Transcript
Page 1: Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING ·  · 2009-07-23Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING Figure 1. ... IntRoduCtIon

�Energeia Vol. 20, No. 4, 2009 | © UK Center for Applied Energy Research (continued, page 2)

Vol. 20, No. 4 | 2009

Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING

Figure 1. Schematic of the carbon-recycling bioreactor.

DAVID BAYLESS and BEN STUARTOhio University

IntRoduCtIon and ChallEngESThe U.S. faces three significant energy challenges. As the world addresses global climate change, carbon emissions will most likely be constrained. In ad-dition, traditional “cheap” energy sup-plies are decreasing as competition for them grows. Finally, much of the cheap energy supplies, especially natural gas and petroleum reserves, exist in coun-tries that are unstable or unfriendly to the U.S. Economics, the global environ-ment and national security are all strong reasons for the nation to pursue a more sustainable energy production route.

Commercialization of algal technolo-gies is of great importance, not only for economic growth, but also to address critical environmental and energy issues facing our nation. Growing algae pho-tosynthetically for either fuel produc-tion (from a non-food resource) or as a source of bioproducts (e.g. bioplastics) or even animal feed, creates a renewable feedstock that reduces the amount of carbon dioxide (CO2) in the atmosphere. Microalgal production and processing represents not only a potential path for producing biofuels and mitigating CO2 emissions, but also an enabling technol-ogy for producing fuel from coal via synthesis. Algal-based systems could be used anywhere in America. They could significantly improve the nation’s

energy security by decentralizing en-ergy production and could reduce our dependence on foreign energy sources.

WoRk at ohIo unIvERSItyBioreactor Work for Biofuels ProductionOhio University and its partners are de-veloping photobioreactor technologies to facilitate producing and harvesting algae for carbon recycling and en-ergy production. The original concept, shown in Figure 1, was for a bioreactor system that could be placed directly into scrubbed flue gas with minimal footprint, low pressure drop, reduced water usage, and photon management to optimize biomass growth and thus optimize CO2 remediation.

In the bioreactor, microalgae (micro-scopic algae) or cyanobacteria (blue-green algae) are grown on vertical sub-strates that are spaced much like plates in an electrostatic precipitator. The membranes are constantly wetted via gravity-assisted capillary flow of water and nutrients. Once saturated, film flow is established, creating a semi-aquatic environment for the algae attached to the surface of the membrane. Carbon dioxide from the flue gas diffuses into the water film at high transfer rates, providing carbon for the phototrophic conversion to biomass.

Photons are delivered to the membrane surface via fiber-optic cables. Visible light from the sun reflected from the collector dish and secondary optics (Figure 2) are directed into an array of optical fibers. The sunlight collected by tracking mirrors (optimized solar collection) can provide over 2000 μmols m-2 s-� of suitable photons throughout the day – depending on geographic location. Light intensities required for

Page 2: Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING ·  · 2009-07-23Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING Figure 1. ... IntRoduCtIon

Energeia Vol. 20, No. 4, 2009 | © UK Center for Applied Energy Research 2 (continued, page 3)

Microalgal Engineering (cont.)

photosynthesis are dependent on the algae strain, but typically range from 20-200 μmols m-2 s-�. Light intensities above these levels either are wasted, or worse, may cause the algae to experi-ence photo-inhibition (reduced activity). By controlling light attenuation through the cables and using specially-designed distributors to hold the fibers in place at specific locations in the bioreactor, a more uniform distribution of photons may be supplied at the specific light intensity that maximizes uptake of CO2 and therefore, biomass production.

The ability to utilize solar photons (as opposed to artificial lighting) is the primary factor that determines system efficiency. In order to utilize solar photons at maximum effi-ciency, the light delivery subsystem must deliver a sufficient quantity and quality of usable photons deep within the bioreactor and minimize the light loss due to reflection and adsorption.

While the film bioreactor is useful for cyanobacteria and quick carbon fixation, bubble-column reactors are better suited for a larger number of algae strains and thus have wider possible application for production of biofuels. In the bubble column reactor (Figure 3), CO2-enriched gas is injected through a distribu-tion plate located in the bottom of

a column and allowed to rise through a water-based algae slurry to the top of the reactor where it is separated from the liquid. The algae-liquid slurry is fluidized (moving up, then falling back down) by the motion of the gas. Where additional control of the slurry flow is required, pumps direct the algal bio-mass in a direction counter to the flow of the gas (top to bottom).

The flow of algal suspension is carried over regions of fiber optic bundles, se-cured at fixed locations in the bioreactor by a series of hangers. The fibers ter-minate at the height of the hangers and emit full-spectrum photons (sunlight), which are then available for use by the autotrophs. As the slurry moves past the hangers, the algae move into darker regions, which promote the dark-cycle reactions (which may be shorter than one second in duration). The continuous motion of the algal slurry past a series of light sources stimulates photosyn-thesis (dark and light cycle reactions). It also keeps the fiber ends free of algal buildup and ensures nutrient transport. The harvesting system removes mature organisms, reducing cell density, pro-moting cell division, and maximizing uptake of CO2. A fraction of the biomass slurry is drained from the bioreactor and filtered to remove algae, which is available for further processing into a useful bio-product or energy feedstock. The transport of the remaining algae within the bioreactor promotes disas-sociation and further development in exponential growth.

Processing TechnologiesWhile numerous algae growth systems have been or currently are being devel-oped, considerably less effort has been devoted toward downstream processing, including harvesting, dewatering, oil extraction and purification, and water re-source management. The success of any biofuels production facility using algal feedstocks requires the development of highly efficient and cost-effective sys-tems for handling the generated biomass and subsequent fuel purification. Cur-rent systems for removing microalgae from aqueous streams include several traditional water-treatment technologies such as coagulation and flocculation, sedimentation, dissolved air flotation, centrifugation, and several types of vacuum/pressure filtration units.

The challenges in processing technolo-gies from engineered algae cultivation systems are extensive. However, technologies being researched by Ohio University and our commercial partners, including: membrane separation, novel belt-driven drying technology, and natu-ral processing, offer great promise for advancing commercial algal processing.

Carbon Interfacing TechnologiesFor microalgal processes to be a practi-cal method for CO2 mitigation, the costs of separating, compressing, treating and delivering the CO2 must be as low as possible. The vast majority of CO2 in enhanced gas streams (>4% CO2 by vol-ume) is found in combustion sources. It is also potentially the lowest cost source of CO2, even lower than air, as future

carbon restrictions may give significant value to removing CO2 from combustion gases.

Ideally, CO2 could be used directly from an emissions source to grow the microalgae, but the practical-ity of that is questionable. Carbon dioxide from combustion sources is usually delivered at extremely low pressures (inches of H2O) and cannot be sparged through any depth of water without compres-sion. Therefore, unless a low pres-sure drop bioreactor that allows for the return of the processed flue gas and products of photosynthe-sis to the stack for atmospheric dispersion is employed, there are limited options for direct flue gas usage. Such options include using separated CO2 (from amine absorption-desorption processes) that is compressed or using enhanced mass-transfer reactors

Figure 3. Side view schematic of the bubble-column bioreactor design. The squares are alignment guides developed by the graphics software and not part of the reactor.

Figure 2. Solar collector mounted above pilot-scale bioreactor.

Page 3: Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING ·  · 2009-07-23Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING Figure 1. ... IntRoduCtIon

�Energeia Vol. 20, No. 4, 2009 | © UK Center for Applied Energy Research

Microalgal Engineering (cont.)

Figure 4. Schematic of the integration of a bioreactor with a Coal/Biomass-to-Liquids Plant to Produce JP8.

in the flue gas train to put carbon species in the aqueous phase for transport to the microalgal growth facility.

Further, combustion flue gas contains numerous pollutants that would not be permitted for widespread dispersion at ground level. These pollutants include, but are not limited to, mercury, particu-late matter, sulfur dioxide, nitrogen-ox-ides, and other heavy metals (notably arsenic and selenium). If large quantities of flue gas are introduced (sparged) into a body of water at ground level, all the contaminants in the flue gas will be distributed at ground level. In addition to increasing the direct exposure of humans and animals to potentially harmful neu-rotoxins (heavy metals) and respiratory-damaging gases (sulfur dioxide, nitrogen dioxide), the potential for asphyxiation also exists. Therefore, the introduction of point-source flue gases requires a CO2 mass transfer system to get carbon into the aqueous phase while protecting the surrounding environment. Selection of the appropriate system depends on en-ergy consumption, maintenance require-ments, and minimal pressure drop on the gas side of the transfer unit.

Separated and pressurized CO2 from combustion sources may or may not be inexpensively available in the distant fu-ture, as plans are being considered for a supercritical CO2 pipeline network. This pipeline is being proposed to facilitate large-scale geological sequestration of CO2. However, such a network would not be ready for operation by 2020, and the current estimated cost of liquefied CO2 would make its use cost prohibitive under almost any circumstance.

Making such CO2 sources viable for interfacing with microalgal growth facili-ties will require efforts in gas cleanup, enhanced aqueous phase mass transfer, or development of growth chambers with low pressure drop where CO2-con-taining gases could be easily recovered and dispersed from stacks. A significant advantage of a bioreactor system is that it can be tied directly to an industrial source of flue gas, which helps maximize direct carbon recycling and considerably increases the microalgae growth rate.

Coal-to-Liquids TechnologiesOne of the more intriguing applications, and one that could be critical to securing domestic energy security for the United States, is coupling carbon recycling using microalgae with Fischer-Tropsch Syn-thesis (FTS) of liquid and gaseous fuels. This is a process that combines hydrogen (H2) and carbon monoxide (CO) to form

long-chain hydrocarbons of any desired length, such as methane (natural gas), mixed alcohols (used as a replacement for gasoline), jet fuel (JP-8), and synthetic diesel fuel. The bioremediation of CO2 is an important factor in the widespread implementation of FTS, as current FTS technology converts only about 50% of the carbon in the gasification feedstock (biomass or coal) to fuels. The remain-ing carbon is discharged to the atmo-sphere as CO2. The release of substantial quantities of CO2 is the major stumbling block to financing such units, each of which costs billions of dollars. Without technology to mitigate CO2 emissions in some fashion, capital markets fear the environmental pushback and financial risk associated with FTS.

With the technology being developed at Ohio University, the CO2 emitted from the FTS process could be recycled using microalgae. This biomass, which is rich in hydrogen, could then be used as a feedstock in the gasification process, cre-ating new and hydrogen-rich syngas for the FT reactor. This recycling not only reduces direct CO2 emissions, but also creates a feedstock for fuel production (such as diesel or natural gas), as shown schematically in Figure 4.

Ohio University has spent considerable effort in developing bioreactor technol-ogy that makes growing microalgae much more efficient and controllable. It is the promise of this bioreactor technol-ogy, coupled with genetic manipulation of algal strains to produce a “super-al-gae,” that has garnered the attention of numerous parties in this field.

ConCluSIonS and FutuRE WoRkWhile algal products offer the potential to provide sustainable solutions for both liquid transportation fuels and CO2 mitigation, important challenges must be overcome to make them cost-effective. Unlike terrestrial crops that have been cultivated and harvested for centuries, the infrastructure and knowl-edge needed to cultivate and harvest algae using industrial processes is in its infancy. For example, within the field of plant biotechnology, algal research is one of the least explored fields and in-dustrial-scale algae energy systems have yet to be demonstrated. Carbon dioxide delivery and conditioning, integration and systems engineering, energy and water use, algal areal and volumetric productivity, cultivation system design, strain optimization, synthetic biology, downstream processing, value-added co-product development, and carbon life-cycle analysis are all issues facing researchers in an effort to create a viable algal production industry.

Drs. Bayless and Stuart are professors in the Departments of Mechanical and Civil Engineering, respectively, at Ohio Univer-sity in Athens, OH. They may be reached at: [email protected] and [email protected].

Page 4: Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING ·  · 2009-07-23Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING Figure 1. ... IntRoduCtIon

Energeia Vol. 20, No. 4, 2009 | © UK Center for Applied Energy Research 4

World of Coal ash | 2009

The third World of Coal Ash (WOCA) Conference was held in Lexington, Kentucky this May. As with the previ-ous two meetings, the 2009 conference was organized by the American Coal Ash Association (ACAA) and the Uni-versity of Kentucky Center for Applied Energy Research (UK CAER).

We would like to thank our generous sponsors and exhibitors for their sup-port and participation, without which the meeting literally would not exist.

One of the highlights of this year’s con-ference was a corner of the exhibit hall devoted to ‘fly-ash furniture’ created by students of UK’s College of Design, along with the technical assistance of CAER researchers. It isn’t often that

such divergent areas of the university (i.e., artists and scientists) can collabo-rate. The furniture made by the students shows the high-value products that can be dreamed up when worlds collide.

Another new dimension of the meeting was the first Student Oral Presentation and Poster Awards. We were pleased with student participation, with six post-ers presented and 20 oral presentations made. In addition, the Midwest Coal Ash Association (MCAA) reached out to universities by providing four, $500 scholarships to students who presented papers or posters.

The next iteration of the meeting will take place in Denver (home of ACAA) in 20��. We hope to see you there.

New ACAA Director, Tom Adams

UK Design Student shows her work to attendee

Attendee questions speaker

A well-attended poster session

The newly established University of Kentucky Biofuels Laboratory is dedicated to improving processes for biomass use and aims to support the development of the biofuels indus-try in Kentucky. The facility is based at UK’s Center for Applied Energy Research (UK CAER) and the Depart-ment of Biosystems and Agricultural Engineering (BAE). It is an open access laboratory, i.e., its equipment is avail-able to researchers in other Kentucky institutions working in the field of biofuels. For more information please contact either:

Mark Crocker [email protected] (859) 257-0295, or:

Czarena Crofcheck [email protected] (859) 257-�000 x 2�2

University of Kentucky BIoFuElS laBoRatoRy

Though WOCA was mentioned briefly in the last issue of Energeia, because it is one of our signature events, we are featuring it here.

Page 5: Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING ·  · 2009-07-23Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING Figure 1. ... IntRoduCtIon

5Energeia Vol. 20, No. 4, 2009 | © UK Center for Applied Energy Research (continued, page 6)

COMMENTARY

CAP and BILL TRADE Gets Us Nowhere THOMAS L. ROBL PHD

University of Kentucky, Center for Applied Energy Research

The current carbon cap and trade bill is not a new direction in Ameri-can energy policy, but an attempt to cling to the status quo. It is not only bad economics: it is bad science, bad policy and bad politics. It will have little benefit to the environment, and in the longer term, may be damaging. Here is why.

It plays the ends against the middle.Cap and trade represents the Balkanization of American energy policy. It picks winners and losers and sets the coasts against the indus-trial Midwest. Kentucky is a good example. A recent study released by a major California university found that Lexington had the highest “carbon footprint” in the U.S. mainly because we use a lot of coal-gener-ated power. This should not come as a surprise. We have southern sum-mers and northern winters. We have limited capacity for wind, frequent cloudy skies, and fully developed hydro. We must rely on coal-gener-ated electricity to meet both heavy heating and cooling loads.

There is another reason for our carbon footprint —heavy industry.

We have about two fifths of America’s aluminum refining capacity along with one of the largest stainless steel mills in North America. We don’t just build Toyotas, Fords and Chevys —we also make the steel. You can’t do this heavy lifting with windmills. It takes about �,000 of them to equal a good size coal plant and we just don’t have that much wind in the Eastern U.S.

If we have learned anything in the last two years, it should be that wealth is not created on Wall Street. It is cre-ated in our power plants, mills, mines, factories, farms and laboratories. Jobs counting carbon credits and shuffling paper cannot replace those we will lose as we make our already stressed basic industries even less competitive.

It’s headed in the wrong direction. The bill not only favors carbon capture and storage (CCS): it mandates it. The CCS strategy requires that the carbon dioxide from coal combustion be cap-tured, compressed and pumped under-ground where it will be “permanently” stored. There are practical problems with CCS that must be overcome such as liability, transportation issues, reser-voir development, etc. The bigger issue is that it will create power plants with enormous parasitic power demands. It is a big step away from the energy- efficiency pathway we need to travel.

CCS will force us to mine and burn between 25 - �5% more coal for the same power.

Coal is neither the devil nor the sav-ior. It is a precious, limited, hard-won resource. It also causes environmen-tal damage. For these reasons alone it should not be wasted. But more importantly it is a finite resource. The idea that there is a lot of it, some say 250 years worth, so we can waste it is irresponsible.

It doesn’t address the big energy issue.Every day we take all the oil that is produced in the United States and throw it away. We simply waste it. We do no work with it. Nothing, just simply dump it in the air along with a lot of CO2. We do this by our driv-ing around in vehicles powered by a �9th century invention —the internal combustion engine. We use extremely high heating value fuels (gasoline and diesel) to create a rapid phase change to power an air pump to motivate our vehicles. We do not use the heat in these fuels; in fact we must get rid of it, quickly and efficiently so the pistons’ valves don’t melt and seize up. The bulk of the energy goes out in radiators and tailpipes as waste. The thermal efficiency of the internal com-bustion engine is somewhere between

The CAER allows it own Dr. Tom Robl (Associate Director for the Environmental and Coal Tech-nologies Group) space to rant once a year in Energeia. Last year’s edi-torial created enough controversy to assure us that our readers are still reading the publication with interest. We hope you enjoy Tom’s latest comments on what he sees as the long-term misdirection of energy and politics.— mm

�5 - 20% in practice. We consume about 8.4 million barrels of gasoline a day. Thus about 6.8 million barrels of gasoline are consumed for wasted heat every day. We produce about 5.� million barrels a day of crude oil do-mestically, thus our waste heat from internal combustion exceeds the total energy equivalent to all to the crude produced in the United States. We can no longer afford this. Improving our average fuel efficiency from 20 to 25 or �5 miles per gallon does nothing to change the paradigm. Displacing the internal combustion engine with

...about 6.8 million barrels of gasoline

are consumed for wasted heat

every day.

Page 6: Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING ·  · 2009-07-23Sustainable Energy and Carbon Recycling through MICROALGAL ENGINEERING Figure 1. ... IntRoduCtIon

Energeia Vol. 20, No. 4, 2009 | © UK Center for Applied Energy Research 6

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, 2540 Research Park Drive, University of Kentucky, Lexington, KY 405��-8479, (859) 257-0224, FAX: (859)-257-0220, e-mail: [email protected]. Current and past issues of Energeia may be viewed on the CAER Web Page at www.caer.uky.edu. Copyright © 2009, University of Kentucky.

Center for Applied Energy Research2540 Research Park DriveUniversity of KentuckyLexington, Kentucky 405��-8479

Non-Profit OrganizationU.S.Postage

PAIDLexington, Kentucky

Permit No. 5�

more efficient electric vehicles--plug in hybrids and eventually full electrics--would allow us to increase coal-based power and simultaneously reduce carbon emissions without CCS. Any bill that purports to address energy must deal with the internal combustion engine head on, not just by provid-ing incentives. If anything needs to be mandated it is the end of the internal combustion engine, not CCS.

It’s based on yesterday’s theory.Climate-change theory is largely based on computer models. It is speculative and has launched a lot of fear, but also a few satellites which have been provid-ing something that was originally lack-ing in the theory, actual data. And not surprisingly, the picture of the earth’s climate emerging is more complex than first thought. It is more local and less global than anticipated. Methane, dark particulate and tropospheric ozone (the bad kind in the lower atmosphere) play a major role. The cap-and-trade bill is focused on carbon dioxide and may be

off the mark entirely in terms of near-term climate change.

It’s a hidden regressive tax.Cap and trade will need a large bureaucracy to judicate, verify and certify emissions and compliance. It will create a large, complex and expen-sive system that will affect everybody. It is designed to increase the cost of en-ergy to force conservation. Much of the added costs will go to feed the system, not reduce the Federal debt or support our economy in some other way or even build more efficient mass transit. It is the worst kind of regressive tax. It will also not work, at least the way it is envisioned. Our university trains both accountants, to help you pay your taxes, and tax attorneys, to help wealthy people avoid theirs. The cap and trade system will almost certainly be mas-sively gamed.

Is there a plan B instead?Yes, plan B would be a simple carbon energy tax with an efficiency bias. A car-bon tax on motor fuel will favor efficient

vehicles. By taxing electric generation on dollars per ton of carbon per kilowatt and allowing the plants to adopt the most efficient boiler technology, we will get more power and mine less coal. These are issues that most Americans see as important to our economic well being and would support. Polls show that most Americans are skeptical of global warming or climate change. A new expensive bureaucratic, forced cap and trade system will eventually generate push-back from the public. Politics are temporary; sustainability is permanent. We need to start making the market work on these problems.


Recommended