Open access publications in the SLU publication database

Abstract

Renewable fuels such as rape methyl ester (RME) and ethanol for heavy diesel engines can be produced with different systems solutions regarding e.g. scale of production. The main purpose of this thesis was to assess the environmental load during small-scale production of RME and ethanol. This was achieved by carrying out limited LCAs, including air emissions and energy requirements. The influence of using alternative plant sizes and fuel production strategies, as well as systems for making organic farms self-sufficient in farm-produced RME, ethanol and biogas, was also evaluated. For using natural resources as efficiently as possible, it is important that the machines for making the fuels are optimised. Therefore, the influence of some press parameters on capacity and oil extraction efficiency of a small rapeseed oil expeller was studied. It was found that to achieve a high capacity and a high oil extraction efficiency, the press was best operated with a small nozzle and a rather high screw speed. On a systems level, the LCAs showed that the dominating step in the production of RME and ethanol was crop cultivation, in which production of fertilisers, followed by soil emissions and tractive power, made major contributions to the environmental load. The differences in environmental impact and energy requirements between small-, medium- and large-scale plants were small for both fuels. The longer transport distances to a certain degree outweighed the higher oil extraction efficiency, higher energy efficiency and more efficient use of machinery and buildings in the large-scale system. The results were largely dependent on the method used for allocation of the environmental burden between the fuels and the by-products, whereas the influence of uncertainty in input data and of some alternative production strategies was small. For organic farming, the production and use of RME had a favourable energy balance and resulted in valuable by-products, but was less positive in other aspects, while the production of ethanol was very energy consuming. Biogas production had a low relative requirement for arable land and thus lower cultivation and soil emissions. For all fuels studied, the global warming emissions were approximately halved in comparison to conventional farming.