NANOWET project : characterization of nanoparticle emission from high temperature incineration of nano-/halogen-/sulfur-containing wastes and performances of wet-scrubber units
Résumé
In order to address the health and environmental problems potentially raised by the incineration of nanowastes, the NanoWet project (supported by the French Agency for Environment and Energy Management -ADEME- CORTEA funding scheme - Grant No. 1581C0096) focuses on the treatment of nanowastes by high-Temperature (T) incineration required when halogen- and sulfur-containing wastes are disposed of. The objectives of the project are i) to assess the effect of both high postcombustion T of 1,100°C and presence of acid gases in raw fumes, on the potential emission and behaviour of nanoparticles originating from nanowaste incineration, and ii) to quantify downstream nanoparticle capture by the wet-scrubbers equipping the fume treatment lines before the exhaust. First, three wastes were selected and characterized: PDMS waste from polyorganosiloxane polymerization processes containing 24.4% dwt of SiO2 nano-fillers (waste previously studied in the framework of NanoFlueGas project [1]); soft PVC from flexible PolyVinyl Chloride production containing 36% dwt of Cl and nano-fillers mainly composed of TiO2; Resin waste from soiled strong acid cation exchange resins of sulfonic type exhibiting 15.4% dwt of S, but no nano-filler type identified. A lab-scale incinerator device composed of a tubular horizontal furnace was designed to operate in representative key conditions of a high-T incineration process dedicated to industrial wastes (T of 1,100°C in both combustion zones, residence time at least of two seconds in the post-combustion zone, air excess from primary and secondary air flows contributing to achieve adequate turbulence conditions). A fume sampling device allows to characterize O2, CO2, CO, SO2, HCl contents as well as particulate matter concentrations in various granulometric ranges. When present, the solid residue after incineration is analyzed to estimate the presence of nano-fillers. Incineration tests were carried out in single-waste or mixed loads. The interactions between the PDMS nanowaste and the halogen- /sulfur- wastes will be discussed in terms of behavior/fate of particles in the fumes. In order to study the performances of wet-scrubbers regarding nanoparticle capture, a lab-scale spraying scrubber will be developed based on real data inferred through a measurement campaign which was carried out on a full-scale industrial unit (TREDI - Groupe Séché Environnement), out of specific incineration of nanowastes but in prevalence condition of halogen-/sulfur-containing wastes. In particular, the particle concentration and size distribution were measured in the core-process, at the inlet of the wet-scrubber columns (after dedusting by electrofiltration). The lab-scale spraying scrubber will thus operate in realistic conditions of temperature, humidity, particle load, liquid/gas ratio, height/diameter ratio of the column, residence time, turbulent flow regime, droplet diameter and relative velocity between particles and droplets.