Influence of Water Content on the Coal Spontaneous Combustion Behavior during Low-temperature Pre-pyrolysis Processes

ABSTRACT

In order to study the influence of water addition in the low-temperature pre-pyrolysis process on the coal spontaneous combustibility, programmed heating experiments were carried out to test secondary oxidation characteristics of coal which was pretreated by isothermal pyrolysis at 80°C with different water content of 5.96%, 10.11%, 13.92%, and 17.48%. The results showed that the concentration of CO and CO₂ decreased, and tended to be constant along with time during the pre-pyrolysis process in which moisture had a positive effect on CO₂ release. The thermostatic pre-heating at 80°C inhibited the spontaneous combustion of coal, while the presence of water during the pre-pyrolysis process showed the competitive characteristics of promoting and inhibiting the coal spontaneous combustion at the same time. From the perspective of CO and CO₂ production, oxygen consumption rate, and exothermicity, it was found that the coal pre-pyrolyzed with water content of 10.11% was easiest to self-heat, followed by the cases with water content of 5.96%, 13.92%, and 17.48%, respectively. The Pearson correlation coefficient method was adopted to conduct correlation analysis on values of ∆CO/∆O₂, CO/O₂, and CO₂/O₂ concentration with respect to coal exothermic intensity. It was found that the value of CO/O₂ concentration has the highest correlation with the exothermic intensity, which could be used as an index of exothermic degree in the stage of spontaneous combustion above 80°C.

KEYWORDS:

• Coal oxidation
• Exothermic intensity
• Moisture
• Pre-pyrolysis
• High mine gas

Additional information

Funding

This work was supported by the National Key R&D Program of China(2018YFC0807900), the National Natural Science Foundation of China (51704226), Natural Science Basic Research Plan in Shaanxi Province of China (2017JQ5047), and China Scholarship Council (201708615022).