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There are many “Rules of Thumb” (ROT) and a few empirical equations that have been developed to estimate the airflow requirements for mines. Some are realistic and based on recent mechanised mines but many are unrealistic and based on older non-mechanised mines. All are based on past experience. There use is acceptable as long as they are taken exactly for what they are that is an idea of the magnitude of the result that will be achieved by calculation. Some time the results will be surprisingly close to a calculated result and many times it will be way off the mark.

Determination of the primary airflow requirement is the starting point for ventilation design. The design airflow needs to be known before the required number, and size of surface ventilation shafts can be estimated.

Design primary airflow requirements are almost always under-estimated, probably due to the use of ROT or some empirical equation, but also due to a failure to allow for increases in mine size, depth and complexity beyond initial estimates. Even then the cost of providing the necessary airflow under-goes “pruning” in an effort to keep project capital and operating costs to the minimum. Under-estimated (or reducing) primary airflow rates will adversely affect the project economics in the following ways:

Operating Costs: Power costs increase dramatically with airflow rate. If airflow rates need to be increased beyond initial estimates, there will be a substantial increase in operating costs, particularly if airways are inadequately sized:

3 Rate Flow Old Rate Flow New Increase Cost Power _      α

Capital Costs: An increase in airflow rate may require the purchase of new fans and excavation of new airways. The cost and just as importantly the disruption to mining in doing so are usually considerably greater than would be the case if the original airways sizes were based on realistic primary airflow estimates.

7.1.1 Determining Primary Air Quantities.

When estimating primary airflow requirements, we need ask ourselves why ventilation is being provided in the first place. In many cases, in mechanised mines the criterion for dilution of diesel exhaust emissions is the overriding factor. It is however also necessary to consider equally

relevant requirements such as control of thermal conditions and adequate dilution of dust and mine gasses.

Analysis of airflow requirements for individual work places is usually carried out when determining primary airflow requirements. Design airflow rates are often based on exceeding 0.04 to 0.06 m3_{/s of airflow per rated kW of diesel engine power in all active mining areas. This}

analysis can become quite complex for larger operations and requires a thorough understanding of the individual facets of the development and production process. The design airflow rate must include an allowance for leakage (both primary leakage and leakage in secondary ventilation ducts) and service areas such as ore passes, grizzlies, crushers, conveyor drives, fuel bays, pump stations, workshops etc.

The first process is to work with the designers and schedulers to allocate air quantities and with consideration to predicted heat loads, strata gas emissions, diesel exhaust emissions, legislation, OH&S and Industrial relations to allocate airflow requirements for;

Location Airflow required for

Scheduled production activity

Drilling, blasting, loading, filling. Equipment in use in each area _{Dimensions and layout of access and loading routes} Scheduled development activities _{Equipment in use in each area}

Dimensions and layout of access and loading routes Auxiliary ventilation system

Haulage routes _{Equipment in use in each area}

Dimensions and layout of access and loading routes Rock handling including:

Rock breaking Crushing, Loading station, Hoisting

Equipment in use in each area Dust dilution/collection/removal Operator protection

Servicing areas including:

Maintenance workshops, Electrical sub- stations, Pumping stations, General maintenance and construction work areas, Refrigeration plants

Equipment in use in each area

Dust & fume dilution/collection/removal Fire protection

Operator protection Storage and supply areas:

Explosive, Diesel fuel, General consumables and stores

Equipment in use in each area Dust & fume dilution/collection/removal Fire protection

Operator protection Lunch rooms and waiting areas _Airflow

Temperature

Obviously not all of the above locations/activities will apply to all mining operations. Circuit design is ultimately determined by the production schedule.

The siting of dedicated ventilation airways will be determined by mining methods and production design layouts. The determination of total mine airflow is only the first step toward a mine ventilation system and requires the most attention because it is at this point that the final and cost to the operation will be determined.

Ventilation planning and design is complicated and those who are responsible for ventilation and believe otherwise have the potential to cost their organisation a great deal of money.

Example

Lets consider a new narrow vein mine with an optimum production rate of 300,000 tonnes per year. It has been decided that predominately one pass ventilation will be required. Ore will be loaded from the stope to an orepass from where it will be trucked in the main decline out of the

BASIC MINE VENTILATION MANAGEMENT

mine. Backfill will delivered to the stope void using a 10 tonne truck. Assume a “ROT” for narrow vein mechanised mine to be 0.5 m3_{/s per 1000 tonne. (0.5 x 300 = 150 m}3_/s)

The production and development schedule has been evaluated and the active locations during each month have been determined. In this case an active location is taken as any development face, raise bore location, production drilling location, production bogging location or stope filling location. The number of active locations during any one-month is then summed. For this example assume the results shown graphically below.

Active Locations 0 20 40 60 80 100 120 140 160 0 6 12 18 24 30 36 42 48 54 60 Month Nu m b er

Development Raisebore Mining Backfill

After consideration to diesel exhaust emissions, dust and heat etc. the air quantities for each activity have been determined as:

Activity Airflow (m3_/s) Decline development 80 In ore Development 12 Production 5 Raiseboring 5 Backfill 8

This airflow was then allocated to the respective activity and summed for each month.

This particular schedule will require primary airflow ranging from 80 m3_{/s during initial}

development peaking at 227 m3_{/s during the start up of production then tapering off to less than}

Airflow Requirements 0 50 100 150 200 250 6 12 18 24 30 36 42 48 54 60 Month Qu a n ti ty (m 3 /s )

Development Raiseboring Mining Backfill Initial Development

Production

Start up Production _{Production Taper}

191 m3_/s

157 m3_/s

There are four distinct periods that require some comment.

1. Initial development (month 1 to 12) to establish the access decline and the exhaust ventilation shaft will be ventilated with secondary fans and will not form part of the primary ventilation requirements.

2. Production Start-up (month 13 to 18). The peak airflow during this period is 227 m3_{/s. This}

peak at the end of initial access development and the commencement of production is common. This occurs because of the flurry of activities necessary to bring the mine into full production in as short a time as possible.

The difficulty of this period is the cost for providing extra air when it is not required over the longer term. Most designers opt to bypass this period and attempt to manage their way through it. (Not a good time to be the ventilation officer). The alternative is to purchase and install primary fans with some form of control that will enable the airflow requirements to be “turned down” after production settles down.

3. Main production period (month 19 to 46). In a new mine there will be ‘teething problems’ and the production and development schedules will undergo constant updating before eventually settling down. With input from the ventilation engineer the airflow peaks and troughs will be smoothed settling somewhere around the median of 160 m3_{/s. (Always}

round UP its hard enough to get so don’t give it away).

4. End of the life of the project (month 47 onwards). A detailed mining schedule is only valid until the next update. Any schedule beyond three years should be viewed with some scepticism. Because of increasing geological information, changing economics etc most mine schedules beyond year three do not have the same confidence level contained in the three-year plan. Because of the very nature of mining there will be an end and the tapering off period will vary from mine to mine, and year to year.