Abstract
The development of modern cities favours the formation of metropolitan zones with urban and industrial areas. The central metropolitan area (CMA) of the Principality of Asturias (northwest Spain), takes up 9.6% of the territory and represents 78% of its population. The first and second wood transformation industries of the CMA generate rather large amounts of biomass residues suitable for both reclaim and energy valuation considering technical, economic, and environmental restrictions. The results obtained from the evaluation of the biomass and the bioenergy of these residues are 7.9 kt/year and 114.7 TJ/year, respectively. The location for the development of a densified solid biofuels plant to produce pellets from these available residues is proposed for the Siero municipality, which is in the CMA. The plant would have an annual potential production capacity for the conventional pelletization process equivalent to 10 MW of fuel output.
Introduction
Several studies have evaluated the potential of biomass resources in Europe (Van Dam et al., 2007). In general, bioenergy systems are suggested to be important contributors to the energy sustainable future for the carbon dioxide emissions reduction (Gustavsson et al., 1995). Biomass residues particularly have the potential to become a significant primary energy source (Cornelissen et al., 2012).
Wood residues collection contribute positively to the conservation of natural resources and can be used for making densified solid biofuels, such as pellets (Paredes and Xiberta, 2010a; Saidur et al., 2011). It is worth mentioning that the pellet prices in Spain are 134 and 179 €/t before taxes (without value added tax) in bulk and in bags, respectively (Spanish Institute for Diversification and Energy Saving, 2013).
Asturias is located in southwest Europe in northwest Spain. The economic activity of the region is concentrated on services and industry, mainly related to coal-mines, steel, and other manufacturing industries (Moreno and López, 2008). The wood transformation industry is formed by sawmills, packing factories and carpentries which contribute to around 5% of the gross domestic product of the industrial sector, by processing over 400,000 m3 per year from Asturian cut wood (Asturian Society of Economic and Industrial Studies, 2013). The central metropolitan area (CMA) of the Principality of Asturias takes up 9.6% of the territory and represents 78% of its population. The CMA generates large amounts of these residues, suitable for both reclaim and energy valuation considering technical, economic, and environmental restrictions.
No studies have been carried out in Asturias concerning the current magnitude of the residues produced by either the first or second wood transformation industries. The main objective of this paper is to evaluate the biomass and the bioenergy of these residues in the CMA. Natural resources, good communications by road and proximity to the final consumers have led to locate over 50% of this sector industry in this area (Asturian Society of Economic and Industrial Studies, 2013). Figure 1 shows the municipalities that comprise the CMA.
Location of the central metropolitan area in the Principality of Asturias (Asturian Society of Economic and Industrial Studies, 2013).
Materials and methods
The BIORAISE (2013) GIS database has been used in order to determine the chemically untreated residues such as wooden cuttings and chips or sawdust, excluding the bark, so they are not impregnated with paint or varnish and they are suitable for energy use. These residues do not always have an established market or a steady price. They are normally managed as raw material or fuel to dry wood in the industry itself. Sometimes, they are stored in a landfill managed by the Consortium for Solid Waste Management in Asturias (Rodríguez-Iglesias et al., 2003).
For the calculation of the resource of each municipality, the area of a circle with origin at the centre point of the municipality and a radius which is the maximum distance between this point and its border have been considered. The centre point is where the collecting point will be located.
The available residue (mAR), that is to say, the residue suitable to be energetically exploited, is calculated from equation 1.
where γ is the useful index that takes the value 0.35 for chemically untreated wood residues from the total residue (mTR) (ALTENER, 2002).
The global assessment of the potential of the energy of the wood residue can be carried out through the lower heating value (LHV) (López-Rodríguez et al., 2009). The potential of the available energy (EAR) of the mAR is obtained from equation 2.
where ETR is the energy of the total residue that has not been chemically treated. The wood residues mixture of this industry to be recovered has been estimated on average to have a LHV of 14,442 kJ/kg with 20% moisture content (ALTENER, 2002).
Results and discussion
Table 1 shows the mass and the energy of the total residue and the available residue in the CMA.
Mass and energy of the total residue and available residue from the first and second wood transformation industries in the CMA municipalities.
20% moisture content. (-) no quantity value.
AR, available residue; E, energy; M, mass; TR, total residue.
The BIORAISE GIS data base has also been used to determine the cost of the residues at the wood transformation plant and global transportation cost (including driver, vehicle, and fuel) from the plant to the collecting point in each municipality. Table 2 shows these costs in terms of dry tonne (dry t) at an average estimated diesel fuel price of 1.45 €/l. Only those municipalities producing residues above 70 t/year have been considered. These municipalities generate 99.9% of the AR.
Residues costs per dry tonne at the wood transformation mill gate and their transportation costs of the plant to the collecting point.
Siero municipality stands out for having high production of available residues at low cost which makes it an ideal location as a CMA collecting point. Residues costs in dry tonne (dry t) at the wood transformation plant and their transportation costs from the plant to the collecting point at La Belga in Siero are indicated in Table 3.
Residues costs in dry tonne at wood transformation mill gate and their transportation costs from the plant to the collecting point at La Belga (Siero).
The total cost of the residues (i.e. the biomass cost plus the transportation cost) to La Belga (Siero) is below 54 €/dry t (Table 3), that is to say the costs are much lower than the wood biomass supply costs in the European pellet production plants. The wood biomass supply costs are 83–110 €/t or 119–160 €/t, including both biomass and transportation costs to destination (customer or harbour, respectively) in the European pellet production plants (Trømborg et al., 2013).
Conclusion
The study carried out in the CMA of the Principality of Asturias indicates that the total residues chemically untreated (excluded the bark) of the first- and second-transformation industry come to 22.7 kt/year. The available residues, having a carbon content of 50% on dry basis, come to 7.9 kt/year and 114.7 TJ/year, which generate 11.6 kt/year of CO2 neutral emissions (Paredes and Xiberta, 2010b).
Siero municipality stands out for having high production of available residues at low cost which makes it an ideal location as a CMA collecting point. It is therefore justified the construction in Asturias of a plant of densified solid biofuels such as pellets in La Belga in the Siero municipality. The potential production capacity of the pelletization process is 8 kt/year, which is equivalent to 10 MW of fuel output per 3200 operating hours (Bergman, 2005; Nilsson et al., 2011).
Footnotes
Declaration of conflicting interest
The author declares that there is no conflict of interest.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.