Moving the Crushing Process Underground

Moving the Crushing Process Underground

We found this interesting article presented by Darcy Flath, Technical Support Engineer, Metso Mineral Industries highlighting the careful planning required to make underground crushing a viable option.

“Underground Primary Crusher Plat Design”

Underground mining requires careful planning as the processes and challenges are very different from open pit mining. Underground mining obviously also has additional safety and maintenance issues. Excavating for and assembling a primary crushing plant underground is complicated and costly.

The planning process requires careful consideration of the following steps:

1. Capacity

The required capacity determines the type of equipment required and also the number of parallel crushers needed to fulfil the production rate. Today’s simulation software is able to easily and effectively calculate the specific requirements that the mine site will need. Capacity is also determined by the feed size and material type introduced to the plant, as well as the required product curve.

2. Machinery

Jaw crushers are the most common solution in underground applications. However, any throughput above 1000 tph is often better suited to gyratory crushers. The crusher settings are adjusted to achieve the required particle size for adequate transportation. Underground mining methods mostly produce a feed that is finer than in a typical open pit mine, resulting in higher capacity through the plant.

3. Scalping

Scalping is usually recommended before a jaw crusher – gyratory crushers can handle excavated ore. Primary gyratory crushers are not as sensitive to fines. They are large, steep and have a relatively short stroke compared to settings that allow fines to flow more easily. Scalping is primarily recommended for a jaw crusher as the energy consumption is lower. Similarly, a jaw crusher usually wears more manganese steel per crushed ton than a gyratory crusher. Feeding fines into the crusher may increase peak stress loads due to packing. The most compact way to scalp is with a vibrating grizzly feeder. Using a separate feeder and a scalper allows both components to be optimised for improved process control and performance.

 

Further to this, adequate planning for future capacity requirements is very important. What the mine is producing now may be very different from what it is required to produce in five or ten years’ time, so the initial planning phase needs to allow for these anticipated changes.

In order to achieve high process reliability and availability, it is important to consider future maintenance needs. Routine maintenance includes lifting wear and spare parts. For large crushers, lifting devices are required. Automation and centralised lubrication are cost-effective ways to improve maintenance processes. Underground plants are mostly operated with automated devices so diagnostic systems need to be properly located during the planning and design of the mine site.

And as always, safety considerations need to be factored in at all times. Preventing people and objects from falling through the crusher is a crucial planning factor. There is often limited time allocated for routine maintenance procedures. Typical issues include not using the proper lifting devices which can have severe consequences. Dust suppression on the feed side of a primary plant is always a challenge, so the correct water mist, suction and filtering solutions need to be installed at all critical points. Fire suppression and fire safety procedures should be given careful consideration, particularly in underground mining activities as evacuation procedures are very different from open pit mines.

Main image courtesy of Mining Australia