A Research On The Methane Adsorption/desorption In The Mid And High Rank Bituminous

People are more concerned about the study of coalbed methane adsorption characteristics for a lang time.With the formation of coal-bed methane industry,many problems of coal-bed methane extraction have been encountered,it is only then people gradually to focus on desorption law research.Mid and high rank bituminous which at the high rank of coal and has high potential for large gas is the preferred zone for coalbed methane development,so the author collected 20 coal samples in the mid and high rank bituminous coal mines to obtain the adsorption/desorption characteristics of coal in this rank.The pore structure is the direct cause of coalbed methane adsorption characteristics while material components is the carrier of the pore structure,so it is the indirect cause of coalbed methane adsorption.Tt is necessary for both comprehensive analysises of the pore structure and material components to clarify the features of methane adsorption and desorption in coal.The identification of coal substance characteristics which include the microscopic and industrial components are made in this paper.The pore structure characteristics of the coal sample which include the pore size, pore volume, pore surface area and porosity are determinationed by liquid nitrogen adsorption and mercury injection experiment.The adsorption/desorption experiments are made by the method of high-pressure volumetric and the excess data of adsorption/desorption which then been corrected into corrected adsorption (the approximation of absolute adsorption)by mass conservation principle were got.The Langmuir adsorption equation was named Langmuir desorption equation after been transformed. In this paper, the data of adsorption was fitted by Langmuir adsorption equation and the data of desorption was fitted by Langmuir desorption equation.Both the square of correlation coefficient R2 of adsorption data and desorption data were up to 99%.The orther proposed three concept which include theoretical desorption residue c,theoretical desorption rateη,theoretical desorption residue rate 1-ηin the base of Langmuir desorption equation.The author analyzed the effect of material composition and coal pore structure on Langmuir volume VL and theoretical desorption residual c.The results showed that it is metamorphic grade,Vitrinite content,fixed carbon content and millipore volume of coal that promote adsorption and obstruct desorption while equilibrium moisture content,ash content,pore surface area,and Pore volumes of micropores,mesoporous,macropores have no obvious effect on methane adsorption/desorption.