Pyrolysis Of Coal To Acetylene By Magnetically Rotating Plasma Arc

The partial oxidation(POX)method and calcium carbide(CaC2)method,are the two main approaches to produce acetylene.Thermal plasma with characteristics of high enthalpy density,high chemical reactivity and adjustable medium,provides a direct and clean way for the production of acetylene.Plasma conversion of carbonaceous materials such as coal,biomass and hydrocarbons,has been the research focuses recently.The target product varies from low hydrocarbons(C2H2,C2H4)to syngas or the combination of both.However,plasma conversion of chemicals suffers from poor mixing efficiency in heterogeneous reaction system,which is attributed to the asymmetric and inhomogeneous features of the plasma arc.In order to overcome the disadvantage,external magnetic field is one promising way to disperse the plasma arc,which will improve the arc uniformity.The rotating plasma is driven by the Lorentz force caused by the external magnetic field.The thesis is divided into two sections,the first is the characteristic of the magnetically rotating plasma reactor,while the latter focuses on the pyrolysis of carbonaceous materials to acetylene.Effects of various operating parameters on the rotating plasma are investigated by CFD method.And the shape of the rotating arc will transfer from radial-based to axial-based,the latter is similar to the pilot-scale plasma arc.The arc length will be prolonged by increasing gas flow rate,resulting in the increase in the voltage and power input.Also the plasma arc will be dispersed by the external magnetic field,while the arc root will be pushed back to the inlet direction with increasing magnetic flux density,which is called magnetic compressing effect.Effect of arc current on the plasma behaves the same trend as the magnetic effect due to the effect of the Lorentz force.Also Voltage-Current characteristics and thermal efficiency variation with various operating conditions are studied with two plasma reactors,50 kW and 1 MW, respectively.Voltage shows negative trend with the increase in arc current,and will increase with the increase in gas flow rate.On the contrary,thermal efficiency shows rather complicated trend with variation in arc current.Mixing efficiency was substantially improved due to the mixing effect in the magnetically rotating reactor.And the plasma conversion ratio of propane is approaching 100%in all the experimental tests.Attributed to the ultra-fast reaction rate under high temperature,plasma pyrolysis of propane usually complets in less than 1 millisecond.Acetylene is the primary product when carbonaceous materials was pyrolysed under high temperature(>1700 K).The mechanism of plasma pyrolysis of coal includes the evaporation of the water,devolatilization of the volatile matter,and char reaction.And the reaction of volatile is the crucial step for the formation of acetylene.Generally,acetylene yield is determined by both the content and constituent of the volatile matters released from coal particles.Effects of particle size,pressure and input power etc.,on the heat transfer and release of the volatile matters from the particle were studied.Results show that particle size is the key parameter for the pyrolysis of coal.Plasma pyrolysis of pulverized coal is carried out in one self-designed 1 MW magnetically rotating plasma reactor,and results show that compatible coal mass input with the specific hydrogen energy is the key parameter for the pyrolysis process.The optimum operating conditions are screened with abundant experimental data,and the range is H2 specific energy(SE)(1.40?1.90 kWh/Nm3-H2)with coal/H2 ratio(0.40?0.65 kg/Nm3),with the values of acetylene mole fraction(5%?6.5%),yield(?25%),coal conversion(?75%)and SER(11?15kWh/kg-C2H2).