Published in the May 2009 Coal USA Magazine
Because a chain is only as strong as its weakest link, the group worked to develop a checklist for operations to ensure all areas are addressed – making for a much more efficiently run total fluid circuit.
“It’s necessary to address all areas of critical operation and/or areas where there is high probability that dirt will be introduced into the hydraulic system, which could impede mining operations and/or cause downtime,” according to the three, who added that their checklist idea came from years of experience with mining operations and both listening to and having a comprehensive understanding of mining issues.
The men said mines that didn’t consider a comprehensive approach could be left with maintenance risks, such as equipment breakdown, and even worse, slowdowns or stoppages that could bring crews – and output – to a halt.
“The dark, wet and dirty environment underground presents some of the most difficult conditions for operating equipment, where fluid cleanliness is of the utmost importance to keep longwall machinery up and running,” Welch said.
So, how strong is your mine’s weakest link? Lynch, Welch and Hersh outline a five-pronged evaluation.
1. Filtration of the source water being used to make 95/5 fluid onsite
This filter’s most important characteristic is its ability to handle large volumes of fluid and large volumes of dirt.
It is necessary to install a coarse strainer at the intake point to prevent large items, including fish, acorns, leaves, muskrats, fish or other wildlife, being sucked into the filter. Filters used here do not see much pressure and must be made of non-corrosive materials, such as stainless steel or possibly aluminum.
A backflushing type filter is a good option at this location due to its capability to manage high volumes. It is also virtually maintenance-free and continues to filter even during the backflushing operation.
Backflushing filters typically utilize slotted tubes to capture solid particulates, which are then released to the backflush line during the periodic cleaning operation. A large-capacity return line filter may also be used in this capacity, with special consideration given to material construction and fluid handling capability.
Another option could be Schroeder’s new cyclone-style filter, the TwistFlow Strainer, a hybrid system consisting of a centrifugal separator and an in-line filter.
2. Protection of the mixing valve
A filter is necessary to allow accurate performance of the valve for mixing of the 95% water and 5% concentrate, which includes lubricants and fluid enhancers.
3. Filtration at the pump station
The pumping station supplies the working fluid and the power to operate the longwall machinery. It includes a reservoir and multiple pumps, motors and valves to supply a steady stream of working fluid to the longwall.
To perform properly, each pump should be protected by a filter on the pressure side. Additionally, fluid returning to the pump station’s reservoir should pass through a return line filter to maintain cleanliness of the reservoir fluid.
As the longwall machines advance and the coal face progresses forward, the pump station will also periodically need to be moved. This requires the disconnection and relocation of hoses and the station itself and the recoupling of all connections at the end of the move.
Since it is quite probable that contaminants will be introduced into the system during this activity, it is imperative that effective filtration is built into the pump station.
4. High-pressure, high-efficiency filtration on the pressure side of a longwall circuit
There can be as much as 1000 feet between the pump station and the coal face, so it is imperative that the working fluid being fed to the shields’ cylinders be kept as clean as possible.
5. Last-chance filtration
Last-chance filtration is dedicated to keeping clean the valves that operate the shields’ cylinders. The shields are responsible for supporting the roof for safety reasons as well as for protecting mining machinery from damage.
To help mines follow this list most effectively, Schroeder says it has three on-call individuals on its sales staff that deal exclusively with mines and can be onsite quickly if needed, as well as members of its distribution chain. “We recognize that longwall mines operate around the clock, and can require assistance at any time of day,” Lynch, Welch and Hersh said.
The three also noted that this checklist approach was not exclusive to longwall fluid circuits. The method can also be used to examine other systems that process coal, such as conveyor belts transporting coal from the face, surface mining operations and coal preparation plants, and even the shearers and continuous miners that are extracting the product.
