Plate Heat-Exchanger Reactors

Ceramic foams (see also Section 10.2.1) are excellent catalyst supports [461]. They have a high porosity of between 40 and 85% formed from pores of 40-1500-pm diameter. Owing to the laminar flow regime, the pressure drop is low in ceramic foams. The first application of ceramic foams was catalytic combustion. 

The application of plate heat-exchanger reactors carries advantages for all types of fuel processing reactors, namely for the reformer, the water-gas shift reactor and the 

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Figure 5.9 Plate heat exchange reactor. Source Reproduced from Ref [64] O 2014 with permission from Elsevier B. V.

Reuse et al. [16] combined endothermic methanol steam reforming with exothermic methanol combustion in a plate heat exchanger reactor, which was composed of a stack of 40 foils (Figure 24.5). Each foil carried 34 S-shaped channels. Cu/ZnO catalyst from Siid-Chemie (G-66MR) was coated into the channel system for the steam reforming reaction. Cobalt oxide catalyst served for the combustion reaction. The reactor was operated in co-current mode. The steam reformer was operated at a S/C ratio of 1.2. At reaction temperatures between 250 and 260 °C, more than 95% conversion and more than 95% carbon dioxide selectivity were achieved. 

O Connell et al. [41] reported stable evaporation of their fuel injection system for an oxidative steam reformer, which worked similar to ATR-8 by mixing superheated steam and fuel, while the air was added downstream, right in front of the stack of their plate heat exchanger/reactor. 

The channels of most plate heat exchanger/reactors are switched in parallel, which reduces the pressure drop compared to alternative flow patterns such as serpentine flow fields. However, flow equipartition is crucial for parallel flow arrangements. It is achieved by perforated plates [89] when a whole stack of plates is fed in parallel from the plate front. Such pinhole plates create additional pressure drop. In case the feed gas is distributed to each plate first and then by a dedicated inlet section to each channel of the plate, a sophisticated geometry of this inlet section [90] helps to achieve flow equipartition. An alternative is the variation of the channel width over the reactor length axis [91]. 

Specific Features Required from Cataiyst Formuiations for MicroChannel Plate Heat-Exchanger Reactors... 

Another aspect is the low catalyst mass per unit reactor volume that can be introduced into the plate heat-exchanger reactor. This drawback is counterbalanced by much better utilization of the catalyst owing to the improved heat and mass transfer. Consequently, more active catalysts are required which compensate the lower mass. At the same time, the cost of the catalyst is less of an issue compared with, for example, fixed-bed reactor technology. These statements will be confirmed by a practical example below. 

Heat Management of MicroChannel Plate Heat-Exchanger Reactors I 193... 

A typical temperature profile, which was determined experimentally in a plate heat-exchanger reactor, is shown in Figure 7.8a. After a slight temperature peak at the reactor inlet, which originated from the high initial heat of reaction, the reactor temperature decreased towards the outlet of the reactor (see Figure 7.8b). 

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. 

The Alfa-Laval Plate Heat Exchanger reactor... 

Figure 7.31 shows a microstructured plate heat-exchanger reactor developed by Kolb et al. [312], which was designed for a power equivalent of 2 kW of the corresponding fuel cell. The temperature profile, which was determined experimentally in... 

Laser welding is a viable option for the fabrication of plate heat-exchanger/reactors. 

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