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

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.

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.

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.”