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SUMMARYThe emission of toxic metals from the combustion of fossil fuels is an important global environmental issue. Solid absorbents can be used to control the emission of toxic trace elements from coal combustion. In this paper, limestone, CaSO , bauxite, kaolinite and CaO are employed for this purpose and experiments are carried out in an electrically heated drop-tube furnace. The trace elements investigated are Pb, Cd, Cr and As. It is observed that the absorptive capacity is related to the qualities of the absorbents (type, amount and particle size) and the combustion temperature. The results also show that some absorbents can reduce SO emission simultaneously, but no in#uence on NO V emission.

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Pressurized oxy-fuel combustion is regarded as a new generation of oxy-fuel technology. The ignition delay times of methane in an O2/N2 atmosphere (0.21O2 + 0.79N2) and an O2/CO2 atmosphere (0.21O2 + 0.79CO2) were measured in a shock tube at a pressure of 0.8 atm, an equivalence ratio of 0.5, and within a temperature range of 1501–1847 K. The present experimental data and the experimental data of Hargis and Peterson at 1.75 and 10 atm were adopted to evaluate five representative chemical kinetic models. This paper studied the chemical effects (chaperon effects of CO2 and the effects of reactions containing CO2) and physical effects of CO2 on the ignition of methane at different pressures and temperatures in detail using a modified model. Artificial materials X and Y were employed to analyze the chemical and physical effects. The analysis showed that the physical effects of CO2 inhibit the ignition of methane and are not sensitive to the temperature. The chemical effects of CO2 vary greatly with the pressure and temperature. At 0.8 and 1.75 atm, the chemical effects of CO2 promote the ignition of methane at a high temperature while suppress the ignition of methane at a low temperature. The chaperon effects of CO2 promote the ignition of methane in O2/CO2 atmospheres at a high temperature mainly because of HCO + M ⇔ CO + H + M. The chaperon effects of CO2 suppress the ignition of methane at a low temperature because of 2CH3 (+M) ⇔ C2H6 (+M). The chemical effects of CO2 offset half of the physical effects of CO2 at a high temperature, and those two effects are great at a low temperature, which is the reason for the fact that the effect of CO2 is subtle at a high temperature and evident at a low temperature. At 10 atm, the chemical effects of CO2 suppress the ignition of methane at 1350–1700 K. The chaperon effects of CO2 suppress the ignition of methane mainly as a result of 2CH3 (+M) ⇔ C2H6 (+M) and are strengthened with the decrease of the temperature. The inhibition of reactions involving CO2 is mainly attributed to CO + OH ⇔ CO2 + H and weakened with the decrease of the temperature; thus, the chemical effects of CO2 on the ignition are almost not sensitive to the temperature. The effects of CO2 have almost not change with the temperature at 10 atm.

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