GB1008553A - Improvements in steam-electric generating units - Google Patents

Abstract

1,008,553. Steam turbine plant. C. STROHMEYER JR. Nov. 15, 1961, No. 17571/61. Heading FIT In a steam-electric generating plant, throttle and shut-off valve T is disposed between the waterwalls of the steam generator and the superheater outlet to permit operation of the generator at two pressure levels and is responsive to a variable condition of the turbine or of the steam downstream of the superheater to vary the pressure in the portion of the superheater which is downstream of the valve. As shown in Fig. 4a the valve is disposed between two superheaters but it may be disposed upstream of a single superheater. The generator may be of the once-through type operating at either subcritical or supracritical pressure and temperature levels, a steam drum D being provided upstream of the throttle in the former case. The location of the throttle gives greater efficiency at starting up and shutting down and during periods of reduced load and can be so operated as to regulate temperature differences between steam and its containing metal walls downstream of the valve. The valve can be replaced by several valves in parallel and can be controlled by the temperature difference between downstream steam and its containment metal, by the steam temperature between turbine stages or by downstream temperature or pressure. The controlled temperature or pressure may be maintained constant. A by-pass BP upstream of the throttle T may provide steam for supply to the inlet of low pressure turbine at start-up or during light load so that the exhaust temperature therefrom is maintained. The by-pass may also be used to establish the flow through the water walls at start up or to prevent condensation in the superheaters or to remove condensate therefrom. As shown in Fig. 5, throttle valve 14, corresponding to valve T, is regulated by controllers 12, 13 operated by the difference in temperature between the metal parts of governor valve 17 of the turbines (detected at point 11) and the steam supplied to the valve (detected at 10). Alternatively temperature detectors 15, 16 associated with a throttle valve 18 in the steam supply to the turbines can operate controller 12. A control 19 may regulate the pressure upstream of valve 14. A controller 3 is responsive at 5 to the steam temperature on leaving the superheaters, at 21 to the steam temperatures upstream of valve 14 and at 1, 6 or 2, 7 to the exhaust temperature and metal temperature of the first stage outlet or the exhaust stage outlet of the high pressure turbine. An outlet 4 from controller 3 may influence an internal flow by-pass valve in the steam generator, or a fuel feed control, or air or gas controls in the generator or attemperation or desuperheating spray water controls, or a device to vary the heat absorption ratio between the evaporating and superheating sections to maintain constant the steam temperature at the control point. If the temperature of the nozzle chest to the high pressure turbine should rise excessively then a detector 22 operates controller 3. It may also control the rate of load change by altering the setting of the turbine governor or speed changer. A continuous recording chart 25 may trace the temperature of 22 and the electrical output from the system, the relative juxtaposition of these traces indicating whether the rate of load change is acceptable for satisfactory rates of change in metal temperature. As shown in Fig. 6, to prevent rise in the temperature of exhaust steam from a low pressure turbine 32 during start-up or under light load, steam from the generator before complete superheating or after desuperheating is mixed by pipe 33 with the steam supplied by pipe 30 from intermediate pressure turbine 31. Valve 34 in pipe 33 is controlled by controller 38 responsive at 39 to the temperature of the exhaust steam or at 40 to the temperature of the metal of the exhaust structure.