Dynamics and control study on the low temperature methanation reactor with mass and heat recycle

• Nonlinear and linear characteristics of the methanation reactor are analyzed.
• Effects of mass, heat recycle and split ratio on reactor stability are revealed.
• Linear model implies that the integral element is necessary for reactor control.
• The High Selector module can maintain the real peak temperature well.

Both nonlinear and linear dynamic characteristics of the low temperature methanation reactor with recycle loop are analyzed for the process safe operation and effective control. Aspen Dynamics tool is adopted to get transient behaviors of the reactor under step changes of the inlet temperature and CO mole fraction. A double-input-multi-output linearized system based on the nonlinear dynamic model is developed for further insight into the process stability, response rapidity and controllability. Similar responses are obtained in the nonlinear and linear models for commendable mutual authenticating. The presence of material recycle because of the unconverted reactants, together with the thermal recycle for energy saving, renders a more sensitive stability of the system, where thermal feedback has the major effect, but the existing of mass feedback may weaken this effect when considerable heat is recycled. Moreover, the transfer function of the linear model indicates that the integral term is necessary for the reactor variables control, and the proposed control strategy using a High Selector module in Aspen Dynamics can successfully maintain the hot spot temperature within the reactor by considering the migration of the peak temperature under the two disturbances.