| The low calorific value gas fuels whose calorific value is under1464kcal/Nm3are widely used in process of coal production, coal chemical industry, petrochemical engineering, steel industry, metallurgical industry and textile industry. For instance, blast-furnace gas, converter gas and carbon black off-gas can be categorized as low calorific value gas. The calorific values of the gas that mentioned above are above600kcal/Nm3, which can be utilized in industrial areas extensively and efficiently. However, the industrial applied research of super-low calorific value gas has come to public attention in last several years. What is worth mentioning is that this kind of gas fuel can be obtained easier in productive process than so called low calorific value gas. And for its large quantity in industrial areas, to develop the methods for its cyclic utilization is beneficial to both energy conservation and environmental protection.As stated above, the super-low calorific value gas whose calorific value is300kcal/kg is chosen as the research subject under this study. According to the characteristics of the fuel evolved in this study, there propose two enhanced burning methods using low calorific value gas as working fuel. The first method is combined firing of both high and low calorific value gas, while the second one is combined firing of coal and low calorific value gas. The research is conducted both experimentally and theoretically and the results can be used for future academic and industrial references. More details are as follow:1) Combined firing of both high and low calorific value gas fuelIn this study, we experimentally investigate the stabilized combustion performance of the turbulent burner whose structure has been optimized with different ratios of mixed gas fuel--high and low calorific value gas. The analytical data show that when the swirl angles of both secondary air flow and main fuel are60°, the stable combustion condition can be achieved using low calorific value gas with the calorific value300kcal/kg as main fuel. In this case, the ratio of high and low calorific value gas is21:79with the mean calorific value379kcal/kg. However, the mean calorific value of main fuel can be depressed to300kcal/kg if acetylene is added to main fuel as supplement, due to the moderate ignitability and stabilized combustion performance of acetylene.Furthermore, this combined firing method has proven to be efficient when it is applied to pyrolysis gas furnace which is used in lignite upgrading process.In this case, the ratio of high and low calorific value gas is23.5:76.5. As a result, we can draw the conclusion that the gas burner which is designed based on grading fire principle of recirculation zone has its own superiorities in ignitability and stabilized combustion performance.2) Combined firing of coal and low calorific value gasCompared with the separated device, the performance of integrated device is more predominant. The low calorific value gas can obtain stable combustion condition when the temperature of hearth can be guaranteed to exceed850℃, even if the calorific value of gas fuel is just273kcla/kg. Meanwhile, according to the experiment, the decreased edge effect is existed in the relationship between the feeding speed of coal and the temperature of fuel-gas. The similar conclusion can be seen in the relationship between temperature of fuel-gas emitted from combustion-supporting coal and the calorific value of low calorific value gas.Based on the previous study, we also find that coal can substitute for LNG as the post combustion, which is more reliable and economical in running lignite upgrading process. In detail, the running cost of lignite upgrading process can be cut down for13.6217million Yuan per year after reforming and the reform cost can be recovered in five months. In other word, The running cost would be dramatically decreased and the technology of lignite upgrading process would be improved if the reforming scheme is up and running. |
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