Effect of Lignite Properties on Its Suitability for the Implementation of Underground Coal Gasification (UCG) in Selected Deposits

Abstract

Two experimental simulations of underground coal gasification (UCG) processes, using large bulk samples of lignites, were conducted in a surface laboratory setup. Two different lignite samples were used for the oxygen-blown experiments, i.e., “Velenje” meta-lignite (Slovenia) and “Oltenia” ortho-lignite (Romania). The average moisture content of the samples was 31.6wt.% and 45.6wt.% for the Velenje and Oltenia samples, respectively. The main aim of the study was to assess the suitability of the tested lignites for the underground coal gasification process. The gas composition and its production rates, as well as the temperatures in the artificial seams, were continuously monitored during the experiments. The average calorific value of gas produced during the Velenje lignite experiment (6.4 MJ/Nm3) was much higher compared to the result obtained for the experiment with Oltenia lignite (4.8 MJ/Nm3). The Velenje lignite test was also characterized by significantly higher energy efficiency, i.e., 44.6%, compared to the gasification of Oltenia lignite (33.4%). The gasification experiments carried out showed that the physicochemical properties of the lignite used considerably affect the in situ gasification process. Research also indicates that UCG can be considered as a viable option for the extraction of lignite deposits; however, lignites with a lower moisture content and higher energy density are preferred, due to their much higher process efficiency.

Investigation of the Evolution of Stratum Fracture during the Cavity Expansion of Underground Coal Gasification

“…Obviously, temperature decreased dramatically away from the inner face of a cavity. Specifically, the temperature at the inner face of a cavity is 1200 • C, which was decreased to about 500 • C at a depth of approximately 2 m and around 200 • C at a depth of about 3.5 m. This result is close to the data obtained by Xin et al [58], Kapusta [59]. Figure 2 suggests that the mechanical performance of coal and sandstone have a small change below the temperatures of 200 • C and 500 • C, respectively.…”

Physicochemical Properties of Biochar Produced from Goldenrod Plants

“…Compared with solid fossil fuels, the calorific value of the obtained torrefaction from goldenrod is similar. The calorific value of hard coal is 20.9–33.4 MJ∙kg −1 [ 54 , 55 , 56 , 57 ] and brown coal (lignite) 5.9–24.9 MJ∙kg −1 [ 58 , 59 , 60 , 61 , 62 ].…”

Investigation of Underground Coal Gasification in Laboratory Conditions: A Review of Recent Research

“…Large bulk lignite samples were experimentally gasified by Kapusta [71]. The research focused on the possibilities of gasification of two different types of lignites, i.e., "Velenje" meta-lignite (Slovenia) and "Oltenia" ortho-lignite (Romania), with an average moisture content of 31.6 wt% and 45.6 wt%.…”