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

摘要

The general objective of study was to develop and extend multi-stage steam-jet-ejector vacuum systems with competitive technical-economic characteristics for Bulgarian refineries of vegetable oils. The energy efficiency of these systems was improved by solving the following main tasks: (i) systems analysis of these multistage 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 30o 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 sections of ejectors were specified. Linear correlations between the roughness recommended and the section diameter were derived as well. The results show that the highest smoothness in the range of Ra= 0.06÷0.12 μm should be required for the narrowest critical section of the nozzle. A family of four-stage vacuum systems with suction flow from 10 to 75 kg/h vapour-air mixture at a suction pressure 300 Pa was developed and commercialized. Twelve vacuum systems have manufactured and introduced successfully for deodorizing vegetable oils in Bulgarian enterprises.