metanol

PEP Process Module 1 25 Aug 1999SRI Consulting

Methanol from Natural Gas by ICI’s LP Process(High Efficiency Design)

Aspen Model Documentation

Index

• Process Summary

• About This Process

• Process Definition

• Process Conditions

• Physical Property Models and Data

• Chemistry/Kinetics

• Key Parameters

• Selected Simulation Results:BlocksStreams

• References


Process Summary

The Methanol from Natural Gas by ICI’s LP (Low Pressure) Process Model illustrates the use of ASPEN PLUSto model a Methanol reforming and synthesis process using ICI’s LP process. The design capacity for a typical plant is825,000 Metric Ton/yr, at 0.90 stream factor. The whole process includes three sections: natural gas reformingsection, methanol synthesis section, and distillation section. The final product is Methanol.


About This Process

There are three types of processes commonly employed for the manufacture of Methanol fromNatural Gas. These are the ICI’s LP Process, the Lurgi Combined Reforming Process, and the ICI’s LCMProcess. Table 1 provides basic information on these processes and examples of some of the companies thathave commercialized the process technology. All of these processes use Ni based catalyst in Natural Gasreforming reactors and Cu based in the Methanol synthesis reactor.

Table 1. Summary of Processes for Methanol Synthesis

The original ICI process rejected substantial quantities of heat energy into cooling water and air. In late 1974,ICI introduced the ‘Reduced Energy Concept’. Several changes were made at that time and thereafter:

• Replacement of LP stream reboilers in the distillation train by ones that were heated by reformerprocess gas.

• Inclusion of a boiler feedwater heating system in the reformer gas cooling system and in the methanolsynthesis loop, to recover energy which had been discarded in the original 1967 design.

• Enhanced heat recovery from flue gases by the introduction of an air preheater in the reformerconvection section.

The “Improved Distillation” design was added to the design package in 1977. Instead of the conventionaltwo-column system, a four-column arrangement was deployed, which produced chemical grade overhead and

Process Reactor Catalyst CompanyPrimary Secondary Temp. Pressure Reforming Synthesis

ICI LP Steam saturated None 520 F 1500 psi ICI 574 ICI 100% Natural Gas Properietaryflow Cu based

Lurgi Steam saturated Primary reforming 500 F 1480 psi Ni based Cu based TennecoCombined 50% Natural Gas gas, 50% Natural Productivity Chemical,

flow Gas flow, and is 1kg / liter Sabah Gaspure Oxygen Catalyst / hr Industries

Steam/Carbon = H2 : CO =2.5:1 2.02 :1

ICI LCM Steam saturated Primary reforming 220-270 C1100 psi Primary Proprietary BHP100% Natural Gas gas and pure Proprietary Cu based Petroleumflow Oxygen Ni based Productivity ConocoSteam/Carbon = H2 : CO = Secondary is 1kg / liter1.42 : 1 2.02 :1 Proprietary, Catalyst / hr

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rejected water in the bottom stream. The first of these columns is operated under pressure. This permits thecondensation of overhead vapor at a sufficiently high temperature for use as reboil energy in the next column,which operates at near atmospheric pressure. The pressure column produces slightly impure methanol, rejectswater that is virtually methanol free and removes most of the higher alcohols as a sidestream. Theatmospheric pressure column does the final refining. The reduction in energy is obtained through the use oflower reflux ratios.

The High Efficiency Design (1979) version of the process introduced additional energy saving features:

• The use of a “feedstock saturator”. The natural gas is scrubbed countercurrently with hot water.Energy for heating the water is low grade and comes mainly from the methanol synthesis loop.

• A greater extent of heat recovery from the reformer product, flue gas, and synthesis product streams.


Process Definition

An ASPEN PLUS model is developed to simulate the ICI’s LP process. The whole process includesthree sections: natural gas reforming section, methanol synthesis section, and distillation section.

1) The Reforming Section:In the ICI LP process, there is only one reformer. Unlike the Lurgi or LCM process, there is also only

steam reforming process in this section. A feedstock water saturator (C101) is employed to furnish 50% ofthe process reformer steam. The natural gas feed is desulfurized in M101 with active carbon. Preheating ofthe reformer reactants to 1000F takes place in E101, and the reaction is carried out in the radiant section ofreforming furnace F101. The reformed stream, stream 6, comes out of F101, and through a series of heatexchangers (E105, 306, 106, 107, 108, 109, 110), flows into the synthesis section. The reforming gas stream6 comes out of the reformer at a temperature of 1600 F, and leaves the section at a temperature of 100 F.V102, V103, V104 and V105 separate the water like de-saturators, and discharge the water into the recyclestreams 32 and 10.

2) The Synthesis Section:The synthesis section consists of reactor R201 and heat exchangers and flashes. The Syngas stream

comes out of the reforming section and is compressed by K201 to 1500 psia. After exchanging heat with thesynthesis reactor R201 product in heat exchangers E202, E203, E204 and E205, the syngas reacts in R201 toproduce crude methanol, stream 17. V201 and V202 separate uncondensed gases. The impure methanolsynthesized, stream 20, flows to the distillation section for purification.

3) The Distillation Section:The distillation section includes four distillation towers, C301, C302, C303 and C304. The overhead

vapor from C301 is cooled in E302, and the condensate, mainly methanol with some light ends, is returned asreflux. The uncondensed vapor mainly consisting of dimethyl ether is removed from reflux drum V301 toblend with the synthesis section purge. The bottom product from C301 is fed to C302, the refining column,which is operated at 100 psia at the base. Most of the water is separated in the bottom, stream 26, and the wetmethanol is further purified in C303. C304 picks up some methanol left in the bottoms of C303 which is thensent to the final product, stream 31.


Process Conditions

The process conditions are as listed in Table 2.

Table 2. Process Conditions

Component Description

Methane Raw materialCO2 Inert gas and Intermediate productCO Intermediate productHydrogen Intermediate productNitrogen Inert gasOxygen Reforming componentEthane Raw materialPropane Raw materialMethanol ProductDimethyl Ether Intermediate productN-Butanol Intermediate productAcetone Intermediate productWater Reforming component

Operating Conditions

ReformerInlet Pressure: 295 psiaTemperature: 1460 F

Synthesis ReactorPressure: 1500 psiaTemperature: 520 F

All reactors use ASPEN PLUS REQUIL and RSTOIC reactors.


Physical Property Methods and Data

The NRTL-RK thermodynamic method is used with Henry’s Law. All the major binary interaction parameters are in theAspen data bank.


Chemistry/Kinetics

Primary Reformer: F101

Reaction Conversion/Extent

CH4 + H2O = CO2 + 4 H2 2543.41 lbmol/hrCH4 + H2O = CO + 3 H2 3884.45 lbmol/hrC2H6 + 2 H2O =2 CO + 5 H2 100% Conversion of EthaneC3H8 + 3 H2O =3 CO + 7 H2 100% Conversion of Propane

Aspen’s RSTOIC model is used to model this reactor.

Combustion Reactions in Reformer Furnace: F101S

Reaction Conversion/Base Component

CH4 + 2O2=CO2+2H2O 0.995/CH42C2H6+7O2=4CO2+2H2O 0.994615/C2H62CO+O2=2CO2 1/CO2H2+O2=2H2O 0.998/H22CH3OH+3O2=2CO2+4H2O 0.998/CH3OHC3H8+5O2=3CO2+4H2O 0.9945/C3H82CH3OCH3+6O2=4CO2+6H2O 1/CH3OCH3H2S+1.5O2=SO2+H2O 1/H2S

Aspen’s RSTOIC model is used to model this reactor.

Synthesis Reformer: R201

Reaction Reaction’s Extent

CO + 1 H2O = CO2 + 1 H2 55.8 F Temperature ApproachCO2 + 3 H2 = CH3OH + 1 H2O 27 F Temperature Approach2CH3OH =DM-Ether + H2O 0.441 lbmol/hr4CO + 8 H2 = 1 Butanol + 3 H2O 1.764 lbmol/hr3CO + 5 H2 = 1 Acetone + 2 H2O 0.661 lbmol/hr

Aspen’s REQUIL model is used to model this reactor.Molar Extent is used to control the low yield of by-products.


References

58074 Scott, R.H. (to ICI), “Process for Purifying Methanol by Distillation” US 4,013,521(March 22, 1977)

58097 Pinto, A. (to ICI), “Methanol Distillation Process” US 4,210,495 (July 1, 1980)58111 Dunster, M., et al., “Reduced Natural Gas Consumption for Methanol Production,” Inst.

Chem. Eng. Symp. Ser. 44,5 (1976), 47-5258144 Pinto, A. et al., “Optimizing the ICI Low-Pressure Methanol Process” Chem. Eng., 84,

14, July 1977, 102-858145 Pinto, A. et al., “Impact High Fuel Cost on Plant Design” Chem. Eng., 84, 14, July

1977, 95-10058150 Masson, J.R. “Energy Saving in LP Methanol Industries,”, March 3-8, 1980415230 Pinto, A. (to ICI), “Steam Hydrocarbon Process” US 4,072,625 (Feb 7, 1978)415329 Camps, J.A., et al. “Synthetic Gas Production for Methanol”: Current and Future Trends,

“Am. Chem. Soc., Symp. Ser., 116 (1979, publ. 1980), 123-46

472134 Rowell, G. M. (to Humphreys & Glasgow), “Synthesis Gas Production”, British2,066,841 (July 15, 1981)

472157 Supp, E. “Improved Methanol Process”, “Hydrocarbon Processing”, 60, 3 (March 1981)71-5

472158 “Methanol (ICI Low Pressure Process”, “Hydrocarbon Processing” 60, 11 (November1981), 183.

472165 Strelzoff, S., “Methanol: Its Technology and Economics”, paper in “MethanolTechnology and Economics”, Chemical Engineering Progress” Symp.Ser., 66, 98 (1970), 54-68.

472167 Dybkjaer, Ib., “Topsoe Methanol Technology”, Chem. Econ. Eng. Review, 13, 6 (149),(June 1981), 17-25.

475322 Brennan, J. R., “Recover Power with Hydraulic Motors”, Hydrocarbon Processing, 60, 7(July 1981) 72-4.

Reports

Satish Nirula , Methanol , Process Economics Program Report No. 43 B (August 1982).

Report by: Sherif AlyAugust 25, 1999

metanol

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