Pulsar Process Measurement Ltd.

Pulsar Sludge Finder 2`s, Wirelessly Helping with Final Treatment Compliance

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Source: Pulsar Process Measurement Ltd.

Pulsar have supplied 14 Sludge Finder 2 sludge blanket detectors to Severn Trent for their Barnhurst STW near Wolverhampton, automating the critical final treatment process to aid Compliance and reduce out of hours call-outs. On this large, well-established site, it would have been impossible to cable the units back to the control cabin, so Pulsar developed an integrated wireless system connecting the field-mounted Sludge Finder 2 unitsto the site control and telemetry systems.

Equipment used

Sludge Finder 2 is an ultrasonic interface measurement system, which generates an ultrasound pulse that reflects from the sludge interface and reliably helps staff to optimise sludge production.It also automatically starts the flushing sequence.

Barnhurst is a large site, with fourteen final settlement tanks. A failure in the process within any one of the tanks could lead to a breach of Consent, so an early warning and control system is important. The challenge was to identify an instrument capable of reliably measuring the interface level, and then delivering that measurement to the on-site SCADA and telemetry system so that, when required, sludge can be withdrawn at an increased rate to protect effluent quality.

Pulsar are acknowledged leaders in acoustic signal processing, with global expertise in non-contacting ultrasonic level and flow measurement. The key to their success has been the development of powerful acoustic discrimination software. By applying that experience to Sludge Interface measurement, Pulsar have brought confidence and automatic control to an area where, previously, measurement was largely manual, inefficient and unreliable.

At Barnhurst, the Sludge level in the settlement tanks is maintained at a level termed 'healthy'. If the sludge level rises above that point, reaching a 'flush' level, the bellmouth valves are activated, returning the level to the setpoint. There may be a number of reasons that a tank reaches the flush level under normal circumstances, but it may also be an indication of a problem. The system allows four flush events within an hour before an alarm is generated. This is only possible because of the confidence with which the staff view the measurement that Sludge Finder 2 is making.

Visits by staff to resolve issues are substantially reduced, an important saving in vehicle miles and man hours. A further benefit is that the settlement tanks can be controlled more effectively, reducing pumping hours and saving further energy.

The Barnhurst site is well-established, and cabling the Sludge Finder 2's through the existing slip rings on the tanks would have been very difficult. Pulsar worked along with Severn Trent to identify and develop an effective radio system that could be integrated with Sludge Finder 2 for ease of installation.

The results have been extremely positive, and Severn Trent now have confidence that the process is well controlled. Following this successful project, many more installations are in progress, improving control and helping to guarantee Compliance across the network.

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