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A smaller footprint: How can it be done?

March 18, 2012 12:10 am

BLACKSBURG

Since no energy option--not coal, not nuclear, not oil and gas, not renewables--is currently unproblematic and ready to assume the bulk of our clean energy needs in the near future, everything--every energy option--ought to be on the table. Research and development is needed for each option and for all greenhouse gas mitigation technologies; it will cost money and we must start investing now if we want to mitigate climate change.

Reasonable projections based on scientific data suggest how pursuing a portfolio of options could add up to an overall solution to the problem. Efficiency and conservation measures have to be increased to reduce demand wherever possible. There is a role for nuclear, natural gas, wind, solar, and yes, coal.

The best projections show coal, the burning of which has already become much cleaner and can be made cleaner still, when carbon dioxide (CO2) is captured, transported, and stored safely underground in various geological formations, to be part of our energy mix for the foreseeable future. As is well-known, the U.S. has a lot of coal, more reserves than any other country in the world, and already has a huge coal-based infrastructure to utilize it. Bringing this infrastructure to a halt isn't currently a serious option; increased efficiency measures are to be supported, but we simply don't know how to meet our energy needs economically without utilizing coal.

In major parts of the world such as China and India, doing without coal is even less of an option; the development of new coal-fired power plants is proceeding exponentially faster than in the U.S. in order to quench their thirst for affordable electricity.

MORE CO2 THAN WE NEED

The major greenhouse gas released from fossil fuel-fired power plants is carbon dioxide. While CO2 is necessary for life, emissions from these power plants are far beyond what we need to sustain life and carbonate our beverages. The basic idea of carbon capture and storage (CCS) is to capture the CO2 at the source, either prior to or after combustion, transport it to a suitable geological formation, and store it safely underground. Each part of that chain requires further research and testing, but in the U.S. we are well into that process. The transportation infrastructure requires little new innovation; we know from years of transportation of oil and gas, and to a lesser extent CO2, the basics of how to do it.

Capturing CO2 may be the element that will require the most innovation. Research scientists have several methods for CO2 capture, but the "energy penalty"--the increased amount of energy needed to do the capture-- is still too high to make it feasible on a large scale. Innovations, already under way, are essential. Recent breakthroughs are promising and predictions are that the cost can be reduced to an acceptable level in the next 10 years.

Estimates by the U.S. Department of Energy show that there is between 2.1 trillion to 22.6 trillion tons of geologic storage capacity for CO2. Given that our current output of CO2 from coal-burning power plants is 2.1 billion tons, this is sufficient for 1,000 to 10,000 years of burning coal and, at current rates of consumption, 350-4,000 years for all fossil fuel consumption in the U.S.

ENHANCED OIL RECOVERY

There are hundreds of recently finished and ongoing injection projects in the U.S. and in the world, including two injection projects in Virginia, that are proving the feasibility of injecting CO2 underground in various geologic formations. There are five projects in the world that are storing CO2 safely underground at a rate of more than one million tons per year. A number of these projects utilize CO2 to enhance the recovery of oil and natural gas from existing production wells.

There is currently a thriving Enhanced Oil Recovery industry in the U.S., which uses CO2 to revive depleted wells and produce more oil. Utilizing CO2 for enhanced recovery of oil or gas can give us the benefit of reducing GHG emissions while simultaneously allowing for increased recovery of domestic energy resources. The economic development potential of enhanced recovery will most likely be a driving factor as we move toward commercial deployment.

The big question is surely, is this safe? In dealing with questions of technology and science, there is no certainty. Still, there are excellent reasons to believe that this is safe. First of all, CO2 is not a toxic substance, and storing it is not in any way comparable to storing radioactive nuclear waste. In some geological environments the stored CO2 will bond closely with the reservoir rock so that it isn't likely to come out. In other cases the CO2 will either dissolve in the briny water of saline aquifers or mineralize within the rock.

In all cases, suitable geological sites will have multiple impermeable rock layers, the "caprock" or geologic seals, that will keep the CO2 from escaping upward to the surface. In many cases these same geologic seals have held oil or natural gas in a reservoir for millions of years. Clearly, earthquake-prone or highly faulted areas are not ideal for storage, which is why geological characterization of storage sites is of utmost importance. Underground sources of drinking water, which could be potentially harmed by CO2 contamination, are protected by EPA regulations and are avoided or protected by sufficient caprock.

Some argue that what the U.S. does is all well and good, but unless China and India go along, everything we do will be futile. What is clear is that China and India are proceeding quickly in utilizing their own extensive reserves of coal for power generation. By pioneering CCS techniques and demonstrating that they can not only work but are economically feasible and safe, the U.S. can offer this technology to other countries. The Chinese have shown great interest in employing and developing CCS technologies; many collaborations with U.S. corporations and agencies are well under way.

A PART OF THE SOLUTION

The argument is not that CCS technologies are a sure bet, or that they should be the only option. They are only one element of the strategy for meeting energy needs while mitigating greenhouse gas emissions. If you are against coal and think it should be phased out, CCS can be seen as part of that phase-out strategy. If you think coal can't be phased out in the foreseeable future--the opinion I hold--CCS is then even more essential. We don't have to decide that question in the debate of investing in CCS or not.

If you believe that natural gas will replace coal as our primary electric generation fuel, CCS from these power plants will be necessary as well. If we move toward plug-in electric vehicles, as many predict, once again CCS is critical because fossil fuels supply nearly 70 percent of our electricity in the U.S. Under various scenarios of our energy future, CCS is an important element of the overall solution to mitigating greenhouse gas emissions.