White Paper


Energy recovery technologies such as the PX Pressure Exchanger (PX), have previously focused on seawater RO applications due to the rather quick payback. This leaves brackish water RO (BWRO) facilities to turbochargers that yield less efficient transfer of energy than their PX counterparts. Recently, the first municipal BRWO application of a PX energy recovery device was designed for the City of North Port, Florida’s Southwest Water Treatment Plant and will be started up in 2nd quarter 2022.

This will be the first Brackish Water municipal installation of the Brackish pressure exchanger within the U.S. This paper will present and discuss the design considerations and key parameters including impacts to RO system operation and water quality, energy saving considerations, and data from the facility startup in 2nd quarter 2022. Municipalities with brackish-water supplies will be shown the way to reduce operating costs and maintain water quality from their RO treatment facility.

White Paper: Keys to High Efficiency, reliable performance and successful SWRO operations

Isobaric energy recovery devices (ERDs) have attained nearly universal acceptance by the seawater reverse osmosis (SWRO) desalting world. These devices are operating in the largest SWRO trains in the world and continue to be an integral component in small, containerized systems. Systems incorporating isobaric ERDs are being installed and supported on all seven continents. This has lead to an accumulation of a wealth of knowledge based on practical operating experience.

White Paper: Desalination and energy efficiency for mining in Namibia

The authors present energy-saving solutions for desalination water supply for mining applications. Detailed design data for the Uranium mining desalination plant are given. Environment and economic conscious owners and operators will learn methods of design and operation of desalination systems in mining, which can be easily extrapolated to many other industrial needs, and how to minimize the total cost of ownership of a desalination process.

Upgrading ERDs within an operating desalination plant in Israel

The Palmachim Desalination plant is one of the largest seawater reverse osmosis (SWRO) desalination plants in Israel with a capacity of 120,000 cubic meters per day. Built by the Via Maris Desalination Ltd. consortium, the plant consists of six (6) parallel SWRO trains, each with a permeate production capacity of up to 20,000 cubic meters per day. In addition to its high-capacity SWRO trains, the Palmachim plant is unique because it was designed to be easily turned on, off or slowed down. Electricity tariffs in Israel are significantly higher during the day than at night with a cost ratio of up to six to one. The plant’s flexibility allows the operators to minimize energy consumption during the day when the power cost is high by shutting down up to 85% of the plants capacity.

The lifetime durability of ceramic PX energy recovery devices

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.

The economics of downtime

A key cost that is seldom estimated during evaluation of various technologies in seawater reverse osmosis (SWRO) projects is the cost of downtime, both planned and unplanned. This paper will prove that these downtime costs are significant to both the investors and the operators of the plant. Therefore, plant availability must be a primary factor to be considered in the design phase. Plant availability is even more critical in evaluating the energy recovery technologies as they can cripple production if they break down often and require high maintenance.

Energy recovery devices (ERD) cost less than 2% of initial capital costs but could cost twice that due to lost margin and capital costs. Due to large initial capital expenses, long project life, and criticality of water for end-users, every component should be designed for longevity and robustness along with highest performance. As many plant operators have to pay for liquidated damages when missing the minimum production requirements, it is imperative that the plant is designed for the highest availability possible.

The advantage of reliable ERD technologies

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.

Highly efficient energy recovery devices

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.

Desalinated water powers China’s economic growth

Location: YuHuan, Zheijang Province, China
Project: YuHuan Power Plant
Capacity: 36,000 m³/ day
Energy Savings: US$ 2.7 million or 27 million kWh/year*
CO2 Savings: 16,000 metric tons/year**
* energy savings estimates based on China’s power cost of $0.10/kWh)
**based on Energy Recovery’s proprietary Power Model analysis.

The Challenge: Desalinated Water Powers China’s Economic Growth

As electricity production increases in China to keep pace with the nation’s rapid economic growth, power providers are caught in a bind: energy generation requires processed water, but desalinating seawater to feed power plants requires significant energy. The 4,000 MW power stations expanding China’s electrical grid in preparation for the 2008 Olympics required a seawater reverse osmosis (SWRO) plant capable of processing significant quantities of water and a careful balance of energy considerations. Beijing CNC Technology, Inc. built the YuHuan desalination facility in Zheijang Province as the largest desalination project to address the water needs of the new power generating plants. The client wanted to avoid the power drain of waste-heat processing and take advantage of reverse osmosis’ higher yields.

The Innovation Solution: PX Pressure Exchanger 220

To save energy and money, the East China Electric Power Design Institute Ministry (ECEPDI) and Beijing CNC specified Energy Recovery PX-220s for YuHuan based on its proven high efficiency and two-year trouble-free track record of the PX-220 installation at the Dalian Petrochemical Plant. The PX Pressure Exchanger® solution created for YuHuan features six trains processing 6,000 m3/day, each with six PX-220s, for a total of 36,000 m3/day.

The Result: 
Significant Energy and Cost Savings Drive Rapid Adoption

Energy Recovery’s YuHuan PX configuration, which has operated since 2006 without issue, achieves real energy transfer efficiencies up to 97% and has cut the energy required for YuHuan’s facility by 68%. Using the PX device has created an economically viable way for China’s residents and industries to benefit from the new electrical power because the PX technology recovers enough energy at YuHuan to reduce power costs by $2.7 million per year. This reduction has cut the carbon footprint of the plant by almost 260 tons of carbon dioxide each year. Because of the success at YuHuan and of the China Petrochemicals Dalian Plant, China leads the world in adoption of efficient PX solutions, with more than 90% of SWRO installations in China using Energy Recovery’s technology.

China’s mega-desalination plant experience

The gap between fresh water supply and demand is steadily widening in the People’s Republic of China, home to approximately 20% of the world’s population. Demand for water supplies continues to grow as both personal and industrial consumption surges. Underground water resources, meanwhile, are already overused and badly polluted, and the deep wells now being drilled are frequently tapping into arsenic-rich aquifers, posing safety risks to as much as 30% of the country’s population.

To help combat shortages, desalination, in the form of sea water reverse osmosis (SWRO), has become an integral part of China’s long-term water management strategy. Historically used on a small scale, desalination is now becoming more widely accepted for large-scale water production, particularly in highly populated coastal areas. In recent years, China announced plans to grow its desalination capacity to 2.2 million m3/d (581 million GPD) by 2015, and Chinese water authorities formed partnerships with global water treatment companies to construct large SWRO facilities.

So far, this initiative has resulted in the construction of the nation’s two largest SWRO plants — the Qingdao and Tianjin Dagang SWRO desalination facilities. Designed, constructed and operated by Abengoa and Hyflux, respectively, the two plants together add 200,000 m3/d (52 MGD) of installed capacity to China’s water network. Half of that comes from the Tianjin facility, which began delivering desalinated water to the northern China city’s industrial zone in July 2009. Three years later in eastern China, Qingdao’s municipal water supply began receiving a comparable amount of water from the new SWRO plant there. Both of these state-of-the-art facilities use the latest desalination technologies, including rotary-type isobaric energy recovery devices (ERD).

By considering not only initial capital expenses, but also operational and maintenance expenses, material alternatives and expected uptime of the Energy Recovery System (ERS), these plants demonstrate how sustained long-term energy efficiency can be achieved in large-scale SWRO plants. By displaying proper system design and energy recovery device (ERD) selection, both mega-plants provide an excellent model for future desalination projects in China.

Brackish water desalination: energy and cost considerations

Energy recovery devices are employed in nearly all seawater reverse osmosis (SWRO) desalination plants to recover pressure from the membrane reject stream and return it to the process. Because of the high pressures and low membrane permeate recovery rates common in these systems, the membrane reject stream contains a considerable amount of energy. The use of energy recovery devices in seawater RO is readily justified on the basis of operating cost savings. However, the application of energy recovery is much less common in brackish water RO systems, primarily because of the relatively low feed pressure and low flow rate of the membrane reject stream. The fear is that energy recovery devices can also potentially limit the flexibility of a brackish RO process because of efficiency losses or flow-rate constraints encountered during off-peak operation.

Accelerating & Sustaining the Water Innovation Ecosystem: What’s next?

In September 2013, Cleantech Group hosted its second annual Water Innovation Summit. Leaders from across the water sector—including venture capital firms, corporates, startups, and municipalities—gathered to discuss the technological, financial, and social challenges related to water innovation. We at Energy Recovery participated in this executive summit along with small to large water and oil & gas industry companies such as Grundfos, Chevron, and MIOX. Download the white paper to learn more.

White Paper: Permeate recovery rate optimization in Alicante, Spain

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.