Oxidative Torrefaction of Poultry Litter in a Pilot Unit: A Numerical Assessment of Process Parameters

Abstract

A numerical model of oxidative torrefaction of poultry litter in a pilot unit was developed. The model accounts for the process steps of biomass preheating in feed hopper, feeding of biomass into the reactor, applying flue gas as a fluidization medium, and electric heating of the reactor walls for additional heat supply. Following a “black box” approach, a major assumption of the model is that the behavior of the fluidized bed reactor is similar to a completely stirred tank reactor (CSTR). The properties of the particles and gas held inside do not depend on their location inside the reactor. During the process, the poultry litter biomass is heated to a predetermined temperature and begins to decompose, generating biochar and a gas phase (torgas), depending on the content of inert ash in biomass particles. Variable optimization in the model has been performed using Matlab software. The model estimates the optimal duration required for completion of the torrefaction process under various conditions: temperature, batch weight, reactor dimensions, etc. The model was validated using experimental data obtained from a series of torrefaction experiments performed in a fluidized bed, and provided reliable estimations of the duration of the process depending on the properties of the material, the size of the reactor and the portion of the material fed.