GB693910A - Improvements in and relating to water tube boilers - Google Patents

Abstract

693,910. Water-tube steam boilers, superheaters. FOSTER, WHEELER, Ltd. March 28, 1951 [March 28, 1950], No. 7756/50. Class 123 (ii) and 123 (iii) In a steam boiler comprising a furnace 18 from which combustion gases flow through a bank 14 of steam-generating tubes, extending from an upper steam drum 10, to a lower water drum 12, to an exhaust duct 22, the latter locates final and initial steam superheaters 34, 26 respectively followed by an economizer 52 and air preheater 54; a desuperheater 30 is also fitted in the air supply duct 44 between the preheater 54 and the furnace burners 20. The flow of gases through the superheaters is controlled by dampers 40, 42, and the flows of combustion air through the preheater 54 and an associated by-pass by dampers 56, 58 respectively, these dampers being controlled by pistons 64, 65 actuated by a change-over valve 62. With the dampers in the positions shown a high degree of superheat is possible; when low superheat is required the dampers are set in the opposite positions so that the superheater 34 is by-passed by the gases and the preheater 54 by air, relatively cool air thus flowing to the desuperheater 50. Instead of, or in addition to, causing the air to by-pass the preheater, the combustion gases may be caused to by-pass said preheater by operation of a damper 60. The final high or low steam temperature is maintained constant by one of two thermostats 66, 67 which are fitted in the main steam outlet pipe 36 and are brought selectively into action upon operation of a valve 63, said thermostats controlling, through a regulator 69 and piston 73, dampers 46, 48 in the duct 44 associated respectively with the desuperheater 30 and a desuperheater by-pass.