Use of membranes for energy efficient concentration of dilute streams

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