A novel sensible heat driven desalination technology

[Truncated] Sensible waste heat sources and hot liquids generated from renewable energies are a promising sustainable energy source for desalination processes. Constrained by their inherent design, conventional thermal desalination technologies fail to access the full potential of these lowgrade heat sources.

This thesis presents a novel desalination technology capable to expand the economically viable range of thermal desalination to low-grade heat sources in the range of 65 – 100ºC.

Part I of the thesis follows the evolution of this scheme, labeled Boosted MED. Starting from a thermodynamic process analysis, the limitations of conventional MED layouts are identified and it is demonstrated that conventional performance measures are incongruent with sensible (waste) heat sources. The Waste Heat Performance Ratio is posited as a new benchmark.

Based on a thermodynamic steady state simulation an optimisation model is developed and used for the system design and evaluation. The model is validated against both published data of market available systems and the pilot plant performance, showing a very good accuracy within a 5% band. Heat transfer coefficient and auxiliary power consumptions modules are developed for a comprehensive process assessment.

A benchmark of the Boosted MED design against conventional parallel feed MED layouts, with and without feed pre-heating, shows a superior performance of the Boosted MED layout for most operational conditions germane to sensible heat sources, with up to 35% and more additional freshwater yield compared to optimal conventional MED configuration with only moderate impact on the heat exchanger surface area and auxiliary power consumption.

An experimentally evaluation of the principle design basis of the novel system is undertaken based on a 2.5m³/day pilot plant that is developed by the author. Tested at heating medium temperatures from 68ºC to 93ºC, cooling water temperatures from 20ºC to 35ºC and feedwater qualities of 400 mg/L and 22000 mg/L TDS, additional vapour production rates ranging from 33% to 57% at sufficiently high temperatures prove the general viability of the design concept. The stable performance and very high distillate quality demonstrate the favourable characteristics of the system.