Characteristics of Water Contaminants from Underground Coal Gasification (UCG) Process—Effect of Coal Properties and Gasification Pressure

Magdalena Pankiewicz-Sperka,Katarzyna Stolecka,Wioleta Basa,Krzysztof Kapusta

doi:10.3390/en14206533

Magdalena Pankiewicz-Sperka, Katarzyna Stolecka + Show 2 more

Open Access

https://doi.org/10.3390/en14206533

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Abstract

One of the most important issues during UCG process is wastewater production and treatment. Condensed gasification wastewater is contaminated by many hazardous compounds. The composition of the generated UCG-derived wastewater may vary depending on the type of gasified coal and conditions of the gasification process. The main purpose of this study was a qualitative and quantitative characterization of the UCG wastewater produced during four different UCG experiments. Experiments were conducted using semi-anthracite and bituminous coal samples at two distinct pressures, i.e., 20 and 40 bar. The conducted studies revealed significant relationships between the physicochemical composition of the wastewater and the coal properties as well as the gasification pressure. The strongest impact is noticeable in the case of organic pollutants, especially phenols, BTEX and PAH’s. The most abundant group of pollutants were phenols. Conducted studies showed significantly higher concentration levels for bituminous coal: 29.25–49.5 mg/L whereas for semi-anthracite effluents these concentrations were in much lower range 2.1–29.7 mg/L. The opposite situation occurs for BTEX, higher concentrations were in wastewater from semi-anthracite gasification: 5483.1–1496.7 µg/L, while in samples from bituminous coal gasification average BTEX concentrations were: 2514.3–1354.4 µg/L. A similar relationship occurs for the PAH’s concentrations. The higher values were in case of wastewater from semi-anthracite coal experiments and were in range 362–1658 µg/L while from bituminous coal gasification PAH’s values are in lower ranges 407–1090 µg/L. The studies conducted have shown that concentrations of phenols, BTEX and PAH’s decrease with increasing pressure. Pearson’s correlation analysis was performed to enhance the interpretation of the obtained experimental data and showed a very strong relationship between three parameters: phenols, volatile phenols and CODcr.

Highlights

Nowadays meeting the challenges of energy supply safety and provision of competitive energy costs is one of the most important challenges in the energy sector today
The average physicochemical characteristics of the post processing water samples obtained during all four underground coal gasification (UCG) experiments are presented in the Table 4
The studies conducted revealed that the type of coal used and gasification pressure have a significant impact on the wastewater parameters

Summary

Introduction

Nowadays meeting the challenges of energy supply safety and provision of competitive energy costs is one of the most important challenges in the energy sector today. One of them is underground coal gasification (UCG) which offers many potential advantages over the traditional mining methods [5,6]. UCG is a method of in-situ (directly in the underground coal seam) thermochemical coal conversion into a synthetic gas [7,8,9]. The basis of the UCG process is direct injection of gasifying reagents to the ignited coal seam and receiving the gas product at the surface [10]. Compared to traditional mining UCG process has lower surface impact and may contribute to the reduction of air pollutants and greenhouse gas emission [11]. The most desirable product for UCG process is methane, which strongly improve calorific value of gas [1,15]. Methane is formed in methanation reaction and directly from solid carbon in hydrogenation reaction [1]: CO + 3H2 → CH4 + H2 O (∆H= −206 kJ/mol)

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