GB777249A - Improvements in and relating to governing systems for reheat turbines - Google Patents

Abstract

777,249. Turbines. GENERAL ELECTRIC CO. Sept. 24, 1953 [Sept. 24, 1952], No. 26363/53. Class 110 (3). [Also in Group XXIX] A power plant having in series a boiler, superheater, high-pressure turbine, reheater, main intercept valve, intermediate pressure turbine, low-pressure turbine and condenser has by-pass conduits and valves so arranged that in starting and warming up the boiler the cool steam may be by-passed around the turbines. The purpose of the arrangement is to allow a quick restart of the power plant before it has cooled down an appreciable amount. The valves in the drawing are shown in the quick starting position with the steam boiler 1, superheater 2 and reheater 5 shut down. In this position the hand wheel 32 is screwed down and the lever 19 depressed so that the main operating servopiston 17a is at the bottom of its stroke and the valves 13b, 46a closed. The hand wheel 48 is then rotated so that the nut 48a is at the lefthand end of the lead-screw 48b so that pivot 49a engages the left-hand end of slot 51a and pulls link 50 to the right so as to cause link 29 to move downwardly and overpower the preemergency governor 30. This causes the pilot 6f to drain the liquid from the motor 6c and the spring 6g to close the main intercept valve 6b. The manually-operated valves 39, 42 are then opened. With the condensate extraction pump 10 and boiler feed pump 11 operating, the boiler is fired. When the superheater discharge pressure reaches a value slightly higher than the rated pressure, a pressure detector 35 opens the valve 34 and maintains the pressure constant by allowing steam to pass through the pressure reducing orifice 41 to the inlet of the reheater 5. A temperature detector 38 maintains the temperature at the outlet of the reheater 5 constant by controlling a valve 37 regulating the supply of boiler feed water injected into a desuperheater 36. When the pressure at the discharge of the reheater 5 reaches a predetermined value, the pressure detector 45 opens the valves 43a, 43b and allows steam and boiler feed water to pass through the pressurereducing desuperheater 33 to the condenser 9 so that this pressure is maintained constant. The firing rate of the boiler is then increased until the steam conditions at the superheater outlet 2a have reached the normal working values. Under these conditions the temperature detector 38 is arranged so that the controlled temperature is within a safe differential from the temperature of the turbine parts. The turbines 4, 7 may now be started by rotating hand wheel 32 so that pilot 18a moves upwards and causes piston 17a to move up and open the pilot valve 13b and intercept by-pass valve 46a. Since the main intercept valve 6 is still closed, steam discharged from the turbine 4 passes through conduit 4a to the reheater 5 and if the flow through the valve 13b is larger than that through the valve 46a, a part of the steam will flow through conduit 5b to the condenser 9. When the valves 13b and 46a are three quarters open, the screw 32a may be backed away from the lever 19, and the turbine is then under the control of the main governor 23. Load may now be put on the turbines. When the governing valves open, the superheater and reheater outlet pressures tend to drop and thus the valves 34, 43a, 43b progressively close. At the same time, the link 51b moves to the left so that the pre-emergency governor 30 will gradually cause pilot 6f to lift and open the intercept valve 6 in proportion to the control valve movement. The hand wheel 48 may be rotated when the normal load is reached, so that the pin 49a on the lever 49 is moved to the dotted line position and floats in the slot 51a. The governor 30 is arranged to operate at a speed just below a predetermined overload value. At a higher speed emergency governors 28, 28a are arranged to shut down the emergency stop valve 3 and valves 40, 47. The pressure reducing desuperheater 33 comprises a plurality of pressure reducing orifices 33a, 33b, 33c arranged in series with a plurality of water spray nozzles 33d, 33e between them. The solid arrows indicate the flow in normal operation and the dotted arrows the flow during the quickstarting cycle.