Improving the energy efficiency of traditional multi-stage steam-jet-ejector vacuum systems for deodorizing edible oils

Abstract

The energy efficiency of multi-stage steam-jet-ejector vacuum systems was improved by solving the following main tasks: (i) systems analysis of these multi-stage plants and (ii) a selection of eligible surface roughness of steam-jet- ejectors as a way for reducing their hydraulic losses and steam consumption. The systems analyse reveals that the consumption of motive steam and cooling water can be reduced when (i) the last stage of vacuum systems employs a water-ring vacuum pump instead of steam ejectors; (ii) four-stage vacuum systems are applied when cooling water with temperature above 30° is used; (iii) the first stage of vacuum system is without a condenser when the plant uses cooling water with temperature above 30°C; (iv) the values of intermediate pressures in the end of the first and the second stages are optimized by means of a minimization of the total consumption of motive steam and cooling water in these stages. An engineering approach was developed for determining the eligible surface roughness of ejectors depending on Re number and the diameter of actual section. This approach assures to be obtained a minimal linear friction factor in each section. On this basis the eligible values of roughness average Ra for seven representative sec- tions of ejectors were specified. A family of four-stage vacuum systems with suction flow from 10 to 75kg/h vapour- air mixture at a suction pressure 300Pa was developed and commercialized. Twelve vacuum systems have manufac- tured and introduced successfully for deodorizing vegetable oils in Bulgarian enterprises.