Comparison of Different Flue Gas Treatment Sections in the Abatement of Ultrafine Particles Emitted by Waste Incinerators, 15th ETH Conference on Combustion Generated Nanoparticles

In the waste field, incineration represents a favorable technique for reducing the volume of waste streams and recovering its energy content for the generation of electricity and district heating. The incineration sector has undergone rapid technological development over the last 10–15 years, due to specific legislation applied to industry that has obliged several European countries to reduce toxic emissions from municipal waste incinerators (MWI). Nevertheless, in Western countries, there is a strong debate on the emission of ultrafine particles (UFPs) at the stack of waste‐to‐energy plants. Currently, as regards particle emission, only a mass-based threshold value need to be observed; otherwise, fine and ultrafine particle stack emission has not yet been fully characterized. Furthermore, a key aspect to be investigated is the influence of the flue gas treatment section on the sub-micrometer particle emission. To this purpose in the present study a comparison of measurement data in terms of particle number concentrations and distributions obtained from six incineration plants supplied by different treatment sections is reported. The apparatus used in the experimental analysis is made up of: i) differential mobility particle sizers to measure particle number distributions, ii) particle counters to evaluate total number concentrations, and iii) thermo-dilution systems to ensure proper sample conditioning. Flue gas treatment sections provided by either dry or semi-dry or wet process were considered. Both Selective Catalytic (SCR) and non-Catalytic Reduction (SNCR) systems for NOx abatement were found, whereas, as regards particle, plants with and without fabric filter were encountered amongst the plants under examination. The preliminary analysis of the measurements lead to the following remarks: - particle concentration at the stack are generally lower than 1×103 part cm-3 in flue gas treatment sections provided by fabric filter; - the mode of the particle size distributions are in the range 60-90 nm; - plants where the particle abatement is obtained through an electrostatic precipitator solely show number concentrations up two order of magnitude higher than plants provided by a fabric filter; - total particle concentrations before the fabric filter were about 2×107 part. cm-3, thus, the resulting removal efficiency of the fabric filter in terms of number concentrations can be evaluated higher than 99%.