Aerosols and fine particles produced during the combustion of solid fuels such as biomass and lower rank coals impact the thermal performance and have an impact on post-combustion strategies to control NOx emissions. The aerosol-forming species of focus in this paper include alkali elements such as sodium and potassium, and alkaline earth elements (magnesium and calcium) which are mainly associated with the organic matrix of the fuel or as carbonates. Upon combustion, the alkali components are vaporized and condense to form aerosols upon gas cooling. The alkaline earth elements form fine particles or react with other minerals during combustion. The aerosols and fine particles interact with other gas species such as sulfur oxides to form sulfates or may condense on the surfaces of entrained ash particles to form silicate, aluminosilicate and other particle types. The partitioning of alkali earth elements between sulfate and other forms is dependent upon the fuel composition, system design, and operating conditions.
The aerosols are transported to surfaces within the combustion system by diffusion and small particle mechanisms. The fine particles react and the phases present cause ash deposit formation on heat transfer surfaces, reducing heat transfer. They also deposit in and on selective catalytic reduction catalysts, causing poisoning, plugging and masking. This paper will provide information of the formation, fate, and behavior of alkali and alkaline earth containing phases and their impacts on system performance.
