HP LP BYPASS SYSTEM:The HP LP Bypass System is designed to maintain the M. S. Pressureat Turbine end at a pre-set desire value during the different Load Conditions of the mahine.Functions:The main funtions of HP-LP Bypass System are! MaintainsTurbineendMainSteamPressureat apre-set desirevaluebydumpingthee"esssteam# $hihisgeneratedintheBoiler# diretly to the Condenser by bypassing its normal flo$ path. %edues Start-up Time by irulating huge &uantity of steam in thebypass path# $hih auses faster rise of steam parameters 'mainlysteam temperature and pressure(# during start up period. )ntrodues *onomi +peration by saving ,. M. -ater losspartiularly during start-up. ,rastially uts do$n the Sound Pollution Levelpartiularly duringstart-up. ProtetsSuper-heaterand %e-heater Coilagainstover-heatingbyirulating steam through it partiularly during start-up.HIGH PRESSURE BYPASS i.e. HP BYPASS SYSTEM:Introduction: .sthenameindiates# theHPBypassSystemdumpstheMainSteam 'MS( from MS Line to C% Line diretly by bypassing the H. P.Turbine. The main ob/et of H. P. Bypass System is to maintain Main SteamPressure at H. P. Turbine end at a pre-set desire value by dumpingthe e"ess main steam to the C. %. Line in suh a $ay so that theparameters 'Pressure and Temperature( of the dumped steam $ill1 / 25 mathes $ith the design parameters 'Pressure and Temperature( ofthe C. %. Pipe Line. The shemati diagram of HP Bypass System is sho$n in Fig - bello$.2 / 25 0rom the shemati diagram of HP Bypass Station# it is lear thatthere are t$o numbers Steam 1alve namely HBP2 3 HBP4 andthree numbers Spray -ater 1alve namely BP*2# BP*4 3 B,. .ll these five valves are basially Control 1alve.HBP ! HBP": 5o$# HBP2 3 HBP4 are the Pressure Controller# $hih ontrolsits6pstreamPressurei.e.HBP23HBP4ontrolstheM. S.Pressure at H. P. Turbine inlet at a pre-set desire value by dumpingthe e"ess main steam# if there# diretly to the C. %. Line. The valve HBP2 3 HBP4 starts to 7+P*58 $hen M. S. Pressureat H. P. Turbine inlet rises above the pre-set desire value and startsto 7CL+S*8 $hen M.S. Pressure at H. P. Turbine inlet falls belo$the pre-set desire value.BPE ! BPE": 5o$# BP*2 3BP*4 are the Temperature Controller# $hihmaintains the ,o$n StreamTemperature of HBP2 3HBP4respetivelyat apre-set desirevaluebyspraying$ater intothedumped steam. Basially it ontrols the &uantity of attemperation flo$'Spray-ater(. So# BPE- ! BPE" are the Spray -ater 0lo$ Controller. The valveBPEstarts to 7+P*58 $hen the ,o$n StreamTemperature of HBP2 valve rises above the pre-set desire valueandstarts to7CL+S*8 $henthe,o$nStreamTemperatureofHBP2 valve falls belo$ the pre-set desire value. The valveBPE"starts to 7+P*58 $hen the ,o$n StreamTemperature of HBP4 valve rises above the pre-set desire valueandstarts to7CL+S*8 $henthe,o$nStreamTemperatureofHBP2 valve falls belo$ the pre-set desire value.B#:3 / 25 Basially#B#isaPressureController# $hihontrolsits,o$nStream Pressure i.e. the Spray -ater Pressure at the inlet of BP*23 BP*4 valves at a pre-set desire value 'Say 299 :g;m4(. Pratially# B, is the Spray -ater Pressure Controller. The valve B# starts to 7+P*58 $hen its ,o$n Stream Spray -ater Pressure falls belo$ the pre-set desire value es plae inside thevalve. To redue the pressure further# a T+rott)ing #e/ice is ereted onthedo$n steamof eah HP Bypass 1alve and pressuredrop isassuredbyinreasingthearea'i.e. volume( of thesteamflo$path# /ust after the Throttling ,evie# suddenly. )n the Fig. ". an attempt has been ta>en to e"plain the onstrution of P%,S 'Pressure%eduing and ,e-super Heating( unit and Throttling ,evie of the H. P. Bypass Station.5 / 25 HP Bypass Station dumps main steam to C% Line by ontrolling the +P*5)5? of its t$o steam valve BP-2 3 BP-4. +ne Pressure Master Controller and t$o Slave Controller ontrol the opening of steam valve BP-2 3 BP-4. The Pressure Master Controller is ommon for both BP-2 3 BP-4 but Slave Controller is separate and independent for BP-2 3 BP-4.+ut of above said t$o Slave Controller# one is for BP-2 and other oneis for BP-4. The Pressure Master Controller omprises of Pressure Transmitter'PT( and Current to 1oltage onverter ');*(# Pressure Setter# *rror ?enerator and one P) Controller. The Slave Controller omprises of Memory Card# Position 0eedba> Transmitter and Current to 1oltage onverter ');*(# *rror ?enerator# +utput amplifier and *letro-Hydrauli .tuator. .tual MS Pressure at HPT end is sensed 'measured( by PressureTransmitter 'PT( and Position 0eedba> Transmitter '0;B Transmitter(is used to measure the atual opening the valve 'here either BP-2 or BP-4(. Pressure Setter is to generate ,esire Set 1alue for main steam at HP turbine end. ,epending upon the differene bet$een .tual MS Pressure and Set Pressure# Pressure Master Controller generates the signal 'P) position demand signal( for final opening position of BP-2 3 BP-4. 5o$# if the memory is in .6T+ mode then the Slave Controller $ill ta>e ation to re-position the valve# if re&uired# after omparing the atual valve position '+utput of 0;B Transmitter( $ith P) position demand signal. Control Sheme for BP-2 is sho$n in Fig. 0 bello$s.6 / 25 7 / 25 Ho$(ontro))er is Functioningto contro) MS Pressure 't HPT end1 ToControl the6pstreamPressurei.e.M. S.Pressureat HPT)nlet# theM. S. Pressure'Patual( isompared$iththePre-setdesire Pressure 'P set(. )f theatual M. S. Pressure'Patual( ishigher thanthePre-setdesire Pressure 'P set(# then HP Bypass 1alve $ill start to 7+P*58. )f the atual M. S. Pressure 'P atual( is lo$er than the Pre-set desirePressure 'P set(# then HP Bypass 1alve $ill start to 7CL+S*8. )nboththeaboveases# theHP Bypass1alves$ill ontinueto+P*5 ; CL+S* till the atual M. S. Pressure is not mathing $iththe Pre-set desire Pressure. .s soon as the atual M.S. Pressure mathed $ith the setPressure# the HP Bypass 1alve $ill stand hold at its last position. The shemati diagramof the Pressure Control Loop of HPBypass System is sho$n in Fig.- 0 bello$.8 / 25 Fig. - 0: Loo& #i'gr', o- t+e Pressure (ontro))er o- HP B%&'ss S%ste,.9 / 25 HP B%&'ss St'tion2s #o$n Stre', Te,&er'ture (ontro) i.e. HP B%&'ss St'tion2s S&r'% 3'ter F)o$ (ontro): For $+'t Te,&er'ture (ontro) o- du,&ed ,'in ste', is essenti')1 -hen High Temperature Steam mi"es $ith the omparatively Lo$ Temperature Steam# then there are the hanes of development of thermal stress. Some times# the energy of this thermal stress may be so high that it may be the ause thermal failure of the system. So# $henever# $e $ill mi" high-temperature steam $ith omparatively lo$temperature steam# then $e have to ta>e are to avoid thermal stress. 5o$# HP Bypass Station dumps the hot main steam# having temperature in the range of @A9 oC# to the C% Line# through $hih omparatively lo$ hot old reheat steam# having temperature in the range of BC9 oC - BD9 oC# is flo$ing. 5o$# $ithout ta>ing any preautionary measure# if HP Bypass Station diretly dumps the hot main steam to the C% Line# then huge thermal stress $ill be develop inside the C% Line $hen hot main steam $ill try to mi" $ith the omparatively ool Cold %eheat Steam. The energy of the said thermal stress $ill be so high that it $ill totally destroy the $hole C% Line. To avoid this# the HB Bypass Station redues the temperature of the dumped steam before dumping it into the C% Line.Ho$ t+e Te,&er'ture o- du,&ed ,'in ste', is contro))ed1 To redue the temperature of the dumped steam# in the 1alve Chamber# attemparation $ater is sprayed into the dumped steam. -esaid early that the HB Bypass 1alves are itself a P%,S unit. The valves are designed ; onstruted in suh a manner so that its attemparator brea>s spray $ater into partile before in/eting it into the dumped steam.10 / 25 Spray $ater is sprayed after brea>ing it into partile for the reason so that it an easily mi" $ith the dumped steam ompletely and no $ater partile an reah into the re-heater oil. )t is lear that by in/eting attemparation $ater# HP Bypass Station ontrols the temperature of the dumped steam i.e. the do$nstream temperature HP Bypass Station. Ho$ t+e HP B%&'ss Te,&er'ture (ontro))er i.e. HP B%&'ssSt'tion2s S&r'% 3'ter F)o$ (ontro))er is Functioning 1 The HP Bypass station has t$o steam valves# $hih dumps mainsteam into the C% Line. 5o$# these t$o valves may dump different&uantity'Tonnage(of mainsteam. So# do$nstreamtemperatureofthese valves may be different. .s a result# the do$nstreamtemperature of eah HP Bypass 1alves is ontrolled separately. Toontrol thetemperature# theatual do$nstreamtemperature'Tatual(of eahvalveisseparatelyompared$ithapre-set desirevalue 'Tset(. )f TatualETset# thentheorrespondingattemparationflo$ontrolvalveTPP( by means of speial eletroni >t. 5o$# to ontrol Hot %e-heat Steam Pressure at )P Turbine inlet# the steam valves LBP 3 LBP " of LP Bypass System dumps the e"ess %e-heat steam# if any# diretly into the Condenser in suh a manner so that the parameters i.e. the pressure of dumped %e-heat steam mathes $ith the allo$able design steam pressure of the Condenser. )n short# the steam valves LBP 3 LBP " of LP Bypass System maintains the Hot %e-heat Steam Pressure at the pre-set desire value and if neessary# bypassing the )P Turbine and LP Turbine# dumps %e-heat Steam# after hanging its pressure $hih isin the allo$able ; permissible limits of the Condenser# diretly in to the Condenser. To ontrol i.e. to redue the pressure of the dumped steam# speialare has been ta>en in the design of the valve LBP 3 LBP ". 18 / 25 These t$o valves are designed in suh a fashion so that they at as PR Unit 'Pressure %eduer(. So# basially# the valve LBP 3 LBP " are the pressure ontrol valves $hih is driven by a single Master Pressure Controllerand t$o separate Slave Controller.LBPE 3 LBPE ": The tas> of Spray -ater 1alves LBPE 3 LBPE " are to ontrol the Temperature of dumped Steam at the do$nstream of LBP 3 LBP " respetively. To ontrol the Temperature of dumped steam at the do$n stream of LBP 3 LBP " i.e. in short# the do$n stream temperature of LBP 3 LBP " at a pre-set desire value# the valves LBPE 3LBPE " sprayed $ater# $hih is ta>en from the ,isharge Header of C*P# in to the dumped steam is suh $ay so that the attemperated $ater mi"es $ith the dumped steam properly. Pratially# by means of attemperator# $ater is sprayed in partile form. Actually, the valves LBPE 1 & LBPE 2 are the Spray Water Flow Control Valve, which is driven by two separate Temperature Controller.19 / 25 LP Bypass Pressure Controller: The shemati diagram of Pressure Control Loop is sho$n in Fig.: : bello$. ToControl the6pstreamPressurei.e. H%SteamPressureat )PT)nlet# theH%SteamPressure'Patual( isompared$iththePre-setdesire Pressure 'P set(. )f the atualH% Steam Pressure 'Patual( is higher than the Pre-setdesirePressure'Pset(# thenLPBypass1alvesLBP-!LBP-"$illstart to 7+P*58.20 / 25 )f theatual H%SteamPressure'Patual(islo$erthanthePre-setdesirePressure'Pset(# thenLPBypass1alvesLBP-!LBP-"$illstart to 7CL+S*8. )n both the above ases# the LP Bypass 1alvesLBP- ! LBP-"$illontinue to +P*5 ; CL+S* tillthe atual H% Steam Pressure is notmathing $ith the Pre-set desire Pressure. .ssoonastheatual H%SteamPressuremathed$iththesetPressure# the LP Bypass 1alve $ill stand hold at its last position.21 / 25 LP B%&'ss Te,&er'ture (ontro))er i.e. LP B%&'ss S&r'% 3'ter F)o$ (ontro))er: The shemati diagram of Temperature Control Loop of LBPE - issho$n in Fig.: ; bello$. TheLP Bypassstationhast$osteamvalves# $hihdumpsH%Steaminto the Condenser. 5o$# these t$o valves may dumpdifferent &uantity 'Tonnage( of H% Steam. So# do$nstreamtemperature of these valves may be different. .s aresult# thedo$nstreamtemperatureof eahLPBypass1alveisontrolledseparately.22 / 25 Toontrol thetemperature# theatual do$nstreamtemperature'Tatual( of eah valve is separately ompared $ith a pre-set desirevalue 'Tset(. )f TatualETset# thentheorrespondingattemparationflo$ontrolvalve