Design, Development and Evaluation of an ‘Oscillatory Flow Bioreactor’ (OFBR)

Oscillatory baffled reactors (OBR) are a relatively new design of ‘intensified’ plug flow reactors. They provide a new type of mixing device, which can be used for continuous or batch applications (Jian and Ni, 2003). In contrast to the conventional plug flow reactor, the oscillatory baffled reactor has equally spaced orifice plate baffles (Stonestreet and Harvey, 2002). The baffles divide the tubular reactor into single chambers. When the fluid is oscillated, the baffles cause the formation of vortices, which leads to both radial and axial mixing. Thus, the chambers each act like a single stirred tank reactor, while the fluid is streaming through them. The chaotic flow patterns lead to instability and turbulence within the reactor and provide intensive, uniform mixing. Oscillation can be carried out in two different ways: by oscillating the fluid itself or the baffled device.

The OBR has a number of advantages over other reactors which might make it useful for special applications. One major advantage is the good, uniform mixing, which provides a good heat and mass transfer. The good mixing in OBR also results in shorter reaction times. Shorter reaction times lead to a reduced length-to-diameter ratio in comparison to conventional plug flow reactors and therefore a more compact design. Thus the OBR is ideal for long reactions. The shear in OBRs is more uniform than in stirred tanks, which might be an advantage especially for biological applications. Scalability is a particular advantage of the OBR because the mixing does not change with scale, which makes a linear scale-up possible and predictable.

As the technology can easily be configured to suspend particles and for gas contacting, the oscillatory baffled reactor seems to be a valuable invention for different types of process industries such as pharmaceutical production, polymerisation and biochemical engineering (Jian and Ni, 2003). One of the most commercially important classes of long reactions are fermentations. Currently, new methods of continuous fermentation are required to allow conversion of a range of batch fermentation processes to inherently more efficient continuous processing.

As one major advantage of the OBR is very good uniform mixing, providing a good mass and oxygen transfer, it seems ideal for microbial purposes. The possibility of continuous fermentation is a second advantage as it will minimise the substrate and product inhibition. Lower shear rates compared to a stirred tank reactor may be an additional advantage depending on the shear sensitivity of cultures such as mammalian, insect and plant cells, fungi and certain types of algae.

This project will initially entail some design consideration of the new design features required when bioreactions, as opposed to chemical reactions, are to be performed. That design will then be fabricated, and the reactor assessed for a range of applications provided by other partners within ‘Bioproduction’ and compared to conventional technology, to determine when and how the OBR is a good solution. The main emphasis herein will be to evaluate the reactor for bioprocesses (various, including microbial production of intermediates and functional biomaterials e.g. biopolymers and enzymic biotransformations).

For more information please contact Prof Adam Harvey.

References

1. Harvey, A.P., Mackley, M.R. and Seliger, T.: Process intensification of biodiesel production using a continuous oscillatory baffled reactor, Journal of Chemical Technology and Biotechnology 78 (2003): 338 – 341

2. Jian, H. and Ni, X.-W.: On modelling turbulent flow in an oscillatory baffled column  -RANS model or large-eddy simulation? Journal of Chemical Technology and Biotechnology 78 (2003): 321 - 325

3. Stonestreet, P. and Harvey, A.P.: A mixing-based design methodology for continuous oscillatory baffled reactors, Trans IchemE 80 (A) (2002): 31 - 44