Power plant chemistry ion exchange process

Power Plant Chemistry

Ion Exchange Process

Prepared By : -

Umar Farooq Chemist “A” Chemical Section

MSC ( Chemistry ) MBA ( Marketing )

[email protected]

[email protected]

SEC Shoaiba Jeddah

Saudi Arabia 1

mailto:[email protected]





Power Plant Chemistry

Table of Content

External Water Treatment

RO Desalination

MSF Desalination

Lime Soda Softening

Zeolite Softening

Demineralization

Weak Cation Resin

Strong Cation Resin

Weak Anion Resin

Strong Anion Resin

Mix Bed


It is the removal of impurities from water

out side the ( Condenser ) in power plant

because raw water taken from the river or

sea contain a large number of impurities

with respect to surrounding ,so it is very

necessary to make cleaned and purify the

water before it entrance to wards

( Condenser boiler )

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“A” Shoaiba Jeddah 4


Practically all surface water contain small

amount of mud, clay ,silt ,decayed, vegetation,

Micro Organisms etc.

To obtain required quantity of water

various techniques are applied Such as

Clarification ,Filtration ,Evaporation ,Softening,

Desalination (MSF & RO ) , Ion Exchange , De

Aeration , Aeration Note: External water treatment for Pretreatment System and RO

System already discussed in earlier training module

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What is RO Desalination

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Reverse osmosis is a membrane process where salty source water is supplied under pressure to a semi- permeable

membrane resulting in the passage of fresh water through the membrane prevents the passage of the dissolved minerals

leaving them in the concentrated brine

Seawater supply Pump

D M F

Cartridge

filter

H P Pump

Booster Pump

1st pass R O

E R D

2 nd pass R O 2 nd pass

Feed pump

Permeate

Transfer pump

Potabilisation

Backwash water

Tank

Out fall

To SWCC Shuaibah II

Storage Tank

S MBS

Anti scalant

Anti Scalant

Caustic soda Acid

Coagulant

Polymer

Back wash

7 Umar Farooq Chemist

“A” Shoaiba Jeddah

What is MSF Desalination

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Multi-stage flash distillation (MSF) is a water desalination process that distill sea water by flashing a portion of the water into steam in multiple stages of what are essentially counter current heat exchangers .Multi-stage flash distillation plants

produce 85% of all desalinated water in the world

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CEP

Sea Water Inlet

Starting Ejector

Brine Heater 1 2 3 4 10 19 20 21 D / A

Duty Ejector 2nd stage Ejectors

I P Steam

After Condenser Inter Condenser Pre Condenser

B V P

1st stage Ejectors

Quick filling

Sea Water Discharge

Make Up

Sea Water Outlet

L P Steam

BRP 1

Cond. Rtn

DP

BRP2

Prodn.

BBDP

Cooling water to

vacuum condensers

The process by which Ca ++ and Mg ++ ion

removed from water is known as water

softening. There are two method is used

Lime soda softening or precipitation

method

Ion exchange method

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Water Softening

Lime soda softening It is the process by which calcium and magnesium salt that cause

hardness in H2O are chemically precipitated and removed by

treatment with lime and soda ash .

Mg(HCO3)2 + 2Ca ( OH) Mg(OH )2 + 2CaCO3+2H2O

Ca(HCO3)2 + Ca(OH) 2CaCO3 + 2H2O

Soluble Insoluble

Most of CaCO3 and Mg(OH)2 from a sludge can be removed by

settling and filtration. So lime can be used for removal of temporary

hardness

MgSO4 + 2Ca ( OH) Mg(OH )2 + 2CaSO4

MgCl2 + 2Ca ( OH) Mg(OH )2 + 2CaCl2

The soluble CaSO4 and CaCl2 are produced and contribute “non carbonated hardness” There must be removed to attain complete

softening of water

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This is done by treating soluble salt of Ca SO4 and CaCl2 with soda

ash ( Na2Co3).when these salt are precipitated as insoluble

carbonate.

CaSO4+Na2CO3 CaCO3+ NaSO4

CaCl2+Na2CO3 CaCO3+ NaCl

Insoluble Soluble

CaCO3 formed is precipitated as sludge the resulting NaSO4 and NaCl

are highly soluble non scale forming

Use of Coagulant in lime soda process

Coagulant serve to agglomerate the particles in softening process

They speed up settling of sludge

Sodium Aluminates has a special advantage as a coagulant in lime

soda softening .practically in reducing magnesium .

Effective use of coagulant to remove silica in the softening process.

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Advantage of Lime soda Softening

Main advantage is reduction of hardness alkalinity TDS

and Silica

Prior Clarification of water in not usually necessary

Reduction of TDS can decrease the conductivity of feed

water, there by decreasing blow down and conserving

heat.

Energy can be saved because of solid reduction in hot

process

With hot process lime soda softening removal of oxygen

and CO2 can be achieved up to same extent

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Disadvantage of Lime soda Softening

The main disadvantage is that while

hardness is remove it is not completely

finished.

Since this process involves adjusting the

amount of lime and soda ash being feed

there fore wide variation in water

composition and flow rate also make

control of this method difficult.

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Ion Exchange Zeolite Softening (Na2Al2Sio2O8.XH2O)

Zeolite softening consist of passing water through a bed of material

that possess the property of removing calcium and magnesium from

water and replacing these ion with sodium or potassium. The

exchange takes place rapidly, so that hard water is passing through

Zeolite bed can be almost completely softened ,regardless of

variation in solution, bicarbonates, sulfate , chlorides etc. Considering only chloride as an example ,for the sake of simplicity

the softening reaction are.

Na2Z+CaCl2 CaZ+ 2NaCl2

Na2Z+MgCl2 MgZ+ 2NaCl2

Material usually applied for this purpose can be naturally occurring

Zeolite I.e. green sand , sulfonated coal or alumina silicate or

synthetic resin based on poly styrene or poly acryllates.

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Advantage of Na2Z Softening

Softened water has low scaling

tendency

Operation is simple and

reliable

Regeneration is easy to handle

Waste disposal is not a

problem

Softener's are easily available

and efficient

Variation in water flow rate up

to large extent have not effect

on treated water quality

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Disadvantage of Na2Z Softening

Softening process has no effect upon alkalinity.

Turbidity and the presence of iron and aluminum

can be deter mental for the ion exchanger.

Strong oxidizing agent like chlorine present in

the water will attack the resin.

At higher pressure and temperature the

exchange capacity of resin is effected.

Zeolite material is unstable in high acidic and

alkaline media

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Demineralization Removal of all kind of ion from water by ion

exchange is called demineralization. Any

salt dissolved in water consist of two types

of ions, +Ve ion called cat ion and -Ve

ion's called anion . In demineralization

process cat ion and anion present in water

are removed one after other by organic ion

exchange resin

The organic resin's are of four

types

Weak Cat ion resin R-COOH Carboxylic group

Strong Cat ion resin R-HSO3 Sulphonic group

Weak anion resin R-NH2OH Phenolic hydroxyl group

Strong anion resin R-NH3OH Amino group

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Ion exchange material

Ion exchange material are either natural or

synthetic. The natural ion exchangers are

termed as Zeolite e.g. green sand aluminous

silicate and sulphonated coal. These can be

regenerated by NaCl solution and are used for

the removal of hardness from water.

Synthetic resins are polymer and co-polymers of

organic compounds like phenol, al dehydes,

styrene's and vinyl derivatives. They differ in

properties due to difference polar group.

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Cat ion Exchangers

Weak Cat ion

This filter bed removers cat ion of salt of weak

acids from water in the following manner e.g. 2RCOO.H + CaSiO3 (RCOO)2 Ca+H2SiO3

2RCOO.H + Ca(HCO3)2 (RCOO)2 Ca+2H2CO3

2RCOO.H + CaCO3 (RCOO)2 Ca+H2CO3

2RCOO.H + Mg(HCO3)2 (RCOO)2 Mg+2H2CO3

2RCOO.H + MgCO3 (RCOO)2 Mg+H2CO3

2RCOO.H + NaHCO3 (RCOO)2 Na+H2CO3

2RCOO.H + NaCO3 (RCOO)2 Na+H2CO3

The water at the outlet of weak cat ion exchanger contain weak acids

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Weak Cat ion Regeneration

Normally 2% HCl is passed

through bed for half hour .All cat ions

that had bed absorbed by resins during

normal service operation are replaced

by H + ion of acid and soluble chlorides

produced in the process of regeneration

are drained to waste

(RCOO)2 Ca + HCl 2RCOOH+CaCl2

Exhausted Resin Regenerated Resin

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Cat ion Exchangers Strong Cat ion

A regenerated strong cat ion resins has

sulphonic functional group (-HSO3) and

removes cat ion of both weak and strong

salts of acids from water as given below. 2RSO3.H + CaSO4 (RSO3)2 Ca+H2SO4

2RSO3.H + CaCl2 (RSO3)2 Ca+2HCl Strong Acid

2RSO3.H + Ca(NO3)2 (RSO3)2 Ca+2HNO3

2RSO3.H + Ca(HCO3)2 (RSO3)2 Ca+2H2CO3 Weak Acid

The water at the outlet of strong cat ion exchanger cat

ion strong acids ( HCl , H2SO4 , & HNO3 )

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Cause of Strong Cat ion Exhaust When strong cat ion filter bed exhausted . It has no H + ion to

exchange with the cat ion (Ca++,Mg+ +,Na+) These cat ion escape in

outlet water. In absence of H + ion . The conductivity of effluent water

decreases and pH is increases , Because H + ion are lightest of all

NaCl escape unchanged form 2nd stage to 3rd stage filter and are

release as NaOH in water

RNH2OH+NaCl RNH2Cl+NaOH

When weak anion filter is exhausted the conductivity

of effluent water increases stately but when strong cat ion resin gets

exhausted. The conductivity of effluent water of weak anion filter

more repaid. It is due to the formation of NaOH is 3rd stage filter by

leaking of Na+ from strong cat ion filter.

Acid Treatment

Fresh 7% HCl solution prepared in deionized water is passed

through the filter almost 40 minute

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Anion Exchanger

Weak anion A regenerated weak anion resin which has amino (-NH2) functional

group will remove all the anions of strong acid from water.

RNH2.OH + HCl RNH2Cl +H2O

RNH2.OH + H2SO4 (RNH2)2SO4 +H2O

RNH2.OH + HNO3 RNH2NO3 +H2O

The water at the outlet of weak anion exchanger will contain only

anion of weak acid . If any e.g. CO32- , SiO3

2- in the form of H2CO3

and H2SiO3

Alkali Treatment

Fresh 3% NaOH solution prepared in deionized water is passed

through the filter almost 70 minute

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Anion Exchanger

Strong anion This filter remove anion of both weak acids and strong acids.

2RNH3.OH + H2CO3 (RNH3)2CO3 +2H2O

2RNH3.OH + H2SiO3 (RNH3)2SiO3 +2H2O

2RNH3.OH + HCl RNH3Cl +H2O

2RNH3.OH + H2SO4 (RNH3)2SO4 +2H2O

Alkali Treatment

4% NaOH is used pass the alkali through the filter for one hour. This

filter is stopped for regeneration when SiO2 content increasing trend.

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Mix Bed Filter

The filter bed contain strong cat ion

The cat ion and anion resin are so

intimately mixed that water following

through the bed may be considered to

have comes across a large number of

small strong cat ion and strong anion

beds. The water at the outlet of mix

bed is of higher quality purity and its

conductivity may be low as 0.5 µs/cm.

Increase in silica content

of effluent water of the mixed bed is a

signal of exhaustion of strong anion

resin and increase of conductivity

means exhaustion of cat ion resin.

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Ion Exchange Problems

Excessive

Regeneration

Frequency.

Higher Operating

Costs.

Poor Treated water

Quality.

Insufficient Volume of

Treated Water

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Common Causes of Ion Exchange

System Problem

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Desalination Water Chemistry Variation

Mechanical Malfunction

Resin Fouling and Degradation

Variation and operating and Regeneration Procedure

Variation in Flow Demand

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Demineralizers are used to provide highly purified water to high pressure boilers as feed water make-up. This highly purified water is also used in a vast number of other processes; such as wash water for microchip manufacturing.

Uses of

Demineraliz

ation water

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Power plant chemistry ion exchange process

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