Biogas as a resource-efficient vehicle fuel

Nov 2007

The so-called ‘first generation’ of biofuels is expected to dominate renewable transportation fuels for the next ten years. However, when considering a long-term perspective, new biofuel production systems need to be developed because several of the ‘first generation’ biofuels, such as ethanol from wheat and corn and biodiesel from rape seed, have limitations regarding their resource efficiency. This is particularly relevant if by-products from production processes are not used efficiently. Examples of the emerging ‘second generation’ of biofuels are vehicle fuels based on lignocellulose and fuels produced by thermal gasification, including methanol, dimethylether (DME), Fischer-Tropsch (FT) diesel and methane, as well as bioethanol produced by hydrolysis and fermentation. However, these novel conversion technologies are not yet commercially available.
Another alternative and complementary option is the production of biogas by anaerobic digestion of energy crops. Biogas can also be produced from organic residues from agriculture (e.g. manure and crop residues), from by-products from the production of ethanol from cereals (distiller’s waste) and from by-products from biodiesel production from rape seed (rape meal and glycerol). Current biogas production is mainly based on sewage sludge in municipal waste-water treatment plants. The production and use of biogas as a vehicle fuel is increasing in Sweden and now exceeds the use of natural gas as vehicle fuel. Sweden has taken the lead in this development but biogas as vehicle fuel is also used in Switzerland, and there is emerging interest and continuing development in the area in other countries, including Germany, Austria, France, Spain, India, China and the USA. To date, almost all of the biogas produced worldwide is used for heat and electricity production. The development of biogas production for use as vehicle fuel is hampered by several factors: (i) the poorly developed commercial market in biogas technology and the need to improve the quality of the resulting biogas for vehicle fuel use; (ii) the limited distribution systems and number of biogas filling stations; and (iii) the higher costs of dual-fuel vehicles compared with vehicles using either ethanol or biodiesel.
In this paper, the potential benefits of increased use of biogas as a vehicle fuel are discussed by comparing biogas with other biomass-based vehicle fuels from the points of view of energy efficiency and environmental aspects. The overall conclusion is that biogas has several advantages over the two liquid biofuels (biodiesel and bioethanol) that are the current focus of vehicle biofuels. This provides incentives for further technological developments in biogas production systems with regard to cost reductions, which could increase its competitiveness as a vehicle fuel.

By: P. Borjesson, B. Mattiasson (Lund University)

 
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