Controlled recirculation of mine ventilation air: its effect on blast contaminant dissipation
Date
2014-09-12
Authors
Alexander, Nicholas Anthony
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Abstract
A series of tests was undertaken on a recirculation scheme in a deep
level gold mine to establish the effect of controlled recirculation of
the mine ventilation air on blast contaminant dissipation.
Clarification was needed as to whether the existing re-entry interval
of three hours would have to be extended with the introduction of
controlled recirculation. The re-entry interval is a time interval,
after blasting, stipulated by the Inspector of Mines during which the
workings are being cleared of blast contaminants and during which time
no persons are permitted tc enter the workings.
The fresh and recirculated air flow rates were varied and their effects
on blast contaminant dissipation measured. Gas concentrations of the
oxides of nitrogen (N0X ) and carbon monoxide were monitored
continuously in the return air. Dust levels were monitored in the
return air from two hours before the blast to four hours after the
blast.
Two gas models (mixed-volume and plug-flow) and residence time analysis
were used to analyse the data.
In all the tests, the critical blast contaminant for determining the
re-entry interval was found to be NO*. In addition, the following
parameters affected the re-entry interval; the amount of explosives
ignited daily, the volume of the workings into which the NO* is
dissipated by the ventilating air, the time taken for air to complete
one circuit (the cycle time), leakage and short circuiting of air, and
the fresh air flow rate. The recirculated air flow rate was found to
have negligible effect on the re-entry interval.