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

Krzysztof Kapusta

doi:10.3390/en14185816

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.

Highlights

Despite the current shift to renewable sources of energy, fossil fuels, and, in particular, coal, will remain a meaningful fuel in some parts of the world, for a long time into the future [1]
The study showed that at similar conditions, the gasification of Oltenia lignite took place with a significantly higher coal consumption rate, i.e., 8.2 kg/h compared to 6.1 kg/h for Velenje lignite
The lower energy efficiency obtained for the Oltenia experiment was due to the higher moisture content of the raw lignite sample

Summary

Introduction

Despite the current shift to renewable sources of energy, fossil fuels, and, in particular, coal, will remain a meaningful fuel in some parts of the world, for a long time into the future [1]. Increased energy demand will lead to the mining of deep coal deposits. As a consequence of the increasing depths, conventional underground mining is more difficult, more dangerous, and more expensive nowadays. Underground coal gasification is considered to be a technology that will enable the safe and economical exploitation of coal resources that could not otherwise be mined [2,3,4]. This, coupled with the current energy security issues and the need to reduce the environmental footprint, has sparked a global revival of interest in UCG. During UCG, coal deposits are transformed into gaseous combustible products (syngas) and extracted to the surface. UCG can be a viable extraction technology for coal seams, for which conventional coal mining technologies are technically, economically, or environmentally not feasible [11]. With the high-profile mine disasters, UCG is deemed safer than conventional mining, since it does not require staff below the ground

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