Desalination project Issue

[asg348]

I am working on desalination project. I made a small prototype for desalinate 0.5 gpm but this need to be constructed for 200 gpm.
In our prototype I bring process water (saline water) to bottom part of an auger (please see attached picture) and I cool down the water in bottom part of auger by a cooling coil feed by a 5 ton chiller to around 40 ͦF . When the temperature drops to 50 ͦF salt start to crystallization and with auger I remove the salt from water and pure water over flow from a half pipe we provide for this purpose. (Please see attached picture).

[highlight #FCE94F]The issue I am having is this: When salt start to crystallization it attaches to cooling coil copper piping and get hard and harder and each 5 to 10 minute we have to stop the process and remove the salt from cooling coils and start over. I appreciate for any input.[/highlight]

I need to add that, before using this system I tried to run the salty water through shell and tube heat exchanger but salt crystals was plugging the heat exchanger.

 

[zdas04]

It seems to me like you are taking too big a temperature drop in a single step. Have you considered doing it in 2-3 stages?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[asg348]

Zdas04,
Doesn't mater for desalination we need to go to that low temperature and it will cause the issue.

 

[zdas04]

Doesn't matter? At 40F you are way super saturated. At 60F you are less super saturated. If you can get the solids to precipitate in a sequence of smaller steps you can sometimes keep them more or less where you want them.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[btrueblood]

I'd think you could coat the auger and/or cooling coils with (for instance) a Teflon spray coating, to help it shed adhered salt crystals more easily. Short of that, some method of backflusing/washing the surfaces with warmer or desalinated water on a periodic basis will need to be contemplated. Like descaling a boiler, make it a required periodic maintenance item.