GB913719A - Improvements relating to a furnace installation - Google Patents

Abstract

913,719. Recirculating combustion products. STEIN, ATKINSON STORDY Ltd. Jan. 13, 1959 [Jan. 13, 1958], No. 1313/59. Class 51 (1). A heat treatment furnace, such as a soaking pit, is heated by a burner 14 firing through a Venturi port 13 and flue gases escape through an outlet 19. A passage 26 feeds flue gases entrained by part of the combustion air delivered by a nozzle 25 to mix with the gases issuing from the burner 14 in the port 13. The total amount of air fed to the burner is controlled in accordance with the temperature of the furnace, and the fuel/air ratio is maintained by a control 40. A valve 24 in the line 36 supplying air to the entrainment nozzle 25 is controlled by the furnace temperature in the opposite sense to the main air supply valve so that the proportion of combustion air fed to passage 26 and hence the amount of flue gas recirculated varies inversely with the fuel and air supply to the burner 14. The ratio control 40 is adjusted by a device 30 in dependence on the furnace temperature, its deviation from the required value, the combustion air temperature and the air flow through the passage 26 so that as the proportion of the combustion air fed through passage 26 increases, the fuel/air ratio of the supplies to burner 14 increases, so that when the furnace is at its maximum temperature, the whole of the combustion air flows through passage 26 entraining combustion products, and the fuel flow to the burner 14 is a minimum, and when the furnace is cold the whole of the combustion air is fed to the burner 14 with the maximum amount of fuel. Instead of using a temperature-sensitive device to adjust the ratio control unit, a fuel line may by-pass the ratiocontrol operated valve, the fuel flow through the by-pass being controlled in accordance with the flow of air through the recirculation passage.