PhD Thesis - Energy Systems Research Unit - University of Strathclyde

The performance of a steam turbine is not significantly affected by ambient
temperature or altitude and, therefore, does not require derating [18].
Otherwise, steam turbine performance may be modelled in the same way as an
ICE, as described in section 5.2, using percentage part load efficiency values as
the measure of performance. Again, as with an ICE, while the efficiency of the
steam turbine drops with partial loading, the amount of waste heat produced
increases proportionally, increasing the heat to electricity ratio, and keeping the
overall efficiency (heat plus electricity) fairly level [18].
As the steam turbine uses an external heat source to produce the steam necessary
to turn the turbine, the efficiency of the boiler employed to produce the required
heat to raise the necessary steam must be taken into account when calculating
the overall fuel requirement. This is done by calculating the fuel consumption
figure using Equation 5.33, 5.35 or 5.36 as appropriate, multiplying this by 100
and dividing by the percentage boiler efficiency. Due to the external nature of
the heat source, and fairly slow start-up time, the options to follow heat demand,
electricity demand or both are not appropriate for steam turbines, and are,
therefore, not available. Again, multiple turbine sets may be used, and these are
subject to a minimum recommended load. The output from this procedure is a
graph of percentage turbine loading, and fuel use is calculated and dealt with as
before in section 5.2. An example of the definition window for a steam turbine
is given in Appendix 1, Figure A1.35.
5.6 Fuel Cell Model
Various models exist to predict the performance of fuel cells [19,20,21], but
these rely on large volumes of information that are specific to a particular fuel
cell design. To allow development of a generic model that can be easily applied
to the different fuel cell types, manufacturers’ performance data will again be
used. This will allow the performance of any fuel cell type (e.g. Phosphoric
Acid Fuel Cells, Molten Carbonate Fuel Cells) to be simulated under various
load conditions, using the same procedure.
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