Computational Model For Transient And Steady State Analysis Of A 1-dimensional Auto-thermal Reformer

This study presents a 1-dimensional mathematical model of steam reformer to be used with high temperature solid oxide fuel cell (SOFC). Steam reforming (SR) is widely used in industries to produce hydrogen from hydrocarbons. There are various physical processes associated with chemical reactions in the SR of methane such as mass, heat and momentum transport. In this study a one-dimensional SR reactor with built-in preheater and mixing chamber connected to fuel gas and steam reservoirs is modeled and analyzed. The main part of the reformer is a metallic tube with catalyst coating on the inner walls, and it can be modeled as a one-dimensional flow channel. The transient continuity, flow momentum and energy equations are applied for discretized control volumes along the flow channels and the energy equation is applied to the tube wall with appropriate heat transfer model. The preheater is modeled as part of the tube without catalyst coating. The mixing chamber is modeled as an adiabatic control volume and transient mass continuity and energy equations are applied to find gas pressure and temperature in the mixing chamber. All transient governing equations are solved using a time-marching technique to simulate the transient thermal dynamics and concentration profiles within the reformer, preheater and mixing chamber. In addition, steam to carbon ratio at the mixing chamber is calculated and used as a numerical control parameter to achieve required fuel and steam reservoir pressures. Results in terms of local temperature and reformate composition are discussed for different prescribed reformer wall temperatures for various pressure gradients along the flow direction. The developed preliminary SR model is extended to Auto-Thermal Reformer (ATR) by introducing controlled flow of air into the reactor leading to combustion within the mixing chamber and the tube. The ATR operates at high temperatures due to combustion and hence the need for preheater and external heating source is eliminated. The developed computational model provides a very effective simulation tool for optimizing reformer design.