Study On Coal Gasification Reaction And Radiation Characteristics For Coal Resource And Solar Energy Utilization

The total global energy consumption has rebounded with the economic recovery in 2021.Chinese energy endowment,“rich coal,poor petroleum,and low fuel-gas”,has determined that coal will be the main supply of energy consumption for a period of time.One of the challenging tasks in the energy sector under the“dual carbon goals”is the efficient,clean,and low-carbon utilization of coal resources.Coal gasification is an important technology that meets this demand and is widely used in the coal chemical industry.However,there are currently few studies on the pyrolysis technology under coal gasification conditions,and traditional coal gasification processes still require coal combustion for heat generation,which consumes a large amount of oxygen.Meanwhile,while ensuring energy security,China is accelerating its energy transition and upgrading its energy structure.Renewable energy is continuously increasing its share in the energy consumption structure and will become a pillar of the energy consumption structure in the near future.The northwestern of China has abundant solar energy resources and is home to a large number of coal gasification plants.Utilizing solar energy to drive the coal gasification process is of strategic significance.However,the mechanism of introducing solar energy into coal gasification and its impact on the gasification reaction and radiation characteristics are not clear.To address the aforementioned issues,this study conducts systematic research,combining experimental studies and numerical simulations,to investigate coal pyrolysis models under coal gasification conditions,the gasification process in a traditional dry pulverized coal entrained flow gasifier reaction chamber,the reaction characteristics of solar-driven coal gasification,the gas radiation characteristics under a solar-driven coal gasification atmosphere,kinetic parameters of solar-driven gasification reactions,and the design of a new solar-driven gasifier and the gasification process in the reaction chamber.First,in response to gasification conditions,the pyrolysis model of coal gasification was developed and optimized by incorporating the advantages of the Chemical Percolation Devolatilization（CPD）pyrolysis model and the Kobayashi pyrolysis model.The CPD model was optimized by expanding its database of structural parameters for 17 typical Chinese low-rank coals Bayesian pseudo-lattice structures.Experimental data were obtained using thermogravimetric and pyrolysis test benches to validate the optimized CPD model for coal gasification conditions and calculate the model parameters and corresponding coefficients.The Kobayashi pyrolysis model was also optimized for gasification conditions and compared with the newly developed CPD model for validation.The combined pyrolysis model was applied to the numerical simulation of a 2200 t/day GSP-type dry pulverized coal-entrained flow gasifier to investigate the gasification process fluid,heat transfer,and reaction characteristics in the three-dimensional gasifier,and optimize the operational conditions.The results showed that the gas temperature in the gasifier reached 1655 K at the output,which was higher than the ash melting temperature point.As the jet intensity in the central circulation zone decreased,the temperature gradually became uniform,with mole fractions of CO and H₂ at 66.14%and 27.03%,respectively.With an increase in the operational oxygen-to-coal ratio（from 92%of the design condition to 108%of the design condition）,the output temperature rose from 1610 K to 1750 K,but the mole fraction of syngas（CO+H₂）decreased from 95.1%to 90.8%.Secondly,renewable energy is introduced into the gasification process,using solar energy to replace the traditional coal combustion energy supply in gasification,and using the CO₂ emissions from industry as a gasification agent instead of the CO₂produced by traditional coal combustion.A novel concentrated solar energy radiation gasification and thermogravimetric analysis experimental setup is independently designed and built.The gas production rate and thermogravimetric online process of solar coal gasification under two different radiation forms,direct radiation,and indirect radiation,are compared.The influence of Na₂CO₃ and K₂CO₃ with different ratios on solar gasification is compared.Based on the experimental data,the evaluation performance indicators of solar energy gasification（carbon element conversion rate and cold gas efficiency）are compared and analyzed.A simplified system model of the disc solar coal gasification system in the Hangzhou area is established and energy and exergy analyses are conducted.The results show that the direct radiation form can increase the weightlessness rate compared with the indirect radiation form.After adding K₂CO₃,the weightlessness rate can reach 90%（the rest is basically ash）,and the cold coal gas efficiency can reach 0.86 in the experiment.In the disc solar gasification system,the synergistic effect of solar energy and catalysts can achieve a system energy efficiency of 41%.The gasification module with the highest exergy efficiency is the direct radiation catalytic gasification,reaching 29.7%.Subsequently,a new gas radiation model is developed for solar coal gasification conditions.Existing gas radiation models are developed for combustion or oxy-fuel conditions,where the gas radiation medium is primarily made up of CO₂ and H₂O.However,in solar coal gasification（with CO₂ as the gasification agent）,the gas atmosphere primarily consists of CO and CO₂.Additionally,gasification processes in the industry often utilize high pressure to increase gasification efficiency.Therefore,we introduce CO as a radiation medium and couple the pressure term into the absorption coefficient of the model,developing a novel gas radiation model.The results show that compared to existing models,the newly developed WSGG gas radiation model provides results that are closer to the benchmark SNB model in terms of emissivity calculations under different pressures（1,5,and 45 bar）,temperatures（500～2500 K）,and ratios（0.125～4）.Meanwhile,by simulating gasification temperature fluctuations and solving the radiation transfer equation under fluctuating gas atmospheres at different pressures,the model calculates radiation heat flux and radiation source terms.The errors in the calculated results,compared to the benchmark SNB model,are within8.42%and 4.71%for radiation heat flux and radiation source terms,respectively.Furthermore,user-defined function（UDF）programs are developed based on the new WSGG radiation model.Finally,numerical simulation calculations are conducted on a 5 k W-scale entrained flow bed solar coal gasifier.The solar coal gasification process is numerically simulated using the kinetic parameters of solar coke gasification obtained from solar gasification experiments,the Gaussian distribution user-defined function（UDF）of the heat flux at the receiver calculated by the Monte-Carlo method,and the newly developed UDF of the WSGG gas radiation model.A new design of a solar coal gasifier is implemented,and operational conditions are optimized.The results show that the optimized gasifier design effectively concentrates the coal particles along the central axis to maximize solar radiation absorption.The cold gas efficiency sees an increase with increasing coal feed rate,decreases with an increase in the gasification agent and solar energy input,and can reach a maximum value of 1.53.The solar energy conversion into chemical energy efficiency increases with increasing coal feed rate,initially rises and then decreases with an increase in the gasification agent,and decreases with an increase in solar energy input,with a maximum value of 29.46%.The outlet gas temperature decreases with increasing coal feed rate and gasification agent,increases with an increase in solar energy input,and reaches a minimum value of 1572K under different design conditions,which is higher than the ash melting point to ensure smooth liquid slag discharge.