Experimental investigation of the minimum auto-ignition temperature (MAIT) of the coal dust layer in a hot and humid environment

• Improved sight into the mechanism of coal dust layer auto ignition temperature.
• Clarified the influence of moisture on coal dust ignition by using the Minimum Auto Ignition Temperature (MAIT) apparatus and Thermogravimetric analysis (TGA)
• Clarified the influence of volatile matter and Particle Size Distribution (PSD) on the MAIT of a coal dust layer.
• Provided important data and explanation of the influence of packing force on the MAIT of coal dust Shows the influence of packing force on the MAIT of coal dust layer.
• Tested and compared different dust MAIT measurement standards, consequently, a wider range of coal particles sizes have been applied to the ASTM E2021.

Ventilation Air Methane (VAM) abatement technology is recognized as a promising and value adding technique for reducing fugitive methane emissions, however, it also increases the potential fire and explosion risks of overheated coal dust. To eliminate these risks from the abatement systems it is necessary to determine the critical combustion characteristics of the minimum auto ignition temperature (MAIT) for a coal dust layer.This study investigates the auto-ignition behavior of coal dust layers in a humid environment with Relative Humidity (RH) >80%. The MAIT of four different coal dust samples (Australian coal) with particle sizes below 212 μm and dust layer thicknesses of 5, 12 and 15 mm were measured using a dust layer auto ignition temperature apparatus in accordance with the ASTM E2021 standard.It was concluded that the MAIT of the coal dust layer significantly decreases with decreasing particle size. The MAIT for the coal samples with a smaller D50 size were observed to be lower in comparison with samples with a larger D50 size. The dust layer thickness was shown to significantly impact on the MAIT. The MAIT increased proportionally with the increasing thickness of the coal dust layer. The effect of the coal dust moisture content and humidity on the MAIT for compacted dust layers was noticeable, whereas, this effect was less important with loose dust layers. In addition, this work investigated and compared the MAIT for a typical coal dust sample based on the existing ASTM and International Electrotechnical Commission (IEC) standard procedures for ignition of coal dust layers.