Condensate Polishing Unit - CPU

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Condensate Polishing Unit - CPU

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CONDENSATE POLISHING UNIT

HIGH SPEED MIXED BED(A RESIN BASED ION EXCHANGE SYSTEM)


CPU-SYSTEM


WHY CPU ?• IT MAKES COST-EFFECTIVE OPERATION OF BOILER

WATER SYSTEM:

• By reducing blow-down & make-up water requirements.

• Improvement in boiler water quality for drum type boiler.

• Quick start-up and as a result full load condition are

reached early.

• Orderly shutdown possible in case of condenser tube leak

condition.

• Improvement in quality of steam which results in enhanced

turbine life.


WHAT IT CONTROLS• CPU CONTROLS:

• Corrosion (crud) transport.

• Ingress of impurity through make-up water.

• Condenser cooling water leaks.


POTENTIAL FOULING SOURCES


HOW IT CONTROLS• BY REMOVING:

• Dissolved contaminates: Chloride, Silica, Sodium etc.

• Suspended contaminates: Iron, Copper etc.


WHAT AFFECTS ITS PERFORMANCE• FACTORS AFFECTING ITS PROCESS:

• Flow-rate

• Regeneration

• Composition of water to be treated

• Quality & quantity of treated water


FLOW RATE• High flow rate results in:

I. Increased pressure: Lead to physical breakdown of resins due to osmotic stresses.

II. Large beads proportionately decreases the surface area available for ion exchange resulting in inferior quality of water.

• Low flow rate results in:

I. Inferior quality: Due to improper ion exchange for want of proper velocity with insufficient bed volume


REGENERATION• At Service• R – H+ + NaCl → R – Na+ + HCl• R – OH- + HCl → R – Cl- + H2O

• At Regeneration• R – Na+ + HCl → R – H+ + NaCl • R – Cl- + NaOH → R – OH- + NaCl

• Reduces residual ions (cations and anions) leaked from the water system.

• CPU works on the same principle on which MB works in the DM plant.


HOW ION EXCHANGE RESIN WORKS


MIXED BED RESINS


REGENERATION• Improper resin separation will result in inferior

outlet water quality because:

i) Anion resin will be converted to Cl- form

ii) Cation resin will be converted to Na+ form


RESIN CLEANING METHODS• Back Washing: Prior to and after acid or caustic injection. Back

washing flow rates are such that bed expansion is 100% and whole beads are not lost during this process, fine/broken beads are also eliminated.

• Air Scrubbing/Rinsing Operation: Air scrubbing of resins is done in the tank with water up to resin top surface (for one minute), vessel pressurized with air (0·4 to 0.5 kg/cm2) and down flow rinse given by releasing pressure through rinse outlet for two minutes.

• Ultrasonic Cleaning: Ultrasonic cleaning devices have now been developed to clean the resins by ultrasonic transducers mounted outside a cleaning tank. The resin slurry is introduced from top of the tank with reverse water flow from bottom to top to carry away loosened crud and resin fines.


CPU REGENERATION STATION


REGENERATION STEPS

1. Transfer of the full resin charge from the operating vessel (MB) to

the cation regeneration tower CRT.

2. Transfer of the small mixed resin stored in the interface isolation

vessel IIV to the CRT.

3. Backwashing the resin in the CRT.

4. Transfer of the anion resin only from the CRT to the anion

regeneration tower ART.

5. Transfer of the small layer containing mixed resin to the IIV.

6. Acid injection in the CRT for regeneration of the cation resin which

doesn't contain any anion resin


REGENERATION STEPS

7. Injection of caustic soda into ART for regeneration of the anion

resin which doesn't contain any cation resin; this can be made

simultaneously with step 6.

8. Transfer of the regenerated cation resin into the mixing and

storage vessel MSV.

9. Transfer of the regenerated anion resin into the mixing and

storage vessel MSV.

10. Mixing the resin in the MSV with clean air or nitrogen.

11. When needed, the regenerated resin charge is transferred

back to of the operating units


Action to be taken for better efficiency• Cross contamination of resin to be tested after every 5

regenerations.• Screen testing of resin to be tested after every 10

regenerations.• Chloride content in caustic used for anion regeneration should

be compatible with rayon grade • A.R. grade ammonia to be used for boosting pH in

condensate. • Both cation and anion resin quantities are to be made up to

the design quantities so as to maintain their interface level in resin separation unit.

• Complete resin transfer from service vessel to regeneration vessel and vice versa to be ensured.


Composition of Water to be Treated• Cation: Ammonia,

Copper,

Iron,

Sodium.

• Anion: Chloride,

Sulphate,

Phosphate,

Silica.

• Others: TSS & Residual TDS


Quality & Quantity of Treated Water

• It largely depends upon leaching particularly Na

• H-Cycle gives ideal result

• NH3-Cycle susceptible in passing of Na more than in

comparison to H-Cycle.


CYCLES OF DEEP BED MB• Hydrogen Cycle

• [RES]-H+ + NH4+ → [RES]-NH4+ + H+

• 7 days (168 Hours)

• Ammonia Cycle

• [RES]-NH4+ + Na+ → [RES]-Na+ + NH4+

• 14 days (336 Hours)


CPU DESIGN OPTIONS

Cylindrical Mixed Bed Unit (4Mpa)


CPU DESIGN OPTIONS

Spherical Mixed Bed Unit (>4MPa)


Tentative Limiting ParametersParameters Units Normal Starting

Suspended Solids

ppb 10 100

Na+ ppb <1 <5

SiO2 ppb <10 <50

Fe ppb <5 <100

Cu ppb <3 <15

Cl- ppb <1 <10

Cation Cond. uS/cm <0.15 <0.2

pH - 6.7-7.5

TDS ppb <20 <50


Tentative Limiting Parameters

• Condensate Temperature: a) Normal operating Temperature: < 50°C

b) Max. Temperature: 60°C

• Maximum Pressure Drop: <0.35MPa


LIMITATIONS• Precautions should be taken to avoid the following:• In case of deep bed CPU, immediately after regeneration the bed

may leak-out some residual regenerant chemicals thus contaminating

feed water quality.

• Any disintegration of resin in CPU will directly cause contamination of

feed water by disintegrated resin.

• Since CPU is installed in the main steam water circuit, it may result in

operational disturbances such as excess pressure drop across CPU.

• Pressure and temperature of influent to CPU may not be always

compatible with the design conditions. This may impair the resin

characteristics.


Equipment Description @ SPGCL

S. No. Equipment Description

1 Mixed Bed 3 No's/Unit

2 Flow (M3/Hr) 391

3 Max Pressure (Mpa) 4.0

4 Max Temperature (°C) 60

5 Max DP (Mpa) <0.2


Presentation byRama Chandra Reddy Butcha

Group Head – Chemical & EnvironmentTata Power Company Limited


Presentation byRama Chandra Reddy Butcha

Group Head – Chemical & EnvironmentTata Power Company Limited

Science

Condensate Polishing Unit - CPU