Intrinsic Characteristics Combined with Gaseous Products and Active Groups of Coal under Low-Temperature Oxidation

ABSTRACT

Coal spontaneous combustion (CSC) characteristics were identified by their different types of coal. In this study, the samples of lignite, non-caking coal, lean coal, and anthracite were chosen to investigate the variations of gaseous products and main active groups during the low-temperature oxidation. The law of indicator gases was obtained by temperature-programmed experiment, and active groups of four coal samples had specific and different probabilities of spontaneous combustion via Fourier transform infrared spectrometer (FTIR). The relationship between the indicator gases at different stages and the main functional groups of coal were explored by Grey correlation analysis. The results indicated that the characteristic temperatures of water evaporation and gases desorption period of four types of coal showed the similar variation with those in thermal storage stage (Stage 1). Moreover, temperature ranges (TRs) in Stage 1 of lignite, non-caking coal, lean coal, and anthracite were 20–60, 20–60, 20–60, and 20–80°C, respectively; TRs in Stage 2 were 60–100, 60–140, 60–120, and 80–200°C, respectively; TRs in Stage 3 were 100–180, 140–180, 120–180, and 200–240°C, respectively. Based on the correlation analysis, the hydroxyl, carboxyl, and methylene had a sound temperature correlation with indicator gases emission. Eventually, the prediction system for CSC during the low-temperature oxidation was revealed.

KEYWORDS:

• Indicator gas
• temperature-programmed
• coal oxidation process
• characteristic temperature
• grey correlation analysis

Nomenclature

Aad	=	Mass fraction of ash of coal in air-dry basis (mass%)
FCad	=	Mass fraction of fixed carbon of coal in air-dry basis (mass%)
Mad	=	Mass fraction of moisture of coal in air-dry basis (mass%)
R	=	Pearson correlation coefficient (dimensionless)
T1	=	Temperature of maximum water evaporation and gases desorption in coal (°C)
T2	=	Temperature of minimum mass of coal before ignition (°C)
T3	=	Temperature of mass of coal increased beginning (°C)
TR	=	Temperature range (°C)
Vad	=	Mass fraction volatility of the coal dust in air-dry basis (mass%)
r0i	=	Grey relative correlation coefficient (dimensionless)

Conflicts of interest

There are no conflicts to declare.

Additional information

Funding

This study was financially supported by National Key R&D Program of China (Grant no. 2018YFC0807900), National Natural Science Foundation of China (No. 51974233 and No. 51974234), Xi’an University of Science and Technology Outstanding Youth Fund (2019YQ2-03), and Shaanxi Province Innovative Talent Promotion Plan-Youth Science and Technology New Star Project (No. 2019KJXX-050).