Transcript Slide 1

WATER CHEMISTRY
ASPECTS FOR
SUPERCRITICAL UNIT
V Chandrasekharan
Sr. Manager
NTPC SIPAT
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
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
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
SUPERCRITICAL DRUMLESS (ONCE THROUGH)
BOILER WITH OXYGENATED TREATMENT
THE KEY WORDS ARE
SUPERCRITICAL+DRUMLESS BOILER +OXYGENATED
TREATMENT
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
SCHEMATIC OF OXIDE GROWTH AND
MORPHOLOGY UNDER 0XIDISING AVT AND OT
2 Fe3O4 + 0.5 02 = 3 Fe2O3
CHEMICAL CLEANING OF SUPER
CRITICAL BOILER
BY FORMIC ACID
AREAS UNDER CLEANING
Economiser
Bottom ring Header
Vertical waterwall
Spiral Waterwall
Separaters
Separator storage tank
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
Inhibitor efficiency test
Acceptable limits
corrosion rate should be less than 0.1 Mg/cm2/hr
Formic Acid
10.0 %
Inhibitor Coronil200 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 / SA213T-12 / SA213 T-22 /
SAT-23 / SA-335 P91.
Temporary arrangements for chemical cleaning of boiler
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
2
Sorbic Acid
98.0
0.15
540
Formic Acid
85.0
10.0
36000
INHIBITOR
(CORRONIL 200S)
100.0
0.3%
1070
Citric Acid
98.0
0.1
360
Non Ionic Detergent
100
0.05
3
Hydrazine
50
0.001
750
Rinsing
4
Citric Acid
98.0
0.1
360
Ammonia
25
0.075
1050
Hydrazine
50
0.050
350
Pre-Neutralization
Neutralization
Passivation
Pre-cleaning,
Hydrotest
Simultaneous
Degreasing and
Descaling
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
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
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.
PASSIVATED COUPON
QUALITY OF
MAGNETITE LAYER
FORMATION AFTER
PASSIVATION AS
VISUAL INSPECTION.
FEED WATER SPECIFICATION
S.NO
Parameter
Units
Normal Operation
During
Start up
Alkaline water
Treatment
Combined
water
Treatment
Min 9.0
8-8.5
Min 9.0
1
pH
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
ppb
<2
<2
< 20
5
Sodium
ppb
<2
<2
< 10
6
Silica
ppb
<10
< 10
< 30
7
Turbidity
NTU
<2
<2
<5
FEED WATER RECIRCULATION VIA BOILER TO ACHIEVE FEED WATER
QUALITY.
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.
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.
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.
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
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
CATION CONDUCTIVITY(ACC)
10
TG ECW COOLING WATER
pH
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
D/A O/LOxygen
: 9 ~ 9.5
: ≤ 7 ppb
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