Using Baffles for Tank Mixing Applications

Mixing chemicals and other substances is a lot like mixing cake batter. A container is involved, as is a stand (or bracket) to support the blades or mixing arm. But, if you’ve ever made a cake, you know that you have to move the bowl around to mix all the ingredients. It doesn’t work to stick the beaters down in the bowl and keep them in one place. Obviously, in a chemical storage and mixingscenario, moving the tank around to get all the chemical that can’t be reached is not an option. That’s where baffles come in.

What Are Baffles?

Baffles Used For MixingBaffles are long flat plates attached to the interior of the tank and protrude inward to interrupt and prevent swirling of a fluid. (see figure) These plates are typically about 4 feet long and ½ to ¾ inches thick. This is sometimes an alternative to a mixer, and sometimes additional to a mixer. Baffles can make extra work on a mixer, however, and often one or the other is used for mixing. With just a mixer impeller, mixing can create sections of the solution that don’t move. Also, in a cylindrical tank, the mixer can create a vortex effect that causes the entire mixture to move as it is and no real mixing takes place. The baffles prevent the vortex effect and cause the tank contents to move from top to bottom. Three or four baffles will be used in a given tank, depending on its size, and they will be mounted 4-6 inches off the inside of the wall.

How are Baffles Attached?

Baffles are not welded to the inside of the tank. Rather, they are installed with PE encapsulated bolts and closed with a gasket to prevent leaks. These are the same bolts that are used for internal/external pipe support and the gasket material is dictated by the chemical. Since the baffles are made from cross-linked polyethylene and are bolted onto polyethylene, there are no concerns about chemical compatibility. The same properties of XLPE that provide 500% more tensile strength over weaker polyethylene, also make it a thermoset and thus not suitable for welding, and that is a good thing. Welds often break, causing a baffle to hit the mixer and cause significant damage. Bolted baffles result in a safer tank mixing system and allow for some fluid to move behind the baffle.

Mixing Considerations

Different chemicals require different mixing systems. Some chemicals create sludge, and it needs to be mixed to avoid buildup at the bottom of the tank. A baffle system is great in this scenario of keeping top to bottom fluid movement. Mixers can also be put on an angle to create a different mixing pattern. This is not recommended for more viscous chemicals and those that contain sludge because there is a risk of bending the shaft. Some food, pharmaceutical, and wastewater applications will require a clean in place (CIP) application to prevent contamination.

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Topics: Fittings and Accessories