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 ms/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. AREAS UNDER CLEANING Economiser Bottom ring Header Vertical waterwall
Spiral Waterwall
Separaters
Separator storage tank

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 Acid
10.0 %
Inhibitor Coronil-200 S
0.30 %
Sorbic Acid
0.15 %
Citric Acid
0.10 %
Wetting agent
0.05 %
Temperature
85oC
Duration
6 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
CHEMICAL CLEANING OF SIPAT *Total volume of boiler including temporary pipelines-370 M3 No
Chemical
Purity (%)
Working
Conc. (%)
Q'ty (Kg)
Remarks 1
Hydrazine 50
0.001
Pre-cleaning, Hydrotest 2
Sorbic Acid
98.0
0.15
540
Simultaneous
Degreasing and
Descaling
Formic Acid
85.0
10.0
36000
INHIBITOR (CORRONIL 200S)
100.0
0.3%
1070
Citric Acid
0.1
360
Non Ionic Detergent
100
0.05 3
750
Rinsing 4
Pre-Neutralization
Neutralization
Passivation
Ammonia 25
0.075
1050
0.050
350

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. COUPON PLACEMENT
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.

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

18. FEED WATER SPECIFICATION
S.NO
Parameter
Units
Normal Operation
During
Start up
Alkaline water Treatment
Combined water Treatment 1 pH
Min 9.0
8-8.5 2
Cation Conductivity, ms/cm
ms/cm
Max 0.2
<0.15
Max 0.5 3
Dissolved Oxygen
ppb
< 5
30-150
Max 100 4
Iron
< 2
< 20 5
Sodium
< 10 6
Silica
<10
< 30 7
Turbidity
NTU
<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.

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.NO
SYSTEM
TYPE OF MEASUREMENT 1
MAKE UP DM WATER
SP.COND., CATION CONDUCTIVITY (ACC) 2
CEP DISCHARGE
pH, ACC, Na, DO, SP.COND., 3
CONDENSATE POLISHER O/L
pH, ACC, Na, SILICA, SP.COND., 4
DEAERATOR OUTLET DO 5
FEED 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.NO
SYSTEM
TYPE OF MEASUREMENT 6
VENT HEADER OF BOILER (SEPARATOR OUTLET STEAM)
ACC, SP.COND., HYDRAZINE, SILICA 7
MAIN STEAM
pH, ACC, Na, SILICA, SP.COND., 8
WATER SEPARATION STORAGE TANK OF BOILER
CATION CONDUCTIVITY(ACC) 9
REHEATED STEAM 10
TG ECW COOLING WATER pH

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

27. THANK YOU