Combustion Characteristics Of Low Calorific Gases In Porous Media And Its Industrial Applications

Combustion in a porous medium offers advantages such as high power density, low NOx and CO emission, high thermal efficiency, high flame stability and extended flammability limit. The thesis introduces the combustion characteristic of low calorific gases in porous media combustor and the combustion wave propagation in porous media through experimental and numerical method, and those results are used to design and develop meso-scale and large-scale reciprocal combustion system.The first chapter focuses on the background and the literature review. The utilization of natural gases and low calorific gases in China is introduced. The research groups of porous media combustion all over the world and their research areas are summarized. The literature review focuses on the heat transfer in porous media, temperature distribution and temperature measurements, combustion wave propagation and flame stabilization, flame variation and flame instability, and reciprocal combustion system. Several further research trends of porous media combustion are recommended. The motivation and the main work in the thesis are also presented in this chapter.The second and third chapters focus on the experimental researches. A novel method was used to measure the gas and solid temperature in porous media combustor. The temperature distribution, combustion wave propagation, excess enthalpy flame was also studied by experimental method. A packed bed porous media combustor system was built, the bare and coated thermocouple junctions were installed in the centerline of the porous combustor and the temperatures of solid phase and bare junctions were recorded simultaneously. The preheating procedure is used to reduce the effect of the junction placement. It is found that the uncertain position of junction have limited influence on the gas phase temperature correction. The temperature profiles measured by thermocouples provide a complete temperature distribution in porous combustor, while a time-based method offers detail gas and solid temperature distributions near the reaction zone. Meanwhile a SiC foam porous media combustor was built, the temperature was measured, and the effects of inlet velocity, equivalence ratio, and pore density on excess enthalpy, combustion wave propagation and the temperature distribution were studied. The damage of porous media caused by over temperature limit was also initially studied.The forth and fifth chapters focus on the numerical studies. The two-dimensional and two temperature porous combustion model was used to study the two dimensional flame variation and inclinational instability. A two-dimensional model was developed based on the combustor built in the laboratory to show the combustion wave propagation in the cylindrical porous combustor. The two-dimensional contours of solid temperature are applied to show the combustion wave propagation. The inlet velocity, equivalence ratio, heat losses and pore density were discussed to show the effect on the combustion wave propagation and the flame variation. The results were compared with the experimental results to show accuracy of the model. Meanwhile, the model was modified to show the inclinational instability in porous media. The flame inclination development and reduction with a finite angle during the combustion wave propagation was studied. The mechanism of inclinational instability of filtration combustion was analyzed. The parameters affecting development of the inclinational instability at various conditions were studied. Finally, the regions where the combustion waves could be stabilized and instability grows were obtained in a model porous media combustor.The sixth and seventh chapters focus on the industrial applications of porous combustor. A50,000Nm3/h low calorific gas combustion system was designed based on the previous work. The design approach, design program, the drawing of furnace, and the layout of gas system were completed. The results show that the thermal efficiency can be as high as88.67%; the reduction of CO2emission is equal to15.4%of a300MWe coal-fired power plant per year. A meso-scaled reciprocal smelting furnace was built and experimentally studied. The best operational condition, the length of regenerative section, the flammability was obtained based on this reciprocal furnace. These results will be benefit for the design of large-scaled reciprocal smelting furnace and low calorific gas combustion system.The eighth chapter focuses on the conclusions of the work, the main results were presented, and the innovation and the future work were discussed. The gas and solid temperature distribution, temperature variation, combustion wave propagation, and excess enthalpy was experimentally studied, the two-dimensional flame propagation, flame variation mechanism, and inclinational instability mechanism was numerically studied. The economic benefit and environmental benefit of the large-scaled low calorific gas combustion system was industrially studied, the experiments of meso-scaled reciprocal smelting furnace would be benefit for increasing the thermal efficiency of metal smelting industry and for design of large-scaled reciprocal porous combustion system.