Three-dimensional modeling of olive cake combustion in CFB

• A three-dimensional Eulerian-Lagrangian numerical model was established.
• The gas–solid flow and chemical reactions were simultaneously simulated.
• The temperatures of gas and solid phases increase along the riser.
• The predicted NO and N2O emissions increase with the increasing excess air ratio.
• No obvious change is observed for the SO2 emission when excess air increases.

A comprehensive three-dimensional numerical model which includes gas–solid flow, chemical reaction, heat transfer and mass transfer has been established, to simulate the combustion of olive cake in circulating fluidized bed (CFB) reactor. The gas flow is solved by large eddy simulation (LES) approach. The particle phase is modeled by discrete particle method, in which the drag force, gravity, particle contact force and static-dynamic friction force are taken into account. The reactive model includes pyrolysis, combustion of char and volatile matters, SO2 emission, NO and N2O emissions, which has been coupled with gas–solid flow. Simulations were carried out in a CFB riser (diameter of 0.125 m and height of 1.8 m). Flow patterns, axial and radial distributions of voidage, gas and particle velocities, profiles of temperature and gas compositions under different operating conditions were obtained. The gas pollutant emissions in a riser were highly focused on. The results showed that gas and solid temperatures increase along the riser which reveals that waste combustion mainly takes place in the upper regions of the riser. The NO and N2O concentrations reach the peak values above the fuel inlet level owing to the equilibrium between the formation and reduction reactions. The SO2 concentration peaks close to the fuel inlet. An increase in excess air ratio causes the increase of NO and N2O emissions. However, no obvious variation tendency is observed for the SO2 emission.

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