olein vacuum drying

[miguelandrade]

Hello,
I have been asked to build a palm olein moisture remover. The process-system consist in heating the olein in a plate heat exchanger and then introducing it in a vacuum tank so the water which it contains evaporate. Beside the mass flow, which are the variables that determine the vacuum tank dimensions? and how do I know the capacity of the vacuum pump I need?
Just to let you know, it's my first project asigned in my first internship job!
thanks a lot

 

[StoneCold]

Hello Miguel
I will try to give you some help.
So lets start with the size of the tank. A good place to start for liquid level if you are pulling vaccum is half full, that gives you room for foaming etc. You don't mention if this is a batch process or if this is going to be a continuous flow through tank. That is obviously going to affect the tank size. If it is continuous then we need to talk about residense time. Since I don't have any experimental data or any knowledge about palm olein, I do not have any idea how easy this water separaration is. So I am going to choose a random time of 5 minutes for the residense time. You might ask around at your company for feedback on this. So we have a tank size and we need to size the vacuum pump. The absolute minimum size for the vacuum pump is the capacity for it to pump out the same amount of vapor as there is water coming in. So taking the mass flow of water coming in you need to convert that to a vapor volume at some temperature and pressure. The pressure being the level of vacuum you ware wanting operate the system at. The vacuum level is going to be a function of how dry you want the material to be and how hot the palm olein is. The water vapor flow rate will give you the ideal minimum size vacuum pump, however you need to factor in leaks, and entrained air that you will have to suck out as well as low boiling products in the feed that can be vaporized and pulled over in the pump. I hope this gets you started. If you need more help post some more information about your process and I will try to add some additional details.

Regards
StoneCold

 

[miguelandrade]

Thanks StoneCold!
Yes, it is a continouos flow process. I have been asking around and they don't have the evaporation rates neither, so what I did to get the residence time is that I used the dimensions of an already existing dryer which handles 4500L/h, I divided its tank volume to the volume flow and with that residence time I calculated the volumen needed for the new dryer, which is supposed to dry 10000L/h. Is it correct?
How do I obtein the leaks and entrained air factor?
Thanks again.

Regards,
miguel

 

[StoneCold]

Miguel
If you already have a running unit that should make things easier. How is the smaller unit working? Did the operations people say this was an excellent unit to copy? One note of caution is that when you scale things up they tend to be less efficient. Meaning that if I was creating a unit that was more than double my existing unit I would add maybe 10% to the residence time to help factor that in. If the small unit is working fine then you can approach the vacuum pump the same way. Though you may want to calculate the pump based on the ideas I gave you last time and compare that to your scaled up model and see if it is reasonable. Sounds like you are on the right track.

Regards
StoneCold

 

[Latexman]

How do I obtein the leaks and entrained air factor?

From the technical information on the existing vacuum pump, you can calculate this for the smaller system. Then, scale it up. You should know the water flow rate. Vacuum pump capacity at the system pressure - water flow rate = air leakage rate. This, IMO, is the best way.

There are some correlations in some vacuum system references and books. Start by searching on Google.

Good luck,
Latexman

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[StoneCold]

Miguel
One more comment on the vacuum pump. Since vacuum pumps come in descrete sizes you don't need an exact value for your leak rate, etc. You don't want to excessively oversize the pump but there will definately be some excess capacity as you try to fit into a vacuum pump model number. I guess what I am saying is when you take the existing vacuum pump size from the 4500 L/hr and multiply that capacity by 10000/4500 to get the new capacity you need. Then when you go to the manufactures table of capacities for diffenent models you are probably going to end up with a unit that gives you some excess capacity and that will help cover the leaks and air entrainment,etc.

Regards
StoneCold

 

[miguelandrade]

Ok guys, thank you for your help! i'll bring you up to day as this project progess,

regards,
miguel