Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage
The global issues of water scarcity and climate change are driving the utilities sector, primarily water and electricity, to transit toward more sustainable sources. Water supply increasingly relies on energy-intensive desalination in recent years, hence renewable energy is suggested to be used as i...
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| Other Authors: | |
| Format: | Thesis-Doctor of Philosophy |
| Language: | English |
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Nanyang Technological University
2025
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| Online Access: | https://hdl.handle.net/10356/182848 |
| _version_ | 1826111517716643840 |
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| author | Li, Dan |
| author2 | She Qianhong |
| author_facet | She Qianhong Li, Dan |
| author_sort | Li, Dan |
| collection | NTU |
| description | The global issues of water scarcity and climate change are driving the utilities sector, primarily water and electricity, to transit toward more sustainable sources. Water supply increasingly relies on energy-intensive desalination in recent years, hence renewable energy is suggested to be used as its power origin under the decarbonization framework. However, the intermittent availability of most renewables (e.g., solar energy and wind energy) escalates the gap between supply and demand in not only electricity but also water sectors. To address this issue, osmotic energy becomes a promising choice as it can be stored easily by depositing two solutions with salinity gradient in separate containers and converted into electricity when needed by pressure-retarded osmosis (PRO). However, the low capacity and efficiency of conventional single-stage PRO (SSPRO) processes deteriorate its practical feasibility.
First of all, two novel PRO configurations and operating modes, atmospheric batch PRO (ABPRO) and semi-closed PRO (SCPRO), are designed to improve the energy production performance of PRO. Both ABPRO and SCPRO can realize 100% energy production efficiency (EPE) ideally facilitated by the multi-cycle operation and variable-pressure mode. However, a significant decay of performance is observed in all PRO processes under practical conditions. ABPRO shows a comparable performance with SSPRO at high PRO water recoveries (PR) due to the entropy generation caused by mixing. Due to the avoidance of mixing by storing the influent and effluent of draw solution (DS) in two separate tanks, SCPRO features the highest SEP and EPE at PR > 0.3. Utilizing a 1.2 M NaCl solution as the DS and a 0.05 M NaCl solution as the feed solution (FS), the EPE of SCPRO approaches 67.6% at PR = 0.5, which is approximately 15% higher than SSPRO and 8% higher than ABPRO.
Furthermore, effective solutions to achieve the coordinated management of energy and water are crucial to establish a sustainable society. Therefore, a desalination-osmotic energy storage (DOES) system integrating reverse osmosis (RO) and PRO is proposed in this study to further enhance the practical feasibility of PRO and strengthen the water-energy resilience. The DOES system features multiple functions, which uses the renewables or waste energy as the power origin to produce water via RO and utilizes partial RO permeate and brine to generate electricity via PRO. Employing the superior semi-closed (SC) mode in DOES substantially reduces energy losses arising from over-pressurization in RO and under-pressurization in PRO. Benefiting from the variable-pressure mode, the DOES system is characterized by 100% energy efficiency in ideal scenarios. The practical maximum efficiency can be maintained at ~75% in the SC mode for both RO and PRO stages at high RO recovery (R) and permeate utilization ratios (∅), attributed to the flexible adjustment of the number of cycles in the SC mode for performance optimization. The specific energy production (SEP), termed as the total energy normalized by the RO permeate volume, approaches 0.48 kWh·m-3 at R = 0.5 and ∅ = 0.5, which is doubled when R and ∅ increased from 0.5 to 0.75.
Finally, the module-scale performance of the DOES system is simulated with the comprehensive consideration of inefficiencies. The results reveal that an increase in R can lead to higher SEC, SEP, and PD simultaneously. However, given the SEP defined as the total energy production normalized by the volume of RO permeate used in PRO in this chapter, it may exhibit an initial rise followed by a decline when ∅ increases. In addition, an increase in PD due to the rise of water flux may result in a deterioration of energy efficiency. Nevertheless, this trade-off between PD and energy efficiency can be mitigated by operating DOES at a higher R. As R rises from 0.5 to 0.75, the EPE, SEP and PD escalate from 62.6%, 0.83 kWh·m-3 and 11.6 W·m-2 to 65.3%, 1.29 kWh·m-3 and 18.1 W·m-2, respectively, At a constant ∅ of 0.50 and a fixed water flux of 14 LMH. The energy production capacity at R = 0.75 is comparable to that of a pumped hydro system with a vertical height of approximately 530 meters while DOES has less topographical constraints and construction loads.
Given its various performance advantages and multi-functionality, the DOES system with the novel SC mode can potentially enable it to effectively enhance energy and water resilience and contribute to a low carbon future. |
| first_indexed | 2025-03-09T10:20:53Z |
| format | Thesis-Doctor of Philosophy |
| id | ntu-10356/182848 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2025-03-09T10:20:53Z |
| publishDate | 2025 |
| publisher | Nanyang Technological University |
| record_format | dspace |
| spelling | ntu-10356/1828482025-03-07T15:37:49Z Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage Li, Dan She Qianhong School of Civil and Environmental Engineering QHSHE@ntu.edu.sg Earth and Environmental Sciences Engineering The global issues of water scarcity and climate change are driving the utilities sector, primarily water and electricity, to transit toward more sustainable sources. Water supply increasingly relies on energy-intensive desalination in recent years, hence renewable energy is suggested to be used as its power origin under the decarbonization framework. However, the intermittent availability of most renewables (e.g., solar energy and wind energy) escalates the gap between supply and demand in not only electricity but also water sectors. To address this issue, osmotic energy becomes a promising choice as it can be stored easily by depositing two solutions with salinity gradient in separate containers and converted into electricity when needed by pressure-retarded osmosis (PRO). However, the low capacity and efficiency of conventional single-stage PRO (SSPRO) processes deteriorate its practical feasibility. First of all, two novel PRO configurations and operating modes, atmospheric batch PRO (ABPRO) and semi-closed PRO (SCPRO), are designed to improve the energy production performance of PRO. Both ABPRO and SCPRO can realize 100% energy production efficiency (EPE) ideally facilitated by the multi-cycle operation and variable-pressure mode. However, a significant decay of performance is observed in all PRO processes under practical conditions. ABPRO shows a comparable performance with SSPRO at high PRO water recoveries (PR) due to the entropy generation caused by mixing. Due to the avoidance of mixing by storing the influent and effluent of draw solution (DS) in two separate tanks, SCPRO features the highest SEP and EPE at PR > 0.3. Utilizing a 1.2 M NaCl solution as the DS and a 0.05 M NaCl solution as the feed solution (FS), the EPE of SCPRO approaches 67.6% at PR = 0.5, which is approximately 15% higher than SSPRO and 8% higher than ABPRO. Furthermore, effective solutions to achieve the coordinated management of energy and water are crucial to establish a sustainable society. Therefore, a desalination-osmotic energy storage (DOES) system integrating reverse osmosis (RO) and PRO is proposed in this study to further enhance the practical feasibility of PRO and strengthen the water-energy resilience. The DOES system features multiple functions, which uses the renewables or waste energy as the power origin to produce water via RO and utilizes partial RO permeate and brine to generate electricity via PRO. Employing the superior semi-closed (SC) mode in DOES substantially reduces energy losses arising from over-pressurization in RO and under-pressurization in PRO. Benefiting from the variable-pressure mode, the DOES system is characterized by 100% energy efficiency in ideal scenarios. The practical maximum efficiency can be maintained at ~75% in the SC mode for both RO and PRO stages at high RO recovery (R) and permeate utilization ratios (∅), attributed to the flexible adjustment of the number of cycles in the SC mode for performance optimization. The specific energy production (SEP), termed as the total energy normalized by the RO permeate volume, approaches 0.48 kWh·m-3 at R = 0.5 and ∅ = 0.5, which is doubled when R and ∅ increased from 0.5 to 0.75. Finally, the module-scale performance of the DOES system is simulated with the comprehensive consideration of inefficiencies. The results reveal that an increase in R can lead to higher SEC, SEP, and PD simultaneously. However, given the SEP defined as the total energy production normalized by the volume of RO permeate used in PRO in this chapter, it may exhibit an initial rise followed by a decline when ∅ increases. In addition, an increase in PD due to the rise of water flux may result in a deterioration of energy efficiency. Nevertheless, this trade-off between PD and energy efficiency can be mitigated by operating DOES at a higher R. As R rises from 0.5 to 0.75, the EPE, SEP and PD escalate from 62.6%, 0.83 kWh·m-3 and 11.6 W·m-2 to 65.3%, 1.29 kWh·m-3 and 18.1 W·m-2, respectively, At a constant ∅ of 0.50 and a fixed water flux of 14 LMH. The energy production capacity at R = 0.75 is comparable to that of a pumped hydro system with a vertical height of approximately 530 meters while DOES has less topographical constraints and construction loads. Given its various performance advantages and multi-functionality, the DOES system with the novel SC mode can potentially enable it to effectively enhance energy and water resilience and contribute to a low carbon future. Doctor of Philosophy 2025-03-04T05:26:47Z 2025-03-04T05:26:47Z 2025 Thesis-Doctor of Philosophy Li, D. (2025). Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/182848 https://hdl.handle.net/10356/182848 en This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). application/pdf Nanyang Technological University |
| spellingShingle | Earth and Environmental Sciences Engineering Li, Dan Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage |
| title | Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage |
| title_full | Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage |
| title_fullStr | Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage |
| title_full_unstemmed | Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage |
| title_short | Developing novel pressure-retarded osmosis (PRO) systems for renewable energy harvesting and storage |
| title_sort | developing novel pressure retarded osmosis pro systems for renewable energy harvesting and storage |
| topic | Earth and Environmental Sciences Engineering |
| url | https://hdl.handle.net/10356/182848 |
| work_keys_str_mv | AT lidan developingnovelpressureretardedosmosisprosystemsforrenewableenergyharvestingandstorage |