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More Update Post: 01_29_2009;
03_07_2009; 04_07_2009
Quite a bit of interest exists
currently globally on the development of ethanol production processes.
However, the basic concept of
fermentation is well known and well-studied for many years. Fundamentally an ethanol
process may be deemed to be of two main components:
Fermentation Substrate-Feed Process and
Biochemical Fermentation Process. The former
handles the processing of the feed prior to being pumped into the
latter, Fermentation Process,
while the latter beginning with the Fermentation Reactor carries
through the rest of production of the alcohol and has a process
engineering that is, more or less, generic for all ethanol
processes.
The Substrate Feed
process have evolved over time from global interest on the development of ethanol production
process; and in course of the experimenting development with a myriad of feed sources for the sugar-feed
for the fermentation reactor. However,
three or four feed sources: Grain, Cellulosic [Grass] Source,
Sugar-cane and Palm Sap; are used most commonly and so constitute
the primary sources. With each of these newer
substrate-sources has come newer ad hoc approaches to ethanol
production, and each of which has the potential of becoming an
industrial process. Also the empirical utilization of these
substrate-sources
has evolved a set of
process step and correspondingly engineering equipment set for
the processing of the feed into the feed-sugar [also the substrate]
as synopsized:
Grain Ethanol Feed Process
Cellulosic & Hemicellulosic Feed Process
Palm Juice Feed Process
prior to being transfer into the fermentation
reactor vessel, in which the fermentation microbe effects the
oxidative digestion of the sugar into ethanol.
The technology of the
Fermentation Process, of
course, for production
operations, which is a continuous
operating process plant, consists of virtually the same equipment
set:
Fermentation Reactor
Distillation System(s)
Storage Tanks
The operation of the
components follows this progression: Basically, during operation,
the feed mixed with other supplementary additives is charged into
the Fermentation Reactor to initiate and sustain fermentation. The
Fermentation reaction is allowed to proceed up to a level of completion as
determined by the reaction time allowed, either by the batch
operation or by the residence time in the reactor. At the set time
the fermentation reaction product is transferred to the distillation
system for distillation. The product of the distillation process
should yield grain alcohol.
The specifics of the
reactor configuration depends on the process technology. However, a
process technology may be based on a homogeneous well-mixed
fermentation reactor, or for purposes of cost control a
heterogeneous biofilm fermentation reactor may be adopted,
although a
homogeneous bioreactor is equally suitable. Each one comes with
its advantages and disadvantages. However, each
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class of reactor can by design be
implemented in all the various known chemical reactor types
including Batch
Fermentation Reactor Analysis, Continuous Flow Fermentation
Reactor Analysis, and Tubular Flow Fermentation Reactor Analysis.
However, irrespective of the type of reactor that is deployed,
material balance analysis for these reactors allows for
accounting for the consumption and
assimilation of the nutrients
into microbial mass. The consideration of the metabolic reactions as
such part of the analysis
foundation enables the adoption of
fermentation
reactor design material balance
method that is intrinsic for fermentation reactor designs.
The homogeneous
bioreactor generally is operated with the fermentation microbes
mixed directly into the reaction matrix or broth. This mode of
operation while allowing for intimate access to the substrates by
the microbes also introduces some issues. The most significant of
these issues is the
choice of the microbes
to be used for a particular fermentation process. Generally, the
microbes can not be pathogenic, if particularly the products are
intended for consumption; and even if consumption is not necessarily
the objective for the products, but such must be used on the human
body in anyway, then the microbes can not even be deemed
opportunistic pathogens, which are microbes that are non-pathogens
under certain conditions and are pathogenic in other conditions.
Accordingly, homogeneous reactors are operated such as to completely
disable the microbes at the end of the fermentation period. These
are accomplished often
with the operation of the reactor up to a state when product
inhibition sets in and ultimately causes death of the
microbes. A classic example of such state of operation is given by
the heuristic determination of completion of fermentation as the
cessation of
bubbling of the broth.
The heterogeneous bioreactor
by design and object has the microbes immobilized onto a collection
of carrier which are then dispersed in the reaction mixture.
This class of reactor provides the most flexibility of
configuration, and operating method. In general, the class of the
reactor is defined by the implementation of the support for
maintaining the carriers within the reactor, and as a result some of
the forms of this class of reactor even implemented as a batch
reactors are operated as
packed bed
reactor,
fluidized bed batch reactors, among others. In
particular, when the bio-reactions need to be sequenced to effect
multiple reaction, the reactor can even be packed as
multi-packed
bed bioreactor. The
immobilization
of the microbes on carriers, of course, impacts the
efficiency of the microbes in
effecting the fermentation reaction.
Implementation of the bioreactor as a heterogeneous reactor also has
attendant issues worth analyzing during the
bioreactor design phase.
However, irrespective of the
choice of bioreactor as per the
specification of the general design rationale bioreactor must
have an integrated
Fermentation
Mash Feeder equipment. The configuration of
the Mash Feeder must be based on the general
requirements of nutrients
for a
fermentative glucose utilizing reactor. By the nutrients
requirements, the configuration of a Mash Feeder at a minimum will
have several feed-ports, say eleven feed-ports, and of different
types. Some of the feed port will be feeding solid powders into the
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substrate, some will be
pumping liquids into the substrate. Further, the Mash Feeder
configuration must be such as to dissolve the proper concentration of the
oxygen into the mash just before discharge into the reactor;
in all these cases even the oxygen concentration in the mash must
not be allowed to fall below the optimal concentration at exit of
the mash into the bioreactor.
Distillation systems
design is standard Chemical engineering and once the
technology developer has successfully concluded the development of
the fermentation reactor, a team can be put together to move the
project forward; at that time the Distillation systems design may be
undertaken.
The alcohol produced
usually from the distillation process of any of the generic
fermentation processes reflected here has the highest proof of 190
[proof]. However, for the purposes of using the alcohol as a fuel alternative,
for example, sieve based secondary distillation may be required to
obtain 200 proof ethanol. In general, the desired proof depends on
the application need and, in terms of the number of distillation
columns that is supported, determines the level of complexity of the
bioprocess, as well as other factors of design consideration.
The analysis and
consideration elicited in this report are, even if a known
industrial process has long been established and has become the
de facto ethanol fermentation process.
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