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CARBON DIOXIDE SEQUESTRATION: WHAT IS IT AND CAN IT BE DONE? A BRIEF OVERVIEW

By Kathryn G. Arlen

Just 150 miles south of the Arctic Circle proudly sits the University of Alaska Fairbanks (UAF,) one of the world’s foremost facilities dedicated to geological engineering and atmosphere/climate research. Global warming debates frequently heat both university and community members’ intellectual discussions, and a current modish question revolves around the engineering option of sequestration, or removing carbon dioxide (CO2) from atmospheric emissions by separating carbon from nitrogen and oxygen and storing it elsewhere. How feasible and economical is this process?

It’s a challenging concept: we’ve put it in our air — can we take it out? “Yes,” but at a price. “It makes little economic sense to attempt to remove the CO_{2
from combustible fossil fuels or curtail the use of fossil fuels which will
result in significant economic hardship,” declares Dr. Paul Metz, Director of
the Mineral Industry Research Laboratory at UAF, adding: “This is not going to
supplant the use of coal for energy or use of petroleum for transportation.”
Cost effectiveness of human-induced sequestration hinges on the basic economic
concept of dollar value return: can we get enough back to justify our
investment?”}

Alaska State Geologist Bob Swenson adds, “It is expensive, because you have to use specific type of equipment to do the injection. You have to drill very, very expensive wells if you don’t have existing wells. [And] much of the equipment has to be stainless steel because CO2 can be very corrosive. So the expense of this can be quite prohibitive.”

In addition to expenses for special equipment and drilling efforts, you need to also factor in the actual energy cost of sequestration effort. Swenson explains: “It takes a lot of energy to do this. So if you’re burning 100 BTU’s of energy in just the normal stream to capture the CO2, then liquefy it, and inject it back into the ground, you’re using probably a third again as much energy.”

Sequestration of carbon dioxide also applies only to earth-based features, such as power plants, and does not address auto exhaust or jet chem. trails. The process itself generally involves cryogenic separation, as Metz elaborates, cooling the gas to –56 degrees C allowing CO2 to become liquid. Then it can be injected into the ground where it regains its gaseous state. One of the more practical, proven uses for sequestration today is enhanced oil recovery (EOR), used on the Alaskan north slopes and in Cook Inlet. In this procedure CO2 is injected into porous rock and its reconstituted gas pressure reduces the oil’s viscosity enabling easier recovery. To date this is our proven technology.

This leaves the unproven technology, including several projects the Department of Energy is working on, Swenson adds, emphasizing that “[CO2 storage] in deep saline reservoirs…is one piece of research we’re trying to get a better handle on.” This process entails deep drilling beneath the fresh water aquifer level, to reach saline reservoirs that, like ocean water, can sequester CO2. However, carbon dioxide’s natural buoyancy dictates its upward migration. Oil and gas accumulation in the subsurface (as in the oil fields) serves as a viable “trapping mechanism” for surfacing CO2, as occurs in proven EOR technology (see figure.) For other purposes, especially addressing global warming/greenhouse gas reduction, Swenson again emphasizes: “If we are going to sequester CO2, to capture it and put it in the ground, we have to know that it’s going to stay there.”

Other possibilities include chemical sequestration, directly applying CO2 to any basalt formation for permanent storage, one of Dr. Metz’ current research projects. Another possibility is adsorption, sequestering CO2 in coal seams by replacing methane molecules.

But all, as geologist Swenson reminds us, are “unproven and part of ongoing research,” adding “the problem is that the technology does not exist to actually get all the CO2 out of the emission streams.”

Kathryn G. Arlen can be reached at mindmerger@hotmail.com