Heat management

We noted earlier in this chapter that many reactions in the chemical industries are exothermic and require heat removal. A simple way of meeting this objective is to design an adiabatic reactor. The reaction heat is then automatically exported with the hot exit stream. No control system is required, making this a preferred way of designing the process. However, adiabatic operation may not always be feasible. In plug-flow systems the exit temperature may be too hot due to a minimum inlet temperature and the adiabatic temperature rise. Systems with baekmixing suffer from other problems in that they face the awkward possibilities of multiplicity and open-loop instability. The net result is that we need external cooling on many industrial reactors. This also carries with it a control system to ensure that the correct amount of heat is removed at all times. 

The control system must manipulate heat removal from the reactor, but what should be the measured (and controlled) variable Temperature is a good choice because it is easy to measure and it has a close thermodynamic relation to heat. For a CSTR. temperature control is particularly attractive since there is only one temperature to consider and it is directly related to the heat content of the reactor. However, in a spatially distributed system like a plug-flow reactor the choice of measured variable is not so clear. A single temperature is hardly a unique reflection of the excess heat content in the reactor. We may select a temperature where the heat effects have the most impact on the operation. This could be the hot spot or the exit temperature depending upon the design of the reactor and its normal operating-profile. 

To summarize, we find that heat management is required for many industrial reactors and that this task can be accomplished by controlling a reactor temperature. WTe start our discussion of unit control by reviewing several reactor temperature control schemes. 

Continuous stirred tank reactors. The simplest method of cooling a CSTR is shown in Fig. 4.14. Here we measure the reactor temperature and manipulate the flow of cooling water to the jacket. Using a jacket for cooling has two advantages. First, it minimizes the risk of leaks and thereby cross contamination between the cooling system and the pro- 

Fortunately we can readily solve many of the problems associated with a direct supply of cooling water. For example, in Fig. 4.15 we have provided a water recirculation loop to maintain a large constant flow of water through the jacket. Fresh cooling water is added to the loop to maintain the desired reactor temperature. This arrangement keeps 

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Heat management is another important consideration in the implementation of a reactive distillation process. Conventional... 

Instead of electrically conductive additives, thermally conductive additives have also been used to construct thermally conductive tapes used for heat management [ 132]. A particular example of an electrical conductive tape is a z-axis conductive construction shown in Fig. 17. In this case, the conductive particles make contact in the z-direction of the tape without doing so with neighboring particles in the... 

The CFSTR is readily adaptable to both heating and eooling beeause the fluid ean be stirred to promote heat transfer, ensuring better heat management with minimum heat transfer area. A eombination of both jaeket and internal eoil may be neeessary to provide the required heat exehange area. Chapter 7 reviews the heat transfer eoeffieient and the... 

Other important aspects to consider during the scaling-up of ionic liquid synthesis are heat management (allcylation reactions are exothermic ) and proper mass transport. For both of these the proper choice of reactor set-up is of crucial importance. 

Li ion batteries are heavily advertised as the future power sources for electric vehicles. This seems premature because the technology of heat management and many questions of safety are not solved. Fuel cells and several types of secondary batteries have a long history in the field of electric vehicle propulsion, with successes and failures. For information on electric vehicle batteries, see [16-22],... 

Fig. 1. Schematic of the pilot unit used for catalyst life and heat management testing.

The investigations refer to the general capability of micro reactors to perform short-time processing with highy intensified mass and heat transfer. A special focus of most investigations on the oxidation of ammonia was the heat management. The use of new concepts for heat supply and removal opens the door to operation in new process regimes with very different product spectra. 

Heat management is of crucial importance for ethylene oxide synthesis (see original citahons in [4]). The reachon enthalpy of the total oxidation to carbon dioxide (AH = -1327 kj/mol) is more than 10 times larger than that of the partial oxidahon (AH = -105 kJ/mol), which induces locally very hot temperatures (hot spots) with corresponding negative consequences on the reaction course. 

Beneficial micro reactor properties mainly refer to improving heat management as a key for obtaining a partial reaction in a consecuhve sequence, when large heats are released by reaction steps other than the partial one (see also Section 3.3.1). 

The main expectations of industrial researchers focused on improving heat management and increasing safety for hazardous process [71]. 

Fig. 13. Heat management with an infinite number of beds...

Steam reforming is an endothermic process that requires complicated heat management of the system. 

Reversible metal hydrides On-board refueling High volumetric densities Lowering desorption temperatures Improving kinetic response Heat management during refill... 

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