Research Paper
The use of additives and fuel blending to reduce
emissions from the combustion of agricultural
fuels in small scale boilers
J.P. Carroll
*
, J.M. Finnan
Crops, Environment and Land Use Programme, Crops Research, Teagasc, Oak Park, Carlow, Ireland
a r t i c l e i n f o
Article history:
Received 6 February 2014
Received in revised form
9 September 2014
Accepted 8 October 2014
Published online 22 October 2014
Keywords:
Biomass combustion
Agricultural fuels
Fuel blending
Additives
Emission reduction
The results of tests to determine the efficacy of fuel blending and additives to reduce
emissions from the combustion of agricultural fuels are presented. It was shown that peat
blended with miscanthus and tall fescue has the potential to significantly reduce both PM
1
emissions and problems related to ash melting. However, the high nitrogen content of the
peat (1.5%) compared to the two agricultural fuels tested (miscanthus
e 0.33 and tall fes-
cue- 0.69) leads to increased NO
x
emission with increasing proportions of peat in the blend.
The results also showed that for both fuels a kaolin addition rate of 4% gave significant
reductions in PM
1
emissions. With increasing peat/kaolin addition ash sintering temper-
ature increased while potassium release decreased. With further developments in the use
of additives and fuel blending it is foreseen that pellets from agricultural fuels may form a
viable alternative to wood pellets.
© 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Rising oil prices and increasing concern about the impact of
greenhouse gas emissions from the use of fossil fuels have
stimulated interest in renewable forms of energy including
biomass. Combustion is the most mature technology for
biomass utilisation but emissions from biomass combustion
are typically greater when compared to the combustion of
natural gas or light fuel oil and can contribute significantly to
concentrations of particulate matter, ozone and nitrogen di-
oxide in ambient air (
). Nitrogen in the fuel
is the principal source of NO
x
emissions as during combustion
fuel nitrogen is almost entirely converted into gaseous nitro-
gen and nitrogen oxides (
; Obernberger
et al., 2003). Particles of solid carbon (soot) may also emanate
from incomplete biomass combustion (
). Howev-
er, under conditions of complete burnout, particle emissions
primarily result from the release of inorganic material from
the fuel, such particles consisting mainly of K, Cl, S, Na
although the principal element is K (
Epidemiological studies have demonstrated a relationship
between negative health effects and air pollution (
). However, the increasing demand for biomass
together with limited wood supplies are forcing markets to
consider non-woody forms of biomass such as agricultural
* Corresponding author.
E-mail address:
(J.P. Carroll).
Available online at
ScienceDirect
journal homepage:
www .e lsev ie r.com/ locate/issn/153 75110
b i o s y s t e m s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 2 7 e1 3 3
http://dx.doi.org/10.1016/j.biosystemseng.2014.10.001
1537-5110/
© 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.
crops (cereal straws, energy grasses, miscanthus). Such fuels
differ in their chemical composition to wood as they typically
have higher ash content and higher concentrations both of
ash forming elements and of elements which produce
elevated levels of gaseous emissions such as nitrogen and
sulphur (
). Thus,
emissions from the combustion of agricultural fuels are likely
to be higher than those from the combustion of wood fuels.
Strategies which can be used to reduce emissions include
the use of air staging and fuel staging (manipulation of the
atmosphere in the primary and secondary combustion
chambers to create optimised conditions during combustion,
) strategies. Such primary strategies can be
very effective as a means of reducing NO
x
emissions but are
not as successful as a means of reducing particulate emissions
as the primary cause of biomass particulate emissions is the
chemical composition of the fuel (
). Partic-
ulate emissions from biomass combustion can be reduced by
the use of secondary measures such as filters and electrostatic
precipitators (Obernberger
& Mandl, 2011). Alternatively,
particulate emissions may be reduced by altering the chemi-
cal composition of the feedstock through the use of additives
or fuel blending (
€afver, R€onnb€ack, Leckner, Claesson, Tullin,
om, €
).
Combustion additives can be classified according to their
chemical composition (Bafter et al., 2008). The principal ad-
ditive groups are those based on calcium, phosphorus,
sulphur and aluminium-silicate additives. The most popular
and best understood additives are those containing lime or
clay minerals (
€afver et al., 2009; Lindstr€om, Sandstr€om,
€om, & €Ohman, 2007; €Ohman, Hedman, Bostr€om, &
). Kaolin is the most studied clay additive, it
consists principally of the mineral kaolinite (Al
2
Si
2
O
5
(OH)
4
)
and acts by binding alkali compounds to the mineral, forming
potassium-aluminium silicates which have higher melting
temperatures than pure potassium silicates.
added either calcite or
kaolin additives to oat grain prior to combustion and found
substantial reductions in particle mass in the flue gases with
both additives, a greater proportion of potassium was
captured in ash as a result of kaolin addition.
added both limestone and kaolin to oats grains and
found that particle emission could be lowered by adding
kaolin (2
e4%). A consequence of kaolin addition was that a
higher proportion of potassium was found in the bottom ash
and chlorine was almost eliminated in fly ash particles.
om, and €
reported that the addition
of 1
e2% kaolin resulted in a significant reduction in fine par-
ticle emissions from wood pellets although the addition of
calcite only had a marginal effect.
B€
onnb€
reported that the addition of kaolin (3% and 6% wet
basis) decreased particle emissions from the combustion of
straw pellets but that there is a clear risk of over-dosing.
Kaolin has been shown to be an effective additive for
reducing fine particle emissions from biomass combustion. It
acts by binding potassium to form high melting K
eAL silicates
reducing the release of potassium to flue gases.
In addition to the use of additives, the chemical composi-
tion of the biomass feedstock can be altered by blending the
fuel of interest with another fuel with a different chemical
composition.
found that the addition of
<30% peat (an accumulation of
partially degraded vegetation) to biomass reduced fuel bed
agglomeration.
also found a decrease in
agglomeration when 20% peat was added to biomass but they
also found a decrease in fine particle emissions and an in-
crease in coarse emissions. The mechanism for the positive
effects of adding peat was identified as the removal of po-
tassium in the gas phase to a less reactive form.
€om,
added both
peat with a high ash content as well as peat with a low ash
content to wood biomass in different ratios. They found an
increase in slagging tendency with both types of peat although
the slagging tendency was considerably reduced when the low
ash peat type was used.
reported a
reduction in fine particle and deposit forming alkali when peat
was blended with straw and suggested that the capture of
alkali was most probably related to the reaction of potassium
with reactive silicon or clay minerals in the peat. It was sug-
gested that slagging could be reduced, or avoided with the use
of peats with high silicon to calcium ratios.
Energy crops (miscanthus, tall fescue, cocksfoot, etc.) are
likely to be major contributors to renewable energy mix in the
future and have been shown to have great potential to miti-
gate carbon emissions (
Smith, Powlson, Smith, Fallon,
). Perennial grasses have proven to be good
candidate energy crops, their advantage over trees is that they
establish more quickly and produce an annual harvest with
low moisture content (
).
However, emissions from the combustion of energy crops are
a potential concern particularly if energy crops are to be uti-
lised as a feedstock in small and medium scale combustion
units. Previous research had demonstrated that additive and
fuel blending strategies can be successfully used to reduce
emissions from a range of biomass feedstocks (
B€
2009; Boman et al., 2008; Lindstr€
). However, research to date has concentrated on
biomass feedstocks such as wood, grain and straw with
comparatively little work done on energy crops. The objective
of our study was to quantify how emissions from the com-
bustion of two contrasting perennial grass energy crops
(miscanthus and tall fescue) could be reduced through the use
of additive and fuel blending strategies. Miscanthus is already
well established an energy crop while native grasses such as
tall fescue have recently been proposed as potential energy
crop (
) which offer the advantage of reduced costs
of establishment compared to miscanthus.
2.
Materials and methods
For combustion of these energy crops and to ensure complete
mixing it was necessary to pelletise each of the samples. Pel-
leting was carried out at University College Dublin
's Lyon's
Research Estate using a Jiangsu Dehui pellet mill (Jiangsu Dehui
Machinery
& Electric Equipment Co., Ltd, Jiangsu, China).
The peat for blending tests was harvested in Ireland and
was received in milled form with particle size of
<3 mm. The
kaolin for the additive tests was in powdered form with par-
ticle size
<1 mm. Miscanthus and tall fescue were firstly
b i o s y s t e m s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 2 7 e1 3 3
128
milled for ease of mixing in a Jiangsu Dehui hammer mill with
a 3 mm screen size. The materials were then weighed on a dry
mass basis and mixed manually to ensure that the materials
were mixed fully. After mixing, each of the individual blends
was pelletised through an 8 mm die. The blends/addition
levels used are shown in
. Kaolin was added to both
energy crops in percentages of 1, 4 and 7%, a control with no
kaolin was also used as a treatment. Peat was blended with
both energy crops varying in proportion from 0 (control) to
100%. For miscanthus, blends which gave a good range of
values between 0 and 100 % were chosen. For tall fescue
blends were chosen based on 20% being the maximum level of
addition for a pellet not to be considered a blend, 40% which
gave interesting results in research with straws and 60% and
100% for completion.
Gaseous emissions were measured using a Horiba portable
gas analyser (PG-250, Edison, NJ, USA) with a heated sampling
line. This gas analyser used non-dispersive infra-red detection
for CO, SO
2
, and CO
2
; chemiluminescence (cross-flow modu-
lation) for NO
x
; and a galvanic cell sensor for O
2
measure-
ments. A serial computer connection enabled continuous
online measurements to be saved and processed.
Particulate emissions were measured using a Dekati
(Tampere, Finland) 3-stage low-pressure impactor with 10
mm,
2.5
mm, 1 mm and filter collection stages. This method of par-
ticulate sampling involves a known quantity of flue gas being
drawn through the impactor under isokinetic conditions and
the weighing of impactor plates and filter before and after
testing. For this particular flue and boiler combination a 9 mm
diameter nozzle was required for isokinetic sampling. PM1, i.e.
all particles below 1
mm was used as the comparison value in
all tests as this is a commonly used value to describe fine
particulate emissions.
An ETA Hack35 (ETA Heiztechnik GmbH, Hofkirchen,
Austria) tilting grate biomass boiler with a rated output of
35 kW and the capability to recirculate flue gas beneath the
combustion grate was used for the combustion tests. The
boiler was ignited and the temperature limited to 900
C at
steady
state
using
flue
gas
recirculation
before
the
commencement of tests. It was then run for 1 h in this state,
during which the particulate and gaseous emissions were
monitored. This was repeated 5 times for each of the pellet
types. The gaseous and particulate sampling set up is shown
in
. Visual inspections were also made of the combustion
chamber prior to and after each combustion test to identify
the degree of ash melting which had taken place.
The ash content of each fuel was conducted using the BS
EN 14775:2009 standard method. Samples of bottom ash from
each combustion test were taken for laboratory analysis of the
main ash forming elements (K, P, Al, Si, Mg and Ca) according
to EN standard 15290 using an Anton Paar Multiwave 3000
(Anton Paar GmbH, Graz, Austria) microwave digester for
digestion of samples and a Perkin Elmer Analyst 400 (Perkin
Elmer Ltd., Waltham, MA, USA) atomic absorption spectrom-
eter for determination of the element concentrations. The raw
fuels were also analysed in this way. All emission data was
collected and analysed using the Genstat (VSN International,
Hemel Hempstead, UK) statistical analysis software and is
expressed in units of mg Nm
3
@ 13% O
2
.
Fuel indices on a molar basis, describing the effect of given
elements on; ash sintering temperature (A) and Potassium
release (B) adapted from those described by
Brunner, and Obernberger (2012)
were calculated based on
both the fuel and ash chemical composition.
Table 1
e Pellet matrix.
Miscanthus
Tall fescue
% Peat
% Kaolin
% Peat
% Kaolin
0
0
0
0
25
1
20
1
50
4
40
4
75
7
60
7
100
100
FGR
Flow rate
and
temperature
Primary air inlet
with flow
Secondary air inlet
with flow
Flow rate and
temperature
measurement
Flue gas
Temperature
measurement
DLPI = Dekati Low
Pressure Impactor
FGR = Flue gas
recirculation
SCC = Secondary
combustion chamber
PCC = Primary
combustion chamber
Fuel
SCC
PCC
CO, NOx, O
2
, CO
2
DLPI
Water to heating system with
heat output measurement
Fig. 1
e Biomass combustion test stand set up.
b i o s y s t e m s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 2 7 e1 3 3
129
A
ðAsh sintering temperatureÞ ¼
Si
þ P þ K
Ca
þ Mg þ Al
B
ðPotassium releaseÞ ¼
Si
K
3.
Results
3.1.
Peat blending
As can be seen in
there was a very strong linear rela-
tionship between the percentage peat addition and the amount
of NO
x
emitted during combustion for both miscanthus (r
2
value of 0.98) and tall fescue (r
2
¼ 0.99). For miscanthus/peat
blends the amount of NO
x
emitted increases from 170 mg Nm
3
for 100% miscanthus to 340 mg Nm
3
for pure peat (statistically
significant differences between all treatment levels at p
< 0.01)
and for tall fescue/peat blends there is a similar rise from
250 mg Nm
3
(100% tall fescue) to 340 mg Nm
3
(100% peat)
with a statistically significant treatment (p
< 0.01).
shows the PM
1
emission values for the mis-
canthus/peat and tall fescue/peat blends. There was a linear
relationship between PM
1
emissions and percentage peat
addition with PM
1
emissions decreasing with increasing per-
centage peat in the pellet blends. Both miscanthus (r
2
¼ 0.98)
and tall fescue (r
2
¼ 0.99) blends display this strong linear
trend. For miscanthus/peat pellets the PM
1
emissions
decreased
from
50
mg Nm
3
(100%
miscanthus)
to
25 mg Nm
3
(100% peat), (statistically significant treatment
effect at p
< 0.01) while for tall fescue/peat pellets the PM
1
emissions decreased dramatically from pure tall fescue pellets
with a value of almost 350 mg Nm
3
to 25 mg Nm
3
from pure
peat pellet combustion (statistically significant differences
between all treatment levels at p
< 0.01). For standard wood
pellets in this particular boiler under similar conditions NOx
emissions of approximately 80 mg Nm
3
and PM
1
emissions of
under 15 mg Nm
3
were observed.
3.2.
Kaolin addition
For both miscanthus and tall fescue pellets an addition level of
4% kaolin gave a significantly lower PM
1
emission value
(p
< 0.01) compared to addition levels of 0 or 1% (
). For
miscanthus PM
1
emissions were reduced by over 50% from
50 mg Nm
3
to 24 mg Nm
3
, while for tall fescue PM
1
emis-
sions were reduced by over 40% from 340 mg Nm
3
to
200 mg Nm
3
. There is no significant difference (p
< 0.01) be-
tween 0 and 1% or between 4 and 7% addition for either mis-
canthus or tall fescue pellets.
3.3.
Fuel indices
showed that with increasing
Si
þPþK
Ca
þMgþAl
(A) ratio there was a corresponding decrease in ash
sintering temperature. As can be seen in
, for indices
based on both fuel and ash chemical composition, the higher
the peat addition the lower the ratio, thus implying a higher
ash melting temperature than for pure miscanthus or tall
fescue pellets. This was seen in test observations with a large
degree of ash melting occurring especially for tall fescue pel-
lets at temperatures close to 900
C and lesser amounts of ash
melting noted with increased peat addition.
A similar pattern is shown for kaolin addition with
increased levels leading to a lower ratio and thus a higher ash
melting temperature as compared to the 100% miscanthus or
tall fescue pellets (
).
0
50
100
150
200
250
300
350
400
0
20
40
60
80
100
mg Nm
-3
@ 13
%
O
2
% Peat
Miscanthus
Tall Fescue
Fig. 2
e NOx emissions for peat blend pellets.
0
50
100
150
200
250
300
350
400
0
20
40
60
80
100
mg Nm
-3
@ 13 %
O
2
% Peat
Miscanthus
Tall Fescue
Fig. 3
e PM1 emissions for peat blend pellets.
0
50
100
150
200
250
300
350
400
0
1
2
3
4
5
6
7
mg Nm
-3
@ 13 %
O
2
% Kaolin
Miscanthus
Tall Fescue
Fig. 4
e PM1 emissions for kaolin additive pellets.
b i o s y s t e m s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 2 7 e1 3 3
130
also described how with
decreasing Si/K (B) ratio there was a corresponding increase in
K release and hence PM
1
emissions. As can be seen in
,
for both miscanthus/peat and tall fescue/peat pellets the Si/K
ratio increased with increasing peat addition and this corre-
sponded to a decreased PM
1
emission as shown in
. This
is also true for miscanthus/kaolin and tall fescue/kaolin pel-
lets (
) with increased Si/K ratio at 4% and 7% addition
levels leading to significantly decreased PM
1
emissions (
).
Indices calculated using the chemical composition of ash
were similar to those calculated using the chemical compo-
sition of the corresponding fuel.
4.
Discussion
4.1.
Peat blending
From the peat blending tests it is clear that the increase in NO
x
emissions resulted from the addition of peat with a nitrogen
content of 1.5% to agricultural fuels with lower nitrogen con-
tents (miscanthus
¼ 0.33%, tall fescue ¼ 0.699%) (
). All
the NO
x
emitted originated from fuel bound NO
x
as the com-
bustion temperatures (900
C) are too low for thermal and
prompt NOx formation (
; Obernberger et al.
2003). These high NO
x
emission levels could possibly be
reduced by the use of advanced air staging.
In general peat has very low PM
1
emission levels
(25 mg Nm
3
). One causative factor contributing to these low
emissions is the very low concentration of K in the fuel
(255 mg kg
1
) and hence very low aerosol formation due to low K
release during combustion (
). For miscanthus
a significantly increased K level of 4810 mg kg
1
leads to an in-
crease in fine particle formation and hence an increased PM
1
emission value (50 mg Nm
3
). Therefore, tall fescue with a K
concentration of 23,000 mg kg
1
in the raw fuel has very high PM
1
emissions (up to 340 mg Nm
3
). The strong linear relationship
between decreasing PM
1
emissions and increasing percentage
peat is an indication that the peat acts as a diluent. The chemical
composition of peat also gives rise to a higher ash melting point
and hence less associated slagging problems than either pure
miscanthus or tall fescue pellets. Similar results were shown by
who stated that a decreasing fine particle
emission level was possible with increasing peat percentage in
peat/forest residue blends and by
, who
showed that a significant reduction in fine particle emission
from combustion of ash rich biomass (wheat straw and forest
residues) is possible by blending with peat.
As there is a conflict with NOx increasing and PM
1
decreasing with increasing peat content, it very much de-
pends on the situation as to what the most appropriate level of
addition should be. If the primary goal is to create a low NOx
emission then a lower level of peat addition is required and
the converse if the requirement is for lower PM
1
emissions.
4.2.
Kaolin addition
Kaolin has very high concentrations of both Si (46%) and Al
(40%) and thus decreases in PM
1
emissions and increases in
ash melting temperature are caused by chemical interactions
involving these elements. Increasing kaolin addition coun-
teracts the high K release from both miscanthus and tall fes-
cue and thus decreases the PM
1
emissions. Hence the reduced
PM
1
emissions at kaolin addition levels of 4 and 7%. For both
miscanthus and tall fescue it is clear that an addition level of
4% is most appropriate, with 1% giving very little reduction in
PM
1
emissions compared to pure pellets and an addition level
of 7% not being significantly different from the 4% levels.
Increased Si and Al concentrations in the fuel/additive
mixture increase the ash melting temperature significantly
and thus there is less slagging and associated combustion
problems caused. These results are supported by the findings
of
B€
and
where significant
reductions in fine particle emissions from kaolin addition to
straw and wood pellets were shown. The addition level of 4%
kaolin was also shown to be the most appropriate level in
these research papers.
Table 2
e Fuel chemical compositions.
Peat
Tall fescue
Miscanthus
Calorific value (MJ kg
1
)
21.52
18.36
18.59
Ash content (%)
2.2
4.96
2.5
N (%)
1.5
0.699
0.33
K (mg kg
1
)
255
23,000
4810
Si (mg kg
1
)
3220
12,300
4970
Ca (mg kg
1
)
3570
4920
2380
P (mg kg
1
)
886
3750
211
Al (mg kg
1
)
672
240
130
Mg (mg kg
1
)
1930
1740
601
Cl (mg kg
1
)
902
814
739
S (mg kg
1
)
432
924
2860
Table 3
e Fuel indexes based on fuel and ash chemical composition of peat blend pellets [( ) values tall fescue blend levels].
% Peat
Miscanthus
Tall fescue
Ash sintering temp index
Index of K release
Ash sintering temp index
Index of K release
Fuel
Ash
Fuel
Ash
Fuel
Ash
Fuel
Ash
0
3.21
3.17
1.03
1.24
5.63
5.22
0.54
0.62
25 (20)
2.25
2.15
1.3
1.46
4.71
4.45
0.57
0.64
50 (40)
1.48
1.44
1.77
1.95
3.85
3.55
0.62
0.70
75 (60)
1.02
0.99
2.94
3.39
2.81
2.64
0.74
0.79
100
0.6
0.59
12.63
13.42
0.6
0.59
12.63
13.42
Ash sintering temperature and K release decrease with increasing index value.
b i o s y s t e m s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 2 7 e1 3 3
131
4.3.
Fuel indices
Fuel indices can be a very useful tool in providing a quick pre-
evaluation of any combustion problems that may arise. A high
potassium release index (Si/K), leads to the formation of po-
tassium silicates, which are bound in the bottom ash. This
results in decreased potassium release and hence decreased
fine particle emissions.
state that it is generally well
known that Ca and Mg increases the ash-melting tempera-
ture, while Si in combination with K decreases the ash melting
temperature. The molar Si/(Ca
þ Mg) ratio is often used to
describe ash melting behaviour in ash rich systems domi-
nated by Si, Ca, Mg and K. However, for P and Al rich systems
this correlation is not valid, hence a modified index is intro-
duced [(Si
þ P þ K)/(Ca þ Mg þ Al)]. Results from Brunner et al.
(2012), and
correspond with results
from this research and all show that a linear relationship
exists between this index and ash sintering temperature.
As can be seen in both
, the indices based on
both fuel and ash concentration follow very similar patterns
with only small differences relating to the amount of the
respective elements being lost in PM emission. Thus, it is put
forward by the authors, that indices based on ash could
possibly be used as a reliable substitute for those based on fuel
chemical composition in research where this is deemed
necessary.
4.4.
General discussion
It is clear from the results that the use of both peat blends and
kaolin additives are promising methods for PM
1
emission
reduction. The very low PM
1
emissions from peat blends are
due largely to the very small amounts of K present which has a
diluting effect on the PM
1
emissions of both of the high K fuels,
miscanthus and tall fescue. The higher ash melting temper-
ature of peat also helps to counteract the ash melting prop-
erties of these two energy grasses. The main concern is that
peat, with a high N content causes increased NO
x
emissions
compared to either of these fuels.
Kaolin as an additive in energy grass pellets has the po-
tential to be a very effective method for decreasing PM
1
emissions but also for ameliorating the problems associated
with ash melting in these fuels. The addition of 4% kaolin
reduced PM
1
emissions by over 40% for both fuels and the fact
that no ash melting was noted in either fuel following this
addition means that both miscanthus and tall fescue could be
utilised in many more boiler types than would be the case for
these fuels in their pure form, where large degrees of ash
melting can lead to extreme combustion problems.
The use of novel fuel indices has the potential to charac-
terise fuels PM
1
emission and ash melting temperatures in a
clear, straightforward manner and thus help select what
conditions to use these fuels and what PM
1
emission abate-
ment measures might be required for combustion of these
fuels.
5.
Conclusions
It can be clearly seen that both peat blending and kaolin
addition are very promising strategies for PM1 emission
reduction with decreases
>40% possible. These two strategies
can also be very useful in amelioration of ash melting related
problems in energy grass combustion. With further research
into fuel blending and additives and the development of
biomass boilers to handle the differing properties of these
pellet types it is hoped that in the future pellets from agri-
cultural fuels will compete favourably with wood pellets in the
domestic heating sector.
Acknowledgements
The authors would like to thank the Sustainable Energy Au-
thority of Ireland for funding this research through the ERA-
NET Bioenergy scheme. The help and support of Professor
Christoffer Boman and Jonathan Fagerstrom from Umea
University, Sweden and Professor Ingwald Obernberger and
Dr. Fritz Biedermann from Bioenergy 2020
þ, Graz, Austria are
also much appreciated by the authors. The authors are also
grateful to Dr Kevin McDonnell and Dr Gerard Devlin of Uni-
versity College Dublin for the use of pelleting equipment.
r e f e r e n c e s
Bafver, L. S. (2008). Particles from biomass combustion-characteristics
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.
B€
ack, M. (2011). Reduction of particle
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e29 January 2011, Graz, Austria
Table 4
e Fuel indexes of kaolin additive pellets.
% Kaolin
Miscanthus
Tall fescue
Ash sintering temp index
Index of K release
Ash sintering temp index
Index of K release
Fuel
Ash
Fuel
Ash
Fuel
Ash
Fuel
Ash
0
3.21
3.22
1.03
1.04
5.63
5.66
0.54
0.53
1
2.27
2.27
1.65
2.01
4.00
4.02
0.74
0.74
4
1.50
1.48
4.67
5.04
2.54
2.49
1.31
1.37
7
1.36
1.35
7.54
8.26
2.08
2.06
1.82
2.05
Ash sintering temperature and K release decrease with increasing index value.
b i o s y s t e m s e n g i n e e r i n g 1 2 9 ( 2 0 1 5 ) 1 2 7 e1 3 3
132
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onnb€
ack, M., Leckner, B., Claesson, F., & Tullin, C.
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e03 September 2010, Saariselk€a, Finland
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e14). Oak Park, Carlow: Published by Teagasc Head
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e1521
e3 July 2009, Hamburg, Germany
Obernberger, I., & Thek, G. (2004). Physical characterization and
€Ohman, M., Hedman, H., Bostr€om, D., & Nordin, A. (2004). Effect of
€om, D., Burvall, J., Backman, R.,
Salzmann, R. (2001). Fuel staging for NOx reductions in biomass
combustion: experiments and modelling. Energy and Fuels, 15,
575
Smith, P., Powlson, D. S., Smith, J. U., Fallon, P., & Coleman, K.
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e539
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