Low Concentration Coal Bed Methane Research Articles

Room-temperature photooxidation of low-concentration coalbed methane to methanol over CuOx/D-WO3 combined with gas-solid-liquid interface: From pollutant to clean fuel

Direct transformation of CH4 in low-concentration coalbed methane (LC-CBM) to clean fuel methanol is a more sustainable route as industrial CH4 transformation is usually energy-intensive. Solar-driven photocatalysis with near-zero carbon emissions can activate and transform CH4 at ambient temperatures, whereas the reported methanol productivities of traditional solid-liquid photocatalysis are still far from satisfactory. Herein, amorphous CuOx decorated defective WO3 nanocomposites (CuOx/D-WO3) were first synthesized and used as full-spectrum responsive photocatalysts for selective oxidation of LC-CBM to methanol. Introducing oxygen vacancies endows CuOx/D-WO3 with near-infrared (NIR) response. Loading CuOx boosts the separation of photogenerated charge carriers and the generation of ·OH via H2O2 reduction by photoelectrons on CuOx sites, confirmed by photoelectrochemical characterizations and in-situ XPS. Under simulated solar light irradiation, CuOx/D-WO3 exhibited significantly promoted activity of CH4 oxidation compared with the counterpart D-WO3. Even under NIR illumination, the optimal 3.0 % CuOx/D-WO3 showed a methanol production of 1.57 mmol·gcat−1 with selectivity of 79.8 %. Furthermore, a gas-solid-liquid triphase interface was constructed by immobilizing hydrophilic 3.0 % CuOx/D-WO3 on superhydrophobic carbon fiber paper (CFP) to promote methanol generation through strengthening CH4 mass transfer. This triphase photocatalysis exhibited a methanol production of 25.42 mmol·gcat−1, which was ∼4 times higher than solid-liquid diphase catalysis. Methanol selectivity of CuOx/D-WO3/CFP triphase photocatalysis was up to 95.3 %. It was mainly due to enhanced mass transfer of CH4 from gas phase to photocatalysts layer through hydrophobic-hydrophilic wettability abrupt interface of CuOx/D-WO3/CFP, which could be evidenced by significantly increased ·CH3 radicals from in-situ EPR spectra. This work broadens the avenue toward cleaner and efficient utilization of LC-CBM in a sustainable way.

Development of Coal Slime Drying System with the Low Concentration Coal Bed Methane Regenerative Oxidation

The pollutants exceeding the standard exists in the coal furnace in the current coal slime drying system. In order to solve the industrial application difficulty of coal slime in coal mine, by using low concentration coal bed methane regenerative oxidation reactor instead of coal furnace to produce the high temperature flue gas and combining with slime drying system, a low concentration coal bed methane regenerative oxidation slime drying system which is applied to coal slime drying is formed. Taking the scale of a single regenerative oxidation reactor which processing capacity is 100,000m3/h as an example, the thermal calculation of the whole coal slime drying system is carried out. The results show that the system can dry coal slime 39t/h and has a large-scale effect.

Highly efficient conversion of oxygen-bearing low concentration coal-bed methane into power via solid oxide fuel cell integrated with an activated catalyst-modified anode microchannel

Efficient utilization of oxygen-bearing low concentration coal-bed methane (LC-CBM) via solid oxide fuel cell (SOFC) device to generate power is highly attractive and receives tremendous attention. However, it is highly limited by the conversion efficiency and carbon formation during the operation. Hence, in this study, a microchannel reactor coupled with highly active catalysts (Ni-Y2O3-Ce0.5Zr0.5O2) are integrated in the SOFC anode to boost the partial oxidation of methane (POM) efficiency and enhance the coking tolerance. Benefiting from the integrated SOFC reactor, the methane conversion efficiency is increased from 23.59 % to 43.22 % at 750 °C when using 16 % CH4-4 %O2-80 %N2 as fuel. Meanwhile, the related peak power density is increased from 904 mW cm−2 to 1208 mW cm−2. The conversion efficiency and electrochemical performance both can be improved significantly. Besides, the integrated SOFC reactor can work at 750 °C for more than 100 h, indicating the excellent anti-coking performance. The proposed integrated SOFC reactor provides a great application potential for the efficient utilization of LC-CBM.

Molecular Simulation of the Effects of Cyclic Organic Compounds on the Stability of Lccbm Hydrates.

CH4 can be separated from low-concentration coal bed methane (LCCBM) by using the hydrate-based gas separation (HBGS) method. To study the contribution of different cyclic organic compounds to the separation of CH4 in LCCBM, an LCCBM hydrate model was constructed. Based on the Monte Carlo and molecular dynamics theory, we simulated the effect of three cyclic organic compounds—cyclopentane (CP), cyclopentanone (CP-one), and cyclopentanol (CP-ol)—on the stability of the LCCBM hydrate at P = 2 MPa, various temperatures, and discussed the structural stability of the hydrate in depth in terms of final snapshots, radial distribution function, mean square displacement, diffusion coefficient, and potential energy change. The results showed that for the CH4-N2 LCCMM gas mixture, CP showed the best facilitation effect compared to the other two cyclic compounds by maintaining the stability of the LCCBM hydrate well at T = 293 K. The promotion effect of CP-one is between CP and CP-ol, and when the temperature increases to T = 293 K, the oxygen atoms in the water molecule can maintain the essential stability of the hydrate structure, although the orderliness decreases significantly. Moreover, the structure of the hydrate model containing CP-ol is destroyed at T = 293 K, and the eventual escape of CH4 and N2 molecules in solution occurs as bubbles. The research results are important for further exploration of the mechanism of action of cyclic promoter molecules with LCCBM hydrate molecules and promoter preferences.

Enhanced conversion efficiency and coking resistance of solid oxide fuel cells with vertical-microchannel anode fueled in CO2 assisted low-concentration coal-bed methane

Clean and efficient utilization of the abundant low concentration coal-bed methane (LC-CBM) via solid oxide fuel cells (SOFCs) is highly attractive for saving energy and mitigate the emission of greenhouse gases. However, it still remains a great challenge because of the low conversion efficiency and carbon deposition. Herein, an improvement strategy is proposed via incorporating dry reforming reaction of CO2 assisted LC-CBM. By introducing CO2 in LC-CBM, the methane conversion improves significantly. A maximum methane conversion is achieved by incorporating 5 %CO2 and the value is increased from 31.69% to 50.03%. Meanwhile, a high CO2 conversion of 74.58% is also achieved. The maximum power density of the single cell with vertical-microchannel anode fueled with 5 %CO2 in LC-CBM is 1321.5 mW cm−2 at 800 °C, which is a bit lower than that without CO2 participation. This is probably ascribed to the open circuit voltage decrease caused by the increased partial pressure of oxygen at anode. The coking tolerance of the single cell with CO2 participation can be improved owing to the high conversion efficiency, leading to a stable power output performance. CO2 assisted LC-CBM for SOFCs provides a potential solution for the efficient conversion of the low calorific value fuels.

The failure behavior of buckling pin valve: Theoretical, numerical, and experimental study

At present, buckling pin in the bypass of piping as pressure relief valve has been gradually utilized in the low-concentration coal-bed methane (CBM), which bends to release pressure when the main valve fails leading to pipeline blockage. However, current researches mainly focused on the buckling behavior of hydraulic cylinder rod or rod string, and less consideration was given to the operational reliability of buckling pin valves. This paper deduced the calculation formula of the critical failure load based on Euler formula in the buckling pin under buckling load. Besides, three finite element models (FEM) based on Johnson−Cook constitutive model were compared to predict failure strength of buckling pin which were verified by experiment. In addition, the defect sensitivity analysis of the buckling pin under different initial geometric defects rate was carried out. The results showed that a) the experimental value of the critical failure load in the buckling pin was 206.04 N and the bending position was in the middle of the buckling pin; b) the analysis result adopting explicit dynamic method was in best agreement with the experimental results within deviation of 0.24%; and c) the initial geometric defect of buckling pin should be controlled within 1%. This study provides an important reference to predict the critical failure load of the buckling pin valve and achieve safe transportation of low-concentration CBM.

Review on Hydrate-Based CH4 Separation from Low-Concentration Coalbed Methane in China

The consumption of natural gas is of great importance to optimize China’s energy structure toward reduced CO₂ emissions and is projected to increase in the next 10 years. Coalbed methane (CBM) is a primary unconventional natural gas and has been recognized as a significant energy resource to supplement conventional fossil fuels (oil and coal) as a result of its huge potential. It has been established that the hydrate-based gas separation is a promising method for the purification of low-concentration coalbed methane (LCCBM). In this work, the research on hydrate-based CH₄ separation from LCCBM conducted by Chinese researchers over the past 10 years has been reviewed. It is found that significant progress has been made to understand the hydrate-based CH₄ separation technology. On the other hand, the challenges related to achieving milder pressure operating conditions and enhancing the rate of hydrate formation should be overcome. Hence, further work is required to bridge the gap between the gas separation science and the technology. In this regard, future research directions are proposed in this work to help advance the research of hydrate-based CH₄ separation from LCCBM.

Study on comprehensive utilization technology of low concentration coal bed methane

Aiming at the problems of low utilization rate and serious environmental pollution caused by low concentration coal bed methane emission in a coal mine, the utilization technology of low concentration coal bed methane was studied by means of field investigation and theoretical calculation, and the technical solution of comprehensive utilization of low concentration coal bed methane combining regenerative oxidation and cryogenic liquefaction was obtained, which realized the “coal and gas are co-mined and shared” and constructed the virtuous cycle development of “use to promote pumping, pumping to promote safety”. The research shows that: the low concentration coal bed methane with concentration of about 5% is converted into high temperature flue gas by regenerative oxidation, and the heat energy is extracted to realize the heating in the mining area; the coal bed methane with concentration of more than 35% is purified and liquefied into LNG product by cryogenic liquefaction, so as to realize long-distance transportation. The technology improves the utilization rate of coal bed methane in the mining area and eliminates the burning of coal for heating. The annual utilization of pure gas is 53.38 million m3, generating economic benefits of 211 million yuan and reducing CO2 equivalent by 767,000 t. The safety, economic and environmental benefits are remarkable. This technology has practical significance to improve the utilization rate of gas and promote the realization of the goal of zero gas emission.

Improvement of solid oxide fuel cell performance by a core‐shell structured catalyst using low concentration coal bed methane fuel

Improvement of solid oxide fuel cell performance by a core‐shell structured catalyst using low concentration coal bed methane fuel

Improving gas hydrate-based CH4 separation from low-concentration coalbed methane by graphene oxide nanofluids

This paper reports an investigation of using graphene oxide (GO) nanofluids to improve CH4 separation from low-concentration coalbed methane (LCCBM) via gas hydrate formation. The effect of GO nanofluids on LCCBM purification was evaluated by performing experiments at different concentrations of graphene oxide nanoparticles (GONs) and operation pressures. It was found that both the rates of hydrate formation and gas consumption were enhanced when graphene oxide nanoparticles were added to the liquid phase. Moreover, CH4 separation efficiency was greatly increased as compared to the systems without GONs. With the elevation of operation pressure, the hydrate formation kinetics was enhanced but the CH4 separation efficiency was reduced. The experimental conditions of 286.6 K, 2.0 MPa, and 500 ppm GONs were preferred for CH4 separation from LCCBM. The energy consumption for gas compression and system cooling at this temperature and pressure condition is lower than other LCCBM purification systems reported in the literature. The CH4 concentration in LCCBM was increased from 30 mol% to 76 mol% after two-stage hydrate-based separation. Therefore, the GO nanofluids have a great potential to improve the kinetics of hydrate formation as well as the purification efficiency of LCCBM.

The Design of Shell-and-tube Heat Exchanger in the Project of the Coal Bed Methane Electrical Power Generation

Coal-bed-methane (CBD) electrical power generation is an active and effective measure to reduce emissions of greenhouse gases. Using shell-and-tube heat exchangers to reduce the water content of pipeline gas can improve the efficiency of the generator set. Designing heat exchanger by ASPEN EDR software can save a lot of manual calculation process, so as to improve the efficiency of the heat exchanger designer. The general method of designing and verifying shell-and-tube heat exchanger by EDR ASPEN software is described in this article by the example of the local process of low concentration gas power generation project. Because of the heat flux medium is low concentration coal bed methane with high explosion risk, anti-explosion measures must be taken to ensure safety beyond the requirements of normal heat exchangers of heat transfer, pressure drop.

Separation of methane from low concentration coal bed methane by hydrate-based process

Separation of methane from low concentration coal bed methane by hydrate-based process

Enhanced methane recovery from low-concentration coalbed methane by gas hydrate formation in graphite nanofluids

Coalbed methane (CBM) is a primary type of unconventional natural gas adsorbed in coal seams. Its amount around the world is estimated to be 260 × 1012 standard cubic meters (SCM). The low-concentration coalbed methane (LCCBM) with CH4 content less than 30 mol% is difficult to utilize because of its low combustion efficiency. This work reports an investigation of employing a graphite nanofluid to enhance CH4 recovery from LCCBM via gas hydrate formation. The CH4 separation efficiency was evaluated by comparing CH4 recovery ratio, the separation factor, and gas consumption with those reported in the literature, and the behavior of gas hydrate growth in graphite nanofluid was observed. The results indicated that hydrate nucleation was promoted when adding a mass fraction of 0.5% graphite nanoparticles (GNP) into the tetrahydrofuran and sodium dodecyl sulfate solution (THF/SDS solution) and gas consumption increased significantly in comparison with that obtained without GNP. The graphite nanofluid containing 0.5% GNP is preferred for CH4 separation among the three GNP mass concentrations (0.1%, 0.5%, and 3.0%) tested in this work. CH4 recovery ratio and the separation factor obtained in graphite nanofluid were higher than those obtained in other systems such as water-in-oil emulsions. CH4 concentration in LCCBM was increased from 30 mol% to 57.1 mol% via a one-stage hydrate based gas separation process. As a consequence, it has the potential to be an efficient approach to recover CH4 from LCCBM by forming gas hydrates in graphite nanofluid.

Modified with Transition Metals (Cu, Fe, Ni, Co) as Efficient Deoxidizers for O2 Removal from Low-Concentration Coal Bed Methane

Deoxidizer Na2S/AC was modified with transition metal ions (Co2+, Ni2+, Fe3+, and Cu2+) by co-impregnation and step-by-step impregnation methods. Those deoxidizers were characterized and tested for the removal of O2 from low-concentration coal bed methane. Results showed that the effective deoxidizing amount of deoxidizers (QO2) and conversion rate of Na2S (CNa2S) of the deoxidizers are in the following order: Co-Na2S/AC > Ni-Na2S/AC > Fe-Na2S/AC > Na2S/AC > Cu-Na2S/AC. As compared to that of the deoxidizer Na2S/AC, the content of reactive oxygen species (O£–) of the modified deoxidizers was enhanced with the doping of transition metal ions (Co2+, Ni2+, Fe3+, and Cu2+). The more content of O£– on the deoxidizer was, the higher deoxidizing activity there was when the dispersion of Na2S and metal ions of deoxidizers was higher. The deoxidizer Co-Na2S/AC had the largest content of O£– and higher dispersion of Na2S and Co2+, and this made it the largest QO2 (54.88 mL/g) and CNa2S (75.50%) at 200 °C. However, ...

Effect of Surface Chemistry and Textural Properties of Activated Carbons for CH4 Selective Adsorption through Low-Concentration Coal Bed Methane

A series of activated carbon were prepared, modified, and characterized by FTIR, Boehm titration, and N2 adsorption/desorption isotherms. Adsorption breakthrough experiments of CH4 through low-concentration coal bed methane (CBM) were carried out for measuring adsorption capacities (Qm) of adsorbents toward CH4 at 293 K. Adsorption isotherms of CH4, N2, and O2 were measured between 25 mm Hg and 760 mm Hg at 293 K and fitted by Langmuir model to calculate separation coefficient of CH4 against N2 and O2 (αCH4/N2 and αCH4/O2). Results show that CH4 adsorption occurs mainly at the micropore of activate carbon, and the surface basic group of activate carbon can strengthen its adsorption ability toward CH4. Adsorption capacities of CH4 on modified AC are higher than that on original AC. The adsorbent KCl/AC has the largest micropore volume and more amount of basic group and this makes it the largest uptake of CH4 (7.89 mL/g) at 293 K and 1 atm; it is 38.9% higher than that of original AC (5.68 mL/g). Separation...

Optimal power generation from low concentration coal bed methane in Iran

Development of a model for optimal power generation from the thermal oxidation of a low concentration coal bed mine has been considered as the main objective of this investigation. The model has been applied to identify the optimal thermodynamic characteristics of the power generation system through using a mixture with 1.6% methane concentration in a recuperative lean-burn gas turbine and coupling a gas engine to the system for more power generation from the remaining coal bed methane. The implementation of the model based on the real site condition would lead to the generation of 6.97 MW electricity in Tabas coal mine of Iran.

Catalytic combustion of low-concentration coal bed methane over CuO/γ-Al2O3catalyst: effect of SO2

The purpose of this work is to report the results of an experimental study devoted to investigate the effects of SO2 in feed gas on the catalytic combustion of low-concentration coal bed methane (1 vol%) over CuO/γ-Al2O3 catalyst with 10 wt% Cu prepared by incipient wetness impregnation in a fix-bed reactor. The study deals with researching a regular low-concentration coal bed methane combustion with lean SO2, which is vital in utilizing low-concentration coal bed methane and in eliminating greenhouse emissions. The concentration of SO2 varied from 0 ppm to 200 ppm, and the accumulation of sulfur on the catalyst surface was examined by X-ray fluorescence (XRF) and Scanning electron microscopy (SEM). The reaction temperature was in the range of 450–700 °C controlled by an electric heater, and at two key reaction temperatures (550 °C and 650 °C), the effect of altering SO2 concentration on low-concentration coal bed methane combustion was studied experimentally. A sulfur poisoning mechanism of CuO/γ-Al2O3 catalyst was proposed. The results showed that the presence of SO2 in feed gas led to the phenomena of sulfur poisoning over CuO/γ-Al2O3 catalyst, and the effect of sulfur poisoning aggravated with increased SO2 concentration. Meanwhile, it had significant influence when temperature was below 575 °C due to the faster decomposition of sulfates at higher temperatures. A high reaction temperature promoted the decomposition of sulfates produced simultaneously, which provided more activating sites on the catalyst for methane catalytic combustion. Sulfates (CuSO4 and Al2(SO4)3) were detected by Fourier transform-infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), resulting in both the reduction of activating sites and specific surface area of the catalyst. The absorption of methane molecules on activated sites was hindered and the catalyst activity decreased.

Impact of Bed Length on Low-Concentration Coal Mine Methane Enrichment by Proportion Pressure Swing Adsorption

The enrichment and utilization of low-concentration coal bed methane (LCCMM) will provide a fuel source, will ensure safety from flammable gas release and will prevent significant greenhouse gas emissions. One of the special challenges in dealing with LCCMM originates from the presence of O2, which is difficult to process economically and explodes easily. In this work, we studied oxygen-bearing LCCMM with a CH4 concentration of 20% and developed a safe and effective enrichment method for LCCMM: Proportion Pressure Swing Adsorption (PPSA), which used a mixture of active carbon (AC) and carbon molecular sieves (CMS) as adsorbents. With this method, CH4 and O2 in LCCMM can be adsorbed simultaneously because CH4 is mostly adsorbed by active carbon and O2 is mostly adsorbed by the CMS. Therefore, the concentration of CH4 and O2 is well controlled and does not exceed the explosive limit during the adsorption and desorption processes. The impact of bed length on LCCMM by PPSA was investigated. We have demonstrated the safety and feasibility of PPSA for obtaining 30% CH4 from LCCMM, with 20% CH4 in air as a feed stock. Our results showed that the O2 concentration can be controlled well and does not exceed the explosive limit in both adsorption and desorption, and the CH4 concentration in the desorption gas can be increased to more than 30% by adjusting the bed length and mass ratio of the AC and CMS.

Combustion of Low-Concentration Coal Bed Methane in a Fluidized Bed

Low-concentration coal bed methane combustion tests were carried out in a bubbling fluidized-bed reactor with a mixture of limestone and crushed catalyst as bed material. The effects of bed temperature (723−923 K), inlet methane concentration (0.15−3 vol %), and superficial velocity (0.1−0.25 m/s) on methane conversion were studied. Gas was sampled from the bed and the freeboard to analyze the axial profiles of methane in the reactor. With kinetic parameters obtained in a fixed-bed microreactor, predictions from a two-phase model were compared to the experimental data from the fluidized bed. The results showed that bed temperature greatly affected the conversion, with a higher methane conversion obtained by increasing the temperature, reducing the inlet methane concentration, and decreasing the superficial gas velocity.