Low-grade waste heat holds promise for desalination

Low-grade, waste heat produced by industry may be applicable to distillation desalination to make fresh water where revere osmosis is not suitable according to findings by the University of Western Australia (UWA).

The study found that by supplementing distillation-desalination with multi-stage flashing increased the overall efficiency of existing multi-effect distillation by 40-50%.
UWA School of Mechanical and Chemical Engineering’s Professor Hui Tong Chua said the technology was designed to maximize the low-grade – below 100ºC – heat which is often considered to be waste.

Hui said the process was suitable for use with wastewater that was unsuitable for reverse osmosis: “For rejected process streams from refineries, and for high-saline, off pH, and/or high-silica content groundwater, the technology is most suitable” he said. “The technology is best suited to refineries, such as alumina refineries, where the conservation of steam is of paramount concern, and where the process fluid cannot use reverse osmosis technology,” he says.

The flash-boosted multi-effect distillation (MED) require more energy than reverse osmosis for pumping and averages a 22-34% energy penalty. “The new technology is essentially comparable to optimised MED, to within one per cent,” said Hui.

The system was scalable and had the potential for industry-wide adoption to produce or recover fresh water from process effluent according to Hui. “The same technology can also be coupled with renewable energy, such as biomass, to provide a stable supply of water to remote communities,” he added.