Measurement of Particle Properties: Concentration, Size Distribution, and Density

Various methods are available to investigate the particular emissions of combustion processes, and a brief survey of these is presented in this chapter. Within the flue gas of combustion, particle numbers may be measured continuously using either nucleus counters or light-scattering instruments. The particle mass concentration is typically measured discontinuously by using filtering systems. Particle size distributions may be determined by applying fractionation to the aforementioned concentrations. On this basis, size-classified particle number distributions or mass distributions may be measured. Typical fractionation methods can distinguish between aerodynamic separation on the basis of inertia (impactor, cyclone) and the electrical mobility of the particles. By comparing size distributions based on aerodynamic diameter with mobility diameter, the effective density of a particle collective can be calculated. A dilution system is normally required for the continuous measurement of particle concentrations in combustion flue gases, to reduce the dew point (avoiding condensation), and to adapting the concentrations to the instrument range. Ejector diluters, porous tubes and dilution tunnels are typically used to investigate stationary combustion processes. When analyzing the particle collective, it is essential to draw a representative sample; thus, in order to avoid sampling errors, certain criteria such as isokinetic sampling or transport losses must be respected.