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.

1


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).

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At the end of 2010 there was a capacity to produce 2.5 GW of biomass electricity

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).

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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

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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).

6


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

11


weights. The weight loss was calculated and became the mass of water. The

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.

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The results data were formatted and put into the statistical analysis software ‘R

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

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(one way Anova, n= 6, p= 0.798). Bracken pellets compared to IVP pellets gave

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,

14


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).

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

bracken pellets compared to VP pellets was recorded, which was statistically

18


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. Pine95% CI

[4.00, 2.80]MD = 3.40

<0.001 <0.001 <0.001

Bracken95% CI

[0.88, 2.08]MD = 1.48

95% CI [2.52, 1.32]MD = 1.92

<0.001 NS

Heather95% 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

Reeds95% 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(No Statistical Significance = NS)

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(No Statistical Significance = NS)

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


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

woodTable 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


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

industrially produced counterparts. The VP pellets had a lower calorific content

35


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

Koppejan, 2007).

36


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

example, the moisture content.

37


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.

Whilst bracken, heather and reeds are more malleable, virgin pine is denser and

38


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

counterparts. A recommendation would be to use an industrial pellet machine to

39


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

biomass based pellet fuel to potentially provide the UK with an efficient, clean

40


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 1Bomb Calorimetry method, undertaken by staff at London South Bank 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 2Industrially made virgin pine pellet’s, ‘Koolfuel’, specification.

53


Appendix 3Raw 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