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Level measurement in the reactor: ceramic and metallic VEGA measuring cells easily handle high temperatures and aggressive substances

Meeting the highest safety standards in all process steps is an indispensable requirement in the chemical industry. There is a small but important building block of BASF’s highly effi  cient, global safety management at its Swiss site in Kaisten. It’s in the form of a guarantee that all processes are completely free of silicone oil. This is why traditional differential pressure transmitters can reach their limits when monitoring the levels during the production of additives for paints and plastics. They work by means of capillary lines filled with silicone oil, which – in the unlikely event of an accident – could come into contact with the medium. In contrast, VEGA electronic differential pressure measuring systems have provide perfect safety – with the innovative combination of ceramic and metallic measuring cells.


Silicone oil-free measurement

While conventional differential pressure transmitters were previously used for level measurement, BASF’s measurement and control engineers in Kaisten have now decided to replace their instrumentation. They have switched their process control over to electronic differential pressure, which is silicone oil-free, without capillary lines and therefore without mechanical pressure diaphragms. Thanks in no small part to the ceramic measuring cell, this system is ideal for vacuum and high temperatures. “The decision for electronic differential pressure on the basis of ceramic CERTEC® measuring cells was obvious, in view of their reliability in withstanding abrasive substances. Our plant is completely automated and operates 24 hours a day, 7 days a week,” emphasizes Markus Stoll, BASF’s Head of Specialist Workshops EMSR, who together with his team ensures the highest possible plant availability.

Strong demand for additives

BASF is one of the leading manufacturers of plastic additives with production sites around the globe. These large-volume substances are produced by around 260 employees in Kaisten, Switzerland, from where they find their way into plastics and lubricating oils. Under precisely defined pressure conditions, the raw materials are converted into additives in several chemical reaction steps. A fully automatic process control continuously records each measured value and ensures the exact dosing, as well as the highly efficient operation of the plant. Reliability is crucial, because the end product is an essential intermediate for BASF. Downtime in this section has far-reaching consequences. “Even the smallest failure,” explains Stoll, “interrupts a complex process. In practical terms, this means weekend work and overtime for us.” Complex readjustments and meticulous analysis would then become necessary.

One system for two extremes

Electronic differential pressure with VEGABAR is silicone oil-free, without capillary lines and requires less installation effort.

The highly robust ceramic CERTEC® measuring cell in the BASF vacuum reactor was ideal for the perfectly flush application in hot, aggressive solvents in the lower reactor section. In the upper reactor area, however, completely different conditions prevailed: Here, the extreme steam caused condensation in the measuring cell and led to inaccuracies. Initially, the obvious solution was to use the differential pressure system based on metallic METEC® measuring cells instead of ceramic measuring cells. Condensate and humidity no longer had any negative influence. “The upper measured value remained acceptable and highly accurate in all situations,” recalls Markus Stoll. However, the high temperature of the solvent in the lower reactor area repeatedly caused measured value drifts.

Dream team for heat and condensate

Plastic additives, including so-called large-volume antioxidants and many customer-specifi c mixtures: They are produced about 40 km east of Basel, where BASF’s Kaisten production site is located in the Swiss canton of Aargau.

It took expertise, a willingness to experiment and above all, hand-in-hand work between BASF’s Measuring and Control Technology department and Jürgen Feser, the Key Account Manager at VEGA, until everything was running smoothly. The surprising solution was to use an innovative electronic differential pressure measurement system – with a combination of a ceramic and a metallic measuring cell. Both pressure transmitters record their respective values separately and calculate the differential in the master sensor. This is made possible by structurally identical instrument electronics behind the two very different measuring cells. They work perfectly, even in a mixed team. “For our application, this combination is a real dream team,” says Feser with satisfaction. “As far as I know, only VEGA offers this combination capability.” 

The bottom line result is “one” solution for two challenges: The ceramic measuring cell easily handles the high temperatures and aggressive substances in the lower reactor area (HP side). In the upper part, or LP side the metallic measuring cell performs perfectly in the presence of condensation.

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