Nanowaste incineration: performances of a bag filter in a pilot scale device under real operating conditions
Résumé
Up to now, there is no peculiar approved procedure for the waste management of nanoobjects at their end of life, mainly because the current regulation does not consider the typical nanospecificity of such emerging products. The French project “NANOFlueGas” (2011-2014) aims to provide data and to assess nanosafety aspects during the final destruction of nanomanufactured products by incineration. The two main objectives of this project are firstly, to better understand possible mechanisms of nanoparticle release during the incineration of nanowastes, and secondly, to evaluate the efficiency of the current pollution control processes and procedures implemented on waste incineration facilities. This study deals with the evaluation of the performances of a bag filter regarding its clogging with a representative nanosized aerosol emitted from nanowaste incineration in boiler output. A laboratory-scale filtration unit was developed, where a single bag filter was implemented (reduced height to 0.44 m). The aerosol used for clogging tests was a condensation aerosol generated from graphite monoliths (generator DNP 2000, Palas). Its particle size distribution and shape were accurately chosen in order to be representative of the aerosol emission profile previously determined from incineration tests performed on a nanowaste mainly composed of black carbon within a laboratory-scale furnace [1] In order to meet with the real operating conditions in the flue gas treatment line, the airflow and the bag filter were heated to 150°C, the filtration unit was insulated, and 10-12% moisture was maintained in the airflow by water injection. Filtration velocity throughout the bag filter was set to 2 cm/s. Moreover, the influence of upstream sorbent injection (typically sodium bicarbonate with activated carbon) was also tested in our small-scale device. The evolution of performances were evaluated throughout the clogging in terms of both pressure drop generated by the hot gaseous flowrate through the filter, and particle collection efficiency evaluated from particle concentration measurements upstream and downstream to the filter using an ELPI impactor (Dekati) after hot sampling and dilution.