Improvement of pure ammonia combustion performance using the catalytic pre-cracking method

Asa storage and transportation medium for hydrogen and a clean fuel with zero carbon emissions, ammonia (NH3) plays an important role in promoting hydrogen energy economy and renewable energy utilization. However, NH3 faces issues of low combustion intensity and the difficulties of ignition when used as a fuel. To address these problems, a novel combustion method with high temperature resistance and strong activity catalyst for NH3 pre-cracking is proposed in this paper. The cracking product, hydrogen, has a higher combustion rate, lower ignition temperature, and higher combustion intensity, which can improve the combustion characteristics of pure NH3. Firstly, Computational Fluid Dynamics was used to simulate the whole process of catalytic cracking and combustion of NH3. An Eulerian multiphase flow model with a granular phase was employed to simulate the catalyst particles and a porous medium to simulate the support carrier for the catalyst particles. Secondly, the Langmuir-Hinshelwood model was built using user-defined functions (UDF) to describe the reaction kinetic rates of the adsorption, cracking, and desorption processes of NH3 on the surface of Ni/Al2O3 catalyst. Then, species indexing in the flow field was implemented using UDF to couple the catalytic reaction rate with the surface coverage concentration to improve the simulation accuracy and reliability. Finally, the simulation results revealed that the catalytic pre-cracking combustion method can significantly improve the thermal efficiency and stability of NH3 combustion.