Primary measures for cleaner biomass combustion to reduce NOx: A narrative review on solid biomass fuels, NOx sources, small-scale boilers, axillary equipment, fuel management and fuel quality improvement
Morteza Jafarsalehi, Mohammad Mashayekh, Mohammad Bagher Miranzadeh, Nezam Mirzaei, Mehdi Ebrahimi
Abstract
Building heating systems largely rely on the combustion of fossil fuels. However, renewable heating technologies are on the rise to low carbon emissions. Among these, biomass is increasingly recognized as a renewable and sustainable source for building heating, particularly in decentralized, small-scale boilers. However, NOx emission during biomass combustion due to health and environmental risks is a significant air pollution source. While secondary measures are often discussed, primary measures are relatively less at the center of attention. The previous literature has shown that NOx emission from small-scale boilers is typically influenced by fuel-N. According to this, the focus of the present review is the improvement of fuel quality and biomass properties. This is followed by the enhancement of thermal efficiency and the utilization of thermal energy storage (TES) and solar heaters. In addition, fuel modification, including fuel-blending and combustible waste management, are analyzed. Finally, decreasing fuel-N by agronomic practices is discussed. The paper concludes with summary results implying primary measures for NOx control as well as some suggestions for future study to solve the remaining challenges.