Corrosion reduction in waste- and demolition wood fired ... · • The corrosion attacks are due to...
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© Vattenfall AB Corrosion reduction in waste- and demolition wood fired boilers by means of additives: A very corrosive case NextGenBioWaste WP 1.2 Second Conference on Biomass and Waste Combustion Oslo, 16 – 17 February 2010 Anders Hjörnhede Rikard Norling Vattenfall Power Consultant, Sweden
Transcript of Corrosion reduction in waste- and demolition wood fired ... · • The corrosion attacks are due to...
© Vattenfall AB
Corrosion reduction in waste- and demolition wood fired boilers by means of additives: A very corrosive case
NextGenBioWaste WP 1.2Second Conference on Biomass and Waste CombustionOslo, 16 – 17 February 2010
Anders HjörnhedeRikard NorlingVattenfall Power Consultant, Sweden
© Vattenfall AB 2
Test of corrosion reducing additive; ChlorOut
• ChlorOut is based on sulphate - containing solutions, developed and patented by Vattenfall
• ChlorOut converts alkali chlorides, NaCl + KCl, into less corrosive alkali sulphates
• ChlorOut is sprayed into the flue gases after combustion, but before the superheaters
• The sulphate-containing solution is normally ammonium sulphate, (NH4)2SO4, therefore, a significant reduction of the NOx emissions is also achieved
© Vattenfall AB 3
Test plant: HKW-Mittelfeld, Kassel
CFB boiler, built 1987 by Götaverken Energy, SwedenCapacity 36 MWth, two steam turbines: 12 MWelSteam data: 525ºC (540ºC), 83 bar and flue gas temperature of
900ºCSuper heater material: 10CrMo910 (2,25%Cr steel)
“No” corrosion since commissioningFuel change from lignite, which was the design fuel, to waste wood
chips late 2008
Shortly after the fuel change, the superheaters failed due to corrosion and the superheater bundles had to be replaced
© Vattenfall AB 4
Plant sketch
Furnace (bubbling bed)Two cyclonesConvection draft with superheaters, economizer and air preheaterFurnace is water-cooled.No cooling of cyclones; generate high temperatures
Fluegas cleaning: Bag filters No SNCR-system is installed
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ChlrOut injections
ChlorOut solution, (NH4)2SO4, concentration of 37% (by weight)
ChlorOut was injected; 1) before two cyclone inlets2) after the cyclone inlets3) a few meters before the convection pass
Cross section area of the duct is about 10m2
The temperature at the injection positions was estimated to 720 –1000°C
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Measurements and analysis
• IACM: Insitu Alkali Chloride Monitor, on-line measuring of NaCl + KCl. A cross-stack IACM was mounted permanently
• OxyMap: Oxygen measurements and temperature measurements at 8 different positions simultaneously
• Triple temperature deposit probe with controlled surface temperatures. Collects deposits from the flue gas at three different temperatures simultaneously (520, 565 and 600°C)
• DOAS: Differential Optical Absorption Spectroscopy, NH3-, NOx- and SOx-concentration measured on-line. Located after bag filters, after the flue gas fan
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Flue gas duct (from top)
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Analysis of the corroded superheaters
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Kassel: super heater 3 (highest temperature)
Super heater tube (10CrMo910, Cr:2,25%) after less than 6 month of exposure
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Analysis of corroded superheater tube
From superheater tube
Loosely sitting scale removed
Pitting corrosion on surface
Depth 0.1mm or more
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SEM/EDX mapping of corroded SH-tubeFe
Cr
O
Cl
Cl detected in the corrosion front
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SEM/EDX mapping of scale/metal - interfaceb) Fe
c) O
d) K
e) Cl
f) Ca
g) S
Cl enriched in the corrosion front
S detected in the outer part of scale
© Vattenfall AB 13
Point analysis of scale/metal interface
Area O S Cl Cr Mn Fe Mo11 25,7 2,2 1,1 4,9 0 65,4 012 21,5 2,7 2,8 6,3 0 66,7 013 26,8 1,4 0,8 3,7 0 66,9 014 27,2 3,1 1,8 6,4 0 59,8 015 26,5 0,5 5,4 3,2 0 64,1 016 12,8 0,9 27,1 5,4 0,5 52,9 017 25,3 0 33,8 0,9 0 37,2 018 0 0 0 2,9 0,6 95,3 1,2
Concentrations does not add up to 100%
18: super heater material
11 – 14: ”high S”, ”low Cl”
15 – 17: enriched Cl- but lowS-concentration
© Vattenfall AB 14
Results from the tests and analyses
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Temperature fluctuation measured at the tested injection positions
Temp. Kassel 27/5-09
700
750
800
850
900
950
1000
1050
12:21:36 12:50:24 13:19:12 13:48:00 14:16:48 14:45:36 15:14:24 15:43:12
1 2 3 4 Left cyclone exit Right cyclone exit
Left - Rightcyclone 10 –100°C difference
Left - 200°C difference
© Vattenfall AB 16
Deposit growth rate (deposit probe)
Deposit weight
0,0
0,1
0,2
0,3
0,4
0,5
600 °C 565 °C 520 °C
Sam
ple
wei
ght g
ain
(g)
Reference 1150 l/hReference 275 l/h
© Vattenfall AB 17
Cl content in deposit (deposit probe)
Cl content
8,2
9,6 9,8
0,07
2,6
9,7
7,8
0,07
0,02
0,05
0,10
0,05
0
1
2
3
4
5
6
7
8
9
10
600 °C 565 °C 520 °C
Depo
sit c
ompo
sitio
n (w
t.%)
Reference 1150 l/hReference 275 l/h
© Vattenfall AB 18
Sulphur content in deposit (deposit probe)
S content
0
2
4
6
8
10
12
600 °C 565 °C 520 °C
Depo
sit c
ompo
sitio
n (w
t.%)
Reference 1150 l/hReference 275 l/h
© Vattenfall AB 19
Alkali chloride concentration in flue gas
ChlorOut Kassel
0
20
40
60
80
100
120
140
160
180
200
15:20 16:32 17:44 18:56 20:08
Tid [hh:mm]
KC
l [pp
m]
0
20
40
60
80
100
120
140
160
180
200
SO2
[ppm
]
KCl [ppm] SO2 [ppm]
AN
M
LK
J
I
H
G
F
EDC
B
A 15:26 - 16:02, 100 l/h , right cycloneB 16:02 - 16:18, stopC 16:18 - 16:43, 100 l/h, left cycloneD 16:43 - 17:15, stopE 17:15 - 17:50, 50 + 50, both cyclonesF 17:50 - 18:11, stop
G 18:11 - 18:25, 50 l/h, 3 lancesH 18:25 - 18:27, stopI 18:27 - 18:40, 50 l/h, 3 lancesJ 18:40 - 18:57, stopK 18:57 - 19:43, 100 l/h, 3 lancesL 19:43 - 19:54, 150 l/h, 3 lancesM 19:54 - 20:03, 200 l/h, 3 lancesN 20:03 - , 60 l/h 3 lances
18:57 - 19:43, 100 l/h,
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Relative and absolute reduction of alkali chloride concentration in flue gas
Injection Load Ratio
0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6
Red
uctio
n [%
]
20
30
40
50
60
70
80
Injection ratio vs absolute Alkali chloride reduction [ppm] Injection ratio vs Reduction [%]
Ex:30MW x 1,2 = 36l/h
22MW x 1,2 = 26 l/h
© Vattenfall AB 21
NOx, SO2, CO and O2-concentration
NOx (blue) 175 –> 65, CO-spikes (green) reduced
© Vattenfall AB 22
Low temperature deposit formation
No SNCR
Adding of NH3
Temperature: 90 – 120°C
Indiacte salmiac NH4Cl
© Vattenfall AB 23
Flue gas components measured by DOAS in Kassel week 48 (wet gas)
0
30
60
90
120
150
09-11-23 12:00 09-11-24 00:00 09-11-24 12:00 09-11-25 00:00 09-11-25 12:00 09-11-26 00:00 09-11-26 12:00 09-11-27 00:00
NO
; SO
2
0
3
6
9
12
15
NH
3
NO [mg/nm3] SO2 [mg/nm3] NH3 [mg/nm3]
0 l/h 32-38 l/h 30-35 l/h
*boiler load drops
*
*
© Vattenfall AB 24
Summary
• The corrosion attacks are due to the presence of alkali chloride in the fuel
• The chlorine content in the deposits was reduced up to 99 % during injection of ChlorOut
• During ChlorOut injection the alkali chloride concentration in the flue gas was reduced by up to 75 % (60%)
• The NOx emissions were reduced up to 75% (60%) during ChlorOutinjection
• There are strong indications of reduced corrosion rates during ChlorOut injections
• An increase with 200% - 350% of SO2 was measured before the flue gas cleaning during ChlorOut injection
