Air Staging and Reburning to Achieve Low Emissions During Co-firing Coal and Biomass

Abstract

In this paper results of research of co-firing coals from Middle Bosnian basin with waste woody biomass are presented. Tested fuels were subjected to pulverized combustion under various temperatures and various technical and technological conditions: different mass ratio of fuel components in the mixture, different coefficient of excess air for combustion, staged air supply into the reaction zone and application of natural gas as an additional fuel (reburning technology). The results are related to the emission of flue gas components (CO2, CO, NOx and SO2) with respect to the technological conditions of combustion. In addition to the valorization of the influence of the primary fuel composition and process temperature on the emission values of the flue gas components, it has been shown that the application of primary measures in the combustion chamber results in lower or higher positive effects in terms of reducing the emissions of individual components - e.g. the NOx emission is reduced from 837;mg/mn3 in conventional combustion to 710;mg/mn3 using air staging. It is also shown that when using natural gas as additional fuel there is an additional reduction in NOx emissions, and this is proportional to the amount of natural gas - e.g. for process temperature of 1350 °C and 10% of natural gas energy share co-firing with coal, a NOx emission reduction of more than 250;mg/mn3 was recorded, compared to emissions without additional fuel.