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

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 mu g/L, while in samples from bituminous coal gasification average BTEX concentrations were: 2514.3-1354.4 mu g/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 mu g/L while from bituminous coal gasification PAH's values are in lower ranges 407-1090 mu g/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.

Automated summary

The study focused on qualitative and quantitative characterization of UCG wastewater produced during four different experiments, showing significant relationships between wastewater composition and coal properties as well as gasification pressure, especially for organic pollutants like phenols, BTEX, and PAH's. The concentrations of these pollutants were found to vary depending on the type of coal and gasification pressure, with phenols having the highest concentrations. Additionally, the study found that concentrations of phenols, BTEX, and PAH's decrease with increasing pressure.