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Energy 50 (2013) 429e437

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Energy

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On-farm storage of baled and pelletized canola (Brassica napus L.) straw:Variations in the combustion related properties

Leticia Chico-Santamarta*, Richard John Godwin, Keith Chaney, David Richard White,Andrea Claire HumphriesHarper Adams University, Edgmond, Newport TF10 8NB, UK

a r t i c l e i n f o

Article history:Received 2 August 2012Received in revised form7 November 2012Accepted 11 November 2012Available online 21 December 2012

Keywords:Canola strawPelletStorageChemical compositionCombustion properties

* Corresponding author. Tel.: þ44 (0)7799387383;E-mail addresses: lchico-santamarta@harper-ada

iagre.biz (L. Chico-Santamarta).

0360-5442/$ e see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.energy.2012.11.026

a b s t r a c t

Brassica napus L. (canola/oilseed rape) straw presents a suitable alternative combustion fuel due to itsavailability, relatively high calorific value and low moisture content. Pelletization enabled the bulkdensity of canola straw to be improved, enhancing its potential as an alternative combustion fuel. Theaim of the paper was to determine the effect of on-farm storage on the gross calorific value, ash content,volatile content and elemental composition of canola straw bales (stored for up to 20 months) and pellets(stored for up to 12 months). Statistically significant changes occurred to the elemental composition ofstraw bales and pellets during on-farm storage, but these changes were not of practical significance interms of the materials suitability as a combustion fuel.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The global harvested area of canola (Brassica napus L.) increasedfrom 258 thousand km2 to 316 thousand km2 between 2000 and2010. This is as a consequence of a global increased demand forcanola oil, which significantly increased from approximately 13million tonnes in 2000 to over 22 million tonnes in 2010. In theUnited Kingdom, the total harvested area increased from 4020 km2

to 6420 km2 during this time [1]. There is not a significant marketfor canola straw with the majority of it being chopped and incor-porated into the soil through ploughing. Canola yields a consider-able volume of straw, but because it breaks down into small pieceswhen it is harvested, it is associated with a relatively low yield of2.5 tonnes per hectare [2]. More pessimistic authors suggesta lower yield of 1.5 tonnes per hectare [3,4]. Based on these figures,and taking 2010 as a reference year, the amount of recoverablecanola straw produced in the UK was between 963 thousandtonnes and 1.6 million tonnes. The gross calorific value (GCV) ofcanola straw is on average 17.4 MJ kg�1 [5], suggesting between4.6 TWh and 7.7 TWh of energy was contained in the canola straw

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produced in the UK in 2010. Furthermore, previous research hassuggested that the use of agri-residues based pellets as a source ofenergy has the potential of reducing greenhouse gases (GHG)emissions by 50%, 250% and 350% compared to wood pellets,natural gas and coal, respectively [6]. As a consequence, it has beensuggested canola straw presents a potential source of biomass forenergy generation [7]. The main disadvantage with straw forcombustion purposes is its relatively lowdensity when baled. Strawtypically has a bulk density ranging from 50 kg m�3 for forageharvested straw to 240 kg m�3 for high density baled straw [8]. Therelative low density of straw makes it more expensive to transportcompared to woodchips (150 kg m�3 to 300 kg m�3), house coal(850 kgm�3) and anthracite (1100 kgm�3). This also means a largerstorage area/volume is required for baled straw compared to othercompressed material (e.g. straw pellets with a bulk density of600 kg m�3 or briquettes with a bulk density of 320 kg m�3).Densification increases the bulk density of biomass [9,10] and asa result, the net calorific content per unit volume is increased [11]and the storage, transport and handling of thematerial is easier andcheaper [11e13].

The use of canola straw as a fuel could involve the storage of thebiomass for variable periods of time, for example if year-round fuelsupply is required. One of the main advantages of using canolastraw is that it is associated with a low moisture content (typicallybelow than 16%) that means the material does not need to be dried

Table 1a) Description of canola straw storage periods and b) description of the canola strawpellets storage periods.

a) Storage Length of storage of canolastraw bales (months)

Year ofharvest

B3 2008 3 2008B4 2008 4 2008B7 2008 7 2008B10 2008 10 2008B20 2008 20 2008B0 2009 0 2009B1 2009 1 2009B3 2009 3 2009B7 2009 7 2009

b) Pelletsample

Length of storage of canolastraw bale beforepelletization (months)

Length of storage ofcanola pelletsafter pelletization (weeks)

B3 2008 2 3 2B3 2008 4 3 4B3 2008 12 3 12B3 2008 24 3 24B3 2008 48 3 48B7 2008 2 7 2B7 2008 4 7 4B7 2008 12 7 12B7 2008 24 7 24B10 2008 2 10 2B10 2008 4 10 4B10 2008 12 10 12B10 2008 24 10 24B3 2009 2 3 2B3 2009 4 3 4B3 2009 12 3 12B3 2009 24 3 24

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437430

before it can be used as a combustion fuel or for the production ofpellets [14]. Drying of biomass is considered a long process and it isassociated with large storage areas of material and high transportand storage costs [15].

However, research has shown that the storage of biomass canalter the properties of the material. Variations in the carbon andhydrogen content were found during the storage of logging resi-dues [16] as well as a decrease in the calorific value as a conse-quence of a carbon increase during the storage of pine woodchips[17]. Furthermore, the properties of the unprocessed raw material(i.e. canola straw bales) can be significantly different from those ofpelletised biomass, which can consequently result in differences inthe physical, chemical and biological characteristics of the biofuel[18]. Pellets have been shown to have higher ash content andlower heating value than the raw materials used to produce thepellets [18]. Thus, it is important to understand the effects ofstorage on the properties of canola straw if it is to be used forcombustion.

To date no research has been conducted that investigates (i) theeffect of on-farm storage of canola straw bales and pellets on theproperties of the material that are relevant to its use as a combus-tion fuel or (ii) the effect of storage of canola straw bales prior topelletisation on the properties of the pelletised straw.

The aim of this paper was to determine the effect of on-farmstorage on the physical and chemical properties of canola strawbales (stored for up to 20 months) and pellets (stored for up to 12months). The effect of storage time on the fuel’s gross calorific value(GCV), ash content, volatile content and chemical analysis wasstudied. The moisture content, ambient temperature and theinternal temperature of the bales were monitored and presented inprevious work [14] and related to the properties presented in thecurrent paper. Possible relationships between the variations in thebaled straw properties and those of the resultant pellets were alsoexamined.

2. Materials and methods

2.1. Canola straw, pellets and storage conditions

Canola straw bales and pellets were supplied and/or producedas described previously [14]. Bales of canola straw, harvested in2008 and 2009, were stored under cover in a shed (with roof andthree open sides) at Harper Adams University (HAU) Farm atambient temperature and for varying lengths of time, as shown inTable 1a. At each storage period, samples were taken from threebales in triplicate. Samples were taken from the centre and twoouter points within the bale [14], and analysed for GCV, ashcontent, volatile content and elemental composition. Canola strawpellets were stored as 10.0 kg � 0.5 kg lots in plastic airtight zipbags (305 mm � 405 mm) (Harrison Packaging, Lancashire, UK) inan enclosed shed at HAU for varying lengths of time, as shown inTable 1b. Samples were taken from three bags of canola strawpellets and analysed in triplicate for GCV, ash content, volatilecontent, and elemental composition.

Calcium lignosulfonate (Borregard-Lignotech, Sarpsborg,Norway) was added to milled straw prior to pelletisation ata concentration of 5% (w/w) as a lubricant/binder. The compositionof the binder was analysed by TES Bretby Laboratory (Burton-upon-Trent, UK) and is shown in Table 2.

2.2. Elemental composition

Samples from canola straw bales and pellets were milled to1 mm and analysed to determine the content of carbon (C), sulphur(S), nitrogen (N), hydrogen (H), oxygen (O), sodium (Na),

magnesium (Mg), aluminium (Al), phosphorus (P), chlorine (Cl),potassium (K), calcium (Ca) and iron (Fe).

The content of C and S (% weight d.b.) were determined usinga LECO automatic analyzer (LECO SC-144 DR, LECO Corp., St. Joseph,USA); Hydrogen content (% weight d.b.) was determined by TESBretby Laboratory (Burton-upon-Trent, UK) using an ExeterAnalytical CE 440 Analyzer. Samples of H were analysed once (andnot in triplicate). The oxygen content was calculated by subtractingfrom 100% the sum of (C, H, N, S and ash) contents in percentage.Hydrogen and oxygen concentrations were used as indicativevalues to ease the discussion.

The total N (% weight d.b.) of straw and pellets was determinedusing a LECO automatic analyzer (LECO FP-528, LECO Corp., St.Joseph, USA). The concentrations of the remaining elements (i.e. Na,Mg, Al, P, Cl, K, Ca and Fe) were determined using a DigiPREPdigestion system (Qmx Laboratories, Thaxted, Essex, UK).0.25 g � 0.02 g of dried and milled sample was weighed witha Precisa XT220A balance (Precisa Instruments Ltd, Dietikon,Switzerland) in a DigiTUBE (Qmx Laboratories, Thaxted, Essex, UK)and 7.5mL of HNO3 (69%; BDH Laboratory Supplies, Dorset, UK)wasadded to each tube. The tubes were placed in the DigiPREP andheated in three steps:

� From ambient temperature to 40 �C (Ramp over 40 min andhold for 30 min).

� From 40 �C to 65 �C (Ramp over 35 min and hold for 5 min).� From 65 �C to 95 �C (Ramp over 15 min and hold for 60 min).

The samples were diluted to 50 mL with puerile water in thecalibrated DigiPREP tube. Calibration graphs were produced for theelements Na, Mg, Al, P, Cl, K, Ca and Fe (Romil Ltd, Cambridge, UK)by analysing ‘calibration elements’ diluted to four concentrations.All standards and samples include 10 mg kg�1 of Ga, Rh and Ir as

Table 2Calcium lignosulfonate composition.

Moisture content (%) Ash (%) Sulphur (%) GCV (kJ kg�1) Carbon (%) Hydrogen (%) Nitrogen (%)

51.3 8 3.1 9050 24.0 2.4 0.2Elemental composition (%m/m)Antimony Arsenic Cadmium Chromium Cobalt Copper Lead<0.5 <0.5 0.5 4.8 0.6 230.0 9.8Manganese Mercury Molybdenum Nickel Thallium Tin Vanadium1118.0 <0.1 0.5 14.6 <0.1 0.7 2.1Zinc Chlorine206.8 364.0Elemental oxide (%m/m)SiO2 Al2O3 Fe2O3 TiO2 CaO MgO Na2O0.5 0.3 0.3 < 0.1 46.0 1.0 7.5K2O Mn3O4 P2O5 SO3

0.9 0.3 0.1 45.4

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437 431

internal standards. Samples were analysed using InductivelyCoupled Plasma Mass Spectrometry (ICP-MS; Thermo FisherScientific Inc, Hemel Hempstead, UK) to determine the level of Na,Mg, Al, P, Cl, K, Ca and Fe in the straw and pellets.

2.3. Gross calorific value

The GCV at constant volume on a dry basis was determinedaccording to CEN 14918 [19]. A 0.50 g � 0.02 g sample of driedmilled straw and pellet sample was weighed with a Precisa XT220Abalance and burnt in the presence of high-pressure oxygen in a Parrbomb calorimeter (Parr Instrument Company, Moline, Illinois,U.S.A.). There were three replications for each sample.

2.4. Ash content

The ash content of samples was determined according to CEN14775 [20]. 1.0 g � 0.1 g of oven-dried sample was heated ina furnace (Gallenkamp muffle furnace, size 3, GAFSE 620, Galle-kamp, Loughborough, UK) to 550�C � 10 �C for 60 min. There werethree replications for each sample.

2.5. Volatile content

The volatile content of biomass was measured according to thestandard CEN 15148 [21]. 1.0 g � 0.1 g of milled straw or pelletsample was burnt in a Gallenkamp muffle furnace (size 3, GAFSE620, Gallekamp, Loughborough, UK). The furnace temperature wasmaintained at 900�C � 10 �C for 7 min. Samples were analysed intriplicate.

2.6. Statistical analysis

Statistical analysis was completed using GenStat Release 13.1[22]. Three different statistical analyses were carried out for thecanola straw:

(i) For the straw harvested in 2008, a 2 � 5 analysis of variance(ANOVA) was completed with a level of probability of 5%(P < 0.05) to identify the possible effect of canola straw balestorage time and bale sample point (i.e. inner and outerpoints) on the GCV, ash content, volatile content andelemental composition of the straw. Thus, the two factors usedin the factorial experiment were: (a) storage of the strawwhich is defined by the experimental treatments 1, 3, 4, 7, 10and 20 months and (b) the point within the bale with insideand outside as experimental treatments.

(ii) For the straw harvested in 2009, a 2 � 3 ANOVA was used forthe same purpose as described in (i) above. However, thefactor storage of the straw was defined for the experimentaltreatments 1, 3 and 7 months.

(iii) A simple linear regression with groups where the responsevariables were GCV, ash content, volatile content andelemental composition. Two explanatory variables weredescribed, the variate which was the storage period and thefactor, which was the year. Thus, the difference between years2008 and 2009 was estimated to determine if the relationshipbetween the response variables and the storage period wasdifferent in the two years. The results were analysed based onthe P values.

In the case of canola straw pellets, two different ANOVA analyseswere completed:

(i) The effect of canola straw pellet storage time and bale storagetime prior to pelletization on GCV, ash content, volatilecontent and elemental composition was conducted witha 3 � 5 ANOVA analysis. The ‘pellet storage’ factor had fiveexperimental treatments: 2, 4, 12, 24 and 48 weeks. The factor‘bale storage time prior pelletization’ had three experimentaltreatments: 3, 7 and 10 months.

(ii) The effect that the year of harvest of the canola straw couldproduce in the pellets was analysed with a 2 � 4 factorialanalysis. The factor year is defined by the experimentaltreatments year 2008 and year 2009, while the factor pelletstorage was defined by the experimental treatments 2, 4, 12and 24 weeks.

3. Results and discussion

3.1. Elemental composition

The variation in the elemental composition (i.e. carbon,hydrogen, oxygen, nitrogen, sulphur, chlorine, sodium, magnesium,aluminium, phosphorous, potassium, calcium and iron) of canolastraw bales with the storage is shown in Table 3. The elementalcomposition of canola straw pellets stored for different periods andproduced from straw harvested in different years and stored fordifferent periods is shown in Tables 4 and 5. Table 6 shows thestatistical significance of (i) bale storage time, the sample positionand the year of harvest on the elemental composition of canolastraw and (ii) the pellet storage time, bale storage time and year ofharvest on the elemental composition of canola straw pellet.

The elemental composition of baled canola straw harvested in2008 and 2009 did not vary significantly with the point fromwhich

Table 3Elemental composition of canola straw harvested in 2008 and 2009, and stored for varying lengths of time.

Storage period B3 2008 B4 2008 B7 2008 B10 2008 B20 2008 B0 2009 B1 2009 B3 2009 B7 2009

C % dry fuel 43.858 42.740 43.078 43.570 44.545 43.878 44.251 43.991 44.247s.e. 0.094 0.054 0.065 0.047 0.142 0.093 0.253 0.569 0.159

H % dry fuel 5.05 4.94 5.19 4.79 5.04 5.00 4.99 4.98 4.83N % dry fuel 0.845 0.937 0.911 0.848 0.719 0.490 0.726 0.707 0.646

s.e. 0.011 0.025 0.013 0.007 0.026 0.016 0.014 0.022 0.023S % dry fuel 0.162 0.190 0.193 0.178 0.236 0.408 0.334 0.353 0.286

s.e. 0.004 0.008 0.007 0.004 0.027 0.014 0.014 0.013 0.020O % dry fuel 45.411 41.171 44.934 45.769 44.219 44.998 44.101 44.598 44.475Cl % dry fuel 0.162 0.251 0.110 0.122 0.093 0.154 0.339 0.224 0.173

s.e. 0.009 0.013 0.010 0.004 0.009 0.013 0.016 0.023 0.015Na mg kg�1 dry fuel 1008.393 500.022 514.089 454.074 927.618 584.589 1740.911 1175.606 1076.128

s.e. 79.623 34.910 52.444 51.056 141.888 47.224 246.695 113.603 106.750Mg mg kg�1 dry fuel 578.330 670.170 689.400 503.489 697.018 455.422 775.667 676.900 659.500

s.e. 17.291 33.560 37.147 16.976 41.648 9.968 17.623 39.815 47.777Al mg kg�1 dry fuel 9.696 40.311 52.053 49.481 20.790 7.680 17.359 31.852 12.778

s.e. 0.687 8.244 6.790 6.517 3.600 0.635 4.373 7.112 1.585P mg kg�1 dry fuel 285.281 346.004 352.648 255.600 293.600 172.589 197.878 171.206 199.733

s.e. 10.385 23.004 23.218 7.791 22.011 7.271 6.123 10.072 16.956K mg kg�1 dry fuel 8075.741 9315.000 9495.481 7308.074 7380.765 10916.556 10864.389 11079.722 9783.889

s.e. 142.953 344.301 739.222 350.748 352.716 239.015 373.976 383.335 436.157Ca mg kg�1 dry fuel 11081.074 12750.000 12347.074 12393.333 12048.941 13397.222 12578.889 13162.222 12043.389

s.e. 187.466 283.828 231.423 167.515 325.687 410.771 365.848 289.103 376.997Fe mg kg�1 dry fuel 34.249 76.091 68.036 62.415 28.574 25.619 28.589 32.174 22.971

s.e. 1.259 11.764 7.441 7.593 2.588 0.793 1.886 2.882 1.457

Nomenclature: B’X0 2008 refers to raw material stored for ‘X’ months in 2008; B’X0 2009 refers to raw material stored for ‘X’ months in 2009; s.e.: standard error.

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437432

samples were taken suggesting the elemental composition ofcanola straw was uniform throughout the bale, with the exceptionof S (%) in 2009. Whilst there was a statistically significant variationin the S content of straw sampled from the inner and outer points ofstraw bales, this variance was not considered of practical signifi-cance. In all instances the S content of straw bales was aboveconcentrations that are expected to result in operational issuesduring combustion. Concentrations of S higher than 0.1% arebelieved to cause corrosion and those higher than 0.2% can causeproblems of SOx emissions [23]. However, no problems were foundin the combustion of canola straw pellets regarding SO2 emissions[24] or ash deposition [25].

The carbon content (C) (%) of a fuel is important because itpositively affects the heating value of the material [9]. Whilstthere was a statistical variation in the C (%) with the year of

Table 4Effect of storage on the carbon (C), nitrogen (N), sulphur (S), chlorine (Cl), sodium (Na) a

C H N S O

% dry fuel s.e. % dry fuel % dry fuel s.e. % dry fuel s.e. % d

B3 2008 P2 42.636 0.085 e 0.654 0.012 0.416 0.009 e

B3 2008 P4 42.618 0.926 4.82 0.650 0.009 0.432 0.008 43B3 2008 P12 43.312 0.179 4.95 0.660 0.015 0.429 0.002 42B3 2008 P24 42.275 0.110 4.91 0.728 0.023 0.433 0.006 43B3 2008 P48 44.039 0.065 4.81 0.647 0.004 0.488 0.004 40B7 2008 P2 42.611 0.582 e 0.749 0.034 0.494 0.005 e

B7 2008 P4 43.088 0.248 4.91 0.696 0.013 0.495 0.007 43B7 2008 P12 43.774 0.114 5.11 0.670 0.019 0.488 0.002 43B7 2008 P24 44.585 0.161 5.54 0.745 0.009 0.520 0.001 40B7 2008 P48 47.309 0.208 4.97 0.749 0.009 0.533 0.009 38B10 2008 P2 43.356 0.122 e 0.674 0.009 0.372 0.003 e

B10 2008 P4 42.719 0.594 4.95 0.704 0.009 0.432 0.008 43B10 2008 P12 43.648 0.363 5.52 0.847 0.026 0.380 0.008 41B10 2008 P24 43.977 0.056 4.49 0.840 0.010 0.452 0.014 42B10 2008 P48 44.339 0.309 4.66 0.768 0.008 0.444 0.016 43B3 2009 P2 43.023 0.127 e 0.615 0.016 0.631 0.008 e

B3 2009 P4 43.828 0.062 4.52 0.652 0.005 0.640 0.013 41B3 2009 P12 45.903 0.227 4.66 0.605 0.006 0.637 0.006 38B3 2009 P24 45.843 0.156 4.64 0.663 0.014 0.636 0.006 41

Nomenclature: B ‘X’ 2008 ‘Y’ refers to pellets stored for ‘Y’weeks and produced with strawproduced with straw stored for ‘X’ months in 2009.

harvest (i.e. 2008 and 2009) and length of storage, this is notconsidered important from a practical point of view because thevariations were minimal and the GCV did not vary greatly withthe carbon content. For example, there was a significant increasein the C (%) content from 42.07% � 0.05% after 4 months storageto 44.54% � 0.14% after 20 months storage. This result is inagreement with Nurmi [16] who found a significant increase inthe C (%) during 10 months storage of hammermilled loggingresidue. An equation was developed to calculate the GCV basedon the C, H, S, O, N and ash content of biomass [26]. The equationassumes the GCV of a fuel is directly related to the carboncontent. In the current study, the GCV decreased slightly witha slight increase in carbon content. There was no clear evidencethat the variations in the C (%) affected the GCV (MJ kg�1) of thecanola straw.

nd magnesium (Mg) content of canola straw pellets.

Cl Na Mg

ry fuel % dry fuel s.e. mg kg�1 dry fuel s.e. mg kg�1 dry fuel s.e.

0.090 0.003 1234.111 7.268 1814.556 56.751.19 0.099 0.020 1183.333 15.849 1639.333 83.576.19 0.250 0.013 1339.000 31.625 1981.333 109.141.70 0.221 0.017 1286.333 11.688 1675.667 75.970.37 0.138 0.017 1350.666 8.575 2103.667 102.863

0.117 0.003 1202.778 20.472 990.967 18.186.32 0.105 0.004 1264.500 26.455 977.275 25.814.08 0.086 0.001 1049.666 5.530 736.544 8.549.99 0.093 0.002 1117.222 7.352 805.967 6.348.84 0.094 0.002 1168.556 9.932 902.467 12.207

0.075 0.006 713.933 55.441 568.889 45.04.29 0.090 0.003 1039.167 10.994 739.980 14.455.57 0.095 0.004 886.167 21.464 662.156 20.879.76 0.123 0.011 981.744 38.143 683.587 21.998.03 0.096 0.004 942.333 29.729 683.100 19.073

0.139 0.003 1707.111 6.257 1021.111 5.961.07 0.134 0.003 1796.889 6.270 1084.556 4.779.44 0.138 0.006 2013.111 14.362 1220.889 8.806.46 0.137 0.006 1875.000 23.614 1207.250 21.477

stored for ‘X’months in 2008. B ‘X’ 2009 ‘Y’ refers to pellets stored for ‘Y’weeks and

Table 5Effect of storage on the aluminium (Al), phosphorous (P), potassium (K), calcium (Ca) and iron (Fe) content of canola straw pellets.

Al P K Ca Fe

mg kg�1 dry fuel s.e. mg kg�1 dry fuel s.e. mg kg�1 dry fuel s.e. mg kg�1 dry fuel s.e. mg kg�1 dry fuel s.e.

B3 2008 P2 404.711 11.712 300.989 1.684 8593.444 54.516 16126.667 99.958 532.878 6.040B3 2008 P4 300.322 7.847 303.844 3.790 8424.556 118.639 15718.889 251.078 496.722 20.682B3 2008 P12 462.844 12.815 328.233 6.747 9452.444 234.344 17824.444 438.426 628.022 19.878B3 2008 P24 401.956 5.408 308.656 5.683 8811.111 65.581 16875.556 125.179 537.922 6.517B3 2008 P48 482.711 4.561 300.044 1.698 9787.222 68.402 18223.333 138.082 636.100 6.402B7 2008 P2 354.767 8.894 353.489 2.697 8721.778 139.225 15874.444 255.979 417.889 11.061B7 2008 P4 316.112 15.546 364.338 9.076 8825.750 1916.645 16022.500 342.229 389.087 8.364B7 2008 P12 228.189 3.304 338.944 1.300 6624.778 34.515 134866.667 73.786 346.711 4.717B7 2008 P24 265.356 2.571 363.656 1.605 73805.556 52.766 14155.556 88.977 3509.667 1.376B7 2008 P48 336.178 4.568 366.344 14.869 78438.889 68.159 16100.000 106.314 441.033 6.935B10 2008 P2 151.503 12.273 305.633 24.215 8285.778 646.450 13327.444 1055.408 281.932 41.527B10 2008 P4 280.470 17.350 350.700 3.926 10058.200. 112.378 16709.000 214.219 507.220 31.593B10 2008 P12 132.211 5.767 349.000 9.583 10892.222 249.882 15744.444 388.047 266.311 13.264B10 2008 P24 158.137 4.761 375.112 16.571 10883.000 356.241 16947.500 455.740 300.887 7.211B10 2008 P48 149.289 6.489 350.533 8.118 10692.667 257.094 17175.556 328.054 304.256 4.917B3 2009 P2 389.100 4.019 306.478 3.162 13658.889 85.593 18228.889 73.285 582.889 8.466B3 2009 P4 434.611 9.683 332.689 5.524 14725.556 224.321 19016.667 47.929 653.389 24.954B3 2009 P12 468.044 4.159 360.544 4.367 17581.111 121.455 20838.889 125.060 698.589 6.795B3 2009 P24 463.462 3.804 360.962 4.880 15962.500 306.671 20250.000 191.759 696.025 8.118

Nomenclature: B ‘X’ 2008 ‘Y’ refers to pellets stored for ‘Y’weeks and produced with straw stored for ‘X’months in 2008. B ‘X’ 2009 ‘Y’ refers to pellets stored for ‘Y’weeks andproduced with straw stored for ‘X’ months in 2009.

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437 433

In contrast to the current study, a decrease in the C (%) wasfound by other researchers when woodchips were stored for up to12 months [17]. They attributed these changes to an increase in theO content, indicating the biomass underwent oxidation or degra-dation during storage. However, in the present work the O contentof canola straw bales did not vary greatly, and no trend wasobserved in the O content during storage. Furthermore, the currentstudy found no relationships occurred during the storage of canolastraw bales between the C (%), H (%), O (%) or GCV (MJ kg�1).

The C (%) of the canola straw pellets was affected by the strawused to produce them. The general tendency was the C (%) in thepellets was approximately 1% lower than in the straw used toproduce them. Although there is no clear evidence to explain whythe C (%) was slightly lower in the pellets compared with the strawused to produce them, the results do demonstrate that the additionof calcium lignosulfonate as a binder did not increase the C content(%) of the pellets. The C (%) in canola straw pellets was also affectedby the length of storage and the year of harvest of the straw.However, the variations in the C (%) of the pellets with storagewere

Table 6Statistical significance of the effect of storage on the elemental composition of canola st

Biomass Canola straw

Stats analysis 2 � 5 ANOVA 2 � 3 ANOVA

Year 2008 2009

Element Factorb

Storage Sample position

SignificanceCarbon (%) S(P < 0.001) N.S. S(P ¼ 0.792) N.S.Nitrogen (%) S(P < 0.001) N.S. S(P ¼ 0.012) N.S.Sulphur (%) S(P ¼ 0.002) N.S. S(P ¼ 0.012) S(P ¼ 0.0Chlorine (mg kg�1) S(P < 0.001) N.S. S(P < 0.001) N.S.Sodium (mg kg�1) S(P < 0.001) N.S. S(P ¼ 0.007) N.S.Magnesium (mg kg�1) S(P < 0.001) N.S. N.S. N.S.Aluminium (mg kg�1) S(P < 0.001) N.S. S(P ¼ 0.005) N.S.Phosphorous (mg kg�1) S(P < 0.001) N.S. P ¼ 0.084 N.S.Potassium (mg kg�1) S(P < 0.001) N.S. S(P ¼ 0.023) N.S.Calcium (mg kg�1) S(P < 0.001) N.S. S(P ¼ 0.028) N.S.Iron (mg kg�1) S(P < 0.001) N.S. S(P ¼ 0.002) N.S.

a The significance of the factor pellet storage is not presented, as the results agree witb The significance of the interaction between factors is not presented here.

minimal (See Table 4) and the variations between years were due tothe C (%) of the canola straw used to produce the pellets (Table 3).

The hydrogen content (H) (%) did not seem to follow anyparticular trend for straw bales harvested in 2008 and showeda decrease during storage in 2009. Previous research showed thatthe hydrogen content of logging residues decreased during storageand was likely to be caused by a loss of volatile matter [16]. Norelationship between the variations of volatile content andhydrogen were found in the present work.

The nitrogen content (N) (%) of canola straw bales (%) wasslightly higher in straw harvested in 2008 compared to 2009.Although, the farm practice was the same in both years, a seasonalvariation in the uptake of nitrogen by the crop can be expected. TheN (%) of canola straw bales harvested in 2008 and 2009 variedsignificantly during storage. The N (%) of canola straw was lowestwhen it was taken directly from the swath (i.e. 0.49% � 0.02%).There was no evidence to explain why the N (%) was higher oncethe straw was baled. Similar result was found previously in thespruce needles of logging residue [16]. A nitrogen content of

raw bales and pellets.

Canola straw pellets

Regression 3 � 5 ANOVA 2 � 4 ANOVAa

2008

Storage Sample position Year

S(P < 0.001) S(P < 0.001) S(P < 0.001) S(P < 0.001)S(P < 0.001) S(P < 0.001) S(P < 0.001) S(P < 0.001)

32) S(P < 0.001) S(P < 0.001) S(P < 0.001) S(P < 0.001)N.S. S(P < 0.001) S(P < 0.001) S(P < 0.001)N.S. S(P < 0.001) S(P < 0.001) S(P < 0.001)N.S. S(P < 0.001) S(P < 0.001) S(P < 0.001)N.S. S(P < 0.001) S(P < 0.001) S(P < 0.001)S(P < 0.001) S(P < 0.001) S(P < 0.001) S(P < 0.001)S(P < 0.001) S(P < 0.001) S(P < 0.001) S(P < 0.001)N.S. S(P < 0.001) S(P < 0.001) S(P < 0.001)S(P ¼ 0.002) S(P < 0.001) S(P < 0.001) S(P < 0.001)

h the 3 � 5 ANOVA presented.

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437434

9.8mg g�1 wasmeasured in the live trees, whilst a nitrogen contentof 11.65 mg g�1 was measured after 9 months storage of theresidue. No clear explanation of this fact was given [16].

The N (%) of canola straw pellets was significantly affected by thestraw used to produce the pellets, the year that the straw washarvested and the storage period which is similar to the trendobserved for the C (%). The N (%) of the pellets was lower than thatof the straw used to produce the pellets suggesting the addition ofcalcium lignosulfonate (i.e. 0.2%) did not increase the N (%) of thepellets.

The N (%) of canola straw pellets was significantly different inthe pellets produced with the straw harvested in 2008 and 2009.This was due to differences in the N (%) of the straw harvested in2008 and 2009 that was used to produce the pellets. The variationsin N (%) during storage were minimal for the pellets produced withcanola straw harvested in 2008 and stored for 3 and 7months priorto pelletisation and with canola straw harvested in 2009 and storedfor 3 months prior to pelletisation. However, the N (%) in the pelletsincreased during storage for the pellets produced with straw har-vested in 2008 and stored for 10 months prior to pelletisation. TheN content (N) (%) of a combustion fuel is important because of NOx

emissions. It is recommended that values of N should be less than0.6 wt % (d.b.) to reduce these emissions [27]. Whilst the N (%)was lower in pellets of canola straw than in bales, the contentremained higher than 0.6%, suggesting NOx emissions duringcombustion may be problematic. However, no problems werefound in the combustion of canola straw pellets regarding NO orNO2 emissions [24].

The content of S (%) in canola straw bales harvested in 2008increased significantly during storage. However, these variationsdid not follow a continuous incremental trend over the period ofstorage.

The S (%) of the canola straw pellets was affected by the strawused to produce the pellets, the storage period and the year ofharvest. However, no trends were found in the S (%) duringstorage. In 2008, the canola straw had a lower S (%) than in 2009,resulting in a lower S (%) content in the pellets produced from thisstraw. The S (%) of canola straw pellets was significantly higher(P < 0.001) than the S (%) of the canola straw used to produce thepellets. The highly significant increase in S (%) in the pellets can beattributed partly to the addition of lignosulfonate at a concentra-tion by weight of 5%, which mathematically would give a 0.15%increment in the S (%). However, the increment of S (%) was higherthan this mathematical value in all cases, except for the pelletsthat were stored for 2 weeks and produced from canola strawbales harvested in 2008 and stored for 10 months prior to pel-letisation. This may be due to an uneven distribution of binderwithin the pellets, or due to the inaccurate application of binder tothe milled straw prior to pelletisation. These levels of sulphurcould be a potential problem, as together with Cl, high Sconcentrations in the canola straw could result in corrosion andSOx emissions.

The content of Cl (%), in the canola straw fluctuated significantlyduring storage, but it did not follow any particular trend. It is notedthe Cl (%) was lower in the swath than once it was baled and the Cl(%) continued to decrease during storage.

The straw, the length of storage and the year of harvest affectedthe Cl (%) in the pellets. The variations during the storage of thepellets did not follow any clear trends, so they might be attributedto natural variations. The Cl (%) in the canola straw pellets is ofimportance because it could cause corrosion and HCl emissionproblems during combustion because the concentration of Cl in thefuel is above 0.1 wt % (d.b.) [27]. However, no problems were foundin the combustion of canola straw pellets regarding HCl emissions[24] or ash deposition [25].

The storage of canola straw bales had a significant effect on therest of the elemental composition, [Na (mg kg�1), Mg (mg kg�1), Al(mg kg�1), P (mg kg�1), K (%), Ca (%) and Fe (mg kg�1)] in 2008 and2009, except for the Mg in 2009 and the P in 2008. There was noclear tendency in the variation of any of these elements withstorage (i.e. an increase or a decrease in the concentrations withstorage), except for the concentration of Na in the straw harvestedin 2009, which decreased from 1740.91 mg kg�1 � 246.69 mg kg�1

to 1076.13 mg kg�1 � 106.75 mg kg�1. There was no evidence thatany contamination from the farm environment affected the bales,as no differences were found between the inside and outside pointsof the bales, suggesting the changes during storage were caused bynatural variation. It has been demonstrated previously thatalthough elemental variations during the storage of spruce needleswere statistically significant, they were considered only unimpor-tant minor changes in the concentration [16].

The content of Na, Mg and Al were significantly lower in theswath and the values increased after baling for straw harvested in2009.

It was noticeable that for some of the elements, such as Mg, Al,Ca or Fe, the concentration was higher in the pellets than in thebaled straw, which can be explained by the addition of the binder.

The fluctuations of the elemental composition in the canolastraw pellets did not follow any particular trend, as was the casewith the canola straw bales, and the small changes are believed tobe caused by natural variations. Also, the variability of the elementsin the canola straw bales was much higher (as shown in the stan-dard error) than for the pellets, suggesting that the pellets are moreuniform than the straw.

3.2. Gross calorific value

The variations in the Gross Calorific Value (GCV) of canola strawbales and pellets during storage are shown in Fig. 1. The pointwithin the bale fromwhich straw samples were taken (i.e. inner orouter points) did not significantly affect the GCV of straw harvestedin 2008 and 2009 (P ¼ 0.822 and P ¼ 0.234, for 2008 and 2009respectively). Linear regression suggested the GCV (MJ kg�1) ofcanola straw bales did not change significantly with the year ofharvest (P¼ 0.162) suggesting that the GCVwas uniformwithin thebale and harvest season.

The GCV of canola straw bales varied significantly during storagefrom straw harvested in 2008 (P < 0.001), but did not changesignificantly in 2009 (P ¼ 0.85), suggesting that the GCV of canolastrawwas uniform during storage in 2009. Although the GCV variedsignificantly during storage in 2008, it is not considered importantfrom a practical point of view because the variation was relativelysmall; the GCV ranged between 16.91 MJ kg�1 � 0.06 MJ kg�1 and17.89 MJ kg�1 � 0.06 MJ kg�1after 7 months storage. The variationsdid not follow any particular trend. A slight decrease in the GCV ofwillow chips during storage was found in previous research, butthese were considered marginal [28]. Similarly, other authors [17]found a decrease in the lower heating value. However, the varia-tions were attributed to the changes in C during storage. In theresults presented here, the changes in the GCV did not follow anytrend with the chemical composition as discussed in Section 3.1.Thus, the changes in the GCV of the canola straw were attributed tonatural variations within the straw bales.

The GCV of canola straw pellets was significantly affected by thestraw used to produce the pellets (P ¼ 0.01) and the length ofstorage (P < 0.001). The year of harvest of the canola straw hada significant effect on the GCV of the canola straw pellets(P< 0.001) (Fig.1c). The GCV of the canola straw pellets was slightlyhigher than that of the straw, contrary to the results found byLehtikangas [18]. Lehtikangas suggested the reduction in the CV in

Fig. 1. Effect of storage time on the GCV (MJ kg�1) of (a) baled canola straw from 2008(-) and 2009 (,) harvest, (b) canola straw pellets produced from straw harvested in2008 and stored for 3 months (-), 7 months ( ) and 10 months (,) and (c) canolastraw pellets produced from canola straw harvested in 2008 (,) and 2009 (-) andstored for 3 months prior to pelletization. Error bars are � SEM.

Fig. 2. Effect of storage time on the ash content (% w.b.) of (a) baled canola straw from2008 (-) and 2009 (,) harvest, (b) canola straw pellets produced from straw har-vested in 2008 and stored for 3 months (-), 7 months ( ) and 10 months (,) and (c)canola straw pellets produced from canola straw harvested in 2008 (,) and 2009 (-)and stored for three months prior to pelletization. Error bars are � SEM.

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437 435

the pellets was due to the loss of volatile extractive compoundsduring drying [18]. However, no drying was required in the canolastraw. This fact, together with the addition of the binder may be thereason for a higher GCV in the pellets.

3.3. Ash content

The point within the bale fromwhich straw samples were taken(i.e. inner or outer points) did not significantly affect the ashcontent of straw harvested in 2008 (P ¼ 0.995) or 2009 (P ¼ 0.55).Simple linear regression analysis suggested the ash content (%) didnot change significantly with year of harvest (P ¼ 0.864), demon-strating the uniformity of the canola straw bales because therewere no significant variations in the ash content within the baleand harvest season.

The ash content of canola straw bales harvested in 2008 and2009 varied significantly with the length of storage (P < 0.001 and

P¼ 0.003 for 2008 and 2009, respectively). The variations in the ashcontent did not seem to follow any particular trend and no rela-tionship between the volatile and ash content was found. The ashvariations during storage were attributed to natural variations [29].Previous research has shown the ash content of willow chips storedin piles marginally increased with storage but the changes wereconsidered not to be significant [28]. Significant changes in the ashcomposition with the storage were found by [17], and it waspostulated these changes were due to the exposure of the wood-chip pile to the weather conditions (e.g. rain). Rain water may havedissolved soluble compounds (e.g. soluble salts) [30,31]. The ashcontent of switchgrass bales increased during 26 weeks outside,

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437436

unprotected storage [32]. However, it was found that it could bea systematic error in the determination of the ash content [32]. Inthe current study canola straw bales were stored under cover (i.e.protected from rain water). Variations in the ash content duringstorage of the canola straw bales are considered to be due to naturalvariations.

The ash content of canola straw pellets was significantly affectedby the straw used to produce the pellets (P < 0.001) and the lengthof storage (P < 0.001) (Fig. 2b). The year of harvest of the canolastraw had a significant effect on the ash content of the canola strawpellets (P < 0.001) (Fig. 2c). The ash content of the pellets wassignificantly higher than the ash content of the straw, which wasalso found by other researcher [18] who attributed this incrementto the thermal treatment in the process that could have caused

Fig. 3. Effect of storage time on the volatile content (% w.b.) of (a) baled canola strawfrom 2008 (-) and 2009 (,) harvest, (b) canola straw pellets produced from strawharvested in 2008 and stored for 3 months (-), 7 months ( ) and 10 months (,) and(c) canola straw pellets produced from canola straw harvested in 2008 (,) and 2009(-) and stored for three months prior to pelletization. Error bars are � SEM.

a reduction in the extractives, leading indirectly to an increase inash content of the material. Also, in the present work, the increasein the ash content could be due to the addition of binder.

The ash content of canola straw pellets ranged from6.74� 0.08%to 9.75 � 0.03% overall. The ash content of a fuel is importantbecause high ash content could affect the carbon monoxide (CO)emissions and efficiency requirements when the pellets are burnt.Previous research, has shown that the combustion of pelletisedherbaceous (i.e. Brassica) pellets resulted in CO emissions andefficiency requirements that were within the European require-ments. However, the CO emissions and efficiency of Brassica pelletswere worse than for poplar pellets, which was attributed to thehigher ash content of the Brassica (10.7%) compared to poplar [33]).Further work could be completed to investigate how the ashcontent of canola straw pellets could be reduced. Previous researchhas shown the ash content of grape pomace was as significantlyreduced when it was mixed with Pyrenean oak pellets [34].

3.4. Volatile content

The point within the bale fromwhich straw samples were taken(i.e. inner or outer points) did not significantly affect the volatilecontent of straw harvested in 2008 (P ¼ 0.535) or in 2009(P ¼ 0.462) and did not change significantly with the year(P ¼ 0.729) according to the simple linear regression analysis. Thissuggests the canola straw bales were uniform, as mentioned forprevious properties (Fig. 3).

The volatile content of canola straw bales varied significantlywith the length of storage for straw harvested 2008 and 2009(P< 0.001 for both cases) (Fig. 3b). Although, the changes in volatilecontent were statistically significant the volatile content appears tobe stable over the storage period.

The volatile content of canola straw pellets was significantlyaffected by the straw used to produce the pellets (P < 0.001) andthe length of storage (P < 0.001). There was a statistical interactionbetween the raw material used to produce the pellets and thelength of storage post-pelletisation (P < 0.001). The year of harvestof the canola straw had a significant effect on the volatile content ofthe canola straw pellets (P < 0.001) (Fig. 3c).

3.5. Conclusion

� No variations between inside and outside points within thecanola straw bale were found and hence they can be consid-ered uniform throughout the bale. Thus, it can be concludedthat the canola straw bales did not suffer any contaminationfrom the farm environment.

� Generally, the storage of canola straw bales and pellets signif-icantly affected the elemental composition, gross calorificvalue, ash and volatile content of the straw and pellets(p< 0.05). However, the variations are considered minimal andare believed to be caused by natural variations, as no correla-tions between properties were found.

� The concentrations of nitrogen, sulphur and chlorine of thecanola straw taken from the swath were significantly lowerthan the composition of the straw after baling.

� The content of sulphur, magnesium, aluminium, calcium, andiron increased when the straw was pelletised. In contrast thecarbon, sulphur and chlorine content were lower in the pellets.

� The concentration of sulphur, magnesium, aluminium, calcium,and iron increased when the straw was pelletised, potentiallyattributable to the addition of the binder. In contrast thecarbon, sulphur and chlorine content were lower in the pelletscompared to the baled strawwhichmay be due to volatilisationduring the pelletisation process.

L. Chico-Santamarta et al. / Energy 50 (2013) 429e437 437

� The variations in the GCV of canola straw bales and pellets withstorage were minimal, and no correlations between the GCVand the chemical composition were found.

� The ash and volatile content of canola straw bales and pelletswere stable during storage. However, the ash content washigher in the pellets, hence consideration should be given toa reduction in the amount of binder used to keep the ashcontent to a minimum.

Acknowledgements

The authors would like to thank the staff at the Princess Mar-garet Laboratory, the Farm and the Crop and Environment ResearchCentre (CERC) at Harper Adams University. We also would like tothank the Douglass Bomford Trust and Claas Stiftung for supportingthis project.

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