New and improved slagging and corrosion
control techniques for biomass firing
Martti Aho
IV Liekkipäivä 23.01.2008
Organisation of the research project
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t
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Research organisations:VTT (Co-ordinaator)
Åbo Akademi University
Main funding:
Tekes (Climbus)
Supporting companies: Metso Power Oy (boiler manufacturer)
Kemira Oyj (chemical manufacturer)
Pohjolan voima Oy (energy company)
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Project duration:
1.1.2005-31.12.2006
Kemira Chemicals Oyj
Research project ”CORRAWAY”
Martti Aho
IV Liekkipäivä 2008
3
Background of operational risks during
biomass combustion
4
On furnace view… .
Recycled fuel
Peat, coal
Sawdust Forest
residues
= safe or protective
= some risks or risky
= very risky
Martti Aho
IV Liekkipäivä 2008
5
CASE 1. BARK/FOREST RESIDUE
Heat transfer
surface
COMPOUN
D
ALKALI
CHLORIDES
S
RI
Y
SK
Cl releases
ä corrosion
KCl
NaCl
Lack of
protecting
compounds
Risk description:
Cl deposition
which
can lead
to high
temperature
superheater
corrosion
Contains 0.01-0.04 wt% Cl but it
can produce about 10 wt% Cl
To critical deposit locations
Low ash
content
BARK/FOREST RESIDUE
Martti Aho
IV Liekkipäivä 2008
6
Presence of melt in fly ash makes it sticky. Presence of Cl in the fly ash
lowers strongly start T of melting ( ref.:Åbo Academi’s calculations)
7
Recycled fuel with high Cl content, but usually <1 wt%
Example: 40% REF in bark (Cl 0.24wt%)
+ High heating value!
Can produce 25wt% Cl to deposits
Martti Aho
IV Liekkipäivä
8
Superheater tubes after high temperature Classisted corrosion
Martti Aho
IV liekkipäivä 2008
9
Destruction of alkali chlorides carrying Cl
to the deposits
Na Cl
Additive or
protective
fuel
HCl + X
Protective fuel
is fossil!
K Cl
Martti Aho
IV liekkipäivät 2008
10
Additive spraying at critical position to the furnace.
Advantage: S is immendiately in its right form (SO3) at right place
Strong and selective effect-> SO2 emissions will not be a problem
’
2MCl + SO3 + H2O -> M2SO4 + 2 HCl
SO3 residue reacts with
CaO etc.
Na2SO4
K2SO4
HCl
SO3 direct
”attach”
Cl carriers:NaCl, KCl
Martti Aho
IV liekkipäivät 2008
11
Reagents invented and tested in the project:
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Ammonium sulphate “Chlorout“ patented by Vattenfall for
comparison:
(NH4)2SO4 -> SO3 + 2 NH3 + H2O
(thetmal destruction at 235 oC:) ( 2-functional: NH3 reduces NO)
*Al (III) and Fe (III) sulphates (Corr 1 ja 2) used earlier as water
chemicals. The new innovation enlargens their application to
energy production (1 functional)
*Patent rights transferred from VTT to Metso Power & Kemira (2007)
Al2(SO4)3 ----à Al2O3 + 3 SO3 (thermal destruction at 770 C
Fe2(SO4)3 à Fe2O3 + 3 SO3 (thermal destruction at 440 C)
t Dosage parameter used: Sreagenssi / Cl2 polttoaineessa
Martti Aho
IV Liekkipäivä 2008
12
Question 1 at the start:
Is the molar flow or sulphur forming ”quantitatively”
SO3 the only effecting parameter from the reagent?
Mx(SO4)y -> SO3 + --Please, note: the real reactions are very complicated
and there are differences for example in the thermal
decomposition temperatures of the additives studied
Martti Aho
IV Liekkipäivä 2008
13
Question 2 at the start:
How selective are the ”vital”reactions (see red arrows) in
relation to the ”wrong”reactions consuming SO3?
’
.
.
M
M 2S O 4
(s ta b le )
SO3
MOH
MOH
MCl
SO3
HCl
(u n s tab le )
HCl
MOH
MCl
A d d itiv e
CaO
SO3
2 CaC O 3
MCl + Cl
M C l + H 2O
C aS O 4
(s ta b le )
CaO
O
SO2
S fu e l + O 2
M = K or Na
Martti Aho
IV liekkipäivä 2008
14
Fractionation results 40% REF 60% bark
14000
12000
mg/kg D.S.
10000
Insoluble
Leached in HCl
Leached in acetate
Leached in H2O
8000
6000
4000
No HCl leaching
with Cl!
from PVC
2000
0
Si
Al
Fe
Ti
Mn
Ca
Mg
Martti Aho
IV liekkipäivä 2008
P
Na
K
S
Cl
15
BFB combustion tests with bark containing
40% recycled fuel on energy basis (Cl 0.24
wt%). Very corrosive fuel when burnt alone
with high steam values!
Martti Aho
IV Liekkipäivä 2008
16
Typical temperature distibution in the 20 kW BFB
8
Residence time, [s]
7
6
5
Freeboard top
Deposit probe
(Ts= 500ºC)
Impactor
sampling
Chemical addition
Tertiary air
4
3
2
Secondary air
1
Bed zone
0
650
700
750
800
850
T, [ºC]
900
950
Martti Aho
IV liekkipäivä 2008
1000
1050
17
dib. air
Ejektor
ELPI
Cyclone
T 800-1000°C
VTT diluter
Ejektor
Cyclone
MFC
Cooling system
DLPI
Exh
nitrogen
Ftir & CO2
Sampling to impactors from 20 kW BFB reactor
18
Results with and comparison of Al2(SO4)3 and Fe2(SO4)3
with two dosage levels
19
The effect of water soluble sulphur-containing chemical to
concentrations of HCl (blue) and other chlorines (red part of columns).
Fuel 40% REF 60% bark with 0.24 wt% Cl
400
in < 4um ash
in HCl
350
300
S/Cl2 = 1.5
Cl, mg/Nm3
S/Cl2 = 0.45
250
200
Risky
Cl
150
100
50
0
No additives
Al2(SO4)3
Fe2(SO4)3
Al2(SO4)3
Martti Aho
IV liekkipäivä 2008
Fe2(SO4)3
20
Cl in vapours and in fine fly ash, fuel 40% REF 60% bark
140
Fly ash particle size range
120
Cl mg/Nm3
100
Dosage S/Cl2 = 0.45
80
1.61-4.02 µm
0.64-1.61 µm
0.26-0.64 µm
0.1-0.26 µm
0.03-0.1 µm
60
40
Dosage S/Cl2= 1.5
20
0
No additives
Al2(SO4)3
Fe2(SO4)3
Al2(SO4)3
Martti Aho
IV liekkipäivä 2008
Fe2(SO4)3
21
Analysis of deposits in Åbo Akademi University by Tor
Lauren
t
The deposit samples were collected from wind and lee sides and from 50
degrees up from the centre of the wind side position for SEM EDS analysis.
Lee side
=50°
50o from Wind side
Wind side
Flue gas flow
22
Deposition of Cl: 40% REF 60% bark
35
S/Cl2= 0.45
30
Cl wt%
25
Wind
50o
Lee
20
15
10
S/Cl2= 1.5
5
0
No additives
Al2(SO4)3
Fe2(SO4)3
Al2(SO4)3
Martti Aho
IV liekkipäivä 2008
Fe2(SO4)3
23
Comparison of the new reagents to the only one existing
in the markets ((NH4)2SO4
24
40%RDF+60%bark, molar dosage factor Sadditive/Cl2fuel is 1.5
140
120
1.61-4.02 µm
0.64-1.61 µm
0.26-0.64 µm
0.1-0.26 µm
0.03-0.1 µm
mg Cl/Nm3
100
80
60
40
20
0
No additives
(NH4)2SO4
Al2(SO4)3
Martti Aho
IV liekki-päivät 2008
Fe2(SO4)3
25
Cl depositon with S/Cl2 W=Wind S= Side L = lee
S
W L
30
30
25
25
20
Pa ino -%
P a in o -%
20
15
15
10
10
5
5
0
0
Alkutila
0.45
0.75
1.5
2.25
Alkutila
0.45
Al2(SO4)3
(NH4)2SO4
Martti Aho
IV Liekki-päivät 2008
0.75
1.50
2.25
26
Conclusions
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There are many (stil unknown) other additive-originated paramerets
effecting to the sulphation power of alkalies than just the molaric
sulphur flow:
The power of the reagents with constant sulphur mass flow in the
reaction: 2MCl + SO3 + H2O -> M2SO4 + 2 HCl was:
Al2(SO4)3 > Fe2(SO4)3 >> (NH4)2SO4
This order is directly proportional to the temperature needed to thermal
destruction. Probably ammoniun sulphate decomposes faster than the
other sulphates which then produce fresh SO3 at longer furnace zone.
Complete decomposion to SO3 at short furnace zone leading to high
local SO3 concentr. may strengthen other SO3 consuming reactions
than sulphation and reduce alkali sulphation selectivity to SO3
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With the new reagents, sulphation of alkali chlorides dominates
strongly over the other SO3 consuming reactions which is a significant
advantage: chemicals can be used with low dosages with small or
insignificant increase of SO2 emissions
Martti Aho
IV Liekki-päivät 2008