Design and Control of a Fixed-Bed Recycle Reactor with Multicatalyst Layers: Methanation of Carbon Dioxide
Youngmin Jeong, Jonghyun Park, Myungwan Han
Abstract
The power-to-gas (PTG) process plays a significant role in transforming renewable electric energy into methane via electrolysis and methanation. Critical issues in the PTG process include the fluctuating nature of renewable electric energy and the safe operation of the methanation reactor. The high exothermicity of methanation and the variable load caused by renewable energy imperil the stable operation of the reactor. A cooled recycle reactor with a multilayered catalyst is introduced for methanation. The intensified reactor provides better performance than conventional reactors, but its complexity poses challenging design and control problems. An optimization problem is formulated for the design of the reactor. The catalyst dilution profile and the product recycle ratio are optimized to improve both the reactor efficiency at steady state and the flexibility to load changes while satisfying the major constraint, i.e., safe operation. The objective function considers the reactor performance in terms of the total annual cost and flexibility against a load change. Load variation is a major disturbance affecting the operation of the methanation reactor. A dynamic control strategy is proposed to address load variation. The proposed control system stabilizes the reactor temperature in each layer and properly distributes the reaction load to the layers, enabling the flexible operation of the reactor under a load change.