Experimental Study And Simulation In Natural Gas Cracked And Converted To Acetylene In Thermal Plasma

This thesis is concerning the acetylene production procedure through pyrolysis natural gas by thermal plasma jet. A high speed plasma jet is formed by means of arc discharging of the working gas, such as nitrogen, argon, hydrogen, etc., and natural gas is leaded to the high temperature jet. Under the conditions of oxygen-free, high temperature and normal pressure, natural gas is pyrolysed, and then converted into the acetylene by coupling reaction. It is a new method, which is different from the calcium carbide-hydrolyzing. Also, comparing with the early arc discharging and partly oxygenating techniques, plasma jet pyrolysis natural gas has more advantages, by which, for example, more suitable temperature, more favorable reaction condition, as well as higher production yield for methane conversion can be got.The thesis consists of four parts: First of all, the project background and its progress are reviewed. Natural gas is a rich natural resource, it has promising future of industry application. According to thermodynamics principle, plasma jet method has more advantages comparing with several kinds of acetylene producing. Emphases are given on the actual acetylene preparation through pyrolysis natural gas by thermal plasma. It is that the temperature grade in reactor must be as small as possible, the mixture of natural gas and plasma jet must be as quickly as possible. Therefore, it is necessary to study the feature on heat transferring and material flowing in plasma reactor systematically, and to develop a new reactor that has above characteristics. By means of computer simulation, the second part systematically simulate the mixing and heat transferring between plasma jet and the reactant in adiabatic reactor with 3D digital features. The fluids velocity, temperature distribution and the mixing are given. To get the boundary condition of simulation more practicability, two relative equations are deducted: one is the conjunction equation of equilibrium pyrolysis degree and temperature of jet gas according to the thermodynamics equilibrium; the other is the temperature of jet fluid and arc power by the energy conservation. By means of the two equations, the dependence of jet gas temperature and pyrolysis degree on arc power are resolved. With the typical technical parameters, the digital simulation indicates that there is a distinct mixing surface of the temperature and the concentration between jet gas and natural gas in the adiabatic reactor with 3D feature. At the mixing surface, the temperature reaches 3500k and the concentration of CH4 is 35%, it can be concluded that the plasma pyrolysis natural gas reaction mainly occurs at the mixing surface. The 3D digital simulation result not only verifies the rationality of the reactor design, but also provides referential data for the further study and application of plasma reactor.The third part is experimental research. Making use of the 200kw plasma reactor with the normal pressure condition, the pyrolysis action of natural gas in the N2 thermal plasma is studied. The dependence of reaction on input power, methane flux and length of reactor are investigated. The best result is natural gas conversion 97%, acetylene yield 90%, and the specific energy 13kwh/kg. Moreover, different yield of acetylene and carbon black is gained by adjusting the length of reactor. Experiments show a good agreement with thermodynamic equilibrium and indirectly verify our simulation for the typical technical parameters.Two important conclusions are given in last part. The process of natural gas converse to acetylene in thermal plasma jet is a thermodynamic equilibrium process, the adiabatic reactor with lateral double-hole inlet introduced in this thesis improves effectively temperature profile and mixing situation in plasma reactor.