Climate change is a major global concern with the urgent need to reduce greenhouse gas emissions and stop global warming. Unfortunately, it is difficult for the developed countries, which are the key environmental pollutants, to shift from their current industrial structures to environmentally friendly ones. To this note, development of alternative solutions to reduce the greenhouse gas emissions have recently attracted significant attention of researchers who have identified pressure retarded osmosis (PRO) as a promising energy generation method.
Generally, PRO generates energy by mixing a lower and higher concentration solution and thus does not give off carbon compounds. In the field of PRO, three categories including thermodynamics, process hybridization, and new membrane modules are generally interconnected and linked to power density, that determines the performance index as well as the quality of the generators. However, large-scale PRO membranes still exhibit low power density so that have low productivity unsuitable for the desired applicants. Other than the issue regarding the large-scale PRO modules, PRO process has another big problem about the incompatibility of the energy units between the subunit processes within a PRO-hybridized process. In spite of the equivalent significance of both aforementioned problems, it has been difficult to simultaneously address the large scale and hybridization problem.
Recently, scientists at Gwangju Institute of Science and Technology: Mr. Sung Ho Chae, Dr. Jangwon Seo and Professor Joon Ha Kim in collaboration with Jihye Kim at K-water Research Centre and Young Mi Kim at Korea Research Institute of Chemical Technology developed a new performance index for the PRO-hybridized process. They assessed the performance of two PRO-hybridized processes, that is, one hybridized only with seawater reverse osmosis and the other hybridized with both seawater reverse osmosis and membrane distillation. Eventually, simulations were performed under various conditions to estimate the performance of the PRO-hybridized processes after which they were compared to each other. The work was published in the journal, Desalination.
The authors observed that the PRO-hybridized process combined with seawater reverse osmosis and membrane distillation exhibited higher energy efficiency as compared to the one combined with seawater reverse osmosis. On the other hand, simulation results at different conditions showed different energy efficiencies for the hybridized processes. For example, the total water recovery in PRO-hybridized processes showed a tendency to have a relationship proportional to the dilutive factor of PRO. In definition, the dilutive factor is considered the degree of the water flow rate in PRO. Thus, the increase of the total water recovery essentially results in the higher water flow rate of PRO. However, in PRO-hybridized processes, a higher water flow rate did not guarantee higher energy efficiency rates as witnessed in the stand-alone PRO process. Such a difference implies that the energy optimization for the PRO-hybridized processes should be applied differently from that for the stand-alone PRO and even from those for seawater reverse osmosis and membrane distillation.
The current study of Professor Joon Ha Kim and his colleagues is the first to successfully investigate the dimensionless performance index for PRO processes hybridized with membrane distillation and seawater reverse osmosis. Therefore, this work is expected to provide the necessary fundamentals to PRO-hybridized processes as well as the future research works.
Chae, S., Seo, J., Kim, J., Kim, Y., & Kim, J. (2018). A simulation study with a new performance index for pressure-retarded osmosis processes hybridized with seawater reverse osmosis and membrane distillation. Desalination, 444, 118-128.Go To Desalination