(454a) A Dynamic, Heterogeneous, 2D Model for Water Gas Shift Reactors

The water gas shift (WGS) reaction has been used in industry for several decades, but has seen a recent resurgence in interest due to new applications in environmentally friendly energy. For example, the WGS reaction can be used to generate hydrogen gas for applications such as the integrated gasification combined cycle (IGCC) to produce electricity from coal with carbon capture, for the Fischer-Tropsch process to produce liquid fuels from biomass, as carbonless fuel for automotive fuel cells, and many others.

The WGS reaction produces hydrogen using steam via the following reaction:

CO + H₂O (g) ↔ CO₂ + H₂

Typically, this takes place in a bed packed with catalyst, although other configurations are possible. Several steady-state models have previously been developed to describe packed-bed WGS reactors. However, dynamic models with sufficient detail are lacking in the open literature. Therefore, we have constructed a dynamic model which considers the temperature and concentration variations in the reactor axial direction, as well as across the individual catalyst pellets. The model is applicable from small to large scales using any type of heterogeneous catalyst for which kinetic information is known, and shows excellent agreement with available experimental data at non-equilibrium conditions.

With this level of detail, we are able to predict several interesting effects that can occur during dynamic operation that other models are unable to capture. For example, we have applied the model to WGS reactors in an industrial-scale polygeneration plant (electricity and liquid fuels), where the feed conditions change with a high degree of frequency. When transitioning between operational steady states, for example, temporary hot spots can develop in the centers of the catalyst pellets at certain locations inside the reactor, raising sintering concerns. Similarly, temporary cold spots can also develop during other transitions. These effects, which may be detrimental to the functionality of the catalyst, cannot be predicted by examining steady state conditions alone. Thus, the model is a very useful tool for the design and operation of any water gas shift reactor.