Comparisons Of NO_x Reduction Via Different Coal Combustion Methods And Application Of Decoupling Combustion

There are about 570 thousand industrial boilers in China, and chain grate boiler is the major industry combustion equipment accounting for 60% of the total number of industrial boilers. NO_x control was not carried out for small and medium scale coal-fired boilers with low-efficiency and serious pollution to environment due to no effective technologies and the corresponding environmental standards. Thus, the technologies to reduce NO_x for small and medium scale coal-fired boils are urgently needed.Decoupling combustion and reburning of combustible gas from pyrolysis and gasification are new low NO_x combustion technologies suitable for medium and small scale coal-fired boilers. The Decoupling Combustion divides the coal combustion process into two steps, pyrolysis and combustion. Coal is first pyrolyzed, and the resulting volatiles and char are in turn combusted in a reorganized way allowing the use of their capabilities for reducing NO_x. At present, comparisons of NO_x reduction via different coal combustion methods are not carried out systematically. Therefore, in this paper the reduction of NO_x emission via different combustion processes occurring in real furnace, such as normal combustion, air-staged combustion, pyrolysis gas reburning, partial gasification gas reburning and decoupling combustion, were investigated experimentally with a specially designed two-stage reactor using different coals. Furthermore, a 1.4MW industrial boiler designed according to the principle of decoupling combustion technique was tested and compared with traditional combustion boiler.The NO_x formation was effectively suppressed by reburning the gas from pyrolysis and partial gasification of coal, making the NO_x emission obviously lower than that of the air-staged combustion. It was found that the decoupling combustion led to the highest NO_x reduction rate over 32% in comparison with the normal combustion. The NO_x reduction ratio was depend on the difference of coal, which showed that the higher the fuel ratio (fixed carbon/volatile matter)at per nitrogen content in coal, the lower NO_x emissions in reburning of combustible gas from pyrolysis and gasification and decoupling combustion. The NO_x emission due to partial gasification gas reburning varied with the oxygen amount applied to gasification, which showed the lowest value in the oxygen concentration range from 8% to 10%. The running data from the 1.4MW industrial boilers based on degoupling combustion showed that the decoupling combustion reduced 32.9% NO_x emission in comparison with the boiler based on traditional combustion.