GB831674A - Improvements in or relating to vapour generating and superheating units - Google Patents

Abstract

831,674. Water-tube steam boilers; superheaters. BABCOCK & WILCOX CO. March 25, 1958 [March 26, 1957], No. 9488/58. Classes 123(2) and 123(3) [Also in Group XII] A high capacity, high pressure, natural circulation water-tube boiler has an upright setting 20 including tube-lined front and rear walls 21, 22 and side walls 23 defining a lower furnace and gas cooling section 24 and a superposed convection heating section 25. The lower section 24 includes a common gas mixing or primary radiation chamber 24A formed by the side walls 23 and inwardly offset vertical portions of the front and rear walls 21, 22. The chamber 24A is connected to an upper radiation chamber 24B by a transition section 24C formed by the side walls and upwardly diverging portions 21A, 22A of the front and rear wall respectively. The unit is fired by cyclone furnaces 26, such as that described in Specification 552,747, which are adapted to burn low quality, high ash content, coarsely pulverized coal. Five furnaces 26 discharge combustion gases and molten slag through the front wall 21 and four through the rear wall 22 into the chamber 24A, the axes of the rear wall furnaces lying midway between those of the front wall. The spinning motion of the gases from one set of furnaces is in opposite sense to that from the other. The cyclone furnaces are lined with steam generating tubes which extend from a ring header 44 through the furnaces and pass as risers 27A through the front and rear walls 21, 22 into the chamber 24B wherein they alternate with some of the generating tubes lining the front and rear walls of the chamber 24A and extending from a header 30. All the tubes discharge into a drum 40. Others of the tubes lining the chamber 24A are bent inwardly to form L-shaped platens 35 the lower inclined legs of which are studded and refractorycovered and form a slag screen 35A across the path of the slag-carrying gases. The tubes of the upper vertical legs 35B are aligned to form a vertical partition 35C dividing the chamber 24B and the convection section 25 into two passes 36, 37, the partition being continued above the passes by a baffle 71. Gas flow is proportioned between the passes by outlet dampers 68, 69. The upper parts of the passes 36, 37 below economizers 48 respectively locate a primary superheater 49 and a reheater 50. Extending across the lower parts of both the passes, where the partition 35C is opened to form pressure equalization ports 52, is a section 49B of primary superheater and a secondary superheater 51. To ensure that slag particles still remaining in the gases after their passage through the screen 35A have solidified before contacting the superheater 51, cooled gases are recirculated by a fan (not shown) from the gas exit flue 63 to a distributing manifold 64. From the manifold the gases enter the setting through ports 65 in the front and rear walls just above the screen 35A, each port being located opposite but above the level of a cyclone furnace in the opposite wall so that a gas stream flowing upwardly from any cyclone furnace is impacted by a horizontally directed high velocity stream of tempering gas to give intimate mixing and rapid decrease in temperature as the gases expand in passing into the chamber 24B. Final steam temperatures are controlled by adjusting the dampers 68, 69 and by the use of a superheater interstage attemperator 57.