Feeding tank; 2. Pump; 3. Elastic
membrane pulsator; 4. Sampling ports;
S. Air difusor; 6, 7. Inlet, outlet of
thermostated water; 8. Liquid outlet; 9.
Sensors (T, pH, etc); 10. Meters; 11.
Gas exit; 12. Data Acquisition and
Control Unit. 2b) Pulsing device: 1.
Inlet stream; 2. Heads; 3. Elastic
rubber tubes; 4. Electrovalve; 5.
Connection to the control loop; 6.
Outlet stream.
ELASTIC MEMBRANE PULSATOR
The elastic membrane pulsator (EMP) consists of a system formed by one or more elastic
tubes connected in parallel by means of two heads with defined internal diameters, wall
thickness and length, which are coupled to an electrovalve which is opened and closed by
a timer or a computerised system (DAC system). A diagram of a packed-bed bioreactor
coupled to the pulsing device is presented in Figure 11.2.
The pulsation is produced when the gas or liquid retained within the elastic tubes
(when the valve is closed), is impelled into the reactor once the valve opens. According
to the flow provided by the feeding pump, the volume of the fluid retained is regulated by
the shutting time of the electrovalve, which therefore determines the volume of pulsed
fluid and, accordingly, the amplitude of pulsation.
The pulsation frequency f and the amplitude a in the bioreactor are expressed through
the following equations:
(1)
(2)
where t 0 , ts, F, ε and D are the opening and shutting times, liquid flowrate, void fraction
and column diameter, respectively. The electrovalve opening time is fixed in a
determined value and therefore the pulsation frequency and amplitude are regulated by
varying the electrovalve shutting time.
HYDRODYNAMIC BEHAVIOUR OF A PULSED PACKED-BED
REACTOR
The effects of pulsation on the modification of hydrodynamics of packed-bed reactors
were studied in different sets of conditions (Roca et al., 1994) (different feed flowrates,
Multiphase bioreactor design 334