10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
High-Temperature Sampling and Characterization of Corrosion-Relevant Particles in Waste Incineration Plants
STEFAN SCHUMACHER, Jörg Lindermann, Burkhard Stahlmecke, Dirk Jarzyna, Amit Khot, Till van der Zwaag, Hermann Nordsieck, Jens Harpeng, Ragnar Warnecke, Christof Asbach, Institut für Energie- und Umwelttechnik e.V. (IUTA)
Abstract Number: 664 Working Group: Combustion
Abstract Although the particulate phase in boilers of waste incineration plants has already for a long time been under suspicion to essentially drive the corrosion of the superheater tubes, it has not been comprehensively characterized to the present. This is mainly attributed to the extreme conditions present in the boilers such as high temperatures, the presence of condensable salt vapors, and high dust loads. These cause tremendous artifacts when using conventional aerosol sampling and measurement techniques that extract the aerosol from the boiler (Deuerling 2010).
Therefore, we developed a novel two stage sampling probe, which allows the collection of particles in the interesting size range from a few 10 nm up to several 100 µm and minimizes condensation artifacts (Schumacher 2016). Larger particles are sampled on an impaction plate, whereas the remaining smaller particles are collected on a nickel membrane filter with well-defined pores. Together, the broad particle size range is covered. The (aerodynamic) cut-off diameter of the impactor is between 16 and 37 µm and depends on the temperature and thus the location within the boiler, where the probe is used. The substrates are well-suited for scanning electron microscopy (SEM), which provides a comprehensive investigation of the size distribution, morphology, and chemical properties of individual particles. Using computational fluid dynamics (CFD), the collection efficiencies of the impactor as well as of the membrane filter have been studied in detail, which allows to deduce the airborne particle number and mass size distributions from counting the collected particles in SEM images. Furthermore, the probe can easily be adapted for total dust sampling and analysis (Schumacher 2017).
The probe has been successfully employed for measurements in the combustion chamber (1250°C) and the four passes (950°C down to 250°C) of two waste incineration plants with strongly different corrosion rates to characterize the evolution of the aerosol on its voyage through the boilers. On the course, the concentration of submicron particles grows by condensation of salt vapors during cooling, whereas the concentration of larger particles decreases due to deposition losses. This behavior was also modeled by CFD simulations of the particle dynamics in the boiler. We show that especially the coarse particles which have been difficult to measure up to now contain a substantial share of chlorine. Since they are efficiently deposited on the superheater tubes, deviations in this size regime might explain the different corrosion rates of the plants.
This work has been supported by the Federal Ministry of Education and Research (BMBF) within the project VOKos (Grant No 03X3589).
References 1. C.F. Deuerling et al. Aerosol Sci. Technol. 44 (2010) 1-9. 2. S. Schumacher et al. Corros. Sci. 110 (2016) 82-90. 3. S. Schumacher et al. Aerosol Sci. Technol. 51 (2017) 1047-1056.