Pre and post treatment of water

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Welcome to Training Programme

Water Treatment Pre Treatment & Demineralization

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WATER

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Molecular Formula – H2O Properties: Available in three different states. High heat storage capacity. High latent heat of evaporation. Universal solvent. Easy to handle.

Water is used in power plants for steam generation

& as cooling water

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SOURCES

Surface Water – Lakes, River, Dam.

Ground Water – Wells, Deep Springs.

Sea Water.

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IMPURITIES Insoluble Silt, Mud, Colloidal matter, Organics,

Microbes, Algae. Soluble Organic - Natural organics Inorganic Cations – Ca, Mg, Na, K, Fe, Al, As, Anions – HCO3, CO3/ Cl, SO4, NO3, PO4, F,

SiO2 Gases - Oxygen, Carbon di oxide, Ammonia etcIf impurities are not removed from water they

cause Scale formation, fouling & corrosion in user

systems

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Water in Nature Contains Suspended impurities – Silt, Mud, Organic

debris, Colloidal matter, etc.

Organic matter – Bacteria, Algae, Dissolved Organic matter.

Dissolved Matter – Mainly Salts of Alkali and Alkaline earth metals.

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Raw Water TreatmentRaw water treatment is divided in two main

partsExternal Treatment – Commonly known as Pre-Treatment. Used to remove un-dissolved as well as

dissolved impurities from water. Treatment choice varies with water

characteristics and application.Internal Treatment – Commonly known as chemical treatment. Main objective to eliminate problems likes

scaling, corrosion, microbial growth. Treatment choice varies with make-up water

quality, equipment used & economy.

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Organic Matter – Chlorination. Suspended Matter – Coagulation /

Flocculation Dissolved Matter – R.O, Ion Exchange Steps 1 and 2 Comes Under Pre

Treatment. Pre Treatment is done to meet the

process and drinking water requirement and also to maintain the plant cooling water system and the DM Plant.

Recommended Treatments

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The process of removing suspended matter.- Coagulation- Flocculation- Sedimentation

Coagulation is the process of destabilisation by charge neutralisation.

Finely divided particles suspended in surface water repel each other because their surfaces are predominantly negatively charged. Once neutralised, particles no longer repel each other and can be brought together. This is achieved by adding inorganic salts of aluminium or iron which neutralise the charge on the turbidity particle.

Eg. Alum.

CLARIFICATION

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Flocculation is the process of bringing together the destabilised or coagulated particles to form a larger agglomeration or floc.

Coagulation and flocculation are aided and enhanced by Coagulant / Flocculant aids like polyelectrolytes.These are long chain polymer molecules with higher charge density. They help form larger floc which settles faster.Unlike inorganic coagulants they do not decrease the pH of the treated water nor increase the TDS.Sedimentation refers to the physical removal from suspension or settling that occurs once the particles are coagulated and flocculated.

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CoagulationFinely divided suspended particles in water repel each other because most of the particles are negatively charged .The coagulants neutralize the charge and also hydrolyze to form insoluble precipitates. pH plays animportant role

Accomplished by inorganic salts of Aluminium and Iron or by organic polymersAl2(SO4)3 + 6NaHCO3 =2 Al(OH)3+3Na2SO4+6CO2Best coagulation in pH range 6 - 7

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Inorganic CoagulantsAl2(SO4)3 + 6NaHCO3 = 2Al(OH)3 ¯ + 3Na2SO4 +

6CO2pH 6-7Fe2(SO4)3 + 6NaHCO3 = 2Fe(OH)3 ¯ + 3Na2SO4

+ 6CO2pH 5 -11Na2Al2O4 + 4H2O = 2Al(OH)3 ¯ + 2NaOHpH 7-9

1 ppm of alum adds0.45 ppm of sulfate ion as CaCO3

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PolyelectrolyteThey are water soluble organic polymers used

in Clarification.Low molecular weight(<500000) polymers used

for primary CoagulationHigh molecular weight polymers are used for flocculation

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Types of poly-electrolytes

Anionic: ionize in water to form negatively charged sites along the polymer chain. It is a copolymer of acrylamide and acrylic acidCationic: ionize in water to form positively Charged sites along the polymer chain. It is a copolymer of acrylamide and acrylic acid Nonionic: ionize in water to form slightly negatively charged sites along the polymer chain.It is basically polyacrylamide

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Chlorine, Sodium hypochlorite Ozone etc. are some of the chemicals used for Oxidation

Cl2 + H2O = HOCl + H+ + Cl-

Ozone is a powerful oxidizing agent but requires on site generation equipment

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The Three processes happening in a clarification equipment are

- Rapid mix for coagulation- Moderate mixing for flocculation and- Floc and water separation.

The most common design is the upflow clarifier where the water flows up while the floc settles.The two types are

- Sludge blanket type and- Solids contact type

Both utilise part of the settled floc to enhance sedimentation

Clarification

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JSW Energy LtdRemoves bulk of turbidity & sediment. The particles with a settling velocity exceeding the upward velocity of the fluid settle out and are separated

STOKES LAW

Vs = g(ρs –ρl)d2

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18μVs is terminal settling velocity m/sg is acceleration due to gravity m/s2

d is particle diameter m ρs, ρl density of particle, liquid,Kg/m3

μ is liquid viscosity Pa.S

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Clariflocculator "Solids-contact" refers to units in which large

volumes of sludge are circulated internally. The term also describes the sludge blanket unit and simply means that prior to and during sedimentation the chemically treated water contacts previously coagulated solids.

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Clarifier JSW Steel Ltd

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The efficiency of coagulation – flocculation is increased by repeated soilids contact.

The sludge formed in the Process is utilized to contactthe coagulated –flocculated water and increase the probability of collisions resulting In better flocculation.High rate solids contact clarifiers work on this principle

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JSW Energy LtdSolids contact Clarifier

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Filtration Used to remove any remnants from clarification process brings down turbidity from 10-20 NTU to 0.5 – 2 NTU.If raw water has less turbidity, directly filtration can be applied.It is a separation process where in solid liquid mixture is passed through porous media which retains solids and allows liquid to pass through.During filtration the retained solids gradually build up and block the interstices of the filter media and cause head loss.

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Gravity filters – Pressure filters

Down flow filters – Up-flow filters

Automatic gravity filters

Filter washing gravity filters

Pre coat filters

Self cleaning filters

TYPES OF FILTERS

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Gravity Sand filter

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Pressure sand filter

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The filter needs to be back washed :

Once the head loss reaches a preset value

The treated water turbidity deviates from the preset value

Back wash is performed using

1.Air and Water simultaneously 2.Air and water in succession

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The different types of filter media used are

Quartz sand Anthracite Dual media of sand and Anthracite / garnet Multi media of sand, anthracite Garnet, Granular activated carbon (GAC)

Typical filter media is 15 -30 inch deep bed. Dual media filters allow high filtration rates, requireLess back wash water than stand alone filters GAC additionally removes organics and free chlorine

FILTERMEDIA

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DEMINERALIZATION

The process of removing the dissolved solids from Water is known as Demineralization

This is accomplished at JSW Energy by using Ion Exchange Process

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JSW Energy LtdDM Plant Flow Diagram

DMFDegas blower

Degas waterStorage

Tank

Raw water tank

SAC

DM STORAGETankSBA

Mixed Bed

UF STORAGETank

UF

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Dual Media Filter

Carbon steel vessel containing Sand & AnthraciteCapacity :45 m3/hrAnthracite Qty : 1.64m3, 0.508 m depthSize of Anthracite : 0.9 – 1.0 mmSand Qty :2.07 m3, 0.405 m depth Size of sand : 0.45 – 0.55 mmTurbidity Inlet water : <20 NTUTurbidity Outlet water : <2 NTU

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JSW Energy LtdIon Exchange Resins

Made by co polymerization of Styrene cross linked with Di-vinyl Benzene. Ion exchange resins exchange one ion for another, hold it temporarily and release it to a regenerant solution.

New forms of resins with acrylic structures are also available with more resistance to organic fouling

In addition to plastic matrix ion exchange resin has ionizable functional groups. This contains one mobile and one immobile Radical. Mobile radical is exchanged

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Strong Acid Cation Resin (R-SO3.H)

SAC has sulfonic acid (HSO3) functional groupConverts neutral salts into respective acids

Ca 2(HCO3) Ca 2H2CO3Mg SO4 + 2RSO3.H = 2RSO3. Mg + H2SO42Na 2Cl 2Na 2HCl

The exchange reaction is reversible. When capacity Is exhausted the resin is regenerated with excess quantity of mineral acid

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Strong acid Cation Resin

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SAC is a rubber lined carbon steel vessel with inlet distributor, regenerant distributor, ion exchange resin free board space and resin retaining under drain system

Resin is retained using strainers which allow only water to flow and prevent resin

The volume of resin employed depends up on capacity of resin and salanity to be removed

Selectivity for cation exchangeCa > Mg > Na

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ION EXCHANGE VESSEL INTERNALS

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STRAINERS

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Strong acid cation is regenerated when

1.Designed quantity of water is processed OR2.Sodium content in outlet water is more than design usually >1 ppm OR3.Conductivity comparator reading crosses stipulated value

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Regeneration Co – flow Counter flow

Service Regeneration Service Regeneration

Counter flow results in

High quality out put, better regeneration efficiency

Requires down flow water to keep resin bed intact

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Hydrochloric acid Regeneration 4 – 5% HCl

Sulphuric acid Regeneration H2SO4

Step 1 : 1.5 – 2 %

Step 2 : 3 %

To avoid Calcium Sulphate precipitation

Regeneration

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Degasser Tower

Water Inlet

Air Inlet

Air Vent

Water Storage

Packing

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De carbonator works on the principle of Henry’s law

Solubility of any gas in liquid is directly proportional to the partial pressure of gas at the liquid surface C total = K P

C total : total concentration of gas in solution

P : Partial pressure of gas above solution

K : constant

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Hence a dissolved gas can be removed from solution By lowering the partial pressure of the gas above solution

This can be done by

1. Vacuum is applied over the system and unwanted gas is vented

2. A new gas is introduced and unwanted gas is vented

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Strong Base Anion

Strong base anion has quarternary ammonium Functional group and is used in hydroxide (OH-) form CH3 l (R – N – CH3)+. OH-

l CH3

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In hydroxide form SBA can remove all anions commonly encountered

H2SO4 SO4

2HCl 2Cl 2H2SiO3 + 2R.OH = 2R. 2HSiO3 + 2H2O2H2CO3 2HCO3

The reactions are reversible and once exhausted The resin can be regenerated with sodium hydroxide to return to hydroxide formThe selectivity for anion exchange SO4 > Cl > HSiO3

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Treated water quality parameters for SBA

pH 7.5 to 8.5

Conductivity < 6.0 μ s/cm

Silica < 0.1 ppm

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Strong base anion is regenerated

1.When designed quantity of water is processed OR2.Silica content in treated water goes beyond limits OR 3.Conductivity of treated water increases beyond limits& pH of treated water is lower then limits

Regeneration is carried out using 4% Sodium hydroxide

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MIXED BED

As the name suggests it consists of both Cation and Anion Resins. This is a polishing unit and is the last stage of Demineralization process to get final qualityDM Water. The two resins are in thoroughly mixed state in service condition and are separated for regeneration using Back washAfter back wash Cation resin settles at the bottomand Anion resin remains at top due to density differenceBlocking flow arrangements are designed to prevent entry of regenerant chemicals into other resin duringregeneration

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Treated water quality after Mixed Bed

pH 6.5 to 7.2

Conductivity <0.1 μ s/cm

Silica < 0.02 ppm

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Mixed bed is regenerated

1.When designed quantity of water is processed

OR

2.Silica content in treated water goes beyond limits

OR

3.Conductivity of treated water increases beyond limits

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JSW Energy LtdULTRA FILTRATION

Ultra filtration is a membrane process in which higher molecular weight solutes are concentrated from feed streamIn JSW Energy it is employed to remove colloidal Silica which can not be removed in Ion exchange process. Colloidal Silica removal efficiency > 95%

Ultra filtration membranes are hollow fiber membranes made of Polysulphone (PS)Polyethersulphone (PES)Polyvinylidenefluoride (PVDF)

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UF Hollow Fiber Membrane

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The filtration system is inside out cross- flow filtration

Fast flush : In this water will flow in the same direction as in service with higher flow rate membraneGets pressurized and adhered material gets dislodged

Back flush: In this water flows in opposite direction toService cycle. This takes away the remaining dirt afterFast flush

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DMT

Fast flush pump

Feed pump

Pre-filter

UF MODULE

Back flush pump UFT

UF PERMEATE

Reject To CW Forebay

To Neutralizing pit

Cleaning tank

UF SCHEMATIC

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Thank You