oil and gas separation process

7/25/2019 Oil and Gas Separation Process

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OIL AND GAS SEPARATION PROCESS

Introduction

The well-streams (or well fluids) produced from well platforms may consist of crude oil,

gas, condensates, water and various contaminants. The purpose of the separator is tosplit the flow into desirable fractions. An oil/gas separator is a pressure vessel that is

installed either in an onshore processing station or on an offshore platform. Based on

the vessel configurations, the oil/gas separators can be divided into horiontal, vertical,

or spherical separators. !n teams of fluids to be separated, the oil/gas separators can be

grouped into gas/li"uid two-phase separator or oil/gas/water three-phase separator. !n

this paper, the three phase separator is used as the basis for the discussion and

presentation of the #iping and !nstrumentation $iagram (#%!$) of an oil and gas

separation process.

The figure below shows a simplified flow diagram of the oil and gas &st

stage separationprocess.

Figure 1: Oil and Gas 1stStage Separation Process lo! Diagra" #Si"pliied$

!nlet temperature is often in the range of &''-&' degrees . *n the e+ample platform,

the well stream is colder due to ubsea wells and risers.


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The pressure is often reduced in several stages but commonly, three stages are used,

and these allow controlled separation of volatile components. The purpose is to achieve

ma+imum li"uid recovery and stabilied oil and gas, and separate water. A large

pressure reduction in a single separator will cause flash vaporiation leading to

instabilities and safety haards.

The retention period is typically minutes, allowing the gas to bubble out, water to settle

at the bottom and oil to be taen out in the middle. !n the first stage separator, the water

content is typically reduced to less than .

igure 0 show the #iping and !nstrumentation $iagram (#%!$) of the & st stage (1-#hase)

separator.

Figure %: P&ID o an Oil and Gas 1stStage #'(P)ase$ Separator


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Piping

#iping is a system of pipes used to convey fluids (li"uids and gases) from one location

to another. The engineering discipline of piping design studies the efficient transport of

fluid.

&. !nlet #ipe for the 2ell luids

Figure ': Inlet Pipe Diagra" o an Oil and Gas Separation Process

rom oil or gas well, well fluids will enter the &st stage separator vessel where its

constituent components3oil, gas, and water will be separated. A gate valve is situated

along the pipeline at the vessel4s entrance in order to allow or stop the flow of fluid.

igure 1 shows illustrates the diagram of this pipe flow.


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0. lare ystem (5as ection)

2hen the set pressure inside the separator

vessel e+ceeded, the relief valve becomes the

6path of least resistance6 as the valve is

forced open and a portion of the fluid (gas orli"uid-gas mi+ture) is diverted through the

au+iliary route. The diverted fluid cis usually

routed through a piping system nown as a

flare header or relief header to a central,

elevated gas flare where it is usually burned

and the resulting combustion gases are

released to the atmosphere. igure at the left

shows the diagram for this system

1. *utlet #ipe for the eparated 5as (7apor)

The gas

that has

been separated from the well fluid mi+ture is directed through a pipe which is e"uipped

with several valves including a pressure valve which by means is an actuator valve. The

actuator valve wors hand in hand with a pressure transmitter (#T) and control (#) in

order to monitor and regulate the pressure of the gas flowing through the piping system.

8. *utlet #ipe for the eparated *il

Figure *: Flare S+ste" Diagra" in an Oil andGas Separation Process

Figure ,: Gas Outlet Pipe S+ste" in Separation Process

Figure -: Oil Outlet Pipe S+ste" in Separation Process


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The oil that has been separated from the well fluid mi+ture is directed through a pipe

which is e"uipped with several valves including a level valve which by means is an

actuator valve. The actuator valve wors hand in hand with a level transmitter (9T) and

control (9) in order to monitor and regulate the flow of the oil through the piping

system. The same system is applied in the outlet pipe for the separated water. ee

igures : and ; accordingly.


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Figure .: /ater Outlet Pipe S+ste" in Separation Process

Separator 0essel

Below are figures showing e+ternal (igure ).


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Figure : 2a3or Co"ponents inside t)e Separator 0essel

At the crude entrance there is a baffle slug catcher that will reduce the effect of slugs

(9arge gas bubbles or li"uid plugs). ?owever some turbulence is desirable as this will

release gas bubbles faster than a laminar flow. At the end there are barriers up to a

certain level to eep bac the separated oil and water. The li"uid outlets from the

separator will be e"uipped with vorte+ breaers to reduce disturbance on the li"uid table

inside. This is basically a flange trap to brea any vorte+ formation and ensure that only

Figure 4: Separator 0essel


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separated li"uid is tapped off and not mi+ed with oil or water drawn in though these

vortices. imilarly the gas outlets are e"uipped with demisters, essentially filters that will

remove li"uid droplets in the gas.

S+ste" Control and Instru"entation

5ate 7alve with spectacle blind flange

5ate valves are

primarily designed to

start or stop a flow (in this case the flow of well fluids)

when a straight line flow of fluid and minimum flow

restriction are needed. !n service, these valves

are pretty much ept either fully open, or fully closed.

2hen turned open, the disc of the gate is completely removed allowing contents to

pass. Although this gives the valve good shut-off properties and is bidirectional, they

cannot be "uicly opened or closed and are sensitive to vibration when open.

A spectacle blind is a safety device used to isolate a section of line or piece of

e"uipment when the line or e"uipment needs to be inspected or removed from service.

!t is different than a valve in that the blind is a permanent or long term isolation device.

*ne end of the blind will have an opening to allow flow through the pipe during

operation and the other end is solid to bloc flow during maintenance.

@elief 7alve


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The relief valve is a type of valve used to

control or limit the pressure in a system

or vessel which can build up for a

process upset, instrument or e"uipmentfailure, or fire. !t is designed or set to

open at a predetermined set pressure to

protect pressure vessels and other

e"uipment from being sub=ected to

pressures that e+ceed their design limits.

ormally losed 7alve

+amples of normally-closed valves are sampling valves,

which are only opened while a sample is taen for test.

*ther e+amples of normally-closed valves are emergency

shut-down valves, which are ept open when the system is

in operation and will automatically shut by taing away the

power supply. This happens when there is a problem with a

unit or a section of a fluid system such as a lea in order to

isolate the problem from the rest of the system.

lange

The flange in oil and gas applications can be a plate or ring to form a rim at the end of a

pipe when fastened to the pipe (for e+ample, a closet flange). A blind flange is a plate

for covering or closing the end of a pipe. A flange =oint is a connection of pipes, where

the connecting pieces have flanges by which the parts are bolted together.

Actuators ($iaphragm or 5lobe)


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Actuators are a means by which a valve can be automated so that no human interaction

with the valve pacage is necessary to cycle the valve. Actuators can be remotelyoperated and can act as shutdown mechanisms in case of an emergency situation,

wherein human interaction can be dangerous.

The diaphragm-style actuator includes a rubber diaphragm and stem in a circular steel

housing. This style of actuators is ideal for valves re"uiring shorter travel, such as

diaphragm valves and globe valves.

@educer / +pander

5enerally, the control valve sie is smaller than the corresponding line sie. This change

in diameter should be clearly indicated in the #%!$ with reducer and e+pander. The

former is the component in a pipeline that reduces the pipe sie from a larger to a

smaller bore (inner diameter). 2hile the latter on the other hand, e+pands the pipe sie

from a smaller to a larger bore.

Ball 7alve (ormally losed)


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An increase in fluid pressure to the actuator is re"uired to cause this valve to open.

#ressure Transmitter

A pressure transmitter senses a pressure and outputs a proportional current signal

which is then transmitted to a monitor or controller

#ressure ontroller (mounted in the control room)


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.

#ressure controller receives data reading from pressure transmitter, compared that

reading to a programmed setpoint, and signals a control element (in this case, anactuator valve) to either close or open depending on the corrective action needs to be

taen.

9evel Transmitter

9evel transmitter provides an electrical output proportional to the well fluid level in the

separator vessel. !t may provide an output upon reaching a specified value (point level)or repeatedly after each measurement (continuous level).

9evel ontroller (mounted in the control room)


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!t regulates the level of the well fluids by processing the reading it receives from the

level transmitter and then, compares the reading from a specified setpoint before itgives signal to the actuator valves which will either open or close depending on the

corrective action that needs to be taen.

oil and gas separation process

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