Comparative study of throttling and variable speed drive operation of parallel pumps for cooling stations in sugar production

Cooling systems contribute to reduce water consumption in sugar production by recycling vapour condensate using refrigerant pumps. These setups operate at nearly continuous duty over several months, with high demand for electrical energy. In this paper, we compare the energy performance of parallel operated centrifugal refrigerant pumps with two flow control schemes, namely adjustable speed operation and throttle valve control. Both systems are modeled to represent typical cooling stations used in sugar mills. The variable speed driven pumps are shown to have significantly lower energy consumption over a wide range of flow rate commands. A lifecycle cost analysis of the two schemes also shows that the additional investment in the variable speed control method is offset after the first year of operation. Moreover, it has a much lower lifecycle cost, compared to the valve throttling system.