Dynamic modeling and analysis of ethanol reformer for fuel cell applications.

摘要

Fuel cells that utilize hydrogen are promising energy conversion units that have a high intrinsic efficiency. However there are operational difficulties in storing hydrogen. One way to alleviate this problem is to generate hydrogen in situ from a liquid fuel such as ethanol. However, when power demand fluctuates with time, the ethanol feed rate into the reformer also fluctuates. For this reason, it is important to study the dynamics characteristic of the reformer. In this thesis, a mathematical model for an ethanol reformer is developed that captures the temporal and spatial variation of the species involved in the reforming reactions. The reformer is modeled as a tubular non-isothermal, non-isobaric packed-bed reactor operating at unsteady state. The partial differential equations resulting from this model are solved numerically after estimating the model parameters from the literature. Simulations are conducted to study how the flow rate of hydrogen is affected by the system parameters. The reformer model is coupled with a fuel-cell stack model and the effect of fluctuating power demand from an experimentally determined power profile from a 3-bedroom house on the hydrogen and ethanol flow rates are studied. Based on these dynamic studies, battery backup systems of three different sizes are analyzed.