|
A Batch fermentation Reactor is
the vessel within which the
fermentation
reaction is conducted, and is such that the reaction mixture can
be charged into and then left within undisturbed until the reaction
is complete, and after which the final reaction product mixture is
emptied from. The vessel interior generally is not accessible and is
not accessed during the course of the reaction. In effect, neither
addition nor removal of substances, to and from respectively the
vessel, are made once the reaction has started. Further, this class
of bioreactors also exhibit mixedness heterogeneity: Mixing of the
microbes with the broth almost certainly never achieves a state
of well-mixedness and as such the reaction mixture does not have
uniform concentration through out the reactor and as a result, the
operations of this reactor must plan for and account for
heterogeneity.
The design of the
fermentation reactor entails two tasks: Equipment design and
Computational design; however, only the former must be performed by
every reactor designer, the latter is optional but strongly
suggested for well-funded projects, as this aspect of the design can
be quite expensive.
Designing, in essence, is the
formal synthesis of the results of analysis, on the other hand,
analysis is the formal validation of design; as such the two tasks
are the same in some respects. In that regard the analysis of the
fermentation reactor is a validation of the design of the reactor.
The equipment design of the
reactor task, actually, is the determination of both the
external and internal structure of the equipment as well as the
dimensions. The equipment design of this type of reactor must
implement all means necessary to ensure the virtual elimination of
heterogeneity of the broth or mash during the reaction. The
computational design is a
mathematical assessment of the equipment design prior to shipping
off the design specification, otherwise called blueprint, to an
equipment fabrication shop for manufacture.
Mathematical analysis of this type of reactor should aim to include
various forms of reaction mixture partitioning coupled with
stochastic dispersion to aim to capture the heterogeneity.
Equipment Design
The equipment, for all intents and purpose, is a manifestation
of that which was subsumed in the
material balances
calculations undertaken to ensure compliance with the Laws of
Conservation of Mass, for supporting the annual production-volume of
ethanol determined to ensure ensure compliance with the Laws of
Conservation of Mass, for supporting the annual production-volume of
ethanol determined to ensure profitability. So obviously
the feed volume and mass will be the same as was assessed for the
material balances; and the feed state must also be consistent with
the
constituents of
typical ethanol fermentation reactor stream used in the material
balance calculations.
In this context, the
equipment design becomes the development of features for handling
different aspects of the operational consideration of the |
fermentation reaction:
- as a closed system
equipment, the pre-operations charging of the reactor with the
feed is a matter of import to be addressed, while taking care to
note also that the equipment can not be accessible while in
operation; moreover, and in particular, the feed must be
charged into the reactor through an integrated microbe-specific
Mash Feeder specially designed to avert reaction mixture
heterogeneity;
- the decision to stir the
reaction-mixture during the progress of the reaction is equally
important as such stirring should eliminate potential
boundary layer around the microbes, as well as enable
sustained intimate mixing of the broth, and the
design that must
support such stirring is necessary;
- the manner of dispersion of
the microbe in the broth or reaction-mixture is also very
important design consideration; the reactor could be operated
homogeneously in which case the microbes are simply mixed into the
Broth, or possibly heterogeneously in which case the
microbes are immobilized on an
effective
carrier dispersed in the
broth;
- some
fermentation reactions,
also produce gases either hydrogen or carbon dioxide, hence raising for address the issue
of the removal of the gases in course of the reaction,
while perhaps making sure that the vessel remains closed,
- a feature for
maintaining the pressure level in the reaction vessel that sustains
the applicable dissolved oxygen pressure, making sure that operation is anaerobic
is critical, given that as a closed system the sugar concentration
reduces with the progression of the reaction and hence
aerobic
fermentation can not be supported through the course of the
reaction;
- the feature to enable
igniting the reaction is also an important one, the
Embden Meyerhoff
pathway requires Magnesium and Potassium to sustain the
glycolysis reaction and hence ignite the reaction, and the timing
and introduction of these minerals into the reactor is of careful
design as well;
The designer may have to
consider other factors as the operations may require, however, the
aforementioned features must be designed for. After the design of
the operation-specific features of the reactor, the final task of
sizing the main body of the vessel comes up. Two approaches can be
taken to deal with this consideration, however: The use of rule of
thumb and full-scale iterative engineering cost analysis based on
the practices of engineering economics. Yet irrespective of the
approach adopted the initial dimensions can be based on the rule of
thumb calculations: The height of the reactor should be no
more than 12-feet, and the interior diameter of the reactor should
be no more than 6-feet; such that the following
calculations are made;
Volume of reactor (Vrxtor)
= π(D/2)2H
where D = 6 and H = 12 as per
the rule of thumb, next compare batch volume Bvol - as determined
|
|
advertisement |
|
now available... Click Image↑
to Buy |
|
Coming soon !
details |
by
material balances - with Vrxtor: If Bvol is less than Vrxtor then
reduce reactor size ratio to match Bvol in ratio of height:diameter::2:1;
If Bvol is more than Vrxtor then adjust
reactor size to half the size of Bvol as to use two reactors;
finally if Bvol is the same as Vrxtor then do nothing. The equipment design is
then complete, after the appropriate adjustments of the other devices
designed for the batch-operations features.
Computational Design
The equipment design evaluation through the computational design is
performed in two parts. Though highly valuable this aspect of the
design is very intense requiring both the software developer to
develop the program and the engineer to develop the mathematical
descriptions of the equipment as designed and of the fermentation
reaction dynamics.
The first part develops to the extent possible a mathematical
description of the fermentation reaction dynamics and conducts simulation
of the performance to ascertain that the production volume output
and other calculations are within tolerable or pre-set bounds of
variation. Mathematical analysis and
performance assessment of the fermentation reactor essentially
entails use of the reaction rate equation of the catabolic reactions
that contribute to the fermentation, and the
Monod equation
for analysis of the catabolic reaction that contribute to anabolic
reaction for cell maintenance. These equations are solved
simultaneously over the reaction-time together with the mash constituents depletion rate equation(s) as
defined by the
mass balance analysis for a specified extent of reaction.
The second part again develops a mathematical design of the
equipment structure and performs a simulation in-operation to test
the robustness of the design. The computational analysis of design-robustness usually aims to assess the equipment by performing stress analysis,
vibration analysis if
mixing and other test are planned, and other appropriate mechanical
robustness tests. This second part of the computational design is
usually computation-intensive.
|
