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Design of Bioreactor:Material of construction 2:Pilot scale and large…
Design of Bioreactor:Material of construction
2:Pilot scale and large scale bioreactors:
Pilot scale and large scale vessels are normally constructed of stainless steel or at least have a
stainless steel cladding to limit corrosion.
steels containing less than 4% chromium
Mild steel coated with glass or phenolic epoxy materials
Wood, concrete and plastic have been used when contamination was
not a problem in a process.
The minimum amount of chromium needed to resist corrosion will depend on the corroding agent
in a particular environment, such as acid, alkalis, gases, soil, salt or fresh water.
Increasing the
chromium concentration enhances the resistance to corrosion,
The inclusion of nickel in high percent
chromium steels enhances resistance and improves their engineering properties.
a reliable aseptic seal
glass and
glass, glass and metal, metal and metal joints such as between a fermenter vessel and a detachable top or base plate.
With glass and metal a seal can be made with a compressible gasket, a lip seal or an ‘O’ ring. With metal to metal joints only ‘O’ ring is suitable.
VESSEL SHAPE
vertical cylinders with specialized top plates and bottom plates
A tall, thin
vessel is the best shape with aspect ratio (height to diameter ratio) around 10:1.
a
conical section is used in the top part of the vessel
to give the widest possible area for gas
exchange.
Stainless steel top plates.
The top plates are of an elliptical or spherical dish shape. The top plates can be either removable or
welded
A removable top plate provides best accessibility, but adds to cost and complexity.
Bottom plates.
most of the large vessels
have a dish bottom,
the smaller vessels are often conical in shape
Height-to-diameter ratio (Aspect ratio).
a symmetrical
vessel maximizes the volume per material used and results in a height-to-diameter ratio of one
most vessels are designed with higher ratio. The range of 2-3:1 is more appropriate