Reformers fixed-bed

A prominent example of a fixed-bed reactor applied for auto-thermal reforming is the HotSpot fuel processor developed by Johnson Matthey. Platinum and chromium catalyst were introduced as fixed bed. The reformer could be started from ambient temperature when methanol was used as feedstock [49, 50]. The reactor was preheated initially by methanol combustion and then operated under autothermal conditions. 

Lindstrom et al. [55] developed a fixed-bed autothermal methanol reformer designed for a 5 kW fuel cell operated with copper/zinc oxide catalyst doped with zirconia. The system was started without preheating from ambient temperature by methanol combustion in a start-up burner, which was operated at sixfold air surplus to avoid excessive temperature excursions. Because significant selectivity toward carbon monoxide was observed for the autothermal reforming process, a WGS stage became mandatory [55]. 

Lattner and Harold [56] performed autothermal reforming of methanol in a relatively big fixed-bed reactor carrying 380 g BASF alumina-supported copper/zinc oxide catalyst modified with zirconia. The 01C ratio was set to 0.22 while the SIC ratio varied from 0.8 to 1.5. The axial temperature profile of the reactor, which had a length of 50 cm, was rather flat, the hot spot temperature did not exceed 280° C which was achieved by the air distribution system through porous ceramic membrane tubes. More than 95% conversion was achieved. Very low carbon dioxide formation was observed for this reactor only 0.4 vol.% was found in the reformate. However, the WHSV calculated from the data of Lattner and Harold [56] reveals a low value of only 6 l/(h gcat) for the highest CHSV of 10 000 h reported. 

Lee et al. [58] from Samsung reported development of a fixed-bed natural gas reformer coupled to a WGS reactor with an electrical power equivalent of 1 kW. The steam reformer was placed in the center of the subsystem, while the annular WGS fixed bed surrounded the reformer separated by an insulation layer. Commercial ruthenium catalyst served for steam reforming, while a copper-based catalyst was used for WGS. A natural gas burner supplied the energy needed by steam reformer. The reformer was operated between 850 and 930 C, while the shift reactor worked between 480 and 530 C. The carbon monoxide content of the reformate was reduced to 0.7 vol.% downstream the shift reactor despite its high operating temperature, because the reformer was operated at high S/C ratio between 3 and 5 the water surplus affected the equilibrium of the WGS reaction positively. At full load, the efficiency of this subsystem was 78% which decreased to 72% at 25% load. 

Moon et al. [59] presented a breadboard fixed-bed fuel processor for isooctane, which was composed of an ATR and high-and low-temperature shift reactors. The fuel processor was applied for testing different catalysts. A NiO/CaO/Al203 catalyst performed equivalent to a Ni/Fe/MgO/AlaOs catalyst for the autothermal reforming reaction. 

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Aromatics are petrochemicals. Fixed-bed reforming of virgin naphthas is one source of these materials. Aromatics fiom the high temperature of coking of coal, the main source prior to 1940, now only account but for a small proportion of the total production. 

An isothermal, plug flow, fixed bed reforming pilot plant (shown in Fig. 14) was used to generate the kinetic data. The reactor was U shaped and contained roughly 70 ml of catalyst. Five sample taps were spaced along the reactor length to determine compositions over a wide range of catalyst contact times. The reactor assembly was immersed in a fluidized sand bath to maintain isothermal conditions. 

Figure 17.13. Multibed catalytic reactors (a) adiabatic (b) interbed coldshot injection (c) shell and tube (d) built-in interbed heat exchanger (e) external interbed exchanger (f) autothermal shell, outside influent-effluent heat exchanger (g) multishell adiabatic reactor with interstage fired heaters (h) platinum-catalyst, fixed bed reformer for 5000 bpsd charge rate reactors 1 and 2 are 5.5 ft dia by 9.5 ft high and reactor 3 is 6.5 x 12.0 ft.

Fig. 1.5. Effect of heat transfer limitation in industrial steam reformers, (a) Scheme of a single catalytic fixed-bed reformer tube with typical heat transfer and operating parameters.

FIG. 19-3 Fixed-bed reactors with heat exchange, (a) Adiabatic downflow, (b) Adiabatic radial flow, low AP. (c) Built-in interbed exchanger, (d) Shell and tube, (e) Interbed cold-shot injection, (f) External interbed exchanger, (g) Autothermal shell, outside influent/effluent heat exchanger. (h) Multibed adiabatic reactors with interstage heaters, (t) Platinum catalyst, fixed-bed reformer for 5000 BPSD charge rates reactors 1 and 2 are 5.5 by 9.5 ft and reactor 3 is 6.5 by 12.0 ft temperatures 502 433, 502 => 471,502 => 496°C. To convert feet to meters, multiply by 0.3048 BPSD to m3/h, multiply by 0.00662. 

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... 

Owing to the high ratio of the reactor-to-particle diameter in technical fixed bed reforming reactors ( i>100), radial gradients of the 02-content and temperature are neglected. 

Data used in this study were obtained on an isothermal fixed-bed reforming pilot plant. The reactor section was equipped with five sampling taps spaced along the length of the reactor. Online gas chromatograph analyses of the axial reformate san les provide composition profiles of 285 hydrocarbon conponents with increasing residence time through the catalyst bed. 

MSR conversion is limited by the thermodynamic equilibrium, and this is one of the most serious constraints related to the MSR reaction. Indeed, in order to achieve complete conversion of methane in conventional fixed-bed reformers, the reaction temperature has to be in the range of 800-900°C. At this elevated temperature the catalyst undergoes deactivation due to carbon formation it also results in blockage of reformer tubes and increased pressure drops (Trimm, 1997). 

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