AUSTRALIA’S mining industry adds about $60b to the country’s GDP. It is an important industry, both in terms of export revenue as well as OH&S issues.
More than most industrial activities, mining is constantly under close scrutiny from all angles over occupational health and safety matters. Although Australia is arguably a world leader in workplace safety for the mining industry, the sheer scale of the industry and its activities have its inherent dangers.
Mine ventilation is one such area, which calls for a number of significant work practices and technologies to be well developed so as to assure the safety of all mining employees.
Eximo, which supplies ducting technologies that often form an integral part of an overall ventilation and/or filtration system for mine ventilation, has worked closely with its technical partners to make sure such installations and identified key objectives are implemented.
General Manager at Eximo, Melissa Phelps, says that when designing a mine auxiliary ventilation system, 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.
Phelps says the quantity of air required, physical restraints present, and other factors must all be considered, and taken into account. She claims 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 horsepower 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 1000 m.), such as drill and shoot operations, and single use applications.
Fibreglass, the most durable of suction ducting materials, is flame resistant, holds up well to abuse, is light-weight, gives high positive and negative pressure, has a low friction factor, and is best suited for: Short-length ventilation runs (less than 500 m.), multiple reuse operations, drill and shoot operations, and mine development. Phelps says 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. She says 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 airflow on OSHA jobs.
Phelps claims 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”, according to Ms Phelps.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.
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