Model-Based Design of a Control System for the Upgrade of Biogas with Zeolite Sorbent Reactors

To remove carbon dioxide from biogas so as to produce biomethane, a fixed-bed tubular reactor filled with a zeolite pelleted solid sorbent is considered. To generate biomethane continuously, three batch reactors are operated in coordinated cycles. The control system operates in a two-level structure: a high-level coordination algorithm determines the shift from a process stage to another for each single reactor and computes the setpoints for the low-level controllers of each reactor; the low-level controllers regulate the process variables, such as the inlet gas flow rate, the inlet or outlet gas pressure and the sorbent temperature, according to the setpoints. In this paper, we first investigate the modelling of the batch process by means of mass, energy and momentum conservation equations. The concurrent adsorption of methane is also taken into account. The model parameters are identified by means of a two-stage procedure using experimental measurements from two plants, a laboratory-scale one located in Piacenza (Italy) and a pilot-scale one located in Camposampiero (Italy). With the identified model we design a control system for the coordination of three batch reactors.