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Dynamic microfiltration with a vibrating hollow fiber membrane module
Desalination 199 (2006) 499–500
Dynamic microfiltration with a vibrating hollow fiber membrane module So/ren Prip Beier, Gunnar Jonsson* CAPEC, Department of Chemical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark email: [email protected] Received 19 October 2005; accepted 6 March 2006
1. Introduction
2. Experimental
The idea of dynamic microfiltration is to decouple high feed flow velocity and high surface shear rate. These terms are normally connected in conventional cross-flow microfiltration, but by creating a relative motion between the feed stream and the membrane, high surface shear rate is induced and the feed flow can be kept low. A low feed flow velocity results in a low module pressure drop. Thus it is possible to maintain a low and uniform transmembrane pressure which together with the high surface shear rate reduces the fast and compact fouling of the membrane. In this work a dynamic microfiltration system is presented. The necessary surface shear rate is created by vibrations of a membrane module that consists of hollow fiber membranes. Filtration of baker’s yeast suspensions are evaluated by using the “critical flux concept” formulated by Field et al. [1]. It is also investigated how the critical flux varies with the surface shear rate.
The membrane module consists of 54 hollow fibers each with a length of 12 cm placed parallel in a plastic cylinder. The polyethersulfone hollow fibers have the skin layer on the outside and an average pore size of 0.45 mm. Each fiber is closed in one end and the other end is connected to a progressive cavity pump that sucks permeate through the fibers. The pump operates at a constant rate which means that the flux is kept constant at that specified pumping rate. The pumping rate is adjustable and controlled by a PC. The fibers are fixed between two steel plates that can be vibrated up and down at variable frequency and amplitude. Compared to other dynamic microfiltration systems [2,3] it is possible to vary the frequency and amplitude independently, and the shear rate on the surface is uniform on the whole membrane area. The feed fluid is circulated between the feed tank and the plastic cylinder. Permeate is collected on an electronic scale connected to the PC from which the flux can be calculated. A pressure transducer connected to the PC measures the transmembrane pressure. Using suspensions of baker’s yeast (5 g/L dry weight) the critical flux is determined at different levels of vibration
*Corresponding author.
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.114
500
S.P. Beier, G. Jonsson / Desalination 199 (2006) 499–500
membrane which is almost constant when operating below the critical flux.
Critical flux [L/(m2 h)]
100 y = 8.2167x0.2643 R2 = 0.8751
4. Conclusion
10
1 10
100 1000 Shear rate [1/s]
10000
Fig. 1. Critical flux as a function of the average surface shear rate in the filtration of baker’s yeast suspensions (5 g/L dry weight).
frequency (5–30 Hz) and vibration amplitude (0.2–1.175 mm). 3. Results and discussion At each combination of frequency and amplitude the average surface shear rate is calculated by use of an equation derived by solving the Navier–Stokes equation of motion. The corresponding values of critical flux and average surface shear rate are plotted in Fig. 1 in a log–log plot. In the figure it is shown that the critical flux varies with the average surface shear rate as a power function which is the same kind of correlation found by other authors working with dynamic microfiltration systems [2–4]. The transmembrane pressure during filtration is very low (<100 mbar), which reduces the fouling problems. This is also seen by looking at the permeability of the
A vibrating dynamic microfiltration system has been presented, and results from filtrations of baker’s yeast suspensions have shown that the critical flux varies with the surface shear rate as a power function. It was possible to filtrate at a very low transmembrane pressure and with a membrane permeability almost constant, when the flux is kept below the critical flux. The fouling problems were therefore reduced. Further filtration results from filtrations of yeast suspensions containing different enzymes will be presented, and the fouling mechanism and enzyme transmission will be discussed.
References [1]
[2]
[3]
[4]
R.W. Field, D. Wu, J.A. Howell and B.B. Gupta, Critical flux concept for microfiltration fouling, J. Membr. Sci., 100 (1995) 259–272. M.Y. Jaffrin, L. Ding, O. Akoum and A. Brou, A hydrodynamic comparison between rotating disk and vibratory dynamic filtration systems, J. Membr. Sci., 242 (2004) 155–167. J. Postlethwaite, S.R. Lamping, G.C. Leach, M.F. Hurwitz and G.J. Lye, Flux and transmission characteristics of a vibration microfiltration system operated at high biomass loading, J. Membr. Sci., 228 (2004) 89–101. O. Al-Akoum, L.H. Ding and M.Y. Jaffrin, Microfiltration and ultrafiltration of UHT skim milk with a vibration membrane module, Sep. Purif. Technol., 28 (2002) 219–234.
Dynamic microfiltration with a vibrating hollow fiber membrane module So/ren Prip Beier, Gunnar Jonsson* CAPEC, Department of Chemical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark email: [email protected] Received 19 October 2005; accepted 6 March 2006
1. Introduction
2. Experimental
The idea of dynamic microfiltration is to decouple high feed flow velocity and high surface shear rate. These terms are normally connected in conventional cross-flow microfiltration, but by creating a relative motion between the feed stream and the membrane, high surface shear rate is induced and the feed flow can be kept low. A low feed flow velocity results in a low module pressure drop. Thus it is possible to maintain a low and uniform transmembrane pressure which together with the high surface shear rate reduces the fast and compact fouling of the membrane. In this work a dynamic microfiltration system is presented. The necessary surface shear rate is created by vibrations of a membrane module that consists of hollow fiber membranes. Filtration of baker’s yeast suspensions are evaluated by using the “critical flux concept” formulated by Field et al. [1]. It is also investigated how the critical flux varies with the surface shear rate.
The membrane module consists of 54 hollow fibers each with a length of 12 cm placed parallel in a plastic cylinder. The polyethersulfone hollow fibers have the skin layer on the outside and an average pore size of 0.45 mm. Each fiber is closed in one end and the other end is connected to a progressive cavity pump that sucks permeate through the fibers. The pump operates at a constant rate which means that the flux is kept constant at that specified pumping rate. The pumping rate is adjustable and controlled by a PC. The fibers are fixed between two steel plates that can be vibrated up and down at variable frequency and amplitude. Compared to other dynamic microfiltration systems [2,3] it is possible to vary the frequency and amplitude independently, and the shear rate on the surface is uniform on the whole membrane area. The feed fluid is circulated between the feed tank and the plastic cylinder. Permeate is collected on an electronic scale connected to the PC from which the flux can be calculated. A pressure transducer connected to the PC measures the transmembrane pressure. Using suspensions of baker’s yeast (5 g/L dry weight) the critical flux is determined at different levels of vibration
*Corresponding author.
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.114
500
S.P. Beier, G. Jonsson / Desalination 199 (2006) 499–500
membrane which is almost constant when operating below the critical flux.
Critical flux [L/(m2 h)]
100 y = 8.2167x0.2643 R2 = 0.8751
4. Conclusion
10
1 10
100 1000 Shear rate [1/s]
10000
Fig. 1. Critical flux as a function of the average surface shear rate in the filtration of baker’s yeast suspensions (5 g/L dry weight).
frequency (5–30 Hz) and vibration amplitude (0.2–1.175 mm). 3. Results and discussion At each combination of frequency and amplitude the average surface shear rate is calculated by use of an equation derived by solving the Navier–Stokes equation of motion. The corresponding values of critical flux and average surface shear rate are plotted in Fig. 1 in a log–log plot. In the figure it is shown that the critical flux varies with the average surface shear rate as a power function which is the same kind of correlation found by other authors working with dynamic microfiltration systems [2–4]. The transmembrane pressure during filtration is very low (<100 mbar), which reduces the fouling problems. This is also seen by looking at the permeability of the
A vibrating dynamic microfiltration system has been presented, and results from filtrations of baker’s yeast suspensions have shown that the critical flux varies with the surface shear rate as a power function. It was possible to filtrate at a very low transmembrane pressure and with a membrane permeability almost constant, when the flux is kept below the critical flux. The fouling problems were therefore reduced. Further filtration results from filtrations of yeast suspensions containing different enzymes will be presented, and the fouling mechanism and enzyme transmission will be discussed.
References [1]
[2]
[3]
[4]
R.W. Field, D. Wu, J.A. Howell and B.B. Gupta, Critical flux concept for microfiltration fouling, J. Membr. Sci., 100 (1995) 259–272. M.Y. Jaffrin, L. Ding, O. Akoum and A. Brou, A hydrodynamic comparison between rotating disk and vibratory dynamic filtration systems, J. Membr. Sci., 242 (2004) 155–167. J. Postlethwaite, S.R. Lamping, G.C. Leach, M.F. Hurwitz and G.J. Lye, Flux and transmission characteristics of a vibration microfiltration system operated at high biomass loading, J. Membr. Sci., 228 (2004) 89–101. O. Al-Akoum, L.H. Ding and M.Y. Jaffrin, Microfiltration and ultrafiltration of UHT skim milk with a vibration membrane module, Sep. Purif. Technol., 28 (2002) 219–234.