GB903012A - An improved method of and apparatus for generating superheated vapour - Google Patents

Abstract

903,012. Regulating forced flow steam boilers. BABCOCK & WILCOX Ltd. March 20, 1961 [March 22, 1960], No. 10045/60. Classes 123 (2) and 123 (3). In a forced flow, once-through steam boiler comprising economizer sections 10, 12, an evaporator section 14 and superheater sections 16, 18 disposed in an upright, cylindrical pressurevessel 8 and heated by a throughflow of coolant from a nuclear reactor 2, the heat output of which is regulated to give a substantially constant temperature of coolant at the reactor outlet, the feedwater supply to the boiler is controlled in response to the deviation from a preset value of a signal representing a comparison of a measure varying with the rate of coolant circulation and a measure varying with the rate of flow of working fluid in the unit in a manner tending to restore the actual value of the ratio to the preset value and hence to maintain the transition zone within preset limits, thus maintaining substantially constant the temperatures both of coolant and steam leaving the unit. In the boiler unit shown in Fig. 1, respective flows of coolant and superheated steam are measured and converted by transducers 45, 40 into signals which are transmitted along lines 46, 41 to a controller 36. In the controller the ratio of the flows is compared with a preset ratio which is varied with the load on the unit in response to a signal of steam pressure transmitted to the controller from a transducer 42. Any out-of-balance is transmitted to an actuator 54 which appropriately adjusts the feedwater regulator 56. As a fine or trimming control for the out-of-balance signal the rate of flow of feedwater as measured at'the orifice 30 is matched in the controller to the rate of steam flow. In a modification. Fig. 2, not shown, the coolant flow is compared with the rate of feedwater flow giving a ratio which is then compared with the load-dependent pre-set ratio. In further modifications, Figs. 3 and 4, not shown, no direct measurement is made of coolant flow, but measures of steam temperature in the superheater 18 or of pressure drop between the intermediate headers 26, 28 are taken, both these measures varying with coolant flow. The measures are compared with steam flow to give the control ratio. The measures may also be used as fine or trimming controls in conjunction with the arrangement of Figs. 1 or 2.