Quantitative calculation of gases generation during low-temperature oxidation of coal

Abstract

The gases evolution during the low-temperature oxidation of coal is an essential parameter used to assess the state of coal oxidation and to estimate the gaseous pollutants. However, the current semi-quantitative method, which employs gas concentration as the measurement standard, is flawed. This paper presents a quantitative calculation method for gas products during coal oxidation. N₂ is used as the tracer gas in the experiment, because nitrogen is an inert gas that will not participate in the reaction, and the amount of matter will not change in the reaction. According to the formula [Formula: see text], the corresponding mass flow rates of each gases component were calculated, and the gas yields during the reaction period were determined by comprehensive calculation. To this end, experiments were conducted on the low-temperature oxidation of coal using a flow reactor. After undergoing quantitative calculations, the main gas products' mass flow rates, yields, and energies, including CO, CO₂, CH₄, C₂H₄, C₂H₆, C₂H₂, and C₃H₈ between 30 and 180 °C were obtained. The findings showed that CO₂ > CO > CH was generated in all the coal samples. The amount of gases produced in the low-temperature oxidation of coal is proportional to the level of oxygen concentration. When the oxygen concentration ranges from 0 to 21%, the gaseous production of MTH coal ranges from 381.44 g/ton to 8562.80 g/ton. The results of gaseous energy calculations showed that the energy loss for low temperature oxidation of the four coal samples ranged from 4334.14~26,772.73 kJ/ton under air atmosphere. Energy loss is also significantly affected by the oxygen concentration, and the energy loss of MTH coal increases significantly from 520.52 kJ/ton at 0% oxygen concentration to 26,772.73 kJ/ton at 21% oxygen concentration, an increase of about 50 times. Significantly, this method not only reflects the real gas evolution during low-temperature oxidation of coal but also computes the gas emission and energy loss, which is crucial for studying the mechanism of coal spontaneous combustion and assessing gases pollutants.

Keywords: Carbon emissions; Energy dissipation; Mass flow rate; Quantitative evaluation; Spontaneous combustion of coal.