GB1060962A - Improvements relating to vapour generating, superheating and reheating units - Google Patents

Abstract

1,060,962. Once through vapour generators. BABCOCK & WILCOX CO. June 4, 1965 [June 5, 1964], No. 23925/65. Heading F4A. A once through forced flow vapour generating, superheating and reheating unit comprises a vertically elongated pressure vessel 12 having a bank of helically coiled vapour generating tubes 98 supported by steel grid 134, extending upwardly from a feed water inlet 48 and water inlet tubes 74, 100, to four equi-spaced steam outlet chambers 102. The steam formed passes to four equi-spaced superheater inlet chambers 110 to pass through helically coiled superheater U-tubes 112, supported from brackets 118, contained in an annular pass between the casing of the vessel 12 and a depending baffle 116 also supported by brackets 118, to exit through four equi-spaced superheater outlet chambers 122 to the point of use. Steam for reheating enters through four equi-spaced reheater inlet chambers 124 to pass through the helically coiled reheater U-tubes 128 supported by steel grid 136 and located in the parallel annular pass defined by the baffle 116 and an escape tube assembly 78, to exit through the four heated outlet chambers 132 to a further point of use. Liquid sodium is supplied through superheater inlet conduit 142 and reheater inlet conduit 140 to respective ring main distribution systems 154-158 and 148-152 to heat the superheater and reheater tube banks 112, 128 respectively, the liquid metal from both passes combining to heat the vapour generating tube bank 98 on its way to the liquid sodium outlet 70. The metal is normally maintained in the vessel 12 at a level 160. The escape tube assembly 78 constructed in sections 80, 82, 84 provided with a rupture disc 166 at the top provides relief means for gases generated due to possible interaction of the sodium and water. The vessel 12 is constructed from five wall sections 20, 22, 24, 26, 28 and upper and lower closure heads 30, 14 all bolted together to facilitate dismantling and reassembly. Cylindrical liners 32, 34, 36 adjacent these sections define annular spaces 38, 40, 42 forming protective argon or stagnant liquid metal jackets to protect the shell from thermal stresses. On dismantling of the unit after drainage, the upper closure head 30, the heating fluid distribution system piping and section 80 of escape tube assembly 78 may be removed as a first unit. The fifth wall section 28 and the reheater tube bank 128 may be removed as a second unit; the fourth wall section 26, the superheating tube bank 112, the baffle 116 and the supporting brackets 118 all together as a third unit; the third wall section 24 and section 82 of escape tube assembly 78 as a fourth unit; and the second wall section 22, the vapour generating tube bank 98, the feed water inlet tubes 74, 100, tube sheet 52 and section 84 of escape tube assembly 78 as a fifth unit, leaving only the first wall section 20 and lower closure member 14 remaining.