GB758465A - Improvements in tubulous steam generators - Google Patents

Abstract

758,465. Water-tube steam boilers. BABCOCK & WILCOX, Ltd. Dec. 21, 1954 [Dec. 23, 1953], No. 35759/53. Class 123(2). In a water-tube boiler comprising a furnace 1 having a gas outlet 9 leading to a downpass 10 followed by an up pass 12 locating a superheater 13 and in which the walls of the furnace and gas passes are lined with steam generating tubes 21, 23, 30, 40 respectively extending from lower headers 22, 24, 31 and 41 to an upper steam and water drum 20, downcomers 46 .. 49 supplying water from the drum to the headers, the water space 90 of drum 20 is divided into three separate spaces 90a, 90b, 90c by transverse partitions 95, 96 which project slightly above the highest working level, spaces 90a and 90b being respectively about twice the volume of spaces 90b and 90c. A feedwater supply pipe 105 is disposed in space 90a whilst space 90c has a blow-down connection at 109. The drum is provided along its interior sides with longitudinally extending pockets 50, 70, the pockets being respectively divided into three parts 50a, 50b, 50c and 70a, 70b, 70c by baffies 61, 62 and 81, 82, the baffles 61, 81 and 62, 82 being slightly displaced from the adjacent partitions 95, 96. The steam-water mixture from the generating tubes discharges into the pockets, that entering pockets 50 being conveyed into pockets 70 through cross-over tubes 84.. The upper parts of pockets 70a, 70b, 70c are connected to a row of centrifugal separators 100, for example as described in Specification 526, 825, disposed in the space 90. Water removed from the steam in each separator is returned to the water space of the drum, whilst the steam passes upwardly and leaves the drum to flow up the superheater 13 through a purifier 111 and conduit 113. The steam generating tubes are divided into three groups A, B and C each containing some of the tubes 21, 23, 30, 40, the number of tubes in each group being such that the heat absorbing capacities of groups A, B and C are in the ratio of 22 : 11 : 7. The lower headers 22, 24, 31, 41 are each divided into three sections each feeding the tubes of the respective group A, B, or C, and each being fed with water from spaces 90a, 90b, 90c respectively through the downcomers 46 .. 49. With the exception of a small number of tubes, all the generating tubes of groups A and B discharge into pockets 50a, 70a and 50b, 70b respectively. The remaining small number of tubes of groups A and B discharge into the adjacent pockets 50b, 70b and 50c, 70c respectively. All the tubes of group C discharge into pockets 50c, 70c. In operation, the major part of the steam is generated in the group A tubes fed with comparatively pure, fresh feedwater from pipe 105. Water spaces 90b, 90c and, therefrom, the tubes of groups B and C are fed respectively from spaces 90a, 90b by water transferred through the small number of steam generating tubes referred to above. There is thus a progressive concentration of impurities in the water from the feed to the blow-down end of the drum. Since a high proportion of the steam is generated in those sections of the drum where water is relatively pure, the total of impurities in a given quantity of the steam due to water entrainment is less than it would be with no sectionalisation of the drum.