| Underground coal gasification(UCG)is a new and efficient green coal mining method,which has the advantages of environmental protection and economy,such as no manual mining of coal,recovery of uneconomical and unrecoverable coal resources mined by traditional methods,reduction of ground subsidence and gas and solid pollution waste discharge,saving mining cost and so on.The technology has been developed by domestic and foreign scholars for many years.However,it is difficult to achieve deep insitu observation of underground coal gasification,and it is difficult to accurately simulate the actual coal gasification process with existing infrastructure equipment and scientific analysis experiments.There is also a relative lack of relevant studies on the evaluation of the gas production energy of underground coal gasification and the influence of different gasification parameters on the rule of gasification product output.Aiming at these problems,this paper,on the basis of UCG in the laboratory simulation experiment,combining with the underground coal gasification based on theory of stoichiometric energy recovery evaluation model to explore the specific gasification parameters on the influence law of underground coal gasification process and product,to obtain the basic gasification tuning parameters,to verify the effectiveness of the evaluation model for energy recovery.It provides scientific basis and research method for subsequent field experiment and engineering control of underground coal gasificationThe research contents and conclusions of this paper are as follows:(1)Based on the analysis of operation process and gasification reaction principle of underground coal gasification,a laboratory UCG simulation experiment system was constructed,and the simulation experiment of specific parameters was carried out by using independently developed experimental equipment of underground coal gasification,and relevant experimental results were obtained.A calculation model for energy recovery evaluation of underground coal gasification process was established based on stoichiometry theory,and the gasification process and effect were evaluated by simulation experiments under specific design parameters.(2)Through transverse longitudinal contrast experiment and evaluation of energy recovery as a result,to study the different gasification channel types(V,L and coaxial type,horizontal channel type),different gasification process(process for the pure oxygen and rich oxygen process,rich oxygen steam gasification process),a specific gasification agent injection flow rate and concentration of oxygen gasification parameters,such as gasification agent on the UCG process and the influence of gasification products.(3)The type of gasification passage has a significant effect on the gasification process,and the calorific value of gasification gas is the best under coaxial gasification in laboratory.Under the same oxygen concentration gasification condition,the heat value of L-type gasification channel is higher than that of V-type.In the late stage of pure oxygenation process,excessive oxygen concentration will cause some oxygen not involved in gasification reaction to overflow and aggravate the secondary combustion loss of gasification gas,and reduce the content of combustible components and calorific value of gas to a certain extent.In UCG simulation experiment of coaxial artificial coal seam,the calorific value of gasification gas is slightly higher than that of sleeping flat passage,but the gasification efficiency is lower.(4)In the oxygen-rich UCG simulation experiment(Experiment 2),on the basis of similar injection flow rate of gasification agent and the same oxygen concentration of gasification agent,the calorific value and gasification efficiency of gasification gas under the injection conditions of 50% and 70% oxygen concentration and different flow rate of gasification agent(30-53 L /min)were compared.The results show that in the initial stage of gasification,the calorific value and gasification efficiency of gasification gas with 70%oxygen concentration are higher than those with 50% oxygen concentration.Under the same oxygen concentration of gasifier,the calorific value and gasification efficiency of gasifier increase with the increase of gasifier flow rate,but the increase rate decreases gradually.The results show that gasification activity is high in the early and middle stages of gasification,increasing oxygen concentration can significantly improve gasification efficiency,and increasing the flow rate of gasification agent can slow down the decay rate of gasification degree.(5)In UCG simulation experiment(Experiment 3),the preferential effects of10L/min gasifier flow increment and 10% oxygen concentration reduction on gasification efficiency and calorific value of gasification gas were investigated in the range of 45%～55%ygen concentration.The results show that the improvement of gasification efficiency with the increment of gasification agent flow rate of 10L/min is higher than that with the reduction of oxygen concentration of 10%.In the early and middle stage of gasification,the increase of gasification agent flow rate can improve gasification rate,increase gas production and improve gasification efficiency to a certain extent.(6)UCG simulation experiment of oxygen-rich water steam(Experiment 3)Experimental results of oxygen-rich water steam stage show that the participation of water steam in gasification reaction can significantly increase the content of H2 in gasification gas,thus improving the calorific value and gasification efficiency of gasification gas.Compared with the oxygen-rich gasification condition with the same gasification parameters,the gasification efficiency is increased by about 4%.However,the peak time of gasification in the phase of oxygen-rich water steam is short,so high oxygen concentration and flow rate need to be satisfied to ensure sufficient high temperature field of the gasifier if the high efficiency gasification state is maintained for a long time.(7)By comparing the coal consumption calculated from the energy recovery evaluation of the experimental gasification process in this paper with the actual coal consumption monitored before and after the experiment,the error value is basically within 10%,which verifies that the energy recovery evaluation model of the gasification process based on the stoichiometry theory proposed in this study is scientific and reliable. |
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