Page 66 - Handbook of Energy Engineering Calculations

(3.66 m) to 15 ft (4.57 m) is needed between the bottom of the primary
superheater and the top of the economizer. This space is required for the
installation of the induct burners or for the adequate mixing of gas streams if
the furnace or an external combustor is used to supply the additional heat.
Another approach is to install a separately fired external economizer in

series or parallel with the existing economizer, which could be fired by a
variety of fuels. The most attractive possibility is to use waste heat from a
gas-turbine exhaust, Fig. 5. The output of this simple combined-cycle

arrangement would actually be higher than the combined capabilities of the
derated plant and the gas turbine.

FIGURE 5 Gas-turbine exhaust gases can be used in place of high-

pressure heaters, using a compact heat exchanger. (Power.)

The steam-cycle arrangement for the combined plant is shown in Fig. 5.
Feedwater is bypassed around the high-pressure regenerative heaters to an