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POST COMBUSTION CARBON CAPTURE
By Steve Blankinship, with additional reporting
by Amethyst Cavallaro
Page 64, Copyright 2007 "POWER ENGINEERING," MARCH 2007 http://www.power-eng.com
Regardless of how well coal-fired power technologies remove various emissions, CO2 dominates today's debate about new coal plants because it is the primary greenhouse gas that coal plants produce. Conventional wisdom has held that the technology with the most promise to capture CO2 is IGCC. That's because capturing all emissions - CO2 included - is easier when coal is in a gasified state prior to being burned, than captured from flue gas after combustion.
But a 5 MW pilot plant in Wisconsin scheduled to go into operation later this year could change that thinking. The plant will test ALSTOM's Chilled Ammonia Process tha
t captures CO2 from conventional pulverized coal plants post-combustion. If successful, the process could be incorporated into new PC plants and retrofitted to existing ones.
The pilot, at We Energies' 1,224 MW Pleasant Prairie plant, will use chilled ammonia to capture CO2 from a portion of the flue gas coming from one of the Pleasant Prairie units. The process captures and isolates CO2 in a highly concentrated form at high pressure. In laboratory tests, the process has shown potential to capture more than 90 percent of the CO2 less expensively than other carbon capture technologies. The captured CO2 can then be used commercially or geologically sequestered. The process is also expected to remove high levels of residual SO2, hydrochloric acid, hydrogen fluoride, SO3 and condensable particulate matter (PM2.5).
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The pilot is being funded privately. In addition to ALSTOM, funding is coming from 19 ERPI-member utilities. "Evaluating and developing technology for economical post-combustion CO2 capture is critical to ensure that we keep coal as a viable electricity generation option," says Chris Larsen, vice president of generation for EPRI. In addition to We Energies, 19 other U.S. utilities have committed to support the project.
Sean Black, manager of CO2 programs within ALSTOM's Environmental Control Systems business, said the process takes fl ue gas, which typically leaves the boiler/flue gas desulfurization unit at about 130 F, and cools it to 32 F to 50 F. After it cools, it passes through a CO2 absorber where it is absorbed with ammonia carbonate. The fl ue gas then passes through a water wash system, after which the CO2 solution moves to a regenerator where the CO2 is stripped off under pressure and high temperatures. (See Fig. 1.) The process leaves lit
tle byproduct - essentially a small amount of water than can either be treated in a wastewater treatment facility or possibly recycled for use in another part of the power plant. "The process is designed to take advantage of the attractive characteristics of the ammoniated solution while preventing the ammonia from escaping from the system," says Black. The CO2 will be pressurized in accordance with anticipated standards for commercial use, such as transport for enhanced oil recovery or sequestration. If purity standards are required for commercial CO2,
Black sees no problems in achieving those standards. One feature of this technology is that it does not require extremely low levels of SO2 coming into the sys
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tem for it to work. About 95 percent of the modern designed FGD is sufficient. So most plants already have or will be retrofitting their plants with modern selective catalytic and FGD systems. That means if they have the footprint to install the chilled ammonia CO2 system, a retrofit may be possible with minor adjustments to the steam cycle to accommodate for the process's low pressure steam requirement.
The Pleasant Prairie pilot project is expected to run about a year, after which ALSTOM expects to build one or more demonstration projects, each in the range of 20 to 30 MW. The company expects the chilled ammonia process to be ready for commercial application in 2011.
For more information, please see:
http://www.alstom.com
Editor's note:
Practical and profitable downstream applications for the generated CO2 and extracted sulfur include the mass production of ammonium sulfate, one of the world's most widely used fertilizers for many years. This is already being done in bulk at the Black Hills project: Agrium also looks to use post combustion carbon capture in the near future for production of their excellent line of fertilizers. This then would complete the full cycle of plant-based carbon sequestration of excess CO2, while in the process creating a food production boom.
So show us your new Branson Award, Alstom! Good work…..and "On, Wisconsin!"
FOR MORE DETAILS, SEE THE ENERGY HANDBOOK BY CLICKING HERE
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