Working diagrams to identify the operating range of a bubbling fluidized bed reactor for the CO2 methanation

Abstract

AbstractFluidized bed reactors for the catalytic CO2 methanation is a promising concept within the power‐to‐gas (methane) process. Due to the intermittency of renewable electricity generation and thus hydrogen production, the subsequent methanation reactor should also be able to operate at lower feed flow rates, while maintaining fluidized bed conditions. Bubbling fluidized bed reactors offer the required flexibility as shown with the new type of working diagrams. These working diagrams visualize a decision window for (a) determining the reactor diameter and (b) operating the fluidized bed reactor with a turndown ratio of 0.5‐1.1. Reducing the turndown ratio (ie, inlet flow rate) could lead to defluidization, thus increasing temperature or reducing the pressure are alternatives to maintain fluidization conditions. The former method is not desired, as a temperature increase would significantly reduce the CH4 yield due to thermodynamic constraints and therefore reduce the overall efficiency. An industrial CO2 methanation reactor, for example, that is designed for 10 bara (1 bara = 100 kPa) and 340°C with a total inlet flow rate of 5000 m3N · h−1 (H2/CO2 = 4) can be operated at a turndown ratio of 0.5 (2500 m3N · h−1) at the same temperature and the same u0/umf ratio by reducing the pressure to 5 bara with only a slight decrease in the CO2 equilibrium conversion from 96.7% to 94.6%.