TECHNOLOGY ROUNDUP
Two very different flow measurement applications have been found for Pulsar’s MCERT-ified flow measurement system. Keith Flint of Pulsar explains how its DUET transducer is helping at Manchester Airport and Premier Foods
control unit to a Premier Foods processing plant in Newport as part of an open channel measurement project for the MCERTS certification scheme. The accuracy achieved by Premier Foods has allowed the company to make a substantial saving on effluent charges. Siris led the project, supplying and installing the primary measurement device together with the flow and sampling equipment. Pulsar’s DUET non-contacting ultrasonic transducer array was chosen for the extraordinary accuracy achievable. Siris’ sales manager, Simon Richardson, explained the process: “To achieve the most accurate flow measurement system, both the design and the installation of the weir tank and associated equipment was undertaken to the highest possible standards. It is vital that upstream flow conditions are controlled, the weir tank was constructed to be very rigid, the weir
Contrasts and connections
S
iris Environmental of Durham has installed Pulsar Process Measurement’s DUET transducer array and its associated
Substantial savings: Premier Foods’ processing plant in Newport
plate was reinforced and the chamfering of the edges of the weir plate was closely controlled.” Ultrasonic systems work by bouncing a sound
pulse from the surface being measured and calculating the distance from the time taken for
the pulse to return to a transducer. The accuracy of the measurement depends on the speed of sound, which can vary with temperature. Temperature changes can be compensated
for, but a temperature compensation circuit cannot respond immediately and there may be temperature variations in the column of air below the transducer face. DUET uses two transducers a known distance apart, and by comparing the returning signal from both transducers, variations in the speed of sound are dynamically compensated for. This was critical to the success of the project. A 2mm variation in measurement accuracy would result in an error of 40m3/d. Richardson explained the advantage of MCERTS: “Many companies see the MCERTS Certification Scheme as another additional expense, they often don’t appreciate that the scheme ensures accurate measurement of their effluent discharge and in this case we have proved that a well implemented installation can save real money.”■■■
Up and away: take-off for run-off monitoring
Like any other airport, surface water runoff at Manchester Airport is considerable, and in certain areas may be mixed with aviation fuel, oil and other contaminants. For this reason it has to be treated like any other industrial effluent before it can be discharged. To assist with separation, treatment and measurement of the final effluent flow, Pulsar supplied a non- contacting, ultrasonic, open channel flow measurement system, featuring the company’s DUET transducer array. The DUET is used in
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14 Sampling & Monitoring May 2010
the airport’s critical API hydrocarbon separation unit. Pulsar supplied a V-notch
weir plate and a DUET transducer array and FlowCERT control unit to measure effluent flow through an open channel. The channel was in an exposed position, where solar radiation can be a significant factor affecting the accuracy of the measurement. The V-notch weir plate was
sized for a maximum flow rate of 25l/s. Although the flow can be low in dry periods of the year, it is vital that the measurement remains reliable
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and accurate. In this case, because the head varies by around 200mm between high flow and zero, it is crucial that the measurement is accurate, repeatable and records a genuine zero when there is no flow. DUET is perfect for this type of application, consisting of two transducers that fire simultaneous ultrasonic pulses which are then received at the lower transducer only. Mark Stewart, the airport
water services engineer in charge of the project, said: “We have been delighted with the performance of the DUET.”
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