Most Pyro-metallurgical processes and certainly all furnaces in the Ferro-Alloy industry use water-cooled components in one form or another. These range from simple steel components used in the roofs and gas ducts to sophisticated copper components in the sidewalls of PGM smelters.
All these systems have one principle in common in that they are all cooled by water and the energy that the water collects from them needs to be dissipated in some way.
Usually this is in the form of a heat exchange cooler, either fin-fan (air cooled) or evaporative type, which transfers the energy from the water to the atmosphere, cooling it down for recycle to the furnace components.
Besides the obvious waste of energy to the atmosphere, additional considerations extend to the energy required to drive the components (pumps and fans) to actually remove the waste energy from the water, as well as the loss of water in systems using evaporative cooling techniques.
Cooling water systems normally contain very large amounts of thermal energy but at relatively low temperatures. This is because of the limitations of water itself, with surface boiling experienced at temperatures as low as 65°C inside the water-cooled components.
As an alternative to this traditional way of cooling, Vuselela proposes the use of thermal oil for cooling since it does not have the surface boiling restrictions and then using this thermal oil source as feed to an ORC plant. The use of thermal oil for cooling is not a new concept, but its application in the Ferro-Alloy industry is unique.
Besides saving water and the energy previously required to drive cooling equipment, investigations are currently underway to establish the temperature tolerance of components cooled with thermal oil.
If the temperatures of the oil can be increased sufficiently without damage to the cooled components, high efficiencies can be expected from the ORC systems connected to the thermal loop. Alternatively, and depending on the results of Vuselela’s investigations, these may be used as preheating streams to the ORC if the temperatures cannot be increased.