Open-loop dynamics of a parallel-plates reactor for ethanol steam reforming

IZURIETA, EDUARDO MIGUEL; CUÑADO BENÍTEZ, IGNACIO; CASEY, VALENTIN; PEDERNERA, MARISA NOEMÍ; LÓPEZ, EDUARDO

Buenos Aires

Congreso; 11th World Congress of Chemical Engineering; 2023

Asociación Argentina de Ingenieros Químicos

Hydrogen is considered a very interesting energy vector, particularly when it comes from raw materials of biological origin as a source of renewable energy to solve the problems of energy availability, environmental protection and regional development. A practical implementation of these hydrogen production processes at small scale requires operation with high efficiency, specifically considering the strong endothermicity of the reforming reactions. For these purposes, the implementation of reactors capable of transferring high heat fluxes per unit area is required. To achieve this goal, a parallel-plates reactor with thermal coupling of endothermic and exothermic reactions have been proved useful. Some authors reported that systems with integration of endo- and exothermic reactions exhibit complex dynamics [1]. This can lead, in the absence of an appropriate control system, to reaction extinction after small disturbances. Then, reliable and computationally efficient mathematical models are of great importance in the study of parallel-plates reactors dynamics and their implementation in power generation systems.Previous contributions showed that ethanol combustion and steam reforming thermal coupling is plausible and an adequate reactor behavior in terms of hydrogen yield and ethanol conversion is predicted in stationary-state simulations [2]. This work presents a study on the thermal coupling of ethanol steam reforming and combustion in a non-stationary parallel-plates reactor.The main disturbances are studied to identify the parallel-plates reactor dynamics. The effect of flowrate and streams temperatures variations on the product distribution and thermal profiles are analyzed. The reactor operation is represented by transfer functions, relating each input disturbance to each output. Second-order functions are applied due to their low error with respect to the simulation results and their low computational costs. The model is later used to design a feedforward control loop. The most important disturbance comes from changes in ethanol flowrate to the combustion section and from changes in both inlet temperatures. For this reason, the proposed control system contemplates them as the variable to be manipulated by the final control element and the main external disturbances, respectively. It was observed that the outlet temperature and the product distribution are strongly affected by these disturbances. The mass balance has a considerably faster dynamic than the energy balance, which causes the latter to be the one that governs the dynamic behavior.References1.Baldea, M., Daoutidis, P. (2007). Dynamics and control of autothermal reactors for the production of hydrogen. Chemical Engineering Science, 62(12), 3218–3230.2.Izurieta, E. M., Pedernera, M. N., López, E. (2019). Study of a thermally integrated parallel plates reactor for hydrogen production. Chemical Engineering Science, 196, 344–353.