Compressor aids Norfolk waterway de-silting

Published:  11 August, 2009

An Atlas Copco compressor is at the heart of an aeration system using compressed air to agitate the water and overcome the build up of silt against the tidal doors that protect the guillotine gates of the Denver Sluice on the River Great Ouse, near Downham Market in Norfolk.

The sluice controls the water levels over parts of the fens and prevents high tides from flooding low-lying areas. Over the past couple of years the Environment Agency has had to dredge up to four metres of silt from in front of the gates and downstream of Denver Lock because only a limited amount of water had been allowed to flow from the three 'eyes' of the sluice due to a prolonged period of dry weather. The decision to bring the ‘eyes", which include the upstream guillotine gates back into full service was hampered by the inability to move the silted up tidal doors (mitre gate type) protecting them.

Rob Barker, the project manager from the Environment Agency, Anglian Region, sought the expertise of their NEECA Framework Consultants, Royal Haskoning, to develop his concept for an aeration system. The task fell to David Goodman, principal mechanical engineer with Royal Haskoning based in their Leeds Office, who developed the initial concept to outline design stage and produced the specification and tender drawings for the system.  The final details for the design, along with the supply and installation of the equipment was provided by Atlas Copco’s main distributor in the area, Anglian Compressors, based in Peterborough.
The complete installation comprised a GA15 VSD 15 kW rotary screw compressor together with an LV500 air receiver and a PD 60 oil filter, housed in a purpose-built GRP kiosk located on site, together with associated pipework and control valves/manifolds.

The aeration system itself comprised three concentric loops of galvanised steel pipework installed in front of each gate. Four mm holes were drilled at 100mm intervals in sections of the pipework loops with each concentration of holes covering a different section of the individual gate/sill. A set of ball valves was configured to allow independent control of each loop for concentrated aeration at higher pressures and also flushing of the system in either direction.

The decision to install a variable speed drive version of the GA15 compressor - capable of delivering air at the rate of 16 - 48 l/s at a pressure of 7 bar(e) –  was influenced by the ability of the VSD compressor to match output to demand for optimum energy efficiency and to minimise starting currents without energy penalty.
The system is now operated regularly during outgoing tides which carry the silt downstream and all the indications are that the system will continue to be effective in keeping the front of the tidal gates free from any silt build-up.

Commenting on the project, Rob Barker said: "The Environment Agency is very pleased with the early results of the compressed air aeration process.  We would certainly consider installing similar systems in other locations experiencing this type of problem."

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