GB1386555A - Reheating furnace - Google Patents

Abstract

1386555 Gas fired reheating furnace MIDLAND-ROSS CORP 15 Feb 1973 [17 March 1972] 7444/73 Heading F4B In an annular reheating furnace through which metallic workpieces are carried by a conveyer, hot gases rich in partial combustion products are introduced near the discharge end, and additional air is introduced between the charge and discharge ends of the furnace in amounts such the atmosphere is only slightly oxidzing in the intermediate zone and the temperature of the work is maintained below the temperature at which oxidation takes place in any zone. An annular rotary hearth furnace, Fig. 1, has a charging aperture 22 and discharge opening 24 separated by a radial partition 25. A flue outlet 26 at the charge end of zone 1 is connected to a flue stack 32 having an air heating jacket 34 and a burner 77 and air inlet 93 controlled by a temperature sensor 106 to regulate stack conditions. Burners 46, 47 in zones 1 and 2 are supplied with air from a fan 66, and are controlled by temperature sensors 96, 96<SP>1</SP>, 98, 98<SP>1</SP> in conjunction with air inlet devices 84, 86. Burners 48, 49 in zones 3 and 4 and a discharge end burner 50 are supplied with preheated air from the stack jacket 34 and are controlled by thermostats 100, 100<SP>1</SP>, 102, 1021 and 104 so that the fuel/air ratio in zone 4 is between 5 and 6 to 1 and that in zone 3 is between 6 and 8 to 1. Air inlets 86, 84 at the discharge ends of zones 2 and 1 are arranged so that the air flow reaches the inner wall at the same cross-section at which it reaches the roof, so that good mixing and the combustion of the fuel gas is completed in zone 1, while the atmosphere in zone 2 remains neutral. The burners in zones 1 and 2 are used to start up the furnace, the completion of the combustion of the gases from the burners in zones 3 and 4 providing sufficient heat during normal operation. During held periods, excess fuel is burnt off in the stack.