News
| Mine ventilation demands serious analysis | 12-02-07 |
We often receive correspondence from the mining industry and related companies. Mining can be dangerous at the best of times, but it is comforting to know that in Australia we have workplace standards that rank among the best in this global industry.
Out technical partners and wholesalers work closely with the supply chain for mining. All the way along the mining supply chain people are constantly asking questions on various areas of mine ventilation and assisting with specifying to gain the optimum result.
So, to help shed a little light on many mysteries, we can help with the following advice.
The basic objectives are: the sufficient provision of clean air for individuals and equipment, and adequate ventilation for the removal, or dilution of hazardous gasses or dust.
The quantity of air required, physical restraints present, and other factors must all be considered, and taken into account.
Air Quantity must be considered in terms of both velocity and volume: the air velocity in the entry or tunnel; and the volume of air required for workers, the operation of diesel equipment, the dilution or removal of gasses and dust, cooling, and, or other needs.
There are also physical constraints which demand consideration. These include: head room over haulage, or material transport equipment; length of duct, and associated handling and hanging problems; potential for damage from blasting, and other activities; the correct sizing of duct and fans to ensure that the fans are not working in a stall, i.e. attempting to move a volume of air greater than the duct’s capacity. A larger duct allows for a more efficient and lower horse-power system.
Other considerations include: the legal and contractual requirements for fans and duct, the preferred directional airflow: suction, or blowing; the acceptable levels of leakage for the determination of duct lengths; with most leakage occurring at the joints, longer lengths have significantly less leakage.
When evaluating the different types of duct available, there are four broad categories to consider: steel, fibreglass, flexible suction, and lay-flat.
For suction ducting, steel requires the lowest initial investment, it is non-flammable, holds high positive and negative pressure, allows medium leakage, is low friction, and is best suited for: moderate length ventilation runs (less than 3,000 ft.), such as drill and shoot operations, and single use applications.
Fibreglass, the most durable of suction ducting, is flame resistant, holds up well to abuse, is light-weight, holds high positive and negative pressure, has a low friction factor, and is best suited for: Short-length ventilation runs (less than 1,500 ft.), multiple reuse operations, drill and shoot operations, and mine development.
While flexible suction has the distinct advantage of being both expandable and contractible in length so it can be stored in small areas, its weight is dependent on the negative pressure rating.
It is also flame-resistant and best suited for starter tunnels, short ventilation runs, and flexible connections with other types of duct.
Lay-flat, also of a low initial investment, has a pressure rating dependent on material and construction, has a medium friction factor and low leakage in long lengths, but requires an additional fan for reversing air flow on OSHA jobs.
This technology requires special expertise in applications for booster fans. It is flame resistant, available in many grades, and is best suited for short ventilation runs using low cost duct, long ventilation runs using high-quality long-length ducts, and TBM tunnels.
When calculating ducting air pressure losses, losses can be categorised as either dynamic or friction induced.
With dynamic losses, the pressure loss in each fitting, inlet and outlet must be calculated separately and is based on the velocity pressure of air at that point in the system, while with friction losses, friction loss curves and formula are used to give the pressure loss due to friction in the duct.