A major environmental project to help rejuvenate a lake at the heart of Berlin attributes much of its success to unique submersible blowers from UK manufacturer Adams Ricardo.
Since the fall of the Wall in 1989, Berlin has seen continuous development with the reunification of East and West Germany, and Berlin's resumption of its role as capital. One of the city's most radical environmental projects was to reestablish a nature reserve around parts of the Rummelsburger See, a 740-acre lake, as well as the rebuilding of the residential area. Luxury apartments have been built and more are under construction around the once thriving harbor side area.
To attract residents, the Berlin Senate knew that they would need to solve a major problem: the Rummelsburger See was stagnant. Years of use as a harbor and the lack of oxygenated water flowing through it had resulted in a lake empty of any wildlife and discolored due to the huge amounts of algae that had formed there.
AGO HydroAir GmbH was contracted to solve this problem, but they knew that the answer would not be a straightforward one.
The solution was to aerate the water. However, a typical land-based blower solution capable of aerating the entire Rummelsburger See would have caused major noise pollution not only for the residents living in the area, but also for the planned nature and wildlife park.
Tests conducted by Adams Ricardo and HydroAir showed that land based blowers would operate with a noise level of 86 dB(A), a level far above what is acceptable for a residential area. (A jumbo jet taking off creates 80 dB(A) at a distance of 1,000 feet.) The cost of silencing the blowers would be astronomical since the permissible noise above the background level was almost zero.
This requirement was particularly severe as the background noise level drops at night, the very time when people are most aware of noise, and any noise would have been propagated with minimal loss across the surface of the water.
Adams Ricardo applied their expertise and presented a unique solution — the submersible blower. A technical innovation in the field of water and sewage treatment, the blower is submerged in the water, dramatically reducing the noise level. In addition, the cooler temperature underwater increases the air density and enables the blowers to run more efficiently.
HydroAir specified the Adams Ricardo submersible blowers. Each blower, made of cast iron and coated with epoxy paint, was supported in a galvanized steel cradle suspended from a floating pontoon moored in the middle of the lake. The benefit of this approach was that there was no need to erect a building to house the blowers, saving on both construction costs and the acquisition costs of land on which to site it.
Furthermore the visual impact was minimized due to the low profile of the equipment and its distance from the shore. The blowers were each capable of blowing 268 ft/min) free air delivered (inlet air at 15°C at sea level) against an operating pressure of 630 millibar. The air then passed via a common manifold down two separate coarse air bubble diffusion pipes of 2,950 feet and 4,265 feet respectively, which went in different directions from the pontoon to give overall coverage of the lake. These pipes had been secured to the bed of the lake by T.O.P.P. Anlagenleasing GmbH, the main contractors of the project.
AGO Hydroair tested the noise of the blowers from the shore at 4 a.m. on a still morning at a distance of 660 feet, and recorded a level of below 41 dB(A) — well within acceptable environmental limits.
Following completion of successful trials by Adams Ricardo, the blowers were installed in March 2002 and found to be more efficient than had been anticipated for a land based equivalent.
Both T.O.P.P. and HydroAir decided that operating just two blowers at a time was adequate as the backpressure was found to be less than originally expected. So they rotated the use evenly between all four blowers.
Operating experience elsewhere has shown that for a blower operating continuously the lubricant can last three years. With blowers operating on an intermittent duty each blower should only require a service every five years.
Hydroair was delighted with the solution, and it was estimated that the submersible blowers would save the Berlin Senate around 15 percent in reduced energy usage. In addition, substantial further savings would be made due to the extension of service intervals.
Chris Davis, managing director of Adams Ricardo, comments, "This application has been a perfect opportunity to demonstrate the unique benefits of the submersible blower. HydroAir had three specific requirements; a blower had to be quiet, economical to run, and not spoil the visual impact of an up and coming area of Germany's capital city. Our system was the perfect match."