Design of the Overall Fuel Processor

the first design step of fuel processor development is an overall net heat balance of the system. 

Afterburner Cel I Parameters 18 180 Cells Voltage 0.75 V Fuel Utilization 80 % Cross Flow 

Amphlett et al. calculated that for a methanol steam reformer the hydrogen utilisation needs to be maintained around 80% to avoid methanol combustion in the burner of the fuel processor. The maximum overall system efficiency had a weak maximum at the lowest possible hydrogen utilisation 407]. 

For a methane steam reforming fuel processor, more than 15% higher fuel processor efficiency was determined experimentally by Mathiak et al. [433] when utilising fuel cell anode off-gas compared with combustion of additional methane. Doss et al. analysed an autothermal gasoline fuel processor and found improved efficiency by utilisation of anode off-gas [434]. 

It has already been mentioned, in Section 2.2, that anode off-gas re-drculation can increase the fuel processor efficiency to values exceeding 100% where efficiency is 

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A compact design for a gasoline fuel processor for auxiliary power unit (APU) applications, including an autothermal reformer followed by WGS and selective oxidation stages, was reported by Severin et al. [83]. The overall fuel processor efficiency was about 77% with a start-up time of 30 min. 

The results of these tests will be used to validate the heat transfer model. Once the heat transfer characteristics are understood, the model will be expanded to include the effects of using a fuel air combustion mixture to generate the hot gas to heat up the system. An overall start-up strategy will be defined that will achieve rapid start and transition to steady-state operation. The strategy will identify the necessary components, the hot gas flow specifications, and the heating sequence. These data will be incorporated into the design of a 5-kWe engineering-scale fuel processor that will demonstrate a start-up time of 2 minutes or less. 

The PEM fuel cell stack system consists of the fuel cell stack and supporting gas, thermal and water management systems as shown in Figure 1. Overall system performance depends on the careful integration of these subsystems. The system developed under this contract was designed to accept reformed gasoline from a fuel processor. Development of the fuel processor was not part of this program. 

Another important design issue is the overall water balance of the fuel processor, because external water addition by the end-user is not favourable, especially with... 

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). 

To meet the requirements of the 20-kW fuel processor, which was the overall aim of the investigations, the reactor design described above was scaled up to a dual stage design of total volume 4 L. Each reactor was now 108-mm high, 108-mm wide and... 

Qi et al. presented a 1-kW breadboard gasoline fuel processor [451]. The device consisted of a concentric reactor arrangement, similar to the design developed by Ahmed et al. [448], see Section 5.4.5. The overall dimensions were very low, a diameter of 150 mm and length 150 mm were reported by these workers [451]. The preferential oxidation reactor was a separate device, but the autothermal fixed bed reformer was positioned in the centre of the fuel processor and surrounded by annular high and low temperature water-gas shift fixed bed reactors, as shown in Figure 9.40. The feed... 

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