Intercomparative measurements of particle emission from biomass pellet boiler with portable and stationary dilution devices

Three portable dilution devices (a two-stage dilutor, a one-stage dilutor and an axial dilutor) and a stationary dilution tunnel were compared by employing them in an experimental setup for particle emission measurements from a 40 kW pellet boiler. Total concentrations and number size distributions of particles were detected by an ELPI + analyzer. Averaged values of total particle emission per MJ received from measurements with available dilution devices were within the range between 3.14 × 1013 and 1.15 × 1014 for the full power regime, and between 1.54 × 1013 and 5.03 × 1013 for the reduced power regime. Measured particle concentrations decreased by using dilution devices in the following order: a two-stage dilutor, a one-stage dilutor, a dilution tunnel and an axial dilutor. The number size distributions of particles for the majority of cases are qualitatively similar for all devices for similar combustion regimes of the boiler. Applying dilution air with or without heating did not significantly affect the results of measurements. During multiple series of measurements the degree of dilution was varied when possible for different devices within a range between 8 and 102. No dependence of particle concentrations on the degree of dilution could be determined from these experiments. Applying a method of one-way analysis of variance revealed the statistically significant difference in particle concentrations measured with different dilution devices. Implementing this method to CO, and CO2 gas emission components of different series it was determined that the boiler operation was stable as the measured data belong to the same distribution. Thus, the statistical differences in particle concentrations most likely relate to the varied measuring equipment, i.e., dilution devices.