Replacement seal solves ongoing challenge

When Regeneron Pharmaceuticals Inc. purchased a new mammalian bioreactor skid, it had the same high expectations that surround any major process improvement. But during the initial start-up, it became apparent that the vessel would not maintain sterility reliably, due in part to the design of the OEM bottom-entry agitator seal. According to Regeneron facilities engineering supervisor Kyle Cherry, the reactor was ‘problematic’.

“The main issue with the OEM seal was that the sterilization requirement hadn’t been observed and sealing integrity was compromised,” said Cherry.

Sterilization of the interior vessel bore was absolutely essential. Once this requirement was met, the bioreactor had to cool to a temperature appropriate for introducing the cell culture medium.

The hitch was that the OEM seal faces were not oriented suitably to foster complete sterility. In addition, the port locations were not optimal for total evacuation of air, causing the inner seal to let in vapour. Because clean steam was used for sterilizing the bioreactor, a moderate flow of clean steam condensate became the barrier fluid to the mechanical seal assembly during certain phases of production.

Undisrupted production did not begin until shortly after the OEM agitator shaft seal was replaced with a custom-engineered design from Flowserve Flow Solutions. While both the OEM seal and the replacement featured a dual mechanical seal to protect the sterility of the cell culture medium and a secondary sealing device to protect the gearbox, the difference, said Cherry, “is that the OEM seal had cleanability issues, making it unable to maintain a sterile environment.

“Flowserve customized a model ST seal to address the repetitive seal problems,” he said. The new seal was designed as a dual-cartridge seal that mounted directly to the gearbox, as well as to the bioreactor’s mounting pad.

An additional part of the challenge was that the European design and the transverse angle of the drive required detailed field measurement by Flowserve for proper fit and function.

Installing the ST seal as a complete unit provided numerous advantages. The ST seal required no handling of integral sealing components, had fewer components to stock and maintain, and included a complete cartridge that could be aerostatically pressure-tested to ensure integrity before installation.

Relocating the springs outside the process media and contouring critical sealing components to resist pooling also fostered optimal cleanability and sterility. Adding a flexible stator design compensated for misalignment and mixing anomalies that can occur under normal operation.

The new seal maintains absolute containment of the clean steam condensate during each phase of production. By incorporating an internal flow deflector, the primary seal is kept lubricated to eliminate dry-run conditions. A Flowserve Bearing Gard II unit was added to eliminate condensate weepage from penetrating the gearbox.

When asked why Tarrytown, NY-based Regeneron chose the Flowserve seal, Cherry explained that Flowserve had engineered sealing solutions for several Regeneron reactors over the years, and that those had performed as promised.

In this case, because the reactor was too large for a magnetic drive, a mechanical seal was needed. “Although this is a bottom-entry agitator at a slight transverse angle, and the previous Flowserve-Regeneron projects were for top-entry agitators, Flowserve didn’t seem to have any problem getting the job done,” said Cherry

MRO

For more information from Flowserve Canada Inc., visit http://www.flowserve.com