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The flow control valve maintain a constant flow through the stope
cooling car, irrespective of the demand for service water from the
stope, providing that the system upstream pressure do not vary more
than 20% from the designated set-point.
High water demand from the stope causes low downstream pressure
conditions, resulting in the opening of the flow control valve to a
position which maintains a constant flow across the stope cooling
car.
Low water demand from the stope causes high downstream pressure
conditions, resulting in the closing of the flow control valve to a
position which maintains a constant flow across the stope cooling
car.
The bleed control valve maintain a constant flow through the
stope cooling car when the water demand from the stope is lower than
the designated flow rate of the stope cooling car, providing that
the system upstream pressure do not vary more than 20% from the
designated set-point.
High water demand from the stope causes low downstream pressure
conditions, resulting in the closing of the bleed control valve.
Low water demand (below the stope cooling car flow rate) from the
stope causes high downstream pressure conditions, resulting in the
opening of the bleed control valve to a position which maintains a
constant flow across the stope cooling car.
The N.G.D’s flow control system allows the utilization of the
cooling water as stope service water for approximately 11 hours a
day.
The pumping power saving for one 8.0 lit/sec cooling car, in a
1400 meters deep shaft, with a conventional pumping system (80% pump
efficiency, 90% motor efficiency, 95% power factor and 5% column
friction losses), is R7,963 per month @ R0.14/kWh.
The refrigeration power saving for one 8.0 lit/sec cooling car,
with a conventional refrigeration surface plant (C.O.P =7, dT =
25OC), is R5,518 per month @ R0.14/kWh.
Preventing low flow through the cooling car as a result of low
system pressure and the maintaining of a sufficient cooling to the
stope provides tolerable working conditions in the stope and
improves stope’s productivity. This benefit should be added to the
overall savings.
Preventing high flow through the cooling car as a result of high
system pressure, results in a major water saving. The pumping power
and refrigeration power saving for 1.0 lit/sec is R3,677 per month @
R0.14/kWr.
The reduction of the overall chilled water consumption, results
in the reduction of the required water treatment in the shaft and
should be added to the overall savings.
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