[Editor's note: Images have been updated.]
Since the advent of the Adelaide Desalination Plant at Londsdale, South Australia, a political storm has surrounded the $1.83 billion facility.
Most recently, SA Water announced that the facility would be "mothballed", prompting many to decry the "waste" of resource spent building the plant.
Other issues have included worker safety during the construction of the plant, the high energy consumption associated with the reverse osmosis desalination process, and the environmental impact of the concentrated saline discharge.
But to talk to some of the engineering brains behind the desalination facility is to gain a perspective into just how much expertise and thought went into every stage of the plant, with energy use, efficiency, reliability and transparency being just some of the key considerations.
Process and power use
The Adelaide Desalination Plant runs on renewable energy from AGL, which, while boosting its green credentials, costs 20 percent more than regular power.
According to Andrew Evenden of ACCIONA Agua, a key focus of the AdelaideAqua consortium was in the effective use and re-use of energy.
"The largest cost for desalinated water is power," Evenden told PACE magazine. "[But] there are some unique process features of this plant which make it quite efficient."
The desalination plant is situated on two levels. RL32, which houses the intake and outfall buildings, is 32m above sea level, while the main buildings are situated on RL52, 52m above sea level.
"We have to lift the water from sea level all the way up to RL52 to process it," said Evenden. "There is a lot of energy involved in doing that."
With the pump station situated 8m below sea level, 12 intake pump motors are gravity-fed the sea water from a 1.4 km long intake tunnel.
This water is run through three rotating band screens which remove solids larger than 3 mm, and then pumped through two separate headers to the RL52 main process area.
In the main process area, the water flows through disc filters, which remove particles larger than 100 micron. This system is cleaned by backwashing every one to two hours.
The water is then ultrafiltered (UF). This system, utilising porous Polyvinylidene Fluoride (PVDF) membranes, removes particles larger than 0.04 micron.
The UF system is also cleaned by backwashing, and also has a clean-in-place facility using chlorine and acidic solutions.
When the desalination plant is running at full capacity, it takes in 600 megalitres of water a day, approximately 50 percent of which emerges as fresh water.
The other 300 megalitres, which consists of seawater used for backwash and saline concentrate, is returned to sea via the outfall shaft.
[Pictured alongside and above: The two energy recovery hydro turbines where specially manufactured in super duplex stainless steel by Australian manufacturer Pentair Southern Cross Tamar. Each turbine generates up to 685kW, operating on a net head of 41m and flow rate 1480-1980 litres per second, for export into the grid.]
The turbines each provide 700 kW of energy which is then reclaimed and used in the process.
To prevent any accidental damage to the highly fragile and expensive reverse osmosis membranes, cartridge filters are situated between the ultra-filtration and reverse osmosis systems.
The reverse osmosis process, which is spread across two buildings of the plant, gets rid of dissolved particles and salts to yield pure molecules of water.
The Adelaide Desalination Plant utilises over 40,000 individual RO membrane units each with a surface area of over 40m2.
Saline concentrate
In order to overcome the natural osmosis pressure of seawater, the water is pumped through the membrane at high pressure.
At such pressures, the fresh water passes through the membrane more readily, while leaving the dissolved salts behind in the form of a saline concentrate.
The saline concentrate, which emerges from the reverse osmosis rack at high pressure, provides another opportunity to recover some energy using spinning rotors.
"We have an energy recovery system that converts the high pressure output of the RO rack to use that energy mechanically to boost the pressure of the feed going into the rack. They provide a significant benefit in terms of saving and efficiency," Evenden explained.
According to SA Water, about 50 percent of the water entering the reverse osmosis membrane racks is partly pressurised by energy recovered from the wastewater stream.
Distribution and control
With all these power requirements, it is no surprise that the Adelaide Desalination Plant is the biggest single electricity user in South Australia.
The facility takes 66 kV from the main grid, and steps it down to 11 kV. This then feeds 2.4 megawatts of power to each of the 12 pumps for the reverse osmosis process, as well as the other pumps used in the plant.
Besides the pumps, a variety of other control equipment is present at the facility, necessitating 270 columns of switchgear on the site. Schneider Electric-owned Magellan Power's converters, support systems and power monitoring systems enact a key support role.
"In total, we have 280m of low-voltage switchboards on our site, [with a] maximum rating of 6.6 kA, and we are rated to 60 kA for one second on those switchboards," Evenden said.
In order to provide power to the Schneider Electric motor control centres, ATS soft starters and variable speed drives, the 11 kV feed is further dropped down to 690V and 400V.
According to Evenden, transparent monitoring and control over all this equipment was a key focus for the project, and this was achieved by implementing a number of networks around the plant.
The facility utilises a decentralised control architecture, with the 16 different areas of the plant each covered by a Quantum PLC.
"The main network is the level 3 ring around the entire plant," Evenden said. "The level 3 ring connects the main [Quantum] PLCs between the different facilities within the plant. It connects to the CITECT-based SCADA system and also to the State Government network."
This connection to the State Government system allows SA Water to monitor the performance of the plant in real time.
"Below that level, there's a series of level 2 rings, which connect the individual plant assets in each of those areas. All those connect together as one network, is visible throughout the whole plant, and the data is available for trend analysis."
ACCIONA Agua, as part of the AdelaideAqua consortium, opted to use Schneider Electric technology based on existing relationships and experience with the company, especially in past projects around the world.
"This is technology we know. When we looked at Adelaide, we looked for someone who could provide this technology we knew, who could provide a global solution for this, and was supported in the country," Evenden said.
"The range of [Schneider Electric] products we have in the plant is fairly broad – we probably have one of everything."
Evenden said the choice to use Schneider Electric's equipment meshes with the constant conversation that the plant partners had around power consumption.
"There are benefits of using the level of automation and infrastructure that Schneider has. The configurability and the flexibility of those drives [we have in the plant] allow us to optimise power consumption," he said.
Partnership in design
But ACCIONA Agua would not be simply installing off-the-shelf Schneider Electric products. Rather, as a Global Strategic Account for Schneider Electric, both companies designed the solutions together, predominantly through partnerships in Europe, where both companies are based.
"Schneider Electric participated in the design of many aspects of the electrical side of the plant," Evenden said.
"For example, the computer network in plant was a joint ACCIONA Agua/ Schneider Electric design. The protection systems within the plant were also a joint design."
On its part, Schneider took on feedback from the AdelaideAqua team, and the feature requests from the customer, working them into the R&D of the products.
However, the journey has not been a totally smooth one, with both parties encountering issues with bringing solutions developed in Europe into Australia's regulatory environment.
"When we buy equipment from around the world, we must ensure it meets the strictest requirements in Australia. That was something we fell down on earlier on," Evenden explained.
"We bought equipment from lots of different sources, and they met a lot of international and European requirements. But bringing them back into Australia, there needed to be some work on the equipment before they met Australian requirements."
As a result, the partners had to make augmentations to the equipment upon delivery to ensure they met Australian standards.
"I think there are some lessons to be learned, the biggest one of which is to involve the Australian Schneider Electric more actively, earlier on," said Evenden.
"We left that a little bit late, but we did catch up. We had an incredible amount of support over the last 18 months from Schneider Electric, to overcome some of our core international issues."
Schneider Electric, on its part, noting the issues faced by international customers, is addressing the challenges internally via a program called "Schneider One", which aims to unify operations to deal with international buying and localised standards.
Implementation
The jointly-designed equipment was put in place around 18 months ago, and the plant is still in the commissioning phase.
In December, it will be handed over to its operator, which is a joint venture between ACCIONA Agua and Trility, who will run the facility for 20 years.
According to Evenden, the equipment has worked very well over the past 18 months, and he is confident that it will continue working well for the next 20 years.
"The amount of effort we put in during the design phase sorting out the issues with local standards has paid off," Evenden said.
While energy efficiency is built into the design of the climate-independent water supply, flexibility and the capacity for future optimisation was also provided for.
This means the operator will have the insight and capability to tweak various areas and features to improve energy consumption in the future.
Evenden's response to comments relating to the plant being mothballed is a measure of his confidence in this built-in flexibility.
"We've designed the plant to be able to use a range of capacities. It can be shut down for a short or prolonged period. It was all part of what was contemplated in the design," he said.
"From a design point of view, it's a flexible plant which can be shut down and started up quickly. Which is why it's there: it's an insurance policy."