Study On Adsorption-desorption Characteristics Of Undeformed Coal And Soft Coal In Shanyang Mine Field

So far, coalbed methane of the country hasn’t reached the degree of large-scalecommercial exploitation because of the excessive dependence on United States system ofcoalbed methane theory founded on the simpler geologic structure, except some regions ofQinshui basin in which the coalbed methane has made many breakthroughs. Research onadsorption-desorption characteristics of soft coal considered as "restricted zone" of coalbedmethane development is little at home and abroad, but it urgently need be in-depth study inChina because of the complexity of coalfield structure to expand new fields of research oncoalbed mathane. So it is urgent to strengthen the research on adsorption-desorptioncharacteristics of soft coal.In this paper, the adsorption-desorption characteristics of undeformed coal and soft coalwere studied thoroughly in Shanyang mine field through mercury injection, low-temperaturenitrogen adsorption, scanning electron microscopy and isothermal adsorption-desorptionexperiments of the5#coal in shanyang coal mine of chenghe mining Co. Limited combiningwith the interdisciplinary theory of structural geology, coal geology, gas geology, coalbedmethane geology, physics, chemistry and numerical simulation and so on.Results show that differeence of adsorption capacity between undeformed coal and softcoal is mainly reflected in different characteristics of coal pores. Compared with undeformedcoal, porosity, pore volume and specific surface area of soft coal enlarge. The pore volumeand specific surface area of big pores decrease, while that of medium pores and little pores,and that of micropores are same. Micropores constitute space of methane adsorbed by coal,which leads to adsorption capacity of soft coal is little larger than that of undeformed coal. Toundeformed coal, capacity of methane adsorbed by coal decreases and the velocity slow downwith increasing grain size and temperature. The desorption curve of coal all lags behindadsorption curve with different temperature, granularity and structure. Isothermal adsorption-desorption process of methane is not reversible, which could cause desorption hystersis. The calculating results indicate that the adsorption heat in process of adsorption is less than that indesorption to different structural and varigrained coal, and the different value in heat explainswhy the desorption hysteresis of coalbed mathane take place from the thermodynamics.