'Cleanest Coal Plants Ever' Coming to Minnesota
September 19, 2013
Boasting about the cleanest coal-fired power plant seems comparable to feeling good about devouring the lowest-calorie banana split. Each might not cause much damage, but we're still talking about damage.
Minnesota Power would likely take umbrage with the comparison. The utility company says it is spending $350 million to make its coal-fired facility "fully-compliant with both state and federal regulations.”
This achievement is particularly noteworthy because America still depends on coal for its energy. The U.S. generated about 4 trillion kW-hr of electricity last year and “about 68 percent of the electricity generated was from fossil fuel (coal, natural gas, and petroleum), with 37 percent attributed from coal,” according to the U.S. Energy Information Agency.
Contrary to what some people think, mining and burning coal for energy and heat isn't choking America. From 2005 to 2011, coal production in America remained essentially unchanged, at about a billion metric tons. Yet, the nation's air quality is overall much cleaner compared to a decade ago, the American Lung Association reported in its "State of the Air 2013."
Cheaper, Cleaner, and More Plentiful Than Coal? We're All Ears.
So far, there are no energy sources that are cleaner and more economical than coal, though fracked natural gas is in the running. Besides, coal is getting cleaner. Minnesota Power is installing Alstom's Novel Integrated Desulphurisation (NID) emission control system for Unit 4 of its Boswell Energy Center and “once installed alongside the 585 MW coal-fired unit, will reduce the plant’s environmental footprint by cutting mercury emissions by 90 percent and significantly curbing emissions of sulfur dioxide and other pollutants,” according to Daily Fusion.
In the NID system, “dry scrubbers inject water into the gas stream to lower its temperature to the optimum level for reacting with the lime, but not more water than can be fully evaporated, so there is no large steam plume,” according to industry journal Power Engineering.
Then “they pass the gas through a fluidized bed of the raw reagents where the chemical reactions occur to remove the pollutants.”
Tim Hartmann, product marketing manager for Alstom Environmental Control Systems, told Power Engineering that “NID requires reactor residence time of less than one second because of the low moisture content of the reagent/fly ash, which is mixed, hydrated and metered into the duct just in time.”
At that point, the flue gas -- with the reagent and reactants -- “then passes to a baghouse where cloth filters allow the clean air to escape while the solids are captured and fed back to the reactor or removed for landfill disposal. The solids are sent through the reactor numerous times in order to fully use the lime, with only a small portion being disposed of.”
"Cleanest Coal-Fired Units In the Nation."
Al Hodnik, president and CEO of Allette Inc., Minnesota Power’s parent company, said in a statement to Daily Fusion that when completed, “Boswell 4 and our recently retrofitted Boswell 3 will be two of the cleanest coal fired units in the nation.”
The efficiency that comes with the particular technology is that it can capture multiple pollutants with a single unit, so the company doesn’t have to install multiple emission control systems. “A retrofitted Boswell 4 will help ensure the continuation of reliable and competitively priced baseload energy for our large industrial customers that fuel our region’s economic engine,” Hodnik said. “This project will create 500 construction jobs and result in significant environmental benefits for years to come.”
Data Fusion described Alstom’s NID technology as “an all-in-one emission control system that captures many of the most common pollutants associated with fossil fuel-fired power generation.” It can be scale up or down depending on power plant emission control requirements.
Minnesota Power officials say their goal is to “reduce emissions at existing plants,” and find “additional generation from renewables and natural gas, creating a diverse energy mix of one-third coal, one-third renewable, and one-third natural gas.”
Alstom technology is also being installed by Tekniska verken in Linköping for a turnkey delivery of a flue gas treatment and heat recovery system for their new waste-to-energy plant in Gärstad, Sweden. The company's advanced flue gas cleaning system “will reduce emissions well below European Union requirements and also recover heat for the district heating system in Linköping,” according to Penn Energy.
The power plant will primarily use waste as fuel, Penn Energy says, “resources that would otherwise have been lost. Tekniska verken has for a long time been working to phase out fossil fuels from its production mix." The flue gas treatment system includes an Alstom NID semi-dry cleaning step, cleaning the gases by injecting lime and activated carbon, Penn Energy reports, adding that the process removes and prevents most of the hazardous substances of the combustion process from reaching the environment.
Coal: Get Clean Or Die.
Coal needs to get cleaner if it wants to survive. In early September the Obama Administration floated proposals to set “an emissions limit of 1,100 pounds of carbon dioxide per megawatt hour for coal plants and 1,000 pounds per megawatt hour for large gas-fired plants,” according to reports published in The Wall Street Journal.
As the Journal wrote, this would pretty much deep-six any new coal plants, “which generally release about twice as much carbon dioxide as the proposed limits.”