Underground Coal Gasification Process Research Articles

Analytical justification of the thermochemical interaction between blast reagents and carbon-containing products under the influence of magnetic fields

Purpose. To justify and develop a model that describes the effect of magnetic treatment of blast reagents and carbon-containing products on the gasification process for predicting the intensification of gas formation. Methodology. The study involves theoretical modeling based on experimental data to investigate the influence of magnetic fields on the underground coal gasification process and co-gasification of coal and carbon-containing products. The Arrhenius equation was used to estimate the rate constants of gasification reactions in the temperature range of 800–1,000 °C. The effect of the magnetic field was incorporated by adjusting the activation energy (Ea). The results of analytical and experimental studies were processed using methods of computer and mathematical modeling. Findings. The results show that the application of magnetic fields significantly intensifies the gasification process of carbon containing products. Increasing the reactivity of the blast reagents, particularly water and oxygen, leads to a higher overall yield of combustible gases. The use of magnetic fields in the gasification process substantially increases the reaction rate (k) due to the reduction in activation energy (Ea), improving the overall efficiency of gasification. Originality. For the first time, an analytical model has been developed to describe the effect of magnetic treatment of blast reagents and carbon-containing products on the gasification process in the temperature range of 800–1,000 °C. The obtained reaction rates follow an exponential trend. The established and correlation-validated pattern shows the relationship between changes in the approximation coefficient (F ) and the change in the carbon fraction (C, %) during the magnetic treatment of blast components within the specified temperature range. Practical value. The results of this study can be applied to enhance the efficiency of industrial gasification processes, particularly underground coal gasification and co-gasification of coal and carbon-containing productss.

Mathematical model for heat transfer during underground coal gasification process

Purpose. To develop a mathematical model of the “coal-gas” medium heat transfer during underground coal gasification to predict the combustion face advance velocity and the duration of gasification column mining. Methodology. To detect the temperature fields in the coal seam and gas, depending on the displacement length of the phase transition boundary, a boundary-value problem of mathematical physics has been developed. To solve this boundary-value problem, Boltzmann transformations, as well as methods for solving ordinary differential equations, are used. Newton-Raphson method, which has quadratic convergence, is used to find the roots of the transcendental equation. Findings. Tendencies in the formation of mathematical models when studying temperature fields around an underground gasifier have been analyzed, with highlighting their disadvantages. A mathematical model of heat transfer during underground gasification has been developed, taking into account the phase transition boundaries of the “coal-gas” medium. A computational experiment was conducted to determine the temperature of the phase transition boundary based on the length of the gasification column and the duration of the process. Originality. A mathematical model for heat transfer during coal gasification in the form of a boundary-value problem of mathematical physics, which consists of parabolic heat-transfer equations, the Stefan condition at the phase transition boundary, and the Dirichlet boundary conditions, has been constructed. As a result of solving the boundary-value problem, a self-similar solution has been obtained for the distribution of the coal seam and gas temperature fields, as well as the position of the phase transition boundary depending on the gasification duration and on the medium density, thermal conductivity coefficients, specific heat capacity of gas and coal, specific calorific value and temperature of coal combustion, initial coal temperature and constant temperature of the gasification process. The conducted analysis of numerical calculations provides a deeper understanding of the dynamics of underground coal gasification process and makes necessary corrections to achieve the maximum process efficiency. Practical value. A methodology for determining the displacement length of the phase transition boundary of the “coal-gas” medium has been developed, taking into account the change in the combustion face temperature along the gasification zone length depending on the duration of this process. Application of the methodology makes it possible to predict the time of mining the gasified coal column for drawing up a calendar plan for mining operations.

Effects of water injection on reaction temperature and hydrogen production in horizontal co-axial underground coal gasification

Underground coal gasification (UCG) is process of directly recovering energy as combustible gases such as hydrogen and carbon monoxide by combusting unmined coal resources in situ. During UCG process, the temperature in the gasification zone can exceed 1,300 °C, raising concerns about the potential melting of the steel pipe for oxidant injection. To control the temperature in the gasification zone, the use of water injection as an injection agent can be an option. Injecting water during UCG process serves two purposes: it decreases the temperature in the reaction zone by the endothermic effect of water, and it enhances the production of H2 by the reduction reaction of water. However, injecting excessive amounts of water may lead to a significant decrease in the temperature in the reaction zone, consequently cannot maintain the temperature range required for the UCG reaction. This study discusses the effects of water injection on the temperature of the gasification zone and the product gas by developing a chemical reaction model of UCG using COMSOL Multiphysics® software. The model was developed based on the temperature and produced gas results obtained from laboratory-scale artificial coal seam UCG experiments. Our findings reveal that water injection significantly influences the gasification process, controlling temperature in the reaction zone and promoting H2 production through steam gasification and water-gas shift reactions. Moreover, under the experiment and analysis conditions of this study, it is revealed that water injection up to an H2O/O2 molar ratio of 3.9 can effectively control the temperature of the gasification zone with enhancing H2 production.

Holistic insight into the viability of employing cerium(IV) sulphate to oxidise toxic contaminants in effluent from the coal gasification process: Optimisation studies

The coal gasification (CG) process, while beneficial for producing syngas, poses environmental risks due to the production of highly toxic wastewater containing high concentrations of polycyclic aromatic hydrocarbons (PAHs), phenolics, and cyanides. This study examines the oxidation of pollutants in wastewater from a simulated underground coal gasification (UCG) process, with initial pollutant levels of pH 1.8, total cyanides 21.00 mg/L, total phenols 61.95 mg/L, heavy metals 7.68 mg/L, PAHs 2459 μg/L, and dissolved organic carbon (DOC) 148.0 mg/L. Three oxidation systems (Ce(SO4)2·4H2O, Ce(SO4)2·4H2O + H2O2, and Fenton process with FeSO4 + H2O2) were used to remove pollutants from wastewater from the coal gasification process. In the first system, the oxidising agent was Ce4+ ions, while in the second and third systems, where hydrogen peroxide was added, the oxidising agents were hydroxyl radicals. Using central composite design and response surface methodology (CCD/RSM), the most favourable oxidation conditions were identified for Ce(SO4)2·4H2O (35 min, Ce4+:C molar ratio of 5:1, pH 2.5, temp. 40 °C). For the Ce(SO4)2·4H2O + H2O2 system DOC:Ce4+:H2O2 molar ratio of 1:2:10. Results showed significant reduction in pollutants: Ce(SO4)2·4H2O reduced PAHs, phenols, cyanides, DOC, and heavy metals by 99.40 %, 99.97 %, 97.67 %, 65.34 %, and 90.01 %, respectively; Ce(SO4)2·4H2O + H2O2 achieved reductions of 99.91 %, 99.66 %, 98.14 %, 76.35 %, and 81.45 %; and the Fenton process achieved reductions of 99.91 %, 99.95 %, 95.07 %, 56.49 %, and 89.33 %. An application of alternative oxidation processes (Ce(SO4)2·4H2O and Ce(SO4)2·4H2O + H2O2) is a viable option in removing toxic pollutants with simultaneously cerium recovery.

Experimental investigation of alterations in coal fracture network induced by thermal treatment: Implications for CO2 geo-sequestration

Hydrogen-rich syngas, produced by underground coal gasification (UCG) process, is a valuable feedstock for chemical industry. However, it can contain large quantities of carbon dioxide (CO2), which requires separation and sequestration to reduce the carbon footprint of the process. This study explores mechanisms influencing coal permeability when CO2 is injected back into the coal through existing gasification chambers. Two main mechanisms affecting permeability are thermal effects associated with underground coal gasification and CO2-related coal matrix swelling.The effects of thermal processes and CO2 flooding on the fracture network of the coal are investigated through a series of comprehensive experiments. Thermal treatment of the studied sample at a temperature of 210 °C shows a notable effect on fracture morphology, increasing width and permeability by up to a factor of 2 and 5, respectively. CO2 flooding, on the other hand, impairs fracture network due to chemisorption driven processes, leading to irreversible changes. Following CO2 flooding experiment, fracture porosity decreases by a factor of three and subsequently permeability declines by 70–80 % within the studied effective stresses range. Our characterization study indicates that thermal treatment significantly increases permeability, compensating for impairments to the fracture network associated with CO2 injection.

Experimental study on coagulation and adsorption treatment of wastewater in combustion cavity for underground coal gasification

Underground Coal Gasification (UCG) is a promising mineral resource development technology that can transform in-situ coal into combustible gas by controlling combustion. However, wastewater generated during the UCG process can lead to environmental pollution in adjacent areas through diffusion or infiltration. In order to seek an efficient and inexpensive in-situ treatment method for underground gasification combustion zone wastewater, UCG model experiments were conducted to obtain wastewater, and the treatment effects of chemical coagulation and physical adsorption methods were compared in this work. The COD concentration in wastewater from underground combustion zone ranges between 555 ∼ 703 mg/L, with a pH value between 8.26 ∼ 8.85. The organic pollutants mainly come from the dissolution of high carbon components, mainly aromatic compounds in tar, which leads to high toxicity and pollution risk of wastewater. For chemical coagulation method, the removal effect of organic pollutants in combustion zone wastewater by ferric sulfate is better than that of aluminum sulfate due to excellent hydrolysis reaction of Fe3+. The corresponding COD removal rate and COD removal cost are 24.34 % and 0.176 ¥/g, respectively. For physical adsorption method, due to the large total pore volume and wide specific surface area of organic bentonite, it can effectively remove COD content. The COD removal rate and COD removal cost, and COD adsorption capacity are 60.23 %, 0.213 ¥/g, and 89.75 mg/g, respectively. Comprehensive comparison shows that physical adsorption is more suitable for in-situ treatment of combustion zone wastewater.

Insights into bacterial diversity in industrial post-processing water from underground coal gasification (UCG) process

This study represents the first culture-independent profiling of microbial diversity in post-processing wastewater from underground coal gasification (UCG) processes. Three types of post-processing wastewater, named W1, W2 and W3, were obtained from three UCG processes involving two types of coal and two gasification agents, namely oxygen-enriched air and oxygen. Very high concentrations of BTEX (benzene, toluene, ethylbenzene, xylene), polyaromatic hydrocarbons (PAHs), and phenol were detected in the wastewater, classifying it into the fifth toxicity class, indicating very high acute toxicity. The values for the Shannon (H), Ace and Chao1 indices in W2 were the lowest compared to their values in W1 and W3. The dominate phyla were Proteobacteria, contributing 84.64% and 77.92% in W1 and W3, respectively, while Firmicutes dominated in W2 with a contribution of 66.85%. At the class level, Gammaproteobacteria and Alphaproteobacteria were predominant in W1 and W3, while Bacilli and Actinobacteria were predominant in W2. Among Bacilli, the Paenibacillus and Bacillus genera were the most numerous. Our results suggest that the main differentiating factor of the bacterial structure and diversity in the wastewater could be the gasification agent. These findings provide new insights into the shifting patterns of dominant bacteria in post-processing wastewater and illustrate the spread of bacteria in industrial contaminated wastewater.

Numerical simulation study on chemical ignition process of underground coal gasification

Underground coal gasification (UCG) is a process that produces combustible gas by the in-situ gasification of coal seams. For a steady and efficient gasification project, the ignition of coal seam is a prerequisite. The heating method and reacting process of coal seam play an essential role to the ignition. A coal seam ignition model coupled with heptane combustion was created to simulate the deep UCG ignition stage employing the chemical ignition method. A 1700 K heptane jet flame and a U-shaped pyrolysis gas flame formed the heat source. The flame temperature of pyrolysis gas was around 1300 K. The effective heating length of the flame increased with the heating time, which reached 600 mm at 400 s. The coal seam reaction process was divided into four stages: (1) heptane flame stabilization, (2) coal seam heating, (3) pyrolysis gas release, and (4) pyrolysis gas flame stabilization. It was the third stage when the coal seam ignited. The coal seam would ignite faster with a lower excess air coefficient, and the ignition time ranged from 225 to 275 s when the excess air coefficient was 1.39. The outlet carbon dioxide concentration increased by about 5 %–17 % when the coal seam ignited.

Simulation of Underground Coal-Gasification Process Using Aspen Plus

In order to study the underground coal-gasification process, Aspen Plus software was used to simulate the lignite underground gasification process, and a variety of unit operation modules were selected and combined with the kinetic equations of coal underground gasification. The model can reflect the complete gasification process of the coal underground gasifier well, and the simulation results are more in line with the experimental results of the lignite underground gasification model test. The changes in the temperature and pressure of oxygen, gasification water, spray water, and syngas in pipelines were studied, and the effects of pipe diameters on pipeline conveying performance were investigated as well. The effects of the oxygen/water ratio, processing capacity, and spray-water volume on the components of syngas and components in different reaction zones were studied. In addition, the change tendency of gasification products under different conditions was researched. The results indicate that: (1) The depth of injection and the formation pressure at that depth need to be taken into account to determine a reasonable injection pressure. (2) The liquid-water injection process should select a lower injection pressure. (3) Increasing the oxygen/water ratio favors H2 production and decreasing the oxygen/water ratio favors CH4 production. (4) The content of CO2 is the highest in the oxidation zone, the lowest in the reduction zone, and then increases a little in the methanation reaction zone for the transform reaction. The content of CO is the lowest in the oxidation zone and the highest in the reduction zone. In the methanation reaction zone, CO partially converts into H2 and CO2, and the content of CO is reduced. (5) The injection of spray water does not affect the components of the gas but will increase the water vapor content in the gas; thus, this changes the molar fraction of the wet gas.

Constructed wetland as a green remediation technology for the treatment of wastewater from underground coal gasification process.

The wastewater from underground coal gasification (UCG) process has extremely complex composition and high concentrations of toxic and refractory compounds including phenolics, aliphatic and aromatic hydrocarbons, ammonia, cyanides, hazardous metals and metalloids. So, the development of biological processes for treating UCG wastewater poses a serious challenge in the sustainable coal industry. The aim of the study was to develop an innovative and efficient wetland construction technology suitable for a treatment of UCG wastewater using available and low-cost media. During the bioremediation process the toxicity of the raw wastewater decreased significantly between 74%-99%. The toxicity units (TU) ranged from values corresponding to very high acute toxic for raw wastewater to non-toxic for effluents from wetland columns after 60 days of the experiment. The toxicity results correlated with the decrease of some organic and inorganic compounds such as phenols, aromatic hydrocarbons, cyanides, metals and ammonia observed during the bioremediation process. The removal percentage of organic compounds like BTEX, PAHs and phenol was around 99% just after 14 days of treatment. A similar removal rate was indicated for cyanide and metals (Zn, Cr, Cd and Pb). Concluded, in order to effectively assess remediation technologies, it is desirable to consider combination of physicochemical parameters with ecotoxicity measurements. The present findings show that wetland remediation technology can be used to clean-up the heavily contaminated waters from the UCG process. Wetland technology as a nature-based solution has the potential to turn coal gasification wastewater into usable recycled water. It is economically and environmentally alternative treatment method.

Searching of Phenol-Degrading Bacteria in Raw Wastewater from Underground Coal Gasification Process as Suitable Candidates in Bioaugmenation Approach

Searching of Phenol-Degrading Bacteria in Raw Wastewater from Underground Coal Gasification Process as Suitable Candidates in Bioaugmenation Approach

Influences of removable gas injection methods on the temperature field and gas composition of the underground coal gasification process

In this paper, the effects of changing the injection position of a gasification agent on temperature fields and gas compositions are investigated through an experimental model of the underground gasification of coaxial coal. A 3D model of the temperature field is constructed based on the experimental temperature parameters using kriging interpolation; the 900 °C isothermal surface is used as the reference plane to define the oxidation zone, and its plane and volume expansion rate are analyzed. The underground coal gasification experiment is divided into five stages according to the injection location. The average expansion rates of the oxidation zone in each stage are 2.04 cm/h, 1.93 cm/h, 3.44 cm/h, 3.68 cm/h, and 3 cm/h along the X-direction and 0.69 cm/h, 0.09 cm/h, 0.56 cm/h, 1.69 cm/h, and 1.01 cm/h along the Z-direction; the expansion rate along the X-direction is greater than that along the Z-direction. The expansion volumes of the oxidation zone after the five stages increase from 0.0097 m3 to 0.0168 m3, 0.0321 m3, 0.0521 m3 and 0.0657 m3. An analysis of the expanded volume of the oxidation zone compared with the volume of the cavity shows that both features are similar in shape and that the final volume of the cavity is smaller than the final expanded volume of the oxidation zone; the volume of the cavity is approximately 77.3 % of the expanded volume of the oxidation zone. The formation of a cavity requires the temperature to reach the conditions for the oxidation reaction of the coal and the rupture and flaking of the ash layer that accumulates after the reaction by the actions of certain stresses, such as thermal. The composition of the product gas and the strength of the chemical reactions involved are evaluated based on stoichiometric conservation. A short period after a shift in the injection position of the gasifier greatly impacts the chemical equilibrium of the UCG process with a large change in the strength of the chemical reaction, followed by a relatively small change when the gasification process stabilizes.

Research on the underground gasification of lignite through an oxygen enrichment process: insights from experimental study and Aspen Plus process model.

Underground coal gasification (UCG) can convert coal resources to high-calorific value syngas, which is important for the exploration of resources and the application of clean coal technology. This study investigated the gasification process of lignite in Heilongjiang Province through an oxygen enrichment approach and examined the impact of the oxygen concentration on the gasification efficiency. Furthermore, a high-fidelity Aspen Plus process model was designed to predict the gasification products of lignite. These findings indicate that the abrupt increase in the gasification temperature and pressure is governed by the concentration of oxygen in the gasification agent. An increased concentration of oxygen results in a higher gasification temperature, thereby influencing the thermodynamic reaction processes within the gasifier. The combustion reaction of lignite transitions into a coke reaction when the oxygen concentration is elevated to 90%. At this time, the relative concentration of CO2 generated from lignite combustion progressively diminished from 78.33%, while the relative concentrations of H2 and CO produced through coke reactions gradually increased from 3% and 2.07%, respectively. When the oxygen concentration reaches 100%, the relative contents of H2 and CO generated through gasification reach their respective maxima, measuring 18.90% and 23.91%. The calorific value attained a peak of 6.65 MJ N-1 m-3 simultaneously. Furthermore, the ash yield of lignite may be a critical factor influencing the process of underground coal gasification. The gasification efficiency of lignite near T 6 is suboptimal when the oxygen concentration falls below 100%, potentially attributable to the influence of ash. In summary, lignite in Heilongjiang Province can be effectively developed through underground gasification technology via an oxygen enrichment process. Furthermore, the Aspen Plus model we developed can effectively assist in predicting the products of lignite gasification in Heilongjiang Province.

ФОРМУВАННЯ МЕТОДИКИ ДОСЛІДЖЕНЬ ВОДНЕВООРІЄНТОВАНОЇ ТЕХНОЛОГІЇ ПІДЗЕМНОЇ ГАЗИФІКАЦІЇ ВУГІЛЛЯ

Purpose. Establishing correlations between analytical and laboratory research in underground coal gasification with a focus on hydrogen production. Methodology. Analysis of experience in conducting analytical and laboratory research in the field of underground coal gasification in situ. Analysis of the application specifics of the Darcy-Weisbach equation to establish optimal conditions for supplying steam-air mixture to the combustion face considering the relationship between the volumetric flow of the specified mixture through the controlled pipeline and its cross-sectional area. Results. The proposed algorithm for conducting research on underground coal gasification processes focuses on hydrogen production. Analytical formulas are provided to determine optimal parameters for supplying the blowing mixture to the combustion front via the controlled pipeline. An author's technological scheme of a laboratory setup for studying gasification processes and the peculiarities of researching it are presented. A diagram illustrating the relationship between blowing system parameters, which vary depending on the hydrogen raw material requirements, the energy capabilities of the system itself, and the parameters of the controlled pipeline, is provided. Originality: Scientifically grounded development of a methodology for conducting analytical and laboratory research on coal gasification process to determine parameters for supplying the blowing mixture through the controlled pipeline with a focus on hydrogen production. Practical implications: Practical implications: Conducting research according to the developed research methodology of underground coal gasification technology allows for a systematic and structured approach to assessing all aspects of the gasification process. The use of a clear research methodology helps to avoid subjectivity and simplifies the process of data collection and analysis. The research methodology ensures high reliability and accuracy of the obtained data, which is critical for making informed decisions. Effective use of the research methodology minimizes resource usage, such as time, costs, and equipment, by avoiding unnecessary duplications and unjustified expenses. Practical implications: Practical implications: Conducting research according to the developed research methodology of underground coal gasification technology allows for a systematic and structured approach to assessing all aspects of the gasification process. The use of a clear research methodology helps to avoid subjectivity and simplifies the process of data collection and analysis. The research methodology ensures high reliability and accuracy of the obtained data, which is critical for making informed decisions. Effective use of the research methodology minimizes resource usage, such as time, costs, and equipment, by avoiding unnecessary duplications and unjustified expenses. Keywords: underground coal gasification, hydrogen, methodology, analytical research, Darcy-Weisbach equation, laboratory research.

Research on Temperature Simulation of Underground Coal Gasification Wellbore

This study aims to integrate the theoretical distribution calculation of temperature and pressure during the gasification process through the derivation of heat conduction, thermal radiation and pressure control theory in the underground coal gasification process, and analyze the temperature of the underground coal gasification process through finite element modeling. Field influencing factors and pressure changes over time. It is of great significance to obtain the relevant parameters of the gasification chamber in the underground coal gasification process.

Aquifer hydraulic conductivity characterization by inflatable packer method in the underground coal gasification process

Underground coal gasification technology is a technology that converts coal into gaseous products through the gasification process. UCG technology is known as clean energy technology. The potential risk of UCG that can occur is groundwater contamination, this is due to gas leaking into the rock layers and the aquifer above it. An important parameter of groundwater contamination is hydraulic conductivity, obtained by the double inflatable packer method. The test results of aquifer-03 (142-151 m), the hydraulic conductivity value is 1.82 e-6 m/s - 2.16 e-6 m/s, the aquifer zone order range from the upper limit to the lower limit tends to be homogeneous in sand lithology. fine. The top layer of aquifer-04 (213-230 m), is silt lithology, the middle is silty sand lithology and the bottom is silty sand lithology. The hydraulic conductivity value is 1.22 e-6 m/s - 3.88 e-8 m/s, the range is quite wide with a difference of 2 orders, this is due to differences in grain lithological composition with finger type aquifer layers and are not interconnected. If there is a gas leak, then aquifer-03 lithology is more affected as a medium for spreading groundwater pollution than aquifer-04 lithology.

Visualization of Movement and Expansion of Coal Reaction Zone by Acoustic Emission Monitoring in Underground Coal Gasification System

Underground coal gasification (UCG) is the process of directly recovering energy as combustible gases such as hydrogen and carbon monoxide by combusting unmined coal resources in situ. The UCG process is an invisible phenomenon, in which fracturing activity at high temperature (>1000 °C) in coal seams expands the gasification zone and increases the combustible components of the product gas. However, excessive expansion of the gasification zone may cause environmental problems such as gas leakage, deformation of the surrounding ground, and groundwater pollution. Therefore, visualization of the gasification zone of UCG is required for both improving gasification efficiency and developing UCG systems with low environmental impact. In this study, the large-scale model UCG experiments conducted on a laboratory scale (size: 625 mm × 650 mm × 2792 mm (H × W × L)) were carried out to discuss the visualization of the gasification reaction zone of coal in UCG by Acoustic Emission (AE) technique with uniaxial and triaxial acceleration transducers. As the results of temperature monitoring and AE source location analysis show, AE sources are located near the high-temperature zone (>1000 °C). In addition, the located AE sources move and expand with the movement and expansion of the high-temperature zone. AE measurement can be a useful technique for monitoring the progress of the UCG reaction zone. AE measurement with triaxial sensors is also useful to predict a high-temperature zone though the measurable range, which has to be considered.

A thermo-mechanical simulation for the stability analysis of a horizontal wellbore in underground coal gasification

The stability analysis of horizontal wells is essential for a successful underground coal gasification (UCG) operation. In this paper, a new 3D coupled thermo-mechanical numerical modeling is proposed for analyzing the stability of UCG horizontal wells. In this model, the effect of front abutment stresses, syngas pressure, syngas temperature and thermal stresses is considered to predict the mud weight window and drilling mud pressure during UCG process. The results show that the roof caving in UCG panel has a greatest impact on the stability of horizontal well. Moreover, when the time of coal gasification is increased, the well convergence increases and for more stability it is necessary to increase the drilling mud pressure. This research was carried out on the M2 coal seam in Mazino coal deposit (Iran). The results showed that the mud weight window for horizontal well drilling is between 0 and 33 MPa. The appropriate stress for the maximum stability of the horizontal well, taking all the thermal and mechanical parameters into account, is 28 MPa. The suggested numerical method is a comprehensive and consistent way for analyzing the stability of horizontal wells in UCG sites.

Quantitative Evaluation of Underground Coal Gasification Based on a CO2 Gasification Agent

Using carbon dioxide as a gasification agent for underground coal gasification (UCG) can not only reduce carbon dioxide emissions but is also expected to lead to a new natural gas technology revolution and ensure national energy security. To explore the effect of the oxygen content in oxygen-enriched carbon dioxide gasification agents on the results of gasification experiments, underground gasification experiments under different oxygen-enrichment conditions were designed, and quantitative parameters were used to analyze and evaluate the gas produced in the gasification experiments. The results showed that as the oxygen content in the oxygen-enriched carbon dioxide gasification agent increased, the CO and H2 in the combustible gas gradually increased, and the calorific value of the combustible gas also slowly increased, reaching a peak value under the gasification condition of 60% oxygen concentration, and then decreased slightly; the product formation rate and the gas production per unit mass of coal fluctuated. The coal consumption rate increased with time and was relatively stable. According to theoretical calculations for the gasification energy recovery evaluation system, the overall energy recovery rate was 56.34%, and the energy utilization rate was relatively high. Research on quantitative indicators based on gas production data has good practical significance for evaluating the gasification efficiency of UCG, which can be used to better evaluate and control the reaction process of UCG.

Nonlinear-Control-Oriented Modeling of the Multi-Variable Underground Coal Gasification Process for UCG Project Thar: A Machine Learning Perspective

The Underground Coal Gasification (UCG) process is a complex and multi-physics phenomenon, thus making it difficult to develop a mathematical model that encapsulates all dynamical aspects. In this regard, data-driven modeling techniques offer a reliable alternative for prediction, control, and optimization of dynamical systems, but their application in UCG is still in the early stages. This work aims to bridge this gap by implementing three cutting-edge nonlinear identification structures: Non-linear Autoregressive with Exogenous Inputs (NARX), Hammerstein–Wiener (HW), and State-Space Neural Networks (SSNN) on the UCG process to obtain a multivariable control-oriented model. The contributions include synthesizing an excitation signal for data acquisition, outlining the non-linear system identification procedure, and comparing predictive capabilities using statistical tools. The simulation results demonstrate a rigorous comparison of various techniques for the heating value and flowrate of the syngas, which are the outputs of the UCG process. The results of the analysis show that NARX outperforms other structures in statistical metrics, with MAE, RMSE, and Best fit values of 1.51,1.9, and 0.9, respectively, for the heating value; and 0.25,0.31, and 0.94, respectively, for the flowrate. Consequently, the outputs of the NARX model are compared with the experimental data obtained from the UCG project Thar, which show a good match for both outputs.