coal based thermal power plant water management.pdf
TRANSCRIPT
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KaushikKaushikKaushikKaushik ChaudhuriChaudhuriChaudhuriChaudhuri
CESC LimitedCESC LimitedCESC LimitedCESC Limited
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Global distribution of Water
2% 1%
% Distribution
97%
Ocean
Ice
Fresh water
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Use of Fresh Water
10%5%
3%
Fresh Water Distribution
70%
12% Evaporation
Power Plants
Irrigation
Industries
Domestic
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Sources of Raw Water for Power
Plants� Ocean
� River
� Dam
Lake� Lake
� Canal
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Raw water contains� Suspended solids
� Dissolved solids
� Dissolved gases
Organics� Organics
� Industrial effluents
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Types of Water used in a Power
Plant� Raw
� Clarified
� De-mineralized
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Points of UseRaw Water
� Mainly Condenser cooling (once through)
Washing/Cleaning� Washing/Cleaning
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Points of UseClarified Water
� Condenser cooling
� Auxiliary cooling (Turbine Lub oil cooler, Vacuum pump � Auxiliary cooling (Turbine Lub oil cooler, Vacuum pump cooler, DMCW HEX etc)
� Service water system (Cleaning, washing, gardening, Ash handling system, dust suppression, water fogging, ESP hopper cooling, Air washery , Sludge conveying, Intake pump gland cooling)
� Hydrant/Mulsifier system
�Drinking water (after proper chlorination)
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Points of UseDe-mineralized Water
� Boiler makeup through RFW tank� Condenser emergency makeup� DMCW system makeup � DMCW system makeup � Stator coolant makeup� Oil Centrifuge sealing� Chemical preparation� Laboratory� Boiler cold filling� Deaerator cold filling
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Raw Water TreatmentTypical impurities in River Water (like Ganga)
1. Non-ionic & undissolved impurities (Suspended Solids)
e.g. mud,dirt,slime,clay and other suspended matter,organicmatters etc.matters etc.
2. Ionic & Dissolved impurities (Dissolved Solids)
e.g. Salts of calcium, magnesium, sodium etc.
Fulvic , Humic acids,Tannins,Lignins as organics.
3. Gaseous impurities (Dissolved Gases)
e.g. Oxygen , carbon dioxide, hydrogen sulphide,
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Pre-treatment of Raw Water1. Clarification
a) Coagulation
b) Flocculation
c) Sedimentationc) Sedimentation
2. Filtration
3. Chlorination
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RAW WATER TREATMENT PLANT
R A W W A T E R C I R C U I T
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Clarification Process� Flash Mixture Tank
� Flocculation Tank/Clariflocculator
� Inclined Surface Settler
Effect : Lowering of Turbidity (NTU)
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Filtration� Pressurized Sand Filter
or
� Gravity Sand Filter
Effect : Further lowering of Turbidity (NTU)
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FILTRATIONClarified Water (Turbidity: 2 NTU)
Sand
Pebbles
Gravels
Filtered Water (Turbidity: 0.2 NTU)
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CLARIFICATION• Al2(SO4)3 Al(OH)3 + H2SO4
• Fe2(S04)3 Fe(OH)3 + H2SO4
Chemical reactions in water is as followsChemical reactions in water is as follows.
•Coagulation Mechanism : Lowering of ZETA POTENTIALZETA POTENTIALZETA POTENTIALZETA POTENTIAL.
CrabingCrabingCrabingCrabing action as well as reduction of Z PZ PZ PZ P found in PE.It also increases sludge density and increases efficacy of alum.
Poly electrolyte : Cationic form (0.2Poly electrolyte : Cationic form (0.2Poly electrolyte : Cationic form (0.2Poly electrolyte : Cationic form (0.2————0.5 %. Alum soln. : 20.5 %. Alum soln. : 20.5 %. Alum soln. : 20.5 %. Alum soln. : 2------------5% Is 5% Is 5% Is 5% Is generally used as generally used as generally used as generally used as coagulantcoagulantcoagulantcoagulant
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Jar Test Apparatus
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CHLORINATION
Na(OCl)H2O HOCl
HOCl H+ + Ocl-HOCl H+ + Ocl-HOCl as well as Ocl enters into the cells of
bacteria and destroy the protein structures
of living beings
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Typical River Water Parameters
pH COND.
(ms/cm)
TURB.
(NTU)
ALK.
(ppm)
TH.
(ppm)
Ca-H
(ppm)
Mg-H
(ppm)
NaCl
(ppm)
SiO2
(ppm)
7.7-8.3 200-500 50-1200 70-170 55-175 30-100 25-75 12-35 7-14
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RWTP GSF FWR DMSP
ACFSACDegasserDGP
WBA SBA MB DMStorage
DM Water Production
Storage
RWTPRWTP Removes Suspended & Colloidal particlesRemoves Suspended & Colloidal particles
GSFGSF Reduces TurbidityReduces Turbidity
ACFACF Removes Oil, grease, colour, odour, ChlorineRemoves Oil, grease, colour, odour, Chlorine
SACSAC Removes Cations like Ca,Mg,NaRemoves Cations like Ca,Mg,Na
DegasserDegasser Removes CO2Removes CO2
WBAWBA Removes strong acids like Chloride, Removes strong acids like Chloride, SulphatesSulphates
SBASBA Removes weak acids like Silica, carbonatesRemoves weak acids like Silica, carbonates
MBMB Final polishingFinal polishing
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Some Facts about DM Water ProductionRegeneration Requirement (sample)
� SAC : Requires about 1 Te of HCL (33% bulk conc), resins are regenerated using 5% HCL
� WBA & SBA : Require approx 400 Kg of NaOH (46.5% bulk conc), 4% NaOHfor SBA & 2% for WBAfor SBA & 2% for WBA
� MB : Requires 260 Kg of HCL & 170 Kg of NaOH� Regeneration waste goes to Neutralizing Pit where it is neutralized before
discharging
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High Pressure Boiler Water Treatment
Methods
� Co-ordinated Phosphate –Ph control
� Congruent control
� All volatile treatment
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Coordinated Phosphate -Ph control method.
•In this method only TSP solution is used.
•PO4 content : 10 ppm•PO4 content : 10 ppm
•pH : 9.8---10.0
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Congruent control Method
In this process TSP & DSP
are mixed 4:1 ratio
externally and dosed to externally and dosed to
boiler. Na:PO4=2.66:1
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All Volatile Treatment (AVT) � Hydrazine Hydrate : 40—100 ppb
(in Economizer inlet water)
� Ammonia : 1.5---2.00 ppm� Ammonia : 1.5---2.00 ppm(in Main Steam sample)
� Advantage : Zero blowdown
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AVT Control of Power Cycle Water
Drum Water
Parameters
Range
PH 9 – 9.5
Conductivity (ms/cm) 5 - 15
Silica (ppm) 0.2 (max)
Chloride (ppm) 0.13
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AVT Control of Power Cycle Water
Main Steam
Parameters
Range
PH 9.3 – 9.7
Conductivity (ms/cm) 6 - 15
Silica (ppm) 0.02 (max)
Ammonia (ppm) 1.4 – 2.5
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AVT Control of Power Cycle Water
Economizer Inlet
Water Parameters
Range
PH 9.3 – 9.7
Conductivity (ms/cm) 6 - 15
Hydrazine (ppb) 40 - 200
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AVT Control of Power Cycle Water
CEP Discharge Water
Parameters
Range
PH 9.3 – 9.7
Conductivity (ms/cm) 6 - 15
Silica (ppm) 0.02 (max)
Ammonia (ppm) 1.4 – 2.5
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AVT Control of Power Cycle Water
Deaerator Water
Parameters
Range
PH 9.3 – 9.7
Conductivity (ms/cm) 6 - 15Conductivity (ms/cm) 6 - 15
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Chemical Control of Stator Coolant Water
Stator Coolant Water
Parameters
Range
PH 6 – 7.5
Conductivity (ms/cm) 2 (max)Conductivity (ms/cm) 2 (max)
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Chemical Control of Closed Circulating
Condenser Cooling Water
Forebay/CW Water
Parameters
Range
PH 8.5 – 8.7
Turbidity (NTU) < 20Turbidity (NTU) < 20
M- Alkalinity 150 - 200
Ca - Hardness < 650
Chloride (ppm) 500
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Corrosion Limits
Type of Water Control
Power Cycle Iron < 10 ppb
DMCW Iron < 50 ppbDMCW Iron < 50 ppb
Stator Coolant Copper < 80 ppb
Cooling Tower < 4 MPY
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Problems faced with closed loop
Condenser cooling water
�Scaling
�Corrosion�Corrosion
�Biofouling
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Scale is a dense coating of predominantly inorganic material formed from the precipitation of water-soluble constituents. Some common scales are
Scaling
� Calcium phosphate� Calcium phosphate� Magnesium salts� Calcium Carbonate� Silica
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Calcium Carbonate deposition in
tube
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Corrosion
Some common types of Corrosion
1. General Corrosion
Corrosion is the mechanism by which metals are reverted back to their natural“oxidized” state
1. General Corrosion2. Galvanic Corrosion 3. Localized Pitting Corrosion
• General Corrosion
The metal loss is uniform from the surface. It is often combined with high-velocity fluid erosion, with or without abrasives.
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• Galvanic Corrosion :-Occurs when two different metals are in the same system. Can occur when two different metals are in contact. The more active metal corrodes rapidly.
• Localized Pitting Corrosion :- exists when only small area of the metal corrodes. Pitting may perforate the metal in short time. The main source for pitting attack is dissolved oxygen.
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Bio-fouling� Biofouling or Biological fouling is the deposition &
growth of micro-organisms on wet surface.
� Biofouling severely impede heat exchange in Condenser, HEX and Cooling towerCondenser, HEX and Cooling tower
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Bio-fouling in BBGS Unit-3 CT
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Bio-fouling in BBGS Unit-3 CT
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Bio-fouling in BBGS Unit-3 CT
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Microbiological Growth
Mainly three kinds of troublesome micro-organisms found in Cooling tower water
Algae , Fungi , Bacteria
Classifications of Bacteria
Planktonic:Free-floating bacteria in bulk water.
Sessile:Sessile:Bacteria attached to surfaces.Over 95% of bacteria in a cooling system are sessile and live in Biofilms.
Biofilms can generally be described as a physically coordinated community ofbacteria and other microorganisms, embedded in a protective glycocaylx withentrained organic and inorganic debris attached to a surface.
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MIC (Microbiologically influenced corrosion)
o Corrosion caused or promoted by micro-organisms.
o MIC does not involve direct attack of bacteria on metal. Rather, MIC refers to corrosion that is induced or accelerated by the presence of products of microbiological metabolism.
o The most commonly seen cases of MIC are caused by Sulphate-o The most commonly seen cases of MIC are caused by Sulphate-reducing bacteria (SRB).
o Other bacteria can also cause MIC to occur - Acid-producing bacteria (APB).
o Anaerobic bacteria, specially Sulfate Reducing Bacteria (SRB) and Acid Producing Bacteria (APB) can accumulate under-deposits. Metabolic reactions of these bacteria produce acids, dropping the pH low enough to cause serious localized or pitting attack.
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Outer surface of the Fire Water & Service water line at Turbine house
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The common types of bacteria can form gelatinous masses in pipes. they adsorb suspended matter and form a physical obstacle to the water flow. In addition, they create local conditions favorable to the growth of ferruginous and sulfate reducing bacteria.
Inside the Fire water
pipe at pipe at Turbine house
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Condenser
CW bus
Fo
rbay
Vent
Controls Microbiological growth by reducing nutrient food source
Air for backwash
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Chemical Management of Closed Circulating
Condenser Cooling Water
� Dosing of Sulphuric acid
� Dosing of antiscalant & corrosion inhibitor (Organophosphonate)(Organophosphonate)
� Dosing of Bio-dispersant
� Dosing of Oxidizing Biocide (Sodium hypochlorite/ClO2)
� Shock dosing of Non-oxidizing Biocide followed by Blowdown
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In Forebay
Ca(HCO3)2 + H2SO4 = CaSO4 +CO2 + 2H2O
NaClO2 + Cl2 + HCl � ClO2 + NaCl + NaoHNaClO2 + Cl2 + HCl � ClO2 + NaCl + NaoH
For Recirculated water
Ca(HCO3)2 + NaOH = CaCO3↓ + NaHCO3+ H2O
CaSO4+ 2NaHCO3 = CaCO3 ↓ +Na2SO4+H2O+CO2
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Oxidizing BiocidesBacteria Fungi Algae PH range
Chlorine (Cl2) Excellent Good Good 5 - 8
Chlorine-di-oxide (ClO2)
Excellent Good Good insensitive
Bromine Excellent Good Poor 5 - 10Bromine Excellent Good Poor 5 - 10
Ozone Excellent Good Good 7 - 9
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� When chlorine is added to water, the initial chemical reaction creates a mixture ofhypochlorous acid (HOCl) and hydrochloric acid (HCl):
Cl2 + H2O → HCl + HOCl� HOCl is the actual oxidant that attacks the microorganism. As pH increases, HOClstarts to dissociate into hypochlorite (OCl-):
HOCl ↔ H+ + OCl-
Chlorine is the most popular oxidizing Biocide
HOCl ↔ H+ + OCl-� OCl- is also an oxidant, but a much weaker one than HOCl. Together these chlorine species are known as free chlorine. At a pH of 5.5, the HOCl concentration in the solution is near 100%. As the pH of the solution increases to 8.5, the HOCl concentration drops to near 10% and the OCl- concentration is now 90%.
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Chlorine Dissociation Curve
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Non-oxidizing BiocidesNon-oxidizing Biocides are Organic Biocides, normally slow acting and are applied periodically in high concentration for maximum efficacy
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Measurements & Implications� Langelier Saturation Index (LSI)
� Corrosion rate (CR)
� Oxidation Reduction Potential (ORP)
Total Bacterial Count (TBC)� Total Bacterial Count (TBC)
� Sulphate Reducing Bacteria (SRB)
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Langelier Saturation Index� It is used to predict the calcium carbonate stability of water
LSI = pH - pHs
Where:� pH is the measured water pH� pH is the measured water pH� pHs is the pH at saturation in calcite or calcium carbonate and is
defined as:
pHs = (9.3 + A + B) - (C + D)Where:� A = (Log10 [TDS] - 1) / 10� B = -13.12 x Log10 (oC + 273) + 34.55� C = Log10 [Ca2+ as CaCO3] - 0.4� D = Log10 [alkalinity as CaCO3]
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Corrosion RateCorrosion Rate (MPY) =
22.3 X Difference of weight of coupon in gm X 1000
-------------------------------------------------------------------------
Surface area of the coupon (sq inch) X Density (gm/cc) X no.
of days exposed
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Corrosion Rack
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Total Bacterial Count
Before Shock Dozing After Shock Dozing
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Sulphate Reducing Bacteria
Day 2 sample Day 4 sample
Day 5 sample
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