Engineers from the Lawrence Livermore National Laboratory have developed a combustion method that results in lower power plant pollutant emissions by combining stage-combustion with nitrogen-enriched air.
The new technology, named Staged Combustion with Nitrogen-Enriched Air (SCNEA), could help power plants comply with US Environmental Protection Act requirements for decreasing plant emissions.
According to LLNL, SCNEA can replace or enhance current pollutant control technologies at a lower cost while at the same time further reducing pollutants. In addition, existing power plants can be easily retrofitted to use the SCNEA combustion method without incurring large costs.
‘As EPA requirements become tighter and tighter on emissions, most solutions become more difficult and more expensive to implement,’ said Larry Fischer, LLNL principal investigator for SCNEA. ‘With our technology, consumers will see cleaner air at a minuscule increase in their utility bills.’
Before concerns about oxides of nitrogen (NO and NO2, termed NOC) and their relationship to photo-chemical smog and acid rain came to light in the late 1980s, fuel was typically burned in boilers and furnaces with single-stage combustion using air as the oxidant stream.
NOC emissions are regulated in the US under the provisions of the Clean Air Act and its 1990 amendments. Those requirements demand that dry bottom wall-fired boilers can emit no more than 0.50 lbs. of pollutants per million British thermal units (Btu) and that tangentially fired boilers can emit not more than 0.45 lbs. of pollutants per million Btu.
To date, low-NOX technologies, including low-NOX burners, overfire air and reburning, have been used to reduce NOX production in coal-fired boilers. But they must reach significantly lower emission levels by 2005.
Fischer said SCNEA is expected to lower corrosion and slagging rates, extend the lifetime of equipment and decrease down time and maintenance costs in power plants. He estimates that a 350-megawatt coal fired boiler plant would cost about $60 million to retrofit for SCNEA operation.
The SCNEA combustion method is said to burn fuels in two or more stages, where the fuel is combusted fuel-rich with nitrogen-enriched air in the first stage, and the fuel remaining after the first stage is combusted in the remaining stage(s) with air or nitrogen-enriched air.
‘You get the NOX reduction but you’re not taking a significant hit in efficiency (energy output) of the power plant,’ said Kevin O’Brien of New Business Development in the Engineering Directorate.
This method is said to substantially reduce the oxidant and pollutant loading in the effluent gas and is applicable to many types of combustion equipment including boilers, burners, turbines, internal combustion engines and many types of fuel including coal, oil and natural gas.
LLNL is working to form a consortium of representatives from the EPA, utility companies, boiler manufacturers, emission control equipment companies and a company that produces nitrogen-enriched air. The next stage is to do a small scale-pilot program.