Reforming autothermal process

The aim of this study is to convert as much as the hydrogen in the fuel into hydrogen gas while decreasing CO and CH4 formation. Process parameters of fuel preparation steps have been determined considering the limitations set by the catalysts and hydrocarbons involved. Lower S/C (steam to carbon) ratios favor soot and coke formation, which is not desired in catalytic steam and autothermal reforming processes. A considerably wide S/C ratio range has been selected to see the effect on hydrogen yield and CO formation. 

The promising and efficient reforming options are the steam reforming and autothermal reforming processes, as can be seen in Table 6. We can compare these two efficient systems in order to observe the equilibrium behavior in the reforming section of the whole micro CHP system. Here, the results of the most efficient options, namely natural gas with steam reforming and autothermal reforming. 

The ATR (Autothermal Reforming) process makes CO-enriched syngas. It combines partial oxidation with adiabatic steam-reforming and is a cost-effective option when oxygen or enriched air is available. It was developed in the late 1950 s for ammonia and methanol synthesis, and then further developed in the 1990 s by Haldor Topspe2. The difference between Steam Methane Reforming (SMR) and ATR is in how heat is provided to activate the endothermic steam reforming reaction. In SMR, the catalyst is contained in tubes that are heated by an external burner. 

The CAR (Combined Autothermal Reforming) process is used to make syngas from light hydrocarbons, and the heat is provided by partial oxidation in a section of the reactor. It was developed by Uhde and commercialized at an oil refinery at Strazske, Slovakia, in 19912. 

The ATR (Autothermal Reforming) process makes CO-enriched syngas. It combines partial oxidation with adiabatic steamreforming. It was developed in the late 1950s for ammonia and methanol synthesis, and then further developed in the 1990s by Haldor Topsoe.2... 

In an autothermal reforming process, lOOOkmol/h of methane at 20°C is compressed to 10 bar, mixed with 2500 kmol/h of saturated steam and reacted with pure oxygen to give 98% conversion of the methane. The resulting products are cooled and passed over a medium-temperature shift catalyst that gives an outlet composition corresponding to equilibrium at 350°C. 

It should be noted that these space velocities are similar to those typically found in autothermal reforming (ATR) so that catalyst volumes will not be excessive compared to autothermal reforming processes. Catalyst activity was found to be reasonably stable for the short duration tests in this work. However, the extremely endothermic nature of the reaction and the integral operation of the test reactor made it difficult to extract reaction kinetics. A new test reactor design was developed and fabricated, and work is in progress to obtain simplified kinetics for the gasoline steam reforming reaction adequate to model the catalytic process in the plate reactor simulation. 

In the autothermal reforming process (ATR), a conversion of hydrocarbon feedstock with oxygen (as oxygen, air, or enriched air) takes place in combination with the conversion of hydrocarbons with steam (Fig. 7). ATR is basically a combination of HSR and partial oxidation (POx) technology (19). 

Lindstrom et al. [55] developed a fixed-bed autothermal methanol reformer designed for a 5 kW fuel cell operated with copper/zinc oxide catalyst doped with zirconia. The system was started without preheating from ambient temperature by methanol combustion in a start-up burner, which was operated at sixfold air surplus to avoid excessive temperature excursions. Because significant selectivity toward carbon monoxide was observed for the autothermal reforming process, a WGS stage became mandatory [55]. 

For processes on a smaller scale, the entire autothermal reforming process is usually performed in a catalyst bed. Alternative concepts are the catalytic prereforming of higher hydrocarbons or cool flames (see Section 3.5 and 5.1.5). 

FIGURE 9-28. Schematic representation of an autothermal reforming process. 

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