Use of aMDEA in Ammonia Synthesis Gas

1. aMDEA for Carbon
Dioxide absorption from
Process Gas
Vivek Sharma
Assistant Manager

2. CONTENTS
1. Need of Carbon Dioxide Removal from synthesis Gas
2. Various processes for Carbon Dioxide Removal
3. Desirable properties of Solvent for CO2 removal
4. Commercially available processes for CO2 removal
5. Difference between physical & chemical absorption
6. Selection criteria of various CO2 removal processes
7. aMDEA process & various constituents & reactions involved
8. Why Rectisol process not possible for CO2 removal in new plant
9. Favorable parameters for absorption & regeneration of aMDEA
& monitoring of parameters in absorption & regeneration.
10. Problems encountered with aMDEA process.
11. Various handling precautions associated with aMDEA solution.
12. Various Process Interlocks involved
13. Common Problems & mistakes

3. NEED OF CARBON DIOXIDE REMOVAL
(1) Removed CO2 is utilized in Urea formation as
a raw
material for UREA plant
(2) CO2 formed in reforming section, are not tolerable in
Ammonia Synthesis Loop. CO2 under high
temperature and pressure oxidizes the iron catalyst
in synthesis reactor which ultimately results in
temporary poisoning of catalyst as described by
following reaction
CO2 + 4H2 ⇌ CH4 + 2H2O
2Fe + 3H2O ⇌ Fe2O3 + 3H2

4. (3) CO2 reacts with the ammonia in
synthesis gas loop to form solid
deposits of ammonium carbamate
results in the corrosion .
(4) Also, Carbon Dioxide slips from the
Decarbonation unit results in the
consumption of expensive Hydrogen in
the methanation section.

5. DESIRABLE PROPERTIES OF SOLVENT FOR
REMOVAL OF CO2:-
i. HIGH CO2 SOLUBILITY
ii. HIGHLY SELECTIVE IN NATURE
iii. LOW VISCOSITY
iv. HIGH THERMAL STABILITY
v. NON CORROSIVE IN NATURE
vi. LOW VAPOUR PR UNDER OPERATING TEMP
vii. BIODEGRADEABLE, NON TOXIC & ENVOIRNMENT
FRIENDLY
viii. EASILY AVAILABLE & LOW COST

6. Commercially used Absorption ProcessesCommercially used Absorption Processes
1). Physical Absorption Process
2). Chemical Absorption Process
3). Combination of Physical & Chemical Absorption
Process
1). Physical Absorption Process
2). Chemical Absorption Process
3). Combination of Physical & Chemical Absorption
Process
Various Physical Absorption ProcessesVarious Physical Absorption Processes
 Rectisol Process (Methanol as solvent ) Lurgi
 Purisol Process( N Methyl – 2 Pyrrolidone as solvent )
 Fluor Solvent ( Propylene carbonate as solvent ) Fluor
 Selexol Process (Polypropylene Glycol of Dimethylether as
solvent) UOP Process Licensor

7. Various Hot Potassium Carbonate Solution based processes
1). Benefield process
2). Gimmarco Vetrocoke Process
3). MEA(Mono Ethanol Amine) Process
Chemical Absorption ProcessesChemical Absorption Processes
Mixed Chemical /Physical Absorption ProcessesMixed Chemical /Physical Absorption Processes
1). aMDEA(activated Methyl Diethanol Amine) Process
2). DIPA ( Diisopropanol amine )

8. COMPARISON B/W PHYSICAL & CHEMICAL ABSORPTIONCOMPARISON B/W PHYSICAL & CHEMICAL ABSORPTION

9. Selection Criteria of CO2 removal process
depends on the following factors:
 Type of feedstock used and choice of process
route selected for raw gas generation.
 Amount of CO2 recovery and purity desired.
 High energy consuming Ammonia plant based on
Partial Oxidation of Fuel oil or Coal gasification
employ physical process- Rectisol where CO2
partial pressure in Reformed gas is compartively
high.

10.  Ammonia plant based on Natural gas Steam
Reforming route involving low partial pressure
of Carbon dioxide adopts mostly either a
Chemical Absorption Process like Benfield
Process/ GV process/ Hybrid Physio-Chemical
Process-a-MDEA.

11. aMDEA at glance
aMDEA solution in CO2 absorption process at NFL Panipat
Absorbing media.- MDEA (METHYL DIETHANOL AMINE) Tertiary
Amine
MDEA is clear, water-white, hygroscopic liquid with an ammonical odor.
Typical Physical Properties
Boiling Range, o
C 247
Flash point, PMCC, °C (°F) 116 (240)
Freezing Point, o
C (o
F) -21 (-5.8)
Specific gravity, 20/20oC 1.0431
Vapor pressure, 20oC, mm Hg <0.01
Viscosity, cSt, 100oF 36.8
Water solubility Complete

12. ACTIVATOR : Piperazine acts as a activator/promoter with MDEA solution
Synonyms: Piperazine Anhydrous,
Diethylenediamine
Molecular Formula: C4H10N2
Formula Weight: 86.13
Boiling point 1460
C
Flash point 820
C
Purpose of use of Piperazine along with MDEA : The
rate of
the reaction can be increased by using promoters,
without diminishing the MDEA advantages. So it
increases the mass transfer rate of CO2 from gas to
liquid phase.ROLE OF PROMOTER IN INCREASING RATE OF REACTION
CO2 + promoter = intermediate
Intermediate + OH-
= promoter + HCO
_
3

13. aMDEA process at NFL Panipat
Activated MDEA process for CO2 removal is a physical/chemical
absorption process. It behaves as a physical absorption process
at higher partial pressure of CO2 and as a chemical absorption
process at low CO2 partial pressure.
The main constituents of aMDEA solution
aMDEA 34 wt%
Piperazine 6 wt%
Water 60 wt%

16. CHEMICAL
CO2 LOADING CAPACITY OF SOLVENTS
aMDEA
PHYSICAL
CO2-LOADING,
m3
/m3
0
20
40
80
60
2 4 6 8 10 12
CO2 PARTIAL
PRESSURE, BAR

17. DIFFERENT CO2 REMOVAL PROCESSES
PROCESS T
0
C
P
Kg/cm2
g
SOLVENT CO2
SLIP
ppm
ENERGY
REQIRD.
Kcal/Nm3
CO2
RECTISOL
MEA
BENFIELD
GV
aMDEA
- 70
30-60
70-115
60-120
750
C
44
20
27-28
27-28
27 - 28
METHANOL
MONOETHANOL
AMINE
K2CO3
DEA
V2O5
K2CO3
GLYCINE
DEA
V2O5
aMDEA
2
500
1000-
1200
500
500
2700
2245
795
612
430-640

18. Benefits of using aMDEA solution for CO2 absorption from
Synthesis Gas
1. Higher CO2 removal rate in activated MDEA process as
process involves low partial pressure of Carbon
Dioxide.
2. Lower energy requirement.
3. No requirement of refrigerant as in case of Rectisol
Process.
4. Lower MDEA make up requirement due to its low
volatility.
5. MDEA (Methyl diethanol amine) is environment friendly
and biodegradable chemical.
6. MDEA is non-corrosive. Hence MDEA system does not
require any corrosion inhibitor

19. aMDEA REACTION FOR CO2 ABSORPTION
1) CO2 (gas) CO2 (sol’n)
Fast
2) CO2 (sol’n) + H2O H2CO3 (sol’n)
Slow
3) H2CO3 (sol’n) +R3N R3NH +
(sol’n) + HCO3-
(sol’n) Fast
So, overall reaction for tertiary amine is described
below :
CO2 (gas) + H2O + R3N(sol’n) R3NH+
(sol’n) +
HCO3- (sol’n)
R’(NH)2 + 2CO2 R’(NHCOO)2
The activator PZ may react with CO2 in liquid lm to form an intermediate
R’(NHCOO)2 + 2H2O R’(NH
+
2 ) + 2HCO3
-
Using Piperazine as an activator
Tertiary Amine MDEA reactions
(R3NH)+
+ (HCO3
)-
+ Heat → R3N + CO2 + H2 O
Tertiary Amine Regeneration reaction

20. DECARBONATION PROCESS OF SYNTHESIS
GAS USING aMDEA AS SOLVENT AT NFL
PANIPAT

21. Major Parts of CO2 removal section
1. CO2 absorber Column F302
2. CO2 stripper Column F301
3. HP Flash drum B302
4. LP Flash drum B301

22. OLD DECARBONATION UNIT V/S NEW DECARBONATION UNIT

23. Gas to
stripper
Flash
gas
CO2
gas
Treated
gas
Absorber
I/L gas
Stream
Description

24. WHY Rectisol Process could not used with new Set up of Plant???
 As in new plant CO2 generation is low due to the low C/H ratio
as result the partial pressure of CO2 in the process gas is low
which result in the ineffectiveness of the rectisol process which
is purely based on physical absorption.
 There is not huge surplus Nitrogen availability due to properly
regenerate the Methanol solvent.
 No need of set up of extra refrigeration unit
 Lesser make up rate of solvent required due low volatility of solvent

25. Bulk CO2 is absorbed in the bottom beds of the column
Only refining of CO2 takes place in the top two beds

26. aMDEA THEORY
a. FAVOURABLE PARAMETERS FOR ABSORPTION
1. HIGH PRESSURE
2. BETTER ACTIVATOR ( PIPERAZINE)
3. LOWEST OPTIMUM TEMPERATURE
4. OPTIMUM SPLIT STREAM TEMP
5. IMPROVED PACKED BEDS AND INTERNALS
b. FAVOURABLE PARAMETERS FOR REGENERATION
1. LOW PRESSURE
2. PROPER DISTRIBUTION OF RICH SOLN
3. IMPROVED PACKED BED AND INTERNALS
4. REGN. STREAM FLOW / TEMP OPTIMUM

27. Absorber parameters to be kept
under control:
 CO2 content in purified gas (main parameter).
 Circulation pumps flow rate.
 Solution temperature.
 Pressure drop.
 Operating pressure.
 Solution composition.
 Temperature profile of the CO2 absorber.
 Foaming tendency of the solution

28. Stripper parameters to be kept
under control:
 Top Temperature of the stripper.
 Bottom temperature of the stripper.
 Pressure drop across the stripper.
 Operating pressure of the stripper.
 Reboiler duty of the stripper

29. MAIN PROBLEMS ENCOUNTERED WITH
HANDLING
aMDEA SOLUTION PROCESS FOR CO2
CAPTURING
 Formation of Heat Stable Salts.
Foaming of the aMDEA solution
FORMATION OF HEAT STABLE SALTS WITH aMDEA
MDEA is the most forgiving amine from a corrosion standpoint,
as compared to other amines i.e. MEA & DEA it does not leads
to the formation of bicarbonates which are mostly resulted in
the lower of PH value of solution leading to corrosion.
Regardless of amine type for the CO2 capture process,
the formation of heat stable salts (HSSs) in amine solutions
has long been a problem.

30. HSSs are formed in the presence of acids which are substantially
stronger than CO2 . These acids are formed from amine
degradation product which are mostly resulted from the
overheating in case of CO2 stripper or from the impurities present
in synthesis gas.
For example, if formic acid is produced, it will react with MDEA to
form a formate HSS
Absorber reaction :
R3N + HO2CH → (R3
NH)+
+ (O2CH)-
[amine plus acid → salt]
Regenerator reactions :
(R3NH)+
+ (O2CH)-
+ Heat → No Change
Thus HSSs typically promote corrosion in the systems because
they lower the pH and increase the conductivity of amine
solutions. This can decrease the efficiency of CO2 capture
because of the irreversible reaction with the amine.

31. Remedy to remove Heat Stable Salts & monitoring the process:
Installation of activated carbon filter for the removal of the
degraded amine products and organic acids from lean solution
split stream.
Periodical inspection of corrosion in the line by the installation of
Corrosion coupons at the critical positions.
Periodical sampling of aMDEA solutions
Remedy to remove Heat Stable Salts & monitoring the process:
Installation of activated carbon filter for the removal of the
degraded amine products and organic acids from lean solution
split stream.
Periodical inspection of corrosion in the line by the installation of
Corrosion coupons at the critical positions.
Periodical sampling of aMDEA solutions

33. PRECAUTIONS IN HANDLING aMDEA SOLVENT
Use Demineralized water for diluting aMDEA premix and
presence of oxygen in make up water severely increase the
corrosivity of aMDEA. Make up water having < 10 wppm is
Recommended for use.
Make up water should have lower chloride level as higher
levels leads to higher localized corrosion. Also, aMDEA is
A chloride free product only chance of getting high chloride
content is from make up water. Max. recommended chloride
content in make up water is 2ppm by wt.
Annual solvent losses are 5% to 10% of aMDEA premix
inventory, which are mainly due to mechanical reasons such
as pump leakage, filter replacement and cleaning liquid
entrainment in off gas stream.
Another major area of concern is loss of activator as it is
more volatile than MDEA which is balanced by enriched
aMDEA make up solution.

34. aMDEA premix can be stored as delivered drum in a warehouse or
in storage tanks which are necessarily blanketed with Nitrogen gas
To avoid the contact with air which can turn the solvent colour
from Light yellow to brownish, due to the formation of degradation
products in ppm range.
Another important reason behind Nitrogen blanketing of solution
storage tank is to prevent explosion due to the release of residual
Hydrogen and other flammable gases from the solution when it is
transferred from system to the storage tank. So, do not transfer the
Rich solution to the storage tank.
Another important thing is maintain the proper temperature of
aMDEA premix in the solution storage tank as too low temperature
Leads to the precipitation of the activator.
Enriched aMDEA composed of 40% MDEA, 40% activator, 20% H2O
Below 200
C activator start to precipatate and solidifies at minus
10O
C

35. PROBLEMS FACED DURING OPERATIONS OF C02 REMOVAL SECTION
1. CO2 stripper Top Temperature fluctuation which should be maintained in range (940
C to 960
C)
Reason behind CO2 stripper Top Temperature fluctuations
1. During Level make in B301
2. Plant Load reduction & increase
3. Increase or decrease of the Carbon number of the NG feed as its composition
changes
Consequence of High CO2 stripper Top Temperature
High Temperature results from high heat duty of Stripper reboiler E302 which ultimately
overheating of aMDEA solution resulting in its degradation leads to the formation of heat stable
salts(HSS) which finally resulting in increase in the foaming tendency and lessens the CO2
Loading capacity of the solution
Consequence of Low CO2 stripper Top Temperature
Low temprature results in the insufficient stripping of semilean solution which
will results in the Lowering of the CO2 Loading capacity of the solution
1. CO2 stripper Top Temperature fluctuation which should be maintained in range (940
C to 960
C)
Reason behind CO2 stripper Top Temperature fluctuations
1. During Level make in B301
2. Plant Load reduction & increase
3. Increase or decrease of the Carbon number of the NG feed as its composition
changes
Consequence of High CO2 stripper Top Temperature
High Temperature results from high heat duty of Stripper reboiler E302 which ultimately
overheating of aMDEA solution resulting in its degradation leads to the formation of heat stable
salts(HSS) which finally resulting in increase in the foaming tendency and lessens the CO2
Loading capacity of the solution
Consequence of Low CO2 stripper Top Temperature
Low temprature results in the insufficient stripping of semilean solution which
will results in the Lowering of the CO2 Loading capacity of the solution

36. 2. High CO2 slip in the outlet of CO2 absorber F302
Possible reasons behind high CO2 slip in the outlet of CO2 absorber
1.Insufficient Semi Lean & Lean solution circulation rates
2. Higher %CO2 in the inlet gas to the absorber due to high plant load or high content of
heavier components in the NG feed.
3. Weak concentration of the aMDEA solution.
4. Low Temperature operation of the CO2 strippper Column.
5. Low Pressure operation of the CO2 absorber Column
2. High CO2 slip in the outlet of CO2 absorber F302
Possible reasons behind high CO2 slip in the outlet of CO2 absorber
1.Insufficient Semi Lean & Lean solution circulation rates
2. Higher %CO2 in the inlet gas to the absorber due to high plant load or high content of
heavier components in the NG feed.
3. Weak concentration of the aMDEA solution.
4. Low Temperature operation of the CO2 strippper Column.
5. Low Pressure operation of the CO2 absorber Column

37. FOAMING CAUSES
 Dust of activated carbon
 Suspended metallic compounds, which may disturb surface
tension
 Decomposition products
 Organic substances, grease, lube oil, paint bitumen epoxy
resins. Sulphides
 High temperature operation CO2 stripper reboiler which
resulting in HSS which are responsible for foaming

38. FOAMING INDICATORS
 High PDI across the beds in the Absorber and regenerator.
 High CO2 slip in the outlet process gas fro the absorber.
 Amine solution carry over with the product gas from the
absorber.
 Solution Hold up in bed packing.
 High instability in the levels of the absorber.
REMEDY FOR CHECKING FOAMING PROBLEM
 Provide Cartridge type of filter in U/S & D/S of activated
carbon filter bed having filtration pore size of 10 micron.
 Use antifoaming solution and ensure its continuous dosing of
antifoaming solution.

43. TRIPS & INTERLOCKS
INVOLVED
IN
CO2 REMOVAL SECTION

61. Some Common Mistake which can be possible in the CO2 removal section
High aMDEA circulation rate during plant load reduction which will result in the
Unnecessary demand heating steam in the CO2 stripper reboiler E302 and also
Leads to high power consumption on the account of high circulation rate.
Lower CO2 stripper top temperature which results in the high CO2 slip
High flow of the heating steam in the CO2 stripper reboiler E302 without
optimising the temperature of steam flow through TIC 316 to make the
availability of the Saturated steam in the CO2 stripper reboiler E302 during
start up.
Not maintaining Pressure in the HP Flash drum during the shutdown/tripping/
Startup of the Plant by not opening nitrogen on time leads to the difficulty in the
Transfer of level to LP Flash drum.