Combustion Guide BOOBT Foreword

Although the price of fuel has reduced of late, energy costs still constitute the largest single refinery operating cost. The Combustion Guide Book has been written in response t? the established need to ensure that the combined combustion expertise within the Group operating centres is mair;tained at the highest possible level.

OperztirL~ fired heaters consistently at their peak efficiency Lhrougl: careful attention to the cornbcs~.is;: I;:-ocess has a significant and beneficial effect on d\e ref.inery’s overall profitLability. ln tod.2.y’~ competitive environment it is essential that all managers , supervisors, operators and en~~~:riccrs xe axvare of yhis and h,ave the ;pprcpriate toois nr35 lx d--up to ac~iicve the oSj’~;7ti-v,?s. EEi.cjci:~ bEii?er operation will, in the future, become even more ii-nportant. Planned Ellropean !egiGh.iicn covering err&sions (SO,, NO, and particxla?e.-;), ai0n.g iu-ih economic incentives for JJ.drJ+ -:g hea-g?eY fuel oils and vacuum flashed fuels, will place 2.~7 even greater r-eliance on efficient b>umc.rs 2nd good. burner practice.

The lnro!-marion presented in this book i- ; 3 ,ntended to pro-“ridi. ol~crz ting certtres with the Lzlow&edge they require to appropriately opttie and, if necessary. update their burner operatior=. -2 wide distribution has been arranged to ensure all involved personnel have tile necessa~ I-eference.material, and I would urge that refineri<?:> use tile guidebook as a workn-ig docurncnt v~lth feedback on their comments and criticisms to tl~e authors so that timely updates can he is?:ll<d

1 TYPES OF BURNERS

INTRODUCTION 1.1

I .2 NATURAL DRAUGHT BURNERS (FIRED I-IEATERS)

/11r Reqisler Oil Alomiser Primary Block Gas Guns

Refraclory Quarl Gas Pilot

I .2. I I.2 2 123 1 .2.4 1.2.5 1.2.6

EXAMPLES OF NATURAL DRAUGHT BURNERS

1.3.1 The John Zink MA Burner 1.3.2 The Airoil Unimax 1.3.3 Gas Only Naturai Draught Burners 1.3.4 Colnbuslion Performance

1.4 F0RC.E.D DRAUGHT BURNERS

Quark Stabilised Burner Suspended Flame Eurner Siab!liser (Swirler) Windbox 011 Atornlser Gas Guns Gas Pilot

1.4.1

1.4.2 1.4.3 1.4.4

1.4.5 1.4 6 1.4.7

1.5 lilG:--1 INTENSITY BURNERS

1.6 RADIANT WALL BURNER

1.6.1 lnsplranng Radiant Wall Burner 1 .G.% Forced Drauqh! Radiant Wa!I Burner 1.6.3 Ignition -

1 .?

1.8 ROTARY CUP BURNER

Z.!

2.2

2.2 I 2.22 2.2.3

2.3

2.4

2-G

2.7 ii(i’l‘i:,R‘i Cl.JP A’I’OMISER

, :

CFIAPTER 3 GAS GUNS

3.1 FUEL GAS GUN

3.2 GASGUN JETTING

3.3 CENTRAL GAS GUNS

3.4 CONCENTRIC GAS GUNS

3.5 IlUlINEtC GAS GUN SIZING

CHAPTER 4

4.1

4.2

4.3 IGNITERS

4.3.1 High Energy Igniter-s 4.3.1.1 Lodge Igniters 4.3.i .2 Di. Be11 1cm~cr.s J

4.3.2 High Tension ignite;.s 4.3.3 Carbon Arc Igniteis

GAS PILOTS AND XGN1TERS

PILOTS

EXAMPLES OF PILOTS

CHAPTER 5 COMBUSTION

5.2 THE COMUUSTIGN REACTION

521 llse of the Chemical Equations

5.2.2 Air for Combustion 5.2.3 Calculation of Air Requirement from Oxygen Usage

5.3 CALOR!FIC VALUE

5.3.1 Calculation of Calorific Value of a Multicomponent Mixture 5 3.1.1 Volumetric tiasls 5.3.1 2 Mass Basis

5s I API Gravity 5 5.’ Calculation ol5; 1: :;I;~c: Gravity for a Multi(:orily,oilc!li Mixture

5.6 Ail?/FUEJ, i?/‘.‘!‘l?;

p t i ( , ‘E j \ !

, - 1 ’ I

f

CHAPTER 6

6.1 FIRING OF A MULTI-COh4I’ONEN-l’ FUEL

6.2 DETERMINATION 01 EFFICIENCY

6.3

6 2, I 6.3 2

G 4 DCTCRMINA’i‘lON C!i‘ i:l.i-iCIENCY BY C;R/\l’I llC/iL MEANS

6.5 FACTORS AFFECTirQ;; f:Ff‘ICIFNCY

6.5. I 6.5.1.1 6.5.2 6.5.3 6.5.4

Excess Air Benelits of Low Excess AIM Operation Energy Losses Preheat Dewpoint

CXIAPTER ? .,. . .

7.1

PE-ORMANCE

PERFORMANCE REQUIREMENTS

7.2 SE:LECTION FOR DUTY

7.3 EFFECTS OF DIFFERENT PARAMETERS

7.3.1 7.3.1.1 7 3.1 2

‘pr,b.,. 7.3.1.3 7.3.1.4 7 3.1.5 7.3.1 5 7 3. 1 ‘7

Flame Length Effect of Liberation Effeci of Excess Air Effect of Atomising Steam Pressure Effect of Viscosity Effect of Combination F!r-lng Effect of Air Preheat Effect of Burner Tip i?c:;!i;:-

7.3.2 13 2.1 7 3.2.2 7.3.2.3 7.3.2.4

Particulates Effect of EXcX?.% Ai: Effect of Atomisir!g Si221!1 ?Lt:ssure Effect of Viscosity Effect of Air Preheat

Nitrogen Oxides Effect of Excess Air Effect of Atomising Sieam Pressure Effect of Viscosity Eifnct of Air Preheat

EFFICIENCY /

il.! 1 Fuel Gun Sizing :i 1 : 8 1.i

Fuel Disrribution Combustion Air DUisli ll)ul:on

8 I s: Tucl Condition !j I ‘i 8.1 G

Flame Stability f“lJCI Filtralion

II ~ ’

‘I /ICCEPTABI,F COI\IIflUSTION ,

OPTIMISATION OF A MULTI BURNER INSTALLATION

Balancing Air (FD Burners) Balancing Air (NO Burners)

FIRING FUELS SINGLY AND IN COMBINA’TION

Firing Oil and Gas Sepsraieiy Combin;irion F17-1ng

IlADlRNT WAl,i,-I’YPE INSPIRATING BURNERS

CHAP?‘ER 9 TROUBLE SHOOTING

9.1 INTRODUCTION

9.2 APPROACHlNG A PRORLEM

9.2.1 New Burners 9.2.2 Existing Burners

10. 1 MAINTENANCE FACiLITIES r-.y?+.i.+

10.2 SPKRY TEST ,&G

10.2 I Use of Spray Test Rig

!0.3 OIL ATOMISER CLEANING

IO.5 GAS PIL0-K

i

Chapter1 r

TYPE OF BURNERS

1.1 INTRODUCTION

To utilise the heat released by the combustion process it is necessary to control it. The burner is a mechanical device designed to produce a stable flame with a pI-CC!iCitZd flame size and shape. The liquid futl = s are broken down into small droplets by means of an atomiser. Dot11 oil and gas are carefully directed into the combustion air IO ensure good mixing and to stabilise the root of tlie i!;~rlre.

There are many types of burners available varying from L 1 simple bunsen burner to the giant burners used for cement kilns. It is important tiiat the burner which is selected is most suited for the application. The refinery industry has traditionally been served by two main burner manufacturers, John Zink and Airoil. They have offered, over the years,‘a very diverse selection of designs many of which are now only found on very old heaters.

Refinery burners can be classified in two main types, Natural Draught (ND) and Forced Draught (ED). A further type of burner encountered on chemical plant (e.g. +~t.hylene ~eformerir) is the radia.r-1? v\r2y Iyl:x<T.y\ c.:‘.

This t-ype of burner- relies ., ~-ix the sucli~c inside the hearer to draw the necessary conibustion air through the burner. The burner is sized ,311 tile suction (hearth draught) available. This draught is determined by tile draught under the convection section, which is set to be slightly negative, plus the additional draught created by tie height of the radiant section.

The nl;aila.ble hearth draught is normally in the regio:: ci 10 :o 12 i:lm W.C. (v:atei- colum~r) ;II~ the burner throat is sized to pass the necessdry air. converting the availab!e draught into velocity. Cornpared with a fo;-ctJ.id clracgh: burner the air -:~:!oci~; is relatively lo ;‘i and therefore there is less erl~::rgy available to mix t~he ali and Luel. As the energy input is low the combustion in:ensi:-f and efficiency are reduced, resulting in a large flame envelope and requiring higher excess air to complete combustion. Excess airlevels for a single burner of lS% when oil firing ,:rtd lO”,G when gas firing are r-calistic.

The ad-lsntage of ND burners is the low nutial cost of the mst~llation. ‘The burners themselves are relatively cheap and there is no requirement for combustion air fans

- and ililcr.vork. If there is no air preheat requirement .!nti :i :!l<~ fuel to be burnt is i~rccl.omi;larr;ly gas, then it may be hard to justify tie add.ior~ai cost of a FD installation. The specific parts of a natural draught bum;-; ;II e described.

‘!‘o avoid oil dripping and coking of burner parts it is !mjrortant that the oil gun p<>sition and the tip jet included angle is matched cn relully with the primary block anti ciuarl. The tip jet included angle provides an itrtilca~l(lIi oi the atorniser spray ;l!lqlC

f

c \ ~ II : I A ill

1.2.3

1.2.4

1.2.5

Primary BIock

To stabilise the oil flame the oil gun is positioned inthe primary block. IS to 20% of the combustion air enters through the block which should be shaped internally to allow the correct recirculation of partially burnt fuel and air back to the root of the flame.

Gas Guns

A gas only burner may have a single central gas gun. Combination burners will have a number of gas guns positioned symmetrically between the primary block and the quarl. Jets in the gas gun tips are angled to direct the gas into the air stream and pro-Jidc stabilisation zones .+tithin the gnarl.

Refractory QuaI

This is mounted in the furnace floor or wall. The internal diameter is sized to produce a pressure drop which converts the available draught, i.e. static pressure into velocity preskure. The internal shape of the quarl helps determine the final flame shape and is instrumental in promoting flame stability.

.3

&xarnples of these early burners are given heiow (see Ficpre.5 1-i and I.2). Inspiratig type burners are still used in reformers as radiant walI burners and inspirating pilots arc rlnivei-sa!ly used.

I-‘igurc I.1 Type VIJMP Inspirating Jet Mix C:a,; Burlier

/

-

Figure 1.2 Hydrocool Air lnspirating Gas Burner

In principle the early oil fired natural draught burners varied very little from those offered today. It was usual to have separate primary and secondary air control Iouvres, the adjustment of which in relationship to orie another is not always understood by the operator. In principle the “tiemary air, which is jntrodxxxl through the primary block, is reyuia.- +-cl to st&ilisc the oil flame. The secondary zir Xouvres xegdat\e :,:xJ;~t i?x/;, cf ti:c ,-’ i; F,<-> 1.1s i; 0 j i ;:.j 1’ c;-tci are thereforc iiiic tJk~.i:;i~~ij 2i.r control. See figures 1.3 and 1.4.

~‘iguxe 1.3 JLiroil CP Burner r‘igure 1.4 John Zink UBA Burner

Figure 1.5 Airoil Unimax Burner

The variety of differ-ent desiqns of ND burn ers still available c;in be seen by looking at a John Zink catalogue. It is suspected, however, that many of ihC+Se designs are no longer fit:ed to modern heaters with the exception of certain crkting ‘neater designs which arc available from Licensees.

1.3.4 Cornbusti6nPerforInance ’ .m.>

Due to the low vc!ocity of the combustion air there is less energy available for mixing and some air is not entrained into the flame, and as a result of this, minimum excess air levels to give acceptable combustion are in the region of 15% for oil firing and 10% for gas firing. The flame length is longer than a FD burner and as a general rule of thumb can be estimated from the burner liberation using the value 1/2 million Kcal/metre. Due to the lower combustion intensity the maximum flame temperature is also lower. 12; iilgh fiarne temperatures increase the formation of nitrogen oxides (NO,), it can be seen from test results that NO, levels are lower than [or FD burners. Conversely. the !c-~eI:; for particulate emi ssions are higher reflectiy the less efficient air/fuel mixinq.

1.4

There are a very wide range of designs available, with all the manufacturers making plausible claims ior Ihe performance efficiency of their design. Unfortunately the buyer normally has to seIect the burner on trust and price- The result being a iail accompli, the buyer has to make the best of his doubtful purchase.

The forced draught burner test programme carried out on the Sunbury Burner Test Zig @TX) bet.ween 13BCi and 1984 produced some surprising results. The burners actually tes:ed, were chosen from manuiactur-ers , -vho were ah! *L’ to d.ei-mm 1 rate 0-ia t

iheir Su;-~-ter ilad a good cha.nce 01 meetiilq. BP’s requirements. -2~ actuA?ty not one of the burners mei 1112 requirements of BP Standard 101 as originally suppiied. Basically, humcrs can be divided into tr;ro types, Quark Stabi!.Lsed (see Figure 1.8) andSu.sl?ended F-lame;.

Cl-IAPTI:I? I - P.sqc 5

i I ! l.‘.l”l-l 1; i #,.I,

8

Stabiliser (Swirler) r

The swirler is designed to swirl a proportion of the combustion air at the root of the flame thus creating an internal and external recirculation. The flame is stabilised by recirculating par:islly burnt hot combustion gases back to the root of the flame. To promote this recirculation the angle of the individual blades is important. The shape of the blade has also proved an important factor. It was found that the flat blsded sw~rler was prone to coke formation in the area around the imer hub vihereas this

problem.did not occur with a curved bladed swirler. Tests by the manufacturers showed that the air distribution along the length of a curved blade was even, whereas on a flat blade the air ffow near the hub was greatly reduced. ‘i’he Inch of air at the hub will allov~ t-he solids in the partially bur-n: con&ustion gases, which are intentionally recil-culatec !, to collect on the swirler in this region.

(‘

i -4.4 Windboj:

The suspended flame burner is quite simple in construction. The windbox is carefully designed to ensure an even distribution of the combustion air into the burner throat (air tube). There is no reliance on adjustable air louvres, as with certain quarl stabilised burners. The air flow through the burner throat is linear with only the portion which goes through the stabilk& (swirler) being swirled. The firr~~I flame s!-,z.r;.z !z deter~Ane-j! by tl,e t?l!c;i!, swirler and fuel jet ~~tiomei;~.

: -4.5

i-4.6 G a 5 e un s

A nlrmber of gas guns are Iocated around the central oi1 gun with their tins positioned in *&e swirler area. The pOSiiiOIliilg oi tile qin tips either jus, ;lil-oTzgil or partiall; through the swirler blades is to give the increased stability required by tic BP Std. !C? out of ratio stab&t-f ck~e. Positioning of the tips around the outer circumference of the swirler hzs given stability at normal conditions but hz-s not met the requirc~m!n+~ of nn stc1 !. 07.

I_ ! ,,l.r(‘i or ::iz i:?a[ures whi(:!1 !)-!!;,j,~:?.: c:on!r)usilon are ;-aAp!a i!.niicrn~ ;-I -I .r-Llel I-ili,i!IC~ ,!!lVl -: a high temperature enviroilmeni. ?he high intensity burner sets out to try and achieve these fea:ures by containing the flame in a small refractory lined ch;:mbc~ i ~conihustor). To prorno!c rapid air fuel mixing the comhus!ion air is eilher swlrli+~i at the point of entry or introtiuced li,rough jets arranged to promoie a vortex w1t11i11 !l~i> chamber.

Cd‘! IAl 1r.i; I I’d(_)‘2 n

windcasing gas connection I /

RRADIKNT WALL BURNER

As the name suggests, this type of burner is designed to increase the radiant heat

!rsnsier from a gas or light 09 flame by utilking the radiaiing capabilities of the

adjacent xfradories. The flame is directed onto the refractory \vhich then radiates

:.!-I 2 I : 8~~:; .0 ,ilC ‘DI?TOCCSS iiib2S.

There arc IFXO types of burners available for firing gas, an inspirating type and a

force6 draught type. The latter is also available for firing li~;ht fuel oils such as

nal3iitli;:.

GAS IN, FT -- INSULATING

BLOCK NOZZLE

PILOT OPTION

Figure 1.15 Inspirating Radiant Wall Bu mer

CTORY

FCJRNACE WALL

Figure 1.16

Forced Clraught PILOT

GAS INLET

Radiant Wall Burner

This t-p,: of burner is normally ~CJT .iied direct from a portable electric or gasjclectric Igniter. I f required, smal! pilot l~uixers are available. The reliability of the plloi:; sllould be checked before Ell!li!i; liicri; lo ail the burners.

1.7 PIICKKGE BURNER

‘I‘llis name is used basically for the want of some better description. Any burner can

be sold in a package, that is. complete with all its integral controls and interlocks. The

type of burner referred to is usually used on smaller boiler plant and is mass

produced to a set specification. A package burner is shown in figure 1.17.

Package

The combustion air fan is integral with the air tube. T~IE oil atomiser and stabiliser

arc fitted at the tube exit. T’ne electric motor which drl..,cs the fart is also used to drive

a fuel oil pump. The ignition transformer, Elan1c failure ~Jo~71.Yol with integral start/stop

timer,.pressure switches and safe-@%?%t-off valves are all mounted off the fan/burner

casing.

The quality of combustion will vary depending on the model used. In general, for

heavy oil firing they are not suitable for very low excess air operation and the tiser

,.a;il! have to be satisfied with 20% or more excess air ok Teration to achieve acceptable

cC~idIUStiO1~.

(:li:TI”l~l:li I I’.lljJ’ I . !

ADJUSTABLE CASCADE VANES

Chapter 2

OIL ATOMXSATXON

2.1

22.1

INTRODUCTJlON

To achieve efficient controlled combustion of a fuel oil. it is necessary to break the Liquid dovin into tiny droplets and to then introduc c these into the combustion air stream by creating a specific spray pattern. The rnec?~anisrri for producing t!lis spray (atomisation) is effeCiCd using ~111 ‘Atomiser’ \tihiclI is loc~~t~d correctly in t!lc !,U~~~lCi throat by means of a ‘Fuel Oil Gun’. There are several different methods used for atomisation and for each of these methods there are different designs of atorniser- available. The effectiveness of an atomiser is dependent on: the fineness of atomisation, its turndown range whilst still giving good atomisation, the ability to produce the required spray pattern and finally the energy required to achieve all this. Other desirable features are robust design and ease of maintenance, however, as efficient atomisation contributes to efficient combustion, higher maintenance required by precision atomisers can be justified by fuel saving.

The atomiser produces droplets of varying sizes, the diameter of which are measured in microns. It is desirable that these droplets are as small as possible, however. the range of droplet size produced h-y a specific atomiser is also important. It is of little use if the atomiser conver-t s 904L afthe rue1 now to the finest cl.Yoplets ever seen, if the remair,i.i-rg i Ci’% are as bit; as bullc’~. The smaii droplets wi.11. burn cut within the flame envelope whereas the large ones will be seen leaving the flame as >parklers. Droplets which do not completely combust leave the combustion zone as particulates which foul the heat exchange surfaces and lower efficiency. The remainder leave via the stack causing more problems.

Pressure Jet

This re!ies solely on pressure to force the oil through a speciahy shaped orifice. The oti is first swiried through angled ~10:s before entering the orifice. To give a reasonable turndown range with satisfactory atomisation, a high maximum oil r2ressure is required with fuel delivery systems clesic~~ed from SG to 60 ijar. 3 l]>rt2ssur<> j;:i atUil:j:;ei 1s StilJ.s.iil iii I‘lg’Ji ‘1 2:. 1.

Figure 2.1 Pressure Jet Atomic;er

PRESSURE JET SPRAYEFc INNER

Spill Return .

To improve the turndown capability of the pressure’jet atomiser, oil can be returned

back from within the atomiser swirl chamber. By returning oil from the atomiser, the

pressure at the tip is maintained while the actual oil flow for combustion is reduced. A

spill return pressure jet atomiser is shown in Figure 2.2.

SPILLATOMISER

Figure 2.2 Spill Return Pressure Jet A;omiser

Twin Fluid Atom.isers .“.. . .T

By ustig an atomising medium, high !um do~.ril c’an be acltielred with lcwer fuel oil

pressures than required for a pressure jer atom&r. There are v-arious designs of

twin Lluid atomiser and tile basic principie is tital tile alomising medium is directed

into the oil flow brea!!g it down into droplets. (A typical twin fluid aiorruiser is shown

in Figul e 2.3.)

Figure 2.3 Typical Twin Fluid Atomisrr

2.3 ~T~MISER DESIGN ‘. .i

..~ .

The quality of atomisation is determined by the atomiser design plus the energy input. The energy input is a function of the oil and atomising medium pressure and flow rate. As seen vtith the pressure jet. oil pressure alone can be used to atomise the oil. The twin fluid atomiser, working at lower oil pressures, still achieves a degree of

atomisation without the atornising medium. The amount of atomising medium

required to achieve satisfactory atomisation increases as the oil pressure drops. This

is illustrated in Figure 2.4 which is based on the IIamworthy intetn:~l iloZ,Izlo mix

atomiser. II can be seen from this graph that there will be a financial saving in

aromising medium (in this case steam) by using a higher oil pressure. Growing that I

kg of oil is required to produce 12 kg of steam, if the atomisiny steam flow r-ate at 5.5

bar oil pressure is 0.22 kg/kg of oil, the energy required to produce this steam is equal to 1.83% of the oil being atomised. I f the oil pressure is 8.25 bar the amount of atomising sieam required is reduced to 0.10 kg/kg of oil, this wiii give a fuei saving

of over 0.9%.

Twin fluid atornisers can be listed under three main types:

(a) Internai I< o::ilc Mix

(Is) Emulsion

(c) Extexna! Til: {‘,ii;;

The quest for iinp:ovcd alomiser desi~ is still being pursued. !qew designs of

internal nozzle mix atomisers are giving encouraging- results.

2s ATO.MISER I-LOW . .

*’

With internal nozzle mix and emulsion type atomisers there is a two stage pressure drop. The first is via the jets which introduce.the oil and atomising medium into the mixing area and the second is throuyh’the dischdrge jets. As the pressure in the mixing area is the sum.of the remaining pressure‘s for both fluids, it can be seen that if the pressure/flow rate on qne fluid alters. the pressure/flow rate of the other will be affected. Figure 2.8 shows the required oil pressures for two dilfc-rent atomisinq steam pressures; the higher is the correct operating pressure.

For %::I ~::~.r.~-nal mix atomizer i1\c: aro;r:isin~~ medium dots not c;l:-:y alit !iz, function until after the oil has left the tip. Therefore. rhe oil flow/pressure relationship is not affected b;, variation s in the s:omislng medium pressure

Figure 2.8 Fuel Oil ‘O” -__- MP Pressure Against Heat Liberation with Different ,D __ Atomising Steam

Pressures .lDvYIC I,,*., Trtsw .,,b, ,.lr,,r*ll.u,

IO F

r

.~.. -.-____ / IJ c..

*....+.I 4--v

1 “Ml 0% WUOIllT >I dl -. .__- -.____ .--- ..__ _

AIR INLET S‘~YlSLEfi SWIALER REGULATIIJG ZPINDLE _ OIL INLEI

‘. ‘\ -‘\ 011. REGUtA:O!i I

Low and Medium Pressure Air AtGrillSei~

ROTARY CUP ATOMISER I_.

The atomiser housing is hinge mounted onto the burner air register unit to allow ease of access to the atomiser cup for cleaning and maintenance. A rotary cup atomiser k shown in Figure 2.10.

The atornising cup and primary air fan are mounted on the same shaft and driven through a rear multi-vee belt drive from the electric motor mounted externally on the atorniser housing. Typical cup ,zreeds are between 4,600 r-pm and 5.400 rpm.

A Inetered oil supply is fed to the interior oi the spinnilng cup via a distributor. The centriiug;ii action causes the oil to be spread in a Titan fillr; o.ver tile interior and towards the cup lip, where it is thrown off tangentially at high velocity. The primary air ian iecds air through the cup shr-oud, dir-ected by swirl v&nes, into Ihe oil fihTL (0

ensure complete atomisation and provide the required spray angle for the atomised fuel oil. The main combustio~l air is supplied to the quarl annulus by the forced draught fan. discharging to the burner airbox, controlled by the airbox damper.

8

8

FUEL GAS GUN

The function of the fuel gas gun is to direct the gas into the air stream in such a way as to promote good fuel gas/air mixing and LO provide stabilisation zones for the flame.

The gas gun should. like the oil qu11. L.)t? removable for cleanir><j v.rhiir: the heater/boiler remains in operation. The gas tip which contains the yas jetz will, depending on the manufacturer, he a screW-on or welded-on type. The numl,er alld locatiorl of the gas guns will also vary depending on the manufacturer.

Every possible arrangement of gas gun with jetting has been tried by one manul’acturer or another over the years. The most complicated probably being the

. . . fan mix type burner, which claims to use the gas pressure to induce full combustion air. The burner uses the-gas pressure to rotate an air fan, on much the same principle as a rotating garden water sprayer.

For refine:-)i needs, it is essential that tie gas burner is as maintenance free as possible, with no moving parts <and easy to remove for clea.ninq wlri.l.st the h:r~r>~ i.- skili able to fi:;cc c~i; oil- ‘ihere axe mo ~~rrangements whicii :;Ct th& purpose; the fjr-s;, and most common, is amanifold with usually 4 to 8 gas pokers (qms) arranged concentrically around th&‘&ntr-EFe oil gun; the second method, used for gas only burners, $ a single central gasgun which occupies the position normally occupied. by the oil gu:t- Examples of both types 51-e shown in Figkes Cj. i and 3.2 respectively-. Gas rings, as ofiered by some manufac+xrers are not corlsid,ered s~~ti~~o1iz.; they cannot be removed for cleaning without removing the burner 2nd have a large rrr~-&e~: oi sitnsii j e‘s v;iiich <rail easily biock.

GAS GUN ‘JETTING

I-iqurt 3.3 Pepper Pot Tip

Ti’he Pepper pot tip may be satisfactory with cle,u, sweet 13;“s QNatural Gas, Propane. eic.), but sufIfers from blockage with dirty refinery gas. ‘;‘he solution is to either clean up the gas or iit a tip with larger diameter holes. The tv;o tips shown in Figures 3.4 and 3.5, both meet the requirements of BP Standard 107. A.. q csx he seen, one has a single hole, the other a, slot.

3.3

3.4

3.5

CENTRAti’GAS GUNS

Information given in 3.2 applies to all gas guns. This additional information applies to central gas guns only.

The central gas gun can be used on gas only burners and occupies the position vScated by th& oil gun. It therefore has the advantage of using the stability zone :_ created for.&& oil flame and. unlike the manifold gas guns, the jetting geometry is mor&.predictablt. The variables are the number of jets, the included angle of the jets which, if swirled, should be in the same direc:tion as the swirler stabiliser. and finally, the operating gas 13:iiT.s lirc: range. An axial hole is sometimes used to aid stcIi2iiity bllt can, by creating a fuel I 1c11 zone, cause coke formation on the tip of the gun.

Although more predictable. central gas guns should be tested before acceptance. .,

COiWENTRIC GAS GUN

This-e of.vti is similar to the central gas c&n: It.is made up using two concentric tubes, the Eei;fral tube acting as the guide tube for the oil qin. The,disadvantage is that&e $a?&& cannot be removed for clkaningwithout,removing the oil gun and the?efore the burner must 5e shut do&n.

The formlrl3 is Ued iI5 Ie!Io.i.,rs by an example to size 2 burner wiLh 12 orliiciis w!Ilch is to fire 888 kg/h of nat*ural gas, having a specific gravity of 0.6, at a fue1 pressure of 1.55 bar g and ambient temperature (156°C). When using this formula, all values should be taken at the same stipulated conditions, i.e. either n.t.p. or s.t.p. 111 tilis cticulation, the vaiues ar s.l.p- will be taken.

For gun with 12 orifices, e.~cl~ orifice is:

581.6 12

=z 56 8 inm’ , equiva!ent to a diameter of S.S mm.

4.1 PILOTS

A gas pilot is fitted to a burner to provide an ignition source for thk main flame. There are two main types of $lot, a forced air piiot and an inspiratingpilot. The ierms describe the method by which the pilot is supplied xxrith the air for combustion oi the nilor fuel. The forced air pilot requires an c -xternal forced air supply. The inspirating pi101 uses the fuel gas pressure to inspirate the air necessary to establis!I c0Ild3l:stion.

_ The forced air pilot i- 7. ., A~orrnally used for forced draught burners in which the pilot flame can b% stibjectcd to very high main burner combustion air velocities and therefore has to operate under more arduous conditions than with a natural draught burner. The inspirating t)?,e is normally used for natural &aught burners and provides a low cost installa?ion due to there being no need for an independent external air supply. More recently inspirating pilots suitable for operation with forced draught burners have also become available. Inspirating pilots capable of remaining alight at RDL’s of up to 250 rqn W.C. (10” w.c.) have been introduced.

The natural draught'bnmer pilot has tie insy:ir:ltc>r- sjt~:ited external to the bu,rner register and remo1k+ fl-or.2 ihE l>Lli:t &me I*? ,, .~Ji;l-. j,i: stal.:,ili:-;ec~ llr;iriq Fi c<)1-tTi<r-ltior!al reterziion tip. Ii is only sujkblcl’or operation \v’iti:t. the iow kelocity ccmbustion air as found in natural draught burners.

: .’

.-

.:

Two acceptable suppliers of portable high eneigy igniters are:

(a) Lodge c

(b) Dr. Bell

Lodge Igni.ters

The Lodge pdrtablti igniter unit uses a blocking oscillator inverter to step up a 12 V dc input supply from n battery pack to approxim atcly 2000 V Jc. A main storage capacitor contained in the ignition unit is ihen charged to this voltage. The energy is then rapidly discharged in the form of a high energy spzrk at the end of the probe tube c2cross the semi-co:rductor between the central conductor 2nd surrounding metal tube. ‘;-

The Lodge igniter equipment consists 0: a porrabfe battery pack, an ignition unit and the igniter. To &able an igniter- to be operated from a safe distance whilst a piIot burner ignition is being attempted, sufficient cabling should be provided between the ignition unit and portable battery pack, and the operating switch or push button should be located on the portable pack. ‘I?he Lodge igniter and portable batter pack are shown &Figures 4.6 and 4.7.

The igniter is connected to the ignition unit which-$&r&&s the electrical circuitry required to cause the high energy spark. The igniter consists of a nimonic or stainless steel tube containing the concentric electrode +d ceramic insulator. An outer stailless steel sleeve can be fitted around the igniter tube to allow any positioning clamp to be fixed to the sleeve rather than risk damage to the electrode on tightening. An adjustable sliding collar is fitted around the sleeve to aid correct positioning of the iqniter for the pilot. The insertion distance is determined by measurement and the collar is set on the igniter at this distance from the firing end so that the igniter can be.placed into the correct pdsition on each ignition attempt. Once in the correct position, the igniter should be fixed in position by a clamp and the operator should retire from the burner vicinity before acti./atir~cj [he i~~nirer-. When the pilot is alight, deactivate the igniter and then the holding clamp can be unscrewed and the igniter withdrawn.

The Lodge igniter provides a fixed sparking rate of 1 per second. Any alterations to the sparking rate can o& be made by the manufacturer by changing the internal circuitry of the iqnitioti unit:The igniters can provide 100,ooO discharges before replacement is necessary. The battery pack supplied with)he Lodqr- Qniter has been found by experience to be capable of providing up to 3 hours of i&ition sparks.

4.3.1.2

The igniter co~~si:;:lr of z tmtertight steel box ccntainirrg the e!ec!rc~~li~.?~ pC‘w3lr

supply connecLi:Tn, optical fault indicator and a potentiometer WitiCl; i-; ii.Yed to vary *he sparking rate (varied between 10 and 20 sTar!c- per second). ‘The ele~:trnnics box of the portable iTtiter is fitted with a handle incorporating a pzh b;:!tc>l ior operahon oi rhe lgrtiter. The box is supplied ~vith 2 connection to ruhich 0:e probe tube containing the electrodes is fitted. ‘The spark end of the ele5:~rodes are constructed of liea; resistant stainless steel to withstand the high temperature conditions everienced. The Dr. Bell igniter is shown in Figures 4.8 told 4.S.

.

An axial stainless steel conductor rod is fitted through the core of ti1-c: ;>l-obe tie. This rod is insulated from the outer tube by means of - * Lemmic iei-ruies disposed at reguIar intervals. The Egh energy spark created at the firing end passes between tile cent& conti.uctor rod and theprobe tube.

4.3.2

.-* ‘. ,,, : _ ~ HighTension Igniters

High lension igniters are considerablycheaper &&I high energy igniters and if maintained properly will give a reasonable service for gas pilot ignition in permanent installations. The spark created by the high tension igniter is not capable of lighting,heavy fuel oil directly but issufficient to ignite light fuel oils if carefully positioned. However high tension (HT) is not us&d for main flame ignition on process burners for refinery applications.

Eigh tension igniters consis: 0 i 2 transformer capable of supplying up to 10.000 V 10 ;I pair oi insuIated clectrod\c!s z+e*par ated by a small air gap 3~1~0s~ vihich a spark il; created. The igniter is insex-ted so thai the spark gap is positioned adjacent to or \rrithin the pilot burner nozle.

The igniters consist of threaded body units with an extended central alIoy electrode or straight insulator in standarci lengths surrounding a central electrode. The igniters can be arranged in pairs to provide a Spark gap of approximately 5 mm (“/,,,“). The insulators are composed of ceramic materials.

4.3.3

Figure 4.10 Carbon Arc Igniter and Transforl!lzr Figure 4.1 I Carbon Arc Ignirer ‘i‘!p

. . .

INTRODUCTION

Combustion equipment in the small scale environment, such as a fac:ory boiler house or home central heating system, is primarily designed to fire a set fuel of relatively consrant composition. The engineer responsible for setting up rhe firing equipment VJill have a! his disposal in graphical form, il:e most relevant coi::tlL:s[ion characteristics of the fuel, such as liberation against pressu,re, densliy. calorific value and air/fuel ratio, to aid him in his war!<.

On a refinery, the fuel supply is of a rnore varied nature. The fuel composition may change daily, and even hourly, and therefore the combustion characteristics of the fuel are not as readily determined as those for a ftiel of standard composition. It is therefore necessary to be able to determine the properties of the fuel mixture knowing its composition.

A set of operating curves are provided by the burner manufacturer for each burner. For a burner firing oil, curves of liberation against fuel pressure and atomising steam pressure are proxkded. For a burner firing refke!y gas , a gmph showinq liberation 2: .~:.!tlc’ ?,I ;; 1. j.1 -1 37-es:;7.;I-e for~t!lf: >,i~:]~~:+:7: 2;: ICI jr;\;-‘;... .’ , c ,; 1 , A I.y;)y:e>:;r;_r; .l.’ t, )<w,i’; lli CCTfii~~~X>tL~Iit Oi i.ktC gas is i-zq+red. S+‘Figuxe 5.1 for a t-ypicai fu.e’l press:jj:c acpinci qa:; flow curve for gas components pf different molr:zalr-.r weights. A refti-le.ry <-z-, wi!! however have a variab!e composition and iis operakg characzeristic- a liTair i7.01. be readily obtairtzhle from a fuel pressure-flow curve. It is necessary therefor-e to obtaiii a composition analysis and from this, determine ii!e specific gravity and iom-cr calorific value of the *efinery gas.

When tix:+ specific gravity and lo-b, t. r---r caloriiic value have bec:~-~ i!e;errr-lined, the operating pressuS f6;r the reiknery gas at a specified Itiex[ron can be found using the iol!ow21g formula:

acsinst Tliherntion for Two Gases of Different Molc&lnr ‘Wetc;jIi l‘ired On a Burner

For example, if as in Figure 5.1 the fuel pressure for a gas of molecular weight 15 at 4.0 MW liberation from a psrticuIar burner is 0.645.x lo5 N/m2 the approximate fuel- pressure required for a fuel of molecular weight 45 to be burnt on the same burner would be found thus:

P, = 0.645 x 10’ x 1.5676 o.sszg x ( ,$$To ) ‘, = 0.26 x lO’N/m’

= 0.26 bar

To achieve the same liberation from the burner, the higher molecular weight gas would need to be supplied at a pressure of 0.26 x 10SN/m2 (0.26 bar).

This chapter &ill now demonstrate with exampies how the properties of fuel mixtures are calclculated +oxying the proportions in which its constituents are present. It commences with an introduction of the basic chemical formulae which are

~fundamcntal to combustion calculations.

THE COMEXUSTXON REACTION

Combustion is, in general terms, an exothetic oxidation reaction of fuel anti air durirq xvhich physical processes such a s energy, mass 2nd momentum transfer are occuring simultaneously. The extent of completion of the exothetic reac%on 1 2 ‘3 ‘1: n CL ‘c on the titeraction of the &ove proce- -es in -space and time.

a Fuel

c + 02 + co, Carbon + Oxygen - Carbon dioxide

2H, + 0, -* ZIi,O

FIydl-Og6ZX -t Oxyger-I -+ Water

s i- 0, ~~_ so, Salphu I + Oxygcm -A S?;$hur dioxide

and also under the right conditions and in the presence of excegs oxygen the

following reaction may 0ccu.r:

zso, + 02 -+ ZSO,

Sulphu~ dioxide + Oxygen --i Sulphur trioxide

As the carbon and oxygen will aIways react in ihe same proportions described by ” the equation, then x atoms of carbon will react Ethic molecules of oxygen to produce x molecules of carbon dioxide. This leads to a useful concept, the xnole, which is defined as the amount of a pure substance containing the same number of chemical units (atoms or molecules) as there are atoms in exactly 12 gramrnes of the isotope carbon - 12. The number of units in a mole is termed Avogadro’s Number and is equal to 6.023 x 10”. A mole of any substance will have a ,pecific atolmic or molecular weight e.g.

One mole of carbon atoms has a mass of 12 grammes.

One mole of oxygen molecules has a mass of 32 grammes.

One mole of carbon dioxide molecules has a mass of 44 grarntnes.

Atomic and molecular weights are usually expressed for convenience in integers although the true values usually differ slightly from these figures. Ln some of the later examples of calculations, more exact values of atomic and molecular weights may be used. For analogous terms, one kilogramm e-mole of carbon would have a mass of 12 kgs.

Kir for Combustion

A combustion reaction needs a source ol o;~~~c~L. 70 C i?rOi;t $u~Tp05es, air is Lt-ed 2s the oxygen source. Air is composed rnainiy oi nitrogen and oxygen with a small proportion of inerts such as carbon dioxide and argon. For ease of use, the inerts content will be ignored and the air composition cpoted in terms of nitrogen and o.xygcn only.

i

Therefore Mass Composition of Air is ?6.?“i, Nitrogen (N,) 23 :i ‘!h c:xygen (0,)

As air is used as’th& oxidant, the quantity of air reguir’ed ;o sat&y the sioichiometric oxygen requirement needs 10 be determined. From tile volumetric composition of air already given. for every mole or volume of oxygen.used, thg following number of moles or volumes of nitrogen are present:

79 21

= 3.76 moles ol nitrogen for every mole oi oxygen

The principal reactions can thus he re-written for combustion in air as follows:

C -t 0, + 3.16 N, -+ CO, -1. 3.76 N,

ZH, -t- 0, -t X76 Nz p. X1,0 t 3.76 N,

S + 0, i- 3.76 N, --) SO, + 3.76 N,

The stoichiometric quantity ofair required for the complete combustion oi a fuel. is defined as the theoretical quantity of air required to just completely bum the fuel to produce carbon dioxide, water and sulphur dioxide with no oxygen in the resulting gases. These equations will be used later in the calculation of air requirements and excess air levels.

Calculation of air requirement from oxygen usage

Figure S-3 Relationship between Lower Heating Value and Specific Gravity for Hydrocarbon Gases

u-8 L-.

r

Jcc.7 --

tm-

calorific value of fuels. A number of empirical relationships are used for the estimation of the calorific value of Iiq-uid iuels, such as:

Gross calorific value CV,= 0.339 C + 1.140 H + 0.105 S MJ/kg

It is also desirable to be able to deiermllle tile c2orific value of a multi-component mixture kno;v::lg ii:e calo-ific vzllues oi . 21~: ii&ividuai componentr; ~i;d ii& w-21 nova be demonstrated.

Volumetric Basis

A fuel to be comh~ted ii3s the following composition on a percent volume basis of 0.9% carbon dioxide (CO,), 14.0% nitirogen (Pi,), 81.8% methane (Cli,), 2.1% ethane (C,&), 0.4”/, propane (C3Hn), 0.1% bulsne (C,;-‘i,, ) and 0.1% penkane (C,Ii,,). 73e calorific value of tie mixture is to be cietermizted.

The Gro&s &&&S~+hue of the’&xture is 33.3 MJ/rn’ ”

The Net Calorific Value of the mixture is 30-O MJ/m’

~ ..

The values were calculated by performing the following steps:

(a) The individual component calorific values, both gross and nett were found from tables. Carbon dioxide (CO2 and nitrogen (FJL> king inerts have a zero calorific

value.

(h) The contribution of each component to the overall caiorific value of the mixture

was calculated from the product of the composition by volume (column 2) and the

component caiorific values (columnns 3 and pi lo; :?cti and gross ~e~pccii~cly) e.g.

Contribution of metllane (CH,) to overall nett and calorific values was

81.8 loo x 37.8 = 30.9 MJ/m3 gross

81.8 100 x 34.0 = 21.8 w/m3 nett

(81.8% is equivalent to !s, 2.1% is equivalent to $$ )

SimiIarly, for the other comp&ents;

Ethane -f$j x 66.8 = 1.8MJ/m3gross

s x 6i.?. = 1.61vlJ/m3nett

Propane $$ X 96.5 = 0.4F&J/m3 gross

s >: 88.9 = 0.4 MIJ/m3 nett

(cj _’

The contrtiutions of each individual componer~; LIZ c,uklned to pro-i!de .he

calorific value of the mixture. In the example:

Gross Calorific Value of mixture = Summation of Column 5

(X3.3)

PJe:t Calorific Value of ;nixture = Summztioil oi Co!umn 6

(30.1)

Contribution of rnethxw to overall gross calorific value is

18& x 55.4 = 48.2 MJ/kg P

Similarly. ContributioIl of ethane to overall gross calorific value is 5.2 MT/kg

R /

II I I ~I

5.4

5.4.:

(1)

Gas

Contribution of propane to overall gross calorific value is 1.5 MJ/kg

Similarly, nett calorific value Of mixture is 43.6 t 4.8 -TV i.4 = ,l?.sMJ/kg

The fuel to be cornbusted may often be a composite of a number of different components. It is useful to know the contribution that the individual components make to the overall physical properties of the fuel. It is’also necessary to be able to convert the composition of a fuel from a quoted percentage volumetric basis to a percentage mass basis an d vice versa. Some examples and the calculations necessary are shown iii the fo!!ow~~~cJ p+ges.

A fuel to be combii::~~:~i has the following composition on a percent voi~lm~ bzsls oi

0.9% carbon dioxide (COz), 14.0% nitrogen @?a, 81.8% methane (CClH,), 2.7”/, ethane (C,H,), 0.4”/, propane (C; EJ, 0.3% butane (C,H,,) and 0.1% pentane (C.&-J,,). The overall den-sil-;q si I.~.L 4) - f:!fij mixture and the comoosition expressed 011 3 l2ercent ma.ss basis are required.

(2) (3)

Composition Density of

by volume components

(%I (b/m?

(4)

Actual mass of

component peg

unit volume (kg/m3)

(a>

Molecular weight of, carbon dioxide (CO;)

= Atomic weight of carbon + molecular weight of oxygen r

= 12 + 32 = 44 mass units

Density = ,~~~,

Therefore, density of carbon dioxide = 44.00 379 = 0.1 16 lb/f?

or in SI units = 44.00 23.7

= I .t?6 kg/m’

(bj Knowing the density ol each component and its proportion oi tlie whole by volume, the contribution of each component to the overall mass of the mtiture can be calculated from the product of columns (2) and (3) e.g.

The actual mass of each component per unit volume (kg/m’). (column 4) is given by the following:

actual mass for each = composition by volurne x denzity of component component

(c) The summation of columin (4) provides the sum of the contribution of each component to the overall mass per unit volu.me of the mixture and therefore proTidt2 1’ . - ’ -c t IC .OVCrZll d.Ens;17,J 0t Iilk fU.ili rrij;::uj: 2. i __ “ile c0;npsitiOi~ by IrlnSs iOr

each compor,ent can then be calculared by dividing the actual mass of each component present in unit volume of the liLL:hiZ” (colurmn 4) by thhc o-~crslj rn<Xs of the mixture per unit volume {found from tie summation of colmnn 4) e.g.

for carbon dioxide, cornposition by mass 0.02

= I_ = 0.02.52 Q-795

As a percentage = 0.0252 X 100

Composition by Mass

for nitrogen, O-l?

=mp loo

for methane, = $$& x 100

Conversion frona a Mass Basis to a Volumetric Basis. “,,,

_, 5.4.3

5.4.4

ii 1

;’ ‘3 s .- L

Rciationship between Molar and Volumetric Term&

[t is easy :o convert from a molar to a volumetric basis and from a voiumetric to a

molar basis because of the relationship whereby one mole of a gas occupies a

standard volume (23.7 dm’ or 379 ft3 at standard temperature and pressure of 15.6”C

and 1.01325 Y. 105N/mZ) i.e.

one mole of gas is equivalent to oL1 _ -i’ volume of gas and therefore the terms are

readily inlerchangeable oil a pe;cen; basis.

For cxarnple, 2 gas mixture co~npr~:;~rion of 90% methane and lo”/, ethane by vciu!ile

would have a molar composition of 90% methane and 10% ethane.

Conversion from a Molar Basis to a Mass Basis

A fuel to be cornbusted has a composition on a molar basis of 85% methane, 10%

ethane ;utd 5% propane. The composition of the gas mixture on a mass basis is

required.

85 16.04 1 13.635 -. 1 r..i3 ‘-) 3 r

10 30.067 3.007 15.95 5 44.092 2.205 11.70

----.

18.847 i 00.00

(a) FLnd from tables the rno1ecuIs1 vieights of the components in the fuel mixture

(b) The acmzl mass of eac‘rt co:r,po;;i-n: is then calculated irom the product of ti.te

molar composition (column 2) 2nd the rnolecvlar weight (col~nn 3).

for merhanc, is 16.041 x -;;; -= 13.635 mass units

for etha.ne, 10

is 30.067 X - = 3.007 mass units 100

(1)

Gas

CiH, C,H, C,H,

1 co2

I

Conversion from a Mass Basis,to a Mola~~B$s&’ J

I .- . . _

A fuel to be combusted has the following composition on a mass basis of 80% methane (CH,). 10% ethane (C,H,), G%pro&e (C,Hd and 4 % carbon dioxide. The composition of the gas mixture on a molar:basis.is required-

(2) (3) (4) (5) (6)

Co:npos;rion SpilCifk VclUme Actual hlUWie of &fiJai nUmbef COrnposition by mass of components each’component of moles molar terms

( Y/u ) (““/1(g) (m’/kg) lx) .-.-__-.._____

80 1.47 1 .I 8 0.0498 90.05

10 0.79 0.08 0.0034 6.15 6 0.54 0.03 0.0013 2.35 4 0.54 0.02 0.0008 1.45

0.0553 100.00

The foll0wk.g sleps are perfomled:

(a) Find thee T~XX~IYC volume (reciprocal of the density, s;& ) io!- each component

The specific volume of e&me is & = 0.79

(b) From the specific volume of each component, the actual volume that each component would occupy can be cakulated knowing the composi~jon by mass.

1

Actual volume of each component per unit mass

for each component = composition by mass X specific vo!ume of component

for methane, actualvolume = s X 1.47 = I..iE; Il-L.‘/ko

for etj::n ‘_ accg& -golu~ne = +j& :c 0.19 :: fJ.CS nir’/!;~ i,

for propane, acF&l volume = & X 0.54 = 0.03 m’/lrg

for carbor: dioxide, actualvolume = & x 0.54 = 0.02 m’jkg

s i IT-, i 1 ;i ; i “.: : / number 0; moles of ethanc = 0.0034 moles

number of rmoles of propane = 0.13013 moles

number of moles of carbon dioxide = 0.0008 moles

CHAPTER 5 --- i’,ig)e 12

.--.. _.,_-

1’ i II ., I !

(d). The summation bf colutin (5)provides the total nun&r of.moles of the mixture.

I -’ The molar composition is found by dividing th’e actual number of moles of each

I

component by the total number of moles of the mixttire.

II / The total moles of mixture = 0.0498 I- 0.0034 t 0.0013 -1. 0.0008 = 0.0553 moles

5.5

for methane, molar composition = 0.0498

0.0553 Yi 100 = 90.05%

for ethane. molar composition .= 6.1i%

for propane. molar composition = 2.35%

for carbon dioxide, lnolar trornpc)s::loii -; 1.45%

SPECIFIC GRAVITY

A useful physical property of a fuel is its specific gravity. The specific gravity of a substance provides a measure of its density in ratio terms against an accepted base standard material which is taken to have a specific gravity of 1 .oO.

For gases, air is taken as the base material.

I4 . For liquids (and solids), water is taken as the base material.

,I The specific gravity for gases can therefore be defined as:

The ratio of the mass of gzs i:\er unit volume (density) at a stated temper-ati-t-c. to the mass of air per unit \~oiume ai. the sume - _ ̂ . _ ten ii,“: <:.!.lJ re

/ Similarly, the specific Gravity for licyuids or solids can be defined as:

The ratio of the mass ofliquid or solid per unit volume at a stated temperature to the mass of water per unit volume at the 5X7152 teinperature.

The relationship betweer, the specific gravity and volumetric lower calorific value of gases has already been shown in FigliT-e 5.2.

Some examples of gaseous and liquid fuel specilic gravities follow.

Example of Gaseous Specific Gravities

Air

The molecular weight of air is 28.9 and its density is 1.22 kg/m” at standard temperature (lS.SS*C or SO”!L=J and pressure (1 a:m).

The following specific gravities are calculated ai standard temperature slid pressure.

The molecular weight of lrnethane is i 6.04 1 and its density is 0.67 kg/m3.

Ratio of methane density to air density = o.57 = 0.549 1.22

Methane has a specific gravity of 0.549.

li’ydrcgen

‘The inoiecuiar vqeiq!ht of iiydrog,An 1s :,;.() 16 ;d,;;(-j .‘:; -i ,, c.ensity is 0.08 kg/m’

Ratio of hydrogen density tc sir denslq -z 7:: Q.OSG.

:-Xycirogen has a specific gravity of 0.066.

0.84s Specific gravity for gas oil is 1 = 0.815

For a heavy fuci oil, having a density of G I. ! 79 !b/lr’ or 0.98 kg/dm’

0.98 Specific gravity for fuel oil is 1

= 0.98

. - . . - I , , “ , _ , , , .

1 I

I

II ‘: I

55.1

:. _

i; _ 5.2

An API graviry may often be quoted as a physical property of a liquid fuel, particularly in America. The API gravity of a fuel is usually expressed in degrees and is related to the specific gravity of a.liquid fuel in the following way:

API gravity = 141.5

specific gravity - 131.5 degrees (‘>

For hea-vy fuel oiI;having a specific gravity of 0.98

APIgravity = +!$ - 131.5 = 12.89’.

These worked examples demonstrate the inverse relationship between API and specific gravity i.e..as the specific gravity is higher, .tie API gravity would be lower.

To calculate the specific gravity of a fuel given its AF’I ,gravity, the following equation is used:

Example

The following fuel is to be combusted having a volumetric compositon of 15% rncthar.-: (CH,), 10% ethane (C,H,) and 15% ;3ropane (C,Ii,). The specific gravipy of the mixture can be calculated.

(2) (3) Compositicn by Density of

volume component

(I/;) (kg/n’)

(2) Specific gravity

of component

(5)

Contribution to specific gravity

of mixture

.L

(d) -Find the specific’gravity.of the mixture from the sum of the specific gravities contributed by the individual componenrs i.er from tht s SUiTlKl2tion of column (5).

The specific gravity of the mixture is

= 0.412 -1. 0.103 4 0.229 = 0.144.

5-s AIR /FUEL RATIOS

5.6.1 Stoichiomctric Air Requirement

In order to bUi-I\ 3 fuel, it is necess;i ry to icnOW llow much aiT ll<iS t0 ‘UC Supplied. ‘r’l\e

air requirements can be calculated on the basis of the simple stoichiometric chemical

equations first proposed in Section 5.2. Again, calcr~laiion of :hc fuel/air

requirements is best illustrated by example.

Example

Propane is to be burnt in air. The amount of air required for the combustion of the propane needs to be calculated. The appropriate balanced equation for combustion of the propane provides the necessary. information. The appropriate equation is:

C,H, -t 50, + 3C0, + 4H,O

i.e. one lnoie 01’ ijrie u-oltune of pr3pane has a stoichiometic oqgen rt5aA*3i~-einea~ of

five moles or five volumes of okygen. As detailed before; the composition of air can be taken to be 79”/, of nitrogen and ‘21% of oxygen- Therefor-e the total air

requirement would be calculated as foLlows:

Nitrogen fed to i~el with oxygen = g x 5 = i8.8 volumes or mo!es

I ‘i’o~al ax requirement = 18.8 + 5 4 23.8 volumes or moles of air.

The molecu!,i!- ,x-~l;rr 1~ *,.-LyI.. (hlTlii) of air = 38.9 (0.79 j: &f&V cfT,J, +- (].2i :-: I,~~j‘:i c>[ @a. Tile

mo!ecular weight of propane is 44. I. Therefore, this equation indicates lhat for every

44.1 mass units of propane, 681.8 (28.9 x 23.8) mass units of air are required for

complete conibusiion.

The example ifiusrrates a further useful renu in combustion, the air:fuei ratio. The

air:fuel ratio provides an indication of the amount of air that is required for the

COITlplete conl~~us~iorr Oi the fLIei based on its St0iCh~OrileiriC COi&uS;iO!i ~2qu.atiOn. In

the example, Ir can be see11 that the stoichiometric air:fuel ratio requirement for

COlnpiete combustion IS 23.8~1 for propane.

The air:fue! ratio can thus br- easiijr calculatea ̂’ from the balanced cornr~icie

COtiusiion reaction. To illustrate the point further, here are some more fuel

combustion equations and the 3 c.ppr-opriaie air:liiel ratio obtained usilng ihe methods ShO\*JIl ii7 ihF e:inrllo!c:

(a) CH, ~!- 2G2 ~_ 2!13o f co,

1 nlOlC Oi 7..;O!lliIicf Of methane rec;LIires 2 rnolcs or volumes of o:i;‘<-je~i -i-

t ;: x :3.7,q of Ili!rogcIi.

Air:iu(:i -‘:2tio = 2 -I- (2 x 3.76):1 -~~ ~ 9.52:i for riletl~ane.

(b) C,H,,-i- 6.50~ -+ 5~~0 + 4c0,

1 nlolr: c-r v3Iu11nc ci butane roquircs 6.5 iuoles or volu~~~cs oi oxyy;:n -t

(6.5 % 3.76) of nitrogen.

. . i’\ir:fuel ratio = 5.5 -t (6.5 x 3.761.1

= 30.94:1 for *3L a,‘;. 1 4 I\ *

The sto~cl~~ometric combustion requirements for various i~ieis can be found from

tabies and in this gcide are provided in TabIe 1 1.1.

(;i IAl’l’I:li :i !‘.“J’! ii;

Excess I&- Levels

In practice. to ensure full combustion of a fuel; air in excess of the stoichiometric

requirement is normally required. Therefore, the excess air level and the excess

oxygen which is unreacted and cal-ried away in the flue gases are of inferest. In the

case of the first example that was shop-n. it may be that an excess air feed of 30% may

be required to ensure full combustion of the propane.

In this case. tile sir iced wouid bz 3O”/k gI-ester than the stoiclliornetric requirement:

(23.8 x ];:, ) i- 23.8 = 30.94 moles or volumes of air (23.8 being tile stoichiomerric air

requirement ior the combustion of propane).

This equation can be simplied to (1 t i.e. 1.30 X 23.8

and hence:, .,

iii R&&&d for a Fuel at a Specified Exckss Air Level is

(1, -I- &) :: Ct,’ f-c u c,lc ~ornetrl~: __ ib il- Reo-jlirer,7eAq;

where Xis the excess air level qecified in percent.

21 is (30.94 X --) = 6.50 moles 01 volumes

103 : . -. _.

from the equation:

C,H, t- 50, t (3.76 x 5)N, --i X0, f 4&O + (3.16 x 5)N,

it canbe seentiM 1.5 (6.5 less 5.0) cccess - moles or volumes oi ox-ygen are present

and as they are unreacted wonid be present with the combustion products. To

calculate the excess oxygen level in the products at 30% excess air feed, we need to

do the fol!owing:

Combustio?products would be 3 volcmes oi CO,, 4 volumes oi i-&O, 24.4 (excess air

figure 30.94 Iess oxygen 6.5) volu.mcs of nitrogen and 1.5 volumes of oxygen.

Therefore ti1’3 excess o:rygen p,~-r‘si;:t :a, i’l2 flue ps V.rOuld be:

1.5

3 + 4 + 24.4 + I.5 X 1@) = 4.6”/; 211-y lrolume wet basis.

5.6.3 Calculation of Excess Air Level from Known l?lue Gas Ox+gen~Lev~ls *

For a combustion reaction. the excess oxygen level in the flue gas may be given and the excess air level to which this corresponds needs to be known. This will again be illustrated by an example with-the combustion of ethane, being given that there is a 6.5 % excess oxygen level on a dry basis. The stoichiometric equation for the combustion of ethane is:

C,H, -i- 3.50, + (3.76 x 3.5)N, -+ Z,CO, -t 3H,O + (3.76 x 3.5)N; a -b

On a dry basis, the water in the combustion products is ignored. Therefore only the carbon diox~cie, nitrogen and the oxygen ln tile flue cp s Is oi interest. I f IlIe tolai air requirement is represented as Xand moles of oxygen and carbon dioxide in the equation as a and b respectively, then

Number of moles OT volumes of nitrogen involved = 3.76 X x’ X a

Number of moles or volumes of oxygen in flue gas = aX - a. The number of moles or volumes of carbon dioxide (represented by b) can be found from the combustion equation.

Excess oxygen content can be written as follows:

% excess oxygen = aX-- a , ._ _ _ _ _ _

b + 3.16Xa -t (ax - a) . . from the stoichiometric equation:

5.6.4

5.6.4.1

Ca!culation of #ir/r72el Ratios fox S Multicomponcn\ Mixtllre

Volumetric Basis

A fuel to be cornbusted has the following compositon on a percent volume basis of 67% metharre (CK,), !09/0 ethane (C&id and 3% pi-opane (C,H,). The ctir:iuc! ratio for the mixture is to be dctemuned.

(2) (3) (4) Volumetric composition Component Air:Fue! Contribution to filiXli.ltee

-: v9jLme (%) Ratio (Volumetric) Air:Fuel Ratio

..’ . .

(b) CaIc&te the contribution of each component airrfnel ratio to the overall airrfuei

ratio of the fuel mixture from the product of columns (2) and (3). e.g.

Contribution of zz

component aikfuel ratio

Vdlutietric composition X Component

air:fuel ratio

for methane, contribution = i?& X 9.52 = 828air:fuel.

Similarly,

for ethant, contribution = 1.66 airrfuel

for pxoi>anc. contribution = 0.71 airrfuel

Air:fuel ratio for mixture = 8.28 + 1.66 -t- 0.71 = 10.65.

5.6.4.2 Mass Basis

Example l-Gaseous Fuel

A fuel to be cornbusted has the fbllowing mass composition of 80% methane (CH,),

15% ethane (C&-I,) and S% propane (C,Hd. The air:fuel ratio on ;? mass bask is to be determined

(1)

Gas

(2)

Mass cor7position

(9/a)

(3)

Component .Air:Fuel

Ratio (mass)

16.869

(cj Add ihe contribution of each component together to find tile mass air:fuel ratio oi

the 1nixture. ‘.

i~ir:F~;el ratio for mixture = 13.694 -i- 2.397 -1. 0.778 = 16.869.

..,: ExampI& Z--Liquid Fuel

?

This example will demonstrate how io find the air requirements for a heavy fuel oil when the elemental mass composition is given instead of a component fuel composition. A heavy fuel oil has a composition on a mass basis of 86.3% carbon, l1.Oo/o hydrogen and 2.7% sulphur. The air:iuel ratioT0r the oil can be determined.

(2) (3)

Mass Theorclicnloxygen

composition Req~~iremenr

(%I 01 elemenl

c 86.3 2.66 11 41 9.85

l-l ) 11.0 7.94 34.06 3.75

s 2.7 1.00 4.29 0.12

13.72

For every mass unit of fuel, 13.7’2 mass units of air are required.

The following steps have been performed in this calculation:

(a) The theoretical oxygen requirerkkit (column 3) for each element can be determined either from tables or from simple equations knowing the atomic and molecular weights of the elements and oxygen.

For ca.xhon, c -I-- 0, 4 co, 12 m.u. 32 rn.u. 44 11n.u. where m.u. = mass units

- . . for one mass unit of carbon, 32

oxygen requirement = E mass UIIils = Z-66 m-u.

Knowing the oxygen requirern,l --lb. tPc. Lileoretical air ruquiremctit c::n also be

determined (based on the mass cornp0siiion of zir of 76.7% N, and 23.3% O,), then

air requirement = 2.66 x 4.29 = il.41 1n.u.

The theoretical air requirement value has been entered in column (4). To further illustrate *ais CT _ ~icuiaiion, the steps used !or the llydrGgei1 and sdphur vcili also be shown e.g.

for hydrogen,

HZ + 0.50, + H,O 2.016 m-u. 16.00 m-u. 18.016 m-c.

’ . . for one mass unit of hydrogen,

15.03

__x .

;_ ..;. Chapter6. ~ '.- ;

EFFICIENCY

Whenever heat is applied in a process, it is commercially desirable td fully utilise the available

energy which would be released on combtistion of a fuel. Improvements in the efficiency of

uriiisation of ftiel provides fuel savings and consequently, cost savings which are of considerable

beneIit to any energy consumef. The extent to which the available energy is used is normally

expressed in terms of the efflclenq of heat recovery (thermal efficiency) and this is ~rsually quoted

on ;I percentage i~as~s. The overall eificiency \%JouId also have to take into account the electrical power requirement of the process. ‘iThe efficiency desqibes in fractional terms the actual enerryf

[ilat is [raii:;ItZrrCCl f;om the combusiion Aorocess to the process strewn. TlGs can b-e represented

simply by the following equation:

Energy received by desired_product stream x loo Efficiency (“/) zz ---- ----_I ___- Energy supplied by combustion of fuel

In the ideal case where all the available energy supplied by the fuel-on combustion is successfully

transferred to the desired stream, a 100% thermal efficiency would.be achieved-Inpractice, heat

losses occur and it is the aim of the combustion operator, therefore, to mini&se the heat losses as

far as practicable in order to maintain as high an efficiency as possibIe. If the heat losses accotit for

all the energy supplied by the fuel c:ombustion tilat is not received by tlLe ini\+r::‘lerj s:re<am then the ecruation above can be rewritten thus:

Energy supplied in fuel

The energy supplied in a fuel is determined from the product of the fuels caloriiic: u-due and ELZSS

fio?J T&Ii-.

Fuel oil is being fed to a burner at 300 kg/hr. and the fuel has a ilett C~OI%C v,due of 40.2 .&Ii/kg of fuel.

Energy supplied to burner in fuel = 300 x 40.2 = 12 050 MJjhr. = 3.35Mw

Total energy supplieiiby fuel mixture is therefore:

1.1 .I 1.3 = 2.4MVI:

Therefore, for a multicomponent fuel mixmie. the total energy available can be summarised from the following equation:

.

Energy supplied = C,(M, x LCV,)

where M is the mass fIow rate LCV .js~the nett or lower calorific value and i 1s the individual component.

In the example, Mi for each component w%s found from the product of the total mass flow and the fraction of the overall mass which was clue to the component ‘I’.

In calculating the energy availability for combustion, any further additional heat must also be accounted for. The additional, or external, heat may be supplied by preheat&g the fuel (atomising steam input would also have to be included) and by preheating the combustion air su@pIy in a unit external to the fired unit under consideration. The energy supplied.on combustion of a fuel can thus be represented by the following general equation;

Energy supplied. = 2 iM; x LCV, f exter&l additional energy input. ‘.

Calculation of the efficiency maybe effected by perfor?ning an energy balanec-. According to the law of conser-vation of energy, the total energy or heat entering a system is.equal to the total energy or heat leaving the system. The total energy leaving the system Includes all the available heat losses in addition to that heai ieating the system in tie (desired product stream. The over-al1 energy balance may

- be sl~own as :olloi~~,-s:

Energy supplied = Energy Received in desired stream + additional losses

As can be seen, the energy balance has already been used io define the process efficiency (section 6.1).

Using &he above equation, an example of <an effrclency calculation on this basis ~;?II be ShGWn.

. I * d’

. . -

6.3 CALCIJLATION OF EFFICIENCY r

6.3.1 Example Without Preheat

A heavy fuel.oil, having a lower calorific value of 40.4 Ml/kg is to be burnt with 10% excess air- The flue, gas leaves the fired heater at a temperature of 370-C. The composition of the fuel on a mass basis is 86.3% carbon, 11 .O% hydrogen and 2.7% sulphur and 4,500 kg/hr. of fuel are fed to the burners.

‘Jsing the equation,

Encrc;y ~uoplied = M.LCV + cxternaf heat input MC,AT

where &I is the ma;: flo~v rate of fuel 4,5% ?<g/hr. LCV is the lower calorific value of fuel 40.4 MJ/kg

C; isthe specific heat of fuel 1.88 X 10e3 MJ/kg’C (value obtained from literature)

AT is zero since there is no preheat.

The energy supplied is 4,500 x 40.4 = 181,8fXlMJ/hr. = 50.5Mw

The air:fuel ratio for a standard heavy fuel oil is 13.8:l. However, this may vary - depending on the fuel carbon:hydr-ogen ratio so it is u.-;efuI to know how it can be calculated- Some typical air:fuei ratios are given below (‘l’echnical Data on Fuel, J.W. Rose and. J.R. Cooper)‘:

Light distillate 15.09 Kerosene 14.69 Gas oil 14.44 Light fuel oil 13.95 Medium fuel oil 13.88 Heavy fuel oil 13.84

The sioichiometric air require;n2n! ior the fuel c2.n be calculated as follows:

The fuel oil composition is 86.3”/” carbon, II.O% hydrogen> and 2.7% sulphur.

Using the simple equations introduced in the previous section

c + 0, + co, (12 ;:iass unirs + 32 mass un::s -- 4G mass units) H, + r/$0, -+ H,O (2 mass units + 16 mass units 4 18 mass units) s + 0, -+ so, (32 mass units + 32 mass units -t 64 mass units)

then

3,653.S Icy of carbon (0.863 :+ .l,XC) require 10,356 kg ol ox-ygen to produce 14,2X.5 kg of carbon dioxirio.

495 !.:g of iiydrogm (C. 1 ! x 4 ,501J) require 3,9GO l.:ij ol cl::-ygcn to produce 4,Gij !.z<j of water.

121.5 kg of sulph&(b.027 x 4:X0) require 121.5 kq of oqqen to produce 243 kg of sulphur dioxide.

For 4,X0 kg of fuel oil, the stoichio metric o.xygen requirement is 10,356 + .3,$x30 + 121.5 kq WlliCh is 14,4X.!< kcr of o:‘:;~q?~l.

The composi’tion of air on a pzro2rit m ass basis Is 76.7”/L liit:oa n _e and 23.3”/, oxzygc:?.

Knowing that 14.439 kg of ~‘;ygl;~. 7” axe required. for the h?ei., then *ale total ,

stoichiometric air requirement !s i 1.4,4X.5 7 6.7 \

\ x ~3 ) -1 1-1.43’1.5 = 61,964 kg/lx-.

iis a lo”,/, ~:;~c~>ss a.lr feed was ic ijc !~s~:c?, *dle ;I:-< 1-m ._..I’!” <‘lii’,‘ill woi\ld therefore bo S1,964 X 1.1 = 68,1X kg/j21. ofair

‘P 1-L 2 :o!si riass of the product S;;-CZ;I 2i t-he stoiciCoxie~:k ~ruiluirement is i 4 J39.5 kg Co, -t ii;?55 k,g H,O -!- 253 kg of SO, 4~ / 76.7 X 14,fi37.S 1-g >r2 :-: FjG,4G4iig/~.Li:. ii 23.3 :i

At lo”/,, e::cess air. a li’rther 6,196 kg of air are c&I-: ((2ci \,;ITii t-he Froduct Stre,a?IT1 YViliCh is made up of

1,444 kg of oxygen i 6,197 x IO0

23.3 >

and 4.752 kg of nitrogen (6,196 less 1,444).

Therefore at 10% excess air ihe tota products are 66,[:64 -1. 6.196 = 12,660 lig/hr.

(Cl l?\l’f!-!i C P.lcjr 3

Alternatively. the total product mass can be.calcuQted knowing the total mass of feed and applying a mass balance principle:

Total air feed at 10% excess = 61,964 x 1.1. = 68,160 kg/hr.

Total heavy fuel oil flow = 4,500 kg/hr. +

Total mass of feed = Tota! mass of products

Therefore total mass of products = 68,160 + 4,500 = 72,660 !KJ/!".

To calculate the efficiency of this process, the heat loss UT) the stack has to be calculated. Some heat loss through the heater casinys also has to be allov~ed for.

The specific heat for the products can be found from a specific heat chart. (See Figure 6.1, which shows heat capacity against temperature for different excess air levels when firing a heavy fuel oil. A number of similar charts can be found in the literature.) From Figure 6.1 the mean specific heat between 31O’C and 15’C at 10% excess air isapproximately 1.094 X 1O-3 MJ/kcj’C.

Figure 6.1

Flue Gas Heat capacity- qainst temperature

, i.

for different Excess Air Levels

11s

The etficiency is therefore 50.5 - 9.3

50.5 x 100 = 81.6%.

: EtiampZe Width heheat ,

The previous example will now be illustrated for the case when the flue gas leaving

the heater is used to preheat the incoming combustion air to 200’C.

The final flue’gas temperature is determined fro& a&eat balance around the

combustionairjflue gas heat exhanger. The following values are known:

Combustion air flow 68.160 kg/h;.

Mean specific heat capacity 1.02 10T3 MJ/kg’C (obtained from literature) Inlet temperature 15°C Outlet tcmpersture 2CO’C

Flue gas floiv 72,660 kg/hr. klean specific hea: capacity 1.12 x 10-3MJ/kg’C

(average value over temperature range of

212-c to 37d’C) Flue gas exit heater 370-c

Heat balance

68.160 x 1.02 x 1O-3 x (200 - 15) = 72.660 .X 1.12 x IO-‘(370 - x)

x = 370 - -.-Lm.-- 68 160 x 1.02 x 10-3x (200-15~ = 212.c 72,660 x 1.121 x -10-j

Erie:-g;: supplied

Energy in preheated air

= 50.5 IViW -t- enerqy in preheated ai,

= 68,160 x 1.02 % 10-3x (200 - IS)

= 12,862MJlkg -1 3.6MW

Total energy supplied = 54.1 MW.

At new flue gas temperatllre of %!%“C, heat loss tiu-ough the stack is (taking mc;in specific heat to be 1.1 x IV3 i”;Jj!:g’Cj,

72,660 x 1.1 x iO-3 s (212 -- is) = 15,145 Mj/kg = 4.4Mw.

Casing losses assuming Lhe same 3”% loss as previous,

= & x 54.1 = 1.6 INTSV.

Total heat losses = 1.6 + 4.4 = 6.0 IKW.

Combustion efficiency is t!l,~re:ore,

Hea! a;rai!a!3ility at 2 paI-ticl:!ar ccnd.itior! is calcillated by subtracting the c21:i?ldpy

v,lues ui the flue gas prSducis at ihe chosen conditions from the lower calorific va!ue of the fuei. The eificiency can be fourld csiny the curves and knowing ttle lower calorific or neti value of !he fuel.

i :

i i Ii

A r).picaI heat available cufle is she . . . .-~~‘(Figu?e’6.i) for a fuel oil having a “,b sulphur and a loaner con-,i>asiti,on of 86.3% carbon, : 1 .C”/L hydrogen and 2.7

do:-ificvalue of 17.400 Btc/.- , I;- :<O.S MJ/kg), The use af thus graph is illustrated by the fl>:lowing exam?,!e:

&,owmg the LCV of the fuel to be 17,400 Eitu/lb (40.5 MJ/kg) the efficiency of the process at conditions of 1,200.F (650-C) and 30% excess air level 1s thus found to

be:

‘yen fuel oil at 30% excess air with a flue The efficiency of a system burning the (51 gas exit temperature of 1,2CQ% (650°C) wodd be 66.7%. TO obtain a true assessment of the heater/boiler efficiency., 2.-3% should he allowed for casing

11 dficienq of a.l’r:‘c~“i.rnately 64 @A. losses giving XI OVera.

fb) The &icienLy can &o be determined irolrt efficiency against ellcess air CUWeS

at various flue gas temperatures (scL A r’irjlrres 6.3 and 6.4 ior curves for a fuel oil and a refmery gss). The efficiency can be read directly from these curves knowing the excess air level and the operating flue gas temperature. Using the

‘he efficiency can be read directly from Figure 6.5 and same example as in (a), L found to be 66.7 %.

To facilitate‘.convel-~:iol’ c.f excess all Lr2 7 I-vr-Ii i>iiO e:ccess oxygen levC?lS, Figures .-

6.6 and 6.7 have been provided iur a fuel oil 2nd a typical refmery gas on both a dry and wet basis.

) It )) /

,$igure 6.3 Eff’ f lclency C%) against Excess Air (%) fol- an API 10’ temperatures

G eavy FuelOil at various Flue Gas z

95

90

95°C

205-c

!I 5-c:

30°C

,. Figure 6-4 Efficiency (%) against E xcess Air.(%) for a Refinery Gas at various Flue Gas :emperaitires

N-

-__

.‘- -_------_- 1--._\ ‘-I\

‘-,:: _- I 1 I--- 1;-

’ 1 _.I..

1- -’ --._-_

-l- -----

-_-_ --I

/.

20

--T---r- T- - 1 - -- --- 3 --_ --_

- - .J .-I -_ -_ ---. . \

L +..

-I---

-._

205’C

0 ? 0 50

-C

35

205

430

f’50

760

070

980

1090

::\A:, loo

t I

-

00

800

_- 1

---=I 1000

--.-- - 1?00 JO

Figure 6.5

Efficiency against Excess Air for Hea> he1 Oil at various Flue C-S temperatures

_-.-j ----_

..__

-.-

,,/

/4 7---,- /

I r-- - T - _ .-- ----- __.-

i-

I

-.----+-.

Figure 6.1

Flue Gas Oxygen II

content against Excess

Air Level for Fuel Oil 10 and a Refinery Gas on

a WET basis

a

6.5

6.5-I

i

6.5.3 . . . Preheat. r

Some of the energy contained in the flue gases can be recovered by using the flue gas stream to preheat an incoming feed to the combustion chamber before being exhausted to atmosphere. The use of the sensible heat in the flue gas stream to preheat the combustion air leads to an improvement inthe combustion efficiency. This is demonstrated by Figure 6.8 in which the effiency of combustion of a heavy fuel oil is shown at 5% excess air both with and without preheat. The example in 6.3.2 demonstrates the,benefit of installation of an air preheat system.

6.5.“: Dewpoint

When the exhaust system for a contin:lous combustion process burning gas. oil or solid fuel is designed , 1: is :mportai~t :o :2n::?i r:: ~~1~. ” it the tcmuexst~.?rrz ofsurfaces in A contact with the waste gases are no! belc,v: the dewpoint of the gases so as to avoid corrosive attack. The dewpoint is the temperature at which moisture in air or flue gas condenses. If only water is present, then it is known as the-water dewpoint. Water will begin to condense out of the flue gases at about 4S’SS’C depending on the hydrogen content of the fuel. I f a fuel cor.taining sulphur is burnt, then in addition to the water dewpoint there will be an acid dewpoint. The acid dewpoint normally occurs between 115-C and 150°C according to operating conditions.

It is important to ensure that waste gas handling systems and chimneys are designed SO that the inner surfaces in contact vrith the flue gases areBbove the acid dewpoint temperature during operation of the p?a.nt.

100

90

! 5% Excess Ait with Prehear ,

1

Figure 6.13 Example of Effect of PieilC,?l on Efficienq

Ic .., .; Chapter I ,’

PERFORIWDJCE~ ‘.

7.1 PERFORMANCE REQUIREMENTS

The requiiemeflts for the mechanic& construction, perforn&ce and testing of burners are given in the following El Standards:

105 Forced draught burners for water tube land boilers

The performance requirements cover efficient and safe combustion, stability and minimum maintenance during operation. As an example of these, the stack emissions @articulates , NO,, SO,, CO and Hydrocarbons) are monitored for aI1 fuels specified over the required turndown range and excess airs. Stability is checked at all loads and excess airs, and in addition, an out of ratio stability test is carried out to deteznine the minimum fir-ing rate a.: which one fuel wiii stay &iqht when the other is lust, the relnaining fuel being subjecied io very high exce:s ai;,.‘;.i;e burners are given a continuous running test to check that there is no deterioration in corr&ustion, oil cirip: o: coke io-mation anywhere hl the burner or furnace tubes, and refractories.

Burners approved by BP are tested to the requirement of the BP Standard on the Sunbury- liurlrer Test Rig. A report is rhen produced. +-iaqr details of hovr the humer perforn-ied a_;id commenting on its abiliiy io ~lleet BP’s req&ements.

1

t I 1

7.3

Fuji throughput xccj\:ired for S ?CW Iiheration Is

Flow, kg/s = & = 0.1238 kg/s or 445 kg/hr (980 lb/hr.).

The effects of excess air, atomising steampressul-e, !iberation and viscosity on bunler- perfor-mance have been determined esTerimentally for a number oi difierent ‘bur-ners. The results and t.ihe specification for some of tilese burners are tC&ulsled.

7-3.1.5 ‘I Effect of Co+Gjktion- Firing

EIurnerA Burner 6 ”

Comb. Visibk F’la& .‘..: .Comb. Visible Flame Ratio length. ‘tiia’th.’ Ratio length width

NG/HFO (m) (m) NG/HFO (m) (m)

100/o 3.0 0.6 100/o 4.5 0.6

TO/30 3.5 6.5 * 1 .o 0.6 70130

5Ol.50 3.5 0.7 5oi50 7.0 0.9

30/70 3.5 0.8 30/70 8.5 1 .o

o/100 4.0 0.8 O/l 00 5.5 1 .o

Burner C Comb.. Visible’Flame Ratio length width

NG/HFO (m) (ml

1,00/o 3.5 0.8

70/30 5.0 1 .o

50/50 5.5 0.9

30/70 5.0 0.9

O/l 00 6.9 1 .i

When co.mbination &ring the visible iTlam e size increases as the proportion of oil fired illcrease.

Experience has shown that for Burner i., 7 a high hydrogen content in the fuel gas can have the effect of increasing the visible flame leng?h when firing in combination with oil. This is thought to be due to hydrogen having a greater aKinity.for the combustion

_.- air than *e fuel oil.

For Burner B, the visible flame size increases as the HFO proportion is increased but drops when only HFO is fired. This is due to the burner design.

2.3.1.6 Effect of Air Preheat

B u rn e r- C,

NG i-i I-’ {.;I

Combustion Visible iziame air temp. len.cjlh widtjl !,*r.*n;i- I

I-iii<,., I >*,;’ , Cl I h

(‘Cl (ml (nil ( TTI j Cm)

Ambient 3.5 0.8 6.9 1.1

150 3.3 . 1 .o 7.5 i .o

300 4.0 0.9 5.5 1 .o

A definitive relationship between vxxJAe -1-1 flame dimensions and the effect of air DTehEZlt COUld not be dE!;t?r?7.inEd frGI7l il!” d-,:2. ob!;i.~.nncc! rlon t:;e dmve axi other

burners. The relationship may be aEected by the burner design. (Burner D is also a forced draught burner.)

7 _ 3.2: i

Padicalates a, ..: .,. ‘.<I

The smoke seen coming from a slack suggests I& a flame is short of air. The smoke is comprised of submicron &zk,carb&‘particles which diffuse light and can therefore

be se&ii: -. .‘..

Par!iculates are micron size (l,,to. 1,CjOjcarbon cenospheres formed by the oil droplet

not bein$completely combusted.Th.eir s’tie renders them incapzible of diffusing light and thereftiie they cannot be seen 16aSing the stack. Evidence of high particulates can be visually detected at the top of a flame and in some instances breaking away from the’side of a flame. Therefore it is-possible to have no smoke but still have high particulates.

The comparison of particulate levels measured for different burners at a se; test condition v~iil Indicate ivhioh burner is giving the best perf’oxnance. In otl~er words, the burner with the lowest particul+te level coupled witi\ a low smoke n&tier gives the best performance.

Effect of Excess hir

Burner A Burner B Burner C Exces: Air Particulates Excess Air Particulates Excess Air Part’iculates

(%) : (46 At. of fuel) WI (% wt. of fuel) WI (% wt. of fuel)

‘H Fo’ ..: ..i 5 0.40 5 0.36 5 0.38 25 0.27 20 i7 1 :i 2 0 0.1 ij 50 0.23 50 <j!J t:; 5; ‘3 0.10

The particnlates level decreases with increasing excess- air due to the improved 2~r/fuel11~xixg obk.i1ed.

Effect of Atornising Steam Pressure

Burner A Burner Eli 8 !J I- I? e i- r,

Atomising Atomisiny Aiomising Steam Press. Particulates Steam Press. i%;liculaieS Steam Press. Particulates

(bar 9) (% wt. of fuel) (bar g) (% wt. of fuei) (bar g) (% wt. of fuel)

i-i FS 4.6 O.Gi 5.7 (j 2Ej ; . 3 4.48 0.39

6.5 0.40 8.6 0.36 5.52 0.37 - 9.5 0.25 9.10 0.37

Increased atomising steCam pressure improver - , ,tomisation (smaller droplet sizes). Farticulates, which are folmed by the larger droplets leaving the flame envelope without having f&ly cornbusted, are thereby red::c.S.

Viscocity

(CSi)

Burner A Zurnei- I3 Particulates ?a :-? I c L’ I 2 t es

(% wt of fuel) (76 bw oi fuel)

Burner c Pzrticrllates

(% VJt of fuel) , /

._.-- ~.._ ,.. .:. i : '2 c 0 jlik^A. .: .._ - -.

13 jJ r ,-, ,d :- !-: i; r*--r) ,.> ,. i-1 ._I \ , i’ ,.ci-nbilstion air te:xp.

(‘C) Fariicuiaics F;: i 1. i c ‘! I 3 L (i 5

(% wt of fuel) (% w; of :uci j

.ii:mbient Tj.3il -7 0.2 2

150 0.21 !<J ] 6

3G9 0.16 0.13

Particulate levels are seer, here t6 decrease with an increase in air pr-chest. This is due to faster air fuel mixing dtie tdincreased air velo.liFf and tb fastcz Lur~~out due to increased flame temperature.

Nitrogen Oxides

Nitrogen oxides formed on combustion of a fuel originate from two main sources:

- Atmospheric nitrogen (from which the emissions are often termed thermal

NOJ.

i -- Fuel bound nitrogen (from which the emissions arc often termed fuel NOx)

The formation of NO, from atmospheric nitrogen is related to the intensity

(tcn;LTerature) of combustion. [he availability of oxygen (excess air levels) and

nitrogen residence times in the hottest combustion zones. The formation of IVO, from

frrel bor:nd nitrogen is related io I!le cjuantity of nitrogen present in tire fuel.

The rabies in sections 1.3.3.2 and 7.3.3.3 show that NO, can be rednced by

decreasing atomising steam flow and increasing viscosity. This solution however is

not acceptable because both have the reverse effect on particulates which are

increased thus making combustion less acceptable.

1.3.3.1 Effect of Excess Air

Burner A Burner B Burner C Burner D

Excess Excess Excess Excess

iii: NO, Ai! I\: 0 Air N 0, Ait i\! 0

(o/6) iiwmvj (%) (ppf?-h)

(T&j (ppriw j (yG>j ’ .( j~pf-lv)

ii FO 15 183 5 235 ., c. 145 5 2 4: ‘ !

25 199 20 249 20 21 5 20 315

50 186 50 205 50 185 50 257

NG 10 96 5 34 5 39 5 59

25 70 2 0 39 20 45 20 6 i!

50 43 - - -

iNO: levels increase kth csccss air IO a peak, and then reduce. The increase &I j.,JDz

is due to the availability of excess oxygen. However, eventually. the introduction of

further excess oxygen ieads to a flame cooling effect and hence a reduction u-t iu’OL

leve!s.

1.3.3.2

Brurner D

Atomtsing Steam Press. NO,

(bar g) (p,pmv)

6.3 209 3.3 257

Burner t3

Viscosiiy i;J 0

(cSt) (pprrw)

15 2 8 0

30 2 2 :i

Increasing fuel viscosity leads to a reduction in NO, !evels due to the poorer fuel

burn out and hence louver combustion temperatures achieved.

Effect of A& Preheat

Combu$kn’air Burner c -NO,

(ppr&) Burner D

temp. (‘C) NG NO, (wmv)

HFO NG HFO

Ambient 39 145 59 241

150 48 161 80 295

300 72 259 125 340

increasing combustion air temperature results in an increase in NO, levels. This is

due to the contribution of the extra heat input to the increase in flame temperature.

EFFECT OF FUEL OIL PtiSSURE, ATOMISItiG iTEAM PRESSURE

AND IJBERA~ION ON STEXM CONSUM$TION

The relationship between 1he above parameters and effect on steam consumption

will now be demonstrated with experimentally determined values for some burners.

(See also Chapter 2 Oil Rtomisation.) Steam consumption is represented in terms of

th’e ratio of the steam to fuel oil flow.

Peabody Turbulent Chamber Atomiser

This atoliiis?-i operaies :.;i:h ;i . ..~.I;.c- f-i 7 c r?rit diIferen!ial pressu- i ~c iln vihic!I the ntornisin~

steam pressure is kept at approximately 2.5 bar above ~.he fuel oil pressure.

EXCtZSS Fuel Siesrr Sre;!m

Air Liberation Flow Presstire Flow Pressure Consumption

(“/I (%I (kg/hr.) (bar 9) (kg/hr.) (bar 9) (%)

20 110 469 5,9 71 8.4 15.1

20 60 253 3.2 51 5.8 20.2

30 34 141 1.9 41 4.5 29.1

The fuel oil pressure, atomising steam pressure and steam consumption have been

plotted against liberation in Figure 7.3.

Atomising Steam Pressure

( -..-- )

Steam Consumption

(‘36) (- - .--)

Figure 7.3 Fuel Oil pressure, Atomising Steam Pressure, Steam Consumption (%)

against Liberation for Constant Differential Firing Heavy Fuel Oil

7.4.2

. . . . . .c

-Earn-worthy Internal Nokzle IHi* Atomiser. ” ,

This atomiser operates with a.constant aiomising steam pressure (in this case 8.28 bar g)-

EXtXSS Fuel Steam Steam Air Liberation Flow Pressure Flow Pressure Consumption

(%I (%) (kg/hr.) (bar o) (kg/hr.) (barg). (%I

50 100 620 6.4 106 8.3 17.1

50 GO 372 4.6 106 8.3 28.5

50 33 214 3.2 101 8.3 50.0

The fuel oil pressure, atornising steam pressure and steam consumption have been plotted against liberation for this atomiser in Figure 7.4.

To conclude, for applications where the burners will be firing mainly on turndown or incombination (oil and gas fired simultaneously), the savings in atomising steam provided by constant differential control should be considered. The supplier must demonstrate however that this saving is not accompanied at the expense. of an increase in particulate emissions.

Atomizing Steam Pressure

(------- 1 t-*52

50

45

40

35

30

25

2 0

15

10

5

There are tvro l~ype’i of Airoil en~ulr;io~~ :~ypc atolnisers:

A SAR COIlsl2nt differ-ent.ial pI.essllrr: 2;c~ri-1iSeI- ii1 W hi& the atomisinq 5tcrnrn !?rcssure

is kept at approximately 1.4 bar a.bove the !-uei oil pressure.

A Dual Stage constant atomising steam pressure atomiser. The Dual S!age atomiser uses low pressurL 3 3 -team at constanr pressure and requires a higher oil pressure. The different atomisbrs are shown in Figure 7.5.

Figure. 7-5 S.A.K. and Dual Stage Oil Guns

, Swirl diw

SAR Atomiser ,I ~ ‘..I.cess Fuel :.; 1. (?,i, j-i-# Steam

* PLli Liberation Flow Prf3StJE Flow Precs;!!re Consumptiori Particulate (yJ!,ii (%I) ; (kg/hr.) {bar s) \‘\J, I, ., /lrr /I,,, \ ( b i , -1 ‘) (“XJ” ,

25 110 256 -4.3 78 5.7 30.5 0.27 25 60 138 2.1 50 3.4 36.2 0.40 30 33 79 1.2 45 2.5 57.0 0.50

EXCXSS Fuel Sieam Steam Air Liberation FIOW Pressure FIOW .P:essuie Consumption Particulare : Q/ ’ \,@I (%) !kg/hr.) (bar c]) (kg/hi.) (bar ~1 (5%).

25 110 253 13.7 40 2.4 15.8 0.46 25 60 170 6.8 40 2.3 23.5 0.50 30 33 81 2.E /!5 2.2 55.6 0.32

The results for the hvo different atornj%ers have been platieci 111 Figures 7.6 and 1.7.

3.5

To concl[lde. if particulates at 110% load and 15% ex’kess air are compared. the parriculates levels for.the Dual Stage atom+zrwe;e found to be SO%greater than that for the SKR atomiser (0.59% wt and 0.40% b? wt of fuel burnt respectively). VVhen the atomking steam corkumptick of &Dual Stage atomiser was increased from 14% to 18%. 12le particulate level was found to be only 22.5% higher (0.49% particulate level). This would app&r to indicate that’the Dual Stage atomiser using a higher steam rate at fuIl load should at least match the SF@ atomizer. The particulate levels 0x1 iuinciowrl were 36% lovrer for the Dual Stage (O-32”/,) t?ian COl- the SAR atomiser (0.50%).

The comparative data provided in this section covers only four of the many atomisers whit!: 11;iv_: _ e., i‘ F, rn testci! under various operating conciitiox ,-ii Sunbuiy. John Zink submitted five different types of atorniser for test with their iMJik20 natural draught burner.

There are detailed performance reportsav+&le for all the bumers/atoeers tested on the Sunbu+ bum& test rig.

‘HEAVY RESIDUES FUELS

The dx~ve vd!ues were obtzLned with fuels supplied at IS cz: 3: the burner, apart from tile vacuum residue which was supplied at 22 est. The results reflect the etira aronking steam and excess air levels required to ex::re satisfactory combustion of

the poi:;cr quality fuels.

(a) that all burners are correctly installed and ale in a seryiceable cunclitlon

(h) that operating instructions and performance graphs for the burners are available.

(d) inspect the heater/boiler to find possible entry points for tramp air. A smoke bomb test will detect these entries and +Aey should all be sealed in *he latest approved manner.

Start-up procedures are or should be given til. the rnanufacrurers instmctior~ and, for fired heaters, in the BP handbook. However, to ensure maximum efficiency, the following points are worth mentioning.

8.1.1 Fuel Gun Sizing --

It is not uncommon for the manufacturer to incorrectly size the oil and gas cqms or perhaps the fuel composition has changed, tin requiring different operating pressures. When, due to fuel pressure Lritations, it is notpossiblc to achiev- fX1 1 ,ocd, the opera:or is immediately on the phone :o ::he manufactiircr as!&:-.g for larger capacity tips. U full load is achieved at a lower pressure than design, nobody seems to notice. Occasionally a complaint about poor btimer performance on turndown is heard, but in general the burners are accepted and carry on operating for many yeaX3.

As vii11 be aonreciated, operation with low iuel pressures wiU affect oil ilring far more *an & firing. Ato&sers designed to operate at say 6 bar i;ave bzn found to be operating at 2 to 3 bar. The result of this rS lower quality atomisation z~d, in an attempt to obtaLn satisfactory combustion, higher atomising steam flows ??nd higher excess ;i!T are 1rz;12c!. _

i

I f the burners are new and the actual operating pressures do not confcjrm ~tiLh the agreed operating conditions and manufacturers graphs, insist that the correct tips are suop!ied. if Lhe equipment has been in operation for some years and is therefore outside aq gu;:; 1 antete period, omtain lrom the :malTi:i’actll ;e.rs, new -co rrec:1-;,i 2.-.- .i-&

:ips.

8 . I .2 Fuel Distribution

AS the object is to operate%‘& low excess air and give an even heat disiribution within the furnace, ihe correct distribution of fuel and air to each byrne-r is importmt. Fuel headers and combustion air duqting should have been designed to ensure good distribution. Undersized fuel hea’deis’will give high pressure-drops resulting in the pressures at the lurthest burner being lower than at the first. %t un~!cr.Ged burner fuel header with the entry at one end could be modified so that the entry is in the centre of the row; the initial&w rate in the header wG then be 50% qi the original. An alternative method is to fit orifice plates or trim valves a; each burner to give equal distri’bution.

8.1.3 Combustion Air Distribution

When a heater is changed ov$r,tcfforc,e.d draught bqJ?s,qs and ai: p&heat,-the combustion air ductin,ghas.to:be.fitted in the space available and h’iglkr than normal .

Fuel Conditions

The fuel oi1 system must be in a serviceable condition- The oil must reach the burners at the correci temperature to give a visco.:iiy of 15 tit. Trace hea:ing lines and steam traps mus! be maintained in correct working order. Lagging must be in good condition and the pipework lagged right 1.:~ to the burner-. This aiso applies to atomising steam lines and fue1 gas hnes (wi:zn iiquid carry Over is poss&!e). One of the major causes for bad combustion is wet atomisingsteam. This steam may have been superheated at source but by the fine it reaches the burners it can be wet.

A useful-item to have is a fuel oil gun whidl has been adapted to monitor both the pressure and temperature of the oil ancl s;S,mising steam. (See figure 0.1.) This gun can then be moved from burner !o bc-::-l~~ :o &ec!c conditions. I;’ *he conditions of the fu‘els are not correct then satisfactory low excess air combustion cannot be expected.

Figure 8.1 Oil Burner Gun with Pressure and Temperature Gauges

ATO&,lISING MEDIUM INLET BUSH

OUTER PIPE ( ATOMISING MEDIUM ) /’

INNER PIPE LOli I

?iYne burner must be checked for cosreci fhmi. ._ 1 crability under all possibie operating conditions. When a &me is unstable the flame root lifts away from the burner front then returns. This happens usually several times per second and it is accompanied by a dramatic change innoise level and with \&ration of the furnace casing. In extreme cases the flame may establish its& some distance from the burner continuously moving but never completely back to the burner. Wh .b n a flame is in this condition it is extremely dangerous and XI-~ small ch,ange in operaiing conditions may bIovr it out.

It is reassuring to see a flJme burning right on the fuel gun tip and many burners operate in this manner: It is howeve, r no: inco:rect for the flame to start burning several centimctres from the tip provided it Is stable.

Reasons for flame instability are covered in the chapter on trouble-shooting. Checking a burner for stability should be carried out at-the burner maximum firing rate and over the agreed turndown range with maximum and minimum excess air. Instability is’usually associated with high excess air,.but it has been known to occur &hen reducing excess air, the flames being stable at high excess air.

8.1.6 Fuel Filtration

Du;i~~g the first iel:/ ii;;;:; or Eve n weeks 0; GpeFc?tiG:l, bloCkage of fIlei gCi1 iii-a; (:,i:L c2llce a major mainten once problem. This shows up as distorted and uneq!“<~i i?Lirncr; with an increase in fuel pressure without an increase in flow. The fuel filters C~CL’ normally positioned upstream of the fuel controi valve and therefore cam-Lot ~::move debris, such as welding- slag, in the downstream lines. To prevent blockage;, new lines and lines upon ~lhich repairs have been carried out should be cleaned b:.:ol-E

._

i

The problem is more pronounced on small burners with small diameter jets and a solution is to fit commiSsioLtig filters which usually screw into-the oil gain &elr;. With some atomisers such as :‘jets, it is advisable to fit these on both the oil and stecVn side.

For gas tips, due to the larger jet diameters, the problem is not as common (see Chapter 3). however for small gas burners a Y type filter can be fitted adjacent to the burner.

._ ̂Very fine particles can pass through a correctly sized’filter. later lodging in valves or adhering to pipe walls. These fine particles will conglomerate together ior;nLng larger particles, which will eventually break away and carry on through the piping, finally Iodging 111 CR? tile! jei. ShGillC! his prcblern e;;ist on a fuel system, Lhcri Lhe source of the fine particles should be identi,fied and if possible, corrected. if noi, then it may be necessary to fit a small filter at each burner.

Partial blockage of fuel jets makes satisfactory low excess air operation impos~;ibLz. It cart cause damage to burner parts due to flazte Distortion and coking. Distorted flames cm impinge on tuk?cs csusiilg ovefhe sting. Add to this the increased

mmtenance costs due co the need for continual stripping and cleaning of fuel guns mci replacement of damaged parts. The cos’t of all Titus should justi@ tilroving the fuel system filtration.

AS is shown in Chapter 7 {Performance) particulates increase as’excess air is reduced when oil firing. Ignoring for one moment the local authority limits on emissions, if the excess air- is reduced until the particulate emissions are high, efficienq is, in the short term, increased due to low excess air op&ation. Ln the long term, however, the eificiency drops significantly (about 3%) due to increased fouling Of convection SCctloIl iUl3~~S.

.

Modern forced draught burners are suitable ior operation with acceptable combustion at 5% excess sir. !fiJhen several are fired together, making allowances for small variationi in fuel and ai< flow, 10% excess air in the combustion chamber IS possible. For natural draught burners suitable for 15 76 excess air operation, 20% to 25% excess air .sijoul+,Qe possible when several are fired togeil?.er. These excess air levels are based on the air flows through th$ burners ?nd d&, not,l,nclude tramp air. ._ As the inside.of the heater is a! a $igfi! negative prez+ure,,,<,$ w’!‘,be drawn through any opening. Heat&k n&uiactu.rers Live not, in rh’e past, paid much, attention to

8.3

_-

8.3.1

ic iz assumed that the burners fitted are of a t-;ii?t? ~&lct~ ha.-; i ‘xen test&c Xld a’p”:!.c?vc-d at the Sunbury Burner Test Rig to the BP standard. Copies of the relevant test reports are avSl’5ble and it is advisabl6 to study these prior to optimisation. These reports give detkils of the optimum conditions determined and should be checked against conditionsrecommended by the burner manufacturer. It has been known for the burner manufacturer to advise wrong conditions, such as atomising steam pressure, to the refinery.

-Y.----L.’

Lfpressures and temperatures are not monitored at or vei7 near to the burner, LFEXL a specially adapted fuel CJLUI canbe obtained. ‘I’ll; pa x41 be fitted iT;i!h prssure gauges and thermocouples and is moved from burner to burner to check conditions. S’nould a variation in the pressures of the fuels ;illC: atomising steam he found (in excess of *Z2/2%). then it is advisable to fit or&e plates or trim valves. If this is not ~pxsible then the combustion air can be adjusir-d IO co.r.,~pensate for ;i\iS V~LriaLion providing +Ae resulting uneven ‘neat distrikrrricxx :S axe,prC201e.

&fore attempting to balance the burners. check all fuel guns axe c1-3an, with no debris present in the jets. I f this is not done it may all be a waste of time.

The combustion air for forced draught bumel-s, being supplied via ducting from a fan, can be trimmed using the intividuai burner isola5r~~ dampers. &A pressure qa~:je 6r water manometer is used to checlc the pressure in each windbox. This pressure must be added to the draught ITT~~~SUI~ fi at tile heater floor @e:zrt& &casght)

to dete:tie the burner register draught !o:;:; (XDi,). There itG17f be 3 slight variation Ln heater draught so it is advisable to moiiitor it at sevzrni positior=. this can be done by-using a gauge or inclined manometer 2nd a long probe.

The procedure for setting the stops on the burner air dampers is as follows

1. Determine the burner register draught ioss for the burners at horrrd liberation by referrit:g to the burner manufac;u;eri; ciwr~s i LL I- -j--d set the comiiustion air fan damper to give this pressure at the burners.

Note: Combustion air should be balanced before the burners are fired and then r&checked once the burners are firLng at normal liberation under balanced conditions. However; if &&heater is already operational, the baLancinq can still ‘be cariied out. The heater should be at normal load or just below it anh the com&stiori air set to Give d&i@ excess air through the burners at normai load. Should there be a slight descrepancy between the measured RDL and that shown oti’ihe ~;rner’n;an~i~ciu~~~~‘~h~~~. then use the mkastired RDL. If the ‘di&z~~pa’nFy is la?g& i&fei thkptobl&!m back to the burner-manufacturer. ,. I- ,- ‘.

4 Adjust the stop on eaclt da:n?c: so that the damper ~a.17 only be opened to [he siri position.

5. Once satisfied that the balancing has been correctly carried out a tack weld can be applied to the stop !o prevent it from being inoved.

Note: Ii balancing is carried out before firing +he heater the EIC% weld should not ‘be -. applied until normal load has been reached and balancing checked.

This procedure relies on *he fact that alI the burners are manuiactured to the same dimensions; hence the air flow through each burner should be the same. If once balanced, one of the &zrnes !ooks .short of air then chic!.: the fu& and atossing steam pressure to that burner. ii everything appears correct, open the burner air darrper slightly to improve the flame andi when it is next possible to enter the heater, check the burner dimensions.

8.32 Balancing Air (ND burners)

Combustion air-is drawn through the burner by the draught (suction) in the heater. Compared with a FD burner the XDL is very low, normal?y til the region of 10 to 15 mm W.C. Owing to the design of conventionaiiY2 burners it is difficult to 1Lse the same procedur’e, b&id on RDL, to set the burner lo~~~res TS recommended for FD burners.

Any variation of hearth draught will affect the air Llow through the bum&s and on a long cabin heater the draught mayva.x7/, being h?‘g+.er Ln the rr,iddl& th& at the ends. This variation will be dependent on tie design of the h.eater- and the position and number of flue gas outlets above the convection section Bakncing the combustion air on a multi burner heaier is &rried out pr;LmaAy fjy visual i&pe&n of the flames aided by a knowledge of the hearth draught variation an-d then r&f&ed by probing the top of the radiant section at several pOsitioi7s for oegeti.Ad combustibles.

As the balancing is primarily visual it will be easier to carq it oqt whilst (if possible) firing fuel oil. The oil flame will smoke when short of air azd the visible flame length will shorten w,ith high excess air. A gas flame length will also vary with excess air blut will not norm&prqduce srr~.o!~:~ :vi en sikor; 0I z&m FI

1. Wit21 all the burners aligh< and firing at noIms1 liberation, set the draught ~der the convection section to 2.5 mm T.V.;. The hearth draught should;ifthe burners are the correct size, induce the necessary combustion air. ’

Note: The burner regLt@r air louvres should be almost fuLly openat design maximum liberation with the correct hearth draught. i

2. Maintaining the correct r!raught conditions in 61% heate;, adjust all’the burner air louYvres to the same position and to give XI c::cc’ss oxygen !evel,of about 6% at the heater exit or the minimum oxygen level above this where no.fl+mes are smoking.

Note: For burners witi separate primary and secondary air control, the primary air is set tq gi-ve a stable oil flame. The secondaq air louvres will,correct the excess air..Use a.steel ruler, or calipers to cl7eck that all the louvresaxe set the same. ;.._-,, .

3. Check’t~e-‘hea.rt~‘drau’g~7t.at sevei-al positions along th@~h&ai&~I‘~ihe draught is lower in &iiaiii-$gas.this must be allowed for whe.& adjusti~~:~~-l~uvres.

8.4

8.4.1

8.4.2

5. Close the air louvres on each burner in turn. by a smal! equal amount. vis~lally checking the f!ame. When a flame’shows smoke, open !he air Iouvres on the lhrlrner by a srnalI amount until the flame i:;‘ciear. Rctpcs! thi

:__ 5 excrci.sr as m;iiii,-

times as is necesssq to achie ve mnumum excess ,371r ope:-,3 tion with r:atislac:ior y combustion. Maintair, the heater draught at the correct conciition.

No:e: When there is a hearth draught variation, burner-s in the low draught :egion will need their air !ou- ii-es open further tha:~ those i~n 3 high d.--.?i;rc;hr r3$011.

5. Whe~n the halancing exorcise ltas been completed , that is, iminimum exci,‘ss ~.iir operationwith satisfactory combu’stion,~note a!2 operating conditions on the heater including the o:cygen and combustibles at the top of the radiant section.

Luck all louvres in Position ,utd mark the position on the register; keep a record of CL” lo*avre posi[ion L0.c ’ .,f;2_211 tllri:er, This exercise ial! bc! r-epeati-ri 7.: several dZferent heater loads, keeping a record of the louvre positions The burner louvres.can then be set to the recorded positions as heater load changes.

Should the louvres be aLmost closed when,set for normal liberation with the correct hearth draught, ‘hen the burners are probably well oversized or there is excessive air inleakage. This must be investigated.

Znould it be necessary with the air louvres fully open, to increase heater draught above design to achieve the correct excess air level, then the burner-s are probably undersized. This also must be investigated.

Prevailing weather conditions, and high winds, can upset the air flows at the burners. When this occurs, a wind shield can be erected adjacent to the heater to reduce wind,e&,ects.

The combination burner is equipped to fire both oil and gas singly or together. When a heater/boiler is fitted with a number of combination burners, there are two i3 zthods of operation nom~aJJ~- 72sed. The first is ko fire oil 2nd gas on sepa;aic burners. The second is to fire 02 and gas together on each bu.rner.

The time and effort spent in balancing air and fuel flows to each burner can quickly be rendered useless by adopting this method of operation without keeping i: under stric? control. When both oil and gas are fired on a heater, the existing method of control is usually that one fuel is selected to be automaticaLly controlled by the process load and tie other is adjusted manually. To operate with low excess air it is necessary to have eq~~al file! and air to each burner. Therefore the manual.!y col-~L~ollecl Lh~el must ix? x~j:j~~txl to match the controiled iuei to ensure ail burners are liberating at the same rate. The fuel oil ivill ha% a fairly consistent mlorik m.Iue but the dorific value of rehem; gas will vary from hour to hour and, unless a caIorliic value meter is fitted, can oniy be determined by sending a sample for analysis. Knowing the calorific value and flow for each fue1, the total liberation is calculated. The number of burners firing either gas or oil is set to ensure that they are aI1 liberating at the same rate. To maintain this balance, it will be necespary to change burners from firing one fuel to the other, subject to the availabilty ofkach fuel. TO

ensure. as far as possible, that the heat is distribute d !kfordy within the heater. burnersiiring oil and those firing gas should be arranged alternately.

Combination firing

Firing of oil and gas together on each burner facilitate s a more labour efficient method of control. The manually controlled fuel is set to provide a base load which is equally distributed to all burners. The-automatically controlled fuel is modulated to give the required process heat load. Every burner will be liberating at the same rate and it will not be necessary to change.over burners from one fuel to the other to ., _. maintain a balance.

The fuel gas pressure is used to inspirate the combustion a.11 using a venturi and jet system. Additional air is induced via secondaryair louvres by rhe furnace draught

Rz cl. i ;> . $11 v,yal! bur-ners may radically be found i.n an ethylen- ~::raclie:.+ f~irnace where large numbers of the burners are situated arranged in ~G:vY;. Vt’ith such a large nuder of burners, it would take a considerable time to set up a furnace by adjustment of air to each individual burner. A generaliscd procedure for balancing radiant wall inspirating burners will now be given. It is to be noted that a similar baiancing procedure can also be followed for forced draught radiant wall burners.

l_ Carry Out preliminary ‘as found’ survey.of the operating furnace. Check burner-s are complete and in good working order. Check all gas jets are clean and correctly sized. Take measurements of excess air levels/combustibles and draught at variouspoints, both horizontally and vertically within the furnace. At the same time, the position of all burner air louvres and the stack dampers should also be noted.

The excess air and combustile~ levels are mcnito i:zil using a p”rtable gas zna!yser and a probe for inserting into the ,krnace. I\lOrmal sm,all bore stainless steel tubing is susceptible to bending in the furnace heat. Care should be taken to ensure that the end of a tube does not fall dire&y into a burner flame or.near process tube entries as misleading analyses wiLl arise. The use of ceramic tubes for s.~mpling would provide an alternative so1utio.t~.

‘i-3 _ ,?e i'u~x~ce should preferably he set up whilst <>pcraiktg at or near full load and under s&&y conditions, i.e. no change in load. The kinace draught will be set to be slightly negative at the top of the radiant section and under the convection section. When the~optimum burner settings for each burner level are found at this load, the burner air settings kill be at their posiiior-1 of greatest flow.

2. Examine results of~preltiinary survey analyses and determine manner in which burner combustion air adjustments are to be commenced.

The survey ITBY reveal high Orqyen at the hearth viltIh combustibles present at the upper levels. I f balancing vlas commenced. at the hearth under these conditions;excess air Tvould be reduced and t. J 7~ er: more ~oniou.s%ies WOLIM be produced. Therefore, combustion air to the upper level burners will have to be increased to a safe excess air condition prior to commencement of burner combustion air adjustment at the lower furnace levels.

lf a reasonable excess oxygen Ievel is found throughout the f&ace at all levels, then balancing of the burners can commence with adjustment of those at the lowest level.

2a. If low excess oxygen levels are found, then the following will have to be performed bef0r.e balancing of the furnace can commence.

Adjust the primary air door of each burner to allcw up to the maximum inspirated air. I f further air is required then this is provided by opening the secondary air doors. The primary air door should not be opened any further than that position necessary to provide maximum inspiration- This allows some protection against air fluctuations at the inspirator inlet due to gusting wind.

3.

adjusted according to ti:e draught and excess oxygen values at each burner level. At the higher b\lzn+?r ! e~:cls the draught wiil’ne lower and therefor-: . the sir doors will have 10 i;e lurther open. Rdjustir?cj burners !o reduce excess oxygen through tht: iurnace will.+lso affec; t‘ne draught conditiom. It is therefore necessary !o r;lAintsin a regular chec!< on the draught, adjuscinq tite stack dar+er :,/he2 r>~;i-~::s;l.ry.

The draughr will bz hiyhc-3 <?Z ihe bottom row of burners. The draught wili

assist the iILS”$iKCltOI iI1 >I ~;~i:ding the necesscr ~-~r sir. Viith !he inspirator sic adjjtstor fully OE)~IL, ailL I!IC :;tco::dary air doors, say, half open on the botCom PC%/0 ros~i; ol bI!r7i:ri:, checlc the’&yqen and combL!stihle levek asing the portable anaiyjs*;r. L’ the burners have been correctly sized for- :;l~: duty, the measured o::>i<wjc;l levc! will be high CLI~CI it fill be necessary to reduce the cbmbustior; air by first, closing the secondary air door and secondly, by adjusting LIP inspirator air adjustor.

Wheti a r&asonable (. ex:.:-ZT.T oxygen valukhti been established at each burner I&vel, thei? I3a’ i=ncl~~~ GL me burners CDTI cOYr:n:ei:<::::. ‘3 -’ : ”

With a safe level of excess.oqgen established throughout the iurnace, con&u&on air to each of the burners at+e IoMest level is altered by first reducing the secondary aiz AII~ only after the secondary air is closed, reducing the primti’iy’air to obtain a p-,eliminary &.ie. of~Z-4°/o excess oxygen at that level.

When the r,equiTed oqgen hs~ been establ&ed, progress to the next level oi burners and carry out the shoe procedule..Wqrk progressively up the furnace until all thk burner air flows have been a&@ !b,provid& 24% excess oxygen at each level.

Having adjusted excess air levels, reduce arch draught by closing stack damper slightly and monitor draught as adjustment is made. For optimum operation, an arch draught of approximateiy 2S3.5 mm W.C. should eventually be airned [or.

Carry out further f&l survey from bottom to top of furnace and adjust burner combustion air flows iC0 r e 1. lmely to obtain required lower excess air levels at each furnace level without showing high cdmbustible (over 200 ppm). -..

Recheck arch draught and adjust stack dampers accordingly.

Recheck excess oxygen throughout the furnace from bottom to top and LTC~,{ adjust burner combustion air ilows a s required. Recheck arch draught.

To achieve a reasonable balance of the burners; the furnace should be traversed, performing the adjustments and monitoring, from bottom to top at least three times. To ensure &er tuning~of &he fU~ilaC+Z, fsur sad possibly five complete surveys may

be necessary- Sett;rs up of a furnace containing a considerable number of burners is therefore quite a time coilsumk~g task.

After completion of khis exercise. ;h,e ~2~ ’ Anced furnace will consist of burners with the following settings: primary ;u, ‘I doors of all burners at up to pre-deterrnir~ed rnaximurn; secondary air doors fr(>iii dosed $nd then progressively opened thro?lgh. the upper reaches of the ium2ce where the draught is lower. As an aid, the settings of the primary and secondary air doors at each burner should be marked or recorded.

lnhereni burner fault

Incorrec! burner selection

?YkLX~d2CllKLrarJ error

Incorrect spares fitted

Incorrect installation

Burner duty changed GoA design

Fuels have changed

Control faults

Operating condition& incorrect

Bad maintenan&

Worn burner parts

Cpnrator error

I: Lhe a.bo~e !.isi is now considered, oniy the first cause is the ~.ciu~J, faxIt of the bummer. BP Standard 101 coupled with the test progr amme carried out on the Burner Test Rig (ETR) at Sunbiiry has provided us with precise information on the performan ce and reli&~ility of a number of forced and natural draught burners. Burners now h&g installed should be selected from those approved by the Surtbu~-f tests. There are a large number oi bamers that were Installed prior to the B’i’R programme which do have inherent design faults and in many instances replacement parts are available from the burner manufacture? which will rectify the fault.

The Airoi! iirtimzc andJohn Zink natural draught burners ori~%naLiy sufi’ered from oil dripping and co.kLng in the primary block. This was found to be due to the internal s&p-2 of tip,= :>I.or: 1; i\Ot allowing for the recircuGtion~$tl&n at the root Of the flame. The proS!eru VKG overcome by changing Lhe inte,qal &ape to allow ior recirclxiation. There are however many burners still ir~pperation which have the original prim.ary blocks.

The Hamworthy LU range.of forced draught burners had the problem of coke forming on :he swirler. This showed up during the long term run 250 hr.) on the BTR.

i Hamworthy attributed the problem to their use of a flat bladed SWI Ier and changed the design to a curved blade. The curved blade swirler was tested on the JjTR and there were no coke deposits foxmed.

Most problems are operational’ , such as: iow combustion air Row causing smok or

high combustibles; bad combustion due to low oil tempe,rature or.wet atomeing steam; partially blocked oil or.gas guns. These can be resolved quickly by iaking the relevant actions as given on the fault sheets. When a problem cannot be resolved by taking the necessary-actions, it musi be investigated in detail.

C~IAPTER 9 -.- Page I

9.3

9.3.1 Fault List Index

._ (b)

(z >

Burner has been correctIy selected for rhe duty and has !3? approval (Sunbury BTR).

Burner has been mannfacrured corruct!y and inspeci?u:~wns carried out before di!TAp:t,~:h.

2:urner has been instaliec’, c3,::recrly a:lC: the positicn ot :l!e i~.!el ~iuns, stabiliser .d (swirler), primary block and quarl d!mensionally checked Sciore the corib~~sticn chamber is sealed.

If the above is found to be correct th<:n refer to the fault sheets

Exis tirlg i-~nrnexs

Burners which have been operadn g sz..tisfactor-ily for a pe:i.oci ‘o-iole tile problems otxur, can normally be rectified by referring to the fault lists.

When changing burr& duty or fuels, it is advisable to ask +che m.anufacturer if his equipment will be suitable before m aking the c^hange. It is probable that he wilI recorr:lencl replacing fuel gun tips arrd possibly other bui-er parts ?o ensure the burner will perform correctly under the new conditions.

THE FAULT LIS;rS

These lists cover all comrrq burner iault~. When usin rhem go t;rirough the ‘first check list’ tiien ii the problem persists use the ‘seconcI chcci: ikt’. ,There k 20 fault hi covering vibration other than to refer to sheet 6 ‘flame u;rstable’. Should a vibration problerr\ ;Ipi;ear not to be due to Ls~aAil?ty ti:\ei1 tiie pro’blem should Se referred to zn experienced engineer.

I

I I

PJLOT

Sheet No. Fad:

1 Pilo: wiu not light

---

2 Pi10 t flame urs:abIe --_ 3 Pilot overheating 4 Pilot will not light main flame

Sheet No. ran1t

5 Will not light 6 Flame unstable 7 Smoke from flame 8 Sparklers in flame 9 Flar;le distorted

10 Carbon build up (dripping)

Sheet No.:. .X‘?Ult

11 Blocked atomiser jets 12 Blocked gas tip jets

4. If line has been nitrogen purged, i0110w instructions in

%Ie Operation of Fired Hea:ers h.andbook to ensure nit:-ogen is cleared from the

pilo! gas system.

5. Check burner combustion air flov; (XDL) is set at manufac- turers recommended start condjtion.

6. Cp,ec;: e!eccric igniter is

nperating correctly and that the ti0 is located in the correct

posiiion for pilot ignition.

(a) Check pilot against manufacturer’.; draWtilgs.

(h) Check all jet diameters.

9. If information no: available:

(b) Check against an identical pilotwhich is firing correctly.

10. Clean pilot gas fi!t0rs

13. Reduce burner contbusiion air llow(RDL). For FD burners a RrlL of 50 nun shoulc1 h!

sufficient.

14. Adjust gas and pilot air pressure by a small amount

one at a time.

15 Lf pilot gas is off spec. calculate pressure required 10 give pilot design liberation.

16. Contact manufacturer and/or Engineering Department. London for advice.

Figure 9;1 Normal PiIot Flame .

----__-. __-- __-

Second Check List Pilot still Faulty

Replace if suspect

(c) Pilot gasjetr~.

8. Lncorrect part could have

been fitted.

(a) a!eck pi!c c ?-~~LixiS:i manufacturer’s drawings.

@) Check all jet diameters. - - ‘-j.’

9. Lf information not available:

piiot iiesicjn iiieratio;

(a) Request it from manufac- turer.

(b) Check parts acqainst a pilot which is operating

1-i. Contact manufacturer and/or

correctly. fiqineering Department, London for advice. If stability resolved by Action (12) or (13)

inform manufacturer and ask for his confirmation that the

I

h I neb7 co!l~diiions are XCeptable.

FAULT SXEET No. 3

2. :-‘ucl gx analyses (Lcv and

MOL WT) are within design specification.

4. Pilot is corxectlypositioned.

S. Maiz burner guns may be patinUy blocked. distorting Ciames. Clean as necessary.

7. Check main burner for mechanical damage. Elockage

due to fallen refractory oi cokiig.

(a) Quarl. @) Oil and gas guns. (c) StabiIiser.

8. Main burner quns may bc -hzorrectly positioneii.

9. Check that pilot matelial of construction is correct for

duty. Ifsuspect contact manufacturer.

Il. Observing pilot ti,~. Adjust by

a smalJ amount at a t&rc :he pilot gas and pilot air pressure umtil pilot run5 coo!. ‘i?tcn

check that pilot flame is big enough to light ;?~ii.l flame.

12. Lf pilot positioned in main

flame zone. Move pilot. Check for satisfactory &in flame ignition.

13. Contact m,mi~kxurer and/or

Engineering Department, London for advice. Eproblem resolved by (11) or (12).

inform manufacturer and ask him to con&m new comditions are acceptable.

Tirs! Check 1,ist

2. Fuel gas analyses (LCV and

MOL WT) are wirhin design

spcciflcation.

4. Burner combustion air flow (RDL) is set at manufacturer’s recommfznded burner iow fire

star:.

5. Pilot is correctly positioned in

the burner relative to stabiliser (swirler) and burner

quarl.

6. Pilot frame is in main name ignillon zone.

7. Fault may be with main burner. Refer to main burner fault shee:s.

Check pilot retention tip and 12. Ifpilot gas oi! 5p;c c,3!cul.2lc

pilot rube for blockage. pressure requFr::(t i0 c;ivc

6;oken refractory or oil/coke pilot design II~,::I-IIO~

may have fallen into pilot. 13. Reduce main Byrne!

Clean pilot gas filiers. combustion air nolii (iXD1,).

14. Adjust pilot air. Reducing pilot

air should increas- i’lame

length.

1.5. Increase pilot gag prc-ssure. Check pilot stabilliY ai increased pressure.

.~? . . . .

/

16. Contact manufacturer and/or Engineering Department,

London for advice. II problem resolved by ( I 2) n r (i 5) inicrm manufacturers 23ct ask for his

confirmation thzi the new conclitions cart‘ acc::;Icab!e.

Figure 9.2 Pilot Flame Too Small

3. Fuel coind!tioni IIUI correct at

burner

4. If line has been ril:rogen purged follow ti~~tructions in

‘Safe Operation, ci Zred Heaters hanrdbook’.

5. Atomising steam conditions are correct for start up.

6. Combustion air flow (RDL) correct for start up.

,.

‘_

8. Check guru are correctly positioned in burner

throat/quarl a,,d relative to stabillser/primary block/ CpXl.

9. Check bul?;er stahiliser]

primary bioc’k/quarl for damage. Replace as Il,eCeSSarj.

10. Check gun jet drilling and

mg!es agatist manufac-

turers drawjngs and/or a

burner which is operating correctly.

1 ,i. Adjust atomising steam pressure by a small am0w.t.

Usucally a reduced pressure vj?U heip.

is. Contact manufacturer and/or Engineering Department, London for advice. Ifproblem resolvedby (12), (13) or (14)

advise manufacturer.

Cl IAPTER 9’-- [‘age 7

. . I

Iiigh exess air- flow can cause instability. Permanent

measuring instruments may be faulty. Reduce excess air.

Visua?ly check flame for smoke, monitor for combustibles.

“urge valve not shut tight or leaking. Safety interlock purge

valve leaking.

Ffigh atomising steam flow can

cause tis:shility. Measuring Lxtru:nents may be faulty.

zldjust manually for visibly acceptabie flame.

Atomising steam temperature too high causing oil over- ilelting hence catitation’in the

gun. Atomising steam should ie dr-{ ,?nd sliqhtIy super- i,,z-:&J.

Fuel oil temperature too high

causing cavi:ation at pumps and in fuel gun.

Liquid carry over in fuel gas.

Figure 9.3 Good Gas Flame

(13) Jets worn. Check ova!iry. (c) internal seals leaking

hcorrecr tips could have been

iittcd. Check qainst manL&c- iurers drawing or burner that is operating correctly.

Fuel i;3-? tips nOi Ln correct position- Sc-rew on type gas gxn tips not In correct position.

Burner stabilisers. primary block, quarl. damaged or incorrectly located.

;.;;-. :r, Strip m.achanIcal safrqr

interlock. Check purge valves seaiing correctly.

Gas buriner dcsignzd for and firing with iuel gas COniair!klg

hydrogen may no: operate correctly if the hydrogen is no longer available.

An atomizing steam flow which proves satisiactory when firing heavy duel oil may cause

an unstable flame if the fuel is changed to light fuel oil.

A burner can usually be modified io achie;:c good stability but this should only

be carried out by an experlenced combus;ion engineer.

‘Figure 9.4 Good Oil Flame Figure 9.5 Unstable Flame

Oil firiiCJ

2. Monitor oxygen levels in combustion chamber. Adjust air flow rate to give 10 to 20% excess air depending on type of burner. Check analyser

calibration.

3. for na&rd clrauqh: bLIiXers open register air louvres. 11

fully open increase draught.

4. Chec!< heater/boiler for air inleakage and sea1 off h&age points.

5. Oil temperatures too lobv.

6. Low atomising steam flow can cause smoke. Check isolating

valves fully open.

Smoke from a

9. Incorrect, ovzrsizcd, atom&r tip could have been litted.

Check agains; manufacturers drawioqs or burner that is I:*ing correc!ly.

10. A:omiser rip badly worn,

orifices oversized.

11. Burner quarl/air tube partially blocked with debris or Z?rbO:i:

12. 3urner or fz &mper damaged or :-g&ted out of line with indicator.

In- Combustion chamber draught low due to damaged stack

damper 0: excessive air inleakage.

Stick-

17. l-!av~ngproved there 1s suificient air for comb:lstion Iaul: could be caused by b~.d air/fuel mixing or bad atomisation. Contact manu-

facturer/Engineering Department, London for advice.

t

. .

see Figure 9.7 - SparkIers in a flame

2. Oil temperature must give a vi,~cosi?y of IS cSr al the

burner.

3. Atomising steam must be dry and preferably slightly super-

heated.

4. Check atomising steam isolating val~ic is fully open

and purg- I’ valve is shut tight

5. Checli s:eam traps are operating correctly.

6. Fit a clean oil ~XII

Note:

If new forced draught burners have been fitted to aheater,,

originally designed for natural .. draught burners. steam usa’ge,.m be much lower

lower velocity will increafe.

Figure 9-i’ S ;parklers in a Flan

. . Therefox

, heat loss

-e, at

in system

13. If correct then increase

atomising steam flGW by 3 sma!! amiount at a time (5%). Keep a visual check on tlame

to ensure stability is not Gfected. Dependifig on

atomiser type, oil pressure inay have to be increased to

rdntain the same oil DoW rate

1~1. Contact manufacturer andjo-

Engineering Department. Lontdon ior advice. Ii problem resolved by (13) advise

inanufacturer of increased steam operating pressure and ask him to comment.

11. Inspect pipework lagging and trace heating- Pipework shouldbe lagged right up to the bur-ners.

CHAbTER 9 -- Psge 10

c. _:

I

. - - _ . . . __.. . - - - . : - - . . . - _

8

8

‘8

8

8

8

8 I( ’ j 8

3

8

8

8

8

1

8

1 1 1 I

Figure 9.8 Distorted Flame

due to Blocked Atomiser

,

2. Look for sips of fuel impirigemeit, flame Assiortion

(sheet 9).

3. Atomising steam Cow too low. Check isolating valve fully

ape*

4. Check purge >alve shut tight.

f. Check for v;esr in jets (ovaiiiy) espec.izll>- if caialys; c;lrry

over suspected.

8. Check for leakage between oil

and ste;mm in fuel gun and safety in:criock.

9. Check oil/gas gun position and concentricitv with

stabiliser/prima& block and quarl.

10. Intf2rn;il shape of primary block on early inatural drsughi burners caused dripping and

cokt,. RF:-desiqncdprimary blocks are available from

n7.;!1llll~Cil~reT.

11. Suspended flame type forced draught burners with flat bladed swirlers prone to

cokir~$. Problem resolved by Fitting curved bladed swirlers

5. Fuel oil quali?- ch.anged

(a) Visbroken resid~~es are

krlown to cause problems (under investigation).

@) Catalyst carry over.

12. Burners which have all

combustion air swirled prone to co!&g on quarl.

13. Contact manufacturer/ Engineering Depay:ment. London for advice.

Figkk.9.9,

Carbon B&ld-up

(cl) Jointing material.

(e:! Catalyst carry over

Effects:

-,-, , i?.ctio;1s:

(a) Partial blockage will cause distorted flames and reduce oil flow.

(b) Blockage of steam jets can result in increased oil flow with deterioration in atornisation.

(CT) Uneven heat distribution.

(d) Lmpede low excess air operation.

(a) Check iilters are !xnciioning correctly.

(b) Check filter mesh size is correct for duff. Ask burner manufacturer to recommend mesh size.

(c) With the fuel Line isolated and already purged, remove atomiser tip and place the fuel oil gun in burner. With pilot alight crack open ste,am valve XKL purge ‘Lhe s;earn line through t&e burner. Crac k open purge valve and purge it?c emppf oil Line through the burner.

(d) liproblem persists clean complete pipework system.

Effects: (a) Blockagewillcause distortedflameand reducegasflow.

@) Partially blocked jets may misdirect gas in burner throat causing overheating of burner parts.

(c) Uneven heat distribution in comk~ustion chamber.

(d) Lmpede low excess air operation.

Actions: id (3) cc> Cd)

(e> RI

Check filters are functionmy correctly.

zf filters not fitted consider fitting them.

Check filter mesh size is correct for duty.

Pilot jets are very small. Staink~~ steel pipingshould be installed downstream oi filters.

Clean fuel system.

Correct oil firing, when cause of fouled gas tips.

t

For a burner 70 continue to operate at its optimum efficiency, it is essential that it is r-ai::iuliy maintaine:d. If this is not done then eiiiciency will drop off rspidiy and damage ma-y bc: -;cstained by the tubes and refractories in the combustion chamber due to flame impingement. The iin;tncial penalty for eiftcicncy loss due to had maintenance can be equal to severalp?rcent of ftic.i uurn[.

This does noi include the cost of rrrsiring damage to the hea:er or boiler due to fIa.tt!i. irnpi”rJ”r~?‘!:i.

correcrl~

IO.2

10.2

102.1

lMirINTENHN CE X’~CILITIES

This should comprise the following:

(a) A work bench with a wooden (not steel) top and fitted with a normal vice with jaw protectors and a pipe vice.

(b) Correct burner tools.

(c) Bronze brushes (not Steel).

(d) Fine copptr wi-re ior clearing jets.

(e) High temperature anti-seize compound.

(i) Solvent for dissolving carbon deposits.

(g) A suitable ~i:;iln rac!c to store clean qr.s.

(h) Protection fo : gun inlets and tips to prevent the ingress of dirt while in storage.

(i) A spray test rig which is used to purge gun and visually test atomisacion once cleaned.

6) A steam or compressed air supply for bIowing through fuel qrrr

A burner ~le~~nincj station is illustrated LnFigure 10.1.

SPRAY TEST RIG

TNs facility is a great asset and fairly simple to install. Purchase from the burner manufacturer a spare stationaq inlet (not with safety interlock) This is the part on to which the oil qun iocates when it is placed in the burner. Mount this inlet on a st‘and and locate it adjacent ?o the maintenance fa&lity so that the oil g-trn, when in position, is pointing towards ~11 unused open area. Connect steam to the atotising stsm {bYlet and water to the oil inlet. Water at mains pressure (normally 3 bar} wiU SLL%CC. Fit

isolating valves and pressure gauges on both the water and steam; Wters ma.y also be neccssar,~. EL;-.- :: 3 purge connection bet->Jeen the steam and VJait2r from upsirea^t of the steam isoia~mg valve to downstream of.the water isolatig valve so that steam can be turned on to the oil (water) side of the gun.

Use of spxay test rig

(a) When the atomiser has been removed for cleaning, the oil. gun should be placed in the test rig and purged with steam, both on the oil side and the stem1 side, to clean out any dirt which will be present inside the rgun. If this is not done, then the clean atomiser may block up &mediately it is used.

(b) When the clean gun and atomiser have been assembled it should be placed in the rig and spray tested. First turn on the wa’ter. lf an oil jet is blocked this will then show up. Next turn on the steam, poor atomisation will show up in the form of large water droplets. The operators will learn by experience to differentiate between good and bad atomisation. ‘:‘I

10. .?

3

I 1 I

I I

10.4 GAS TIP CLEANING

(a) Remove the c;lp nut carefully using the: corccct spanner

(b) If the atom&r is stuck in the cap nut, LIP 11 out using a correct shaped hard wood br soft metal driit.

(i) Remove the atomiser from the so! ‘.:!ln: <anr! clean ~vith a bronze br~!sh

(g) Visually check all jets are clear. This is no! possible with the oil jets on ak jet type a:omiser, so use apiece of soft copper ,,“~ire to check that they are not hiocked.

(11) Check a!1 jointing faces and threads ior ri&mage including &OS,- ox 02 gun body; do not r*use suspect parts.

(i). Using a high temperature anti-seize compound on the threads careiuiiy replace the atomiser &d cap nut. Tighten using the correct spanner.

(j) Place the clean gun in the spray test rig and turn the water onto the oil side. Visually check all jets are discharging equally and at the same angle.

(k> Turn on the a:omising stearr. The SIE;IIII pidzL.sure should be that required from the manuiacturur’s graphs, for the fuel oil pressure equal to the water pressure. Visually check the atomisation.

(1) Lithe gun is not to be used immediately, place it Ln a suitable gun rac!~. Cover the atomqser axcl ~11~ tilets to prev-r\l th.2 i;:.g;es~ of dirt.

Emulsion type guns, ,?s,fitted to most nz.a~::;il c’lr,~.ugh! burizers ‘naive a cone tip and an internal mixing tip. Both these should be remo-zecl and cleaned follo>;;mg the above procedure.

StiLsons should never be used to remove atomiser tips. Unfortunately certain sizes of Airoil guns have no spanner flats and for these stilsons have to be used. To minimise the damage done by the stilsons a piece of rag or leather can LS placed under the jaws, however, t&e real solution is to insist t?lar the mandacturer (Ahoil) modify their funs to include spanner fla.ts or provision for a C spanner.

Gas guns vdl either have the @ps scrL’,iti. --z. =,-i ~1: 0 I- ,;;~>l::ied ~JII. The !oIn.r rnc-Lkes cleaning easier but leaves open the possibility for the tip jets to be wrongly positioned when tile tip is replaced.

(a) Remove the screw-on gas tip from the gas gun. Soak in solvent to soften any carbon deposits.

(b) Purge gun with steam or compressed air to remove any dirt. Ii there is an oil or grease 5Lm on the &ide of the ~a”, then c,se s!e~7_~n to dean.

(c) Remove tip from solvent and clzan \-vlih ;I bronze brush.

(d) Visually check jets are clear. Use soft copper wire to dislodge slly dirt blocking the jets.

(e) Inspect ffireads for wear; do not re-use suspect parts. !

(f) Replace tip using a high temperature anti-seize compound on threads.

(g) Align jets correctly on gas gun, according to manufacturers drawing.

(h) If tips are welded on, back flush with steam ok- air through jets pushing dirt back out of gun inlet. Clean tips using solvent, bronze brush and copper wire.

Noler ‘CViien removing gas &uns mark them with a number so that, Lvhen they are replaced, they are fitted into the same position on the same burner.

I f a new spare gun is being fitted check it dimensionally against original gun, other guns on the same burner and manufacturers drawings.

(,I) Srrip the pilot anti clc,~ri al! parts.

Great care must be ~&XI Avis en handling fue1 guns. Y&en removing or replacing them in the burger &PSczaretul not to knock the tip. Be prepared for the gun to he hot. Do not drop it ar throw it; carry it to the work bench.

Darrage whilst in ppera;ion:

(a) Overheating.

(b) Mechanical damage due to falling refractory or even a falling stack darnper blade.

(c) Jet erosion due to dirt. catalyst c;!rry over or 7;ct stream. (FigLIre.5 10.2 anti 10.3 show the damage caused by catalyst and viet steam respectively.)

Damage by manhandling:

(a) Accidental damage.

@) Using the wrong tools.

(c) Incorrect assembly, iorcing.parts together.

(d) Using the wrong cleaning tools.

(e) Incorrect storage when not in use

Corrosion Damage

By following the instructions on stomiser clea&y ai?cl by careful storage when not in use, the fuel guns will, when required, function correctly. However, the fuel 9111 stationary inlets or mountings must aIso be protected. Whe‘n a has fired on gas for a long period of time it is not uncommon t& see the ts for the fuel oil guns in a badly corroded condition. When the oil gun is cIamped &position, there VsriU be little ch&de of creating <an effective seal due to the amount of mt pitting on

the sealing surfac’es. Add to this that both the oil and steam outlets &e oken to the ingress of dirt, the gun will veFf likely block up as soon as a light up is attempted.

TO protect the qil and steam staiionary inletsa closure plate,shouId;be.obtained from the mantifdctu&r- An example of.a do&&,plate is shown i<Fi&&+&0.4. This plate can also f;e exierided to cover the’oil-g&eide hlb&,preve&ng the passage of air through’it: The stationary inlets shouId’b&-lightly greased 2nd.tlie cloSure plate clamped in position to protect it. The closure plate can be attached to the burner with .I a short length of chain, to pievent it getting lost whe’n not in use.. ’

I

: ‘! i;.,i.q : : . : : . . !

Figure

:

The real solution is relatively easy. ‘ihe following procedure siould be adopted.

(a) The s-prayer must be held r-igiclly on a bench, locating on the sprayer hexagon adlacent io the cap nut- Loosen the cap n91 and undo approximately 1 to 2 iLlrET.. llsing a piece of wood

or soft metal, tap the atom&r back into the nut until it contac :s the sprayer end. i iolcl it in this position and screw oil rlie cap .iu!, Figure number 2. “Pins procedure keeps the

atomiser square with tie cap nut and prevents wedging. Care must be taken no: io drop the atomiser when the cap ;urt fiially clears the sprayer.

(b ) I f an.atomiser has become wedged in a cap nut th+ can usually be squared up again 1;~ simply screwing back onto the sprayer. ‘I?& srOc$ure above can then be eimployed.

hl the case of a severely l,tfedgeC 1 atomisdr~ if’may be necessary to use a soit metal cl\ift in order‘@ square up then tap out. Under these cir~nnn&mces both the atomiser anrl ths cap nut shouId be Closely exsrnined and.rejected if.dai&aged..

Sefore any exa_l-cGnation can ho *nadL:, d:e atomiser must bi o C!Cated. T[‘Pcis is liOi??taliji do;ic: b;i

soaking in a paraffin bath to wash any heavy oil films, this also has the action of loosening carbon deposit. It may,;,also be necessary to use asoft metal scraper to lift away any heavy carbon depositsA hardened scraper could possibly damage the atomiser.

The use of &rasiv~-blast equipment or muElk furnaces shpuld not be used without consultation. Incorrect’use of these method.? can reduce component life seriously.

The cleaned atdmiser should then be examined for’damag&. T’ne nozzle sizes should be

checked using ‘go and no go’ pin gauges. This action will also determine if any nozzles are blocked and should, in fact, clea c them. Compressed air will normally clear any debris left in

the nozzles after cleaning. The seahng iace of the atomiser is checked by rubbing on a surface plate withmarking blue. If the face is not square and flat it is necessary to correct this by lapping.withafine carborundum paste.

If a s&ace plate and marking blue are not available a light rub on the lapping plate TNlth. fine paste wiIl also indicate the c;irdi!ion of tile sealing face. The atomiser should only be lapped 2 the se@ng face is found to be unsatisfactory. Do not carry out unnecessary lapping.

,- lt is import;li:: t0 inspect the !?.?pkt g -!aia a; rqdar ii:k!~V;25-. Tkk ph. :e must be ~-n,3~mts’iiiE:c‘!

flat if it is to be of any use. The atomiszr should be lapped by using the figure eight p?.ttcrrL

Figure number 3, employing the ms:ttinum sutface area of the plate to prevent local ~cal.

Finally the atomiser must be washed to remove all lapping paste. II the atomiser is not to be used immediately,- it must be kept in a plastic or similar container to preven t, damage or scratching‘of the sealing face.

It is false economy not to reject an atomiser if it is found to be unsatifactory, i.e.,

(a) Not possible to produce a complete sealing face across atom&r.

(b) NozzIes excessively worn (see note).

(c) Nouies damaged by hammering, etc.

Note: Accebtabie atomiser wear can be derermined by using a ‘go/no go’ pin gauge, referred to

above.

The ‘nogo’ pin wilt be normally sized at 101 .S% of the top limit for the particular nozzle.

The action cm i,i~~p~r~c~ a sprayer ’ - erICI c;ill:; (Or cJr;:i(f?rZible Cil.i-2 ,irlt! 7!li::il~lOIl. ?‘hC lSppii;i. plate which mI:st be hand held, must be regularly maintained for fiaintss~ figain the fig”re of eightpat!er!l is ~~rr:~loyed and much care mssi be taken to ensure th,?.i thi: “Iate does not rock. creating a CO;LV~X end. Figure number 4.

When a sprayer is not in use a protective cap or cover must alweys be fitted to protect the sealing face and threads. The sealing face and threads are not bar dened and particular care must be talcen.

FITTING ATOWIISER ASSEMBLY ONTO THE SPRAYER

Before locating tt?e atomiser into the cap nut, check that no inclusions are ~rapned between the atom&r shoulder and cap nut. Care must he taken to keep the atomiser sc[uare lvith the cap nut as it is located, otherwise wedging may occur.

The threaded portion of the sprayer should be cot-eredwith’anon-hardPr~~~~~ high temperatxre lubricating compounc!. ?‘hA facilitates subsequen: remox& P&tic&ar car-e must, however, be taken to ensure Fiat no compound is trapped berween the se&g faces.

The cap nut is run 1~‘s u;\til the atomiser comes into contact with the. spraye I, a itid tightening torque of 150 to 200 ft.lbs. s'noulcl +&en be applied:

Provided due attention has been paid to all the aforementioned pbints, no difficulty should be experienced in achie~::~g a satisfactory sea! jetw33. at*r&ey and ~~xayer. LL dOVAt eXiStS l”iTlO V” L - the atorniser immediately- and examine, the witness marks on.the atorniser iace, there should be two corqlete rings corre,sponding to the sprayer end seal face. 1

b%%en a clean sprayer is fitted into a burner, it is imperative that the cooling steam isolating valve is opened Lmmecliatel;:, otllerT*/ise overheating may occur. L

By the same token, when a sprayer is removed for maintenance,.the cooling steam’khould not-be isolated until the moment of removal.

Regular checks must be made to ensure that blockages of the cooling steam valve have not occured.

The design and asserr&!y of the steam atomiser described is very simple. The maintenance and fitting procedure is not particularly demanding when considering the function that this component plays in the overall plant performance.

It can, therefore, not be overs:ressed the importance of rigidly following these rules if efficient operation is to be achieved and maintained.

A Hamworthy Steam Atomiser Figure 1

-

I/l’ gyq-\AToM,sE- ‘- N”-i- THRO?IGH CENTRE ‘:

I ATOMISED I

OIL SPRAY

8, I :

12.01

%.OlF

32.m

2a.016

28.01

4*k.O!

16.041

30.067

4 4.092

Z-6. 1 18

58.118

_. ., I&..lGC

72.144

7 2 1 ‘! 4

86.169

28.05 1

42.077

CS.1GZ

56.102

70.128

78.107

92.132

100. ISI”,

26.036

128.162

32.04 1

46.067

17.031

32.06

34.076

64.06

18.016

28.9

0.0853 I 1.?23

1.3553 3.733

1.1916 0.839

1.1860 0.843

1.8-742 cl.524

0.6797 1.471

1.2861 cl.?78

1.9158 0.522

2.534 1 0.395

2.534 1 0.395

3.0499 0.322

3.0‘399 0.328

3.0499 0.32s

3.6426 0.275

1.1943 0.837

1.7781 0.562

2.3707 i3..122

2.3707 0.422

2.9666 0.337

3.2998 0.303

3.853 1 0.257

4.49CO 0. % 23

1.1166 0.896

5.4207 0.184

1.3552 0.733

1.9478 0.513

0.7304 1.369

1.459 1 0.685

2,776O 0.360

0.7622 1.312

1.2262 0.815

12.11

11.99

37.75

66.77

I;t6.50

125.56

125.30

119.U

149.s3

148.77

177.42

60.13

87.04

1. l‘f.9 1

114.31

142.93

135.76

167.07

19Jt.86

q3.99

218.11

32.34

59.63

16.43

24.11

32.7

142.1

10.1

555

51.9

so.4

49.5

49.4

49.1

48.9

48.8

48.7

50.3

48.9

.\8.5

48.2

48.2

42.4

42.9

+3:1

50.0

40.2 I L 23.9

30.6

22.5

9.3

16.S

32.7

i%O.!

10.1

so.1

47.5

46.4

4 5 -8

45.7

-IS.<

45.3

45. I

4s. 1

47.2

45.8

lir’, 3 .

45.1

45.0

40.7

41.0

4 ! -3

48.3

38.9

21.1

27.7

18.6

9.3

15.2

r

Gas Combustion Const;ants jconlinuecf)

0.5 1.882 2.382 1.0 1.882 0.571 1.9co 2.471 1.571 1 CJw

2.0

3.5

: 5.0

6.5

6.5

8.0

8.0

8.0

9.5

3.0

4.5

6.0

5.0

7.5

7.5

9.0

10.5

2.5

12-k

1.5

3.0

0.75

7.528 9.520

13.ilS 18.525

18.821 73.821

24.457 30.967

24.457 30.967

30.114 38.114

30.114 X3.114

20.1 I.1 &LF I.&::?

35.7M 45.260

11.233 14.293

16.939 21.439

22.23s 28.585

22.585 28.585

23.232 35.732

20.232 35.732

33.878 42.873

39.524 50.024

1.0 2.0

2.0 3.0

3.0 4.0

A!.0 5.0

4.0 5.0

5.0 5.0

5.0 6.0

50 6.0

6.0 1.0

2.0 2.0

3.0 3.0

‘1.0 -LO

co 4 .c

S-0 5.0

6.0 3.0

7.0 4 0

8.0 5.0

2.0 I 0

IO.0 JO

1.0 2.0

2.0 .?.O

I.5

3.990 13.275 !I.275

3.125 l2.;cJ: 16.1!9

3.629 12.07~ I 1~.7c!3

3.579 11.9@! 15.487

3.579 11.9c-8 15.487

3.548 11.805 IS.363

3.!%8 1 ME 15.3E.3

3..54a 1 I 1?!05 15.363

3.528 11.735 15.266

3.4?.2 il.?.% 14.301

3.422 11.385 14.007

3.422 11.3m 14.807

3.422 11.3-85 14.807

3.422 11.3.35 14.807

3.073 10.224 13.297

3.126 10.401 13.527

3.165 lOSN3 13.695

3.073 l&22(. 13.29i

2.996 9.965 12.964

1.498 4.784 6.483

XC84 6.934 9.ola

1.409 4.cxB 6.096

2.744

2.927

2.994

3.029

3.029

3.050

xcxx

3.050

3.064

3.130

3.138

3.1~38

3.138

3.13a

3.38 1

3.344

3.317

3.m36!

3.434

1.374

1.911

2.246

1 .ma

1.634

1.5X

1.550

1.498

1.498

1.498

1.464

l.ZEL!i

1.285

1285

I.285

1.285

0.692

0.782

0.849

0.692

0.562

1.12s

1.170

1.587

9.,1 1. 1 !I.911

45.170 57.160

5.646 7.146

11 .?A3 1 -I 293

2.a23 3.5T3

=4 1.998

SO, 1.B.30

Salp2u 0.998 3.2al 4.“& 3.28~7

HydrogenSulphide

Sulphm Dioxide

SVater Vapour

Air

1.5 5.646 7.146 ij.646 1.109 4.688 6.097 0.529 4.6%

!

i”

t$j”- - Kincmalic ViSco;iIy icS$

These are siable residual oils or Sle~tI:; r;lk:cring the requirements of DS2869 Classes E. F and C. Tlley arc used in genera! !nti~;; including boiler firing for both sre;i;:7

ria1 and Coinmerci~I ;:pplic;i!ions C!l.~’ j ,.oi-Lxiater. furnaces 3ilci iarge air healers i.

and dryers. They are also suitable iu~:!h (or medium and large siaiionary diesel

engines.

Min Mu Typicti Min Max Typical hlin Max Typic-al

0.980 0.910

66 - .lO 13.5. 13

3.2 2.2 0.5 0.1

2524x.b Nfi

- 0.1. 0.02

0.c -

0.05 0.02

-

56

7s

0s

-

,41.8 39.5

2 30

1010

-

(!) Measured by Peak-/ - Martens (clbsed) riwthod

(2) To convert MJ/kg to Dtu/lb multiply by 429.932.

0.999 0.970 -

35 34

3.5 2.5 0.75 0.1 Nil

0.15 0.03

0.07 0.03

- 86.3 11.1

- 42.7 - 40.3

- 1030

0.4s

- 66 5s

-

c; 5

41.6

39.3

40

50

0.980 -

85 78

3.5 2.6 I.0 0.1

lNi1 -

0.2 0.04

0.10 0.04

86.3 11-O

42.4

NJ.4

1020

0.45 c O.UX-38

-

(3) As recommended by lZX4 10: 1978. To convertkW to 3tu/hr multiply kW by 3415. Fa an approximation for steanlboilers 1 k’N equals 3.4 15 lb/hr maximrrm continuous rating.

! . ! I Typical vaIues reflect mrrent production from BP oil mainland refineries. Ructuarions within rhe minimum and maximum values will OCCUI as refinery production varies to suit changing crude supplies <and other factors.

This guide has been writtern to provide operarions staffwith a speciailst insight into ihe workings of combustion equipment. It is specifically directed towards the big rning”of liquid kd gaseous fuels on refineries and chemical p!ani.

ir is inrended that sections of the guide will be updated to include the iaiesr acceptable advances in burner design and operation techniques. Your comments oil the content and suggestions for future addlt~ns should be-sent to:

Messrs J.F. Brazier and J. Ellis Hea; Tr,:nsfer Group Chemical Engineering Support Branch Processing Technology Division Engineering and Technical Support Departmenr BP Internaiional Limited

BP Research Cent::e

Chertsey Road

Sunbuy-on-Thames

Middlesex

‘I‘W16 ?LN

Project 106

Burner Test Rig Facfiity

Available for:

Perfon;iiance Testing oi Burr-lers

Burner Perfor~~.nce b;<Lh Specific Fuels

Resolvtig Burner ?roblems

Operator Training

Mobile Combustion Laboratory

Available for:

Monitoring FruLssio?s

Qptirnising C0rnLbusti0r1

This course is held annually at Sunbury and is designed to give an understanding of Combustion

Equipment, covering Burner Cperaiion, ‘l’rouhleshooting, Maintenance and provides an imsight

into Heater, Boiler and Flare Operation.

Details available from: Engineering and Tecltical Support

Processing Technolow Division

Training Films

The following films are available to assist in on-site training of Operations Staff for G:ired Heater

Operation.

(1) Operation and Tnaintcnance of Natural Draught Burner (2) Operation and Maintenance of Forced Draught Burner

(3) Refinery Heater Multi Burner Operations

Films available in-video forrn only from: BP Oil International Ltd. Operations Branch

OMF, Operations Division

,- ;

/ ,& ‘;

B

;’ .’

.., : ,, ..j .: I

.- -. / , . .

i ‘.. -. ;L;

I-:.,:;:.:.. ..y ..,I.., ‘.

.?’

” .’ :.

.-‘.

., WII ..^. . . . . .? .,.. _.. . . .,.- . . ..,_-__,.