Wood Chips Compaction: First Energetic Analysis

Transcription

1 Applied Mathematical Sciences Vol. 8, 2014, no. 130, HIKARI Ltd, Wood Chips Compaction: First Energetic Analysis Alessio Facello Istituto per le Macchine Agricole e Movimento Terra (IMAMOTER) Consiglio Nazionale delle Ricerche (CNR) Strada delle Cacce, Torino, Italy Niccolò Pampuro Istituto per le Macchine Agricole e Movimento Terra (IMAMOTER) Consiglio Nazionale delle Ricerche (CNR) Strada delle Cacce, Torino, Italy Marco Manzone Department of Agriculture, Forestry and Food Sciences (DISAFA) University of Torino Via Leonardo da Vinci 44, Grugliasco, Italy Paolo Balsari Department of Agriculture, Forestry and Food Sciences (DISAFA) University of Torino Via Leonardo da Vinci 44, Grugliasco, Italy Eugenio Cavallo Institute of Agricultural and Earthmoving Machines Italian National Research Council, Torino, Italy Copyright 2014 Alessio Facello, Niccolò Pampuro, Marco Manzone, Paolo Balsari and Eugenio Cavallo. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract The need to mitigate climate change and the progressive fossil fuel exhaustion have engendered a great interest for renewable fuels. This boosted the demand for wood fuel in all industrialized Countries creating a considerable business opportu-

2 6548 Alessio Facello et al. nity for the different stakeholders of the forestry sector. To increase the efficiency of the entire wood fuel supply chain, it is necessary to reduce the cost of harvesting, processing and transportation. One possible way to cut the handling costs is the densification of the chips. This paper reports the results of a study conducted on the densification process of chips, with particular focus on the demand of energy required by the process and on the density achieved. The investigation has been carried out on chips from hybrid poplar (PC) chestnut (CC), and a mixture of spruce and eastern white pine (MC) at different pressures (20, 30, 50, 80 and 110 MPa). The study pointed out that average values for density ranges between , and kg m -3 for PC, CC and MC respectively. Specific energy demand ranges between , and kj kg -1 for PC, CC and MC respectively. Keywords: pressure agglomeration, specific energy, wood chips 1 Introduction The progressive fossil fuel exhaustion and the need to mitigate climate change have generated a strong interest for renewable fuels [Berndes et al., 2003]. Various new prospective of biomass use have been introduced giving a growing importance to these materials and boosting the demand for wood fuel in all industrialized Countries [Kraussmann et al., 2008]. Wood biomass is very plentiful in all European countries and is largely underutilized [De Wit and Faaij, 2010]. The energy conversion of wood biomass may offer a significant contribution in heat generation, for cost-effective substitution of fuel oil, electricity or natural gas [Aebiom, 2011]. One fundamental step in the biomass energetic exploitation is the comminution process that usually is performed with different kinds of chippers adopting various cutting technology that affect the overall process efficiency [Spinelli et al., 2012 and Facello et al., 2013]. In order to optimize the entire wood fuel supply chain, is useful reduce the cost of harvesting, processing and transportation. One of the most penalizing chips characteristics is the final low density ( kg m -3 ) that increases the handling costs in terms of storage and transportation volume occupation. One possible way to reduce these costs is represented by the densification that, increasing the density, can improve the overall handling costs. This paper reports the results of a study conducted on the densification process of chips, with particular focus on the energetic demand required by the briquettes production and to the final density values obtained at different applied pressures and with different biomasses. 2 Materials and methods 2.1 Compression test and energy calculation Three types of woody materials hybrid poplar (Populus x euramericana

3 Wood chips compaction 6549 Guiner) (PC), chestnut (Castanea sativa L. ) (CC) and a mixture of spruce (Picea abies L.) and eastern white pine (Pinus strobus L.) (MC) were studied. Wood chips used for the trials were G40 quality class with average moisture content of PC, CC and MC were 7.1, 7.9 and 8.1% (wb), respectively. The moisture content was determined using American Society of Agricultural and Biological Engineers (ASABE) Standard S358.2 [ASABE, 2006]. The initial bulk density of PC, CC and MC were 119, 212 and 152 kg m -3, respectively. The bulk density was determined using ASABE Standard S269.4 [ASABE, 2007]. The mass of samples used for making compacts was g. Five preset pressures of 20, 30, 50, 80 and 110 MPa corresponding to loads of 31.5, 47.3, 62.3, and kn, were used to compress samples in the chamber. For each woody material investigated, 10 samples were produced at each pressure level applied (Fig. 1). Fig 1: Chestnut samples obtained applying 20, 30, 50, 80 and 110 MPa. Raw material on the left. Details of the hydraulic press used for the experiment have been previously described by Pampuro et al. [2013a]. After compression, samples length and diameter were measured using a digital caliper, while a digital balance accurate to 0.01 g was used to measure the final mass of the densified materials. Density was calculated from the ratio of mass to volume. As reported by Li and Liu [2000], the densities of the briquettes were measured 2 min after the logs were ejected from the mold. During the compression of individual compacts, force-displacement data were recorded. Specific compression energy (SCE) was calculated following the methodology of Adapa et al. [2006], Mani et al. [2006] and Pampuro et al. [2013b]. The area under the force-displacement curve was integrated using the trapezoid rule [Santamarta et al., 2012]; when combined with the briquette mass, it yielded the specific energy values in kj kg Statistical analysis Data have been submitted to statistical analysis using SPSS statistical software package (Version 17.0). Differences among treatments has been tested using one way analysis of variance (ANOVA) while regression analysis was performed

4 6550 Alessio Facello et al. using the proc reg" function. Experimental data have been plotted using Microsoft Excel (Microsoft Office 2007).. 3 Results and discussion Results from the experiments showed that the average density values ranged from 546 to 898 kg m -3, from 543 to 913 kg m -3 and from 559 to 1,082 kg m -3 for PC, MC and CC respectively, upon application of pressure in the range of MPa (Tab. 1). Tab 1: Density values (kg m -3 ) of PC (hybrid poplar), CC (chestnut) and MC (mixture of spruce and eastern white pine) obtained using different pressure levels (20, 30, 50, 80 and 110 MPa). Mean value and standard error (in parentheses) of 10 replications. Applied pressure Materials (MPa) PC CC MC a 559 a 543 a (18) (6) (10) 622 a 695 b 615 a (7) (7) (6) 714 a 840 c 764 b (9) (12) (9) 817 a 990 c 908 b (7) (3) (9) 898 a 1,082 b 913 a (3) (5) (9) Values with different letters in each row are statistically different at p<0.05. Table 1 shows that in the pressure range of MPa, CC has density values significantly (p<0.05) higher than PC and MC. For pressures of 20, 30, 50, 80 and 110 MPa the average specific compression energy required to form the briquettes ranged from 22.5 to 58.1 kj kg -1, from 19.4 to 50.2 kj kg -1 and from 18.8 to 43.3 kj kg -1 for PC, MC and CC (Tab. 2).

5 Wood chips compaction 6551 Tab 2: Specific compression energy values (kj kg -1 ) of PC (hybrid poplar), CC (chestnut) and MC (mixture of spruce and eastern white pine) obtained using different pressure levels (20, 30, 50, 80 and 110 MPa). Mean value and standard error (in parentheses) of 10 replications. Applied pressure Materials (MPa) PC CC MC a 18.8 b 19.4 b (1.0) (0.7) (1.0) 32.1 a 22.7 c 25.7 b (0.5) (0.4) (0.6) 42.5 a 29.2 c 37.1 b (1.0) (0.5) (0.6) 49.9 a 38.1 c 42.3 b (0.5) (0.4) (0.4) 58.1 a 43.3 c 50.2 b (0.3) (0.5) (0.4) Values with different letters in each row are statistically different at p<0.05. As shown in Table 2, in the pressure range of MPa, CC has specific compression energy values significantly (p<0.05) lower than PC and MC. The relationship between density and specific energy recorded on the different samples of chips are showed in Fig. 2. Fig 2: Relationship between density and specific energy values and linear regression predicted values.

6 6552 Alessio Facello et al. Collected data have been analysed to detect relationship between density and specific energy required for the densification. Linear regression gives the simplest model of the process. The general equation is reported below: SCE = k ρ + c Where ρ is the density, k is a material-dependent coefficient and c is a constant offset value. For each material the characteristic components were computed and the results are showed in the following table: Tab 3: Parameters for the SCE linear equation. Material Parameter k c R 2 PC CC MC These equations are valid in the range MPa. The specific compression energies calculated for the densification of hybrid poplar, chestnut and a mixture of spruce and eastern white pine were higher than the values reported by Santamarta et al. [2012]. Using a moisture content of 10.8% and an applied pressure of 47.7 MPa, The specific energy required to obtain the oilseed rape (OSR) straw briquettes with moisture content of 10.8% and applying 47.7 MPa pressure was 24.9 kj kg -1. To produce PC, MC and CC briquettes with moisture content ranging from 7.1 to 8.1% and applying 50 MPa pressure 42.5, 37.1 and 29.2 kj kg -1 was required respectively. However the investigation point out that the average specific compression energy values were lower than the specific energy required to manufacture pellets from biomass feedstock (typically kj kg -1 ) [Colley et al., 2006]. As stated by Mani et al. [2004], the energy requirements depend mainly upon the applied pressure and moisture content, but also on the physical properties of the material and the method of compaction. 4 Conclusions The study indicates that the final density value is strongly affected by the type of biomass and by the different properties of the materials. In particular, poplar and pine require more energy per unit of processed material to obtain the same density in the final densified products. This suggest a lower efficiency of the process when processing low density woods. These data have to be paired with those coming from an economical analysis in order to evaluate the overall cost of the operation and design sustainable applications.

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