Before being fed to the blast furnace, iron ore is first converted into pellets by, for example, a traveling-grate (TG) pelletizing plant. In this plant, so-called green pellets are conveyed through a furnace that heats the pellets to high temperatures to perform drying, partial calcination and induration. The pelletizing process generates considerable emissions of oxides of nitrogen (NOx) due to the high process-air temperature. Primary NOx-reduction measures used in different industries are less effective for TG applications, and secondary deNOx measures, such as selective catalytic reduction (SCR), have high capital and operating expenses, explains Andreas Munko, senior product manager, Ferrous & Heat Transfer at Metso Outotec Corp. (Helsinki, Finland; www.mogroup.com).
Because NOx emission limits have been established in many countries, and are also becoming more stringent, Metso Outotec has developed a new burner to solve this challenge. Commercially launched at the end of March, the Ferroflame LowNOx burner for TG pelletizing plants (diagram) substantially reduces NOx emissions by up to 80%, says Munko.
The main operating principle of the new burner is a high-speed dilution of fuel with air using a specially designed burner lance (diagram), along with a slight increase in the primary air-to-fuel ratio, explains Munko. This leads to an improved mixing of fuel and air and a lower fuel content in the combustion mixture. The average and peak temperature in the flame is also reduced in the new burner, which is important because NOx emissions increase at higher temperatures, he says.
The first commercial full-scale application of the burner has been operating since 2019, and the company is now working on a new project that is scheduled for delivery this year. The new burner works seamlessly with natural gas fuel, and tests demonstrate that diesel and coke-oven gas can also be used.