Gota Deguchi

Laboratory Studies on Evaluation of Gasification Effect for Conversion of Coal Resources in Underground Coal Gasification (UCG) Reactors

Underground coal gasification (UCG) as a clean energy technology and efficient way for the conversion of the coal resources into energy in-situ has attracted wide public attention in recent years. Laboratory-scale experiments on coal blocks can provide significant insight into UCG process. The main goal of this study was evaluation of the gasification effect applying L-shape linking-hole and Coaxial-hole UCG models. Experimental results show the gas composition, AE activity and the temperature distribution inside the combustion reactors under similar operating parameters. Positive correlation was found between the temperature and cumulative AE events. The results shown that the gasification of L-shape linking-hole model obtained the average calorific value, as high as 11.3 MJ/m3, whereas in the Coaxial-hole model, the average calorific value of gas produced was only 5.79 MJ/m3 under the experimental conditions. Even so, the results of conducted Coaxial-hole UCG experiment provide the original and sorely lacking data base for future new-style UCG research.

Coal Mining Technology. Visualization System for Roof Rock using the Mechanical Data of Roofbolter.

It is important to obtain information about geostructure of roof rock for effective rock bolting at the roadway in underground coal mine. Information on the variation in rock types and the distribution of discontinuities, such as layer boundaries, separation of strata and cracks, is especially important. For in situ evaluation of roof rock, we developed a measurement-while-drilling (MWD) system using mechanical data obtained from a drilling machine. The hardware of this system detects the torque, thrust, revolution and stroke of the machine as the mechanical data, and the software analyzes the mechanical data log and displays the locations of discontinuities by Neural Network techniques. This system also enables estimation of the 3-D geostructure of roof rock with regard to the change in rock types and distribution of discontinuities in the case of an array arrangement of drill holes. For displaying images inside the 3-D geostructure, animation consisted of slicing images and/or a 3-D model describing the boundary plane of layers by VRML(virtual reality modeling language) in virtual space are employed. We conducted some feasibility studies of this system using a pneumatic and a hydraulic drilling machine in roadways of Taiheiyo Coal Mine, Japan. The results of feasibility studies confirmed that the 3-D geostructure, including the distribution of crack density, can be reconstructed by the analysis system. Animation and display by VRML for the 3-D geostructure were useful for understanding inner structure of rocks.

Ex Situ UCG model experiments with oxygen enriched air in an artificial coal seam

Underground Coal Gasification (UCG) demands precise evaluation of the combustion area in the coal seam. Especially, the monitoring of fracture activity in the coal seam and around rock is important not only for efficient gas production but also for estimation of subsidence and gas leakage to the surface. For this objective, laboratory experiments were conducted using the simulated UCG models. This paper also investigated gas energy for coal consumption, the production gas quantity and heat value, the application of oxygen element balance in the gasification reaction process, and the gas composition obtained in this study. During burning of the coal, temperatures inside the coal, contents of product gases and acoustic emission (AE) activities were monitored successively under the control of feeding gas (air/oxygen and steam) flow rate. Comparison of the temperature variation and accumulated AE event curves revealed a close correlation between them. The local change of temperature inside the coal induced fractures with AE. The AE activity was related closely to the local changes of temperature inside the model. The evaluation of gas energy recovery calculated from the obtained product gas provided a fair evaluation for the coal consumed, and the quantity of gas product and calorific value obtained from the UCG process.

Joint R & D projects on coal mine gas control

JCOAL and CSIRO commenced a co-operation project on mine gas control in 1997 based on the agreement between Australian and Japanese government. The aim of the project is to develop effective post-mining goaf drainage technology for highly gassy longwall mines. A suitable site in Australia has been identified at Dartbrook in Hunter Valley. Overall scope of the project include field experiments with gas drainage technologies such as long horizontal holes, cross measure holes and surface goaf holes, and other field experiments of tracer gas studies, goaf gas distribution, gas analysis and ventilation monitoring. The project also include computational fluid dynamics modeling of gas flow in goaf environments and 3D visualization of the workings and gas drainage holes.Dartbrook Colliery is one of the gassiest mines in Australia, with longwall goaf gas emissions in the order of 420 to 540 m3/min. The capacity of the post-drainage system designed should be large enough to capture a major proportion of these goaf gas emissions. The susceptibility of the coal seam to spontaneous combustion and large quantities of broken coal left in the goaf compound the gas problem at Dartbrook. The spontaneous combustion issue demands that oxygen ingress into the goaf should be minimised. Requirement for high goaf gas drainage capacity and the need to prevent oxygen ingress into the goaf are contradictory to one another and should be considered during design and implementation of goaf gas drainage system.This report presents the details and results of the joint R & D project.