Evaluation of Energy Recovery from Laboratory Experiments and Small-scale Field Tests of Underground Coal Gasification (UCG)

Abstract

Coal, the most abundant fossil fuel resource in the world, has proven reserves that are expected to be primary energy source for the 21st century. From the perspectives of safety and efficient resource utilization, coal is the subject of great expectations to satisfy the rapidly increasing demand for energy. As a clean coal technology, Underground Coal Gasification (UCG) is used to create a combustion reactor in an underground coal seam, thereby enabling the collection of heat energy and gases (hydrogen, methane, etc.) through the same chemical reactions that are used in surface gasifiers. As early as 1912, the first plan for UCG experiments was proposed by Sir William Ramsay. They were conducted on a small-scale in Durham, UK 1). A f ield study of UCG technology was done in the 1930s in the Union of Soviet Socialist Republics (USSR) 1). The technology was developed to a limited degree in the US, Europe, China, and Japan later during the 1960s and 1970s 2-10). However, many countries have recently shown increased interest in this method: modern sensing and control techniques can reduce UCG environmental effects by curtailing greenhouse gas emissions to the air and by leaving no ash aboveground. The relevant literature describes experimental tests and modeling experiences of UCG that have been pursued in recent decades. Theoretical and experimental studies have increased year-by-year in many countries since the 1930s 1, 11-14). A typical UCG system is presented in Fig. 1. It includes a coal seam with two boreholes drilled down into it: one for injecting reaction gas for in-situ burning of coal and the other for extracting the product gas. Actually, UCG minimizes health hazards and improves miners' safety because it requires no underground work, eliminates environmental hazards, and

Effect of Injection Flow Rate on Product Gas Quality in Underground Coal Gasification (UCG) Based on Laboratory Scale Experiment: Development of Co-Axial UCG System

“…Additionally, the total amount of oxygen inflow was almost the same in these ranges. Figure 9 shows the monitoring results of the main compositions and the calorific value of the product gas, which can be calculated with the concentration of the combustible gas contents such as CO, CH 4 , H 2 , and other hydrocarbons [24]. The calorific value of the product gas in experiment 2 decreased dramatically with a decrease of the combustible gas contents after 2 h elapsed, while that of experiment 1 decreased slightly.…”

Monitoring and evaluation of simulated underground coal gasification in an ex-situ experimental artificial coal seam system

“…Furthermore, the AE source was located using the parameters obtained from recorded signals during the gasification process to discuss the correlation between the clustered AE region and the temperature of coal seam. Next, the gas quality, gasification efficiency, and coal consumed in the tests were estimated to discuss the energy recovery using the stoichiometric approach proposed in our previous work [43]. For comparison, the method of balance computation (reported by Wiatowski et al [44]) was also applied to investigate the coal consumption during the gasification process.…”

“…In this study, a useful method of balance computation [44] is applied to discuss the amount of coal gasified over the experiment. Additionally, the amount of coal consumption is compared with the results from a proposed stoichiometric method (reported in our previous work [43]) which can be calculated by the product gas composition and oxygen injection rate. Fig.…”

“…Comparison of the results shows that the coaxial UCG system has a lower rate of energy recovery from coal than the linking-hole UCG system under the experimental conditions. Additionally, the results from a proposed stoichiometric method [43] were employed to predict coal consumption. This method is a simple assumption to calculate the coal consumption; the product gas is assumed only typical components, i.e., hydrogen, carbon monoxide, carbon dioxide, and methane as shown eq.…”

Model Calculation of Heat Balance of Wood Pyrolysis

“…For heat of pyrolysis, some researchers conducted micro-scale analysis of wood pyrolysis by thermogravimetric analysis to determine heat of pyrolysis 3) 4) . For the heat and material balances of macromolecular conversion, the authors proposed a new stoichiometric approach to analyze coal gasification 5) 6) , and, recently, it was applied to coal gasification both on surface 7) and in underground 8) . The stoichiometric theory was used to obtain theoretical heat of gasification, and adiabatic gasification temperature was also given rather than a simple matching of stoichiometric coefficients.…”