Underground » Maintenance
This project aimed to establish if longwalls with Hi-Set systems could successfully operate with much lower main emulsion system pressures. Reducing the main emulsion system pressure would reduce the safety hazards associated with high levels of energy stored in the longwall hoses. The stored energy is proportional to the system pressure squared. As such, reducing the pressure from 350 bar to 200 bar would reduce the energy by a factor of ~3. Additionally, the power of the pump motors could be reduced by a factor of 1.75, resulting in lower operating cost. Furthermore, the fatigue lives of fittings and hoses could increase by a factor of 5.
However, the analysis established that operation at lower pressure would require valve upgrades to retain the existing cycle times and productivity. This is not because roof support functions (other than leg set) require high pressure, but because the existing valves are optimised for single pressure systems; such valves are no longer required if a Hi-Set system is dedicated to leg setting.
Field trials of a low-pressure system would be possible to prove the concept, but this would be limited to pressures above 300 bar (or possibly down to 250 bar with changes to existing Hi-Set control parameters and accumulator pre-charge levels). Successful testing to prove that cycle times and setting performance could be retained would be required to justify design of new systems optimised for low-pressure operation (including the installation of higher flow valves and lower power motors).
In addition to lower pressure operation of the main emulsion system, the use of in-shield intensifiers could achieve set pressures up to 500 bar. This would provide 25% higher set densities or enable the existing set densities with smaller leg cylinders (note, the lower fluid demands of smaller leg cylinders would allow greater function speeds and higher productivity).