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putting Carbon In Its Place

Although climate change is a recent problem, the government agency most responsible for addressing it, has roots that go back to 1910 when the United States Bureau of Mines (BOM) came into being.  A hundred years ago the Bureau was born to secure a safe workplace for miners and a reliable supply of fossil energy for a growing nation.  Today, BOM's successor, the National Energy Technology Laboratory (NETL) functions in similar fashion by ensuring the development of affordable fossil fuel technologies that will meet the nation's future demand for energy without diminishing our quality of life.


TECHNOLOGY LEGACY

In 1910 the United States Geological Survey established the Bureau of Mines at the Allegheny Arsenal in Lawrenceville, just a couple of miles up the Allegheny River from Pittsburgh.  The Bureau's headquarters housed administrative offices as well as laboratories and outdoor apparatus for conducting explosive experiments and emulating mine explosions.  In the same year, the Bureau leased a thirty-eight acre site in the village of Bruceton, about twelve miles south of Pittsburgh, where it punched a pair of tunnels which would serve for the next fifty-odd years as the Bureau's Experimental coal mine.  In the tunnels, coal mine explosions which had killed thousands of miners through the years were transformed from tragic and inexplicable catastrophes into a set of manageable and methodical scientific events.


Although the Bureau's initial efforts focused on miner safety, as time went on the needs of a growing nation began to occupy a larger role in defining its agenda.  During the first and second World Wars, the Bureau's expertise in the field of explosives was tapped for the development of bombs and ammunition.  When New York City’s Holland Tunnel needed an automotive exhaust system, a fleet of test automobiles traversed Bruceton's Experimental Mine to test tunnel exhaust system prototypes. When oxygen made hospitals dangerous, the Bureau of Mines found a way to make them safe.  When natural gas explosions became commonplace, the Bureau of Mines developed an aromatic additive to alert consumers of gas leaks.  When the nation needed helium gas, the Bureau of Mines prospected for and developed helium wells in the American southwest.  When the Manhattan Project needed an explosive trigger for the first atom bomb, they came to Bruceton for the answer.  When the budding field of nuclear energy needed a metal with superior performance characteristics, the Bureau of Mines developed an affordable way to refine titanium.  Between the World Wars, when mineral resources became scarce, the Bureau of Mines prospected for new sources of supply.  And when air pollution rose to a higher level of public concern, the Bureau of Mines helped to establish air quality standards.


Through the years, the Bureau split its duties between those involving physics, chemistry and engineering issues and those involving human health and safety issues. The hard sciences went to a series of Energy Technology Laboratories.  Safety and health issues went to the National Institutes of Occupational Safety and Health.  Finally, in 1999, Congress established the National Energy Technology Laboratory.  It was and is the only national federal laboratory wholly owned by the federal government.  Now a subsidiary of the United States Department of Energy, NETL is charged with identifying affordable technologies that will meet the nation's future demand for fossil fuels without diminishing our quality of life.


Quite appropriately, the National Energy Technology Laboratory is nestled in Pittsburgh’s rolling South Hills atop the same idyllic hillside into which the Experimental Mine was opened a century ago.  Today, the site serves as headquarters for more than 1,400 employees, at five locations, including Pittsburgh, Pennsylvania (Bruceton), Morgantown, West Virginia, Albany, Oregon, Houston, Texas and Fairbanks, Alaska.  The bulk of the work is divided about equally between Bruceton and Morgantown, each of which have about 650 employees more than half of whom are scientists and engineers.  I visited two of them, Sean Plasynski and John Litynski.


Plasynski’s official title is too long to say in one breath: Sequestration Technology Manager in the Office of Coal and Power R&D within the Strategic Center for Coal at the National Energy Technology Laboratory NETL) of the Department of Energy (DOE). Prior to his current position, Plasynski worked on energy infrastructure and reducing vulnerabilities related to homeland security.

Alongside Plasynski was John Litynski, Carbon Sequestration Division Director in the Strategic Center for Coal.  An environmental engineer, Litynski is responsible for managing a $1 billion portfolio of applied research, development, and demonstration.


BALANCING ACT

While ensuring adequate fossil energy for the future is a daunting task, doing so without compromising the environment or our lifestyles raises the technology bar to a befuddlingly high level.  The problem takes many forms, but at base, it revolves around the conflicting social and economic consequences of climate change. On one side of the equation, the quality of human life is threatened by global warming; on the other side, productivity is threatened by impending cost increases associated with reducing the greenhouse gases that produce global warming, carbon dioxide being the most notorious.  NETL’s mission is responsive to what many believe will be a new regulatory regime for carbon emissions.


Although a debate about the validity of greenhouse gases and global warming continues to smolder, if not rage, the topic has risen to a level of sufficient concern at high levels of national governments around the world to warrant the attention of any and all players in the energy policy arena.  In recognition of the political, legislative and regulatory landscape of the moment, NETL assumes a non-partisan, scientifically objective approach to the issues. 


"We operate under the concept that there's going to be policy coming down on climate change." said John Litynski, NETL's Sequestration Division Director.  "We don't dictate what technology industry should adopt.  Our goal is to develop technologies that industry can use to address those policies, whatever they may be.  Before passage of the Clean Air Act we worked on SOx (sulfur oxides) and NOx (nitrogen oxides) mitigation technologies that didn't yet exist.  We're doing the same thing in anticipation of carbon regulation."


NETL's work is driven by data developed by the U.S. Energy Information Agency that projects coal to continue to dominate power generation for the next twenty-five years.  While natural gas, nuclear, renewables and petroleum production are expected to remain flat, coal is expected to increase its share of the electricity generation pie. The reason is twofold: first, with a two-hundred year supply, the United States is considered by many to be the Saudi Arabia of coal and second; the vast majority of our electricity production comes from pulverized coal plants, whose productive lives may be as long as fifty years.  However, if nothing is done to limit carbon emissions, coal's anticipated growth is expected to be accompanied by an increase in carbon emissions in excess of fourteen percent over the next quarter century – bad news for global warming. "Every model shows that coal will be in the energy mix, which means we must have carbon capture and storage (CCS)," Litynski said.


STORAGE OPTIONS

True to its name carbon capture and storage, also called sequestration, puts the carbon we create when we produce energy in a stabile place other than the atmosphere.  It can be deep underground (geologic), in forests or fields (terrestrial), in the ocean (not currently viable), or in commercial products and processes (e.g. soft drinks, synthesized fuels, polymers and enhanced oil recovery).  According to Litynski, geologic storage holds the greatest potential for long term CO2 storage.


Stepwise, geologic storage strips gaseous CO2 out of a fuel, either before or after combustion; compresses it to a supercritical fluid at 2,200 psi; pipes it to a suitable underground storage site; pumps it underground; and watches the site for a long time to ensure the carbon stays where it's supposed to.  In terms of infrastructure, the ideal CCS system requires a power plant near a source of cooling water, alongside a chemical processing plant, built atop a coal mine, near a suitable underground storage site, along an electric transmission corridor.  Although meeting all those criteria may pose significant challenges, the grand challenge is finding a way to do it all without producing a larger quantity of carbon than that which is being stored.  Termed the "energy penalty" by the carbon cognoscenti, the problem is sufficiently pressing that NETL is approaching it from a great many angles with a large pool of domestic and international resources.


PIECES OF THE PUZZLE

According to Plasynski, NETL's CCS program is comprised of three pieces: Core R&D; Infrastructure and; Global Partnerships.  Core research and development, which focuses on small scale research, is conducted by NETL staff researchers as well as under cooperative agreements with universities, industry partners and other national laboratories. The infrastructure component addresses larger issues, such as field testing for storage of throughout the United States and Canada in collaboration with seven regional carbon sequestration partnerships and almost 400 industry partners.  The global partnerships and collaboration program extends the program's reach by sharing information and experience with CCS enterprises throughout the world, including projects in the North Sea, Algeria, Germany, Canada and Australia.  "Except for Weyburn in Canada, we don't put money into the infrastructure for these projects," Plasynski explained.  "We send researchers to work on what might be a fifty million dollar project, so this is a nice way to leverage our money. They learn from our research expertise.  We learn from the field experience."


On the capture side of the picture, NETL scientists are investigating both pre-combustion and post-combustion capture.  Pre-combustion capture typically means gasifying coal by heating it and running steam over it to produce a water-gas shift reaction in which the oxygen atom in H2O breaks away and binds with a carbon monoxide molecule (CO), to yield a concentrated stream of CO2 for sequestration and hydrogen (H2) for combustion.  The gas is then separated into its component parts by running it through a separation medium, either a liquid solvent, a solid sorbent or a synthetic membrane.  The same principles hold for post-combustion separation, except that because the CO2 is less concentrated, extraction takes more energy.


However, as with all problems, there's an easy part and a hard part.  Getting the CO2 to bind to a medium is the easy part.  Getting it to come off so the medium can be re-used is the hard part.  Fortunately, the answer is simply heat.  Unfortunately, heat is energy, and energy is money, so the problem is how to release the CO2 using as little energy as possible. "You want a sorbent, solvent or membrane to capture the CO2 well enough to take it where you want it, but then go back and get some more," Plasynski explained.  "If it binds so tightly that it takes a lot of energy to get it off and let it go back to get more, you're no further ahead. At the same time, if it doesn't grab it tightly enough, it's not going to hold it and you won't be able to get the CO2 where you want it to go."


John Litynski elaborated upon the actual process: "The process uses an absorber column and a desorber, or stripper, column and there's a temperature and pressure difference between them.  We're trying to reduce the amount of steam it takes to strip the CO2 off the desorber column."


GETTING IT THERE

In any event, once CO2 is separated from a flue gas, the next step is to get it to a suitable storage site, which means either building a power plant on top of one, or piping it to one.  In either case, the CO2 must be compressed to 2,200 psi to transmute it into a supercritical fluid, which lowers the cost of transport, facilitates injection into a geologic formation and improves stability while it's there.


"There are over 3,500 miles of CO2 pipelines in the U.S. already," Litynski said. "And they all transport CO2 at supercritical pressure because the cost of bringing it to supercritical pressure is less than the cost of building a much larger pipeline to move it as a gas.   When you reduce a volume of gas to a supercritical fluid you reduce it to 1/300 of its original volume, so it doesn't make sense to transport or store CO2 as a gas.  Also, changing it from a gas to a liquid helps it flow through a pipeline. And when you inject it down-hole, the increased density helps it move into the formation."


"The formations that we're looking at are below 2,600 feet," Sean Plasynski added.  "You need enough CO2 pressure to overcome the pressure in the formation.  Once it’s there, the pressure at that depth is high enough to keep it in a supercritical state.”


Porosity, permeability and stability are the essential characteristics of a good geologic sequestration formation.  Porosity and permeability are inherent in the microstructure of the rock.  Stability is provided by geologic cap structures that prevent the upward movement of the CO2 after it is injected.   Saline formations, depleted gas or oil wells, unmineable coal seams and certain other organic formations typically serve as geologic storage sites.  Since every geologic formation is different, characterization of each formation's capacity to absorb and retain CO2 is an essential part of the site assessment process.  For instance, depending on a formation's physical characteristics, CO2 may or may not mix with residual oil, gas or water. In unmineable coal seams CO2 sticks to the coal.  In other geologic formations the CO2 traverses the formation and enters the pores.


While CCS is very new, the oil and gas industries have almost forty years experience injecting CO2 underground and monitoring its movement.  Since the 1970s the practice of enhanced oil recovery (EOR) has used supercritical CO2 to force residual oil across a field from a line of injection wells to a line of extraction wells.  During the process some of the CO2 mixes with the oil, some is left behind in the oil-bearing formation and some is extracted for reuse.  Using CO2 for EOR has made a market for CO2 captured by power plants.  Another commercial use is the production of high-purity, food-grade CO2, such as that used in soft drinks.


"Within our program we have a focus on CO2 use and reuse," Plasynski said. "If there's a way to make an economic product out of it, or another way of binding the CO2 up to be permanently stored, we're interested.  For instance, we think it may be possible to use CO2 for polymers, or to combine it with hydrogen for fuels.  The big issue with fuels is where to get the hydrogen.  In most cases it's from methane, but that doesn't gain you anything.   But then, there are alternatives - everything from hydrogen-producing algae to the solar-powered electrolysis to separate hydrogen from water. They all have their challenges, either in cost or practicality.”


KEEPING IT THERE

Advanced technology notwithstanding, once the CO2 is in the ground, decades-long monitoring begins.  Fortunately, through the years the oil and gas industries have learned how to detect the location and movement of geologic structures and substances by using seismic, chemical, pressure, atmospheric and global positioning techniques.  According to Litynski, a cooperative project at an ethanol plant at ADM world headquarters will inject a million tons of CO2 into the Mount Simon sandstone, which is over a thousand feet thick on average and underlies the entire state of Illinois.  “The CO2 probably won’t move more than three hundred feet vertically and a quarter mile horizontally,” he predicted.


THINKING OUTSIDE THE BOX

"We've been working on both novel concepts and novel molecules," Plasynski said. "We have a molecular metalorganic framework with a cage-like structure.  You can think of it like a crate with a molecule on each corner of the crate. The CO2 slips between the corner molecules into the crate where it is held and released with low heat, allowing it to go back and get more.  The approach is attractive because you just can't afford to get more new material every time you strip a CO2 molecule out of a flue-gas stream."


"Another novel approach is ionic liquids, where you can absorb the CO2 and release it using less energy than with other methods," Plasynski continued. "Some researchers have proposed coating a membrane with an ionic liquid to help facilitate the transfer across the membrane." 


But not all ideas about CCS are complex.  For instance, the relatively simple concept of hybridizing terrestrial and geologic sequestration calls for co-firing biomass with coal in a capture-enabled power plant.  Because the biomass inspires CO2 during photosynthesis and leaves a portion of it in its roots and the earth in which it grows, capturing the carbon contained in the top of the plant results in a net reduction of atmospheric CO2.  "Retrofitting a pulverized coal plant for biomass co-firing means having a holding tank, a transport system and a blower," Plasynski said. "It comes down to economics.   If coal is $40 a ton and biomass is $70 ton it becomes a premium fuel and up goes the cost of electricity.  But if you could get carbon credits for the biomass that would change everything."


In addition to the advantages of including biomass in the CCS picture, agricultural productivity also stands to benefit. “We have funded research with Oak Ridge and Pacific Northwest National Laboratories as well as Virginia Tech on using soil amendments such as char and flyash to increase productivity on degraded soils,” Litynski said.  “In general it has been fairly successful since these materials seem to aid the soil in retaining moisture, increasing humification processes, and increasing plant productivity.  Some environmental issues need to be addressed such as the potential to leach metals form the fly ash, although the R&D completed to date suggests that this may not be an issue to be concerned about.  Sampling of lands treated with flyash 15-30 years ago have also shown higher levels of carbon in the soil than those not treated.”


In another example of novel thinking, at the far reaches of carbon sequestration research, NETL scientists are at work on a potentially revolutionary technology called chemical looping combustion (CLC).  The process splits the oxidation-reduction (redox) reaction normally associated with burning fuel into its two half reactions, oxidation and reduction.  The system concentrates atmospheric oxygen on a metal carrier in one chamber and then exposes the oxidized metal to syngas produced from coal in another.  The ensuing reduction reaction yields as much heat as if the fuel were consumed in a fire, but without the flame. Because the metal is oxidized at temperatures too low to form nitrous oxides, nitrogen compounds are completely avoided.  And because the coal is converted to a gas before the metal is reduced, CO2 is greatly diminished and concentrated.  According to Litynski, who considers the method very promising the technology is probably about fifteen years away from commercialization.


It is clear that in any case, our energy future will be very different from the present. “We recently launched a training and education program comprised of seven regional training initiatives located throughout the country aimed at developing the workforce of scientists and engineers that carbon capture and sequestration will need when the technology becomes fully commercialized,” Plasynski said. “Our goal is to have available information for the wide scale deployment of CCS by 2020.”


In light of the enormity of the problem, the difficulty of the challenges and the variety of potential solutions, that’s not very far off.


This article first appeared in Progressive Engineer E-zine.

©Copyright 2007 Thomas P. Imerito/ dba Science Communications


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©2009 Science Communications
thomas@science-communications.com