Agile Operation of Renewable Methanol Synthesis under Fluctuating Power Inputs

The fluctuating production of renewable energy constraints the operation of Power-to-X processes such that steady-state conditions are unattainable without energy storage. It seems eminent to establish operation strategies considering significant disturbances along the process and to determine those scenarios where the operation becomes unfeasible. In this work, an industrial methanol Lurgi-type reactor, embedded in a Power-to-Jet process (Figure 1), is evaluated under fluctuating feed conditions. The simulated scenarios consist of step functions up to 20 % (w/w) increments in the feed flowrate as consequence of the fluctuating power input on the electrolysis stage. A one-dimensional dynamic model for a multi-tubular fixed bed reactor is implemented, considering both the gas and catalyst phase. The mathematical model is solved numerically using orthogonal collocation at the spatial domain and backward differences at the time domain. The system shows rapid response to disturbances, reaching steady state conditions in 1.5 minutes. Furthermore, it is evidenced that the feasible region to increase the production of methanol is narrowed down by rises of carbon dioxide feed flowrate up to 5 % (w/w).