Put Carbon in Its Place

Engineers at the National Energy Technology Laboratory are researching carbon sequestration as a possible solution to climate change, revealing several technologies for doing it.

By Tom Imerito

Although climate change has emerged as a recent problem, the government agency most responsible for addressing it has roots that go back to 1910. The United States Bureau of Mines (BOM) was created 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 to meet the nation’s demand for energy without destroying the environment or diminishing our quality of life.

In particular, the lab makes an ideal venue for researching carbon sequestration, a promising technology for mitigating carbon dioxide buildup. “We recently launched a training and education program consisting of seven regional training initiatives 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,” says Sean Plasynski, sequestration technology manager at NETL. “Our goal is to have available information for the wide-scale deployment of CCS by 2020.”

The United States Geological Survey established the BOM at the Allegheny Arsenal in Lawrenceville, Pennsylvania just a couple of miles up the Allegheny River from Pittsburgh. BOM’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 38-acre site in the village of Bruceton, about 12 miles south of Pittsburgh, where it punched a pair of tunnels that would serve for the next 50-odd years as the bureau’s experimental coal mine.

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, the only national 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.

Strict Security in an Idyllic Setting
Quite appropriately, NETL nestles in Pittsburgh’s rolling South Hills atop the same idyllic hillside into which the Experimental Mine was opened a century ago. The mine is still there, but the test explosions ceased a few decades ago when suburbanization began to take hold. While it serves as a grade school trip attraction, nobody gets into NETL without an invitation, an escort, and a thorough vehicle search. Booted guards searched under my car with a mirror-on-a-stick device.

Inside, my escort took me to the receptionist who transcribed my license information to the visitor log and asked me to verify that I was a United States Citizen and that I was unarmed by signing in the designated box. This energy business is serious stuff. Serious enough to warrant the efforts of more than 1,400 employees at five locations, including Pittsburgh (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 has about 650 employees, more than half scientists and engineers.

Today I would visit two of them, Plasynski and John Litynski. Throughout his career at NETL, Plasynski, who works in the Office of Coal and Power R&D within the Strategic Center for Coal, has been involved in power and environmental systems. He started at NETL in 1989 as a postgraduate researcher in NETL’s Coal Combustion Division and concurrently works in project management for the Coal Preparation and Solids Transport Division. He holds B.S., M.S., and Ph.D. degrees in chemical engineering from the University of Pittsburgh and also an MBA from the University of Pittsburgh’s Katz Graduate School of Business.

An environmental engineer, Litynski serves as director of the Carbon Sequestration Division in the Strategic Center for Coal. Previously, he coordinated the Regional Carbon Sequestration Partnerships at NETL, a $750 million initiative responsible for bridging the gap between the applied research efforts and demonstration of CCS technologies in the field. He is a registered Professional Engineer and Project Management Professional, having received his B.S. in Civil Engineering from Virginia Tech University.

While ensuring adequate energy for the future is a daunting task, doing so without compromising the environment or our lifestyles raises the technology bar to a high level. The problem takes many forms, but at the base, it revolves around the conflicting social and economic consequences of climate change. NETL’s mission responds to what many believe will be a new regulatory regime for carbon emissions.

“We operate under the concept that there’s going to be policy coming down on climate change,” says Litynski. “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 25 years. While natural gas, nuclear, and petroleum production are expected to remain flat, coal is expected to maintain a strong share of the electricity generation pie until renewable energy becomes viable on a large scale. With a 200-year supply, the United States is considered by many the Saudi Arabia of coal, and the vast majority of our electricity production comes from pulverized coal plants, whose productive lives may be as long as 50 years. However, if nothing is done to limit carbon emissions, an expected increase in carbon emissions in excess of 14 percent over the next quarter century will accompany coal’s use – 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 states.

Away from the Atmosphere
True to its name, carbon capture and storage, or 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 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 many angles with a large pool of domestic and international resources.

NETL’s CCS program consists of three pieces: core research and development, infrastructure, and global partnerships. Core R&D, 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 carbon throughout the United States and Canada in collaboration with seven regional carbon sequestration partnerships and almost 400 industry partners. The global partnerships and collaboration extend 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.

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, so the problem is how to release the CO2 using as little energy as possible.

It Must Be Transported
In any event, once the 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 United States already,” Litynski reveals. “And they all transport CO2 at supercritical pressure because the cost of bringing it to supercritical pressure outweighs 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 we’re looking at are below 2,600 feet,” Sean Plasynski adds. “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 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 new, the oil and gas industries have almost 40 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 created a market for CO2 captured by power plants.

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 predicts.

Other Ideas Abound
Novel ideas abound in the field, some immediately practical, others theoretically promising. 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 explains. “It comes down to economics. If coal is $40 a ton and biomass is $70 a 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 amendment such as char and fly ash to increase productivity on degraded soils,” Litynski reports. “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 a concern. Sampling of lands treated with fly ash 15 to 30 years ago have also shown higher levels of carbon in the soil than those not treated.”

“Within our program, we have a focus on CO2 use and reuse,” Plasynski says. “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.” Another commercial use of CO2 is production of the high-purity, food-grade variety such as that used in soft drinks.

In another example of novel thinking, at the far reaches of carbon sequestration research, NETL scientists are working 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 promising, the technology is probably about 15 years from commercialization.

With such cutting edge research into a modern problem as complex as global warming, it’s clear NETL has come along way since its beginnings as the Bureau of Mines. It will probably continue to morph as carbon sequestration comes to the forefront in years to come.

Tom Imerito is president of Science Communications, a Pittsburgh technology communications consultancy. To learn more about Science Communications, visit www.science-communications.com.

To learn more about the National Energy Technology Laboratory, visit www.netl.doe.gov.