•The preferential adsorption of CO2 over CH4 improves with coal rank.•Pore structure of coal affects the thermodynamics of adsorption of CO2 and CH4.•Adsorbed CO2 has a more ordered configuration ...than CH4 on different rank coals.
In this paper, the pore structures of three different rank coals sampled from China (anthracite, bituminous coal and lignite) were characterized by CO2 and N2 adsorption. The isothermal adsorption curves of CO2 and CH4 on three samples were measured by gravimetric method and fitted by Langmuir model. The preferential selectivity (αCO2/CH4) was calculated using the Langmuir parameters of CO2 and CH4, and the Henry’s coefficient (KH) was obtained with the help of virial equation. More importantly, a comparative analysis of adsorption thermodynamics of CO2 and CH4 on three different rank coals, including surface potential (Ω), Gibbs free energy change (ΔG) and entropy loss (ΔS), was presented according to the adsorption data. It is found that the uptakes of CO2 and CH4 on anthracite are the largest, followed by lignite and bituminous coal in sequence. αCO2/CH4 increases with the increase of coal rank. Low temperature helps injected CO2 to displace pre-adsorbed CH4. The KH values on anthracite are the biggest, while KH values on bituminous coal are the smallest. Ω, ΔG and ΔS of CO2 and CH4 all exhibit a U-shaped function with maturity. Anthracite has the highest Ω, ΔG and ΔS, while bituminous coal has the lowest Ω, ΔG and ΔS. The thermodynamics parameters of Ω, ΔG and ΔS are affected by pore size distributions of three coals. Ω, ΔG and ΔS of CH4 are smaller than those of CO2. CO2 adsorption on coal is more favorable and spontaneous, and adsorbed CO2 molecules form a more efficient packing on coal.
Carbon dioxide phase transition blasting (CO2-PB) technology is an effective and economical technology used for breaking rocks. The use of CO2-PB can significantly reduce the vibration damage to ...surrounding rocks. There is little research on the shockwave generated by the CO2-PB, and simulation can better show the flow field characteristics. In order to clarify the mechanism of its blasting load process, a theoretical analysis and a numerical model were developed to study the flow-field characteristics and the impact pressure of CO2-PB. Our results show that the CO2 absorbs heat from the surrounding environment, producing a significant low-temperature area. The overpressure is significantly lower than the driving gas pressure to the ambient pressure, limiting the maximum over-pressure that can be obtained. When the pressure in CO2-PB reaches 100 MPa, the shockwave is about 4.25 MPa. As the distance increases, the peak value of the shockwave decays rapidly. As the dimensionless distance increases from 1 to 5, the dimensionless overpressure decreases from 1 to 0.23. Under the same blasting pressure, increasing the filling pressure and increasing the filling volume slightly reduce the initial pressure of the shockwave. In the shock stage, strong compression is formed on the surface of the shockwave, resulting in a higher peak pressure value. Meanwhile, the stable pressure is influenced by the target distance, blasting pressure, and CO2-PB length.
In order to improve the reliability and scientificity of the path of agriculture sustainable development, guided by the concept of circular economy, this paper combines data mining technology to ...construct a path analysis system of agricultural sustainable development and establishes a one-dimensional discrete dynamic model of the interaction between the stock of renewable resources and the output. Moreover, this paper discusses the impact of resource-based industries’ output on the sustainable use of resources and establishes a two-dimensional discrete dynamic control model for resource stock and resource development speed. In addition, this paper mainly studies the relationship between resource stock and output when the speed of resource development is managed and controlled, and builds a system structure model based on the actual needs of agricultural development. Finally, this paper designs an experiment to analyse the performance of the system model constructed in this paper. The research results show that the system constructed in this paper has a certain guiding effect on the sustainable development of agriculture, and it can be applied to practice.
Properties of coal surface and pore structure are important aspects to be investigated in coal preparation and utilization. In order to investigate the limits of different probe methods, a ...comprehensive approach was comparatively used to probe surface properties and pore structure of anthracite, bituminous coal and lignite. Surface morphology of the three coal samples was analyzed by scanning electron microscopy (SEM). Combining mercury intrusion porosimetry (MIP), physisorption method with carbon dioxide (CO2) at 273 K and nitrogen (N2) at 77 K was used to quantify a broad pore size distribution of coals, while FT-IR and water vapor sorption methods were used to study the coal surface properties. The results show that wedge-shaped pores develop with the increase of coal rank due to compression effect. The determined specific surface area (SSA) and pore volume of N2 decrease with the increase of coal rank, while CO2 SSA and pore volume are of a kind of U-shaped function of coal rank. MIP results indicate that that the pore size of 10–100 nm accounted for 70.7–97.5% of the total volume in the macropore range. Comparison of different methods indicates that micropores cannot be fully covered by the standard probes. CO2 adsorption technique can only probe micropores in the range of 0.5 nm to 0.9 nm. Water vapor is not an effective probe to detect the micropores in coals, due to that the water clusters is mainly filled in mesopores and macropores. The results also show that both water vapor adsorption and FT-IR analysis can provide qualitative information of coal surface, rather than qualification of functional groups.
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The combined effects of surface chemistry and pore structure on water vapor adsorption characteristics of coal were studied by evaluating the equilibrium, thermodynamic and kinetic ...properties. Four coal samples of different rank were fully characterized with gas (N2 and CO2) sorption and Fourier Transform infrared spectroscopy (FTIR) methods. Then measurements of water vapor adsorption equilibrium and kinetics were undertaken at elevated temperatures. Equilibrium and kinetic data were fitted by the modified BET model and the unipore model, respectively. The thermodynamic parameters, as well as diffusion activation energy were estimated based on the adsorption data. The results demonstrate that water vapor adsorption depends on the surface chemistry but unrelated to the pore structure, because the pore space is not completely filled by water molecules even at the saturation pressure. The monolayer adsorption capacity decreases with increasing coal rank. Moreover, water vapor needs lower work to attain equilibrium on high-ranked coal. Also, the binding affinity of water molecule with primary sites is stronger than secondary sites. Furthermore, the diffusion coefficient decreases with coal rank, and the diffusion activation energy for high-volatile bituminous is higher than the other coals, as a result of the complexity and poor connectivity of its pore network.
The physico-chemical effects caused by supercritical CO2 (ScCO2) exposure is one of the leading problems for CO2 storage in deep coal seams as it will significantly alter the flow behaviors of gases. ...The main objective of this study was to investigate the effects of ScCO2 injection on diffusion and adsorption kinetics of CH4, CO2 and water vapor in various rank coals. The powdered coal samples were immersed in ScCO2 for 30 days using a high-pressure sealed reactor. Then, the diffusion and adsorption kinetics of CH4, CO2 and water vapor in the coals both before and after exposure were examined. Results indicate that the diffusivities of CH4 and CO2 are significantly increased due to the combined matrix swelling and solvent effect caused by ScCO2 exposure, which may induce secondary faults and remove some volatile matters that block the pore throats. On the other hand, the diffusivities of water vapor are reduced due to the elimination of surface functional groups with ScCO2 exposure. It is concluded that density of the surface function groups is the controlling factor for water vapor diffusion rather than the pore properties. The unipore model and pseudo-first-order equation can simulate the diffusion and adsorption kinetics of CH4 and CO2 very well, but the unipore model is not capable of well describing water vapor diffusion. The effective diffusivity (De), diffusion coefficient (D) and adsorption rates (k1) of CH4 and CO2 are significantly increased after ScCO2 exposure, while the values of water vapor are decreased notably. Thus, the injection of ScCO2 will efficiently improve the transport properties of CH4 and CO2 but hinder the movement of water molecules in coal seams.
The isothermal sorption experiments of CH4, CO2 and CH4/CO2 mixture gases on shale were performed. The sorption affinities of CH4, CO2 and CH4/CO2 mixture gases were compared using Henry’s ...coefficient (KH). The thermodynamics of sorption of CH4, CO2 and their mixture were discussed based on surface potential (Ω), entropy loss (ΔS) and change of Gibbs free energy (ΔG). It is shown that the uptakes of CO2 is largest, followed by CH4/CO2 mixture gases and CH4 in sequence. The introduction of a small amount of CO2 into mixture gases can significantly enhance the adsorption quantity of mixture gases and suppress the adsorption of CH4. The lower pressure and the smaller CO2 mole fraction in bulk phase (yCO2) improve separation factor and boost the displacement of adsorbed CH4 by CO2. KH, Ω and ΔS for CO2 are higher than those for CH4, and KH, Ω and ΔS for CH4/CO2 mixture gases are between those for CH4 and CO2. Increasing yCO2 increases KH, Ω and ΔS. ΔG of CO2 and CH4/CO2 mixture gases are bigger than that of CH4. CO2 adsorption is more spontaneous and the introduction of CO2 enlarges the spontaneity degree of adsorption of mixture gases.
This article has been retracted from publication in the Taylor & Francis journal, Acta Agriculturae Scandinavica, Section B - Soil & Plant Science.
Following publication, concerns were raised by ...multiple third-parties around the content of the special issue and the decision-making process.
Following an investigation by the Taylor & Francis Publishing Ethics & Integrity team in full cooperation with the Editor-in-Chief, it was confirmed that this article included in Special Issue titled "
Envisage Computer Modelling and Statistics for Agriculture", guest edited by Gunasekaran Manogaran was not peer-reviewed appropriately, in line with the Journal's peer review standards and policy.
As the stringency of the peer review process is core to the integrity of the publication process, the Editor and Publisher have decided to retract all of the articles within the above-named Special Issue.
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There are some errors and lags in the way of judging the cutting load type of the mining machine manually. In order to solve the above problem, a classification method of mining machine cutting load ...based on wavelet packet decomposition and sparrow search algorithm optimized BP neural network (SSA-BPNN) is proposed. The method comprises two parts of signal feature extraction and mode classification. In the part of signal feature extraction, the collected vibration signal of the mining machine rocker arm is decomposed by wavelet packet to obtain the energy of each subband and the total energy of the signal. After normalization, feature vectors representing different load types are obtained. The principal component analysis is used to reduce the dimensions of the feature vector. In the mode classification part, SSA is used to optimize the initial weight and threshold of BPNN. The feature vector is used as the input of SSA-BPNN to realize the load classification and recognition. Taking the MG500/1170-AWD1 mining
Carbon dioxide (CO2) has been used to replace coal seam gas for recovery enhancement and carbon sequestration. To better understand the alternations of coal seam in response to CO2 sequestration, the ...properties of four different coals before and after supercritical CO2 (ScCO2) exposure at 40 °C and 16 MPa were analyzed with Fourier Transform infrared spectroscopy (FTIR), low-pressure nitrogen, and CO2 adsorption methods. Further, high-pressure CO2 adsorption isotherms were performed at 40 °C using a gravimetric method. The results indicate that the density of functional groups and mineral matters on coal surface decreased after ScCO2 exposure, especially for low-rank coal. With ScCO2 exposure, only minimal changes in pore shape were observed for various rank coals. However, the micropore specific surface area (SSA) and pore volume increased while the values for mesopore decreased as determined by low-pressure N2 and CO2 adsorption. The combined effects of surface property and pore structure alterations lead to a higher CO2 adsorption capacity at lower pressures but lower CO2 adsorption capacity at higher pressures. Langmuir model fitting shows a decreasing trend in monolayer capacity after ScCO2 exposure, indicating an elimination of the adsorption sites. The results provide new insights for the long-term safety for the evaluation of CO2-enhanced coal seam gas recovery.
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