At the beginning of the year, a large desalination plant was put into operation on Australia’s Gold Coast. It delivers 125 million liters of drinking water each day, which in this dry region corresponds to 20% of drinking water requirements. For this project, Nijhuis Pompen BV of Winterswijk — part of the Norit Group — delivered and installed 42 pumps. At the customer‘s request, some pumps use condition monitoring, where the vibrations are measured using sensors and measurement modules on the Wago-I/O-System.
Precisely on the day on which André Betting visited the seawater desalination plant, the Gold Coast Desalination Plant in Tugun, Southeastern Queensland in Australia, it was raining cats and dogs. André Betting is a project manager at Norit Nijhuis who was on-site for some final work on the pump systems. It is almost a little depressing after people have worked for nearly two years on this 1.2 billion dollar project when shortly before start-up, fresh water (rain) simply falls from the sky. The necessity of such a plant is nevertheless controversial: it should bring to an end the threatened shortage of drinking water in a region whose economy is growing steadily. For years, this region has struggled with ever-drier conditions, and the population is growing by 55,000 people per year, which puts constant pressure on the water supply.
Drinking water from the sea
To make drinking water from sea water, a 2.2 km tunnel with a diameter of 3.7 m had to be drilled in the bedrock in Tugun in order to draw sea water from the coast approximately 1.4 km away. At the height of the desalination plant, a 70 m deep shaft was dug that opens into this tunnel. The other side of the tunnel ends in the sea approximately 40 m under the subsiding sea floor. Here too a shaft was dug, from which sea water is drawn at low speed via an intake approximately 20 m under sea level in order to protect the sea flora and fauna. The law of “communicating pipes“ (Blaise Pascal) ensures that the sea water climbs passively until approximately 20 m below the ground level of the system. The remaining level difference is pumped up with four vertical turbine pumps. Each of these pumps has a capacity of 5,000 m³ per hour — with a hydrostatic head of 23 m. In a pre-treatment phase, organic material is removed from the water. Subsequently, the water is subjected to additional treatments in order to correct the acidity and chlorination, and it is then pressed at high pressure through several membrane filters (reverse osmosis). The reverse osmosis procedure performs the actual desalination: the water molecules pass through the membrane, while the salts and other particles are left behind. This process is very effective and filters out 95 to 99% of the salt. In a post-treatment step, the water is brought up to drinking water quality and stored in huge containers. From there, it travels through two newly-built pump systems and a 24 km pipeline into the drinking water network. The volute casing pumps used for this have a capacity of up to 2,400 m³ per hour, with a hydraulic head of up to 135 m. Various pump models from Norit Nijhuis are used in the whole project.
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