1. Title, Journal and Authors
Title: A simulation study with a new performance index for pressure-retarded osmosis processes hybridized with seawater reverse osmosis and membrane distillation
Authors: Sung Ho Chaea, Jangwon Seoa, Jihye Kimb, Young mi Kimc, Joon Ha kima,c,*
aSchool of Earth Scinces of Environmental Engineering, Gwangju institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea
bWater Research Center, K-Water Research Institute, Korea, 125, Yuseong-daero 1689beon-gil, Yuseong-gu, Daejeon, Republic of Korea
cAdvanced Green Chemical Materials Division, Center for Membranes, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeongro, Yuseong, Daejeon 34114, Republic of Korea
PRO was on the rise as an excellent alternative to conventional energy generation processes. Many researchers have studied PRO with a viewpoint of Power density (PD). Now, we faced two problems. First, PD value varied drastically depending on the process scale. Second, it was incompatible of energy units between subunit processes. Therefore, in this paper, a new dimensionless performance index of PRO performance was introduced.
In materials and methods parts, some dimensionless performance indexes of the subunit processes were introduced. Dimensionless number could adapt any system and process regardless of scale. Specific energy consumption (SEC) was introduced for RO and MD and specific energy recovery (SER) was introduced for MD. In addition, total water recovery rate (Tot) and dilutive factor (DF) were proposed.
In results and discussion parts, Nr/c that was a new dimensionless performance index of PRO was introduced. It was a ratio of the total energy recovered by PRO to the total energy consumed by SWRO and MD. Using it, various simulations were performed with two processes (SWRO-PRO-hybridized process and SWRO-MD-PRO-hybridized process). Then, following conclusions could be drawn.
1) In SWRO-PRO-hybridized process, when Rec increased, Nr/c decreased and increased around 0.5. So, we could infer RecRO that had 0.4~0.6 should have lower Nr/c.
2) A positive correlation was indicated between Tot and DF. At then, SWRO-MD-PRO-hybridized process was slightly higher than that of SWRO-PRO-hybridized process. And DF value varied with a membrane’s specification. Plus, in SWRO process, a higher permeate flow rate did not guarantee higher energy efficiency.
3) Because MD process was operated on the basis of distillation, heat source that was affected to economics played an important role when process operating. The lower heat source was, the higher Nr/c was. And, when heat source was higher, Nr/c of SWRO-MD-PRO-hybridized process was lower than Nr/c of SWRO-PRO-hybridized process. However, as RecRO was higher, Nr/c of SWRO-MD-PRO-hybridized process was higher than that of SWRO-PRO-hybridized process.
4) As all the indexes were considered, a conclusion was clarified that it was difficult to overcome the present energy limit of PRO-hybridized process. So, a new state-of the art membrane like aquaporin and graphene membrane was needed to improve it.
5) In SWRO stand-alone process, reduction of energy consumption which could be induced by enhancing membrane physical properties was already close to the limit. Therefore, some breakthroughs like PRO and reverse electrodialysis were suggested.
3. Application to research
Nr/c that was a new dimensionless performance index for PRO was first introduced in this paper. At now, we could adapt it coming research.
Dae Seong Jeong / Intern student
Environmental Systems Engineering Lab.
School of Earth Sciences & Environmental Engineering
Gwangju Institute of Science and Technology
1 Oryong-dong Buk-gu Gwangju, 500-712, Korea
Phone : +82-10-2003-7860
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