Patent GB-1114441-A (GB)
Title: Multiple pass arrangements for once-through steam generators
IPC: F22B29/06
Filed: 1965-05-17
Abstract: 1,114,441. Once through vapour generators. FOSTER WHEELER CORPORATION. 17 May, 1965 [27 May, 1964], No. 20780/65. Heading F4A. A forced flow once through vapour generator, comprises a gas-tight rectangular furnace enclosure 12 formed from a number of flow tubes continuously welded together in a plurality of passes. Feedwater from economizer 32 in a convection downpass, passes through downcomer 32b to a radiantly heated tubular division wall 22 extending upwardly through the furnace enclosure. From the division wall outlet header 22g a downcomer 22h transmits the fluid to furnace pass No. 1, formed of tubes which partly define the rear wall 20 and the rear parts of the side walls of the lower part of the furnace enclosure 12, and which extend between I- shaped inlet header 42b and U-shaped outlet header 42j. From outlet header 42j, the fluid flows through downcomer 42k to furnace pass No. 2 formed of tubes partly defining all four walls of the lower part of the furnace enclosure 12, which extend between double I-shaped inlet header 44b and rectangular shaped outlet header 44e. From outlet header 44e, the fluid flows through downcomer 44f to furnace pass No. 3 formed of tubes partly defining the front wall 18 and front parts of the side walls of the furnace enclosure 12 which extend between I-shaped inlet header 46b and U-shaped outlet header 46e. In the rear half of the furnace enclosure, the tubes of furnace passes Nos. 1 and 2 are intermingled in a two-to-one ratio, Fig. 14A, whilst in the front half of the enclosure the tubes of furnace passes Nos. 3 and 2 are similarly intermingled. Due to the plurality of furnace passes and the interleaved arrangement of the tubes of the passes, the temperature differential between adjacent tubes always remains less than 100 F. In a modification the furnace enclosure may have a flat bottom with U-shaped inlet headers (Fig. 16). From outlet header 46e, Fig. 2, the fluid flows through four risers 46f to furnace pass No. 4, formed from tubes defining the front and side walls of the upper part of the furnace enclosure which extend between U-shaped inlet and outlet headers 48c, 48d, respectively. The fluid then passes to a first convection pass from distributers 50b, 50c on opposite sides of the furnace, which feed both tubes 26 forming a front screen for a pendant finishing superheater 28, and tubes 30, and 50 forming the rear screen and the side walls of the finishing superheater enclosure. A subsequent second convection pass is then formed from tubes 52 lining the walls of the rear convection gas pass, and division walls 52d, 52e which divide that gas pass into economizer, high-pressure reheater, and lowpressure reheater passes 32, 34, 36, respectively, and from roof tubes 54. From roof tubes 54, the fluid flows through downcomers 54e to the platen superheater 24 which comprises a plurality of J-shaped drainable tube banks 24a offset from one another and situated in the upper part of the furnace enclosure 12, extending between inlet headers 24b and outlet headers 24c. The fluid finally flows through U-shaped platen finishing superheater tubes 28. The tubes of furnace passes Nos. 1 and 2 in the rear wall 20 are supported from above by the screen tubes 26 and 30. The tubes of passes Nos. 1 and 2 leave the rear wall 20 at differing levels, Fig. 14A (and see Fig. 14, not shown), whilst the screen tubes 26 and 30, here designated (5), also enter the wall at differing levels. Adjacent tubes of furnace passes Nos. 1 and 2 and tubes (5) are welded together where they overlap. The tubes of furnace passes Nos. 1 and 2 in the rear part of the side walls, and the tubes of furnace passes Nos. 3 and 2 in the front wall and the front part of the side walls are similarly supported from the tubes of furnace pass No. 4.