Carbon Monoxide Clean-up

The CO selox becomes thus a fundamental stage also in the integrated membrane systems for H2 production. Recently, in the literature it was demonstrated that the use of an MR for this reaetion stage can improve the depletion of CO content. The membrane, constituted of a ceramic tube, most often zeolite, on which is deposited the catalyst, opportunely distributed in the pore, does not have the function of separating/purifying a stream, but to improve the reactant/catalytic phase contact, to reduce by-passing 

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The third chapter deals with the reforming chemistry of conventional and alternative fuels, and with the chemistry of catalytic carbon monoxide clean-up, sulfur removal and catalytic combustion. 

Even if the reformate is purified by catalytic carbon monoxide clean-up to well below 50 ppm carbon monoxide and if other impurities are reduced to the ppb level, performance losses are to be expected when running a fuel cell with reformate. A 7% lower power production was observed by Shi et al. [31] when mnning a 2 kW PEM fuel cell stack with reformate produced from liquid hydrocarbons. 

Design of the Carbon Monoxide Clean-Up Devices 1167 Temperature [°C]... 

The effect of operating conditions of the reformer and the carbon monoxide clean-up reactors on their individual performance was discussed in Sections 5.1 and 5.2. However, the operating parameters of the reformer also affect the performance of the clean-up reactors. Increasing the reformer temperature increases the load on the water-gas shift reactors downstream, because the carbon monoxide content is higher... 

The catalytic carbon monoxide clean-up worked with a two-stage water-gas shift in tubular reactors cooled by steam generation. The kinetics for a rhenium-alumina catalyst for high temperature water-gas shift and for a copper/alumina catalyst for low temperature shift had been extracted from the literature. 

Figure 5.63 shows the fuel processor that was designed, based upon the results of the simulation work. It had a concentric design, with the hottest components positioned in the centre. The reformate passed through two annular paths dedicated to carbon monoxide clean-up. The reformer and the four water-gas shift reactors... 

Residual propane would damage catalytic carbon monoxide clean-up catalysts downstream of the reformer in a practical application. 

Figure 9.5 P2 HotSpot fuel processor (top) linked to a Demonox carbon monoxide clean-up unit (bottom) the manifolds were placed in the centre [575].

A methane or natural gas fuel processor with 2.5-kW thermal energy output was described by Heinzel et al. [17]. It consisted of a pre-reformer, which made future multi-fuel operation possible, the reformer itself, which carried a nickel catalyst [433], it was operated between 750 and 800 ° C, and had catalytic carbon monoxide clean-up. The preferential oxidation reactor was operated at an O/CO ratio of 3.5 [433]. A carbon monoxide content of between 20 and 50 ppm could be achieved during steady state operation. An external burner suppUed the steam reforming reaction with energy. The natural gas was desulfiirised by a fixed bed of impregnated charcoal. Figure 9.21... 

Seo ct al. reported on the development and operation of a 100-kW natural gas fuel processor, tvhich tvas developed for a molten carbonate fuel cell [609]. The molten carbonate fuel cell does not require any carbon monoxide clean-up (see Section 2.3.2), and thus the system consisted merely of a burner to supply the steam reformer, a compressor, heat-exchangers, the desulfurisation stage and the reformer itself. The reformer was built by relying on conventional technology with tubular reactors top-fired externally from the natural gas burner. The 16 steam reformer tubes shown in Figure 9.33 were operated at a S/C ratio of 2.6 and 3-bar pressure, while the design operating temperature was 700 °C. Seo et al. reported that the efficiency of their system was still too low. Therefore, an improved version of the fuel processor is under development. 

A completely different system, which worked with cracking of liquefied petroleum gas was presented by Ledjeff-Hey et al. [79]. The system had the charm of being, at first glance, much simpler compared with conventional reforming coupled with catalytic carbon monoxide clean-up. It was very similar to the concept presented... 

The fuel processor worked with autothermal reforming [620] and with conventional carbon monoxide clean-up, namely high and low temperature water-gas shift and preferential oxidation. Substrates coated with catalyst that were not specified further were used to build the reactors. A catalytic afterburner was used to utilise ... 

Rosa et al. [251] set up a complete 5-kW diesel fuel processor based on autothermal reforming and catalytic carbon monoxide clean-up, which was dedicated to a low temperature PEM fuel cell. The breadboard system was composed of the autothermal reformer operated between 800 and 850 °C with a ruthenium/perovskite catalyst (see Section 4.2.8), a single water-gas shift reactor containing platinum/titania/ceria catalyst operated between 270 and 300 °C (see Section 4.5.1), and a preferential oxidation reactor containing platinum/alumina catalyst operated between 165 and 180 °C. Figure 9.54 shows the gas composition and reactor temperatures achieved. The hydrogen content of the reformate was in the range from 40 to 44 vol.% on a dry basis. The carbon monoxide content of the reformate was 7.4 vol.% and could be reduced to values of between 0.3 and 1 vol.% after the water-gas shift reactor and to below 100 ppm after the preferential oxidation reactor. 

Another application for diesel fuel processors is the propulsion of naval systems. Krummrich et al. [626] reported from a conceptual study of a 2.5-MW fuel processor/fuel cell system, which was dedicated to submarine applications for the German ship manufacturer HDW. The system consisted of a desulfurisation step, an adiabatic pre-reformer operated between 400 and 550 °C, steam reforming at 800 °C and catalytic carbon monoxide clean-up. The critical step turned out to be the desulfurisation of F76 diesel fuel, which in Europe contains as much as 0.2 wt.% sulfur, world-wide as much as 1 wt.%. These workers then set up and operated a 25-kW demonstration model of the fuel processor, which achieved an efficiency of 82%. 

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