LARGE SCALE PRODUCTION FERMENTER DESIGN AND
ITS VARIOUS CONTROLS
Suman Kumar Mekap
CUTM BHUBANESWAR
INTRODUCTION
Fermentor - industrial usage microbes
grown in large vessels.
Bioreactor
Complicated in design
IDEAL FERMENTOR PROPERTIES
Supports maximum growth of the organism
Aseptical operation
Adequate aeration and agitation
Low power consuming
Tempurature control system
pH control system
Sampling facilities
Minimum evaporation loss
Minimum use of labour
Range of processes
Smooth internal surfaces
Similar in geometry to both smaller & larger vessels in pilot
plant
Cheapest material usuage
Adequate service provisions
Provision for control of contaminants
Provision for intermittent addition of antifoams
Inoculum introduction facility
Mechanism for biomass/ product removal
Setting for rapid incorporation of sterile air
Withstands pressure
Ease of manipulation
BASIC DESIGN OF AFERMENTOR
Various components of an ideal fermenter for batch
process are
Monitoring and controlling parts of fermenter
are
SHAPE OF FERMENTER:
Fermentation Are Available In Different Shapes Like
Conical Fermenter
Cylindrical fermenter
Spherical fermenter
Pear In Shape Fermenter
SIZES OF FERMENTER :
The sizes of the fermenter are divided into the following groups.
1. The microbial cell (mm cube)
2. Shake flask (100-1000ml)
3. Laboratory fermenter (1-50 L)
4. Pilot scale (0.3 -10m cube)
5. Industrial scale (2-500m cube)
MATERIAL OF CONSTRUCTION
Laboratory scale bioreactor:
In fermentation with strict aseptic requirements it is important to select materials
that can withstand repeated sterilization cycles. On a small scale, it is possible to
use glass and/or stainless steel.
Glass is useful because it gives smooth surfaces, is non-toxic, corrosion proof and
it is usually easy to examine the interior of vessel. The glass should be 100%
borosilicate, e.g. Pyrex® and Kimax®.
The following variants of the laboratory bioreactor can be made:
1. Glass bioreactor (without the jacket) with an upper stainless steel lid.
2. Glass bioreactor (with the jacket) with an upper stainless steel lid.
3. Glass bioreactor (without the jacket) with the upper and lower stainless steel
lids.
4. Two-part bioreactor - glass/stainless steel. The stainless steel part has a jacket
and ports for electrodes installation.
5. Stainless steel bioreactor with peepholes.
Vessels with two stainless steel plates cost approximately 50% more than those
with just a top plate
Pilot scale and large scale bioreactors:
When all bioreactors are sterilized in situ, any materials use will have to assess
on their ability to withstand pressure sterilization and corrosion and their
potential toxicity and cost.
Pilot scale and large scale vessels are normally constructed of stainless
steel or at least have a stainless steel cladding to limit corrosion.
The American Iron and Steel Institute (AISI) states that steels containing
less than 4% chromium are classified as steel alloys and those containing more
than 4% are classified as stainless steel.
Mild steel coated with glass or phenolic epoxy materials has
occasionally been used. Wood, concrete and plastic have been used when
contamination was not a problem in a process.
Vessel shape: -
/Typical tanks are vertical cylinders with specialized top plates and
bottom plates. In some cases, vessel design eliminates the need for a stirrer
system especially in air lift fermenter. A tall, thin vessel is the best shape with
aspect ratio (height to diameter ratio) around 10:1. Sometimes 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. Various ports and standard nozzles are provided on
the stainless plate for actuators and probes. These include pH, thermocouple, and
dissolved oxygen probes ports, defaming, acid and base ports, inoculum port, pipe
for sparging process air, agitator shaft and spare ports.
Bottom plates:
Tank bottom plates are also customized for specific applications. Almost
most of the large vessels have a dish bottom, while the smaller vessels are often
conical in shape or may have a smaller, sump type chamber located at the base of
the main tank. These alternate bottom shapes aid in fluid management when the
volume in the tank is low. One report states that a dish bottom requires less power
than a flat one.
In all cases, it is imperative that tank should be fully drainable to recover
product and to aid in cleaning of the vessel. Often this is accomplished by using a
tank bottom valve positioned to eliminate any “dead section” that could arises
from drain lines and to assure that all content will be removed from the tank upon
draining.
If the bioreactor has a lower cover, then the following ports and elements should
be placed and fastened there:
1. Discharge valve;
2. Sampling device;
3. Sparger;
4. Mixer's lower drive;
5. Heaters.
Height-to-diameter ratio (Aspect ratio).
The height-to-diameter ratio is also a critical factor in vessel design.
Although 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 and in some situation, where stratification
of the tank content is not an issue or a mixer is used, will allow still higher ratio to
be used in design.
The vessels for microbiological work should have an aspect ratio of 2.5-
3:1, while vessels for animal cell culture tend to have an aspect ratio closer to 1.
The basic configuration of stirred tank bioreactors for mammalian cell culture is
similar to that of microbial fermenter but the major difference is there in aspect
ratio, which is usually smaller in mammalian cell culture bioreactor.
FERMENTOR’S STRUCTURAL COMPONENTS IN
AERATION & AGITATION SYSTEM:
The agitator
Stirrer glands & bearings
Baffles
The aeration system
AGITATOR
Synonym : impeller
Mounted to a shaft through a bearing in the lid
Driven by an external power source or direct drive
Direct drive - action varied by using different impeller blades
Recent designs – driven by magnetic coupling to a motor mounted beneath
the fermenter
High speed of rotation marked vortex occurs
Spinning of medium in circular direction
MIXING OBJECTIVES IT ACHIEVE
Bulk fluid & gas
Heattransfer phase mixing
Air dispersion
Suspension of solid particles
O2 transfer
Maintenance of uniform environment throughout the vessel
CLASSIFICATION
Disc turbine
Vanned disc
Variable pitch open turbine
Marine propellers
DISC TURBINE:
A disc with series of rectangular vanes set in a vertical
plane around the circumference.
Break up a fast air stream without itself becoming flooded in
air bubbles
VANED DISC
A series of rectangular vanes attached vertically to the underside
Air from sparger hits it’s underside & the air gets displaced towards
the vanes
Results in destruction of air bubbles
VARIALBLE PITCH OPEN TURBINE:
Vanes are attached directly to a boss on the agitator shaft
Air bubbles hit any surface by its action
Flood when super fial velocity exceed 21m/h
MARINE PROPELLER
Blades are attached directly to a boss on the agitator shaft
Air bubbles hit surface
A single low shear impeller
Mainly used in animla cell culture vessel
Flood when superfial velocity exceed 21m/h
MODERN AGITATORS
Rushton disc turbine
Scaba 6SRGT
Prochem max flow T
Lightening A315
Ekato intermig
BAFFLES
Metal strips
1/10th of the vessel diameter
Attached radially to wall
4 baffles (normal)
Wider baffles -high agitation effect
Narrower baffles – low agitation effect
Can be attached with cooling coils
Not found in lab scale fermentors.
Vertical baffles – increased aeration
AERATION SYSTEM
Syn : sparger
A device that introduce air into medium
Has a pipe with minute holes (1/64 - 1/32 inch or large)
Hole – allows air under P to escape into medium
For mycelial growth – ¼ inch holes
Impeller blades disperses air released through sparger into medium
SPARGER TYPES
Porous
Orifice
Nozzle
POROUS SPARGER:
Made of sintered glass, ceramics or metal
Used mainly on a large scale fermenters
Bubble size produced – 10-100 times larger than pores
Throughput of air is low – P drop across it
Clogging of pores
ORIFICE SPARGER
Those with drilled air holes on their under surface of the tubes making up ring
or cross
Without agitation used to a limited extend in yeast manufacture & effluent
treatment
NOZZLE SPARGER
Modern mechanically stirred fermentors use them
Single open or partially closed pipes
Ideally, positioned centrally below impeller
Causes lower P drops
no clogging of pore
Common Measurement And Control Systems
STIRRED TANK REACTOR
Mixing method: Mechanical agitation
High input required
Baffles are constructed within the built-in.
Applications include production of antibiotics and
free/immobilized enzymes
Draw back is that high shear forces may break the cells
AIR LIFT REACTORS
Mixing method: airlift
Central draft tube
Up-flowing stream and down flowing stream
Homogenization of all
components present
Applications include bacterial, animals, plants, fungi and
yeast cells
FLUIDIZED BED REACTOR
When the packed beds are operated in up-flow mode, the bed
expands at high liquid flow rates due to upward motion of
the particles.
Energy is required
Waste water treatment
PACKED BED REACTOR
Column with attached biofilm
Biocatalysts
Pump is required to make fluid move through the packed
bed.
Applications include waste water treatment
BUBBLE COLUMN REACTOR
Mixing method:
Gas sparging
Simple design
Good heat and mass transfer rates
Low energy input
Gas-liquid mass transfer coefficients depend largely on bubble diameter and
gas hold-up
TRICKLE BED REACTORS
• Liquid is sprayed onto the top of the packing and trickles down through
the bed in small rivulets.
• In the process, the gaseous pollutants on the surface of the carriers is
adsorbed and immediately biologically mineralized (degraded) by the
microorganisms
