Expolitation of coalbed methane (CBM) involves production of a massive amount saline water that needs to be properly managed for environmental protection. In this study, direct contact membrane distillation (DCMD) was utilized for treatment of CBM-produced water to remove saline components in the water. Simulated CBM waters containing varying concentrations of NaCl (1, 20, and 500 mM) and NaHCO 3 (1 and 25 mM) were used as feed solutions under two transmembrane temperatures (∆40 and 60˝C). In short-term distillation (~360 min), DCMD systems showed good performance with nearly 100% removal of salts for all solutes concentrations at both temperatures. The permeate flux increased with the feed temperature, but at a given temperature, it remained fairly stable throughout the whole operation. A gradual decline in permeate flux was observed at ∆60˝C at high NaHCO 3 concentration (25 mM). In long-term distillation (5400 min), the presence of 25 mM NaHCO 3 further decreased the flux to 25%-35% of the initial value toward the end of the operation, likely due to membrane fouling by deposition of Ca-carbonate minerals on the pore openings. Furthermore, pore wetting by the scalants occurred at the end of the experiment, and it increased the distillate conducitivity to 110 µS¨cm´1. The precipitates formed on the surface were dominantly CaCO 3 crystals, identified as aragonite.

Coalbed methane (CBM) content is generally estimated using the isotherm theory between pressure and adsorbed amounts of methane. It usually determines the maximum content of adsorbed methane or storage capacity. However, CBM content obtained via laboratory experiment is not consistent with that in the in-situ state because samples are usually ground, which changes the specific surface area. In this study, the effect of the specific surface area relative to CBM content was investigated, and diffusion coefficients were estimated using equilibrium time analysis. The differences in adsorbed content with sample particle size allowed the determination of a specific surface area where gases can adsorb. Also, there was an equilibrium time difference between fine and lump coal, because more time is needed for the gas to diffuse through the coal matrix and adsorb onto the surface in lump coal. Based on this, we constructed a laboratory-scale simulation model, which matched with experimental results. Consequently, the diffusion coefficient, which is usually calculated through canister testing, can be easily obtained. These results stress that lump coal experiments and associated simulations are necessary for more reliable CBM production analysis.

-In order to asses gas production behavior for CO2 ECBM, the sorption charcteristics on coal are considered to be a key factor. In this study, we have investigated the change of the sorption rate of adsorbed gas as a function of pressure and temperature below the appropriate depth for CO2-ECBM. The experiment were carried out under four different temperatures varying from 15℃ to 45℃, while the coal pressure was varied from atmosphere to 1,400 psi for every temperature. From this results, the sorption rate both CO2 and CH4 increased with increasing the coal pressure. Otherwise, the sorption rate both CH4 and CO2 decreased linearly as the coal temperature increased. From the sensitivity studies on pressure and temperature change, it was experimentally identified that CO2 sequestration rate and CH4 production rate are better at deeper depths below a depth of 800 m in coal seams. However, the results showed continued decline in the increasing ratio of ECBM with formation depth.

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