| At present,mine fires are still one of the major disasters threatening the safe production of mines in China.Among them,coal natural ignition has become a kind of multiple mine disasters with great difficulty in prevention and control because of its characteristics of wide distribution underground,hidden ignition source,oxygen-poor combustibility and easy repetitive oxidation.Therefore,it is of great theoretical and practical significance to propose efficient suppression methods to effectively reduce the oxidation rate of coal relics and retard natural ignition for the prevention and control of coal spontaneous combustion.In this thesis,based on the extensive research of various coal spontaneous combustion prevention and control technologies at home and abroad,we try to propose a new method principle of microbial induced calcium deposition to inhibit coal spontaneous combustion,and reveal the blocking mechanism of microbial blocking agent on coal oxidation process through multi-scale analysis,and the research results can provide theoretical basis and technical support for mine fire prevention and control.In this thesis,a combination of mechanistic analysis,experimental tests and modeling calculations was used to demonstrate the effectiveness of microbial blocking agent on coal spontaneous combustion by using Bacillus pasteurii as the microbial blocking material and conducting comparative tests and simulations on microstructural properties,coal spontaneous combustion properties and oxidation kinetic properties under multi-scale and controlled temperature rise conditions.The main results are as follows:(1)The culture environment of Bacillus pasteurii was optimized,and the comparison of biological and chemical calcification effects was carried out.The mechanism of induced calcification was demonstrated by comparative analysis of OD600,urease activity and calcium carbonate production quality,and significant coal surface wrapping effect could be achieved by using the urease produced by Bacillus pasteurii to decompose urea and produce carbonate ions combined with calcium ions to produce calcium carbonate precipitation.The comparison results showed that the microbial OD600 and urease activity were at the highest value when the incubation time was 48 h and the p H of the culture solution was 7.5;the mass of calcium carbonate produced by bio-inhibition reached the highest when the concentration of the culture solution was 1 mol/L,the ratio of colloidal solution to bacterial solution reached 1:1,and the ratio of urea and calcium source was 1:1.(2)In terms of microstructural characterization of coal spontaneous combustion,SEM,pore size analysis and FT-IR tests were carried out on 20 coal samples of 5 coal types and 4 preparation methods to study the microscopic properties of surface morphology,pore structure and active functional groups of raw coal,bio-resisted,chemically resisted and leached coal samples,and to analyze the resistances mechanisms and change laws.The results showed that compared with the original coal,a large number of calcium carbonate particles were attached to the surface of the bio-blocked coal samples,which reduced the total pore volume and specific surface area of the coal samples,e.g.,68.49% and 74.01% for lignite,indicating that bio-blocking could effectively seal the native pores.The hydroxyl group content of long-flame coal was reduced by 40%,the carboxyl group content of poor coal and gas coal was reduced by 50.6% and 51%,respectively,and the methyl/methylene content of lignite was reduced by the largest amount of 96.5%,which indicated that bio-resistance could significantly enhance the thermal stability of coal and revealed the inerting effect of microbial resistances to inhibit coal spontaneous combustion.(3)Based on the simultaneous thermal analysis and programmed warming experiments,the oxidative exothermic characteristics and spontaneous combustion characteristics of five coals treated with different resistances were analyzed.The results showed that the characteristic temperature points of the bio-resisted coal samples were higher than those of the original coal,and the T3 characteristic temperature of the low-temperature oxidation stage of lignite was delayed by 71.62℃,and the T5 characteristic temperature of the rapid oxidation stage was delayed by61.31℃;the oxygen consumption and oxygen consumption rate of each coal sample were significantly reduced after bio-resisting,and the gas production detection temperature was delayed by about 10℃ on average;the crossover point temperatures of lignite and long-flame coal after resist treatment were delayed by 13.6℃ and10.6℃,respectively,compared with those of the original coal.The cross-point temperatures of lignite and long-flame coal were delayed by 13.6℃ and 8.5℃,respectively,and the results of oxidation kinetic test showed that the spontaneous combustion propensity of long-flame coal was reduced from easy to spontaneous combustion coal to spontaneous combustion coal after bio-inhibition,and the test also verified that the blocking rate of bio-inhibitor was the maximum,and the bio-inhibitor has the effect of promoting the etherification of the active functional group,which indicated that bio-inhibitor could effectively reduce the risk of spontaneous combustion of coal.(4)Based on the kinetic model of coal spontaneous combustion and oxidation,the activation energy of the reaction of five coal samples before and after blocking was calculated at different oxidation stages,and the most probable mechanism function was determined by the Coats-Redfern method.It was found that the activation energy and the finger front factor of the coal samples increased significantly after bio-resistance treatment,and the activation energy of the poor coal after bio-resistance in the heat decomposition stage increased 124.4% compared with the original coal,while the activation energy of the lignite after bio-resistance in the combustion stage increased 153.4% compared with the original coal,indicating that the coal oxidation process could be significantly inhibited by using bio-resistance treatment of coal samples.The thesis has 64 figure,42 table,and 132 reference. |
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