Dynamic simulation of a solar-autothermal hybridized gasifier: Model principle, experimental validation and parametric study

Abstract

Solar thermochemical fuel production technologies, such as biomass gasification, are confronted to the intermittency of solar irradiance. The development of dynamic simulation tools is thus required to design around-the-clock control strategies. An innovative model was developed here, based on unsteady mass and energy conservation equations, considering gas-phase thermodynamic equilibrium and heterogeneous char oxidation kinetics. The char accumulation and gas species production rates were therefore tracked throughout operation, giving insight into the reactor dynamics with optimized computational cost. The model was validated via a comparison with experimental results, regarding both thermal and chemical reactor performances. Simulations reliably predicted the evolution of reactor temperatures and syngas production rates, under both solar-only and hybridized (solar-autothermal) operation. Parametric studies regarding the impact of reactants injection rates on steady-state performances were finally proposed. Steam addition (0.22 to 0.60 g/min) increased the syngas H2:CO molar ratio significantly (1.13 to 1.47). Biomass addition (1 to 3 g/min) boosted the solar-to-fuel efficiency (0.22 to 0.47), but altered the reactor temperature. Finally, oxygen addition kept the reactor running despite fluctuations of solar power, while decreasing the total H2 + CO production and cold-gas efficiency linearly. A constant H2 + CO production (2.17 NL/min) could however be achieved by feeding additional biomass and oxygen during hybridization, thus limiting the cold-gas efficiency decrease and improving the reactor energy efficiency (0.29 to 0.40). Such a dynamic reactor model can be further applied to hybridized gasification process optimization and dynamic control under real fluctuating solar irradiation conditions.