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Power requirement for a constant stirring vessel

Q: What is the power requirement (motor specification, gearbox size and the shaft size) for a constant stirring vessel that is an open type with a 60-degree inclined pitched blade agitator running at 14-15 rpm? The contents of the vessel can be UF (Urea Formaldehyde resin), Melamin formaldehyde resin, MUF, phenol formaldehyde resin, etc. The diameter of the tank is 3,500 mm and the height is 5,500 mm. The stirring is required to not let the liquid gel-up.

A: This request contains about half the information that is really needed, since UF (Urea Formaldehyde resin), Melamine formaldehyde resin, MUF, and phenol formaldehyde resin could exist at several viscosity levels, and the only clue is the reference to a possible gel problem.

For minimal, but adequate mixing intensity, capable of maintaining liquid motion throughout the batch, I recommend two 60-degree (angle measured from the horizontal), pitched-blade impellers 1,600 mm in diameter. Each impeller should be with four blades 320 mm wide. One impeller located about 1,500 mm from the bottom and the other about 3,000 mm from the bottom. The tank should have four vertical baffles if the typical viscosity is less than 2,500 cp, and does not need baffles for higher viscosities. Rotating at 15 rpm, the impellers will require at least 1kW, so a 2- or 5-kW motor is recommended to prevent overloads. The drive output torque needs to be 1,275 or 3,200 Newton meters, depending on the selected motor size. An 80-mm diameter shaft is recommended.