WATER TREATMENT FOR BOILERS

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TREATMENT OF WATER FOR HIGH PRESSURE BOILERS & STEAM-WATER QUALITY PARAMETERS BY DILIP KUMAR

1. PRETREATMENT PLANT AERETOR BY GANGA MAKEUP PUMPS RIVER GANGA •Suspended particles •Dissolved inorganic salts •Dissolved organic compounds •Micro organisms & •Dissolved gasses IMPURITIES IN 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; Fe(HCO3) + O2 -- FeO(OH) + CO2 + H2O Mn(HCO3) + O2 -- MnO2(OH) + CO2 + H2O
2. 3. 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; Fe(HCO3) + O2 -- FeO(OH) + CO2 + H2O Mn(HCO3) + O2 -- MnO2(OH) + CO2 + H2O •Alum Al2 (SO4)3, 18H2O : For coagulation. •Lime Ca (OH)2 : To maintain the pH. •Chlorine Cl2 : As a disinfectant. DOSING OF CHEMICALS Al2(SO4)3.18 H2O + 3 Ca(HCO3)2 =2AI(OH)3 + 3CaSO4 + 18H2O + 6CO2 Al2(SO4)3.18 H2O + 3 Ca(OH)2 = 2AI(OH)3 + 3CaSO4 + 18H2O Cl2 + H2O HOCL + HCl CLARIFIER CASCADE AERATOR Clarifier outlet turbidity < 20NTU Clarifier outlet residual Cl2: 0.2-0.5 ppm
3. 4. RAW WATER INLET CLARIFIED WATER OUTLET SLUDGE OUTLET
4. 5. Clarified water turbidity < 20NTU Clarified water residual Cl2: 0.2-0.5 ppm CLARIFIER Turbidity reduced Micro-organisms are killed GRAVITY SAND FILTER (GSF) Sand Gravel Rapid rate gravity filtration is the most widely used technology for removing turbidity and microbial contaminants from pretreated surface water and groundwater. FILTERATION Filtered water turbidity < 5 NTU Clarified water residual Cl2: 0.2-0.5 ppm
5. 6. FOR DRINKING FOR DEMINERALIZATION TO DM PLANT FILTERED WATER SUMP Filtered water turbidity < 5 NTU Clarified water residual Cl2: 0.2-0.5 ppm REMAINING IMPURITIES Dissolved inorganic salts Dissolved gasses Dissolved organic compounds
6. 7. Degasser FW water ACF WAC SAC WBA SBA MB CST Processes ….. DEMINERALISATION STREAM
7. 8. 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) Processes …..
8. 9. Degasser FW water ACF WAC SAC WBA SBA MB CST WAC resin is capable to exchange cations of alkalinity producing salts only i.e., for carbonate hardness removal purpose. 2 R-COOH + Ca(HCO3)2  (RCOO)2Ca2+ 2 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. Processes …..
9. 10. Degasser FW water ACF WAC SAC WBA SBA MB CST SAC resin works over wide pH range & is capable to exchange any type of cations present in salts as sulphonic acid group is strongly acidic. 2 R-SO3-H+ + CaCl2  (RSO3)2Ca2+ 2 (H+ + Cl- ) Processes …..
10. 11. 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 CO^ and water. carbon dioxide escapes into the atmosphere. Water is pumped back to anion exchanger bed Processes …..
11. 12. 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 Processes …..
12. 13. 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. Processes …..
13. 14. 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, H 7.0 and silica content less than 0.02 ppm. Processes …..
14. 15. CATIONS Ca2+,Mg2+ Na+,Fe3+, K+ ANIONS Cl-,SO4 2-, NO3 -,CO3 2- HCO3,SiO2 2 WATER SAC R-H+R-H+ R-H+ R-H+ R-H+ R-H+ R-H+ CATIONS H+ ANIONS Cl-,SO4 2-, NO3,CO3 2- HCO3,SiO2 2- AIR DG CATIONS H+ ANIONS Cl-,SO4 2-, NO3 -,SiO2 2- WATER WATER R-OH- R-OH- R-OH- R-OH- R-OH- R-OH- CATIONS H+ ANIONS OH- WBA+SBA CO2 ION EXCHANGE - PROCESS CHEMISTRY WAC +
15. 16. REGENERATION PROCESS 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+ NaCl,CaCl2 etc. TO DRAIN SAC SAC R-Cl R2-SO4 R-NO3 R-Cl NaOH TO DRAIN R-OH- R-OH- R-OH- R-OH- R-OH- R-OH- SBA SBA+ WBA R2-SiO2 R2-SiO2 R2-SiO2 WBA
16. 17. Parameters pH Conductivity Turbidity Residual Chlorine Silica ACF 6.5 – 7.5 -- <2.0 NTU Nil -- Anion 6.5 – 8.0 <10 Nil Nil <200 ppb Mixed Bed 6.5-7.0 <0.2 Nil Nil < 20 ppb
17. 18. 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.
18. 19. CONDENSER CEP LPH DEAERATOR H P H ECONOMISER WATER WALLS BOILER DRUM TURBOGENERATOR GT SWITCHYARD BOTTOM RING HEADER UPPER RING HEADER D O W N C O M M E R S SH TO STACK TO ESP BFP CT
19. 20. BFP DOSING OF CHEMICALS TO PROTECT THE BOILER AND PREBOILER SYSTEM FROM CORROSION
20. 21. BFP AMMONIA IS USED TO INCREASE THE pH OF THE SYSTEM & NH3+ CO2 = (NH4)2CO3 N2H4 + O2 =N2 + H2O 3N2H4 =4NH3 + N2 ( this reaction takes place in the boiler drum AMMONIA DOSING
21. 22. BFP Tri-sodium phosphate hydrolyses & gives Na3PO4+H2O= Na2HPO4 + NaOH Na2HPO4+H2O= NaH2PO4 + NaOH NaOH + HCl (As Impurity)= NaCl + H2O TRISODIUM PHOSPHATE DOSING IN BOILER DRUM
22. 23. BFP SAMPLING POINTS AND PARAMETERS CONDENSATE SAMPLE COLLECTED FROM CEP DISCHARGE PH 9.0-9.2 K 3.0-4.0 µs/cm SILICA 10 ppb DO <40 ppb NH3 1.0 ppm Fe <10 ppb Cu <3.0 ppb
23. 24. BFP SAMPLING POINTS AND PARAMETERS FEED SAMPLE COLLECTED FROM ECONOMIZER INLET PH 9.0-9.2 K 3.0-5.0 µs/cm ACC 0.2 µs/cm SILICA 10 ppb DO <5 ppb Fe <10 ppb Cu <3.0 ppb
24. 25. BFP SAMPLING POINTS AND PARAMETERS BOILER DRUM(BD) SAMPLE COLLECTED FROM BOILER DRUM PH 9.1-9.4 K <20 µs/cm SILICA 0.1 ppm PHOSPHATE 1.0-2.0 ppm CHLORIDE 0.5 ppm TDS 10 ppb
25. 26. BFP SAMPLING POINTS AND PARAMETERS SATURATED STEAM SAMPLE COLLECTED FROM BOILER DRUM OUTLET PH 9.0-9.2 K 3.0-5.0 µs/cm ACC 0.2 ppm SILICA 10 ppb Na <5.0 ppb NH3 <1.0 ppm Fe <10 ppb
26. 27. BFP SAMPLING POINTS AND PARAMETERS MAIN STEAM SAMPLE COLLECTED FROM SUPER HEATER OUTLET PH 9.0-9.2 K 3.0-5.0 µs/cm SILICA 10 ppb Na <5.0 ppb NH3 1.0 ppm Fe <10 ppb Cu <3.0 ppb
27. 28. BFP SAMPLING POINTS AND PARAMETERS DEAERATOR OUTLET SAMPLE DO <5 ppb