The use of coflowing jets with large velocity differences for the stabilization of low grade coal flames

Abstract

A new method of flame stabilization—the COFLOWING JETS WITH LARGE VELOCITY DIFFERENCES, is described. This is an improvement on the basic principle of creating a recirculation zone of high-temperature combustion gases as an ignition source and a means for flame stabilization. One or more small, high speed jets of air or steam, injected off the axis and in the same direction as the low-speed main fuel-air flow in the combustionn, chamber, create a large recirculation zone of high turbulence intensity in which the combustibles and high temperature gases are effectively mixed, and stable and intensive combustion can be maintained even for fuels with poor ignition qualities. After the traditional swirl and bluff body principles, this is another effective and practical method of flame stabilization. A pulverized coal combustor based on this method is shown to have excellent combustion characteristics and is very simple in construction. A number of precombustion chambers of this type have been installed and are being used in utility and industrial boilers in China. Using these precombustion chambers, successful startups and part-load operation of the boilers have been consistently achieved with unpreheated air and low grade coals having volatiles as low as 15% and ash content as high as 30%. This method shows good promise as an attractive technology in combustion.