Blowers, compressors and vacuums come in handy when recovering spillage material that conventional types of equipment are unable to access.
This collected material sometimes are of very high grade making it a profitable undertaking for any mine.
Multistage centrifugal blowers are available in various sizes to provide flows from 1000CFM to 35000CFM and up to 15psi. PD blowers in two-lobe and three-lobe designs are the backbone of the low pressure market place. For instance Hibon PD blowers offer flows from 20CFM to 5500FCM and pressures up to 15psi. Acoustical enclosures are common accessory to the meet sound level requirements.
In addition, to ensure that every particle of precious ore is captured requires a constant and reliable low pressure air solution, PD blowers are used as the air supply to flotation cells and leach tanks.
There are three basic types of air compressors reciprocating, rotary screw and rotary centrifugal. They are further specified by the number of compression stages namely cooling method whether air, water or oil, drive method which can be either motor, engine, steam, etc.) and the type of lubrication thre being a choice of oil, Oil- Free where Oil-Free means no lubricating oil contacts the compressed air and packaged or custom built.
Various types of compressor component technologies are available as possible candidates to provide the typical 12-13 psig air pressure required. A universal specification is 100 pounds-per-minute air flow at this pressure. The design of the discharge nozzle at the business end accomplishes this- more on that in a bit.
Factors for selecting any of the technologies hinges on available package size and weight, operating efficiency or power consumption at a particular operating point, noise, durability and cost. Other more subtle factors include the general performance characteristic and stability at a given operating point.
Many people are not aware that heavy duty industrial vacuum technology has been around for many years. It has always been a niche product with very specific uses but in terms of mining these have mostly been for the cleaning of spillages and the recovery of high grade materials.
Generally, moving ore or spillage material is possible by means of several conventional types of equipment such as skid steer loaders and front-end loaders and this equipment can outperform a vacuum unit in terms of tonnage per hour quite easily when the material is accessible. However, as soon as material is in difficult to reach areas such as under low conveyors or in places that the conventional machinery cannot access such as certain shaft bottoms, bucket elevator pits, confined space areas or even tailings dams with plastic linings that risk damage, then you have a situation where vacuums can make a real positive impact.
The only other alternative in these types of situations would be manual labour with shovels and even buckets at times but there are several inherent risks and disadvantages to this approach. Safety is the first shortly followed by the tonnage per hour that is possible which is relatively low considering that workers with shovels have a limited range within which they can be effective. If the material is very dry then you also have the added disadvantage of dust being generated by the use of shovels which can be a health hazard for the workers. Vacuums allow the material to be contained within the hoses or pipeline that is being used. This can eliminate the dust generated at the point of collection. Vacuum systems can convey up to a distance of 100m or more depending on the material. In certain cases vacuums allow for a drastic reduction in the use of water to clean spillage materials which is a benefit to mines wanting to conserve a precious resource even though the right vacuum can handle dry material, mud or even water.
One of the big advantages of using a vacuum system is that it is possible to discharge directly back onto a moving conveyor which means the material only has to be handled once making it a more efficient operation. In South Africa the law prohibits cleaning near a moving conveyor to minimise the risk of injury to workers so the collection point can’t be under the conveyor that’s moving but it is still possible to clean other areas and discharge onto a moving conveyor that is at a safe distance away. The biggest advances in the use of vacuum technology in the near future will be in the mechanising of the nozzles for example, a robotic solution that will allow cleaning under a moving conveyor by being fully remote control and allowing the operator to be untethered from the nozzle and a safe distance from the working area. This will be a great advantage for mines that are currently only able to clean spillages during shutdowns as they will now be able to do it at any time. This challenge has been identified by organisations such as the Coaltech Research Association as one of the major issues to tackle in underground coal mines but any mine that has to deal with spillages under conveyors has the same challenges.
Vacuums are also very good at collecting material that conventional equipment just can’t handle. Often, very high grades of material are found in fine dust, especially in gold mines. When moving material with conventional equipment such as LHDs most of the fine dust material is left behind. This is a perfect opportunity to recover this high grade material by using vacuums which can collect even the finest of dust particles. The overall quantities of material collected will be fairly low but the quality of the material recovered can be quite phenomenal. Double and even triple digit grades have been recorded and often a dedicated vacuum team will focus on this type of recovery work which becomes a very profitable part of the overall operation. Recovering material in confined stopes is another application of vacuums.
Vacuums do have certain key limitations, some of which we have already covered, but if these are understood then they can have a key part to play in a mines arsenal of technology to improve safety and productivity.