Plate heat exchanger fuel processors

Plate heat exchanger fuel processors on the meso- and microscale... 

Additionally, highly efficient heat exchangers are required in fuel processors and the micro si rue lured plate heat exchanger design seems to be the best solution so far to maintain the crucial system efficiency competitive. 

A micro-reactor as part of a practical fuel processor is generaUy designed as a plate heat exchanger, a conventional heater being shown in Figure 7.3a. If only one... 

The choice of materials for plate heat exchanger/reactors also depends on the desired dynamic properties of the microsystem. One important parameter is the energy demand for fuel processor start-up, which results from the product of specific heat capacity and density of the construction material. For a given geometry and volume of the device, aluminum is favored over copper and stainless steel. 

Few reports address the challenges of mass production of the fuel processors. Work at IMM in Mainz, Germany has resulted in an assessment of costs associated with production runs of 1(X) 000 units per annum for a heat exchanger reactor for a fuel processor (Kolb et al., 2007). The structure is based upon micro-structured plate heat exchanger technology (see Chapter 4). The plate heat exchanger unit has... 

Figure 5.53 shows the flow scheme of a 10-kWei diesel fuel processor/fuel cell system based on steam reforming, as designed by Cutillo et al. (443). The energy required to run the endothermic reaction was generated in a directly coupled catalytic afterburner, which could be realised as a plate heat-exchanger, as described in Section 5.1. The S/C ratio fed to the steam reformer was substantially higher compared with the system discussed above in order to prevent coke formation. 

Taking into consideration that another two reactors (low temperature shift and preferential oxidation reactors) are required downstream of the high temperature water-gas shift, at least in a conventional fuel processor/low temperature PEM fuel cell system, the calculations demonstrate that it is difficult to pre-heat a chain of reactors without an excessive time demand. Other measures and functionalities become possible when plate heat-exchanger technology is applied, which may help to solve this problem. 

However, monolithic reactors and plate heat-exchangers are more suitable than fixed-beds for the rapid start-up and transient operation requirements of fuel processors on the smaller scale [57]. 

Microstructured plate heat-exchangers, which require no electrical heating, or only for start-up, are more likely to be future applications in fuel processors. Some of these devices will be presented below. 

Catalyst cost may play a significant role in the overall fuel processor cost and could reach values as high as 38% [633]. In this situation, tailor-made catalyst formulations of enhanced activity are required along with meastues to increase the utilisation of the catalyst. This may be achieved by coating the catalyst into small channel systems of ceramic or metallic monoliths or into microstructured plate heat-exchangers, which improves the mass transfer, as described in Chapter 6. 

For reformate flow rates up to 400 Ndm3 min-1, the CO output was determined as < 12 ppm for simulated methanol. The reactors were operated at full load (20 kW equivalent power output) for -100 h without deactivation. In connection with the 20 kW methanol reformer, the CO output of the two final reactors was < 10 ppm for more than 2 h at a feed concentration of 1.6% carbon monoxide. Because the reformer was realized as a combination of steam reformer and catalytic burner in the plate and fin design as well, this may be regarded as an impressive demonstration of the capabilities of the integrated heat exchanger design for fuel processors in the kilowatt range. 

Because the reformer was a combination of steam reformer and catalytic burner in plate and fin design, this was regarded as an early and impressive demonstration of the capabilities of the integrated heat exchanger design for fuel processors in the kilowatt range. 

An early stage of plate a heat-exchanger for water-gas shift in the kW size range was described by Kolb et al. [543]. The reactor still had a three stage cross-flow design for the sake of easier fabrication. Platinum/ceria catalyst was wash-coated onto the metal plates, which were sealed by laser welding. The reactor was tested separately and showed equilibrium conversion under the experimental conditions. It was subsequently incorporated into a breadboard fuel processor (see Section 9.5). 

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