RO Desalination
According to the project, we aim to produce hydrogen to decarbonate the O&M activity. The primary input of hydrogen production is water or H2O. Desalination is one of the essential steps to complete the process. It is the process of separating the salt molecule from the water molecule. The concentrated salt is called brine. The brine that used particular chemicals in the pre-treatment process can be returned to the ocean. The water output from the process name freshwater or permeate. This water will proceed into the hydrogen production execution [2]. The diagram is shown in Figure 1.
Figure 1: Desalination Flowchart
In addition, renewable energy has much popularity in the modern world. It has been applied to the desalination system as well. There are two main possible combination of wind energy to desalination technologies as the presented Table 1. The definition for each desalination technologies is following below.
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1. Reverse Osmosis (RO)
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Reverse osmosis (RO) is a process that relies on a specific threshold known as the osmotic pressure. It is the point at which a semipermeable membrane separates a high-concentration water solution from a low-concentration solution while maintaining a state of equilibrium between them [3].
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The energy consumption of the RO process is directly related to the osmotic pressure, which in turn is influenced by the concentration of solutes in the incoming water. The typical seawater with a salinity level of 35,000 ppm, requires a pressure ranging between 50-70 bar to drive the RO process [3].
2. Mechanical Vapour Compression (MVC)
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Mechanical Vapour Compression (MVC) technology utilizes a compressor to drive the compression process. Moreover, it does not require an external heat source. Due to its compatibility with wind energy, MVC is often integrated with this renewable energy source. This integration can be achieved through the use of a turbine rotor to mechanically drive the compressor by way of the low-speed shaft, or via the generation of electricity through the turbine's generator to power an electrical motor and compressor assembly. [3]
RE Desalination Process | Typical Capacity (m3/day) | Energy Demand (kWh/m3) |
|---|---|---|
Wind/MVC | <100 | 7-12 |
Wind/RO | 50-2000 | Seawater 4-6
Brackish water 1.5-4 |
Table 1: Renewable energy (RE) Desalination
As demonstrated in the table presented, the process of MVC (Mechanical Vapor Compression) produces three types of waste, whereas the RO (Reverse Osmosis) desalination process only generates one. Additionally, the RO desalination process, when coupled with a wind turbine, has become a widely preferred choice for desalination purposes, owing to its capability of catering to a vast range of water capacities with relatively low energy consumption. This combination has proven to be both simple in design and easy to operate. As a result, the selection of RO desalination process for our system has been deemed suitable.
Reverse Osmosis Desalination System
Figure 2: RO Desalination System
The Figure 2 shows that the sea water is feeder into the filter to remove the impurities. After that, it is passed through a chemical pretreatment (CPT) unit to eliminate the harmful microorganisms. Then, it is entered into the RO module where the desalinate the sea water in this unit. The desalinated water, upon exiting the RO unit, is blended with a minor quantity of saline water within the mixing chamber to attain the desired level of water salinity. At state 19, which is the end-product of the desalination process, and it will be continued to Hydrogen Production (PEM)[4]. The proposed list enumerates the suppositions taken into account during the evaluation of the designed system in the table 2 below.
Parameters | Value |
|---|---|
Salinity of Sea water | 35,000 |
Salinity of Freshwater | 450 |
Freshwater Flow Rate (m3/d) | 37.5 |
Pump Efficiency (%) | 80 |
Membrane Recovert Ratio (%) | 40 |
Membrane Salt Rejection Ratio (%) | 99.8 |
Table 2: RO Desalination Parameters
Reference
[1] Al-Karaghouli, A., Renne, D. and Kazmerski, L.L. (2009). Solar and wind opportunities for water desalination in the Arab regions. Renewable and Sustainable Energy Reviews, [online] 13(9), pp.2397–2407. doi:https://doi.org/10.1016/j.rser.2008.05.007.
[2] Do Thi, H.T., Pasztor, T., Fozer, D., Manenti, F. and Toth, A.J. (2021). Comparison of Desalination Technologies Using Renewable Energy Sources with Life Cycle, PESTLE, and Multi-Criteria Decision Analyses. Water, 13(21), p.3023. doi:https://doi.org/10.3390/w13213023.
[3] Greco, F., Heijman, S.G.J. and Jarquin-Laguna, A. (2021). Integration of Wind Energy and Desalination Systems: A Review Study. Processes, 9(12), p.2181. doi:https://doi.org/10.3390/pr9122181.
[4] Siddiqui, O. and Dincer, I. (2018). Examination of a new solar-based integrated system for desalination, electricity generation and hydrogen production. Solar Energy, 163, pp.224–234. doi:https://doi.org/10.1016/j.solener.2018.01.077.