Natural autothermic reforming

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. 

In addition to SMR, other technologies are used for syngas production from natural gas that involve addition of oxygen or air. The catalytic partial oxidation (CPO) reaction is given in Reaction (3) and in autothermal reforming (ATR) this reaction is combined with Reactions (1) and (2). 

Natural Gas Autothermal Reforming an Effective Option for a Sustainable Distributed Production of Hydrogen... 

Natural gas is reacted with steam on an Ni-based catalyst in a primary reformer to produce syngas at a residence time of several seconds, with an H2 CO ratio of 3 according to reaction (9.1). Reformed gas is obtained at about 930 °C and pressures of 15-30 bar. The CH4 conversion is typically 90-92% and the composition of the primary reformer outlet stream approaches that predicted by thermodynamic equilibrium for a CH4 H20 = 1 3 feed. A secondary autothermal reformer is placed just at the exit of the primary reformer in which the unconverted CH4 is reacted with O2 at the top of a refractory lined tube. The mixture is then equilibrated on an Ni catalyst located below the oxidation zone [21]. The main limit of the SR reaction is thermodynamics, which determines very high conversions only at temperatures above 900 °C. The catalyst activity is important but not decisive, with the heat transfer coefficient of the internal tube wall being the rate-limiting parameter [19, 20]. 

Heinzel et al. [77] compared the performance of a natural gas autothermal reformer with that of a steam reformer. The ATR reactor was loaded with a Pt catalyst on a metallic substrate followed by a fixed bed of Pt catalyst. In the start-up phase, the metallic substrate was electrically heated until the catalytic combustion of a stoichiometric methane-air mixture occurred. The reactor temperature was increased by the heat of the combustion reaction and later water was added to limit the temperature rise in the catalyst, while the air flow was reduced to sub-stoichiometric settings. With respect to the steam reformer, the behavior of the ATR reactor was more flexible regarding the start-up time and the load change, thus being more suitable for small-scale stationary applications. 

An experimental study by Lee et al. [72] reported the development and testing of a natural gas fuel processor, which incorporates a catalytic autothermal reformer, a sulfur trap and a WGS reactor. The fuel processor was successfully run over 2300 h of continuous operation. The ATR reactor gave over 40% H2 (dry basis) in the ATR reformate and 96-99.9% methane conversion over the entire test duration. 

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 primary ways in which natural gas, mostly methane, is converted to hydrogen involve reaction with either steam (steam reforming), oxygen (partial oxidation), or both in sequence (autothermal reforming). The overall reactions are shown below ... 

ATR [AutoThermal Reforming] A process for making CO-enriched syngas. ATR combines partial oxidation with adiabatic steam-reforming. Developed in the late 1950s for ammonia and methanol synthesis. Further developed in the 1990s by several companies for making liquid fuels from natural... 

Description Natural gas is preheated and desulfurized. After desulfurization, the gas is saturated with a mixture of preheated process water from the distillation section and process condensate in the saturator. The gas is further preheated and mixed with steam as required for the pre-reforming process. In the pre-reformer, the gas is converted to H2, C02 and CH4. Final preheating of the gas is achieved in the fired heater. In the autothermal reformer, the gas is reformed with steam and 02. The product gas contains H2, CO, C02 and a small amount of unconverted CH4 and inerts together with undercomposed steam. The reformed gas leaving the autothermal reformer represents a considerable amount of... 

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