As U.S. policymakers consider how to tackle the challenge of greenhouse-gas constraints, the U.K.’s approach to the problem offers instructive examples.
Capture and storage tech developments secure coal’s future.
Carbon capture and storage or sequestration (CCS) involves isolating carbon dioxide (CO 2) from other power plant emissions before it is emitted from the stack, compressing it into a liquid, and pumping it into underground geological formations such as spent oil or natural gas wells, saline reservoirs, or inaccessible coal seams.
A 2007 study released by the Electric Power Research Institute (EPRI), found that U.S. electric utilities can help the nation cut its CO 2 emissions to 1990 levels by 2030 by taking aggressive steps in seven areas. The most significant reductions, according to the study, would come from CCS technologies.
The National Energy Technology Laboratory (NETL), in its “NETL 2007 Carbon Sequestration Atlas,” reports that North America has enough storage capacity at its current production rate for more than 900 years of carbon dioxide.
A great deal of progress has been taking place during the last year related to CCS. Some activity is focused solely on the capture side, some solely on the sequestration side, and some on both. The two projects that have advanced the furthest involve a We Energies plant—which will demonstrate technology for capturing CO 2 emissions—and an American Electric Power (AEP) plant—which will both capture and sequester CO 2. These projects make up two phases of a three-phase rollout by Alstom, a French CO 2 capture technology provider that was involved in both projects. But many types of organizations, from Battelle to Siemens, are moving CCS technology forward in different ways.
Phase I: Pleasant Prairie
We Energies’ Pleasant Prairie power facility in Pleasant Prairie, Wisc., has two plants with combined generating capacity of 1,210 MW, burning low-sulfur pulverized coal.
Alstom and EPRI tested a pilot-scale version of CO 2 capture on a 1.7-MW portion or slipstream ( see Figure 1 ). The project started in early 2008 and wrapped up Oct. 8, 2009, capturing about 40 tons of CO 2 each day. Although the project was a small-scale test, it was important because it showed how the technology would operate commercially in a state-of-the-art, base-load coal-fired power plant. “The plant has the latest air quality controls in place, similar to what will probably be the case in other coal plants when commercial CCS processes are in place in the future,” explains Brian Manthey, senior communications specialist for We Energies.
Alstom is working on three different CO 2 capture technologies. The We Energies project used chilled ammonia technology. The chilled ammonia withdraws about one percent of the exhaust (flue) gas between the outlet and the stack. The gas is first cooled to condense and remove moisture and residual pollutants. It then enters a CO 2 absorber, where the CO 2 is absorbed by an ammonia-based solution, separating it from the flue gas. Then, the CO2-laden solution is heated, releasing a pure stream of CO 2.
In a commercial-sized application, the CO 2 stream would be compressed and transported for use in industrial processes, such as