raw water.ppt

8/13/2019 Raw Water.ppt

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Power Plant Chemistry

Pre-Treatment Post-Treatment Boiler

preservation

EnvironmentalMonitoring

EfficiencyImprovement

Fuel QualityMonitoring

Lube OilMonitoring

Plant & Materialinspections Safety

Inventory MgMt

Compliance tolegal

requirements

Stator cooling

system



Watercontd..

• Hence, water is called as

“Universal solvent”• Because of that, water will

contain impurities.



Sources of Raw water

• 1. Meteoric water : Rain water /snow/ hail:

• 2. Surface Water : River, lakes, ponds.

• 3. Ground Water : Wells, Springs,• 4. Sea water .



Sources of Raw water contd…..

• The mineral composition of sea water varies from7.5g/l(Baltic sea) to 43 g/l (Red Sea)

• The composition of sea water:• Nacl : 83.67 %• MgCl 2 : 8.50 %

• MgSO 4 : 3.60 %• CaSO 4 : 4.20 %• KCl : 0.03%



Impurities in Raw Water

• These are of three main types

• 1. Suspended solids• 2. Dissolved solids• 3. Dissolved gases



Impurities in Raw Water• Suspended solids : These are

colloidal systems consisting of aggregated

molecules, the particle size ranging from 1to 100 mu; such as starch, glues andminerals such as Si0 2, Al(OH) 3, Fe(OH) 3 and organic substances (humins and fulvicacid).




• Dissolved solids: These are substancescompletely dissolved in water and present as

separate molecules or ions. The water can not bedistinguished from absolutely pure water , except by taste or by chemical analysis .

• Contains many gases eg. O2, N2 ,CO2, H2S and

others, soluble salts of Sodium , potassium,calcium, ammonium, magnesium, aluminium,iron, manganese etc.




• Suspended solids: These are

particles of sand, clay, andorganic matter

• These types of impurities getsettled on standing.




• Biological Contaminations

• Water bodies are polluted withorganic matter of plant and animalorigin indicated by BOD and COD.




• Planktons: Plants and animals whichremains suspended in water

• Benthos : Plants and animals whichremains at bottom.




• Turbidity• Imparts unsightly appearance to water.• Deposits in water lines, process

equipments.

• Interferes with most process uses.



Impurities in Raw Water -Turbiditycontd….

• Means of treatment :

• 1. Coagulation• 2. Settling

• 3. Filteration



Impurities in Raw Water contd….

• Hardness

• Chemical nature- Calcium andMagnesium salts expressed as CaCO 3

• Difficulty caused : Chief source of scalein heat exchange equipments, Boilers,pipelines. Forms curds with soap,interferes with dyeing



Impurities in Raw Water: Hardness

contd …

• Means of Treatments

• Softening• Demineralisation



Impurities in Raw Water contd..

• Alkalinity : Chemical nature-

• Bicarbonate( HCO 3)-

• Carbonate ( CO 3) –

• Hydrate ( OH) –

• all expressed as CaCO 3



Impurities in Raw Water :Alkalinity

contd.. • Difficulty Caused

• Foaming and carrying over of solidswith steam

• Embrittlement of boiler steel

• CO 2 from carbonate and biocarbonatecauses corrosion in condensate lines



Impurities in Raw Water :Alkalinity

contd..

• Means of Treatments• Lime and lime soda softening• Acid treatment• Hydrogen Zeolite softening

• Demineralisation• Dealkalisation by anion exchange




• Free Mineral Acidity

Chemical nature-• H2SO 4, HCl etc. expressed as

CaCO 3




Free Mineral Acidity contd

• Difficulty Caused

• Corrosion• Means of Treatments

• Neutralisation with alkalies




• Carbon dioxide• Chemical nature - CO

2

• Difficulty Caused - Corrosion in

water lines and particularly in steamand condensate lines.•




Carbon dioxide contd..


• Aeration• De-aeration• Neutralisation with alkalies




• PH• Chemical nature - Hydrogen ion

concentration defined as• PH = log 1/(H +)

• Difficulty Caused - PH varies accordingto acidic or alkaline solids in water. Mostnatural water have a PH of 6.0-8.0



Impurities in Raw Water PHcontd..


• PH can be increased by alkalies anddecreased by acids.




• SULFATE (SULPFATE)• Chemical nature - SO

4

- -

• Difficulty Caused – Adds to the solidcontent of water. Combines with Calcium toform Calcium Sulfate scale

• Means of Treatments• Demineralisation




• Chloride• Chemical nature - Cl -

• Difficulty Caused Adds to the solidcontent and increases corrosive character ofwater





• Nitrate• Chemical nature - (NO

3) -

• Difficulty Caused Adds to the solidcontent. High concentration causemathemo-globinemia in infants .





• Floride• Chemical nature - F -

• Difficulty Caused : Cause mottledenamel in teeth. Not usually significantindustrially.

• Means of Treatments• Adsorption with Mag. Hydroxide, calcium phosphate or bone black. Alum Coagulation




• Sodium• Chemical nature - Na +

• Difficulty Caused : Adds to the solid content.When combined with OH - , causes corrosionin boilers under certain conditions





• Silica• Chemical nature - SiO

2

• Difficulty Caused : Scale in boilers and cooling waterssystems , Insoluble turbine blade deposits

• Means of Treatments• Demineralisation• Adsorption by highly basic anion resins




• Iron

• Chemical nature - Fe++

(Ferrous)Fe ++ + (Ferric)

Difficulty Caused : Discolors water on

precipitation , Source of deposits in water lines, boilers etc. Interferes with dying, tanning, papermaking etc.



Impurities in Raw Water : Iron contd..

Means of Treatments

• Aeration.• Coagulation and filtration• Lime softening

• Cation exchange• Surface active agents for iron retention




• Manganese

• Chemical nature - Mn ++

Difficulty Caused : Discolors water on precipitation , Source of deposits in water

lines, boilers etc. Interferes with dying,tanning, paper making etc.Means of Treatments : Same as Iron




• Aluminium

• Chemical nature - : Al +++

Difficulty Caused : Usually present as aresult of floc carry over from clarifier. Can causedeposits in cooling systems and contribute to

boiler scalesMeans of Treatments : Improved clarifier

and filter operation




• Oxygen

• Chemical nature - : O 2• Difficulty Caused : Corrosion of water

lines, Heat exchange equipments, boilers ,return lines, etc .

Means of Treatments : De-aeration,Sodium sulfate, corrosion inhibitors




• Hydrogen Sulfide

• Chemical nature - : H 2S• Difficulty Caused : Cause of “rottenegg” odor, Corrosion.

• Means of Treatments : Aeration,Chlorination, Highly basic ionexchange




• Ammonia

• Chemical nature - : NH 3

• Difficulty Caused : Corrosion ofcopper and zinc alloys.

• Means of Treatments : Cationexchange, De-aeration, Chlorination,




• Dissolved solids• Chemical nature - : None

• Difficulty Caused : It is measure of

total amount of dissolved matter : causesfoaming in boilers.

• Means of Treatments : limesoftening, Demineralisation




• Suspended solids• Chemical nature - : None

• Difficulty Caused : It is measure of un-dissolved matter : causes deposits in heatexchange equipments, boilers, water lines etc.

• Means of Treatments : Subsidence,Filtration usually preceded by coagulationand settling.




• Total solids

• Chemical nature - : None

• Difficulty Caused : It is sum ofdissolved and suspended solids.

• Means of Treatments : same asdissolved and suspended solids

raw water.ppt

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