Power plant chemistry
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The document outlines the water treatment processes used in a thermal power plant, focusing on the demineralization (DM) plant and chemistry activities. Key stages include raw water treatment, coagulation, flocculation, and filtration to remove impurities before water is used in boilers. It highlights the importance of maintaining pure water to prevent corrosion and scaling in power generation systems.
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Power plant chemistry
- 1. Presented by Raghab Gorain A Maharatna Company Date- 28/05/2020NTPC TSTPS
- 2. Coal Storage Conveyer Belt Coal Pulverizer Furnace Boiler Turbine Condenser Generator Transformer Fly Ash Chimney ESP DM Plant PT Plant Cooling Tower Bus Bar Overview OF Thermal Power Plant Eco Bottom Ash Raw Water
- 3. WATER TREATMENT PLANT MAIN PLANT CHEMISTRY COAL & OIL ENVIRONMT & SPECIAL LAB CW& ETP TREATMENT Role Of Chemistry In Power Plant Chemistry Activities
- 4. DM Plant (Stg-1)Alum PAC Lime DM Tank-1 (2000m3) DM Tank-2 (2000m3) WAC Sludge Backwash Filter (3+2)175m3/hr Sand Filter Sump Filter water p/p(4) 3*130m3/hr 3*130m3/hr Degasser Tower Clarifier Aerator River MB A B C Cl2 ACF A AB S B S A B S A B S SBA Degasser Tank WBA SAC SBA Air Blower Main Plant DMP Boiler Fill p/p Make up p/p DM Reg. p/p A B S 4*2300m3/hr 4*2300m3/hr 3*130m3/hr 3*50m3 Degasser p/p 140m3/hr (3w+1S) 2*100m3/hr 3*100m3/hr 2*50m3/hr
- 5. Sources of water Sources Of Water
- 6. Water Requirement Requirement of Water in Power Plant
- 7. Dissolved form Suspended Form Colloidal form ORGANICS Impurities in Water Impurities Present in water
- 8. Pretreatment of water Impurities present in Raw water Suspended impurities Ionic solids Micro-organisms Dissolved Gasses Treatment of water in PT plant Mainly four steps are used to remove the impurities in raw water Oxygenation- Aeration of the water to precipitate out the ferric salt. Here ferrous salts are converted to ferric salt and also it removes the dissolved CO2 Coagulation-In this process a flux mixture is produced by the addition of FeCl3 and polyelectrolyte. Flocculation & Settlement-It is the process to precipitate out the solids from the clarifier. Filtration- To remove the impurities Aeration of water 4
- 9. Raw water Aeration Exposing Water to Atmospheric air thereby oxidizing some of the dissolved salts. During aeration, two impurities viz. Ferrous Bicarbonate and Manganous Bicarbonate are oxidized as follows; 4Fe(HCO3)2 + O2 + 2H2O =4Fe(OH)3 + 8CO2 2Mn(HCO3)2 + O2 = 2MnO2 + 4CO2 + 2H2O Raw Water To Clarified Water Treatment Process
- 10. Raw water (disinfection, to control bacteria, virus & org. mat) (coagulant) (pH adjustment, softening) Raw Water Clarified Water Treatment Process
- 11. Clariflocculator Coagulation & Sedimentation Raw Water Clarified Water Treatment Process Dividing Chamber
- 12. Clarified water from clarifier IN FILTERED WATER OUT 5th layer 4th layer 3rd layer 2nd layer 1st layer For back washing of the GSF water is passed through filter in reverse direction BACK WASH WATER OUT BACK WASH WATER INLET FROM FILTER WTR. O/H TANK Gravity Sand Filter 1st layer - 50 mm X 37 mm gravel 2nd layer - 37 mm X 12 mm gravel 3rd layer – 12 mm X 6 mm gravel 4th layer – 6 mm X 2.5 mm grit 5th layer – 0.35 mm X 0.5 mm sand
- 13. Pretreatment of Water Exposing the raw water to atmospheric air. So some of the dissolved salts oxidized, specially ferrous and manganous bicarbonate as follows 4Fe(HCO3)2 + O2 + 2H2O =4Fe(OH)3 + 8CO2 2Mn(HCO3)2 + O2 = 2MnO2 + 4CO2 + 2H2O Aeration Clarification Cl2: As disinfectant Alum: Used as flocculating agent Lime : To maintain pH Schulze-Hardy rule Greater the valency of the flocculating ion, greater will be its coagulation power. Fe3+ ion is 1000 times more effective than that of monovalent ion. So FeCl3 is used in clarifier. Fe3+ + PO4 3- = FePO4 Cl2 +H2O = HOCl + HCl Gravity Sand Filter(GSF) It is used to remove the suspended particles and the microbial organisms from the clarified water. Filtered water turbidity: <5 NTU Residual Cl2: 0.2-0.5 ppm GSF 5
- 14. DM Plant Raw water contains various dissolved salts & suspended solids. For use as feed in boiler these are to be removed as they may get deposited in heat transfer zones thereby restricting heat transfer & may lead to corrosion also. Why Demineralization Require? What is DM water? DM water defined as that water which does not contain any mineral or ions. It is also called De – ionized water.
- 15. Degasser FILTER water ACF WAC SAC WBA SBA MB CST DM Plant
- 16. Degasser FW water ACF WAC SAC WBA SBA MB CST ACF Acts on principle of adsorption which is a surface active phenomenon It removes residual turbidity (<2 NTU) of water to its 1/10 level. It removes organic molecules to control colour and odour. It removes free residual chlorine present in filtered water(0.5 ppm Nil) Activated Carbon Filter(ACF)
- 17. Cation Exchange Resin 2R-H + Na2CO3 2R-Na+H2CO3 Reaction mechanism of Cation exchange Resin During service condition During Regeneration condition R-Na + HCl R-H + NaCl R= 20
- 18. Degasser FW water ACF WAC SAC WBA SBA MB CST WAC resin is capable to exchange cations of alkalinity producing salts only ie, for carbonate hardness removal purpose. 2 R-COOH + Ca(HCO3)2 (RCOO)2Ca2+ + H2CO3 WAC resin can exchange ions only in neutral to alkaline pH range. WAC results efficient TDS reduction in high carbonate hardness water. Efficient regeneration takes place even with very dilute acid solution. Weak Acid Cation Exchange Resin
- 19. Degasser FW water ACF WAC SAC WBA SBA MB CST Strong Acid Cation Exchange Resin
- 20. Degasser FW water ACF WAC SAC WBA SBA MB CST Water from the ex-cation contains carbonic acid which is very weak acid and difficult to be removed by strongly basic anion resin and causing hindrance to remove silicate ions from the bed. The ex-cation water is trickled in fine streams from top of a tall tower packed with rasching rings, and compressed air is passed from the bottom Carbonic acid break into CO2 and water. carbon dioxide escapes into the atmosphere. Water is pumped back to anion exchanger bed DM Plant (Degasser Tower)
- 21. Anion Exchange Resin Reaction mechanism of Anion exchange Resin 2R’-OH + H2SO4 R’2SO4+2H2ODuring service condition During Regeneration condition R’2SO4 + NaOH2R’-OH + Na2SO4 Anion Exchange Resin Chemicals NaOH Level(g/L) 30-150 Flow Rate(BV/hr) 3-5 Concentration(%) 5-8 Min. contact time 30 min R’= 21
- 22. Degasser FW water ACF WAC SAC WBA SBA MB CST Weak anion resins derive their functionality from primary (RNH2),secondary(R-NHR’)& tertiary amine (R3N)groups. The weak weak-base anion resins remove free minerals acidity(FMA) such as HCl & H2SO4 but doesn’t remove weakly ionized acids such silicic acid and bicarbonates Weak Acid Anion Exchange Resin
- 23. Degasser FW water ACF WAC SAC WBA SBA MB CST The Strong base anion resins derived their functionality from quaternary ammonium exchange sites. These are capable of exchanging anions like Cl- ,HCO3 -,Silica. Strong Base Anion Exchange Resin(SBA)
- 24. Degasser FW water ACF WAC SAC WBA SBA MB CST Ex-anion water is fed to the mixed bed exchanger containing both cationic resin and anionic resin. This bed not only takes care of sodium slip from cation but also silica slip from anion exchanger very effectively The final output from the mixed bed is an extra-ordinarily pure water having less than 0.2/Mho conductivity, pH 7.0 and silica content less than 20 ppb. Mixed Bed
- 26. R2-Ca2+ R2Mg2+ R-Na+ R-K+ R3-Fe+3 R3-Al+3 HCl R-H+ R-H+ R-H+ R-H+ R-H+ R-H+ TO DRAIN (NaCl, CaCl2 etc SAC WAC R-Cl R2-SO4 R-NO3 R-Cl NaOH TO DRAIN R-Cl R-SO4 R-NO3 R2Ca2+ R2Fe2+ R-K+ SBA MB R2-SiO2 R2-SiO2 R2-SiO2 WBA DM Plant during Regeneration HCl NaOH TO DRAIN
- 27. Parameters pH Conductivity Turbidity Residual Chlorine Silica ACF 6.5 – 7.5 -- <2.0 NTU Nil -- Anion 6.5 – 8.0 <20 Nil Nil <200 ppb Mixed Bed 6.5-7.0 <0.2 Nil Nil < 20 ppb DM Plant Parameters
- 28. MAIN Plant Why DM water can’t be used directly in boiler? - Principle says if water is acidic – Corrosive. - Principle say if water is alkaline – Scale forming. As DM water (also called as hungry water) is having no salt, when it comes in contact with metal surface attacks the metal. DM Water is called ‘Hungry Water’
- 29. 14 Boiler Water Treatment 9 GEN. R Y B C P U TURBINE DE-AERATOR CONDENSER H P HEATER L P HEATER CONDENSATE EXTRACTION PUMP By Pass v/v LP Dosing (Ammonia) BOILER FEED PUMP BOILER BLOW DOWN H P Dosing (Phosphate) BOILER SUPER HEATED STEAM
- 30. HP Dosing Na3PO4+H2O= Na2HPO4 + NaOH Na2HPO4+H2O= NaH2PO4 + NaOH NaOH + HCl (As Impurity)= NaCl + H2O
- 31. AMMONIA IS USED TO INCREASE THE pH OF THE SYSTEM. LP Dosing
- 32. Condensate Polishing Unit(CPU) 24 Removes dissolved solids from feed water (sodium, silica, sulphate ,chloride etc.) by ion-exchange method in an extremely low level Removes suspended solids from feed water(crud of ferric oxide and other impurities) by filtration Function of CPU Stabilizes the steam- water parameters very rapidly during start up Reduces boiler tube failure Reduces turbine maintenance related to steam purity Provides protection against condenser tube leakage Reduces boiler blow down hours Reduces DM water make up Benefits of CPU
- 33. CPUBoiler De aerator IPT LPTHPT HP Heaters LP Heaters Condenser CPU I/L Parameter Sample Limit Sodium, ppb C <2 ACC, µS C <0.10 Silica, ppb C or S <10 Parameters Sample Limit pH C or S 9.2-9.6 ACC, µS C <0.2 DO, ppb C <5 Silica, PPB C or S <20 Parameters Sample Limit Sodium, ppb C <2 ACC, µS C <0.2 Silica, ppb C or S <20 Parameters Sample Limits pH C or S 9.2-9.6 Silica, ppb C or S 400/100 Chloride, ppb C or S <100 Parameter Sample Limit Sodium, ppb C <2 ACC, µS C <0.20 DO, ppb C <20 Silica, ppb C or S <20 MAIN STEAM CPU O/L BOILER WATER FEED WATER Legend: C = Continuous, Online S = Grab, Once in shift Cycle Chemistry Diagram For A Drum Unit- Core Parameters Only
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