Boiler fuel savings by heat recovery and reduced standby losses

Abstract

This paper is concerned with an investigation into the fuel savings that can be achieved in a fuel-fired package boiler by the use of an economiser which incorporates a flue damper, linked via a controller, to the burner. The fuel savings are accomplished by two means. 1. 1. By direct heat recovery from the flue gases leaving the boiler and 2. 2. By a reduction in boiler draught and cooling losses by closing the flue damper which is activated on burner shut down. These losses occur during normal burner cycling and standby periods. Experimental heat recovery data were obtained from a hot gas boiler simulation test rig, and shown to be dependent on the exhaust temperature, excess air level and boiler size. Standby savings were predicted from a boiler cooling model, based on measured boiler cooling rates and draught conditions. Details of the cooling model are given in the paper. The standby savings were found to depend on boiler operating time, the number of burner cycles during boiler operation and the boiler cooling rate time constant, burner purge time and flue gas damper delay time. Overall the fuel savings that can be achieved were found to be in the range 6–16% depending on the operating conditions prevailing, and additional tests on boilers confirmed these findings.