Heat shell/tube reactors

Heat exchanger-like, multi-tube reactors are used for both exothermic and endothermic reactions. Some have as much as 10,000 tubes in a shell installed between tube sheets on both ends. The tubes are filled with catalyst. The larger reactors are sensitive to transient thermal stresses that can develop during startup, thermal runaways and emergency shut downs. 

Design a shell-and-tube reactor that has a volume of 24 m and evaluate its performance as the reactor element in the process of Example 6.2. Use tubes with an i.d. of 0.0254m and a length of 5m. Assume components A, B, and C all have a specific heat of 1.9 kJ/(kg-K) and a thermal conductivity of 0.15W/(m-K). Assume 7 ,>, = 70°C. Run the reaction on the tube side and assume that the shell-side temperature is constant (e.g., use condensing steam). Do the consecutive, endothermic case. 

All conventional reactors, tested before using the micro reactor (simply since micro reactors were hardly available at that time), only fulfilled the demands of one measure, at the expense of the other measures. For instance, a single-tube reactor can be operated nearly isothermally, but the performance of the oxidative dehydrogenation suffers from a too long residence time. A short shell-and-tube reactor provides much shorter residence times at improved heat transfer, which however is still not as good as in the micro reactor. 

Exothermic processes, with cooling through heat transfer surfaces or cold shots. In use are shell-and-tube reactors with smaii-diameter tubes, or towers with internal recirculation of gases, or muitipie stages with intercooiing. Chlorination of methane and other hydrocarbons results in a mixture of products whose relative amounts... 

Because the large heat of reaction must be removed, it is expected that a shell-and-tube reactor will be needed, with the catalyst packed inside the tubes. The heat duty for the reactor is... 

Small production units employ 4 inch diameter brass tubes 16 inches long, heated by electric resistor ribbons, while large production units require shell and tube reactors heated by a molten salt circuit. Organic heat exchange media are not recommended as at 250 °C they would undergo a fairly rapid thermal degradation. 

The design of pipeline, coil, and heat exchanger (reaction on tube or shell side) reactors and their optimization are illustrated and discussed. 

Transformation of the alcohol, pure or mixed with water, in the azeotrope composition (bpi.013 — 79.9°C. water content 12 per cent weight , previously vaporized, with air and steam added, and then raised to the required temperature in a multi-tube reactor operating at around 330°C aud 035.106 Pa absolute. The thermal level is controlled by removing the heat generated by the reaction by meaos of the shell-side circulation... 

Reaction it takes place on a feed preheated to around 220°C of ammonia, propylene and compressed air (0.3. 10 Pa absolute) in controlled proportions. It takes place in a multi-tube reactor (catalyst tube dimensions inside diameter 25 to 30 mm, height 3 to 3.5 m), with shell-side circulation of a bath of molten salt intended to remove the heat generated by the reaction, and which is then cooled to produce high-pressure steam. 

For many reactions, the microstructured mixers are simply followed by tube reactors, e.g., double-mantled tubes or shell-in-tube heat exchangers. The benefit from mixing in combination with the benefits of the continuous-flow process through the tube give process intensihcation, while providing reliable operation, especially when for larger volume flow ranges. 

Thermal Effects in Membrane Reactors - The problem of how to supply or remove heat from membrane reactors is an important practical concern. In a shell-and-tube configuration, the catalyst can be put on the shell side, which can then be encased in yet another shell containing a heat-transfer fluid. It is likely that other geometries will, in fact, be used. For example, the burner unit of Ohta et al. is shown schematically in Figure 10. 

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