Mount Maunganui chemical manufacturer Dominion Salt has selected Auckland’s APD for the design, delivery and installation of multiple new storage tanks which improve the company’s production processes. By choosing APD, Dominion Salt has received cost-effective, reliable plant with proven longevity.
Dominion Salt harvests salt from the waters of the Southern Pacific, then refines and delivers the product to a range of diverse industries and destinations around the world. Founded by George Skellerup in 1942 and operating initially from Lake Grassmere in the South Island, the company opened its Mount Maunganui plant by 1974. The Bay of Plenty refinery receives raw salt from Australia, processing it into finished food, pharmaceutical, industrial and agricultural grade salt shipped to customers internationally.
Dominion Salt Site Engineering Manager Tim Knowles explains that on arrival, raw salt is mixed with water to form a brine which undergoes a purifying process. “We required two new vessels for this process, one with a 30-kilolitre capacity and another of 16-kilolitres, for pharmaceutical and food grade salt, respectively.”
The selection of APD for the job, says Knowles, was somewhat straightforward. “There are basically two options for this application: steel or High-Density Polyethylene. We already have several HDPE tanks on site supplied by APD which have been performing well since 2009, so the choice was obvious.”
Manufactured in Auckland from HDPE PE100, both tanks are open topped (exposed to the atmosphere). This required care in shipping, as the weight of the vessels could cause their collapse.
Unique designs for the vessels include, in the case of the 30-kilolitre tank, an offset agitator which required welding a bush to the base which now accommodates a shaft running 4.7 metres from top to bottom. Additionally, both tanks feature horizontal baffle plates which prevent settling. “The way APD welded and secured these features is brilliant. The tanks have a long-life expectancy and that includes the fixtures and fittings inside them. The manufacturing is top notch and can be expected to last,” Knowles notes.
Furthermore, it is well known that even stainless steel will corrode in the presence of sodium chloride. By contrast, chemically inert HPDE doesn’t react with any of the chemicals used in the salt production process, combining longevity with low maintenance and reliability. The APD tanks are also far lighter than a steel counterpart, easing handling and installation.
While the Coronavirus lockdown struck during the delivery of the project, Knowles says APD responded rapidly to keep matters on track. “There were impacts on costs and timings, but we can’t complain. APD kept us posted at all times, so we could adapt together to an evolving situation.”
The new tanks are deployed towards the end of a production process designed to eliminate impurities by holding the liquid and allowing completion of a chemical reaction. “The tank is a delayed reaction vessel which allows all solids to dissolve and remain suspended in the brine, after which the solids are removed,” says Knowles.
Rather than increasing production per se, he says the new tanks increase the volume available to complete the purification process. “Before the introduction of these tanks, we were encountering issues with sediment build-up in the filtration systems owing to limited volumes. Now we have an improvement in efficiency as there is more room for the chemical reactions to fully take place before the next phase in our process.”
In conclusion, Knowles says APD is a trusted partner relied upon for the delivery of lightweight, cost-effective and chemically resistant tank solutions. “The tanks are built solid and fit for purpose. And, in fact, they work so well on site that we already have another order in for more.”
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