Ammonia Decomposition in a Micro-Reactor, CFD Simulation
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- This report presents a simulation which investigates the production of hydrogen gas from ammonia, using the heat of the propane-air reaction.
- The ammonia conversion rate and the overall system efficiency were calculated.
- The geometry of the ammonia decomposition micro-combustor was created using ANSYS SpaceClaim software.
- A high-quality tetrahedron elements mesh was generated using ANSYS Meshing software.
- Appropriate species transport settings and boundary conditions were applied to correctly simulate the rate of ammonia decomposition.
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Description
Ammonia Decomposition: Using Micro-Reactor to Produce Hydrogen from Ammonia.
In the pursuit of sustainable energy solutions, hydrogen production from ammonia decomposition has emerged as a promising pathway for clean energy storage and utilization. Micro-reactors for ammonia decomposition offer significant advantages due to their compact size, enhanced heat and mass transfer characteristics, and improved process control. However, the endothermic nature of ammonia decomposition presents challenges in providing efficient and uniform heating while maintaining optimal reaction conditions. This study focuses on a paper-based novel micro-reactor design that utilizes the heat generated from propane-air combustion to drive the ammonia decomposition process.
Using ANSYS Fluent software, a comprehensive numerical investigation was conducted to analyze the coupled heat transfer and reaction kinetics in the micro-reactor system. The reactor geometry was designed using ANSYS SpaceClaim and a high-fidelity mesh comprising tetrahedron elements was generated using ANSYS Meshing (463220 elements) to ensure accurate resolution of the complex flow and reaction phenomena. The study evaluates key performance metrics including ammonia conversion rates and overall system efficiency, providing valuable insights for optimizing the micro-reactor design for enhanced hydrogen production efficiency.
Methodology
A pressure-based, steady-state solver was employed to capture the combustion processes and decomposition of ammonia. Propane-air mixture was used as the working fluid, with a two-step reaction mechanism implemented to simulate the combustion process. The Realizable k-epsilon turbulence model was adopted for this simulation due to its robust performance in predicting flow separation and recirculation zones, which are crucial features in micro-reactor systems. A suitable wall function was implemented to accurately resolve the near-wall region, which is essential for capturing the heat transfer and flow characteristics near the reactor walls. The species transport model with eddy dissipation concept was utilized to simulate the chemical reactions and mixing processes, providing detailed information about species concentrations and reaction rates throughout the domain.
Results and Conclusion
From the simulation, the following results are obtained:
- NH3 mass fraction contour indicates progressive decomposition from inlet to outlet, demonstrating effective thermal decomposition.
- H2 mass fraction contour increases along the flow direction, reaching maximum concentration (0.177) near the outlet, confirming successful NH3 decomposition.
- Temperature distribution peaks at 1960K in the combustion zone and gradually decreases downstream, providing necessary heat for NH3 decomposition.
- Propane (C3H8) mass fraction shows highest concentration at inlet with gradual consumption along the combustion chamber.
- The NH3 decomposition rate is about 99.6% which is very good and acceptable for ammonia decomposition reactors.
- Overall efficiency of the reactor system is about 21.07%. Thus, the present configuration can be applied to practical micro reforming systems.
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