Small wastewater treatment works (WwTWs) frequently present significant physical challenges for instrumentation and control engineers. However, a compliant flow measurement facility has been installed at a plant in Fowey, in the south-west of England, by a partnership involving a water company, a contractor, an instrumentation provider and an inspection company.
THE CHALLENGE
The flow monitor at Fowey WwTW needed to be replaced as part of a capital maintenance programme which was challenging due to the constrained nature of the site. Therefore, more innovative solutions were considered as an alternative to a like-for-like replacement.
Engineers from Tecker, a MEICA contractor for South West Water, therefore reviewed the available options. “The channel is in-between two aeration ditches, and there was insufficient room to extend or divert the channel,” explains Tecker Project Engineer Ben Finney. “We therefore considered repairing or replacing the flume, but an alternative suggestion was made that we contact Nivus to see if their cross-correlation flow meter might be able to deliver accurate flow measurements without the costs and problems associated with capital works.”
THE SOLUTION
Following Tecker’s request, engineers from Nivus visited the site and specified the instrumentation requirements, based on the Nivus NF750 transmitter, a cross-correlation velocity sensor combined with ultrasonic level measurement. “The popularity of this technology has grown enormously in recent years,” says Rob Rhyder from Nivus. “This is frequently because the flow meter can be quickly and easily retro-fitted to damaged or ageing channels, without having to implement significant capital works.”
Explaining the advantages of this solution, Ben Finney says: “The cross-correlation flow meter was delivered within a month of the order and installation took less than a week. In contrast, work to repair or replace the flume would have taken much longer to organise and implement; it would have cost a great deal more; normal operations of the plant would have been impacted, and there would have been no guarantee of MCERTS compliance. We were therefore delighted that the Nivus solution was implemented so quickly, and that it passed the MCERTS inspection.”
RESULTS
Following the installation of the Nivus NF750 transmitter, the flow measurement facility was tested and passed MCERTS, without any impacts on the plant’s treatment processes. Looking forward, Ben Finney says: “It is likely that we will utilise area velocity flow meters in more applications because they are sufficiently flexible to be able to accommodate a wide variety of hydraulic systems. In addition to the reduced costs and faster installation times, one of the most important advantages is the minimised requirements for process impact.” Emphasising the importance of a partnership approach, Ben adds: “Obviously, we were keen to ensure that the flow installation received MCERTS approval, so it was highly beneficial to accommodate the views of all stakeholders from the beginning, including the MCERTS inspector.”
– Dave Curtis, MEICA Specialist, South West WaterMore demanding requirements from the regulator combined with challenging process scenarios mean that the need to consider alternative technologies is essential…The technique offers a valuable tool in our armoury where the application does not suit other closed pipe or noncontact methods.
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