Methanol Synthesis Loop Troubleshooting INTRODUCTION TROUBLESHOOTING CONVERTER PROBLEMS OPERATING PROBLEMS CATALYST PROBLEMS TROUBLESHOOTING Common Problems APPENDIX Design Case Study #6752014GB/H

1. Plus Design Case Study
#6752014GB/H

2. CONTENTS
INTRODUCTION
TROUBLESHOOTING
CONVERTER PROBLEMS
OPERATING PROBLEMS
CATALYST PROBLEMS
TROUBLESHOOTING
Common Problems
APPENDIX
Design Case Study #6752014GB/H

3. Introduction
This presentation details some common problems that
can occur in a methanol synthesis loop.
Examples of Converter Problems
Example Operating Problems
Example Catalyst Problems
Some typical examples include, but are not limited to,
Rapid catalyst deactivation due to poisoning, Failure of
vessel components, High by-products levels, Temperature
excursions.

4. CONVERTER PROBLEMS

5. Quench Converter: “Cold Core” Problem
The term “Cold Core” usually refers to a problem observed
with the old Quench-style converter.
This traditional converter design (as shown on the right), in
which the synthesis reaction is quenched by the addition of
shots of cold gas between catalyst beds.
The quench is added to the gas reacting within the converter
by means of banks of transverse sparge pipes which have a
regular pattern of holes.
These spargers are in void space within a horizontal mesh
covered structure whose vertical shape is that of a lozenge

6. Quench Converter: “Cold Core” Problem
However, there have been problems due to the
phenomenon known as 'Cold Cores'.
This originates from portions of the catalyst that have a
high voidage and therefore a high gas flow whilst other
portions had a low voidage and therefore a low flow.
This causes a zone that is hot (due to low flow) and a
zone that is cold (due to high flow).
When shot is added to these hot and cold zones at an equal rate
through out the converter this causes a wide variation in the
temperature inlet the next bed. As there is essentially no cross
mixing within the converter, the effect passes down through the
whole converter leading to severe operational difficulties.

7. Quench Converter: Dust in Lozenges
Some quench converters suffered from blockage of the lozenge mesh,
see figure below which illustrates the design of the lozenge.
This can lead to problems of gas distribution between the hot bed exit
gas and cool shot gas.
This causes some problems in terms of operation since
such blockages prevented good mixing between the
effluent from the previous bed and the shot gas.

8. (TCC) Tube Cooled Converter Issue
A similar problem was also evident in early TCC (Tube Cooled
Converters), due to the spread of temperatures exit the tubes / inlet the
catalyst bed.
The problem here was that if the bed side temperature was
low due to high gas flowrates, then there would be a
localized reduction in the total heat transferred.
This causes a smaller than expected temperature rise up
the tubes, thereby reducing the inlet bed (turn)
temperature.
This causes the catalyst local to that tube to have a low
inlet temperature and therefore the bed temperatures will
be low.

9. (TCC) Tube Cooled Converter Issue
This problem was resolved through
design of a gas collection / mixing
device as shown to the right.
This then caused low tubeside
temperatures and a feedback loop
was developed.
The same effect occurred for zones
of low flow which led to high
temperatures etc.

10. (TCC) Tube Cooled Converter Design Issue
Generic Design
Tubesheet installed in the
bottom of the converter
Modified Design

11. (TCC) Tube Cooled Converter: Exit Collector
During the discharge of an Asia Pacific
Methanol Plant converter, it was found that the
mesh that should have been installed over the
exit collected had never been installed.
The collector consists (as illustrated to the
right) of a truncated cone which has 1 cm
wide holes in it side to allow for gas flow out
of the converter.
During the loading and normal operation, this cone was surrounded by
inert balls and therefore there was no catalyst ingress into the cone
and downstream outlet pipe.

12. (TCC) Tube Cooled Converter: Exit Collector
To rectify this situation, the outlet pipe had to
be cut and the catalyst emptied out; this spool
piece has been fitted with flanges.
Due to the problems associated with the
Manways (only 10” diameter), it has been
impossible to place a mesh over the outlet
collector and therefore at every catalyst
discharge the spool piece will have to be
removed.

13. OPERATING PROBLEMS
E1113E1112
E1110
V1107
Shot Gas
Converter
Inlet Gas
180 °C
0
0
0
0
Shot Flows
kNm3/hr
From C1102
210 °C
E1111
Loop start
Up Heater
100
bar
steam
TIC
060
HIC 007
240 °C
ShutOpen
180 °C
210
190
230 100
220
210
240 150
25 %
50 %

14. Operational Problems: Temperature
Excursions
On a loop trip that affects the circulator, there will be complete loss of
circulation around the loop.
Since there is still hydrogen and carbon oxides in the converter at
high temperature, there will be some methanol synthesis.
These reactions cause a volume decrease as outlined below, and
there will be a pressure reduction which will in turn lead to further
reactants being sucked into the converter.
CO2 + 3H2  CH3OH + H2O ΔH = +49 kJ/kmol
4 volumes 2 volumes
CO + 2H2  CH3OH ΔH = +90 kJ/kmol
3 volume 1 volume

15. Operational Problems: Temperature
Excursions
At an Americas Methanol plant, during a plant trip,
there was a temperature excursion.
This plant had a
separate circulator
and synthesis gas
machine, but in this
case, the minimum
stop on the valve
downstream of the
saturator water
heater (see figure)
failed and closed
shut.

16. Operational Problems: Failure of Mesh on
Exit of Quench Converters
The outlet collector of the Quench Converter is
covered in a mesh to prevent catalyst passing
through the collector during discharge.
During normal operation, the collector is
surrounded by inert balls.
However, if the mesh fails, inert balls and
catalyst will be passed into the outlet pipe of
the reactor.
This will lead to very high pressure drop, which
will cause the plant to be shut down and then
synthesis catalyst to be changed out.

17. Operational Problems: Leakage of Balls from
ARC Bottom Beds
In ARC converters, there is a sealing
ring at the bottom of the converter
which is aimed at preventing inerts
balls and subsequently catalyst
passing into the outlet pipe work and
then on to downstream equipment.
This ring is not welded to the shell (an
important feature of the ARC converter
which makes it simple to install).
Catalyst Support
Plates Individual / Separate
Catalyst Beds
Gas Mixing
System

18. Operational Problems: Oil Leaks
Many circulators use oil on the
seals to prevent damage to the
shaft of the machine.
This oil can and does leak into the synthesis gas and is passed
to the converter where it is converted into longer chained
alkanes commonly known on methanol plants as waxes.

19. Operational Problems: Impingement
Corrosion
Severe corrosion can result from the high
velocity impingement of liquid droplets
entrained in a gaseous stream on a metal
surface, even though the environment would
not be considered corrosive under still
conditions.
Mild and low alloy steels are among the metals which are
particularly susceptible to this form of attack.
Problems can often be solved simply by upgrading to a higher alloy.
Conditions which could lead to impingement attack occur in those
parts of the loop where condensation takes place, or condensate is
present.

20. Operational Problems: Impingement
Corrosion
The actions which must be taken to eliminate
this problem are:
 Reduction of gas velocity by increasing of
the inlet pressure to the compressor.
 Adjusting the level within the MUG separator
to maximize efficiency.
 Balancing the heat load in the cooler and
condenser prior to the MUG separator.

21. Operational Problems: Fouling of Crude
Cooler
There are two ways of fouling the crude
cooler.
The first is from wax formation which will
foul the tube side.
The second is from shell side fouling – normally due to
excessively high (50-60°C) return cooling water temperatures
leading to the hardness in the cooling water plating out on
the outside of the tubes

22. Operational Problems: Make Up Gas
Compositions
There is theoretical evidence that shows that synthesis
gases with high CO2 levels can lead to surface oxidation of
the methanol synthesis catalyst.
This in turn leads to an apparent loss of activity.
Comp Mole Frac (Methane) 0.111%
Comp Mole Frac (Nitrogen) 0.490%
Comp Mole Frac (Hydrogen) 69.028%
Comp Mole Frac (CO2) 6.054%
Comp Mole Frac (H2O) 0.094%
Comp Mole Frac (CO) 24.222%

23. Operational Problems: Boiler Feed Water
Quality
At a small South American methanol
plant there was a serious failure of the
tubes within their Steam Raising
Converter.
It was found that the cause was poor
boiler feed water quality which lead to
stress corrosion cracking of the tube
sheet to tube weld.

24. Operational Problems: Deposits on the
Synthesis Gas Machine and Circulator
At a South American methanol plant it was found that the
synthesis gas machine capacity was dropping; that is for a fixed
power usage, the flowrate through the machine dropped.
On inspection, it was found that there was a thick deposit on the
blades of the machine.
This was analysed and found to be a mixture of iron of nickel.
A similar effect was seen on the circulator.

25. Operational Problems: Methanol carryover
from catchpot
Some plants have suffered from liquid carry
over from the loop catchpot which can lead
to damage to the circulator.
This also increases the methanol content of
the gas entering the converter, thereby
giving a less favorable equilibrium position.

26. CATALYST PROBLEMS

27. Low Activity
There are a number of reasons
for apparent low methanol
synthesis catalyst activity
including:
Poisoning
Poor catalyst loading
Excessive localized breakage leading to flow mal-
distribution.
Catalyst Problems

28. Catalyst Problems
Sintering
Sintering is caused by operation at high temperatures which causes
the migration of copper between crystallites which causes a loss of
copper surface area as illustrated below;

29. Catalyst Problems
Sintering
The activity of the catalyst is
proportional to copper surface
area, and therefore with time,
activity is lost.
0.175
0.275
0.375
0.475
0.575
0 12 24 36 48
Time Months
Activity
The figure illustrates the typical effect of temperature on activity

30. Catalyst Problems
Catalyst Breakage
Catalyst breakage does occurring during loading and operation,
however it is rare that the breakage is so bad that it affects
production.
There are of course some instances were catalyst breakage does
cause a problem.

31. Catalyst Problems
Byproducts
In the synthesis loop there are a number of by-products
formed, including,
 Ethanol and higher alcohol’s such as propanol, butanol etc,
 Dimethyl ether,
 Acetone,
 Ketones including Methyl Ethyl Ketone and Methyl Iso
Propanyl Ketone,
 Methyl Formate,
 Alkanes from heptane through to C40’s,
 Methane.

32. Catalyst Problems
Byproducts
TMA
TMA or Tri Methyl Amine is a problem in the product
methanol since is gives the methanol a fishy smell –
methanol has a limit in all product specification that it
“shall be free from odour”.
TMA is formed by the reaction of ammonia produced in
the primary reformer with methanol formed in the loop.

33. Methanol Synthesis Catalyst: Poisoning
In order to avoid poisoning of the methanol synthesis catalyst, the following
limits MUST NOT be exceeded:
COMPONENT. LIMIT. Effect
Sulfur (as H2S). Such that the maximum accumulated S on the
catalyst charge be less than 0.20% of the total
mass of catalyst.
Poison
Chlorine (as HCl). Such that the maximum accumulated Cl on the
catalyst charge be less than 0.02% of the total
mass of catalyst.
Poison
Iron. Such that the maximum accumulated Fe on the
catalyst charge be less than 0.15% of the total
mass of catalyst.
Poison and wax
formation
Carbon
(elemental).
Absent. ∆P increase
Metals e.g. V, K,
Na.
Absent. Poisons
Nickel. Such that the maximum accumulated Ni on the
catalyst charge be less than 0.04% of the total
mass of catalyst.
Poison
Ammonia. 10 ppmv in the MUG. TMA formation
Ethene. 20 ppmv in the MUG.
Ethyne. 5 ppmv in the MUG.
Particulate
matter.
Absent. ∆P increase
Hydrogen
cyanide.
Absent. Poison

34. Methanol Synthesis Catalyst: Poisoning
Oxygen
Oxygen is not normally expected to be present in the
synthesis gas.
Although oxygen is not a catalyst poison, it is advised that the
level does not exceed 0.1% (molar) in the MUG, due to the
associated temperature rise and hydrogen consumption.
If the oxygen is present at a high enough level, it will lead to
bulk oxidation of the catalyst which will be seen as a loss of
apparent activity.

35. Methanol Synthesis Catalyst: Poisoning
Sulfur
There have been a
number of instances
of sulfur poisoning of
methanol synthesis
catalyst.
The mechanism of
sulfur poisoning is
highlighted 

36. Methanol Synthesis Catalyst: Poisoning
DMS Formation
DMS or Dimethyl Sulfide can be formed by the reaction of
methanol with hydrogen sulfide.
This is normally a problem on methanol plants for the
reformer since there is methanol in the purge gas added
to the HDS section.
The DMS is formed over the HDS catalyst and ZnO but is
not removed in the ZnO bed. Therefore is passes straight
on to the primary reformer where it causes hot banding.

37. Methanol Synthesis Catalyst: Poisoning
Ni/Fe Carbonyl
Iron and nickel react with carbon monoxide, under certain
conditions, to form metal carbonyls.
As the reaction is exothermic and involves a reduction of
volume in forming Fe(C0)5 or Ni(CO)4, the equilibrium
concentration of carbonyl falls with rising temperature
and increases rapidly with pressure.
Against this, the rate of reaction increases with
temperature.

38. Methanol Synthesis Catalyst: Poisoning
Ni/Fe Carbonyl
At 1 bar partial pressure of CO the rate of formation of
carbonyl is at a maximum in the range 60-100°C, and
decomposition occurs at temperatures over 150° C.
At 10 bars partial pressure of CO the rate of formation
reaches a maximum at 180-190° C.
The maximum rate is also higher, but there should be no
significant nickel carbonyl formation above 250° C at low
pressures.

39. Methanol Synthesis Catalyst: Poisoning
Chloride Poisoning
Chlorides are a very severe
poison for methanol
synthesis catalyst, however,
it is rare that they are a
problem.
The figure illustrates the
mechanism,

40. Methanol Synthesis Catalyst: Poisoning
HDS Catalyst of Choice
Some methanol plants have experienced methanation of
the CO from the hydrogen recycle gas in the HDS vessel.
The recommended catalyst to be used is CoMO but some
plants have removed the HDS catalyst completely,
thereby leaving themselves vulnerable to poisoning by
organic sulfur compounds.

41. Methanol Synthesis Catalyst: Poisoning
Catalyst Discharge
Methanol synthesis catalyst in its
reduced form is pyrophoric and as such
will heat up very rapidly to 600°C or more
in the presence of air.
There have been numerous instances of such incidents during
catalyst discharge.
With the advent of discrete catalyst bed converters such as the ARC
and CMD converter, a requirement for a safer method of catalyst
discharge has developed.

42. Methanol Synthesis Loop: Common Problems
Problem Effect Solution
Low Circulation Rate High Converter Pressure Drop. Check valve position.
Check converter DPI meter
Mesh damage and catalyst passing
into outlet pipe.
Catalyst breakage.
Low Heat Recovery Fouling of Exchanger. Chemically clean exchanger.
Low exit converter temperature.
Too little gas through heat recovery
exchanger.
High Converter
Temperature Spreads
Cold Core. Raise converter temperature.
Change catalyst and ensure good
catalyst loading.
Instability ARC Low temperatures in converter – large ATE’s exit
bed 1.
Drop circulation rate. If this fails then
raise converter inlet temperature by
0.5°C.
Instability TCC Operating below minimum stability point. Raise turn temperature.
High Turn Temperature in
TCC and loss of
Production
Too high a recycle rate.
Too high a UA.
Gag in circulator.
Modify converter internals.
High Temperature on Trip Methanation. De-pressure on loop trip.
Valve failure.
Increasing Crude Cooler
Exit Temperature
Wax deposition.
Shell side fouling.
Reduce CW flow and raise exit
temperature.
Chemically clean shellside.
Maximise CW flow to keep return CW
temperature down.
Low Catalyst Activity Catalyst poisoning
Temperature excursions.
Check for sulphur/chlorides etc.
De-pressure loop on trip.

43. Conclusions
To conclude, a number of
potential issues have been
highlighted that can affect both
the hardware (equipment) and
the catalyst in the methanol
loop

44. APPENDIX: Design Case Study #6752014GB/H

45. Design Case Study #6752014GB/H

46. Stream Component: Material Balances
Table 1

47. Stream Component: Material Balances
Table 2

48. Stream Component: Material Balances
Table 3

49. Stream Component: Material Balances
Table 4