scavengers This H circulation pipeline mole/mole DGA Diglycolamine pressure has are but DEA, Diethanolamine process removed has to MEA Monoethanolamine used aminoethoxyethanol/ commonly Monoethanolamine equipment for increase incorporating H The Amine as alkyl Amines Amine 2

S 0

Primary,

2 . common less can

a . . . .

amine 30

been

is or over to is used GATEKEEPER S lower

commonly

– are selectively aryl usually of

be corrosive

by Cyclic Tertiary Secondary Primary Solution specs selectivity, and

via

0

. ;

rates stripping observed Scavenging

in

.

CO selected, loaded in alkyl 35 organic Secondary, higher Preferentially used

affinity groups,

filters

short 25

amines the more 2

(

moles , – DGA)

unless used (

and

– DEA) or – – Either

mole

Oil

than

used

35 forms strip One loading

to All residence

( – aryl and compounds

for H MEA) loading, (MEA), focuses Selection

than retaining

diglycolamine lower

with as

& acid Two 2 1 in have

three weight - S

to

gas

MEA Tertiary, CO of Gas secondary mole/mole in H groups well reclaimer to

50

-

2

mole selective

S three gas one

15 of of stainless 2

may

freezing

export

been hydrogen industry

stream and and –

diethanolamine and

as and

the time, on

%

–

a per amine

70

amine,

be

derived

20

the hydrogen basic

acid

or solutions,

CO H

three reclamation

Amine . degradation

given specs

2

weight

mole

or

achievable

DEA S Due (DGA)

when weight Cyclic for point 2 . concentration steel

has

from and

tertiary nitrogen atoms gas

in hydrogen

CO

as

.

from can to amine

. :

in

. .

Systems, high

using

may

DGA

are 2 % atoms

gas an % is well the Degradation

loading,

Table

over

Amine be

are

also

ammonia

(DEA)

solutions is amines acid aqueous

with

characteristics

also

not with CO atom is high

selective stainless sweetening not as

replaced is atoms

also H

- 2 limited

of gas 1

produce 2 stainless

used replaced

specialty . one S, carbon content

practical pH

and with and the with Acid

able

.

but rich solutions

with

. are

Corrosion of products

for

steel of

solution to A

by

one

degradation methyl

a to ll

has MEA, hydrocarbon gas ; steel

.

pipeline replaced

H

0 steel substitution

by the

cyclic

are alkyl of due . designed absorb Higher 2

30 Systems although, or S lone

a alkyl

. loading ; the

over

aqueous

all

corrosion most Due – or higher loading

to used,

or are

issues diethanolamine structure

pair

0

final spec CO

CRA the . or

by aryl COS,

35 CO solution

to

extremely

2

aryl

commonly amine

of

of alkyl

gas will values 2 of

mole/mole

need

pH corrosion will systems solution . groups

gas as diisopropanolamine also

solutions

CS electrons

inhibitors one

the

groups

stream result high than with

or 2 essentially

for , for

strength

prevent

molecules,

SO or are aryl

amine

.

.

some as

hydrogen

corrosive

MEA vacuum 2 all Typical

issues, in

, .

used (MDEA) .

of loading based groups .

0 and

They of different . Degradation

70 .

alkylamines

allowing

loading systems the

results be Blended SO

– regenerative

loading operating r can can

on eclaimers 0 3 removed in hydrogens atoms and . are

.

90

carbon selectivity

(DIPA) be carbon .

be above

in it

mole/mole Under should

the

is classified

solutions products to replaced that reduced used

limited ranges

in .

reach - steel,

most steel 0

with DEA

and H low . the are

35 be 2 to of S

Amine MDEA Loading values are based on use in carbon steel systems systems steel carbon treatment* in use inhibitor on based corrosion are values without Loading MEA DGA DEA

Table 1: Amine Operating Ranges

Solution Solution Figure (wt%) 50 25 15 20 Figure Primary 1: Amine Figure Tertiary 3: Amine - - - -

70 35 20 50

2 :Secondary Amine (mole / mole) 0.30 0.30 0.30 0.30 0.70 0.70 Loading - - - -

0.80 0.35 0.35 0.35

Selectivity H

Dependent Condition 2 Limited S

No No

>

CO

2

JUNE 2014 JUNE 2014 GAT2004-2014.06

H2S Scavenging: Amine Systems

Methyl Diethanolamine (MDEA) By contact between the gas and the amine solution,

acid gasses (CO2 & H2S) are stripped into the amine Generally, MDEA is used in 20 – 50 weight % solution. The sweetened produced gas exits the top solutions, but lower weight % solutions have been of the tower; Rich (acid-gas containing) amine used in very low pressure systems. Loading ranges stream exits the bottom of the tower. of 0.70 – 0.80 can be achieved due to significantly reduced corrosion issues. Oxygen exposure will Heat Exchanger produce corrosive acids and can result in build-up of iron sulfide. MDEA is also selective towards H2S over Rich amine passes through the Heat Exchanger and CO2, has a lower vapour pressure, has lower heats is pre-heated by the hot regenerated Lean amine of reaction, and has higher resistance to degradation from the Reboiler. An optional Flash Tank for the compared to other amines. Rich amine and Filters can be used on the Rich (Inlet) and Lean (Outlet) amine streams. Mixed Amines Regeneration Tower Mixed amines are generally combinations of MDEA with DEA or MEA as up to 20% of the total amine. Like the Contactor Tower, the Regeneration Tower is

DEA or MEA are added to enhance the CO2 removal also filled with plates or packing. Heated Rich amine where MDEA alone allows too much CO2 to slip into is fed into the top while steam and vapor from the the absorber or in low pressure systems where Reboiler enter from the bottom. Acid-gas-rich vapor

MDEA alone is unable to remove CO2 to pipeline exits the top of the Tower to the Condenser and specs. Lean amine leaves the bottom of the Tower, entering the Reboiler for further acid-gas stripping. Amine Sweetening Process Reboiler The primary components of an amine sweetening system include: Heat is added at the Reboiler, generating steam and Figure 4: Amine Gas Treating helping to break the chemical bonds between the Process . Contactor Tower amine and the acid gasses. The CO2 and H2S-rich vapor is sent into the bottom of the Tower, where . Regeneration Tower the lower partial pressure of the rising steam helps . Reboiler liberate acid gasses from the falling amine. References . Heat Exchanger Optionally, the Lean amine may be sent to a . Condenser & Accumulator/Reflux Drum Reclaimer to remove contaminants such as salts. 1. “Production Chemicals for the Oil and Gas . Makeup Tank Industry.” Malcolm A. Kelland, CRC Press, Condenser & Accumulator/Reflux Drum 2009.

Optional components of an amine sweetening The acid-gas rich vapour from the Regeneration system include: Tower is passed through a Condenser to drop out water & any remaining amine, feeding into the . Mechanical Filters Accumulator / Reflux Drum. The remaining acid-gas . Flash Tank stream is sent for disposal; the water/amine solution . Inlet Separator is fed back into the top of the Regeneration Tower . Charcoal Filters as reflux. . Reclaimer Makeup Tank . Outlet Separator Some amine and solvent are lost due to heating, Filters can be used to remove solids & contaminants. refluxing, and wetting of the gas stream; An Inlet Separator may be used to remove additionally, the amine in the selected solutions hydrocarbons & water from the produced gas to break down or degrade over repeated cycles and fall reduce contaminants; an Outlet Separator may be out as solids. Periodically, fresh amine solution from used to remove any residual amine or solvent from a Makeup Tank will have to be added to the system the sweetened gas stream. A Flash Tank may be with the Lean amine stream. used to recapture hydrocarbons from the Rich amine. A Reclaimer unit is used for semi-continuous Conclusion distillation with MEA solutions. DEA’s higher boiling temperature and lower degradation rate makes it A few key points should be considered before less practical, less economical, and unnecessary to finalizing Amine System design and amine selection. use a Reclaimer; filtration and caustic wash are Treated gas composition, including CO2, sufficient purification for DEA. H2S, and other acid-gas contributors, must be understood to select the best amine for application. Contactor Tower System pressures and re-circulation rates, as well as the use of stainless steel or a corrosion inhibitor, will The Lean (acid-gas free) amine is circulated from impact amine selection, loading, and efficiency. top to bottom over plates or packing as the Optional subsystems may improve performance and produced gas to be sweetened enters from the reduce degradation of the amine. For optimal bottom of the Tower. operation and highest efficiency, all system components should be carefully selected.