NETL Studies Ecology of Cold Air Traps in Temperate Climates

Ice stalagmites at Spruce Creek talus slope in Pennsylvania.

Recent studies have shown that cold air traps in temperate climates often harbor flora and fauna that are usually only found in far colder climates. These unusual sites of low temperature create unique “bio-geographical islands,” the function and fate of which may serve as valuable indicators of current and future global climate change.

The first scientific report on cold air traps in eastern North America was published in the 1890s. Climatologist Edwin S. Balch visited 33 unusually cold sites, including ravines and gorges, taluses and boulder heaps, as well as man-made wells, mines and tunnels where ice had been reported to persist into the summer months. Although many cold traps were believed by local residents to “make ice” (which they used to make ice cream and cold drinks) in the summer, Balch demonstrated that most summertime ice was formed when cold air stored during the winter in rock slopes and caves froze water from snow melt and spring rain, producing ice that lasted for several months in protected environments.

Ice formations in the Trough Creek ice mine.

As a result of an NETL investigation that began in 2009, a cold talus slope near Spruce Creek in Huntingdon County, PA was found to harbor numerous boreal (subarctic) lichens not found elsewhere in Pennsylvania. Lichens are symbiotic associations of fungi and algae that result in hardy plant-like organisms that require few nutrients to survive. Ice formations in rock vents at Spruce Creek can persist well into early summer, and the cold air flowing out of the bottom of the rock slope during the summer allows the lichens and other boreal plants to survive. Many other small or microscopic species undoubtedly exist here as well - boreal mites have been shown to be biological indicators of similar cold habitats in Europe, for example. As a result of NETL scientists’ efforts, more than ten lichen species previously unknown in Pennsylvania were identified at the Spruce Creek site.

In collaboration with West Virginia University, NETL researchers also monitored the temperature in the Trough Creek ice mine, another well-known cold site in central Pennsylvania. Here the temperature inside a talus cave was recorded on an hourly basis for 3 years using temperature data logging sensors. NETL scientists found that the cave is isolated from the external environment and does not provide a cooling effect on the environment outside the cave. Instead, the microscopic organisms within the cold cave may be more significant. Psychrophilic, or cold-loving, bacteria with an optimal growth temperature <10°C were found to be abundant inside the cave, consistent with the cool temperatures maintained within the cave year-round. The study was recently published in the peer-reviewed journal Permafrost and Periglacial Processes.

NETL research on the characteristics of regional cold sites and their ecology led to an invitation from the National Park Service to help evaluate the proposed designation of the Ice Mountain Preserve in Hampshire Co., West Virginia as the newest site in its National Natural Landmark program. Future research may show that these unique sites serve as sensitive indicators of subtle changes in temperature rise associated with global climate change.

NETL Carbon Capture Sorbents Support U.S. Energy Independence

Carbon dioxide (CO₂) is considered one of the major greenhouse gases affecting climate change. An estimated one-third of anthropogenic CO₂ emissions to the atmosphere results from the combustion of fossil fuels used for electricity generation. One technique for preventing CO₂ emissions from entering the atmosphere is to capture and concentrate it for beneficial re-use or permanent storage in a geologic formation, assuaging a major concern with the continued use of abundant fuel sources that are domestically available.

Parametric field testing of ADA-ES 1 kW pilot carbon dioxide capture reactor at Martin Lake TX electric generation station.

Capture and separation of CO₂ can be achieved by using solvents, cryogenic techniques, membranes, or solid sorbents. Large-scale operation of any of these technologies is energy intensive when applied to capturing CO₂ from the combustion stream or flue gas, where it accounts for only about 15 percent of the volume. While wet scrubbing systems using regenerable, amine-based, solvents are the most commercially advanced, they are extremely energy intensive due in part to the large amount of processing water involved.

The NETL Basic Immobilized Amine Sorbent (BIAS) process is a "dry" sorbent-based CO₂ capture technology that is both technically and economically viable for removing CO₂ at low concentration from flue gas streams. The technology uses a sorbent made from an amine that is synthesized for high carbon dioxide selectivity and polymerized around a high surface area silica gel for ease of handling. The amine releases adsorbed carbon dioxide when heated at steam temperatures and can then be reconditioned as a solvent with no need for water.

BIAS sorbents.

Independent laboratory testing of over 100 sorbents demonstrated that NETL BIAS sorbents had the best overall performance. BIAS sorbents showed the greatest working capacity, a measure of the net ability of the sorbent to absorb CO₂, were readily regenerated by heating, and had among the lowest projected regeneration energies—the amount of energy necessary to desorb CO₂ from the sorbents.

An initial systems analysis indicates that solid sorbents, such as BIAS sorbents, could adsorb CO₂ over a range of temperatures typically encountered downstream of flue gas desulfurization units in coal-burning power plants, and with their relatively low heat capacities would reduce the energy required for regeneration by 40 percent. Moreover, compared to state-of-the-art alternatives, BIAS sorbents are more thermally stable, exhibit little or no degradation , and produce less corrosion, eliminating the need for corrosion inhibitors. All these advantages combined to earn NETL BIAS sorbents a 2012 R&D 100 award, which recognizes 100 most technologically significant products introduced into the marketplace over the past year. Members of the award-winning NETL BIAS team are: McMahan Gray, Henry Pennline, Daniel Fauth, James Hoffman, and Kevin Resnik.