METHANOL PLANT ARC RETROFIT Case Study

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Methanex Motonui
GBH Enterprises, Ltd.
METHANOL PLANT ARC RETROFIT
-
Methanol Casale Advanced
Reactor Concept (ARC) Converter
Retrofit CASE STUDY #10231406
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ACME – Methanol (Middle East)
For older methanol plants, efficiency is worse than for a modern plant
• To maximize profit we must improve either
– Plant efficiency
– Plant production rate
This case study highlights the revamp of a Middle Eastern Methanol Plant ARC
converter with part IMC internals, to improve efficiency and production; with no
CO2 addition to the Synloop, and with CO2 addition to the Synloop.
- 250 TPD CO2
- 500 TPD CO2
Note: ARC refers to Methanol Casale Advanced Reactor Concept (ARC)
Converter (See Fig 1. ARC Converter below)
IMC refers to Casale Isothermal Methanol Converter (IMC)
(See Fig 2. IMC Converter below)
OVERVIEW
The nominal 2500 MTPD ACME methanol plant currently operates with a
Methanol Casale-JMC ARC converter retrofit.
Previous studies have looked at a further revamp involving overall replacement
of the ARC internals with those forging Methanol Casale’s IMC plate-cooled
system.
This additional study now looks at a part retrofit of the 5-bed converter by way of
replacing only the bottom two ARC beds (ca. 60 % of total catalyst volume) with
IMC plate-based internals.
It is envisaged that CO2 will become available for injection into the synloop. Two
foreseen cases are examined; one with the addition of 250 TPD CO2, the other
500 TPD.

Figure 1.

Figure 2
.

DESIGN BASIS
The pertinent assumptions to this work are as follows:
General loop layout as used for previous IMC Vs. ARC revamp study.
Key temperature and pressure values as for previous study
e.g. Converter inlet pressure = 81.2 bar(g)
Converter quench temperature = 126 ºC
Separator temperature = 37 ºC
Synthesis loop make-up gas (MUG) composition:
CO = 14.47 mol. %
CO2 = 7.97
H2 = 73.39
CH4 = 3.12
N2 = 1.05
Flowrate = 15810 kgmol/h
155491 kg/h
The recirculation flowrate (from separator unit) utilized in the simulations was
maintained at the value used in the previous IMC study (Recirculation / MUG =
4.2 mol/mol or {MUG + Recirculation} / MUG = 5.2). This recirculation rate is
also maintained for the cases involving CO2 addition. The addition of this ‘heavy’
CO2 gas will significantly alter the density of the fluid and may invoke a power
limit on the circulator, reducing the obtainable recirculation rate, unless prior up
rating of this unit is carried out.
Total catalyst volume maintained as for ARC reactor (201.5 m3
reduced, ca. 229
m3
installed) neglecting additional volume occupied by IMC internals applied to
the bottom two discretized beds (ca. 121 m3
reduced), at this stage in the study.
Pressure drop across reactor maintained at ca. 1 bar, similar to that incorporated
in the 5-bed ARC simulations.
This current study does not incorporate the impact of CO2 addition, which may or
may not become available or indeed utilized.
The general configuration set-up of this part IMC revamp involved two main
possibilities regarding the connection of the warmed IMC plate-side effluent gas.

Firstly this stream may be mixed with the gas that has by-passed the calculated
IMC plate ‘coolant gas’ feed stream and together enters the first bed of the
existing ARC part of the retrofit. Another option exists which involves connecting
the IMC plate-side effluent stream to the existing ARC total quench flow. Based
on pipe sizing and capacity of existing equipment, either one of these options
may not be practically feasible without the need for extensive modifications. This
current study investigates both of the aforementioned options in view of
comparison of their general loop productivity attributes.
CO2 Addition to Reformer/Loop
• If local source of CO2 is available then can be added to either reformer or the
loop
• Addition to the reformer does mean synthesis gas composition will be more
carbon rich
– Potential issues with metal dusting downstream of the reformer in waste
heat boiler
• In either case, molecular weight of circulating gas is increased and circulation
rate will be reduced
– Often this effect is overlooked and in reality predicted production rates
will not be achieved
There is an optimum amount of CO2 that can be added
• As more CO2 is added then carbon efficiency does drop
• But production steadily increases
– However, the reduction in recycle ratio can be so large that the
production rate is reduced
– Effect is worse if recycle ratio is low to start with
• CO2 addition to the reformer will produce more incremental methanol per ton of
CO2

SIMULATION RESULTS
The results of a preliminary simulation study of this concept are depicted in the
tables below (Tables 1 - 7). The simulation results from the current ARC loop
flowsheet are included as the base case comparison, together with previously
predicted results for a full IMC revamp.
a) Without CO2 Addition
Table 1. IMC Plate-side Effluent to Bed 1 ARC, No CO2 Addition.
Parameter
Base case 5-
Bed ARC
Internals
3-Bed ARC +
Part IMC
Internals
*
Full IMC
Internals
EO
R (4
yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4
yrs)
SOR
(0 yrs)
Recycle Ratio
(Recirculation/MUG)
4.2 4.2 4.2 4.2 4.2 4.2
Methanol Production
(MTPD in Crude)
257
3
2633 2644 2662 2653 2661
Carbon Efficiency
(mol.%)
94.3 96.5 96.9 97.6 97.3 97.5
Production Increment
Over Existing ARC
(MTPD)
- - 71 29 80 28
*
Original IMC revamp study utilized 220 m3
reduced catalyst volume (250 m3
installed). Similar results obtained for an inventory of 201.5 m3
reduced (229 m3
installed) as used in this work, especially under SOR conditions. At EOR, the
make is reduced by up to 11 MTD (500 TPD CO2).
Also, the inlet calculated temperature to the IMC at EOR was ca. 120 ºC arising
from the cold-gas interchanger, compared with 126 ºC used in this current study.
This lower temperature would yield benefits with all of the reactor configurations
including the existing ARC (quench temperature), although not so readily
obtainable without increased cooling capacity because the reactor outlet
temperatures are higher than those resulting from a full IMC, especially with the
ARC.

The calculated flows through the hot-gas interchanger are significantly less when
compared with the base case ARC (e.g. at EOR mass flow = 34064 kg/h
compared with 127040 kg/h for base case ARC).
Therefore, the omission of the hot-gas interchanger in the loop was briefly
examined. As a consequence of this configuration change, the saturator water
heater originally operating in parallel to the hot-side of the aforementioned
interchanger will experience an even greater heat load increase than without the
interchanger, when compared to the base case ARC. The figures are included in
Table 2.
Table 2. IMC Plate-side Effluent to Bed 1 ARC, No CO2 Addition. (No Hot-Gas
Interchanger).
Parameter
Base case 5-
Bed ARC
Internals
3-Bed ARC +
Part IMC
Internals
3-Bed ARC +
Part IMC
Internals
(No Hot-Gas
Interchanger)
Full IMC
Internals
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
Recycle Ratio
(Recirculation/MUG)
4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2
Methanol Production
(MTPD in Crude)
2573 2633 2644 2662 2653 2663 2653 2661
Carbon Efficiency
(mol.%)
94.3 96.5 96.9 97.6 97.2 97.6 97.3 97.5
Production
Increment Over
Existing ARC
(MTPD)
- - 71 29 80 30 80 28
Parallel Heat
Exchanger (To Hot-
Gas Interchanger)
Duty (KW)
59200 60700 61500 61700 61700 61700 59000 59130

Table 3. IMC Plate-side Effluent to ARC Quench Flow, No CO2 Addition.
Parameter
Basecase 5-
Bed ARC
Internals
3-Bed ARC +
Part IMC
Internals
Full IMC
Internals
EO
R (4
yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4
yrs)
SOR
(0 yrs)
Molar Recycle Ratio
(Recirculation/MUG)
4.2 4.2 4.2 4.2 4.2 4.2
Methanol Production
(MTPD in Crude)
257
3
2633 2643 2661 2653 2661
Carbon Efficiency
(mol.%)
94.3 96.5 96.8 97.6 97.3 97.5
Over Existing ARC
(MTPD)
- - 70 28 80 28
b) With CO2 Addition
i) 250 TPD CO2
Table 4. IMC Plate-side Effluent to Bed 1 ARC, 250 TPD CO2.
Parameter
Base case 5-
Bed ARC
Internals
3-Bed ARC +
Part IMC
Internals
*
Full IMC
Internals
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR (0 yrs)
Recycle Ratio
(Recirculation/MUG)
4.2 4.2 4.2 4.2 4.2 4.2
Methanol Production
(MTPD in Crude)
2687 2787 2802 2830 2812 2825
Carbon Efficiency
(mol.%)
92.3 95.8 96.3 97.2 96.6 97.1
Over Existing ARC
(MTPD)
- - 115 43 125 38

Table 5. IMC Plate-side Effluent to ARC Quench Flow, 250 TPD CO2.
Parameter
Base case 5-
Bed ARC
Internals
3-Bed ARC +
Part IMC
Internals
Full IMC
Internals
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR (4
yrs)
SOR
(0 yrs)
Molar Recycle
Ratio
(Recirculation/MU
G)
4.2 4.2 4.2 4.2 4.2 4.2
Methanol
Production (MTPD
in Crude)
2687 2787 2797 2827 2812 2825
Carbon Efficiency
(mol.%)
92.3 95.8 96.1 97.1 96.6 97.1
Production
Increment Over
Existing ARC
(MTPD)
- - 110 40 125 38
ii) 500 TPD CO2
Table 6. IMC Plate-side Effluent to Bed 1 ARC, 500 TPD CO2.
Parameter
Base case 5-
Bed ARC
Internals
3-Bed ARC +
Part IMC
Internals
*
Full IMC
Internals
EO
R (4
yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR (4
yrs)
SOR
(0 yrs)
Recycle Ratio
(Recirculation/MUG)
4.2 4.2 4.2 4.2 4.2 4.2
Methanol Production
(MTPD in Crude)
277
1
2929 2946 2991 2955 2983
Carbon Efficiency
(mol.%)
89.
6
94.7 95.3 96.7 95.6 96.5
Over Existing ARC
(MTPD)
- - 175 62 184 54

Table 7. IMC Plate-side Effluent to ARC Quench Flow, 500 TPD CO2.
Parameter
Base case 5-
Bed ARC
Internals
3-Bed ARC +
Part IMC
Internals
Full IMC
Internals
EO
R (4
yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR
(0 yrs)
EOR
(4 yrs)
SOR (0
yrs)
Molar Recycle Ratio
(Recirculation/MUG)
4.2 4.2 4.2 4.2 4.2 4.2
Methanol Production
(MTPD in Crude)
277
1
2929 2936 2987 2955 2983
Carbon Efficiency
(mol.%)
89.
6
94.7 95.0 96.6 95.6 96.5
Over Existing ARC
(MTPD)
- - 165 58 184 54

SUMMARY OF RESULTS
As envisaged, the simulation-based study has shown that the part IMC retrofit
yields productivity benefits to the existing ARC-based synthesis loop of the
ACME Methanol plant, with and without CO2 addition. However, with addition of
CO2 to the loop, the production benefits are amplified.
Both of the design configurations for the connection of the warmed IMC plate-gas
effluent give comparable results especially for the cases without CO2 addition.
With CO2 addition, the connection of the plate effluent to bed 1 ARC generates
the higher production figures (ca. 5 %).
In quantitative terms, the increase in crude make is ca. 30 MTPD (1.1 %) at SOR
and 70-79 MTPD (2.7-3.1 %) at EOR, when compared to the existing 5-Bed ARC
productivity for the cases without CO2 addition. With reference to a complete IMC
overhaul, the part-IMC design simulation results show the production benefits to
be very comparable at SOR conditions and between ca. 88-100 % (No hot-gas
interchanger for 100 % case) of those at EOR, with further possibilities to explore
of reducing ARC quench temperatures via by-passing of the cold-gas
interchanger.
For the cases involving CO2 addition, the benefits of the part-IMC benefit are
greatly enhanced. Depending on the amount of CO2 injected into the synloop
(250 or 500 TPD CO2) the increase in methanol make is between 43-62 MTPD at
SOR (1.5-2.1 %) and 115-175 MTPD at EOR (4.3-6.3 %). Compared with the
full-IMC projections that used a 120 ºC inlet temperature, this amounts to at least
as good or even better performance at SOR and between 92-95 % of the gains
at EOR. Due to the use of a EOR inlet temperature of 120 ºC also fixed at SOR,
this results in an non-fully ‘optimized’ full-IMC design which is why the part-IMC
revamp is so very similar or even better at SOR. Naturally a fully ‘optimized’ IMC
utilizing a significantly lower inlet temperature at SOR would generate the highest
production figures.
It should also be noted that the full IMC simulations were themselves performed
with an additional 18.5 m3
catalyst volume which produces more methanol,
notably at EOR (up to an extra 11 MTPD crude methanol with 500 TPD CO2
addition).

CONCLUSION
In conclusion, the data obtained from this ACME Methanol plant case study,
indicate that the fundamental benefits of a full IMC retrofit are also exhibited to a
high extent, especially with CO2 addition, by converting only part of the ARC
reactor with IMC internals (bottom two beds - around 60 vol.% of the catalyst
inventory), with the advantage being that the package could be offered to the
POTENTIAL customer at a reduced capital cost.

METHANOL PLANT ARC RETROFIT Case Study

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