Study On Scheme For Acetylene Production From Coal By Plasma Pyrolysis With Coal-bed Methane As Refrigeration

Because of relative scarcity of oil reserves in the world, coal will replace oil as the main raw material of chemical industry in the future. New-style coal chemical engineering industry must be energetically developed in China. Acetylene can be directly produced by coal plasma pyrolysis, which can realize efficient and clean conversion from coal to chemical products.It is showed by thermodynamic study on volatile matters system of coal and reactions of carbon and hydrogen under plasma conditions in this paper that acetylene is mainly converted from the volatile matters deducting CO released by coal pyrolyzed in plasma torch when the temperature is below 4000K and so the conversion ratio of carbon in coal to acetylene is too small but the specific energy required (SER) of acetylene is very high. So the temperature of reaction system must be raised above 4000K in order to improve the conversion ratio of carbon in coal to acetylene.Thermodynamic systems of total elements of coal are studied in this paper to obtain approaches to improve the conversion ratio of carbon in coal to acetylene. As a result, the optimized reaction conditions are determined for the process to produce acetylene from coal by plasma pyrolysis: the temperature of the initial reaction system must be above the sublimation point (about 4000K) of graphite;before quenching process, the H/C ratio of the system should be about 6 and the total pressure should be about 0.5MPa;the system must be quenched at the temperature of about 3460K with adequate quenching rate. Approaches are further studied in this paper to reduce SER of acetylene, where, considering reduction of the initial energy inputted for the reaction system and recycle of the energy released during the quenching process of the high temperature system, a new method to produce acetylene from coal by plasma pyrolysis with coal-bed methane as refrigerant is proposed in this paper: first, the initial system with H/C ratio as 2.25 (Baode coal is taken as an example andcarbon in CO is deduced in this text) is heated to a temperature over 4000K;then, certain H2 is added to cool the system and to adjust H/C ratio of the system to 6 at the temperature of 3460K with total pressure as 0.5MPa and just no solid carbon;later, coal-bed methane is added as refrigerant to quench the system, where the temperature of total system is about 2000K;finally, the total system is quenched by water or liquid hydrocarbon to room temperature. The conversion ratio of carbon in coal to acetylene in this method can be improved to 94.9% and SER of acetylene can be reduced to 6.38 kWh /kg-C2H2, which has obvious advantages in economical and environmental profits compared with other method to produce acetyleneIt is showed by chemical kinetic study in this paper that initial quenching rate of (0.88-1.0)X108K/s is needed for the quenching process from 3460K to 2000K of high-temperature gaseous system with coal-bed methane as refrigerant and initial quenching rate of (0.7-2.5) X 107K/s is needed for the quenching process from 2000K to 500K of the total system.Experiments on pyrolysis of graphite carbon substituting coal in hydrogen plasma torch are studied in this paper, in which the results of thermodynamic studies above are proved and the feasibility of the new method is also basically proved by the experiments with graphite sublimating in hydrogen plasma torch.