Page 213 - Advanced Gas Turbine Cycles

Chapter 9. The gas turbine as a cogeneration (combined heat and power) plant 177

temperature is limited, at the level corresponding to (QNU)CG/FCG = 3/16 as in the basic
plant, then corresponding limits on A’, are 27/4 for + = 1.5 and 27/2 for + = 1.2.

9.5. Design of gas turbines as cogeneration (CHP) plants

Both the heat to work ratio kG and the various performance parameters such as
EUF and FESR are affected by the choice of design parameters within a gas turbine.
However, for the gas turbine with a WHR, the range of &-G that can be achieved by
varying these parameters is not large and operation may have to involve firing a WHB,
or running in parallel with conventional plants, as explained earlier. But some variation
in kc can be achieved by varying the ‘internal’ design parameters (e.g. pressure ratio
and turbine inlet temperature), achieving matched operation for each of the different
designs, i.e. by varying kG to match AD. Porter and Mastanaiah [2] calculated kc for
a gas turbine with a WHR supplying process steam at pp, Tp. Plots of the heat to work
ratio A,-G against Tp are shown in Fig. 9.7, for a maximum temperature of 1200 K and
various pressure ratios, and with a limit on the stack temperature and compressor and
turbine efficiencies of 0.9.
The EUF and FESR are then simple to derive and typical area plots of the range of EUF
and FESR against the derived &G, for gas turbines with varying practical design
parameters, are illustrated in Fig. 9.8.
It is concluded that such simple gas turbines with WHRs have good energy utilisation at
kc = I with respectable FESR. The introduction of a WHB will move the operable area
to higher values of A, usually with comparable EUFs but lower FESRs, as has been
illustrated in the examples calculated in Section 9.2.

9.6. Some practical gas turbine cogeneration plants

There are many gas turbine CHP plants in operation for a range of purposes and
applications. Here we describe the salient features of two such plants, each operating with
a WHR but also with supplementary firing which can be introduced to meet increased heat
demands.

9.6.1. The Beilen CHP plant
A gas turbine CHP scheme, with a heat recovery steam generator producing process
steam, operates at the DOMO plant at Beilen in the Netherlands. The plant, which
produces dairy products, originally took its electric power (up to 3.2 MW) from the grid
and its heat load was met by two gas-fired boilers with a steam production of 25 t/h at
13 bar.
The CHP plant which replaced these two separate energy supplies is based on a
Ruston TB gas turbine (rated at 3.65 MW) which can meet the electrical demand of
3.2 MW and is connected to the grid so that excess electrical power can be sold. By
providing full gas power, up to 12 t/h of saturated steam can be produced at 191°C
and 13 bar. Five supplementary gas burners can be engaged to increase the steam