(521en) Repurposing Existing Steam Reformers for COX-Free Hydrogen Generation through Catalytic Ammonia Decomposition

With growing environmental awareness and a combined effort towards reducing our carbon footprint, greener alternatives to energy-fuels are being implemented. Hydrogen is vital, futuristic energy as its burning is CO_x-free. Hydrogen is generated through multiple established routes, of which hydrocarbon steam reforming is the most widespread. Steam reforming is a mature technology with readily available resources, and moderate-high operating conditions. However, the use of hydrocarbons inevitably brings the production of CO_x. It, therefore, needs to be avoided in the long-term carbon neutrality goal. Cleaner, greener routes for H₂ production have been proposed to overcome the issues posed by steam reforming, one of them is ammonia cracking. Ammonia is a carbon-free hydrogen vector that is easier to store, transport, and convert to hydrogen via catalytic ammonia decomposition. Compared to methane steam reforming, ammonia decomposition is less endothermic (220 vs. 46 kJ mol^–1) and needs milder conditions (800 vs. 500 °C). Therefore, a steam reformer can be repurposed as ammonia cracker with minimal modifications.

Towards that effect, we present a combined process simulations and computational fluid dynamics (CFD) approach to repurpose an industrial steam reformer as an ammonia cracker. The proposed reformer is modeled in a shell-and-tube configuration, with a Ba-Co-Ce catalyst loaded in multiple tubes and heated from the shell. Firstly, laboratory-scale ammonia decomposition runs were performed in a packed-bed reactor from which intrinsic kinetics were obtained as a modified power-law rate expression. Coupling them with a 2D cylindrical catalyst pellet incorporating heat-mass transfer effects in a cracker tube, process optimization is performed using gPROMS®. The optimization studies suggest using a profiled wall temperature to effectively use the entire tube length; avoiding cold spots (Figure 1). In the following stages, LES-based CFD simulations are performed using Barracuda Virtual Reactor® to further propose effective temperature control strategies for this endothermic reaction.