GB915627A - Improvements in and relating to heat exchangers - Google Patents

Abstract

915,627. Heating steam boilers by hot gases; superheaters. HEAD WRIGHTSON CO. Ltd. July 22, 1959 [Aug. 7, 1958], No. 25385/58. Classes 123 (2) and 123 (3). A boiler generating steam at a high and a low pressure is heated by the coolant gas from a nuclear reactor which flows from an inlet duct 17 and header 18 through a large number of tubulous heat exchange elements to a header 19 and outlet duct 20 whence it returns to the reactor for reheating. The heat exchange elements are disposed one above the other to form vertical grids, several of which are arranged side-by-side to form the complete boiler, each element consisting of a series of aligned outer pipes 2 which enclose a number of parallel connected inner tubes 21 extending between headers 18, 19 and which may be straight or arranged helically to absorb differential expansion. The tubes 21 carry the hot gas whilst the working medium flows through the space between the outer and inner tubes. The bank of tube elements is divided into five main sections, namely, an L.P. and H.P. superheater section I, a H.P. evaporator II, a H.P. preheater section III, an L.P. evaporator IV, and an L.P. and H.P. preheater section V. Sections I, III and V are respectively divided into subsections Ia, Ib, IIIa, IIIb and Va, Vb. Water enters the L.P boiler through a header 3 and flows successively through the sub-sections Va, Vb of alternate grids, the outer tubes of the sub-sections being serially connected at alternate ends to give oppositely directed flow in vertically adjacent tubes. The sub-sections are connected by a tube 5. The heated water leaves the preheater via a header 6 and passes to an L.P. drum, not shown, whence it flows via a header 7 through the serially connected outer tubes of the L.P. evaporator IV. Steam-water mixture returns to the drum whence separated steam flows through the L.P. superheater constituted by alternate grids in the sub-sections Ia, Ib which are connected by a pipe 10 to an associated L.P. turbine. The H.P. superheater and preheater are constituted by the grids which alternate with the L.P. grids in the sections I, V, the flow of H.P. working medium being the same as that for the L.P. medium except that water circulates from the H.P. drum through the additional preheater III before passing to the H.P. evaporator II. Adjoining sections in each element are separated by a tube plate 22, Fig. 5, to which aligned outer tubes 2a, 2b are welded, the inner gas-carrying tubes 21 passing through the tube plate. Further to minimize thermal stresses in the grids the external connections to the various sections and sub-sections thereof are arranged so that fluid flow in adjoining aligned outer tubes 2 is in opposite directions, whilst the end connections between outer tubes of one section or sub-section are displaced one tube pitch from those of the adjoining section or sub-section.