Balancing the heat requirements of an endothermic reaction with heat generated by an exothermic reaction

Reactor designs suffer from a fundamental limitation resulting from the flow configuration in which a reacting stream flows parallel to a heat transfer surface through which the majority of heat is transferred perpendicular to the direction of fluid flow. Regardless of the reaction taking place in the reaction channels, its reaction rate will vary along the flow length of that channel due to changes in concentration and temperature. Balancing the heat requirements of an endothermic reaction with heat generated by an exothermic reaction flowing parallel to and on the opposite side of a separating plate is extraordinarily difficult since the endothermic reaction is likely to have a very different dependence upon concentration and temperature than the endothermic reaction. Along the flow length of the plate that divides these reactions, the heat flux through the plate that is perpendicular to fluid flow will vary due to temperature and reaction rate differences along the flow length of the plate. Since the thermally coupled reactions are so closely coupled, neither reaction can run at a significantly different reaction rate at any point along the channel length. Thus, each reaction will exhibit a peak in reaction rate at nearly the same position within the reactor with slower reaction rates before and after this peak, which leads to the need for a long reactor channel to ensure complete conversion.反应器设计普遍存在一项根本性局限，其源于特定流动构型：反应流（reacting stream）与传热表面（heat transfer surface）平行流动，而绝大多数热量的传递方向与流体流动（fluid flow）方向垂直。无论反应通道（reaction channels）内进行何种反应，受浓度（concentration）与温度（temperature）的变化影响，反应速率（reaction rate）都会沿该通道的流动长度发生改变。要平衡吸热反应（endothermic reaction）的需热需求与平行流动于分隔板（separating plate）另一侧的放热反应（exothermic reaction）所释放的热量，这一过程难度极大——由于吸热反应对浓度与温度的依赖特性，与另一侧的放热反应往往存在显著差异。在分隔两类反应的隔板的流动长度方向上，垂直于流体流动方向、穿过隔板的热通量（heat flux），会因隔板流动长度上的温度与反应速率差异而发生变化。由于这类热耦合反应（thermally coupled reactions）的耦合程度极高，在通道长度方向的任意位置，两类反应的反应速率都无法出现显著差异。因此，两类反应的反应速率峰值几乎会出现在反应器内的同一位置，峰值前后的反应速率均相对偏低，这就需要更长的反应通道才能确保实现完全转化（conversion）。