Experimental Studies On Combustion Characteristic Of Syngas Swirl Diffusion Flame By Dilution

Integrated gasification combined cycle (IGCC) system is a new power generation cycle which can improve the efficiency of energy use. Considering the large concentration of hydrogen in medium or low-heat-value syngas, the problem of flashback and high pressure loss is arising in dry low NO_x (DLN) combustion system technology. However dilution combustion can efficiently reduce flame temperatures while not markedly lower fuel reactive, so it becomes one of the main solutions of syngas low emission combustion. To more deeply understand the concept of dilution combustion, 5 modes of steam and nitrogen dilution in syngas diffusion flames has been studied on an atmospheric-pressure, small-scale and preheated test facility system: fuel diluted with steam, combustion air diluted with steam, steam injected directly into the combustor, nitrogen diluted with steam and nitrogen injected directly into the combustor.First of all, the influence of dilution on flame root temperature fields, NO_x and CO emissions and the efficiency of combustion of the five different dilution modes were studied experimentally. It was found in the experiments that dilution have little influence on the efficiency of combustion, but NO_x emissions could be effectively decreased with the increase of dilution in five different dilution modes, and CO emissions increased in varying degrees. It can be concluded that steam injected directly into combustor and fuel diluted with steam are more efficient in reduction of NO_x and CO emissions.Then the stability of diffusion flames was studied. It was found that there were no lean blowout problems in these modes: steam injected directly into combustor, combustion air diluted with steam and nitrogen injected directly in combustor. However ,the fuel diluted with steam or nitrogen modes both have lean blowout problems, and steam dilution to fuel mode have narrower LBO limit than the nitrogen dilution. But they could work well on combustion stability in generally used NO_x emissions reduction ranges. The critical dilution is existent, and combustion flame will blowout when dilution degree is higher than it.In the condition of the same adiabatic flame and exhausting temperature, NO_x emissions could be effectively decreased with the increase of dilution degree in five different dilution modes while the CO emissions were still low because the flame temperature was high enough. Low NO_x emissions and designed outlet temperature would be achieved when the optimum equivalence ratioφand dilution degree of the fuel supply (DOH) were chosen.Finally, inner concentration and temperature field and combustor outlet emissions were measured in a typical status in different dilution mode. It could be concluded that both steam injected directly into combustor and fuel diluted with steam may more effectively lower flame temperature and steam injected directly into combustor may more effectively lower oxygen concentration in high temperature region of flameroot.