THE MAGAZINE FOR THE DRAINAGE, WATER & WASTEWATER INDUSTRIES
SPECIAL WORKS
Three channels with new actuated penstocks
‘magflow meter’ demonstrated a 60% saving in cost and 95% saving in embodied carbon. The magflow option was therefore also disregarded.
The solution
“Before making the final decision, a number of internal ‘surgeries’ were conducted involving hydraulic, mechanical and process engineers,” explains Josh Sparks, MMB Contracts Manager & EICA Regional Practice Lead. “As a company, we are always looking for innovative solutions that over-deliver on a number of fronts, and that is exactly what we managed to achieve at Five Fords.”
The preferred solution involved the deployment of three actuated penstocks that would be lifted into the first three channels. The fourth channel would be isolated, but could be made available if necessary, in the future. Effective control of the penstocks would depend heavily on the reliable measurement of flow in each channel downstream of the penstocks. “This was also a major challenge,” Josh explains. “Most traditional flow measurement methods were ruled out due to the physical constraints of the
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site, along with the cost of solutions involving significant civil works. As a result, we engaged with NIVUS and determined that their cross-correlation flow meters offered the best solution.”
NIVUS was contracted to install flow meters in the relief pipe, in the main inlet channel, and in each of the three ASP inlet lanes. All of these instruments are MCERTS and EX-rated and employ the NIVUS cross- correlation flow measurement method.
Two NIVUS POA wedge sensors were fitted to L-shaped bed-mounted brackets – one on either side of the main inlet channel. These sensors were connected to a (NF750 M9) transmitter, to which the pipe insertion probe (velocity profiler and ultrasonic level) was also connected.
Each of the ASP lanes was fitted with a radar level sensor, working together with POA wedge sensors, which were also mounted on L-shaped bed-mounted brackets. Each of these sensors was connected to a single input transmitter (NF750).
Cross correlation flow measurement method
The ultrasonic cross-correlation method
developed by NIVUS measures individual velocities continuously at different levels within the flow. This area velocity flow measurement technique provides a 3- dimensional flow profile that is calculated in real-time to provide reproducible and verifiable flow values in full or partially filled channels or pipes.
The method is based on the principle of ultrasonic reflection, in which reflectors such as particles, minerals or gas bubbles within the water body are scanned using an ultrasonic impulse with a defined angle. The resulting echoes are saved as images or echo patterns, and a further scan is conducted a few milliseconds later. This creates echo patterns which are compared with previously saved signals, and the positions of unambiguously identifiable reflectors are identified in order to determine velocity, by using the beam angle. This means that the particle velocity, which is equivalent to the wastewater flow velocity, can be calculated from the temporal shift of the reflectors. The method produces highly accurate readings without the need to perform additional calibration measurements.
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