A CFD ANALYSIS OF THE FLOW OF FINE PARTICLES IN A TURBULENT MEDIUM AND CONTROLS FOR DUST IN LONGWALL MINING

Author

Akshat Chandna, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2015

Degree Name

Master of Science

Department

Mining Engineering

First Advisor

Chugh, Yoginder

Abstract

Worker exposure to coal dust in underground mines remains a major health hazard. This research has: 1) Analyzed the wetting characteristics of less than 10 micron dust particles using a novel micro-emulsion technology (MET) at bench scale and prototype scale with emphasis on agglomeration of dust particles, and 2) Simulate airflow and dust dispersion patterns on a longwall mining face using CFD modeling techniques to compare the current and proposed spatial distributions of water sprays around a longwall shearer. With the “Final Dust Rule” adopted by MSHA in 2014 and slated to go into full effect August 16, 2016, this research is a significant contribution to the coal industry. A suitable micro-emulsion containing 0.2% oil and 0.0125% didodecyl-dimethyl-ammonium bromide (DDAB) was identified. For assessing the wettability of coal dusts, a slightly modified version of “Fixed Time Wettability” or FTW (Chugh et al., 2004) was employed. These wettability tests however, did not yeild true wettability using the MET. An analysis for both unwetted and wetted portions of coal dust using particle size distribution curves (PSD) confirmed agglomeration when treated with the emulsion. For the unwetted portion, 96.6% of the particles had sizes greater than 25 μm after treatment with MET. Similar data for wetted dust was 100%. Experiemental studies in a 4 ft x 4ft x 10 ft chamber showed 12-15% improvement in respirable dust when using MET as compared to water alone.. Validated computational fluid dynamics (CFD) models were used to study airflow patterns and the interaction between sprays and airflow for designing both engineering and administrative controls around a longwall face. Two important zones – low air velocity (LAV) and recirculation (RC) – were identified around the model of a longwall face. These zones were located: 1) Behind the headgate drum and 2) Above the shearer chassis. Analysis of a modified geometric configuration of sprays on the shearer chassis showed improved coverage for wetting the dust on the longwall face. Numerical modeling comparisons were made between current spray systems and spray systems proposed by Dr. Y. P. Chugh using the concepts of “Continuous and Discrete Phase Modeling”. Analyses included changes in airflow patterns caused by spray systems and dust dispersion tracks generated from the cutting face. Chugh’s spray system was able to effectively eliminate RC zones existing above the shearer body, thereby minimizing the extent to which coal dust enters the walkway of the longwall face where workers are located. The proposed spray system used concepts of multiple wetting points for dust, air-locks, and venturi to wet the dust and direct the dust-laden air from mine workers. These improvements can be used in longwall mines as engineering controls for meeting new dust control standards.