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Flow Measurement

Non-invasive Flow Measurement With Clamp-on Ultrasonic Sensors In Titanium Dioxide Production

| Editor: Dr. Jörg Kempf

Staying on the safe side: clamp-on ultrasonic sensors mounted on the outside detect the flow of dilute acid and boiler feed water. The WaveInjector extends the application range to 400 °C. (Pictures: Flexim)
Staying on the safe side: clamp-on ultrasonic sensors mounted on the outside detect the flow of dilute acid and boiler feed water. The WaveInjector extends the application range to 400 °C. (Pictures: Flexim)

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Non-invasive flow measurement based on ultrasonic sensors mounted on the outside of a pipe is no longer a well-guarded secret. Clamp-on solutions have now reached the mainstream. We discuss two non-invasive measurement technology applications in titanium dioxide production to highlight the advantages of high-performance ultrasonic measurement systems.

Since 1877, dyes (initially azo and aniline dyes) have been produced in Krefeld-Uerdingen in Germany’s lower Rhine region for the local textile industry. Later on, pigment dyes became the predominant colorant product. Titanium oxide and iron oxide are produced at the Krefeld-Uerdingen Chemical Park, which is now the world’s largest producer of inorganic pigments. Even a relative newcomer like crenox has been in business for more than 50 years, and like most companies at the park it is closely associated with the name Bayer.

In 1957, Bayer built a titanium dioxide plant in Uerdingen to produce raw materials for paint, coatings, washing detergents and toothpaste. After a joint venture and subsequent divestiture, the plant was known as Tronox. When the US parent filed for Chapter 11 protection, the fully independent entity crenox emerged. Since May 2009, the new name has been synonymous with titanium dioxide made in Krefeld.

Turning Black Into White

Making titanium oxide is like industrial alchemy. Pure white color pigments are produced from black ore, and crenox uses the sulfate process to perform this bit of “white magic”. The plant has an annual output capacity of 107,000 metric tonnes, making it one of the world’s largest titanium oxide production facilities. Sulfuric acid is used to leach titanium from the raw materials. As has been the case for many years, the dilute sulfuric acid which is left over at the end of the leaching process is put through a treatment process where it is concentrated and returned to the production process.

During recycling, the dilute sulphuric acid first passes through three vacuum evaporators in series, which raise the concentration to about 45%. In the next step, the salts from the titanium ore leaching process are then crystallized and filtered out. The concentration of the clarified acid is brought up to around the 75% level, which is necessary for the titanium oxide process.

The recycling line has to be shut down several times a year for inspection and maintenance. Due to the quick rise in temperature, the special pumps which drive the dilute acid stream to the evaporator are subject to severe stress, particularly when the line is restarted. To minimize stress and wear, the engineers wanted to find a good way of measuring the flow to the evaporators.

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