| The production of coal gangue increases with the increase of coal mining activities.Combustion for power generation is one of the effective ways to realize the comprehensive utilization of coal gangue.During the oxy-fuel combustion process,the pure O2 and recycled flue gas is mixed as oxidizer,which can easily made CO2 enrich in the flue gas and further realize CO2 capture.Meanwhile,oxy-fuel combustion technology can be applied in coal gangue combustion power plant,and can provide a new solution for the CO2 emission control.This thesis studies the reaction characteristics of coal gangue under O2/CO2/H2O atmosphere,and the effect of O2 and H2O concentrations on reaction characteristics is studied.Furthermore,the correlation between the combustion reactivity and the structural parameters of coal gangue char is analyzed,and the influence mechanism of CO2 and H2O on the structure and reaction characteristics of char is revealed.Meanwhile,a single particle combustion technique is employed to observe the ignition mechanism and combustion characteristics of millimetre-sized single coal gangue particles under O2/CO2/H2O atmosphere.The main conclusions are as follows:(1)The reaction characteristics and kinetics of Pingshuo coal gangue under O2/CO2 atmosphere are studied by thermogravimetric analyzer.The results show that with the increase of O2 concentration from 5% to 21%under O2/CO2 atmosphere,the ignition and burnout temperature decreases by 26?and 75?,and the maximum weight loss rate and comprehensive combustibility index increases,which indicated that increasing O2concentrations can improve the comprehensive combustion performance.Furthermore,the increase of heating rate can enhance the comprehensive combustion performance.Under the same O2 concentration,the ignition and burnout temperature in O2/CO2 atmosphere is higher than that in O2/N2atmosphere,which is not conducive to the combustion of coal gangue.The combustion reaction of coal gangue in O2/N2 and O2/CO2 atmosphere follows the first-order reaction in the range of 5%to 21%O2 concentration.At the same O2 concentration,the apparent activation energy of coal gangue in O2/CO2 atmosphere is higher than that in O2/N2 atmosphere,and the apparent activation energy decreases with the increases of carbon conversion rate.(2)The reaction characteristics of Pingshuo coal gangue in O2/CO2/H2O atmosphere also are studied by thermogravimetric analyzer.The results indicate that the ignition and burnout temperature decreases with increases of O2 concentration from 5 to 50%under O2/CO2/H2O atmosphere at H2O concentration of 10%.When O2 concentration is greater than 30%,the combustion reaction rate slightly increases in O2/CO2/H2O atmosphere.The ignition temperature decreases first and then increases with increases of H2O concentration at the O2 concentration is less than 30%.When O2concentration is greater than 30%,the effect of H2O concentration on ignition and burnout temperature is not obvious.Under the same O2concentration,the combustion performance of coal gangue is the best in O2/CO2/H2O atmosphere at H2O concentration of 10%.In the range of O2concentration between 5 to 50%,the combustion reaction of coal gangue in O2/CO2/H2O atmosphere follows the first-order reaction.At lower O2concentration(?10%),the total reaction order changes from first-order to0.5 order when increasing H2O concentration;at higher O2 concentration(>30%),with the increase of H2O concentration,the total reaction order of coal gangue is closer to 1.5 order.(3)The structural characteristics of the Pingshuo and Yangquan coal gangue chars are prepared in different atmospheres are analyzed and characterized by Raman spectroscopy and N2 adsorbent,the correlation between the reactivity parameter and structure parameters of char is analyzed,and the influence mechanism of CO2 and H2O on the structure and reaction characteristics of char is revealed.The results show that for PS and YQ coal gangues,the occurence of C-CO2 and C-H2O gasification reaction decreases the char yield,and with increases of fixed carbon content in the coal gangue,the gasification reaction rate increases.The occurrence of gasification reaction results in the abundant mesoporous structure,and the effect of H2O on the pore structure of char are significantly greater than that of CO2.The large aromatic ring is destroyed when the occurence of C-CO2and C-H2O gasification reaction,which leads to decrease of the graphitization degree of char,the combustion reactivity increases.(4)A single particle combustion technique is employed to observe and analysis the ignition mechenism and combustion characteristics of millimetre-sized single Yangquan coal gangue(YQ)particles under O2/CO2/H2O atmosphere in a fixed bed reactor.The results indicates that the ignition of coal gangue particles under O2/N2 atmosphere followes the homogeneous ignition mechanism.Under O2/CO2 atmosphere,reducing particle size,increasing furnace temperature and H2O concentration can change the ignition mechanism from heterogeneous to homogeneous ignition.The larger and brighter volatile flame and longer flame duration are observed in O2/CO2/H2O atmosphere with increasing the H2O concentration at 750°C.When the particle size increases from 3 mm to 6 mm at 850°C,the brightness of volatile flame decreases,the ignition delay time increases by7.09 s,and the volatile flame duration is shorten.As the furnace temperature increases from 850°C to 950°C,the ignition delay time and volatile flame duration is shorten.The change in ignition delay time causes by increasing O2concentration is less significant compared with the increasing furnace temperature and particle size,and the volatile flame duration increases by1.24 s with the increase of O2 concentration from 10%to 30%.The minmum ignition temperature Ti,min of coal gangue particles in O2/CO2 atmosphere increases by 157°C compared to that in O2/N2 atmosphere at 10%O2concentration.The Ti,min gradually decreases with increasing H2O concentration under O2/CO2/H2O atmosphere.Under O2/CO2 atmosphere,compared with coal combustion,the longer volatile ignition delay time,shorter volatile flame duration and higher ignition temperature are observed during the coal gangue combustion process,which indicates that coal gangue is more difficult to ignite than coal in oxy-fuel combustion atmosphere.This paper clarifies the reaction characteristics of coal gangue in O2/CO2/H2O atmosphere,and the results can provide a certain theoretical basis for the development and utilization of oxy-fuel combustion technology in the process of coal gangue combustion for power generation. |
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