煤的微生物气化动力学建模研究

Kinetic modeling of biogenic methane production from coal

  • 摘要: 煤的微生物原位气化开采技术在未开采的遗留煤炭、原位煤层具有广阔的应用前景。为了更好地了解煤微生物气化过程,掌握煤微生物气化的关键影响因素,根据煤微生物气化的研究进展,建立了一个煤生物气化的动力学模型,模型包含煤降解的5个过程,即煤的增溶、水解、产酸、产氢产乙酸和产甲烷。每个过程采用生化反应式表示,采用元素平衡和电子平衡确定生化反应方程化学计量数。采用Monod动力学方程来描述微生物的生长和死亡过程,同时考虑生物自身生长抑制和产物抑制。为校核该模型,在实验室开展了煤的厌氧发酵试验,利用试验获得产甲烷数据校核该模型。结果表明:建立的模型对煤的微生物气化和营养强化煤产甲烷过程均有较好的描述。对模型参数进行了敏感性分析,通过改变模型敏感性参数,分析中间参数变化规律和产甲烷特征。结果表明:煤炭初始物质的量浓度越大,甲烷产量越大,但存在一个最大浓度,超过该最优煤炭添加浓度将会抑制甲烷生产。煤炭溶解速度可以缩短煤产生物甲烷的启动时间,采用煤预处理的方法可提高煤的平衡溶解浓度,提高甲烷产量。微生物浓度同样影响煤产生物甲烷的特征。改变溶煤细菌和水解菌的初始浓度,可以缩短产气的延滞期,溶煤菌浓度增大10倍(1 mol/m3至10 mol/m3),延滞期可缩短83.33%,乙酸营养型产甲烷菌浓度影响最大产甲烷速率。添加蓝藻可以为微生物生长提供底物,同时也为产甲烷菌提供了产甲烷底物,显著提高模型的有机负荷率,提升甲烷产量,添加1.0、1.63、2.5、4.0 mol/m3蓝藻,甲烷产量分别提升了12.9、20.8、27.7、54.3倍。研究结果丰富了煤炭微生物气化领域的数据建模方法,为该技术的实验室试验提供了重要的理论支撑和指导。同时,通过实验室试验与数值计算相结合的研究方法,可以提高对煤产生物甲烷机理的认识。

     

    Abstract: Microbial in situ gasification mining of coal has a great application prospect in unmined remnant coal and in situ coal seams. To better understand the process of coal microbial gasification and grasp the key influencing factors of coal microbial gasification, a kinetic model of coal biogasification based on the research progress of coal microbial gasification was established. The model contains five processes of coal degradation, i.e., coal solubilization, hydrolysis, acid production, hydrogen and acetic acid production, and methane production. The model uses elemental and electron balances to determine the stoichiometric numbers of the biochemical reaction equations. Monod kinetic equations were used to describe the microbial growth and death processes, taking into account the organisms' own growth inhibition and product inhibition. To calibrate the model, anaerobic fermentation experiments with coal were carried out in the laboratory, and the model was calibrated using the methane production data obtained from the experiments. The calibration results show that the model has a good description of both microbial gasification of coal and nutrient-enhanced coal methanogenesis. A sensitivity analysis of the model parameters was carried out. By changing the model sensitivity parameters, the change rule of model parameters and the characteristics of methane production were analyzed. The numerical calculation results show that the larger the initial coal concentration, the larger the methane production, but there exists a maximum coal addition amount, and exceeding this optimal concentration will inhibit the methane production. Coal dissolution rate can shorten the initiation time of coal producer methane, and the use of coal pretreatment can increase the solubility of coal and methane production. Microbial concentration similarly affects the characterization of coal producer methane. Changing the initial concentration of coal-solubilizing and hydrolyzing bacteria can shorten the delay period of gas production; a 10-fold increase (1 mol/m3 to 10 mol/m3) in the concentration of coal-solubilizing bacteria can shorten the delay period by 83.33%, and the concentration of acetic acid-nutrient methane-producing bacteria affects the maximum methane production rate. The addition of cyanobacteria can provide substrates for microbial growth and also provide methanogenic substrates for methanogenic bacteria, which significantly increased the organic loading rate of the model and enhanced methane production. Adding 1.0, 1.63, 2.5, 4.0 mol/m3 of cyanobacteria enhanced the methane production by 12.9, 20.8, 27.7, and 54.3 times, respectively. The present study enriches the data modeling methods in the field of coal microbial gasification and provides important theoretical support and guidance for the laboratory test of this technology. At the same time, the method of combining laboratory experiments and numerical calculations for the study can improve the insights of coal producer methane.

     

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