There is a small but important building block at BASF’s highly efficient Swiss production site in Kaisten. It is 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 provide additional safety through the innovative combination of ceramic and metallic measuring cells.
Plastics today can be colourfast and elastic, crystal clear, high gloss, abrasion-resistant or even heat-resistant, thanks to a variety of special additives. The vapour pressure of liquids plays a decisive role in the production of such additives. Their precise measurement not only contributes to BASF’s highly efficient control of special processes, but also provides additional information on how process components can be optimised and plant availability increased.
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 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,” emphasises Markus Stoll, BASF’s head of Specialist Workshops. “Our plant is completely automated and operates 24 hours a day, 7 days a week.”
One system for two extremes
The highly robust ceramic Certec measuring cell was ideal for the perfectly flush application in hot, aggressive solvents in the lower reactor section of the BASF vacuum reactor. 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. Condensate and humidity no longer had any negative influence. “The upper measured value remained acceptable and highly accurate in all situations,” recalls Stoll. “However, the high temperature of the solvent in the lower reactor area repeatedly caused measured value drifts.”
Dream team for heat and condensate
It took expertise, willingness to experiment and above all, close cooperation 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 Stoll 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.”
Conclusion
Even the most ingenious manufacturing process for additives is only as good as the equipment of the production plant. In the case of BASF’s distillation reactors in Kaisten, the sensors of the pressure transmitters really get the job done, even in the most inhospitable locations. The combination of a ceramic Certec and a metallic Metec measuring cell has proved to be the perfect combination from VEGA.
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