BROMINE AND CHLORINE IN AEROSOLS AND FLY ASH IN
CO-FIRING OF SOLID RECOVERED FUEL, SPRUCE BARK
AND PAPER MILL SLUDGE IN 80MWTH BFB BOILER
PASI VAINIKKAa, JAANI SILVENNOINENb, ARI FRANTSIc, RAILI TAIPALEa,
PATRIK YRJASd, JANNE HANNULAe
a
VTT, Koivurannantie 1, FI-40101 Jyväskylä, Finland
Metso Power, Kelloportinkatu 1, FI-33101 Tampere, Finland
c
Stora Enso Publication Papers, Anjalankoski mills, FI-46900 Anjalankoski, Finland
d
Åbo Akademi Process Chemistry Centre, Biskopsgatan 8, FI-20500 Åbo, Finland
e
Lassila&Tikanoja, Sepelitie 6, FI-40320 Jyväskylä, Finland
b
Corresponding author: pasi.vainikka@vtt.fi. Tel. +358 40 5825 987
ABSTRACT
Aerosol and fly ash sampling was carried out at a 80MWth bubbling fluidised bed (BFB)
boiler plant co-incinerating solid recovered fuel (SRF), spruce bark and paper mill
wastewater sludge in two experimental conditions. SRF-Bark ratio was kept constant at
50%-50% on dry mass basis but two sludge proportions were used: 15% and 4% on dry
mass basis. Aerosol samples were collected from the superheater region of the boiler
furnace and fly ash from the electrostatic precipitator (ESP). Na, K, Cl and S were
found to be the main elements in the aerosols sampled by the means of a Dekati type
Low Pressure Impactor (DLPI). Also bromine was found in several weight percentages
in aerosols and it was amongst the main elements in some of the samples collected.
Bromine is supposed to be mainly originated from flame retarded plastics and textiles in
the SRF. According to the measurements the fate of Br seems to be analogous to the
other main halogen, Cl, and its conversion from fuel to aerosols was high indicating the
formation of bromine bearing salts.
Keywords: Fluidised bed combustion, co-incineration, co-combustion, aerosols, fine
particles, halogens, bromine, chlorine, solid recovered fuels.
INTRODUCTION
The Anjalankoski BFB plant
Stora Enso Anjalankoski co-incineration plant started as pulverized coal boiler in year
1971 with a small fixed grate for bark combustion. The first commercial size BFB
boiler in Finland was connected to coal boiler in 1983 to combust wet sludge from
paper mill’s wastewater treatment. Grate of the coal boiler was converted to BFB in
1995. Wet scrubber was also installed after the ESP to improve flue gas cleaning and
establish heat recovery to scrubber water. Plant’s emissions to air and water are shown
in Figure 1.
After the start-up of the BFB co-incineration of SRF initiated in order to solve paper
mill’s waste treatment, and was later widened to the use of package wastes which could
not be recycled. Simultaneously the live steam values were reduced to the level of
500°C/80bar from 525°C/87bar in order to allow safety margin for more corrosive
combustion gases.
109%
100 %
% from environmental permit limit
BAT BREF
Measured yearly average
80 %
60 %
40 %
20 %
80 %
60 %
40 %
20 %
Zn
/f
ur
an
s
io
x
in
s
Tl
Pb
Ni
Hg
Cu
Cr
d
C
As
D
O
x
(n
o
C
d
+
Tl
O
th
er
Hg
he
av
y
m
D
et
io
al
xi
s
ns
/f
ur
an
s
O
Du
st
C
HF
Cl
H
2
C
TO
SO
R)
SC
Du
st
0%
0%
N
Figure 1. Anjalankoski plant’s emissions to air (left) and water (right). With bars are shown values for
combustion plants based on Best Available Technology (BAT) according to the Reference Document on
the Best Available Techniques (BREF) for Waste Incineration (European Integrated Pollution Prevention
and Control Bureau 2006) and with crosses are marked the measured yearly average values, as percent
from the plant’s environmental permit, for the Anjalankoski plant.
Indirect thermal sludge dryer was invested in year 2000 in order to combust all adjacent
paper mill’s sludge in dry matter content of about 70-80 wt-%. This also made it
possible to increase the amount of SRF in the fuel mix. In 2006 the boiler received new
environmental permit according to the European Waste Incineration Directive (WID)
with SRF capacity of 50 000 tonnes per year. SRF share from all fuels was increased to
60 % (on energy basis) after long term tests and investigations.
140
70 %
SRF amount
120
60 %
100
50 %
Paper industry
strikes 2005
80
40 %
e2
00
8
e2
00
9
20
07
20
06
20
05
20
04
0%
20
03
0
20
02
10 %
20
01
20
20
00
20 %
19
99
40
19
98
30 %
19
97
60
SRF share, enb
SRF share
19
96
SRF amount, kt/year
% from environmental permit limit
100 %
Figure 2. Annual SRF amount and share from all fuels (on energy basis) at the Anjalankoski BFB plant.
Objectives
A suspension of solid fine particles or liquid droplets in a gas is called aerosol. In this
paper the term aerosol is specifically used for the suspension particles less than 1 m in
aerodynamic diameter. With the sampling system applied in this research these particles
are supposed to be mainly formed from compounds that are vaporized at fluidized bed
combustion temperatures. (Valmari, Kauppinen et al. 1998, Pyykönen, Miettinen et al.
2007, Sippula, Lind et al. 2008)
The objective of this study was to measure the composition and concentration of
aerosols in the superheater area of the boiler and compare these results to the fuel and
ESP ash elemental analyses in order to characterise the fate of chlorine and bromine in
the combustion gases.
It is widely known that alkali chlorides induce hot corrosion of boiler superheaters. One
of the questions for the experimental work was that if bromine, analogously to the other
halogen, chlorine, can be found as vaporised salts in the furnace superheater region.
In the experiments two experimental trials were carried out: day one was a business-asusual situation with the normal fuel ratios, and, on day two the share of the paper mill
sludge was reduced to one third (on dry mass basis) from the normal operating
conditions. The objective was to find out if any change in the composition or
concentration of aerosols can be seen. As the sludge is a high sulphur, high kaolinite
fuel it is postulated to influence alkali halogen chemistry in the furnace.
Bromine and chlorine sources
There is a general agreement that the Cl in SRF originates mainly from chlorinated
plastics such as PVC or food residues which contain dietary salt (Ajanko, Moilanen et
al. 2005). In addition, chlorine is used in flame retardants (Hornung, Donner et al.
2005).
Commonly referred source of Br is flame retarded plastics and particularly Waste
Electrical and Electronic Equipment (WEEE). Halogenated flame retardants have
traditionally been used because of their efficiency and suitability with various types of
plastics. Bromine is generally preferred over chlorine because it requires lower
quantities of flame retardant and minimizes the impact of the additive on the polymer’s
performance. The high content of bromine, chlorine and heavy metals in waste electric
and electronic equipment (WEEE) has led to the need for establishing separate
collection and recycling scheme for this type of waste, in order to reduce environmental
impacts. (Hornung, Donner et al. 2005). For this reason, this type of material is not
found in large quantities in SRF.
However, flame retarded plastics can be found everywhere where thermal stability is
required, also in waste fractions commonly found in SRF. These could be: polystyrene
foams in construction; textiles in sofas, chairs and upholstery; decorative profiles;
construction and protective films; polyamide or nylon based heat protective hoods and
pipes; different types of polypropylene (lamp, gadget) holders, sockets and kitchen
hoods etc. A good summary on the brominated flame retardant applications is published
by the Bromine Science and Environmental Forum (BSEF). (Bromine Science and
Environmental Forum (BSEF) )
The use of brominated compounds has also drawbacks because of the possible
formation of polybrominated dibenzo-p-dioxins and -furans and the evolution of very
corrosive bromine-containing gases in case of fire, incineration or recycling.
(Balabanovich, Hornung et al. 2004)
Flame retarded plastics can contain several weight percentages of halogens, some
examples are given in Table 1. They also contain significant amounts antimony (Sb)
and led (Pb). On top of these, circuit boards have many other metallic impurities.
Table 1. Concentration (mg/kg dry basis) of Cl, Br and selected other elements
in some plastic fractions. (Vehlow, Bergfeldt et al. )
Cl
K
Cr
Fe
Ni
Cu
Zn
Br
Sr
Sb
Sn
Ba
Pb
WEEE
56 400
70
6
80
8
80
40
17 400
4
7 190
935
<25
1 010
TV housings
19 040
<20
<1
<2
<1
<1
<1
34 900
<1
23 980
170
<20
220
Circuit boards
23 000
720
220
3 095
470
66 200
1 310
18 540
160
5 730
5 550
770
4 960
EXPERIMENTAL
Anjalankoski BFB utilises three main fuels: SRF, spruce bark and dried paper mill
sludge. SRF and bark samples were collected during the experiments from the plants
conveyor belts and sludge from the thermal dryer drum. Proximate and ultimate
analyses were carried out according to standards: CEN/TS 14774-2 (mod.), ISO
1171:1997 (mod.), ASTM D 4239 - 05 (mod.), CEN/TS 14918 (mod.), CEN/TS
15104:2005 (mod.), CEN/TS 15289/15408 (mod.) and SFS-EN ISO 10304-1:1995
(mod.). Fuel fractionation was carried out according to (Zevenhoven-Onderwater,
Blomquist et al. 2000).
Aerosols were sampled at two locations in the furnace 1.5m depth from the furnace
walls within the superheater area, see Figure 3. The sampling system has been described
by Aho et al. (Aho, Vainikka et al. 2008, Aho, Gil et al. 2008). The corresponding
combustion gas temperatures measured by k-type thermocouples, also approximately
1.5 meters’ depth from furnace wall, are shown on the adjacent data table.
FTIR was measuring the flue gas composition at the entrance of the second pass. The
ESP had two fields in flue gas flow direction. Ash was collected from the hoppers and
combined into one sample.
Location 1
Location 2
FTIR
Experiment 1
Experiment 2
Location 1
724±20
758±25
Location 2
555±11
604±16
FTIR
477±5
No data
Figure 3. Schematic picture of the Anjalankoski BFB boiler indicating the aerosol, FTIR
and temperature measurement locations. In the data table are shown the corresponding
average combustion gas temperatures with standard deviations in degrees centigrade.
RESULTS AND DISCUSSION
Fuels and fuel properties
SRF utilised at Anjalankoski plant originates from wholesale business and small and
middle scale industry from southern Finland. Suitable wastes are source-separated
package and other solid industrial non-recyclable wastes which are separately collected
by the SFR supplier. In fuel preparation plant material is crushed and hazardous
materials removed (by magnets, screens and eddy current). SRF is transported to the
BFB plant as wrapped bales or fluff.
The spruce bark originates from the adjacent paper mill where stem wood is used for
mechanical pulping.
The wastewater sludge consists of wood fibre and paper filler and coating rejects which
are mainly kaoline and calcium carbonate. In the treatment some 30-40 kg of ferric
sulphate per ton of dry sludge is added to the wastewater stream as a flocking agent. In
addition aluminium sulphate is used at the paper machines which may entrain in the
wastewater. Proximate and ultimate analysis results of the fuels are shown in Table 2.
Table 2. Proximate and ultimate analysis results of the fuels.
SRFI
SRFI
Bark
Sludge
*
Exp. 1
Exp. 2
Moisture (wt-%, ar)
18.3
18.1
54.8
Ash (wt-%, db)
7.5
7.5
2.1
ULTIMATE ANALYSIS OF DRY SOLIDS (wt-%, db)
8.3 (67 )
21
38.6
7.2
42.7
5.6
C
41.7
51.0
52.4
5.2
0.73
29.74
1.63
6.5
0.18
34.4
0.69
6.7
0.12
34.6
0.43
NA
0.011
0.013
0.021
0.21
0.23
16.33
14.77
20.54
11.68
21.17
11.08
H
S
O
N
54.9
55.1
50.4
7.6
7.6
5.9
0.15
0.15
0.02
29.06
29.06
41.31
0.79
0.48
0.27
0.0010.001Br**
NA
0.026
0.026
Cl
0.46
0.44
0.015
HEATING VALUE (MJ/kg)
LHV, db
23.56
23.51
19.00
LHV, ar
18.80
18.81
7.25
*
For wet sludge in Experiment II
**
MIN-MAX values from SRF suppliers long term follow-up
The shares of fuels on energy basis were: in Experiment I 51%-36%-13%; and
Experiment II 60%-38%-2%. On energy basis the ratio of the SRF and bark was close
to 60%-40% in both experiments (59%-41%, 61%-39%), and this as a base line the
sludge content was varied. This arrangement was somewhat challenging to carry out as
in Experiment I the plant was run as usual, but for the reduced sludge flow case the
sludge dryer was shut down, as it can not be run in partial loads, and wet sludge was
mixed with bark. In normal operating situation dried sludge is injected pneumatically
into the furnace in a separate feeding line.
Bark is typical Scandinavian spruce bark with high calcium, mobile potassium and
moisture content. The SRF fuels were sampled separately during both test trials. Their
results are shown here separately, although they are very similar in composition. The Cl
content of the SRFs was 0.46 and 0.44 wt-% for Experiment I and II, respectively. This
is indicated with a line in the Figure 4. In the Figure are also shown Cl and moisture
content variation for five separate samples from both experiment’s SRF collected in the
course of the experiments. This was done in order to establish understanding on the
possible Cl content fluctuations during the experiments. The average values for Cl
content based on the individual five samples are 0.52 and 0.53 wt-% for Experiments I
and II, respectively.
Heating value of SRF is the highest amongst the fuels used. Sludge’s heating value (ar,
as received) is twice as high as that of bark due to its low moisture content. Sludge’s ash
content is 21 wt-% which is the highest of the fuels.
Bromine content has been analysed only for the SRF and the values shown in Table 2
are the minimum and maximum values analysed by the supplier.
30
Cl, wt-%
Cl, wt-%
1
1.2
Moisture, wt-%
0.8
0.6
30
Cl, wt-%
Experiment I
25
1.0
20
0.8
15
0.6
Experiment II
Moisture, wt-%
25
20
15
0.46 m-%
0.44 m-%
0.4
10
0.4
10
0.2
5
0.2
5
0
0.0
0
SRF Ia
SRF Ib
SRF Ic
SRF Id
SRF Ie
0
SRF IIa
SRF IIb SRF IIc
SRF IId
SRF IIe
Figure 4. The variation of the Cl and moisture content in the SRF.
Chemical fractionation result for the main ash forming elements found in the fuels are
shown in Figure 5. The bar charts are shown for the fuels individually and for the fuel
mixes utilised in the experiments. The SRFs show typical fractionation result for the Cl
with high share of insoluble, chlorinated plastic originated Cl. Na is to large extent
water soluble which can, together with Cl, originate from dietary salt.
The sludge contains large amount of aluminium silicates which is assumed to consist
mainly of the kaoline filler and pigment in the paper mill rejects. It has quite large
content of sulphur which is assumed to originate from Al and Fe sulphate used at the
paper machines and water treatment. Ca originates mainly from the paper pigment
calcium carbonate and to some extent from wood fibres. For bark and sludge the
vertical scale has been adjusted.
The chemical fractionation results for trace elements are shown for the SRFs in Figure
6. The concentration of trace elements is higher in the Experiment I SRF. Zn is the
dominating element in both samples. Br has not been traditionally included in the
fractionation elemental analyses. In the bar charts are shown by cross the maximum
values of Br from Table 2. Also a flame retardant compound, Sb, can be found in low
concentration, in slightly higher concentration in Experiment II.
Moisture, wt-%
1.2
35 000
35 000
SRF, Experiment I
SRF, Experiment II
30 000
Rest fraction, analysed
30 000
Leached in HCl
Rest fraction, analysed
25 000
Leached in Acetate
25 000
Leached in HCl
Leached in H2O
Untreated Fuel
Leached in H2O
20 000
mg/kg
mg/kg
Leached in Acetate
Untreated Fuel
20 000
15 000
15 000
10 000
10 000
5 000
5 000
0
0
Si
Al
Fe
Ti
Mn
Ca
Mg
P
Na
K
S
Cl
Si
10 000
Al
Fe
Ti
Mn
Ca
Mg
P
Na
K
S
Cl
40 000
Paper mill sludge
Spruce bark
Rest fraction, analysed
35 000
Leached in HCl
8 000
Leached in Acetate
Rest fraction, analysed
30 000
Leached in HCl
Leached in H2O
Untreated Fuel
Leached in Acetate
mg/kg
25 000
mg/kg
6 000
4 000
Leached in H2O
Untreated Fuel
20 000
15 000
10 000
2 000
5 000
0
0
Si
Al
Fe
Ti
Mn
Ca
Mg
P
Na
K
S
Cl
Si
Al
Fe
Ti
Mn
Ca
Mg
P
Na
S
Cl
35 000
35 000
Experiment II
Experiment I
30 000
30 000
Rest fraction, analysed
Rest fraction, analysed
Leached in HCl
25 000
Leached in HCl
25 000
Leached in Acetate
Leached in Acetate
Leached in H2O
20 000
mg/kg
mg/kg
K
Untreated Fuel
Leached in H2O
20 000
15 000
15 000
10 000
10 000
5 000
5 000
Untreated Fuel
0
0
Si
Al
Fe
Ti
Mn
Ca
Mg
P
Na
K
S
Si
Cl
Al
Fe
Ti
Mn
Ca
Mg
P
Na
K
S
Cl
Figure 5. Fuel fractionation results for main elements in the individual fuels and corresponding blends
utilised in experiments.
600
600
SRF, Experiment I
500
Rest fraction, analysed
Leached in HCl
Leached in Acetate
Leached in H2O
Untreated Fuel
500
400
mg/kg
400
mg/kg
SRF, Experiment II
Rest fraction, analysed
Leached in HCl
Leached in Acetate
Leached in H2O
Untreated Fuel
300
300
200
200
100
100
0
0
Br
As Cd Co
Cr
Cu Hg Mn
Ni
Pb
Sb
Tl
V
Zn
Br
As Cd Co
Figure 6. Fuel fractionation results for trace elements in the SRFs.
Cr
Cu Hg Mn
Ni
Pb
Sb
Tl
V
Zn
ESP ash samples
25 000
25 000
20 000
20 000
15 000
15 000
mg/kg
mg/kg
Fly ash samples were collected from the ESP during both experiments. Leaching test
was carried out for the ashes based on the leaching test developed for biomass fuels
(Zevenhoven et. al) which has also been applied for fly ashes (Pettersson, Zevenhoven
et al. 2008). In Figure 7 is presented results for the total analysed content of Cl, K, Na, S
and Br and their water soluble fractions in the ESP ash. The main water soluble element
was calcium with 28 500 mg/kg for both experiments.
10 000
10 000
5 000
5 000
0
H2O
ESP, Total
Cl
K
Na
S
Br
7 431
5 820
5 680
15 600
3 666
16 700
5 830
15 600
411
523
0
H2O
ESP, Total
Cl
K
Na
S
Br
21 218
18 800
10 834
20 200
7 481
19 200
3 843
19 700
1 902
1 610
Figure 7. Total concentrations and water soluble fractions of Cl, K, Na, S and Br in the ESP ashes for
Experiment I (left) and II (right).
The character of the two halogens, Cl and Br, are similar in terms of solubility. They are
forming to large extent compounds that are water soluble. K, Na and S form also
compounds that are insoluble in water.
Also it can be seen from Figure 7 that concentration of all these elements are higher in
Experiment II and their water soluble fractions are at least doubled, with the exception
of S. This is an indication of higher concentration of alkali halogen compounds in the
furnace in Experiment II even allowing for the lower ash content of the fuel mix in this
experiment. If this is the case, it should show through also in the in-furnace aerosol
sampling for vaporised ash forming compounds.
It has been found out (Vehlow, Bergfeldt et al. ) in co-combustion experiments of flame
retarded TV housing plastics with organic waste that some 25 to 40% of bromine ended
up in fly ash. Some 5 to 10% was retained in the bottom slag of the grate fired unit and
the rest was found in the gas phase mainly as HBr or in some cases Br2. Vehlow wt al.
also found out that volatilisation of Zn and Pb increased with increased inventory of Cl
and Br in the feedstock. HBr was included in the FTIR gas analyses of Anjalankoski
experiments but it was not present in the spectrum, with the exception of some
occasional 1-2 ppm peaks.
Aerosol samples
Water soluble Br-, SO42-, Na+, K+, Cl- were analysed from the samples by Ion
Chromatography (IC) and Flame Atomic Absorption (FAAS). Aerosol samples were
collected from locations indicated in Figure 3.
The fine mode, i.e. particles with aerodynamic diameter less than 1 m, consists mainly
of Cl, K, Na and SO4. Sulphate is found in higher concentration in Experiment I. This
was expected, as sulphur content of the fuel mix was then higher due to the higher
sludge proportion.
100 %
100 %
Experiment I, location 1
80 %
60 %
Experiment I, location 2
Br
SO4
Na
K
Cl
Br
SO4
Na
K
Cl
80 %
60 %
40 %
40 %
20 %
20 %
0%
0%
<0.03
0.03 - 0.1
0.1 - 0.26 0.26 - 0.64 0.64 - 1.61 1.61 - 4.02
4.02 - 10
100 %
<0.03
0.03 - 0.1
0.1 - 0.26 0.26 - 0.64 0.64 - 1.61 1.61 - 4.02
4.02 - 10
100 %
Experiment II, location 1
80 %
60 %
Br
SO4
Na
K
Cl
40 %
Experiment II, location 2
80 %
Br
SO4
Na
K
Cl
6%
7%
5%
60 %
40 %
2%
20 %
0%
<0.03
1%
20 %
0%
0.03 - 0.1
0.1 - 0.26 0.26 - 0.64 0.64 - 1.61 1.61 - 4.02
4.02 - 10
<0.03
0.03 - 0.1
0.1 - 0.26 0.26 - 0.64 0.64 - 1.61 1.61 - 4.02
4.02 - 10
Figure 8. Composition as wt-% (on vertical axis) of different particle size fractions (horizontal axis)
collected by DLPI. In the lower right chart the numbers indicate the weight percentage for Br in the
corresponding particle size fraction sample.
In the bar chart in Figure 7 it was shown that the bromine content of the fly ash was
significantly higher in Experiment II. This seems to show through also in the aerosol
samples as water soluble Br can be found in several weight percentages particularly in –
and during – sampling in Location 2.
In this case it can be stated that Br is becoming one of the major elements in the
aerosols.
Based on these mass fraction values it can be calculated that 17% of the halogens in
submicron particles are bromides. The concentration of Br bound in the submicron
fraction in the combustion gases is 2 ppm, which already is 65% of the maximum
conversion from fuel. This includes the assumption that SRF contains Br the maximum
analysed amount indicated in Table 2 and in the other fuels the content is negligible. If
larger particulates, up to 10 m, collected with the impactor are also accounted for, the
corresponding gain is 80%.
For the other halogen, Cl, it is more convenient to establish a balance in the furnace, as
its concentrations is significantly higher. In Figure 9 is shown the split of Cl in aerosols
and HCl gas measured by FTIR. ‘Cl MAX’ lines are the calculated maximum possible
Cl concentrations in the combustion gases based on the Cl content in the fuel mixtures
shown in Table 2. The conversion of fuel bound Cl to HCl can be calculated to be 90%
and 78% for Experiment I and II, respectively.
250
200
Experiment I
SO2
HCl
200
Experiment II
150
175
ppm, 6% O2
125
ppm
Dry sludge
feeding
stopped
225
175
Cl in aerosols
Cl in HCl
Cl MAX
100
75
150
125
100
75
50
50
25
25
0
Location 1
Location 2
Location 1
Location 2
0
0:00
2:00
4:00
6:00
8:00
Figure 9. The split of Cl between HCl and submicron aerosols. HCl measurement was carried out at the
location shown in Figure 3.
On right in Figure 9 is FTIR data on HCl and SO2 during the transition period where the
feeding of the dried sludge stopped. There are fluctuations in the SRF proportions
during this period which is seen in the HCl concentration fluctuations of the gas.
Nevertheless, HCl concentration of the gas decreases when shifting to Experiment II
operation mode and all the sulphur in fuel is bound in the ash.
CONCLUSIONS
The aerosol and ESP ash analyses show that Br can be present in significant amounts in
these fractions. Alongside Cl, Br should be included in the alkali halogen and salt
studies regarding ash behaviour of SRF in combustion. This can also be justified by the
Br content found in SRF, which can be several hundreds of ppm.
Br and Cl were found to form in large extent water soluble ash compounds, as for K,
Na, SO4 and Ca compounds insoluble in water were also present in the ash.
The yield of Br in aerosols can be high; however the reliability of fuel Br analysis may
be questionable due to small number of analyses carried out. More analyses are required
from aerosols and fuel in order to built confidence for establishing reliable Br balance
and in-furnace behaviour characterisation.
Higher concentration of sulphates were found in the aerosols in Experiment I where the
high sulphur sludge was co-fired at higher proportion in the fuel mix than in Experiment
II. Still, alkali halogens were present in the aerosol and ESP samples in both
experiments.
Alkali halogen concentration was higher, especially based on the ESP ash analysis for
water soluble compounds, in Experiment II. During this experiment the highest
concentration of Cl bound in aerosols was reached and conversion of Cl from fuel to
HCl gas was lower than in Experiment I. The reasons for this and the role of sulphur
and kaoline in alkali capture should be assessed.
ACKNOWLEDGEMENTS
Financial support from the Finnish Funding Agency for Technology and Innovation
(Tekes), Metso Power Oy, Lassila&Tikanoja Oyj, UPM-Kymmene Oyj and Bioenergy
NoE (through contract SES6-CT-2003-502788) is gratefully acknowledged. We are
grateful to Stora Enso for providing the Anjalankoski BFB plant available for
experimental work. We thank Hannu Vesala, Marko Räsänen, Raili Taipale, Kauko
Tormonen and Sari Kauppinen for their comments, hard work and commitment.
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