By Amethyst Cavallaro
Online Editor, Power Engineering
A lot of attention is being focused on a 5 MW pilot project in Pleasant Prairie, Wis., where the breakpoint may be reached between the technical viability to decrease carbon dioxide emissions and the cost of its implementation.
The collaborative effort of Alstom Power Inc., the Electric Power Research Institute (EPRI) and We Energies has attracted the support of 19 other utilities, which EPRI says represent a large portion of the coal-burning utilities in the United States. EPRI hopes positive results from data analysis will encourage even more participation from the power sector.
The pilot project managers claim the experimental system has the potential to remove over 90 percent of post-combustion CO2 at a cost that is far less expensive than other carbon capture technologies. They also believe that controlling CO2 is no longer a technology issue, it’s a competitive cost, political and social problem.
“The real problem of CO2 is the installed base today; it’s not a future problem,” Philippe Joubert, President of Alstom’s Power Turbo-Systems and Power Environment Division, told reporters at a POWER-GEN press briefing. “We need to clean the installed base now.”
Alstom will design and construct the pilot and operate it during its yearlong trial. We Energies has provided the use of its Pleasant Prairie Power Plant site and EPRI will conduct performance testing and an engineering/environmental performance and cost analysis during the operation.
A portion of the boiler flue gas generated by the two-unit 1,224 MW plant will be piped to the pilot project where the flue gas will be chilled to 0 to 10 C and directed to the CO2 absorber where an ammonia carbonate compound will be used to isolate the carbon dioxide in a highly concentrated form. The gas coming out of the absorber will then be processed through a water wash system to remove any ammonia slip. The resulting gas will then be exhausted up the stack.
Stuart Dalton, EPRI director for generation, said the project participants chose the Pleasant Prairie site because it is representative of what most new coal-fired facilities will look like. The plant uses Powder River Basin (PRB) coal, has flue gas desulfurization (FGD) and selective catalytic reduction (SCR) technology already in place, and, therefore, reflects the type of emissions that will be in the flue stacks of most new units under construction or being permitted.
Because of modern emissions control systems, the concentration of gases in the flue stacks would be similar for many different fuel systems, making the technology applicable to most modernized coal-fired plants across the country using different grades of coal.
“The CO2 absorber system won’t know what coal was being used to get the gas there,” said Sean Black, Manager of CO2 Programs within Alstom’s Environmental Control Systems Business. “It only matters what the CO2 concentration is and, for coal-fired plants, that’s in the 12 to 15 percent range.”
The biggest difference, according to the project participants, between this and other technologies is cost. The chilled ammonia allows higher loading of CO2 and becomes a type of ammonia bicarbonate slurry, “like a conventional limestone slurry, but different chemistry,” Dalton said. The steam needed in the regeneration process to break the bond created by the chemical reaction to capture CO2 is much lower than other technologies, like monoethanolamine (MEA) absorbers. MEA and amines are very good at absorbing CO2 because they form strong chemical bonds, but it takes more energy to break those bonds in the regenerator than when using ammonia as an absorber. Black said the chilled ammonia process is also advantageous because it removes large amounts of CO2 without creating any significant chemical byproducts.
The project is in the detailed design stage and modular construction and onsite building of the absorber is expected to begin soon. The system should be in operation by mid-2007 and run for a year.
“We’re all looking to move this forward quickly,” Dalton said. EPRI plans to analyze the project data and help Alstom convert the project into a full-scale commercial process. Black said he would expect one or more demonstration projects to soon follow the pilot at the 20 to 30 MW scale with the technology ready for commercial release by early 2011.
While EPRI, Alstom and We Energies has been putting together its pilot project, many utilities have announced plans to incorporate “carbon-capture ready” engineering considerations into current construction plans.
“As carbon capture comes closer to becoming a reality, we want to be ready to implement the technology that comes along,” said OG&E Electric Services Spokesman Brian Alford. “We are watching some EPRI pilot projects very closely to see what viable technology may come in the near future.” OG&E is planning to reserve extra space for future carbon capture technology at the proposed Red Rock ultra supercritical generating facility in northeastern Oklahoma. Project partners include Public Service Co. of Oklahoma, a subsidiary of American Electric Power, and the Oklahoma Municipal Power Authority.
In conjunction with its major building initiative, TXU announced in November that it is investing to ensure each reference plant is “carbon capture ready.” Of the 11 units it plans to build, eight will be advanced coal reference plants. The carbon capture ready investment includes mainly site preparation work such as designating sufficient space in the plant’s critical access locations in ductwork and near the chimney. TXU is conducting geological studies of enhanced oil recovery (EOR) sites and saline aquifers where concentrated CO2 can be permanently stored near the reference plant sites.
Black said a retrofit of a baseload plant already in operation can be done without a major overhaul of plant systems, and a proposed plant that is proceeding with the understanding that it’s likely to later include post combustion capture technology can make the process even more simplified.
“If you’ve got an SCR and you’ve got FGD systems and you have the footprint available, then we can retrofit the plant fairly easily,” Black said. The steam cycle may need to be modified to provide the low-pressure steam required for the CO2 absorber with some interchange of heat to regulate the flue gases. He said some electrical and mechanical adjustments might also be needed to accommodate the new technology.
In fact, the developers of the project believe in the technology to the point of not pursuing the abundant amount of federal aid available for clean coal initiatives. The market is moving and they’re getting ready to meet its needs.
“Alstom is really excited about this technology and we want to control the speed of its development,” Black said. “We see that there’s a market there because of what’s happening in Europe and the EU’s cap-and-trade program. We think the same thing will materialize in North America as well.”