Radiant Tube Burner for Liquid Fuels

摘要

In a project supported by the Arbeitsgemeinschaft Industrieller Forschungsvereinigungen e.V. (A1F) (research association) an oil burner for radiant tubes has been developed at the Department of Heat and Mass Transfer EST, RWTH Aachen [1]. The capacity range of the burner is 20 kW to 40 kW, as combustible fuel oil (Heizol. Extra Leicht) is used. The radiant tube burner was investigated at furnace temperatures of 1000 deg C. Despite of the fact that the combustion air was preheated to a temperature of 850 deg C, extremely low emissions were achieved. At a firing rate of 39 kW the NO_x-emissions were at approx. 100 ppm (3 percent O_2), the CO-emissions were clearly below 25 ppm. By balancing the radiant tube temperature of + - 15 K a very low value could be achieved, which is necessary for optimal heat transfer to the material to be heated. By the determination of the recirculating mass flows and validation of these values by computer-aided simulation, the understanding for the phenomena taking place couid be clearly improved. The total recirculation ratio with a value of r approx = 1.5 explains the minimal NO_x-emissions. By means of the. software code CFX numerical simulation computations were carried out, the aim of which was the computation of reacting flows and the calculation of the ratio of the recirculating waste gas. The computation method was successfully tested at a simplified two-dimensional model of the radiant tube. The comparison between measurements carried out and the results of the simulation amounts to deviations of up to 10 percent for the relevant range of application and up to 30 percent in total.