Integrated Knowledge-Based Analyses of Socio-Economic Issues

Report Catalogue Data

  Report Class   General Public Report
  Analysis Type   Situation Analysis
  Issue Category   Technology Analysis
  Release Date   06_08_2008
  Last Update   06_11_2009
  Reference Code   GPR-SA.TA.FT-20080608-EFP

Fermentation Technologies
Ethanol Fermentation Process Analysis

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

 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



Available at Okumaye Publishing

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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