GB1043889A - Improvements in steam generators having flue gas recycling - Google Patents

Abstract

1,043,889. Forced flow steam boilers; recirculating combustion gases. SULZER BROS. Ltd. Dec. 6, 1963 [Dec. 21, 1962], No. 48345/63. Headings F4A and F4B. A steam generator in which flue gases are recycled through the space between the combustion chamber tube wall and a solid wall extending over at least part of the combustion chamber, consists of a vertical combustion chamber 1, Fig. 1 (not shown), fired by burners 35 and containing panel type superheating surfaces 8. Flues 7, 9 extend from the top of the combustion chamber and contain contact heating surfaces 31 . . . 34 for superheating, reheating and preheating. The chamber and flues are bounded by tube walls 2, 3, 10, 11 which are spaced from solid walls 4, 12, 13 forming spaces 30, 37, 38 respectively. A portion of the flue gases are drawn by fan 6 from the flue 9 and recycled via an annular duct 5, approximately half way up the combustion chamber, through the passages 30, 37, 38. The tube walls are thereby heated on both sides which considerably reduces their thermal stresses, further by varying the recirculation flow the combustion chamber flame temperature can be influenced. Gases passing downwards through passage 30 enter the combustion chamber through opening 41, between the bottom of the tube walls 2 and the top edge of the funnelshaped tube wall 3, and opening 42 in the bottom of wall 3 through which combustion air enters. Additional outlets of various sizes can be arranged in wall 2 to increase the area of mixing of flame and recycled flue gases. If the outlets are distributed over the entire height of the combustion chamber the hot flame gases can be prevented from touching the walls, thereby reducing the formation of S0 3 and the consequent cold corrosion. The solid walls may consist of a sheet metal skin and thermal insulation 25 and may be of circular cross-section particularly if the generator is operated at a pressure above atmospheric.