Adsorption-transport Mechanism Of Ch₄ , Co₂ ,n₂ And Their Mixture In Coalbed

The global climate change induced by anthropogenic greenhouse gas(carbon dioxide,methane et al) emissions has become a very important factor which has great influence on world economic order,political situation and international relation,and is also a determining factor for the future of world energy development. If deep reductions in anthropogenic greenhouse gas emissions are to be achieved, alongside these technology such as use renewable energy, improve energy efficiency and fuel switching .would be deployed,the introduction of CO₂ capture and storage in geological reservoirs is likely to be necessary. These geological reservoirs can be used to store CO₂.include depleted and disused oil and gas fields, deep saline aquifers and deep unminable coal seams. among of them,The injection of carbon dioxide (CO₂) of flue gas(the mixture of CO₂/N₂) in deep, unmineable coalbeds(CO₂-ECBM)is a very attractive option for geologic CO₂ storage as it with CO₂ stored and at the same time the recovery of coalbed methane is enhanced. The process involved in the CO₂-ECBM include multi-components gas adsorption,diffusion,and flow in coalbed. Otherwise,the mechanism of multi-components gas adsorption and transport in coalbed.is also very important for coal and gas outburst prediction and management in the process of coal mining. Based on this , the research was focused on the the mechanism of multi-components gas adsorption and transport in coalbed,and some results gained:(i)The adsorption experiment of pure CO₂,CH₄,N₂ and their binary/ ternary mixture were conducted. the results indicated that the gas separation coefficient is a function of gas pressure and composition,the gas separation coefficient of CO₂/CH₄ decreased with gas pressure increase. Two adsorption model were used to simulate the adsorption behavior of CO₂/CH₄ binary gas mixture,the results suggested that the IAS model fitted the laboratory data better than the extended Langmuir model.as it is more sensitive to dynamic changes in pressure and composition.Another,Grand canonical ensemble Monte Carlo(GCMC)simulations which is a molecular simulation method was carried out to investigate the competitive adsorption and separation of CO₂/CH₄ in slit-shape pores, and the influence of temperature,pressure,pore width and mole fraction of carbon dioxide on competition adsorption of carbon dioxide and methane. The results suggested that there is a optimum pressure and temperature conditions occurred in which the equilibrium separation factor of CO₂ with respect to CH₄ reached maximum value .therefore,optimization of the conditions is needed in practical CO₂ sequestration in unminable coalbed. based on the thermodynamics principal, an adsorption induced coal deformation model was development,and incorporated with the molecular simulation method , it found that adsorption induced coal deformation was primary caused by micropore adsorption.(ii) The results of diffusion experiment indicated that the diffusion coefficient of CO₂ is greater than CH₄.and there was a negative correlation between diffusion coefficient and gas pressure,Gas diffusion coefficient in the coalbed should be treated as a dynamic variable.then based on the Maxwell-stefan theory,an multicomponents gas adsorption-diffusion model was developmented,the model can describle the co-direction diffusion behavior in the process of CO₂-ECBM,and the numerical simulation results indicated that the impact of interaction of components could not be neglect.(iii) laboratory experiments measured the change of the permeability of coal samples as a function of gas pressure and injected gas composition at constant effective stress were carried out. The results suggested that adsorption induced swelling will reduce coal permeability.the coal permeability is a function of effective stress and the injected gas composition.. the permeability versus pressure curve followed a similar type with the gas adsorption/desorption hysteresis phenomenon on coal.so the permeability of coal is pressure path dependent. A permeability model considering adsorption induced swelling effect and the effective stress was development,and the coal permeability is depend on the initial stress and boundary conditions.(iii)a multiphysics coupled model describle multi-components gas flow in coalbed was developed,and through numerical simulation,some factors impact on the process of CO₂-ECBM was studied, these results are very important for site selection and technological parameters optimum of CO₂-ECBM project.(â…³) the site stability for CO₂ storage was studied,and the method for determine the sustainable maximum injection pressure of CO₂ was proposed.base on the real reservoir conditions and reservoirsimulation,a integrated method was proposed to estimate the CO₂ storage potential in coalbed.