Kinetic Study Of Coal Char-steam Gasification Under Microwave Heating

Coal gasification is one of the important technologies to achieve high efficiency and clean utilization of coal.Although the coal gasification technology has been developed for a hundred years in China,the traditional gasification technology still has a large number of problems,such as large equipment,complex process,large investment,serious pollution and so on.As a new and efficient way of heating,microwave heating technology has been paid more and more attention.Interestingly,coal char is a strong absorbing material,which can rapidly heat up in the microwave field,making the application of microwave heating technology in coal gasification has infinite possibilities.And there were a large number of researchers have done a great deal of research about coal char-CO₂ gasification.But few studies have carry out in coal char-steam gasification.Because of the complexity of gasification,the mechanism of microwave gasification is still not clear.In this paper,using Inner Mongolia lignite char as raw materials,steam as the gasification agent.The effect of heating methods ?microwave and conventional heating? on the gasification reaction of coal char was studied,and the effect of different alkaline catalysts on the gasification reaction under microwave heating was also researched.The kinetic parameters of the two different heating methods were discussed,and the mechanism of the influence of microwave heating on the gasification reaction was analyzed.The results show that:?1?Under the same experimental conditions,with the increase of gasification temperature,the conversion rate of carbon conversion rate of coal char increases gradually,either in the traditional heating or microwave heating.?2?Under the same experimental conditions,the conversion rate of carbon for microwave heating is greater than that of conventional heating with the gasification temperature of 600-900?.Especially at temperature 700?,the carbon conversion rate of microwave heating is 2.3 times as high as conventional heating,and the spillover rate of the generated gas is 3.4 times as high as the conventional heating.So the microwave heating is more beneficial to increase the gasification reaction rate,and this phenomenon is more obvious at low temperature.?3?For two different heating methods,the content of H₂ and CO₂ gradually decreased with the increase of gasification temperature,while the content of CO increased gradually.?4?As for the coal char-steam gasification,the activation energy and the pre-experiment factor for microwave heating are 114.3 kJ·mol^-1?6.7×10⁴min^-1,and the conventional heating are 82.8kJ·mol^-1?4.7×10³min^-1.It can be refer that microwave heating can obviously reduce the activation energy of the gasification reaction of coal char-steam gasification.?5?Microwave gasification using de-ashing the coal char samples and loaded with different alkaline catalysts was conducted,and found that the catalytic activity of alkaline catalyst on coal char-steam gasification in this order:K-char>Na-char>Ca-char>Fe-char>Mg-char>de-ash char.And the KNO₃ also promotes the formation of CO₂ in the reaction.In addition,the Ca?NO₃?₂ has the effect of promoting the formation of CO in the generated gas.?6?By comparing the loading different content of KNO₃,it is found that undermicrowave heating when the loading amount is 5%,the catalytic activity of coal char-steam gasification is the best,the conversion efficiency of carbon is the highest,and the spilling rate of gas generation is the largest.When the loaded content is 5%,the activation energy of the catalytic gasification of conventional heating is 91.02 kJ·mol^-1,and the microwave heating is 55.52 kJ·mol^-1.