Agitators
IMPELLERS

Mixing technology represents a balance between the requirements of the process and the output efficiency of the impeller within the process. Often referred to as propellers, the impellers selected for a specific agitation system are required to produce one of three basic fluid regimes: Flow (Q), Shear (H) and Pressure (P); and there is also the possibility of producing a combination of the three.

Agitator impellers all obey the relationship whereby Power is dissipated into Flow or Shear:

Power = Q x H

     

This type of impeller, also known as a hydrofoil impeller, is used in applications where high flow velocity is required, and is one of the most commonly used impellers throughout our vast industry. The F3 is called upon in many applications because of its robust and efficient structure. The impeller can meet the demands of the process at lower installed power than most other impellers within the range. Widely employed throughout the various industries, these F3 impellers are used where the generation of flow determines the agitator selection. The impeller is multipurpose (by varying the blade pitch angle, one can alter the impeller’s flow and shear characteristics) and can provide high axial flow with low shear whenever required.

This impeller is industry proven and boasts a solid track record with thousands of successful installations in multiple industries. Some industry applications and examples include:

  • Mining: CIL & CIP, ore (copper and gold), leaching, lime makeup and storage, solid suspensions, chemical reaction tanks, slurry tanks.
  • Agricultural: Fertiliser makeup tanks, water storage tanks, Jojo tank mixers.
  • Pharmaceutical: Batch mixers, laboratory mixers, homogenising reactors, pressured vessel agitators.
  • Waste and Water Treatment: Flocculent plants, water treatment plants, chemical reaction applications.
  • Paint & Ink: Mixing tanks, batch and blending tanks, pre-mix within 210-litre drums, large and small scale applications.
  • Chemical Industry: IBC bin agitators, soaps, cleaners and detergent mixing, fine powders and liquid blending, household cleaning products.

This type of impeller, also known as a pitch blade turbine impeller, is used in applications such as blending, high viscosity blending, applications requiring shear, and re-pulping where some flow and addition of power is still required. The FS4 impeller pitched blade turbine, consists of four blades and is very limited to its performance tasks within process application parameters. This type of impeller is used for applications which require higher power draw and a lower efficiency in terms of mixing. There is still a demand for this type of impeller through some applications needing high flow and some shear.

Some industry applications and examples include:

  • Mining: Re-pulping applications.
  • Agricultural: Blending applications with some solids needing to be broken up and dispersed throughout the tank.
  • Pharmaceutical: Lower impeller in high viscosity batch mixers.
  • Waste & Water Treatment: Aerators, sludge tanks to break up the “cake” crud collection.
  • Paint & Ink: Viscous mixing tanks, batch and blending tanks, addition of solids into batches.
  • Chemical Industry: Addition of solids into solutions where high power is required to assist with breaking down the solids.

This type of impeller is also known as a high solidity hydrofoil impeller, similar to the P4 impeller but with three blades instead of four. These types of impellers are used in applications where a macro flow is required, specifically in high viscosity, low Reynolds number fluids. They are also used when effective dispersion, as well as blending and solid suspension, is required. These impellers have been adopted in applications where close clearance impellers, such as scrappers, spirals and gate anchors, have traditionally been used. They are capable of blending in liquids where the viscosity is more than 40 000cP (Centipoise).

Some industry applications and examples include:

  • Pharmaceutical & Personal Care: Shampoos and conditioners, hand wash liquid soaps, as well as relaxers (thixotropic products).
  • Paint & Ink: High viscosity resins, high viscosity paint blends, bulk addition of solids to a viscous solution.
  • Chemical Industry: Chemical reactions where the solutions thicken with time (anti-thixotropic).

This type of impeller, also known as a high solidity hydrofoil impeller, has been designed especially for the induction of large volumes of gas. Having a solidity value greater than 90%, these impellers ensure that the gas being introduced is not able to bypass the impeller. The result is increased absorbed power under gassed conditions. This is opposite to that of the Rushton impellers or Smith Turbine, both of which experience a reduction in power under gassed applications.

These high-efficiency axial gas dispersion impellers are used within the following applications:

  • High-pressure autoclaves
  • BIO oxidation reactors
  • Bacterial leaching
  • Fermentation and hydrogenation
  • Iron removal
  • Cyanide detox applications

These impellers, also known as a shear disc or sawtooth impeller, provides very high shear compared to other open bladed mixing devices. It can be used for the purpose of incorporating powders into liquids, breaking down or shearing agglomeration or to form stable emulsions. Results of the S1 impeller are increased with the use of a F-type impeller to aid circulation within the tank.

Some industry applications and examples include:

  • Chemical: Fermentation of stable emulsions Shearing of powder agglomerations

  • Paint: Dispersion of pigments Fermentation of emulsions for paint

AFX offers a broad range of unique folding axial flow impellers. These impellers have been adapted to suit applications whereby the mixing process takes place inside a vessel, which has a limited opening diameter. Before the development of folding impellers, applications such as these were approached by using impellers with fixed blades that had a diameter small enough to pass through the vessel opening. This meant that the agitator would run at speeds much higher than those whose impeller’s DT ratios had been created to meet the desired specification, thus increasing the power requirements of the agitator and reducing its overall efficiency.

Nowadays, as we have adapted our axial flow impellers to incorporate the moving or folding blades, we can select the impeller which would be the closest fit in terms of your vessel dimensions and application demands. These impellers provide an economical and energy efficient agitator solution suitable to your application.

This unique radial flow impeller is designed for pumper mixer applications. The impeller discharges the fluid radially outward to the vessel wall. This particular type of radial impeller provides a more informal radial flow pattern when compared to the radial impellers that do not feature a disc. The progressive design ensures advanced flow, maximum dispersion, and provides a specified and desired head generation. The curved blade pump turbine design assists with reduced power consumption, minimum shear generation and turbulence. Radial flow impellers are most commonly used in gas-liquid or liquid-liquid dispersion applications.

These impellers are used in applications such as:

  • Solvent extraction (SX Mixing)
  • Thickener dilution systems

AFX’s application engineers have been working alongside its R&D department in an effort to find improved solutions for wastewater treatment plants. A common problem, called “ragging”, has been identified as a headache in the industry, causing many process failures and mechanical breakdowns of the agitators. Mechanical agitators are found in many wastewater treatment processes such as anoxic, anaerobic and denitrification tanks, as well as flocculation, chemical make-up, storage, sludge mixing and neutralisation and equalisation mixing tanks.

“Ragging” is the collection of fibrous solids in and around the hub and leading edges of the impellers. Historically, a number of impellers have been used to achieve mixing in these processes. These impellers included the axial flow impellers, hydrofoil impellers, pitch blade turbines and radial flow backswept impellers.

The axial flow and hydrofoil impellers were the most recent introduction in terms of mixing turbines in the industry due to their high pumping number (Nq) and low power number (Np). These impellers could deliver the required mixing efficiency in the tank for the process requirement, which is keeping solids in suspension. The bioreactor process is typical of this requirement, as this process requires high-efficiency mixing to avoid solids settling.

To remove the entangled collection of fibrous materials (the result of ragging) from around the impeller, wastewater treatment plants resort to reversing the mixers after daily operations and emptying the bio-reactor tanks every three to four months to manually detangle and strip the hub and impeller of the entangled mass. This is known as a fouled impeller. Rag buildup around the impeller not only restricts the process flow which results in settled solids but also increases the load on both the motor and gearbox. This increased loading reduces the expected bearing life, as well as inducing a possible motor overload, resulting in premature failure of the mechanical agitator.

The most commonly found agitator solutions employ radial backswept turbines, which have a large power draw with a very low pumping/flow delivery. It was assumed that the backswept, curved blade design would assist in limiting the rag buildup around the turbine. The radial flow, backswept impeller demands high power inputs to provide a marginal pumping delivery into the mixing tanks, but rag buildup still occurs around the impeller blades and hub.

AFX was driven to find the “perfect” solution. Keeping our focus on efficiency for the process demands, as well as offering cost savings to the plants, AFX developed a clean edge impeller, also known as a ragless or non-stringing impeller. The impeller, FCE3, boasts an impressive design. Eliminating areas where common rag build-up occurred, this impeller still produces the desired output pumping rate. The FCE3 impeller ensures that the high-efficiency demands of the process are met, and provides a solution which is energy efficient. The inputted power required for the FCE3 is far less than the typical bio-reactor agitators with outdated turbine technology.

The welded hub and blade design, in conjunction with the blade geometry ensures that any fibrous solids and materials that come into contact with the impeller surface are pushed over the top edge and entrained back into the high-velocity zone by the leading blade. The impeller has a high pumping number (Nq) similar to the F3 axial flow hydrofoil impeller. The power number (Np) is almost five times less than that of a radial flow backswept blade impeller. The FCE3 impeller delivers not only a solution to eliminating rag buildup, but provides you with a sound solution to the mixing process. The FCE3 impeller slots into AFX’s energy saving endeavour, providing you with the best possible mechanical solution that saves you both time and money.

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