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Energeia Vol. 19, No.6, 2008 © UK Center for Applied Energy Research

Vol. 19, No. 6, 2008

Hydrogen Production by Biomass Gasification in Supercritical WaterJun ZhangSoutheastern University, China

INTRODUCTION

Currently, there is a great deal of interest in hydrogen as an alternative fuel. The majority of energy fueling our society is furnished by fossil fuels such as coal, natural gas, and crude oil. However, fossil fuel resources are finite and will be depleted eventually. There is a worldwide movement to explore the practical, reliable, and economic use of renewable energy. For these and other reasons, alternative fuels are increasingly being pursued all over the world.

There have been many proposals brought forward to produce sustain-able alternative fuels, such as biomass, solar, wind, bio-oils, ethanol and hydrogen. Among these, hydrogen is considered to be a key fuel in the future because it:

produces no carbon emissions. In the process of utilizing hydrogen as a fuel, water is the only combustion product;is abundant. It is the most plentiful element found in the universe;is efficient. The reaction of hydrogen with oxygen is extremely fast;is renewable. Hydrogen in the water can be obtained again by splitting the water or other hydrogen-con tained sources in which the hydrogen also comes from water such as biomass.

Since hydrogen can be produced from abundant domestic resources, it is expected that the use of hydrogen as an alternative transportation fuel will in-crease dramatically in the future. This is especially attractive to the United

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States due to the lack of domestic petro-leum resources. In the U.S., over half of the petroleum consumed is imported. To decrease dependence on foreign oil, the U.S. Department of Energy (DOE) has created programs concerned with hydro-gen utilization, such as “The Hydrogen, Fuel Cells & Infrastructure Technologies Program.” In Europe, the “Hydrogen and Fuel Cell Technology Platform” has being established. The establishment of the HFP has been facilitated by the European Commission. The platform assists in the co-ordination of European, national, regional and local research, development and deployment programs

and initiatives and ensures participation of the major stakeholders

HOw TO ObTaIN HyDROgeNHydrogen doesn’t occur naturally as a gas on earth, although it is the simplest and most abundant element. Hydrogen is always combined with other ele-ments. Water is a common example of this combination. It can also be found in many organic compounds, notably the hydrocarbons that make up many fuels, such as gasoline, natural gas, methanol, and propane. Therefore, splitting hydro-gen-containing sources into hydrogen is

Energeia Vol. 19, No. 6, 2008 © UK Center for Applied Energy Research � (continued, page 3)

Hydrogen Production (cont.)

the only viable way to obtain hydrogen. This also means that hydrogen is not a primary energy source, and like electric-ity, is only an energy carrier.

Traditionally, hydrogen has been produced by the electrolysis of water or directly from fossil fuels. Electrolytic processes are simple, but energy con-sumption is very high, leading to a high operational cost. It is very hard to imag-ine that hydrogen can be produced for fuel by this method in the future unless electricity can be generated cheaply and by renewable energy sources such as solar, wind, tides, or by nuclear sources.

To satisfy the need of hydrogen consumption as an alternative fuel, a few innovative process technologies have being developed. Among them are photolytic processes including photo-biological water splitting and photo-electrochemical water splitting, in which sunlight with microorganisms for the former (photo-biological) or with electrochemical materials for the latter is used directly to split water into hydro-gen and oxygen with no extra external energy. With this method, the environ-mental impact is very low, making these very attractive technologies. However, the efficiency of transfer in the processes is still very low, and they cannot pro-vide sustainable hydrogen production.

Biomass, as a unique carbon-containing renewable resource, has properties simi-lar to fossil fuels, in regards to hydrogen production. Therefore, the technolo-gies of hydrogen production from the fossil fuels may also be employed using biomass as the feedstock. Unlike fossil fuels, the process produces zero net emissions of carbon dioxide (CO�) and fewer pollutants such as sulfur dioxide (SO�). Thus, hydrogen production from biomass is considered to be one of the feasible and attainable methods for large-scale hydrogen production in the future.

A variety of processes for hydrogen pro-duction from biomass have been (or are being) developed. The most common is gasification technology. In traditional gasification technology, steam, air, or oxygen is usually used as a gasifying agent, which has resulted in low hydro-gen content in the product stream with much unwanted tar as well. Plus, the moisture content of the biomass feed-stock is limited to less than 35 percent for gasification, which may increase the drying costs because a large portion of biomass waste is wet, containing up to 95 percent water.

SUpeRCRITICal waTeR TeCHNOlOgy fOR bIOmaSS gaSIfICaTIONIn the last two decades, a novel gasifi-cation technology called supercritical water (SCW) gasification has been de-veloped, in which water having a pres-sure of over ��MPa and a temperature of over 374 °C (i.e. supercritical condi-tions) is used as the gasifying agent. In the SCW technology, the biomass will be gasified almost completely and the produced gas usually contains mainly H� and CO� with a very small portion of CH4 and CO. The overall chemical conversion can be presented by the simplified reaction:

CHxOy+((2-y)H2O→CO2+(2-y+x)/2H2

This reaction may be divided into two steps: steam reforming and water-gas shift

CHxOy+((1-y)H2O→CO+(1-y+x/2)H2 CO+H2O→CO2+H2

The conventional biomass gasification process also includes these two steps which occur in two reactors: the steam-reforming reactor and the water-gas shift reactor. Differing from the conven-tional process, SCW gasification only requires a single reactor and has the advantages of:

Wet biomass can be used. The bio-mass slurry is the feedstock for SCW gasification. So there is no minimal dryness requirement in the mois ture content and it is particularly suiable for high moisture biomass,like sew-age sludge, VGF (vegetable,garden and fruit) waste, vinasse (waste-product ethanol production), trester (residue of wine production), wastewater, etc.There is high gasification efficiency. When water is in the supercritical state, its dielectric constant (the ratio of the permittivity of a substance to the permittivity of free space) is much lower; the number of hydrogen bonds is much lower; and their strength is much weaker. As a result, SCW behaves like many organic solvents so that the organic compounds origi- nating from biomass can be dissolved completely in SCW, i.e. the fluid in the reactor is a single phase, which provides a good environment for the gasification reactions. There is a high molar fraction of hydrogen in the gaseous products, meaning lesser cost for the separation of the hydrogen from production gas. With SCW, the biomass decomposes

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rapidly into small molecules or gases. Consequently, neither tar nor char occurs. So hydrogen’s volumetric ratio of greater than 50 percent is eas- ily achievable.It is a simpler, more concise system. All reactions and gas separations are carried out in one reactor.Clean gas can be obtained. Some con taminants like H�S, NH3 and HCl may be formed in the SCW gasifi cat-ion of biomass. However, these contaminants are easily captured due to their higher solubility in the water at evaluated system pressure.

Despite the significant advantages of the SCW gasification process, it is still in an early stage of development and the work has been mostly done on a labora-tory scale. The main reasons are:

Plugging Plugging is caused by char and saltsformed during the gasification process. Char may be formed at the inlet of the reactor when the heating rate of the feedstock is low. Usually a pre-heater is used to control char formation. However, it may occur at a high feed rate or a high biomass ra-tio, which could result in a more cost effective solution. On the other hand, inorganic compounds in biomass that have low solubility in the water could agglomerate into a larger particle and plug the reactor tubes.Corrosion When it is in the supercritical state, H�O may be decomposed forming OH, which is transferred further into H�O� , especially in the existence of O�, leading to the increase of SCW corrosion ability. Moreover, alkali metals and chlorine in the biomass also promote corrosion of the reactor material. Little knowledge on the corrosive ability of biomass in SCW gasification is available so far. Economy

In the SCW process, external energy is needed to pre-heat the biomass slurry and the reactor in order to minimize plugging. Although nearly 100 percent conversion could be obtained in the SCW process, the high temperature required to pre- heat the slurry and the low bio- mass/water ratio required for high transfer efficiency could mar the system economics.

Research Although much work has been performed in biomass gasification using SCW, the fundamental knowl- edge of the biomass reaction in the SCW is still lacking because the reac- tor in the environment of high

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3Energeia Vol. 19, No. 6, 2008 © UK Center for Applied Energy Research

Hydrogen Production (cont.)

Eighteen energy researchers and support staff spent three late summer days on the road touring important energy sites throughout Kentucky to learn more about the business of energy. The com-panies that graciously allowed the crew to tour were: Armstrong Coal’s surface and underground mines (Centertown); Owensboro Grain’s biodiesel plant (Owensboro); Century Aluminum’s Smelter (Hawesville); Cemex Cement Plant (Kosmosdale); Lafarge’s Wallboard Plant (Silver Grove); and EKPC’s Spur-lock/Gilbert Power Station (Maysville). The CAER wishes to thank each of these organizations that took time out of their business day to educate those whose business is energy research. Also, thanks to CAER researcher Bob Rathbone for ar-ranging the visits. Below are some of the impressions those tours made:

aRmSTRONg COal mINeS – Jim Hower

The CAER Energy Industry field trip visited Ohio County surface and under-

ground mines. The western Kentucky coal industry has been seeing a renewal of interest in the high-sulfur coal mined in the region, largely due to increasing flue gas scrubber installations at Ohio Valley power plants. The surface mine, operated by Armstrong Coal, mines multiple coal seams. They operate the only working drag line remaining in the coalfield. The underground Big Run coal mine operates in the Western

Kentucky No. 9 coal, traditionally the top producing coal in the region. Due to the logistics associated with taking nearly �0 people underground, most never having previously been in a mine, we did not get to the working face of the unit. The CAER staff did participate in some of the experiences associated with underground mines, including not be-ing able to walk upright in the 4.5-foot coal.

CAER Group in front of Wombles bus

Energy Road Trip

The roads less taken

pressure and temperature makes it difficult to physically get to the areas needed for experimental research; and the water in the supercritical state leads to difficulty in theoretical research.

In general, the SCW gasification technol-ogy of biomass is one of the promising

technologies of hydrogen produc-tion. However, there are still some technological challenges such as the gasification and continual deliverance of high-concentration biomass, reac-tor plugging, material corrosion, and catalysts. It will require a long time to perform the R&D work for its commer-cialization, possibly 15-�0 years.

Jun Zhang is a Professor at the School of Energy and Environment of Southeast Uni-versity, China; His expertise is in thermo-chemical utilization of biomass; fossil fuel combustion and pollutant (SOx, NOx and PM) Control. He is currently a visiting scientist at the CAER. He may be reached at: jun.zhang@caer.uky.edu

Energeia Vol. 19, No. 6, 2008 © UK Center for Applied Energy Research 4

OweNSbORO gRaIN – Courtney fisk

While everyone always talks about fully automated plants, I don’t think I’ve ever seen one quite like Owensboro Grain’s Biodiesel Plant. Although the plant itself looked similar to any number of chemi-cal plants, the programs they designed to monitor and control their process was impressive. I was surprised at how few people I saw throughout the facility. I

also enjoyed seeing the quality control lab, as well as hearing their opinion on not only what is the most vital test for their process, but about their outlook on the industry as a whole. CeNTURy alUmINUm – matt weisenbergerAs a researcher, the opportunity to get out of the lab and behold real-world in-dustrial processes is, in my opinion, vital. We were privileged to visit Century Alu-minum -- and they did not disappoint. Here, amidst the cauldrons of molten aluminum, and mega-amps of current, we all walked away with a deeper ap-preciation of the material that makes the modern 1� oz. can, and the modern �00 passenger can (fondly known as com-mercial aircraft), possible. Aluminum, once more valuable than gold, is now an affordable and essential metal, whose production and sustainability massively rely on the availability of abundant, inexpensive, and efficiently-produced electric power. At Century, to see it all come together was a treat.

CemeX KOSmOSDale CemeNT plaNT – bob Rathbone

The first impression of the Kosmosdale facility was the sheer size of the kiln; I’m always amazed at how big they are. It’s even more astounding that something that large is raised to a temperature of Exploring the turbine

greater than �,600 degrees Fahrenheit. Seeing that large, hot kiln definitely imparts a more practical understanding of how important energy costs are to their business. Another impression was how enthusiastic the Cemex personnel were to show us the operation, despite our rather tardy arrival. I especially enjoyed discus-sions with the technicians in the kiln control room and would have liked to have stayed longer. However, I realized that if I had tried to stay longer many of

our tired and dazed group would have fed me to the kiln.

lafaRge wallbOaRD plaNT – bob Jewell

The size of the 643,000 square foot Lafarge wallboard plant was absolutely staggering. What was even more im-pressive was to learn that they produce 1.6 billion square feet of half-inch thick wallboard annually. That equates to the utilization of a large amount of gypsum

Suiting up for the mine

produced from two local coal com-bustion power plants; and that’s only at this particular plant. I was very surprised by the complexity of the entire network of conveyors and hy-draulics all choreographed to a fast paced rhythm to produce something as simple, at least in appearance, as wallboard.

eaST KeNTUCKy pOw-eR’S SpURlOCK plaNT – mark warren

The most interesting part of the energy tour for me was the visit to East Kentucky Power Cooperative’s (EKPC) power plant. The first thing I noticed at the Spurlock power plant was the investment being made to install new pollution control equip-ment. The tour guide informed me that over $900 million dollars was being invested at the Spurlock plant in clean coal technologies. These technologies included two new SO� scrubbers that required new flue gas stacks to be built. We also saw the on-going installation of the new fluidized bed combustor (FBC), which will burn coal cleaner. The new FBC will also generate power cheaper, keeping electricity rates low for EKPC’s customers.

a mORe pHIlOSOpHICal VIew – marybeth mcalister

While some of the researchers were asking in depth questions about syn-thetic-gypsum chemistry or biofuels composition, my English major’s mind wandered down a different path. As someone who has always

worked in offices, the sheer mag-nitude of manufacturing involved in these industries almost made me feel guilty about how easy I have it. True, we all work hard at our lab, but if an experiment doesn’t work, we can always try again. If these companies don’t create their materials on schedule, or without quality products, there can be catastrophic repercussions. The current economic downturn is affecting these companies in a direct bread-and-butter way. If anything, this tour gave me more respect for the manufacturing sec-tor that made our country great, and continues to do so, although those of us who sit in front of a computer have forgotten.

Energy Road Trip (cont.)

5Energeia Vol. 19, No. 6, 2008 © UK Center for Applied Energy Research

CommEnTARy

Indiana Jones and the Cornstarch of Doom

By Rodney AndrewsDirector, CAER

My past ‘mandatory end-of-year editori-als’ have been written over the Thanks-giving holiday weekend, generally fueled by tryptophan-induced euphoria, a com-pulsion to avoid too much family interac-tion, and fear of an irritable editor. These have been upbeat listings of CAER’s an-nual accomplishments and awards, with little bad news to report. This year will depart from that theme; not that we have bad news or funding disasters, or any fewer staff accolades, but rather because my Thanksgiving didn’t go as planned…

I spent the break working with my son, Kelden, on his Science Fair Project. This is a big deal when you are 6, and more so if your sister has won her grade three years in a row. AND, you managed to find a way to focus your kindergarten project the previous year on making fake Sasquatch footprints that all the 5th-grad-ers thought were really cool and wanted to talk to you about even though you’re a kindergartener…. It’s a lot of pressure for 1st grade. Getting him to focus on valid experimental science was not helped by his fascination with the titular mythical archeologist – Indiana Jones. He has the last movie memorized (which was as good as the others when viewed without nostalgic bias), and was determined to do something related. Aliens being too difficult, he settled on how to escape from quicksand.

Unfortunately (from a certain point of view), quicksand is not common in Kentucky, so we needed another source of non-Newtonian fluid behavior. Luck-ily, as with everything else, Google had the answer. Here we get to the point captured in the picture: Kelden, me, the table, and most of our kitchen covered in a fine layer of cornstarch. If mixed in the correct proportions with water, this fluid will become non-Newtonian. (It acts like water if you move through it at slow speeds, but acts like a solid if you try to move quickly). The experiments went well, except that Lego Indiana Jones floats, requiring a switch to Tony Hawk on a skate board, and we determined how much cornstarch is required and how slowly to move for Indy/Tony to escape from the “quicksand.” How does this relate to CAER, energy and Kentucky? As I walked him to the school bus on Monday discussing the difference (one more time) between Newtonian and dilatant fluid behavior, and listening to him dream up ways that you could use this stuff to stop cars, trains and bad guys, it occurred to me that somewhere between here and col-lege, we go off track with math and sci-ence education. Somewhere the fun gets knocked out of it and the interest slides into apathy. How and why do we miss the excitement of discovery in teaching about science, technology, engineering and math (STEM)?

The Pritchard Committee on Academic Excellence recently released an update on the Kentucky educational system’s progress in achieving Top �0 status by �0�0. Kentucky fourth grade students rank 9th in the nation for science scores. This drops to ��nd by the eighth grade, and by the time they reach college, only �9% of bachelor degrees are awarded in STEM fields. This places Kentucky 44th in the nation in our ability to produce a workforce to meet the demands of an increasingly STEM-dominated future. There are opportunities to recapture the imagination of students and interest them in STEM careers. Talking to stu-dents and communities about the chal-lenges of providing enough energy in the future certainly sparks this interest:

How do we use biomass? How do we burn coal without releasing CO�? Can we use algae to solve both problems? Their ability to imagine a future, dif-ferent than what we now know are the limits, holds the opportunity to rein-vent Kentucky and create prosperity for its students.

We have some good examples of how this can happen. The Kentucky Legislature last session instructed the STEM Taskforce to explore how to use renewable energy issues to attract students to STEM courses, recogniz-ing this as a key need for developing future innovators. Doug Keaton at the Russell Area Technology Center has developed a popular Alternative & Renewable Energy program, with his students designing, constructing and operating a small wind genera-tor, solar array, and storage system to power the hallway lighting. Energy can spark the imagination of students, and keep them interested in STEM disciplines if we can make the links to keep this interest alive. I am very excited that the keynote speaker at the 3rd Energizing Kentucky Conference (www.energizingken-tucky.org) is Jared Diamond (one of my all time favorite authors). His book, Collapse: How Societies Choose to Succeed or Fail explores how the choices we make as a society in using and preserving our environment can determine our success or failure in the future. One such choice we face now is how we will provide our children with the tools they need to address the energy and environmental needs they will inherit from us. If we do not increase our success in STEM educa-tion, we run the risk of leaving them unprepared. But, to get there, our students must be allowed to know the fun and fascina-tion of discovery. Hopefully, Kelden, who is cursed with two engineer parents, will someday look back at what is quickly becoming known as the cornstarch weekend as the time he realized “I can come up with things they didn’t think of.”

Energeia Vol. 19, No. 6, 2008 © UK Center for Applied Energy Research 6

WOCA is an international conference organized by the American Coal Ash Association (ACAA) and the University of Kentucky Center for Applied Energy Research (CAER). The 2009 confer-ence marks the two organizations’ third joint biennial meeting. It will again focus on the science, applications and sustainability of coal ash worldwide. As such, it will encompass all aspects of coal combustion products (CCP’s) as well as gasification products.

For more information, go to: www.worldofcoalash.org

WoRLD oF CoAL ASH ConFEREnCE

Center for Applied Energy Research�540 Research Park DriveUniversity of KentuckyLexington, Kentucky 40511-8479

Energeia is published six times a year by the University of Kentucky’s Center for Applied Energy Research (CAER). The publication features aspects of energy resource development and environmentally related topics. Subscriptions are free and may be requested as follows: Marybeth McAlister, Editor of Energeia, CAER, �540 Research Park Drive, University of Kentucky, Lexington, KY 40511-8479, (859) �57-0��4, FAX: (859)-�57-0��0, e-mail: mcalister@caer.uky.edu. Current and past issues of Energeia may be viewed on the CAER Web Page at www.caer.uky.edu. Copyright © �008, University of Kentucky.

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