Autothermal reactor

Fig ure 6-9. An autothermal reactor with an external heat exchanger. 

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Autothermal reactor for methanol synthesis using a numerical search technique... 

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... 

The design of novel autothermal reactors and catalysts holds promises for efficient reforming of oxygenates such as methanol and ethanol. However, up to now, only limited studies have appeared in the literature. 

Bird, R. B., Stewart, W. E., and Lightfoot, E. N., Transport Phenomena. Wiley, New York, 1960. Bonvin, D., Dynamic Modeling and Control Structures for a Tubular Autothermal Reactor at an Unstable State. Ph.D. thesis, University of California, Santa Barbara (1980). 

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... 

The following also discusses autothermal reactors, the conversion of ammonia, and finally, the optimum-temperature progression, with derived equations for reversible exothermic reactions for which profiles are not readily available. 

B. Glockler, A. Gritsch, A. Morillo, et ah, Autothermal reactor concepts for endothermic fixed-bed reactions. Chem. Eng. 

G. Eigenberger, A simplified procedure for the optimal design of autothermal reactors for endothermic high-temperature reactions. Chem. Eng. Sci.,... 

A completely different design of an autothermal reactor has been proposed and developed by Boreskov and Matros [41-43], Fig. 24A gives a sketch of the basic concept, showing an adiabatic fixed bed reactor with fecd/cxit tubes and two valves for periodic flow reversal. Before start of operation the fixed bed has again to be heated above the ignition temperature of the catalytic reaction. If the reactor is then fed with cold feed from one side the cold feed gas is heated up... 

Figure 26. Alternative arrangements for autothermal reactor design with periodic flow reversal A) Radial-flow concept B) Multiple-bed arrangement...

Interesting aspects of autothermal reactor operation arise if an endothermic synthesis reaction is coupled with an exothermic reaction in such a way that the combination is weakly exothermic An example has been given by Amoco for the oxidative steam reforming of methane [48] The application to styrene synthesis has so far been limited to simulation studies (see [49] and references therein)... 

In addition to the well-established fixed-bed reactor configurations mentioned above, new concepts are being discussed where specific features like educt addition and selective product removal are integrated in the fixed bed. From these multifunctional reactors , autothermal reactor concepts where the heat exchange between the cold feed and the hot effluent is integrated in the fixed-bed have already been established in industrial practice. 

This extremely exothermic reaction is successively suppressed in favor of Eq. (33) as the temperature increases, ft should be possible to use a simple autothermal reactor for the slightly exothermic reaction of Eq. (33). Proper design and an appropriate catalyst are required to avoid excessive reaction via Eq. (34) at the entrance to the reactor, causing a hot spot. The ratio H2/CO = 2 is more convenient for downstream processes than that obtained by steam reforming ... 

The heat duty to the reforming reactor is specified as zero. The oxygen flow rate can then be adjusted until the desired methane conversion is achieved. For 98% conversion, the flow rate of methane in the autothermal reactor product (stream 502) is 2% of the flow rate in the reactor feed (stream 501), i.e., 20 kmol/h. For the purpose of this example, the oxygen flow rate was adjusted manually, although a controller could have been used, as described in Section 4.8. The results are shown in Figure 4.11. 

Hagh, B.F. Optimization of autothermal reactor for maximum hydrogen production. Int. J. Hydrogen Energy 2003, 28 (12), 1369-1377. 

The overall reactions in Route 2 cure those previously indicated along with the following combustion reactions of the autothermal reactor. 

Integrated ATR Assembly Autothermal reactor Water gas shift reactors Sulfur removal Water boiler N/A... 

Exercise 6.20 The effect of heat transfer in an autothermal reactor... 

Some Reactor/Heat-Exchanger Systems 6.2.1 Autothermal Reactors... 

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