Design of a Bearingless Bubble Bed Reactor

In the past, several studies have found bubble aeration in animal cell cultures, especially the bursting of bubbles in the foam region, to be responsible for significant cell death. In order to reduce these detrimental cell-bubble interactions, the so called "bubble bed reactor was developed at the Swiss Federal Institute of Technology (ETH) Zurich. This modified loop reactor accumulates oxygen bubbles in the downcomer and has thereby a more than 10 times higher oxygen uptake than standard air-lift reactors. With the example of a 250L bubble bed reactor it has been shown that an oxygen yield in excess of 90% is reachable and that the bubble bed reactor is a gentle aeration method for animal cell cultures. One of the main remaining sources for cell death in the bubble bed reactor is the shaft seal of the impeller. In this paper we present a concept for a bubble bed reactor with a totally magnetically suspended impeller. It is based on the technology of the "bearingless motor" and is therefore called the "bearingless bubble bed reactor". A single bearingless motor with a ring shaped rotor is at the same time a motor and a bearing system. The ring shaped rotor with the axial flow impeller is arranged around the downcomer inside the tubular reactor housing. The motor/bearing stator is arranged around the housing. The six spatial degrees of freedom of the rotor are stabilized magnetically through the housing wall which is in the air gap. Three degrees of freedom are stabilized actively (the rotation and the radial displacement of the rotor). The axial and the angular displacement are stabilized passively.