The use of novel materials to make biomass based fuel pellets compared to traditional pellet fuels

Biomass pellets compared to Industrial pellets
‘The use of novel materials to make biomass based fuel
pellets compared to industrially produced fuel pellets’
By Richard Charles Allen Jee
Key Words: Biomass pellets, Bracken (Pteridium aquilinum ), Heather (Calluna
vulgaris), Reed (Phragmites australis), Virgin Pine (Pinus spp.)
Abstract
As the world looks for future sources of energy, biomass stands out as one of the
leading solutions. This study looks at how three novel materials for pellets;
bracken (Pteridium aquilinum), heather (Calluna vulgaris) and reeds (Phragmites
australis), compare to an industrially made market leader in the biomass based
pellet field; ‘Koolfuel’ virgin pine pellets (Pinus spp.). Pellets were made using
each of the three novel materials and a virgin pine pellet was produced from
chips of the same crop as the industrially made (IVP) pellets, for comparative
reasons. Six samples of each of these pellets were tested for their calorific,
moisture and ash contents and were compared to the IVP pellets values.
The results showed that bracken and heather were both comparable to the IVP
pellets and that, if modified, will produce a similar calorific content. Both bracken
and heather cohered to the ENplus pellet rating system, used to assess pellets
worldwide. The reed pellets did not perform as well, having an undesirable high
ash content and low calorific value, and so did not fit into all of the guidelines
necessary for the ENplus certification. Heather and bracken are worth pursuing
as materials for the biomass material market.
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Introduction
Energy security and the impact of energy use on the environment are of
increasing global concern. Renewable energy sources are slowly integrating into
the global energy mix and biomass has been suggested as one of the most
important (IEA, 2013). Biomass is biological material originating from living, or
recently living organisms that, either directly or indirectly, have been derived from
contemporary photosynthesis reactions (van Dyken, et al., 2010). It most often
refers to plant-based materials (Quark et al., 1999: Van Loo and Koppejan,
2007). Plant-based fuel primarily comprises two types of materials: lignin and
cellulose (Van Loo and Koppejan, 2007). These are the well-understood
materials that largely define woody fuels, however, the amount of each change
depends on the plant.
Plant-based fuels, including biomass-based pellets, are increasingly being used
throughout the UK, Europe (Skea, 2006: British Forestry Commission, 2007:
Aylott, et al., 2008) and the world (Berndes, et al, 2003: Thornley, et al., 2009) as
a fuel to heat buildings and provide electricity. It is renewable and largely carbon
neutral in comparison to fossil fuels when combusted (Rowe, et al., 2009), so it is
becoming increasingly important to expand the biomass energy sector to help
meet the objectives of the UK Government’s Renewable Energies Roadmap
(DECC, 2011).
At the end of 2010 there was a capacity to produce 2.5 GW of biomass electricity
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in the UK (DECC, 2011). It is the single largest contributor to the UK’s total
renewable energy generation (DECC, 2011). Globally, biomass pellets are most
commonly used for this (IEA, 2013). Co-firing fossil fuels and biomass based
fuels together is possible (Al-Mansour and Zuwala, 2010) with the upgrading of
existing plants, but is subject to technical limits and the amount of biomass used
(Hansson, et al., 2009: DECC, 2011). It is possible to convert fossil fuelled power
stations to run on 100% biomass, for example Tilbury Power Station, UK (DECC,
2011). Both energy generating plants co-firing, and those dedicated to biomass
only, were generating 21% and 17% of this the total biomass energy in the UK
energy (DECC, 2011).
The potential energy produced in the UK from biomass generators is predicted to
rise up to 6GW by 2020 (Figure 1). This depends on a high industry production
rate, the construction of new generating plants, the applications for construction
being approved (Figure 2), and whether there is enough sustainable feedstock
for fuel (DECC, 2011).
3

Figure 1 – Shows the potential for biomass electricity produced in the UK from
2010 to 2020 (DECC, 2011). There could be an industry high of up to 6GW and
an industry low of around 3 GW.
Figure 2 – Shows the target capacity and timeline of the biomass electricity
projects for the UK by 2020 (DECC, 2011).
4

Heat generation from biomass, is also taken into account in the Department of
Energy and Climate Changes (2011) report. It estimates that biomass boilers
could contribute the majority of up to 50TWh of heat in non-domestic buildings by
2020 (Figure 3).
Figure 3 – Shows the potential for biomass heat for non-domestic buildings
produced in the UK from 2010 to 2020 (DECC, 2011).
Pelletising is a method that mechanically increases the bulk density of a material
(Mani, et al., 2006a: Van Loo and Koppejan, 2007). Biomass based fuel pellets
are an upgraded biomass fuel with several advantages to accomplish efficient
combustion (Boman, et al., 2003). Wood pellets are a clean, dry, easily stored
and fed fuel (Van Loo and Koppejan, 2007) that are particularly well suited for the
5

domestic market (Boman, et al., 2003). In well-designed boilers, generators and
stoves, they have exceptionally low emissions of the products of incomplete
combustion compared to fossil fuels (Boman, et al., 2003). The ideal material for
a pellet would be one with a high calorific content with a large, renewable supply
and ideally the waste product of another process. Current materials include virgin
pine and miscanthus, Miscanthus giganteus, which are grown especially for the
biofuel industry (Everard, et al., 2013), along with waste wood from saw mills
(Taylor, 2008).
This paper looks into three novel pelleting materials: heather, Calluna vulgaris,
Bracken, Pteridium aquilinum, and the common reed, Phragmites australis.
Heather (Calluna vulgaris) is a low growing perennial shrub, commonly found on
heaths mires and some woodland throughout the UK and Europe (Rodwell,
1991: NBN, 2013). It grows in acidic soil and is found in the open moorland and
heathland or in moderately shaded woodland (Rodwell, 1991).
The common reed (Phragmites australis) is a stout, coarse perennial that forms
extensive beds with its creeping rootstock (Fitter, et al., 1984: Rodwell, 1995).
Often found in marshes and estuaries, it sometimes persists in apparently
unsustainable habitats of differing trophic states and a variety of substrates
(Fitter, et al., 1984: Rodwell, 1995). Traditionally it has been used as thatching,
however this is not a common in the UK anymore (Hawke and José, 1996).
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Bracken (Pteridium aquilinum) is one of the most common cosmopolitan ferns in
Europe (Fitter, et al., 1984: Rodwell, 1991). It grows in extensive, often closed
communities, which can often cover whole hillsides on dry heaths, moors and in
open woodland (Fitter, et al., 1984: Rodwell, 1991). It exists in a brown, dead
state throughout the winter (Fitter, et al., 1984).
Each of these plants was chosen due to its historical background of being
controlled by burning, which is not as common as it once was (DEFRA, 2007:
DEFRA, 2008). The Department of Environment, Food and Rural Affairs
(DEFRA) (2011) suggests that cutting and swiping are good alternative to
burning as they are not weather dependent and there is a lower risk of
unnecessary damage to the other parts of the heath and its habitat (DEFRA,
2011: Everett, 2012). However, the cut material can become a problem if it does
not decay quickly enough to allow the underlying vegetation to continue to grow
(DEFRA, 2011). To counter this, the cut material can be collected and therefore
becomes of use to humans. This experiment looked at whether it could be made
into viable biomass pellets.
Aims and Objectives
The aim of this study was to compare the energy efficiency of these novel
materials used as biomass pellets against a market leader. The objectives of the
report are to (1) compare the energy efficiency of these novel materials to the
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efficiency of industrial virgin pine pellets by looking at the calorific content, the
ash content and the moisture content, (2) research whether these novel materials
are as readily available as their industrial counterparts, and (3) explore the
environmental impact of the collection, transportation and the ultimate burning of
the pellets.
Method
A literature review was performed to help determine the choice of novel materials
and determine the factors important to measure. Three quantitative analyses
experiments were undertaken on four types of pellets sourced from bracken,
reeds, heather and virgin pine. The energy efficiency of each material was
compared against the existing, industrially produced virgin pine (IVP) pellet,
‘Koolfuel’. Tests included finding the energy output after complete combustion,
the moisture content and the ash content after combustion.
Desk Study
Literature searches were undertaken on the online scholarly databases
Academic Search Premier, ScienceDirect and Google Scholar from January to
May. Search terms included were ‘UK Bioenergy’, ‘Biomass Pellets’, ‘Biopellets’,
‘Renewable Energy Outlook’, ‘Bioenergy Strategy’, ‘Department of Energy and
Climate Change’, ‘Energy roadmap UK’, ‘Phragmites australis’, ‘Pteridium
aquilinum’, ‘Calluna vulgaris’, ‘Energy Policy UK’, ‘DEFRA’, ‘Grass burning code’,
‘Calorific content of pellets’ and ‘Biomass and Bioenergy’. References were
8

chosen based on the their relevance, if the information was up to date and
whether they were reputable sources.
Sample Collection
Samples of each novel material were collected from within 3 kilometres of each
other within the perimeters of Dale, Pembrokeshire, UK. The points of collection
are shown in Figure 4. The samples were collected on Thursday 8th
March 2014.
Figure 4 – Shows the points of collection of each novel material sample (Google
Maps, 2014).
9

The Scottish IVP pellets, were acquired from Strawson Energy along with the
Scottish virgin pine (VP) chips used to make control pellets.
Pelleting
The pelleting method was designed specifically for this experiment.
The samples were dried in a drying oven at 102ºC for 48 hours (MAFF, 1986).
They were then placed in paper bags, weighed to 2 decimal places and put back
in the drying oven at 102ºC for an hour and weighed again. This process was
repeated until there was less than 0.1g difference in the weight before they went
into the oven and the weight after. The samples were then ground and sieved to
pieces >1mm - <2mm. These were then sealed in airtight containers.
The press’s aluminium block, in Figure 5, was heated to 125ºC in an oven.
Between 0.7g and 0.9g of the bracken material was put into the 0.6mm hole in
the block, 135ul of distilled water was added and it was compressed to a force of
75N, measured with a 100N force gage from specific spot marked on the screw
press handle. The press was then put into the oven at 125ºC for 10 minutes. The
pellet was extracted from the press and left to cool at ambient temperature for 30
minutes before being sealed in a labelled, airtight container. Six pellets were
made for each of reeds, bracken, heather and virgin pine.
10

Figure 5 – Shows the press designed for and used in this experiment.
Calorific Content
The calorific content was determined using calorimetry and was performed using
a bomb calorimeter, (type FTT EN ISO 1716 Oxygen Bomb Calorimeter) at the
London South Bank University, UK. The methodology followed that of Appendix
1.
Moisture content
36 small beakers were weighed to 4 S.F. Six pellets of each different material
were weighed in the beakers to 4 S.F and had their beaker weight deducted to
acquire their wet weights. These samples were then put into drying oven at
102ºC (MAFF, 1986) for 12 hours. The samples in the beakers were reweighed
on the same scales and had their beaker weight deducted to acquire their dry
weights. The weight loss was calculated and became the mass of water. The
11

results were put into the Equation 1 below and the outcome was recorded.
Moisture content (%) =
Mass of Water
X 100
Mass of Biomass sample
Equation 1 – How to formulate the moisture content of the biomass pellets.
Ash content
36 small beakers were weighed to 4 S.F. Six pellets of each different material
were weighed in the beakers to 4 S.F and had their beaker weight deducted to
acquire the sample weights. These samples were then put into a furnace at
671ºC (Mendez-Vilas, 2012) for 8 hours. When cool, the samples in the beakers
were reweighed on the same scales and had their beaker weight deducted to
acquire their ash weights. The weight loss was calculated and became the mass
of ash. The results were put into the Equation 2 below and the outcome was
recorded.
Ash content (%) =
Mass of Ash
X 100
Mass of Biomass sample
Equation 2 – How to formulate the ash content of the biomass pellets.
Statistical Analysis of Results
Data were initially explored with boxplots and then analysed using an analysis of
variants (ANOVA) to determine statistical significance and generate confidence
intervals.
The results data were formatted and put into the statistical analysis software ‘R
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2.13.2’ (R Core Team, 2013). Confidence intervals were calculated to illustrate
the certainty with which the results were determined. Boxplots of the calorific,
moisture and ash content were created from the results as a non-parametric way
to display the data. A Tukey ANOVA test was run to show the comparisons of
means in the results.
Results
Calorific Value Analysis
Each calorific value measured was within 1467.5 J/g of each other from the
highest value in the industrially made virgin pine (IVP) pellets of 18513.9 J/g,
95% Cls [18453.1, 18574.6], to the lowest found in the reed pellets of 17046.4
J/g, 95% Cls [16950.2, 17142.5], shown in Figure 6. The calorific value of the
reed pellets was significantly less than all of the other pellets, shown in Figure 6.
Heather and Bracken pellets both had higher calorific content means than the VP
pellets, but lower than the IVP pellets, which were superior.
There was not a statistical significance in the difference in the calorific content
values of the heather and bracken pellets against each other and every other
pellet with the exception of reeds (Figures 7, 8 and Table 1). A mean difference
of 263.3J/g, 95% CI [-387.38, 859.98], less energy output from heather pellets
compared to bracken pellets was recorded, which was not statistically significant
(one way Anova, n= 6, p= 0.798). Bracken pellets compared to IVP pellets gave
13

a mean difference of 507.8J/g, 95% CL [-115.87, 1131.49]. This is not statistically
significant (one way Anova, n= 6, p= 0.151), displayed in Table 1. A mean
difference of 319.7/g, 95% CI [-943.38, 303.98], less calorific content from
bracken pellets compared to VP pellets was recorded; this showed no statistically
significant difference (one way Anova, n= 6, p= 0.569). IVP pellets compared to
heather pellets gave a mean difference of 271.5/g, 95% CL [-352.17, 895.19].
This is not statistically significant (one way Anova, n= 6, p= 0.706). Finally, the
mean difference of VP pellets and heather pellets was 556J/g, 95% CI [-1179.68,
67.68]. It was also not statistically significant (one way Anova, n= 6, p= 0.097).
There was a statistical significance in the difference in the calorific content values
of the reed pellets against each other pellet along with the IVPs and VPs (Figures
7, 8 and Table 1). A mean difference of 959.68J/g, 95% CI [1583.39, 336], less
energy output from bracken pellets compared to reed pellets was
recorded, which was statistically significant (one way Anova, n= 6, p= <0.001). A
mean difference of 1,195.98J/g, 95% CI [2091.17, 843.81], less energy output
from heather pellets compared to reeds pellets was recorded, which was
statistically significant (one way Anova, n= 6, p= <0.001). A mean difference of
827.51J/g, 95% CI [1451.19, 203.83], less energy output from IVP pellets
compared to VP pellets was recorded, which was statistically significant (one way
Anova, n= 6, p= <0.001). A mean difference of 639.98/g, 95% CI [16.30,
1263.66], less energy output from VP pellets compared to reed pellets was
recorded, which was statistically significant (one way Anova, n= 6, p= 0.042).
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Figure 6 – Boxplot shows the range and means of the calorific values in each
pellet.
15

Figure 7 – Shows the higher and lower confidence intervals between each set of
pellets for the calorific content. If the line crosses 0 at any point then there is not
a statistically significant difference between the two pellets contents. It does,
however, show that there is 95% confidence that the real difference lies between
the upper and lower confidence intervals.
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Table 1 – Output of Tukey – test, ANOVA. Multiple Comparisons of Means of
calorific value of 6 pellets of each material on the top part of the table. It also
shows the mean differences, MD, (J/g) and the 95% CIs, on the bottom half of
the table. Statistically significant difference is shown in bold text.
I. V. Pine V. Pine Bracken Heather Reeds
I. V. Pine <0.001 NS NS <0.001
V. Pine
95% CI
[1451.19,
203.83]
MD =
827.51
NS NS 0.04
Bracken
95% CI
[1131.49,
-115.87]
MD =
507.8
95% CI
[-943.38,
303.98]
MD =
319.7
NS <0.001
Heather
95% CI
[-352.17,
895.19]
MD =
271.5
95% CI [-
1179.68,
67.68]
MD = 556
95% CI
[-387.38,
895.98]
MD = 263.3
<0.001
Reeds
95% CI
[2091.17,
843.81]
MD =
263.3
95% CI
[16.30,
1263.66]
MD =
639.98
95% CI
[1583.36,
336.0]
MD =
959.68
95% CI
[1819.66,
572.30]
MD =
1195.98
(No Statistical Significance = NS)
The IVP pellets consistently gave a superior output of calorific content to all of
the other pellets. Heather pellets gave a marginally lower energy output than IVP
17

pellets but were higher than bracken. Equally bracken was higher than the VP
pellet’s output. The reed pellets had a consistently inferior calorific content
compared to every other pellet.
Moisture Analysis
The moisture values of each pellet were all under 10% (Figure 8). The IVP
pellets had the highest mean moisture at 7.89%, 95% Cls [7.80%, 8.0%] and the
lowest was the heather pellets at 2.87%, 95%Cls [2.63%, 3.11%].
There was not a statistical significance in the difference in the moisture content
values of each of the pellets against each other, with the exception of bracken
and reed pellets (one way Anova, n= 6, p= 0.707), (Figures 8, 9 and Table 2). A
mean difference of 0.26%, 95% CI [-0.86, 0.34], less moisture content from reed
pellets compared to bracken pellets was recorded.
There was a statistically significant difference in the pellet moisture content
between every other pellet type against each other. A mean difference of 3.53%,
95% CI [4.14, 2.94], less moisture content from bracken pellets compared to
heather pellets was recorded, which showed a statistically significant difference
(one way Anova, n= 6, p= <0.001). A mean difference of 1.48%, 95% CI [0.88,
2.08], less moisture content from IVP pellets compared to bracken pellets was
recorded, which was statistically significant (one way Anova, n= 6, p= <0.001). A
mean difference of 1.92%, 95% CI [2.52, 1.32], less moisture content from
18

bracken pellets compared to VP pellets was recorded, which was statistically
significant (one way Anova, n= 6, p= <0.001). A mean difference of 5.02%, 95%
CI [4.42, 5.62], less moisture content from heather pellets compared to IVP
pellets was recorded, which was statistically significant (one way Anova, n= 6, p=
<0.001). A mean difference of 3.28%, 95% CI [2.68, 3.88], less moisture content
from heather pellets compared to reed pellets was recorded, which was
1.62%, 95% CI [1.02, 2.22], less moisture content from heather pellets compared
to VP pellets was recorded, which was statistically significant (one way Anova,
n= 6, p= <0.001). A mean difference of 1.74%, 95% CI [2.34, 1.14], less moisture
content from IVP pellets compared to reed pellets was recorded, which was
3.40%, 95% CI [4.00, 2.80], less moisture content from VP pellets compared to
IVP pellets was recorded, which was statistically significant (one way Anova, n=
6, p= <0.001). Finally, a mean difference of 1.66%, 95% CI [2.26, 1.06], less
moisture content from reed pellets compared to VP pellets was recorded, which
was statistically significant (one way Anova, n= 6, p= <0.001).
19

Figure 8 – Boxplot shows the range and mean percentage of moisture found in
the different pellets.
20

Figure 9 – Shows the higher and lower confidence intervals between each set of
pellets for the moisture content. If the line crosses 0 at any point then there is not
a statistically significant difference between the two pellets contents. It does,
21

moisture content of 6 pellets of each material on the top part of the table. It also
shows the mean differences, MD, (%) and the 95% CIs on the bottom half of the
table. Statistically significant difference is shown in bold text.
I. V. Pine <0.001 <0.001 <0.001 <0.001
V. Pine
95% CI
[4.00, 2.80]
MD = 3.40
<0.001 <0.001 <0.001
Bracken
95% CI
[0.88, 2.08]
MD = 1.48
95% CI
[2.52, 1.32]
MD = 1.92
<0.001 NS
Heather
95% CI
[4.42, 5.62]
MD = 5.02
95% CI
[1.02, 2.22]
MD = 1.62
95% CI
[4.14, 2.94]
MD = 3.53
<0.001
Reeds
95% CI
[2.34, 1.14]
MD = 1.74
95% CI
[2.26, 1.06]
MD = 1.66
95% CI
[-0.86,
0.3393]
MD = 0.26
95% CI
[2.68,
3.88]
MD = 3.28
There is no statistical significance in the difference in the moisture content for
reed and bracken pellets set against the other pellet types. Every other
comparison showed a statistically significant difference. The heather pellets had
22

considerably lower moisture content than the other pellets and VP pellets were
substantially lower than their industrial counterparts, IVP pellets, which had a
higher moisture content than all of the other alternatives. The bracken and reed
pellets had similar moisture contents and were higher than the VP and heather
pellets.
Ash Analysis
The ash values of each pellet were all under 5%, shown in Figure 10. The reed
pellets had the highest mean moisture at 3.57%, 95% Cls [3.24%, 3.90%] and
the lowest was the IVP pellets at 0.12%, 95% Cls [0.05%, 0.18%].
There was no statistically significant difference in the moisture content of the IVP
pellets against the VP pellets and each against the heather pellets (Figures 10,
11 and Table 3). A mean difference of 0.19%, 95% CI [-0.15, 0.52], less ash
content from IVP pellets compared to VP pellets was recorded, which showed a
statistically significant difference (one way Anova, n= 6, p= 0.485). A mean
difference of 0.30%, 95% CI [-0.64, 0.03], less ash content from IVP pellets
compared to heather pellets was recorded, which showed a statistically
significant difference (one way Anova, n= 6, p= 0.095). A mean difference of
0.11%, 95% CI [-0.45, 0.22], less ash content from VP pellets compared to
heather pellets was recorded, which showed a statistically significant difference
(one way Anova, n= 6, p= 0.858).
23

Statistically significant differences were found in the ash content of bracken and
reed pellets against every other type of pellet (Figures 10, 11 and Table 3). The
reed pellets ash levels were much higher than any of the alternatives (Figure 10).
A mean difference of 1.31%, 95% CI [1.64, 0.97], less ash content from heather
pellets compared to bracken pellets was recorded, which showed a statistically
significant difference (one way Anova, n= 6, p= <0.001). A mean difference of
1.61%, 95% CI [1.94, 1.27], less ash content from IVP pellets compared to
bracken pellets was recorded, which showed a statistically significant difference
(one way Anova, n= 6, p= <0.001). A mean difference of 1.84%, 95% CI [1.51,
2.18], less ash content from bracken pellets compared to reed pellets was
recorded, which showed a statistically significant difference (one way Anova, n=
6, p= <0.001). A mean difference of 1.42%, 95% CI [1.76, 1.08], less ash content
from VP pellets compared to bracken pellets was recorded, which showed a
statistically significant difference (one way Anova, n= 6, p= <0.001). A mean
difference of 3.15%, 95% CI [2.81, 3.48], less ash content from heather pellets
compared to reed pellets was recorded, which showed a statistically significant
difference (one way Anova, n= 6, p= <0.001). A mean difference of 3.45%, 95%
CI [3.11, 3.79], less ash content from IVP pellets compared to reed pellets was
recorded, which showed a statistically significant difference (one way Anova, n=
6, p= <0.001). A mean difference of 3.26%, 95% CI [3.60, 2.93], less ash content
from VP pellets compared to reed pellets was recorded, which showed a
statistically significant difference (one way Anova, n= 6, p= <0.001).
24

Figure 10 – Boxplots show the range and mean percentage of ash found in the
different pellets.
25

Figure 11 - Shows the higher and lower confidence intervals between each set
of pellets for the ash content. If the line crosses 0 at any point then there is not a
statistically significant difference between the two pellets contents. It does,
26

ash content of 6 pellets of each material on the top part of the table. It also shows
the mean differences, MD, (%) and the 95% CIs on the bottom half of the table.
Statistically significant difference is shown in bold text.
I. V.
Pine
NS <0.001 NS <0.001
V. Pine
95% CI
-0.15,
0.52]
MD = 0.19
<0.001 NS <0.001
Bracken
95% CI
[1.94,
1.27]
MD = 1.61
95% CI
[1.76,
1.08]
MD = 1.42
<0.001 <0.001
Heather
95% CI
[-0.64,
0.03]
MD = 0.30
95% CI
[-0.45,
0.22]
MD = 0.11
95% CI
[1.64,
0.97]
MD = 1.31
<0.001
Reeds
95% CI
[3.11,
3.79]
MD = 3.45
95% CI
[3.60,
2.93]
MD = 3.26
95% CI
[1.51,
2.18]
MD = 1.84
95% CI
[2.81,
3.48]
MD = 3.15
The reed pellets had a substantially greater ash content than the other alternative
pellets. The bracken pellets had a higher content than the VP, IVP and heather
pellets, which all had similar ash contents, with the IVP pellets having the lowest
ash content.
27

Availability of materials
Bracken, Pteridium aquilinum, is abundant throughout the British mainland
(Figure 12). There is 1058 hectads (BSBI, 2012a) and nearly every white space
on the figure is within 100 kilometres of a source of it.
Heather, Calluna vulgaris, is also largely present throughout the UK (Figure 13),
especially in Scotland, Northern Wales and Southern England. There is 753
hectads of it (BSBI, 2012b). However, there is a large white space on the figure
in central England where heather frequency is limited, but this is all still within
100 kilometres of a source.
Reeds, Phragmites australis, are not as abundant throughout the UK as the other
two materials (Figure 14), with only 517 hectads (BSBI, 2012c). It lies
predominantly around the coastlines and needs to be near a source of water, so
is restricted.
The VP and IVP pellets are very abundant (NBN, 2011) shown in Figure 15,
more so than the alternative materials. There is an even coverage throughout the
UK with a much higher abundance in England.
28

Figure 12 – Shows a map of the abundance of Bracken, Pteridium aquilinum, in
the UK (BSBI, 2012a) in hectads. The lines show a 100km2
grid.
29

Figure 13 - Shows a map of the abundance of Heather, Calluna vulgaris, in the
UK (BSBI, 2012b) in hectads. The lines show a 100km2
grid.
30

Figure 14 - Shows a map of the abundance of Reeds, Phragmites australis, in
the UK (BSBI, 2012c) in hectads. The lines show a 100km2
grid.
31

Figure 15 – Shows a map of the abundance of Pine, Pinus spp., in the UK (NBN,
2011) in hectads.
32

Discussion
It is conceivable from the results that of the three novel materials used, there are
two that could be deemed successful when pelleted: bracken and heather, and
one that did not perform as well: reeds.
EPC Ratings
The European Pellet Council, EPC, (2013) categorises wood pellets for heating
purposes, which has become not only a European but, a worldwide standard.
The standards in Table 4 are relevant to the pellets used in the practical and from
this the pellets could be categorised, with ENplus-A1 being the best. However,
there was not sufficient testing to actually grade these pellets, as many
properties were not tested in this experiment.
33

Table 4 – Shows the threshold values of the pellet parameters for the ENplus
rating system (EPC, 2013).
((1
= as received, (2
= dry basis)
From the results, it can be deduced that each pellet type would be in the ENplus-
A1 category for the calorific content, which ranges from the reed pellets 17046.4
J/g [16950.2-17142.5] to the IVP pellets 18513.9 J/g [18453.1, 18574.6],
moisture content, which ranges from heather pellets at 2.9%, with an lower CI of
2.63%, to IVP pellets at 7.9%, with an upper CI of 8.0%, and additive content.
34
Property Unit ENplus-A1 ENplus-A2 EN-B
Diameter mm 6 or 8
Calorific
Content
J/G 16500≤Q≤19000 16300≤Q≤19000 16000≤Q≤19000
Moisture
Content
w-
%(1 ≤10
Ash
Content
w-
%(2 ≤0.7 ≤1.5 ≤3.0
Additive
content
(Lubricants,
binding
agents)
w-% ≤2
Wood type
Stem wood,
Chemically
untreated
residues from the
wood processing
industry
Whole trees
without roots,
Stem wood,
Logging residues,
Bark, Chemically
untreated residues
from the wood
processing
industry
Forest, plantation
and other virgin
wood, Chemically
untreated residues
from the wood
processing
industry,
Chemically
untreated, used
wood

In terms of ash content, only the IVP 0.12%, upper 95% CI 0.18%, VP 0.31%,
upper 95% CI 0.37, and heather 0.42%, upper 95% CI 0.49%, pellets would be in
the ENplus-A1 category, the bracken pellets 1.73, 95%CI [1.66%, 1.79%], would
be in the EN-B category and the reed pellets with a mean ash content of 3.57%,
95% CI [3.24%, 3.90%], wouldn’t make it into any of the categories, and so could
not receive the certification from the EPC.
All pellets would fall into the diameter brackets for any of these classifications as
they were all made in a 6mm press and the specification of the IVP pellets shows
that they had a diameter of 6mm (Appendix 2).
Whilst the IVP and VP pellets would be associated with the ENplus-A1 category
for their wood type, the other pellets are all plantations and so would comply
within the EN-B category.
Analysis of results
These pellets were not made using industrial machines, with the exception of the
IVP pellets. Both the IVP and VP pellets were made from the same source of
virgin pine. In principle, the only difference between them is how they were
made. Therefore, the difference between these two pellets could show what the
difference would be between the bracken, heather and reed pellets and their
35

industrially produced counterparts. The VP pellets had a lower calorific content
than the IVP pellets having a statistically significant, mean difference of
827.51J/g, 95% CI [1451.19, 203.83] (Figures 6 and 7, Table 1). However, both
the bracken and the heather pellets had a higher mean calorific content than the
VP pellets. Suggesting that industrial bracken and heather pellets have the
potential to have a higher calorific output than the IVP pellets.
Moisture, with the help of heat, can promote a range of chemical and physical
changes in a pellet, such as thermal softening of the biomass, denaturation of
proteins, gelatinization of starch and solubilisation and recrystalisation of sugars
and salts (Kaliyan and Morey, 2010). This aid allows the pellet to get, and keep,
its form (Mani, et al., 2006b). The optimum moisture content for a pellet is
between 6% and 12% (Li and Liu, 2000: Obenberger and Thek, 2004: Kaliyan
and Morey, 2009: EPC, 2013). The IVP pellets at 7.89%, 95% Cls [7.80%, 8.0%],
the bracken pellets, at 6.41%, 95% Cls [5.94%, 6.88%], and reed pellets, at
6.15%, 95% Cls [5.83%, 6.48%], could all potentially fit between these levels
(Figures 8 and 9, Table 2).
Low moisture content decreases the risk of mould, fungi and general decay
(Alakangus, 2010). Increasing moisture content reduces the highest possible
combustion temperature and increases the resistance time in the combustion
chamber. This can lower the potential energy output and will give less room in
preventing emissions as a result of incomplete combustion (Van Loo and
36

Koppejan, 2007).
Air pollutants can reduce the air quality of an area, which can have negative
effects on public health, ecosystems, biodiversity and habitats (Granier, et al.,
2011: DECC and DEFRA, 2012). The combustion of biomass in renewable heat
generation produces emissions and air pollutants, such as CO2 and nitrogen
oxide, which fall under the EU air quality targets (DECC and DEFRA, 2012). The
impact is currently small, however, the increasing size of the renewable energy
sector could result in higher levels of air pollution, so emission performance
standards are being introduced by the DECC (2011). Whilst there was no actual
testing of air pollutants or emissions undertaken in this experiment, they would
need to be taken into account if applying for ENplus certification.
Ash is the product of pyrolysis: the thermal degradation in the absence of an
externally supplied oxidizing agent (Van Loo and Koppejan, 2007). Products
include carbonaceous charcoal, low molecular weight gases (CO and CO2), but
mainly tar (Van Loo and Koppejan, 2007). Ash can cause abrasion and erosion
of biomass generators and boilers (Van Loo and Koppejan, 2007). The reed
pellets failed to reach the ENplus rating for their ash content due to it being over
the ≤3.0% needed (Table 4), at 3.57%, 95% CI [3.24%, 3.90%] (Figures 11 and
12, Table 3) suggesting that they might not be useable. The reeds could be
mixed with an alternative biomass material to lower the amount of ash produced.
However, this could change the positive attributes of the reed pellets, for
37

example, the moisture content.
The environmental impact of cutting reeds in the winter, at appropriate water
levels, will be minimal and the species will retain its dominance in its habitat
(White, 2009). It also preserves the habitat as it slows the natural succession of
the reed swamp to scrub and woodland (White, 2009). Summer cutting reduces
the competitive ability and can ultimately eliminate it from the habitat (White,
2009). This would impact on when the reeds would be available to pellet, as they
cannot be harvested year round or intensively whereas a pine plantation can
(Framstad, 2009: Singh, 2013). Equally bracken and heather both have seasons
to be harvested, in the autumn and winter (DEFRA, 2007: Everett, 2012). The
spring and summer provide habitat and nesting sites for ground dwelling birds,
and so the Department of Environment, Food and Rural Affairs has set up
regulations against harvesting at that time (DEFRA, 2007). However, pine trees
take years to grow, and are usually harvested on 20-25 year rotations (Framsted,
2009), whereas these alternative sources and bio-crops can be harvested
annually.
In the long-term, other infrastructure constraints are likely to dominate, such as
the transportation of these materials around the UK. Densification of materials
destined to be pellets is of vital importance to simplify and reduce the cost of
handling, transporting and stowing (Kaliyan and Morey, 2009: Serrano, et al.,
2011). The transportation of these novel materials could differ dramatically.
38

Whilst bracken, heather and reeds are more malleable, virgin pine is denser and
can have a greater mass fitted into a smaller space. Therefore, more of it can be
transported at once. Thus transport costs for virgin pine would be lower than the
novel materials in question. However, depending where the pelleting plant is
located, there would be little difference as generally all of the materials are
evenly distributed throughout the UK (Figures 12, 13, 14 and 15). The harvesting,
transportation, manufacturing and utilisation of the resources could provide jobs
for the UK population (DECC, 2011).
Using these resources in the UK could reduces the dependency on imported
fuels as they start to diminish and rise in price and could provide a source of
trade value if exported. Global forest stocks are rapidly declining, and a
significant reason for this is their use as fuel (FAO, 2005: Johnson, 2009). There
are global concerns regarding the limited amount of space needed to grow both
food and biofuel crops (Tilman, et al., 2006). There is potential for a huge global
capacity of biomass if properly exploited with 10% of the net international market
available to the UK (DECC, 2011).
Limitations and Recommendations
The machine used to make the pellets fundamentally limited this study. It was
designed specifically for the experiment, but was not what would be used if the
pellets were to be mass-produced. Therefore, the results collected cannot
accurately reflect the values that would be found in their industrially produced
39

counterparts. A recommendation would be to use an industrial pellet machine to
make the pellet samples, to accurately portray the values that could be present in
these material’s pellets.
Due to the lack of resources available to the author, there were limitations as to
what could be measured in this experiment, such as emissions, which are an
important part of the ENplus rating system (EPC, 2013). A recommendation
would be to measure these whilst being combusted in order to provide a wider
outlook on how the pellets could be rated.
The author was unable to determine the calorific content of the pellets, as the
resources were unavailable at the place of study. The London South Bank
University calculated them using their bomb calorimeter. A recommendation
would be for the author to have gone to that university to use the bomb
calorimeter.
Conclusion
To conclude, the IVP pellets had the lowest ash content, the highest, but
optimum, moisture content and the highest energy output. They are, therefore,
the quintessential product to strive towards to meet the pelleting needs. The reed
pellets, as they are, can be ruled out as an alternative biomass based pellet fuel
due to their failing to reach the EPC standard. Within the parameters of this
study, the bracken and heather pellets could be a good alternate option for a
40

biomass based pellet fuel to potentially provide the UK with an efficient, clean
and economic source of energy.
Acknowledgements
Firstly, I would like to express my sincere gratitude to Professor Tony Marmont,
without whom; I would never have developed my fascination with renewable
energy.
Thank you to Graham Smith for his constructive suggestions and patient
guidance during the writing of this paper.
I would like to thank Darrell Watts for helping with the statistical analysis, Geoff
Baker for helping make the pelleting device, and Laura Dodge for organising my
laboratory work.
Special thanks must go to The London South Bank University for using their
equipment to measure the calorific content and to Dr Anil Sequeira for providing
this contact.
A thank you must also go to my family and friends for their support and
encouragement through the study.
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Appendix
Appendix 1
Bomb Calorimetry method, undertaken by staff at London South Bank
52

University.
A sample pellet was weighed using an analytical balance to between 0.7-0.9
grams. Fuse wire and a cotton fuse of appropriate lengths were cut and weighed
with the same balance. The fuse wire bridged the two electrodes inside the bomb
and the cotton fuse was looped over it so that it draped into a crucible containing
the sample suspended from an electrode. The calorimeter was assembled and
tightened. The oxygen hose was connected and the machine automatically
pressurised the calorimeter to 20 atm of pure oxygen. One litre of 25ºC water
was measured. This was drained into the bucket, which was placed into the
machine. The bomb was sealed into the bucket and the electrodes connected.
The relevant weights are inputted into the machine. Water was continually
circulated from the water bath (25ºC) into the outer jacket to maintain a constant
temperature. When the temperature of the water in the bucket was the same as
the temperature of the jacket (it will have cooled upon leaving the bath) the bomb
automatically fires. A current was passed across the electrode causing the fuse
wire and cotton to ignite; this in turn ignited the sample. The temperature rise
was measured and the temperature peaked. The machine then calculated the
SHC of the sample. No adjustments were made for enthalpy changes caused by
reactions between oxide gases/halogens and water, nor was there an attempt to
quantify ash/soot deposits.
Appendix 2
Industrially made virgin pine pellet’s, ‘Koolfuel’, specification.
53

Appendix 3
Raw data from ‘R’ Printouts (R core team, 2013)
54

Calorific Content
> AnovaModel.2 <- aov(J.G ~ material, data=pellets)
> summary(AnovaModel.2)
Df Sum Sq Mean Sq F value Pr(>F)
material 4 7677581 1919395 14.19 3.58e-06 ***
Residuals 25 3382005 135280
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
> numSummary(pellets$J.G , groups=pellets$material, statistics=c("mean", "sd"))
mean sd data:n
Bracken 18006.05 126.28538 6
Heather 18242.35 377.58884 6
I.V.Pine 18513.86 75.87983 6
Reeds 17046.37 120.18098 6
V.Pine 17686.35 705.46324 6
> .Pairs <- glht(AnovaModel.2, linfct = mcp(material = "Tukey"))
> summary(.Pairs) # pairwise tests
Simultaneous Tests for General Linear Hypotheses
Multiple Comparisons of Means: Tukey Contrasts
Fit: aov(formula = J.G ~ material, data = pellets)
55

Linear Hypotheses:
Estimate Std. Error t value Pr(>|t|)
Heather - Bracken == 0 236.3 212.4 1.113 0.79830
I.V.Pine - Bracken == 0 507.8 212.4 2.391 0.15083
Reeds - Bracken == 0 -959.7 212.4 -4.519 0.00113 **
V.Pine - Bracken == 0 -319.7 212.4 -1.506 0.56856
I.V.Pine - Heather == 0 271.5 212.4 1.279 0.70625
Reeds - Heather == 0 -1196.0 212.4 -5.632 < 0.001 ***
V.Pine - Heather == 0 -556.0 212.4 -2.618 0.09721 .
Reeds - I.V.Pine == 0 -1467.5 212.4 -6.911 < 0.001 ***
V.Pine - I.V.Pine == 0 -827.5 212.4 -3.897 0.00528 **
V.Pine - Reeds == 0 640.0 212.4 3.014 0.04224 *
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
(Adjusted p values reported -- single-step method)
> confint(.Pairs) # confidence intervals
Simultaneous Confidence Intervals
Fit: aov(formula = J.G ~ material, data = pellets)
Quantile = 2.937
95% family-wise confidence level
Linear Hypotheses:
56

Estimate lwr upr
Heather - Bracken == 0 236.2967 -387.3833 859.9766
I.V.Pine - Bracken == 0 507.8083 -115.8716 1131.4883
Reeds - Bracken == 0 -959.6800 -1583.3599 -336.0001
V.Pine - Bracken == 0 -319.7033 -943.3833 303.9766
I.V.Pine - Heather == 0 271.5117 -352.1683 895.1916
Reeds - Heather == 0 -1195.9767 -1819.6566 -572.2967
V.Pine - Heather == 0 -556.0000 -1179.6799 67.6799
Reeds - I.V.Pine == 0 -1467.4883 -2091.1683 -843.8084
V.Pine - I.V.Pine == 0 -827.5117 -1451.1916 -203.8317
V.Pine - Reeds == 0 639.9767 16.2967 1263.6566
> cld(.Pairs) # compact letter display
Bracken Heather I.V.Pine Reeds V.Pine
"bc" "bc" "c" "a" "b"
> old.oma <- par(oma=c(0,5,0,0))
> plot(confint(.Pairs))
Moisture Content
> AnovaModel.2 <- aov(moisture ~ material, data=pellets)
material 4 89.26 22.315 177.9 <2e-16 ***
Residuals 25 3.14 0.125
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
57

> numSummary(pellets$moisture , groups=pellets$material, statistics=c("mean",
"sd"))
mean sd data:n
Bracken 6.413833 0.5879124 6
Heather 2.870833 0.2992320 6
I.V.Pine 7.890333 0.1185558 6
Reeds 6.152667 0.4065758 6
V.Pine 4.494833 0.1116771 6
Fit: aov(formula = moisture ~ material, data = pellets)
Linear Hypotheses:
Heather - Bracken == 0 -3.5430 0.2045 -17.329 <1e-04 ***
I.V.Pine - Bracken == 0 1.4765 0.2045 7.222 <1e-04 ***
Reeds - Bracken == 0 -0.2612 0.2045 -1.277 0.707
V.Pine - Bracken == 0 -1.9190 0.2045 -9.386 <1e-04 ***
I.V.Pine - Heather == 0 5.0195 0.2045 24.551 <1e-04 ***
Reeds - Heather == 0 3.2818 0.2045 16.052 <1e-04 ***
V.Pine - Heather == 0 1.6240 0.2045 7.943 <1e-04 ***
Reeds - I.V.Pine == 0 -1.7377 0.2045 -8.499 <1e-04 ***
58

V.Pine - I.V.Pine == 0 -3.3955 0.2045 -16.608 <1e-04 ***
V.Pine - Reeds == 0 -1.6578 0.2045 -8.109 <1e-04 ***
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
Fit: aov(formula = moisture ~ material, data = pellets)
Quantile = 2.9371
Linear Hypotheses:
Estimate lwr upr
Heather - Bracken == 0 -3.5430 -4.1435 -2.9425
I.V.Pine - Bracken == 0 1.4765 0.8760 2.0770
Reeds - Bracken == 0 -0.2612 -0.8617 0.3393
V.Pine - Bracken == 0 -1.9190 -2.5195 -1.3185
I.V.Pine - Heather == 0 5.0195 4.4190 5.6200
Reeds - Heather == 0 3.2818 2.6813 3.8823
V.Pine - Heather == 0 1.6240 1.0235 2.2245
Reeds - I.V.Pine == 0 -1.7377 -2.3382 -1.1372
V.Pine - I.V.Pine == 0 -3.3955 -3.9960 -2.7950
59

V.Pine - Reeds == 0 -1.6578 -2.2583 -1.0573
"c" "a" "d" "c" "b"
Ash Content
> AnovaModel.2 <- aov(ash ~ material, data=pellets)
material 4 50.75 12.688 321.9 <2e-16 ***
Residuals 25 0.99 0.039
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
> numSummary(pellets$ash , groups=pellets$material, statistics=c("mean", "sd"))
mean sd data:n
Bracken 1.7250000 0.08689074 6
Heather 0.4183333 0.08328665 6
I.V.Pine 0.1166667 0.08382521 6
Reeds 3.5666667 0.41171187 6
V.Pine 0.3050000 0.07791020 6
60

Fit: aov(formula = ash ~ material, data = pellets)
Linear Hypotheses:
Heather - Bracken == 0 -1.3067 0.1146 -11.399 <1e-04 ***
I.V.Pine - Bracken == 0 -1.6083 0.1146 -14.031 <1e-04 ***
Reeds - Bracken == 0 1.8417 0.1146 16.067 <1e-04 ***
V.Pine - Bracken == 0 -1.4200 0.1146 -12.388 <1e-04 ***
I.V.Pine - Heather == 0 -0.3017 0.1146 -2.632 0.0947 .
Reeds - Heather == 0 3.1483 0.1146 27.466 <1e-04 ***
V.Pine - Heather == 0 -0.1133 0.1146 -0.989 0.8579
Reeds - I.V.Pine == 0 3.4500 0.1146 30.098 <1e-04 ***
V.Pine - I.V.Pine == 0 0.1883 0.1146 1.643 0.4853
V.Pine - Reeds == 0 -3.2617 0.1146 -28.455 <1e-04 ***
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
61

Fit: aov(formula = ash ~ material, data = pellets)
Quantile = 2.9369
Linear Hypotheses:
Estimate lwr upr
Heather - Bracken == 0 -1.30667 -1.64331 -0.97002
I.V.Pine - Bracken == 0 -1.60833 -1.94498 -1.27169
Reeds - Bracken == 0 1.84167 1.50502 2.17831
V.Pine - Bracken == 0 -1.42000 -1.75665 -1.08335
I.V.Pine - Heather == 0 -0.30167 -0.63831 0.03498
Reeds - Heather == 0 3.14833 2.81169 3.48498
V.Pine - Heather == 0 -0.11333 -0.44998 0.22331
Reeds - I.V.Pine == 0 3.45000 3.11335 3.78665
V.Pine - I.V.Pine == 0 0.18833 -0.14831 0.52498
V.Pine - Reeds == 0 -3.26167 -3.59831 -2.92502
"b" "a" "a" "c" "a"
Appendix 4
62

Appendix 3 – Figure 1 – Line graph to show the relationship between calorific
value and moisture content
63

Appendix 3 – Figure 2 - Line graph to show the relationship between calorific
value and moisture content
64

Appendix 3 – Figure 3 - Line graph to show the relationship between moisture
value and ash content
65

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