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Savannah, GA -- TSG Technologies, Inc., a wholly owned subsidiary of TSG Water Resources, Inc., has completed the design, construction, and commissioning of a 1.25 million gallon per day seawater reverse osmosis desalination plant on the island of St. Kitts under a design-build agreement with the DeZen group based in Toronto, Canada. The plant provides both potable and irrigation water for the Marriott St. Kitts Royal Beach Resort and Spa, a 648 room hotel with an 18 hole golf course. The plant has been initially fitted with four trains of 250,000 gallon per day each for a total capacity of 1,000,000 gallons per day. The plant is designed so that a fifth train may be added to bring the total capacity to 1.25 million gallons per day.
Pre-Assembly
The contract was executed in September 2003 with a target completion date of December 19, 2003. In order to achieve this delivery schedule, a decision was made to prefabricate as much equipment and interconnecting piping system as possible in Gainesville to minimize on-site staffing. TSG also utilized a number of University of Florida students currently in the Rinker School of Construction Management to assist with equipment fabrication. This provided these students with hands on experience. Unfortunately, the installation schedule and their class schedules did not permit any of the students to participate with on-site equipment installation.
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| Seawater Intake Structure |
Equipment installation began on December 9th, 2003. The client requested work be suspended on December 19th for the Christmas holiday. Equipment installation resumed on January 6th and was completed on January 16, 2004. Following 10 days of system start up and commissioning, the plant went into full production on February 2, 2004.
Open Seawater Intake And Inland Pump Station
The island of St. Kitts is located in the Windward region of the Caribbean Sea, dividing the Atlantic Ocean and the Caribbean Sea. The Marriott St. Kitts Royal Beach Resort is located on the Atlantic side of the island, which is subject to continuous heavy surf and periodic destructive waves with the passage of regional hurricanes. To insure a reliable feedwater supply, the project was designed to obtain seawater from a horizontal beach gallery. However, in response to a shortage of potable water, the result of a prolonged island drought, the decision was made to install and open seawater intake with provisions to add a horizontal beach well at a later date.
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| Capping of Intake Conduit with Ballast Blocks |
After performing an underwater survey of the coastal region, the optimum location for the positioning of the intake structure was between two large reefs outside of a man-made breakwater. This location was approximately 300 feet off shore.
Land constraints limited to location of the intake pump station to either directly in front of the resort or 1,500 feet inland, adjacent to the desalination plant. The location in front of the resort was eliminated as an alternative due to concerns with appearance. In order to minimize the vacuum on the intake pump seals, the intake pipeline was laid using the groundwater table as a reference from the pump station to approximately 200 feet from the ocean. At this point, the pipeline elevation dropped to approximately six feet below sea level out to the man-made breakwater.
The anchoring system for the intake pipeline consisted of 2,000-pound reinforced concrete saddles and 15-ft. long, three-inch diameter sand screws. Experience with other intake projects had shown that maintaining the intake conduit in tension reduced pipeline motion during heavy seas and thus, increase the chances of surviving a major storm event. A total of eight sand screws and 12 reinforced concrete ballast blocks were installed.
Large Diameter Fiberglass Reinforced Media Filter Housings
With the decision to utilize an open seawater intake media prefiltration was added to reduce the potential for membrane fouling. However, up to this point, the largest commercially available non-metallic filter housing available was only 60-inch in diameter. To meet the feedwater filtration requirements for the initial four RO trains, four of these filters would be required per RO train. An alternative option was to use more conventional rubber lined, carbon steel housings. Manufacturing of these housings would take up to 5 months and therefore would not meet the project delivery schedule.
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| Cartridge Filtration Final Installation |
We evaluated the feasibility of designing, fabricating and testing larger diameter fiberglass housings. After determining that existing low-pressure designs could be modified to yield an ASME code design, 100 psig housing within our time restrictions, TSG ordered eight of these filters in October for delivery of the first housing within four weeks. All eight housings were completed, crated, and shipped out of the Port of Jacksonville by the middle of November 2003. Each housing has over nine miles of reinforcement fiber.
Energy Usage
One of the biggest concern for any seawater desalination project is the energy consumed by the process. This was especially true for this project as a large percentage of the water was initially being used to complete the 18-hole golf course. In order to maximize the energy efficiency, the plant was designed with the following features:
1. Positive displacement high-pressure pumps were to be used in parallel with pressure exchanger energy recovery units;
2. Variable frequency drives would be used to control the energy recovery boost pumps;
3. A low membrane flux (8.6 gfd) was selected to reduce the membrane operating pressure; and
4. A membrane recovery rate of 45 percent was selected to reduce seawater-pumping requirements.
The implemented design resulted in a unit energy consumption of 9.7 kilowatt-hours per 1,000 gallons of water produced for the entire process. At a unit cost of $0.15 per kilowatt-hour, the total energy cost to produce 1,000 gallons of water is approximately $1.46.
Inland Lake Restoration
The Marriott St. Kitts Royal Beach Resort golf course includes a chain of interconnected small lakes that serve as drainage for the golf course and surrounding geography. The golf course was originally built as part of an older resort that utilized treated wastewater effluent for irrigation. The performance of the wastewater plant was below specification; resulting in significant carryover to the lakes.
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| Membrane Process Room |
One of the design missions of the desalination project was to provide source water for flushing of these lakes with a goal of restoring aquatic life to the lakes. The proposed design call for the disposal of the membrane concentrate to the highest lake within the chain. As an addition feature, the media influent piping included a seawater by-pass to allow blending of the membrane concentrate stream with fresh seawater. The lake conductivity is monitored and record twice daily as part of the lake restoration project.
Following the first month of plant operation, the water transparency had improved to the point the lake bottom was visible for the first time in years. Fish have also migrated into the lake system.
Royal Building System
As part of their overall business operation, the owner of the resort complex has a division that manufactures an interlocking PVC building system, known as the Royal Building Systems™. This system consist of rigid extruded polymer components that serve as the finished formwork for a variety of concrete walls including bearing, non-bearing, retaining, and foundation wall applications. This patented wall system is available in a variety of sizes, shapes and colors to meet every building need, from the simplest enclosure to complex architectural designs. Window and door openings and jambs are easily incorporated. Insulation and electrical raceways can be built-in. Assembly is simple, and finished interior and exterior walls are ready for immediate use.
This building system was very appealing to TSG as it can be installed extremely fast and provides a corrosion resistance end product with tremendous strength. The wall support system can be fastened using expansion wedge anchors. Unfortunately for this project, the building was provided without any acoustically treatment to reduce sound. This shortcoming is currently being resolved through the implementation of acoustical tiles.
The project scheduled called for the main RO building to begin construction in early October 2003 with substantial completion by the end of the month. This schedule was delayed by four weeks due to heavy rains in the region. Actual site clearance started in early November 2003.
Web Based Remote Monitoring
The control system that manages the facility is comprised of PLCs and a Touchscreen all linked with Ethernet Connectivity. This universal Ethernet connectivity standard is the same standard utilized by most networked offices world-wide. TSG has expanded upon this standard with existing technology and created a secure “tunnel” through the Internet to provide real-time monitoring and data transfer between the SWRO facility and TSG’s Engineering office in Gainesville, Florida. This real time data flow allows TSG to remotely monitor and diagnose the client’s problems or questions. Additionally this streaming data can be collected and trended to provide long term troubleshooting assistance to the client as well as provide valuable operational feedback for future design improvements. This mainstream connectivity is one of the first steps towards TSGs expanding training and assistance system that will be used by its clients and own operational staff.
Project Economics
The desalination facility is part of Royal Utilities that also operate the power station and wastewater treatment plant. The plant is staff full time for eight hours each day with on-call personnel for the balance of the time. The plant controls include an Autodialer to alert staff of any system problems.
Assuming 10-year debt service at 5.5 percent, the fixed costs associated with the capital for this project is approximately $1.11 per 1,000 gallons. The total cost of water produced by this plant is approximately $3.90 per 1,000 gallons.
This project, along with many others completed in the Caribbean, demonstrate the viability of seawater desalination as a solution to help meet Florida’s growing water demand. This project was completed in less than five months through the cooperation of Owner and local government. It further supports the benefits of the design-build format as a means of developing and implementing cost effective solutions
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