Horizontal vapor generating unit

966,995. Indirectly heated steam boilers. BABCOCK & WILCOX CO. March 27, 1961 [March 28, 1960], No. 11066/61. Heading F4A. In a steam boiler comprising a horizontal, cylindrical pressure vessel 12 containing below a water level 14 therein a bundle of U-shaped tubes 20 which convey hot vapour or vapourliquid mixture from an inlet header 34 to an outlet header 36, rapid circulation of water over the tubes 20 is promoted by enclosing the tube bundle between outer and inner baffles 52, 54 to provide a generally U-shaped space 56 for the upward flow of water over the tubes and outer and inner downflow spaces 58, 60 conveying water to the bottom of the space 56. Downflow of water in the inner space 60 is assisted by a flow of feedwater from a pipe 32 located in the top of this space and having downwardly directed perforations therealong. Water treatment chemical feed lines 62 and blowdown lines 64 are positioned above the downflow spaces 58 on each side of the tube bundle. Steam coming from the tube bundle is released more uniformly from the surface of the water in the vessel 12, thus promoting a more effective separation of the steam and water by locating a triple baffle 66 consisting of three spaced perforated plates just below the surface. Specification 775,156 is referred to.