Sizing 2-phase Horizontal Vessel 1

[Abiodun1]

Hi guys,

I want to size an horizontal Surge Vessel to handle 50,000 bopd.

The % height of the LSL, LAL, LAH, LSH has been given. There respective respective retention times required has been given.

How can i determine the diameter and length of the vessel?

I try using DEP but bit confuse!

Useful information is appreciated.

Regards,

 

[BigInch]

Surge vessels do not require a retention time. Are you sure you want to design a surge vessel or a separator? Separators do require a retention time.

For a surge vessel, you must know the maximum volume of liquids that will be slugged from (usually a 2-phase pipeline or a predominately gas pipeline with liquid condensates or minor voumes of condensates and oils) pipeline into the surge vessel. That will depend on the ratio of gas to liquid flow and the hydraulic characteristics of your pipeline (see 2-Phase flow regimes).

For a separator, if your flow is 50 KBOPD, and your retention time is 2 days, you will need 50Kbbl/day x 2 days =100,000 bbl capacity to start up the separator, during which time all flow will be diverted and feed into the separator. You will open the outlet in 2 days. Once the separator is started up, you can continue operating it at a steady state. You will probably also require some degassing volume above the oil's surface, so account for a reasonable vapor space to allow for degassing that 50Kbopd, according to the gas to liquid production ratios you expect to have, gas drawoff rate and the allowable pressure of the tank.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[ChEMatt]

Don't know what DEP is. I've sized a few surge vessels, or as we call them "slug catchers". What BigInch says is correct for a surge vessel. Look at the system upstream of the vessel and determine the maximum slug of liquid that may be spontaneously pushed into the vessel. Doesn't matter what the driving force is as much as the volume of pipe in which the liquid might settle (due to altitude changes).

Worst case is all your pipes slugging at the same time. A less conservative approach is to reasonably assume that all pipes will not slug at the same time; so you take your best educated guess, document it, and therefore you can possibly reduce the size of your slug catcher.

A helpful simulation program might assist in determining how much liquid might reasonably develop in the pipes.

I'm talking from a midstream background here, so if some of this does not apply my apologies.

Onwards,

Matt

 

[BigInch]

Carefull with the slug volumes if you have multiple 2-phase flow lines upstream. Be conservative! 2-phase flow methods (correlations or rigorous calculations) are not reliable. If there's one thing that's not very nice, that would be to fill your slug catcher to the top, or OTT or have very high gas velocities arriving after the slug that tend to blow through the vessel and carry out excessive liquids with the accelerated gas flow. Small amounts of liquids hitting a compressor do lots of damage.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Abiodun1]

The information given to me by the client is that they want to convert a rectangular shaped surge tank to a horizontal vessel capable of handling 5oKbopd with adequate retention time which was given for each level swicthes.

The information i need is to determine the diameter and length of the required vessel.

Thanks

 

[BigInch]

A value corresponding to a level in a tank of unknown horizontal dimensions doesn't have too much meaning.

Neither does a retention time given for various levels of a tank, even if the dimensions are known. (at least it dosn't mean anything to me).

Retention time should be dependent on the solids that must be settled, hence dependent on density of the solids, average or maximum diameter of the solids and the viscosity of the oil in which they are being transported.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Abiodun1]

the value given was 13 feet diameter and 40 feet long. All, i wanted to do was to confirm if the dimension given for the vessel is capable to handle the fluid.

 

[BigInch]

I think you're still confused. You question refers to settling times, but the size you give now is obviously not sufficient to retain anything for allowing a settlement period.

If its a surge vessel for a liquid line, you must do a hydraulic surge analysis to find out if releasing that volume from the pipeline into the tank during a surge event will keep the pipeline's pressure below the pipeline's maximum allowed operating pressure.



BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Abiodun1]

Am not.
May be you don't understand me.

The detail given to me by the client is to design a vessel that will handle a 50K bopd of crude per day.

The initial vessel is a rectangular tank, but they want to change it to horizontal vessel.

They propose the size i.e. 13'x40' and gives the reaction time btw the level switches.

All i wanted to do was to check if the proposed size is sufficient.

 

[BigInch]

OK

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[SeanB]

Well I will try to throw my 2 cents in here. I think you are talking about a feed surge drum and you are trying to define the Hold Up and Surge Volumes required. I think you confused people when you said retention times. Hold Up is the volume between the low liquid level and normal liquid level. Surge is the volume between the normal liquid level and the high liquid level. So it sounds like you already have the levels defined. So based on a rate of 50,000 BPD you can calculate how many minutes of Hold Up and Surge you have. If these times are not sufficient then the vessel is not large enough.

 

[ifreeman]

Abiodun1,

As you do not give detailed information, I will do my own calculation here.

1) According to DEP 31.22.05.11(You mean Shell's DEP,right?)

LSL : > 150 mm
LSL to LAL : > 100 mm or 60 seconds holdup for control room and 5 mins for outside intervention.
LAL to LAH : Should be calculated from retention time
LAH to LSH : > 100 mm or 60 seconds holdup for control room and 5 mins for outside intervention.
LSH to Top of Vessel(Vap. Compartment) : should be enough for v/l separation (In this calculation this was ignored, virtually no vapor flow...)

2) Given Dimension : 13' x 40' (3962mm x 12192mm, L/D = 3)

LSL : 150/3962 = 4%
LAL : 250/3962 = 6%
LAH : 3712/3962 = 94%
LHL : 3812/3962 = 96%

BTM to LSL Partial Volume : 1.858 m3
LSL to LAL Partial Volume : 2.109 m3
LAL to LAH Partial Volume : 142.378 m3
LAH to LSH Partial Volume : 2.109 m3
LSH to TOP Partial Volume : 1.858 m3

You can change the dimensions above applying % of height given by your client.

W/ above dimensions, holdup+surge volume(from LAL to LHL) is 142.4m3.

3) 50,000 BPSD = 50000*0.158988 /24/60 = 5.52m3/min
Therefore the retention time from LAL to LAH = 142.4/5.52 = 25.8 minutes. (Check with the holdup+surge time criteria given by client)

4) If there is a need for V/L Separation, LSH shall be checked based on other variables such as density etc.

Regards,
ifreeman

 

[MortenA]

Listen to the last poster. If you are working for Shell then i can only recommend that you follow the DEP to the letter (or don't question the requirements unless so required because quite often Shell people can be a little "touchy" about the DEP if you get my meaning)!

Best regards

Morten