Opportunities of improvement of the MED seawater desalination process by pretreatments allowing high-temperature operation

Abstract

In this work, the effect of increasing the top brine temperature (TBT) in a multi-effect distillation (MED) process and its influence on the main design and operational parameters, as gain output ratio (GOR) and specific heat transfer area is investigated. To that end, a detailed and advanced steady-state mathematical model for MED process with forward feed arrangement is developed and validated against data found in the literature. First, a comprehensive sensitivity analysis including key design parameters is carried out. The model is then used to simulate three different heating steam temperatures of 70°C, 100°C and 120°C with a variable number of effects between 9 and 34 and mean temperature difference between effects within 2°C‒4°C. Results showed that, given a mean temperature difference between effects, the simultaneous increase in the number of effects and heating steam temperature leads to a significant improvement of the GOR, and a reduction of the specific heat transfer area. Particularly, for a mean difference of temperature between effects of 2.5°C, if the heating steam temperature is increased from 70°C to 120°C, the GOR is improved about 70%, the specific heat transfer area is reduced a 11% and the specific thermal energy consumption a 45%. This analysis provides meaningful results for the preliminary design of MED plants with high-temperature operation.