Autothermal process operation

The submerged-flame technique developed by BASF represents the latest de> cIopment in autothermal processes. Within a liquid hydrocarbon, a flame creates a suf ciently high temperature in its vicinity to cause the formation of light products, tnduding acetylene. The gases are quendied in the cold zones of the liquid, and the carbon black formed is sent with the hydrocarbon to the burner. The reactor can operate undo pressure with any hydrocarbon oomponnd, without the substandal producdon of carbon black. The weak point of the device is the control of the burner, which is difficult to achieve due to the bi gas flow velocity (Fig. 5.13). 

All the industrial processes are autothermal, 30 to 40% of the coal utilized being burnt to attain the required high reaction temperatures. This is also the case for the Lurgi pressure gasification process carried out in a mechanically agitated solid bed at ca. 1200°C (as used e.g. in Sasolburg in South Africa), for the Koppers-Totzek process in which the coal is used in the form of flyash (atmospheric pressure, 1400 to 1600°C) and for the Winkler process operating with a pressureless fluidized bed at 800 to 1100°C. 

This combination of technologies was originally developed for ammonia plants in which e air is used in the autothermal process, to introduce nitrogen into the system. Nowadays this concept is also used for production of synthesis gas. The HSR reactor in combination with a downstream located auto thermal reformer is often selected to achieve an optimum balance between capital investment and operating costs. The choice for combined reforming technology is... 

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... 

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. 

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.)... 

SWITGTHERM A catalytic process for oxidizing volatile organic compounds (VOCs). It involves regenerative heat exchange, which permits autothermal operation at VOC concentrations in the range 250 to 650 ppm. Developed in Poland and now used in over 100 installations there. 

There are reactions where the heat of reaction can be employed to preheat the feed when an exothermic reaction is operated at a high temperature (e.g., ammonia N2 + 3H2 <-> 2NH3 or methanol CO + 2H2 CH3OH synthesis, water-gas shift reaction CO + H20 <-> H2 + C02). These processes may be performed in fixed-bed reactors with an external heat exchanger. The exchanger is primarily used to transfer the heat of reaction from the effluent to the feed stream. The combination of the heat transfer-reaction system is classified as autothermal. These reactors are self-sufficient in energy however, a high temperature is required for the reaction to proceed at a reasonable rate. 

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