Boiler operation influence on the emissions of submicrometer-sized particles and polycyclic aromatic hydrocarbons from biomass-fired grate boilers

The emissions of particles, and gaseous compounds, into the ambient air from biomass-fired moving grate boilers were characterized under different boiler operation conditions. The boilers had a thermal capacity of similar to1 MW. The flue gas cleaning systems consisted of multicyclones for the removal of coarse particles. Dry wood fuel that consisted of shavings, wood chips, and sawdust from a local wood industry and wood pellets were fired at two plants. The influence of boiler load on the emissions was characterized. An electrical low-pressure impactor (ELPI) was used to determine the particle number concentration with high time resolution. A low-pressure cascade impactor (LPI) was utilized for the mass size distribution and the size-differentiated chemical composition. Elemental analysis of the fly ash collected on impactor substrates was made by particle-induced X-ray emission (PIXE) analysis. The concentration of elemental carbon under different load conditions was also measured. In addition, emissions of polycyclic aromatic hydrocarbons (PAHs) from the boiler that was operating on dry wood fuel were compared with PAH emissions from two different biomass-fired boilers (one was operating on forest residues and the other on pellets). The boiler load had little influence on the particle mass concentration of submicrometer-sized particles, which was in the range of 50-75 mg/m(3) (0 degreesC, 101.3 kPa, dry gas, 13% CO2). The total particle number concentration increased and the particle size decreased as the boiler load increased. The elemental analysis revealed that potassium and sulfur were the dominating components in the submicrometer size range, whereas potassium and calcium were major components in the coarse fraction. The PAH emissions between the three boilers varied by almost 3 orders of magnitude.