7 replies to this topic

[nastaran]

as you know there is a rule for 3or 2 seprator sizing based on stoke's law , when we use some internals like:vane pack,coalese pad,.. the size is smaller,but I don't know how I can attend this point in sizing and how much they decrease the size.would you please help me?
with Thanks

[Andree]

What you are after is a proprietary information related to performance of internal used. Generally, the issue is that you base sizing calculation on maximum velocity that given internal element can handle and it refer also to performance in terms of minimum droplet size captured as well as enlarged (coalesced) size in the case of coalescing internals.

Your question is rather general and refers to many types of equipment. If you could refine it, I could probably help more

[JoeWong]

You may also refer to section 7 Separation equipment in GPSA (12th ed. that i have).

[nastaran]

What you are after is a proprietary information related to performance of internal used. Generally, the issue is that you base sizing calculation on maximum velocity that given internal element can handle and it refer also to performance in terms of minimum droplet size captured as well as enlarged (coalesced) size in the case of coalescing internals.

Your question is rather general and refers to many types of equipment. If you could refine it, I could probably help more

thanks alot
I exactly don't know what internal should I apply in a separator but I have seen it 's common to use a vane pack at the inlet and gasoutlet.How much they decrease the size?
and another question is about outlet purity How can i consider this point in sizing for example:

- Maximum Oil droplet size in vapor 150 μm
- Maximum Oil droplet size in water 125 μm
- Maximum water droplet size in oil 400 μm

- Oil content in the produced water outlet to be less than 2000 ppmV.
- Water content in the produced Oil outlet to be less than 0.05 ppmV.
- Oil content in the gas outlet to be less than 20 Lit/MMSCMD .
How canI be sure seprator is suitable for this purity

[Andree]

I exactly don't know what internal should I apply in a separator but I have seen it 's common to use a vane pack at the inlet and gasoutlet.How much they decrease the size?

depends on the design of specific internal... in the case of higher separation efficiency required, you can go to coalescence mats (both gas/liquid and liquid/liquid)... but vanes usually have less pressure drop and life cycle is also in favour to them... manufacturers of coalescing cartridges define different values of minimum droplpet size to be captured for different design - mimimum for liquid/liquid os said to be "below 1 micron", for gas/liquid I met 0.3 micron... when you look of products offered in the market, the manufactirers claim efficiency defined as "X" ppm of carryover - this is related to both element performance and assuring reasonable process condition (vessel sizing etc.)


and another question is about outlet purity How can i consider this point in sizing for example:
- Maximum Oil droplet size in vapor 150 μm
- Maximum Oil droplet size in water 125 μm
- Maximum water droplet size in oil 400 μm

maximum droplet size will depend on hydrodynamic in the system - in vigorous turbulent flow the stresses acting upon droplets lead to breakup (and surface or interfacial tension forces tend to keep droplet in one piece - very simplified description, neglects surface interaction if suraface active compounds or electrostatic charge are present)... the flow conditions, for gas as a continuous phase it will be much different than for liquids, should be so that this maximum stable size >> droplets after coalescence (>> design size - you probably meant this)

the design size you proposed seems to be quite reasonable, only for gases seems for me a little to large... however, I am curious how did you arrive to those figures? I ask about this, because I can see trend which is not exactly in agreement with physical phenomena of the process


- Oil content in the produced water outlet to be less than 2000 ppmV.

usually in oil removal from water the limit is much less (e.g. 200ppmV or even 15ppmV in wastewater treatment technologies)

- Water content in the produced Oil outlet to be less than 0.05 ppmV.

not realistic


How canI be sure seprator is suitable for this purity

you can't be
you cannot say and subsequently design a separator for 15, 50 or 100ppmV - you obtain such efficiency as declared by manufacturer when:
- you do not exceed critical process parameters (velocity through element, whcih can be detrimental from the point of view of performance - this is variable, depending on liquids to be separated, dispersed phase concentration etc.)
- you perform vessel sizing as advised by internal provider (that's why many companies provide complete designs, i.e. vessel with internals)

[nastaran]

thanks again

would you please see the attached file that a company has guaranteed for these purity of oil&water&gas?

Attached Files

•  3_phase_separator.pdf   87.66KB   135 downloads

[Andree]

Sorry, I cannot say much and guarantee if the company design proposal is sensible, bacause:
1. I do not know what is performance of offered internals
2. I do not know the flowrate and volume fraction of each phase

And what is HHLL? I suspect that this is level control height (distance between LG connections on the right hand size head of the vessel on your sketch).

Efficiency (cleanliness) for gas and water seems to be attainable (especially for water - 2000ppmV is really high concentration), but it is completely not realistic to reach 0.05ppmV of water in oli phase... Are you sure this is 0.05ppmV and not 0.05%vol., which is 500ppmV? - This could be realistic figure.

[Andree]

I recommend you to get through Schell DEP 31.22.05.12-Gen. "Liquid/Liquid and Gas/Liquid/Liquid Separators - type selection and design rules" - there you will find answers for many of your questions