Page 208 - Advanced Gas Turbine Cycles

Chapter 9. The gas turbine as a cogeneration (combined heat and power) plant 173
with AD = &G = 2.25,

(0.4/0.25)
FESR= 1 - = 0.2.
1 + (2.25 X 0.410.9)
For the supplementary fired plant of Fig. 9.2b with AD = 7.2 and with the parameter J,
taken as 1.2, so that F2 = 6, the fuel energy savings ratio is

FESR’ = 1 - (4 + 6)/(2.5 + 730.9) = 0.048.

Thus the FESR is less attractive when there is a large heat load and a WHB with
supplementary firing is used. In general, the FESR is probably the most useful of the CHP
plant performance criteria as it can be used directly in the economic assessment of the
plant [ I].

93. The unmatched gas turbine CHP plant

In general, a gas turbine CHP plant may not exactly match the electricity and heat
demands. A plant with a recuperator may meet the heat load (Qu)cG = AD but not the
power load ( WcG < WD = 1) so extra power from the grid is required (W,) as illustrated
in Fig. 9.4. Following a procedure similar to that given in Section 9.2.3 it may be shown
[ 11 that the performance parameters for the total plant are then

Fig. 9.4. Unmatched CHP plant laking power from the grid.