Choosing the Right Portable Mixing Tank

Choosing the right tank mixer for your process requires consideration of a number of factors. These include the desired mixing speed and intensity, viscosity of the liquid being mixed, and tank size and geometry.

Mixers can be clamped to the side of a drum, drum tote, or tank. Angling the mixer 15 to 20 degrees off-center or on-center provides effective mixing patterns.

Propeller and Shaft Positioning

Whether a portable mixer is being used to blend, dissolve or disperse, the positioning of the propeller and shaft in the tank will determine the overall mixing efficiency. Incorrect angling will cause the contents of the tank to swirl around the walls instead of having proper top-to-bottom turnover and could lead to uneven blending, dissolving or dispersing.

For tanks with a capacity of more than 1,000 gallons, it is recommended that the mixer be mounted directly in the center of the tank with the shaft in a vertical orientation. This configuration is preferred when good top-to-bottom tank turnover is required, portable mixing tank for example in the case of a slurry. Baffles should be attached to the tank walls and positioned so they prevent the contents from turning in the direction of the mixer and creating an inefficient vortex. Neptune offers a wide range of mixer types and styles that will perform well in this type of tank-mixing application.

The paddle agitator is the most common and basic mixing device that consists of several paddles or blades mounted on a shaft. These agitators push the material up and down and around by rotating, and are suitable for low to medium viscosity liquids and some powder materials. The spiral agitator has spiral-shaped blades that are mounted on a shaft and is suitable for high-viscosity liquids or more viscous powder materials.

Mounting Configurations

A variety of mounting configurations are available to suit portable tank mixing applications. Non-drum and tote mixers can be threaded into the bung opening of a drum, tote or bulk tank, c-clamped above the vessel or attached with special brackets designed for the particular container. The c-clamp mounts typically feature an adjustable angle of entry controlled by a ball-and-socket design. Flange mounts attach to a flange on the tank lid or can be used with special angled risers that provide a fixed 10-degree angle of entry into the mixing vessel.

Larger tanks may require the mixer to be positioned vertically and on-center in the tank. In this situation, baffles are recommended to prevent the contents of the tank from turning in the direction of the mixer and creating an inefficient vortex. This baffling will also promote proper top-to-bottom turnover.

Direct drive portable mixers can be mounted on a pedestal or structure above the tank to address asymmetrical flow patterns and dead spots in larger tanks. They offer maximum versatility and can be equipped with an electric, compressed air or explosion proof motor for hazardous environments.

Baffling

Baffles are internal, flat plates used to optimize and stabilize mixing flow patterns in agitated tanks, minimize variation in agitator power draw, and improve process results. Proper baffle implementation dramatically impacts mixer performance and tank mix times.

In unbaffled cylindrical tanks, the agitator creates a deep vortex with surface swirling and little top to bottom fluid turnover. Particle tracing in these tanks shows minimal motion with the exception of the vortex, indicating poor mixing performance.

Baffling prevents the formation of these vortices, reducing overall energy requirements for agitator operation. The baffles also reduce segregation of particles by creating a symmetrical, circular movement pattern within the vessel. When a baffling system is used, the mixer can be used to mix low viscosity liquids and solid suspensions with good results.

Traditionally, three or four baffles are installed in a rectangular tank. They portable mixing tank manufacturer are affixed with polyethylene encapsulated bolts and closed with a gasket to ensure chemical compatibility and prevent leaks. The baffles are not welded to the inside of the tank, which allows them to be removed easily for cleaning and servicing.

For high viscosity applications, the baffles are spaced closer together, allowing a gap to form between the base of the baffles and the tank wall. This gap is required to avoid sludge buildup and facilitate rapid resuspend of solids.

Viscosity Chart

The higher the viscosity of a fluid, the more resistance it has to flow. Low-viscosity liquids, such as water, flow easily, whereas high-viscosity materials, like honey and tar, resist deformation much more vigorously. Viscosity can range from a few centipoise (cP) to hundreds of millions of cP.

Mixing highly viscous materials presents unique challenges. Optimal mixing results in these applications require detailed knowledge of the rheologies and agitation forces involved. This expertise helps to choose the right mixer for the application and avoid costly product losses caused by agglomerates, emulsions, shear and thermal shock.

High-viscosity mixers need to be designed to generate sufficient shear to disrupt agglomerates while avoiding excessive power demands and heat generation. This requires careful engineering of the blade profile and geometry, speed, blade width, the number of blades and their proximity to each other.

In larger cylindrical tanks, the mixer is often positioned vertically on-center. It is recommended to attach baffles to prevent the tank contents from rotating in the direction of the mixer and creating a vortex that hampers effective top-to-bottom turnover and mixing.