Introduction to Eductor nozzles

Introduction to Eductor nozzles 

Eductor nozzles, are an indispensable component in many industrial applications that require mixing, have issues with sedimentation and beyond. They operate on the Venturi principle, utilizing the pressure differential to create a suction effect that draws in and mixes surrounding fluids. This mechanism makes them highly effective for mixing, agitating, and circulating liquids within tanks, ensuring uniformity and preventing sedimentation. Their ability to move large volumes of fluid with minimal energy input makes them a cost-effective solution. 

Why Eductor nozzles are used 

Eductor nozzles are primarily used to maintain homogeneity in liquid tanks. They are particularly beneficial in applications where sedimentation or separation of liquids is undesirable. By continuously circulating the liquid, eductor nozzles ensure that the contents of the tank remain well-mixed, preventing solids from settling at the bottom. This is crucial in industries such as chemical processing, water treatment, and food and beverage production, where consistent fluid properties are essential for product quality and process efficiency. 

Key considerations for using Eductor nozzles 

1. Specific Gravity (SG) of the Liquid: The SG of the liquid in the tank is crucial as it affects the flow rate and efficiency of the eductor. For instance, the standard flow rate calculations are based on water with an SG of 1. Adjustments need to be made for liquids with different SG values to ensure optimal performance. For example, if the liquid has an SG of 1.2, the flow rate needs to be adjusted accordingly to maintain the desired turnover rate considering the higher viscosity of the fluid. 

1. Volume of liquid in the tank: Knowing the volume of liquid is essential for sizing the eductor correctly. The goal is to achieve a specific number of ‘turns’ per hour, where one ‘turn’ is defined as moving the entire volume of fluid within the tank. This ensures thorough mixing and prevents sedimentation. For instance, in a tank holding 5000 litres, if the desired turnover rate is 10 turns per hour, the eductor system must be capable of moving 50,000 litres per hour. 

1. Material Selection: As there is a limited selection materials available for eductors, having a granular understanding of your application is critical. Typically, eductors are supplied in a chemically resistant Glass-Filled Polypropylene, but can be offered in Carbon Steel, 316 Stainless Steel and Brass, where applications determine that a metallic option is more suitable, such as with harsh chemicals that may quickly corrode or affect polymers.  

Mathematics Behind Eductor Nozzles 

Eductor nozzles move approximately five times the volume of the pumped fluid due to the suction effect created by the pressure differential through the shroud of the nozzle. The flow rate through the eductor is proportional to the pressure drop across the nozzle. Therefore, consulting flow rate vs. pressure charts is necessary to determine the appropriate size and number of eductors required for a given application. 

For example, if an eductor is designed to ‘turn’ 1/5th of the tank’s fluid volume per hour, and the tank holds 1000 litres, the eductor should move 200 litres per hour. Given the 5x multiplier, the actual pumped fluid would be 40 litres per hour. This relationship is crucial for ensuring that the eductor system is neither underpowered nor overpowered for the application, which could be adverse to the desired goal. 

Sizing Eductors 

The sizing of eductors depends on the desired turnover rate, which varies by application: 

• General Circulation: 1-3 turns per hour 

• Mixing Fluids with Solids: 5-10 turns per hour 

• Plating and Rinsing Tanks: 10-25 turns per hour 

• Blending Applications: 20-120 turns per hour 

For instance, in a blending application requiring 50 turns per hour in a 2000-liter tank, the eductor system must move 100,000 litres per hour. Given the 5x multiplier, the actual pumped fluid would be 20,000 litres per hour. This ensures that the fluid is thoroughly mixed and that any solids remain suspended. 

Positioning Eductors 

Proper positioning of eductors is critical for effective mixing. Eductors produce a plume of moving fluid with a length of 4.3 meters per 1 bar of pressure drop and a spray angle of around 12 degrees. They should be positioned to cover as much of the tank as possible, ideally hitting the opposite wall to maximize fluid movement and minimize blind spots. For applications requiring no sedimentation, eductors can be angled downwards to sweep the tank floor, with the plume reach halved to 2.15 meters per bar. 

In a large tank, multiple eductors may be necessary to ensure even coverage. For example, in a 10-meter diameter tank, positioning eductors around the perimeter and angling them to create overlapping plumes can ensure thorough mixing. This setup prevents dead zones where sedimentation could occur. 

Applications of Eductor Nozzles 

Eductor nozzles find applications in various industries: 

• Chemical Processing: Ensuring uniform mixing of reactants and preventing sedimentation of catalysts. 

• Water Treatment: Circulating and mixing chemicals to ensure effective treatment and prevent sludge build-up. 

• Food and Beverage: Maintaining consistency in liquid products and preventing separation of ingredients. 

• Pharmaceuticals: Ensuring homogeneity in liquid formulations and preventing sedimentation of active ingredients. 

Conclusion 

Eductor nozzles are invaluable tools in maintaining fluid uniformity in tanks. By understanding the specific gravity of the liquid, the volume of the tank, and the appropriate sizing and positioning of eductors, one can ensure efficient and effective mixing, preventing sedimentation and ensuring consistent fluid properties throughout the tank. Their versatility and efficiency make them a preferred choice in many industrial applications, contributing to improved process performance and product quality.