Unit 6 Separators

8/13/2019 Unit 6 Separators

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INTRODUCTION

Rarely a reservoir can yield pure natural gas.

Hydrocarbon stream produced is a complex mixtureof several hydrocarbons, intimately mixed withwater.

Often solids and other contaminants are alsopresent.

It is important to remove any solids andcontaminants and to separate the produced stream

into water, oil and gas which are handled andtransported separately.

Gas and liquid separation operations involve theseparation and stabilization of these phases intosaleable products.


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Field processing of natural gas includes:

1. Gas and liquid separation operations to remove the

free liquids- crude oil, hydrocarbon condensate, andwater and the entrained solids.

2. Recovery of condensable hydrocarbon vapors. Stageseparation , or low temperature separation techniquesare used.

3. Further cleaning of the gas and oil streams afterseparation.

4. Gas dehydration processing to remove from the gascondensable water vapor that may lead to theformation of hydrates.

5. Removal of contaminants or otherwise undesirablecomponents ,such as H2S and other corrosive sulfurcompounds and CO2.


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SEPARATION EQUIPMENT

To efficiently perform its separator functions a well

designed separator must Control and dissipate the energy of the well

stream as it enters the separator and provide low

enough gas and liquid velocities for proper gravity

segregation and vapor-liquid equilibrium. Remove the bulk of the liquid from the gas in the

primary separation section.

Have a large settling section, of sufficient volume

to refine the primary separation by removing anyentrained liquid from the gas and handle any slugs

of liquid.


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TYPESOFSEPARATORS

Separators can be categorized into three basic

types:

1. Vertical separators

2. Horizontal separators3. Spherical separators


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VERTICALSEPARATORS


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The well stream enters the vertical separatortangentially through an inlet diverter that causes anefficient primary separation by three simultaneous

actions on the stream :1. Gravity settling

2. centrifugation

3. Impingement

The gas from the primary separation section flowsupwards ,while the liquid falls downward into the liquidaccumulation section.

The smaller liquid droplets that are carried along bythe upwards rising gas stream are removed in the

centrifugal baffles near the top. Finally a mist extractor at the gas outlet removes any

entrained liquid droplets from the gas in the micronsize.


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Advantages :

1. A vertical separator can handle relatively large liquid slugs

without carryover into the gas outlet.2. The tendency of the liquid to revaporize is also minimized ,

because less surface area is available to the liquid for

evaporation.

3. It occupies less floor space, a particularly important

advantage for operations on an offshore platform where floorarea is at a premium.

Disadvantages:

1. They are more expensive to fabricate and more expensive to

transport to location.

2. A vertical separator for the same capacity is usually largerthan a horizontal separator , since the upwards flowing gas

in the vertical separator opposes the falling droplets of liquid.


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HORIZONTALSEPARATORS


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Separation begins with well flow streams entering a vessel

horizontally and hitting a series of perpendicular plates. This

causes liquids to drop to the bottom of the vessel while gas(red) rises to the top. Gravity separates the liquids into oil

(brown) and water (blue). The gas, oil and water phases are

metered individually as they exit the unit through separate

outflow lines. Mechanical meters measure fluids; an orifice

meter measures the gas. Both devices require periodic

recalibration.


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HORIZONTALDOUBLETYPESEPARATOR

In the double tube type separator , the upper tube

acts as the separator section, while the lower tube

merely functions as a liquid accumulation section.

The double type separator is similar to a single tube

separator, but with a greater liquid capacity.

The liquid generated in the primary separation

section near the inlet is immediately drained out

into the lower tube.


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DISADVANTAGES

Liquid level control is critical for horizontal

separators , and the surge space is rather limited.

They are much harder to clean, and therefore not

advisable to use where the well produces a lot of

sand.

They occupy a lot of space.


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SPHERICALSEPARATORS

A ball-shaped vessel used for fluid separation. Aspherical separator can be used for two-phase or three-phase separation purposes.

An inlet flow diverter spreads the entering well streamtangentially against the separator wall.

The liquid is split into two streams that come togetherafter halfway around the circular vessel wall and thenfall into the liquid accumulation section.

A mist extractor is used for the final removal of small

liquid droplets in the gas. Nevertheless, their compact size and ease of

transportation have made them suitable.


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ADVANTAGES

Spherical separators are very inexpensive cheaper

than either the vertical or the horizontal separators.

They are very compact , and offer better clean out

and bottom drain features than even the vertical

type.


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SEPARATIONPRINCIPLES

The several different techniques applied for

separation processing can be broadly classified into

two categories:

1. Mechanical separation

2. Chemical separation

In separators, the mechanical separation methods

that are applied are of three types:

1. Centrifugal action2. Gravity settling

3. Impingement


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CENTRIFUGESEPARATION

Consider a centrifuge of radius R2, height h, andinner shaft radius R1.

Feed enters at a volumetric rate q.

As the centrifuge rotates at an angular speed ,

the heavier liquid droplets are thrown outward tothe centrifuge walls .

The residence time t for the fluid in the centrifuge isgiven by:

t= centrifuge volume/volumetric flow rate of fluid= (R2

2-R12)h / q

In the analysis it is assumed for simplicity that theliquid droplets are spherical, with a uniformdiameter dp.


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The area A projected by a droplet is therefore

equal to (/4)dp2.

Unit 6 Separators

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