Pressurised Black Liquor Gasification - Numerical Modelling of an Entrained Flow Reactor

摘要

Pressurised black liquor gasification is an important new technology for energy and chemical recovery in the pulp and paper industry. However, the technology is still in its infancy and there is potential for improved performance. To this end a numerical model for a pressurised black liquor gasification process has been developed. The model is based on the commercial CFX4.4 CFD code and is used to investigate the flow patterns of gas and black liquor droplets in a gasification reactor. Droplets are modelled via a Lagrangian approach as a modelled spray burner injects them into the reactor together with oxygen. The droplets release their moisture and volatiles as they are being heated, and the resulting char particles are then gasified. A limitation with the model is that the char gasification is with oxygen only even though other gasification reactions are highly important in the real process. Furthermore, transport equations are solved for the mass fractions of volatiles, oxygen, gaseous combustion products, and char combustion products where the Eddy dissipation concept models the homogeneous combustion reactions. The results from simulations do not confirm the presence of two distinct flow patterns predicted by an earlier simplified model. Hence, the process appears to be more robust than what has previously been assumed and the results indicate that the gas flow field is relatively insensitive of the burner spray angle. The model has so far not been compared to experimental data since there is no data available from experiments yet. However, model validation is an important task in future research in our group.