Energy 24 (1999) 141–150
Properties of charcoal derived from hazelnut shell and the production of briquettes using pyrolytic oil Ayhan Demirbas¸* Black Sea Technical University, Science Education, 61335 Akc¸aabat, Trabzon, Turkey Received 6 March 1998
Abstract Hazelnut shells were converted to charcoal and to liquid, and gaseous products using pyrolysis at different temperatures. The chemical compositions and yields of the charcoals were determined as functions of the carbonization temperature. Higher heating values (HHVs) were estimated using both ultimate and proximate analyses. Hazelnut shells and the derived charcoal were densified to briquettes using pyrolytic oil or tar as binder. Briquette properties improved with an increase in briquetting pressures and percentages of binder materials. The best charcoal briquettes were obtained at 800 MPa pressure at 400 K. 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction Hazelnut shell is a potentially important energy source for Turkey. Approximately 3 ⫻ 105 tons of hazelnut shells have been produced annually [1] and their properties investigated [2–7]. Utilization of agricultural residues for the production of biocoal (briquetted charcoal) is a novel procedure for the simultaneous disposal and partial substitution of biomass-derived charcoal for other energy sources. Considerable attention has recently been focused on briquetting of coal fines, peat, charcoal, biowaste, and other combustible wastes [8–15]. It has been shown that heating material to a predetermined temperature interval produces products that are more stable than the unheated materials [9,16,17]. The longer the cellulose fibres are, the stronger the briquette at a given paper to combustible waste ratio, and the lower the ratio of paper to combustible waste to maintain a minimum handling strength, damp and dry. Kraft paper, newsprint, and used paper could be utilized to bind coal dust or other particulate combustible wastes together to make a strong briquette, using processes * Corresponding author. Fax: ⫹ 90-0462-248-7344; e-mail: ayas@risc01.bim.ktu.edu.tr 0360-5442/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 3 6 0 - 5 4 4 2 ( 9 8 ) 0 0 0 7 7 - 2
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similar to those applied in papermaking technology. Kraft paper is highly desirable for briquetting because of its long fibres and the difficulty to repulp. Paper mill waste, sunflower shell, sawdust and brewery waste have also been used as binder materials at different ratios [18]. The test results on the briquette properties of the paper-bonded coal fuel briquette were reported [19]. 2. Experimental studies 2.1. Preparation and analyses of raw materials The raw material consisted of mixed ground hazelnut shells. The samples were of the species Corylus avellana from Trabzon. Air-dried samples were milled and then screened. Only the fraction retained on a 1.5–4.0 mm sieve was used. Hazelnut shells were screened into coarse, mediumcoarse, and fine sizes. Coarse pieces do not pass through 4.0 mm screen openings, medium-coarse pass through a 4.0 mm but not a 2.0 mm screen, and fines (sawdust) pass through a 2.0 mm screen. The samples were extracted by using acetone and an alcohol-benzene mixture (1/1, v/v) before the experiments. The chemical, ultimate, and proximate analyses for of hazelnut shell samples used in the experiments are given in Table 1. 2.2. Pyrolysis and fractioning of pyrolysis products The pyrolysis experiments were performed in a device designed for this purpose. The main element of this device was a tubular reactor of height 95.1 mm, ID 17.0 mm, and OD 19.0 mm inserted vertically into an electrically-heated tubular furnace. A similar fast pyrolysis apparatus was illustrated in our earlier study [20]. A simple thermo-couple (NiCr-constant) was placed directly on top of the sample but not touching it. Fig. 1 shows plots for pyrolysis products. Liquid products obtained from the pyrolysis of hazelnut shell and some wood samples were Table 1 Analyses of hazelnut shells Composition
Ultimate analysis (% wt of daf shell)a
Carbon Hydrogen Nitrogen Oxygen
50.8 5.2 1.4 42.6
Moisture Fixed carbon Volatile matter Ash
8.7 27.6 62.4 1.3
Structural componentsb
% wt of daf and extractive free
Calorific value
(kJ/g)
Lignin Hemicelluloses
44.4 28.7
HHV LHV
18.5 17.3
Cellulose
42.6
Density (g/cm3)
a
daf ⫽ dry and ash free daf and free of extractive
b
Proximate analysis (% wt of shell)
0.32
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143
Fig. 1. Plots for pyrolysis products from hazelnut shell. Heating rate ⫽ 5 K/min.
fractionated by means of gas chromatography into their tar, methanol, ethanol, acetone, acetic acid, and methyl acetate, etc. constituents on a BDS column. The yields of pyrolysis liquid products from these samples are given in Table 2. 2.3. Briquetting procedure The samples of hazelnut shell and pyrolitic charcoal obtained from the hazelnut shell and their Table 2 Yields of pyrolysis products obtained from hazelnut shell and wood samples at 870 K (% wt of daf shell) Product Tar Acetic acid Methanol Acetone Other organics Gases
Hazelnut shell 20.7 15.9 7.9 1.6 4.3 16.1
Pine wood 12.4 4.5 1.4 0.3 10.8 20.9
Spruce wood 11.8 4.3 1.6 0.3 10.8 21.3
Beech wood 26.2 8.1 1.7 0.8 3.0 17.2
Ailanthus wood Poplar wood 27.0 6.8 1.6 0.7 2.2 17.7
26.6 7.1 1.6 0.7 3.0 18.5
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Table 3 Elementary compositions and yields of charcoals from hazelnut shell in relation to the carbonization temperature and their HHVs Carbonization Elementary composition (%) temperature (K) C H O
Yield (%)
HHV (kJ/kg) HHV (kJ/kg) Difference Experimental from Eq. (1) ⫾ %
295 295 295 295 295 295 295
90.8 42.6 38.1 35.0 32.2 31.1 30.7
19846 28714 29140 29665 31041 31464 32008
to to to to to to to
470 550 650 750 850 950 1050
53.3 75.0 82.3 88.4 92.5 94.3 95.7
6.1 5.5 3.6 2.4 1.9 1.5 1.3
40.6 19.5 14.1 8.6 6.0 4.2 3.1
⫺ ⫺ ⫺ ⫹ ⫹ ⫹ ⫺
19383 28682 29132 29948 31204 31485 31815
2.33 0.11 0.03 0.95 0.53 0.07 0.60
Table 4 Ash, volatile material, fixed carbon contents of charcoals from hazelnut shell and their HHVs (in kJ/kg) Carbonization temperature (K)
Ash %
Volatile material %
Fixed carbon %
HHV Exper.
HHV from Eq. (2)
Difference ⫾%
295 295 295 295 295 295
2.28 2.34 2.42 2.65 2.74 2.84
20.61 18.24 16.70 8.20 5.50 3.88
77.11 79.42 81.88 89.15 91.76 93.28
28714 29140 29665 31041 31464 32008
28699 29151 29633 31058 31570 31878
⫺ ⫹ ⫺ ⫹ ⫹ ⫺
to to to to to to
550 650 750 850 950 1050
0.05 0.04 0.10 0.05 0.34 0.41
blends with different percentages of liquid tar or pyrolytic oil obtained from the shell at 295 to 600 K were briquetted at ambient temperature and elevated temperatures in a calibrated laboratory scale Shimadzu hydraulic press (model SSP-10A), using a punch and die set (25 mm ID ⫻ 60 mm height or 13 mm ID ⫻ 40 mm height) for 1–30 minutes (for laboratory tests) under pressures of 300–800 MPa. The briquettes obtained were cylindrical in shape. In order to determine the stability of the briquettes, measurements of the length were taken immediately on removal from the die, after one week of exposure to the atmosphere and again after five weeks exposure. The compressive strengths of the briquettes were determined by a modified version of the TS24 standard tests [21]. 2.4. Physical tests A series of tests were performed to determine the density, ignitability, size, dustiness, moisture content, and water resistance of the briquettes. Another series of experiments were carried out to determine the effects of different binder material percentages and of the briquetting pressures on the compressive strengths of the briquettes. Only the charcoal was heated to the desired temperature before squeezing. As heat was applied externally by means of an electrical element surround-
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Fig. 2. Effect of briquetting pressure on density of briquettes from hazelnut shell. Particle size: 1.5 to 4.0 mm. Binder material: Tar or pyrolytic oil.
ing the die, time was required for heat to penetrate to the centre of the sample. After a period of 12 minutes the centre temperature rise was measured by means of a thermocouple. 2.5. Fuel properties The elementary composition, ash, volatile material, and fixed carbon contents of charcoals from hazelnut shell in relation to the carbonization temperature and their HHVs were determined by bomb calorimeter according to the ASTM D2015 standard method and calculated by using the ultimate and proximate analysis data as given in the earlier studies [22–25]. 3. Results and discussion 3.1. Calculation of HHVs for charcoals The elementary compositions, yields and HHVs (in kJ/g) were calculated from the ultimate analyses given in Table 3 by using the relation
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Fig. 3. Effect of briquetting pressure on density of briquettes from hazelnut shell charcoal. Briquetting temperature: 400 K. Binder material: Tar or pyrolytic oil from the shell. Particle size: > 2 mm.
HHV ⫽ 0.3181(C) ⫹ 0.1423(H) ⫹ 0.1540(O),
(1)
where (C), (H), and (O) are the wt% of C, H and O, respectively. The ash, volatile material, fixed carbon contents of charcoal obtained from the hazelnut shell and their HHVs in kJ/g are given in Table 4. The HHVs may be calculated from proximate analyses in Table 4 by using HHV ⫽ 0.196(FC) ⫹ 13.585,
(2)
where HHV is higher heating value in kJ/g and FC is wt% of fixed carbon in the samples. The correlation coefficient is 0.99 for both relations. The HHVs calculated using Eqs. (1) and (2) showed mean differences of 1.52% and 0.12%, respectively (Tables 3 and 4). 3.2. Densities of briquettes Density is an important parameter in a briquetting process. The higher the density, the higher the energy/volume ratio. Hence, high-density products are desirable in terms of transportation, storage and handling [8]. The bulk densities of conventional wheat straw bales are about 0.10– 0.12 g/cm3. The bulk density of rice husk briquettes produced by tumbling agglomeration, a
A. Demirbas¸ / Energy 24 (1999) 141–150
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Fig. 4. Effect of briquetting pressure on compressive strength of hazelnut shell briquettes. Particle size: 2 to 4 mm. Binder material: Pyrolytic oil or tar.
method to determine bulk density, has been reported to be 0.32 (g/cm3) [26]. The density of extruded rice husk char briquettes has been reported to be 0.81 (g/cm3) [14]. 3.3. Physical tests results The effect of the briquetting pressure on density of hazelnut shell with 1.5 to 4.0 mm particle sizes are given in Fig. 2. The effect of the briquetting pressure on the density of briquettes obtained from the shell charcoal is shown in Fig. 3. The effect of briquetting pressure on the compressive strength of the hazelnut shell briquettes is given in Fig. 4. The effect of the briquetting pressure on compressive strength of briquettes obtained from the hazelnut shell charcoal is shown in Fig. 5. The effect of the briquetting temperature on the compressive strength of the shell briquettes is given in Fig. 6. As can be seen Figs. 2–5, briquette properties increased with an increase in the briquetting pressure. The compressive strength is an important criterion of briquette durability [27–30]. The best charcoal briquette has been obtained under 800 MPa pressure and at 400 K temperature. The effect of binder material content of the briquettes obtained from the charcoal on the compressive strength is shown in Fig. 5. The binder material contents to facilitate stable compaction
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Fig. 5. Effect of briquetting pressure on compressive strength of briquettes from hazelnut shell charcoal. Briquetting temperature: 400 K. Particle size: > 2 mm.
were found to lie between 13.0% and 18.0% by weight for the charcoal briquettes. The effect of binder materials percentage on the compressive strength of the hazelnut shell and charcoal briquettes are given in Figs. 4 and 5, respectively. In general, briquette durability increased with an increase in the percentage of binder material. 3.4. Ignitability A combustible material should not be easily ignitable, particularly for household use. Too low porosity, low volatile content and high ash content are likely to reduce the ignitability [8]. Qualitative observations showed that as the densities of the briquettes increased, their ignitabilities decreased. Due to its very easy ignitability, waste material is not suitable directly for domestic fire purposes. In general, briquetted hazelnut shell is likely to be more difficult to ignite because of low porosity due to the higher density. As a result, as the density of briquette increased its ignitability decreased [31].
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Fig. 6. Effect of briquetting temperature on compressive strength of briquettes from hazelnut shell charcoal. Briquetting pressure: 800 MPa. Particle size: > 2 mm. Binder material: Pyrolytic oil or tar.
3.5. Calorific value Heating value is a major quality index for fuels. The higher heating values for hazelnut shell and its charcoal were found to be 18.5 and 32.0 kJ/g, respectively. It was reported that biocoal produced rice husk by agglomeration showed calorific values around 17.6–18.1 kJ/g [26–32]. 3.6. Size of briquette The briquettes produced were normally around or above 3 cm in diameter. For cooking purposes, the briquettes normally have to be broken into smaller pieces to fit into a combustion apparatus. The size of briquette can be relatively easily controlled to match the needs of the users. Also, binders tend to make the surfaces of the briquettes relatively free from loosely adhering small particles, which would otherwise tend to blacken fingers on touching [8]. 4. Conclusions Prolytic oil or tar may be used as a binder for hazelnut shell and charcoal derived from hazelnut shell. The binder material is important for the briquetting process [33]. The samples used may
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be compressed and stabilized to densities of the order of 3 to 5 times that of normal bales by application pressures of between 400 and 800 MPa. Only the charcoal samples were heated to temperatures between 380 and 400 K before compression. Physical parameters such as the density, binder material content and compressive strength were found to be the best indicators for briquette quality. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33]
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