This is a full course about how the Amine Sweetening Unit works, and all the factors, operations, and problems related to this unit. This course was taken from the IHRDC institute.

1. Amine Sweetening Unit
Operation
A full course about launching and operation Sweetening Unit

2. Overview
 Natural gas sales contract specifications normally allow 1 to 5 grains total sulfur per
100 standard cubic feet (SCF) of natural gas. Hydrogen sulfide (H2S) is limited to
0.25 grains per 100 SCF, which is equivalent to about 4 parts per million (ppm).
Carbon dioxide (CO2) is limited to 1 to 3 percent by volume.
 An amine sweetening unit, when properly designed, operated and maintained, will
remove acid gases from sour gas with minimal difficulty and attendance. However,
process principles and physical limitations of the equipment should be clearly
understood. Knowledge of these limitations will help eliminate many operational
problems which occur directly as a result of improper operating practices.

3. Sweetening Process
 You learned in the principles course that amine sweetening is an absorption
process where lean amine absorbs acid gases from sour gas in the
contactor column. You also learned that amines are expensive; and
therefore, it is important to remove absorbed acid gases from the amine
solution so it can be used over and over again.
 Before we proceed, let's review the two fluid flow paths through a typical
amine sweetening unit.

4. Types of Alkanolamines
Alkanolamines can be categorized on a chemical basis as being primary
(monoethanolamine MEA, diglycolamine DGA), secondary (diethanolamine DEA,
diisopropylamine DIPA), and tertiary (triethanolamine TEA, methyldiethanolamine
MDEA) depending on the number of substitutions onto a central nitrogen atom.
Each of these alkanolamines has its advantages and disadvantages.

5.  MEA is used in low gas feed pressure; it has a high corrosion potential and a high
vapor pressure resulting in higher losses than other alkanolamines. It is non-
selective removal in a mixed acid gas system. It forms irreversible degradation
products which require continuous reclaiming.
 DGA has a tendency to react with CO2 over H2S. It is used in higher concentration
compared with other amines which results in lower circulation rates.
 DEA is used in medium to high pressure treating, it is less corrosive than MEA,
and has low vapor pressure which results in less losses. It has good resistance to
degradation.
 MDEA has several advantages over other types of amines which include lower
vapor pressure, lower heat of reaction, higher resistance to degradation, fewer
corrosion problems, and selectivity toward H2S in the presence of CO2.
 Mixed amines can be used which are generally mixtures of MDEA and DEA or
MEA and are used to enhance CO2 removal by MDEA.

6. Alkanolamine Sweetening
Amine sweetening process uses an aqueous
solution of one of the alkanolamines to react
with acid gases to form weak organic salt
complexes. The amine solution "holds" acid
gases in a chemical manner until the
temperature of the amine solution is increased
or the pressure is decreased. When this
happens, the salt complexes are decomposed
and the acid gases are released.
To better understand what's happening, let's
look at the chemical reactions involved. The
process is based on a neutralization reaction
between a weak base (amine) and a weak acid
(H2S or CO2) which yields a water-soluble salt.

7. Water Quality
 The quality of water used for making an amine solution is very important to the
efficiency of an amine sweetening unit. Deionized or distilled water should be
used. Impurities, such as sand, salt, and minerals, can cause numerous operating
problems. Some of the more serious problems are foaming, corrosion, erosion, and
plugging.
 If treated or well water is used, tests should be routinely conducted to assure water
quality. The water supply can change over time and start causing problems with
the sweetening process.

8. Gas Flow:
 Sour gas passes through an inlet separator to remove free liquids and solid
particles. The sour gas flows from the separator to the lower section of the
contactor. It then flows upward through the tray or packed column contacting the
amine solution. Before leaving the contactor, the sweet gas flows through a mist
eliminator which reduces amine loss due to carryover. Sweet gas leaves the
contactor and flows through an outlet separator to recover any entrained amine
solution. From here, the sweet gas flows into the sales or other process line.

9. Gas Flow Diagram

10. Amine Flow:
 Lean amine is continuously pumped to the upper section of the contactor, where it
flows downward across each tray or over packing. As the lean amine flows
downward, it absorbs acid gases from the rising sour gas.
 Rich amine flows out near the bottom of the contactor and through a flash tank.
The flash tank separates entrained gases and liquid hydrocarbons from the rich
amine.
 From the flash tank, the rich amine flows through particle and carbon filters to the
lean/rich heat exchanger. The warmed, rich amine then flows to the upper section
of the stripper column.
 Lean amine is heated in the reboiler. Some of the water in the amine solution
vaporizes. This vapor rises through the stripper and heats up the counter flowing
rich amine. Acid gases are released, and the vapor carries them to the top of the
stripper.

11. Amine Flow Diagram

12.  Excess vapor carries the released acid gases out the top of the stripper to the
reflux condenser and accumulator. Here the vapor is condensed and separated
from the acid gases. The acid gases are removed from the system and the
condensed vapor is pumped to the upper section of the stripper for reflux.
 Lean amine flows out near the bottom of the stripper to the reboiler. From the
reboiler, the hot, lean amine flows through the lean/rich heat exchanger to preheat
the rich amine flowing to the stripper. Lean amine is stored in the surge tank until it
is pumped through a trim cooler to the upper section of the contactor.
 If a reclaimer is used, a small portion (one to three percent) of the total amine
circulation is distilled in the reclaimer to remove degradation products, heat-stable
salts, and solids.
 The vaporized amine is returned to the reboiler vapor outlet. At the end of the
reclaimer cycle, accumulated contaminants are dumped in a safe and
environmentally acceptable manner.

13. Process Variables
 The degree of acid gas removal is determined by several process variables
which include: inlet gas temperature, inlet gas pressure, gas flow rate, inlet
amine temperature, amine concentration, amine circulation rate, and acid
gas loading. All are major factors which affect the efficiency of an amine
sweetening unit.

14. Process Variables - Inlet Gas Temperature
 inlet gas temperature has a significant effect on the acid gas content of
sour gas entering the contactor. At constant pressure, the capacity of sour
gas to hold acid gas increases as the inlet gas temperature increases. If the
inlet gas contains more acid gases, the unit is required to remove more
acid gas in order to achieve the desired sweetening of outlet gas.
 In cold weather, line heaters are used to heat the sour gas stream ahead of
the sweetening unit to maintain minimum inlet gas temperature, which is
50°F (10°C). Minimum inlet gas temperature is set by gas/amine equilibrium
conditions. Depending on the composition and pressure of the sour gas,
hydrates may form at temperatures well above 50°F (10°C), thus requiring a
higher inlet gas temperature to avoid plugging problems. Low inlet gas
temperatures increase the tendency of amine solutions to foam which can
create significant operating problems.

15. Process Variables - Inlet Gas Pressure
 In the normal operating range of an amine sweetening unit, pressure is not a
critical factor. However, it is important to note that at constant temperature, sour
gas can hold more acid gas as the pressure is reduced. Therefore, acid gas
content of inlet gas will be high if gas pressure is low.

16. Process Variables - Gas Flow Rate
 For the unit to operate efficiently, a specified range for gas flow must be
maintained. If flow rate is outside these limits, problems can develop. Falling far
below the specified range will result in loss of efficiency and may result in
channeling of the amine solution. Channeling could decrease the amount of acid
gas removal, depending on the design of the trays or packing in the contactor.
 If the gas flow rate rises above the specified range, reboiler overload occurs
resulting in insufficient amine solution regeneration and reduced acid gas removal.
The amount of amine solution carried out with the sweet gas will also increase. In
fact, large amounts of amine solution can be carried out of the contactor if the gas
flow rate is high enough.
 A flow rate without rapid surges is necessary to prevent loss of seal in tray
contactors. Seal loss allows gas to bypass the trays and results in high acid gas
content in the outlet gas and high amine losses.

18. Process Variables - Inlet Amine Temperature
 Inlet amine temperature of 5°-15°F (2°-7°C) above the inlet gas temperature is
required to prevent hydrocarbon condensation in the amine solution. Hydrocarbon
condensation increases foaming, reduces carbon filter life, and increases carbon
buildup on the reboiler fire tube.

19. Process Variables - Amine Concentration
 Amine concentration for MEA usually ranges between 10-20 wt.%. The range for
DEA is normally 20-30 wt.%. DGA can be used in relatively high concentration
ranges between 50-60 wt.%, while the range for MDEA is 35-50 wt.%.
 Corrosion in an amine sweetening unit is usually caused by degradation products
in the amine solution or high fluid velocity. Sulfide acid gases (H2S, COS, CS2,
etc.) react with steel to form iron sulfide scale on metal surfaces. This scale coats
the surface and reduces further corrosion. However, high fluid velocity and
particles in solution wipe away the coating and allow further corrosion to take
place.
 There is a relationship between amine concentration and amine circulation rate. If
one is increased, the other can be decreased. For example, increasing the amine
concentration will increase the solution's capacity to remove acid gas and will allow
the amine circulation rate to be decreased

20. Process Variables - Amine Circulation Rate
 The amine circulation rate is established during the design phase of an amine sweetening
unit. It is determined by acid gas content of the inlet gas, amine concentration, and type of
amine used. After startup, rarely does the circulation rate change, unless the acid gas
content or feed rate of the inlet gas changes. If either or both of these conditions decrease,
the circulation rate can be reduced to save energy while still meeting sweet gas
specifications.
 Common practice is to over circulate amine solution to minimize corrosion problems.
However, it is desirable to maintain the lowest amine circulation rate to produce the
desired gas sweetening. Excessive circulation rates can result in the following problems:
• Increased fuel consumption
• Exceeded reboiler capacity
• Increased overhead amine losses
• Increased corrosion
• Increased pump maintenance

21. Process Variables - Acid Gas Loading
 Acid gas loading of rich amine is usually in the range of 0.25 to 0.35 mole of acid
gas per mole of MEA or 0.35 to 0.65 for DEA. A mole is a unit of weight expressed in
grams and equal to the molecular weight of a substance. For example, the
molecular weight of MEA is 61, so one mole of MEA weighs 61 grams.
 Acid Gas Loading
 Common practice is to operate at the lower end of these ranges to minimize
corrosion. However, operating the unit at the upper end of the range can save fuel
input to the reboiler.
 The amine solution should be regenerated to achieve a lean amine loading no
lower than necessary to meet the required sweet gas specifications. Lean amine
loading is usually around 0.1 mole of acid gas per mole of amine. Lower lean
amine loadings increase energy usage in the reboiler and are not required unless
the contactor pressure is lower than 100 psig (690 kPa).

23. Operation and Controls
 Efficient operation of an amine sweetening unit requires a good understanding of
the sweetening process and process variables. Better sweetening and significant
savings result when an amine sweetening unit is operated properly. The operation
of individual components within the unit must be understood to properly operate
and troubleshoot the unit.
 Depending on the type of amine used, the amine sweetening unit at your location
may vary from the typical unit discussed in this course. However, the process and
equipment will be very similar.

25. Inlet Separator
 The inlet gas stream first enters the sweetening unit through an inlet gas separator. Here
solids and free liquids in the sour gas are removed. An inlet separator can be an integral
part of the contactor or a separate vessel.
 Within the separator, a baffle allows most of the liquids to be removed. A mist eliminator,
located near the gas outlet, traps liquids entrained in the gas before it leaves the separator.
 Efficient removal of solids and liquids, such as scale, iron sulfide, liquid hydrocarbons,
water, etc., from sour gas prior to the absorption process can minimize many operational
and maintenance problems. Some of these problems are foaming, corrosion, and fouling.
Results of these problems can be amine loss, equipment failure, and difficulty in meeting
sweet gas specifications.
 A liquid level controller operates a control valve to drain the separated liquids. It is
important that the vessel be large enough to remove all solids and free liquids. The inlet
separator should be checked regularly to prevent any malfunction. Overloading the
separator causes excessive liquid carryover into the contactor which causes foaming.
Therefore, it is important to routinely monitor liquid levels and their controls for proper
operation.

26. Inlet Separator
(Integral Vessel
Inlet Separator
(Separate Vessel)

27. Contactor Column
 The function of the contactor column,
sometimes called an absorber, is to
contact sour gas with amine solution, so
the amine solution can remove acid gases
from the sour gas. Contactors are
designed to accommodate a certain gas
volume and acid gas concentration at a
given pressure. Contactors operate at
elevated pressures in the range of 200-
1000 psig (1379-6895 kPa). If design
specifications are exceeded, amine
losses will increase and reduced
efficiency of the vessel to remove acid
gases will result.

28. Tray With Bubble Caps
For large volumes of sour gas, the
contactor is usually a tray column
containing 16 to 20 trays. On each tray
up flowing sour gas bubbles through
down flowing amine solution. The
number of trays in the contactor
affects the amount of gas sweetening;
more trays mean more acid gas
removal.

29. Bubble Caps
Each tray has a number of openings
with bubble caps bolted over them to
evenly disperse sour gas through the
amine solution as the sour gas is
forced to pass through these caps. The
sour gas gives up acid gases and
becomes sweeter as it passes upward
through each succeeding tray. The
amine solution becomes more
saturated with acid gases as it flows
downward over each succeeding
tray. Also found on the trays are weirs
and downcomers.

30.  Weirs are dam-like devices which maintain a
level of amine solution above the slots in the
bubble caps. Downcomers carry amine
solution to the trays below.
 In smaller capacity units, contactors having
diameters of 18 inches (46 centimeters) or
less, random packing may be used instead of
trays. The packing can be made of metal,
plastic, or ceramic material. Packing is
designed to furnish a large surface area for
the amine solution to spread out and make
better contact with the sour gas. Random
packing is poured into the contactor onto a
support grid.
 Packed columns utilize the same process as
tray columns. Amine solution flows down
over the packing and sour gas flows up
through the packing, contacting the amine
solution. Packed columns are less expensive;
however, the amine solution tends to channel
easier and have poorer flow distribution.

31. Structured Packing
 Contactors being designed today
may contain structured packing.
Structured packing is a group of
corrugated metal sheets welded into
a specific pattern and placed in the
contactor on edge. Amine solution
coats these sheets and sour gas
flows between them. This type of
packing is much more efficient than
bubble caps or random packing.
Structured packing is used in
columns from six inches (15
centimeters) in diameter up to 10 feet
(3 meters).

32.  Before lean amine enters the contactor, two things happen:
• The amine solution is pumped up to contactor pressure.
• The amine solution temperature is lowered to 5°-15°F (2°-7°C) above the inlet
gas temperature.
 It is best to have lean amine entering the contactor 5°-15°F (2°-7°C) warmer
than the inlet gas. Cooler amine solution allow hydrocarbon vapors to
condense which causes foaming, resulting in greater amine loss. Warmer
amine solution reduces effectiveness of absorbing acid gases from the sour
gas.
 Incorrect lean amine temperatures entering the contactor indicate an
imbalance in the amine solution to gas flow rate, a problem in the trim cooler,
or the reboiler temperature is out of adjustment.

33. mist eliminator
 Above the top tray there is
usually space for separation
where most of the entrained
amine solution particles in the
gas stream settle out. Amine
solution not settling out is
removed by a mist eliminator in
the top of the contactor. This
prevents liquid amine from being
carried out of the contactor and
into the gas discharge line.

34. Carryover
Carryover can result from foam buildup caused by
amine solution contamination; however, carryover can
also be caused from a high gas rate. Carryover will
happen continuously when the gas flow rate is high
enough to agitate amine solution on the top tray. A
foam forms that is too thick for the mist eliminator to
handle. When this happens, the gas flow rate must be
reduced to eliminate carryover.
Level control in the contactor is important for
stabilizing operation. The level controller should be
adjusted to hold a uniform flow rate of rich amine out
of the contactor. It is more important to hold a
constant flow rate of rich amine and let the level in the
contactor vary a few inches than to hold a constant
level and let the flow rate fluctuate. Flow rate surges
will cause the reboiler to operate inefficiently and may
overload it.

35. Outlet Separator
Amine sweetening units usually have an outlet separator downstream of the contactor.
This separator is used to recover any amine solution in the sweet gas stream that has
carried over from the contactor prior to sales or further gas processing. An outlet
separator has the same components and operates the same as the inlet separator.

36. Flash Tank
 The flash tank is used to remove a large portion of the physically absorbed gases
in the rich amine. It also removes any liquid hydrocarbons carried out of the
contactor by the rich amine.
 The flash tank is simply a three phase separator in which entrained gases, liquid
hydrocarbons, and amine solution are separated. Entrained gases, which are
usually sour, are recycled to the contactor or flared. A pressure control valve
maintains a back pressure on the vessel, usually 50 to 85 psig (345 to 586 kPa).
 Separating liquid hydrocarbons from the amine solution before entering the
reboiler reduces the load on the carbon filter and helps prevent carbon from
building up on the reboiler fire tube. Problems caused by liquid hydrocarbons
entering the stripper are flooding, amine loss, and possible damage to the stripper.
 Two level control systems are typically installed on flash tanks. The upper system
regulates flow of liquid hydrocarbons from the vessel. The lower system regulates
flow of rich amine from the vessel.

37. Flash Tank

38. Solids Removal Dissolved Contaminants Removal
Carbon Filters
Filters are installed in the amine stream to remove solids and other contaminants which may
cause plugging and foaming. There are two types of filters commonly used in amine
sweetening units: One type is used for solids removal and the other for dissolved
contaminants removal.

39. Solids Removal
 Mechanical filters such as fine screen, sock type or cartridge filters are used for
solids removal. Solid particles can cause erosion of pump pistons, valve seals and
discs, plugging of equipment, and foaming.
 Sock filters are the most commonly used type for solids removal. Sock filters
contain cylindrical elements that are replaced as they become coated. A pressure
drop of 3-6 psig (21-41 kPa) usually occurs as amine solution flows through the
elements; however, the pressure differential increases as the elements remove
solid material and become plugged.
 To measure the pressure drop across elements, a differential pressure gauge is
installed. When the pressure differential rises to 15-20 psig (104-138 kPa), the
elements should be replaced so that collapse of the elements or stoppage of
amine solution does not occur.

40. Dissolved Contaminants Removal
 Activated carbon filters are recommended for the removal of dissolved contaminants. Carbon
filters work well until their adsorption capacity is reached. In cases where the amine solution
contains appreciable quantities of light hydrocarbons, carbon filters must be changed or
reactivated frequently. Most amine units cannot be operated successfully without carbon filtration.
 There are two types of activated carbon filters. Most units use a carbon canister; however, larger
units use a loose fill carbon vessel. When the loose fill vessel is used, care must be taken to trap
carbon fines and keep them from entering the amine solution. This is especially important when a
fresh carbon bed is put into service. The usual method of trapping carbon fines is to route the
amine solution through the carbon bed prior to the particle filter. However, care must be taken to
reroute the amine solution to its proper flow, or the useful life of the carbon bed will be shortened.
 Carbon filters should be replaced or regenerated anytime the level of contaminants in the amine
solution goes up. Watching for an increase in the flash tank gas rate is a good indicator as to when
the filters should be replaced or regenerated.
 Regenerating a carbon bed with low pressure steam can extend the useful life of the bed and will
save money. Disposal of carbon canisters or loose fill must be done in a safe and environmentally
acceptable manner.

41. Lean/Rich Heat Exchanger
 The lean/rich heat exchanger
preheats rich amine going to the
stripper by lean amine exiting the
reboiler. This exchanger reduces the
heat load on the reboiler by raising
the temperature of the rich amine to
approximately 190°F (88°C). It is
best not to preheat the rich amine
above 190°F (88°C) because more
acid gases are released by the
amine solution as temperature
increases and corrosion problems
will result.

42.  Heat exchangers are subject to fouling by salt, coke, or gum deposits which can
reduce the heat transfer rate and increase lean amine temperature. Fouling
reduces operating efficiency, wastes energy, and can keep the amine sweetening
unit from processing the required amount of sour gas. Operating and heat removal
data on heat exchangers will help determine fouling rates and pinpoint corrosion
areas.
 The performance of heat exchangers should be routinely checked. Temperature
differentials across exchanger walls are an excellent way to spot problems. For
example, if the heat exchanger is not operating near design heat transfer rate, the
problem may be caused by severe fouling or vapor trapped in the shell side.

43. Heat Exchangers

44. Stripper Column
 The function of the stripper column, sometimes called a still, is to remove acid
gases from rich amine. Strippers are designed to accommodate a certain vapor
stripping rate. Strippers operate at or near atmospheric pressure. If design
specifications are exceeded, amine losses will increase and reduced efficiency of
the vessel to remove acid gases will result.
 Like the contactor, a stripper is either a tray or packed column which provides good
vapor/amine contact. The rich amine, which has been preheated to approximately
190°F (88°C) in the lean/rich heat exchanger, enters the stripper near the top and
flows downward. Hot vapor rising from the bottom of the stripper heats the rich
amine to about 220°-240°F (104°-116°C). Acid gases are stripped from the rich
amine, and the vapor helps to sweep the liberated acid gases out the top of the
stripper.

45. Tray Stripper Column and Packed Stripper Column
The overhead system in a stripper,
which is the area above the top tray
or packing, is where extreme
corrosion can take place if
regeneration is not closely
monitored. Hydrogen sulfide, carbon
dioxide, and water are present in
the overhead system, and this
mixture is very corrosive. A small
amount of amine (0.5%) in the
overhead condensate used for
reflux will help prevent corrosion in
this section of the stripper.

46.  It is important to remember that the highest levels
of concentrated H2S are in the overhead system of
the stripper. Proper safety procedures must be
followed when working around this area of the
stripper.
 There is usually space in the overhead system
where most of the entrained amine solution
particles in the vapor stream will settle out. Amine
solution not settling out will be removed by a mist
eliminator. This prevents liquid amine from being
carried out of the stripper and into the overhead
vapor line.
 Carryover results from foam buildup caused by
contaminated amine solution and dirty packing or
trays; however, carryover can also be caused from
a high vapor rate. Carryover will happen
continuously when the vapor rate is high enough
to agitate amine solution on the top tray so that a
foam forms that is too thick for the mist eliminator
to handle. When this happens, the vapor rate must
be reduced to eliminate carryover.

47. Level control on the stripper is important
in stabilizing operation. The level
controller should be adjusted, as in the
contactor, to hold a uniform flow rate of
lean amine out of the stripper. Flow rate
surges will cause the reboiler to operate
inefficiently and may overload it.

48. Reflux System
 The reflux system consists of
the reflux condenser,
accumulator and pump.
Overhead vapors from the
stripper, consisting essentially
of water vapor and acid
gases, pass through the
reflux condenser which
condenses most of the water
vapor and the small amount
of amine which may have
vaporized in the stripper.

49.  This two phase stream flows to the reflux accumulator where the acid gases are
separated from the condensed liquids. The acid gases may be sent either to a flare
stack or to a sulfur recovery plant, depending on the amount of H2S present. The
condensed liquids are pumped to the top of the stripper for reflux.
 Reflux accomplishes two things in the overhead system of the stripper. First, it cools
vapors in the top of the stripper to reduce the amount of amine carryover; and
secondly, it cools acid gases in the top of the stripper to reduce their corrosiveness.
However, reflux is an additional heat load for the reboiler.
 Over- or under-refluxing can be an expensive operational problem. A temperature
controller should be used to control energy usage in the reboiler. An overhead
condensing temperature in the range of 190°-210°F (88°-99°C) is usually sufficient for
good stripping.
 Below this range, reboiler duty is increased resulting in excessive firing and fuel waste.
Above this range, the amount of amine solution lost in the overhead will increase.
Optimum reflux should be determined and then maintained by closely monitoring the
process.

50. Reboiler
Lean amine is heated in
the reboiler. Reboiler heat
converts some of the
water in the amine
solution to a stripping
vapor. The heat medium
for reboilers can be low
pressure saturated steam,
hot process fluids, or a
direct-fired heater.

51.  Reboiler temperature is primarily a
function of the pressure at which the
stripper is operated. As the pressure
goes up, the reboiler temperature
must also go up. It has been found
that at temperatures above 240°F
(116°C), the corrosion rate increases
rapidly. Therefore, it is desirable to
maintain a pressure on the stripper
low enough to permit operating the
reboiler below 240°F (116°C).
However, the pressure must be high
enough to force the amine solution
out of the stripper through the
lean/rich heat exchanger to a surge
tank or pump suction.

52.  Stripping vapor requirements
vary depending on the degree
of sweetening required.
Normally, the heat input should
be one pound (0.45 kilogram) of
vapor for each gallon (3.77
liters) of amine solution
circulated. Analysis of the amine
solution entering and leaving
the reboiler will help you
determine efficiency of the
stripping operation.
MEA Temperature/Pressure Relationships

53. Reclaimer
 A reclaimer is not often included in an amine sweetening unit. When used it can
greatly reduce operating problems, such as corrosion, foaming, and fouling. A
reclaimer stores the amine solution by removing high boiling and non-volatile
impurities, e.g., heat-stable salts, suspended solids, volatile acids, and corrosion
products.
 The amine solution is reclaimed by a semi-continuous batch process when the
level of contamination reaches one percent. A side stream of one to three percent
of the total amine circulation is fed from the reboiler to the reclaimer.

54.  Amine which boils from the top of the
reclaimer flows to the vapor outlet of the
reboiler. As amine in the reclaimer
continues to boil out, the concentration of
contaminants will increase, and liquid
temperature in the reclaimer will also
increase. The temperature in a reclaimer
should not be allowed to exceed 305°F
(152°C) because degradation of the
remaining amine will occur at higher
temperatures. A continuous flow of lean
amine from the reboiler maintains a
constant level of fluid in the reclaimer.
 Heat-stable salts can chemically "tie up"
amine so it cannot remove acid gases.
Sometimes up to 50 percent of amine in
solution can be tied up with heat-stable
salts. Past practice was to add sodium
carbonate, or soda ash, to the reclaimer
during the initial fill to free up this amine.
Generally, 0.03 percent by weight of
sodium carbonate was sufficient unless
these impurities were excessive.

55.  The exact amount of sodium carbonate required had to be
calculated and slowly added to the reclaimer to avoid an
upset in the unit. Too much sodium carbonate caused a
number of operational problems, such as additional
sludge, foaming, fouling, corrosion, and inaccurate
laboratory analyses. Current practice is not to use sodium
carbonate except under extreme situations.
 The reclaiming cycle is complete when essentially all
amine has been distilled from the contaminant residue.
The residue, which should be a thick sludge, is flushed
from the reclaimer with water and disposed in a safe and
environmentally acceptable manner. Then another cycle is
begun.
 One way to tell whether reclaimer operation has been
effective is to visually examine the material washed out of
the reclaimer. If this material is thick and concentrated, the
reclaimer efficiency is satisfactory. If on the other hand
this material is thin, the reclaimer has not concentrated
higher boiling compounds and recoverable amine is being
lost. Another possibility is that the amine solution does not
contain a lot of heat-stable salts and the reclaimer is being
operated too often.

56. Heat Medium
 In gas treating facilities, reboiler and
reclaimer heat is usually supplied by a
direct-fired heater, which consists of a
removable fire box and firetube. This
method of heating simply consists of
controlled combustion on the inside of
the firetube surrounded by the boiling
amine solution.

57.  Firetubes should be inspected at periodic intervals for hot spots, corrosion, and
accumulation of scale. The burner flame should aim straight down the center of the
firetube. If it hits the firetube directly, a hot spot will form and premature tube failure
will occur. The burner should come on and burn steadily for a long period of time
rather than blasting on and off. A yellow flame with just enough air to keep soot
from forming is best.

58.  Low pressure saturated steam in the range of 30 to 40 psig (207 to 276 kPa) is
sometimes used as a heat medium for reboilers. The temperature of saturated stream
in this pressure range is 274° to 287°F (134° to 142°C).
 Low pressure saturated steam in the range of 150 to 175 psig (1,034 to 1,207 kPa) is
sometimes used as a heat medium for reclaimers. The temperature of saturated steam
in this pressure range is 366° to 378°F (186° to 192°C).
 Temperature control is extremely important for reboilers and reclaimers. Many
operational problems can develop if temperature controllers are not used or fail to
function properly. For example: If not enough heat is supplied to the reboiler,
insufficient vapor will be generated for the stripper. In the reclaimer, amine losses will
increase due to decreased distillation.

59.  If too much heat is supplied to the reboiler or reclaimer, amine degradation will
result and energy will be wasted. Therefore, temperature controllers should be
installed and properly maintained for efficient operation of amine sweetening units.

60. Surge Tank
 The surge tank is a holding vessel
for the cooled lean amine until it is
pumped to the contactor.
Periodically, water and amine are
added to the surge tank to make up
for losses of these two liquids
during the process.
 The surge tank should be vented
and the vent line kept unplugged.
Vapors which are trapped in the
surge tank could cause the
circulation pump to vapor lock. The
vent line should be piped away from
process equipment.

61. Circulation Pumps
 Most small amine sweetening units use fluid-driven reciprocating pumps while
larger units generally use electrically-driven reciprocating pumps. However,
centrifugal pumps are sometimes used in units with low pressure contactors. In
any case, the pump is a critical part of the amine sweetening unit because it has
the only moving parts in the system. Before entering the pump, lean amine passes
through a strainer to remove large particles.
 Leaks and corrosion are major problems around amine circulation pumps. Proper
packing gland maintenance and the use of manufacturer's recommended packing
can minimize those problems.

62. Electrically-Driven Reciprocating Pump Electrically-Driven Centrifugal Pump

63. Trim Cooler
 Lean amine entering the contactor
should be hotter than the sour gas
being treated; however, high
amine temperatures affect acid
gas removal. A trim cooler lowers
the temperature of lean amine
coming from the surge tank and
controls the temperature of lean
amine entering the contactor.

65. Amine Conditioning and Reducing Amine
Losses.
Efficient operation of an amine sweetening unit is dependent on various factors. One
of the most important is analysis of the amine solution which helps to pinpoint costly
operating problems. Based on analysis results, adjustments can be made to maximize
sweetening efficiency.

66. Temperature and Pressure Conditions
 Inlet Gas Temperature: The temperature of inlet gas is important. As previously
stated, at constant pressure, sour gas can hold more acid gas as the temperature
of the sour gas increases; and therefore, the amount of acid gas that the amine
solution must remove also increases. The inlet gas temperature should be 100°F
(38°C) or lower for good acid gas removal and low amine losses. In some
installations it is necessary to cool the inlet gas prior to entering the contactor. In
other instances it is important to heat the inlet gas to prevent hydrate formation.
 Inlet Amine Temperature: The temperature of lean amine entering the contactor
should be kept to a minimum while still maintaining a 5°-15°F (2°-7°C) higher
temperature than the incoming sour gas. As previously stated, this is to prevent
hydrocarbon condensation.

67. Inlet Amine Temperature

68.  Reboiler Temperature: This temperature controls the concentration of acid gas in
lean amine; higher temperatures at constant pressure result in greater amine purity.
The temperature range varies based on the type of amine being used and the
operating pressure.
 Reclaimer Temperature: This temperature controls the amount of amine restored by
removing high boiling and non-volatile impurities; higher temperatures at constant
pressure result in greater amine recovery. The temperature range varies based on the
type of amine being used and the operating pressure.
 Heat Exchanger Temperature: Amine solution temperatures taken both before and
after passage through a heat exchanger indicates the condition of the exchanger
surfaces. As exchanger surfaces become more severely fouled, the temperature
change or differential across the heat exchanger decrease and energy consumption
for amine solution regeneration goes up due to increased firing of the reboiler.

69. Heat Exchanger Efficiency

70.  Contactor Pressure: Operating the contactor below design pressure creates the
following problems:
• At constant temperature, acid gas content of inlet gas increases as pressure decreases,
causing the unit to work harder to sweeten gas
• At constant gas rates, gas velocity through the contactor increases as pressure is
lowered, causing carryover problems
 Stripper Pressure: A buildup in pressure, above design, usually indicates a plugging or
flooding problem, most commonly in the trays or packing. An increase in pressure also
prevents some acid gas from distilling out of the amine solution. This requires higher
temperatures in the reboiler, which wastes fuel and can lead to amine degradation.
 Filter Pressure: A pressure drop of 3-6 psig (21-41 kPa) is normal as amine solution
flows through the elements; however, pressure differential increases as the elements
become plugged. When this differential increases to 15-20 psig (104-138 kPa), the
element should be replaced.
 Flash Tank Pressure: Operating pressure in the flask tank is 50-85 psig (345-587 kPa).
Back pressure is maintained by a pressure controlled regulator.

72. Reducing Amine Losses
 Some amine losses are to be expected as part of normal operation. A rule of thumb for acceptable
losses is: 0.2-0.4 gallons of amine solution per million standard cubic feet of gas treated (0.03-0.05
liters of amine solution per thousand standard cubic meters of gas treated) if the unit utilizes a
reclaimer. If not, the amine losses are approximately one half the above values.
 Amine losses can be a serious and costly operating problem. Losses commonly occur by
entrainment, vaporization, chemical degradation, or mechanical leaks. The following are ways to
reduce amine losses:
• Maintain an amine solution control program. A large quantity of amine solution can be lost when the
contactor or stripper is dirty and/or the amine solution is contaminated.
• Do not exceed design capacity of the various components in the sweetening unit.
• Keep the amine concentration at the upper end of its range.
• Maintain a corrosion control program. When corrosion rates are high, amine losses increase due to
equipment problems.
• Minimize mechanical leaks by routine maintenance of pump packing, valves, and other system
components.
• Connect all drains from equipment, except the reclaimer, to a common sump.

73. Amine Tests
 In order to prevent costly operating problems such as high amine losses, foaming, and corrosion, it
is essential that meaningful analytical information be collected to pinpoint areas of inefficiency.
 Maximum sweetening efficiency is achieved when sufficient data from amine tests is known, so
proper evaluation of unit performance and correct adjustments can be made. Amine tests should
include the following analyses:
 Amine Appearance: The physical appearance and odor of the amine sample can indicate
operating problems. For example:
• The presence of iron sulfide is indicated by a fine black suspension.
• An amber solution may contain suspended iron oxide.
• A green or blue solution indicates the presence of copper or nickel.
• An oily film or odor indicates hydrocarbon contamination.
• A brown color indicates that air has entered the unit and oxidation has occurred.
• A strong ammonia odor indicates chemical degradation or solution contamination.
 Acid Gas Content: Acid gas content of both the rich and lean amine is determined by chemical
titration method(s). This information helps to determine amine circulation rate and amine
concentration. Operating efficiency and corrosion rate can also be determined for the unit.

74.  Alkalinity by Titration: There are various titration
procedures used; however, test results give the amount of
free amine available for acid gas absorption and thereby,
is a basis for controlling amine circulation and
concentration.
 Water Content: This refers to the amount of water in the
amine solution. Water quality is also very important and
tests should be run periodically on your water supply to
make sure it is still good quality water.
 Inorganic Salt Content: This refers to the proportion of
soluble inorganic salts in the amine solution. These salts
can enter the amine stream from hard water, the gas
stream, or accidental addition of foreign compounds. Salt
accumulation is responsible for corrosion, foaming, and
poor heat transfer.
 Acid Gas Loading: This refers to the H2S and
CO2 content of the rich and lean amine and is essential
for optimizing the sweetening unit's operating conditions.
Once the rich and lean amine loading are known, simple
calculations reveal whether parameters such as
circulation rate, degree of sweetening, regeneration heat
duty, reflux flow, and even equipment integrity are
satisfactory.

75.  Foaming: Foaming is the most common cause of upset in alknolamine systems resulting in
excessive amine losses, off-specification treated gas and a reduction in treating capacity.
 Foaming can be attributed to three main parameters in alkanolamine systems:
• A contaminant acting as a foaming initiator
• Solids stabilizing the foam
• High gas velocity forming the foam
 One or more of these parameters is needed for foaming.
 Amine contaminants such as condensed hydrocarbons, organic acids, water contaminants, iron
sulfide particles, and amine degradation products are considered foam stabilizers.
 Foaming symptoms include the following:
• High or erratic differential pressure in absorber or stripper
• Amine carry over from absorber, stripper, or flash drum
• Fluctuating liquid levels in any vessel
• Decrease in H2S removal with increase in CO2 removal
• Off-specification treated gas
• Poorly stripped amine

76.  Remedies for eliminating foaming focus on identifying and preventing alkanolamine
solution contamination.
 Foaming prevention can be obtained by:
• Maintaining lean amine temperature 10°F above inlet gas temperature to minimize
hydrocarbon condensation
• Adequate inlet gas separation to minimize liquid hydrocarbons, iron sulfide, suspended
particles, and chemicals from entering the system
• Adequate carbon and mechanical filtration
• Temporary use of antifoams (Antifoam usage should be considered a temporary
treatment while the root cause is identified and corrected.)

77. Thank You
SADIQ ALOMESH
Process Engineer