PROJECT:GAS – LIQUIDSEPARATORS

PRESENTED BY:KHUSHBOO N. MEHTAROLL NO. – Y760008

CONTENTSPRINCIPLES OF SEPARATIONPARTS OF SEPARATORTYPES OF SEPARATORDESIGNING OF VERTICAL

SEPARATOR EXAMPLE

PRINCIPLES OF SEPARATIONMOMENTUMGRAVITY SETTLINGCOALESCING

MOMENTUMFluid phases with different densities

will have different momentum.If a two phase stream changes

direction sharply, separation occurs.Usually employed for bulk separation

of two phases in a stream.

GRAVITY SETTLING

COALESCINGVery small droplets such as fog or mist

cannot be separated practically by gravity. These droplets can be coalesced to form larger droplets that will settle by gravity.

Coalescing devices in separators force gas to follow a tortuous path.

Wire mesh screens, vane elements, and filter cartridges are typical examples of coalescing devices.

PARTS OF A SEPARATOR Regardless of shape, separation

vessels usually contain four major sections, plus the necessary controls-

The primary separation section, A Secondary or gravity section, B Coalescing section, C The sump or liquid collection section,

D.

TYPES OF SEPARATORVERTICAL

HORIZONTAL

SPHERICAL

VERTICAL SEPARATORS

Vertical separators are usually selected when the gas-liquid ratio is high or total gas volumes are low.

Compressor Suction Scrubber is an example of vertical separator. In this service the vertical separator:

Does not need significant liquid retention volume.

The liquid level responds quickly to any liquid that enters, thus tripping an alarm or shutdown.

The separator occupies a small amount of plot space.

HORIZONTAL SEPARATORS Horizontal separators are most

efficient where large volumes of total fluids and large amounts of dissolved gas are present with the liquid.

The greater liquid surface area in this configuration provides optimum conditions for releasing entrapped gas.

Following figure illustrates the separation of two liquid phases (glycol and hydrocarbon)

Rich Amine Flash Tank is as an example of horizontal separator. In this service:

There is relatively large liquid surge volume leading to longer retention time.

There is more surface area per liquid volume to aid in more complete degassing.

The horizontal configuration would handle a foaming liquid better than a vertical.

The liquid level responds slowly to changes in liquid inventory.

SPHERICAL SEPARATORS Spherical separators are occasionally

used for high pressure service where compact size is desired and liquid volumes are small.

Factors considered for spherical separators are:

CompactnessLimited liquid surge capacityMinimum steel for a given pressure.

DESIGNING OF SEPARATION VESSEL Following equation can be used to

estimate the settling velocity of the liquid droplets, for the design of separation vessel:

μt = 0.07 [(ρL-ρv)/ρv]1/2

where μt = settling velocity, m/s,

ρL= liquid density, kg/m3,

ρv= vapour density, kg/m3.

If a demister pad is not used, the value of μt obtained from the equation should be multiplied by a factor of 0.15 to provide a margin of safety and to allow flow surges.

DESIGNING OF VERTICAL SEPARATORThe layout and typical proportions of a vertical gas-liquid separator is shown in the figure.

Contd….Minimum allowable diameter will be given

by:

where Dv= minimum vessel diameter, m,

Vv= gas, or vapour volumetric flow

rate, m3/s, μs= μt, if a demister pad is used, and

0.15 μt for a separator without a demister pad.

The height of the vessel outlet above the gas inlet should be sufficient to allow for disengagement of the liquid drops. A height equal to the diameter of the vessel or 1m, whichever is the greatest, should be used.

EXAMPLE

Make a preliminary design for a separator to separate a mixture of steam and water; flow-rates: steam 2000 kg/h, water 1000 kg/h; operating pressure 4 bar.

SOLUTION: From steam table; at 4 bar: saturation

temperature is 143.60C, liquid density 922.5 kg/m3, vapour density 2.16 kg/m3.

μt = 0.07[(922.5-2.16)/2.16]1/2

= 1.45 m/s As the separation of condensate from steam is

unlikely to be critical, a demister pad will not be specified.

So, μt = 0.15 x 1.45

= 0.218 m/s

Contd….Vapour volumetric = flow-rate = = 0.257 m3/s 0.5 = 1.23 m, round to 1.25 m (4 ft).Liquid volumetric = flow-rate = 1000/(3600 x 922.5) = 3.0 x 10-4 m3/s

Contd….Allow a minimum of 10 minutes hold-up.Volume held = volumetric x time in vessel flow-rate = 3.0 x 10-4 x (10 x 60) = 0.18 m3

Liquid depth = required = = 0.15 mIncrease to 0.3 m to allow space for positioning the

level controller.

CONCLUSION THUS, A GAS-LIQUID SEPARATOR IS DESIGNED TO HANDLE STREAMS WITH HIGH GAS-TO-LIQUID RATIOS.

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