GB719423A - Improvements in fluid heat exchange apparatus - Google Patents

Abstract

719,423. Combustion-air heaters. BABCOCK & WILCOX, Ltd. Oct. 26,1950 [Oct. 29, 1949], No. 16302/52. Divided out of 719,378. Class 64(1) . In a method of protecting a heatexchanger, e.g. a combustion air heater, from condensation from heating gases, a first part of a stream of heating gas is passed through a first section of the heatexchanger after cooling in a further heatexchanger and a second and separated part of the heating gas stream is passed through a second section of the heat-exchanger adjacent the cold fluid inlet without passing through the said further heatexchanger. In the form shown, an economizer 91 and two air heaters 75 are associated with a water-tube boiler 76. By a suitable setting of dampers 96, 97, Fig. 1, controlling gas flow to a space 94 above the air heaters 75, and damper 92 in an air heater by-pass duct 88, heating gases from the boiler may be directed through boiler gas outlet 83 to flow in series over economizer 91 and air heaters 75 to gas outlet duct 93, or they may be directed in streams flowing in parallel, one of which flows through gas outlet duct 83, over economizer 91 and through by-pass duct 88 to gas. outlet duct 93, and the other of which flows through a longitudinally extending lower gas outlet 85 to space 94 above the air heaters and then through the tubes or other elements cf the air heaters to the gas outlet 93. As seen from Fig. 2, the air heaters 75 are adjacent one another, each air heater having an inlet 109 for cold air and an outlet 112 for air heated by flowing over the air heater tubes. In order to avoid corrosion of the tubes by excessive cooling of the heating gas when the air heater is operating at relatively low temperatures, a flow of the heating gas from the boiler is caused to pass at all times through further lower gas outlets 85a, 85b, Fig. 2, and through rows 117 of air heating tubes lying adjacent the cold air inlet 109 of each air heater, this flow taking place irrespective of the flow of the remainder of the boiler gases over the main part of the air heater and the economizer as directed by the setting of dampers 92, 96, 97. U.S.A. Specification 2,418,815 is referred to.