Coal Gasification Research Articles

Enhancing coal seam gas pressure measurement accuracy and preventing leakage through dual chamber pressure balancing in borehole

Accurate measurement of coal seam gas pressure (CSGP) is critical to the evaluation of coal mine gas hazards and the potential of coal seam gas extraction. In this study, we investigate gas leakage from chambers and its influences on CSGP measurement results (MR) through numerical simulations. Furthermore, we propose, analyze and validate a novel method that balances gas pressure between two chambers, i.e. the measurement and regulation chambers, in a borehole. The results demonstrate that: (1) Traditional CSGP measurement method utilizing boreholes with a single chamber exhibit a gradual expansion of the gas pressure dropping region around the borehole, accompanied by an initial increase in chamber gas pressure followed by stabilization. The gas leakage process within the chamber undergoes three typical stages. (2) The increase of gas leakage lowers the MR value and raises the CSGP measurement error ratio (R). The relationship between MR, R and the stable value of gas leakage is nearly linear. (3) The proposed novel CSGP measurement method involves continuous gas injection into the regulation chamber to establish a dynamic gas pressure balance region between the two chambers. This approach minimizes gas leakage in the measurement chamber and accelerates gas pressure recovery. Maintaining dynamic pressure equality between the dual chambers is essential for minimizing R. (4) An automatic regulation unit is developed to achieve dynamic gas pressure balancing between the two chambers. With the novel method, R values remain below 3%, yielding higher CSGP measurement accuracy compared to alternative approaches.

Solid carbonaceous materials transformation during pulverised coal and natural gas co-injection

Co-injection of coal and gaseous fuel, such as natural gas (NG), is common practice promoting pulverised coal gasification in blast furnace (BF) ironmaking. The high hydrogen content in NG makes it possible to act as cleaner reductant to reduce iron ore to produce hot metal, which will result in reduced CO2 emissions during the ironmaking process. In this work, selected parameters affecting the overall performance of the pulverised coal and natural gas co-injection system were studied using the CanmetENERGY injection test rig, including coal injection rate, natural gas rate and blast oxygen enrichment. Increase in combustion intensity promotes conversion of injected coal into solid carbonaceous material with relatively low reactivity with CO2. Hence, it reduces the competitiveness of combustion residues for oxygen in the raceway to continue the gasification process. NG co-injection reduces the coal combustion intensity but enhances the reactivity of combustion residues by competing the oxygen in the raceway.

Adsorptive removal of microplastics from aquatic environments using coal gasification slag-based adsorbent in a liquid–solid fluidized bed

Microplastics (MPs) are emerging pollutants in aquatic environments that threaten ecological health. This study investigated the adsorption process and mechanism of a coal gasification slag-based adsorbent in a liquid–solid fluidized bed to remove MPs from an aquatic environment. The results showed that the coal gasification slag-based adsorbent had high MP adsorptive removal efficiency of up to 1400 mg/g and adsorption-removal efficiency of 99.2 %. The adsorption process was mainly dominated by electrostatic attraction, π-π absorption, and surface complexation, supplemented by partial physical adsorption. The adsorbent dosage mo was the dominant factor affecting the adsorption performance of the liquid–solid fluidized bed for the continuous adsorption of MPs, followed by the initial MP concentration co and ascending water velocity vt. At a suitable combination of operating parameters (co = 250 mg/L; mo = 2.5 g; vt = 0.11 m/s), the adsorption saturation level of the liquid–solid fluidized bed reached 0.95, which was higher than that of the traditional fixed bed (0.91), indicating good MP adsorption performance. This study provides a new technical approach for MP removal from aquatic environments that is conducive to the industrial application of fluidized beds in the field of wastewater treatment.

CH4 and CO2 adsorption–desorption-diffusion characteristics in surfactant-modified coal under microscopic conditions

Hydraulic techniques are integral to both coal mining and gas extraction procedures, and the precise inclusion of surfactants in hydraulic fracturing fluids serves as a crucial factor influencing the wettability of coal and facilitating gas desorption. Nevertheless, relatively few investigations have focused on the influence of surfactants within coal on the adsorption–desorption-diffusion dynamics of gases. In this study, Xin Tian high-rank coal was treated with different surfactants, and the pore structure and functional groups of the coal samples were determined by fluid invasion methods, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (13C NMR) spectroscopy. Moreover, molecular-scale models were constructed to simulate the adsorption–desorption-diffusion performance of the gases in the surfactant-modified coal. As per the results, modification with methyltrimethoxysilane (MTMS) and polyethylene oxide (PEO) surfactants reduced the proportion of micropores and relative content of oxygen functional groups, resulting in reduced the adsorption of gases and enhanced diffusion performance, consistent with molecular simulations result. These results provide a theoretical foundation for elucidating the adsorption–desorption mechanisms of surfactant-treated coal and its application in mining areas.

A Review of Exploration and Development Technologies for Coal, Oil, and Natural Gas

Energy is the fundamental prerequisite for human survival and development, as well as the driving force behind the progress of human civilization [...]

Fe–Ni composite oxygen carrier for chemical looping gasification with diverse fuels to produce syngas

Coal-based chemical looping gasification (CCLG) has been proposed as an emergent type of coal gasification technology that produces high-quality syngas by using lattice oxygen from oxygen carrier instead of molecular oxygen. In this paper, the Fe–Ni composite oxygen carrier was synthetized using sol-gel method and the gasification performance of the prepared sample was analyzed by a fixed-bed reactor. The results indicated that the Fe–Ni composite oxygen carrier presented a high carbon conversion of fuel and syngas selectivity during the CCLG process. Additionally, the cycle stability test showed that the carbon conversion of fuel and syngas selectivity did not change significantly with the increase of cyclic frequency. To further study the influence of volatiles released from coal on the gasification performance of oxygen carrier, the interactions between the oxygen carrier samples and char obtained at different pyrolysis temperatures were investigated by a fixed-bed reactor and TG-MS, respectively. The results suggested that the gas products (H2, CO, CO2 and CH4) yields of char-oxygen carrier were significantly lower than those of coal-oxygen carrier. Besides, the pyrolysis temperature for preparing char had a great effect on the carbon conversion of fuel and syngas selectivity due to the distinction of volatiles released from solid fuel.

Carbon-based brilliance: a novel approach to renewable energy in radiotherapy centers.

The energy produced from other sources which does neither come from fossil fuels nor contribute in the production of any greenhouse effects that causes climate changes is called as 'Alternative Energy'. Since our world's primary energy sources such as coal, oil and natural gases are exploited to a greater extent, we are in an urge to switch to an alternative energy. Scattered radiation, a common byproduct in radiation therapy and diagnostic radiology, presents a unique opportunity in the realm of alternative energy. As a potential source of interference, scattered radiation can be repurposed to contribute to sustainable energy solutions. Addressing the issue of scattered radiation wastage and utilizing it for alternative energy, an activated carbon-based solar cell emerges as a solution. This solar cell, a conventional one in which cadmium Telluride is replaced by coconut shell based carbon material, has the potential in producing a significant amount of electrical energy by utilizing scattered radiation from radiotherapy and radiology machines. Furthermore, this activated carbon based-material undergoes thorough characterization into various teletherapy and radiology machines, and it can be seamlessly integrated into clinical practices.

Comparative study of the composition and microstructural properties of semi-coke from microwave and conventional pyrolysis of low rank coal

Microwave pyrolysis technology can effectively realize the clean and quality improvement of coal. In order to study the changes of each component of coal in the process of microwave pyrolysis, the d002, La, Lc, combustion reactivity and conductivity of semi-coke after pyrolysis were analyzed by using XRD, TG, conductivity meter and other testing instruments, and the infrared spectra of semi-coke after pyrolysis were finely resolved by using Origin peak-splitting technique, and the composition of the coal gas in the process of pyrolysis and its percentage content were analyzed. The composition and percentage content of gas in the pyrolysis process were analyzed and compared with conventional pyrolysis. The results showed that compared with conventional pyrolysis, microwave pyrolysis can be completed at a lower temperature and microwave pyrolysis is more favorable to the release of volatile components, in which the content of CO and H2 in the gas fraction increased significantly compared with conventional pyrolysis. At the same pyrolysis temperature, the microwave semi-coke has a higher maximum combustion rate temperature than the conventional semi-coke, which is conducive to improving the thermal stability of semi-coke. The orderliness of the semi-coke increased with the increase of pyrolysis final temperature, resulting in the phenomenon of "similar graphitization". The increase in the number of carbon microcrystalline structures generates off-domain electrons, leading to a significant increase in conductivity. Meanwhile, FT-IR peak fitting analysis revealed that the R value inflection point temperature of microwave semi-coke was much lower than that of conventional semi-coke, which further proved that microwave pyrolysis could be accomplished at lower temperatures, and the C value showed a decreasing tendency with the increase of the final temperature of pyrolysis, which indicated that pyrolysis was an effective method to improve the quality of coal. The above analysis shows that compared with conventional pyrolysis, microwave can prepare high stability and high conductivity semi-coke at lower temperature.

Upgrading low-concentration oxygen-bearing coal bed methane by dual-reflux vacuum swing adsorption

Fugitive methane (CH4) is a typical by-product of mining processes, which is commonly known as coal bed methane (CBM) or coal mine gas (CMG). The capture of these CH4 gases can simultaneously avoid greenhouse gas emissions and provide extra energy benefits. However, the explosion risk of low-concentration CBM (CH4 molar fraction ≤ 30%) requires strictly safe operating protocols to conduct the capture process. Dual reflux vacuum swing adsorption (DR-VSA) is a promising candidate with a vacuum operating condition which can lower the explosion risk and simultaneously reach CH4 enrichment and O2 removal targets in product and effluent streams. Herein, a low-concentration oxygen-bearing CBM (20% CH4, 16% O2 and 64% N2) can be upgraded to 69.7 mol% in the product gas while ensuring an effluent concentration of 2.5 mol% by the DR-VSA cycle using ionic liquidic zeolites (ILZ) as the adsorbents. A rigorous safety analysis has been conducted to investigate the explosion risk in the adsorption column and product tank, suggesting that the DR-VSA process is a safe technology for upgrading low-concentration oxygen-bearing methane.

Study on the grading preparation of multifunctional materials and application from coal gasification fine slag

Alkali activation at high temperatures serves as a significant method for the resource reuse of coal gasification fine slag (CGFS). This experimental approach used CGFS, coal-based solid waste, to prepare multifunctional materials and neither waste acid nor alkali was discharged in the process. Using this method, MCM-41 with hexagonal mesopores and carbon/zeolite composite with NaP-type zeolite structures were prepared hierarchically. It is noteworthy that this synthetic method incorporates Al from CGFS into MCM-41, which enhances the acidic sites of the material. This modification endows MCM-41 with potential application in catalyzing guaiacol. Under the same conditions, CGFS-based MCM-41 demonstrated the capacity to convert guaiacol into cyclohexane. In contrast, commercial MCM-41 exhibited the ability to catalyze the conversion of guaiacol into cyclohexanol and cyclohexane. At the same time, the carbon/zeolite composite retains the Fe in CGFS and can be used for the catalytic oxidative degradation of tetracycline. The carbon/zeolite composite was able to degrade 100 mL of 100 mg‧L−1 tetracycline solution by 99.38 % in 120 min at dose of 30 mg, an H2O2 concentration of 25 mmol‧L−1 and solution pH of 3. This research outlines a promising approach for the innovative concept of "turning waste into treasure."

Reversible operation of solid oxide cells fed with syngas derived from underground coal gasification

Underground coal gasification (UCG) technology can directly convert coal resources to syngas underground, making it important for coal utilization. In this work, the power generation, CO2 electrolysis, and reversible operation of flat-tube solid oxide cells (SOCs) fueled with UCG syngas were studied. The factors affecting the performances of flat-tube solid oxide cells were investigated. Fueled with syngas (Swan Hills, Canada) at 750 °C, the flat-tube cell achieved a maximum power density of 329.4 mW cm−2 and a current density of 650.8 mA cm−2 at 1.4 V. 100-cycle (250 h) reversible operation of flat-tube SOCs running on syngas (Swan Hills) was accomplished. No carbon deposition on the surfaces of the cell fuel channels was detected. The syngas conversion in flat-tube cells was illuminated based on density functional theory calculations.

Experiment and simulation assessment of supercritical underground coal gasification in deep coal seam

To explain the impact of geological and process factors on underground coal gasification in deep coal seam (>2200 m) and promote the efficient and clean extraction and conversion of coal, this study employs the orthogonal experimental design method to investigate the impact of CO2 coefficient (0–1), moisture content (30–80 wt%), calcite content (0–10 wt%), albite content (0–10 wt%), kaolinite content (0–20 wt%), reaction temperature (550–650 °C), and reaction pressure (23–27 MPa) on the characteristics of coal underground gasification under supercritical H2O/CO2 conditions. Furthermore, range analysis and variance analysis are utilized to determine the degree of influence of each factor and the interaction between factors. Finally, the Gibbs free energy minimization method is used to conduct a thermodynamic equilibrium analysis of coal supercritical H2O/CO2 gasification at high temperatures (750–1000 °C). The results indicate that the three most significant factors affecting the process of coal supercritical H2O/CO2 gasification are the CO2 coefficient, moisture content, and reaction temperature. The maximum carbon gasification efficiency at 650 °C in experimental cases and 1000 °C in simulation cases is 22.2% and 88.1%, respectively. Although the addition of CO2 at lower temperatures reduces the carbon gasification efficiency, at high temperatures (>900 °C), a higher initial CO2 concentration increases the carbon gasification efficiency. The addition of CO2 under conditions of low moisture content increases the mole fraction of H2, but reduces it under conditions of high moisture content (≥70 wt%). Among the three minerals, calcite has the most significant influence on the gasification process.

Near-zero carbon emission power generation system enabled by staged coal gasification and chemical recuperation

Generating clean, efficient, and low-carbon electricity from coal is imperative for limiting the global temperature rise to 1.5 °C. This study presents a near-zero-carbon-emission power generation system that utilizes staged coal gasification. The innovation of this system is the division of coal gasification into two stages: intermediate-temperature pyrolysis, followed by high-temperature gasification. This process begins with utilizing waste heat from the exhaust of a gas turbine to drive the partial gasification of coal during pyrolysis. The nongaseous products from this stage are then completely gasified in the gasifier, and chemical recuperation is performed, in which heat from the syngas at the gasifier's outlet preheats the reactants at the inlet and aids in reforming pyrolysis gas. For CO2 capture, an oxyfuel combustion strategy is used. Our system produced net electricity and exergy efficiencies of 43.01 and 47.57 %, respectively, surpassing both pre-combustion CO2 capture systems based on staged coal gasification (improvements of 3.04 and 5.37 %, respectively) and coal-water slurry gasification (improvements of 3.55 and 5.8 %, respectively). Moreover, the carbon emissions from our system are approximately 90 g/kWh lower than those from these systems. Thus, this study offers an environmentally sustainable approach to utilizing coal that may facilitate achieving global environmental goals.

A study on the occurrence modes and distribution characteristics of sulfur and mercury in coal gasification slag

Although coal gasification is recognized as a core technology for clean coal utilization, S and Hg can migrate to gas, wastewater, and slag during the gasification process, causing environmental pollution. It is well known that S and Hg have a strong affinity. Therefore, the interaction between S and Hg during the gasification process warrants further investigation. In this study, the occurrence modes and distribution characteristics of S and Hg in gasification slag were systematically investigated using multiple treatments and various characterization techniques. The results showed that sulfur in the gasification slag exists predominantly as organic sulfur, while mercury mainly exists as HgS/silicate-bound Hg. Although the relative enrichment index of Hg (RE < 0.7) indicates its high volatility, a more pronounced enrichment effect for mercury of fine slag was indicated by its much higher RE than coarse slag. When exploring the relationship among the contents of C, S, and Hg and specific surface area in gasification slag, it was found that the correlation between S and Hg content in fine slag was the strongest, with a correlation coefficient (R2) of 0.96, indicating a significant influence of sulfur content in fine slag on mercury content. Additionally, it was observed that the S and Hg contents in gasification slag increased with the decrease of particle size and density. These results provide an important understanding of the distribution, migration, and transformation behavior of S and Hg during coal gasification, as well as a certain theoretical support and technical basis for the resource utilization of gasification slag.

Возможности и проблемы энергогенерации в Республике Тыва

RELEVANCE. The energy sector forms the basis for functioning of other economic sectors and social services. Presentday technologies of energy generation are based on using coal, gas, oil, hydro, nuclear and renewable sources. PURPOSE. Analysis of the current state of energy generation in the Republic of Tyva, identification of drivers for development and optimization of its structure. RESULTS. A review is made of the current global trends in energy generation. Directions for diversifying energy generation sources are proposed, e.g. using both imported and coal seam gas as well as hydro resources along with coal. CONCLUSIONS. Focusing on only one energy source reduces the energy security of the region. Energy shortages and the presence of costly diesel-based power generation hinder the economic development of the Republic of Tyva. In the republic that has extensive coal reserves, coal generation has to introduce modern “clean coal” technologies. A high share of thermal power plants in the structure of the coal-fired generation capacity will allow the development of cogeneration using innovative, environmentally friendly Russian technologies. Options for solving the challenge of energy shortage in Tuva in the future until 2035 are proposed.

Mechanisms underlying variations in pore structures and permeability in response to thermal treatment and their implications for underground coal utilization

Coal remains a predominant energy source in today's society. However, the coal mining process is associated with severe environmental hazards, and combustion for power generation leads to pollution and carbon dioxide emissions. As a result, many countries have imposed restrictions on underground coal mining. Underground coal gasification, direct combustion for heat recovery and thermal treatment provides serval promising way for cleanly and safely utilizing coal resources. However, the successful operation of these technologies needs to comprehensively understand the physical and chemical properties of coal responding to high temperature. In particular, the pore structures and permeability of coal which are closely related to the transport of gas and liquid in coal seams. Therefore, serval advanced instruments were employed to investigate the variation of the functional groups, pore structures, permeability from room temperature to 500 °C. Their connection was discussed in detail to reveal the mechanism of thermal treatment on the pore structures and permeability of coal. The variations of all physical properties with temperature demonstrated a trend of gradual change followed by a sudden change. This indicated that coal samples possess relatively good stability up to 300 °C. Experimental results revealed significant alterations in the pore structure and permeability of the coal at 400 °C and 500 °C. Correspondingly, the mass of coal samples and the CC functional groups, which constitute the main molecular structure of coal, underwent significant changes at these temperatures. This suggested that the pyrolysis of coal beyond 400 °C led to an increase in both pore volume and permeability. Moreover, observations through scanning electron microscopy indicated that the increase in pore volume at 400 °C and 500 °C also resulted from the thermal stress induced cracks between minerals and organic matters. These mechanisms significantly enhance the pore volume and permeability of coal seams, facilitating the transport of coalbed gases and liquids during the production process of underground coal utilization.

Proposal and performance analysis of a novel hydrogen and power cogeneration system with CO2 capture based on coal supercritical water gasification

To establish a sustainable energy system, it is essential to achieve low-carbon and clean utilization of coal. In this study, a novel hydrogen and power cogeneration system with full CO2 capture that based on coal supercritical water gasification (SCWG) is proposed. Hydrogen is separated from syngas produced by coal SCWG, and the remaining combustible gas is burned to generate power. Moreover, supercritical CO2 cycle is integrated within the cogeneration system to recover the waste heat with high exergy efficiency. Thermodynamic performances, effects of key operation parameters and off-design performances under part-load conditions of the cogeneration system are analyzed. Under the design condition, the cogeneration system produces 20.26 mol kg−1 hydrogen and generates 8746 kJ kg−1 net power, achieving the high energy efficiency and exergy efficiency of 54.77 % and 52.54 %. The exergy efficiency of cogeneration system can be enhanced by optimizing the operation parameters, which is increased by 0.42 %, 4.03 % and 1.10 % with the optimal coal water slurry concentration (17.5 %), higher gasification temperature (750 °C) and higher gas turbine inlet parameters (1500 °C/3 MPa), respectively. The cogeneration system performance decreases with the power load, and the exergy efficiency decreases by 9.61 % when the system power load reduces from 100 % to 30 %.

Suitable promotion scope of different clean heating technology paths in northern China

The Chinese government has implemented a clean heating policy to alleviate the severe air pollution and high energy consumption associated with winter heating in northern China. However, the promotion of clean heating technology paths (CHTPs) is limited by the problems of rising energy prices and insufficient supply capacity. To quantitatively study the promotion scope of each CHTP, this paper adopts the K-means clustering method in machine learning to analyze the clean heating methods suitable for the characteristics of each region in northern China based on 37 pilot cities. The results show that the 10 CHTPs based on coal, electricity and natural gas as energy, the most widely applied is Air-source heat pump technology, accounting for 86.7 % in cities. The least number of cities suitable for application are water-source heat pumps and sewage-source heat pumps due to economic constraints, with a proportion of 44 %. The 3 kinds of CHTPs applying solar, biomass and geothermal energy, accounted for more than 60 %, among them, ground-source heat pumps are recommended to promote the smallest scope, concentrated in Hebei, Henan, Shandong, and Heilongjiang provinces. This study is of great significance in guiding the selection of CHTPs on a large spatial scale.

Gas desorption characteristics of coal particles under dynamic temperature changes: Implication for the lost gas estimation during borehole coal sampling

The estimation of lost gas during borehole coal sampling determines the accuracy of coalbed methane (CBM) content determination. The isothermal desorption data is used frequently for analyzing the estimation error of the lost gas, which is not consistent with the engineering practice that the gas desorption during borehole coal sampling is in dynamic temperature changing condition (i.e., DTC), thus resulting in the result of the lost gas estimation is not accurate. In this study, a DTC adsorption/desorption experimental system was set up to study the gas desorption characteristics of coal particles during borehole coal sampling, and the differences between isothermal desorption and DTC desorption were analyzed in detail. Furthermore, the isothermal desorption data and DTC desorption data were fitted using the unipore diffusion model (UDM) to discuss the influence of DTC desorption on the lost gas estimation. Finally, the fractional diffusion model (FDM) was applied to estimate the lost gas. The results showed that there is a significant difference between isothermal desorption and DTC desorption. For the case of DTC desorption, more gas will be lost at the same exposure time, resulting in the lost gas being underestimated in the CBM content determination. With the exposure time of 12 min, the average fitting errors of lost gas using the FDM with different coal particle sizes and gas pressures are less than 17.9%, while that using the UDM are greater than 57.5%, suggesting that the FDM could improve the fitting accuracy of lost gas estimation in the CBM content determination.

Composition and Structural Characteristics of Coal Gasification Slag from Jinhua Furnace and Its Thermochemical Conversion Performance

Gasification technology enables the clean and efficient utilization of coal. However, the process generates a significant amount of solid waste—coal gasification slag. This paper focuses on the Jinhua furnace coal gasification slag (fine slag, FS; coarse slag, CS) as the research subject, analyzing its composition and structural characteristics, and discussing the thermochemical conversion performance of both under different atmospheres (N2 and air). The results show that the fixed carbon content in FS is as high as 35.82%, while it is only 1% in CS. FS has a large number of fluffy porous carbon on its surface, which wraps around or embeds into smooth and variously sized spherical inorganic components, with a specific surface area as high as 353 m2/g, and the pore structure is mainly mesoporous. Compared to the raw coal (TYC), the types of organic functional groups in FS and CS are significantly reduced, and the graphitization degree of the carbon elements in FS is higher. The ash in FS is mainly amorphous and glassy, while in CS, it mainly has crystalline structures. The weight loss rates of TYC and FS under an inert atmosphere are 27.49% and 10.38%, respectively; under an air atmosphere, the weight loss rates of TYC and FS are 81.69% and 44.40%, respectively. Based on the analysis of the thermal stability of FS and its high specific surface area, this paper suggests that FS can be used to prepare high-value-added products such as porous carbon or high-temperature-resistant carbon materials through the method of carbon–ash separation.