Improving cooling system efficiency with pre-cooling

Mine production water is cooled on the surface by pre-cooling towers before entering the refrigeration process. Poor water quality and broken draft fans reduce the cooling efficiency and utilisation of a pre-cooling tower. The pre-cooling towers and refrigeration plant operate at full load during the summer months to deliver the required cooling. During the winter months, the bulk air coolers are stopped and extra refrigeration capacity becomes available. For this reason maintenance on the pre-cooling tower is scheduled during the winter months. A case study was done on a mine refrigeration system where the water quality was poor. Dissolved salts form crystals on the heat exchanger´s film surface when the temperature of the solution is reduced. Solid particles suspended in the water compounded the situation by further clogging the fill of the pre-cooling tower. The cooling capacity of the pre-cooling tower was greater than required and could be replaced by a lower maintenance fill. The increase in utilisation is at a cost of efficiency. Each of the eight cell´s large fan was replaced by four high-speed direct drive fans with an improved efficiency and better utilisation factor. The overall system efficiency increased and resulted in an average power saving of 1.00 MW over a 24 hour day on average on the mine refrigeration system. The system maintained the same level of service to the mine production process.