Autothermal temperature profile

GP 11] [R 19] For an autothermal reactor, i.e. a device with neither internal nor external heat transfer, steep temperature profiles along the flow axis were found [9]. Via an inspection window, glowing of the front zone of the wire reactor was observed, indicating complete conversion within a few mm reaction passages. The... 

Figure 17.19. Reactors for the oxidation of sulfur dioxide (a) Feed-product heat exchange, (b) External heat exchanger and internal tube and thimble, (c) Multibed reactor, cooling with charge gas in a spiral jacket, (d) Tube and thimble for feed against product and for heat transfer medium, (e) BASF-Knietsch, with autothermal packed tubes and external exchanger, (f) Sper reactor with internal heat transfer surface, (g) Zieren-Chemiebau reactor assembly and the temperature profile (Winnacker- Weingartner, Chemische Technologie, Carl Hanser Verlag, Munich, 1950-1954).

The essential feature of an autothermal reactor system is the feedback of reaction heat to raise the temperature and hence the reaction rate of the incoming reactant stream. Figure 1.6 shows a number of ways in which this can occur. With a tubular reactor the feedback may be achieved by external heat exchange, as in the reactor shown in Fig. 1.6a, or by internal heat exchange as in Fig. 1.6b. Both of these are catalytic reactors their thermal characteristics are discussed in more detail in Chapter 3, Section 3.6.2. Being catalytic the reaction can only take place in that part of the reactor which holds the catalyst, so the temperature profile has the form... 

Kikas et al. [47] operated a micro structured autothermal reformer for methane in the conventional and reverse flow mode. Owing to the reverse flow conditions, a more uniform temperature profile was achieved in the reactor (Figure 2.21). 

Figure 23. Autothermal fixed-bed reactors with recuperative heat exchange. Basic design and typical temperature profiles. A) Conventional design with separate heat exchanger B) Counter-current fixed-bed reactor.

Figure 24. Autothermal reaction control with direct (regenerative) heat exchange for an irreversible reaction [14], A) Basic arrangement B) Local concentration and temperature profiles prior to flow reversal in steady state C) Variation of outlet temperature with time in steady state.

Figure 9.13. Feed-side and sweep-side temperature profiles along the length of the membrane reactor for autothermal reforming syngas. (Reprinted with permission from Huang et al.,6 Copyright...

Figure 9.18. Feed-side temperature profiles along the length of membrane reactor for autothermal...

Figure 17.21. Some recent designs of ammonia synthesis converters, (a) Principle of the autothermal ammonia synthesis reactor. Flow is downwards along the wall to keep it cool, up through tubes imbedded in the catalyst, down through the catalyst, through the effluent-influent exchanger and out. (b) Radial flow converter with capacities to l tons/day Haldor Topsoe Co., Hellerup, Denmark), (c) Horizontal three-bed converter and detail of the catalyst cartridge. Without the exchanger the dimensions are 8 x 85 ft, pressure 170 atm, capacity to 2000 tons/day (Pullman Kellogg), (d) Vessel sketch, typical temperature profile and typical data of the ICI quench-type converter. The process gas follows a path like that of part (a) of this figure. Quench is supplied at two points (Imperial Chemical Industries).

Li B, Maruyama K, Nuruimabi M, Kunimori K, Tomishige K (2004) Temperature profiles of alumina-supprated noble metal catalysts in autothermal reforming of methane. Appl Catal A 275 157-172... 

Dias JAC, Assaf JM (2008) Autothermal reforming of methane over Ni/7-Al203 promoted with Pd. The effect of the Pd source in activity, temperature profile of reactor and in ignition. Appl Catal A 334 243-250... 

Ciambelli P, Palma V, Palo E, Villa P (2010) Autothermal catalytic reactor with flat temperature profile. PCT Int. Appl. WO 2010/016027... 

Figure10.2 Longitudinal temperature profiles at autothermal operation for a H2-air mixture of equivalence ratio 0.6 in (a) a 250 pm gap size ceramic-frame microreactor and (b) a 300 pm gap size thin stainless-steel-based frame microreactor, for different thermal spreaders (material indicated) of thickness 3.2 mm adhered to the framework (redrawn from [6, 7]).

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. 

Aicher et al. [72] measured the temperature profile in their autothermal diesel reformer reactor (see Figure 4.4). Temperatures up to 900 °C were detected upstream of the catalyst honeycomb, while the reformate temperature never exceeded 700 °C at the reactor exit... 

At 290 °C reaction temperature and a feed composition of 9 vol.% methanol and 11% water, which corresponded to S/C 1.2,65% methanol conversion could be achieved at 99% hydrogen selectivity over CuZns samples treated by acid leaching for 20 min. Under autothermal conditions, more than 25% methanol conversion was achieved at S/C 1.2 and 0/C 0.3, while the oxygen was fully converted. Later, Homy et al. improved their catalyst by doping with chromium [482]. At S/C 1.0 and 0/C 0.25, axial temperature profiles were determined over the reactor to determine the hot spot formation. The hot spot did not exceed 3 K due to the high heat conductivity ofthe brass. A fixed catalyst bed showed a hot spot of about 20 K under comparable conditions. 

A microstructured monolith for autothermal reforming of isooctane was fabricated by Kolb et cd. from stainless steel metal foils, which were sealed to a monohthic stack of plates by laser welding [73]. A rhodium catalyst developed for this specific application was coated by a sol-gel technique onto the metal foils prior to the sealing procedure. The reactor carried a perforated plate in the inlet section to ensure flow equi-partition. At a weight hourly space velocity of 316 L (h gcat). S/C 3.3 and O/C 0.52 ratios, more than 99% conversion of the fuel was achieved. The temperature profile in the reactor was relatively flat. It decreased from 730 °C at the inlet section to 680 °C at the outlet. This was attributed to the higher wall thickness of the plate monolith compared with conventional metallic monolith technology. The reactor was later incorporated into a breadboard fuel processor (see Section 9.5). 

Figure 10.1. X-ray diffraction patterns of fresh and used catalysts (a) fresh catalysts (b) Rh/Al203 (c) Pt/Al203 (d) Pd/Al203. (1) fresh (2) the used catalyst at the catalyst bed inlet (3) the used catalyst at the catalyst bed outlet. Fresh reduced in hydrogen flow at 1123 K. Used reaction conditions of 1123 K, CHVHzO/Oz/Ar = 40/30/20/10, W/F = 0.40 gh mol, 4 h [3]. (Reproduced from Applied Catalysis A - General, 275(1-2), Li BT, Maniyama K, Nunmnabi M, Kunimori K, Tomishige K, Temperature profiles of alumina-supported noble metal catalysts in autothermal reforming of methane, 157-72, 2004, with permission from Elsevier.)...

FIGURE 9.29 Reactor with a periodic flow reversal (autothermal fixed bed reactor for catalytic combustion of VOCs). (a) Reactor configuration, (b) temperature profiles at the time of flow reversal, and (c) exit temperature versus time. 

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