Patent GB-957481-A (GB)
Title: Forced-flow once-through steam generators for critical or super-critical conditions
IPC: F22G7/14
Filed: 1961-08-15
Abstract: 957,481. Fluid-pressure servomotor control systems. SULZER FRERES S.A. Aug. 15, 1961 |Aug. 26, 1960], No. 29446/61. Heading G3P. A method of operating a forced-flow oncethrough steam generator designed for normal operation at critical or super critical conditions, comprises regulating the feed, at pressures below the critical pressure, in dependence on the working medium temperature at the end of the evaporator zone, and at critical pressure or above in dependence on the working medium temperature at a point downstream of the conversion zone. The temperature in a tube 63 of the evaporator or conversion zone, depending on the pressure, is measured by a rod 64 which acts through a lever 65 on a control valve 68 to determine the pressure in a pipe 69 acting on a spring loaded piston 71. Similarly the temperature downstream of the zone is measured at 40 to determine the pressure acting on a spring loaded piston 72. The pressure in the generator is fed through a pipe 81 to act on a piston 80 which is loaded by an adjustable fluid pressure determined by a transmitter 131 whereby when the pressure in the generator reaches critical pressure, the piston 80 moves to the right to move a lever 77 from the position shown to the dotted line position thus altering the temperature control from movements of piston 71 to the movements of piston 72. Such movements adjust the position of a leak valve 82 to move piston 84 and a control valve 86. The valve 86 controls the pressure in a pipe 90 which acts on a slide valve 91, which controls a piston-cylinder device 93, and also acts on one end of a piston-cylinder device 95. The opposite ends of the slide valve 91 and device 95 are subjected to pressure existing in a pipe 58 which, with the piston 80 in the position shown (i.e. below critical pressure), is the pressure determined by control valve 106 in accordance with the wetness of the steam but at or above critical pressure, is the pressure determined by a transmitter 127. The piston 80 also acts through a lever 120 on a three-way valve 126 to change this control. Movements of the pistons of the devices 93, 95 act through lever 96 on the control valve 97 of the power device 99 which controls a throttle valve 12 in the feed line. The device 99 is also subjected to the pressure in a pipe 119 which is controlled by a valve 118 actuated by a cam 117 in response to flow. The wetness of the steam is measured by the flow measured by a restriction 110 and diaphragm 112 acting on a cam 114, operating a control valve 109 and by the water level in a separator 14 operating a control valve 102. These control valves determine the pressures in pipes 56, 60 acting on a control valve 104 of a piston-cylinder device 105 which operates the control valve 106. In a modification, the control of the feed may be through the adjustment of an hydraulic coupling between the drive motor of the feed pump. In a further modification, control in response to wetness of steam may be omitted. The temperature signal in the evaporator 3 may be provided by the maximum temperature in the tubes.