Patent GB-885315-A (GB)
Title: Improvements in vapour generating and vapour heating units
IPC: F22B37/10
Filed: 1959-05-15
Abstract: 885,315. Water-tube steam boilers; super-heaters. BABCOCK & WILCOX CO. May 15, 1959 [May 19, 1958], No. 16742/59. Classes 123(2) and 123(3). In a steam generating and heating unit comprising a plurality of burners 40 disposed adjacent the bottom of a vertically elongated furnace chamber 21 which is lined with front, rear, and side steam generating tubes 22, 23, 24 respectively and has a gas exit 25 communicating with a lateral gas pass 26 accommodating a steam generating tube bank 29 connected between upper and lower drums 27, 28 primary and secondary superheater banks 46, 50 extend across the upper high temperature gas zone 21A of the chamber 21. The banks are provided with predominantly radiantly and convectively heated surfaces so that the steam is heated to a substantially constant temperature over a wide load range of the unit. The primary superheater 46 includes a plurality of vertically disposed, transversely spaced, return bend platen tubes 46a which have their discharge ends connected into an outlet header 47 leading to the inlet header 49 of the secondary superheater bank 50. The latter comprises a plurality of vertically disposed, nested, return bent tubes 50A, 50B which are transversely spaced and have their discharge ends connected to an outlet header 51. The ends of the tubes 46A and 50A, 50B, of the superheaters 46, 50 project outwardly through wall openings S, S<SP>1</SP> formed between the tubes 22C, 22E and 23 of the front and rear walls 22, 23 respectively, the tubes 22C, 22E being bent inwardly from the remainder of the front wall tubes 22B to form an arch 39 and provide a screen 22D in the vicinity of the furnace gas exit 25. The remainder 22B of the front wall tubes 22 enter the lower drum 28 beneath a baffle 28 which directs the steam and water mixture through a tube 28B to the upper drum 27. Every third tube 23A of the rear wall tubes 23 is bowed outwardly and, as between the spaced tubes 22C, 22E of the front wall, provide the narrower side wall spaces S for the ends of the secondary superheater tubes 50A, 50B. The upper wider spaces S<SP>1</SP> for the ends of the primary superheater tubes are formed by bowing outwardly further rear wall tubes 23B and by bending the front wall tubes 22E inwardly behind the tubes 22C. One end of each of the lowermost tubes 50A of the bank 50 is supported by a U-shaped bridge casting 62 which is made, e.g. of cast steel, and has channel-shaped leg portions 63A provided with inwardly projecting bosses 65 which are supported on the horizontal legs 61A of a pair of corresponding L-shaped lugs 61 which, with integral reinforcing gussets 61D, are welded to the appropriate pair of front or rear wall tubes 22, 23. A saddle 70, with an arcuate cradle 71, is welded to the end of each tube 50A to rest freely upon the upper surface of the corresponding bridge piece 62 and has a depending projection 74 which, cooperating with an upstanding flange 67 on the bridge piece 62, limits the movement between the latter and the saddle to within normal thermal expansion tolerances. Each bridge piece has a gusset plate 68 between the upper ends of its legs 63A. The supports for the other ends of the lower tubes of the primary and secondary superheaters 46, 50 such as where the wall spaces S<SP>1</SP> are greater, are provided with outer wing portions 66A to support extra saddles 70. The superposed tube lengths of the superheater banks 46, 50 are supported on saddles 75 the arcuate portions of which embrace the lower part of a tube supported thereon with the depending leg portion secured to the tube disposed immediately below the supported tube. The gases leaving the pass 26 are led through a duct 41 to an air heater 42.