Experimental Research On Semi-coke Characterisitic And Hydrogasification Reactivity Of Lignite Coal

The demand of natural gas as a typical clean energy increases due to the contradictions between the energy structure and energy consumption.Hydrogasification of coal to produce natural gas is significant for ensuring the supplement of natural gas,clean and efficient use of coal and ensuring the national energy security.The fixed bed reactor with high temperature and pressure was applied for the hydrogasification of lignite semi-coke.The influence of pyrolysis conditions and hydrogasification conditions on the hydrogasification reaction were investigated in this study.The characterization of lignite semi-coke and the semi-coke with different reaction degree were conducted by XRD,Raman,BET,FT-IR and so on.The mean conclusions of this study were listed as follows:1.At 400⁸00?,the value of d₀₀₂/L₀₀₂02 slightly decreased from 0.521 to0.472,which indicated limited graphitization.When the pyrolysis temperature increased to 900?,the value of d₀₀₂/L₀₀₂02 decreased to 0.365,which indicated that the carbon crystallite structure transformed to more ordering structure.2.With the increase of pyrolysis temperature at 400⁹00?,the value ofI_D1/I_G?I_D2/I_G increased,the value of I_D3/I_G decreased,and the value of I_D4/I_G increased first and then decreased,which illustrated that the disordered carbon structure increased.The value of I_G/I_ALLLL decreased with temperature from400⁸00?,and then increased when the temperature was higher than 800?,which indicated that the observed graphitization started from 800?.This results were consisted with the conclusion obtained from XRD analysis.3.The hydrogen band in the semi-coke were mainly formed by the self associated–OH,which significantly reduced with increasing temperature from600⁷00?.The primary oxygen-contained functional groups were hydroxyphthalic,which decreased with increasing temperature from 400⁷00?,and the variation of different oxygen-contained functional groups could be ignored when the temperature was higher than 700?.4.With the increase of temperature from 400⁹00?,the specific surface area of semi-coke increased from 1.95m²/g?400??to 183m²/g?700??,and then decreased to 180mL/g?900??;the volume of pore increased from0.019mL/g?400??to 0.86mL/g?800??,and then reduced to 0.073m²/g?900??.While the average pore size had the opposite trend with the specific surface area and the pore volume,that the average pore size firstly decreased from?400??.According to the SEM analysis,the surface of semi-coke became loose and rough with increasing pyrolysis temperature.5.The yield of methane increased 47.61%with increasing temperature from 400?to 600?,and then kept constant until 800?,but decreased sharply whent the temperature was increased to 900?.The carbon conversion rate of the hydrogasification reaction first increased and then decreased with increasing temperature,the maximum carbon conversion rate existed at 600?.With the reaction proceed,the maximum of methane concentration appeared at90-110min,which delayed with the increasing temperature.6.The carbon conversion rate and the yield of methane increased first and then decreased with the increasing time of constant temperatre,the maximum of value of these two character belonged to the semi-coke with 10min constant temperature time.The optimal time of constant temperature was 10min.7.With the increase of heating rate of pyrolysis,the carbon conversion rateand methane production of semi-coke hydrogenation increase first and then decrease.Compared with the semi-coke with a temperature of 5?/min,the carbon conversion rate of the semi-coke with a heating rate of 10?/min increased by 10.9%.8.There was no significant change in the yield of hydrogenated methanation gaseous products?CH₄,C₂H₆,C₂H₄,CO,and CO₂?obtained by pyrolysis and carbon conversion of gasification reaction with the atmospheres of nitrogen and hydrogen under the same pyrolysis pressure.When the pyrolysis pressure increases from atmospheric pressure to 4 MPa,the carbon conversion rate increases from 74.45%to 76.46%under the atmosphere of hydrogen pyrolysisan.And the carbon conversion rate increases from 75.31%to 76.36%under a nitrogen atmosphere.9.The semi coke gasification reaction rate of hydrogenation and the conversion of carbon significantly improved with the increasing of reaction temperature,when the reaction time is more than 85 minutes.The methane production and decomposition dropped into balance,the conversion of carbon and the reaction rate kept constant when the reaction temperature was 850?.The output of CH₄ has increased and the output of C₂H₆ has decreased;the output of C₂H₄,CO and CO₂ kept constant with the increasing of reaction temperature.10.The semi coke gasification reaction rate of hydrogenation and theconversion of carbon significantly improved with the increasing of reaction temperature.The methane production and decomposition dropped into balance,the conversion of carbon and the reaction rate kept constant when the reaction temperature was 850?.The output of CH₄ has increased and the output of C₂H₆has decreased;the output of C₂H₄,CO and CO₂ kept constant with the increasing of reaction temperature.11.The reaction rate of hydrogenation increased,the gasification reaction rate and the conversion of carbon significantly increased when the reaction pressure increased form 1 MPa to 4MPa.The semi coke conversion rate and maximum gasification rate kept constant when the reaction pressure increased to5MPa.The production of CH₄ and C₂H₆ increased,the production of CO and CO₂ decreased with the increase of reaction pressure.12.The reaction time redced with the increase of heating rate,But the conversion of carbon was same.The peak of the first reaction rate rised obviously,the production of CH₄ and CO increased,the production of C₂H₆ and CO₂ decreased with the increase of heating rate.