Dave Dickey Forum Moderator 291 Posts
Re: How can I update the efficiency of very old mixers?2 November 2009 at 1:29pm
You left out what could have been an important piece of information, and that is the current impeller diameter. However, I was able to do a sufficient comparison to give you a simple solution to the problem. You can add baffles and replace the two 8-blade Rushton turbines with three 4-blade pitched-blade turbines of the same size as the current Rushton turbines. These three impellers will require slightly less power than the current two impellers, even after adding baffles.
You are entirely correct that the strong vortex, the lack of baffles, and the radial-flow disk-style impellers could not do a much worse job of solids suspension and solids dissolution. Unless your solids dissolve extremely slowly because of equilibrium, I would expect that you could cut in half the time required to achieve solution.
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I am new to the job and have been assigned to look at the efficiency of our very old mixers (salvaged from other plants). We use our mixers to dissolve rubber in solvents to make adhesives. (Final products viscosity ranges from average 5000cP, max around 10,000 cP) Some data I have collected: Tank: vertical cylinder diam = 1.25m, height = 5m, no baffles Stirrer: 2 number of Rushton turbine, 8 blades Motor: belt type 40hp, 330rpm Deep vortexes are noticed during operation. From what I have read this indicates fluid swirling, which is the worst kind of mixing because very little axial mixing is taking place. Using the general guidelines for solid dissolution, I am considering installing baffles and changing the stirrer to a pitched blade turbine in the hope to bring down mixing time and hopefully the hp of the motor as well. Where do I start and how do I estimate the "improvement" quantitatively?
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