Coal combustors cut pollution
1 Jul 2002
Two new, high-tech coal combustors offer the potential for cutting smog-forming emissions to levels that rival more complex chemical devices now being installed on many coal-burning plants.
Equally important, these advanced technologies also could cut the cost of reducing pollutants by at least 25%.
Alstom Power and Praxair both participants in the Energy Department's coal research program, developed the new combustion systems in independent projects.
Each company presented results from their pilot tests at a recent conference on nitrogen oxide controls conducted by the National Energy Technology Laboratory, the US government's lead centre for advanced fossil energy technology.
Both combustor systems employ innovative modifications to low-NOx burner technology. Low-NOx burners - so-named because they lower the levels of nitrogen oxides (NOx) emitted when coal is burned - have become standard for many utilities in the US.
Conventional low-NOx burners reduce nitrogen oxide pollutants by 40 to 45% at relatively low costs. But as emission limits have become more stringent in many states in the US, many utilities are being required to install more expensive pollution controls that cut emissions even more.
To achieve the necessary emission reductions, power generators are turning to the current state-of-the-art NOx control technology called 'selective catalytic reduction' (SCR). Rather than reducing NOx in the combustion zone, SCR uses chemical catalysts to scrub NOx pollutants from a power plant's flue gas before it is expelled from the plant.
SCR can meet the most stringent emission limits set by federal and state standards - 0.15 pounds of NOx per million Btus. But SCR adds a complex and expensive chemical plant to the power station.
Now, new low-NOx technologies developed by Alstom and Praxair can, in many cases, achieve the aggressive NOx reduction required to meet these same stringent emission limits. Like conventional low-NOx burners, however, the NOx is reduced inside the combustor not in a separate chemical plant, resulting in a less complex and lower cost power plant.
The Alstom combustion system uses advances in control systems, combustion process modifications, and special 'carbon burnout' technology to lower the formation of NOx. The Praxair technology enhances the combustion process with oxygen which improves NOx reduction compared to burners using only air.
The next step will be to demonstrate both combustion systems in full-scale, multiple-burner configurations at sizes typical of larger commercial power plants.
The Praxair burner was co-funded by the US Energy Department in co-operation with the University of Utah, The University of Arizona, Reaction International Engineering, and Alstom Power. The Alstom project, also co-funded by the Department of Energy, included participation from Progress Materials and Kennecott Energy.
