Water nucleation on submicronic particles for flue gas cleaning process: preliminary results on experimental and theoretical evaluation in relation to particles chemical-physical properties.

Scrubbers are common and efficient systems for micrometer-sized particles removal from in-dustrial waste gas stream by means of the interaction with liquid jets or flows. Wet scrubbers use liquids (mainly water) to remove pollutants from gas streams incorporating them in liquid droplets through multiple interaction mechanisms (atomization of the liquid or gas stream bubbling through the liquid) whose selection is driven by the nature of the pollutant that has be removed. For particles diameter ranging between 0.1 and 1 ?m, the probability to impact on liquid droplets is extremely low resulting in a very low-efficient removal. In the case of submicronic particles the activation of heterogeneous water nucleation mechanism on a parti-cles surface (water nucleation on foreign particles) is of great interest for flue gases cleaning process. In order to optimize the process is important to understand the dependence of the nucleation efficiency on size, charge, morphology and surface characteristics of the particles and the temperature and the saturation of the environment. In the field of flue gas cleaning by heterogeneous nucleation process there is a continuous need to access to methods for production of aerosol of narrowly distributed nanoparticles, es-pecially methods assuring control, reproducibility and versatility with respect to the chemical-physical nature of the particulate, with the possibility to tune the particle size distribution and concentration in a wide range. The equipment that best meets these requirements is a spark discharge generator (Palas GmbH Aerosol Generator GFG 1000), which provides particles aerosol through the vaporization of two electrodes between which is applied a suitable poten-tial difference. The Palas system offers control, versatility and reproducibility of nanoparticle aerosols coupled with the absence of undesirable combustion by-products (tar-like species or PAH). It provides aerosol nanoparticles in a wide nanometer range (1-100 nm) and beyond [1]. Depending the typology of electrodes, carrier gases and operative condition (spark fre-quency, system dilution level) the nanoparticles can be completely contamination free or com-posed of one or more elements with different compositions. The Palas system is particularly suitable for producing particles with structure similar to carbonaceous particles typically formed in combustion systems (flames, engines). It also offers the possibility, by changing the typologies of electrodes, to obtain particles of different nature such as metal and metal oxides, of peculiar interest for the research typology for which the instrument will be applied for. This issue is of particularly interest since the factor influencing the submicronic particle wetting show a clear dependence on the surface chemical composition and microstructure: phenomena as capillary condensation, occurring in all confined geometries, divided media, cracks, or contact between surfaces [2] become relevant at nanoscale. The goal of this work is the analysis of the effect of particle nature on heterogeneous nuclea-tion activation process. To this aim, a multi-step experimental approach was applied. At first particles of different chemical nature were produced by using electrodes differing for density, melting temperatures, electrical and thermal conductivity which affect the production effi-ciency of aerosols. The particles were characterized as powders by means of different analyti-cal techniques to get structural and chemical insights. Condensation experiments were then performed in a lab-scale apparatus [4]. Finally, the condensation results then have been corre-lated to the chemical features of the nanoparticles.