Experimental study of underground coal gasification (UCG) of a high-rank coal using atmospheric and high-pressure conditions in an ex-situ reactor

Abstract

This paper presents the results of an extensive experimental analysis of underground coal gasification (UCG) using large bulk samples in an ex-situ reactor under atmospheric and high-pressure (30 bar) conditions. The high-rank coal obtained from the South Wales (UK) coalfield is employed for that purpose. The aim of this investigation is to define the gas production rates, gas composition, gas calorific value, process energy efficiency and temperature changes within the UCG reactor during the gasification process based on the pre-defined reactants and flow rates. Two UCG trials, each lasting 105 hours, consisted of six stages where the influences of oxygen, water, air and oxygen enriched air (OEA) under different flow conditions on the gasification process were investigated. Based on the results of two multi-day experiments, it is demonstrated that the gasification under high pressure conditions produces syngas with higher average calorific value (8.49 MJ/Nm 3 ) in comparison to syngas produced at atmospheric pressure conditions (6.92 MJ/Nm 3 ). Hence, the overall energy efficiency of the high-pressure experiment is higher compared to the atmospheric pressure test, i.e. 57.67% compared to 51.72%. This is related to the fact that the high-pressure gasification produces more methane (11.97 vol.%) than the atmospheric pressure gasification (2.30 vol.%). Under elevated pressure, the temperatures recorded in the roof strata are about 100°C higher compared to the UCG process under atmospheric pressure conditions. This work provides new insights into the gasification of carbon-rich coals subject to different gasification regimes and pressures.

Regression Models Utilization to the Underground Temperature Determination at Coal Energy Conversion

“…The methodology of the UCG process physical modeling in experimental equipment is widely used by researchers (e.g., in [34,35]). For this reason, an experimental gasifier was designed and constructed to realize the UCG process experimental measurements.…”

Characterisation of the Contaminants Generated from a Large-Scale Ex-Situ Underground Coal Gasification Study Using High-Rank Coal from the South Wales Coalfield

“…The laboratory-scale UCG simulations were conducted at large-scale laboratory facilities of the Central Mining Institute's Clean Coal Technology Centre located in Mikołów, Poland. The experimental set up was as described in Kapusta and Stańczyk (2011), Wiatowski et al (2019) and Zagorščak et al (2020) (Fig. 1).…”

“…1). Two artificial coal seams (size = 3.05 m × 0.41 m × 0.41 m, mass = 648 kg (atmospheric test) and 650 kg (30 bar pressure test) were prepared using 5 blocks of coal (Zagorščak et al 2020). Two separate gasification experiments, one at atmospheric pressure and other at 30 bar pressure, were performed.…”

“…The experimental conditions, including the reagent supply rates, in different stages of the atmospheric and highpressure UCG experiments are presented in Table 2. The detailed interpretation of the experimental results is presented in Zagorščak et al (2020). The UCG effluents were periodically sampled during the gasification tests from the water scrubber (see Fig.…”

Sequential transformation study of minerals during underground coal gasification: Promising to indirectly reflect the actual reaction condition

“…In addition, it has long been feared that the UCG residuals will cause potential pollution in the adjacent groundwater of gasified coal seams, and the dissolution of harmful trace elements in the ash is closely related to the mineral characteristics of the ash 16 . Therefore, it is of great scientific significance to study the mineral composition and transformation of ash and slag under different gasification conditions to understand the real reaction conditions, improve the efficiency of coal utilization, and identify and control the environmental impact of ash and slag 17–19 …”