Study On Adsorption And Desorption Characteristics Of Different Metamorphic Deformed Coal

CBM is a kind of unconventional source of energy with high efficiency and cleaness whose main component is methane.The development of CBM can alleviate the shortage of oil and gas in our country and be beneficial to the prevention and control of gas disasters,which is of great significance to the enhancement of China's initiative of energy security and the adjustment and optimization of the energy structure.The better development and production of coalbed methane should be guided under a better understanding of the adsorption and desorption characteristics of different types of coal and rock.Therefore,an experiment on the isothermal adsorption and desorption of 12coal samples with various metamorphic deformation sequences were carried out from the perspectives of fitting equation and influencing factors in order to investigate the adsorption and desorption characteristics of different metamorphic deformed coal.An analysis on the result of the experiment shows that:?1?For Langmuir equation,the two parameters V_L and P_L acquired through the linearization of the equation are more explicit compared with the direct fitting method,which makes it more instructive for Langmuir equation in real production.For DR equation,the parameters obtained by direct fitting are all related to temperature which is not consistent with the definition,and the points are also relatively dispersed and not on the same adsorption characteristic curve at different temperatures.Therefore,the direct fitting method is not desirable although the degree of fitting through direct fitting is relatively high.The fitting parameters in DR equation are reduced by calculating V₀thus the resulting fitting parameters are closer to the actual values.DR equation works better in fitting effect after a comparison with Langmuir equation.The volume-filling theory of micropores comes nearer to the actual data in describing the absorbability of coal to methane,especially in high rank coal.Adsorption quantity under different temperature and pressure can also be calculated through the adsorption characteristic curve.?2?The adsorption capacity of air-dried coal-based samples increases with the degree of deterioration.Coals in different ranks have different stages of adsorption quantity difference:adsorption quantity difference in low-rank coals mainly occurs in the low-pressure stage while that in high-rank coal lies in the high-pressure stage.High rank coal has the strongest adsorption capacity and the highest adsorption rate in each stage compared with other coal samples.The adsorption capacity of coal increases with the degree of tectonic deformation.Ductile deformation has a greater influence on the adsorption capacity of coal than the brittle kind.Temperature has a negative effect on coal adsorption capacity while pressure has a positive effect.However,the stages of influence on different metamorphic coal varies:The adsorption capacity of low-rank coal is greatly affected by temperature,and is mainly influenced by pressure in the low-pressure stage and by temperature in the high-pressure stage;The adsorption capacity of high-rank coal is less affected by temperature.?3?The modified Langmuir equation has a good degree of fitting with the desorption curve,and the parameters obtained are more accurate and meaningful.The desorption residuals acquired have a positive correlation with the degree of metamorphism and deformation:The higher the degree of deterioration,the higher the residual amount;the higher the degree of deformation,the higher the residual amount.