Abstract:
As a result of the rising electrical energy costs in South Africa, a
method was sought to reduce the overall electrical consumption of
typical shaft systems. A typical shaft configuration was analysed and
the primary energy consumers were identified. The ventilation fans
for this system were found to consume 15% of the total energy of the
shaft system. It was calculated that more than 50% of this energy is
consumed by the shaft itself, more specifically, by the pressure losses
that occur in the shaft as the ventilation air passes through it. In
order to ensure that the theory being used for the evaluation of these
shaft systems is accurate, a total of five shafts were instrumented
and the actual pressure losses over the shafts plotted against time.
These shafts were then analysed from a theoretical perspective.
Finally, in order to ensure a thorough understanding of the behaviour
of the ventilation air in shaft systems, the systems were simulated
using computational fluid dynamics (CFD) techniques. There were
significant discrepancies between the theoretical analysis and the
CFD simulation during the initial comparisons. This discrepancy
lessened as the complexity of the CFD models increased, until when
the complete shaft was modelled using the full bunton sets, the pipes,
and the flanges, the difference between the theoretical evaluation and
the CFD simulation was small. This result demonstrates that the
theory is insufficient and that the interrelated effect of the buntons
and fittings has not been fully appreciated by current theory. The
final phase of the work presented here was to evaluate the costeffectiveness
of using different bunton shapes and shaft configurations.
It is shown that the increase in the pressure losses and
therefore the direct operating costs of the shaft can vary by as much
as 80%, depending on the bunton configuration chosen. The
placement of the piping in the shaft can increase the pressure losses,
and therefore the direct operating costs of the shaft, by as much as
12%, depending on the placement of the piping in the shaft; this
effect includes the use of flanges. The use of fairings on a large cage
can reduce the resistance that the cage offers to the ventilation flow
by as much as 30%. This, however, does not translate into a direct
saving because as the cage moves through the shaft, the overall
effect is transitory. These savings can be significant when the items
highlighted in this work are applied correctly.
