fuel ethanol production - katzen

7/29/2019 Fuel Ethanol Production - Katzen

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Fuel ethanol production 1

Fuel ethanol production

P.W. MADSON AND D.A. MONCEAUX

KATZEN International, Inc., Cincinnati, Ohio, USA

History

Motor fuel grade ethanol (MFGE) is the fastestgrowing market for ethanol worldwide; andMFGE production dwarfs the combined totalproduction of all other grades of ethanol.

Fermentation ethanol, as fuel (and solvent), hasexperienced several cycles of growth and declinesince the early 1800s. By 1860, production hadreached more than 90 million gallons per year.In 1861 Congress imposed a tax of $2.08 pergallon. About that time, oil was found inPennsylvania. Thus began the cycle of controlof fuel ethanol markets (and thereforeproduction) by taxation policy and oil industryinfluence on government. Petroleum interestsdominated the world fuel industry in the post-World War II era, until a major policy shift byBrazil in the 1970s led to an ethanol-fueled motorvehicle strategy, followed a decade later by theUS (Morris, 1994, personal communication). Asa result, the combined motor fuel ethanolproduction from fermentation in the WesternHemisphere exceeded 5.5 billion gallons per yearin 2002.

In Central and South America the dominantMFGE feedstock is sugar, either in the form ofcane juice directly from crushed cane(autonomous distilleries), or from molasses(annexed distilleries). In North America, thedominant feedstock is starch from grain, with

90% derived from corn. Feedstock choice

follows regional dominant agricultural output(Katzen, 1987).

Since the technology for producing MFGEfrom sugar sources is an abbreviated form of

ethanol production from starch, which is in turnan abbreviated form of production from wholegrain, this chapter will focus on MFGEproduction from whole grain as typicallypracticed in North America. This technology isgenerally known as dry milling (Raphael KatzenAssociates, 1978).

Introduction

A comparative evaluation of potable ethanol andMFGE production processes reveals manysimilarities. As the MFGE industry began todevelop, it looked to the distilled spirits industryfor technology. In the US, many early MFGEplants copied beverage alcohol distilleryprocesses, differing primarily in the addition ofdehydration facilities copied from the industrial-grade ethanol industry (Madson and Murtagh,1991). This generally ensured a plant capableof producing ethanol. This technology strategy,coupled with a strong ethanol market during the1980s, often resulted in positive cash flows.

This technology strategy continued until a

downward trend in ethanol pricing revealed the

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2 P.W. Madson and D.A. Monceaux

critical difference between distillery and MFGEeconomics. Distilleries are traditionally operatedfor consistency in flavor and quality of product.

Other factors such as yield, energy efficiency,labor cost, etc., while being important, did notdominate the economics. For the beveragedistiller it is counterproductive to reduce cost ofproduction at the expense of flavor and qualityand, possibly, market share. Flavor and productconsistency are so important that any benefitassociated with a process change must beextremely high to offset the inherent market risk,which could be catastrophic if the product mustbe aged for several years. This, combined withthe price differential between distilled potable

spirits and MFGE, caused a shift to newtechnology development and differentiation ofthe MFGE industry in order to survive periodsof high grain cost and low MFGE prices.

The MFGE producer has minimum productquality-related constraints. MFGE specificationsfor water content, acidity, solids, etc. (as definedin ASTM D-4806) can be met whileconcurrently minimizing operating costs. MFGEproducers have traditionally operated withnarrow profit margins. The drop in ethanol priceduring the mid 1980s resulted in most of thebeverage distillery technology-based MFGEproducers ceasing operations. Many of theseoperations were labor- and energy-intensive andoperated with poor yields (Madson, 1990).

The design of a successful MFGE facilityrequires a clear understanding of the economicsensitivities. Evaluation of dry milling operatingcosts revealed that feedstock costs comprise over60% of the total (Hill et al., 1986). Energyconsumption, at one time the central focus ofdebate, has been reduced via a rapiddevelopment of technology to less than 40,000BTUs per gallon of product, which is

approaching the point of diminishing returns incost trade-offs (Hill, 1991; personalcommunication). The key issues today arefeedstock conversion efficiency, capitalinvestment, environmental impact and user-friendliness.

Conversion efficiency (yield)

Most MFGE producers have little control overfeedstock pricing beyond hedging strategies

such as trading in futures. The producersprimary edge is therefore to maximize yield.Prior to the major growth of the MFGE industry,

the typical yield in the production of spirits andindustrial ethanol was five proof US gallons perdistillers bushel (56 lbs) equivalent to 2.375undenatured gallons per bushel in MFGE terms.By the early 1980s, the newly-developed MFGEtechnologies had demonstrated (in top-performing plants) achievements of 2.55undenatured US gallons per distillers bushel(gpb) in dry milling plants and 2.45 gpb in wetmilling plants. More recently, some dry millingMFGE plants have achieved sustained yields of2.8 gpb (undenatured basis).

Because of the different industry reportingprocedures, this discussion is based on the pay-to-pay analysis. That is, yields are presented onthe basis of unadjusted distillers bushels of grainpurchased and ethanol sold (undenatured basis)over a time period exceeding three months. Thisresults in a market-based yield figure that refersdirectly to profit.

What brought about this remarkable yieldincrease? The major development in technologyhas occurred in the dry milling industry,primarily because of the variety of technologiestested and the broad-based experience fromwhich to learn (Katzen et al., 1992).

Beginning with the cooking step, it has becomeclear that the controlling factor in design of acooking system is not the cooking of starch, butrather elimination of bacteria in order to achieveand maintain sterility throughout the process(Kemmerling, 1989). Because conditionsneeded to achieve sterility are different fromconditions required to cook starch, other factorsmust be considered. Cooking must beconducted with minimum solubilization ofpotential fermentables in order to minimize

adverse reactivity; yet all fermentables must bereleased during the liquefaction, saccharificationand fermentation processes for completeconversion to ethanol. This includes thefermentable sugars embedded in the fiber matrix.Premature solubilization of potentialfermentables risks side reactions that can resultin unfermentable starch and sugar complexesbecause of high temperature and the presenceof water and other reactive components. Thesereactions may be as simple as retrogradation ofstarch or as complex as reactions between amino

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acids and carbohydrates. An example of amashing and cooking system that hasdemonstrated maximum yield is illustrated in

Figure 1.Competing cooking factors can be balanced

by selecting a grind that allows minimummobility of the sugars and starch within the grainparticle matrix, yet provides necessaryhydration. This is followed by instantaneous jetcooking in the absence of adverse catalysts. Byproper design of the cooking flash-down toliquefaction temperature (including valveselection), the locked in fermentables can bereleased for full access by liquefying andsaccharifying enzymes. Further, the non-starch

fermentables are released from the fiber matrixto become available to the yeast. By keepingthe fermentables locked in within the particlematrix until the liquefaction tank has beenreached, maximum retention and availability offermentable value is achieved.

The next critical step is liquefaction. Byliquefying to minimum dextrose equivalence(DE) at high temperatures for short time periods,adverse reaction conditions that convertfermentables to non-fermentables areminimized. Little of the starch is converted, andis therefore protected from adverse reactionuntil fermentation conditions are reached.

The key to creating maximum availability offermentable carbohydrates is to reach the outlet

of the mash cooler with virtually sterile mashwhile providing minimum exposure ofcarbohydrate to adverse reactions. At the same

time, the system must maximize downstreamavailability of fermentable carbohydrateembedded in the fiber matrix. Upon reachingthe fermentation temperature, undesirable side-reactions in the mixture are minimal.

From the mash cooler forward, yield is strictlya function of enzymatic hydrolysis, fermentationtechnology, sterility and completion. Highsustained yields, above 2.75 gpb (2.9 gpb asdenatured MFGE product), have been achievedwith simultaneous saccharification andfermentation (SSF). SSF technology was

developed in the 1970s to solve a fundamentalproblem in the conversion of cellulose to ethanol.The MFGE industry has advanced thistechnology to provide even higher yields byincorporating simultaneous yeast propagation(from active dry yeast) in the fermentor duringinitial saccharification. Thus, SSYPF (simultaneoussaccharification, yeast propagation andfermentation) has become the low-cost, high-yielding technology of choice (Figure 2).Significant sugar concentrations do not developin the fermentor, thus avoiding sugar inhibitionof both enzymatic hydrolysis and yeastmetabolism. As a further consequence, bacterialgrowth is inhibited due to lack of free sugarsubstrate. Sugars are converted by yeast to

Figure 1. Mashing and cooking.

Recycled condensate

Steam

Cooker

Hotwell

Flashtank

Steam Processwater

Liquefyingenzyme LIquefaction

tank Mash tofermentation

Mashcoolers

Processwater heater

Recycled stillage

Meal

Backset

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ethanol as rapidly as they are produced. Byproper maintenance of pH, nutrients and sterility,full conversion of available starch and sugars toethanol is achieved. Any pH excursions below4.2 at the end of fermentation correlate directlywith losses in yield (Bowman and Geiger, 1984).

This high-yield SSYPF technology has been

employed in four plants in North America forwhich long-term technical results have beenreported (Katzen and Madson, 1991). SouthPoint Ethanol of South Point, Ohio (64+ milliongallons per year undenatured MFGE) was thefirst plant known to have achieved the 2.75 gpbsustained yield milestone with corn feedstockfor more than one year of operation (Hill, 1991;personal communication). Reeve Agri-EnergyCorporation of Garden City, Kansas, operatesan 11 million gallons per year plant with yieldsfrom milo and corn feedstock exceeding 2.75gpb (Reeve and Conway, 1998; personalcommunication). Pound-Maker Agventures LTDof Saskatchewan, Canada, using wheat asfeedstock, has achieved sustained yieldsequivalent to those of South Point Ethanol andReeve Agri-Energy on a raw material starch andsugar basis (Wildeman and McCubbing, 1997;personal communication). More recently,Minnesota Energy Cooperative of Buffalo Lake,MN, in a plant now producing 18 million gallonsper year, has achieved sustained yields of 2.8gallons of MFGE per bushel of corn (Robideauxand Johansen, 1999; personal communication).

On a product sold basis, this yield is 2.95

gallons of denatured MFGE per bushel.It has been suggested that lower yields result

in increased animal feed co-product production;and since the market price of the co-product,distillers dried grains with solubles (DDGS), isgenerally greater than that of grain (per unit ofweight), the production facility generates DDGS

revenue to offset the losses in ethanol revenue.However, several issues need to be considered:

1. Every pound of starch or sugar not convertedto ethanol must remain as starch, sugar, orbe converted to a compound that does notinvolve the production of CO2 (or othervolatile by-product) in the requisitemetabolic pathways. If not, production ofone pound of DDGS will requireconsumption of two pounds of sugar, therebynegating the revenue trade-off.

2. If sugar or products of high-yieldstoichiometric reactions pass directly throughto DDGS, the soluble solids are recovered.Frequently, however, this results incomplications in evaporator and dryeroperations due to carbohydrate fouling andexcess solubles syrup production. This cannecessitate disposal of concentrated solublessyrup at significantly less than DDGS solidsequivalent pricing. It can also result in atemporary decrease in production rate ormay cause shutdown for cleaning.

Figure 2. Simultaneous saccharification, yeast propogation and fermentation (SSYPF).

Yeast

Fermenters

EnzymeWater

Mash

Beer feed todistillation (pH 4.5)

To carbon dioxide scrubber(pH 5.2)

A B C D

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3. Most plants are limited in centrifugation,evaporation or dryhouse capacity becausethese systems are the least productive from

a return-on-investment perspective.Therefore higher ethanol yields maximizeboth plant production and productivity ofthe investment, since lower co-productproduction reduces demand on associatedprocessing equipment.

4. For a plant of a given production capacity,increasing yield reduces the required size ofmost process equipment, with acorresponding decrease in capitalinvestment. Higher yield, therefore, reducesdebt service per unit of production.

What is this yield worth? If corn is priced at$2.50 per bushel, DDGS at $120.00 per ton andethanol at $1.12 per undenatured gallon, the netresult of a yield increase from 2.5 to 2.75 gpb is$0.145 per purchased bushel of grain ($0.053per gallon of ethanol) in additional profit. Thisprofit gain is after deduction of the $0.135 perbushel decrease in DDGS sales owing toreduction in carbohydrate pass-through toDDGS. Actual profit, however, will exceed$0.145 per bushel due to the efficiency valueof increased production with no increase in fixedcost and little increase in variable cost.

What does it cost to achieve these yields?Fortunately, the investment and operating costsassociated with this high-yield technology arelower than those of the common technologiesavailable in the 1970s and early 1980s. High-yield milling, mashing, cooking, liquefactionand SSYPF technology represents one of thosepleasant, but rare, situations in which it costsless to get more.

As the result of this extraordinary advance,

more than 90% of grain dry milling MFGE plantsoperating in 2002 in North America haveadopted SSF, SSYPF or a similar fermentingprocess. Further, more than 90% of plants underconstruction have chosen this simultaneoustechnology (Tetarenko, 2002; personalcommunication).

Cascade fermentation

Although there are substantial variations in the

fermentation technologies applied in grain orstarch conversion to ethanol, current operationscan be described on a general basis. The broad

divisions of technology are wet milling and drymilling. In wet milling, the major objective is toseparate corn into a number of products such asstarch, gluten, germ meal, germ oil, animal feedresidue (gluten feed), dextrose, fructose,modified starches and a variety of specialtyproducts. Production of MFGE from the lowergrades of starch, or from all of the starch in anMFGE-dedicated plant, is an establishedconversion process in which starch slurry iscooked, liquefied and saccharified prior tofermentation.

All fermentation systems in use today arecontinuous with respect to input and output.Fermentation of saccharified starch in the wetmilling process is carried out by eithersimultaneous (SSF or SSYPF) or cascadeprocesses. Figure 3 shows a typical system forcascaded saccharification and yeast propagation.Figure 4 shows the continuation of the cascadewith pre-fermentation and fermentation. Thiscascade technology has been appliedsuccessfully to wet-milled starch feedstock.Application to whole corn dry milling operationshas been carried out on a large scale, but has notyielded results comparable to SSYPF technology.

Not only is less equipment required for SSYPFoperation in dry milling plants, but the externalsaccharification step of cascade systems, a majorsource of infections, is eliminated. Also, SSYPF,which starts at pH 5.2 and ends at pH 4.5, maybe carried out in carbon steel fermentors. On theother hand, the cascade process requiresmaintenance of low pH to minimize bacterialinfection. It operates at a pH near 3.5, thusrequiring stainless steel construction andconsequently higher investment.

Prior to the advent of fully-computerizedfermentor control, including automated cleaning-in-place (CIP) systems, labor costs favoredcascade operation. With todays automation andsimplified design, labor costs associated withoperating either fermentation technology arenegligible.

Distillation and dehydration

The first distillation step in the production of

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Figure 3. Cascade saccharification and yeast propagation.

Figure 4. Cascade prefermentation and fermentation.

EnzymeAcid

Liquefied starch

To preferment A trainand fermenters

Air

Nitrogen

Acid

Yeast

Phosphate

pH 3.6

Air

Mixtank

Dilution

To preferment A train

Yeast B train

Nitrogen

AcidYeast

pH 3.6

Yeast A train

To preferment B trainand fermenters

To preferment B trainCascadesaccharification

Beer feed todistillation(pH 3.4)

To carbon dioxide scrubber

From yeastB train

Fromsaccharification

AirAir

Air Air Air Preferment B train

Preferment A train

Acid

Fermenters

From yeastA train

Fromsaccharification

AirAir

Acid

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MFGE from fermented beers in the range of 8-12 wt % ethanol has been carried out primarilyby techniques similar to those found in the

beverage spirits industry. However, thedehydration step, primarily conducted byternary azeotropic distillation in the past (Figure5), has been superceded by molecular sievedehydration utilizing integrated pressure swingadsorption (PSA) technology (Figure 6),particularly in newer installations.

Considerable research efforts have beenexpended in the field of ternary azeotropicdehydration, utilizing agents such as benzene,cyclohexane, diethyl ether and n-pentane, toreduce the assumed high energy consumption

of this process. However, in reality manysystems have been operating with multistagedistillation such that the dehydration process isoperated entirely with recovered heat from theprimary distillation system. Alternatively,recovered energy from dehydration is used toprovide most of the energy for stripping andrectification. Commercial systems are producingMFGE from fermented beer with thermal energy

consumption of 17,000 BTUs per gallon forcombined distillation and dehydration. Whenmolecular sieves are used in a well-integrated

design, this operation consumes about 14,000BTUs per gallon.

MOLECULAR SIEVE DEHYDRATION

Molecular sieve adsorption technology fordehydrating MFGE has been actively developedsince the late 1970s. Pressure swing adsorptionis now the technology of choice for MFGEdehydration for new plants and retrofits. Oncebelieved to apply only to small productionfacilities, a single-train molecular sieve unit hasbeen in operation in Brazil since 1993 with anannualized capacity of more than 60 milliongallons.

Molecular sieves are hard, granular substances,spherical or cylindrical extrudates manufacturedfrom materials such as potassium aluminosilicates.They are graded according to the nominaldiameter of the myriad of internal pores that

Figure 5. MGFE distillation and dehydration by ternary azeotrope.

Steam

Beer feed

Stillage

Fuel ethanol product

Preheater/exchanger

Decanter

Fusel oildecanter

Preheater/condenser

Preheater/condenser

Condenser/cooler

Dehydrationtower

Productcooler

Entrainerrecoverytower

Condenser/reboiler

Condenser/reboiler

Reboiler

Pressurizedstripping/rectifyingtower

Fuseloil

cooler

Washwater

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provide access to the interstitial free volumefound in the microcrystalline structure. A typicalgrade used in ethanol dehydration is Type 3.This designation means that the averagediameter of the interstitial passageways is 3Angstroms (). (One Angstrom is a unit ofmeasure equivalent to 10-8 centimeters). Thus,the passageways in the structure have a diameterthat is of molecular scale. The water moleculehas a mean diameter less than 3, while theethanol molecule has a mean diameter greaterthan 3. In addition, the water molecules canbe adsorbed onto the internal surface of the

passageways in the molecular sieve structure. Itis this combination of physical properties thatmake molecular sieves useful for the separationof mixtures of ethanol and water.

Water molecules can invade the inner structureof the molecular sieve beads and be adsorbedthereon, while the ethanol molecules are too largeand pass out of the vessel leaving the waterbehind. Thus, dehydration of MFGE from sub-azeotropic concentrations is possible. It shouldbe noted that this sieving process works toseparate ethanol-water mixtures in either the

liquid or vapor phase. Process details of coursediffer for vapor and liquid mixtures.

The earlier systems for such dehydration,particularly in the liquid phase, required hot gasregeneration to displace the water from thebeads. The molecular sieve beads rapidlydeteriorated due to excessive thermal shock.With a half-life for the beads on the order of sixmonths in the liquid systems, operating costswere high.

Application of vapor phase, pressure swing,vacuum purge adsorption (PSA) technology forMFGE dehydration matured in the 1980s. With

PSA technology, molecular sieve beads areregenerated by recycling a portion of thesuperheated, anhydrous ethanol vapors to onebed under vacuum while the other bed isproducing anhydrous ethanol vapor underpressure. With this milder regenerationcondition, molecular sieve bead life is extendedto several years. In some cases molecular sievebeads have operated for more than 10 years withno appreciable deterioration. This results ininsignificant adsorbent replacement expense andreduced overall operating costs.

Figure 6. MFGE distillation and dehydration by pressure swing adsorption molecular sieve.

Beer feed

Stillage

Fuel ethanol

product

Dehydrationbeds

Vacuumpump

Recycledrum

Fuseloil

cooler

Fusel oildecanter

Washwater

Reboiler

Steam

Beerstripper

Preheater/condenser

Recycle water

Rectifierfeed

tank

Steam

Condenser

Steam

Reboiler

Reboiler

Rectifier

Superheater

A B

Regenerationcondenser

Productcondeser/

cooler

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With an automated operation, the vapor feedto the molecular sieve system can be takendirectly from a pressurized rectifier, with the

reprocessing of the hydrous regeneration streamin the same rectifier. In this way, recovery of theethanol from the molecular sieve regenerationsystem adds less than 1% to the distillationenergy consumption.

One of the major shortcomings of the earlymolecular sieve systems was the highmaintenance cost of the compressor used topressurize feed vapor from atmospheric pressurerectifiers. This problem was initially solved byfeeding a liquid spirit to a pressurized vaporizer,thereby eliminating the compressor. However,

higher energy consumption resulted. Theseproblems have been overcome by new pressure-cascaded distillation systems integrated with themolecular sieve beds as shown in Figure 6. Therectifier is maintained at a pressure sufficient toeconomically operate a reboiler to provideenergy to the atmospheric pressure beer stripper.Approximately two-thirds of the overheadrectifier vapor is used to provide this reboilerenergy. The remaining ethanol spirit vapor ispassed through a steam-heated superheater andthen to the molecular sieve beds for dehydration.The thermal energy content of the resultantsuperheated anhydrous ethanol vapor can berecovered in an auxiliary reboiler on the beerstripper. The condensed anhydrous ethanolvapors (MFGE) are then cooled and passed tostorage. The recovered ethanol and water fromthe regeneration phase of the pressure swingadsorption cycle is recycled to an appropriatefeed point in the rectifier for recovery.

Animal feed co-products

The DDGS co-product operation for dry millingplants recovers the residual non-starch materialsin the stillage from the beer stripper. This isaccomplished by combining centrifuged solids(wet cake) with concentrated solubles (syrup)from the evaporated thin stillage after centrifugalseparation, as shown in Figures 7 and 8. Recycleof dried DDGS acts as a base for blending thewet cake and syrup to yield a material suitablefor operation of dryers, which may be either hot-gas or steam-tube type. The DDGS productmeets the commercial specification of 26-30%

crude protein. However, the more efficient drymilling plants produce DDGS containing 30-35% protein and 8-9% fat as well as B complex

vitamins from yeast propagated in thefermentation operation. This is a high-value,triple concentrate of the corn protein and oil,plus the incremental value of the propagatedyeast.

In the wet milling industry, the primary animalfeed co-product is corn gluten meal (CGM), ahigh value, low volume product containing 60%protein, but no appreciable fat or oil. Thesecondary animal feed co-product is corn glutenfeed (CGF), which is a concentrate of theresidual fiber and liquid containing about 20%

protein and very little fat or oil. This is a relativelylow grade product compared to DDGS.

Energy use

Confusion abounds regarding energy use andefficiency of production of MFGE from corn.Some publications refer to very high steamusage, which is related to older practices inproduction of potable ethanol of various typesfrom grain. Those operations hark back to anage when energy was cheap and potable ethanol

had a high value. However, modern MFGE plantsare designed with a high degree of efficiencywith respect to energy consumption.

In wet milling operations, much of the energyuse is charged to products other than ethanol.The ethanol operation itself requires only about30,000 BTUs per gallon.

Dry milling operations charge all of the energyconsumed to MFGE production, although muchof this energy use is associated with productionof the DDGS co-product. As an example of theefficiency of modern operations, thermal energy

use of 35,000 BTUs of fuel and electrical use of1.15 kilowatt hours per gallon is common. Theseusages can be compared with the gross heatingvalue of ethanol, which is 84,000 BTUs pergallon, or the net heating value of about 75,000BTUs per gallon.

Investment

Facilities for production of MFGE from corn varywidely in size and technology base; it is therefore

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Figure 7. Centrifugation and drying.

Figure 8. Evaporation.

Steam

Thin stillage

Syrup to drying

Thinstillage

tank

Feedpreheaters

Evaporator

Compressor

Scrubber

Finisher

Recycle condensate

Syruptank

Fuel

Syrup from evaporation

Thin stillage

To evaporation

and backset

Chiller

Transfer conveyor

Dryer

Cyclone

Dryer

Feed mixer

Feed conveyorConveyor/

Elevator

Centrifuges

Fuel

DDGS

cooler

DDGS

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difficult to set a standard investment factor. Inaddition to large scale wet milling and dry millingfacilities, there are smaller plants built for unique

opportunities, such as low cost waste feedstocks,or adjacent cattle feedlots that can utilize thestillage directly. In effect, investment for anyparticular facility must be developed on a site-specific basis for the conditions at hand.

Experience in developing improved andsimpler technology over the previous decadespermits estimation of approximate costs for wetmilling and dry milling facilities in view of themost advanced and efficient technologyavailable. Total investment relating to large drymilling plants (turnkey) approaches $1.75 per

gallon of annual capacity (denatured basis). Itshould be noted that in general, wet millingMFGE production units require only about halfthe investment of a dry milling plant. This is dueto the fact that an MFGE facility is simply addedon to a wet milling plant. All other facilities, suchas raw material handling, primary processing,waste processing and utilities are already in placeand provide sufficient capacity for the adjacentethanol facility.

At the other extreme, small farm-based ethanolplants with direct acquisition of feed-stocks andaccess to cattle feedlots for direct consumptionof wet stillage can be built to produce in therange of 5-30 million gallons per year forinvestments in the range of $2.00 to $1.50 perannual gallon. However, in special situations,using pre-owned equipment, the requiredinvestment may be less than $1 per annualgallon of capacity.

References

Bowman. L., and E. Geiger. 1984. Optimization

of fermentation conditions for alcoholproduction. Biotechnology and Bio-engineering 26:1492.

Hill, L.L. et al. 1986. South Point Ethanol 60-Million-Gallon-per-Year Fuel-Ethanol PlantFinal Technical Report. Prepared for: USDepartment of Energy, DOE/ID/12188.

Katzen, R. 1987. Large-scale ethanol productionupdate. Alcohol Fuels 1987, Cancun, Mexico.

Katzen, R. and P.W. Madson. 1991. Bio-engineering improvements in cornfermentation to ethanol. Corn-Derived Ethanol

Conference, Peoria, Illinois, May 12-21.Katzen, R., P.W. Madson and B.S. Shroff. 1992.

Ethanol from corn. State-of-the-art technologyand economics. AIChE Annual Meeting,Biotechnology for Fuels, Chemicals, andMaterials, Session No. 154, Miami Beach,Florida, November 1-6.

Kemmerling, M.K. 1989. Effects of bacterialcontamination on ethanol yield anddownstream processing. InternationalConference on Alcohols and Chemicals fromBiomass, Guadalajara, Mexico.

Madson, P.W. 1990. Bio-ethanol experiences inthe USA. Zuckerind 115 No. 12, pp.1045-1048.

Madson, P.W. and J.E. Murtagh. 1991. Fuelethanol in USA: review of reasons for 75%failure rate of plants built. InternationalSymposium on Alcohol Fuels, Firenze 91,Florence, Italy.

Raphael Katzen Associates. 1978. Grain MotorFuel Alcohol Technical and EconomicAssessment Study. Prepared for: USDepartment of Energy, HCP/J6639-01.

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fuel ethanol production - katzen

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