Patent GB-733545-A (GB)
Title: Improvements in or relating to the method and plant for producing superheated steam
IPC: F22B21/34
Filed: 1953-11-11
Abstract: 733,545. Steam superheaters; water-tube steam boilers. COMBUSTION ENGINEERING, Inc. Nov. 11, 1953 (Nov. 22, 1952], No. 31249/53. Classes 123 (2) and 123 (3). In a process for superheating and/or reheating steam generated in a water-tube boiler, a highboiling point heat-transfer liquid such as molten sodium, potassium, sodium-potassium mixtures, sodium nitrite or potassium nitrate or mercury is heated in tubes lining the combustion zone of the boiler furnace and passed to a steam heater which receives saturated steam from the boiler drum or interstage steam from a turbine, the steam being generated in tubes located in a region downstream in the gas flow path from the combustion zone. Fig. 1 shows a steam power plant comprising a natural circulation boiler having a furnace 1 the upper part of which is lined with steamgenerating tubes 2, 3, 4 connected between headers 12, 13, 14 and a steam and water drum 9, the water circulation being completed through downcomers 15. The lower part of the furnace which constitutes a combustion zone is fired by corner-mounted, tilting burners 28 and lined with thin-walled tubes 17, 18 carrying the heat-transfer liquid which are connected between lower headers 20, 22, 24 and upper headers 19, 21, 23. The gases from the combustion zone flow upwardly through the steam generating section of the furnace, then laterally through a steam generating tube lined pass 29 locating a high-temperature superheater 32 and downwardly through a pass 31 in which is mounted a low-temperature superheater 35 and economizer 40. Steam from the drum 9 passes through superheaters 35, 32 in series and thence to a high-pressure turbine 43. The steam is withdrawn at an interstage space in the turbine and reheated in a coil 48 mounted in a heat exchanger 49 which receives a flow of heat transfer liquid from the upper headers 19, 21, 23 through pipes 27, 51, the liquid being returned to the lower headers 20, 22, 24 through pipes 52, 26 by a pump 53. A second stage reheater 61 may be connected in parallel with heat exchanger 49. To provide protection for tubes 17, 18 when starting up the boiler, a third heat exchanger 54 is connected between pipes 27, 26, the internal coil 54c of this heat exchanger being supplied with water from drum 9 through pipes 57, 58, or with cooling fluid from an external source through pipes 59, 60. During starting-up, the liquid circulating in tubes 17, 18 can thus be cooled by the boiler water or by the cooling fluid. Whilst in operation the degree of reheat is controlled by diverting an appropriate part of the flow of heat transfer fluid through heat exchanger 54. The latter may be replaced by a coil disposed in the water space of drum 9. In a modification (Fig. 5, not shown), the steam is generated in tube banks located in downpass 31, water circulation being established by means of a pump. In this case the whole of the furnace is lined with liquidheating tubes, the saturated steam from drum 9 and the interstage steam from the turbine being respectively superheated and reheated in exchangers through which the hot liquid from the furnace tubes circulates.