Agitator Design

Agitator design Q: How do you design the shaft diameter, impeller rpm and power required to drive an agitator? A: For mechanical design information about mixers, see Chapter 21 of "Mechanical Design of Mixing Equipment" in the Handbook of Industrial Mixing, Ed Paul, et.al. editors, John Wiley & Sons, 2004. Here are more of the latest questions on: Mixing What type of impeller and engine power should I use for the following service? What type of impeller and engine power should I use for the following service?

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Tank: Diameter = 2m, L = 5m (17m3 Capacity) Fluid = Vegetable oil (I think viscosity = 60 cP, density = 900 kg/m3) Temperature: Reaches 130 degrees C

What is the best mixer for solids and liquids? I want to mix a solid with a liquid with the ratio of 50/50. But the solid is water wet 30% and I have to drive off the water while mixing the two components. What is the best mixer to use to first get the water to the top of the vessel, evaporate off and also mix the solids and liquid? Solids density is 1.6 g/cc, liquid is 1.5 g/cc. What is causing the mechanical problems with agitators? I am currently mixing 4 tons of product with a density of 8.4lb/gal that is very sensitive to over mixing. My current mixer design has reliability issues. There are two counter rotating agitators in the tank which are about 8' long by 5' wide. While running, the agitators sway due to either fabrication quality or design flaws. I currently have 2" and 4" shafts extending down from the gear box into the tank. I am being sold on two different design options: 1.) Add a steady bearing to bottom of tank to reduce movement and my issues with this are the following: a. Ability to CIP; b. Have not corrected the problem just hid they symptom; c. Failure of the tank due to shaft hitting steady bearing in the repeatedly in the same place. 2.) Increase the size of the shaft to 6" and 3" my issues are the following: a. Work required to perform repair (cut off top of tank and replace with new cover); b. Cost associated with new gear box installs. My question is for this application in a pharmaceutical environment, what would be the best course of action? Is there any published literature on the subject? Lastly are these design solution accurate or should I be looking at other alternatives? What are the motor powers and shaft diameters for these agitators? To be used in various tanks we need to get your answer for agitator motor power and shaft diameter for the following agitator data: Agitator A: •

Liquid in tank: Density = 1.09 t/m3 Dynamic viscosity = 150 mPa.s Temperature = 85 degrees C (average)

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Speed: 95 rpm Length in tank = 3650 mm Impeller: 1 row, 2 blades , 900 mm in dia. Tank volume= 40 m3

Agitator B: • • • • •

Liquid in tank: Density = 1.4 t/m3 Dynamic viscosity = 100 mPa.s Temperature = 80 degrees C (average) Speed: 85 rpm Length in tank = 4750 mm Impellers: 2 rows, 2m between rows, 2 blades at each row , 1300 mm in dia. Tank volume= 28 m3

Agitator C: • • • • •

Liquid in tank: Density = 1.48 t/m3 Dynamic viscosity = 10000 mPa.s (average) Temperature = 70 degrees C (average) Speed: 66 rpm Length in tank = 5630 mm Impellers: 3 rows, 1m between rows, 2 blades at each row , 800 mm in dia. Tank volume= 15 m3

For the above agitators, I need motor powers and shaft diameters. How do I calculate the dynamic force on the agitator? How do I calculate the dynamic force on the agitator? The details are as given:         

Capacity of mixer: 15 Kl Motor: HP 75 HP shaft speed: 48 rpm diameter of vessel: 2450 mm st. height: 3000 mm dish height: 491 mm stirrer: anchor type sweep dia: 2300 mm material viscosity: 40 poise (emulsion-based paint)

How do I calculate the dynamic force on the agitator? Q: How do I calculate the dynamic force on the agitator? The details are as given: • • •

Capacity of mixer: 15 Kl Motor: HP 75 HP shaft speed: 48 rpm

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diameter of vessel: 2450 mm st. height: 3000 mm dish height: 491 mm stirrer: anchor type sweep dia: 2300 mm material viscosity: 40 poise (emulsion-based paint)

A: Explaining "how" to calculate the dynamic force on the agitator is more difficult than providing a value for the conditions described. Further, "how" the "dynamic force" will be used makes a difference in the suggested safety factors to be applied to the calculated values. For the purposes of equipment design, the dynamic forces should be calculated based on the motor horsepower and agitator speed, since at some viscosity the motor could be fully loaded. On that basis, torque will be about 11,000 N-m. An estimate of the bending load on the shaft and drive is about the same, 10,000 N-m. Those loads require a 125 mm diameter shaft. For the purposes designing a support for the agitator, a rigid mounting is necessary. The support should be designed to handle 2.5 times the calculated torque and 3.0 times the calculated bending load. If all that is needed is an anticipated operating load for the dimensions and viscosity described, the agitator will require about 33 hp. That requirement is based on a viscous power number of 360 (for laminar operation), which is multiplied by a factor of 2.2 for the impeller Reynolds number of about 1,000. The resulting viscous (not turbulent) power number is 780.

Impeller Equipment Mixing Technology represents a balance between the requirements of the process and the output efficiency of the impeller. Impellers used in agitation systems are mainly required to produce three basic fluid regimes:

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Flow Shear Pressure

or a combination of these, Agitator impellers all obey the relationship P = Q x H (where Q = Flow and H = Head (Shear) To suit the requirements of the process, all impellers are selected for their ability to produce various combinations of the variables of Power, Flow and Head (Shear).

The main impellers used by CANAMIX in the selection and manufacture of their high technology agitators are:

CANAMIX Type F3 impeller for high flow production This 3 bladed, high efficiency impeller is specifically designed to produce high flow velocity at low installed power. These low solidity impellers are usually selected for the following duties: Leaching , CIP, Neutralisation, Lime Make-up and Storage, Water Treatment, Chemical Reactions, Pulp Mixing, Flocculation, and similar applications where the generation of flow drives the agitator selection.

CANAMIX Type P4 Pressure Impeller for Gas dispersion. This 4 bladed, high solidity impeller is specifically designed for applications involving the introduction of high volumes of gas. With a solidity ratio of greater than 90%, the gas introduced is unable to bypass the impeller. This results in an increase of power under gassed conditions (unlike 6 bladed Rushton impellers which reduce in power under gassed conditions), eliminating the need for variable speed or 2 speed motors to allow for the increased power when gas is reduced or shut down. These high efficiency axial gas dispersions are normally used on the following processes :

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High pressure autoclaves BIO-Oxidation reactors BIOX®, BioCop® and BioNIC® reactors Fermentation and Hydrogenation Iron Removal

CANAMIX Type P 3 impeller for High viscosity applications In high viscosity applications, there is a need for an impeller to produce flow in viscous, low Reynolds number fluids. Normal low solidity impellers do not produce macro flow and high solidity impellers draw excess power. The compromise is the Afromix P3 impeller. This 3 bladed impeller has a solidity ratio of approximately 70%, allowing the production of macro flow in duties with a Reynolds number of 200-300, or effective maximum viscosity of 40 000cps. These impellers bridge the gap between low solidity aerofoils, and close clearance impellers like gates, spirals and anchors, which would have, traditionally, been used for applications in excess of 15000cps.

The CANAMIX F4 impeller Aerofoil impellers, such as the F3, produce higher flow, but are limited where shear is also a requirement. All mixing impellers operate in accordance with the relationship. P = Q x H (where H = Shear). To provide a higher level of shear, whilst maintaining a relatively high pumping capacity, the tried and testedPitched Blade impeller still has the advantages, despite its relatively high power draw and low efficiency. This standard impeller, usually pitched at 45°, or a convenient angle, is named the CANAMIX FS4. Whilst rarely used, it is still an important weapon in the mixing artillery.

The CANAMIX R6 impeller pump mixer The Canamix R6 radial flow impeller is a unique impeller designed for pump mixer application in solvent extraction or thickener dilution systems. The impeller is designed to advance flow, maximise dispersion and provide specified head generation. These curved blade pump turbines offer maximized head and flow while reducing power consumption, minimum shear generation and turbulence.