PhD Thesis - Energy Systems Research Unit - University of Strathclyde

As the time required for one batch is generally between two and four days, the
batch process will run through a number of days longer than the batch length
before starting to record data, when a continuous feedstock supply is being used.
This allows the batches to start working through so that the ethanol production
and energy requirements will start from the beginning, for the different batches
running simultaneously. This is also done in the transesterification process if
the batch length is longer than 24 hours, but this is not generally the case. The
outputs of the batch process simulation are the same as for the continuous
process described in Section 6.4.2. This process is also shown in Figure 6.7.
6.4.4 Use of Residues
If energy crops are used, a certain amount of crop residue may be available.
This may, again, be used as cattle feed, sent to an anaerobic digester or gasifier,
or burned directly to produce heat and/or electricity, depending on the residue
type, and other system requirements. The processes for dealing with this type of
residue are as described in Section 6.3.4. If these crop residues are used to meet
some or all of the process energy needs, the input energy requirements and
amount of residue produced are reduced accordingly.
If a dry animal feed is produced, this can be used or processed in the same way
as the energy crop residues. Determining the feedstock availability for this
residue, however, is more difficult than for the crop residues, as it is produced
more erratically. This is not a problem when gasification is being considered, as
the feedstock is put into a store when available, and used from that store when
possible. The gasification process characteristics are defined, and the outputs
and energy use are calculated, in the same manner as described in Section 6.1,
and the various options for processing the resulting gas are also available. If the
dry animal feed is to be made available for use in boilers, engines or turbines, a
temporal production rate graph for a specified “other” category of fuel is
produced.
If a wet animal feed is produced, this may be sent, if desired, to an anaerobic
digester. This is also an option for the dry animal feed. The erratic nature of
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