L/L separation equipment
L/L separation equipment
(OP)
It's been awhile for me; I have an application where it's necessary to separate 2 immiscible liquids with a contact time of < 5-10 minutes. A centrifuge comes to mind, but would there be any other technology out there worth looking into, such as coalescer's? A decanter requires too much residence time.
Here's some info on the application:
Heavy Liquid sg: 1.15, viscosity ~ 5 cP
Light Liq sg: 1, viscosity ~ 15 cP
Vol ratio Heavy/Light: 4:1
Total vol flowrate: 10 gal/min
Any tips appreciated
Thanks,
Pete
Here's some info on the application:
Heavy Liquid sg: 1.15, viscosity ~ 5 cP
Light Liq sg: 1, viscosity ~ 15 cP
Vol ratio Heavy/Light: 4:1
Total vol flowrate: 10 gal/min
Any tips appreciated
Thanks,
Pete





RE: L/L separation equipment
RE: L/L separation equipment
25362 sets you on the right lines by directing you to Perry's. From the info you have given I'd think closely about hydrocyclones, though the delivery pressure will be a crucial factor, as will the extent of mixing between the two fluids.
You'll need to ask yourself the following questions if you are thinking about applying a hydrocyclone.
- Which is your product stream?
If you need to pump the feed up (generally you require a feed pressure of >3barg) then you could end up shearing the fluids and emulsifying them even further. The key to successful hydrocyclone installation and operation is carefully controlling the pressure drop ratios (dpr) around the unit. The vendor will advise.If you do have a relatively small droplet size (i.e. <10microns) then you may want to consider a fibrous coalescing media upstream of the hydrocyclone (www.owtc.com or www.cyclotech.com).
Hydrocyclones (www.mozley.co.uk) will separate the feed into two streams; light product and reject. The light product should be relatively clean while the reject will comprise the heavy fluid plus some light fluid. The total reject flow may reach up to 5% (by vol) of the inlet flow, and up to 80% of the reject may be light fluid.
I hope that this helps in some way.
Nosey
RE: L/L separation equipment
How relevant this is to you, I couldn't say. I suspect that your viscosities may be against this method.
Centrifuging may be a better option (GEA Westphalia, ALfa Laval for example). In the marine industry they use the centrifuges to seprate water from heavy fuel oil. This is usually at 98degC with typical oil density 981kg/m3 and viscosity 35cst; water, well 1000kg/m3 and 1 cst, near as makes no difference.
RE: L/L separation equipment
1) to recover Heavy or Light (H/L ) or both component(s) ?
How clean ?
2.) To assure that H or L is NOT contaminated with
the other component ( specify !)
<nbucska@pcperipherals.com>
RE: L/L separation equipment
Both Light and Heavy are products that will be recovered.
The 2 phase mixture is not emulsified; it separates easily into 2 clear phases in about a minute or less in a 500 ml size bottle.
Currently, the stream of the 2 liquids flows by gravity. A pump would be required to generate pressure to go into a hydroclone.
RE: L/L separation equipment
You said the mixture easily separates into 2 phases in a minute or less. At 10 gpm, 10 minutes residence time wouldn't mean a very large piece of equipment would be needed. From a cost point of view, centrifuges or hydrocyclones are going to be a lot more money.
RE: L/L separation equipment
A variety of means have been listed to separate these two liquids. I would like to comment on two already mentioned and perhaps add a third.
Coalescer: A coalescer can handle this separation. If emulsions arise, coalescer elements can often break the emulsions as well as separate the phases. Pall has liquid/liquid coalescing elements and housings for this service. The feed will have to be pumped into the coalescer to develop pressure drop across the element. Both liquids will contain the other liquid at its solubility at the separation temperature. If low levels of cross contamination are desired, pre-cooling the feed is advantageous. A pre-filter is necessary for any coalescer. An issue will be chemical compatibility of the liquids with the filter media.
Centrifugal separator: CINC (Nevada) has a centrifugal separator that will make the phase separation. This is a more costly approach. The feed should be pumped into the CINC. Product streams can gravity flow out.
Decanter: Simple, horizontal decanter with heavy phase boot. Level control the heavy phase out (or detect interface with magnetorestrictive gage with float that floats on heavy phase) and overflow the light phase. Feed pumped in subsurface in the light layer.
RE: L/L separation equipment
Gravity separation is the way to go.
RE: L/L separation equipment
It is, however, worthy to try and analyse the bottle experimental results on whether they are indeed reproducible in a plant-size prototype metal-made continuous flow settler.
Besides, are the liquids totally immiscible or do they partially dissolve in one another ? Do they need further treatment for their purification ? How do the given viscosities, surface tension and densities relatively change with temperature ?
Good luck.
RE: L/L separation equipment
Gravity will work for this. In the past, two decanters have been tested on this stream. One was vertical with 1 hr res time for heavy, 30 min res for light. The other was horizontal, with more res time than the vertical.
The problem is that an undesireable solid byproduct forms from contact between the phases, and comes out with the Heavy of either decanter. The horizontal decanter, with more contact area and res time, made more bydroduct than the vertical.
For this reason, I want to minimize contact time and area between the phases. I know in lab tests with a sep funnel that if I can separate the phases after a few minutes, I do not get any byproduct. Unfortunately I do not know the time limit for a batch separation to avoid byproduct formation.
It might be possible to use a smaller decanter to avoid making the byproduct and still get a good L/L split.
I know I could use a centrifuge to get a good sep'n with a few minutes contact time.
RE: L/L separation equipment
If interfacial solids formation limits the use of a gravity decanter, the CINC centrifugal separator is perhaps a good method. Phase contact time and surface area are small.
www.cit-ind.com
Bill Choate
RE: L/L separation equipment
1. Gravity separation in horizontal decanters can be enhanced with the help of smoothening vanes or gratings, thus the vessel can be of smaller dimensions and the time of contact at the interphase may be shortened. Some provisions to continuously remove the "band" near the interphase may be needed.
2. Is there a possibility of using a third immiscible chemically inert liquid with an intermediate density to act as a physical separating wall between the process fluids ?
3. Or can a third "inert" liquid be dissolved in the heavier phase to increase its density and reduce its viscosity to make the phase separation quicker ? This "new" fluid would have to be easily removable as needed at a cost.
4. Can you use a higher temperature to make separations easier and quicker without increasing the phases' chemical reactivity ?
Good luck.
RE: L/L separation equipment
If your solid forming reaction is strongly temperature dependent, even though lowering the temperature of the fluid may increase viscosity and increase separation time, you may want to run decanter colder in order to stop reaction from occuring. If solid is something that you have to filter out or decreases your useful product volume, you might save this expense.
RE: L/L separation equipment
The side reaction to form solids is slowed by reducing temperature, so this might be a viable approach, but I'll have to put some cooling in which will add cost.
Some observations from the lab; if I use a sep funnel and separate batchwise with about 10 minutes holing time of the phases, I don't seem to form any solids. However, if I run continuously with a decanter at average res time of around 10 min, or even less, solids still seem to form. My theoretical explanation for this is that it must be due to a residence time distribution phenomena in the continuous system. i.e. in the continuous system, some fluid from each phase will be in contact for longer than the avg res time.
RE: L/L separation equipment
RE: L/L separation equipment
The difference between the lab sep funnel model and the process decanter with the same residence time is probably due to the difference in interfacial area. The sep funnel model probably has a very low area. The reaction is occuring by mass transfer of some species from one phase to the other with a product that is somewhat insoluble in either phase. The transfer flux is proportional to the concentration of the reactant in whatever phase it is in and the interfacial area. More solids are formed at a fixed residence time in the system having the higher interfacial area.
Several viable options have been offered by contributors to this forum. The reaction slows as the temperature is dropped. Phase separation is slowed as the temperature drops requiring higher residence times. A gravity decanter, to optimize the result desired, would have to be a tall, vertical tank to minimize area and provide required residence time for separation. In addition the feed would have to be cooled to slow reaction.
If centrifugal force is used, the separation may be more easily managed.
RE: L/L separation equipment
Comparing the lab continuous decanter to the plant continuous decanter, they generate roughly the same wt% solids in the heavy stream at the same avg res time. The interfacial surface area/volume is roughly the same between the lab and plant scale.