Mixing Slurry
Mixing Slurry
(OP)
Hello,
I am having trouble figuring out what is typically done in my situation (FYI: I am a new graduate in chemical engineering). I have a cylindrical baffled tank (approximately 60" in height, 30" in diameter) with an agitator (2 impellers). I am mixing a slurry which has a strong desire to separate on me. The system is also equipped with a recirculation pump (whose capacity seems to be nowhere near the appropriate capacity).
The tank takes approximately 8 hours to empty. As long as the fluid is in contact with the agitator, the slurry is well mixed and no problems appear. However, the last 10" or so of the tank, the slurry level is below the agitator and the recirculation pump is the only mixing device in effect. Unfortunately, the last 10" takes about 1 hour to drain and due to the poor mixing, the slurry separates on me. I was looking for some solutions from people with mixing experience... here is what I am thinking and I would appreciate any advice...
1. increase the capacity of the recirculation pump, however, the capacity would have to be increased by a very large amount and the space/cost may be an issue
2. add an air sparging system to bubble gas through the bottom of the tank (is this typically done? could it be capable of creating the turbulence required to keep this slurry in tact?)
3. redesign the tank... a coned bottom would reduce the amount of "dead" material to an acceptable level (which would be discarded as waste. however, i fear a new tank would also require a redesigned agitator to ensure appropriate mixing.
Thank you all in advance.
Roland
I am having trouble figuring out what is typically done in my situation (FYI: I am a new graduate in chemical engineering). I have a cylindrical baffled tank (approximately 60" in height, 30" in diameter) with an agitator (2 impellers). I am mixing a slurry which has a strong desire to separate on me. The system is also equipped with a recirculation pump (whose capacity seems to be nowhere near the appropriate capacity).
The tank takes approximately 8 hours to empty. As long as the fluid is in contact with the agitator, the slurry is well mixed and no problems appear. However, the last 10" or so of the tank, the slurry level is below the agitator and the recirculation pump is the only mixing device in effect. Unfortunately, the last 10" takes about 1 hour to drain and due to the poor mixing, the slurry separates on me. I was looking for some solutions from people with mixing experience... here is what I am thinking and I would appreciate any advice...
1. increase the capacity of the recirculation pump, however, the capacity would have to be increased by a very large amount and the space/cost may be an issue
2. add an air sparging system to bubble gas through the bottom of the tank (is this typically done? could it be capable of creating the turbulence required to keep this slurry in tact?)
3. redesign the tank... a coned bottom would reduce the amount of "dead" material to an acceptable level (which would be discarded as waste. however, i fear a new tank would also require a redesigned agitator to ensure appropriate mixing.
Thank you all in advance.
Roland





RE: Mixing Slurry
JMW
www.ViscoAnalyser.com
RE: Mixing Slurry
RE: Mixing Slurry
If air is OK, you might inject it at the top to force-drain the tank quickly instead of having it trickle out over hours
Unrelated idea: You may wish to throw in an eductor connected to your recirculation pump and mounted to the lowest point in the tank. An eductor uses the energy of the pumped stream to move a lot of flow.
RE: Mixing Slurry
JMW
www.ViscoAnalyser.com
RE: Mixing Slurry
Why are you draining the tank all the time?- is it a batch make up process or is it just a normal shutdown situation
What stops you draining the tank faster once the level is below the blades
Cheers.
RE: Mixing Slurry
You could install a false floor in the tank that slopes towards the drain nozzle. It should'nt affect your mixing dramatically, although you would need to monitor the new tank geometry for wear.
If your looking into air agitation, bear in mind that you will need to keep the slurry out of the air distribution system, which requires careful design.
NB
RE: Mixing Slurry
The tank is used for batch mixing. It drains into another piece of processing equipment, which has a limited capacity... hence the slow drainage.
RE: Mixing Slurry
With an 8 hour drain time is the holding time important- or do you need to clean the tank out between batches.
Can you change your batching process to make a new batch up once you reach the minimum level?