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THE INCINERATION OF

AQUEOUS WASTES

MOO J du Pont de emours & o, n

imington, Deaware

Three bsc methods of tretng qeos wste byncnerton re covered Exmles of ech tye re ven revew of mmble zones s gven These re crtclconcet reqrement n ncnertng sch wstes Clc

lted dt re resented for the sgncnt vrbles thtgovern temertre nd het nt These cn be sedto redct erformnce

ODO

The owng emhss on the redcton of wter ollton n ths contry hs hd rononced effect onthe eld of ncnerton Once ndstrl ncnertorswere led rmrly to fels wth selfsortng combstble chrcterstcs nd to lesser deee to fes wth

only mnor reqrements for xilry fel to stsfctorly brn Tody a ncresng nmber of ncnertorsre beng blt to dsose of qeos wstes whch mycontn only trces of combstble mterl

The sorce of these qeos wste my nclderocesses whch hve drect contct between the rodct nd wter tnk wshngs sry condenser dschrgesetc These wstes my vry from lqds tht re essentlly lwter to lqds tht re wter wth recbleercentges of other mterls The other mterlsresent my be toxc mterls wth hgh bcterl

4

oxygen demnd mterls cble of rodcng trbdtyor mters wth excessve cdc or bsc chrcterstcsThere re mny estblshed wter tretment methods forhndlng sch wstes While the mny fctors tht ffectcosts re too nvolved to be dscssed here there re somesttons where ncnerton s the economcl wy to

dsose of qos wstes

M MHOD

The three bsc wys of ncnertng qeos wstes mybe chrcterzed by the three sttes tht heted wter ssmes The rst of these my nvolve only the hetng ofthe qeos wste lthogh ths s seldom fesble dsosl scheme there re strng or crbonton lctons In these the contct of combston rodcts wthqeos wstes when dded to other rocess stes my

consttte tre ncnertor system n exme s theSchtt rocess shown n g 1 [1]The second bsc qeos wste ncnertng method

covers the re of hetng nd rtl or comete evorton Ths s very fesble oerton nd often coverslctons thoght of ony s hetng When sbmergedexhst combston s sed ths method s the sl reslt The concentrton of orgc comonds th hghbolng onts n the nevorted wter whch s thenncnerted n flme (g ) s n exmle of ths secondbsc method

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A hrd mehod of ncneron s h of combnngheng nd evoron of he wer nd serheng of

he resln vor drecly n me (g 3) Combsbles resen n he qeos wse cn be odzed f he

necessry fndmenl reqemens re me

AW WASTE

ATER WITHOW BOILING

ONTAMINANS

OFF GASES

TO FLARE STACK

COOLINGWATER

BURNER

TAN

WATER LEVELSUBMERGED EXHAUST DOWN COMER

WEIR

FIG. SCHUTT PROCESS INCINERA TOR

SEAMNGEN

AQEOUS

WASE

FEED

LIQUID LEEL ------ ---- -- - _

PUMP

CONCENTRATED WASTE

AIR

SUBMERGED EXHAUST

WEIR

FIL TER(IF USED)

FIG_ EVAPORATING INCINERATOR

5

AIR

AQUEOUSCWASTE

NATURALGAS

FURNACE

FIG 3 SUPERHEATING INCINERAOR

OP

VENT

There re cern bsc condons h ms be followed n qeos wse dsosl f ssfcory resls reo be cheved These re no lwys ndersood ndfndmenl d re no generly vble If combson s o be comlee he sl generlzed reqremensof me emerre nd rblence ms be whn ssfcory lms These re fncons of brner nd frncedesgn nd wll no be del wh here snce hey re welldeveloed n commercl desgns When wer s dded o

15

("

FIG FLAMMABLE ZONES AND WATER INJECTION

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the combstion me the reqrement of mmbilitylimits (or more roerly zones) ssmes imortnce ndmst be nderstood for sccessfl reslts

Fig shows lot of mmble zones for methnend oxygen The Line B reresents the ossiblemethneoxygen combintions in ir The oint L77

reresents the slly reorted len limit nd the ointR77 reresents the slly reorted rich mit Point Sreresents the stoichiometric mixtre The oints L, R,nd S re slly vilble from the litertre (ie, nd3 bt re slly bsed on m bien t conditions Oncecombstion is chieved these limits re chnged The lenlimit will generlly shift only slight mont sch sshown by the sbscrits on L which reresents thelen limit t F The rich lmit will exnd t F greter mont s shon by the reltionshiof R to R77 There is third oint on the m

mble zone which is of imortnce nd this is the ontM This oint reresents the minimm oxygen contentt which iition cn be chieved t the indicted temertre It slly lies on or ner lne drwn fromoint S, which is the stoichiometric r/fel rtio, to thezero ordinte nd bciss oint Point M is redily vilble from the litertre t F bt there is little or nobckgrond informtion on this minimm oxygen lmitt higher temertres The oint drwn s M isfrom the thor's own exerience

It cn redily be seen tht once iition is chievednd the oerting temertre of the me nd its frnce incresed, there is mch eter rnge of mmble limits nd zones thn occrs t the time of initilignition n other words, mixtre which might notignite t ll t room temertre will brn stisfctorlyfter ignition is estblished nd higher temerre isttined

Point C ws selected for demonstrtion of notherimortnt fetre t reresents the ir/fel mixtre formethne with 3 ercent excess r On dry bsis thecombstion rodcts wold contin 5 ercent oxygennd no fel nd line is drn to this oint from oint C

to reresent the combstion rocess The gses t C rewithin the F lmmble zone nd redily ignite ndbrn If we ssme the sme ir/fel rtio of oint C btwith vrying monts of wter dded, we cn investigtethe brning of qeos wstes in mes n order to lotonts similr to oint C, the wter ws ssmed to beevorted s stem

Point D on Fig ws ssmed to hve b of wterdded for every Bt of gross cloric vle in thefel The reslting decrese in the ercentge of oxygen

nd fel resent in the overll mixtre of fel, ir, ndstem is shown by the loction of the oint D otside the77 F lmmble zone f the stem, ir, nd fel wereslied well mxed, iition wold be dfclt if notimossible The dibtic me temertre of this mixtre is 5 F nd since oint D is well wthin the F

mmble zone, the mixtre shold brn once frncetemertre is estblished t is necessry, therefore, toignite the fel nd r lone nd then dd wter slowly sreresented by lne CD to cheve stble me

If more wter is dded ntl rtio of lb of wter er Bt of fel is chieved, the condtion shown byoint E on Fig is reched t this condition the dibtic combstion temertre is F nd theoretcllystble combstion cn be mintined While this is tre,in rctice, the eqiment mst be well designed ndcreflly oerted

If even more wter is dded ntl rtio of b er3 Bt is reched, the condition shown by oint Freslts lthogh oint F is wthin the F mmblezone, its dibtic combstion temertre is only Fnd combstion cnnot be mntined If the wter injected in cses D nd E contns trces o f combstiblemterils nd the brner nd frnce design re correct,the combstible trces cn be exected to be brned comletely if they re injected diectly into the combstionrection The wter cnnot be sryed into the rodctsof comlete combstion wth ny reslts other thn

evortion nd yrolysis of the wsteThis imortnt nd little nderstood ont cn be exlined s follows Referng gin to Fig nd ressming 3 ercent excess mxtre of methne (oint C,it ws stted tht the rodcts of comlete combstonwold be reresented by the 5 ercent oxygen nd ercent fel oint From this oint it is ossible to constrctthe dsh line mrked fel nd dry combstion gs dltionline This lne reresents the ossible combintions ofmethne nd the dry combstion rodcts Since nooint on this lne intersects the known mmble zones,combston of the methne cnnot nd wll not occr

If the wter sed in cse D is dded n even lower line reslts which hs mximm of 33 ercent oxygen If methne or other orgnics re resent in the wter dded,they wll not brn if the wter is injectd fter the initilmethne nd ir combstion is comleted since no mmble mixtre occrs

n terms of the exmle ven, it cn be stted tht if1 ercent orgnics re dded to the strem D nd injectedith the methne nd ir in single combstion rectionof good design, the orgnics will be incinerted t cn

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also be stated that if the same water and organic areprayed nto the products of combustion of the same

methane air ame, little or no incineration will take place

and the stack producs will include the vaporized ornicand its pyrolysis products. If the aqueous stream impingeson the walls of the incinerator, sucient pyrolysis products may accumulate to appear as aparks from the unitwhen they are dislodged

M Y HG OY

Calculatons were made to determine the variables involved when the aqueous waste was only to be heated withcombustion products These calculations are relatvelysimple thermodynamically but are tedious since a tria and

error soluton involving the partal pressure of the watervapor is involved A computer proam was written toperform the calculatons for each of the three states ofwater n equibrium wth combuston products. It wasfound that only the heat input in Btu/lb H20 was a sgnicant factor and the results are sho n Fig 5 Wherediute organc wastes are involved wth water and theyhave low boing temperature chracteristcs, the Schuttsystem shown in Fig has applcation This system is

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/NI L P 6 Fi

20 3 4 5 6 0u/ AR

FIG

5TEMPERA TURE VERSUS HEAT INPUT FOR

HEATNG WATER

8

207

described in detail in [1]. Combustion products fromsubmerged exhaust burners strip the organics from thewaste liquid A partial condenser removes the evaporated

water and the orncs are passed off to a are stack orother combuston process to be burned. f the lare stackhas the proper combustion conditions which produce aammable mxture, the gaseous organics will be incnerated Since a mnimum of auxilary fuel is used to heatthe water, this system is advantageous where oher combustion processes, lames, or ares are available to disposeof the of-gas

Submerged combustion can also be applied to aqueouswastes to carbonate them Carbonaton, pH control, orboth, may be used to achieve desrable chemical reactionswhich improve the aqueous stream before it s discharged

or treated further Whe the choice of fuel does not affect the Btu/lb water required to heat the water, t doesafect the CO2 produced and should be taken nto consideration.

t should be noted on Fig 5 that wth 00 percent excess combustion evaporation start to occur atabout 109 F whle a temperature of 3 F can be achievedwthout evaporation at ero excess combustion Fg. 5should not be used at heat inputs above the excess limits shown in the dotted porton of the curve

M Y D VPO HG

When evaporaton with combuston products occurs, asecond variable becomes sgnicant in addton to heatinput n determining the nal temperature This isexcess air The reason that excess ar is mportant is thatthe increased partal pressure o f the unconsumed oxygenand its accompanyng ntrogen reduce the partal pressure of the water vapor beng evaporated The computedresults for the evaporaton condition re shown on Fig 6The type of fuel used was not found to be signcant

At atmospherc pressure nd wth no excess combustion , a maxmum bong temperature of 191 F occur and wth 100 percent excess combustion themximum boiling temperature will be 176 F. For allpractica purposes a maxmum heat input of 1400 Btu/lb water acheve complete evaporaton regrdless ofthe excess used Ths s shown by the vertcal line atthe upper rit of excess air cues where evaporations complete. There ae many ncinerator appcatons forthe operatng range shown on Fg. 6 f an aqueous wastecontans organcs wth hgh bog tmperatures and theornc not evaporate at the temperatures shown,

then the organc can be concentrated s shown n Fig.

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and sprayed into the combustion ame to burn the organic. The heating value of the organic will reduce theamount of auxiliary fuel required to provide the 1400

Btu/lb water needed for complete evaporation. For example, under adiabatic conditions, a mixture of 5 gallons

of No 6 fuel oil and 95 gallons of water could be evaporated and incinerated with an auxiliary fuel input ofonly 455Btu/lb water.

_ 5 gl x50000Btu/galHeatRequred- 1400 95gax8.345Ib/gal

= 455Btu/lb water

Another area of appication for saturated vapor heating is that of soids emission control and recovery. If the

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208

aqueous waste contains a metallic ion it generay become an oxide partice of submicron size in a combustioname Such partices are difcult to trap but submergedexhaust combustion can often reduce the emission evelto 02 gr/cu ft f submerged exhaust combustion is fo

lowed by a high eciency scrubber, good recovery of themetallic particles is possibe. It is frequently desirable torecover these particles either because they are toxic andcannot be discharged into watersheds or because they are

valuable materials High eciency separators or fltersare expensive and if the arrangement shon in Fig. 2 isempoyed the size of the separating equipment cn be reduced since the residual oxides are concentrated in thesmal amount of aqueous waste that is recirculated andtered

hese two exampes are ony indicative of the manyapplications possibe for evaporative incinerators ithout

superheat hey shoud aways be considered when possible because they require a maximum of 00Btu/b ofwater and frequently ess They are often criticized because the evaporated water at 9 F or ess results in avisibe plume of steam his water vapor is not an a pollutant and shoud not be considered one any more thanthevapor pume from a cooing tower or a steam jet eector

Y HG V

If the aqueous waste is inected into a ame propery

according to the principles previousy stressed, the waterwill be superheated as well as evaporated. For this condition a third factor was found to be significant. his thirdfactor is the hydrogen content of the fue burned Therelativey high specic heat of superheated water formedby the combustion of the fue's hydrogen cannot be ignored. Figs 7a, 7b and 7c represent the computed resultswith three carbon to hydrogen fuel ratios by weight Fig.3 shows a typical burner which can obtain equibriumcombustion of organics in aqueous streams A perusa ofany of the three Figs 7 show the relativey high auxiary

fuel requirements. f we re-examine our previous exampleof a waste consisting of 5 galons of No fuel oi and 95galons of water and assume it is to be fired th auxiliarynatural gas fuel to provide 750 F with 30 percent excessair, we nd from Fig. 7b that 700Btu/lb of water are required he credit for the fue oil is the same as previously and 3755 Btu/lb of water are required from the auxiaryfuel This is 80 times as much auxiary fuel as the evaporative incinerator required This example emphasizes theprobem of fue consumption for direct ame incinerationWith 00 percent water the ratio is over 5 and it increases

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BS CB H2T

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90-

FIG EMPERATURE VERSUS HEAT INPUT FORSUPERHEATING WATER

7a - C/H= 233b- C/H=

c- C/H

09

E CES Al0 Iv: 06080 F- w :

BS CBS N TEW -

BTUB. WRFB

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o infniy as he heaing vale of he aqeos wase increases

Anoher shor-c mehod for predicing he axiliaryfel reqiremen for dec fame incineraion can be madeby sing ig 8. This igre shows he percen of a fes

heaing vale ha is available a varios combsion condiions. or 1750 and 30 percen excess air an availabiliy of 40 percen is read from ig. 8 If b of waeris heaed o 22 from 60 i will reqe 52B Toevaporae a 22 an addiional 970B are reqired Tosperhea o 1750 wih a specific hea of 05 reqires769 moreB for a ol of 189B/lb waer Using heavailabiliy figre of 40 percen from ig 8 we nd ha4730B/lb of waer are reqired This answer is in goodaeemen wih he resl of 4700 B/b obained fromig. 7b

is no o be conclded ha sperheaed vapor incin

eraion shold no be sed becase he fel cos behi n fac he sysem shown in ig 2 ses i a hebrner is also qie applicable for smal sreams where70r-"

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-

x-

o

C cwh exess

gs

20 10 IIL

1 15 2CMUSI MPERATURE _OF

8 X

2

20

he relaively high fel coss may be less han eqipmendepreciaion and mainenance coss reqired for morecomplex sysems or arge size sreams a carefl evalaion of he sperheaed vapor incineraion verss heevaporaing incineraor shold be made.

The choice of axiliary fels for sperheaing vaporincineraors is a sbjec of debae. I is relaively easy oinsall dal gas gns and waer aomizing nozzles in asingle air reser and o obain qaliy combsion Daoi and waer nozzles in a sine reser sffer some deerioraion in performance since he wo aomized spraysinerfere wih one anoher This can be compesaed forin nis wih a flame hoding diffser a he end of heaomizing nozzes by greaer rblence prodced byhigher han norma brner reser pressre drops Theahor has also had some sccess wih direc mixing ofeiher No 2 fe oi or solvens direcly wih he aqeoswase ino a sine line prior o aomizaion a singlenozzle Oils reqiring heaing for proper aomizaion canno be sed in sch an arrangemen

L

) Every effor shold be made o apply proper combsion fdamens when aqeos wases are disposed

of by incineraion These inclde he ammabliy zonesfor which here is need of more fndamenal knowledge

in he viiaed reon2) Of he hree mehods of reaing aqeos wases,

viz heaing evaporaion and sperheaing none serve all appicaions Each ms be evalaed for eachspecic applicaion

[1] Schut, H C. and Lofus Jordan "Waste Waer Recon

ditoned by Carrer Gas il and Ga Jural, Vo. 64 No. 32Augus, 1966.

[2] Coward H. F and Jones, G. W. Limts of Flammabity

of Gases and Vapors Bureau of Mnes Bulletin N. 503, U. S.Governmen Prinng Ofce 1952.

3] Zabearis M. G. "Fammabiity Characerscs of Com

busibe Gases and Vaors Bureau of Mines Bulletin N. 7U. S Governmen Printng Oce 196