ONE-DIMENSIONAL MODELLING OF CONICAL SPOUTED BED
Systematic methods and tools for managing the complexity
Process Simulation & Optimization - I (T4-9a)
Keywords: Spoted bed, flow modelling, hydrodynamics
Conical spouted beds have good perspectives for operations and processes where gas-solid contact is required, as in addition to the characteristics of the conventional spouted beds (cylindrical with conical bottom) they may operate in a wider range of gas velocities, which allows for attaining a vigorous gas-solid contact (Olazar et al., 1992). This versatility makes conical spouted beds especially useful for treatment of solids that are difficult to handle due to their irregular texture or because they are sticky. Likewise, conical spouted beds allow for attaining low gas residence times. A good behaviour of conical spouted beds has been proven in combustion of bituminuous coals (Tsuji et al., 1989), treatment of sawdust and agroforest residues (Olazar et al., 1994a) and pyrolysis of waste plastics and tyres (Aguado et al. 2005)
To improve the knowledge about the gas-solid contact in conical spouted beds a mathematical model have been developed. The aim of the model is to obtain velocity distributions of gas an particles in the different regions of conical spouted beds. Furthermore, design of conical spouted bed reactors for pyrolysis of biomass, plastics and tyres requires to couple the kinetic model with the hydrodynamic one. For this purpose, a simple but realiable hydrodynamic model should be used.
The model incorporates two levels of complexity: The simpler version considers constant bed voidage along the spout, given that this is a dilute region. For this purpose, mass balances have been applied in the spout and annulus for gas and particles but momentum balances have only been applied in the spout region both for gas and particles. In the second version, bed voidage along the spout has been considered to increase with bed level. To obtain the evolution of bed voidage along the spout, the momentum balance for the gas in the annulus has been used.
The great advantage of the model is the requirement of only two empirical equations, one for obtaining the minimum spouting velocity and the other one for obtaining the pressure gradient through the bed. Apart from that, only the geometrical factors of the conical spouted bed and the physical properties of gas and particles are required.
A comparison of the results predicted by the model with the experimental ones shows the version with constant voidage gives poorer predictions except for the solid cross-flow from the annulus into the spout with bed level. The predictions of the second version are quantitatively much better and, especially, those of voidage with bed level. Based on the data obtained at the top of the spout, properties in the fountain have also been calculated, namely fountain height and the voidage at the axis of the fountain.
Referencias
Aguado, R., Olazar, M., Arabiourrutia, M., Bilbao, J. Ind. Eng. Chem. Res., 44, 3918(2005).
Olazar, M.; San José, M. J.; Aguayo, A. T.; Arandes, J. M.; Bilbao, J Ind. Eng. Chem. Res. 31, 1784, 1992
Olazar, M.; San José, M. J.; Llamosas, R.; Bilbao, J.. Ind. Eng. Chem. Res., 33, 993-1000, 1994
Tsuji, T., Shibata, T., Yamaguchi, K., Uemaki, O., Proceedings of the International Conference on Coal Science, Vol. I, p 457 (1989).
See the full pdf manuscript of the abstract.
Presented Monday 17, 11:33 to 11:52, in session Process Simulation & Optimization - I (T4-9a).
