P. Bächler, J. Meyer, R. Ligotski, P. Krug, A. Dittler

Process Safety and Environmental Protection, 2024, https://doi.org/10.1016/j.psep.2024.02.013 (open access)

The nanoparticle emission of a biomass incineration plant for district heating was investigated during a field measurement campaign. Pulse-jet cleaned filters were used as the main waste-gas treatment technology for the plant, downstream of a multi-cyclone which served as a pre-separator for the coarser size spectrum of fly ash particles. These filters feature a characteristic transient emission behavior consisting of distinct emission peaks, lasting from several seconds to many minutes after filter regeneration. This transient behavior required the development of an adapted measurement setup and methodology when using a scanning mobility particle sizer (SMPS) for the determination of the size distribution. The concentration of particle size fractions (during both, SMPS scans and measurements with fixed classifier voltage) and the total concentration were measured simultaneously applying two condensation particle counters (CPC). The decay behavior of the emission peaks of certain size fractions (at fixed classifier voltage) and the total concentration are in good agreement, enabling post-processing of the SMPS scans, which are affected by the inlet concentration decay during measurement. The size distributions of the particle emission from filter bags made of needle-felt media (aged and newly installed) and of membrane filter medium with taped seams (newly installed) were obtained following the measurement methodology. The emission of the aged needle-felt and the membrane filter medium rapidly declined to zero, allowing only for a single scan for each regeneration event. The membrane filter medium shows the lowest emission at an average number concentration of approx. 13 #/cm³ with a number-based median diameter x_50,0 of 70 – 80 nm. The results demonstrate the possible high number based separation efficiency (e.g. above 99.999 % for the membrane filter bag) of pulse-jet cleaned filters regarding particle sizes not properly represented by conventional gravimetrical measurements.