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WATER CHEMISTRY ASPECTS FOR SUPERCRITICAL UNIT V Chandrasekharan Sr. Manager NTPC SIPAT.

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Presentation on theme: "WATER CHEMISTRY ASPECTS FOR SUPERCRITICAL UNIT V Chandrasekharan Sr. Manager NTPC SIPAT."— Presentation transcript:

1 WATER CHEMISTRY ASPECTS FOR SUPERCRITICAL UNIT V Chandrasekharan Sr. Manager NTPC SIPAT

2 DETAILS  WATER TREATMENT  OT – INTRODUCTION  BOILER ACID CLEANING  BOILER WATER PARAMETERS  LP & OXYGEN DOSING SYSTEM  ON LINE MONITORING  CHANGE OVER FROM ALKALINE TREATMENT TO OT

3 WATER TREATMENT - EXTERNAL Depending on the source of water 1. Clarification 2. Filtration 3. Demineralization 4. DM With RO Make up water quality at DM Outlet Conductivity of > 0. 1  s/cm Silica - <10 ppb

4 FEED WATER TREATMENT Type - A: AVT(R) ;using Ammonia and a Reducing Agent (such as Hydrazine) Type – B: AVT (O); Similar to Type – A minus reducing agent Type – C : (OT); Oxygenated Treatment using only ammonia and oxygen

5 SUPERCRITICAL DRUMLESS (ONCE THROUGH) BOILER WITH OXYGENATED TREATMENT THE KEY WORDS ARE SUPERCRITICAL+DRUMLESS BOILER +OXYGENATED TREATMENT

6 OT AN ALTERNATIVE PROVIDES LONG TERM PROTECTION OF PRE BOILER SYSTEM BY FORMING HAMETITE LAYER. CPU OPERATING PERIOD WILL BE MORE DUE TO LOW CONDENSATE AMMONIA CONTENT IRON TRANSPORT WILL BE REDUCED BY 90% LESS GENERATION OF CRUD REDUCTION IN CHEMICAL CLEANING FREQUENCY REDUCTION IN OUTAGE TIME AND FASTER START UP FAC WILL BE MINIMIZED ALL THESE LEADS TO VERY LESS BTF

7 SCHEMATIC OF OXIDE GROWTH AND MORPHOLOGY UNDER 0XIDISING AVT AND OT 2 Fe3O = 3 Fe2O3

8 CHEMICAL CLEANING OF SUPER CRITICAL BOILER BY FORMIC ACID

9  Economiser  Bottom ring Header  Vertical waterwall  Spiral Waterwall  Separaters  Separator storage tank AREAS UNDER CLEANING

10 STEPWISE CHEMICAL CLEANING PROCESS Inhibitor efficiency test Hydro test of the system SH filling & DM Water Flushing of Boiler Chemical Cleaning Of Boiler Rinsing SH Back Flushing Pre Neutralization Neutralization Passivation preservation

11 Inhibitor efficiency test Acceptable limits corrosion rate should be less than 0.1 Mg/cm2/hr Formic Acid10.0 % Inhibitor Coronil- 200 S 0.30 % Sorbic Acid0.15 % Citric Acid0.10 % Wetting agent0.05 % Temperature85 o C Duration6 hrs. Materials Used SA-106 / SA-210C / SA213- T-12 / SA213 T-22 / SAT-23 / SA-335 P- 91.

12 Temporary arrangements for chemical cleaning of boiler

13 CHEMICAL CLEANING OF SIPAT *Total volume of boiler including temporary pipelines-370 M3 NoChemicalPurity (%) Working Conc. (%) Q'ty (Kg)Remarks 1Hydrazine Pre-cleaning, Hydrotest 2Sorbic Acid Simultaneous Degreasing and Descaling Formic Acid INHIBITOR (CORRONIL 200S) %1070 Citric Acid Non Ionic Detergent Hydrazine Rinsing 4Citric Acid Pre-Neutralization Neutralization Passivation Ammonia Hydrazine

14 Function of Chemicals Sorbic Acid: acts as a reducing agent convert Fe3+ to Fe2+ Formic Acid: (HCOOH) Removes mill scale, weld slag Citric Acid: which dissolves the rust. The pH is raised to an alkaline value using ammonia, and the sequestered iron remains in solution

15 Function of Chemicals Inhibitor: Makes a passivation layer to save the parent metal Detergent: Removes oil & grease COMPLETION CRITERIA FOR ACID CLEANING Check point: Fe++, Fe+++,pH, TOC Requirements: Fe++, pH, TOC Should be stable

16 Coupons to be placed in supply & return line prior to chemical addition to circulation tank made of exactly same composition as of boiler tubes of different locations. COUPON PLACEMENT

17 PASSIVATED COUPON QUALITY OF MAGNETITE LAYER FORMATION AFTER PASSIVATION AS VISUAL INSPECTION.

18 FEED WATER SPECIFICATION S.NOParameterUnitsNormal OperationDuring Start up Alkaline water Treatment Combined water Treatment 1pHMin Min 9.0 2Cation Conductivity,  s/cm  s/cm Max 0.2<0.15Max 0.5 3Dissolved Oxygenppb< Max 100 4Ironppb< 2 < 20 5Sodiumppb< 2 < 10 6Silicappb<10 < 30 7TurbidityNTU<2 <5 FEED WATER RECIRCULATION VIA BOILER TO ACHIEVE FEED WATER QUALITY.

19 LP DOSING AND OXYGENATED TREATMENT SYSTEM AT SIPAT – AMMONIA DOSING Cycle pH is controlled by feeding an ammonia from a pump having a automatic stroke adjustment. The adjustment is automatically adjusted by CEP outlet pH and Feed water flow. The dosing system includes two positive displacement pumps with auto stroke adjustment Automatic switching of pumps upon pump failure.

20 LP DOSING AND OXYGENATED TREATMENT SYSTEM AT SIPAT – HYDRAZINE DOSING Cycle oxygen is controlled by feeding an hydrazine from a pump having a automatic stroke adjustment. The adjustment is automatically adjusted by Deaerator outlet Dissolved Oxygen and Feedwater flow.

21 LP DOSING AND OXYGENATED TREATMENT SYSTEM AT SIPAT – OXYGEN DOSING The cycle oxygen is controlled by flow control valve having a automatic controller. The injection control is automatically adjusted by Feed water flow and Condensate extraction pump outlet dissolved oxygen / Deaerator outlet dissolved oxygen. The dosing system includes four(4) flow control valves with auto controller.

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23 STEAM WATER ANALYSIS SYSTEM (SWAS) FOLLOWING IS THE PROCESS MONITORING FOR CHEMICAL CONTROL OF STEAM AND WATER USED FOR BOILER AND STEAM TURBINE S.NOSYSTEMTYPE OF MEASUREMENT 1MAKE UP DM WATERSP.COND., CATION CONDUCTIVITY (ACC) 2CEP DISCHARGEpH, ACC, Na, DO, SP.COND., 3CONDENSATE POLISHER O/LpH, ACC, Na, SILICA, SP.COND., 4DEAERATOR OUTLETDO 5FEED WATER AT ECONOMIZER INLET pH, ACC, COND.,HYDRAZINE,SILICA, TURBIDITY

24 STEAM WATER ANALYSIS SYSTEM (SWAS) FOLLOWING IS THE PROCESS MONITORING FOR CHEMICAL CONTROL OF STEAM AND WATER USED FOR BOILER AND STEAM TURBINE S.NOSYSTEMTYPE OF MEASUREMENT 6VENT HEADER OF BOILER (SEPARATOR OUTLET STEAM) ACC, SP.COND., HYDRAZINE, SILICA 7MAIN STEAMpH, ACC, Na, SILICA, SP.COND., 8WATER SEPARATION STORAGE TANK OF BOILER CATION CONDUCTIVITY(ACC) 9REHEATED STEAMCATION CONDUCTIVITY(ACC) 10TG ECW COOLING WATERpH

25 PROCEDURE TO CHANGE OVER TO OXYGENATED TREATMENT CPU TO BE IN SERVICE WITH FULL CONDENSATE FLOW. UNIT IN FULL LOAD & STABLE CONDITION. THERE SHALL BE 4 CPU VESSELS (3 IN SERVICE OF 33% CAPACITY EACH) REQUIRED WATER QUALITY:  FEED WATER CATION CONDUCTIVITY : < 0.15 us/cm  FEED pH value : 9 ~ 9.5  D/A O/LOxygen : ≤ 7 ppb

26 DURING SHUTDOWN Stop oxygen feed at least one hour before shutdown Increase ammonia feed rate to achieve a pH > 9.0 Open Deaerator vents LP & HP heaters should be vented

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