Patent GB-864527-A (GB)
Title: Improvements relating to steam power installations
Inventor: DAVIS ALLAN WILLIAM
IPC: F01K15/04
Filed: 1956-10-23
Abstract: 864,527. Turbine power plant. FAIRFIELD SHIPBUILDING & ENGINEERING CO. Ltd., and FOSTER WHEELER Ltd. July 11, 1957 [Oct. 23, 1956], No. 32269/56. Class 110(3). A steam power plant in which superheated steam from a boiler plant is supplied to a turbine having reheating between the stages, the steam being reheated in a combustion chamber receiving considerable excess air, has a passage for the main supply of combustion air to the boiler burners, a passage to conduct the exhaust gases from the reheater to the boiler burners and automatic control means subject to the interstage steam pressure to shut off the fuel supply to the reheater in the event that the flow of inter-stage steam reduces below a predetermined value. A water-tube boiler 10 with a superheater 11, 11A supplies steam to a turbine plant consisting of high and intermediate pressure ahead stages 20, 21 and a high-pressure astern stage 23 arranged in tandem and a low-pressure ahead stage 22 and astern stage 24 also arranged in tandem as a separate unit. The steam between the stages 20, 21 is heated in the tubes 31 by the gases from the combustion chamber 32 fed with fuel by an oil burner 33 and with a considerable excess of combustion air by the furnace front casing 34. The exhaust gases are led by a duct 36 to a conduit 14 leading to the main boiler front casing so as to form a separate supply additional to the normal supply of combustion air to the main boiler burners. The fuel supply to the burner 33 is controlled by a valve 60 actuated by a device 61. The valve 60 is closed when the pressure in the piping 47 falls below a predetermined limit. The valve 60, Fig. 2, comprises a valve member 64 carried by a stem 65 having a hand wheel 66 and a screw-threaded portion 67 for hand operation and which is urged by a spring 68 to the closed position. A nut 69, axially movable but held against turning by a guide 70, carries a lever 77 which engages a stop 79 to hold the valve open. The lever 77 is connected to a piston 74 loaded on one side by a heavy spring 75 and on the other by the steam pressure in the piping 47A. If the steam pressure falls below a predetermined value, the spring 75 acts to pull the lever 77 away from the stop and against the fulcrum 81. When the steam pressure is restored the valve 60 is re-set by operation of the hand wheel 66. Valves 86, 87, 88 are provided to isolate the reheater. The combustion air to the burners 13, 33 is supplied by separate fans 90, 91, respectively. This air may be preheated in heaters 93, 94 by steam bled from the turbine. A desuperheater 108 may also be cooled by the combustion air, the amount of cooling being controlled by dampers 110A, 111A. In a modification, Fig. 3 (not shown), a single fan is used to supply combustion air to both of the burners. The air supply to the burners 33 being preheated by passing through a jacket surrounding the reheat combustion chamber. In another modification, Fig. 4 (not shown), a mixer is provided to mix the reheater exhaust gases with the combustion air supply to the burners 13. A further modification, Fig. 5 (not shown) has the suction of the fan supplying combustion air to the burners 33 connected to the discharge of the fan supplying combustion air to the burners 13. In a modification of its arrangement only the primary air to the burners 33 is boosted in this manner. The installation may consist of two or more main boilers to the burners of any one or more of which the reheater exhaust outlet may be ducted and provision may be made for directing the exhaust gases to any one or more burners at choice. The reheater may be used to reheat more than one interstage steam flow in the same turbine. The supply of fuel and combustion air to the reheater may be controlled manually or automatically in accordance with the temperature of the inter-stage steam leaving or entering the reheater.