Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/983801
Water.desalination+reuse June 2018 On Site 17 TECHNOLOGY & EFFICIENCY • Plant performance "significantly improves" on industry average energy consumption • Large size Dissolved Air Flotation and Dual Media Gravity Filtration systems • Proprietary energy recovery technology that utilises brine The project team also took a spark of innovation into its technology and process design. The intake infrastructure and pumping station are to be built new, and the team had to find routes and channels under roads and around neighbouring structures. The plant will use a pipe intake reaching 1.2 kilometres into the sea, and an outfall pipe of two kilometres. This is in line with the Environmental Impact Assessment, and in compliance with the relevant environmental regulations. "We looked at the currents, and at the nearby coral reefs. We decided to go a bit further, to protect those," says Keil. The pumping station is about 16 metres in depth, and water is pumped into DAF unit of 26 metres by 110 metres, which typically has 99 per cent recovery. From the DAF, the water goes to a dual media gravity filtration (DMGF) system of 50 metres by 95 metres, partly above and partly below ground, with a hydraulic design making it more economical. Any sludge from the DAF or DMGF goes to a thickening treatment system, which is later put into a centrifuge and trucked for recycling or fertilisation. "This is something that DEWA will take the benefits from, and we included in our design thinking as a developer, and not just a contractor," adds Keil. A‰er the DMGF, it goes to a typical two-pass RO — seawater RO followed by brackish water RO — and then for remineralisation. "Remineralisation is a difficult process that must be Dubai has big ambitions to rebalance to reverse osmosis Dubai produces 470 million imperial gallons (MIGD) a day (2.1 million m3/d) of desalinated water, of which five per cent is from reverse osmosis (RO). While desalination capacity has remained steady since 2012, demand for potable water supplies is rising by about 22 per cent a year. The goal is to procure additional capacity to take the total output to 750 MIGD (3.4 million m3/d), and to rebalance the emirate's water portfolio in favour of RO technology over thermal. Currently about 95 per cent of desalination capacity in Dubai is multi-stage flash, powered using waste heat. By 2030, DEWA aims to have 41 per cent of desalination capacity come from RO. The second strand to DEWA's desalination strategy is to have the RO capacity powered by solar, in a bid to reduce greenhouse gas emissions and save an estimated $13 billion. The emirate has built the world's largest single-site solar park based on an Independent Power Project model, the Mohammed bin Rashind Al Maktoum Solar Park. Investment in the park has totalled AED 50 billion ($13.6 billion) in three phases, with the third phase awarded to Masdar in 2016 and due to complete by 2020. The first three phases use photovoltaics (PV); longer-term the plant will use concentrating solar power. The goal is to generate 1,000 MW by 2020, and 5,000 MW by 2030. DEWA has established a solar- powered water pumping and desalination station at the site for research and development, using PV solar panels to desalinate water with RO technology, at a production capacity of 50 m3/d. The investment is in line with its plans to decouple water desalination and power production, and for desalination using solar energy. DEWA aims to have 41 per cent of desalination capacity come from reverse osmosis by 2030 2017 2030 Multi-stage flash (MIGD) 445 445 Reverse osmosis (MIGD) 25 305 Total desalination capacity 470 750 Reverse osmosis proportion of total 5.3% 40.7% 2010 2014 2011 2015 MIGD 2012 2016 2013 2017 2018 750 650 550 450 350 250 Installed desalination capacity and peak desalination demand done correctly, that includes limestone filters and all kinds of introduction of minerals to make it good quality, potable water," says Keil. The process is additionally using a proprietary technology for energy recovery from brine, and a brine treatment process before it is discharged back into the ocean. "The design requirements from DEWA and ILF were super challenging, but from our perspective it is a pleasure to work in such an environment, because if they set the technical requirements very high, and you come with real value engineering, it makes a difference. It's not necessarily the quickest and cheapest, but what you can achieve is outstanding. If we had to sell the water as owner of an Independent Water Plant, it would be a very competitive rate," Keil says. The new plant "significantly improves" on industry average energy consumption, he adds. n n n Installed capacity (MIGD) – Peak desalination demand (MIGD) The consultant's original design foresaw two- storey buildings, which Besix was able to avoid, reducing costs