Reactors heat-removal techniques

Temperature is certainly a dominant variable for polymer reactors. Many of the reactor designs that have been discussed in previous sections can be used for polymerization. Any of the techniques discussed for heat removal apply here. However, temperature is never the only dominant variable in these systems. 

The efficiency of the steam reformer fuel processor of 96.6% was much higher than the autothermal reformer efficiency (88.8%), which in turn also increased the system efficiency (38.7% compared with 35.5% for the autothermal reformer) [443]. The heat removal required for the two air coolers was much lower for the steam reformer (about 2.1 kWcompared with 3.4 kW for the autothermal reformer). This in turn reduced the size of these components, which was a substantial benefit because the air coolers contributed significantly to the overall system size. The volume required is a stringent factor, especially in mobile systems. All the benefits of steam reforming clearly have the drawback of a more complex reactor design, which needs to be addressed by suitable manufacturing techniques in order to become competitive in price and not just in performance (see Section 10.2). 

The heat of polymerization can be removed by heat exchangers placed on an externa] recirculation loop. However, low boiling point hydrocarbons and a-olefin comonomers can be introduced into the reactor in the liquid phase to absorb the heat of polymerization by their latent heat of evaporation in an operation procedure called condensed mode. Since most polymerization reactors are limited by their heat removal capability, this technique permits a substantial increase in reactor productivity. 

Until recently, the temperature control of highly exothermic reactions using the microreaction systems was mainly based on the removal of heat in order to prevent hot spot formation and thermal runaway [29]. More recently, however, research has focused on techniques that enable microreactors to be heated because they can efficiently dissipate the heat. If a microheat exchanger is integrated into a microreactor, both effects can be combined, that is, either enabling fast heat supply in the reactor or heat removal from the reactor [30]. In practice, strongly exothermic reactions such as nitration, oxidation, chlorination, and even fluorination with elementary fluorine (in microreactors made of nickel) can be carried out in microreactor systems under nearly isothermal conditions [31]. 

Another option for heat removal from a CSTR or batch reactor is to vaporize some of the contents of the reactor, condense some or all of the vapor in an external condenser, and return the liquid condensate to the reactor. This technique is feasible when the reactor can be operated at a temperature where the rate of vaporization is large enough to allow a significant rate of heat removal. Analyzing vaporization/condensation heat removal is more complex than analyzing heat transfer through a jacket or an internal coil. The following development is based on the latter means of heat transfer. 

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