A PULSING DEVICE FOR PACKED-BED BIOREACTORS .1. HYDRODYNAMIC BEHAVIOR

This paper describes a new pulsing device which permits the insertion in pulsing form of a liquid phase fed into an equipment where a microbial or enzymatic transformation occurs. It also analyzes the modifications of the flow model caused by the pulsation generated by means of three kinds of pulsators: A hydropneumatic pulsator, a selfpropelled pulsator and a newly designed elastic membrane pulsator. The hydrodynamic behaviour of a packed-bed column, to which each of these pulsators has been connected is compared with the correspondent system without pulsation. The flow model is determined by the study of the curves of residence times distribution, obtained by using a stimulus-response technique. A computer programme has been used to determine the axial dispersion coefficients from the response curves. In all cases we worked within a wide range of Re(p) (10-215). The pneumatic pulsing device causes a backmixing in the system due to the alternative movement that communicates to the fluid contained in the column. The application of the pulsation by means of the selfpropelled injector or the elastic membrane pulsator reduces the axial dispersion coefficient in regard to those corresponding to the system without pulsation, a fact which becomes even more significant when operating at high flow velocities. For the study of the hydraulic model of the pulsing system of elastic membrane we worked under different conditions in order to determine the effect of the particle's diameter, the viscosity, and the frequency of pulsation. At the same frequency at which the Re(p) increases, the axial dispersion coefficient also increases, following in all cases an almost linear tendency. For the same Re(p), the dispersion coefficient decreases when the particle diameter increases. On the other hand, the dispersion coefficients obtained for a fluid of a viscosity of 2 cp are, in some cases, up to 3 times higher than the corresponding values for water. All the results indicate that the new pulsator is specially applicable to reactors which, as in many biological transformations, present inhibitory problems by the product, or, in general, to those reactions that require that the flow model in the reactor be a plug flow model.