Mining Contract: Mechanisms of Coal Dust Explosions and Their Prevention

Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

Research on secondary dust explosions has been primarily empirical in nature. Previous attempts to model the complex processes describing dust lifting by air movement induced from a blast, particle heating, and combustion have not been successful. Only recently has numerical modeling been used to solve these multifaceted activities.

This contract will determine the following:

• How much dust (both inert and coal) is removed and lifted by winds induced from a primary explosion.
• When the thickness of a coal dust top layer is dangerous enough to support a dust explosion.
• Conditions under which a second reactive zone ignites.
• Effect of airborne dust on the ignition and spread of a secondary dust explosion.

The University of Maryland has developed and tested a numerical model of the dust explosion process called the Dust Explosion Simulation (DESIM) code. Through simulation experiments with the chemical reactions “turned off,” this code can determine how fluids and particles interact and react in explosion scenarios. Variable parameters for the DESIM code include the thickness of a coal dust layer, strength of a pressure wave that lifts the coal dust, volatility of coal dust particles, dilution of coal dust with inert particles, and the initial size of those particles.

Under this contract, some of the University of Maryland results include:

• The suggestion of dust rises more rapidly with decreasing layer thicknesses, and the thicker layers produce stronger fluctuations than thinner layers;
• faster than particles with higher inertia and can result in a separation between different particle sizes;
• The effects of radiation should be explored more carefully since one-dimensional computations show that thermal radiation may cause large accelerations of coal dust flames and ignite two different coal dust clouds;
• Even a very thin layer of coal dust (~250 µm) on top of an inert dust layer is sufficient to produce a reactive particle cloud dispersed by a shockwave; and
• Ignition may occur behind a reflected shock wave where the temperature, pressure, and turbulence are much higher.

Successful completion of these tasks provide a fundamental theoretical and computational model for understanding the mechanics of coal dust explosions, a better understanding of the relevant existing experimental data, and information on how frequently inert dust should be placed on top of reactive coal dust layers.