Development of a methodology to research the influence of liquid nitrogen exposure on carbon material

Abstract

Recently, studies, which are dedicated to the effect of cryogenic substances on the structure of coal, are gaining popularity. The impact of liquid nitrogen on coal leads to micro- and macrostructural disturbances in the continuity of coal due to drastic cooling of the moisture in the microcracks and pore space of the coal, while the volume of ice microcrystals increases. This approach provides the opportunity to treat the massif without additional injection of liquid agents into seams to create pressure to disintegrate it, unlike traditional methods of increasing the filtration surface in coal. Research work, which are presented in this field, are aimed at studying the multiplicity of increase in porosity and fracturing of coal in the process of single or multiple exposure to portions of liquid nitrogen. A distinctive feature of the ongoing research is the evaluation of the results of cryotreatment of samples by non-destructive methods of measuring the pore space. Thus, the conclusion about the change in permeability is made without direct measurements of the gas filtration rates in the samples. Changes shown by CT scans show an increase in the total number of open pores and channels, however they do not illustrate the increase in gas permeability in general. As a part of this work, we carried out a number of studies on axial gas filtration in dense coal samples, which were under controlled all-round loading. Preparatory work was carried out to dry the samples and further saturate them with moisture to identical values in the entire batch. A scheme for conducting experiments to study the effect of cryotreatment on the internal structure of coal using the methods of stationary axial gas filtration and NMR relaxometry is proposed. The development of this technique contributes to obtaining reliable data on the increase in the gas permeability of coal samples. The data can be useful in designing methods and approaches to increase the degree of degassing by treating degassing wells at coal mining enterprises.