Eductors are devices used to recycle liquid in tanks and vessels to prevent sedimentation and ensure uniform fluid qualities. They work by creating a pressure drop that causes surrounding liquid to be sucked into the nozzle, resulting in a multiplication of the volume of liquid in the tank. This highly efficient process reduces energy use and saves money.
To use an eductor, it is lowered into the tank and motive fluid is pumped through the discharge opening under pressure. The jet of motive fluid enters the venturi area, entraining additional fluid from the tank and moving it through the venturi. A discharge plume of combined motive and entrained fluid leaves the venturi and continues the mixing and agitation action for a significant distance.
Eductors are a lightweight and cost-effective alternative to mechanical mixing methods. They can be used to reduce the settling of suspended solids, improve flow, mix chemicals, or move solids along the bottom of a tank.
The positioning of eductor nozzles is important for optimal results. The moving plume created by the eductor will have a length equivalent to 4.3 meters per 1 bar of pressure drop across the eductor and a spray point of around 12 degrees, forming a tight cone of moving liquid. Ideally, eductors should be positioned so that the plume hits the opposite wall of the tank and further disperses as it does so.
To prevent sedimentation, eductors can be angled downwards to clear along the floor of the tank. However, in this case, the 4.3m/1 bar plume range should be split into 2.15m/bar. It is best to cover as much of the tank as possible with the estimated moving plumes to ensure that there are no "blind" spots where sedimentation can occur.
Eductors are commonly used in tanks for plating, phosphating, slurry, paint, anodizing, agricultural fertilizers and chemicals, pulp, slurries, electrocoating, and pretreatment. They are also used in open tank heating applications, such as cooking grain, cooking starch, and circulating and mixing. Steam is brought into an open tank through the lowered eductor to heat the contents.