Molecular Simulation Research On Mechanism Of Coal Spontaneous Combustion Prevention And Storage Of Flue Gas

There are many problems caused by spontaneous combustion of coal,such as waste of coal resources,generation of toxic gases,gas explosion,and so on,which leads to great loss of life and property then seriously threatens the safety production of coal.On the other hand,coal-fired power plant flue gas is the main source of CO2 emissions.Global warming has caused a series of climate changes,then CO2 mitigation in coal-fired power plants need to be solved urgently.Therefore,injecting flue gas into goaf to prevent spontaneous combustion of coal and at the same time store CO2 is proposed.The method can save the cost of CO2 and N2 production in traditional fire prevention by inert gas.Based on the process above,deeply study on the microscopic mechanism of competitive adsorption of power plant flue gas in goaf was made in this dissertation using molecular simulation,which laid a theoretical foundation for injecting flue gas from coal-fired power plants into goaf to prevent spontaneous combustion of coal and store CO2.The 3D models of macromolecular coal structure and small molecular gases were established.Adsorption of single CO2,CH4,N2,O2 and binary mixtures of them in coal was simulated using Grand Canonical Monte Carlo method.The results show that the ability of competiive adsorption is CO2>CH4>O2>N2.The adsorption sites and interaction energy between coal and gas are influenced by temperature,pressure,bulk fraction,competition from other gases,then the adsorption amount and selectivity can be affected.Based on this,adsorption of flue gas(16.5%CO2+79%N2+4.5%O2)in coal was calculated and the mechanism was analyzed.The results show that the adsorption amount is CO2>N2>O2,and the adsorption selectivity of CO2/O2 is up to 5.66?20.42,which is benefit to inhibit the first step of coal spontaneous combustion-physical adsorption of O2,and CO2 storage.The mechanism is that the adsorption space of CO2 can affected by O2 and N2,and not adsorption sites.On the contrary,the adsorption sites of O2 and N2 are competed by CO2.Then,O2 and N2 adsorb in sites with weak interaction energy.The competitive adsorption of CO2/N2/O2 ternary mixture was calculated to research injecting various fractions of flue gas into goaf with different O2 contents.The simulation results show that flue gas can reduce the adsorption amount of O2 when the O2 concentration in the goaf is higher than 3.7%.The highest reduction rate of O2 adsorption amount is 82.6%.And the more flue gas injectivity,the more CO2 storage.In order to study the effect of H2O on flue gas adsorption in coal,the adsorption mechanism of single H2O in coal was studied first.The priority adsorption site of H2O in coal is stronger than CO2.In addition,the adsorbed H2O can provide a stronger secondary adsorption site.Therefore,for the H2O/CO2/N2/O2 quaternary mixture adsorption systems in coal,adsorption amount of CO2 reduces and the adsorption amount of O2 is almost constant.H2O in wet coal occupies the pore space,so that the large pores are divided and the effective pores are reduced.H2O will compete with CO2 for adsorption sites and occupy the adsorption space of CH4,O2 and N2.In consequence,the adsorption amount of CO2 and selectivity of CO2/O2 in wet coal are lower than that in dry coal,and separation ability between CO2 and O2 is poor.H2O in coal is unfavorable to the competitive advantage of flue gas.The competitive adsorption of CO2/N2/O2/CH4 quaternary mixture was calculated to research the competitive adsorption between various fractions of flue gas and CH4.The results show that the interaction energy between CO2 and coal is the strongest.The priority adsorption site of CO2 is stronger than that of CH4 and the adsorption sites of CH4 are competed with CO2,also the adsorption space of CH4 is occupied by N2 and O2,which promote desorption of CH4.The more injectivity of flue gas,the more adsorption amount of CO2,N2,and O2,and the less adsorption amount of CH4.Therefore,injecting flue gas can replace CH4 and store CO2,thereby better isolating the contact between coal and O2.The more flue gas,the more stable of the adsorption system,and the more difficult it is to spontaneous combustion with O2 adsorption.There are 104 figures,8 tables and 254 references in the dissertation.