Feasibility study of a forward osmosis/crystallization/reverse osmosis hybrid process with high-temperature operation: Modeling, experiments, and energy consumption

doi:10.1016/j.memsci.2018.03.031

Journal of Membrane Science

Volume 555, 1 June 2018, Pages 206-219

https://doi.org/10.1016/j.memsci.2018.03.031 Get rights and content

Highlights

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High temperature operation for FO/crystallization/RO hybrid process was suggested.
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Appropriate draw solute candidates were selected.
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Transport and energy consumption model for the hybrid process were developed.
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Appropriate membrane parameters condition were estimated from experimental data.
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The energy consumption of the hybrid process was calculated for each draw solute.

Abstract

This paper presents a comprehensive analysis of a forward osmosis (FO)/crystallization/reverse osmosis (RO) hybrid process with high-temperature operating conditions to assess its feasibility as desalination technology. A process configuration and draw solute candidates are suggested. A mathematical model was developed to describe transport phenomena at the described operating conditions and an experimental study was conducted to investigate the amounts of water and reverse salt fluxes and to validate the developed model. Based on the experimental data, suitable membrane parameters for each process were estimated, and the applicability of the operating conditions was confirmed. An energy consumption model for the hybrid process was also developed and a comparative study with the conventional seawater reverse osmosis (SWRO) process was conducted. The equivalent work in the hybrid process is around 1.66–2.72 kW h/m³ when heat-electricity energy cost conversion is considered. The energy requirement of the hybrid process is competitive with that of conventional SWRO process. Of the total energy requirement of the process, thermal energy comprises 0.6–1.1 kW h/m³. Thus, the energy requirement can be lowered to less than 1.0 kW h/m³ if very cheap waste energy is available.

Graphical abstract

Introduction

As the human population has increased worldwide, the problem of water scarcity is considered one of the most severe challenges we face in the future [1]. Because more than 97% of water on Earth exists as seawater, there is no doubt that seawater desalination may be the ultimate solution to water scarcity problems [2], [3]. Today, the seawater reverse osmosis (SWRO) process is regarded as the most energy-efficient technology for seawater desalination [4]. The energy requirement of the SWRO process has decreased to around 2 kW h/m³ [1] and water production costs have dropped to lower than $0.7/m³ for medium-sized systems (12,000–60,000 m³/day) [5]. However, the inevitable utilization of high-pressure pumps in SWRO processes leads to many problems, such as severe irreversible fouling at the surface of the reverse osmosis (RO) membrane and high membrane replacement costs [6]. In addition, the theoretical minimum amount of energy required to separate fresh water from 35 g/L seawater is 1.06 kW h/m³ at 50% recovery [1]. Thus, the energy efficiency of seawater desalination can be improved if novel processes can be developed.

Forward osmosis (FO) has received much attention in recent decades, and has been regarded as an alternative technology to RO [7]. A great deal of investigation has been conducted into how the energy consumption of seawater desalination could be decreased by utilizing FO [7], [8], [9], [10], [11], [12], but it has been revealed that the energy requirement of a standalone FO process cannot be lower than that of a conventional RO process [13], [14]. To overcome this limitation, hybrid process designs in which FO is coupled with other processes such as membrane distillation (MD) [15], [16], [17], [18], electrodialysis (ED) [19], nanofiltration (NF) [20], [21], and RO [8], [22], [23], [24] have been explored, as summarized in Table 1. It has been suggested that process hybridizations with FO may have some potential for future desalination technology, although more research should be carried out to replace the conventional RO process.

Recently, a hybrid process of FO/crystallization/RO was suggested. As demonstrated in our previous report, this hybrid process was expected to be competitive in terms of energy consumption relative to the RO process [25]. However, the energy requirement of the FO/crystallization/RO hybrid process is still quite high even in the lowest energy case (~ 2.15 kW h/m³). The main reason of this high energy requirement is the energy-consuming refrigerator used to cool the crystallizer. Because of the low energy efficiency of the refrigerator, the operation mode described in the previous paper cannot easily decrease energy consumption significantly. In other words, the energy efficiency of the hybrid process would be improved if utilization of a refrigerator could be avoided. In our previous report, an operation mode was already mentioned in which the FO process operates above ambient temperature and the effluent stream of the FO process is cooled in a crystallizer with a cooling tower rather than a refrigerator. In this high-temperature operation mode, utilization of refrigerator could be obviated. Thus, the energy requirement for operating the FO/crystallization/RO hybrid process could be significantly reduced. In addition, if waste heat energy could be utilized almost free of charge, the high-temperature operation mode of the FO process would become a competitive design for seawater desalination. Thus, the feasibility of this novel operation mode should be investigated both theoretically and experimentally.

In this study, a high-temperature operating mode for the FO/crystallization/RO hybrid process is proposed and analyzed with experimental results and simulation approaches. Draw solute candidates were carefully selected based on criteria to operate the hybrid process efficiently. An experimental setup for each part of the FO/crystallization/RO hybrid process was used to study the performance of the selected draw solutes in terms of water flux and solubility at each temperature. Membrane parameters and van’t Hoff coefficients of the draw solutes were estimated based on the experimental results. Next, specific energy consumptions were calculated with the proposed model to evaluate the energy performance of each draw solute in the hybrid process. Finally, the energy-feasibility of the hybrid process with a high-temperature operating mode is validated by comparing to the results with those of the conventional RO process, which is a one stage SWRO process. If the energy feasibility is competitive compared with the conventional RO process, the developed models and experimental data may be utilized in commercialization of the hybrid process and cost estimation for detailed design in future works.

Section snippets

Process description

The hybrid FO/crystallization/RO process is composed of three units, as illustrated in Fig. 1. In the FO process, which is considered the main desalination unit, water molecules permeate from the feed (seawater) stream to the draw solution stream spontaneously, driven by the osmotic pressure difference across the membrane. The effluent diluted draw solution from the FO process is fed into the crystallizer to at least partially separate draw solutes from the draw solution based on the solubility

Solubility measurements

The measured solubilities of each draw solution are displayed in Fig. 6 with reference data [41], [42]. The measured solubility data revealed that the solubilities of the selected draw solutes have sufficiently high temperature dependence for the hybrid process to operate efficiently. Especially around 50–70 °C, the solubility variability is extreme. Based on the measured data, it can be concluded that the operating temperature of the FO process should be around 70 °C (at least 60 °C). At

Conclusions

In this study, high-temperature operating conditions for an FO/crystallization/RO hybrid process were investigated. Models for describing the process and its energy consumption were developed and experimental data were obtained to confirm the feasibility of the hybrid process and its operating conditions. A comparative study of the energy consumption of the hybrid process and the conventional RO process was also performed.

Through crystallization experiments, the actual solubility of each draw

Acknowledgements

This work was financially supported by Lotte Chemical Corporation and Korea University grant.

References (59)

A.D. Khawaji et al.
Advances in seawater desalination technologies
Desalination
(2008)
C. Fritzmann et al.
State-of-the-art of reverse osmosis desalination
Desalination
(2007)
I.C. Karagiannis et al.
Water desalination cost literature: review and assessment
Desalination
(2008)
R.L. McGinnis et al.
Energy requirements of ammonia–carbon dioxide forward osmosis desalination
Desalination
(2007)
D.L. Shaffer et al.
Forward osmosis: where are we now?
Desalination
(2015)
G. Blandin et al.
Opportunities to reach economic sustainability in forward osmosis–reverse osmosis hybrids for seawater desalination
Desalination
(2015)
A. Deshmukh et al.
Desalination by forward osmosis: identifying performance limiting parameters through module-scale modeling
J. Membr. Sci.
(2015)
Q. Ge et al.
Hydroacid magnetic nanoparticles in forward osmosis for seawater desalination and efficient regeneration via integrated magnetic and membrane separations
J. Membr. Sci.
(2016)
N. Akther et al.
Recent advancements in forward osmosis desalination: a review
Chem. Eng. J.
(2015)
P. Wang et al.
Evaluation of hydroacid complex in the forward osmosis–membrane distillation (FO–MD) system for desalination
J. Membr. Sci.
(2015)

G.M. Geise et al.

Water permeability and water/salt selectivity tradeoff in polymers for desalination

J. Membr. Sci.

(2011)

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