Rotary screw compressor selected for aeration system

An Atlas Copco compressor lies 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 last couple of years the Environment Agency has had to dredge up to four metres of silt from 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 (of the mitre gate type) that protect them.

Rob Barker, the Project Manager from the Environment Agency, Anglian Region, sought the expertise of the agency's 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, 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 of Peterborough.

Commending the support received, David Goodman says: "The level of assistance provided by both Anglian Compressors and Atlas Copco's technical team was excellent and greatly contributed to the success of the project; and, as expected, the equipment supplied and quality of installation were first class."

The complete installation comprises 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.

In addition, the aeration system comprises three concentric loops of galvanised steel pipework installed in front of each gate. Holes 4mm in diameter 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 for flushing the system in either direction.

The decision to install a version of the GA15 compressor with a variable-speed drive - capable of delivering air at the rate of 16-48l/s at a pressure of 7bar(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 any energy penalty.

Operated regularly during outgoing tides that carry the silt downstream, the system is expected to continue to be effective in keeping the front of the tidal gates free from any silt build-up.

Commenting on the project, Rob Barker says: "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."