Research On Prediction Model And Application Of Joint Coal Measure Gas Mining

The coal in the current shaft coal mine is to be mined mainly in solid state mode.The resulting mining losses mainly include two parts:one is the mining losses caused by the current mining characteristics;the other is the influence of coal seam assignment,and also inevitably some hard-to-mine or unmineable coal seams.For this kind of coal mining,the method of coal microbial in-situ gasification mining is proposed.Microorganisms and nutrients are injected into the coal seam,and coal is converted into gaseous mining by using the technology of anaerobic fermentation.This not only improves the coal recovery rate,but also belongs to an environmentally friendly mining method.In response to the current inadequate understanding of the process of coal microbial conversion.The degradation efficiency of coal microbial gasification strains is not high.This leads to the practical difficulty of large gap between experimental tests and field applications.In this thesis,coal samples from typical coal resource endowment regions in China were selected,and coal microbial gasification experiments were carried out using exogenous composite strains enriched in the laboratory.The mechanism of coal microbial gasification was studied in terms of gas-solid-liquid three-phase of gasification process and microbial community.The feasibility of sustainable nutrient supplementation to promote long-term coal gas production was also explored.（1）Using anaerobic medium,a composite strain of bacteria that can gasify coal samples of different coal grades was enriched in the laboratory,and the composition of the composite strain was analyzed.The bacterial part of the strain was mainly composed of Bacillus and Clostridium,and the archaea were mainly composed of hydrogenophilic and acetic acidophilic methanogenic bacteria.The results of methane carbon isotope ratio showed that the addition of coal changed the carbon utilization priority of the composite strain.This proves that the composite strain can effectively utilize the carbon source from coal.（2）The gas production characteristics of microbial gasification of coal of different coal rank were investigated by using batch anaerobic fermentation.The coal resources were mainly gasified into methane and carbon dioxide,and the gas production and gas production rate of low-rank coal were significantly higher than those of high-rank coal.A large amount of CO₂ was produced in the reactor,and the injected H₂ could reduce CO₂ and increase the methane production in the reactor.The ultraviolet–visible spectroscopy（UV-Vis）test results of the fermentation solution showed that the microorganisms utilized the organic matter containing benzene ring in the coal.The results of three-dimension excitation emission matrix（3D-EEMs）of the fermentation solution showed that the organic matter composition of the fermentation solution differed among coal rank.The surface of the coal samples after microbial utilization was observed using environmental scanning electron microscopy（SEM）and Fourier transform infrared spectroscopy（FI-IR）,and the results showed that only a small fraction of organic matter was utilized on the surface of the coal.Only small changes in the coal surface can be observed at the microscopic level.The lower the coal rank the greater the change,which showed that the smooth surface became rough.（3）The characteristics of microbial communities in the process of microbial gasification at different coal ranks were analyzed by 16S rRNA sequencing technology.The coal sample as a carbon source changed the bacterial community characteristics in the reactor.There was a significant difference in the diversity between low-rank coal and high-rank coal.Bacillus spp.was the core genus of coal microbial gasification.The results of the analysis of archaea at OTU level showed that there were fewer species of archaea and no significant differences between different coal sample groups.The reactor was still dominated by the Methanoculleus spp.in the gas production process.Macrogenetic sequencing was used to reveal the species changes and functions in different gas production stages of low-rank coal.The abundance of reactor species decreased with increasing fermentation reaction time,and the abundance remained unchanged.Nutrients could stimulate the microbial community in the reactor to recover to the initial abundance.The reactor species at the phylum level consisted mainly of the bacterial domains of the phyla Synechococcales,Thick-walled Bacteria,Archaea and Spirochaetes.Among the metabolic functional genes,carbohydrate metabolism was the most abundant,followed by amino acid metabolism.The composition and content of these genes help to study the composition of organic matter in coal.（4）The continuous gasification performance of coal promoted by different nutrient supplements was investigated using a microgas measurement device.The results indicate that the reason for the cessation of gas production in the split-wholesale fermentation reactor is the depletion of non-coal nutrients in the reactor.Continued addition of the medium promoted the re-gas production from coal resources,but the gas production decreased significantly.By comparing the gas production performance of medium,sawdust and cyanobacteria as nutrient supplementation,it was found that the efficiency and yield of methane production from coal gasification could be significantly improved by continuously obtaining cyanobacteria.The gas production potential of different nutrient supplementation was evaluated kinetically using an improved S-shaped bacterial growth curve equation,and the best-fit model was determined.（5）A numerical computational model for methane production from coal microorganisms was developed based on the coal microbial gasification process.The model contains five processes of coal degradation,including coal leaching,coal hydrolysis,acid production from macromolecules,hydrogen production from acetic acid and methane production.The reaction rate of each process is microbially related.Each process is represented using a biochemical equation,using elemental and electron balance equations.The reaction kinetics were expressed using the Monod kinetic equation,cells had growth inhibition,and cell death was expressed using decay coefficients.The model was calibrated using experimental data,and changes in microbial and substrate concentrations during the reactions were analyzed.The results improve the understanding of the complex role between microbial activity,substrate specificity and bioavailability of coal for methane production,providing estimates of product and intermediate concentrations during coal conversion.This dissertation has 100 figures,49 tables,and 217 references.