Patent GB-481668-A (GB)
Title: Improvements in and relating to steam power installations
IPC: F01K15/04
Filed: 1936-08-13
Abstract: 481,668. Steam power plant; fluid - pressure servomotor - control systems. PARSONS MARINE STEAM TURBINE CO., Ltd., and PARNALL, W. R. Aug. 13, 1936, No. 22355. [Class 110 (iii)] [Also in Group XXIX] A steam plant having a prime mover supplied with superheated steam and the auxiliaries with saturated steam from the same source has a desuperheater which is supplied with cooling water, preferably automatically, from alternative sources, i.e. from raw water, from distilled water (condensate) or from both as required. A marine turbine plant, Fig. 1, has a turbine HP, supplied with superheated steam from the boilers B, the auxiliaries A being fed through the desuperheater D, the cooling water supply to which is controlled by valves V<5>, V<6>. The pressure in the auxiliary steam range is controlled by a regulator R<5>, Fig. 3, which consists of a spring-loaded piston 1 subjected on one side to the steam pressure and on the other to the spring 2. If the steam pressure rises, the piston 1 moves upwards and pressure oil previously admitted through a branch PO to the space below a spring-loaded piston 10, Fig. 4, will escape to the leak-off LO and the valve 9 controlling the steam supply to the desuperheater will close, a fall in pressure in the steam range will cause the branch PO to be connected to the underside of piston 10 and allow the valve 9 to open. To vary the pressure in the auxiliary steam range it is only necessary to screw the sleeve 6 in or out of its housing thus varying the amount it is necessary to compress the spring 2 to bring the valve 4 to its balanced position. A main feed tank FT may be provided having automatic means for regulating the raw and distilled water supplies to the desuperheater. An oil relay valve, Fig. 7, controlled by a float in the feed tank is connected to valves V<4>, V<5>, V<6>, of the type shown in Fig. 4. Pressure-oil is supplied to the inlet 18a of the ported rotary valve 18 the ports of which are so formed that at a high level in the tank pressure-oil is only supplied to the valve V<5> i.e. the condensate supply valve is only open. As the level falls, the oil supply to valve V5 is cut off and it is connected to the outlet 18b, the valve therefore closing. At the same time, the valve V<6> controlling the raw water supply is opened. At a still lower level, indicating a shortage of feed water, the supply of superheated steam to the desuperheater is increased by allowing steam to pass through valve V<4> from the desuperheater to the turbine. In this float control the valves V<4>, V<5>, and V<6> are always fully opened or fully closed and while this is a satisfactory method of operating valves V5 and V<6> it is desirable that the valve V<4> should be open only to the extent necessary to meet requirements, and to meet this objection the valves V<5> and V<6> may be controlled by a float-operated relay valve similar to Fig. 7 whilst the valve V<4> is controlled by a float and is opened to an extent dependent upon'the fall of the water level. These two valves may be in a common housing and may be operated by the same or different floats. When the valve V<4> is open the additional desuperheated steam passing therethrough is directed by the valve DV, Fig. 13, to the turbines or to the condenser. The port o is connected to a suitable stage of the turbine so that if the load is low the pressure on the piston 23 will be low and valve 25 will be opened and the valve 25 closed. This will cause the steam to be directed to the condenser and prevent it upsetting the control of the main machine. If the load is high, the valve 25 will be closed and valve 24 opened thus allowing extra steam to be supplied to the turbine. In a further modification a portion of the exhaust steam from the auxiliaries is used in a surface type evaporator. In another modification the steam supply to the desuperheater may be increased when the water in the feed tanks falls to a low level and the valve V4 may be arranged to pass steam when the pressure in the auxiliary range rises above a certain valve.