Pressure Monitoring in Milk Production
The Nestlé research and development centre in Konolfingen, Switzerland, is developing milk-based constitutional food products. The pressure monitoring at the heat exchangers in the new testing facility is conducted by Baumer pressure transmitters, which are equipped with hygienic CombiConnect process connections made of stainless steel.
In Konolfingen, the international nutrition company Nestlé operates the Nestlé Product Technology Centre (PTC) – one of 24 research centres worldwide. For more than 30 years, the company has been developing milk-based products and the respective production processes there, with the main focus lying on infant food, special diet nutrition and health care food. The Konolfingen developers are researching appropriate recipes and testing processes for all operational Nestlé companies worldwide requiring new products for these areas.
Heat Exchangers in the New Testing Facility
For hygienic reasons, all measuring devices in their new testing facilities had to be equipped with an aseptic screw connection according to DIN 11864-1. All over the PTC, pressure transmitters of the ED701 series were already being used in various other applications such as homogenisers, mills and filling equipment. Since Nestlé had been very satisfied with those devices, they were also chosen for the pressure measurement at the new facility’s heat exchangers. Depending on the processes to be tested, up to six heat exchangers are used for heating and/or cooling the products, with the temperatures going up to 150°C.
At high temperatures, the products precipitate protein, which then sediments at the heat exchanger’s metal plates. If there is too much sediment on the exchanging face, the differential pressure between the product and medium side rises and the heat exchangers have to be cleaned. With this application, the PTC developers test the recipes and manufacturing processes with different kinds of liquid products ranging from milk to dessert crème. Among other results, the tests show the possible range of process temperatures between medium and product as well as the time period the production can run without the heat exchanger needing to be cleaned.
Differential Pressure Measurement with the ED701
The differential pressure is measured by the ED701, a piezo-resistive pressure transmitter with a stainless steel diaphragm for industrial and hygienic applications. It is based on a silicon sensor designed for high precision within the widest possible range of temperature. Its downstream digital compensation reduces the signal drift. The piezo-resistive silicon sensor is anodically bonded to a very stable glass base attached to a stainless steel construction, which guarantees an excellent thermal isolation. A stainless steel diaphragm and a specially processed filling liquid isolate the sensor from the process medium.
The electronics are located within the hermetically sealed transmitter housing, making the ED 701 extremely resistant to humidity, shock and vibration. Depending on the choice of the electrical connection, the protection classes vary from IP 65 to IP 67. The electronics’ core piece is a micro-controller compensating any drift effects on the sensor signal due to temperature changes. Therefore, these effects can be eliminated over a wide range of temperatures with a short response time.
The ED 701 is available with a great variety of pressure and electrical connections, a 4…20 mA current loop and various voltage output signals. The line’s most distinctive features are its short response time (max. 5 ms) and an excellent repeatability and long-term stability. The hygienic design makes the ED 701 series most suitable for applications in the food and beverage processing industry as well as in the pharmaceutical and biotechnology industry. Any parts contacting the media are made of stainless steel 316L / 1.4435 and all materials, including the white oil used as standard filling liquid, are compliant with the FDA standards.
For the use in the heat exchangers, the pressure transmitters were constructed with an accuracy of 0.4% FS and a compensated temperature range of -10 to 125°C (on the cooling water side) respectively a high medium temperature of 300°C maximum (on the heating side). The measuring range of the gauge pressure covers 0 to 20 bar.
Connection for the Milk Tube Fitting
Since a new process connection was also required for the new milk tube, the Nestlé PTC developed a special adapter for the ED701 in co-operation with Baumer.
A further challenge this application posed was the very small pipe with a diameter of only 10mm, making it very difficult to clean. The problem was solved by choosing a high flow rate and a pressure transmitter with a small volume compared to that of the tube.
The Nestlé product developers had already been convinced by the reliability of the pressure transmitters used in various other applications. Concerning the heat exchanger applications in the new testing facilities, all upcoming challenges were mastered thanks to the flexible CombiConnect connections and a close collaboration with the manufacturer in developing an adapter. “For a hygienic pressure measurement, the quality of the measuring devices is the decisive criterion. With the ED701, we have had consistently good experiences”, resumes Strahm.