Study On CO₂ Reforming Of CH₄ To Syngas By Thermal Plasma Jet

With the petroleum resources becoming increasingly exhausted, more and more attention has been focused on the exploitation of natural gas that is clean and abundant worldwide. Since both CH₄ and CO₂ are major greenhouse gases and the plentiful sources of carbon, how to utilize them is of great significance for resources utilization and the protection of environment.The major work of this thesis is thermodynamic analysis and the application of plasma jet in CO₂ reforming of CH₄ to synthesize gas, which includes four parts.First, this thesis sums up the development of synthesis gas produced from CH₄ and CO₂ by traditional methods and cold plasma at home and abroad. Meanwhile, the studies and application of conversion of CH₄ by thermal plasma are briefly recounted.Secondly, the physical properties of hydrogen as discharging gas of thermal plasma jet are analyzed. According to the characteristics of the experimental system, the self-consulted equations are established, and the relation between decomposition intensity and temperature of hydrogen is derived at different input power and different flow rates of discharging gas. It is found that the decomposition intensity of hydrogen increases quickly between 3000～6000K, therefore, the plasma jet should work in this temperature region.Thirdly, the high-temperature thermodynamics of the reforming process is also analyzed. The temperature effect on the conversion and selectivity is calculated with different molar ratio of CH₄/CO₂. It is found that not only the temperature but also the molar ratio of CH₄/CO₂ could affect the selectivity of both H₂ and CO. And the optimum reforming reactive temperature and molar ratio of CH₄/CO₂ is 1100K and 4/6 respectively.Finally, the effect of input power, feedstock flow rate and molar ratio of CH₄/CO₂ on conversion and selectivity is investigated respectively with a thermal plasma generator of 15 kW. Experimental results show that the conversion of methane and carbon dioxide is mainly determined by plasma power and feedstock flow rate, and the selectivity of hydrogen and carbon monoxide is sensitive to molar ratio of CH₄/CO₂. These experimental results are consistent with the theoretical analysis. According to the energy balance calculation of the reforming reaction, a method to further improve energy efficiency is proposed preliminarily.Integrating various factors, preferable conditions of reforming reaction, i.e. input power, feedstock flow rate and molar ratio of CH₄/CO₂, are 8.5kW, 1.3m3/h and 4/6 respectively. Under these conditions, the conversion of methane and carbon dioxide is 87.98% and 84.34%, the selectivity of carbon monoxide is 82.27%, and the energy efficiency is 1.63mmol/kJ, all of which are higher than the other methods of CO₂ reforming of CH₄ to synthesis gas by plasma. Accordingly, the CO₂ reforming of CH₄ to synthesis gas by thermal plasma jet could not only bring larger output volume, less by-products and green process, but also higher energy efficiency.