Journal of Sustainable Bioenergy Systems, 2013, 3, 186-193
http://dx.doi.org/10.4236/jsbs.2013.33026 Published Online September 2013 (http://www.scirp.org/journal/jsbs)
Controlled Batch Leaching Conditions for Optimal
Upgrading of Agricultural Biomass
Prabahar Ravichandran1, Duncan Gibb2, Kenneth Corscadden1
1Department of Engineering, Faculty of Agriculture, Dalhousie University, Truro, Canada
2Centre for Renewable Energy, University of Freiburg, Freiburg, Germany
Received June 10, 2013; revised July 15, 2013; accepted July 28, 2013
Copyright © 2013 Prabahar Ravichandran et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Agricultural biomass presents a promising feedstock, which may contribute to a transition to low carbon fuels. A sig-
nificant amount of research has identified a number of challenges when combusting agricultural feedstock, related pri-
marily to energy value, ash, emissions, corrosion and combustion characteristics. The mitigation of such challenges can
be addressed more cost effectively when dealing with large or utility scale combustion. The costs associated with har-
vesting, conversion, transportation and ultimately, market development all create additional roadblocks for the creation
of an agricultural biomass industry. Nova Scotia, an Eastern Canadian province, has significant land resources, however
it is prone to wet spring and as yet does not have a supply chain established for such an industry. The main components
of supply, processing and conversion and demand simply do not yet exist. This research addresses one aspect of this
supply chain by attempting to develop a fuel suitable for a) existing markets (local residential wood and wood pellet
stoves and b) a scale that will support industry engagement. The outcomes of this research have determined that such a
venture is possible and presents empirical preprocessing conditions to achieve a competitive agricultural fuel.
Keywords: Optimal Leaching; Agricultural Biomass; Fuel Design; Ash Reduction
1. Introduction
The drive to reduce Green House Gas (GHG) emissions
and increase renewable energy has created an opportu-
nity for alternative sources of biomass fuel or bioenergy,
particularly for residual applications [1,2]. The term bio-
mass has historically been used to describe wood based
fuel, in either raw or densified form. One common ex-
ample is the wood pellet, compacted biomass, which
results in a homogeneous fuel with better handling and
transportation characteristics than wood logs. Most pel-
lets are made from by-products, such as sawdust and
ground wood chips, inherent in many primary wood
processing operations which help reduce the costs asso-
ciated with waste disposal. The global pellet industry had
an estimated 6 million tons production capacity in 2006,
50% of which originated from Sweden and North Amer-
ica with an additional 1.2 million tons from Canada [3].
This industry has seen steady growth in recent years
reaching 28 million tons [4] by 2010.
Agricultural crops and crop residue are relatively un-
tapped energy sources which present an attractive low
cost local fuel with potential to augment wood based
biomass and to some degree replace a portion of fossil
fuels for the production of heat and power [5,6]. In addi-
tion, the combustion of agricultural biomass is generally
regarded as carbon neutral [7,8] with annual growing
cycles. The presence of alkali metals and other inorganic
elements inherent in agricultural biomass when com-
busted creates elevated ash content, 10 to 20 times that of
wood pellets, corrosion, slag formation and emissions, all
of which may have significant economic or environ-
mental impact and ultimately limit the combustion po-
tential of agricultural biomass [9]. These limitations arise
primarily from inorganic elements such as potassium (K)
and chlorine (Cl) present in the raw material. K is the
largest contributor to ash and slag formation, however
alkali metals such as sodium (Na) can also lower the
melting temperature of the ash, which causes a greater
formation of fused ash known as clinkers [10]. Research
conducted by the National Renewable Energy Laboratory
(NREL) reports that essentially all biologically occurring
alkali material has high mobility, where mobility is de-
fined as the ability of a material to come in contact with
other material [11]. This applies especially to K, whose
mobility is facilitated by Cl, which acts as a shuttle
C
opyright © 2013 SciRes. JSBS

P. RAVICHANDRAN ET AL. 187
transporting K to the surface of the material where the
ash compounds are formed. The presence of K and Cl
also increases its potential for corrosion [12]. When K is
transported to the surface by Cl it tends to form chlorides,
hydroxides and sulfates, all of which are significant in
the corrosion mechanism [13]. Ca is also commonly
found in biomass which forms oxides, and to a lesser
extent carbonates, but is less volatile than K and lacks
similar corrosion potential [14]. Paulrud et al. also sug-
gested a link between high Si concentrations and ash for-
mation [15]. Combustion of the material comprised of
metal oxides and silicon dioxide at temperatures typically
in excess of 800˚C causes K to react with the silicon-rich
substance and form alkali-silicate compounds known as
slag [16,17], the composition and strength of which is
dependent on the fuel ash composition [18]. Fuels rich in,
Si and K also contribute to higher levels of deposits on
furnace heat exchanger tubes [19], resulting in an in-
crease requirement for boiler maintenance. Fuels with
little alkali/silica are reported to produce fewer and more
manageable deposits [20,21], however Ogden et al. de-
termined that K will form oxides, hydroxides, chlorides
and sulfates which also contribute to slagging and foul-
ing of furnaces [22].
Increasing environmental restrictions means that
combustion analysis of fuels should also consider flue
gas and particulate emissions. Biomass combustion re-
leases CO, NO, NO2 and SO2. The presence of N and S
create NOx and SOx oxides released through the flue
which are classified as harmful emissions [23]. NOx (NO,
NO2 and other oxides of nitrogen) and SOx (SO2 and
other oxides of Sulfur) primarily depend on the nitrogen
and sulfur content of the fuel [6]. While wheat straw fuel
has relatively low emissions during combustion, wood
fuel is typically lower [24]. The vapors from incomplete
combustion and fly ash inorganic materials resulting
from potassium, sulfur, chlorine and oxygen [25] parti-
cles condense to form particulate matter [21], which has
been associated with various respiratory and cardiovas-
cular issues [11,26]. It is therefore necessary to reduce
the presence of K and Cl in biomass prior to combustion
before agricultural biomass can be used as a fuel for
residential combustion appliances. While concentrations
of carbon, hydrogen and oxygen remain relatively con-
stant in grass biomass, the grasses vary with respect to
their ash forming constituents [27]. Biomass composition
can be influenced by the management of fertilizers, har-
vesting techniques, time of harvest and climate, all of
which affect the end-composition of the raw material and
thus its combustion suitability. Literature suggests that
the main mitigation option relates to the solubility of
the alkali metals and the potential to avoid the use of
Industrial chemicals or complicated processes and simply
remove the inorganic materials by in-field leaching.
Leaching periods can range from as little as one week up
to a few months, depending on the grass species [22].
Switchgrass performs considerably well if cut in early
fall and left over winter to leach, resulting in low ash
content and a similar concentration of potassium to that
found in wood pellets. Allowing the crop to stand over
winter can have similar results, and has proved promising
for reed canary grass [27], however in both cases a re-
duction in biomass yield is experienced, especially in
geographical locations that experience wet springs. Had-
ders and Olsson [19] reported an average loss of 25% in
yield due to delayed harvesting.
To avoid yield loss, the biomass could be harvested in
fall and the inorganic elements leached in a controlled
manner by submerging biomass in water [23,28]. Jenkins
et al. [17] showed that soaking or flushing in water has
similar effects of in-field leaching, but requires addi-
tional drying before it could be milled and further densi-
fied. This technique should have less contamination and
higher yields than that experienced with in-field leaching.
The results of research on leaching of various types of
grass biomass strongly support the removal of K and Cl.
Si was typically found to increase or decrease slightly,
but with high removal of K the slagging tendency will
fall accordingly. Tonn et al. [29] investigated the effi-
cacy of leaching of two types of biomass: dry calcareous
grass (Mesobromium) and hay meadow (Arrhenatherion).
Their work reported an average 63% reduction for K and
82% for Cl after 120 min of leaching, while Si was found
to increase by 10% over the same period. Skoulou et al.
[30] performed leaching on raw olive kernel biomass and
found that alkali and chlorine were “significantly” re-
duced. Turn et al. [31] leached banagrass for only three
(3) minutes, and reported a 90% and approximately
100% reduction of K and Cl respectively. This study also
found Si to be the most persistent, with reductions of less
than 15%. Jenkins et al. [32] reduced K and Cl concen-
trations in wheat straw by 81% and 92% respectively,
with only 65 mm of natural precipitation. There are po-
tential applications for regions like Nova Scotia to im-
plement controlled leaching. Nova Scotia has sufficient
land which could be utilized for energy crop production.
The region however typically experiences mild and wet
springs which cause significant damage to crops that
have not been harvested in the fall or winter. Producers
have reported wide variability in crop quality and in
some cases lost the harvest completely by delaying har-
vest until spring. This region would benefit from a proc-
ess whereby the biomass material is harvested in late fall
early winter and a controlled preprocessing leaching
method developed that can be implemented over the
winter. This paper presents the results of a study to de-
velop such a process. The study investigates the impact
of several variables on the modification of four feed-

P. RAVICHANDRAN ET AL.
188
stocks native to Nova Scotia, which include reed canary
grass, barley straw, switchgrass and wheat straw. The
input variables include water temperature and residence
time with the objective of identifying the optimal condi-
tions for creating an upgraded agricultural biomass feed-
stock suitable for combustion in residential wood burning
appliances.
2. Materials and Methods
2.1. Feedstock for the Experiments
The following experiments were carried out using four
feedstock (reed canary and switch grass that represent
energy crops, and barley and wheat straw that represent
commonly available crop residue). Reed canary grass
(Phalaris arundinacea) was collected form a dairy farm
near Truro, NS (+45˚22'46.3", −63˚27'38.6"). Switch
grass (Panicum varigatum) was boughtfrom a commer-
cial energy crop grower located in Antigonish, NS
(+45˚33'40.6", −61˚51'9.6"). Wheat (Triticum spp.) and
Barley (Hordeum vulgare) were collected from the ex-
perimental farm plot of Dalhousie University, Faculty of
Agriculture in Truro, NS (+45˚22'23.2", −63˚15'17.2").
2.2. Experimental Design
A 2 × 3 full factorial design was used for the design of
experiments. Leaching experiments were designed to
investigate the potential impact of water temperature and
residence time in controlled batch leaching or washing of
agricultural biomass. Two (2) different residence times
and three (3) different water temperatures were selected
as experimental variables, to yield six (6) experiments
per feedstock for a total of 24 experiments and the ex-
periments have been replicated three times.
In order to obtain a homogeneous sample, for each of
the four raw feedstocks, the following process was used.
Each feedstock was milled separately using a New Hol-
land 358 hammer mill fitted with a 1/8-inch screen. Afew
hundred grams of each feedstock was dried in a Fisher
Scientific - isotemp programmable muffle furnace at
105˚C for 24 hours.
Fifteen (15) grams of each oven-dried feedstock sam-
ple was then added toone (1) liter of millipore water in a
hot water bath, which was heated to the three experi-
mental temperatures of 20˚C, 50˚C and 80˚C. The tem-
perature was maintained using a Julabo refrigerated and
heating circulator. The feedstocksamples were manually
agitated for five (5) minutes and a circular steel mesh
pushed through the top of the beaker to submerge the
sample thoroughly in the water. Samples of each feed-
stock were taken after the two experimental residence
times of 6 hours and 24 hours and filtered through
whatmann 2 filter paper. The filter samples were oven-
dried again at 105˚C for 24 hours.
2.3. Analytical Methods
The leached and unleached feedstock once oven-dried,
were then ground in a mini-wily mill with a 40 mesh.
These ground samples were analyzed for ash, alkali met-
als (K, Na, Ca, Mg), nitrogen and sulfur. The ash content
of each feedstock was analyzed using ASTM E1755-01
(Standard Test Method for Ash in Biomass). Ash content
is represented as the mass percentage of residue remain-
ing after dry oxidation at 575˚C ± 25˚C of the oven-dried
sample.
Atomic Absorption Spectroscopy was performed using
a Varian SpectrAA 200FS to analyze Potassium (K),
Calcium (Ca), Sodium (Na) and Magnesium (Mg). One
(1) gram of each feedstock was placed in a porcelain dish
and preheated in an electric furnace for approximately 20
minutes. After which the samples were ignited in a muf-
fle furnace at 550˚C for atleast 6 hours. The ash sam-
pleswere allowed to cool in a dessicator for at least one
(1) hour and 10 ml of 5% HCl added to the dishes. Ten
(10) minutes later the dishes were rinsed into a 50 ml
volumetric flask through a whatmann 1 filter in a conical
funnel. The extracted feedstock samples were then ana-
lyzed for alkali metals with the concentration represented
in mg/g.
ASTM D4208-13 (Standard Test Method for Total
Chlorine in Coal by the Oxygen Bomb Combustion/Ion
Selective Electrode Method) was used to analyze total
chlorine for each feedstock sample. Total chlorine con-
tent in the sample was presented in ppm. LECO-3000
CNS was used to analyze total nitrogen and sulfur, aap-
proximately 0.2 grams of each feedstock sample was
placed in tin foil, wrapped and loaded in the auto-sam-
pler. The sampler was loaded initially with three blanks
and three standards. Additionally, a standard was loaded
with a blank every tenth sample.
2.4. Statistical Analysis
The results of the leached feedstock representing each of
the experimental variables (time and temperature) were
compared to the unleached control feedstock samples
presented as % x-reduction, which can be defined as,


leached unleached
unleached
% reduction100
xx
xx


% reduction in ash and other elemental concentration
was analyzed using central composite full factorial de-
sign.
The influence of residence time and water tempera-
ture was assessed separately for each feedstock using
ANOVA in a full factorial design. Since the analysis
contains two factors and one of those factors is time, re-
peated statement in MIXED procedure of SAS 9.3 (SAS
Institute Inc.) was implemented. The following model
was used for analysis,

P. RAVICHANDRAN ET AL. 189
ijkijij ijk
Y





  
where, μ = overall mean; αi = effect of temperature factor;
βj = effect of time factor; αβij = interaction effect of tem-
perature and time factor; εijk = overall experimental error.
The statistical assumptions are checked to validate the
ANOVA results. When the ANOVA results are signifi-
cant (if P-value is less than 0.05(α)) for the interaction
effect, Tukey’s test (α = 0.05) were used to compare the
means for different resident time and water temperature
combinations. If and only if, the interaction is not sig-
nificant the significance of the main effect is considered
for means comparison.
3. Results
Ash, nitrogen, sulfurs, chlorine and other alkali metals
such as potassium, sodium, magnesium and calcium are
some of the potential elements that contribute to higher
emissions (NOx, SO2, and particulate) and other boiler
issues (slagging, clinkering and corrosion of boiler heat-
ing surfaces). Ultimate analysis and ash analysis on a per
oxide basis were carried out on the four unmodified
feedstock used for the experiment, the results of which
are reported in Tables 1 and 2. These results provide a
benchmark from which to determine the relative changes
due to the leaching experiment.
The results reported in Tables 1 and 2 show that the
overall ash content was lower in switchgrass than the
other three feedstock and the potassium (K) and chlorine
(Cl) were significantly higher in wheat, barley and reed
canary grass than found in switch grass.
3.1. Energy Crop
Switch grass and reed canary grass are purpose-grown
Table 1. Ultimate analysis for the samples used, expressed
as percentage of initial dry mass and chlorine expressed in
parts per million (ppm).
C % H % O % S % N % Cl, ppm
Barley 46.50 6.15 45.79 0.24 1.32 2446.2
Switch Grass 46.00 6.1 46.41 0.28 1.21 888.1
Wheat 45.53 6.07 47.38 0.3 0.72 5528.5
Reed Canary 45.00 5.9 47.15 0.31 1.64 2295.5
Table 2. Ash analysis and alkali metal composition for the
samples, expressed in milligram per gr am of dry sample.
Ash Mg Ca K Na
mg/g mg/g mg/g mg/g mg/g
Barley 56.63 0.93 3.38 12.14 0.595
Switch Grass 30.5 1.22 2.6 2.03 0.248
Wheat 68.73 0.98 2.47 9.76 0.994
Reed Canary 73.17 1.07 2.47 8.5 0.081
crops used for the production of bio renewable energy.
Improving the quality of biomass produced by these en-
ergy crops is a key for these to be predominantly used in
the energy sector. Leached switch grass and reed canary
grass were tested for ash, nitrogen, sulphur and other
alkali metals and the data is presented in Table 3.
3.1.1. Switch Grass
Potassium, chlorine, sodium and sulfur had a reduction
of 90%, 93%, 75% and 27% respectively, when sub-
jected to a water temperature of 80˚C for 24 hours.
Whereas, in the case of magnesium and calcium the av-
erage reduction of 57% occured at each of the following
three conditions of 80˚C for 6hours, 50˚C for 24hours
and 80˚C for 24hours residence time.
Nitrogen content in switch grass was reduced by an
average 30% with no significant difference between 50˚C
and 80˚C at both 6 and 24 hours resident time. Whereas,
the overall ash content reduced by an average 49% at
80˚C at both 6hours and 24 hours residence time.
3.1.2. Reed Canary Grass
Reed canary grass had a maximum chlorine reduction of
97% and there was no significant difference between the
time and temperature combination. Similarly, the interac-
tion between the two factors was not significantly dif-
ferent for sodium and potassium, which indicates that
there was a consistent decrease to a maximum of 92%
and 48% respectively in potassium and sodium with in-
crease in temperature and time. When magnesium, cal-
cium, nitrogen and overall ash are considered, reduction
was inconsistent. For example, nitrogen decreases with
an increase in temperature at 6 hours, whereas nitrogen
increased with increase in temperature at 24 hours resi-
dence time. However, in the case of sulfur there was a
consistent percentage reduction up to a maximum of 28%
with time and temperature.
3.2. Agricultural Residue
Abundantly available agricultural residue such as wheat
and barley straw could substantially servebioenergy
market demands. Unlike energy crops, wheat and barley
are primarily grown for their grain yield. This demands
the use of fertilizers, which could potentially increase the
inorganic element accumulation in these agricultural
residues. The fuel properties of leached wheat and barley
straw are reported in Table 4.
3.2.1. Barley
Barley had a maximum ash reduction of 75% at 80˚C for
24 hour residence time. A consistent reduction of 93%
and 92% was observed for potassium and chlorine at
80˚C and 24 hours residence time. Whereas, magnesium
and calcium had a maximum reduction of 65% and 57%

P. RAVICHANDRAN ET AL.
190
Table 3. Energy crops (switch grass and reed canary grass)—mean and standard deviation for Ash, K, Na, Mg, Ca, S and N
presented for different temperature and resident time combinations.
Ash, mg/g K, mg/g Na, mg/g Mg, mg/gCa, mg/g Cl, ppm S, % N, %
Time h Temp
˚C μ σ μ σ μ σ μ σ μ σ μ σ μ σ μ σ
SG 6 20 23.9 0.82 0.32 0.01 0.08 0.002 0.83 0.032.12 0.0681.11.510.26 0.003 0.990.06
SG 6 50 23.9 1.44 0.25 0.01 0.08 0.001 0.77 0.052.21 0.1175.20.90.24 0.001 0.90.02
SG 6 80 19.4 0.61 0.21 0.02 0.07 0.001 0.53 0.051.74 0.07 73.83 0.590.22 0.003 0.90.07
SG 24 20 24.2 0.82 0.26 0.03 0.07 0.001 0.63 0.021.96 0.0169.20.620.25 0.004 0.920.03
SG 24 50 20.8 0.81 0.25 0.04 0.07 0.001 0.49 0.011.81 0.0668.10.20.22 0.009 0.860.02
SG 24 80 17.6 0.12 0.21 0.01 0.06 0.001 0.52 0.011.78 0.0263 0.530.2 0.004 0.790.01
RC 6 20 54.6 2.08 1.07 0.07 0.06 0 0.68 0.011.89 0.25 56.33 0.670.29 0.005 1.470.06
RC 6 50 52.1 1.92 0.84 0.04 0.05 0 0.60.02 1.630.09 48.430.780.26 0.004 1.450.06
RC 6 80 42.4 2.38 0.72 0.05 0.04 0 0.56 0.031.41 0.05 42.03 1.690.25 0.003 1.290.04
RC 24 20 53.8 0.35 0.96 0.08 0.06 0.001 0.47 0.011.52 0.0656.31.050.24 0.004 1.360.08
RC 24 50 46.6 1.69 0.8 0.04 0.05 0.0010.36 0.031.20.0647.50.70.23 0.001 1.410.03
RC 24 80 46.8 5.32 0.71 0.07 0.04 0.0010.50.01 1.590.0442.61.080.23 0.002 1.440.04
Table 4. Agricultural residue (barley and wheat)—Mean and standard deviation for Ash, K, Na, Mg, Ca, S and N presented
for different temperature and resident time combinations.
Ash, mg/gK, mg/g Na, mg/g Mg, mg/gCa, mg/g Cl, ppm S, % N, %
Time h Temp ˚C μ σ μ σ μ σ μ σ μ σ μ σ μ σ μ σ
B 6 20 31.5 2.882.33 0.09 0.18 0.001 0.840.022.720.05 326.46.72 0.24 0.002 0.980.05
B 6 50 26.0 2.231.79 0.08 0.150 0.67 0.012.340.07 288.33.27 0.22 0.004 0.920.08
B 6 80 18.2 2.371.61 0.13 0.14 0.0010.60.022.25 0.05 268.50.7 0.21 0.008 0.890.08
B 24 20 28.1 2.591.59 0.14 0.17 0.004 0.630.032.36 0.13 229.6 3.41 0.23 0.006 1.010.04
B 24 50 15.1 2.111.17 0.1 0.140.0030.330.041.450.04221.7 0.8 0.21 0.001 0.790.05
B 24 80 14.3 2.110.8 0.04 0.130.001 0.440.021.73 0.06 200.4 0.89 0.19 0.005 0.830.05
W 6 20 38.8 1.851.39 0.07 0.29 0.003 0.820.031.79 0.07 569.0 1.46 0.27 0.005 0.530.04
W 6 50 35.0 0.671.21 0.14 0.27 0.001 0.650.011.67 0.02 495.7 3.68 0.24 0.002 0.490.05
W 6 80 26.3 1.4 1.12 0.16 0.210.0010.6 0.031.590.13389.2 5.4 0.22 0.002 0.570.04
W 24 20 39.2 1.760.91 0.08 0.24 0.002 0.550.031.52 0.07 485.2 5.16 0.25 0.002 0.590.06
W 24 50 25.0 3.940.88 0.03 0.22 0.002 0.380.031.13 0.07 484.9 5.79 0.22 0.002 0.530.02
W 24 80 24.0 1.7 0.67 0.09 0.190.0010.580.041.490.11440.42.55 0.2 0.003 0.530.02
at 50˚C with 24 hours residence time. Sodium and sulfur
had a maximum reduction of 77% and 17% at 80˚C with
both 6 hours and 24 hours residence time. Furthermore,
nitrogen reduced by an average 35% at 50˚C and 80˚C
with both 6 hours and 24 hours residence time.
3.2.2. Wheat
Similar to barley, the overall ash content reduced to an
average of 63% with no significant difference between
80˚C at 24 hours, 50˚C at 24 hours and 80˚C at 6 hours.
There was an inconsistent reduction in nitrogen with in-
crease in time and temperature. Whereas, with magne-
sium and calcium a reduction of 40% was observed for a
temperature of 50˚C and 24 hours residence time. Unlike
other feedstocks, chlorine reduced by up to 93% at 80˚C
with 6 hours residence time. A reduction of 35% was
observed when wheat was subjected to 80˚C and 24
hours residence time.
3.3. Statistical Interpretation of the Results
Analysis of Variance (ANOVA) was performed on each
response (% reduction in Ash, K, Na, Ca, Mg, Cl, N and
S) separately for each of the four feedstocks. If the re-
sults were significant at 5% (P-value < 0.05), multiple
means comparison was performed on the significant in-
teraction else on the main factors. Multiple means com-
parison is a technique widely used to determine the dif-
ferences and similarities between the means. A range of
means comparison are available, few methods that are
predominantly used for are LSD, Tukey-Kramer, Dun-
can, Scheffe’s method, etc. Tukey-Kramer method at
5% level of significance was used for analyzing the
results.
Letter groups (a, b, c, d and so on) at the top of each
column in Figure 1 will be used to represent all possible
imilarities and differences between means. Letter “a” s

P. RAVICHANDRAN ET AL. 191
Figure 1. % reduction in Ash and other inorganic elements with respect to resident time and temperature factor. Treatments
ithin a feedstock with same letters are not significantly different. w

P. RAVICHANDRAN ET AL.
192
may represent a treatment combination or a group of
ted in this paper has proven the
velop a biomass fuel that, once processed and pelletized
d and combusted in residential
IA), “World Oil
Markets, Official Energy Statistics US Government,”
2006. http://wemissions.pdf
treatment combination with largest mean. Likewise, let-
ter “b” may represent a treatment combination or a group
of treatment combination with the second largest mean.
The treatment combination with letter group “a” is dif-
ferent for the combination that received a letter group “b”.
However, if there is a group of treatment combinations
that received the same letter, there is no significant dif-
ference between those combinations. If the treatment
combination can be further grouped, those means would
be grouped with the letters “c”, “d” and so on. A treat-
ment combination may sometime be represented by more
that one letter (say “ab”). In such cases, “ab” treatment
combination is not significantly different form the treat-
ment combination or a group of treatment combination
that received a letter group “a”or “b”.
For example, Figure 1(a) presents a graph—% ash re-
duction vs. feedstock—resident time with letters group-
ing for each feedstock.
Let us consider reed canary, which is represented as
RC 6 for 6 hours and RC 24 for 24 hours with three
columns indicating temperatures. The letters for each
treatment combination is given at the top if each column.
Treatment combination of 80˚C at 6 hours gets letter “a”
indicating that it has the largest % reductions in ash.
Further, 50˚C and 80˚C at 24 hours group receives a let-
ter “ab”. Since, all of these treatment combinations has
letter “a” there is no significant difference between them
(all three treatments combinations reduces ash to the
maximum). If the best treatment that offers maximum ash
reduction for reed canary was to be chosen among these
three treatment combinations mentioned above, other
factors such as energy used to subject the feedstock to
each treatment combination and the cost associated with
it may be considered (i.e. treatment combination that
reduces ash to a maximum with low energy use or cost).
4. Conclusions
The research presen most
efficient method for batch leaching of inorganic material,
particularly K and Cl, in switchgrass and wheat straw to
be at 50˚C for 24 hours. This temperature and time are the
most effective, however more moderate conditions may
be used depending on the ash content of the unleached
material. Previous literature has identified the leaching
potential for reduction of these properties, but has not yet
determined the effective conditions for performing this
leaching. Using the method established in this research,
switchgrass and wheat straw can be prepared for com-
bustion with the assurance that inorganic material content
has been reduced sufficiently to safeguard against ash
production, corrosion, slagging and harmful emissions in
residential pellet stoves.
The implications of this knowledge can be used to de-
or briquetted, can be sol
appliances. This will give farmers an opportunity to as-
sess the value in their natural grasses by either autono-
mous energy generation (oil and gas independence) or
the commercial application of their natural resource. The
simplicity of the leaching process lends itself to the pos-
sibility of creating a natural grass biomass value chain,
with farmers investing in the harvesting, leaching and
pelletizing/briquetting of their materials.
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