Isobaric Energy Recovery Devices Research Articles

Experimental study of a booster pump-free isobaric energy recovery device (DAC) for reverse osmosis: Performance evaluation and comparison

Reverse osmosis (RO) is a widely used desalination technology known for its high energy requirements. However, the incorporation of energy recovery devices (ERDs) in RO plants has proven effective in reducing specific energy consumption. The booster pump (BP) is an essential component utilized in conjunction with isobaric ERDs. Approximately 5 to 10 % of the capital cost for small to medium-sized RO units is attributed to the BP. The objective of this paper is to investigate the feasibility of implementing a newly designed isobaric ERD called DAC. The study focuses on an RO plant with a capacity of 48 m3/day. The proposed ERD undergoes design, manufacturing, and experimental testing. The major benefit is its ability to utilize the system feed pump as a BP, eliminating the need for a separate BP. This equipment reduction not only lowers the initial cost but also simplifies the system complexity. Furthermore, the system is designed to allow a comparison between the DAC and a pressure exchanger (PX) under the same operating conditions. However, unlike the DAC, the PX becomes unresponsive and does not function when the BP is turned off to allow the system feed pump to take over.

An optimization study on the seal structure of fully-rotary valve energy recovery device by CFD

Leakage in isobaric energy recovery devices (ERDs) is inevitable. Three seal structures are introduced and studied for a fully-rotary valve energy recovery device (FRV-ERD) to reduce leakage. Effects of pressure difference and geometrical parameters of seal structure on leakage are investigated and compared for different seal structures. Results show that, as the key component of this ERD, the fully-rotary valve (FRV) achieves its best seal performance with the bilateral seal. For the FRV-ERD of design parameters, both the efficiency and required clearance are improved by using the bilateral seal to replace the original seal. The calculated efficiency is improved from 89.48% to 92.05% at the clearance of 30 μm under operating pressure and the required clearance increases from 18.1 μm to 20.4 μm. Based on the results of the optimized bilateral seal, an approximate leakage rate equation is proposed and can be used for design calculation. The performance of FRV-ERD with the optimized bilateral seal is improved greatly. Compared with FRV-ERD with the original seal, the efficiency of FRV-ERD with the optimized bilateral seal is improved from 89.48% to 96.33% at the clearance of 30 μm under operating pressure, and the required clearance increases from 18.1 μm to 29.5 μm, easing machining difficulty greatly.

Studies on leakage characteristics and efficiency of a fully-rotary valve energy recovery device by CFD simulation

Seawater reverse osmosis (SWRO) develops rapidly and benefits from excellent performance of isobaric energy recovery devices (ERDs). Leakage characteristics directly affect the ERD performance. In this paper, leakage characteristics of a fully-rotary valve energy recovery device (FRV-ERD) which is a new type of isobaric ERD are studied numerically. Leakage variation of the fully-rotary valve (FRV) that is the key part of the device caused by pressure difference and geometric parameters is investigated. Then performance of the FRV-ERD is discussed. Results indicate that leakage rates of forward and reverse leakage within the same FRV are almost equal to each other and present a good linear relationship with pressure difference. Leakage rate is exactly proportional to the 3.0 power of the clearance height. Effects caused by changing the length and diameter are equivalent. The leakage rate decreases sharply first and then slowly after the length or diameter is larger than a specific value of which the axial length and the half circumference are equal to each other. The performance of the larger size FRV-ERD is much better than the smaller one, and the required clearance is also significantly increased, alleviating machining difficulty to some extent.

Development and experimental studies on a fully-rotary valve energy recovery device for SWRO desalination system

Isobaric energy recovery devices (ERDs) are developing rapidly and playing a significant role in reducing specific energy consumption (SEC) of seawater reverse osmosis (SWRO) desalination systems. However, leakage, abrasion and large pressure loss are still big challenges and remain big problems unsolved among the present ERDs. In this paper, a novel isobaric ERD based on so-called fully-rotary valves (FRVs) is developed to resolve these problems. The key fully-rotary valve energy recovery device (FRV-ERD) consists of only two FRVs and pipelines. The performance of the FRV-ERD is tested by means of an ERD performance test system. The hydraulic performance of the device is tested under laboratory conditions with the test pressure about 3.0MPa. Experiments show that the operation of the FRV-ERD is stable and the pressure fluctuations of high pressure streams are small. The leakage is not detected and therefore excellent seal performance is proved through tests as well. The measured pressure loss is low and the energy recovery efficiency is as high as 98.47% which is among the best of the reported values.

Analysis of the influence of the configuration in ERD retrofit in two-stage SWRO trains

Isobaric energy recovery devices (ERD) have achieved nearly universal acceptance in the seawater reverse osmosis (SWRO) world. Because of this, during the last decade, several SWRO plants have upgraded their energy recovery devices with the aim of obtaining energy savings in the operation of the plant. This upgrade generally involves the installation of isobaric chambers (IC) and the replacement of the existing Pelton wheels. The purpose of this paper is to present the results of a study where specific energy consumption (SEC) savings, water production variation and payback for this retrofit in eight full-scale two-stage trains have been evaluated. The retrofits have been grouped based on their configuration after the retrofit and three different configurations have been considered. In light of the results obtained it can be concluded that the configuration selected when retrofitting a train with IC has a significant impact over those key indicators considered when studying investment feasibility.

Modeling seawater reverse osmosis system under degradation conditions of membrane performance: assessment of isobaric energy recovery devices and feed pressure control benefits

A transient model of seawater reverse osmosis (SWRO) system enables systematic assessment of membrane performance in response to changes in time-series parameters, operating conditions, or ancillary equipment. In this study, we describe the effects of energy recovery device (ERD) and feed pressure control on the SWRO plant in terms of energy consumption (reduced) and water quantity (increased) using a numerical model at pilot scale. In the simulation, two types of isobaric ERD, i.e. pressure exchanger (PX) and dual work exchanger energy recovery (DWEER), were used to quantify changes of the mass flow rates of inflow and outflow in the system. Also, temporal variation in the raw feedwater quality was addressed in the model with adaptive feed pressure control to maintain the amount of produced water under fouled membrane conditions. Results showed that the observed recovery and rejection rates in the pilot-scale plant had an excellent agreement with their predicted values under different seawater feed concentrations varied over a year (NSE = 0.9990 and 0.9987, respectively). Both PX and DWEER were found to affect the concentration and stream of influent directed to the reverse osmosis module, in which PX showed slightly higher recovery rate than DWEER that had the volumetric flow loss of the pressurized feed. While water quality and quantity of the permeate declined progressively in non-steady state simulation of membrane fouling, increasing the feed pressure linearly improved the performance of the pilot plant, higher recovery rate and lower energy consumption than a constant pressure mode. Therefore, this study demonstrates that the dynamic simulation model for the SWRO system not only describes deterioration of membrane performance at the pilot scale, but also can be used to search alternative devices and operation modes that achieve water quality and quantity targets with efficient energy use.

Lahat BWRO plant: technical and economic evaluation of energy recovery alternatives

The Lahat BWRO plant was constructed as part of the southern Israel coastal aquifer rehabilitation project. Two RO trains, with a capacity of 10,000 m3/d each, were commissioned in August 2010. In both trains a turbocharger (TC) energy recovery device was installed, wherein the turbine side utilizes the energy of the second stage brine to boost the second stage feed. Lahat plant expansion with two additional 11,300 m3/d BWRO trains is currently under construction. As part of the pre-design phase, a techno-economic analysis was conducted with the purpose of finding the most cost-effective energy recovery configuration. Comparing existing design of TC added with a booster pump with alternative isobaric energy recovery with ERI PX devices, it was shown that implementation of isobaric PX results in a life cycle saving of 1,091,882$, about 1.5 times more than the TC alternative. Accordingly, in the design of the two additional RO units, isobaric energy recovery device was implemented. Apart from the cost benefit, this configuration has several advantages versus the TC, mainly the control of the second stage booster pressure with increased accuracy and flexibility. This enables a better balance of the first and second stage flux in comparison with TC option. The current paper includes an introduction about the southern Israel coastal aquifer rehabilitation project, and the construction plan of the Gat, Granot, and Lahat brackish water RO BWRO desalination plants. In addition, it presents the complexity of the marine brine disposal pipeline of these inland plants, and the rational that led to the innovative idea of energy recovery in the Lahat BWRO plant. Finally, the technical and economic considerations of energy recovery alternatives in BWRO plants are discussed and summarized.

次世代型エネルギー回収装置

次世代型エネルギー回収装置

Larnaca SWRO upgrade

The Calder™ Energy Recovery Turbines (ERT’s) were installed and operated more than 10 years ago at the Larnaca SWRO plant, on the island of Cyprus. The ERT’s help drive the Flowserve membrane feed pumps. The increased need for potable water drove the owners to investigate improvement plans for the plant, while incorporating isobaric energy recovery devices. Rather than retrofitting the existing installation, a new plant design was chosen that increases the overall capacity while incorporating the most efficient energy recovery devices available on the market. By contracting with one supplier for both the DWEER™ energy recovery devices and all the main pump services, the engineering procurement and construction company was able to gain significant efficiencies not previously experienced. This paper outlines the development of the new SWRO plant at Larnaca and the benefits of having a one-supplier contract.

Energy recovery consideration in brackish water desalination

In brackish water RO desalination, the low feed water TDS and relatively low brine flow make the use of energy recovery devices ambiguous. The decision to implement energy recovery device must always be based on the Life Cycle Cost estimation of the plant. Design considerations concerning the energy recovery device selection and field experience in Lahat brackish water desalination plant (40,000m3/day) are presented in this article.Two types of energy recovery device are generally considered in the brackish water RO desalination, turbocharger and isobaric energy recovery devices. Taking into consideration the simplicity of the turbocharger, it was selected for the 1st phase of the Lahat brackish water desalination plant with the design recovery range of 80%–88%. The turbocharger was designed for max recovery and external bypass line was added to operate the plant at low recoveries. For such wide recovery range the turbocharger entire efficiency range of 30%–40% was achieved.Due to the limitation of the turbocharger to operate efficiently at the broad recovery range and Life Cycle Cost benefits of isobaric energy recovery device, the isobaric energy recovery device was selected for the 2nd phase of the Lahat brackish water desalination plant.

Reduction of energy consumption in seawater reverse osmosis desalination pilot plant by using energy recovery devices

Of paramount importance, seawater desalination plants using reverse osmosis (RO) is reducing the use of energy, which is mostly required for high pressure pumps. Accordingly, energy recovery devices (ERDs) are widely used for reusing hydraulic energy in RO concentrate stream. Nevertheless, few works have been done to investigate the operation characteristics of various EDR systems in actual desalination plants. In this context, we focused on the comparison of ERDs in a pilot plant with the capacity of 1,000 m3/day. One centrifugal ERD (turbocharger) and two different types of isobaric ERDs (pressure exchanger [PX] and pressure exchanger for energy recovery [PEER]) were installed and tested under various conditions. Operation data in the pilot plant were analyzed to estimate specific energy consumption and energy transfer efficiency. The specific energy consumption analysis results showed that the isobaric ERDs have higher efficiency than the centrifugal ERD as also expected in theoretical estimation. The energy transfer efficiencies for PX and PEER were determined to be similar in short-term tests.

Isobaric Energy-Recovery Devices: Past, Present, and Future

AbstractIn the last 25 years, the energy required to desalinate seawater has been reduced by a factor of two. Energy recovery devices (ERDs) are responsible for more than half this reduction. Among commercially available ERDs, pressure-equalizing or isobaric ERDs have demonstrated energy savings of 10–30 percent greater than turbine-based devices or reverse-running pumps. Isobaric ERDs transfer energy from the membrane reject stream directly to the membrane feedstream, thereby reducing the duty of high-pressure pumps. Despite the success, modern isobaric ERDs can experience expensive energy losses over the life of a seawater reverse osmosis plant. This article explores performance of modern isobaric ERDs and potential implications of their improvement, as well as estimated life-cycle costs for investment, maintenance, and optimization.

Energy optimisation of existing SWRO (seawater reverse osmosis) plants with ERT (energy recovery turbines): Technical and thermoeconomic assessment

Reduction of SEC (specific energy consumption) is the field with the most specific technical research focus and effort in SWRO (seawater reverse osmosis) plants. For existing installations with energy recovery systems consisting in Pelton turbines, the most significant challenge is how to reduce energy costs. The highest efficient isobaric ERD (energy recovery devices) are used in order to produce major savings in energy consumption in the desalination process and/or to increase the freshwater capacity of the installations, by taking full advantage of the plant equipment. This paper gives a brief overview of the technology used to recover the energy from brine stream in large desalination plants, with a description of the modifications required if the recovery system with Pelton turbines is to be replaced by systems based on isobaric-chamber devices. All possibilities analysed are deeply justified technically and thermoeconomically within an exhaustive assessment.

Reverse osmosis and osmotic power generation with isobaric energy recovery

Current state-of-the-art seawater reverse osmosis processes require isobaric energy recovery devices to minimize energy consumption and total operating costs. These “pressure-equalizing” devices efficiently recover pressure energy from the reject concentrate stream of the reverse osmosis process. The use of isobaric energy recovery devices in SWRO processes provides a great deal of flexibility in the design and operation of the plant. In a properly designed application, membrane flux and recovery can be dynamically changed without a significant total process energy efficiency penalty. The high efficiency and flexibility of isobaric energy recovery devices makes them logical solutions for other membrane processes such as brackish RO systems and pressure retarded osmosis. Pressure retarded osmosis, sometimes referred to as osmotic power, is a membrane process for generating energy from the osmotic potential between two feed streams such as seawater and fresh water. The process, invented by Sidney Loeb in 1973, will see its first full-scale prototype within 2009. Isobaric ERDs play a pivotal roll in making the pressure retarded osmosis process economically viable. This paper will illustrate how isobaric energy recovery devices work and chart the technological advances they have made through the years. The application of the isobaric ERDs, and specifically the ERI PX device, to reverse osmosis and pressure retarded osmosis processes will be discussed in detail.

Retrofits to improve desalination plants

Legacy seawater reverse osmosis (SWRO) desalination plants used turbine-type energy recovery devices (ERDs) connected with a shaft to the high-pressure pump. These ERDs, commonly known as Pelton wheels or energy recovery turbines, were default equipment in SWRO plants until quite recently. Today, however, over 80% of new SWRO plants are being designed and built to utilize isobaric-chamber ERDs. Isobaric ERDs such as Energy Recovery, Inc. (ERI’s) PX Pressure Exchanger™ (PX™) device are positive displacement devices that operate with energy transfer efficiencies as high as 98%. High SWRO plant operating efficiency can be obtained over a wide range of membrane water recovery rates, typically between 35% and 50%. Recovery rates can be adjusted in response to changes in seawater temperature or salinity or as the membrane elements age. Flexible recovery and low-recovery operation are tremendous advantages for lowcost SWRO operation provided by isobaric ERD technology. Removing legacy ERDs and installing modern isobaric ERDs makes it possible to reduce the power consumption of existing systems by as much as 60%. Such retrofits can also significantly increase the capacity of existing systems while adding little or no additional power requirements. These benefits can be realized at a fraction of the cost of constructing new plants. For these reasons, many owners of legacy desalination plants worldwide are upgrading their processes by incorporating isobaric ERD technology. The authors recognize that each energy recovery technology comes with its own unique advantages and disadvantages, which should be compared and studied for each individual system. This paper, therefore, provides detailed analyses comparing SWRO energy consumption with various ERDs. It presents many examples of retrofits, including replacements of Pelton turbines and turbocharger devices. It also estimates the potential energy savings and capacity increase benefits for retrofitting some of the largest SWRO projects in the world including facilities in Fujairah, UAE and Trinidad.

Operation of the RO Kinetic ® energy recovery system: Description and real experiences

Along with the older style centrifugal energy recovery devices (ERDs), there has been a recent proliferation of ERDs that employ positive displacement mechanisms. These “pressure-equalising” or isobaric ERDs transfer the energy from the membrane reject stream directly to the membrane feed stream. This direct, positive displacement approach results in a net transfer efficiency up to 97% [R.L. Stover, Seawater reverse osmosis with isobaric energy recovery devices. Desalination, 203 (2007) 168–175]. A number of devices have been developed to recover pressure energy from the brine reject stream. These ERDs fall into two general categories: centrifugal and isobaric devices. In order to avoid the efficiency losses associated with the energy-conversion steps inherent in centrifugal devices, in the 1980s engineers developed positive-displacement (PD) isobaric devices for seawater reverse osmosis (SWRO) plants. These devices place the SWRO reject and raw feed in contact in pressure-equalising or isobaric chambers. Current manufacturers of isobaric devices include Calder (DWEER TM) [2], KSB (SalTec DT) [3], ERI ® (PX) [4] and RO Kinetic ® (RO Kinetic ® is a patent of the Canary Islands engineer Manuel Barreto). The RO Kinetic ® is a novel energy savings system for RO desalination plants that implies an enormous advance in the specific energy consumption (SEC) reduction in this type of facilities. With this device, we are able to obtain a SEC of slightly higher than 2.20 kWh/m 3, which approaches the theoretical minimum limit for energy consumption in seawater reverse osmosis processes [5]. The physical principle that serves as the foundation for the RO Kinetic ® system is the “incompressible property of liquids”, making it possible to submit a mass of water to a given pressure without expending any energy. Pressure exchangers are used to put this principle into practice. This article describes the state of the art of the RO Kinetic ® energy recovery device; it explains the way it works and the advantages of using this type of ERD in SWRO plants. Furthermore it shows some operational data of different SWRO desalination plants with the RO Kinetic ®.

Design and optimization of seawater reverse osmosis desalination plants using special simulation software

This paper introduces the Integrated process simulation environment (IPSEpro™) software, and its application to reverse osmosis desalination. The paper introduces the reader to the basic modeling concepts, and how individual process units can be simply simulated with a graphical, flowsheet style interface. The paper then goes on to describe an example simulation for off design of an integrated pump, membrane rack and isobaric energy recovery device, investigating the effects of changing water quality, membrane condition and also, the influence of isobaric energy recovery device overflush.

Effect of recent technological developments on SWRO incorporated in the Red–Dead project

Since the last relatively detailed study of the large SWRO incorporated in the Red–Dead project (Harza 1996), several important technological developments were made. The most relevant are largediameter RO membranes, large and high-efficiency pressure pumps and Pelton turbines, and the isobaric energy recovery device. All have a significant effect on the sizing and economics of this large desalination project. Moreover, the new energy recovery device (ERD), aimed to reduce energy consumption, imposes a revision of the conceptual design regarding location of the pretreatment and combined production of electric power and desalination. The new concept of using an isobaric ERD or the former concept using more efficient RO membranes and more efficient pressure pumps and a Pelton-type ERD, may eventually significantly reduce investment and energy consumption; the number of RO membranes could be reduced by a factor of 4; and total energy consumption, excluding product delivery, could be reduced from about 0.9 kWh/m3 to about 0.6 kWh/m3 or less.

SWRO process simulator

Most large seawater reverse osmosis (SWRO) desalination plants built before 2002 incorporated turbine-type energy recovery devices (ERDs) that were connected with a shaft to the high pressure pump. Both the pump and the ERD had best efficiency points corresponding to specific flow rates and pressures. To obtain the high energy-efficiency necessary for cost-effective operation, SWRO plants were designed and operated at a fixed membrane water recovery rates — typically 45% for Mediterranean Sea waters and 35% for Arabian Sea waters. Most SWRO plants being designed and built today utilize isobaric ERDs. These designs emancipate the ERD and high-pressure pump making their operation independent. High efficiency can be obtained at range of membrane water recovery rates and can be changed as seasonal variations in the seawater occur or as the membrane elements age. Numerous best-efficiency operating points can be found which is a tremendous advantage for low-cost SWRO operation but can be too complex for manual design calculations. For this reason, Energy Recovery, Inc. (ERI ®: ERI SIM is a copyright and trademark of Energy Recovery, Inc. ERI, PX Pressure Exchanger, PX and the PX logo are registered trademarks of Energy Recovery, Inc.) developed the ERI SIM TM program. ERI SIM is an instructional computer program that simulates the pressures, flows and salinities of a SWRO process equipped with ERI’s PX Pressure Exchanger ® technology. The ERI SIM program integrates PX ® device performance, typical pump and valve characteristics and projected membrane responses into an interactive, dynamic model. It is the first program in the public domain that treats an SWRO process as a complete, coupled system. The author demonstrates the ERI SIM program by using it to compute SWRO-process responses to changes in process variables, typical startup and shutdown conditions, and various possible process upset conditions.

Seawater reverse osmosis with isobaric energy recovery devices

The world increasingly depends on desalting seawater or brackish water for producing suitable and sustainable supplies of potable water for local populations, tourism, agriculture and industry. The energy cost component of desalinating seawater has historically been a large factor (up to 70%) of the total cost. There is a limit to the amount of available energy and an environmental consequence associated with every kilowatt consumed. Along with the older style centrifugal energy recovery devices (ERDs), there has been a recent proliferation of ERDs that employs positive displacement mechanisms. These “pressure-equalizing” or isobaric ERDs transfer the energy from the membrane reject stream directly to the membrane feed stream. This direct, positive displacement approach results in a net transfer efficiency of up to 97%. This efficiency advantage makes it possible to dramatically improve the performance of seawater reverse osmosis (SWRO) plants by reducing their energy consumption by as much as 60% compared to systems operating without energy recovery. In addition to energy savings, isobaric ERDs offer significant benefits to SWRO plant designers and operators. These include unlimited capacity, reduced high-pressure pump costs, high efficiency and operational flexibility. The PX pressure exchanger isobaric ERD provides the additional benefits of maintenance-free operation, fail-safe operation, corrosion avoidance, low vibration, ease of control and long life. Although the author of this paper is directly associated with Energy Recovery, Inc., a leading company in isobaric ERD technology, the principles and theories presented in this paper are applicable to all devices that are based on the positive displacement, isobaric chamber approach.