White Paper

In order to ensure the long-term and trouble-free lifetime of the seawater reverse osmosis (SWRO) process and its enabling technology, it is essential to utilize the most advanced and reliable materials of construction. One of the more advanced and unique materials currently in use in SWRO desalination applications is high purity (>99%) aluminum oxide (alumina) ceramics. Due to its hardness, self-lubricating properties, high compressive strength and chemical resistance, alumina ceramics create an ideal fluid bearing for the rigors of seawater applications, which perform in conditions that combine corrosive and potentially two-phase (solid/fluid) environments.

High purity alumina ceramics developed and manufactured by Energy Recovery are particularly unique because of the innovative design of the company’s PX devices and the intense conditions of SWRO plants in which they operate. When in use, the ceramic-based devices are supported by a seawater fluid bearing while rotating and being pressure-cycled millions of times per year. The durability of ceramics in high-pressure, corrosive seawater environments is fundamental to the success of these devices and is quantified and categorized throughout this paper. The enhancement of ERI material science and technological improvements has shown to improve the overall durability of the product and significantly reduce sound levels to below 81 decibels.

Technical data shows that at peak rates, Energy Recovery ceramics inside the PX device wear at less than 3 microns per year (.003 inches over 25 years). The findings identify wear and prove that ERI alumina ceramics can last longer than 25 years in a seawater desalination reverse osmosis plant.

More than 15,000 PX units have been installed worldwide. Some units have been in operation for as long as 12 years. With zero failure as a result of PX technology designed ceramics, research indicates that PX devices will continue operating well into the future.

Availability can be defined as the probability that a system or piece of equipment when used under the specified conditions operates satisfactorily at any given time. The availability of the equipment installed in a seawater reverse osmosis facility (SWRO) is extremely important to the price, quality, and quantity of the final product—water. There are three critical components in the SWRO processes; the main high-pressure feed pumps, the RO membranes, and the energy recovery device (ERD) system. This paper focuses on the economic benefits and importance of the availability of energy recovery devices in SWRO desalination plants.

The largest operating expense for an SWRO facility is the power consumed, which accounts for approximately 30% of the total RO operating expense. Typically for large facilities (>50,000m3/d), the ERDs responsible for reducing energy consumption are only a fraction of the initial capital cost (~1-2%) of the entire plant, but offer major return on investment through energy savings.

The role that ERDs play is undeniably critical to success or failure of an RO facility.

Energy Recovery Devices (ERDs) are at the core of saving energy in the operation of any seawater reverse osmosis (SWRO) desalination facility. Isobaric or “positive displacement” devices such as the PX Pressure Exchanger devices are the most efficient solution available today and can reduce the energy consumption of seawater reverse osmosis (SWRO) systems by up to 60 percent.

Energy Recovery has the largest installed base of ERDs in the industry. Considering only large desalination plants, the Company has a global installed base of over 15,000 individual PX devices in more than 500 desalination plants. Factory acceptance testing is done on 100% of the PX devices.

This paper will examine and quantify the efficiency of PX devices based on an extensive database of actual test results. Significant historical performance data was evaluated and analyzed to validate efficiency figures and guarantee increased efficiencies for several PX device models, including the PX Pressure Exchanger models PX-220, PX-260 and PX-300 units. The existing models offer 96.8% efficiency guarantees, which in turn offer significant energy savings for plant owners and operators. Test data will also quantify the efficiency gains provided by Energy Recovery’s Quadribaric technology.

The company’s newest device, the PX-Q300, incorporates the innovative Quadribaric technology, which doubles the number of pressure exchanges per revolution. This new PX-Q300 improves efficiency—with a warranted minimum efficiency of 97.2%.

Many of the globally installed units have been in operation for as long as 12 years. With zero failure as a result of PX technology designed ceramics, research indicates that PX devices will continue operating well into the future.

Optimization of recovery rate is critical for desalination processes. A high recovery rate gives a high process yield, but requires higher average concentrate salinities in the membrane elements, higher osmotic pressures and higher membrane feed pressures. In addition, supersaturation of the concentrate results in more scaling, and high membrane flux leads to increased fouling. On the other hand, low recovery rate operation directly reduces process yield and can result in excess pretreatment and supply-pumping expenses. Permeate recovery rate optimization, therefore, is a critical exercise for RO process design and operation.