Multi-effect distillation and adsorption cycle (MED-AD)
Global demand for water is ever on the rise due to the surge in population and industrialization. This vital resource is becoming significantly scarce with the bulk of it being held in salty oceans that render it unsuitable for domestic, industrial, and agricultural purposes. Current research on seawater desalination has improved technologies and been implemented in the industry to produce freshwater from seawater. The main challenge that limits broader applications of seawater desalination is its intensive energy use. At present, various aspects of research have been conducted to overcome this challenge. So far, such endeavors have helped establish hybridization of desalination processes, as one of the most promising technologies to overcome the current limitations of desalination technologies while maximizing the advantages of individual processes in practice. Further, innovative industrial processes such as seawater reverse osmosis, multi-stage flash, and multi effect distillation (MED) have been proposed, in the spirit of improving existing technologies by increasing energy efficiencies, advancing pretreatments/membrane cleaning, and developing the hybrid desalination processes. Remarkably, the multi-effect distillation and adsorption hybrid cycle, MED-AD, a hybrid system between an MED with a thermally driven energy efficient technology, has recently yielded promising results.
The fundamental framework of the MED-AD hybrid System has yet to be affirmed despite having the improved system performance confirmed experimentally in published literatures. To address this, researchers from the King Abdullah University of Science & Technology in Saudi Arabia: PI-Professor Kim Choon Ng together with Professor Muhammad Wakil Shahzad at the Northumbria University in the United Kingdom investigated the MED and adsorption desalination (AD), with the objective to maximize the utilization of energy input in desalination. Their focus was also to develop a thermodynamic framework so as to explain the synergetic impacts observed in the previous studies on the MED-AD hybrid system. Their work is currently published in the research journal, Desalination.
In their approach, two different thermal desalination technologies were integrated. The researchers utilized energies of both thermal and flash evaporation in all operation conditions. Further, individual effects were inventoried to analyze the thermodynamic synergy of hybridization. In the sole MED operations, the energy input in the first effect was carried over to the following effects, and part of it was used for thermal evaporation.
The authors reported that both the water production and the universal performance ratio were improved 2–5 times in different quality of the heat source (40–60 °C) to the MED. Moreover, the researchers reported that the MED-AD hybrid process enabled scavenge energy from the ambient temperature below 30 °C for the desalination.
In summary, the study demonstrated a synergetic model, for analyzing the energy distributions in consecutive stages of a MED-AD hybrid system. The study reported improvements attributable to the extended range of operating temperature and additional flash evaporation accrued in the preceding MED stages, demonstrating the excellent thermodynamic synergy to even below the ambient temperatures in the last few stages; a kudos to hybrid integration of heat and mass transfer processes. In a statement to Advances in Engineering, Professor Muhammad Shahzad, corresponding author highlighted that the reported symbiotic integration of MED and AD cycles has great potential for utilizing low-temperature energy sources, such as the solar or geothermal thermal sources, and it will pave the way for sustainable seawater desalination of the future.
Hyuk Soo Son, Muhammad Wakil Shahzad, Noreddine Ghaffour, Kim Choon Ng. Pilot studies on synergetic impacts of energy utilization in hybrid desalination system: Multi-effect distillation and adsorption cycle (MED-AD). Desalination, volume 477 (2020) 114266.