Berkeley Lab's Carbon Cycle 2.0 Energy and Environmental Analysis Team—A Closer Look at Carbon Sequestration

Scientists in Lawrence Berkeley National Laboratory's Environmental Energy Technologies Division (EETD), in cooperation with colleagues throughout the Lab, have formed a team to evaluate the impacts of low-carbon and energy-efficient technologies that are still in the laboratory. Development of these technologies is part of a Lab-wide effort called Carbon Cycle 2.0, focused on sustainable energy solutions such as advanced materials and information technology for buildings; next-generation biofuels; new battery, fuel cell, and thermoelectric energy-storage technologies; and carbon capture and sequestration technologies.

The work of the Carbon Cycle 2.0 Energy and Environmental Analysis Team (E2AT), led by EETD's Eric Masanet, has begun to bear fruit in the form of assessments of several technologies, including next-generation coatings for energy-efficient windows, salt- and drought-tolerant switchgrass for biofuels, and large-scale solar photovoltaic installations. Read more about these results on "Berkeley Lab's Carbon Cycle 2.0 Energy and Environmental Analysis Team Finds Effective Directions for Energy Research".

The pilot project to develop a spatial and temporal life-cycle environmental and cost model for geologic carbon sequestration (GCS) furnishes an illuminating case study on how the Team works. Hanna Breunig, Philip Price and Tom McKone together with Earth Sciences Division scientists Curt Oldenburg and Jens Birkholzer are studying the economic and environmental characteristics of large-scale systems to capture carbon at the power plant and inject it into geological reservoirs.

"Throughout the Unites States," Price explains, "are saline aquifers in large sedimentary basins, depleted oil and gas reservoirs, un-mineable coal areas and other formations which could serve as reservoirs for greenhouse gases produced at power plants." The CO₂ storage capacity of saline aquifers alone is estimated to be between 1,600 and 20,200 billion tonnes (metric tons).

One of the barriers to using these reservoirs is that injecting CO₂ into these formations raises the pressure of saline water (brine) occupying pore space in the rocks. This reduces the amount of CO₂ that can be stored, and may cause small earthquakes or force some of the injected gas into drinking water aquifers. One way to address the problem is to maintain the pressure by removing the brine to the surface.

The brine production poses problems of its own. Geologic carbon sequestration will only be practical if there are cost-effective, sustainable ways of using or disposing of the brine.

For their analysis, the Berkeley Lab scientists selected three saline aquifers in different parts of the United States, to introduce geographic and regional economic variability: the southern Mt. Simon Sandstone Formation in the Illinois Basin; the Vedder Interval in the southern San Joaquin Basin, California; and the Jasper Interval in the eastern Texas Gulf Basin. (See Figure 1.) Each aquifer is near a major greenhouse gas emitting power plant, making it a candidate as a reservoir for those point source's emissions.

"There are several ways of using the brine from these aquifers," says Breunig. "The approach is to treat the brine as a resource, using its minerals, energy, and water in applications such as geothermal energy extraction, salt harvesting, and saline algae ponds for biofuels production. Then the brine would be discharged into wastewater treatment facilities or evaporation basins."

In a basin, the evaporating water would leave behind minerals such as gypsum, magnesium, salt, potash, and boron, which have value, and could be harvested and marketed. Workers would harvest salts year-round in California and Texas, and during warmer months in Illinois. The salts could be used for anti-icing roads during colder months in Illinois, while in all three locations, any remaining brine could be diluted and sent to a saline water body or re-injected underground.

Price and Breunig obtained the mineral concentrations of brine in each of the three locations. They calculated the cost of production, and the value of salts that could be harvested in each location, taking into account the differing regional market prices, and rates of evaporation (the Texas and California locations are hotter and drier, and evaporation continues year-round).

GIS (geographic information systems) software is one of the tools they used in their analysis. It provides a cross-regional perspective, allowing the Team to understand the impacts of new technologies on resource use and emissions in different climates and geographies, with their variations in utility costs and other costs of living.

Their results are summarized in Figure 1. The brine from the Illinois site turned out to have the highest value. It has a very high concentration of dissolved salts, and researchers concluded that "a large profit could be obtained from harvesting salts during warmer months. In addition, the brine from this formation could be used for anti-icing roads in the wintertime. This substitute for mined rock salt would lower the pressure on depleted salt mines, avoid the production of synthetic deicing solutions…"

Even though brine evaporates at the southern California site year-round, its low total dissolved solids content means that harvesting these salts would not be cost-effective.

They also concluded that, "Texas [site's brine] also has high enough total dissolved solids that a profit may be obtained by harvesting salts through evaporation ponds. Due to heavy rain fall in Eastern Texas, ponds could be used for salt tolerant algae production for biofuels…"

Their study illuminates how regional variations in economics and climate affect the viability of geologic carbon sequestration from place to place—and their analysis methods provide scientists developing the technology, as well as future investors, implementers, and policymakers, with results to make better decisions about where and when to use the technology cost-effectively.

This research was funded by the Lab-Directed R&D program of Lawrence Berkeley National Laboratory.