Figure 5. Contour plots of temperature, methanol mole fraction, and hydrogen mole fraction under nominal operating conditions for the heat integrated reactor.
The contour plots of water mole fraction, oxygen mole fraction, and carbon dioxide mole fraction under nominal operating conditions are presented in Figure 6 for the heat integrated reactor. A reaction chamber has dimensions of height, width and length. The length of the reaction chamber is typically longer. Typically, the sides of the reaction chamber are defined by reaction chamber walls. These walls are preferably made of a hard material such as a ceramic, an iron-based alloy, or high temperature nickel-based superalloys. More preferably, the reaction chamber walls are comprised of stainless steel which is durable and has good thermal conductivity. In addition to thermal transfer between adjacent reaction chambers, in some cases, a reaction chamber can be in thermal contact with a microchannel heat exchanger. This combination of reaction chambers and heat exchangers can result in high rates of thermal transfer. The catalyst could also be applied by other methods such as wash coating. On metal surfaces, it is preferred to first apply a buffer layer by chemical vapor deposition or thermal oxidation, which improves adhesion of subsequent wash coats. Preferred reactors and methods of conducting reactions in integrated reactors can be characterized by their properties. The devices may be made of materials such as plastic, metal, ceramic and composites, depending on the desired characteristics. Walls separating the device from the environment may be thermally insulating. However, the walls separating adjacent exothermic and endothermic reaction chambers should be thermally conductive. Introduction of laterally distributed combustion fuel and air in co-flow with endothermic reactant flow concentrates the heat transfer at the endothermic reactor inlet, where the concentration gradient is highest, thus obtaining superior results over systems that distribute the combustion fuel evenly over the entire surface of the combustion catalyst. Although the examples with distributed combustion still exhibit excellent heat flux in comparison to conventional steam reformers. The present design could use alternate exothermic reactions, such as oxidation reactions, including partial oxidation reaction, to drive an endothermic reaction. During operation, a reactant enters a combustion or reaction chamber in a bulk flow path flowing past and in contact with a porous material or porous catalyst. A portion of the reactant molecularly transversely diffuses into the porous catalyst and reacts to form a product or products, and then the products diffuse transversely into the bulk flow path and out of the reactor. A short heat transport distance is desired for good performance. These short heat transport distances, combined with preferred reactor configurations, can provide surprisingly high volumetric productivity and low pressure drop. The 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. A specific example of this reaction rate problem encountered in the parallel flow arrangement is demonstrated by attempts to drive endothermic steam reforming with exothermic combustion in microchannel and alternating parallel plate reactors. A convenient way to supply heat is to couple the endothermic reaction with an exothermic combustion reaction in the heat exchange channels. Thus, the stacked reactor becomes an alternating series of endothermic and exothermic reactors separated by thin heat exchange walls. Unfortunately, the combustion reaction is difficult to control with convenient combustion catalysts and fuels, and most of the combustion occurs near the fuel inlet. This uneven combustion results in uneven heat transfer to the endothermic reaction and poor overall reactor performance. The geometry allows intimate thermal contact whilst keeping the streams from becoming mixed. The reactor body is constructed by modification of a substantially rigid and essentially nonporous monolith honeycomb. Prior to modification the monolith consists of a honeycombed body having a matrix of thin walls defining a multiplicity of discrete channels which pass through the body of the structure from one face to the opposing face. The monolith is modified in such a way as to produce a rigid body containing at least two discreet process flow paths which have a number of dividing walls in common. A channel is defined as any individual passageway through the monolith body and a flow path is the group of channels used for a single reaction. The inlets to the first reaction flow paths and the inlets to the second reaction flow paths are in the inlet manifold such that the reactants run in a co-current configuration. The reactants also leave the reactor in the same outlet manifold via the first reaction outlets and the second reaction outlets. The fuel processor is described using the steam reformation of methane and oxidation of methane reactions to illustrate the concept. The inlets and outlets may be arranged for a countercurrent flow of the reactants.