Overall Basic Engineering of the Fuel Processor

The S/C ratio of the cracking reactors, which were regenerated by carbon gasification with steam, amounted to 3.0 [442]. Calculations revealed that the lowest efficiency was achieved with the autothermal reformer coupled to the adiabatic medium temperature water-gas shift reactor. The fuel cracker was best in terms of efficiency, water management, volume and weight, but lowest in terms of controllability, cost, emissions, dynamics and operability [442]. 

Downstream of the ATR, the reformate was cooled in HX-A, further cooled and enriched with water by the water-injection system WI-1 and then entered the high temperature water-gas shift reactor (HTWGS). About 750 W of energy were removed from the reactor by internal heat-exchange. This made isothermal operation at 390 °C possible. 

Hydrogen conversion of 80% was assumed for the fuel cell. The unconverted hydrogen was then fed into the AFB downstream of an additional water separation (WS2). Part of the low temperature heat contained in the AFB off-gas, which had a temperature of 125 ° C downstream of HX- B was then removed by a second air cooler (about 1.8 kW of heat losses) and left the system at 70 °C. The heat formed by the oxidation reaction in the fuel cell was removed with the cathode air of the fuel cell. The cathode feed required humidification. Part of the water fed to the cathode was regained from the cathode off-gas (WS2) and fed back to the system. This improved the overall water balance. 

The amount of fuel fed to the steam reformer was substantially lower compared 

The efficiency of the steam reformer fuel processor of 96.6% was much higher than the autothermal reformer efficiency (88.8%), which in turn also increased the system efficiency (38.7% compared with 35.5% for the autothermal reformer) [443]. The heat removal required for the two air coolers was much lower for the steam reformer (about 2.1 kWcompared with 3.4 kW for the autothermal reformer). This in turn reduced the size of these components, which was a substantial benefit because the air coolers contributed significantly to the overall system size. The volume required is a stringent factor, especially in mobile systems. All the benefits of steam reforming clearly have the drawback of a more complex reactor design, which needs to be addressed by suitable manufacturing techniques in order to become competitive in price and not just in performance (see Section 10.2). 

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