Modeling and Optimization of a Membrane Reactor for the Steam Methane Reforming Process

Hydrogen has had broad usage in both the chemical and oil industries. However, its use is projected to expand into the transportation and energy markets in the future. Thus, there is a critical need to look further into methods of hydrogen production in order to economically meet those new, emerging demands. The objective in this research is to develop a model for a membrane reactor (MR) for use in the Steam Methane Reforming (SMR) process and to perform an economic analysis for optimization of its implementation into a conventional plant. Initially, the model is developed in Aspen Custom Modeler (ACM) and validated against the literature to compare the performance of three different permeation models of hydrogen through a Palladium (Pd)-based membrane. After validating the permeation models, the one that yields the lowest errors against the validation literature (4%) is chosen to replace the conventional reformer in the Aspen Plus SMR plant simulation.

With the modified design, an economic optimization is performed seeking hydrogen production maximization, using as decision variables the furnace and water-gas shift reactor temperatures, while respecting the operational limits of the conventional plant. In addition, the optimization problem also considers pollutant contamination constraints, regarding the concentration in the pressure swing adsorption tail gas. The optimization results in no changes to the conventional plant temperatures, minimizing operational impacts. The novel membrane reactor design generates reduced equipment footprint, but increases equipment purchase costs by $80,000 and operating costs by $188,000 annually. Conversely, there is an increase in hydrogen production of 1,250 kg/h, which generates a yearly increase of $22 million assuming an average hydrogen sales price of $2/kg. Thus, the developed model corresponds to a promising application of a novel, intensified design for economic hydrogen production.