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Comparison of quality and production cost of briquettes made from agricultural and forest origin biomass
Renewable Energy 57 (2013) 20e26
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Comparison of quality and production cost of briquettes made from agricultural and forest origin biomass a _ ski a, Mariusz J. Stolarski a, Stefan Szczukowski a, Józef Tworkowski a, Micha1 Krzyzaniak , Pawe1 Gulczyn Miros1aw Mleczek b, * a b
Centre for Renewable Energy Research, University of Warmia and Mazury in Olsztyn, Oczapowskiego 2, 10-724 Olsztyn, Poland Department of Chemistry, University of Life Sciences in Poznan, Wojska Polskiego 75, 60-625 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 July 2012 Accepted 11 January 2013 Available online 14 February 2013
This paper presents the quality and cost of small-scale production of briquettes, made from agricultural and forest biomass in north-eastern Poland. The experiment involved production of eight types of briquettes. The highest net calorific value was determined for briquettes made from pine sawdust (18,144 MJ t1). The value measured for briquettes made from perennial energy plants was over 1500 MJ t1 lower, and for those made from straw 2000 MJ t1 lower than for sawdust briquettes. The sawdust briquettes left significantly the lowest amount of ash (0.40% of dry mass). The significantly highest content of hydrogen, sulphur and nitrogen was found in briquettes containing the highest portion of rapeseed oilcake. The quality of briquettes varied and only some of them met the requirements of DIN 51731. Briquettes made from pine sawdust were of the highest quality. The briquette production cost ranged from 66.55 V t1 to 137.87 V t1 for rape straw briquettes and for those made from a mixture of rape straw and rapeseed oilcake (50:50), respectively. In general, briquette production was profitable, except for the briquettes made from a straw and rapeseed oilcake mixture. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Biomass Briquettes Energy plants Calorific value Production cost
1. Introduction Recently in Poland, as well as elsewhere in the EU, renewable sources have been used increasingly often in the generation of energy. In 2009, energy from renewable sources in the EU accounted for 18.3% of the total primary energy, with 9.0% on average in Poland. According to the guidelines set out in the EU directive [1], energy from renewable sources in Poland must account for 15% of total energy by 2020. Currently, most of energy from renewable sources in Poland is produced from solid biomass e 86.1% [2]. The majority of solid biomass for energy generation in Poland is supplied by forests and the wood processing industry. However, the majority of biomass is ultimately to be obtained from perennial energy crops, cultivated on agricultural land, such as Salix coppice (Salix spp.), Sida hermaphrodita (Virginia mallow) and Miscanthus giganteus [3e7] as well as cereal and rape straw as post-production biomass. In order to meet the goals set by the EU with respect to production of renewable energy, the domestic Regulation of the Minister of Economy of 14 August 2008 provides for a significant * Corresponding author. Tel.: þ48 618487836; fax: þ48 618487824. E-mail address: [email protected] (M. Mleczek). 0960-1481/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.renene.2013.01.005
increase in non-forest biomass consumption for energy production [8]. Large power plants and combined heat and power plants buy biomass fuel from large producers, which reduces biomass availability on the local markets. Pellet production in Poland is growing very rapidly. It amounted to about 20 thousand tonnes in 2003, to reach 410 thousand tonnes s in 2009 and about 595 thousand tonnes s in 2010 [9,10]. Pellet consumption for energy production is also growing in the EU; it amounted to 1.3 million tonnes s in 2002, about 10 million tonnes s in 2009 and it is estimated to exceed 11 million tonnes s in 2010 [10,11]. Due to the high demand for pellets, large pellet-producing plants have been established with an annual production output from 10 thousand to 100 thousand tonnes, which has led to an increase in the demand for large amounts of uniform biomass. Paradoxically, this provides an opportunity for smaller plants, with an annual production output of 1e5 thousand tonnes, which process locally obtained biomass and produce briquettes, supplying fuel to individual consumers and to local heat-generating plants. This is currently happening in Poland. These briquette producers generally stand a low chance of purchasing sawdust for briquette production due to strong competition from large pellet-producing plants. Therefore, small briquette production plants seek new sources of biomass, including energy plants. Production of raw material (biomass) on one’s own plantation of perennial plants is
M.J. Stolarski et al. / Renewable Energy 57 (2013) 20e26
one of the possibilities of reducing the cost of material for briquetting. In such a case, the cost of material purchase would be equal to the cost of its production; moreover, such a system would ensure stability of supply of material for production. It should also be emphasised that small-scale briquette production enables local biomass utilisation and limits the money-energy circulation system to a small area, which is important from the economic and environmental point of view. Locally produced briquette is an attractive energy carrier for individual consumers in different parts of the world, especially in developing countries [9,12e17]. In general, briquette fuel has better energy parameters, higher density, higher calorific value (especially per volume unit) and lower moisture content as compared to the raw materials. Briquette production consumes different types of materials and uniform fuel is obtained from mixtures of materials (agricultural residues and energy plants) [18e25]. Considering the facts mentioned above, this study aimed to assess the possibility of producing briquettes from agricultural and forest biomass and to determine the production cost and the quality of the produced fuels. 2. Material and methods 2.1. Experiment design and biomass for briquette production The experiment was conducted with biomass obtained from perennial energy plants (Salix viminalis clone UWM 006 and Sida hemaphrodita Raspy, both from three-year-old rootstocks), rape straw and rapeseed oilcake (Brassica napus L.) and also pine sawdust (Pinus sylvestris L.). Biomass from perennial energy plants was obtained from field experiments (0.2 ha for each plant) conducted at the University of Warmia and Mazury in Olsztyn (UWM) (N: 53 350 E: 20 360 ). In March 2010 all S. viminalis and S. hemaphrodita were collected in three and one year rotation coppice, respectively. The plants were manually cut down with a petrol trimmer at 5 cm above the ground surface. Collected S. viminalis and S. hemaphrodita shoots were stored on special piles for drying up under wind and sun influence to the end of August 2010. After this time, shoots were crumbled to chips (3e5 cm length) with a Junkkari HJ 10 G wood chipper (Junkkari, Finland), connected with a New Holland tractor (New Holland, United Kingdom) with 130 kM power. In this form the material was transported to works of briquette production. Rape straw was transported to the production plant in small bricks with the dimensions of 80/40/40 cm (h/w/d). Rapeseed oilcake was obtained by cold-pressing oil from rapeseed. Pine sawdust was obtained at the briquette production plant, where it is received as a by-product in parquet floor production. 2.2. Characteristics of the soil According to the PTG 2008 classification [26], the plants grew on sandy loam, in which the percentage of sand (2e0.05 mm), silt (0.05e0.002 mm) and clay (<0.002 mm) was 60, 36 and 4%, respectively. Samples of the soil on which the tested plants grew were characterized by selected parameters described in Supplementary material. 2.3. Assessment of quality of biomass raw materials and the obtained briquettes Samples of each kind of biomass (raw material) were taken for analysis before briquette production started. Subsequently, eight types of biomass briquettes were produced from: S. viminalis; S. hemaphrodita; a mixture of S. viminalis and S. hemaphrodita in
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50:50 ratio; rape straw; a mixture of S. viminalis and rape straw in 50:50 ratio; a mixture of rape straw and rapeseed oilcake in 75:25 ratio; a mixture of rape straw and rapeseed oilcake in 50:50 ratio; and from pine sawdust for comparison. For preparation of appropriate mixtures, the materials were ground in an OSMEKA HZ2100 mill (PONAR, qód z), and blended by mixer BWE 260 (ZREMB “50/50 ) about 300 dm3 value. The material was highly Project”, Poznan homogenous (12 mm) The following were determined in all the raw materials and in briquettes: moisture content, gross calorific value, net calorific value, ash content, volatile matter content, bulk density and chemical composition. Each analysis was performed in triplicate at the UWM laboratory in Olsztyn. 2.4. Characteristics of the materials used in briquette production The bulk density of the materials used in briquette production ranged from 89.33 kg m3 to 383.00 kg m3 for chips of S. hemaphrodita and rapeseed oilcake (Table 1). Rapeseed oilcake also had significantly the lowest moisture content (9.80%). The gross calorific value for rapeseed oilcake was significantly the highest and was equal to 22,551 MJ t1 of d.m., and its net calorific value was equal to 20,341 MJ t1. The value was higher by about 23% for S. viminalis chips and by about 20%, 17%, and 14% for straw, S. hemaphrodita and sawdust, respectively. Sawdust contained the lowest amount of ash (0.35% of d.m.). S. viminalis chips contained fourfold more ash and also straw and rapeseed oilcake 16- and 18-fold more ash than sawdust. Rapeseed oilcake contained the highest amounts of hydrogen, sulphur and nitrogen of all the materials. The sulphur content in sawdust was about 155fold lower and that of nitrogen e about 75-fold lower than in oilcake. The content of those elements in S. viminalis and S. hemaphrodita biomass was 14- to 29-fold lower. Rapeseed straw contained the highest amounts of chlorine (0.75% of d.m.); the value found for the other materials was lower, from 16- to 39-fold. 2.5. Production of briquettes and economic analysis Production of briquettes from agricultural and forest biomass was examined at the Max-Parkiet sp. z.o.o. plant. The biomass of each type, as well as their mixtures, was briquetted on a Polish piston-briquetting machine BT86M (WAMAG, Walbrzych). The main unit of the device was a horizontal crank-and-piston briquetting press. An integral part of the press was a briquetting unit, consisting of a briquetting bush, pre-forming bush, a piston and a two-part clamping bush with a pneumatically adjusted clamping pressure. Another integral element of the device was a material feeding-compacting worm unit and the third one was a briquette conveyor, 5 m long, on which the briquette thermal and strength stabilisation took place. The device also included a storage and dispensing container with a worm scraper, a cyclone for pneumatic transport of material and a control cabinet. The set was fitted out with three electric motors. The main motor had the power of 15.0 kW, whereas the two motors of the worm feeders had the power of 2.2 and 1.1 kW. The required air pressure of the clamping
Table 1 Market prices of raw materials used for briquette production. Material
V t1
Natural dried willow chips Natural dried chips of Virginia mallow Rape straw Rapeseed oilcake Dry pine sawdust
56.3 58.8 30.0 180.2 50.1
Source: authors’ data based on market information.
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bush unit ranged from 0.1 MPa to 0.7 MPa. The device output was about 250 kg h1, and the briquette it produced had the form of a cylinder with a diameter and length of 55 and 50e80 mm, respectively. Production of briquettes was conducted on two shifts. Therefore, allowing 30 days a year for stoppages for repair and maintenance, the line annual output was about 1340 tonnes. Briquettes were packed in 25 kg foil bags and loaded on pallets, 40 bags on each. Each pallet was then wrapped in foil. The line was operated by one worker paid an average monthly salary of 615V. The briquette production experiment was conducted separately for each raw material for 3e4 h. The line depreciation was estimated as 10% p.a., and repair and maintenance costs as 5% of the general plant costs. The analysis of the briquette production costs assumed that the materials for fuel production would be bought by the production plant (Table 2). The price of 1 kWh of electrical energy was 0.1317V. The amount in Polish zlotys (PLN) has been converted to Euro (V) according to the average exchange rate of the National Bank of Poland for 2010 (V:PLN e 1:3.9945). The inflation rate in Poland in 2010 was 2.6%.
Table 3 Bulk density, ash, fixed carbon and volatile matter content of the produced briquettes. Type of briquette
Bulk density (kg m3)
Willow Virginia mallow Rape straw Virginia mallow/ willow (50:50) Straw/willow (50:50) Straw/rapeseed oilcake (75:25) Straw/rapeseed oilcake (50:50) Pine sawdust
469.70 363.77 395.92 465.09
Ash content (% of d.m.)
6.61b 15.96e 7.84d 7.99b
1.47 2.83 5.35 2.40
0.15f 0.15d 0.12b 0.04e
Volatile matter content (% of d.m.) 77.04 77.47 74.58 75.92
0.36b 0.45b 0.03d 0.17c
398.70 19.39d
4.64 0.37c
75.01 0.41d
414.95 11.13d
6.30 0.15a
73.94 0.06e
443.08 8.22c
6.31 0.01a
73.89 0.02e
542.42 2.43a
0.40 0.03g
78.84 0.23a
Standard deviation. a, b, c. homogeneous groups.
3. Results and discussion 3.1. Characterisation of the briquettes produced in the experiment
2.6. Theory/calculation The use of biomass in the state of nature (chips, sawdust and straw) is unattractive and potential consumers generally become disheartened from using permanently this kind of fuel. When these types of raw material or their mixes are made into briquettes, they are easier to store, distribute and use for energy generation. Briquetting facilitates utilization of smaller batches of biomass obtained from small farms (less than 20 ha) in whole Europe, which helps to expand the activity over larger rural areas, improving the competitive edge of the market of solid biomass fuels and contributing to the attainment of the EU goals in terms of renewable energy generation and protection of the environment. On the other hand, the quality and production costs of briquettes can be highly varied depending on the raw material. Thus, it is essential to specify categories of different types of briquettes as fuel according to their quality and production costs. In our paper, we point to these dependences under Polish conditions, which have specific importance for other EU states and countries in Asia or South America, where the same issues are being undertaken. Moreover, attention is currently drawn in the EU to pellets as the primary rectified type of biomass fuel. Noteworthy is the fact that production of briquettes, a less important form of biofuel, consumes less energy (is less expensive) than production of pellets, which is why they can compete with pellets on local markets and are more eco-friendly.
The processes of production of briquettes from all the materials did not deviate from the norm. The analysed types of biomass were found to be usable as raw materials in the production of solid fuel such as briquettes. The highest bulk density was determined for sawdust briquette: 542.42 kg m3 (Table 3). Compared to the raw material, the value measured for the briquette was nearly five-fold higher. Briquetting agricultural materials increased the briquette density from 2.6-fold for S. viminalis to more than fourfold for S. hemaphrodita. Sawdust briquettes contained significantly the lowest amount of ash (0.40% of d.m.) (Table 3). The amount increased according to the sequence S. viminalis, mixture of S. hemaphrodita and S. viminalis, S. hemaphrodita, mixture of straw and S. viminalis, straw, by a factor of 3.7, 6.0, 7.1, 11.6 and 13.4, respectively. Ash content in briquettes with rapeseed oilcake was equal to 6.3% of d.m., which was nearly 16-fold as much as in sawdust briquettes. The moisture content of briquettes from pine sawdust was significantly the lowest (8.17%) (Table 4). The highest moisture content was found in briquettes made from a mixture of rape straw and rapeseed oilcake (75:25). The highest gross calorific value and net calorific value was measured for pine sawdust briquette: 19,759 MJ t1 d.m. and 18,144 MJ t1 d.m., respectively (Table 4). In terms of the net
Table 2 Thermophysical properties and elemental composition of the materials used for briquette production. Attribute
Material
Bulk density (kg m3) Moisture content (%) Gross calorific value (MJ t1 d.m.) Net calorific value (MJ t1) Net calorific value (MJ m3) Ash content (% of d m) Volatile matter content (% of d.m.) C (% of d.m.) H (% of d.m.) S (% of d.m.) N (% of d.m.) Cl (% of d.m.)
180.67 18.29 19,265 15,740 2844 1.31 78.61 50.28 5.42 0.026 0.45 0.019
Willow chips
Standard deviation. a, b, c. homogeneous groups.
3.79b 0.02a 35c 32e 55b 0.00d 0.04b 0.01b 0.02c 0.003d 0.01c 0.002d
Virginia mallow chips
Rape straw
89.33 3.06e 11.34 0.05c 19,0905d 16,9266c 1512 51d 1.85 0.00c 78.49 0.02c 48.44 0.09c 5.38 0.03d 0.033 0.003c 0.35 0.00d 0.021 0.004d
130.00 12.04 18,432 16,212 2108 5.57 74.29 43.46 4.91 0.231 1.14 0.747
4.58c 0.05b 40e 45d 70c 0.03b 0.04d 0.05d 0.02e 0.004b 0.00b 0.003a
Rapeseed oilcake 383.00 9.80 22,551 20,341 7790 6.35 74.13 50.39 5.98 0.746 6.42 0.047
16.37a 0.02d 41a 32a 321a 0.00a 0.04e 0.65b 0.03a 0.003a 0.08a 0.000b
Pine sawdust 108.33 10.85 19,517 17,398 1885 0.35 79.80 55.34 5.83 0.005 0.09 0.037
7.64d 0.02c 18b 12b 132c 0.03e 0.00a 0.23a 0.02b 0.000e 0.00e 0.005c
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Table 4 Moisture content, gross calorific value and net calorific value of produced briquettes. Type of briquette
Moisture content (%)
Willow Virginia mallow Rape straw Virginia mallow/willow (50:50) Straw/willow (50:50) Straw/rapeseed oilcake (75:25) Straw/rapeseed oilcake (50:50) Pine sawdust
11.30 11.15 10.59 11.77 10.94 12.33 11.09 8.17
0.00c 0.36c 0.20d 0.06b 0.08c 0.08a 0.11c 0.08e
Gross calorific value (MJ t1 of d m)
Net calorific value (MJ t1)
Net calorific value (MJ m3)
18,758 49d 18,636 16e 18,042 15h 18,4899f 18,280 18g 19,087 17c 19,715 17b 19,7598a
16,638 43d 16,557 82e 16,131 22g 16,3133f 16,2791f 16,734 29c 17,5287b 18,1449a
7815 6023 6386 7587 6491 6944 7766 9842
129b 246e 135d 131b 316d 197c 144b 45a
Standard deviation. a, b, c. homogeneous groups.
calorific value, the two materials were followed by briquettes containing 50% and 25% rapeseed oilcake. The net calorific value of briquettes made from perennial energy plants was lower by over 1500 MJ t1 as compared to sawdust briquettes. The value for straw briquettes was lower by over 2000 MJ t1. Also, the highest net calorific value of 1 m3 of fuel was measured for sawdust briquette (9842 MJ m3). The second homogeneous group with a net calorific value lower by 21e23% included briquettes made from Salix chips, from a mixture of Salix and Virginia mallow, and those containing 50% rapeseed oilcake. On the other hand, the value of this feature for briquettes made from rape straw and S. hemaphrodita was lower by 35e39% as compared to sawdust briquettes. The briquetting process increased the energy concentration in 1 m3 of fuel by a factor of 2.7e5.2 as compared to the raw materials. Among the fuels produced in the experiment, the highest carbon content was found in pine sawdust briquette (52.15% of d.m.) (Table 5). The second homogeneous group included briquette from a mixture of rape straw and rapeseed oilcake (50:50). The other types of briquette were in the third homogeneous group in terms of carbon content. The highest content of hydrogen, sulphur and nitrogen was found in briquettes with the highest proportion of rapeseed oilcake. The lowest sulphur content was found in sawdust briquette; the value was 64 times lower than in the briquette with the highest proportion of rapeseed oilcake. Furthermore, briquette made from perennial energy plants contained about 20 times less sulphur. The nitrogen content in the briquettes ranged from 3.85% of d.m. in briquette from straw and rapeseed oilcake (50:50) to 0.10% of d.m. in sawdust briquettes. The chlorine content was significantly the highest in rape straw briquettes (0.57% of d.m.). The data presented in the paper show that the quality of different types of briquette varied greatly and only some of them met the requirements of DIN 51731 for pellets and briquettes [27]. For example, only briquettes made from pine sawdust and from Salix lay within the acceptable range in terms of ash content, whereas only briquettes made from pure pine sawdust met the requirements of ÖNORM M 7135 [28] with regard to the attribute. The requirements of DIN 51731 with regard to sulphur content were met by briquette from sawdust, Salix, S. hemaphrodita and their mixture. Only pine
briquette met the requirements for nitrogen content. The briquette lay within different categories for each parameter with regard to the requirements set forth in EN 14961-1:2010:E [29] (Table 6). Obviously, the cited norms generally concern fuels produced from timber biomass, but they give us an idea to what extent the examined briquettes from different types of biomass are inferior to fuels from pure wood. Besides, in the future, it might be exciting to work out mixtures of different types of biomass so as to meet the norms but replace the forest biomass by the biomass from agricultural sources. However it must be emphasized that for example combustion of rapeseed cake is connected with emission of specific fumes and smells. It is specially onerous when this fuel is combusted in small capacity boilers. However due to emission of combustion gases at high altitude (large stacks) this effect may be imperceptible in large power/heating plants. Properties of fuel briquettes depend mainly on the type of material they are made from and on the type of the briquetting machine used to produce them. According to data published in Sweden [30], the bulk density of briquettes produced from sawdust, with a diameter of 50e65 mm, ranges from 550 to 660 kg m3. The average ash content in such fuel is about 0.7%, its moisture content about 10%, and the net calorific value ranges from 17 to 18 MJ kg1. Similar values of sawdust briquette characteristics have been found in Poland [31]. According to other studies, the bulk density of briquettes made from groundnut shell (diameter e 35 mm) was 618 kg m3. Moreover, the fuel contained more (7.92%) ash, its moisture content was about 9% and the calorific value was high (18.6 MJ kg1) [32]. In the case of briquettes produced from rapeseed oilcake the net calorific value will depend on oil content. In this research oil was pressed from rapeseed by “cold pressing”. Thus, rapeseed cake contained approx. 12% of oil. If higher efficiency press, with solvent extraction would be used, then only 1e 2% of oil could still remain in the cake. Therefore, net calorific value would be lower due to higher net calorific value of oil than “pure” biomass. This relationship was demonstrated in other research. The gross heating value of cold-pressed oilcake with 8e 10% of oil was 19.8 2.0 MJ kg1 and if the oil amount decreases to 2.6%, the gross heating value was 17.8 1.5 MJ kg1 [33].
Table 5 Elemental composition of briquettes. Type of briquette
C (% of d m)
Willow Virginia mallow Rape straw Virginia mallow/willow (50:50) Straw/willow (50:50) Straw/rapeseed oilcake (75:25) Straw/rapeseed oilcake (50:50) Pine sawdust
49.10 50.16 48.45 50.06 48.53 48.51 50.70 52.15
Standard deviation. a, b, c. homogeneous groups.
0.21b 1.32b 0.77b 1.12b 0.48b 0.74b 0.60ab 1.08a
H (% of d m) 4.69 5.17 5.37 5.14 4.86 5.67 5.93 5.37
0.01d 0.19c 0.05c 0.12c 0.12d 0.02b 0.10a 0.15c
S (% of d m) 0.027 0.023 0.166 0.026 0.132 0.347 0.474 0.007
0.007e 0.006e 0.001c 0.001e 0.002d 0.005b 0.004a 0.001f
N (% of d m) 0.44 0.39 1.21 0.40 0.86 2.59 3.85 0.10
0.01e 0.01f 0.02c 0.00f 0.01d 0.00b 0.03a 0.01g
Cl (% of d m) 0.05 0.05 0.57 0.06 0.36 0.50 0.35 0.04
0.01d 0.01d 0.01a 0.01d 0.01c 0.01b 0.02c 0.01e
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Table 6 Specification of selected properties for briquettes included in EN 14961-1:2010:E. Moisture, M (w% as received)
Ash, A (% of d.m.)
Sulphur, S (% of d.m.)
Nitrogen, N (% of d.m.)
Chlorine, Cl (% of d.m.)
M10.0 10.0% M15.0 15.0% e e e e e e e e
A0.5 0.5% A0.7 0.7% A1.0 1.0% A1.5 1.5% A2.0 2.0% A3.0 3.0% A5.0 5.0% A7.0 7.0% A10.0 10.0% A10.0þ > 10.0%a
S0.02 0.02% S0.05 0.05% S0.08 0.08% S0.10 0.10% S0.20 0.20% S0.20þ > 0.20%a e e e e
N0.3 0.3% N0.5 0.5% N1.0 1.0% N2.0 2.0% N3.0 3.0% N3.0þ > 3.0%a e e e e
Cl0.02 0.02% Cl0.03 0.03% Cl0.07 0.07% Cl0.10 0.10% Cl0.10þ > 0.10%a e e e e e
a
Maximum value to be stated.
Table 7 Cost of briquettes produced from different materials (V t1). Item
Type of briquette Willow
Depreciation Repair and maintenance Purchase of raw material Transport of raw material Drying of raw material Milling raw material Electrical power consumed for briquetting Packaging and storage Human labour Total
Virginia mallow
Rape straw
Virginia mallow/ willow (50:50)
2.80 1.77 61.19 2.45 8.01 6.11 7.41 4.63 11.02
2.80 1.77 58.84 4.55 0.00 5.00 7.41 4.63 11.02
2.80 1.77 30.71 3.20 0.00 5.00 7.41 4.63 11.02
2.80 1.77 60.01 3.50 4.01 5.56 7.41 4.63 11.02
2.80 1.77 43.52 2.73 4.01 5.56 7.41 4.63 11.02
105.39
96.04
66.55
100.71
83.45
3.2. Cost of briquette production The analyses conducted in the experiment showed that the lowest cost was that of straw briquette production: 66.55 V t1 (Table 7). This resulted mainly from the lowest cost of the material purchase. The cost of sawdust briquette production was about 24% and that of briquette made from a mixture of straw and Salix was about 25% higher than that from straw alone. Furthermore, the cost of production of briquette from perennial energy plants was higher by
Straw/ willow (50:50)
Straw/rapeseed oilcake (75:25)
Straw/rapeseed oilcake (50:50)
Pine sawdust
2.80 1.77 68.10 2.72 0.00 3.75 7.41 4.63 11.02
2.80 1.77 105.48 2.25 0.00 2.50 7.41 4.63 11.02
2.80 1.77 51.23 3.84 0.00 0.00 7.41 4.63 11.02
102.21
137.87
82.71
44e58%. The total cost of production was the highest for briquette made from straw and rapeseed oilcake (50:50) e 137.87 V t1 e which included the cost of material purchase of 105.48 V t1. Reducing the proportion of rapeseed oilcake to 25% while increasing the proportion of straw to 75% reduced the cost of briquette production to 102.21 V t1. The cost of the raw material purchase accounted for the largest portion of the total cost of briquette production (Fig. 1). It ranged from 46.15% for straw to 76.51% for a mixture of rape straw and rapeseed oilcake (50:50). This was followed by the cost of human
Fig. 1. Cost structure for production of 1 tonne of briquettes from different raw materials.
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Table 8 Average sale price of briquettes on the local market and estimated profit generated from briquettes produced from different materials. Item
Price (V t1) Profit (V t1) Profit (V year1)
Type of briquette Willow
Virginia mallow
Rape straw
Virginia mallow/ willow (50:50)
Straw/willow (50:50)
Straw/rapeseed oilcake (75:25)
Straw/rapeseed oilcake (50:50)
Pine sawdust
117.7 12.3 16,444.2
112.7 16.6 22,264.0
94.6 28.1 37,627.4
115.2 14.4 19,360.8
106.1 22.7 30,412.6
96.4 5.8 7808.8
100.1 37.7 50,561.3
132.7 50.0 66,963.1
labour (7.99e16.56%), and the cost of electricity consumed in the briquetting process (5.37e11.13%) should also be taken into account. It was estimated in a study conducted in Sweden that regardless of the production output and the material moisture content, the average cost associated with it accounted for 61% of the total cost, i.e. it was in line with the findings of this study. It was followed by costs related to machines (9%), whereas the cost of energy and labour was similar, 8% each [30]. An earlier study conducted in Poland [34] on the production of briquettes, with the same briquetting machine as that used in this study, found that the cost of production of 1 tonne of briquettes, excluding the cost of material purchase, was only 42.2 V t1. When the cost of sawdust (about 8.3 V t1) was included, the cost of production of 1 tonne of briquette amounted to about 50.5 V t1. The labour-related costs (86%) dominated in the cost structure in this case, while the cost of electricity and depreciation accounted for 6% and 4% of the total cost, respectively. It was found in a later study conducted in Poland that the cost of briquette production from sawdust was similar to that calculated in this study. Depending on the variant, it ranged from 69.6 to 93.4 V t1 [31]. That paper found (as in this study) that the cost of the material purchase accounted for the highest portion of the cost (about 35e 38%). The cost of human labour ranged from 15 to 31%, depreciation accounted for 17e32% and electricity for 7e10% of the total cost. The quantities and costs of production of briquette affect the market price of the fuel. It has been estimated in Brazil that about 180,400 tonnes of briquette can be produced annually from agri-food industry residues. Its market price ranged from 68 to 104 V t1, with the average price being 85 V t1. When briquette was packaged in small bags, 25e40 kg in each, and sold to individual customers, its price was higher and ranged from 154 to 191 V t1 [14]. Briquette prices in Poland have been increasing steadily for several years due to the growing demand, both for the raw material and for the fuel itself. The briquette price for individual customers in the period 2006e2009 increased from about 85 to 98 V t1 [13]. The growing demand for the fuel has not changed and the price exceeded 100 V t1 in 2010 and currently ranges (depending on the quality) from 94.6 to as much as 132.7 V t1 (Table 8). Obviously, the price depends on the briquette quality and on the supply and demand for the fuel. The lowest prices were recorded for straw briquettes and the highest for briquettes from pure sawdust. Therefore, it can be assumed that the estimated profit earned from 1 tonne of briquettes would range from 12.3 to 50.0 V t1, for briquettes made from Salix and pine sawdust, respectively. It would generate a profit of 16,444 V year1 for briquettes made from Salix and 66,963 V year1 for pine sawdust. On the other hand, production of briquettes from a mixture of straw and rapeseed oilcake would generate a loss. 4. Conclusions and remarks The quality of briquettes varied and only some of them met the requirements of DIN 51731. Briquettes made from pine sawdust were of the highest quality.
Briquettes lay within different categories with regard to different attributes. Therefore, the percentage share of raw materials in the mixture should be chosen to make it meet the highest standard requirements possible. The cost of briquette production was determined mainly by the raw material price; therefore efforts should be made to find good quality (yet inexpensive) raw materials with stable supply. Moreover, the market price of briquettes is determined by their quality, which makes it unprofitable to produce briquettes from a straw and rapeseed oilcake mixture. Acknowledgement This work was supported by the Polish Ministry of Science and Higher Education through project R12 071 03. Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.renene.2013.01.005. References [1] Directive 2009/28/EC of the European Parliament and of the Council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing directives 2001/77/EC and 2003/30/EC. [2] G1ówny Urza˛ d Statystyczny. Energia ze zróde1 odnawialnych w 2010 roku [Energy from renewable sources in 2010]. Warsaw: Central Statistical Office; 2011 [in Polish]. [3] Stolarski M, Szczukowski S, Tworkowski J, Kopaczel M. Production of willow (Salix spp.) biomass on arable land in short-term harvesting cycles. Polish J Nat Sci 2006;20:53e65. [4] Stolarski M, Szczukowski S, Tworkowski J, Klasa A. Productivity of seven clones of willow coppice in annual and quadrennial cutting cycles. Biomass Bioenerg 2008;32:1227e34. _ [5] Stolarski M, Szczukowski S, Tworkowski J, Wróblewska H, Krzyzaniak M. Short-rotation willow coppice biomass as an industrial and energy feedstock. Ind Crop Prod 2011;33:217e23. [6] Szczukowski S, Stolarski M, Tworkowski J, Przyborowski J, Klasa A. Productivity of willow coppice plants grown in short rotations. Plant Soil Environ 2005;51:423e30. _ [7] Jezowski S, G1owacka K, Kaczmarek Z. Variation on biomass yield and morphological traits of energy grasses from the genus Miscanthus during the first years of crop establishment. Biomass Bioenerg 2011;35:814e21. [8] Rozporza˛ dzenie Ministra Gospodarki z 14 sierpnia 2008 roku w sprawie szczegó1owego zakresu obowia˛ zków uzyskania i przedstawienia do umorzenia swiadectw pochodzenia, uiszczenia op1aty zaste˛ pczej, zakupu energii elektrycznej i ciep1a wytworzonych w odnawialnych zród1ach energii oraz obowia˛ zku potwierdzania danych dotycza˛ cych ilosci energii elektrycznej wytworzonej w odnawialnym zródle energii (Regulation of Minister of Economy concerning detailed scope of duties of obtaining and presenting green certificates, buying of heat and power generated from renewables and confirming the data referring to the amount of power generated in renewable sources of energy e in Polish) Dz. U. nr 156, poz. 969. [9] Wach E, Bastian M. Rynek pelet w Polsce i Europie [Pellet market in Poland and in Europe]. Czysta Energia 2010;6:42e4 [in Polish]. [10] Wach E. Aktualnosci rynku pelet na koniec 2010 roku [Latest developments on the pellet market at the end of 2010]. Czysta Energia 2011;6:42e4 [in Polish]. [11] Tromborg E, Solberg B, Ranta T, Schweinie J, Tiffany DG. Costs and policy means for production of wood pellets e a comparative study between Finland, Germany, Norway and the US. In: 19th European biomass Conference and exhibition, Berlin, Germany; 6e10 June 2011. [12] Stolarski M, Szczukowski S, Tworkowski J. Pellet production from short rotation forestry. In: Proceedings of world sustainable energy days, European pellets conference, Wels, Austria; 2005 [available on CD-ROM].
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_ [13] Stolarski M, Krzyzaniak M, Graban q. Evaluation of energy-related and economic aspects of heating a family house with dendromass in the north-east of Poland. Energ Build 2011;43:433e9. [14] Felfli FF, Mesa JM, Rocha JD, Filippetto D, Luengo CA, Pippo W. Biomass briquetting and its perspectives in Brazil. Biomass Bioenerg 2011;35:236e42. [15] Ferguson H. Briquette businesses in Uganda. The potential for briquette enterprises to address the sustainability of the Ugandan biomass fuel market. London: GVEP International; 2012. [16] Nasrin AB, Choo YM, Lim WS, Joseph L, Michael S, Rohaya MH, et al. Briquetting of empty fruit bunch fibre and palm shell as a renewable energy fuel. J Eng Appl Sci 2011;6:446e51. [17] Shekhar N. Popularization of biomass briquettes e a means for sustainable rural development. Asian J Manage Res 2011;2:457e73. [18] Chou CS, Lin SH, Lu WC. Preparation and characterization of solid biomass fuel made from rice straw and rice bran. Fuel Process Technol 2009; 90:980e7. [19] Chou CS, Lin SH, Peng CC, Lu WC. The optimum conditions for preparing solid fuel briquette of rice straw by a piston-mold process using the Taguchi method. Fuel Process Technol 2009;90:1041e6. [20] Yaman S, Sahan M, Haykiri-Acma H, Sesen K, Kücükbayrak S. Fuel briquettes from biomasselignite blends. Fuel Process Technol 2001;72:1e8. [21] Purohit P, Tripathi AK, Kandpal TC. Energetics of coal substitution by briquettes of agricultural residues. Energy 2006;31:1321e31. [22] Katinas V, Markevicius A, Kavaliauskas A. Current status and prospects of biomass resources for energy production in Lithuania. Renew Energ 2007;32: 884e94. [23] Osadolor OO. Availability of grasses, weeds and leaves as energy resource. Renew Energ 2009;34:486e91. [24] Kwasniewski D. Technologia oraz koszty produkcji brykietów i peletów z wierzby energetycznej [Technology and costs of briquette and pellet
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Contents lists available at SciVerse ScienceDirect
Renewable Energy journal homepage: www.elsevier.com/locate/renene
Comparison of quality and production cost of briquettes made from agricultural and forest origin biomass a _ ski a, Mariusz J. Stolarski a, Stefan Szczukowski a, Józef Tworkowski a, Micha1 Krzyzaniak , Pawe1 Gulczyn Miros1aw Mleczek b, * a b
Centre for Renewable Energy Research, University of Warmia and Mazury in Olsztyn, Oczapowskiego 2, 10-724 Olsztyn, Poland Department of Chemistry, University of Life Sciences in Poznan, Wojska Polskiego 75, 60-625 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 July 2012 Accepted 11 January 2013 Available online 14 February 2013
This paper presents the quality and cost of small-scale production of briquettes, made from agricultural and forest biomass in north-eastern Poland. The experiment involved production of eight types of briquettes. The highest net calorific value was determined for briquettes made from pine sawdust (18,144 MJ t1). The value measured for briquettes made from perennial energy plants was over 1500 MJ t1 lower, and for those made from straw 2000 MJ t1 lower than for sawdust briquettes. The sawdust briquettes left significantly the lowest amount of ash (0.40% of dry mass). The significantly highest content of hydrogen, sulphur and nitrogen was found in briquettes containing the highest portion of rapeseed oilcake. The quality of briquettes varied and only some of them met the requirements of DIN 51731. Briquettes made from pine sawdust were of the highest quality. The briquette production cost ranged from 66.55 V t1 to 137.87 V t1 for rape straw briquettes and for those made from a mixture of rape straw and rapeseed oilcake (50:50), respectively. In general, briquette production was profitable, except for the briquettes made from a straw and rapeseed oilcake mixture. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Biomass Briquettes Energy plants Calorific value Production cost
1. Introduction Recently in Poland, as well as elsewhere in the EU, renewable sources have been used increasingly often in the generation of energy. In 2009, energy from renewable sources in the EU accounted for 18.3% of the total primary energy, with 9.0% on average in Poland. According to the guidelines set out in the EU directive [1], energy from renewable sources in Poland must account for 15% of total energy by 2020. Currently, most of energy from renewable sources in Poland is produced from solid biomass e 86.1% [2]. The majority of solid biomass for energy generation in Poland is supplied by forests and the wood processing industry. However, the majority of biomass is ultimately to be obtained from perennial energy crops, cultivated on agricultural land, such as Salix coppice (Salix spp.), Sida hermaphrodita (Virginia mallow) and Miscanthus giganteus [3e7] as well as cereal and rape straw as post-production biomass. In order to meet the goals set by the EU with respect to production of renewable energy, the domestic Regulation of the Minister of Economy of 14 August 2008 provides for a significant * Corresponding author. Tel.: þ48 618487836; fax: þ48 618487824. E-mail address: [email protected] (M. Mleczek). 0960-1481/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.renene.2013.01.005
increase in non-forest biomass consumption for energy production [8]. Large power plants and combined heat and power plants buy biomass fuel from large producers, which reduces biomass availability on the local markets. Pellet production in Poland is growing very rapidly. It amounted to about 20 thousand tonnes in 2003, to reach 410 thousand tonnes s in 2009 and about 595 thousand tonnes s in 2010 [9,10]. Pellet consumption for energy production is also growing in the EU; it amounted to 1.3 million tonnes s in 2002, about 10 million tonnes s in 2009 and it is estimated to exceed 11 million tonnes s in 2010 [10,11]. Due to the high demand for pellets, large pellet-producing plants have been established with an annual production output from 10 thousand to 100 thousand tonnes, which has led to an increase in the demand for large amounts of uniform biomass. Paradoxically, this provides an opportunity for smaller plants, with an annual production output of 1e5 thousand tonnes, which process locally obtained biomass and produce briquettes, supplying fuel to individual consumers and to local heat-generating plants. This is currently happening in Poland. These briquette producers generally stand a low chance of purchasing sawdust for briquette production due to strong competition from large pellet-producing plants. Therefore, small briquette production plants seek new sources of biomass, including energy plants. Production of raw material (biomass) on one’s own plantation of perennial plants is
M.J. Stolarski et al. / Renewable Energy 57 (2013) 20e26
one of the possibilities of reducing the cost of material for briquetting. In such a case, the cost of material purchase would be equal to the cost of its production; moreover, such a system would ensure stability of supply of material for production. It should also be emphasised that small-scale briquette production enables local biomass utilisation and limits the money-energy circulation system to a small area, which is important from the economic and environmental point of view. Locally produced briquette is an attractive energy carrier for individual consumers in different parts of the world, especially in developing countries [9,12e17]. In general, briquette fuel has better energy parameters, higher density, higher calorific value (especially per volume unit) and lower moisture content as compared to the raw materials. Briquette production consumes different types of materials and uniform fuel is obtained from mixtures of materials (agricultural residues and energy plants) [18e25]. Considering the facts mentioned above, this study aimed to assess the possibility of producing briquettes from agricultural and forest biomass and to determine the production cost and the quality of the produced fuels. 2. Material and methods 2.1. Experiment design and biomass for briquette production The experiment was conducted with biomass obtained from perennial energy plants (Salix viminalis clone UWM 006 and Sida hemaphrodita Raspy, both from three-year-old rootstocks), rape straw and rapeseed oilcake (Brassica napus L.) and also pine sawdust (Pinus sylvestris L.). Biomass from perennial energy plants was obtained from field experiments (0.2 ha for each plant) conducted at the University of Warmia and Mazury in Olsztyn (UWM) (N: 53 350 E: 20 360 ). In March 2010 all S. viminalis and S. hemaphrodita were collected in three and one year rotation coppice, respectively. The plants were manually cut down with a petrol trimmer at 5 cm above the ground surface. Collected S. viminalis and S. hemaphrodita shoots were stored on special piles for drying up under wind and sun influence to the end of August 2010. After this time, shoots were crumbled to chips (3e5 cm length) with a Junkkari HJ 10 G wood chipper (Junkkari, Finland), connected with a New Holland tractor (New Holland, United Kingdom) with 130 kM power. In this form the material was transported to works of briquette production. Rape straw was transported to the production plant in small bricks with the dimensions of 80/40/40 cm (h/w/d). Rapeseed oilcake was obtained by cold-pressing oil from rapeseed. Pine sawdust was obtained at the briquette production plant, where it is received as a by-product in parquet floor production. 2.2. Characteristics of the soil According to the PTG 2008 classification [26], the plants grew on sandy loam, in which the percentage of sand (2e0.05 mm), silt (0.05e0.002 mm) and clay (<0.002 mm) was 60, 36 and 4%, respectively. Samples of the soil on which the tested plants grew were characterized by selected parameters described in Supplementary material. 2.3. Assessment of quality of biomass raw materials and the obtained briquettes Samples of each kind of biomass (raw material) were taken for analysis before briquette production started. Subsequently, eight types of biomass briquettes were produced from: S. viminalis; S. hemaphrodita; a mixture of S. viminalis and S. hemaphrodita in
21
50:50 ratio; rape straw; a mixture of S. viminalis and rape straw in 50:50 ratio; a mixture of rape straw and rapeseed oilcake in 75:25 ratio; a mixture of rape straw and rapeseed oilcake in 50:50 ratio; and from pine sawdust for comparison. For preparation of appropriate mixtures, the materials were ground in an OSMEKA HZ2100 mill (PONAR, qód z), and blended by mixer BWE 260 (ZREMB “50/50 ) about 300 dm3 value. The material was highly Project”, Poznan homogenous (12 mm) The following were determined in all the raw materials and in briquettes: moisture content, gross calorific value, net calorific value, ash content, volatile matter content, bulk density and chemical composition. Each analysis was performed in triplicate at the UWM laboratory in Olsztyn. 2.4. Characteristics of the materials used in briquette production The bulk density of the materials used in briquette production ranged from 89.33 kg m3 to 383.00 kg m3 for chips of S. hemaphrodita and rapeseed oilcake (Table 1). Rapeseed oilcake also had significantly the lowest moisture content (9.80%). The gross calorific value for rapeseed oilcake was significantly the highest and was equal to 22,551 MJ t1 of d.m., and its net calorific value was equal to 20,341 MJ t1. The value was higher by about 23% for S. viminalis chips and by about 20%, 17%, and 14% for straw, S. hemaphrodita and sawdust, respectively. Sawdust contained the lowest amount of ash (0.35% of d.m.). S. viminalis chips contained fourfold more ash and also straw and rapeseed oilcake 16- and 18-fold more ash than sawdust. Rapeseed oilcake contained the highest amounts of hydrogen, sulphur and nitrogen of all the materials. The sulphur content in sawdust was about 155fold lower and that of nitrogen e about 75-fold lower than in oilcake. The content of those elements in S. viminalis and S. hemaphrodita biomass was 14- to 29-fold lower. Rapeseed straw contained the highest amounts of chlorine (0.75% of d.m.); the value found for the other materials was lower, from 16- to 39-fold. 2.5. Production of briquettes and economic analysis Production of briquettes from agricultural and forest biomass was examined at the Max-Parkiet sp. z.o.o. plant. The biomass of each type, as well as their mixtures, was briquetted on a Polish piston-briquetting machine BT86M (WAMAG, Walbrzych). The main unit of the device was a horizontal crank-and-piston briquetting press. An integral part of the press was a briquetting unit, consisting of a briquetting bush, pre-forming bush, a piston and a two-part clamping bush with a pneumatically adjusted clamping pressure. Another integral element of the device was a material feeding-compacting worm unit and the third one was a briquette conveyor, 5 m long, on which the briquette thermal and strength stabilisation took place. The device also included a storage and dispensing container with a worm scraper, a cyclone for pneumatic transport of material and a control cabinet. The set was fitted out with three electric motors. The main motor had the power of 15.0 kW, whereas the two motors of the worm feeders had the power of 2.2 and 1.1 kW. The required air pressure of the clamping
Table 1 Market prices of raw materials used for briquette production. Material
V t1
Natural dried willow chips Natural dried chips of Virginia mallow Rape straw Rapeseed oilcake Dry pine sawdust
56.3 58.8 30.0 180.2 50.1
Source: authors’ data based on market information.
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bush unit ranged from 0.1 MPa to 0.7 MPa. The device output was about 250 kg h1, and the briquette it produced had the form of a cylinder with a diameter and length of 55 and 50e80 mm, respectively. Production of briquettes was conducted on two shifts. Therefore, allowing 30 days a year for stoppages for repair and maintenance, the line annual output was about 1340 tonnes. Briquettes were packed in 25 kg foil bags and loaded on pallets, 40 bags on each. Each pallet was then wrapped in foil. The line was operated by one worker paid an average monthly salary of 615V. The briquette production experiment was conducted separately for each raw material for 3e4 h. The line depreciation was estimated as 10% p.a., and repair and maintenance costs as 5% of the general plant costs. The analysis of the briquette production costs assumed that the materials for fuel production would be bought by the production plant (Table 2). The price of 1 kWh of electrical energy was 0.1317V. The amount in Polish zlotys (PLN) has been converted to Euro (V) according to the average exchange rate of the National Bank of Poland for 2010 (V:PLN e 1:3.9945). The inflation rate in Poland in 2010 was 2.6%.
Table 3 Bulk density, ash, fixed carbon and volatile matter content of the produced briquettes. Type of briquette
Bulk density (kg m3)
Willow Virginia mallow Rape straw Virginia mallow/ willow (50:50) Straw/willow (50:50) Straw/rapeseed oilcake (75:25) Straw/rapeseed oilcake (50:50) Pine sawdust
469.70 363.77 395.92 465.09
Ash content (% of d.m.)
6.61b 15.96e 7.84d 7.99b
1.47 2.83 5.35 2.40
0.15f 0.15d 0.12b 0.04e
Volatile matter content (% of d.m.) 77.04 77.47 74.58 75.92
0.36b 0.45b 0.03d 0.17c
398.70 19.39d
4.64 0.37c
75.01 0.41d
414.95 11.13d
6.30 0.15a
73.94 0.06e
443.08 8.22c
6.31 0.01a
73.89 0.02e
542.42 2.43a
0.40 0.03g
78.84 0.23a
Standard deviation. a, b, c. homogeneous groups.
3. Results and discussion 3.1. Characterisation of the briquettes produced in the experiment
2.6. Theory/calculation The use of biomass in the state of nature (chips, sawdust and straw) is unattractive and potential consumers generally become disheartened from using permanently this kind of fuel. When these types of raw material or their mixes are made into briquettes, they are easier to store, distribute and use for energy generation. Briquetting facilitates utilization of smaller batches of biomass obtained from small farms (less than 20 ha) in whole Europe, which helps to expand the activity over larger rural areas, improving the competitive edge of the market of solid biomass fuels and contributing to the attainment of the EU goals in terms of renewable energy generation and protection of the environment. On the other hand, the quality and production costs of briquettes can be highly varied depending on the raw material. Thus, it is essential to specify categories of different types of briquettes as fuel according to their quality and production costs. In our paper, we point to these dependences under Polish conditions, which have specific importance for other EU states and countries in Asia or South America, where the same issues are being undertaken. Moreover, attention is currently drawn in the EU to pellets as the primary rectified type of biomass fuel. Noteworthy is the fact that production of briquettes, a less important form of biofuel, consumes less energy (is less expensive) than production of pellets, which is why they can compete with pellets on local markets and are more eco-friendly.
The processes of production of briquettes from all the materials did not deviate from the norm. The analysed types of biomass were found to be usable as raw materials in the production of solid fuel such as briquettes. The highest bulk density was determined for sawdust briquette: 542.42 kg m3 (Table 3). Compared to the raw material, the value measured for the briquette was nearly five-fold higher. Briquetting agricultural materials increased the briquette density from 2.6-fold for S. viminalis to more than fourfold for S. hemaphrodita. Sawdust briquettes contained significantly the lowest amount of ash (0.40% of d.m.) (Table 3). The amount increased according to the sequence S. viminalis, mixture of S. hemaphrodita and S. viminalis, S. hemaphrodita, mixture of straw and S. viminalis, straw, by a factor of 3.7, 6.0, 7.1, 11.6 and 13.4, respectively. Ash content in briquettes with rapeseed oilcake was equal to 6.3% of d.m., which was nearly 16-fold as much as in sawdust briquettes. The moisture content of briquettes from pine sawdust was significantly the lowest (8.17%) (Table 4). The highest moisture content was found in briquettes made from a mixture of rape straw and rapeseed oilcake (75:25). The highest gross calorific value and net calorific value was measured for pine sawdust briquette: 19,759 MJ t1 d.m. and 18,144 MJ t1 d.m., respectively (Table 4). In terms of the net
Table 2 Thermophysical properties and elemental composition of the materials used for briquette production. Attribute
Material
Bulk density (kg m3) Moisture content (%) Gross calorific value (MJ t1 d.m.) Net calorific value (MJ t1) Net calorific value (MJ m3) Ash content (% of d m) Volatile matter content (% of d.m.) C (% of d.m.) H (% of d.m.) S (% of d.m.) N (% of d.m.) Cl (% of d.m.)
180.67 18.29 19,265 15,740 2844 1.31 78.61 50.28 5.42 0.026 0.45 0.019
Willow chips
Standard deviation. a, b, c. homogeneous groups.
3.79b 0.02a 35c 32e 55b 0.00d 0.04b 0.01b 0.02c 0.003d 0.01c 0.002d
Virginia mallow chips
Rape straw
89.33 3.06e 11.34 0.05c 19,0905d 16,9266c 1512 51d 1.85 0.00c 78.49 0.02c 48.44 0.09c 5.38 0.03d 0.033 0.003c 0.35 0.00d 0.021 0.004d
130.00 12.04 18,432 16,212 2108 5.57 74.29 43.46 4.91 0.231 1.14 0.747
4.58c 0.05b 40e 45d 70c 0.03b 0.04d 0.05d 0.02e 0.004b 0.00b 0.003a
Rapeseed oilcake 383.00 9.80 22,551 20,341 7790 6.35 74.13 50.39 5.98 0.746 6.42 0.047
16.37a 0.02d 41a 32a 321a 0.00a 0.04e 0.65b 0.03a 0.003a 0.08a 0.000b
Pine sawdust 108.33 10.85 19,517 17,398 1885 0.35 79.80 55.34 5.83 0.005 0.09 0.037
7.64d 0.02c 18b 12b 132c 0.03e 0.00a 0.23a 0.02b 0.000e 0.00e 0.005c
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Table 4 Moisture content, gross calorific value and net calorific value of produced briquettes. Type of briquette
Moisture content (%)
Willow Virginia mallow Rape straw Virginia mallow/willow (50:50) Straw/willow (50:50) Straw/rapeseed oilcake (75:25) Straw/rapeseed oilcake (50:50) Pine sawdust
11.30 11.15 10.59 11.77 10.94 12.33 11.09 8.17
0.00c 0.36c 0.20d 0.06b 0.08c 0.08a 0.11c 0.08e
Gross calorific value (MJ t1 of d m)
Net calorific value (MJ t1)
Net calorific value (MJ m3)
18,758 49d 18,636 16e 18,042 15h 18,4899f 18,280 18g 19,087 17c 19,715 17b 19,7598a
16,638 43d 16,557 82e 16,131 22g 16,3133f 16,2791f 16,734 29c 17,5287b 18,1449a
7815 6023 6386 7587 6491 6944 7766 9842
129b 246e 135d 131b 316d 197c 144b 45a
Standard deviation. a, b, c. homogeneous groups.
calorific value, the two materials were followed by briquettes containing 50% and 25% rapeseed oilcake. The net calorific value of briquettes made from perennial energy plants was lower by over 1500 MJ t1 as compared to sawdust briquettes. The value for straw briquettes was lower by over 2000 MJ t1. Also, the highest net calorific value of 1 m3 of fuel was measured for sawdust briquette (9842 MJ m3). The second homogeneous group with a net calorific value lower by 21e23% included briquettes made from Salix chips, from a mixture of Salix and Virginia mallow, and those containing 50% rapeseed oilcake. On the other hand, the value of this feature for briquettes made from rape straw and S. hemaphrodita was lower by 35e39% as compared to sawdust briquettes. The briquetting process increased the energy concentration in 1 m3 of fuel by a factor of 2.7e5.2 as compared to the raw materials. Among the fuels produced in the experiment, the highest carbon content was found in pine sawdust briquette (52.15% of d.m.) (Table 5). The second homogeneous group included briquette from a mixture of rape straw and rapeseed oilcake (50:50). The other types of briquette were in the third homogeneous group in terms of carbon content. The highest content of hydrogen, sulphur and nitrogen was found in briquettes with the highest proportion of rapeseed oilcake. The lowest sulphur content was found in sawdust briquette; the value was 64 times lower than in the briquette with the highest proportion of rapeseed oilcake. Furthermore, briquette made from perennial energy plants contained about 20 times less sulphur. The nitrogen content in the briquettes ranged from 3.85% of d.m. in briquette from straw and rapeseed oilcake (50:50) to 0.10% of d.m. in sawdust briquettes. The chlorine content was significantly the highest in rape straw briquettes (0.57% of d.m.). The data presented in the paper show that the quality of different types of briquette varied greatly and only some of them met the requirements of DIN 51731 for pellets and briquettes [27]. For example, only briquettes made from pine sawdust and from Salix lay within the acceptable range in terms of ash content, whereas only briquettes made from pure pine sawdust met the requirements of ÖNORM M 7135 [28] with regard to the attribute. The requirements of DIN 51731 with regard to sulphur content were met by briquette from sawdust, Salix, S. hemaphrodita and their mixture. Only pine
briquette met the requirements for nitrogen content. The briquette lay within different categories for each parameter with regard to the requirements set forth in EN 14961-1:2010:E [29] (Table 6). Obviously, the cited norms generally concern fuels produced from timber biomass, but they give us an idea to what extent the examined briquettes from different types of biomass are inferior to fuels from pure wood. Besides, in the future, it might be exciting to work out mixtures of different types of biomass so as to meet the norms but replace the forest biomass by the biomass from agricultural sources. However it must be emphasized that for example combustion of rapeseed cake is connected with emission of specific fumes and smells. It is specially onerous when this fuel is combusted in small capacity boilers. However due to emission of combustion gases at high altitude (large stacks) this effect may be imperceptible in large power/heating plants. Properties of fuel briquettes depend mainly on the type of material they are made from and on the type of the briquetting machine used to produce them. According to data published in Sweden [30], the bulk density of briquettes produced from sawdust, with a diameter of 50e65 mm, ranges from 550 to 660 kg m3. The average ash content in such fuel is about 0.7%, its moisture content about 10%, and the net calorific value ranges from 17 to 18 MJ kg1. Similar values of sawdust briquette characteristics have been found in Poland [31]. According to other studies, the bulk density of briquettes made from groundnut shell (diameter e 35 mm) was 618 kg m3. Moreover, the fuel contained more (7.92%) ash, its moisture content was about 9% and the calorific value was high (18.6 MJ kg1) [32]. In the case of briquettes produced from rapeseed oilcake the net calorific value will depend on oil content. In this research oil was pressed from rapeseed by “cold pressing”. Thus, rapeseed cake contained approx. 12% of oil. If higher efficiency press, with solvent extraction would be used, then only 1e 2% of oil could still remain in the cake. Therefore, net calorific value would be lower due to higher net calorific value of oil than “pure” biomass. This relationship was demonstrated in other research. The gross heating value of cold-pressed oilcake with 8e 10% of oil was 19.8 2.0 MJ kg1 and if the oil amount decreases to 2.6%, the gross heating value was 17.8 1.5 MJ kg1 [33].
Table 5 Elemental composition of briquettes. Type of briquette
C (% of d m)
Willow Virginia mallow Rape straw Virginia mallow/willow (50:50) Straw/willow (50:50) Straw/rapeseed oilcake (75:25) Straw/rapeseed oilcake (50:50) Pine sawdust
49.10 50.16 48.45 50.06 48.53 48.51 50.70 52.15
Standard deviation. a, b, c. homogeneous groups.
0.21b 1.32b 0.77b 1.12b 0.48b 0.74b 0.60ab 1.08a
H (% of d m) 4.69 5.17 5.37 5.14 4.86 5.67 5.93 5.37
0.01d 0.19c 0.05c 0.12c 0.12d 0.02b 0.10a 0.15c
S (% of d m) 0.027 0.023 0.166 0.026 0.132 0.347 0.474 0.007
0.007e 0.006e 0.001c 0.001e 0.002d 0.005b 0.004a 0.001f
N (% of d m) 0.44 0.39 1.21 0.40 0.86 2.59 3.85 0.10
0.01e 0.01f 0.02c 0.00f 0.01d 0.00b 0.03a 0.01g
Cl (% of d m) 0.05 0.05 0.57 0.06 0.36 0.50 0.35 0.04
0.01d 0.01d 0.01a 0.01d 0.01c 0.01b 0.02c 0.01e
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Table 6 Specification of selected properties for briquettes included in EN 14961-1:2010:E. Moisture, M (w% as received)
Ash, A (% of d.m.)
Sulphur, S (% of d.m.)
Nitrogen, N (% of d.m.)
Chlorine, Cl (% of d.m.)
M10.0 10.0% M15.0 15.0% e e e e e e e e
A0.5 0.5% A0.7 0.7% A1.0 1.0% A1.5 1.5% A2.0 2.0% A3.0 3.0% A5.0 5.0% A7.0 7.0% A10.0 10.0% A10.0þ > 10.0%a
S0.02 0.02% S0.05 0.05% S0.08 0.08% S0.10 0.10% S0.20 0.20% S0.20þ > 0.20%a e e e e
N0.3 0.3% N0.5 0.5% N1.0 1.0% N2.0 2.0% N3.0 3.0% N3.0þ > 3.0%a e e e e
Cl0.02 0.02% Cl0.03 0.03% Cl0.07 0.07% Cl0.10 0.10% Cl0.10þ > 0.10%a e e e e e
a
Maximum value to be stated.
Table 7 Cost of briquettes produced from different materials (V t1). Item
Type of briquette Willow
Depreciation Repair and maintenance Purchase of raw material Transport of raw material Drying of raw material Milling raw material Electrical power consumed for briquetting Packaging and storage Human labour Total
Virginia mallow
Rape straw
Virginia mallow/ willow (50:50)
2.80 1.77 61.19 2.45 8.01 6.11 7.41 4.63 11.02
2.80 1.77 58.84 4.55 0.00 5.00 7.41 4.63 11.02
2.80 1.77 30.71 3.20 0.00 5.00 7.41 4.63 11.02
2.80 1.77 60.01 3.50 4.01 5.56 7.41 4.63 11.02
2.80 1.77 43.52 2.73 4.01 5.56 7.41 4.63 11.02
105.39
96.04
66.55
100.71
83.45
3.2. Cost of briquette production The analyses conducted in the experiment showed that the lowest cost was that of straw briquette production: 66.55 V t1 (Table 7). This resulted mainly from the lowest cost of the material purchase. The cost of sawdust briquette production was about 24% and that of briquette made from a mixture of straw and Salix was about 25% higher than that from straw alone. Furthermore, the cost of production of briquette from perennial energy plants was higher by
Straw/ willow (50:50)
Straw/rapeseed oilcake (75:25)
Straw/rapeseed oilcake (50:50)
Pine sawdust
2.80 1.77 68.10 2.72 0.00 3.75 7.41 4.63 11.02
2.80 1.77 105.48 2.25 0.00 2.50 7.41 4.63 11.02
2.80 1.77 51.23 3.84 0.00 0.00 7.41 4.63 11.02
102.21
137.87
82.71
44e58%. The total cost of production was the highest for briquette made from straw and rapeseed oilcake (50:50) e 137.87 V t1 e which included the cost of material purchase of 105.48 V t1. Reducing the proportion of rapeseed oilcake to 25% while increasing the proportion of straw to 75% reduced the cost of briquette production to 102.21 V t1. The cost of the raw material purchase accounted for the largest portion of the total cost of briquette production (Fig. 1). It ranged from 46.15% for straw to 76.51% for a mixture of rape straw and rapeseed oilcake (50:50). This was followed by the cost of human
Fig. 1. Cost structure for production of 1 tonne of briquettes from different raw materials.
M.J. Stolarski et al. / Renewable Energy 57 (2013) 20e26
25
Table 8 Average sale price of briquettes on the local market and estimated profit generated from briquettes produced from different materials. Item
Price (V t1) Profit (V t1) Profit (V year1)
Type of briquette Willow
Virginia mallow
Rape straw
Virginia mallow/ willow (50:50)
Straw/willow (50:50)
Straw/rapeseed oilcake (75:25)
Straw/rapeseed oilcake (50:50)
Pine sawdust
117.7 12.3 16,444.2
112.7 16.6 22,264.0
94.6 28.1 37,627.4
115.2 14.4 19,360.8
106.1 22.7 30,412.6
96.4 5.8 7808.8
100.1 37.7 50,561.3
132.7 50.0 66,963.1
labour (7.99e16.56%), and the cost of electricity consumed in the briquetting process (5.37e11.13%) should also be taken into account. It was estimated in a study conducted in Sweden that regardless of the production output and the material moisture content, the average cost associated with it accounted for 61% of the total cost, i.e. it was in line with the findings of this study. It was followed by costs related to machines (9%), whereas the cost of energy and labour was similar, 8% each [30]. An earlier study conducted in Poland [34] on the production of briquettes, with the same briquetting machine as that used in this study, found that the cost of production of 1 tonne of briquettes, excluding the cost of material purchase, was only 42.2 V t1. When the cost of sawdust (about 8.3 V t1) was included, the cost of production of 1 tonne of briquette amounted to about 50.5 V t1. The labour-related costs (86%) dominated in the cost structure in this case, while the cost of electricity and depreciation accounted for 6% and 4% of the total cost, respectively. It was found in a later study conducted in Poland that the cost of briquette production from sawdust was similar to that calculated in this study. Depending on the variant, it ranged from 69.6 to 93.4 V t1 [31]. That paper found (as in this study) that the cost of the material purchase accounted for the highest portion of the cost (about 35e 38%). The cost of human labour ranged from 15 to 31%, depreciation accounted for 17e32% and electricity for 7e10% of the total cost. The quantities and costs of production of briquette affect the market price of the fuel. It has been estimated in Brazil that about 180,400 tonnes of briquette can be produced annually from agri-food industry residues. Its market price ranged from 68 to 104 V t1, with the average price being 85 V t1. When briquette was packaged in small bags, 25e40 kg in each, and sold to individual customers, its price was higher and ranged from 154 to 191 V t1 [14]. Briquette prices in Poland have been increasing steadily for several years due to the growing demand, both for the raw material and for the fuel itself. The briquette price for individual customers in the period 2006e2009 increased from about 85 to 98 V t1 [13]. The growing demand for the fuel has not changed and the price exceeded 100 V t1 in 2010 and currently ranges (depending on the quality) from 94.6 to as much as 132.7 V t1 (Table 8). Obviously, the price depends on the briquette quality and on the supply and demand for the fuel. The lowest prices were recorded for straw briquettes and the highest for briquettes from pure sawdust. Therefore, it can be assumed that the estimated profit earned from 1 tonne of briquettes would range from 12.3 to 50.0 V t1, for briquettes made from Salix and pine sawdust, respectively. It would generate a profit of 16,444 V year1 for briquettes made from Salix and 66,963 V year1 for pine sawdust. On the other hand, production of briquettes from a mixture of straw and rapeseed oilcake would generate a loss. 4. Conclusions and remarks The quality of briquettes varied and only some of them met the requirements of DIN 51731. Briquettes made from pine sawdust were of the highest quality.
Briquettes lay within different categories with regard to different attributes. Therefore, the percentage share of raw materials in the mixture should be chosen to make it meet the highest standard requirements possible. The cost of briquette production was determined mainly by the raw material price; therefore efforts should be made to find good quality (yet inexpensive) raw materials with stable supply. Moreover, the market price of briquettes is determined by their quality, which makes it unprofitable to produce briquettes from a straw and rapeseed oilcake mixture. Acknowledgement This work was supported by the Polish Ministry of Science and Higher Education through project R12 071 03. Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.renene.2013.01.005. References [1] Directive 2009/28/EC of the European Parliament and of the Council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing directives 2001/77/EC and 2003/30/EC. [2] G1ówny Urza˛ d Statystyczny. Energia ze zróde1 odnawialnych w 2010 roku [Energy from renewable sources in 2010]. Warsaw: Central Statistical Office; 2011 [in Polish]. [3] Stolarski M, Szczukowski S, Tworkowski J, Kopaczel M. Production of willow (Salix spp.) biomass on arable land in short-term harvesting cycles. Polish J Nat Sci 2006;20:53e65. [4] Stolarski M, Szczukowski S, Tworkowski J, Klasa A. Productivity of seven clones of willow coppice in annual and quadrennial cutting cycles. Biomass Bioenerg 2008;32:1227e34. _ [5] Stolarski M, Szczukowski S, Tworkowski J, Wróblewska H, Krzyzaniak M. Short-rotation willow coppice biomass as an industrial and energy feedstock. Ind Crop Prod 2011;33:217e23. [6] Szczukowski S, Stolarski M, Tworkowski J, Przyborowski J, Klasa A. Productivity of willow coppice plants grown in short rotations. Plant Soil Environ 2005;51:423e30. _ [7] Jezowski S, G1owacka K, Kaczmarek Z. Variation on biomass yield and morphological traits of energy grasses from the genus Miscanthus during the first years of crop establishment. Biomass Bioenerg 2011;35:814e21. [8] Rozporza˛ dzenie Ministra Gospodarki z 14 sierpnia 2008 roku w sprawie szczegó1owego zakresu obowia˛ zków uzyskania i przedstawienia do umorzenia swiadectw pochodzenia, uiszczenia op1aty zaste˛ pczej, zakupu energii elektrycznej i ciep1a wytworzonych w odnawialnych zród1ach energii oraz obowia˛ zku potwierdzania danych dotycza˛ cych ilosci energii elektrycznej wytworzonej w odnawialnym zródle energii (Regulation of Minister of Economy concerning detailed scope of duties of obtaining and presenting green certificates, buying of heat and power generated from renewables and confirming the data referring to the amount of power generated in renewable sources of energy e in Polish) Dz. U. nr 156, poz. 969. [9] Wach E, Bastian M. Rynek pelet w Polsce i Europie [Pellet market in Poland and in Europe]. Czysta Energia 2010;6:42e4 [in Polish]. [10] Wach E. Aktualnosci rynku pelet na koniec 2010 roku [Latest developments on the pellet market at the end of 2010]. Czysta Energia 2011;6:42e4 [in Polish]. [11] Tromborg E, Solberg B, Ranta T, Schweinie J, Tiffany DG. Costs and policy means for production of wood pellets e a comparative study between Finland, Germany, Norway and the US. In: 19th European biomass Conference and exhibition, Berlin, Germany; 6e10 June 2011. [12] Stolarski M, Szczukowski S, Tworkowski J. Pellet production from short rotation forestry. In: Proceedings of world sustainable energy days, European pellets conference, Wels, Austria; 2005 [available on CD-ROM].
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