Non-invasive Flow Measurement With Clamp-on Ultrasonic Sensors In Titanium Dioxide Production
Dilute Acid Flow Measurement
Dilute acid is not a very pleasant substance, to put it mildly. To handle the highly corrosive acid, the pipes at crenox are made of fiberglass-reinforced plastic with an FEP inliner. However, the aggressive chemical nature of the acid is not the only problem. There is more involved in the recycling process than restoring the concentration of the dilute sulphuric acid. The dissolved salts from the leaching process in titanium dioxide production also have to be removed. During evaporation, the salts precipitate out as solids. The entrained particles would quickly wear out any flow measurement system which comes into contact with the material stream.
Under these circumstances, non-invasive flow measurement based on clamp-on ultrasonic technology was the only viable solution. However, deployment of this elegant solution with ultrasonic sensors clamped onto the outside of the pipes is not as simple as it sounds. The OD of the evaporator inlet pipes is greater than 60 centimeters, and wall thickness is one centimeter. Fiberglass-reinforced plastic pipe has very pronounced acoustic damping properties, which means that a powerful source of sound waves is needed to penetrate into the pipe interior and produce a good detection signal.
In addition, the process temperature of 115 °C is beyond the operating range of many ultrasonic sensors. Process engineers are pragmatic people by nature, who have a predilection for fair play. The crenox team received the crucial tip at the start of 2005 from a company which supplies magnetic-inductive flowmeters and could only suggest one good solution for this formidable challenge: “Give Flexim a call,” they said to the engineers at crenox. “They can do it.”
Quod erat demonstrandum. Heinrich Brucks, whose sales region includes the Chemical Park, is used to getting calls like that: “Technology leadership really becomes apparent when you reach the outer limits,” he said. He mounted very low frequency 200 kHz ultrasonic sensors on the fiberglass-reinforced pipes. 130 °C is within the operating range of standard Flexim sensors, so the process temperature was not a problem.
The ultrasonic flow meters were installed in June 2005 and have provided dependable, fault-free operation ever since. The Fluxus system was installed during ongoing operation without system shutdown, and it has enabled the crenox engineers to optimize operation of the line. They have reduced wear on the pumps and also reduced caking on the heat exchangers, which degrades energy efficiency.
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