Lecture 5 Compression cont.ppt

7/23/2019 Lecture 5 Compression cont.ppt

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Lecture 5

Compression, cont.



Surge

• Surge occurs at some minimum capacity at each

speed. The compressor does not meet the

discharge pressure and a series of flow reversals

occur.• Anti surge control recycle flow controlled via

flow and differential pressure monitoring



Centrifugal compressor Characteristic Curve



Reminding Compression !"#

Recycle

valve

Check valve

Level

control

>



Surge control shown in Compressor !$%#

PSV

BDVESV

Recycle Valve

Note the PSD function



Scru&&ers

• The scru&&er is a pressure vessel needed for removal of

li'uid (vertical two)phase separator*.

• +here the gas at suction of one compressor stage have a

normal operating temperature and pressure which is far

away from the gas water or hydrocar&on dewpoint curve,and all possi&le variations in operating conditions does not

create any li'uid, the compressor suction scru&&er may &e

avoided.



!$%# upstream a compressor

Overpressure?

Low level

High level



verpressure in Scru&&ers

verpressure scenarios shall &e identified, for e-ample

• verpressure protection of the scru&&er shall tae into account

leaage from the compressor discharge side in case the discharge

chec valve fail to close on compressor shut down. / %f, in case of chec valve failure, the common settle out pressure e-ceeds the

design pressure of the scru&&er, two chec valves shall &e installed in series.

• +hen two chec valves are used, monitoring of the intermediate pressure is re'uired

for leaage detection of chec valves.

/ 0pstream !S1 to &e designed for a predefined leaage through the chec valve,typically 23 opening of the cross sectional area of the chec valve.



Settle out pressure

Recycle

valve

Check valve

>



• The conditions downstream the li'uid control valve

shall &e checed for hydrate formation, and suita&le

precautions taen, i.e.

• control valve type to reduce potential for internal free4ing

• inection point for methanol

• +hen normally no flow of li'uid out of scru&&er is

e-pected, level is to &e controlled on an on6off &asis

Li'uid from scru&&ers



7ydrates

8as hydrates are crystallinecompounds that occur when waterforms a cage)lie structure aroundsmaller hydrocar&on molecules.

These solid formations are

detrimental to oil and gas processing operations since theycan &loc pipelines, and canrender measuring e'uipmentuseless.

7ydrates form at low temperature and high pressureareas,



9a-imum flow

The coolers and scru&&ers

should &e a&le to

withstand the ma-imum

flow that the associated

compressor can handle at

minimum discharge pressure without incurring

mechanical damage.



Layout re'uirements

• Coolers and compressors should &e elevated a&ovescru&&ers. Lines shall slope towards scru&&er.

• Anti surge line should &e sloped with the antisurgevalve at the highest point.

• +hen methanol inection is re'uired upstream thecooler, the main piping shall slope from inection pointtowards the cooler.

• Compressors should, to the e-tent practical, &e locatedaway from large hydrocar&on inventories such as

production separators



%nterface re'uirements

The following utility and support systems may have to &e provided to thecompression system

• Cooling medium or seawater for gas, lu&e and seal oil coolers.

• :itrogen for isolation seal gas.

• 9ethanol if re'uired for hydrate prevention and removal.

• %nstrument air and hydraulic power.

• ;lectric power and 0!S, as re'uired.

• Service fresh water for tur&ine washing. %on e-change filters to &e partof the system.

• "uel gas6diesel.• "lare and drain.



8as may re'uire treatment to remove

/ C< with water = corrosion, may e-ceed sales gas

specification

/ 7<S with water = corrosion> to-ic, may e-ceed sales

gas specification

/ +ater ) may cause hydrate formation, also an essential

ingredient for corrosion

8as Treatment



7ydrate "ormation re'uires

• C2 to C?

hydrocar&ons

• Lowtemperature

• "ree water

• 7igh pressure



• #ehydration can &e &y glycol contactor or adsor&ent

material (silicate*.

• C< removal can &e &y glycol contactor.

• 7<S removal &y amine contactor.

• Contactors and dryers need regeneration ;-pect high

levels of the removed su&stance there@ 7eat is usually

used.

8as Treatment



Acid gas removal processes>

• Chemical solvents

/ Alanolamines

/ Alaline salt solutions

• !hysical solvents

/ Sulfinol

/ Sele-ol

/ "luor Solvents

/ Rectisol

• #ry)&ed adsorption

/ 9ol sieve

/ %ron sponge

• 9em&rane processes



8lycol

contactor inlet

scru&&er

8lycolcontactor inlet

cooler

8lycol

contactor

8as filter 6

coalescer

Rich glycol

Regenerator

Re&oiler

Surge tan 6

accumulator

Lean

glycol

To vent

8as #ehydration with glycol

Lecture 5 Compression cont.ppt

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