An investigation into the efficiency of systems for circulating refrigerant through evaporators in the ice-making plant at the ERPM Gold Mine.
Date
2012-01-30
Authors
Katzeff, Steven.
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Abstract
Although comparisons of relative energy efficiency and cost effectiveness for
small gas and mechanically pumped liquid overfeed refrigeration systems
(arrangements) have been performed, no such comparison has been reported for
large batch type ice-making systems. The ice-making plant at the Far East Vertical
Shaft, East Rand Proprietary Mines (ERPM) Ltd, South Africa, which produced
ice in a batch-type process for cooling its underground workings, utilizes cold
flash gas to pump liquid refrigerant to and through its ice-building evaporators.
Each of this plant’s three operating units manufactured up to 1000 tons of ice per
day to adequately cool this gold mine’s underground workings. For one unit of
this plant, this investigation models the functioning of the existing ‘cold gas’
pumping arrangement, supported by test data. It then investigates, through similar
modelling, a more conventional ‘hot gas’ pumping arrangement, and two possible
mechanically pumped arrangements for this unit, functioning under similar
conditions. The models provide a thermodynamically meaningful comparison of
the different liquid overfeed refrigerant pumping arrangements, principally in
terms of their energy efficiency and electrical cost effectiveness. They predict that
under similar operating conditions, the current cold gas pumping arrangement is
more energy efficient and electrically cost effective than both hot gas and
conventionally mechanically pumped arrangements. This agrees with the
suggestions and conclusions of previous investigations performed on smaller
refrigeration systems. However, compared to a theoretical fully mechanically
pumped arrangement, the existing cold gas pumped system is predicted to incur
larger unproductive refrigeration demand and higher annual electrical operating
cost.