In the future, the location where mixing occurs could change as the size of cleanrooms will be drastically reduced, he believes. "The cost to build a cleanroom is phenomenal, so if you can minimize the size of it, for example, by external mixing, you can reduce the capex. And we are beginning to see some technologies go this way. For example, we are just opening a cleanroom for a company in France. It's very small and the operator passes the powder direct to the vessel from outside the area. In another example, an operator has a 5,000-l vessel in the technical area, with the clean room on the floor above for access."
Rotating jet nozzles are prominent in the efforts of Alfa Laval, Lund, Sweden, and Richmond, Va. It offers mixers with two or four such nozzles positioned under the liquid surface at the top of a tank. A variable speed pump circulates liquid to be mixed through the tank in a closed-loop system. The resulting flow drives a gearing system in the rotary jet mixer that causes the nozzles to rotate around both the horizontal and vertical axes (Figure 3).
This double rotation produces mixing action throughout the entire tank volume, reportedly resulting in fast and efficient mixing of the injected liquid, gas or powder. The rotary jet mixer also may be used for cleaning the tank by feeding cleaning fluids through the nozzles.
For Ekato Mixing Technology, Lörrach, Germany, and Ramsey, N.J., a long-term focus has been on viscous systems. The company's latest equipment is the modular Paravisc system that can handle viscosities from 1 mPas to 1 million mPas. In addition, it can be combined with baffles, wall scrapers or independently driven additional mixers (coaxial or with excentric two-shaft systems) as necessary.
Meanwhile, APV, a unit of SPX, Charlotte, N.C., is working to keep air from entering as powders are added to liquid in a mixing tank. The air can can pose problems in processing foods and beverages, among other products, by causing foaming, clogging and lumps, and hindering full dissolution of powders. The company combats the problem with a surprisingly simple solution. The Flex-Mix Instant inline batch mixer uses vacuum to draw powder under the liquid, minimizing the amount of air that enters the mix.
For its part, Chemineer, Dayton, Ohio, which offers a diverse range of impeller technology for sanitary applications, places an emphasis on cleanability. The company evaluates all components in its mixing systems, from welds to impellers, to ensure mixing surfaces promote free draining of liquids.
Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at email@example.com.