Water and Effluent Treatment Magazine
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O wned and operated by Jersey Water, the La Rosière reverse osmosis (RO) desalination plant provides essential top up water supplies for the island's reservoirs during prolonged dry periods. Last upgraded in 1999, a major modernisation programme is underway to replace plant that has reached the end of its working life. The goal is to bring the plant right up to date, taking advantage of the latest RO membrane technology to provide a highly resilient and efficient fresh water solution, while almost doubling capacity to 10.8 million litres per day to take account of changing climate, population growth and increasing summer demand from tourism and agriculture. Led by ACWA Services, the turnkey solution comprising design and procurement through to installation and commissioning will see the complete redesign and expansion of the existing seawater reverse osmosis (SWRO) process streams, with new pressure vessels, an additional dual media filter, next generation high capacity RO membranes, energy recovery and pre-treatment systems and associated equipment. Cost savings Strict planning constraints and Value engineering a resilient solution • Overcoming strict planning consents, re- use of existing infrastructure and site constraints proved crucial for desalination project on Jersey. ACWA Services' Peter Brewer explains. ONSITE DeSAlinAtiOn uPgrADe the new solution will recover pure water at a rate of 45% limited space availability on site set the tone from the outset and it was agreed that existing buildings would be utilised as far as possible to avoid additional construction. This would remove the potential for extended planning consultations and deliver significant cost savings. But, accommodating the new 10.8 million litres per day capacity in a building originally designed for six million litres per day, with the potential to up-rate this to 15 million litres per day to further future-proof the facility, needed careful evaluation and design input to establish what was suitable for re-use. Reverse osmosis uses hydraulic pressure and semi- permeable RO membranes to diffuse pure water from seawater using osmotic pressure. The new solution at La Rosière is designed to recover pure water at a rate of 45% using the latest RO membranes, which benefit from an additional 25% active surface area for the same volume. These are contained in pressure vessels all of which are being re-used, supplemented with additional vessels to achieve the desired increased capacity. These are designed and manufactured to precisely match the existing pressure vessels to ensure standard pipework connections project specs • Value engineering a resilient solution • redesign and expansion of the existing seawater reverse osmosis (SWrO) process streams • use the latest rO membrane technology to resilient and efficient fresh water solution throughout the system. The original six million litres per day plant capacity was achieved using four streams of filtered sea water to feed the RO pressure vessels. To save energy, the new plant will only use two streams, each with a high pressure pump and energy recovery device to deliver pre-filtered seawater to two banks of 72 RO pressure vessels, 144 in total. This is achieved by modifying the RO vessel support frames and redesigning the feed and discharge pipework. The design is very efficient, reducing the relative specific energy consumption of the new RO system by 40% compared with the old set-up. Extraction To achieve the increased plant capacity, it was also necessary to establish the capacity of existing process units and which elements would need upgrading or replacing. The seawater intake pumps and pipework which discharge into the existing quarry pool were found to be of sufficient capacity to feed the new system. However, seawater extraction from the quarry pool and delivery to the pre- treatment systems needed upgrading and it was found to be more beneficial to replace the existing quarry pool pumps with fewer, larger and more MArCH 2016 Wet NeWs 19 efficient units incorporating inverter drives, as opposed to doubling up the existing pumps. This reduces power consumption and will provide more operational flexibility. The common discharge main from the pumps to the pre- treatment plant was undersized for the new capacity and therefore required replacement. The heart of the pre- treatment plant comprises two filter vessels containing dual media filters to remove suspended matter from the seawater. Trials established that an additional filter vessel would be required to achieve both the desired water quality and capacity, and this has been configured adjacent to the existing filters to simplify manifold pipework and ensure ease of operation and maintenance. A final stage is to condition the seawater using new 5 micron cartridge filters before passing through to the RO system. The existing cartridge filters were under sized for the new duty and an awkward location with difficult access determined a new design arrangement with larger vessels and li˜ing facilities to make future operation and maintenance far easier. All existing chemical dosing systems were at the end of their useful life and will be replaced with much more accurate up to date systems which in turn will