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Product category: Waste-water handling, monitors + treatment
News Release from: ABB Automation Tech (Instrumentation + Automation) | Subject: Swirl meters
Edited by the Processingtalk Editorial Team on 08 March 2006

Swirl meters cut costs in water
treatment upgrade

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Swirl meters from ABB have helped save thousands of pounds off the cost of a recent upgrade to the waste water treatment facilities at Biddulph in Staffordshire

Swirl meters from ABB have helped save thousands of pounds off the cost of a recent upgrade to the waste water treatment facilities at Biddulph in Staffordshire United Utilities was required to upgrade its Biddulph works to meet a revised effluent discharge consent from the Environment Agency

The new consent principally tightened the requirement to remove ammonia, but also included tighter limits on BOD and suspended solids.

As part of AMP 3, United Utilities employed a Galliford-Costain Joint Venture and Degremont to carry out the upgrade, which required the installation of two new aeration lanes.

These improve the supply of oxygen to the bacteria that digest the contaminants.

Six flowmeters measuring the supply of air into the aeration lanes form a crucial part of the operation and control system, but the use of conventional insertion thermal flowsensors would have meant suspending pipework over the tanks, complete with walkways and handrails to gain access to them.

This is because single point insertion meters require relatively long runs of straight pipe both before and after the meters if they are to give accurate readings, typically 15 pipe diameters upstream and 5 pipe diameters downstream.

The ABB Swirl meters typically need just 3 and 2 diameters.

'The extra platforms and pipework would have amounted to between GBP8k and 10k in my estimation,' says Degremont Project Manager Robert Hill.

'The Swirl meters were slightly costlier than the insertion meters, but they have allowed us to install a tighter configuration of pipework in a smaller area that is accessible from ground level.

This has enabled an overall cost saving to the installation.' The meters work by first using static blades at the inlet to set the process fluid rotating, or swirling.

The fluid is then accelerated by a reduction in the cross section of the meter before being decelerated and deswirled as it leaves.

A piezoelectric sensor is positioned in the centre of the meter at the point of maximum fluid velocity.

The primary rotation caused by the swirler has a low-pressure zone at its core.

This low-pressure zone is thrown into a secondary rotation proportional to the fluid flow rate so that it looks like a helical coil.

At low flow rates, the low-pressure swirls are farther apart and the coil is stretched out.

At higher flows, the swirls are closer together and the coil is compressed.

Areas of slightly higher pressure separate the low-pressure swirls.

The sensor will deflect to the left and right as a pressure swirl passes from one side to other.

The frequency of this deflection is proportional to the volumetric flowrate.

The ABB meters were installed at Biddulph WwTW several months ago and have been running trouble free ever since.

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