Power Plant Engineering

198 POWER PLANT ENGINEERING

Steamin

Steam Out

Fig. 6.3

Steam

50 bar

Exhaust to

condenser

Steam

50

Bar

Exhaust steam from

steam engine

1.5 Bar

Condenser

SteamReheater

Condenser

Fig. 6.4

through a reversing chamber, reentering bucket further round the periphery. This process is repeated
several times, the steam flowing a helical path. Several nozzles with reversing chambers may be used
around the wheel periphery.

(C) On the Basis of Means of Heat Supply:
(i) Single pressure turbine,
(ii) Mixed or dual pressure turbine
(iii) Reheated turbine.
(a) Single (b) Double
(i) Single Pressure Turbine : In this type of turbine, there is single source of steam supply.
(ii) Mixed or Dual Pressure Turbine : This type of turbines, use two sources of steam, at
different pressures. The dual pressure turbine is found in nuclear power stations where it uses both
sources continuously. The mixed pressure turbine is found in industrial plants (e.g., rolling mill, colliery,
etc.) where there are two supplies of steam and use of one supply is more economical than the other; for
example, the economical steam may be the exhaust steam from engine which can be utilised in the L. P.
stages of steam turbine. Dual pressure system is also used in combined cycle.

(iii) Reheated Turbine : During its passage through the turbine steam may be taken out to be
reheated in a reheater incorporated in the boiler and returned at higher tempera-ture to be expanded in
(Fig. 6.6). This is done to avoid erosion and corrosion problems in the bladings and to improve the
power output and efficiency. The reheating may be single or double or triple.

(D) On the Basis of Means of Heat Rejection :
(i) Pass-out or extraction turbine, (ii) Regenerative turbine, (iii) Condensing turbine, (iv) Non-
condensing turbine, (v) Back pressure or topping turbine.

(i) Pass-out Turbine. In this turbine, (Fig. 6.4), a considerable proportion of the steam is ex-
tracted from some suitable point in the turbine where the pressure is sufficient for use in process heating;
the remainder continuing through the turbine. The latter is controlled by separate valve-gear to meet the