Synthetic Gas Production for Methanol - American Chemical Society

7 Synthetic Gas Production for Methanol: Current and Future Trends J. A. CAMPS and D. M. TURNBULL

Downloaded by CORNELL UNIV on August 2, 2016 | http://pubs.acs.org Publication Date: March 26, 1980 | doi: 10.1021/bk-1980-0116.ch007

Davy Powergas Inc., P.O. Drawer 5000, Lakeland, FL 33803

Methanol is the one of most easily made organic

compounds and is synthesized from a gaseous mixture of carbon monoxide and hydrogen. CO + 2H2

CH3OH

The carbon monoxide/hydrogen mixture is traditionally referred to as "Synthesis Gas" and typically includes

small percentage of CO2, CH4, nitrogen and other inerts.

Thus, although hydrogen is used in methanol production,

it can be taken straight from the steam-hydrocarbon reformer and does not require further purification and treatment as in the case of pure hydrogen production or ammonia production. The economics of methanol production are significantly affected by the thermal integration of the reformer (or other gas generation unit) with the rest of the plant. Synthesis gas may be prepared from any feedstock containing any ratio of carbon and hydrogen and oxygen and not extreme levels of sulphur and nitrogen. Such a definition covers feedstocks ranging from wood, biomass, coal and heavy fuel oils, to naphtha and natural gas.

Naphtha was the initial feedstock for the ICI low pressure methanol process because it was available to ICI at the time they developed the process. However, it is also the most ideal feedstock from a stoichiometric view-

point; as evidenced by the following reaction.

"CH2" + H2O

CO + 2H2

CH3OH

Naphtha + Steam

Synthesis Gas

Methanol

Depending upon the stoichiometry of the feedstock source, a stoichiometric synthesis gas is achieved by adjusting the carbon/hydrogen ratio via shift conversion 0-8412-0522-1/80/47-116-123$06.00 © 1980 American Chemical Society Smith and Santangelo; Hydrogen: Production and Marketing ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

124

HYDROGEN: PRODUCTION AND MARKETING

and C0~ removal or C0? addition. Alternatively, within certain limits, the flexibility of the ICI LP methanol

process allows a hydrogen rich gas to be economically fed to the synthesis loop. The excess hydrogen is purged from the loop and burned as fuel. The following is a brief description of synthesis gas

generation from the various accepted feedstocks.


Reforming of Natural Gas

By far the most widespread method of producing synthesis gas for methanol production today is via steam reforming of naphtha and lighter hydrocarbons . The process routes for both natural gas steam reforming and naphtha reforming are virtually identical, so we shall consider only natural gas reforming.

Since the ICI LP methanol process was

first introduced in 1967, the design has been modified to enhance energy recovery as it became more economic to do so due to increasing energy costs. Davy's latest process flowsheet is illustrated in Figure 1. Figures 2 and 3 are

photographs of two natural gas based methanol plants built

by Davy.

Brief Process Description of Davy's Latest High Efficiency Design. Natural gas is desulfurized over an

activated carbon bed or zinc oxide to remove sulfur below

0.2 ppm, suitable for natural gas reforming.

The desulfurized gas is then countercurrently contacted against hot water which heats the feedstock and saturates it with water vapor providing 49% of the process steam

requirements. (Over 60% for a plant with C0~ addition). The feedstock is then preheated to the reformer inlet conditions, and the balance of the process steam is added. The mixed steam/feedstock mixture is then passed to the tubular reformer where it is reformed to synthesis gas

over a nickel catalyst contained in high alloy tubes. This reaction is highly endothermic, and the heat of reaction is supplied by firing natural gas and purge gas in a fire box external to these tubes.

The heat is then

transferred through the tube wall into the catalyst packed reaction zone.

The reformed gas leaves the furnace at a high temperature where high grade heat is recovered successively to a reformed gas boiler, steam superheater process feedstock heater and boiler, feedwater heater.

The reformed gas then passes to

the distillation area where low grade heat is efficiently recovered via column reboilers and a demineralized water heater.

Finally, the reformed gas passes to the reformed gas cooler where the gas is cooled from 150°F to 100°F against cooling water.

Smith and Santangelo; Hydrogen: Production and Marketing ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

7. camps and turnbull

Synthetic Gas Production from Methanol

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