Date Published: July 20, 2017
Publisher: Public Library of Science
Author(s): Aitao Zhou, Kai Wang, Lingpeng Fan, Bo Tao, Saima Noreen.
Coal and gas outbursts are dynamic failures that can involve the ejection of thousands tons of pulverized coal, as well as considerable volumes of gas, into a limited working space within a short period. The two-phase flow of gas and pulverized coal that occurs during an outburst can lead to fatalities and destroy underground equipment. This article examines the interaction mechanism between pulverized coal and gas flow. Based on the role of gas expansion energy in the development stage of outbursts, a numerical simulation method is proposed for investigating the propagation characteristics of the two-phase flow. This simulation method was verified by a shock tube experiment involving pulverized coal and gas flow. The experimental and simulated results both demonstrate that the instantaneous ejection of pulverized coal and gas flow can form outburst shock waves. These are attenuated along the propagation direction, and the volume fraction of pulverized coal in the two-phase flow has significant influence on attenuation of the outburst shock wave. As a whole, pulverized coal flow has a negative impact on gas flow, which makes a great loss of large amounts of initial energy, blocking the propagation of gas flow. According to comparison of numerical results for different roadway types, the attenuation effect of T-type roadways is best. In the propagation of shock wave, reflection and diffraction of shock wave interact through the complex roadway types.
Coal and gas outbursts are an extremely complex dynamic phenomenon[1–5], during an outburst, the coals and rocks around the coal mining face are rapidly broken and ejected, releasing large amounts of gas from the pulverized coal[6,7]. The pulverized coal and gas flow induced by an outburst have enormous energy, which can lead to fatalities and destroy underground equipment. In recent years, many coal and gas outburst accidents have occurred in China. For example, on October 20, 2004, a serious outburst occurred in Daping coal mine of Zheng Coal Group in Henan province. In this accident, the outburst coal and rock was estimated 1894 t, plus approximately 250 thousand m3 outburst gases. Because the pressure of outburst gas flow was great, some underground ventilation facilities were destroyed, a large number of gas flowed to adjacent intake roadways, such that the gas concentration within these intake roadways exceeds gas explosion limit, a gas explosion occurred. 148 people were killed and 32 people were injured.
To analyse the influence of pulverized coal on the outburst shock waves, simulations were conducted for different volume fraction of pulverized coal and different roadway types: the volume fraction of pulverized coal is 0% indicates the pure gas outburst, while the other volume fraction of pulverized coal is 5% simulates the process of coal-gas two-phase flow. In the meantime, three different roadway types with straight, branch, bifurcation are also simulated.
(1) The elastic energy of coal only accounts for a few thousandths of the total outburst energy. Thus, in the outburst development stage, the elastic energy of coal can be ignored and the transport energy of coal derives entirely from the gas expansion energy.