PhD Thesis - Energy Systems Research Unit - University of Strathclyde

6.3 Transesterification
Transesterification is the production of methyl or ethyl esters (biodiesel) from
animal or vegetable oils. The feedstock for this process may be continuously
available (waste vegetable or animal oils), or seasonal (energy crops). Smallscale
production is batch-wise, and larger scale continuous processes are being
developed [7]. An example of the transesterification system definition window
is given in Appendix 1, Figure A1.16.
6.3.1 Feedstock Availability
Feedstock availability, for continuous and seasonal supplies, is dealt with in a
similar manner to that described in Section 6.1.1. For seasonal supplies, the oil
availability per day is calculated using Equation 6.3, where the crop yield is in
litres of oil per hectare. The electricity and heat required for oil extraction from
energy crops, if necessary, are calculated using Equation 6.1 or 6.2 (substituting
the heat requirement where appropriate), and are applied during the appropriate
times. As it is common to use the same equipment to process oils from different
harvest crops at different times of the year, to allow a more continual use, up to
five different seasonal supplies may be defined for use by the same processing
equipment. These are all added into the same store, as they become available, as
the performance of the processing equipment and process requirements are not
significantly affected by the use of different feedstocks. This process is shown
in Figure 6.5.
Again, the rate of use of oil from seasonal supplies may be slower than the
production rate to allow fuel production beyond the harvest periods. For
seasonal supplies, if there is excess feedstock left over in the store at the end of
the simulation period, and this is more than the minimum required for the fuel
production process, the entire simulation period is analysed again, and the
results from this second simulation period are used.
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