Corrosion and emission reduction in CHP plants
Experiences from a ChlorOut installation in a BFB boiler
Håkan Kassman, Åsa Astervik
Vattenfall AB, Research & Development
CenBio Final Conference
13-14 March 2017
Confidentiality class: Low (C1)
Content of the presentation
• Alkali-related operational challenges during combustion of biomass
• IACM and the ChlorOut concept
• Plant description of the BFB boiler in Jordbro
• Selected results from two Conference papers. To be presented at
CFB-12 Krakow, May 2017
• Reduced superheater corrosion by injection of ammonium sulphate
in a biomass fired BFB boiler,
• Simultaneous reduction of NO and KCl during injection of ammonium
sulphate in a biomass fired BFB boiler
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Challenges during combustion of biomass
• The alkali-related operational challenges during biomass combustion
include agglomeration, deposit formation and superheater corrosion.
• High levels of alkali chlorides (expressed as KCl) can cause
enhanced deposit formation.
• KCl in deposits may cause accelerated superheater corrosion.
• Superheater corrosion can be reduced by co-combustion or by the
use of sulphur/sulphate-based additives.
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
IACM and the ChlorOut concept
• IACM (In situ alkali chloride monitor) –
Measurement of gaseous KCl
IACM is used for control of the required
amount of additive and for on-line
quality control in the incoming fuel mix
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
I
II
III
60
KCl (ppm wg)
• The ChlorOut concept - Injection of
sulphate containing additives (often
ammonium sulphate, AS). AS converts
KCl to a less corrosive alkali sulphate
80
pure wood
pellets
wood
pellets
+straw
wood pellets
+straw+PVC
40
20
0
0
40
80
120
Time (minutes)
160
IACM – Measurement of gaseous alkali chlorides (KCl)
Transmitter (light source)
Receiver (spectrometer)
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Sulphation of gaseous KCl
Ammonium sulphate (AS)
Direct decomposition into SO3
(NH4) 2SO4  2NH3 + SO3 + H2O
Sulphation of gaseous KCl is more
efficient with AS (KCl-AS) compared
to elemental sulphur (KCl-S).
Sulphur
Oxidation from S to SO2 and SO3
SO2 + ½ O2 ↔ SO3
Sulphation of gaseous KCl from SO3:
2KCl + SO3 + H2O  K2SO4 + 2HCl
Influence of combustibles (e.g. H-radicals):
SO3 + H ↔ SO2 + OH
The SNCR reaction:
4NH3 + 4NO + O2 → 4N2 + 6H2O
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Plant description - Jordbro
63 MWth (20 MWel) BFB boiler
Valmet/Metso design
AS, L1
AS, L2
Start of operation: 2010
Permanent ChlorOut installation in 2014
Fuel: Mainly demolition waste wood
Steam data: 80 bar/470°C, Superheater SH2
made of 10CrMo9-10 (low alloyed material)
EKO
SH1
SH2
IACM
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
The BFB boiler and IACM measurements
IACM measurement location below SH2
IACM - Reduced measurement path
The BFB boiler in Jordbro with IACM &
injection points for AS and NH3 indicated
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
The BFB boiler and injection of ammonium sulphate (AS)
Injection lance
Dosage system & storage tank
The BFB boiler in Jordbro with IACM &
injection points Level L1 and L2 for AS
Nozzle
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Flow control of air and AS
Experimental – Superheater corrosion
• Reduced superheater corrosion by injection of ammonium sulphate in a
biomass fired BFB boiler
• The lower and hottest parts of SH2 were replaced after four years of
operation without any additives to prevent superheater corrosion.
• A permanent ChlorOut installation was fully implemented in regular
operation of the boiler during the summer of 2014.
• Extensive measurement campaigns were performed prior to installation.
They included short-term deposit and long-term corrosion probe
measurements both with and without injection of AS.
• Tube analysis were performed on the replaced tubes and on the tubes
after two years of operation with the ChlorOut concept.
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Deposit probe measurements (short-term)
Chemical analysis of deposits from probe measurements
Less chlorine in deposits during injection of ammonium sulphate
16
Na+K
S
Cl
14
12
Weight %
10
8
6
4
2
0
Reference
ChlorOut 60 l/h
ChlorOut 90 l/h
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
ChlorOut 120 l/h
Jordbro: Corrosion probe measurements (long-term)
Long-term corrosion measurement (1000h). The corrosion rate of 10CrMo910
was decreased by ~80% during injection of AS (1l/MWh) compared to Ref.
Steam temperature 470°C =>
material temperature ~ 500°C
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Corrosion - Operating experience
Four years without an additive
Two years with the ChlorOut concept.
Corrosion rate ~0,75 mm/year.
Corrosion rate ~ 0,25 mm/year.
The superheater corrosion was significantly reduced after
the ChlorOut concept was permanently installed.
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
The BFB boiler and injection of ammonium sulphate (AS)
Injection lance
Dosage system & storage tank
The BFB boiler in Jordbro with IACM &
injection points Level L1 and L2 for AS
Nozzle
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Flow control of air and AS
Experimental - Emissions
• Simultaneous reduction of NO and KCl during injection of
ammonium sulphate in a biomass fired BFB boiler
• The strategy was to inject AS by so-called
transient tests during three different excess
air ratios (λ).
• Increasing amounts of AS were injected in a
sequence in L1 (upper part of combustion
chamber) & in L2 (upper part of empty pass).
• Each sequence consisted of a reference
without any injection of AS (Ref), and
injection of increasing amounts of AS.
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Simultaneous reduction of NO and KCl
Transient test with injection of various flows of AS
Impact on NOx, KCl (obtained from IACM), SO2, HCl.
Reduction of NO and KCl Case 1 - Day 1
KCl (ppm)
HCl (mg/m3)
NOx (mg/MJ)
SO2 (ppm)
100
30
75
20
50
10
25
0
14:00
0
16:00
18:00
Time
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
20:00
NOx (mg/MJ), SO2 (ppm)
KCl (ppm), HCl (mg/m3)
40
Simultaneous reduction of NO and KCl
Increasing amounts of AS were injected in a sequence in L1 (upper part
of the combustion chamber) and in L2 (upper part of the empty pass).
(NOo/NOi) or (KClo/KCli)*100 (%)
100
80
60
40
L1-NOx
L2-NOx
L1-KCl
L2-KCl
20
0
0
1
2
NH3/NO or S/Cl (molar ratio)
Impact on NO and KCl during injection of AS: Air excess ratio λ=1.20
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Summary - Simultaneous reduction of NO and KCl
100
100
80
80
KCl
60
λ=1.17 L1
λ=1.20 L1
λ=1.28 L1
λ=1.17 L2
λ=1.20 L2
λ=1.28 L2
40
20
(KClo/KCli)*100 (%)
NO
(NOo/NOi)*100 (%)
Reduction of NO and KCl versus molar ratio NH3/NO during injection of AS in L1 (upper
part of combustion chamber) and L2 (empty flue gas pass) for λ=1.17; λ=1.20 and λ=1.28
1
NH3/NO (molar ratio)
60
40
20
0
0
0
λ=1.17 L1
λ=1.20 L1
λ=1.28 L1
λ=1.17 L2
λ=1.20 L2
λ=1.28 L2
2
0
0.5
1
1.5
S/Cl (molar ratio)
2
• The air excess ratio and the position (L1 or L2) had an impact on the reduction of
NO as well as KCl during injection of ammonium sulphate.
• A less efficient reduction of both NO and KCl was in general as achieved in earlier
positions in comparison with other positions with the same air excess ratio.
• Sulphation of KCl was somewhat more sensitive for interactions with the O/H
radical pool (i.e. H-radicals).
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)
Acknowledgements
• This work has been funded by CenBio – Norwegian Bioenergy
Innovation Centre.
• CenBio is co-funded by the Research Council of Norway (193817/E20)
under the FME scheme and the research and industry partners.
• The practical support from the staff at the BFB boiler in Jordbro is also
greatly appreciated .
| Corrosion and emission reduction in CHP plants | Håkan Kassman, Vattenfall AB
Confidentiality class: Low (C1)