1568 Figure 1 – Arrangement diagram of the field UCG trial Figure 2 – Drilling core samples obtained from the 5 m section at the co-axial well bottom Figure 3 – Borehole water remaining in Well-1 and Well-2 Table 1 – Results of proximate and ultimate analysis of coal Calorific value (MJ/kg) Proximate analysis (wt%) Ultimate analysis (wt%) Moisture Ash Volatiles Fixed carbon C H N S O 17.98 4.1 38.2 27.9 29.8 45.8 3.64 0.88 0.17 9.61 3. FIELD-SCALE UCG TRIAL 3.1 Experimental Setup The experiment was initiated by igniting the coal section in the co-axial well using LP gas. After confirming ignition, combustion and gasification of the coal were sustained through continuous injection of oxygen-enriched air with an oxygen concentration of 40-50%. The oxygen-enriched air was injected after blending oxygen supplied from a compressed oxygen cylinder and air supplied by a compressor (5.5 kW) at a predetermined mixing ratio using a gas metering and mixing device. The detailed injection conditions are presented in Figure 4. To progressively advance the combustion and gasification into the unreacted coal zone, the tip of the injection pipe (ignition position) was sequentially moved toward the inlet side by approximately 100 mm every four hours. A three-axis borehole geophone (Borehole Pick 3315, Oyo Inc.) was installed in the monitoring well (Well-3) at a depth of 17.5 m from the inlet in order to detect acoustic emission (AE) events associated
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