Dave Dickey Forum Moderator 269 Posts
Re: Can we thoroughly mix without breakage of the CPGs?7 November 2011 at 1:29pm
The mixing requirements for this process are impractical because of the batch size limits. A 400-gram batch is about 0.4 liters, which must be mixed into 4,000 to 8,000 liters of solvent. If the process involves mixing 0.4 liters and 8.000 liters in the same vessel, then the minimum liquid level would be 0.25 mm in a 1,500 mm diameter cylinder, with a maximum liquid level of 4,700 mm. Mixing 0.25 mm in any vessel is going to be impossible, especially in 1,500 mm diameter.
The most likely prospect of a vessel and mixer with some of the required characteristics, would be a vertical, cylindrical vessel, 1,500 mm in diameter with a 5,000 mm straight side and a dished bottom. The mixer could be a helical ribbon mixer, 1,300 mm in diameter, with two flights, blade width of 130 mm, a 1:1 pitch, and 4,550 mm height. The shear will be in the velocity gradient between the edge of the helix and the wall of the tank. Adjusting the rotational speed of the helical ribbon will allow adjustment of the maximum shear and the blend time. For low shear, similar to a wrist action shaker, the rotational speed of the mixer will be very slow, perhaps 5 to 10 rpm. At these speeds, the blend time will be long, especially with the tall tank.
The helical ribbon mixer should give the least shear and the maximum blending for this application. Whether this design meets all of the process requirements is impossible to estimate without more experimental information.
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