Modeling the transient response of a fluidized-bed biomass gasifier

Abstract

The dynamic response of a bubbling fluidized-bed biomass gasifier (FBG) is examined. A transient model is developed by extending a previous steady-state model to account for key processes occurring during the ramp-up and/or changes in loading of fuel and gasification agent. The model is validated against measurements from transient tests in a laboratory-scale FBG. The model results are also compared with steady-state measurements and previous FBG models from the literature. A sensitivity analysis is performed to identify the most influencing parameters. The model is then used to study the transient response of industrial FBG under different operating conditions. It is shown that for given operational conditions (biomass flowrate, equivalence ratio, initial temperature, and initial char inventory in the bed), there is always an optimal start-up procedure (rate of change in feeding the gasifying agent and/or the fuel) leading to the shortest start-up time and lowest peak temperature. The transient period can be reduced by up to 75% compared to the reference value, in which the transient response can extend for more than an hour, due to the slow change in the inventory of char in the reactor. The model can be used to optimize the operation of hybridized power plants with biomass gasification and thermal energy storage.