(189t) Simulation of a High-Flux Riser-Reactor Flow Using Cfd Techniques

The application of Computational Fluid Dynamics (CFD) in industrial operations has been increased not only in the project of new equipments but also in the optimization of the existing ones. The present work shows a set of three-dimensional two-phase and adiabatic conditions, using the two-fluids model for the calculation of gas-solids flow in a high-flux risers of two different geometries, one with 10m of height and 76mm of internal diameter, and the second with 18m of height and 50mm of internal diameter. The k-epsilon model was applied to consider the influence of turbulence over the gas phase. The four-lump and ten-lump schemes kinetic models were used to predict the catalytic cracking reactions in the two different reactors. The first riser had two entrances, one for particles and one for the organic materials. The mesh size for this case was 584,000 control volumes. The second studied riser had one entrance for vapor, one for organic materials, and a third for particles. The mesh generated over this geometry had 650,000 control volumes. The numerical results of gas-solids dispersion flow in a high-flux were compared with the experimental data from the work of Pärssinen and Zhu (2001), the four lump scheme for the mass concentration of chemical species was compared with the work of Ali et al. (1997), and the ten lump scheme was compared with the work of Nayak et al. (2005). The catalytic cracking reactions models show an important role in the prediction of all phenomena present in the reactor. The simulated results show that the kinetics models are important not only because of the variation of the gas phase and the temperature profiles inside the reactor but also because these parameters interfere directly in the dynamic behavior of the gas-solid flows.

KEYWORDS: CFD, gas-solid, catalytic cracking

References

* Ali, H., Rohani, S. and Corriou, J.P. (1997). Modelling and Control of a riser type fluid catalytic cracking (FCC) Unit, Trans. IchemE., 75A, 401-412.

* Nayak, S.V., Joshi, S.L., Ranade, V.V. (2005) Modeling of vaporisation and cracking of liquid oil injected in a gas-solid riser. Chemical Engineering Science, n. 69, p. 6049-6066, 2005.

* Pärssinen, J.H. and Zhu, J.X. (2001). Particle velocity and flow development in a long and high-flux circulating fluidized bed riser. Chemical Engineering Science, 56, 5295-5303.