Success behind advanced SWRO desalination plant

7 min read
World's largest and most advanced SWRO desalination plant.
World's largest and most advanced SWRO desalination plant.

The world's water stress is, if anything, becoming more severe, with countries around the world being hit by severe drought. California, Brazil and South Africa are experiencing their worst droughts in many years; the Caribbean area is facing its worst drought in 5 years record; in Africa millions are dying each year of water-related diseases, even more have no access to clean water. It is clear to all that the world needs sustainable sources of clean water, and it needs these now. The lack of water resources can also impact the development and growth of the economy in severely water-stressed countries, and affect their GDP.

Israel is an arid country, located at the edge of the desert, and its battles over water are described as far back as the Bible. During its many years of water stress, the Government has run many campaigns aimed at encouraging the public to save water as “Israel is drying up”. In 1999, the Government began the implementation of a long-term, large scale SWRO (Seawater Reverse Osmosis) desalination program, designed to provide for the increasing demands on the country's scarce water resources, and to mitigate the drought conditions that have characterized most years since the mid-1990s.

Sorek snapshot:  

Capacity: 624,000 m3/day (26,000 m3/hour)

Technology: Reverse Osmosis (RO)

Project Type: Build-Operate-Transfer (BOT)

Location: Sorek, Israel

Footprint: 100,000 m2 (10 ha)

Commission Date: 2013

Today developer of water treatment technologies, IDE Technologies, has its roots in Israel, having been established half a century ago to try to find a solution to the country's water needs. The company has a rich history of more than 400 plants in over 40 countries, delivering some 3Mm3/day of clean water, and is responsible for the design, erection and operation of some of the world's largest desalination plants. With expertise in project management and financing too, IDE takes full responsibility for the entire process, including water quality and quantity, all environmental aspects, and closure of the financing for large PPP projects.

At the turn of the century, the Government of Israel faced a problem – on the one hand, a water shortage becoming more severe, and a constant need to supply a sustainable source of clean water for the municipal and agricultural needs of the growing population. On the other hand, there were requirements to be met. These included, for example, the need to prevent harm to the environment in a world of ever-increasing awareness of the importance of the environment and the need for its preservation, including the need to preserve shore and marine values; the need for lower power consumption; less use of harmful chemicals; a small footprint, as Israel does not have real estate to spare; and all this, of course, at a competitive price. A tall order indeed! IDE Technologies rose to the challenge, and over the last decade has built, and operates, three mega-size desalination plants: Ashkelon with a capacity of 396,000 m3/day (2005); Hadera with a capacity of 525,000 m3/day (2009); and Sorek, the world's largest operating plant of its type, with a capacity of 624,000 m3/day (2013), at which we will take a closer look.

The Sorek Desalination Plant  

The Sorek Desalination Plant is the world's largest and most advanced SWRO desalination plant which provides some 20% of the municipal water demand in Israel (approximately 1.5 million people). The plant sets several signi?cant industry benchmarks in desalination technology, capacity and water cost. A special purpose company, Sorek Desalination Ltd. (SDL), was established to execute the project. The shareholders in the joint venture are IDE Technologies Ltd. (51%) and Hutchison Water International Holdings Pte. Ltd. (HWIH) (49%). The plant includes a number of technological innovations that are said to contribute to its competitive pricing, small footprint and environmental awareness. Further, as part of IDE's end-to-end responsibility for the project, a unique financing package was compiled for the project.

Technological innovation  

IDE has spent 50 years developing the technologies implemented in the Sorek Desalination Plant. Bearing in mind the State's requirements, the design phase was guided by the principle of implementing the technological innovations that would have the greatest impact on plant capacity and operating costs, while meeting the environmental requirements, and supplying water at the contracted quantity and quality.

This article focuses on the technological innovations below, which are considered as having the greatest impact on plant capacity and operating costs:

  • Pressure center concept: This concept was first used successfully in the Ashkelon Plant, and later also in the Hadera and Sorek Plants. The design has shown increased availability and reliability, higher efficiencies and greater flexibility under variable operational modes, and lower Capex/Opex costs. The pressure center design makes use of horizontal centrifugal axially split High Pressure pumps, with an optimized size in order to achieve the highest efficiency. Optimization is based on the pumps specific speed (Ns), pump flowrate, total dynamic head etc. The pressure center offers economy of scale and simplified erection, and allows feed pressure to the RO trains to be increased/decreased, meaning that all RO trains remain operational during periods of reduced production, thereby decreasing system recovery without increasing the total feed to the plant. The Sorek Desalination Plant produces at peak 26,000 m3/hr through two (2) identical desalination sections of the plant. Israel has a varying electricity tariff that changes according to the seasons, the days of the week, and the times of day. The Sorek plant operates according to this variable tariff, with maximum production during the night when the tariff is low and less water production at the times when the cost of electricity is high. The operating pressure of the seawater section varies from 49 bar to 74 barg, according to the operating regime.  
  • Large diameter (16 in) membrane elements: The Sorek design implements 16 in membrane elements in a vertical pressure vessel (PV) array. Close followup of these membranes since the start of operation of the Sorek plant confirms that they behave in an identical manner to 8 in membranes, with the same salt rejection performance and a correspondingly 4.3 times larger flow rate at the same feed pressure and operation conditions. This configuration meets the State's requirement for a smaller plant footprint, and allows the use of shorter HP pipe headers and an improved membrane loading method. Further, as the volumes of feed water are larger, their tendency for membrane fouling is less, leading to a significant reduction in membrane handling for maintenance purposes.

Sorek features 16 in membrane elements in a vertical pressure vessel array.  

  • Self-generating energy supply system: The Sorek plant has two redundant energy sources in order to minimize the cost of the electrical power needed for the process, without compromising reliability. A self-generating energy supply system (Independent Power Producer – IPP) soon to start operating on site is the plant's primary source of energy; and a 161 KV overhead line from the Israel Electric Company Grid operates mainly during “Off Peak” time, when the cost is lower. The IPP system is fueled by natural gas, which results in lower electricity costs that contribute to a lower overall water price.

Minimizing the plant's environmental impact  

IDE is aware of the increasing need to preserve the environment and promotes the use of environmentally-friendly technologies wherever possible.

  • Pipe jacking: To minimize the plant's environmental impact (air, land and marine), the environmentally superior pipe jacking method was used to install the large diameter feed and brine pipelines. Pipe jacking was used for at least 1100 meters from the shore, and for the all on-shore pipelines. The less environmentally friendly “cut and cover” method used at a minimum for the applications required to complete the installation. There are several advantages to the pipe jacking method that include, but are not limited to, minimal disruption of the sea bed, minimal impact on existing infrastructures, lower emissions, no impact on navigation, and longer overall pipeline lifetime.
  • Other measures: the potential impacts of the Sorek Plant's operation on the environment were thoroughly assessed, and appropriate measures were taken to prevent, minimize and mitigate these. The following are some highlights of thse measures: – The feed water pumping station is located far (2,400 meters) from the coastline, and feed water flows by gravity to the on-site pumping station. – Entrainment and impingement effects at the intake system are minimized, thus minimizing the consumption of electricity and chemicals (especially CO2) and reducing the emission of related greenhouse gases, air pollutants and noise. – Environmentally-friendly antiscalants, and inorganic and treatable cleaning solutions, are used. – Brine is discharged back to the sea approximately 2 kilometers offshore, and at a depth of 20 meters through a specially designed outfall system (diffusers) that enhances quick brine dilution to the seawater body. The critical parameters of the brine disposal are monitored online, 24/7. – The plant is equipped with a special sludge treatment system to treat any effluents generated in the process. This system removes all suspended matter and only clear water is discharged to the sea.

Financing package  

It is claimed Sorek set a new benchmark for the price of desalinated water – $0.58 at the time of the bid (October 2009).

The financial closure took place during a challenging time in the economic market, with unstable international financial markets, and a shortage of liquidity. A project financed structure allowed the consortium to reduce its financing costs. Some highlights are presented below.

  • A unique two-tranche project finance package with a trio of local and international lenders – an Israel-based tranche in New Israeli Shekels, and a EURO tranche.  
  • The capital provided by these tranches represents Senior Debt, which covered 80% of the total project cost. The remaining 20% of the costs was financed by equity injected by the shareholders.  
  • A mechanism is provided to hedge against changes in the exchange rates, relevant inflations and base interest rates applicable to these currencies.

The consortium also structured an Equity Bridge Facility, a Standby Facility and a Working Capital Facility.

Global Water Intelligence highly commended Sorek for the 2011 Water Deal of the Year, “in recognition of the transaction that had a positive impact on private sector participation in the international water sector.”

Conclusion

The commissioning procedure for a plant of this size and complexity is not simple. It is time consuming, requires all disciplines to be available for the entire period and often requires a 24/7 presence on site. A detailed commissioning plan was developed for the commissioning sub-project, which took approximately six months.

All issues encountered during the commissioning were immediately addressed by the team on site.

The Sorek Desalination Plant has been operating for a little over two years, and has continuously produced drinking water at the required quality and contracted quantity, at a lower specific energy than expected. It is worth noting that these successful results were achieved with relatively fewer “teething problems” than other similar size plants.