6 replies to this topic

[Root]

Hi,

Can any one shed some light for L/L separator bucket location (for light phase liquid) as i haven't found any code or standard, only one papaer which mostly referenced here (successfully desig three phase separator)indicating 12" before wier plate.

Toor

 

[Root]

Hi all,

Is my question is  not appropriate on this forum or any one don't have answer for this question.

Regards

Toor

[PingPong]

I assume you are referring to the article "successfully specify three phase separators"

 

The space between the bucket and the oulet weir should be such that heavy liquid flowing pressure drop is minor, and that access for cleaning is possible. These authors simply advise 12 inch (1 foot).

 

Note that the article contains the word assume many times.

 

The space below the bucket is also simply set on such assumption, but there the same applies: pressure drop should be minor.

 

What is strange in their method is that they do not take into account that there is a crest over weir at the inlet weir of the bucket and also at the other weir where the heavy liquid overflows. Crest over weir can be calculated using the well known Francis formula.

 

The crest over both weirs, plus the before mentioned pressure drops (if not negligible), have an impact on the calculation of ΔH and should have been included in equation 57.

 

Also the way they set the vapor space in example 2 is very strange. Although they mention K values in table 2 they don't seem to bother with that kind of details when they simply say: assume H_v = 0.70 D

What kind of ridiculous design philosophy is that?

 

A separator with a light liquid bucket is only used when the amount of light liquid is minor compared to the heavy liquid. One glance at table 10 and you know that that problem should absolutely not be solved with such a separator. One should not need to do any calculation to realise that.

 

I never used that article, and I fear that if I would check everything in detail I would find more dubious assumptions/advices/formulas.

 

Generally: always be carefull when using an article. First of all they can contain typing errors in formulas. But more importantly: the fact that an article was published does not mean that the contents is correct. Always keep an open mind and also use your common sense.

 

Designing a phase separator is not exactly rocket science. There are only a few simple formulas involved: separating liquid drops from vapor (using those K values) and settling of liquid droplets in a liquid with a different density. Those can be found in many textbooks, so use of an article is not really required.

Edited by PingPong, 08 December 2013 - 08:41 AM.

[curious_cat]

I never used that article, and I fear that if I would check everything in detail I would find more dubious assumptions/advices/formulas.

 

Generally: always be carefull when using an article. First of all they can contain typing errors in formulas. But more importantly: the fact that an article was published does not mean that the contents is correct. Always keep an open mind and also use your common sense.

 

Indeed! Wise words of caution. I feel one has to be even more cautious in using canned spreadsheets! just because they seem so "easy". I find a very worrying reliance on using third party spreadsheets on an increasingly common basis. 

 

Validation is key. Even the best intentioned person can so easily make an error in a complex Excel spreadsheet I cringe to think of the consequences on a hastily designed piece of equipment.

Edited by curious_cat, 08 December 2013 - 10:44 AM.

[Bobby Strain]

Whatever separator design, you can check it at my site. Just Google my name to find it.

 

Bobby

[Root]

Bobby,

Your website is silent on bucket sizing, i ready checked.

PinPong,

Its mean their is no such criteria for bucket location and you can specify location based on separation length of light liquid?

Thanks

Toor

[PingPong]

The bucket location is set by L1 (not by L3). L3 merely sets the location of the overflow weir, relative to the bucket.

 

In my opinion however the way these authors calculate L1 is not correct.

L1 should be set by separation of heavy drops out of light liquid, as well as by separation of light drops out of heavy liquid, not by separation between vapor and liquid droplets, as the autors seems to do. They simply assume an Hv and consequently an Av, which is not the way to go. Av should be calculated by Souders Brown type equation (like equation 4) using a K value. I would use K = 0.1 m/s (0.35 ft/s) to size the vapor space in a horizontal drum, but there are other sources that use a somewhat higher K-value.

 

My advice: do not use this article to design a horizontal bucket/weir separator as the authors seem to have no clue what they do.

I have no opinion about the calculation procedure for other type of separators in the article as I did not check those, and I do not intend to spend time to check those either.