Displaying items by tag: Process Innovation

The Centre for Process Innovation Ltd has recently finished accepting proposals for a contract covering thesupply, installation and commissioning of a fermenter seal system

at its Wilton Centre base, near Redcar, UK.

 

CPI operates a number of fermenters in the Wilton facility. One of these, a 10,000 litre working volume fermenter, was installed in 2010 and the seal system has proved troublesome.

 

Reliable seal operation is defined as no failures in a three year period. CPI requests the seal system vendor to propose a seal system which will achieve the required level of reliability, and to guarantee this, subject to any appropriate limitations.

Furthermore the seal system vendor should identify any steps or checks which have to be carried out by CPI to achieve and sustain this level of reliability.

 

The fermenter is part of an experimental development facility, running around 30 weeks per year. Batches typically take three to 10 days in operation; however continuous operation for up to 60 days can also be required.

The vessel is used for biofermentation and uses standard CIP chemicals (NaOH) to clean. The steam and air systems are clean. The fermenter is cleaned in place after every campaign.

Sterilisation of the fermenter and the seal is a requirement before every batch. This is carried out using locally generated low pressure (2barg) steam at 133°C. Sterilising of the seal is carried out with the agitator stationary.

 

The agitator is top mounted with a gearbox and motor mounted on a stool on the vessel top flange (see figures 1 and 2). The seal attaches to the lower flange of the stool. The agitator has an in-tank steady bearing at the bottom end of the shaft.

Shaft diameter is 125mm at the vessel opening and steps down to 123mm under the current seal sleeve. Fermenter design pressure range is -1 to +5 barg; fermenter design temperature is 0 to 150°C.

A bursting disc for 5barg is fitted. Operating pressure is normally in the range 0.5barg to 1barg. A process trip is set at 2.4barg at which point the exhaust bypass opens.

 

Vessel operating temperature is normally in the range 27°C to 30°C. Maximum temperature is during sterilisation (133°C). The agitator speed is 10-170RPM. Normal speeds are in the range 25 to 100 RPM.

 

It is a cartridge double seal using sterile (filtered) air as the pressurizing medium (API piping plan 74). Air pressure is 4.5barg minimum. The lower (process side) seal is a gas seal with hydrostatic lift and is contained within the vessel head space. The upper (atmospheric side) seal is a dry running carbon vs SiC seal. A ball bearing is contained within the seal housing to control the shaft radial position.

 

During commissioning/initial operation the upper seal failed in March 2011 due to excessive wear of the carbon face. The specification of the carbon face was changed. In Dec 2012 the lower seal failed, apparently due to mis-assembly (prior to arriving at site).

 

The upper seal carbon was again found to be heavily worn. At the time of Setember 2013, the upper seal is known to be worn again due to the visible carbon content of the condensate/steam mixture during sterilisation and the seal will need to be changed shortly.