Research On The Mechanism Of Gas Generation During Low-Temperature Oxidation Of Coal

Coal is one of the main energy in China,accounting for 57.7 percent of total energy consumption in 2019.However,coal spontaneous combustion will occur in the process of coal production,which has become one of the key restricting the efficient,accurate and safe mining of coal resources in China.The process of coal spontaneous combustion has multiple reaction paths to produce gas and the complexity of coal structure,leading to the gas generation mechanism were not fully understood.Therefore,this paper focused on the pure oxidation path that can reflect the combination of coal and oxygen by refining the path of heat and gas generation in the process of coal spontaneous combustion,quantified the reaction thermodynamic parameters,and analyzed the change of oxygen-containing intermediate and gas,so as to establish the relationship between them.From the microscopic perspective,the causes of these characteristics were further studied,to explore the reaction process and conversion mechanism of the key active groups,and get the role of the active groups in the gas and heat generated in coal spontaneous combustion.Combining the macro-characteristics and micro-mechanism of the pure oxidation path,to improve the gas production process and mechanism of coal spontaneous combustion.The main research contents and achievements are as follows:(1)In order to solve the problem of multi-path interference in the process of coal spontaneous combustion,based on the analysis of the existing reaction path of coal spontaneous combustion,the concept of pure oxidation path of coal spontaneous combustion was proposed,and a new method of testing the heat generation characteristics of pure-oxidation path and the theoretical model of the method was established.The new method can quickly and accurately obtain the heat generation under the condition of lower temperature,and the heat generation characteristics obtained by the pure oxidation path can well characterize the nature of coal spontaneous combustion.It is found that the value of CO2/CO produced by the pure oxidation pathway of coal with different metamorphic degrees can be divided into four stages with the rise of temperature,and gradual participation of key active groups is the main reason for the segmentation of CO2/CO ratio in pure oxidation process.The contents of hydroxyl have a significant influence on the CO2/CO ratio and equilibrium value.(2)Because of the intermediate state of the oxygen-containing intermediates,it is difficult to measure their heat production characteristics and structures.In order to solve this problem,based on the uniqueness of heat generation source in pure oxidation path,the relationship between gas,oxygen-containing intermediates and heat was established,and the purpose of quantifying the heat production rate of oxygen-containing intermediate was achieved.The model compounds were used to confirm the reaction process of reactive groups in the coal to form peroxides and oxygen-containing intermediates and the chemical structure of the peroxides.Combining the heat production characteristics,it is concluded that the oxygen-containing intermediates play a key role in the process of coal spontaneous combustion,and its stability determines the process of coal spontaneous combustion.(3)Using in-situ infrared to establish the relationship between the macroscopic(heat and gas)characteristics and microscopic changes of coal spontaneous combustion.It is found that the key active structures in the process of coal spontaneous combustion are methylene bridge,hydroxyl,methylene side chain and oxygen-containing intermediate.The function and mechanism of each key active structures in the process of coal spontaneous combustion are clarified.Among them,the number of higher active groups(methylene bridge)is an important factor that determines whether the coal spontaneous combustion can occur,the content of hydroxyl groups has an important influence on the production of CO2,and methylene side chain plays a decisive role in the production of hydrocarbon gas.(4)Based on the reaction process of key active structure and its role in the process of gas generation,combined with the relationship between gas,oxygen-containing intermediate products and heat,the mechanism of gas generation during low-temperature oxidation of coal was proposed.It is concluded that alkanes can only be produced if the side chains contain at least two carbon atoms.(5)Under the guidance of the gas generation mechanism,based on the chemical characteristics of the key active structure,the pre-oxidation method was proposed to prevent coal spontaneous combustion.The chemical inhibitor represented by sodium persulfate was developed,and the mechanism of pre-oxidation method was put forward to prevent coal spontaneous combustion.