Autothermal

Steam Reforming. When relatively light feedstocks, eg, naphthas having ca 180°C end boiling point and limited aromatic content, are available, high nickel content catalysts can be used to simultaneously conduct a variety of near-autothermic reactions. This results in the essentiaHy complete conversions of the feedstocks to methane ... 

MPa (300—400 psig), using a Ni-based catalyst. Temperatures up to 1000°C and pressures up to 3.79 MPa (550 psia) are used in an autothermal-type reformer, or secondary reformer, when the hydrogen is used for ammonia, or in some cases methanol, production. 

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

The first observation of sensitivity-stability was reported by Liljenroth (1918) in connection with the autothermal operation of ammonia oxidation reactors. Papers of Damkdhler (1937) and Wagner (1945) went unnoticed. At Union Carbide Corp. Perkins (1938) used zero order kinetics to define a safe range for ethylene oxidation in an unpublished report. His result,... 

There are reaetions where the heat of reaetion ean be employed to preheat the feed when an exothermie reaetion is operated at a high temperature (e.g., ammonia N2 + SHj o 2NH3 or methanol CO + 2H2 o CH3OH synthesis, water-gas shift reaetion CO -1- H2O o H2 -1-CO2). These proeesses may be performed in fixed-bed reaetors with an external heat exehanger. The exehanger is primarily used to transfer the heat of reaetion from the effluent to the feed stream. The eombina-tion of the heat transfer-reaetion system is elassified as autothermal. These reaetors are self-suffieient in energy however, a high temperature is required for the reaetion to proeeed at a reasonable rate. 

The following also diseusses autothermal reaetors, the eonversion of ammonia, and finally, the optimum-temperature progression, with derived equations for reversible exothermie reaetions for whieh profiles are not readily available. 

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

Figure 6-10. An autothermal multi-tubular reactor with an internal heat exchanger.

Figure 6-11. An autothermal reaotor with a reoyole arrangement.

The recycling of PVC by hydrothermal techniques is described, in which PVC is thermally converted in a steam atmosphere into hydrogen chloride, hydrogen, carbon dioxide, carbon monoxide and some gaseous and liquid hydrocarbons. Whilst gasification with only steam is an endothermic reaction, partial combustion of PVC by the addition of small amounts of air, enables autothermic operation of the process to take place. This work deals... 

Hydrogen production by methanol autothermal reforming with high conductivity honeycomb supports... 

Autothermal reaction of ethanol through Pd-Ag membrane reactor prepared by sequential electroless deposition... 

Oxidations of ammonia display ignition/extinction characteristics and auto-thermal reaction behavior. At low heat supply, only low conversion is observed and temperature remains nearly constant. With increasing heat supply and approaching a certain temperature, the reaction heat generated can no longer be transferred completely totally to the reactor construction material. At this stage, the reaction starts up . Suddenly, the temperature is raised by increased heat production until heat generation and removal are in balance. The reaction can now be carried out without a need for external heat supply, namely in autothermal mode. 

Partial methane oxidation comprises very high rates so that high space-time yields can be achieved (see original citations in [3]). Residence times are in the range of a few milliseconds. Based on this and other information, it is believed that syngas facilities can be far smaller and less costly in investment than reforming plants. Industrial partial oxidation plants are on the market, as e.g. provided by the Syntroleum Corporation (Tulsa, OK, USA). Requirements for such processes are operation at elevated pressure, to meet the downstream process requirements, and autothermal operation. 

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... 

Flow reversal performance is controlled weakly by the period r. Flow reversal is an autothermal operation and as such exhibits parametric sensitivity. Greater stability can be ensured by the conventional expedient of providing cooling in the catalyst bed. It can also be done through bypassing part of the reactor effluent gas around the recuperator section. 

Nieken, U., Kolios, G., and Eigenberger, G., Control of the ignited steady state in autothermal fixed-bed reactors for catalytic combustion. Chem. Eng. Sci. 49, 5507-5518 (1994). 

In the design of processes involving exothermic reactions it is generally desirable to use the energy liberated by reaction at some other point in the process or to make it available for use elsewhere in the industrial plant. For example, it can be used to preheat the feed components, particularly when the reaction takes place at high temperatures and the feed components are supplied at much lower temperatures. The term autothermal operation is applied to modes of processing in which exothermic reactions are carried out such that the energy released by... 

Since operation in an autothermal mode implies a feedback of energy to preheat the feed, provision must be made for ignition of the reactor in order to attain steady-state operation. The ordinary gas burner and many other rapid combustion reactions are examples of autothermal reactions in which the reactants are preheated to the reaction temperature by thermal conduction and radiation. (Back diffusion of free radicals also plays an important role in many combustion processes.)... 

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