Coking Rules And Decoking Technology Of Coal Pyrolysis To Acetylene In Rotating Arc Plasma

Pyrolysis of coal to acetylene by arc plasma is a very promising high-efficiency and green coal conversion technology.One of the biggest problem that restricts the industrialization of this pyrolysis technology is the coking problem of the reactor,which affects the stability and continuous operation of the system.The gasification and coking conditions under different pyrolysis conditions were studied systematically in this work,and CO2 plasma was used as decoking medium.For the first time,the coking/decoking rules under different experimental conditions were quantitatively studied,which were based on the two parameters of coking ratio and decoking ratio,which laid a foundation for the inhibition of reactor coking and the development of efficient and rapid decoking technology.The coal was pyrolyzed to acetylene using hydrogen as working gas in 50 kW rotating arc plasma reactor.The effects of input power,system H/C ratio and feed rate on coal pyrolysis efficiency were studied.The experimental results show that the mainly gas phase products of coal cracking are C2H2,CH4 and CO.The content of C2H2 decreases with the increase of input power,the content of CO increases with the increase of input power,and the content of CH4 is not affected by the change of input power.As the system H/C increases,the carbon conversion rate of the cracking experiment increases gradually.When H/C=5/1,the highest carbon conversion rate can reach 51.33%.The acetylene selectivity and acetylene yield reached a maximum at H/C=4/1,and the highest acetylene yield was 19.6%.When the hydrogen flow rate was 4.4 Nm3/h,and the specific enthalpy was 3.92 kWh/Nm3,acetylene selectivity was 40.19%.Higher carbon conversion at low feed rate and higher acetylene selectivity and acetylene yield at high feed rate.The reactor coking ratio under different pyrolysis conditions was determined experimentally,and the influence of experimental conditions on the coking ratio was quantitatively analyzed.The results show that when the input power is lower than 22?23 kw,the coking ratio remains stable with the increase of input power.When the power is higher than 22?23 kW,the coking ratio will increase rapidly with the increase of power.As the H/C ratio of the system increases,the coking ratio of coal pyrolysis gradually decreases.Increasing the input quantity of HZ can suppress the decomposition of acetylene from the perspective of reducing temperature and chemical equilibrium,and effectively reduce coking.With the same H/C ratio,coking severity is more severe under the lower feed rate,and the coking ratio is even more than 40%.Analysis of the composition of pyrolysis residual coal shows that the higher input power means the higher temperature,the more thorough release of coal volatiles and the more complete pyrolysis.The structure of coke on the inner wall of the reactor was characterized.It was found that the closer to the high temperature zone of arc plasma,the larger the particle size of carbon black.Also it means the more obvious agglomeration,and the higher degree of coke graphitization.The CO2 plasma was used for eliminating coke,and the eliminating coke efficiency was quantitatively evaluated by the decoking ratio.The results show that the eliminating coke process was divided into three stages:the initial stage,the middle of the eliminating coke,and the end of the eliminating coke.The initial stage is generally within 60 s,at the same time the decoking ratio is the fastest.More than 60%of the coke in the reactor is vaporized in a short time,and then the decoking ratio begins to decrease gradually.Generally,the decoking ratio can reach 90%at around 150 s.At a high power and high gas velocity condition,the coke gasification reaction is faster,the eliminating coke speed is faster,and the decoking ratio can reach a higher level in a shorter time.