Dynamic Study On Co-gasification Of Coal Char And Biomass Char

As a sort of chemical energy which stores in biomass, because of its renewable, relatively stable performance, seldom constrained by natural factors and other characteristics,it can be used as a new supply of energy, to a certain extent, solve the problem of limited reserves of coal,oil and other fossil energy. And due to its high content of volatile matter, high gasification reactivity, and low ash content, it is suitable for gasification. Biomass gasification technology has been developped for one hundred years. However, there are some drawbacks in gasification of biomass alone, such as outdated technology, small-scale and low efficiency, but co-gasification of biomass and coal can be a good way to make up the defects of biomass gasification alone, such as unstable supply of raw materials and the bed instability. So, co-gasification of coal and biomass has become a new hotspot, and be taken seriously.Biomass chars which made from three different types of biomass-sawdust,white pine and corn stalks,were selected as study objects in this paper. In addition, Xilinhot lignite was selected to be made the char. Besides basic coal quality analysis of chars, specific surface area and pore diameter distribution test of chars also have been done. On this basis, using the thermal analysis technology, firstly study the reactivity difference of three kinds of biomass chars gasification with carbon dioxide at normal pressure with temperature 1073K.Secondly study the lignite char, wood char and mixed char gasification with steam and carbon dioxide at normal pressure with different temperatures. Finally study the three kinds of partially gasified chars gasification with steam and carbon dioxide with four different temperatures. Homogeneous model, shrinking spherical ashless particle model and mixed reaction models were used to fit the experimental data. The most suitable model was used to calculate kinetic parameters and compensation effect between kinetic parameters was analyzed.At last, we discuss the synergistic effect of co-gasification of biomass char and lignite char with steam and carbon dioxide.Based on thermobalance experiment date,the carbon conversion,reaction rate,reactivity exponent(R) and mean specific rate of biomass char,lignite char and mixed char were calculated,the result show that:(1) The reactivity of three kind of biomass chars from high to low are:wood char> corn stalks char> white pine char.(2) The carbon conversion of lignite char and wood char,at the same reaction time with carbon dioxide and steam all increased,and along with the increase of temperature,the time needed to reach the largest carbon conversion was shorten.(3) When gasification with carbon dioxide,the reaction rate of lignite char,wood char and three kinds of mixed char monotonicly reduce along with the increasing of carbon conversion.lt is a decreasing function of curve,and the curvature of the highest point in the the reaction rate is in turn reducing along with the temperature rising.When gasification with steam,the reaction rate firstly increased and then decreased, finally reduced to zero along with the increasing of temperature.When in the same conversion rate, the gasification rate increases along with the temperature increasing.In addition, the maximum reaction rate increases along with the increasing temperature, and the higher the temperature is,the more obvious of the rate curve peaks are.(4) When reaction with carbon dioxide and steam, with temperature 1073K, the reaction rate of mixed char generally ranged from wood char and lignite char.And when the reaction temperature is greater than 1173K, the reaction rate of mixed char is lower than that of the single char.(5) The reaction exponent and the mean specific reaction rate which with the same gasifying agent all increased along with the increasing of temperature.Except one or two experiment, the reaction exponent and the mean specific reaction rate of mixed chars are lower than that of single char,and all reduce along with the increasing of biomass char content in the mixed char.(6) When the lignite char, wood char and mixed char react with carbon dioxide and steam, the shrinking spherical ashless particle model has a high degree of linear fitting to the experimental data, and the kinetic parameters k, A, Ea were gained. The total reaction order of five chars were 0.0807～19.2618; the activity energy of five chars with carbon dioxide were 149～181 kJ/mriol, with steam were 125～194kJ/mol. The kinetic compensation effect were observed between them, which can be explained by transition state theory.(7) For MX20%XLHT80% mixed char, the activation energy of vapor re-gasification increase along with the gasification rate increasing, but for MX35%XLHT65% and MX50%XLHT50% mixed char, the activation energy of vapor re-gasification reduce along with the gasification rate increasing. However, when the partially gasified chars react with carbon dioxide, the activation energy from kinetic analysis is contrast with that of vapor re-gasification. (8) When the carbon dioxide and steam as gasifying agent, the synergistic effect exists only in 1073K, MX20% XLHT80% mixed char gasification process, and the significant inhibition exists in other experimental conditions.(9) The maximum weight loss rate of three different mixed char is not equal to the sum of biomass char and coal char gasification.Except one or two experiment, on the whole, the maximum weight loss rate of mixed char is lower than the sum of biomass char and coal char gasification.(10) When gasification with carbon dioxide or steam, the experimental value of solid product weight is less than that of calculated values only exists in 1073K, MX20% XLHT80% mixed char gasification process. In other conditions, the experimental value is greater than the calculated values.It is consistent with the comparison between experimental value and calculated values before.(11) The synergistic effect not only exists in 1073K, MX20%XLHT80% mixed char gasification,it also exists in GJ20%XLHT80% mixed char and BS20%XLHT80% mixed char. Therefore, it is primaly prove that the synergistic effect exist in 1073K, BI20%XLHT80% mixed char gasification process.