More than a breath of fresh air

Paul Boughton

Mine ventilation design, including fan installations, is a major element in mines. Maurice Jones reports.

Well designed mine ventilation will, of course, be adequate to pass necessary fresh airflow to all working areas of the mine sufficient to supply oxygen to miners, to remove noxious gases (whether naturally occurring or produced by machinery), and to remove heat from the ground, machinery and electrical apparatus sufficient to allow an acceptable ambient working temperature.

In addition to these basic requirements there should be provision, such as at least one extra fan, to produce at least enough ventilation to allow the evacuation of all miners safely in the case of the main fan breakdown or similar emergency. For the same reason the fan controls must allow adjustment of the air-flow, including perhaps reversal, to avoid aggravating situations such as fires.

Mains fans may be of axial or centrifugal design concept; the first providing principally large volumes of air, and the second providing the pressure to overcome network resistance as well as large air flows. Axial fan blades may be adjustable to accommodate changes in load as mining develops. With centrifugal fans performance can be modified with inlet vane controls, inlet dampers or speed controls. Fans usually operate in the exhausting mode, handling stale and contaminated air from the mine, but sometimes forced ventilation is used in conjunction with cooling systems or for directing flows in secondary ventilation.

In addition to the fans themselves, a main ventilation installation will include a duct system to connect the fans with a working shaft, decline or dedicated ventilation shaft. This will feature the lowest practical resistance to airflow, not only to permit maximum airflow, but also to minimise energy costs – a big factor in efficient ventilation. Long-life mines may have these ducts as concrete structures, but many modern mines, with comparatively sort planned life, ducts are prefabricated in steel. This may remove a requirement for custom design, and speed up installation.

Over the life of a mine it is likely that workings and access drives will extend in length, increasing the resistance to ventilation. Periodically the ventilation system has to be renewed. This may involve uprating the existing fan installation or adding a remote ventilation shaft, with or without a fan there. Underground booster fans may also be added to overcome resistance in particular sectors of the mine.

A mine ventilation system design, including main fan installations, is a major element in engineering the mine. It may be a task handled by the engineers of the owner or operator of the mine or, increasingly, by specialist ventilation consulting engineers. The optimise of the design computational fluid dynamics (CFD) may be employed to analyse local airflow movements with the aim of removing otherwise undetected major eddies and other factors depressing overall efficiency.

The main mine ventilation may also be installed in conjunction with cooling systems of different types necessitated by particularly hot mines, usually caused by depth of working as in several mines in South Africa and others such as Kidd Creek in Canada. As well as designing and consulting on mine ventilation design, including main fan installations, the Snowden Group, including BBE Bluhm Burton Engineering of South Africa, couples the work with ventilation cooling systems when required. However this is subject for another issue.

Major manufacturers of main mine fans include Fläkt Woods, Howden, TLT-Babcock (Turboluft Technik group)  and Zitron. Recent years have seen several acquisitions and mergers between leading firms who now work or are represented worldwide.

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