Electricity and Control September 2023

MEASUREMENT + INSTRUMENTATION

A duo of ceramic and metallic measuring cells Claudia Homburg, VEGA Grieshaber KG Meeting the highest safety standards in all process steps is a critical requirement in the chemical industry. For BASF, at its production site in Kaisten, Switzerland, there is a small but important building block in its highly efficient safety management procedures. It’s in the form of a guarantee that all processes are completely free of silicone oil.

T his is why traditional differential pressure transmitters can reach their limits when monitoring the levels dur ing 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’s electronic differential pressure measuring systems provide the safety required – with the innovative combination of ceramic and metallic measuring cells. Plastics have been produced on an industrial scale for over 100 years. But anyone who spent their childhood in the 1970s or 80s knows that the plastics of yesteryear have little in common with today’s special plastics. The plastic toy figures quickly turned yellow and some of the Lego bricks became brittle. Plastics age due to thermo-oxidative degradation, that is, under the influence of heat and oxygen. That plastics today can be colourfast and elastic, crystal clear, high gloss, abrasion-resistant or even heat resistant, is due to a variety of specialist additives. The eye in the storm The vapour pressure of liquids plays a decisive role in the production of such additives. Precise measurement is key: it contributes to BASF’s highly efficient control of special processes and provides additional information on how pro cess components can be optimised and plant availability

In this BASF application, the combination of ceramic and metallic measuring cells meets the different challenges in the upper and lower reactor areas. increased. The more precise the values, the clearer the processes and the higher the potential for optimisation. In the production environment, conditions are extreme; there are aggressive substances and acids, which can adhere to vessel walls forming deposits, as well as high vacuum and steam levels. Through all this, the reliable measuring results of VEGA pressure transmitters are essential. Silicone oil-free measurement Although previously conventional differential pressure transmitters were used for level measurement, the measurement and control engineers in BASF’s team at Kaisten decided to replace the instrumentation. They switched the process control over to electronic differential pressure, which is silicone oil-free, without capillary lines and therefore without mechanical pressure diaphragms. Due in no small part to the ceramic measuring cell, this system is ideal for vacuum applications and high temperatures. “The decision to switch to 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,” says Markus Stoll, BASF’s Head of Specialist Workshops EMSR, who, together with his team, is responsible for ensuring the highest possible plant availability. Strong demand for additives BASF is one of the leading manufacturers of plastic addi tives, with production sites around the globe. At the Kaisten site in Switzerland, some 260 employees are involved in

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

16 Electricity + Control SEPTEMBER 2023