First Operational Experiences with Advanced NOX Emission Abatement Technology for Large Lignite Fired Power Boilers

摘要

The subject of the paper represents advancement and implementation of new GE LowNOx Firing Technology for large lignite-fired power boilers. Today’s standard solution for such boilers contains primary measures of NOX reduction to comply with the legislation. Primary measures consist of design concepts and adapted configurations of individual steam generators allowing operation with NOX concentrations in the flue gas of average not more than 200 mg/m3(STC dry, 6 % O2) (European Directive 2010/75/EU). Boilers which miss the mark of primary NOX reduction due to individual features of design and/or fuel characteristics demand upgrades. Those are called secondary measures. Secondary measures append devices to reduce final NOX formation by post combustion chemical reactions in the flue gas. Also lignite fired boilers may fail to achieve the emission limits by primary measures due to design and fuel conditions. The quest to avoid the expensive amendment of catalytic reduction led to multiple investigations into applicable Selective Non-catalytic Reduction techniques. GE developed in cooperation with a prominent European utility a technical concept combining LowNOx Firing Technology with Advanced SNCR Technology for large lignite fired steam generators to continue operation or undercut legislative limits. GE LowNOx Firing Technology for large lignite-fired power boilers is based on primary NOX cutback incl. overfire air injection extended by Advanced SNCR Technology. Full-scale tests were conducted at one 1,100 t/h lignite-fired boiler in 2014 and 2015. The boiler was commissioned in the 1980s and was retrofitted from 2009 - 2011. The installed LowNOx firing system consists of jet burners and two levels of overfire air (OFA). The second overfire air level - consisting of ten lances - is located in the final superheater. During the large-scale tests urea solution was injected via the OFA lances. In combination with the LowNOx firing system emission levels below 150 mg/m3 were successfully demonstrated achieving NOX reduction rates of up to 40 %. The paper shall give an outline of the initial results and discuss the potentials of the technology. The promising results motivated the plant owner to implement the technical concept at units of the largest European lignite-fired power station.