Evaluation of Structural Changes in the Coal Specimen Heating Process and UCG Model Experiments for Developing Efficient UCG Systems

Abstract

Abstract:In the underground coal gasification (UCG) process, cavity growth with crack extension inside the coal seam is an important phenomenon that directly influences gasification efficiency. An efficient and environmentally friendly UCG system also relies upon the precise control and evaluation of the gasification zone. This paper presents details of laboratory studies undertaken to evaluate structural changes that occur inside the coal under thermal stress and to evaluate underground coal-oxygen gasification simulated in an ex-situ reactor. The effects of feed temperature, the direction of the stratified plane, and the inherent microcracks on the coal fracture and crack extension were investigated using some heating experiments performed using plate-shaped and cylindrical coal specimens. To monitor the failure process and to measure the microcrack distribution inside the coal specimen before and after heating, acoustic emission (AE) analysis and X-ray CT were applied. We also introduce a laboratory-scale UCG model experiment conducted with set design and operating parameters. The temperature profiles, AE activities, product gas concentration as well as the gasifier weight lossess were measured successively during gasification. The product gas mainly comprised combustible components such as CO, CH 4 , OPEN ACCESSEnergies 2013, 6 2387 and H 2 (27.5, 5.5, and 17.2 vol% respectively), which produced a high average calorific value (9.1 MJ/m 3 ).

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

“…AE monitoring is, therefore, used in the field of rock mechanics, concrete, and mining to predict the damage and the failure of brittle materials because they reach structural failure by accumulating microfracture [18][19][20][21][22]. As many AE activities can be detected attributable to thermal stress during UCG process [23], it is also useful to estimate the progress of gasification process and special events such as collapse of coal in the cavity and extensive propagation of gasification zone. In this study, AE events and AE counts are calculated by means of data processing of the raw AE signal data, as shown in Figure 6.…”

Sensing underground coal gasification by ground penetrating radar

“…The gasification process also changes the coal structure. Around the gasification zone, this creates a space with fissures that enable the process to progress (Itakura et al 2009;Su et al 2013;Bhutto et al 2013). For determination of the shape and size of gasification cavity as well as progress of the process in time domain, various methods are used.…”

Modelling Underground Coal Gasification—A Review

“…Later on, in 1912, famous British chemist Sir William Ramsay expanded the ideas of Betts and proposed gasifying coal underground as a way to avoid air pollution and as a solution for the mining worker [16]. His strong advocacy for the development of this technology created an international surge of interest in UCG that eventually helped him to culminate the first ever UCG experiment being carried out at Hett Hill near Tursdale Colliery in County Durham, North East England, in 1912 [16,18]. Unfortunately, the experiments did not proceed due to the outbreak of World War I in 1914 and Ramsay's death in 1916.…”

“…Although the idea of the UCG was first mentioned by Sir William Siemens of Great Britain in 1868 [16][17][18] and the idea was consolidated independently by the famous Russian chemist Dmitri I. Mendeleev, who also pointed out the economic benefit of UCG over conventional mining [16], most credit goes to an American chemist, A.G. Betts, due to his detailed technical contents and engineering drawing on the UCG method that closely resemble modern approaches presented in his three UCG patents received during 1909-1910 [16,17]. Later on, in 1912, famous British chemist Sir William Ramsay expanded the ideas of Betts and proposed gasifying coal underground as a way to avoid air pollution and as a solution for the mining worker [16].…”