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How an ethanol plant worksHere are the basic steps in an industry thats still evolv ing

Making ethanol is a lot likefarming. Ethanol plantsgrow yeast, a fungusthat has waste products

of carbon dioxide and alcohol.

The main part of the process isa living organism. It is alive. Its likegrowing a crop, says Scott Kohl, aresearcher with ICM, Inc. in Colwich,Kansas, an ethanol plant designingand engineering firm.

When todays ethanol industry be-gan, ethanol was made in wet mill-ing plants that also turn out corn oil,starch, syrup, and gluten meal forlivestock feed. Wet mills soak grainin water and acid to help separate

An ethanol plant is a biological and industrial process. Besides this production flow, a modern plant

recycles some water, recaptures much of its heat, and scrubs emissions from exhaust. Trucks deliver

grain and ship out DDGS. Railcars are filled with ethanol that has double the energy used to make it.

ethanol

Illustration

:PaulBridgford

corn kernels germ and endosperm.Today, nearly all new ethanol

plants are dry mills, which cost lessto build and run. They grind corninto a flour that is used to make two

products: ethanol and livestock feed.Dry mills also make carbon dioxide,but only a few have found marketssuch as soda bottling plants.

A br ief tour of a dry mil lDry milling is getting more so-

phisticated. The Broin Companiesof Sioux Falls, South Dakota, arestarting to use fractionation, whichmechanically mills corn into fiber,germ, and endosperm before mak-

ing ethanol. This allows a plant tomake more high-value productssuch as corn oil.

Most dry mills still use the con-ventional process illustrated above.

The front end resembles a smallgrain elevator, where trucks dumpinto a grain pit that elevates corninto temporary storage. It might holda 10-day supply of corn. From therecorn is conveyed to hammer millswhere it is ground into a fine meal.The meal, with a consistency of

corn meal, is conveyed into threeor four slurry/cook tanks, wherethe process of breaking starch intosugar begins. Water, heat, and en-

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Farmers investing in todaysethanol industry rely heavily onplant designers and builders.

Id say 90% of the plants havebeen a turnkey plant, says J eremy

Wilhelm, an agribusiness loan

officer with Farm Credit Servicesof America. And of those, mostare built by two firms, says ShaneFrahm, another lender at the bank.

At least 60% of dry mill plantshave been built by Fagen, Inc.(www.fageninc.com) of GraniteFalls, Minnesota, Frahm says. Itoften teams up with Kansas plantdesigner, ICM, Inc. (www.icminc.

com), which is working with abouttwo thirds of new plants under con-struction. Broin Companies (www.broin.com) of Sioux Falls, SouthDakota, has designed and built

most of the rest.

These companies will also runplants at start-up, or even per-manently, as well as train staff.Some are involved in marketingplant products. And theyre heavilyinvolved in promoting ethanol.

Other players include Delta-TCorporation (www.deltatcorp.com) and the German firm, LurgiPSI (www.lurgipsi.com).

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Photograph:Ted

Schlaebitz

zymes are added to the meal, cre-ating a slurry. In some plants moreenzymes are added to complete thebreakdown to sugar, but most nowfinish that process during fermenta-tion, Kohl says.This first cooking usually takes

place at about 185F., but newer

enzymes will work at lower tem-peratures. Not shown in the chartare boilers that provide this heatand steam for cooking, fermenting,and distillation. Most run on naturalgas, but as its cost rises, new plantsare being built to run on coal, evenmethane from manure.

Over the last 10 to 15 years, en-ergy conservation has significantlyimproved, Kohl says.Ten years ago, it took up to 60,000

Btus to make a gallon of ethanol.Today its about 35,000. Most of the

savings is from recapturing heat touse in several steps of production.

Into the biological heartNext, the wet mixture called mash

is pumped into fermentation tankswhere yeast is added. Keepingyeast-producing ethanol is both artand science. There is a risk of bac-terial infection, which lowers produc-tion. Urea may be added for nitro-gen, which is food for the yeast. If allgoes well, in 40 to 55 hours at 90F.,the yeast makes a beer that is up

to 16% to 17% alcohol by volume.The chart shows three 730,000-gal-lon fermentation tanks and a largertank, called a beer well, that sendsbeer to the distillation columns.

Extracting the alcoholDistillation does two things. It

separates alcohol from most of thewater and diverts the rest of the wa-ter and solids, called stillage, into aprocess to make distillers grains.

Distillation columns use alcoholslower boiling point, 178.4F., to sep-

arate it from water, which boils at212F. The beer is heated between178F. and 212F. As this gas risesto the top of the column, liquid witha higher percentage of alcohol con-denses. The liquid is passed to thenext column, where an even higherpercentage of alcohol condensesout. The last distillation columnyields 190 proof (or 95%) alcohol.

After distillation, alcohol passesto molecular sieves, columns that

are filled with BB-size zeolite balls.

Each has microscopic holes bigenough for water molecules but toosmall for larger alcohol molecules.Heat and pressure force water intothe balls. Pure alcohol is removed.When the balls fill up with water, itsremoved in a vacuum.

Making livestock feedStillage, with a consistency of

noodle soup, flows from the bot-tom of the distillation columns to acentrifuge, which makes wet cakethat looks like steaming, bright yel-

low sawdust and can be balled upin your hand. The centrifuge alsospins out a mix of water and 7%solids called solubles. Evaporatorsthicken the solubles to the consis-tency of maple syrup. Most plants

add solubles back into the wet cake.

Then its dried to about 10% mois-ture and sold as distillers dry grainsand solubles (DDGS), which areused for livestock feed.

If a plant can sell the wet cakewithout drying, it can cut the energyneeded for ethanol production tounder 25,000 Btus per gallon, a bigcost savings, Kohl says. But at 65%moisture, it must be used in abouta week by nearby feedlots. Someplants now sell modified wet cake at50% moisture, which keeps about amonth. DDGS last a year.

Ethanol plants run year-round, 24hours a day but must be shut down atleast twice a year for maintenance.A lot can go wrong. Theres just aton of moving parts, Kohl says. Asa plant ages, they can break.

At this plant, distillation columns are on the left, molecular sieves

in the center, and fermentation tanks are behind the shed at right.