Effect of Coal Grain Size on Sorption Capacity with Respect to Propylene and Acetylene

Agnieszka Dudzińska,Adam Smoliński,Natalia Howaniec

doi:10.3390/en10111919

Abstract

Propylene and acetylene are released to mine air with the increase in the temperature of self-heating coal. Concentrations of these gases in mine air are applied as indicators of the progress of the self-heating process. Hydrocarbons emitted from the self-ignition center are sorbed on coal, while migrating through the mine workings. Coal crushed during the mining process is characterized by a high sorption capacity, which facilitates the sorption phenomena. This results in the decrease in hydrocarbons content in mine air, and in the subsequent incorrect assessment of the development of the self-heating process. The results of the experimental study on propylene and acetylene sorption on Polish coals acquired from operating coal mines are presented in this paper. Bituminous coal is characterized by a high sorption capacity with respect to unsaturated hydrocarbons, like propylene and acetylene. The sorbed volumes depend on the grade of metamorphism, porosity, and chemical characteristics of coal. Low level of metamorphism, increased porosity, and oxygen content result in higher sorption capacity of coals. The reduction in grain size of coals also results in the increased sorption capacity with respect to hydrocarbons. The most significant increase in the volumes of sorbed propylene and acetylene with the decrease in grain class was observed for coals of low porosity, high grade of metamorphism, and low to medium sorption capacities. The 10-fold decrease in coal grain size resulted in the 3 to 6-fold increase in the volume of sorbed propylene, and 2-fold increase for acetylene. The decrease in grain size results in higher accessibility of pore structure, increased pore volume and area, and higher number of active centers interacting with hydrocarbons of dipole characteristics. For coals with low grade metamorphism, high porosity, and high sorption capacity the volumes of sorbed propylene and acetylene increased only slightly with the decrease in coal grain size.

Highlights

The accumulation of heat released in the process of self-heating of coal often causes endogenous fires, creating a hazard for mining staff and serious financial losses
The volumes of sorbed acetylene increased with coal grains fragmentation of 20–60% with the change in coal grain diameters from 0.500–0.700 mm to 0.125–0.250 mm (V2/V1) for all coal samples except for coal sample 7, for which the value doubled with the reduction in coal size class
The sorption capacity of coals with respect to propylene and acetylene depends on the grade of metamorphism, porosity, and chemical properties of coals

Summary

Introduction

The accumulation of heat released in the process of self-heating of coal often causes endogenous fires, creating a hazard for mining staff and serious financial losses This is why various fire prevention activities are undertaken in mining industry to mitigate these risks [1,2,3]. An example of such activities is a complex control of coal’s self-heating process based on the monitoring of mine air composition, which enables early detection of self-heating centers and their elimination.

Methods

Discussion

Conclusion