Emissions characteristics of NOx and SO2 in the combustion of microalgae biomass using a tube furnace

Abstract

There is a strong motivation for alternative energy sources, such as fuel technologies based on the use of sustainable biomass feedstocks, due to increasing pressure to conserve ever diminishing fossil fuel resources and to reduce greenhouse gas emissions. Microalgae and oil shale are two promising potential alternative energy sources. In this work, an assessment of nitrogen oxides (NOx) and sulfur dioxide (SO2) emission characteristics of a species of microalgae (i.e. Chlorella vulgaris) under conditions that are relevant to large-scale use of biomass for heat and other products is performed. The pollutant emission characteristics of the microalgae samples, when blended with different catalyst materials (SiC, ZnCl2, MgO, and CuCl2) and different oil shale content, are also measured. The microalgae biomass samples are observed to display variation in the devolatization and char oxidation characteristics at different furnace operating temperature conditions. In this work, the reduction in the peak NOx and SO2 emissions are found to decrease in the order of CuCl2 > SiC > ZnCl2 > MgO, and MgO > SiC > ZnCl2 > CuCl2 as the added catalyst, respectively. The co-combustion of microalgae biomass and oil shale is also found to affect the NOx and SO2 emission profiles, which is most likely caused by the inhibitory effects on mass transfer caused by the very high ash content in the oil shale samples used in this work.