Ensuring a protected environment for people and installations, clamp-on ultrasonic flow measurement technology is helping to guarantee air circulation in the processing of wastewater sludge.
A long-term challenge for the water treatment industry, sludge is the by-product removed from the slurry through the course of industrial or municipal wastewater treatment. Removing the water from the sludge through the process of evaporation reduces its weight and volume, which in turn makes storage and transportation much more straightforward.
Why is ventilation flow measurement so important?
During the processing of wastewater sludge, methane is formed through anaerobic processes that produce biogas. Methane has the potential to become explosive when mixed with oxygen, which is why it’s so important for the sludge dewatering installation to be ventilated to prevent high concentrations of methane.
The ventilation flow measurement is a crucial parameter for securing the safety of both personnel and installations. This is where clamp-on flow measurement can offer a convenient and reliable solution.
Used to measure the flow of fluids within pipes, non-invasive ultrasonic clamp-on flowmeters have an uncomplicated design, comprising clamp-on transducers and an electronic converter. There are no moving parts and the internal fluid is never touched, meaning that the need for time-consuming maintenance is greatly reduced, if not removed entirely.
Safe, stable and reliable.
FLEXIM was tasked with optimising the safety of a sludge dewatering installation at a wastewater treatment plant in Amsterdam.
The ventilation had originally been equipped with thermal mass meters, but these were proving unreliable because of their sensitivity to humidity and contamination. So, ultrasonic flowmeters were tested on different sections of the ventilation channels, with these tests demonstrating that the flow measurement was stable and reliable.
Ultrasonic clamp-on flowmeters are not the obvious choice for this type of application, as the process conditions are challenging for non-invasive, acoustic measurement technology. The meters are installed upstream of the ventilators and see a pressure below atmospheric, while the density in the pipes is low and the transfer of acoustic signals through the medium is challenging. However, the pipes are made of HDPE, which has high acoustic damping and allows for measurement by acoustic transducers in a single path configuration.
Ventilation flow measurement
To eliminate any cross interference between the transducers, the pipes were coated with densit tape, which absorbs acoustic noise and provides a much better Signal Correlated Noise Ratio (SCNR). The pipes had a diameter of 200 mm and a thickness of 3 mm, and various frequency transducers were tested to determine which type was best suited for this application. The tests determined the optimum frequency transducers via diagnostic data.
Due to poor inlet and outlet straight lengths at the available mounting locations for the flowmeters, it was decided to equip all measurements with two pairs of transducers in a cross arrangement, as this would allow for good compensation of cross-flow disturbance effects. Currently, three fixed meters have been installed on the main channels of the ventilation system.
Boasting powerful clamp-on transducers and sophisticated evaluation technology, FLEXIM’s clamp-on ultrasonic flowmeters have proven to be a reliable and highly effective solution for measuring ventilation flow in sludge dewatering installations. And most importantly – helping to prioritise safety in operations.
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