Higher COC and ph Independent Operation of Cooling Water Systems

Transcription

1 Higher COC and ph Independent Operation of Cooling Water Systems CONFER-NERTA 2016 S. M. Mahadik President Technical Vasu Chemicals 31/3/2015

2 Conventional Coal based Power Plants: Flue Gases Steam Turbine Generation Ash handling Condenser Cooling Water out Water Cooling Water in Fuel Boiler Pump

3 Power Plant Cooling Water Treatment - Main Consumer of cooling water: T G Condenser - Other Consumer of cooling water: Lube oil coolers, Atomizer - Condensation of Steam at C on shell side in TG condenser. - Maintain Vacuum & Low back pressure in the condenser with proper cooling. - Maintain oil temperature within desire range in oil coolers. - Maintain CT fills free from fouling

4 Factors affecting TG Condenser performance Water side scaling & fouling of condenser tubes. Partial blockage of cooling water flow through the tubes due to deposition of extraneous matter. Inadequate removal of non-condensable gases. Faulty distribution of exhaust steam. Leakage in the vacuum system. Water side scaling / fouling is most common cause

5 Open Recirculating Cooling Water System HOT WATER Steam in Surface Condenser MAKE UP WATER Condensate COLD WATER Blowdown Problems in HEAT TRANSFER Equipments CORROSION SCALE / DEPOSITS MICROBIOLOGICAL FOULING

6 Factors to be considered while selecting treatment program 1. High circulation rate and hold-up. 2. Process side temperature, i.e. steam temperature, which is about 50 C 3.The metallurgy of condenser tubes : Copper Alloy/SS 4. Water box Protective coating, Sacrificial Anode. 5. Pipelines CS 6. Packed PVC fills in Cooling Tower More prone for fouling and deposition 7. Less contamination

7 Conventional Treatment in Power Plant Cycle of Concentration (water use to ash handling) ph control with acid addition Chemical for scale control - HEDP based Antiscalant Microbiological control - chlorine Corrosion control of condenser water box - sacrificial anode / coating Use of Zn and Azole as a corrosion control High water consumption, high quantity of acid handling - Disadvantage Water vapour ash handling steam Antiscalant HEDP based Make up water Chlorine condensate

8 Forward Path Separate arrangement for water for Ash handling system Cycle of Concentration - 5 to 7 No acid addition or very little acid addition Cooling water ph up to 9.2 Water vapour steam Package Treatment chemicals Chlorine / Chlorine Dioxide /Biodispersant Condenser Make up water 2 to 4% Side stream filter condensate

9 Higher Cycle of Concentration/High ph operation Advantages : 1. Water Saving 2. Less or no acid handling Safe operation 3. Reduction in general water corrosion tendency Disadvantages : 1. High tendency for deposition and scaling, CW is more stressed 2. High tendency for Magnesium Silicate precipitation 3. High Alkalinity and ph of Cooling water 4. High Holding Time Index (HTI) 5. Chlorination less effective 6. High tendency for Packed PVC fills fouling and deposition 7. Increase in Turbidity of CW

10 Blowdown,m3 Cycle of Concentration Vs Blowdown Plant Capacity MW Circulation rate m3/hr Temp. Difference 8-10 deg. C blowdown # COC Blowdown, m3/hr COC Water saving 3 COC to 6 COC 3672 M3/Day

11 Higher Cycle of Concentration/High ph operation Advantages : 1. Water Saving 2. Less or no acid handling Safe operation 3. Reduction in general water corrosion tendency Disadvantages : 1. High tendency for deposition and scaling, CW is more stressed 2. High tendency for Magnesium Silicate precipitation 3. High Alkalinity and ph of Cooling water 4. High Holding Time Index (HTI) 5. Chlorination less effective 6. High tendency for Packed PVC fills fouling and deposition 7. Increase in Turbidity of CW

12 Treatment Program for higher COC and higher ph a. ph control Up to 9.2 b. Deposit/Scale Control - - High stress polymer (Ter-polymer) Better control of Magnesium Silicate, Silt deposition along with Zinc and Phosphate stabilization - Stable Organophosphonate such as PBTC along with low Phosphorous Phosphonate (PSA) Better Calcium Carbonate scale control - Hardness Stabilizer, Polymaleic Acid (PMA) based to further enhance scale /deposition control in TG condenser and Cooling Tower fills. c. Biological Control Continuous Chlorination/Bromination with Chlorine Dioxide to maintain ORP mv - - Bio dispersant at least 5 ppm based on B/D - Non oxidizing biocide for contingency application

13 Treatment Program for higher COC and higher ph d. Corrosion Control - - Copper corrosion control : Oxidant Stable Azole - CS pipeline corrosion control : High ph reduces corrosion tendency Addition of Zn (0.3 to 0.5 ppm) and if necessary Ortho Phosphate (2-3 ppm) e. Turbidity Control- - Provide Side Steam Filter

14 High Efficiency PVC Fils Problems More prone for - Slime formation - Deposition of dust and dirt from atmosphere - Deposition of Calcium Carbonate Action - Good control on scale, deposition and bio fouling (Chlorine Dioxide) is must - Avoid channeling of falling water - Cell by cell Running of CT fan without water till deposit get dried, followed by addition of Biodispersant with water. - Regular on line cleaning by addition of special cleaners along with Biodispersant/Sequestering agents.

15 Chlorine Dioxide - Safe O Cl In-Situ Generation of Chlorine Dioxide O NaClO 2 + 1/ 2 Cl 2 -- ClO 2 + NaCl (Chlorine Dioxide ) Can be generated without Chlorine gas also Advantages : True gas hence does not dissociates like Cl2 2.5 times stronger than Cl2 Do not react with Ammonia, Organics. Hence more effective than chlorine in contaminated system. Reduces chlorine consumption. Reduces the chloride built-up due to chlorination. Effective in high ph range also. Negligible delignification of wood.

16 Cl 2 Cl 2 Cl 2 ClO 2 Cl 2 Cl 2 ClO 2 ClO 2 ClO 2 ClO 2 penetrates through slimy deposit, removes & kills SRB

17 Methods of Generation Single pump Use of Chlorinated water from Chlorinator 2NaClO 2 + Cl 2 2ClO 2 + 2NaCl Sodium Chlorine Chlorine Sodium Chlorite Dioxide Chloride

18 Methods of Generation Acid Method No chlorine 5NaClO 2 + 4HCl 4ClO 2 + 5NaCl + 2H 2 O Sodium Hydrochloric Chlorine Sodium Water Chlorite Acid Dioxide Chloride Recommended ClO2 Residal ppm Higher cost than chlorination

19 Performance Monitoring Comparison of Calcium/Cl / Mg/Sio2 Ratio Simple and reliable tool Calcium Ratio = Mg. Ratio = Calcium Hardness in cooling water Calcium Hardness in make up water Mg/SiO2 in cooling water Mg/SiO 2 in make up water No proper Treatment Calcium Mg /SiO 2 or Ratio < Ratio Without Treatment Proper Treatment Calcium Mg/SiO2 Ratio = Ratio

20 Performance Monitoring (contd..) Vacuum Data Vs Plant Load: If Scale formation /Deposition Vacuum Drops Plant load reduces Sudden drop in vacuum physical blockage of water flow in the condenser. Pressure drop across TG Condenser / Exhaust Temperature Increase in pressure drop Deposition / Scaling in TG Condenser. Terminal Temperature difference(ttd): Increase in TTD(at same plant load) Deposition / Scaling in TG Condenser. TTD = Process out let temp. Cooling out let Temp.

21 Control of Evaporation loss from Water Storage Pond- Avoid/reduce water air contact by use of non toxic chemicals, floating cover/plastic balls.

22 HOW DO THE SHADE BALLS/COVER WORK? -The plastic black balls, around the size of an apple -They float on the surface and block the sun's rays reduced evaporation -The balls also form a protective barrier across the surface that helps keep birds, animals and other contaminants out away, also reduces algae formation

23 Think out of Box Can we convert evaporated cooling water into condensate? If yes, then no water scarcity in Industry

24 Conclusion Availability of latest technology and properly designed treatment package, makes it possible to operate power plant cooling water system at higher cycle of concentration with no or very little acid addition with effective performance leading to tremendous savings in water and energy. However, inadequate treatment can lead to disaster.

25 Thank you