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
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