GB974662A - Improvements in or relating to steam producing apparatus - Google Patents

Abstract

974,662. Feedwater supply systems for forced flow steam boilers. P. LEGRAND. March 24, 1961 [March 29, 19601, No. 10935/61. Heading F4A. In a forced flow, once-through steam generator having a low pressure drop between the feedwater inlet and steam outlet, a reserve of water is provided to supply the boiler ternporarily should the pressure in the feed supply line suddenly fall due to feed pump failure, or to supplement the supply in the event of a feed line pressure drop due to excessive demand for steam, by connecting a water storage vessel in parallel with the tube system, the vessel being of such a height or located at such a level that the stored water is automatically delivered by gravity into the feedwater inlet when said pressure, drop occurs. In the form shown in Fig. 1, the generator consists of an upright vessel 1 located within the shield 12 of a nuclear reactor, the coolant gases from the reactor flowing downwardly through the vessel to heat a tube nest 9 therewithin. Connected between the feed inlet 4 and steam outlet 6 of the generator but located outside the shield 12 is a vertical columnar tank 2 with an upward extension 13 of height sufficient to prevent water flowing from the vessel 2 into the steam outlet. The tube nest 9 consists of layers of tubes wound helically around a core 10. In a modification the tube nest is of the type descrided in Specification 970,722, the tubes being grouped in threes connected by trifurcating pieces to the water and steam headers, each tube being double-walled and terminating in fittings as described in Specification 955,147, which constrain the water and steam to flow within the annulus between the double walls and the heating fluid to flow through the inner tube as well as flowing around the outer tube. In a further modification, Fig. 6, several heat transfer cells 35a, 35b &c. are disposed within the shield 12 and connected to coolant gas manifolds 42, 43. The water in the make-up tank 34 connected in parallel with the tube systems of the cells is heated by a coil 41 in a vessel 38, thermosiphon circulation being established between the tank and vessel through lines 39, 40. Steam flows from the generator to a turbine 49 the exhaust from which is reheated by indirect contact with live steam in a reheater 48 and flows to a lowpressure turbine 50. A drum 44 is disposed at such a height that it fills with water under full load conditions providing the auxiliary reserve.