The Development of a Low-Cost Method for Monitoring Methane Leakage from the Subsurface of Natural Gas Fields

The leakage of methane from the subsurface on the coalfield or natural gas field invariably becomes an important issue nowadays. In notable addition, materials such as activated carbon, zeolites, and Porapak have been successfully identified as adsorbents. Those adsorbents could adsorb methane at atmospheric pressure and room temperature. Therefore, in this scholarly study, a new method using adsorbents to detect points of methane leakage that can cover a wide-scale area was developed. In the beginning, the most capable adsorbent should be determined by quantifying adsorbed methane amount. Furthermore, checking the possibility of adsorption in the column diffusion and desorption method of adsorbents is equally necessary. The most capable adsorbent was activated carbon (AC), which can adsorb 1.187 × 10−3 mg-CH4/g-AC. Hereinafter, activated carbon successfully can adsorb methane through column diffusion, which simulates the situation of on-site measurement. The specific amount of adsorbed methane when the initial concentrations of CH4 in a bag were 200 ppm, 100 ppm, and 50 ppm was found to be 0.818 × 10−3 mg-CH4/g-AC, 0.397 × 10−3 mg-CH4/g-AC, 0.161 × 10−3 mg-CH4/g-AC, respectively. Desorption of activated carbon analysis shows that methane concentration increases during an hour in the temperature bath under 80 °C. In conclusion, soil methane leakage points can be detected using activated carbon by identifying the observed methane concentration increase.

The Effect of Static Blasting Materials on Coal Structure Changes and Methane Adsorption Characteristics

Methane in coal seam is always under the dynamic process of adsorption and desorption. It has been demonstrated that the static blasting technology is an effective way to extract methane from coal. Although it is of great significance to understand the role of static blasting materials on methane extraction, the change of methane during static blasting is not well understood due to limited research studies. In this paper, we took the reaction pressure and heat from the hydration of the static blasting materials as the main factors. Microstructure changes in the static blasting materials and coal were analyzed by scanning electron microscopy, gas chromatography, infrared spectroscopy, and mercury injection. Changes of methane adsorption and adsorption rate before and after the static blasting were also measured. Our results demonstrated that the static blasting materials entered the microcracks of the coal body and the porosity of the coal was increased by heat expansion, improving methane migration. During the blasting process, methane began to desorb from the coal and its adsorption content was decreased. In contrast, the adsorption of methane was increased after the reaction. However, methane adsorption rate is higher than that of raw coal, indicating that the adsorbed methane is easier to convert into free methane, which is conducive to emission. This is of great significance to methane extraction and the safety of mines.

Experimental Measurement of Bulk Thermal Conductivity of Activated Carbon with Adsorbed Natural Gas for ANG Energy Storage Tank Design Application

The development of adsorptive natural gas storage tanks for vehicles requires the synthesis of many technologies. The design for an effective Adsorbed Natural Gas (ANG) tank requires that the tank be filled isothermally within a five-minute charge time. The heat generated within the activated carbon is on the order of 150 MJ/m 3 of storage volume. The tank can be effectively buffered using Phase Change Material (PCM) to absorb the heat. The effective design of these tanks requires knowledge of the thermal properties of activated carbon with adsorbed methane. This paper discusses experimental measurements of the thermal conductivity of activated carbon with adsorbed methane. It was found that within the tank the thermal conductivity remains almost constant within the temperature and pressure ranges that ANG tanks will operate.

Experimental and Simulation Studies on Adsorption and Diffusion Characteristics of Coalbed Methane

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.