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Low Drum Level in Boilers - A Major Cause of Concern

written by: Dr V T Sathyanathan • edited by: Lamar Stonecypher • updated: 5/18/2011

Drum leel in a boiler indicate! the leel o" water in the drum aailable "or !team #eneration$Low drum leel operation lead! to aailability lo!! o" the boiler$ Low%leel trip! in a boiler mu!talway! be re!ponded to &uic'ly and correctly$

• The drum leel in a boiler i! maintained near the preiou!ly de"ined normal water leel(

which #enerally i! below the #eometric center o" the drum$ )aintainin# a hi#h drum leel ha! it!

own problem! li'e carryoer o" !alt to !uperheater! etc$( but low drum leel operation ha! muchmore !eriou! e""ect on the boiler tube!$ *heneer thi! happen!( the operator i! warned by alarm

to ta'e correctie action$ +" thi! i! not re!ponded to and the drum leel #oe! "urther down to a

dan#erou!ly low leel( the boiler trip! on auto to protect the boiler$ The !peci"ic cau!e! "or adrum leel trip( the boiler re!pon!e( and the immediate action o" the boiler control room operator

and the local operator are #ien in outline "orm below$

Specific causes

o ,ne "eed pump trip!

o )al%operation o" "eed control auto

o )al%operation o" "eed pump !coop

o )al%operation o" "eed control / re#ulatin# ale

o Sudden reduction in load

o Sudden trippin# o" one or more mill!

o Tube "ailure in water wall with lar#e openin#

o )al%operation o" emer#ency drain ale

o )al%operation o" low point drain

Plant response

o Low drum leel alarm

o Very low drum leel trip

Immediate boiler desk operator action

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o Start re!ere "eed pump i" needed

o -han#e to manual "eed water control i" re&uired

o  .eer by%pa!! the ery low drum leel trip

o Trip the unit i" the i!ible leel #oe! out een i" auto did not act

Immediate local operator action

o -hec' the tripped pump( recti"y cau!e and in"orm boiler de!' operator that it i!

ready "or re!tart

o -hec' "or po!!ible tube lea' in "urnace "ir!t and other area! i" needed

o -hec' drum drain and low point drain "or po!!ible openin#

o -hec' the "eed water auto controller in local and in"orm condition( al!o arran#e

"or recti"ication

o -hec' "eed controller "or any lin' "ailure

The e""ect o" ery low drum leel operation i! ery !eere that it can cau!e the water wall tube!to #et oerheated it can cau!e !na'in# o" water wall tube! leadin# to lot o" proection in and out

o" "urnace$ +t can cau!e in!tant !hort term "i!h mouth tube "ailure! in water wall$ Thi! 'ind o"

"ailure ha! led to "urnace eplo!ion under certain !peci"ic condition! and ba!ed on the location o" the "ailure$ +" the "ailure o" the tube i! in !uch a location in "urnace that the !team comin# out o"

the tube mie! with the coal particle! to "orm producer #a!( then an eplo!ie miture "orm! and

the boiler "urnace eplode!$ The oerheatin# i! !een to happen in many water wall tube! ratherthan a !in#le tube a! eperienced in many ca!e!$

ecti"ication o" the "urnace wall become! more di""icult and time con!umin# a! it re&uire!

eten!ie chec'in# both by an .DT 3non%de!tructie te!tin#4 method a! well a! a !amplin#

method$ Leain# tube! that hae !na'ed may not lead to any ader!e e""ect in per"ormance o" the boiler ecept in certain !peci"ic location!( li'e near the burner where "uel impin#ement can occur 

and cau!e "uel a!h ero!ion$

The rea!on "or !uch maor "ailure o" water wall tube! when the drum leel #oe! to lower than the

ery low limit i! due to the "act that the !team in the drum #et! entrained in the down comer! o"the circulation !y!tem( and thi! up!et! the whole natural circulation in the boiler$ *hen the

circulation in "urnace tube! i! up!et( the coolin# o" tube! doe! not ta'e place e""ectiely( which

lead! to "ailure o" tube! due to !hort term oerheatin#$

 

Low Drum Level

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