Use of membranes for energy efficient concentration of dilute streams

In the chemical-process industries, dilute streams containing valuable ingredients are generated in several unit operations. Mechanical vapor-recompression is the best available technology for vaporization that may be used for concentrating such dilute solutions. Energy consumption for vaporization by compression and membrane technology is 350 and 90 kJ/kg, respectively. In order to save additional energy by recycling water, this study explored the use of membranes for processing a hot feed (70-80 degrees C) containing small amounts of food ingredients. Pilot tests report the effects of experimental parameters on membrane performance. The impact of pretreatment of the feed and membrane-cleaning procedures to maintain performance will also be discussed. Initial results indicate that the use of a membrane to preconcentrate, prior to the final concentration with mechanical vapor recompression, has the potential to save significant amounts of energy. Furthermore, the use of membranes would increase plant capacity by reducing the load on the vapor-compression unit. In this study, it was estimated that a plant processing 15 metric tonnes of feed every day and using membrane technology for concentrating to twice the concentraiton would save about 2 GJ of energy. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.