Underground » Health and Safety
The objective of this project is to determine optimum air velocities for management of both dust and gas concentration levels on longwall faces with different cutting heights. The project aims to obtain a fundamental understanding of the effect of airflow quantities and velocities on dust distribution patterns and dust entrainment at different locations along the longwall face. It also aims to investigate dust entrainment vs dust dilution at different velocities and the influence of air velocity on effectiveness of primary dust control strategies, such as water sprays.
The project included:
- Investigation of the effect of various airflow quantities on gas distribution profiles near the tailgate corner of the longwall face;
- Transient simulations to investigate the effect of airflow quantities on longwall return gas levels during barometric pressure changes.
The field data collected from the mine sites was analysed to obtain an initial assessment of the effect of air velocity on respirable dust levels in various longwalls. Analyses of the data show that there is no direct relationship between air velocities and respirable dust levels.
Two CFD models were developed with face cutting heights of 3.6m and 2.6m, representing mining conditions at two different mine sites. Initial base-case CFD modelling simulations were carried out with a ventilation quantity of 70 m3/s. The results show that dust concentration levels in the front walkway region at different locations along the longwall face vary from 0.3 mg/m3 to 1.5 mg/m3. The modelling results and field data are in close agreement at different sections along the face. Analyses of respirable dust distribution profiles at different face airflow quantities show that respirable dust levels in the walkway region reduce substantially with increasing airflow quantity.
Extensive modelling studies were carried out with 3.6m models to investigate the effect of airflow quantity and velocity on dust re-entrainment on the longwall face. Re-entrainment dust sources were introduced at different locations in different sets of simulations.
CFD modelling studies were also carried out with 2.6m models to investigate the effect of changes in longwall face geometry and associated airflow characteristics on respirable dust distribution profiles and re-entrainment in the longwall face.
Modelling studies were carried out to:
- Investigate the effectiveness of the primary dust control strategy, i.e., water sprays, on dust suppression in longwall faces; and to
- Investigate the effects of various airflow quantities on gas distribution profiles near the tailgate corner of the longwall face.
Transient CFD simulations were carried out to investigate the effect of airflow quantities on goaf gas distribution and longwall return gas levels during barometric pressure changes.
This project suggests that 7.0 - 7.5 m/s is the optimum air velocity on the longwall faces for management of both dust and gas in typical Australian longwall faces. The corresponding airflow quantities with respect to 7.0 - 7.5 m/s air velocity in the longwall face for 3.6m and 2.6m height faces would be around 90 - 100 m3/s and 60 - 70 m3/s respectively, depending on the longwall face equipment configuration. It is recommended that an airflow quantity of around 70 - 90 m3/s is to be maintained on longwall faces to manage tailgate gas distribution pattens, and to minimise the adverse effects of barometric pressure changes on longwall return gas levels.