GB1163555A - Once through vapor generators - Google Patents

Abstract

1,163,555. Once through forced flow vapour generator. FOSTER WHEELER CORP. 21 Oct., 1966 [22 Oct., 1965], No. 47412/66. Heading F4A. A once through forced flow vapour generator operating at subcritical or super-critical pressures comprises a gas tight tube lined rectangular furnace chamber 12, fed by burners 16 in its lower portion front and rear walls, the combustion gases flowing through the upper portion 22 of the furnace chamber into a convection pass 23. In the sub-critical generator, water from the economizer 30 in the convection pass 23 flows through downcomers 30b to the floor tubes 36 of the furnace chamber, forming the furnace pass No. 1. The fluid then passes to inlet header 38a and flows upwardly through a welded finned tube panel 38, comprising most of the lower front wall of the furnace, to outlet header 38b, thereby constituting furnace pas No. 2. From header 38b, the fluid flows through downcomers 39 to L- shaped inlet headers 40a, feeding L-shaped tube panels 40 occupying the remainder of the front and part of the side walls of the furnace and constituting furnace pass No. 3. From the outlet headers 40b of these panels, the fluid flows through downcomers 41 and mixing bottles 43 to the inlet header 42a of tube panel 42 comprising furnace pass No. 4, occupying the remainder of the side walls and the rear wall of the lower half of the furnace. From the outlet header 42b of this pass, fluid flows through risers 44 to the tubes 46 of furnace pass No. 5 lining the front and side walls of the upper part of the furnace enclosure, and extending between inlet and outlet headers 46a, 46b respectively. The fluid then flows through downcomers 48 to tees 50 on either side of the generator, whence it is distributed through lines 52, 56 and 58 to front, rear and sides screen tubes 24, 28 and 60 respectively surrounding a pendant super-heater 27, and through lines 54, 62 and 64 to the tubes lining the convection pass 23 and to a division wall 66 therein. All these tubes feed upper outlet header 68, whence the fluid flows through risers 70 to roof tubes 74 extending between inlet and outlet headers 72, 76 respectively. The fluid then passes through primary superheater 34 in convection pass 23, platen superheater 26 in front of furnace screen tubes 24, and finishing pendant superheater 27. A re-heater 32 is situated in the convection pass 23. The tubes forming the tube panels are 1“ inch outside diameter and of 0À180 to 0À200 inch minimum wall thickness. The number of parallel tubes in furnace passes Nos. 2, 3 and 4 progressively increases, their number and arrangement being such that in normal operation water is fed to the inlets of the tubes 42 of pass No. 4, this pass constituting the transition zone. These tubes may contain turbulators within them, whilst the mass flow rate through them is maintained above 1À65 x 10<SP>6</SP> lbs. per hr. per foot square to maintain " nuclear " boiling. In the super-critical unit, Fig. 6, fluid from economizer 116 flows through a first furnace pass 126 comprising a tube panel forming the front and part of the side walls of the lower furnace enclosure, a second furnace pass composed of opposed side wall panels 134, and a third furnace pass comprising tube panel (144) forming the remainder of the side walls and the front wall of the lower furnace enclosure. Fluid then flows through furnace pass No. 4 comprising tube panels lining the front and side walls of the upper parts of the furnace, and subsequently convection passes Nos. 5 formed of tubes lining the upper rear wall of the furnace enclosure, tube screens 170 and 172 and side and bottom walls 174, 176 of the convection enclosures surrounding pendant superheater 168. Convection pass No. 6 comprises the wall tubes of convection enclosure 114, whence the fluid passes through roof tubes 178 and the platen and finishing superheaters. The tubes of passes Nos. 5 and 6 may be combined in a single pass. In modifications, an additional furnace pass may be provided in the lower furnace side walls between passes Nos. 2 and 3, or a flat bottom furnace as with the subcritical generator may be utilized to provide an extra furnace pass. The tube numbers and arrangements in the passes Nos. 1, 2, and 3 of the super-critical unit are such that the mass flow rate per pass in these passes progressively increases. In both the sub-critical and the super-critical units the tube panels in the lower part of the furnace enclosure are suspended from those in the upper part, which are themselves top supported from a steel structure (not shown). A division wall may be incorporated in the furnace enclosure. With these constructions, temperature differentials between adjacent tubes are maintained at under 100‹ F.