Since 1964 the company has been producing a wide range of polyester textile yarns, geotextiles and carbon and heat resistant polypropylene materials, for products such as special protective clothing or packaging solutions in agriculture and construction.
Capacitance solution in acetone tanks for overfill protection and empty detection
The company conducted preliminary tests in the solvent tanks. During synthetic fibre manufacturing, acetone is used to impregnate the fabric. Each fabric to be produced is passed through a bath of clean, pure acetone, where amongst others excess epoxy resin, which is used for bonding the fibres, is washed off. The majority of the resin is usually cured after the heat treatment, non-hardened epoxy resin can be removed during this process step. Thereafter, the acetone is considered polluted and enters a separate tank, where it is cleaned in a special mechanical process. Subsequently, the purified solvent is filled in the tank container with so-called regenerated acetone.
Acetone is an extremely aggressive substance that secretes corrosive vapours and quickly corrodes ordinary materials. For the individual tanks with clean, contaminated as well as regenerated acetone the synthetic fibre manufacturer needed a reliable, and at the same time robust, level monitoring system. Tests carried out with a variety of sensors made it clear that the robust RFnivo® probe was the most favourable solution. The RF series consists of single-rod probes that require, due to their design, no temperature-limiting components for media detection and can therefore be used in processes of up to 500°C. They work with the capacitive measuring principle, whereby the capacitance is detected independently of the length of the sensor of the medium between the probe and the container wall.
The customer has different tanks measuring from 1.2 to 1.6 meters in diameter. Apart from a reliable measurement, even with frequently occurring pressure fluctuations, it was also essential that the sensor carried a corresponding certificate according to gas explosion protection (Zone1). Firstly, each tank was equipped with an RF probe (standard version) for full signal, that ensured reliable protection against overfilling of the acetone containers. Secondly, an empty detection system was installed in each container, that switches on time to prevent dry running.
As it is common that the sensor probe is exposed to the acetone and the aggressive molecules of the acetone vapour for longer periods of time, especially during the empty detection process – it was realised that an extra robust version of the device was required. So the capacitve single rod was thus refined – 1.4404 (316L) stainless steel and PPS isolators were used with a FFKM seal in the product-contacting probe. The FFKM seal (perfluoroelastomer / perfluoro rubber) has a particularly high chemical resistance against aggressive materials. Perfluoro rubber is considered as the new generation plastic. It is a true high-tech elastomer, which is always used when special demands are placed on resistance to chemicals, temperature and form. The equipping of the probe seals of the capacitance level indicator with the highly robust polymer made them absolutely resistant to the acetone.
Clean and regenerated as well as contaminated acetone tanks can be similarly monitored using the capacitive measuring principle. The Active Shield Technology, which is integrated in the RF probe as standard, also ensures that the measurement result will not be affected by any buildup on the sensor probe.
A total of 16 acetone tanks could be fitted with a reliable content monitoring, which meant the optimal support of a smooth and maintenance-free manufacturing process for the synthetic fibre producer.
Customer statement:
“The capacitive sensor has been operating smoothly in the acetone tanks for some time now and reliably detects the level. It was an exciting project, where we were once again delighted by the quality and reliability of the UWT equipment.
More solutions with the capacitance series for level measurement in liquids, pastes and foams
After gaining valuable experience within liquids applications, UWT has expanded its portfolio to include compatible solutions for all liquids, pastes and foams. The RFnivo® 8000 series was included in the RFnivo® level switch series, which is especially suitable for the detection of pasty, adhesive and corrosive liquids as well as for foam detection. It can also be used for interface measurement of different liquids or sludges and is with WHG and according to Lloyd’s Register certified. The compressive strength of this RF version is up to 35bar. The optionally available PFA coating also provides improved chemical resistance. The devices are equipped with encapsulated electronics and work with the innovative Inverse Frequency Shift Technology, which allows a very precise sensitivity adjustment to the medium. Due to the variation of versions with rod and tube extensions, the sensors can be easily adjusted to the respective container conditions and installation situation.
Experts in Level Measurement
Based in the Allgäu for more than the past 40 years, UWT is the leading manufacturer of level measurement technology on the world market. The company is principally focused on the field of bulk solids and liquids. Its head office, development and production facilities are located in the Allgäu. With an additional production facility in Malta and its own sales subsidiaries in the United States, United Kingdom, Russia and in the growth regions of China and India, the company can meet the needs of the world market with the greatest flexibility that customers expect. The company is certified ISO 9001:2015 and constantly expands its portfolio of product certifications (ATEX, FM, CSA), particularly with regard to the international markets. The products feature easy handling, high reliability and long service life under the motto of the company “Brilliantly simple level measurement in bulk solids.”
