外加直流电场对煤吸附解吸瓦斯的改性机理研究

Coal seam permeability is generally low in our country, it is to be solved in the energy utilization and gas control problem, using the applied electric field of auxiliary mechanical way to strengthen the gas drainage is one of the effective ways to solve this problem.The research contents are as follows: by using the experimental system of the influence of direct electric field on gas adsorption and desorption process in different types of coal, in order to identifies the advantages of different rank coal in the process of gas adsorption/desorption, this paper establishes the relationship between the characteristics of the adsorption/desorption parameters and the field strength before and after adding the field, and then formations the method of determining the advantageous modified field strength of different rank coal; The relationship between the polarization of the direct current electric field and the adsorption energy of the coal surface is analyzed by experiments and numerical analysis, the heat transfer of methane in the isothermal adsorption and desorption process of coal is measured and calculated by micro calorimeter and Clausius-Clapeyron equation, and it couplings the relationship between the adsorption energy of coal surface and the adsorption heat in the process of coal adsorption/desorption; By using characterization of adsorption energy by adsorption heat which is on the basis of Morse potential, this paper establishes the adsorption potential model of coal methane under direct electric field, it is of great significance to improve the gas drainage rate and the development of coalbed methane to study on modified mechanism of adsorption and desorption of coal gas under external direct electric field.

我国煤层透气性普遍偏低，是瓦斯治理和能源利用亟待解决的技术难题，运用外加电场这一非力学方式辅助强化瓦斯抽采是一新途径。研究内容如下：利用直流电场作用下煤瓦斯吸附解吸的实验宏观表征，建立加场前后吸附/解吸参数变化与场强之间的关系，分析外加直流电场下煤瓦斯吸附解吸特征，判识不同煤级的优势改性场强；采用实验和吉布斯方程分析直流电场极化作用下煤表面（煤表面含氧官能团发生改性）和内部结构（孔隙结构参数发生改性）发生改性后的表面吸附能变化特征，采用实验和Clausius-Clapeyron方程分析煤瓦斯等温吸附解吸过程中吸附热的变化特征，耦合两者间的关系，以吸附热表征吸附能，在Morse势的基础上，建立直流电场下煤甲烷吸附势模型，微观角度揭示直流电场对煤吸附解吸瓦斯的改性机理，为提出一种适合不同煤级的辅助强化瓦斯抽采的电场物理激励方法提供理论基础，对提高瓦斯抽采率和煤层气开发具有重要意义。

项目研究了直流电场对不同变质程度煤样瓦斯吸附、解吸、放散特性的影响规律，确定各类煤体优势强化场强，系统分析了直流电场下煤体响应表现出的激发极化效应、热力学效应及孔裂隙变化效应，揭示了直流电场对煤体吸附解吸瓦斯的改性机理。. （1）直流电场下，对不同变质程度颗粒煤样，加电电压和加电时间对解吸量、放散初速度的影响呈抛物线形式，存在一个最大值，其中煤样特征电压均分布在4kv～12kv间，特征加电时间为4h～12h间，加电电压占主导地位，影响煤体解吸性能更加明显；而直流电场对高变质无烟煤作用放散初速度变化不明显，中高变质肥煤、贫瘦煤瓦斯放散特征表现一致，低变质褐煤放散初速度随着电压的升高有所增大，在12kv左右达到最大。. （2）柱状煤样直流电单独强化吸附过程，发现特征场强利于煤样对瓦斯的吸附，吸附量与场强呈抛物线状的关系，存在优势强化场强；吸附解吸强化过程，煤体瓦斯解吸量、解吸速度均明显被强化；单独强化解吸过程，实验现象与前者相同，且强化的结果弱于全过程加电强化的16.7%；直流电强化实验中在60kV/m时瓦斯吸附量、解吸量最大、解吸速度最快，判定是柱状煤样的优势强化场强。. （3）直流电场实时加载下，颗粒煤样吸附甲烷随着施加电场场强的增大而逐渐减小，与未加电场相比电场强度为30、60、90KV/m时，煤体吸附甲烷的能力下降了10.9%、15.7%、18.9%；解吸CH4速率依次提升了6.9%，15.3%，14.6%。并在Langmuir模型和D-R吸附方程基础上，构建了表征电场下的煤体吸附模型，实现了对不同场强下煤体吸附响应特征的预测。. （4）煤体直流电场下的激发极化效应、热力学效应及孔裂隙变化效应：①电场可使煤体中的极性基团发生转向极化，增加煤体电负性，减少吸附位，降低煤体吸附性能；②煤样吸附热力学计算发现，场强60kV/m时吸附热值最小，且吉布斯自由能相对未加电场增加了30.6%，吸附能力得到提升；③核磁共振实验发现，直流电场下煤样T2谱图的P2谱峰面积增加了近9倍，峰值向右偏移，煤体的孔数量得到增加，微裂隙得到扩展，对煤体吸附解吸性能均有促进作用。. 研究成果为加快瓦斯解吸速度非力学电磁技术方案提供依据，对瓦斯抽采辅助增透技术的多样化、瓦斯高效抽采和煤层气开发均具有重要意义。