Boiler Name

8/19/2019 Boiler Name

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Boiler name-plateIn the latter half of the 19th century explosions of steam boilers were commonplace. Asa consequence of this, a company was formed in Manchester with the objective of

reducin the number of explosions by subjectin steam boilers to independentexamination. !his company was, in fact, the beinnin of today"s #afety $ederation%#A$ed&, the body whose approval is required for boiler controls and fittins in the '(.

Fig. 3.7.1

Boiler name-plate After a comparatively short period, only eiht out of the 11 ))) boilers examinedexploded. !his compared to *+) steam boiler explosions in boilers not examined by thescheme. !his success led to the oiler -xplosions Act %1*& which included arequirement for a boiler name/plate. An example of a boiler name/plate is shown in$iure 0..1.

!he serial number and model number uniquely identify the boiler and are used whenorderin spares from the manufacturer and in the main boiler lo boo2.

!he output fiure quoted for a boiler may be expressed in several ways, as discussed in

previous !utorials within this loc2.

Safety valves An important boiler fittin is the safety valve. Its function is to protect the boiler shellfrom over pressure and subsequent explosion. In the '(3


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In -urope, matters relatin to the suitability of safety valves for steam boilers areoverned by the -uropean standard -4 1*950. In the '# and some other parts of theworld, such matters are covered by A#M- standards.

Many different types of safety valves are fitted to steam boiler plant, but enerally theymust all meet the followin criteria3

• !he total dischare capacity of the safety valve%s& must be at least equal to the

"from and at 1))67" capacity of the boiler. If the "from and at" evaporation is usedto si8e the safety valve, the safety valve capacity will always be hiher than theactual maximum evaporative boiler capacity.

• !he full rated dischare capacity of the safety valve%s& must be achieved within

11) of the boiler desin pressure.

• !he minimum inlet bore of a safety valve connected to a boiler shall be *) mm.

• !he maximum set pressure of the safety valve shall be the desin %or maximum

permissible wor2in pressure& of the boiler.• !here must be an adequate marin between the normal operatin pressure of

the boiler and the set pressure of the safety valve.

Safety valve regulations (UK)


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Fig. 3.7.2Boiler safety valve

A boiler shall be fitted with at least one safety valve si8ed for the rated output of theboiler / :efer to -4 1*950 for details.

!he dischare pipewor2 from the safety valve must be unobstructed and drained at the

base to prevent the accumulation of condensate. It is ood practice to ensure that thedischare pipewor2 is 2ept as short as possible with the minimum number of bends, sothat the allowable bac2pressure indicated by the valve manufacturer is not exceeded.

It will be quite normal for the internal diameter of the dischare pipewor2 to be morethan the internal diameter of the safety valve outlet connection, but under nocircumstances should it be less.

oiler stop valves


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Fig. 3.7.3Boiler stop valve

A steam boiler must be fitted with a stop valve %also 2nown as a crown valve& whichisolates the steam boiler and its pressure from the process or plant. It is enerally ananle pattern lobe valve of the screw/down variety. $iure 0..0 shows a typical stopvalve of this type.

In the past, these valves have often been manufactured from cast iron, with steel and

bron8e bein used for hiher pressure applications. In the '(, # *9) %eventually tobe replaced with -4 1*950& states that cast iron valves are no loner permitted for thisapplication on steam boilers. 4odular or spheroidal raphite %#;& iron should not beconfused with rey cast iron as it has mechanical properties approachin those of steel.$or this reason many boilerma2ers use #; iron valves as standard.

!he stop valve is not desined as a throttlin valve, and should be fully open or closed.It should always be opened slowly to prevent any sudden rise in downstream pressureand associated waterhammer, and to help restrict the fall in boiler pressure and anypossible associated primin.

!o comply with '( reulations, the valve should be of the "risin handwheel" type. !hisallows the boiler operator to easily see the valve position, even from floor level. !hevalve shown is fitted with an indicator that ma2es this even easier for the operator.


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down valve, with a disc chec2 valve sandwiched between the flanes of the crown valveand itself.

$eedwater chec2 valves!he feedwater chec2 valve %as shown in $iures 0..= and 0..5& is installed in theboiler feedwater line between the feedpump and boiler. A boiler feed stop valve is fittedat the boiler shell.

!he chec2 valve includes a sprin equivalent to the head of water in the elevatedfeedtan2 when there is no pressure in the boiler. !his prevents the boiler bein floodedby the static head from the boiler feedtan2.

Fig. 3.7.4 Boiler !e" valve

'nder normal steamin conditions the chec2 valve operates in a conventional manner to stop return flow from the boiler enterin the feedline when the feedpump is notrunnin. >hen the feedpump is runnin, its pressure overcomes the sprin to feed theboiler as normal.

ecause a ood seal is required, and the temperatures involved are relatively low%usually less than 1))67& a chec2 valve with a -?@M %-thylene ?ropylene& soft seat isenerally the best option.


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Fig. 3.7.#$oation of fee% !e" valve

oiler water quality control!he maintenance of water quality is essential to the safe and efficient operation of asteam boiler. !he measurement and control of the various parameters is a complextopic, which is also covered by a number of reulations. It is therefore covered in detaillater in this loc2. !he objective of the next few #ections is simply to identify the fittinsto be seen on a boiler.

!@# control!his controls the amount of !otal @issolved #olids %!@#& in the boiler water, and issometimes also referred to as "continuous blowdown". !he boiler connection is typically@415 or *). !he system may be manual or automatic. >hatever system is used, the!@# in a sample of boiler water is compared with a set point if the !@# level is toohih, a quantity of boiler water is released to be replaced by feedwater with a muchlower !@# level. !his has the effect of dilutin the water in the boiler, and reducin the!@# level.


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Fig. 3.7.&'ypial automati 'S ontrol system

Bottom lo*%o*n

!his ejects the slude or sediment from the bottom of the boiler. !he control is a lare%usually @4*5 to @45)& 2ey operated valve. !his valve miht normally be opened for aperiod of about 5 seconds, once per shift.

$iure 0.. illustrates a 2ey operated manual bottom blowdown valve whereas $iure0.. illustrates an automated bottom blowdown valve and its typical position in ablowdown system.

Fig. 3.7.7Key operate% manual ottom lo*%o*n valve


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Fig. 3.7.+

'ypial position for an automate% ottom lo*%o*n valve

?ressure aue All boilers must be fitted with at least one pressure indicator.

!he usual type is a simple pressure aue constructed to -4 1*950.

!he dial should be at least 15) mm in diameter and of the ourdon tube type, it shouldbe mar2ed to indicate the normal wor2in pressure and the maximum permissiblewor2in pressure B desin pressure.?ressure aues are connected to the steam space of the boiler and usually have a rintype siphon tube which fills with condensed steam and protects the dial mechanismfrom hih temperatures.

?ressure aues may be fitted to other pressure containers such as blowdown vessels,and will usually have smaller dials as shown in $iure 0..9.


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Fig. 3.7.,'ypial pressure gauge *it! ring sip!on

;aue lasses and fittins All steam boilers are fitted with at least one water level indicator, but those with a ratinof 1)) 2> or more should be fitted with two indicators. !he indicators are usuallyreferred to as aue lasses complyin with -4 1*950.


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Fig. 3.7.1auge glass an% fittings

A aue lass shows the current level of water in the boiler, reardless of the boiler"soperatin conditions. ;aue lasses should be installed so that their lowest readin willshow the water level at 5) mm above the point where overheatin will occur. !heyshould also be fitted with a protector around them, but this should not hinder visibility of the water level. $iure 0..1) shows a typical aue lass.

;aue lasses are prone to damae from a number of sources, such as corrosion fromthe chemicals in boiler water, and erosion durin blowdown, particularly at the steamend. Any sin of corrosion or erosion indicates that a new lass is required.

>hen testin the aue lass steam connection, the water coc2 should be closed.>hen testin the aue lass water connections, the steam coc2 pipe should beclosed.

'o test a gauge glass/ t!e follo*ing proe%ure s!oul% e follo*e%0

• 7lose the water coc2 and open the drain coc2 for approximately 5 seconds.

•

7lose the drain coc2 and open the water coc2.

>ater should return to its normal wor2in level relatively quic2ly. If this does nothappen, then a bloc2ae in the water coc2 could be the reason, and remedialaction should be ta2en as soon as possible.

• 7lose the steam coc2 and open the drain coc2 for approximately 5 seconds.


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;aue lass uards!he aue lass uard should be 2ept clean. >hen the uard is bein cleaned in place,or removed for cleanin, the aue should be temporarily shut/off.

Ma2e sure there is a satisfactory water level before shuttin off the aue and ta2e carenot to touch or 2noc2 the aue lass. After cleanin, and when the uard has beenreplaced, the aue should be tested and the coc2s set in the correct position.

Maintenance!he aue lass should be thorouhly overhauled at each annual survey. Cac2 of maintenance can result in hardenin of pac2in and sei8ure of coc2s. If a coc2 handlebecomes bent or distorted special care is necessary to ensure that the coc2 is set full

open. A damaed fittin should be renewed or repaired immediately. ;aue lassesoften become discoloured due to water conditions they also become thin and worn dueto erosion. ;lasses, therefore, should be renewed at reular intervals.

A stoc2 of spare lasses and cone pac2in should always be available in the boiler house. :emember3

• If steam passes are cho2ed a false hih water level may be iven in the aue

lass. After the aue has been tested a false hih water level may still beindicated.

• If the water passaes are cho2ed an artificially hih water level may be observed

due to steam condensin in the lass. After testin, the lass will tend to remainempty unless the water level in the boiler is hiher than the top connection, inwhich case water miht flow into the lass from this connection.

• ;aue lass levels must be treated with the utmost respect, as they are the only

visual indicator of water level conditions inside the boiler. Any water levelperceived as abnormal must be investiated as soon as it is observed, withimmediate action ta2en to shut down the boiler burner if necessary.

>ater level controls!he maintenance of the correct water level in a steam boiler is essential to its safe andefficient operation. !he methods of sensin the water level, and the subsequent controlof water level is a complex topic that is covered by a number of reulations. !hefollowin few #ections will provide a brief overview, and the topic will be discussed inmuch reater detail later.


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-xternal level control chambersCevel control chambers are fitted externally to boilers for the installation of level controlsor alarms, as shown in $iure 0..11.

Fig. 3.7.11

ternal level ontrol !amer

!he function of the level controls or alarms is chec2ed daily usin the sequencin purevalves. >ith the handwheel turned fully anticloc2wise the valve is in the "normal wor2in"position and a bac2 seatin shuts off the drain connection. !he handwheel dial may loo2similar to that shown in $iure 0..1*. #ome handwheels have no dial, but rely on amechanism for correct operation.


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Fig. 3.7.12urge valve !an%*!eel

!he followin is a typical procedure that may be used to test the controls when theboiler is under pressure, and the burner is firin3

• #lowly turn the handwheel cloc2wise until the indicatin pointer is at the first"pause" position. !he float chamber connection is baffled, the drain connection isopened, and the water connection is blown throuh.

•

?ause for 5 to seconds.• #lowly move the handwheel further cloc2wise to full travel. !he water connection

is shut/off, the drain valve remains open, and the float chamber and steamconnections are blown throuh. !he boiler controls should operate as for loweredwater level in boiler i.e. pump runnin and B or audible alarm soundin and burner cut/out. Alternatively if the level control chamber is fitted with a second or extralow water alarm, the boiler should loc2/out.

• ?ause for 5 to seconds.

• #lowly turn the handwheel fully anticloc2wise to shut/off aainst the bac2 seatinin the "normal wor2in" position.

#equencin pure valves are provided by a number of different manufacturers. -achmay differ in operatin procedure. It is essential that the manufacturer"s instructions befollowed reardin this operation.


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Internally mounted level controlsCevel control systems with sensors %or probes& which fit inside the boiler shell %or steamdrum& are also available. !hese provide a hiher deree of safety than those fittedexternally. !he level alarm systems may also provide a self/chec2in function on system

interity.

ecause they are mounted internally, they are not subject to the procedures required toblow down external chambers. #ystem operation is tested by an evaporation test to "1stlow" position, followed by blowin down to "*nd low" position.

?rotection tubes are fitted to discourae the movement of water around the sensor.

Fig. 3.7.13nternally mounte% level ontrols


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Air vents and vacuum brea2ers>hen a boiler is started from cold, the steam space is full of air. !his air has no heatvalue, and will adversely affect steam plant performance due to its effect of blan2etinheat exchane surfaces. !he air can also ive rise to corrosion in the condensate

system, if not removed adequately.

!he air may be pured from the steam space usin a simple coc2 normally this wouldbe left open until a pressure of about ).5 bar is showin on the pressure aue. Analternative to the coc2 is a balanced pressure air vent which not only relieves the boileroperator of the tas2 of manually purin air %and hence ensures that it is actually done&,it is also much more accurate and will vent ases which may accumulate in the boiler.!ypical air vents are shown in $iure 0..1=.

>hen a boiler is ta2en off/line, the steam in the steam space condenses and leaves avacuum. !his vacuum causes pressure to be exerted on the boiler from the outside, and

can result in boiler inspection doors lea2in, damae to the boiler flat plates and thedaner of overfillin a shutdown boiler. !o avoid this, a vacuum brea2er %see $iure0..1=& is required on the boiler shell.

Fig. 3.7.14'ypial air vents an% vauum rea"ers

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