Experimental study on combustion and NOx emissions for a down-fired supercritical boiler with multiple-injection multiple-staging technology without overfire air

• Published in: Applied energy 2013-06, Vol.106, p.254-261
• Main Authors: Kuang, Min, Li, Zhengqi, Liu, Chunlong, Zhu, Qunyi
• Format: Article
• Language: English
• Subjects: air; Applied sciences; Boilers; Carbon; Coal; Coal combustion; Combustion; Down-fired boiler; emission; Emissions control; Energy; Exact sciences and technology; Fly ash; Furnaces; Gas temperature; Industrial-size measurement; Multiple injection and multiple staging; NOx emissions; oxygen; temperature
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2013.01.072

► Asymmetric combustion and particularly high NOx emissions appearing in down-fired furnaces. ► Applying a deep-air-staging technology especially for these problems in new down-fired furnaces. ► Experimentally evaluating the air distribution effect on coal combustion and NOx emissions. ► Symmetric combustion, high burnout, and relatively low NOx emissions appearing in the furnace. A deep-air-staging combustion technology was previously developed to achieve reduction in NOx emissions and to eliminate strongly asymmetric combustion found in down-fired boilers. Recently, one of two down-fired 600MWe supercritical utility boilers using this technology (without applying overfire air) began commercial operations. To understand coal combustion and NOx emissions characteristics within the furnace, full-load industrial-size experiments were performed at different air-staging conditions with measurements taken of gas temperatures in the burner region, gas temperatures and species concentrations in the near wing-wall region, carbon content in fly ash, and NOx emissions. As expected, the furnace performance characterized by relatively timely coal ignition, symmetric combustion, and low levels of carbon in fly ash, developed in the furnace at all three settings. Deepening the air-staging conditions could reduce NOx emissions by one-fifth, but varied slightly carbon in fly ash. In view of the still high NOx production (i.e., 1036mg/m3 at 6% O2), adding an overfire air system which was essentially a part of the technology, was recommended for the boiler to significantly reduce the present NOx emissions.