methanol plant arc retrofit case study

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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

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)

2573 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



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


- - 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


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/MUG) 4.2 4.2 4.2 4.2 4.2 4.2


2573 2633 2643 2661 2653 2661



- - 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



*Full IMC Internals

EOR (4 yrs)

SOR (0 yrs)

EOR (4 yrs)

SOR (0 yrs)

EOR (4 yrs)

SOR (0 yrs)


Methanol Production (MTPD in Crude) 2687 2787 2802 2830 2812 2825



- - 115 43 125 38



Table 5. IMC Plate-side Effluent to ARC Quench Flow, 250 TPD CO2.

Parameter



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/MUG)

4.2 4.2 4.2 4.2 4.2 4.2


2687 2787 2797 2827 2812 2825



- - 110 40 125 38

ii) 500 TPD CO2 Table 6. IMC Plate-side Effluent to Bed 1 ARC, 500 TPD CO2.

Parameter



*Full IMC Internals

EOR (4 yrs)

SOR (0 yrs)

EOR (4 yrs)

SOR (0 yrs)

EOR (4 yrs)

SOR (0 yrs)



2771 2929 2946 2991 2955 2983

Carbon Efficiency (mol.%)

89.6 94.7 95.3 96.7 95.6 96.5


- - 175 62 184 54



Table 7. IMC Plate-side Effluent to ARC Quench Flow, 500 TPD CO2.

Parameter



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/MUG) 4.2 4.2 4.2 4.2 4.2 4.2


2771 2929 2936 2987 2955 2983

Carbon Efficiency (mol.%)

89.6 94.7 95.0 96.6 95.6 96.5


- - 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

Technology

total catalyst volume

imc converter

situ exsitu sulfiding

arc internals

mtpd acme methanol plant

older methanol plants

arc beds

acme methanol middle