Session: 09-02-03 WEC performance analysis

Paper Number: 78191

78191 - A Novel Zero-Discharge Supercritical Water-Based Wave Energy Desalination System 

This paper presents a sustainable and innovative wave energy-based water desalination system combined with emerging supercritical water process for a zero liquid discharge technology.  

Seawater desalination is a small but growing part of the global water industry. Most desalination systems use reverse osmosis (RO) or multiple-effect distillation (MED) technologies, both of which generate a considerable volume of brine waste. More than one gallon of waste can be generated for each gallon of clean water produced, which can be challenging to treat. The elevated salinity from concentrated brine waste discharged during plant operation creates significant environmental impacts and can be harmful to the marine ecosystem.

Integrating wave energy, RO, and supercritical water (SW) desalination can address key technological challenges in desalination and help create the needed consistency in the power source to significantly reduce the drawbacks of both technologies. RO have several disadvantages: (1) membrane fouling that reduces the overall lifespan and increases maintenance costs (2) fast membrane degradation and disintegration and (3) a large volume of brine waste that is discharged to the environment; for example, RO typically generates a gallon of brine waste per gallon of clean water produced. The brine waste is directly discharged into surface water, injected into deep wells, and/or treated in an evaporation pond; yet, all these methods have adverse environmental impacts. Since most desalination facilities are located near the water source, discharge of the locally elevated salinity from concentrated brine waste creates significant environmental impacts and threatens the surrounding ecosystem. The SW produce zero liquid waste but the technology is relatively energy intensive. 

With a focus on the blue economy and resilient communities the wave energy converter was designed to operate near shore using wave characteristics common in the central eastern United States, as a case study. This paper will focus on the oscillating surge wave energy converter (OSWEC) as this topology has a high potential for near-shore, small scale direct water pressurization. The OSWEC will convert wave motion in the surge direction into pressurized seawater, through a rotational high-pressure pump power-take-off (PTO) unit, to the RO membrane. A hydraulic pressure accumulator unit is located between the PTO unit and the RO membrane to provide energy storage in the form of pressurized water to improve the hydraulic system efficiency. The highly concentrated seawater (brine) output from the R.O. membrane (T > 25°C and P > 45 bar)  is pressurized and heated to a supercritical point (T > 374°C and P > 221 bar), which will allow precipitation of the salts and recovery of fresh water. The additional energy requirements for this phase can come from renewables such as photovoltaics, concentrating solar thermal (CST) or electricity. After the SW water cycle the resulting byproduct is fresh water (liquid) and salt crystals (solid).  

The final paper will include results from the hydrodynamic models for the near shore OSWEC, such as wave excitation forces and torque vectors. Numerical evaluation and performance analysis of key parameters for the integrated system will be presented, such as the rotational PTO, R.O. elements, pumps, energy storage, supercritical water component requirements to match expected brine flow/pressure from R.O. element, and energy requirements for the SW cycle, among others. In addition, the final paper will contain preliminary experimental results for a small 0.1 gal/hour supercritical water desalination prototype. 

Presenting Author: Faete Filho East Carolina University

Authors:

Faete Filho East Carolina University
Gabriel Glosson East Carolina University
Jason Mcmorris East Carolina University
Tarek Abdel-Salam East Carolina University
Kurabachew Duba East Carolina University
Thanh Toan Tran National Renewable Energy Laboratory
Salman Husain National Renewable Energy Laboratory