March 29, 2013
Rice Team Develops More Efficient Method To Capture Carbon Dioxide
Brett Smith for redOrbit.com — Your Universe Online
"This is just the first step in our effort to better engineer a process for capturing CO2 from flue gas at power plants," said project leader George Hirasaki. The Rice team was one of 16 selected by the Department of Energy in 2011 to create innovative methods for reducing emissions from power plants.
Coal-fired power plants make electricity by generating steam that runs electric turbines. Some of the steam generated by burning coal doesn´t have enough heat to run a turbine. Often referred to as "waste" heat, the Rice team found a way to use this steam to aid in the capture CO2, according to two reports on the project recently published in the International Journal of Greenhouse Gas Control.
The Rice method expands on a currently used technique that removes naturally occurring carbon dioxide from natural gas as it is being extracted from a well. For several reasons, the process isn´t cost-effective enough to be used a power plants.
"The CO2 that comes out of the ground with natural gas is under high pressure, while the CO2 at power plants is not," Hirasaki explained. "There's also a greater volume of CO2 per unit mass at a power plant than at a natural gas well.”
A two-fold process is used to remove CO2 from natural gas. First, gas is piped up through a column while an ammonia-like liquid called amine flows down the column. Amine captures CO2 as natural gas is allowed to bubble out the top of the column.
Second, the amine and captured CO2 is recycled using heat, which drives off the greenhouse gas. This part of the process is the most prohibitive, as the amount of heat required to recycle the gas demands as much as one-quarter of the “good” steam that would have be used to generate electricity, according to Hirasaki. Known as "parasitic" power loss, the steam diverted to carbon capture would lower the amount of electricity a plant can produce for sale.
"It has been estimated that the use of current technology for CO2 capture would drive up the cost of electricity by 70 to 100 percent," said report co-author Sumedh Warudkar.
"There's a great deal of optimization that needs to take place," he added. “The Department of Energy wants us to investigate how our process compares with what's already on the market, and these first two studies are the first step because they will help us identify an optimal set of operating conditions for our process."
According the study results, two parts of the Rice method — an optimized amine formula and the use of waste heat -- can cut parasitic power loss to around 25 percent from about 35 percent.
The team said they are currently working to develop new materials and a single, integrated column that can further economize CO2 capture.