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| Anaerobic digestion plant under construction. |
By Cameron Gray, P.Eng., Donson Engineering and Contracting Ltd., North Bay, Ontario
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| Anaerobic digestion plant under construction. |
The glass-fused-to-steel tank market has been driven by the corrosion-resistant silica glass coating on the steel panels. Today, there are over 180,000 installations in more than 80 countries, with unprecedented growth during the past decade. The system is a storage tank made of sectional steel panels with glass molecularly bound (fused) to the steel surface. This provides a very durable, but flexible surface with excellent corrosion resistance, resulting in a tank, which can provide long life in a wide variety of applications.
The tanks are available in standard sizes, ranging from 2,600 to over five million gallons capacity, with roof, floors, mixing equipment and many other appurtenances available.
Glass-fused-to-steel tanks have found very wide application in the water and wastewater treatment industry. In addition, as simple storage vessels, tanks have become very popular with the engineering fraternity, for the more complex industrial process applications. In potable water treatment, the sectional tank systems are used as clarifiers, shells, filters, contact tanks, thickeners, reservoirs and standpipes. In the waste treatment industry, they are used as aeration tanks, clarifier shells, trickling filters, anaerobic digesters (tanks and/or covers), gasholders, odour control units, biosolids storage and flow equalization.
Glass tankage systems are easily adapted to a wide variety of complex internal requirements that could include clarifier mechanisms, aeration systems, mixers, media support structures, weir troughs, baffles and many other specialized requirements.
Tanks are delivered to site, flat packed, for easy transport and site handling. The prime components of the kit are the glass-fused-to-steel panels, ready for bolting together and complete with any special cut-outs for nozzles and/or manways or other appurtenances as required. The panels overlap and are bolted together and sealed with a high performance seal, chosen to suit the material being stored.
At the top and bottom of the tank, a galvanized steel anchor provides dimensional stability. The bottom angle is leveled on shims and secured to the concrete base, with anchor bolts. The rebate is then filled with concrete and a perimeter seal to ensure a bubble tight interface. Sectional tank designs can be carried out in a wide variety of national codes, including AWWA, DIN, NSF61 and local building codes.
Panel joining is an important feature worthy of closer examination. The sealant (mastic) is applied to the overlap sheet surface and is allowed to dry and cure. Mastic has the benefit of forming an adhesive bond with the glass on the panel. It is also flexible and has high cohesion strength. This means that, as the tank flexes, the seal can move with the tank and remain intact, an improvement over gasket seals.
All the bolt heads are plastic-capped to provide corrosion protection in the process environment. Mastic squeezes out between the panels and the bolt head seals the shank and protects it from contact with process fluids.
Construction with jacks is cost-effective and particularly beneficial for taller tanks. A trained and experienced crew of three people can easily install twenty sheets per day. An example of this efficient construction procedure is the Regional Municipality of Niagara -- Garner Road biosolids storage where the third tank (106' diameter x 33' sidewall complete with geodesic domes) was erected in less than two weeks!
This article was abridged from Environmental Science & Engineering magazine, which also contains many more articles not posted on our Web Site. See our home page on how to order your subscription. We regret we can only accept orders from Canada and the United States.