Underground coal gasification is one of the clean technologies of in-situ coal utilization.Hydrogen production from underground gasification of lignite was investigated in this study based on simulation experiments.Py...Underground coal gasification is one of the clean technologies of in-situ coal utilization.Hydrogen production from underground gasification of lignite was investigated in this study based on simulation experiments.Pyrolysis of lignite, gasification activity, oxygen-steam gasification and the effect of groundwater influx were studied.As well, the advantages of lignite for stable underground gasification were analyzed.The results indicate that lignite has a high activity for gasification.Coal pyrolysis is an important source of hydrogen emission.Under special heating conditions, hydrogen is released from coal seams at temperatures above 350 °C and reaches its maximum value between 725 and 825 °C.Gas with a hydrogen concentration of 40% to 50% can be continuously obtained by oxygen-steam injection at an optimum ratio of steam to oxygen, while lignite properties will ensure stable gasification.Groundwater influx can be utilized for hydrogen preparation under certain geological conditions through pressure control.Therefore, enhanced-hydrogen gas production through underground gasification of lignite has experimentally been proved.展开更多
The problem of the high-level processing of coal into synthetic motor fuels assumes worldwide actual meaning nowadays. Thereat, it is important especially for countries and regions which possess extensive coal resourc...The problem of the high-level processing of coal into synthetic motor fuels assumes worldwide actual meaning nowadays. Thereat, it is important especially for countries and regions which possess extensive coal resources and are forced to be guided by the import of liquid and gas hydrocarbons. However, a greater emphasis is paid to the given issue in Russia-The development of the federal program for highlevel processing of coal into synthetic motor fuels was initiated. This article describes options of underground coal gasification (UCG) use for the generation of hydrocarbons from UCG gas in the process of the Fischer-Tropsch synthesis (FTS). The technical and economic analysis of the integrated UCG-FTS powerchemical factories has detected their investment attractiveness and practicability of experimental-industrial testing at coal deposits of the Russian Federation.展开更多
Coal pillars are critical supporting structures between underground coal gasification gasifiers.Its bearing capacity and structural stability are severely threatened by high-temperature environments.To elucidate the h...Coal pillars are critical supporting structures between underground coal gasification gasifiers.Its bearing capacity and structural stability are severely threatened by high-temperature environments.To elucidate the high-temperature deterioration mechanism of coal pillars at multiple scales,coal strength features as a function of temperature were investigated via uniaxial compression and acoustic emission equipment.The pyrolysis reaction process and microstructure evolution were characterized via X-ray diffractometer(XRD),scanning electron microscope(SEM),thermogravimetric(TG),Fourier transform infrared spectroscopy(FTIR),and computed tomography(CT)tests.Experimental results reveal a critical temperature threshold of 500℃for severe degradation of the coal bearing capacity.Specifically,both the strength and elastic modulus exhibit accelerated degradation above this temperature,with maximum reductions of 45.53%and 61.34%,respectively.Above 500℃,coal essentially undergoes a pyrolysis reaction under N_(2)and CO_(2)atmospheres.High temperatures decrease the quantity of O_(2)-based functional groups,growing aromaticity and the degree of graphitization.These changes induce dislocation and slip inside the coal crystal nucleus and then lead to deformation of the coal molecular structural units and strain energy generation.This process results in a great increase in porosity.Consequently,the stress deformation of coal increases,transforming the type of failure from brittle to ductile failure.These findings are expected to provide scientific support for UCG rock strata control.展开更多
Coal underground gasification(UCG)transforms the physical extraction of coal into the chemical extraction of gas,which is effective for exploiting deep coal deposits.Numerical simulation technology for UCG is a crucia...Coal underground gasification(UCG)transforms the physical extraction of coal into the chemical extraction of gas,which is effective for exploiting deep coal deposits.Numerical simulation technology for UCG is a crucial tool for studying the complex processes involved in coal gasification.This study was conducted to determine the direction in which UCG numerical simulation is developing,specifically by reviewing the research progress and achievements made in this area and identifying the existing problems and future research directions.The findings indicate the following:(1)Research has focused on the reaction issues of coal underground gasification,considering mass and heat transfer effects and gasification cavity expansion.Chemical equilibrium,gasification block,packed bed,and gasification channel models have been developed,which have certain advantages in solving gasification reaction problems influenced by cavity structure and reasonable simplifications capable of describing local issues.(2)The dynamic description of gasification cavity structures is a challenging problem that UCG numerical simulation needs to address.The cavity expansion mechanism includes thermochemical consumption,coal spalling,roof collapse,and debris accumulation.Thermochemical consumption causes the mechanical properties of coal and rock to change,leading to spalling under stress.(3)Process models emphasize dynamic simulations of the gasification process,including cavity evolution and gasification products.The reactor combination model,continuous medium equivalent model,and multimodule integration model are primarily used.(4)Future UCG numerical simulation technology development will prioritize modularity,systematization,and intelligence.There is an urgent need to facilitate the chemical reaction kinetics of large coal blocks,the coupling of discontinuous media,and the integration of multifunctional systems,including that of numerical simulation technology with artificial intelligence.With continuous improvements,numerical simulation technology will play a greater technical supporting role in UCG industrialization.展开更多
In situ coal gasification poses a potential environmental risk to groundwater pollution although it depends mainly on local hydrogeological conditions. In our investigation,the possible processes of groundwater pollut...In situ coal gasification poses a potential environmental risk to groundwater pollution although it depends mainly on local hydrogeological conditions. In our investigation,the possible processes of groundwater pollution origi-nating from underground coal gasification (UCG) were analyzed. Typical pollutants were identified and pollution con-trol measures are proposed. Groundwater pollution is caused by the diffusion and penetration of contaminants generated by underground gasification processes towards surrounding strata and the possible leaching of underground residue by natural groundwater flow after gasification. Typical organic pollutants include phenols,benzene,minor components such as PAHs and heterocyclics. Inorganic pollutants involve cations and anions. The natural groundwater flow after gasification through the seam is attributable to the migration of contaminants,which can be predicted by mathematical modeling. The extent and concentration of the groundwater pollution plume depend primarily on groundwater flow ve-locity,the degree of dispersion and the adsorption and reactions of the various contaminants. The adsorption function of coal and surrounding strata make a big contribution to the decrease of the contaminants over time and with the distance from the burn cavity. Possible pollution control measures regarding UCG include identifying a permanently,unsuitable zone,setting a hydraulic barrier and pumping contaminated water out for surface disposal. Mitigation measures during gasification processes and groundwater remediation after gasification are also proposed.展开更多
Environmental benefits of underground coal gasification are evaluated. The results showed that through underground coal gasification, gangue discharge is eliminated, sulfur emission is reduced, and the amount of ash,...Environmental benefits of underground coal gasification are evaluated. The results showed that through underground coal gasification, gangue discharge is eliminated, sulfur emission is reduced, and the amount of ash, mercury, and tar discharge are decreased. Moreover, effect of underground gasification on underground water is analyzed and CO 2 disposal method is put forward.展开更多
Two-stage underground coal gasification was studied to improve the caloric value of the syngas and to extend gas production times.A model test using the oxygen-enriched two-stage coal gasification method was carried o...Two-stage underground coal gasification was studied to improve the caloric value of the syngas and to extend gas production times.A model test using the oxygen-enriched two-stage coal gasification method was carried out.The composition of the gas produced,the time ratio of the two stages,and the role of the temperature field were analysed.The results show that oxygen-enriched two-stage gasification shortens the time of the first stage and prolongs the time of the second stage.Feed oxygen concentrations of 30%, 35%,40%,45%.60%,or 80%gave time ratios（first stage to second stage） of 1：0.12,1：0.21.1：0.51,1：0.64, 1：0.90.and 1：4.0 respectively.Cooling rates of the temperature field after steam injection decreased with time from about 19.1-27.4℃/min to 2.3-6.8℃/min.But this rate increased with increasing oxygen concentrations in the first stage.The caloric value of the syngas improves with increased oxygen concentration in the first stage.Injection of 80%oxygen-enriched air gave gas with the highest caloric value and also gave the longest production time.The caloric value of the gas obtained from the oxygenenriched two-stage gasification method lies in the range from 5.31 MJ/Nm^3 to 10.54 MJ/Nm^3.展开更多
To optimize the technological parameter of underground coal gasification （UCG）, the experimental results of air gasification, air-steam gasification, oxygen-enrichment steam gasification, pure oxygen steam gasificat...To optimize the technological parameter of underground coal gasification （UCG）, the experimental results of air gasification, air-steam gasification, oxygen-enrichment steam gasification, pure oxygen steam gasification and two-stage gasification were studied contrastively based on field trial at the Huating UCG project. The results indicate that the average low heat value of gas from air experiment is the lowest （4.1 MJ/Nm3） and the water gas from two-stage gasification experiment is the highest （10.72 MJ/Nm3）. The gas productivity of air gasification is the highest and the pure oxygen steam gasification is the lowest. The gasification efficiency of air gasification, air-steam gasification, oxygen-enriched steam gasification, pure oxygen steam gasification and two-stage gasification is listed in ascending order, ranging from 69.88% to 84.81%. Described a contract study on results of a field test using steam and various levels of oxygen enrichment of 21%, 32%, 42% and 100%. The results show that, with the increasing of O2 content in gasifying agents, the gas caloricity rises, and the optimal O2 concentration range to increase the gas caloricity is 30%-40%. Meanwhile, the consumption of O2 and steam increase, and the air consumption and steam decomposition efficiency fall.展开更多
This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions.The results show that in the cultivation ...This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions.The results show that in the cultivation stage of oxidation zone,the main direction of the temperature field expansion is consistent with the crack direction of the coal seam.In the gasification stabilization stage,the main direction of the temperature field expansion is along the channel.The temperature of the coal seam and the overlying rock mass at its interface with the furnace directly above the gasification channel is equivalent to that of the coal seam temperature,and this temperature is much greater than the temperatures observed near both side walls of the gasification channel at the interface.However,temperatures perpendicular to the axis of the gasification channel are similar at a vertical distance of 40 cm away from the interface.The temperature distributions indicate that the transmission of heat through the overlying rock mass is more rapid in the vertical direction than in the horizontal direction.Moreover,some degree of thermal dispersion is observed in the vertical direction near the outlet.The thermal dispersion coefficient is 0.72 and dispersion angle γ is 78.7°.展开更多
The field trail used a mixture of steam and air with various levels of oxygen en- richment.Steady conditions were achieved in the field trail which produced high quality hydrogen-enriched syngas.To understand and opti...The field trail used a mixture of steam and air with various levels of oxygen en- richment.Steady conditions were achieved in the field trail which produced high quality hydrogen-enriched syngas.To understand and optimize the UCG process,a simplified heat and mass transfer model was presented,providing a predictive tool for temperature and the major constituents of the syngas production.The model is compared with the field trail measurements for air and two levels of oxygen enrichment,showing reasonable agreement for the channel temperature and product syngas concentration profile.展开更多
An integrated vacuum pressure swing adsorption(VPSA) and Rectisol process is proposed for CO_(2) capture from underground coal gasification(UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly desi...An integrated vacuum pressure swing adsorption(VPSA) and Rectisol process is proposed for CO_(2) capture from underground coal gasification(UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO_(2) with a CO_(2) purity of 98.35% from UCG syngas(CH_(4)/CO/CO_(2)/H_(2)/N_(2)= 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field,Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO_(2)remained in light product gas from the VPSA process using cryogenic methanol(233.15 K, 100%(mass)) as absorbent. A final purified gas with CO_(2) concentration lower than 3% and a regenerated CO_(2) product with CO_(2) purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg^(-1) of the single Rectisol process to 1.008 MJ·kg^(-1) of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO_(2) capture from UCG syngas. Additionally, the high-value gas(e.g., CH_(4)) loss can be decreased and the effects of key operating parameters on the process performances were detailed.展开更多
During underground coal gasification （UCG）, whereby coal is converted to syngas in situ, a cavity is formed in the coal seam. The cavity growth rate （CGR） or the moving rate of the gasification face is affected by...During underground coal gasification （UCG）, whereby coal is converted to syngas in situ, a cavity is formed in the coal seam. The cavity growth rate （CGR） or the moving rate of the gasification face is affected by controllable （operation pressure, gasification time, geometry of UCG panel） and uncontrollable （coal seam properties） factors. The CGR is usually predicted by mathematical models and laboratory experiments, which are time consuming, cumbersome and expensive. In this paper, a new simple model for CGR is developed using non-linear regression analysis, based on data from 1 l UCG field trials. The empirical model compares satisfactorily with Perkins model and can reliably predict CGR.展开更多
Based on the quasi-steady-state approximation, the dynamic equation of char combustion in the oxidation zone of underground coal gasification (UCG) was derived. The parameters of the dynamic equation were determined a...Based on the quasi-steady-state approximation, the dynamic equation of char combustion in the oxidation zone of underground coal gasification (UCG) was derived. The parameters of the dynamic equation were determined at 900℃ using a thermo-gravimetric (TG) analyzer connected to a flue gas analyzer and this equation. The equation was simplified for specific coals, including high ash content, low ash content, and low ash fusibility ones. The results show that 1) the apparent reaction rate constant increases with an increase in volatile matter value as dry ash-free basis,2) the effective coefficient of diffusion decreases with an increase in ash as dry basis, and 3) the mass transfer coefficient is independent of coal quality on the whole. The apparent reaction rate constant, mass-transfer coefficient and effective coefficient of diffusion of six char samples range from 7.51×104 m/s to 8.98×104 m/s, 3.05×106 m/s to 3.23×106 m/s and 5.36×106 m2/s to 8.23×106 m2/s at 900℃, respectively.展开更多
In this study,the composition of tars collected during a six-day underground coal gasification(UCG)test at the experimental mine‘Barbara’in Poland in 2013 was examined.During the test,tar samples were taken every da...In this study,the composition of tars collected during a six-day underground coal gasification(UCG)test at the experimental mine‘Barbara’in Poland in 2013 was examined.During the test,tar samples were taken every day from the liquid product separator and analysed by the methods used for testing properties of typical coke oven(coal)tar.The obtained results were compared with each other and with the data for coal tar.As gasification progressed,a decreasing trend in the water content and an increasing trend in the ash content were observed.The tars tested were characterized by large changes in the residue after coking and content of parts insoluble in toluene and by smaller fluctuations in the content of parts insoluble in quinoline.All tested samples were characterized by very high distillation losses,while for samples starting from the third day of gasification,a clear decrease in losses was visible.A chromatographic analysis showed that there were no major differences in composition between the tested tars and that none of the tar had a dominant component such as naphthalene in coal tar.The content of polycyclic aromatic hydrocarbons(PAHs)in UCG tars is several times lower than that in coal tar.No light monoaromatic hydrocarbons(benzene,toluene,ethylbenzene and xylenes—BTEX)were found in the analysed tars,which results from the fact that these compounds,due to their high volatility,did not separate from the process gas in the liquid product separator.展开更多
The exact shape and size of the gasification channel during underground coal gasification(UGC) are of vital importance for the safety and stability of the upper parts of the geological formation.In practice existing g...The exact shape and size of the gasification channel during underground coal gasification(UGC) are of vital importance for the safety and stability of the upper parts of the geological formation.In practice existing geological measurements are insufficient to obtain such information because the coal seam is typically deeply buried and the geological conditions are often complex.This paper introduces a cylindrical model for the gasification channel.The rock and soil masses are assumed to be homogeneous and isotropic and the effect of seepage on the temperature field was neglected.The theory of heat conduction was used to write the equation predicting the temperature field around the gasification channel.The idea of an excess temperature was introduced to solve the equations.Applying this model to UCG in the field for an influence radius,r,of 70 m gave the model parameters,u1,2,3...,of 2.4,5.5,8.7...By adjusting the radius(2,4,or 6 m) reasonable temperatures of the gasification channel were found for 4 m.The temperature distribution in the vertical direction,and the combustion volume,were also calculated.Comparison to field measurements shows that the results obtained from the proposed model are very close to practice.展开更多
A 72-h ex situ hard coal gasification test in one large block of coal was carried out.The gasifying agent was oxygen with a constant flow rate of 4.5 m^(3)/h.The surroundings of coal were simulated with wet sand with ...A 72-h ex situ hard coal gasification test in one large block of coal was carried out.The gasifying agent was oxygen with a constant flow rate of 4.5 m^(3)/h.The surroundings of coal were simulated with wet sand with 11%moisture content.A 2-cm interlayer of siderite was placed in the horizontal cut of the coal block.As a result of this process,gas with an average flow rate of 12.46 m^(3)/h was produced.No direct influence of siderite on the gasification process was observed;however,measurements of CO_(2)content in the siderite interlayer before and after the process allow to determine the location of high-temperature zones in the reactor.The greatest influence on the efficiency of the gasification process was exerted by water contained in wet sand.At the high temperature that prevailed in the reactor,this water evaporated and reacted with the incandescent coal,producing hydrogen and carbon monoxide.This reaction contributes to the relatively high calorific value of the resulting process gas,averaging 9.41 MJ/kmol,and to the high energy efficiency of the whole gasification process,which amounts to approximately 70%.展开更多
Underground coal gasification(UCG)is widely regarded as a clean coal technology that holds enormous potential to decarbonize the world's coal industry.It converts coal underground into combustible syngas through a...Underground coal gasification(UCG)is widely regarded as a clean coal technology that holds enormous potential to decarbonize the world's coal industry.It converts coal underground into combustible syngas through a set of complex physiochemical events.Experimental and nu-merical efforts over the past century have contributed to the development of UCG around the world;however,tapping the world's deep-situated coal resources with UCG requires substantial contributions from numerous high-quality researchers.To facilitate effective engagement,this paper will provide a background on where to start if one wishes to undertake UCG modelling.First,a brief description of the fundamental phenomena involved in UCG is given.Then,a succinct introduction of the widely used modelling software is rendered,followed by a description of UCG studies to provide insight how to tune the various software packages for modelling UCG and where their strengths lie.This paper shall serve as guidance to new UCG modellers.展开更多
China has a huge demand for energy.Under the present energy structure of rich coal,lean oil,less gas,limited and low-rising rate renewable energy,discussion focus is now on the high-efficient mining of coal as well as...China has a huge demand for energy.Under the present energy structure of rich coal,lean oil,less gas,limited and low-rising rate renewable energy,discussion focus is now on the high-efficient mining of coal as well as its clean-and-low-carbon use.In view of this,based on an analysis of the problems in the coal chemical industry and the present coal utilization ways such as Integrated Gasification Combined Cycle(IGCC),this paper proposes that underground coal gasification(UCG)technology is a realistic choice.By virtue of its advantages in many aspects such as safety&environment,integrated use of superior resources,economic feasibility,etc.this technology can serve as the front-end support and guarantee for coal chemical industry and IGCC.Under the present situation,the following proposals were presented to promote the development of this technology.First,R&D of technical products should be strengthened,a comprehensive feasibility study assessment system should be established,and the relevant criteria in the industry should be formulated.Second,precise market positioning of UCG products should be made with much concern on the integrated economic indicators of each product's complete flow scheme,following the principle of“Technical Feasibility First,Economic Optimization Followed”.Third,a perfect operation and management pattern should be established with strict control over high-efficient,environmentally-friendly,safe,harmonious&compact objectives in the whole industry chain.In conclusion,to realize the large-scale UCG commercial production will strongly promote the optimization and innovation of fossil fuels supply-side economics in China.展开更多
This research focused on the feasibility of applying the forward and reverse combustion approach to the in situ gasification of lignite with the production of hydrogen-rich syngas(H_(2)and CO).The so-called forward co...This research focused on the feasibility of applying the forward and reverse combustion approach to the in situ gasification of lignite with the production of hydrogen-rich syngas(H_(2)and CO).The so-called forward combustion gasification(FCG)and reverse combustion gasification(RCG)approach in which oxygen and steam are simultaneously fed to the simulated system of underground coal gasification(UCG)was studied.A simulated system of UCG was designed and established.The underground conditions of the coal seam and strata were simulated in the system.The combustion gasification of lignite has been carried out experimentally for almost 6.5 days.The average effective content(H_(2)+CO)of syngas during the FCG phase was 62.31%and the maximum content was 70.92%.For the RCG phase the corresponding figures are 61.33%and 67.91%.Thus,the feasibility of using RCG way for UCG has been demonstrated.The temperature profiles have been provided by using of 85 thermocouples during the model experiment,which portrayed the several nephograms of thermal data in the gasifier were of significance for the prospective gasification processes.展开更多
The global trends of increasing oil and gas costs have compelled coal possessing countries to start long term underground coal gasification （UCG） projects. These enhance national energy security and are among the cl...The global trends of increasing oil and gas costs have compelled coal possessing countries to start long term underground coal gasification （UCG） projects. These enhance national energy security and are among the cleanest, ecologically safest coal utilization technologies. This paper delineates the major characteristics of such technologies and analyzes technical solutions. Highlighting the desire to develop large scale industrial UCG plants, pilot level projects are presented using a new UCG method developed in Russia by Joint Stock Company Gazprom Promgaz. This method is distinct for its high controllability, stability, and energy efficiency. New, efficient technical solutions have been developed over the last 10-15 years and are patented in Russia. They guarantee controllability and stability of UCG gas produc- tion. Over one hundred iniection and gas production wells have been operated simultaneously.展开更多
基金Projects 50876112 and 50674084 supported by the National Natural Science Foundation of China
文摘Underground coal gasification is one of the clean technologies of in-situ coal utilization.Hydrogen production from underground gasification of lignite was investigated in this study based on simulation experiments.Pyrolysis of lignite, gasification activity, oxygen-steam gasification and the effect of groundwater influx were studied.As well, the advantages of lignite for stable underground gasification were analyzed.The results indicate that lignite has a high activity for gasification.Coal pyrolysis is an important source of hydrogen emission.Under special heating conditions, hydrogen is released from coal seams at temperatures above 350 °C and reaches its maximum value between 725 and 825 °C.Gas with a hydrogen concentration of 40% to 50% can be continuously obtained by oxygen-steam injection at an optimum ratio of steam to oxygen, while lignite properties will ensure stable gasification.Groundwater influx can be utilized for hydrogen preparation under certain geological conditions through pressure control.Therefore, enhanced-hydrogen gas production through underground gasification of lignite has experimentally been proved.
文摘The problem of the high-level processing of coal into synthetic motor fuels assumes worldwide actual meaning nowadays. Thereat, it is important especially for countries and regions which possess extensive coal resources and are forced to be guided by the import of liquid and gas hydrocarbons. However, a greater emphasis is paid to the given issue in Russia-The development of the federal program for highlevel processing of coal into synthetic motor fuels was initiated. This article describes options of underground coal gasification (UCG) use for the generation of hydrocarbons from UCG gas in the process of the Fischer-Tropsch synthesis (FTS). The technical and economic analysis of the integrated UCG-FTS powerchemical factories has detected their investment attractiveness and practicability of experimental-industrial testing at coal deposits of the Russian Federation.
基金supported by Young Scholar Program(Category A Continuation Funding)of National Natural Science Foundation of China(No.52525401)General Program of National Natural Science Foundation of China(No.52174125)+4 种基金Outstanding Youth Cultivation Project in Shanxi Province(No.202103021222008)Major Program of National Natural Science Foundation of China(No.52334005)New Cornerstone Science Foundation through the XPLORER PRIZEShanxi-Zheda Institute of Advanced Materials and Chemical Engineering(No.2022SX-TD010)Shanxi Science and Technology Major Project(No.20201102004).
文摘Coal pillars are critical supporting structures between underground coal gasification gasifiers.Its bearing capacity and structural stability are severely threatened by high-temperature environments.To elucidate the high-temperature deterioration mechanism of coal pillars at multiple scales,coal strength features as a function of temperature were investigated via uniaxial compression and acoustic emission equipment.The pyrolysis reaction process and microstructure evolution were characterized via X-ray diffractometer(XRD),scanning electron microscope(SEM),thermogravimetric(TG),Fourier transform infrared spectroscopy(FTIR),and computed tomography(CT)tests.Experimental results reveal a critical temperature threshold of 500℃for severe degradation of the coal bearing capacity.Specifically,both the strength and elastic modulus exhibit accelerated degradation above this temperature,with maximum reductions of 45.53%and 61.34%,respectively.Above 500℃,coal essentially undergoes a pyrolysis reaction under N_(2)and CO_(2)atmospheres.High temperatures decrease the quantity of O_(2)-based functional groups,growing aromaticity and the degree of graphitization.These changes induce dislocation and slip inside the coal crystal nucleus and then lead to deformation of the coal molecular structural units and strain energy generation.This process results in a great increase in porosity.Consequently,the stress deformation of coal increases,transforming the type of failure from brittle to ductile failure.These findings are expected to provide scientific support for UCG rock strata control.
基金supported by Natural Science Research Project of Yangzhou University Guangling College,China(Grant No.ZKZD25002)Youth Science and Technology Special Project of PetroChina(Grant No.2024DQ03221)Basic Research Project of Institute Research Institute of Exploration and Development,PetroChina(Grant No.101001cq0b52394).
文摘Coal underground gasification(UCG)transforms the physical extraction of coal into the chemical extraction of gas,which is effective for exploiting deep coal deposits.Numerical simulation technology for UCG is a crucial tool for studying the complex processes involved in coal gasification.This study was conducted to determine the direction in which UCG numerical simulation is developing,specifically by reviewing the research progress and achievements made in this area and identifying the existing problems and future research directions.The findings indicate the following:(1)Research has focused on the reaction issues of coal underground gasification,considering mass and heat transfer effects and gasification cavity expansion.Chemical equilibrium,gasification block,packed bed,and gasification channel models have been developed,which have certain advantages in solving gasification reaction problems influenced by cavity structure and reasonable simplifications capable of describing local issues.(2)The dynamic description of gasification cavity structures is a challenging problem that UCG numerical simulation needs to address.The cavity expansion mechanism includes thermochemical consumption,coal spalling,roof collapse,and debris accumulation.Thermochemical consumption causes the mechanical properties of coal and rock to change,leading to spalling under stress.(3)Process models emphasize dynamic simulations of the gasification process,including cavity evolution and gasification products.The reactor combination model,continuous medium equivalent model,and multimodule integration model are primarily used.(4)Future UCG numerical simulation technology development will prioritize modularity,systematization,and intelligence.There is an urgent need to facilitate the chemical reaction kinetics of large coal blocks,the coupling of discontinuous media,and the integration of multifunctional systems,including that of numerical simulation technology with artificial intelligence.With continuous improvements,numerical simulation technology will play a greater technical supporting role in UCG industrialization.
基金Projects 20207014 and 50674084 supported by the National Natural Science Foundation of China
文摘In situ coal gasification poses a potential environmental risk to groundwater pollution although it depends mainly on local hydrogeological conditions. In our investigation,the possible processes of groundwater pollution origi-nating from underground coal gasification (UCG) were analyzed. Typical pollutants were identified and pollution con-trol measures are proposed. Groundwater pollution is caused by the diffusion and penetration of contaminants generated by underground gasification processes towards surrounding strata and the possible leaching of underground residue by natural groundwater flow after gasification. Typical organic pollutants include phenols,benzene,minor components such as PAHs and heterocyclics. Inorganic pollutants involve cations and anions. The natural groundwater flow after gasification through the seam is attributable to the migration of contaminants,which can be predicted by mathematical modeling. The extent and concentration of the groundwater pollution plume depend primarily on groundwater flow ve-locity,the degree of dispersion and the adsorption and reactions of the various contaminants. The adsorption function of coal and surrounding strata make a big contribution to the decrease of the contaminants over time and with the distance from the burn cavity. Possible pollution control measures regarding UCG include identifying a permanently,unsuitable zone,setting a hydraulic barrier and pumping contaminated water out for surface disposal. Mitigation measures during gasification processes and groundwater remediation after gasification are also proposed.
基金TheHi TechResearchandDevelopmentProgramofChina (S 86 3)
文摘Environmental benefits of underground coal gasification are evaluated. The results showed that through underground coal gasification, gangue discharge is eliminated, sulfur emission is reduced, and the amount of ash, mercury, and tar discharge are decreased. Moreover, effect of underground gasification on underground water is analyzed and CO 2 disposal method is put forward.
基金financial support of the National Natural Science Foundation of China(No.50876112)the Fundamental Research Funds for the Central Universities (No.2009QH13)the Program of International S&T Cooperation (No.2009DFR60180,No.2010DFR60610)
文摘Two-stage underground coal gasification was studied to improve the caloric value of the syngas and to extend gas production times.A model test using the oxygen-enriched two-stage coal gasification method was carried out.The composition of the gas produced,the time ratio of the two stages,and the role of the temperature field were analysed.The results show that oxygen-enriched two-stage gasification shortens the time of the first stage and prolongs the time of the second stage.Feed oxygen concentrations of 30%, 35%,40%,45%.60%,or 80%gave time ratios（first stage to second stage） of 1：0.12,1：0.21.1：0.51,1：0.64, 1：0.90.and 1：4.0 respectively.Cooling rates of the temperature field after steam injection decreased with time from about 19.1-27.4℃/min to 2.3-6.8℃/min.But this rate increased with increasing oxygen concentrations in the first stage.The caloric value of the syngas improves with increased oxygen concentration in the first stage.Injection of 80%oxygen-enriched air gave gas with the highest caloric value and also gave the longest production time.The caloric value of the gas obtained from the oxygenenriched two-stage gasification method lies in the range from 5.31 MJ/Nm^3 to 10.54 MJ/Nm^3.
文摘To optimize the technological parameter of underground coal gasification （UCG）, the experimental results of air gasification, air-steam gasification, oxygen-enrichment steam gasification, pure oxygen steam gasification and two-stage gasification were studied contrastively based on field trial at the Huating UCG project. The results indicate that the average low heat value of gas from air experiment is the lowest （4.1 MJ/Nm3） and the water gas from two-stage gasification experiment is the highest （10.72 MJ/Nm3）. The gas productivity of air gasification is the highest and the pure oxygen steam gasification is the lowest. The gasification efficiency of air gasification, air-steam gasification, oxygen-enriched steam gasification, pure oxygen steam gasification and two-stage gasification is listed in ascending order, ranging from 69.88% to 84.81%. Described a contract study on results of a field test using steam and various levels of oxygen enrichment of 21%, 32%, 42% and 100%. The results show that, with the increasing of O2 content in gasifying agents, the gas caloricity rises, and the optimal O2 concentration range to increase the gas caloricity is 30%-40%. Meanwhile, the consumption of O2 and steam increase, and the air consumption and steam decomposition efficiency fall.
基金supported by the National High Technology Research and Development Program of China(No.2011AA050106)Hubei Technological Innovation Special Fund(CN)(No.343-0402-YQN-TWEP).
文摘This article presents the evolution law of temperature fields in a large-scale laboratory Underground Coal Gasification reactions using Ulanqab lignite under actual conditions.The results show that in the cultivation stage of oxidation zone,the main direction of the temperature field expansion is consistent with the crack direction of the coal seam.In the gasification stabilization stage,the main direction of the temperature field expansion is along the channel.The temperature of the coal seam and the overlying rock mass at its interface with the furnace directly above the gasification channel is equivalent to that of the coal seam temperature,and this temperature is much greater than the temperatures observed near both side walls of the gasification channel at the interface.However,temperatures perpendicular to the axis of the gasification channel are similar at a vertical distance of 40 cm away from the interface.The temperature distributions indicate that the transmission of heat through the overlying rock mass is more rapid in the vertical direction than in the horizontal direction.Moreover,some degree of thermal dispersion is observed in the vertical direction near the outlet.The thermal dispersion coefficient is 0.72 and dispersion angle γ is 78.7°.
基金the Cultivation Fund of the Key Scientific and Technical Innovation Project,Ministry of Education of Chinese(02019)Anhui Province Science and Technology Tackling Key Project(08010202058)
文摘The field trail used a mixture of steam and air with various levels of oxygen en- richment.Steady conditions were achieved in the field trail which produced high quality hydrogen-enriched syngas.To understand and optimize the UCG process,a simplified heat and mass transfer model was presented,providing a predictive tool for temperature and the major constituents of the syngas production.The model is compared with the field trail measurements for air and two levels of oxygen enrichment,showing reasonable agreement for the channel temperature and product syngas concentration profile.
基金financially supported by the Renewable Energy and Hydrogen Projects in National Key Research & Development Program of China (2019YFB1505000)。
文摘An integrated vacuum pressure swing adsorption(VPSA) and Rectisol process is proposed for CO_(2) capture from underground coal gasification(UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO_(2) with a CO_(2) purity of 98.35% from UCG syngas(CH_(4)/CO/CO_(2)/H_(2)/N_(2)= 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field,Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO_(2)remained in light product gas from the VPSA process using cryogenic methanol(233.15 K, 100%(mass)) as absorbent. A final purified gas with CO_(2) concentration lower than 3% and a regenerated CO_(2) product with CO_(2) purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg^(-1) of the single Rectisol process to 1.008 MJ·kg^(-1) of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO_(2) capture from UCG syngas. Additionally, the high-value gas(e.g., CH_(4)) loss can be decreased and the effects of key operating parameters on the process performances were detailed.
文摘During underground coal gasification （UCG）, whereby coal is converted to syngas in situ, a cavity is formed in the coal seam. The cavity growth rate （CGR） or the moving rate of the gasification face is affected by controllable （operation pressure, gasification time, geometry of UCG panel） and uncontrollable （coal seam properties） factors. The CGR is usually predicted by mathematical models and laboratory experiments, which are time consuming, cumbersome and expensive. In this paper, a new simple model for CGR is developed using non-linear regression analysis, based on data from 1 l UCG field trials. The empirical model compares satisfactorily with Perkins model and can reliably predict CGR.
基金Projects 59906014, 50276066 and 20207014 supported by National Natural Science Foundation of China
文摘Based on the quasi-steady-state approximation, the dynamic equation of char combustion in the oxidation zone of underground coal gasification (UCG) was derived. The parameters of the dynamic equation were determined at 900℃ using a thermo-gravimetric (TG) analyzer connected to a flue gas analyzer and this equation. The equation was simplified for specific coals, including high ash content, low ash content, and low ash fusibility ones. The results show that 1) the apparent reaction rate constant increases with an increase in volatile matter value as dry ash-free basis,2) the effective coefficient of diffusion decreases with an increase in ash as dry basis, and 3) the mass transfer coefficient is independent of coal quality on the whole. The apparent reaction rate constant, mass-transfer coefficient and effective coefficient of diffusion of six char samples range from 7.51×104 m/s to 8.98×104 m/s, 3.05×106 m/s to 3.23×106 m/s and 5.36×106 m2/s to 8.23×106 m2/s at 900℃, respectively.
基金This work was a part of the HUGE 2 project and was jointly supported by the Research Fund for Coal and Steel,under contract RFCR-CT-2011-00002 and by the Polish Ministry of Science and Higher Education.
文摘In this study,the composition of tars collected during a six-day underground coal gasification(UCG)test at the experimental mine‘Barbara’in Poland in 2013 was examined.During the test,tar samples were taken every day from the liquid product separator and analysed by the methods used for testing properties of typical coke oven(coal)tar.The obtained results were compared with each other and with the data for coal tar.As gasification progressed,a decreasing trend in the water content and an increasing trend in the ash content were observed.The tars tested were characterized by large changes in the residue after coking and content of parts insoluble in toluene and by smaller fluctuations in the content of parts insoluble in quinoline.All tested samples were characterized by very high distillation losses,while for samples starting from the third day of gasification,a clear decrease in losses was visible.A chromatographic analysis showed that there were no major differences in composition between the tested tars and that none of the tar had a dominant component such as naphthalene in coal tar.The content of polycyclic aromatic hydrocarbons(PAHs)in UCG tars is several times lower than that in coal tar.No light monoaromatic hydrocarbons(benzene,toluene,ethylbenzene and xylenes—BTEX)were found in the analysed tars,which results from the fact that these compounds,due to their high volatility,did not separate from the process gas in the liquid product separator.
基金supported by a grant from the Major State Basic Research and Development Program of China (No. 2007CB714102)sponsored by the Fundamental Research Funds for the Central Universities (No. 2009B00714)
文摘The exact shape and size of the gasification channel during underground coal gasification(UGC) are of vital importance for the safety and stability of the upper parts of the geological formation.In practice existing geological measurements are insufficient to obtain such information because the coal seam is typically deeply buried and the geological conditions are often complex.This paper introduces a cylindrical model for the gasification channel.The rock and soil masses are assumed to be homogeneous and isotropic and the effect of seepage on the temperature field was neglected.The theory of heat conduction was used to write the equation predicting the temperature field around the gasification channel.The idea of an excess temperature was introduced to solve the equations.Applying this model to UCG in the field for an influence radius,r,of 70 m gave the model parameters,u1,2,3...,of 2.4,5.5,8.7...By adjusting the radius(2,4,or 6 m) reasonable temperatures of the gasification channel were found for 4 m.The temperature distribution in the vertical direction,and the combustion volume,were also calculated.Comparison to field measurements shows that the results obtained from the proposed model are very close to practice.
基金The research presented in this article was performed within the work"Conducting an exsitu experiment of underground coal gasification with a mineral interlayer"commissioned and funded by the Silesian University of Technology in Gliwice,Department of Applied Geology,by order sign ZP/018521/18/ZZ/01987/18.
文摘A 72-h ex situ hard coal gasification test in one large block of coal was carried out.The gasifying agent was oxygen with a constant flow rate of 4.5 m^(3)/h.The surroundings of coal were simulated with wet sand with 11%moisture content.A 2-cm interlayer of siderite was placed in the horizontal cut of the coal block.As a result of this process,gas with an average flow rate of 12.46 m^(3)/h was produced.No direct influence of siderite on the gasification process was observed;however,measurements of CO_(2)content in the siderite interlayer before and after the process allow to determine the location of high-temperature zones in the reactor.The greatest influence on the efficiency of the gasification process was exerted by water contained in wet sand.At the high temperature that prevailed in the reactor,this water evaporated and reacted with the incandescent coal,producing hydrogen and carbon monoxide.This reaction contributes to the relatively high calorific value of the resulting process gas,averaging 9.41 MJ/kmol,and to the high energy efficiency of the whole gasification process,which amounts to approximately 70%.
文摘Underground coal gasification(UCG)is widely regarded as a clean coal technology that holds enormous potential to decarbonize the world's coal industry.It converts coal underground into combustible syngas through a set of complex physiochemical events.Experimental and nu-merical efforts over the past century have contributed to the development of UCG around the world;however,tapping the world's deep-situated coal resources with UCG requires substantial contributions from numerous high-quality researchers.To facilitate effective engagement,this paper will provide a background on where to start if one wishes to undertake UCG modelling.First,a brief description of the fundamental phenomena involved in UCG is given.Then,a succinct introduction of the widely used modelling software is rendered,followed by a description of UCG studies to provide insight how to tune the various software packages for modelling UCG and where their strengths lie.This paper shall serve as guidance to new UCG modellers.
文摘China has a huge demand for energy.Under the present energy structure of rich coal,lean oil,less gas,limited and low-rising rate renewable energy,discussion focus is now on the high-efficient mining of coal as well as its clean-and-low-carbon use.In view of this,based on an analysis of the problems in the coal chemical industry and the present coal utilization ways such as Integrated Gasification Combined Cycle(IGCC),this paper proposes that underground coal gasification(UCG)technology is a realistic choice.By virtue of its advantages in many aspects such as safety&environment,integrated use of superior resources,economic feasibility,etc.this technology can serve as the front-end support and guarantee for coal chemical industry and IGCC.Under the present situation,the following proposals were presented to promote the development of this technology.First,R&D of technical products should be strengthened,a comprehensive feasibility study assessment system should be established,and the relevant criteria in the industry should be formulated.Second,precise market positioning of UCG products should be made with much concern on the integrated economic indicators of each product's complete flow scheme,following the principle of“Technical Feasibility First,Economic Optimization Followed”.Third,a perfect operation and management pattern should be established with strict control over high-efficient,environmentally-friendly,safe,harmonious&compact objectives in the whole industry chain.In conclusion,to realize the large-scale UCG commercial production will strongly promote the optimization and innovation of fossil fuels supply-side economics in China.
基金The work has been supported by the National High Technology Research and Development Program 863 of China(2011AA050106)the Fundamental Research Funds for the Central Universities(2012YH01).
文摘This research focused on the feasibility of applying the forward and reverse combustion approach to the in situ gasification of lignite with the production of hydrogen-rich syngas(H_(2)and CO).The so-called forward combustion gasification(FCG)and reverse combustion gasification(RCG)approach in which oxygen and steam are simultaneously fed to the simulated system of underground coal gasification(UCG)was studied.A simulated system of UCG was designed and established.The underground conditions of the coal seam and strata were simulated in the system.The combustion gasification of lignite has been carried out experimentally for almost 6.5 days.The average effective content(H_(2)+CO)of syngas during the FCG phase was 62.31%and the maximum content was 70.92%.For the RCG phase the corresponding figures are 61.33%and 67.91%.Thus,the feasibility of using RCG way for UCG has been demonstrated.The temperature profiles have been provided by using of 85 thermocouples during the model experiment,which portrayed the several nephograms of thermal data in the gasifier were of significance for the prospective gasification processes.
文摘The global trends of increasing oil and gas costs have compelled coal possessing countries to start long term underground coal gasification （UCG） projects. These enhance national energy security and are among the cleanest, ecologically safest coal utilization technologies. This paper delineates the major characteristics of such technologies and analyzes technical solutions. Highlighting the desire to develop large scale industrial UCG plants, pilot level projects are presented using a new UCG method developed in Russia by Joint Stock Company Gazprom Promgaz. This method is distinct for its high controllability, stability, and energy efficiency. New, efficient technical solutions have been developed over the last 10-15 years and are patented in Russia. They guarantee controllability and stability of UCG gas produc- tion. Over one hundred iniection and gas production wells have been operated simultaneously.
