Ultrasonic flowmeters and the reliable measurement of wastewater in the sewage treatment plant.

Because non-invasive flow measurement is highly sensitive to low flow velocities and can be used flexibly, clamp-on ultrasonic flowmeters are proving invaluable for the accurate measurement of wastewater. They are ideal for this application, or in fact any dirty liquid that’s sonically conductive or water based. Clamped to the outside of the pipe, they use ultrasound to reliably measure flow, even with high solids content. Transducers are robustly clamped on the pipe and sound bounces back and forth, with the difference being proportionate to the velocity.

Flow measurement on a pond treatment plant.

FLEXIM was called in to assist with delivering a fresh approach to flow measurement at a German pond treatment plant. With plans to modernise and convert it into a compact plant, the engineers were looking for an alternative to their current measuring method used to assess the cleaning performance. In order for the plant to go ahead with its expansion plans, the present actual output must first be determined, and dry weather inflow rate must be measured in order to estimate future capacity needs, and to determine the cleaning performance.

The normal way to carry out this measuring task is to direct the water flow that needs to be recorded through a pipe, and to ensure that it’s always full, it needs to be designed as a culvert. A collection container was constructed with an attached pipe with a 90° upwards bend, so that the pipe is always permanently filled.

The engineers were using a magnetic-inductive flowmeter installed on the DN200 line, but this was only proving to be up to the measuring task to a certain extent. Due to the low inflow and the resulting low flow velocities, the amount of wastewater discharged would often remain unrecorded. FLEXIM replaced this with a flowmeter with a lower flow response threshold.

No need to open the pipeline.

A key advantage of clamp-on ultrasonic measurement is that the technology can be used to set up flow measuring points without having to open the respective pipeline. And because the acoustic method works practically without inertia, even the smallest currents are accurately recorded.

Ultrasonic flowmeters are not only used for balancing, but also for valuable leak detection by monitoring the low flow rates during the night.

A future-proof solution.

Following the switch to ultrasonic technology, the bespoke culvert measurement point now reliably records the amount of wastewater fed into the sewage treatment plant. And once the sewage treatment plant has been modified as planned, it will be a simple task to uninstall the clamp-on flow meter and reuse it at a new measuring point, making non-invasive ultrasonic measurement technology truly versatile, and the solution of choice for many years to come.




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