Underground » Mining Technology and Production
Longwall coal mining utilises hydraulically operated roof supports. The roof supports are often separated from the pumping hardware by more than 500m. It is perceived throughout the mining industry that the long hoses connecting the pumps and the roof supports introduce significant flow restrictions into the fluid path and compromise system performance.
The largest flow demands occur during "leg raise" of the roof supports. Due to the large area ratio of the leg cylinders (typically 10:1), only 1/10 of the leg raise fluid volume is required from the pumps during "leg lower", but a large fluid volume (the same as that required for leg raise) must be returned to tank over the long hose path.
"Regenerative" technologies aim to eliminate the transport of large fluid volumes fluid over long distances. Instead, the large fluid volume discharged during leg lower on one support is transferred locally (over a very short/low resistance fluid path) to a nearby roof support undergoing leg raise. As such, only the very small leg lower volume is supplied by the pumps.
This report presents performance predictions for a number of regenerative options and compares them with the predicted performance of a "generic" longwall. The generic longwall is modelled using component details typically found in Australian longwall installations.
The report includes descriptions and details of the hydraulic circuit components and how they affect system performance. Simple static analyses of the main roof support functions are included to help develop an appreciation of the critical hydraulic circuit variables. Dynamic analyses are used for more comprehensive consideration of the real longwall conditions. The dynamic analysis results are used for the final comparisons of the alternatives.
Based on the results of the dynamic modelling WBM concludes regenerative technologies are unlikely to offer a viable benefit to longwall performance. This outcome is driven primarily by the realisation that the long hose runs in modern longwalls are not the critical influence they are commonly perceived to be. Additionally, extra valves are required to implement regenerative technologies, and these further degrade the system performance. Additional valving implementation and maintenance costs could be more effectively invested by purchasing improved conventional hydraulic systems (better valves and control strategies etc.)
The dynamic modelling tools used for assessment purposes during this project were not available at the time the project commenced. Development of the dynamic models forms part of the in kind contribution to the project made by WBM. Having established that regenerative concepts would be less beneficial than had been hoped, rather than expending resources on detailed investigation of these concepts, the time was spent identifying and documenting the principles that will provide the basis of real performance gains in longwall hydraulic systems.
The report concludes with an expected cost-benefit ranking of a number of new options aiming to improve system performance. This ranking should help prioritise further analysis required to validate the options prior to implementation.