Thermal stress is an important reason of coal particle primary fragmentation,during which the role of pore structure is ambiguous.Thermal stress induced fragmentation experiments were conducted with low volatile coal/...Thermal stress is an important reason of coal particle primary fragmentation,during which the role of pore structure is ambiguous.Thermal stress induced fragmentation experiments were conducted with low volatile coal/char particles,and the results show that the fragmentation severity enhances with increasing porosity.Various porous thermal stress models were developed with finite element method,and the influences of the pore shape,size,position and porosity on the thermal stress were discussed.The maximum thermal stress inside particle increases with pore curvature,the pore position affects the thermal stress more significantly at the particle center and surface.The expectation of the maximum tensile thermal stress linearly increases with porosity,making the particles with higher porosity easier to fragment,contrary to the conclusion deduced from the devolatilization theory.The obtained results are valuable for the analysis of different thermal processes concerning the thermal stresses of the solid feedstocks.展开更多
An experimental study on the ignition of single coal particles at low oxygen concentrations (XO_(2)<21%) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal ...An experimental study on the ignition of single coal particles at low oxygen concentrations (XO_(2)<21%) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different XO_(2) values and furnace temperatures Tw. Compared with literature experimental data obtained at a high XO_(2) value, the ignition delay time τi decreases more rapidly as XO_(2) increases at the low XO_(2) region. The responses of Ts and Tc to the variation of XO_(2) are different: Ts decreases while Tc remains nearly constant with increasing XO_(2) at a low XO_(2) value. In addition, τi is less sensitive to Tw while the ignition temperature Ti is more sensitive to Tw at a low XO_(2) value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as XO_(2) decreases. At a low XO_(2) value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.展开更多
Research on coal fragmentation can play an important role in understanding coal and gas outbursts.The study discussed in this paper explored the fragmentation of gas-containing coal particles using the drop-weight imp...Research on coal fragmentation can play an important role in understanding coal and gas outbursts.The study discussed in this paper explored the fragmentation of gas-containing coal particles using the drop-weight impact method.The effects of equilibrium gas pressures and type of adsorbate gas on particle size distributions and fragmentation energy were investigated in detail.We found that the Fractal particle size distribution model can most effectively describe the crushed coal particle sizes.The equilibrium pressure and type of gas can influence the Fractal distribution parameter.The crushing energy is composed of energy to create new surfaces and other forms of energy that are dissipated but the equilibrium gas pressure and type of adsorption gas can affect energy consumption and crushing efficiency.This research will be of guiding significance to the intensity evaluation and mechanism understanding of coal and gas outbursts.展开更多
In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemic...In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.展开更多
As the major primary energy source in China,coal has been proved to be capable to improve its physical and chemical characteristics by the pretreatment of the self-preheating burner.In this study,the effects of alteri...As the major primary energy source in China,coal has been proved to be capable to improve its physical and chemical characteristics by the pretreatment of the self-preheating burner.In this study,the effects of altering operating conditions including preheating temperature(T_(p))and primary air equivalence ratio(λ_(p))on preheating characteristics of three typical pulverized coal were investigated on a bench-scale test rig.The high-temperature coal gas compositions along the axis of the riser and at the outlet of the self-preheating burner were measured,and the coal char and coal tar produced in the preheating process were collected and analyzed separately.The results indicated that with the significant release of volatile and the occurrence of chemical reactions,cracks and micropores emerged on the surface of the particles,making the pore structure on the surface more developed,and T_(p)had the most significant effect on the structure of coal particles.Additionally,there were evident differences in the corresponding operating conditions when the preheating characteristics of the three typical coal reached optimally.And preheating had the strongest influence on the degree of anthracite modification.With respect to coal tar,the increase of T_(p)andλ_(p)further promoted its secondary cracking and oxidation,resulting in a decrease in production yield.In this study,for bituminous coal and lignite,a large amount of coal tar were produced during preheating and the highest production yields could reach 5.74%and 6.15%,respectively.While for anthracite,the production yield was intensely low due to its own coal properties,all below 1.02%.展开更多
Pneumatic conveying of coarse coal particles with various pipeline configurations and swirling intensities was investigated using a coupled computational fluid dynamics and discrete element method. A particle cluster ...Pneumatic conveying of coarse coal particles with various pipeline configurations and swirling intensities was investigated using a coupled computational fluid dynamics and discrete element method. A particle cluster agglomerated by the parallel-bond method was modeled to analyze the breakage of coarse coal particles. The numerical parameters, simulation conditions, and simulation results were experimentally validated. On analyzing total energy variation in the agglomerate during the breakage process, the results showed that downward fluctuation of the total particle energy was correlated with particle and wall col- lisions, and particle breakage showed a positive correlation with the energy difference. The correlation between the total energy variation of a particle cluster and particle breakage was also analyzed. Parti- cle integrity presented a fluctuating upward trend with pipe bend radius and increased with swirling number for most bend radii. The degree of particle breakage differed with pipeline bending direction and swirling intensity: in a horizontal bend, the bend radius and swirling intensity dominated the total energy variations: these effects were not observed in a vertical bend. The total energy of the particle cluster exiting a bend was generally positively correlated with the bend radius for all conditions and was independent of bending direction.展开更多
基金supported by National Natural Science Foundation of China(grant No.21908150)China Postdoctoral Science Foundation(grant No.2019M653404)+1 种基金the Key Research&Development Program of Sichuan Province,China(grant No.22zDYF 1839)Sichuan University Post-Doctoral Interdisciplinary Innovation Initial Funding.
文摘Thermal stress is an important reason of coal particle primary fragmentation,during which the role of pore structure is ambiguous.Thermal stress induced fragmentation experiments were conducted with low volatile coal/char particles,and the results show that the fragmentation severity enhances with increasing porosity.Various porous thermal stress models were developed with finite element method,and the influences of the pore shape,size,position and porosity on the thermal stress were discussed.The maximum thermal stress inside particle increases with pore curvature,the pore position affects the thermal stress more significantly at the particle center and surface.The expectation of the maximum tensile thermal stress linearly increases with porosity,making the particles with higher porosity easier to fragment,contrary to the conclusion deduced from the devolatilization theory.The obtained results are valuable for the analysis of different thermal processes concerning the thermal stresses of the solid feedstocks.
文摘An experimental study on the ignition of single coal particles at low oxygen concentrations (XO_(2)<21%) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different XO_(2) values and furnace temperatures Tw. Compared with literature experimental data obtained at a high XO_(2) value, the ignition delay time τi decreases more rapidly as XO_(2) increases at the low XO_(2) region. The responses of Ts and Tc to the variation of XO_(2) are different: Ts decreases while Tc remains nearly constant with increasing XO_(2) at a low XO_(2) value. In addition, τi is less sensitive to Tw while the ignition temperature Ti is more sensitive to Tw at a low XO_(2) value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as XO_(2) decreases. At a low XO_(2) value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.
基金support from the Science and Technology Foundation of Guizhou Province(No.[2017]2815)the Fundamental Research Funds for the Central Universities(No.2020YJSAQ05)the National Natural Science Foundation of China(Nos.51274206,51404277)。
文摘Research on coal fragmentation can play an important role in understanding coal and gas outbursts.The study discussed in this paper explored the fragmentation of gas-containing coal particles using the drop-weight impact method.The effects of equilibrium gas pressures and type of adsorbate gas on particle size distributions and fragmentation energy were investigated in detail.We found that the Fractal particle size distribution model can most effectively describe the crushed coal particle sizes.The equilibrium pressure and type of gas can influence the Fractal distribution parameter.The crushing energy is composed of energy to create new surfaces and other forms of energy that are dissipated but the equilibrium gas pressure and type of adsorption gas can affect energy consumption and crushing efficiency.This research will be of guiding significance to the intensity evaluation and mechanism understanding of coal and gas outbursts.
基金The first author gratefully acknowledges the Ministry of Research,Technology,and Higher Education(KEMENRISTEKDIKTI)of Republic Indonesia for the scholarship funding through the Research and Innovation in Science and Technology Project(RISET-Pro)program and also the University of Glasgow for supporting this research.
文摘In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.
基金supported by CAS Project for Young Scientists in Basic Research(YSBR-028)Strategic Priority Research Program of the Chinese Academy of Sciences(XDA21040100)Youth InnovationPromotion Association of the Chinese Academy of Sciences(2019148)。
文摘As the major primary energy source in China,coal has been proved to be capable to improve its physical and chemical characteristics by the pretreatment of the self-preheating burner.In this study,the effects of altering operating conditions including preheating temperature(T_(p))and primary air equivalence ratio(λ_(p))on preheating characteristics of three typical pulverized coal were investigated on a bench-scale test rig.The high-temperature coal gas compositions along the axis of the riser and at the outlet of the self-preheating burner were measured,and the coal char and coal tar produced in the preheating process were collected and analyzed separately.The results indicated that with the significant release of volatile and the occurrence of chemical reactions,cracks and micropores emerged on the surface of the particles,making the pore structure on the surface more developed,and T_(p)had the most significant effect on the structure of coal particles.Additionally,there were evident differences in the corresponding operating conditions when the preheating characteristics of the three typical coal reached optimally.And preheating had the strongest influence on the degree of anthracite modification.With respect to coal tar,the increase of T_(p)andλ_(p)further promoted its secondary cracking and oxidation,resulting in a decrease in production yield.In this study,for bituminous coal and lignite,a large amount of coal tar were produced during preheating and the highest production yields could reach 5.74%and 6.15%,respectively.While for anthracite,the production yield was intensely low due to its own coal properties,all below 1.02%.
文摘Pneumatic conveying of coarse coal particles with various pipeline configurations and swirling intensities was investigated using a coupled computational fluid dynamics and discrete element method. A particle cluster agglomerated by the parallel-bond method was modeled to analyze the breakage of coarse coal particles. The numerical parameters, simulation conditions, and simulation results were experimentally validated. On analyzing total energy variation in the agglomerate during the breakage process, the results showed that downward fluctuation of the total particle energy was correlated with particle and wall col- lisions, and particle breakage showed a positive correlation with the energy difference. The correlation between the total energy variation of a particle cluster and particle breakage was also analyzed. Parti- cle integrity presented a fluctuating upward trend with pipe bend radius and increased with swirling number for most bend radii. The degree of particle breakage differed with pipeline bending direction and swirling intensity: in a horizontal bend, the bend radius and swirling intensity dominated the total energy variations: these effects were not observed in a vertical bend. The total energy of the particle cluster exiting a bend was generally positively correlated with the bend radius for all conditions and was independent of bending direction.