Desalination using low grade heat in the process industry: Challenges and perspectives

This paper examines the use of low grade heat from process industries for thermal desalination processes as this is relevant not only to current energy conservation schemes but also may play a role in increasing the capacity to Satisfy future water demands. The study focuses on low grade heat sources from a paper mill located on a British coastal area which presents a large quantity of recoverable waste heat at low temperature (< 100 degrees C). Two scenarios are considered: (i) low grade heat is used directly to feed the desalination process, (ii) low grade heat is upgraded using a heat pump coupled with a desalination system. In the first scenario, a Humidification Dehumidification process was identified as a suitable technology due to its low operating temperature. In the second scenario, the low grade heat temperature was upgraded using a hybrid absorption heat pump and subsequently used to feed a Multiple Effect Distillation desalination system. These two cases were compared in terms of performances and economics. For both cases, a payback period of less than 10 years could be obtained for water price equal to 2 per tonnes of water. This is comparable to the price of home water supply. Environmental aspects were also discussed from the results of a full Lifecycle assessment. Low grade heat utilisation in both cases reduced the Global Warming Potential in comparison with fossil fuel powered systems, but toxicological impacts appeared higher in comparison to a system using natural gas. (c) 2012 Elsevier Ltd. All rights reserved.