| In order to achieve clean and efficient utilization of coal and ensure national energy security,it is of great significance to actively promote the conversion and utilization of coal by classification and quality."High temperature and high pressure rapid hydropyrolysis technology"can greatly improve the yield of pyrolysis tar?oil yield>20%?,which is called"high oil yield technology".However,the compositional characteristics of a large number of pyrolysis semi-coke and the technical means of efficient utilization have yet to be further optimized.In this paper,the semi-coke remaining after extracting the high value-added tar component is used as raw material:the physical and chemical properties of raw coal and semi-coke are analyzed by XRD,Raman,FT-IR and SEM;the gas is investigated by fixed bed reactor.The effect of chemical flow rate,temperature and heating rate on the gasification reactivity of semi-coke water vapor;the influence of catalyst,heating rate and atmosphere on the combustion characteristics of semi-coke was investigated by thermogravimetric analyzer.The main conclusions are as follows:?1?Pyrolysis reduced the content of O element from 13.71%to 6.58%.A large number of oxygen-containing functional groups were removed during the thermal process.H and N decreased from 4.68%and 1.22%to 3.00%and 1.18%respectively.Fixed carbon content increased from 46.08%to 66.83%,Pyrolysis is a process of deoxidation,dehydrogenation and carbon deposition.Thermogravimetric curves show that the quality of raw coal decreases from 97%to about 77%at 400570?,and the maximum weight loss peak occurs near460?with a weight loss rate of 2.2%/min.At this stage,raw coal releases a large amount of volatile and tar products,while the weight of semi-coke decreases from 97%to 94%,with little change.The peak strength of 002 of raw coal and semi-coke are 168 and 210,and the peak strength of 100 is 45and 68,respectively.High temperature and high pressure hydropyrolysis makes ordered carbon content increase relatively,and graphitization degree of semi-coke aggravate.?2?The time required for isothermal gasification to reach the same 80%carbon conversion was reduced from 110 minutes to 35 minutes,with a decrease of 68.18%.Temperature had a great influence on the steam gasification of semi-coke residue,while the time required for the increase of carbon conversion from 80%to 88%was more than 30 minutes,and the effect of temperature on gasification was significantly reduced in the later stage of the reaction.In the initial stage of gasification reaction,with the increase of gasification reaction time,the gasification reaction rate increases gradually.About 10 minutes,the gasification reaction rate peaks,and then the gasification reaction rate decreases gradually.The whole gasification reaction rate curve presents an inverted V shape.After the gasification reaction rate curve crosses the peak value,the higher the reaction temperature,the steeper the rate curve,the larger the decline of gasification rate,and the shorter the time to complete gasification.?3?The gases produced by steam gasification of semi-coke are mainly H2,CO and CO2.The sum of the three gases accounts for more than 99.0%of the total gas production,while the CH4 content is very low.With the increase of gasification reaction temperature,the gas yield of semi-coke decreases gradually.Among them,the proportion of H2 in product gas decreased from 63%to 54.6%;the proportion of CO in product gas increased from 14.4%to 35.4%,and the increase of CO accounted for 70.5%of the total increase.Temperature had a great influence on the production of CO during gasification;the proportion of CO2 in product gas decreased from 21.1%to 9.1%;the content of CH4 gas was less than 1%and had little change.?4?When the carbon conversion reaches 85%,the time required for steam flow rate of 200mL/min,400mL/min and 600mL/min is 80min,64min and47min,respectively;the maximum gasification reaction rate Max is1.832%/min,2.026%/min and 2.412%/min,respectively,with an increase of10.59%and 31.66%respectively,and the maximum gasification reaction rate is greatly increased in the same reaction time.The cumulative gas production rate of semi-coke residue gasification can be significantly increased by flow rate,but the final gas production rate of semi-coke residue has little effect.With the increase of steam flow rate,the proportion of H2 in product gas increased from 58.7%to 60.7%,the proportion of CO in product gas decreased from 29.1%to 25.8%,the proportion of CO in product gas increased from 11.5%to 13.2%,and The content of CH4 did not change much,and the total amount was within 1.00%.?5?When the carbon conversion reaches 95%,the heating rate increases from 7?/min to 15?/min,the reaction time decreases from 146 minutes to 91minutes,and the decrease is as high as 37.7%.Increasing the heating rate has a significant effect on the gasification of most carbon in semi-coke.At different heating rates,with the increase of gasification reaction time,the gasification reaction rate first increases and then decreases,and the trend of the three curves is"inverted V".With the increase of the heating rate of gasification reaction,the gas yield changed little,but the content of gas components changed in varying degrees.The proportion of H2 in the product gas increased from 58.7%to 61.4%;the proportion of CO in the product gas increased from17.65%to 19.88%;the proportion of CO2 in the product gas decreased from18.965%to 17.36%;and the content of CH4 changed little,less than 1.5%.?6?The semi-coke steam gasification reaction can be described by a mixed kinetic model.The model equation is ?=dx/dt=k?1-?n,and the total reaction order is 0.871.39.The activation energy of gasification reaction of semi-coke and steam is 142.11 kJ·mol-1 to 164.84 kJ·mol-1.With the increase of water vapor ratio,the activation energy decreases gradually.There is a dynamic compensation relationship between the frequency factor and the activation energy,and the compensation relation is:InA=0.1109 E-0.8465.?7?Under the same combustion conditions,the peak temperatures of DTG curves of semi-coke samples added with Ca?CH3COO?2,Fe2O3,K2CO3 and CH3COONa were advanced by 10?,21?,53?and 84?,respectively.The catalysts promoted the TG-DTG curves of semi-coke combustion to move to the low temperature zone,and the corresponding temperature of the maximum weight loss peak decreased significantly.The ignition temperature was reduced from 459.2?to 431.1?,441.8?,413.2?and 402?,respectively;the ignition index was increased from 70.49×10-4 to 101.25×10-4,115.17×10-4,139.12×10-4 and 162.56×10-4,respectively;the burnout index is increased from44.44×10-5 to 73.89×10-5,111.1×10-5,128.32×10-5,158.11×10-5;the comprehensive combustion characteristic index is from 85.56×10-9 Increase to115.9×10-9,141.8×10-9,165.79×10-9,159.54×10-9.The addition of catalyst increases the ignition index,burnout index and comprehensive combustion index of semi-coke,and promotes the combustion of semi-coke.?8?The combustion process of the semi-coke at different heating rates showed a similar trend.As the heating rate increases,the mass of the residue does not change much,but the peak width of the DTG curve of the semi-coke gradually increases,and the maximum mass loss rate?dw/dt?max increases.The heating rate increases from 10?/min To 15?/min?20?/min,the ignition index Ci increased from 30.42×10-4 to 170.35×10-4 and 114.36×10-4,respectively;the burn-up index Cb increased from 18.21×10-55 to 44.43×10-5and 64.46×10-5;The comprehensive combustion characteristic index is increased from 55.51×10-9 to 85.25×10-9,98.37×10-9;increasing the heating rate can effectively improve the combustion performance of the semi-coke.?9?The combustion mechanism of the semi-coke in the two atmospheres of O2/N2 and O2/CO2 is basically the same,which is heterogeneous combustion.In the O2/N2 atmosphere,the oxygen concentration is increased from 20%to 50%,the ignition temperature is reduced from 472.1?to455.7?,the ignition index is increased from 320.42×10-4 to 442.99×10-4,and the burnout index is from 526.04×10-5 increased to 991.1×10-5,the comprehensive combustion characteristic index increased from 257.06×10-9 to350.2×10-9;in O2/CO2 atmosphere,the oxygen concentration increased from20%to 50%,and the ignition temperature was 476.2?reduced to 458.3?,the ignition index increased from 290.83×10-4 to 434.48×10-4,the burnout index increased from 468.13×10-5 to 953.3×10-5,and the comprehensive combustion characteristic index was increased from 247.06×10-9 to311.39×10-9;under the same atmosphere,the higher the oxygen concentration,the ignition characteristic index of the semi-coke,the higher the burnout and comprehensive combustion characteristic index,the better the combustion performance of the semi-coke.Under the same oxygen concentration,the ignition temperature and burnout temperature of the semi-coke in O2/N2atmosphere are lower than the ignition temperature and burnout temperature of O2/CO2 atmosphere.The combustion temperature range of semi-coke in O2/N2atmosphere is closer to the low temperature zone than that in O2/CO2atmosphere,and the combustion is relatively concentrated;the ignition characteristic index,the combustion characteristic index and the comprehensive combustion index of the semi-coke burning in the O2/N2atmosphere are larger than the combustion characteristic index in the O2/CO2atmosphere,and the semi-coke is in the O2/N2 atmosphere.The medium has better combustion performance in the O2/CO2 atmosphere.?10?Under the same combustion conditions,the heating rate is increased from 10?/min to 15?/min and 20?/min,and the activation energy E is reduced from 93.662 kJ·mol-1 to 71.786 kJ·mol-1,64.056 kJ·mol-1,the reaction order is 0.70.9;after adding four catalysts of Ca?CH3COO?2,Fe2O3,K2CO3and CH3COONa,the activation energy is reduced from 84.41 kJ·mol-1 to 70.41,81.54,84.07 and 82.25 kJ·mol-1,the reaction order is about 0.8;the oxygen concentration is increased from 20%to 50%,and the activation energy in O2/N2 atmosphere is increased from 159.67 kJ·mol-1 to 216.93 kJ·mol-1,under O2/CO2 atmosphere.The activation energy increases from 131.12 kJ·mol-1 to215.66 kJ·mol-1.With the increase of oxygen concentration,the activation energy of semi-coke increases gradually during the combustion process because the reaction changes from diffusion control zone to kinetics.The control zone leads to an increase in activation energy. |
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