Page 139 - Advanced Gas Turbine Cycles

Chapter I. The combined cycle gas turbine (CCGT) 111

QLR QA
.c

Fig. 7.2. Combined cycle plant with heat loss between higher and lower plants.

Ekj. (7.6) can be written in another form, defining
QL -I-- QHR = -[ (1 vUN %) 1
rlB=-- (7.7)
QHR -
as the fraction of the total heat rejected by the higher cycle which is supplied to the lower
cycle, a form of ‘boiler efficiency’ for the heat transfer process. The combined plant
efficiency may be written as
TLQL QHR
=
VcP= %+ - %+TIL%-- = %+%TL - %%%. (7.8)
QB QB
or

rlCP = % + (rl0)L - VH(rlO)L, (7.9)
where (7)o)L is the overall efficiency for the lower cycle, equal to the product of thermal
efficiency and ‘boiler efficiency’, TL~B.

7.4. The combined cycle gas turbine plant (CCGT)

The most developed and commonly used combined power plant involves a
combination of open circuit gas turbine and a closed cycle (steam turbine), the so-called
CCGT. Many different combinations of gas turbine and steam turbine plant have been
proposed. Seippel and Bereuter [3] provided a wide-ranging review of possible proposed
plants, but essentially there are two main types of CCGT.