Fire progression within coal waste heap in Heřmanice, Upper Silesia, Czech Republic

Abstract

In the Czech part of the Upper Silesian Coal Basin (USCB), there are several places of coal wastes storage. Within improperly protected heaps, the self-heating and spontaneous burning processes may develop, resulting in the emission of gaseous, water-soluble and solid (tars, dust) pollutants.The thermal processes have developed within the heap in Hermanice (Ostrava) since the 1990s. Recently, the most thermally active is the eastern part of the deposit. The purpose of the study was to evaluate the progression of the fire based on temperature measurements, molecular and stable isotope composition of gases emitted from thermally active parts of the deposit. The sampling was conducted in the same places in January, April and September 2023. One of the sampled points was a steel pipe that penetrated the dump to a depth of ca. 12 m, where, according to Diamo Ltd., it was ca. 350 °C. The other 3 sampling points were located in areas of visible thermal activity (steam or smoke emissions). Surface temperature measurements in these spots ranged from 3 to 345 °C, and at the probe depths (50-100 cm), from 66 to 363 °C. Gases were taken at each point twice: directly from the chimney where the outflow of gas/vapour was visible (sample SURF) and after sticking the probe into the ground (sample DEEP).During the study period, in the zone of intense thermal processes (southeastern part of the heap), large changes in temperature and gas concentrations (N2, O2, hydrocarbons (HC), CO, CO2, H2 and S-compounds) were noted. In general, SURF gases were found to be richer in pollutants than DEEP gases. This suggests that the gases coming to the surface flow from much deeper parts of the heap than those reached with the sampling probe. The highest concentrations of CO2 (19.17%), CO (0.67%), HC (2.43%), H2 (6.26%) and S-compounds (844 ppm) were found in April in gas coming out of the pipe (from the highest temperature, ca. 350oC). In September, the zone with the highest temperatures shifted to the north, and the concentrations of monitored gases generally decreased, indicating material burnout in the hot spot. The δ13C(CH4), δ2H(CH4), and δ13C(CO2) values indicate the thermogenic origin of all gases.At a point ca. 100m away from the hot spot, temperatures of ca. 65-75oC were found during all measurements, and the gas composition was independent of the sampling depth. The highest concentrations of CO2 (20.21%), HC (3.30%) and H2 (0.5%) were found during the April campaign. The isotopic composition of selected gases suggests their relation to low-temperature thermogenic processes; the presence of a component of microbial origin is not excluded.The data presented here show that the molecular and isotopic composition analysis of gases is a good tool for tracking processes in thermally active coal waste dumps.This study was financed by the AGH University of Krakow as a part of the programme Excellence Initiative – Research University, Action 4, Grant No. 4113.