Simulation and modelling of hydrogen production by sorption enhanced steam methane reforming in fixed bed reactors

An increased demand for hydrogen as energy-carrier and as fuel for clean power generation is expected during the 21st century. The Kyoto-protocol states that the world has to decrease it’s CO2-emissions to the atmosphere. A concept combining hydrogen production and sequestration of CO2 is the sorption enhanced steam methane reforming (SE-SMR) process. This is an alternative to the traditional steam methane reforming (SMR) for production of hydrogen. SE-SMR is a concept that has received increased attention in recent years. The process utilizes a solid CO2-acceptor to capture CO2 in the reforming reactor and thereby change the normal thermodynamic limitations of steam methane reforming. The work in this thesis has focused on simulation of hydrogen production by sorption enhanced steam methane reforming in a fixed bed reactor. A robust transient one dimensional model has been formulated and implemented for the simulations of the reforming reactor. Three main models have been formulated, one pseudo-homogeneous model and two heterogeneous model that account for intraparticle mass and heat transfer. The two heterogeneous models are different in the way the solid materials are placed in the reactor. The 1-particle model considers one type of pellet in the reactor consisting of both catalytic and sorbent material, while the 2-particle model considers two separate pellet types with catalytic and sorbent material. Kinetic models for all major reactions must be formulated to simulate the sorption enhanced steam methane reforming reactor. The steam methane reforming reactions have been extensively studied earlier, and the kinetic model of Xiu and Froment was used in the simulations. Different solid synthetic materials for the high temperature CO2 capture have been studied, and kinetic models for capture of CO2 on these materials have been formulated in this thesis. Two of the materials, nanocrystalline lithium zirconate and sodium zirconate have been synthesized at NTNU, while the lithium silicate was obtained from Toshiba. The materials synthesized at NTNU showed quite similar kinetic properties, and the capture rate of CO2 was described by a first order rate reaction with respect to fractional conversion of the solid. However, while the shape of the rate expression was similar for the two zirconates, the reaction rates did differ substantially. The lithium zirconate had the slowest capture rate of the materials; with a kinetic constant about 100 times lower than th