cpu-final
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CONTENTS
Introduction of CPU
Need of CPUService cycle of CPURegeneration process
Case studyBenefitsConclusion
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INTRODUCTION
The Condensate polishing units are typically installed for super
thermal power station with the main objective of improving the
boiler water quality. The benefits of condensate polishing is
quicker start up and as a result full load conditions are reached
early giving economic benefits. Orderly shut down is possible in
the case of condenser tube leak conditions.
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NEED OF CPU
The Condensate Polishing Unit removes
'CRUD' - corrosion products consisting
mostly of oxide of iron, copper or nickel
Dissolved Solids - mostly consisting of
sodium, chloride and silica andDissolved Gases-Carbon dioxide.
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1. Contamination from Make up water
2. Use of impure water for dosing system.
3. Use of impure dosing chemicals
4.Residues from Chemical Cleaning operation
5.Condenser tube leakage.
SOURCES 0F CONTAMINATION
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RSTPS 500MW each CPU havingprovision to utilize 50 % for condensatetreatment
AUTO BYPASS allow BYPASSING
of CPU at set pressure
CPU DESCRIPTION
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CPU-A CPU-BBY
PASS
From CEP
To deareator
CPU SERVICE VESSELS
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During service the CPU O/L is monitored for pH, Cation
Conductivity (max 0.1 mhos/cm ) and sodium.
The service cycle of CPU consists of
1.H+ cycle - when cations are exchanged with H +
2.NH3 cycle - when cations are exchanged with NH 4+.
SERVICE CYCLE OF CPU
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During the H + cycle , dosing of Ammonia
at CPU O/L is essential to maintain the pH of the system.
H+ cycle duration is 6 to 7 days
NH4+ cycle duration is 14 days
SERVICE CYCLE OF CPU
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Cation exchange during service cycle
R- SO3 H + NaCl R- SO3Na + HCl
R- SO3
NH4
+ NaCl R- SO
3Na + NH
4Cl
Anion exchange during service cycle
R- NR3OH + HCl R-NR3Cl + H2O
SERVICE CYCLE OF CPU
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R- NR3OH + NH4Cl R-NR3Cl + NH4OH
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SERVICE CYCLE OF CPU
DESIGN PERFORMANCE(under normal operating conditions )
PARAMETERS HYDROGEN AMMONIACYCLE CYCLE
_____________________________________________________ TOTAL CRUD, ppb
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REGENRATION PROCESS
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1. BACK WASH TO SEPARATE RESINS2. INJECT ANION RESIN REGENERANT3. RINSE ANION RESIN
4. INJECT CATION RESIN REGENERANT5. RINSE CATION RESIN6. DRAIN BED7. AIR MIX THE RESINS
8. ALLOW BED TO SETTLE9. REFILL UNIT10.RINSE
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REGENRATION PROCESS
SERVICEWATER IN
ACID IN BACK WASH OUT NaOH IN
NaOH OUT
BACK WASH INMIXING AIR IN
ACID OUT
SERVICE WATER OUT
Mixedcation andanion resin
Anionresin
Cationresin
Anionresin
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TYPICAL REGENRATION CONDITIONS FOR RESINS IN MIXED BED
ANION CATION
Regeneration level , g/l resin 64 64
Regenerant concentration wt% 4 5
Regeneration injection time , h 0.5 0.5
Regeneration flow rate , BV/h 3.2 3.2
Rinse time , h 0.5 0.5
Rinse volume(BV) 5 5
Regenerant NaOH HCl
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CASE STUDY ON RSTPS STAGE 2 CPUAMMONIUM CYCLE
IT IS OBSERVED THAT WHEN RSTPS STAGE 2 CPUOUT LET pH EXCEEDS 6.2 CHLORIDE IS LEAKING
BUT IN STAGE 3 CPU UP TO 9.0 pH THEREIS NOCHLORIDE LEAKING
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IF WE OBSERVE HYDROGEN CYCLE
AT CATION RESIN:R-H + Na+ R-Na + H+
R-H + NH4+ R-NH4 + H+
R-OH + Cl R-Cl + OH
AT ANION RESIN:
FINAL OUT PUT IS:
H+ + OH H2O
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IF WE OBSERVE AMMONIUM CYCLE
AT CATION RESIN:R-NH4 + Na+ R-Na +NH4+
R-OH + Cl R-Cl + OH
AT ANION RESIN:
FINAL OUT PUT IS:
NH4+ + OH NH4OH
SO WE OBSERVE IN AMMONIUM CYCLE THERE IS A RISE IN pH.ALONG WITH RISE IN p H CHLORIDE IS LEAKIG. SO WE CAN NOTGET THROUGHPUT IN AMMONIUM CYCLE WHERE AS DESIGNEDTHROUGHPUT IS 226800M 3 .
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SO WE CAN PREDICT CHEMICAL REACTION AS FOLLOWS
NH4OH + R-Cl NH4 Cl + R-OH
IT IS A EQUILLIBRIUM REACTION AND FORWARDREACTION IS MORE FAVOURABLE
FORWARD EXPLAINS FOR CHLORIDE LEAKING
NH4OH + R-Cl NH4 Cl + R-OH
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ACCORDING TO CHEMICAL KINETICS RATE OF THE REACTIN IS
PROPORTIONAL TO THE CONCENTRATION OF RECTANTS.
FOR CONTROLLING CHLORIDES RATE OF FORWARD REACTIONSHOULD BE LOW.THAT MEANS WE HAVE TO DECREASE NH4OH , R-ClCONCENTRATIONS.
THIS IS NOTHING BUT REGENERATION OF ANION AND CATIONRESIN AND THIS IS THE ONLY PRACTICE.
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BACKWARD REACTION IS:
NH4 Cl + R-OH NH4 OH + R-Cl
THIS IS THEREACTION RESPONSIBLE TRAPING THE CHLORIDES INRESINE.FOR CONTROLLING CHLORIDES RATE OF THIS REACTIONSHOULD BE HIGH.THAT MEANS WE HAVE TO INCREASE NH4Cl , R-OHCONCENTRATIONS.BUT IT IS NOT POSSIBLE.ACCORDING TO CHEMICAL KINETICS RATE OF THE REACTIN IS
DEPEND UP ON THE NATURE OF RECTANTS ALSO.
SO WE HAVE TO UPGRADE THE ANION RESIN IN SUCH AWAYTHAT ANION RESIN SHOULD TRAP THE CHLORIDES.
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1. REDUCTION IN CBD HOURS&MAKE UP2. CONTROL IN DRUM PRESSURE RESTRICTION3. CHEMICAL CONTROL DURING STARTUP IS VERY
EFFECTIVE
4. ORDERLY SHUTDOWN POSSIBLE IN CASE OFCONDENSOR TUBE LEAK CONDITION5. IMROVEMENT IN QUALITY OF STEAM WHICH RESULT IN
ENHANCED TURBINE LIFE6. IMPROVEMENT IN BOILER WATER QUALITY FOR DRUM
TYPE BOILERS7. QUICK STARTUP AND AS RESULT,FULL LOAD
CONDITIONS ARE REACHED EARLY GIVING ECONIMICBENEFITS
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BENEFITS
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CONCLUSION
Condensate polishing is a proven method of maintaining the purity in the steam/water
circuits. It protects against condenser leakages ,removes traces of ionic impurities & crud fromcondensate before it is recycled to boiler. It reduces CBD hours and save water
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