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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


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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


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R- NR3OH + NH4Cl R-NR3Cl + NH4OH

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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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