Simulation of co-pyrolysis of coffee ground and waste polystyrene foam in a tilted-slide reactor

Abstract

Coffee ground is considered one of the promising biomass resources because it is one of the most popular beverages and has higher calorific value than other kinds of biomass. In the previous study on the fast pyrolysis of coffee ground, the viscosity of the pyrolysis oil was found to be very high and it was suggested to mix some amount of alcohol to reduce its viscosity. The quality of the pyrolysis oil also can be improved by mixing synthesis polymer such as polyethylene, polyethylene, or polystyrene as a feedstock. Recently, a tilted-slide reactor for fast pyrolysis was designed with a feeding capacity of 20 kg/h, in which no fluidizing gas is necessary for conveying hot sand. In the previous experiment, the co-pyrolysis of coffee ground and waste polystyrene foam was performed in the tilted-slide reactor. The ratio of waste polystyrene foam in the feedstock mixture was varied from 0% to 100% by weight, and fast pyrolysis was performed near the temperature of 550 °C. In this study, the co-pyrolysis was simulated by a commercial computational fluid dynamics code, and the results were compared with experimental results. A multistep kinetic mechanism was adopted for the pyrolysis of coffee ground and polystyrene. The volatile yields in the simulation approached the pyrolysis oil yields in the experiment by introducing a composite boundary condition to retain the unpyrolyzed polystyrene near the reactor bottom for longer residence time. The elemental composition and moisture contents became similar with measurement when increasing polystyrene blending ratio.