Would you like the opportunity to test biomass-processing technology in a world-class

pilot plant without building a facility of your own? And in a pilot plant capable of

handling recombinant organisms and one where national laboratory expertise is also

available? A U.S. Department of Energy (DOE) user facility operated by the National Renewable Energy Laboratory (NREL) in Golden, Colorado, may provide that opportunity for you.

With funding from the DOE National Biofuels Program, NREL constructed a fermentation

pilot plant facility to test bioprocessing technologies for production of ethanol or other fuels

or chemicals from cellulosic biomass. The Process Development Unit (PDU) of the Bioethanol

Pilot Plant can test biomass fuel or chemical production processes from start to finish at a

scale of about 900 kilograms (1 dry ton) per day of dry feedstock. An associated Mini-Pilot

Plant is ideal for preliminary testing at small scale. As part of NREL’s Alternative Fuels User

Facility (AFUF)—and in keeping with NREL’s role as a U.S. Department of Energy national

laboratory—the PDU, Mini-Pilot Plant, and associated Bioethanol Pilot Plant facilities are

available to support industrial and academic research and development. Projects can be

arranged under cooperative research and development agreements, work-for-others contracts,

or other flexible business agreements. If you are developing a technology that uses biological

organisms for large-scale conversion of biological materials, the facilities and expertise of

NREL that are available at the Bioethanol Pilot Plant may be exactly what is needed to commercialize that technology.

■ The Process Development Unit

The Bioethanol Pilot Plant’s one-ton-per-day Process Development Unit is a complete system for producing ethanol or other

fuels or chemicals from cellulosic biomass sources. PDU operational components include:

■ Feedstock washing and milling

■ Thermochemical pretreatment

■ Enzymatic hydrolysis

■ Fermentation

■ Microorganism seed growth and holding tanks

■ Ion exchange and chromatographic separations

■ Distillation 

■ Solid-liquid separations.

The enzymatic hydrolysis and fermentation equipment

includes four 9000-liter, two 1450-liter, and two 160-liter fermenters. All can be used for aerobic or anaerobic fermentation,

with separate or combined hydrolysis. The distillation equipment

includes a 10-meter stripping column. The PDU is one of relatively few facilities specifically designed to safely handle metabolically engineered as well as native microorganisms. It can also

process high solids material (greater than 20% total solids), which

is crucial for developing cost-effective biomass-based processes. 

The PDU has a very sophisticated control and data acquisition

system for all facets of plant operations in its control room. Spectroscopic monitoring of fermentation-off-gas composition makes it

possible to calculate oxygen transfer rates. The data acquisition system provides information to conduct material and energy balances. 

■ The Mini-Pilot Plant

In addition to the PDU, the AFUF has a Mini-Pilot Plant for preliminary process testing at a more cost-effective small scale. The

Mini-Pilot Plant offers batch and continuous fermentation processing. A flexible system of several vessels ranging from 10 liters to

100 liters allows configuration appropriate to a wide range of

processes. The Mini-Pilot Plant can validate batch, fed-batch, or

continuous bioprocessing technologies. As with the PDU, it can

accommodate high solids concentrations and recombinant organisms and can be used to determine carbon mass balance closure.

A Tool for Commercialization A Tool for Commercialization

Inside one of four 9000-

liter fermentation tanks at

the National Renewable

Energy Laboratory’s

Bioethanol Pilot Plant. The

facility enables NREL and

its industry partners to

move advances in producing ethanol and other

fuels and chemicals from

biomass into the development phase.

The DOE Bioethanol 

Pilot Plant

The DOE Bioethanol 

Pilot Plant
■ Pretreatment Options

Of the various steps for processing biomass, pretreatment is most

feedstock sensitive and the one for which testing at pilot plant

scale is critical. NREL offers three different thermochemical 

technologies for solubilizing hemicellulosic sugars and making

cellulosic sugars more accessible to hydrolysis enzymes and fermentation organisms. The PDU has a continuous dilute-acid pretreatment system from Sunds Defibrator (now Valmet). This

commercially available equipment can be readily included in setting up your own biomass processing system.

■ Steam Gun Thermochemical Pretreatment

As an alternative to the Sunds pretreatment system, the

Bioethanol Pilot Plant offers a batch-process steam gun system

that uses high pressure and high temperature to enhance diluteacid pretreatment. This system is also good for test runs when the

amount of feedstock is limited. Feedstock can be impregnated

with the acid either at atmospheric pressure or in a 14-liter pressurized vessel. After “cooking” the feedstock with steam for a few

minutes, the steam gun expels it into a flash tank. The explosive

pressure drop rapidly cools the material to precisely stop the

reaction. The steam gun system makes it easy to experiment with

a wide range of temperature, pressure, acid concentration, and

other conditions. Although not commercially available, the steam

gun equipment set up can be easily built to include in your biomass processing system.

■ Countercurrent Pretreatment

NREL’s third pretreatment option is a novel countercurrent reactor

system. This patented technology also uses dilute acid, high temperature, and pressure, but in a way that releases and preserves

more of the sugars. Conventional dilute acid pretreatment

Process Flow Diagram of the Process Development Unit

Centrifuge

Ethanol

storage

Condenser

Washer

Debris

Water Feedstock

Mill

Cyclone

Feed

hopper

Plug

feeder

Steam

Acid

Water

Seed

fermenters

Nutrient

tank

Capacity: 1 ton of biomass/day

Enzyme

tank

Flash

tank

Cake

tank

Distillation column

Centrate

tank

Recycle

Solids

Liquids

Hydrolyzer

9000-L fermenters

Belt conveyor

Shaker

Beer

well

The countercurrent pretreatment system removes

sugars quickly after they hydrolize, preventing

degradation and allowing the reactor to “shrink,”

reducing operating costs.

hydrolyzes the hemicellulose (breaks it down to xylose and other

five-carbon sugars), which also physically exposes the cellulose to

hydrolysis (typically enzymatic). At a higher temperature, diluteacid pretreatment will also hydrolyze cellulose (breaking it down

to glucose). Temperatures high enough for cellulose hydrolysis,

however, are also high enough to degrade the xylose and other

hemicellulose sugars. 

NREL’s countercurrent pretreatment technology incorporates

several innovations to make pretreatment more effective. Countercurrent flow in the second stage removes hydrolyzed sugars from

the system more quickly upon their release, limiting exposure of

the sugars to the hot acid, which is fed in the opposite end. Staged

temperature increase takes advantage of the fact that a portion of

the hemicellulose hydrolyzes more easily—removing this portion in

the first stage before the temperature is raised to hydrolyze the rest

of the hemicellulose in the second stage. Both of these innovations

increase yield by reducing degradation of the xylose. They also

allow a third innovation—“shrinking” the required reactor volume

in the second stage via its vertical orientation as first the remaining

hemicellulose and then cellulose is hydrolyzed. The vertical orientation allows the remaining solids to remain compact as the solids
are lifted upward. This not only reduces the amount of hot dilute

acid solution needed—a critical consideration in achieving acceptable process economics—but maintains more effective contact

between the solid particles and the flowing dilute acid. This is

believed to reduce mass transfer reaction resistances, allowing for

lower temperatures and lower acid concentrations to achieve the

same degree of hydrolysis as in more traditional reactor designs. 

The countercurrent exchange pretreatment system is hooked

up to a data control and acquisition system allowing precise control and sophisticated data analysis. Although the equipment is

not yet commercially available, with appropriate agreements for

use of the technology, it could be incorporated in setting up your

biomass processing system.

■ Continuous Ion Exchange and 

Chromatography Separation System 

Hardwood feedstocks present an extra challenge—acetic acid, an

inhibitor of the yeast fermentation process. The liquid solution of

sugars that comes from the pretreatment of hardwoods contains

significant amounts of acetic acid. The PDU includes a continuous

ion exchange system to remove the inhibitory acetic acid prior to

fermentation. The system uses commercially available standard

ion exchange resins, to which the acid adsorbs, removing the

inhibitor from the hydrolyzate. The system—which is sized to be

compatible with the PDU 1-ton/day feed rate—can be readily

connected to the PDU for process testing or to your biomass processing system. The system can also be hooked up to the PDU

systems upstream or downstream of fermentation for ionexchange or chromatographic purification or separation of products from chemical production processes.

■ Expertise/People

The Bioethanol Pilot Plant is far more than just a collection of

state-of-the-art equipment. NREL has more than 50 scientists, engineers, and technicians from a wide range of disciplines with

expertise in biomass conversion and bioprocess development.

They can help you use the facility to move your technology from

a scientific concept to a technically and economically proven

process ready for commercial production—before you commit to

staff and capital investment. NREL has been developing biomassto-ethanol and other biofuels technologies since 1977 and has an

outstanding biofuels staff. They have the scientific and technical

expertise to work with metabolically engineered microorganisms

and enzymatic processes. They also have the operation skills necessary to keep a plant operating smoothly and the engineering

skills to scale up processes. In addition, the NREL biofuels staff is

experienced in working with outside partners, providing needed

help, and protecting proprietary information and processes.

■ Experience/Success

Since opening in 1994, the Bioethanol Pilot Plant has already

been used for numerous cooperative projects to help develop

bioprocessing technologies—several of which are now moving

into commercial production (see below).

Collaborations Using the PDU

Industrial Feedstock Product Key Organism Scale Business

Partner Processes Mechanism

Amoco corn fiber ethanol, pretreatment systems (2), yeast (including PDU CRADA

animal feed glucose/xylose cofermentation recombinant) (9000 liter)

BC International bagasse, rice straw, ethanol pretreatment, fermentation recombinant 20-L, 160-L CRADA

wood E. coli bacteria 

Arkenol rice straw ethanol glucose/xylose cofermentation recombinant 160-L CRADA

Zymomonas 

bacteria**

Sustainable mix of a variety ethanol dilute acid and enzymatic yeast 4-L steam gun, collaboration

Technology of solid wastes hydrolysis with enzyme recycle 30-L fermenter 

Energy Partnership*

Sealaska Corp. softwood ethanol hydrolysis, fermentation Nx7 yeast** 4-L steam gun, memorandum

bench scale of understanding

Quincy Library softwood forest ethanol hydrolysis, fermentation Nx7 yeast** 4-L steam gun, collaboration

Group thinnings bench scale

Collins Pine, softwood ethanol hydrolysis none 4-L steam gun collaboration 

California Energy and 

Commission subcontract

Swan Biomass rice straw ethanol pretreatment, recombinant PDU pretreat- collaboration 

glucose/xylose fermentation Saccharomyces ment, benchyeast scale fermentation

*DOE, NREL, California Energy Commission, California Institute of Food and Agricultural Research at UC Davis, Waste Energy Integrated Systems

**Proprietary NREL organisms available for license
■ From Bioethanol Pilot Plant to 

Biorefinery of the Future

A little less than 100 years ago, the first oil refineries started cracking crude oil to separate it into gasoline and a handful of other

useful products. Today, the petroleum industry converts billions of

barrels of oil per year (approximately 14 million barrels per day in

the United States alone) into a dozen fuels and hundreds of plastics. Our economy is built on these products, but oil and other

fossil fuels are expensive, pose environmental risks to extract and

transport, and their supplies are ultimately limited. Their combustion generates much of our air pollution and most of the greenhouse gases that threaten to change the Earth’s climate.

Instead of importing oil, we can home-grow biomass to provide the feedstock for many of our fuels and chemicals. Hydrolysis of cellulosic material to sugars and then fermentation or other

bioprocessing of those sugars can supply many of the fuels and

chemicals (or equally good alternatives) for which we now

depend on petrochemicals. The more we turn to such a “sugar

platform” instead of petrochemicals, the better off our domestic

economy and environment will be. Producing ethanol from nonfood plant materials for use as an automotive fuel is just one of a

myriad of possible sugar-based bioprocesses. Our user facility is

titled the Bioethanol Pilot Plant, but it is equally available to your

process that produces other fuels or chemicals. Together we can

make the Pilot Plant the forerunner of the biorefinery of the

future.

■ Availability

NREL’s Bioethanol Pilot Plant was explicitly designed to assist

industry and outside researchers develop commercial bioprocessing technology. The PDU and other Pilot Plant facilities—and

associated NREL staff expertise—are available for major trials of

an entire process, for research and development of individual bioprocessing steps, or for cooperative basic research of your or

NREL’s bioprocessing technologies. NREL can work with private

DOE has made the investment in a world-class NREL facility for pilot

testing biomass-processing technologies, so you do not have to.

industry or other research institutions under a variety of flexible

business-venture arrangements. Most typically, cooperative

research and development agreements (CRADAs) are used for

joint projects to advance renewable energy or energy-efficiency

technologies . Work-for-others agreements (WFOs) are used to

apply NREL’s unique facilities and expertise to develop proprietary industrial processes. NREL welcomes inquiries from companies and research institutions interested in using Bioethanol Pilot

Plant facilities to develop and commercialize technology for making valuable fuels and chemicals from biomass. Whether with a

CRADA, a WFO, or some other business device, chances are good

we can work together. 

For more detailed information on the Bioethanol Pilot Plant contact Biofuels Technology Manager Robert Wooley: 303-384-6825;

robert_wooley@nrel.gov. To inquire about setting up a cooperative project using the plant’s facilities, contact Mark Yancey: 

303-384-6858; mark_yancey@nrel.gov

You may also visit our web site at www.ott.doe.gov/biofuels.

Produced for the U.S. Department of Energy (DOE) by the

National Renewable Energy Laboratory, a DOE national 

laboratory.

DOE/GO-102000-1114 • September 2000

Printed with a renewable-source ink on paper containing at least 50%

wastepaper, including 20% postconsumer waste.

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Photo Credits: Page 1: Warren Gretz, NREL/PIX01008; Warren Gretz, NREL/PIX09072. Page 4:

Warren Gretz, NREL/PIX01011.