Autothermal reforming conventional processes

Today, different processes (steam reforming, autothermal reforming, partial oxidation, gasification) are available and commercially mature for hydrogen production from natural gas or coal. These processes would have to be combined with technologies for C02 capture and storage (CCS), to keep the emissions profile low. A power plant that combines electricity and hydrogen production can be more efficient than retrofitted C02 separation systems for conventional power plants. 

Figure 10. A comparison of hydrogen to carbon monoxide molar ratios for different processes for producing hydrogen from fossil fuels (POX = partial oxidation ATR = autothermal reforming CR = conventional steam reforming UMR = unmixed reforming).

Most new large methanol plants are built in areas where low cost natural gas is available. If the synthesis gas is produced by the conventional one-step process, with a steam reformer only, the module will always be around 3 with natural gas as feed. Process studies (Soegaard-Andersen, 1989) have shown that for capacities above 1000-1500 t/d it is economical to adjust the module to the optimum value by adding an oxygen-fired autothermal reformer downstream the steam reformer as shown in Figure 12. This two-step reforming process (Dybkjaer et al., 1985) is similar to the well-known process lay-out with a primary and secondary reformer used in ammonia plants. 

The equilibrium of the methanol synthesis reaction severely limits the conversion in the conventional process. The equilibrium conversion is very sensitive to temperature. The high recycling rate is costly and requires oxygen instead of air in the autothermal reforming or partial oxidation step. The development of low-temperature and continuous methanol removal processes mentioned brieffy in Section 1.3.1, would be very attractive [6365]. Hi single-pass conversion could also be attained with a two-step process methanol carbonylation to methyl formate followed by methyl formate hydrogenolysis to 2 mol methanol [6669]. Research in these areas has yielded promising results. 

The above reactions proceed also in the so-called rich-gas processes of British Gas and Lurgi/BASF, which convert naphtha with steam in autothermal reactions in a vessel filled with a special nickel-containing catalyst. It was formerly successfully used for town gas production from naphtha. This reaction may also used as pre-reformer ahead of a conventional tubular steam reforming furnace to convert higher hydrocarbons at low temperature and low S/C ratio into a methane reach gas which can than be reformed in the primary reformer with a standard methane reforming catalyst instead of an alkalized catalyst (Section 4.1.1.3.1). 

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