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Separator Design Terms

Separator Design Terms

Separator Design Terms

Could you please, explain me the terms given in below?
-turndown ratio
-residence-retention time
-foaming service
-H&MB case

RE: Separator Design Terms

Google would probably give you a reasonable answer for these. But just to get the ball rolling in will give you a few explanations.

Turn-down ratio: This is typically used where something is designed to be able to operate over a range of speeds or capacity. For example if you had a variable speed gearbox which had a full speed of 100 rpm but could be adjusted down to 10 rpm then the turndown ratio would be 100/10 or 10:1. Something to consider with turn down ratio is whether the full range of adjustment or variation is actually able to be used. The gearbox example i just used at a 10:1 turn-down. But maybe at full load it might not get sufficent oil flow at 10 rpm so a minimum of 20 rpm is necessary. In this case the usable turn down is only 100/20 or 5 :1.

Residence and retention times typically mean the same thing. This is an average value of how long it takes for a complete turn over of the contents of a pipe, container , chamber , tank , that has a flow entering and leaving the container tank or pipe.
The maths looks like this. Residence time = Volume(of tank etc)/ flow rate.

Example A tank has a volume of 10m3 and a flow of 1m3/hr is entering the tank and it is overflowing at a rate of 1m3/hr.

Residence time = Volume/flow rate

Residence time = 10m3/1m3/hr
residence time = 10 hrs.

"Any water can be made potable if you filter it through enough money"

RE: Separator Design Terms

Turn down ratio in separators is a term that is very often mis-applied, but it is reasonably easy.

If we start at the top end, we have the mist pad. Mist pads tend to have a narrow operating range, and it is much worse to go under the design velocity than to exceed the design velocity. The design velocity used by competent vessel designers is around 10 ft/s. This requirement is the reason that on larger vessels the mist extractor is often placed inside a plenum that is smaller than the bulk vessel diameter. Velocity greater than 10 ft/s will reduce performance, but very slowly and 30 or 40 ft/s tends to give you results indistinguishable from 10 ft/s.

The maximum velocity is determined by a constant based on vessel orientation and length times the square root of the term difference in species density divided by gas density.

Turn these two velocities into mass flow rates (or volume flow rates at standard conditions) being careful to use the mist-pad plenum diameter for the top end if appropriate and divide the small flow rate into the big flow rate and you have turndown ratio.

For a separator, residence time is a bit messier than ashtree's tank example. The reason we talk about it at all is that many volatile components in crude oil can take some non-trivial time to evolve out of the liquid phase. Allowing that time is important to keeping these valuable components from gong out the tank vents. Most often we calculate the volume of liquid represented by the level controller just opening the dump valve minus the volume in the vessel as the level controller shuts the dump valve with that difference divided by the liquid flow rate into the vessel. If someone is talking about residence time in a gas/water 2-phase separator they are quoting rote "learnings" that they really didn't comprehend.

Foaming service is just what it says, fluids that tend to foam either before or inside the separator. Foam is very persistent and difficult to deal with, which is why it is common to use foam breaker chemicals before the separator to keep the mess under control. It is very difficult to deal with foam mechanically.

"Slugging" is a flow stream that is prone to the multi-phase condition of "slug flow". I'm not sure what you are looking for beyond that.

I'm not familiar with the term "H&MB Case".

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

RE: Separator Design Terms

Only thing to add to ZDAS04's excellent post is

H&MB I think means Heat and Mass balance. This though is not a "case", but simply a document , often a spread sheet, which balances all the heat, and mass of fluids on and out of the system.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Separator Design Terms

Thanks to all of you for the explanation

RE: Separator Design Terms

What does it mean 'The liquid system should be protected from gas blowby using a restriction orifice to limit the gas flow to 1 MMscfd' ? it means that the gas outlet should be 1MMscfd or what?
Flow comes from some land wells. Gas = 10 MMscfd. GOR = 10 bbl/MMscf condensate, no water is produced. Arrival T = 5 to 30°C.
Gas is 2% CO2, 90% C1, 1% C2, 2% C3, 2% iC4, balance C5+
Condensate: density 700 kg/m3
FTHP = 50 barg
CITHP = 120 barg

RE: Separator Design Terms

See my response to the question you posed about the level control valve....

What it means is that if the liquid level control valve fails open and all the liquid drains out of the tank at the pressures and wide open CV of your control valve, the gas dlow rate into the liquid system should be less than 1 MMscfd.

Or if the wide open flow value is > 1MMscfd insert an orifice plate so that if the liquid level control valve fails wide open the restriction orifice limits the gas flow to 1 MMscfd.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Separator Design Terms

Thank you so much for your help. I know you are getting tired of me. I'm so sorry. I will try not to ask basic questions

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