Ceramat retractable sensor fittings: the solution for extreme conditions Process measurement and control specialist Henning Springer of Mecosa presents the key advantages of using Knick Ceramat fittings to protect and manage process control sensors in harsh, corrosive, abrasive, toxic, sticky or fibrous processing applications.
I deal for accurate continuous moni- toring of pH, dissolved oxygen and conductivity in harsh environments, the Ceramat retractable fitting from Knick features advanced flushing, calibration and cleaning functionality for the built-in sensors used for process management. “Ceramat retractable systems are used in several processing plants in South Africa, including minerals processing, petrochemical, food and biotechnology facilities. Most notably, the system uses a ceramic-on-ceramic rotating seal between the measured medium and the outside environment, which delivers resistance to acids and abrasives,” begins Henning Springer, MD of Mecosa, South Africa’s niche process variable specialist. According to Springer, one of the early success stories of the Ceramat system comes from the chocolate industry, where it is used for particle-size measurement and control. “With chocolate, the finer the grind of the cocoa, the better the quality and taste of the chocolate. The problem, though, is that cocoa grinding accounts for 40-50% of production costs. So, a smooth chocolate that melts on your tongue is typically more expensive,” he points out. Today, SOPAT optical sensor systems,
utilising the Knick Ceramat, are used to measure and control the grind size of cocoa used in chocolate production. However, with chocolate and other food products, optical sensors tend to foul quickly, so automatic sensor cleaning is required, with the sensor having to be removed from the process chamber. This separation and subsequent sensor cleaning are performed using the Ceramat solution, which eliminates O-ring sealing issues associated with traditional sensor retraction systems. Instead, two planar ce- ramic discs that rotate towards each other are used to withdraw the optical sensor from the process fluid into a separate, sealed cleaning and calibration chamber with built-in flushing and recalibration systems tailored to the sensors in use. Particle size is also a critical process- control parameter in the mining industry. The electricity cost of grinding ore in mills before it passes into the metallurgi- cal plant for recovery and liberation of the high-value product accounts for the largest share of the processing circuit's cost. Oversized material must be returned for further grinding, while overground material consumes unnecessary energy and may even be lost as ultra-fines in the downstream process.
“So we measure the grind size by put- ting a sensor on the output to minimise the amount of grinding energy needed to liberate the target mineral,” Springer explains, adding that the Ceramat system is not yet used for these applications. Instead, Mecosa offers a purpose-built particle-size probe for the mining industry. Electrochemical sensing The Ceramat retractable fitting has found a niche in applications where pH, redox, dissolved oxygen, and conductivity mea- surements are critical to managing pro- duction processes or reactions. These are all electrical-based sensors. A Clark cell, for example, works by diffusing dissolved oxygen across a membrane to a platinum cathode, where it is electrochemically reduced. The current produced from this reaction is proportional to the dissolved oxygen concentration of the process fluid. Measuring pH also uses the electro- chemical cell principle, in which hydrogen ions migrate across a gel-based membrane in the sensing tube. The direction and extent of this transfer are directly related to the pH in the process vessel. Control of dissolved oxygen and pH is used in fish farming, for example, to optimise healthy growth and survival rates and to promote conditions for ben- eficial microorganisms. “The typical Knick Ceramat units used for many industries in- clude control and evaluation systems and pond cleaning solutions,” says Springer. They are also used in wastewater treat- ment due to the chemical processes in- Knick Ceramat fittings protect and manage process control sensors in harsh, corrosive, abrasive, toxic, sticky or fibrous processing applications.
Ceramat retractable fittings have found a niche in applications where pH, redox, dissolved oxygen, and conductivity measurements are critical for managing production processes or reactions.
22 ¦ MechChem Africa • January-February 2025
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