15% Lime tank: Guidance.. 1

[jamesbanda]

Hello all,

I'm looking for a decent reference for specifying a 15% solids content lime tank.. specifically,
1. mixing type of device..(top agitator or other)
2. Type of sloping on tank..

is there a reference or design guideline i can purchase for these kinds of systems? (outside of my normal chemical experience..)

 

[geesamand]

Typically a top-entry agitator is employed here. With solids suspension, tank geometry is very important. My company has made many such agitators. Unfortunately I'm not a process expert so that's all I can share.

One important question is whether the agitator impeller would be even partially buried if the unit is off and the solids are allowed to completely settle. Mechanically the torque loads on a buried impeller are very high, so if this is unavoidable you'll need to oversize the entire agitator, prevent the agitator from stopping, or jet water on the impeller to loosen things before startup.

If you're interested I can put you in touch with one of our mixing process experts.

Dave

 

[shahyar]

I am not dealing with 15% lime. I usually design for much lower Lime strengths. In those cases, I try to limit the tank diameter to less than 4 m and L/D around one. The reason for D<4 m is to avoid using side-entry agitators which have problems.L/D around one help us to be able to use single agitator on a shaft. The other thing is baffles inside of the tank. If you can avoid them it is excellent. They will plug quickly. If your system is small you might use off-centre agitators if the extra vibration on the tank is manageable.
hope this help.

 

[jamesbanda]

Would you design a square tank to avoid baffles.. i'm looking at a 7m,7m,7m square tank..

or would you use a jet mixing system with a pump..?
it is only a buffer lime tank..

 

[shahyar]

Your both options look ok, even though I personally haven't tried them.
I am not very familiar with square tanks, it could be because there is no(?) famous standard for their design and in the oil industry we try to avoid them.
Hope this help

 

[GHartmann]

The conversion of lime (CaO or soda ash) into a slurry is quite common for Flue Gas Desulphurization in the power industry and for use in waste water treatment.

However the slurry can freeze at 80 deg (it is essentially like cement / mortar and is a main ingrediant in such).

You will need to know if it quick lime (CaO) or hydrated lime (Ca(OH)2) and follow some of the ideas here:

http://bromatco.com/costs.html

I've never seen a rectangular mixing vessel.

Good luck.