Sizing and counting of particulate emissions

J. Aerosol Sci. Vol. 29. Suppl. I, pp.S433-S434. 1998 0 1998 Published bv Elsevier Science Ltd. All riehts reserved Printed in &at Britain 0021-8502/98 $19.00 + 0.00

SIZING AND COUNTING OF PARTICULATE EMISSIONS

R. FRIEHMELT,

H. BUTTNER,

and F. EBERT,

University of Kaiserslautem, Particle Technology and Fluid Mechanics, Postfach 3049, D-67653 Kaiserslautern, Germany, Phone: ++49 63 1 205 2121, Fax: ++49 63 1 205 3055

Measurement

Techniques,

Particulate Emissions, Optical Particle Counter, Nonspherical Particles

Calibration,

Optical particle counters, that determine particle sizes and concentrations by analyzing scattered light, have become a common tool in aerosol measurement technology. Devices of the type Umhauer (1983) described are able to measure particle sizes and concentrations fast, non-intrusively and on-line. The measureable range of concentrations amounts to some 10 up to lo6 particles/cm”, which means for spheres of unit density and a diameter of 1 pm mass concentrations of approximately 0.005 mg/m3 up to 500 mg/m3. Compared to a common measuring device like the cascade impactor, measurements with an optical particle counter are much faster and a higher resolution both in time and in particle sizes can be achieved. An important reason not to use white light optical particle counters in modem emission control systems is their relatively high detection limit of approximately 0.5 urn. However, in many emissions most of the emitted particles are smaller than this limit. Under environmental aspects especially these small particles are dangerous to human health. The goal of our investigations was to develop a measuring system suitable for measurements over a wide range of both particle sizes and concentrations. In order to meet these requirements the white light optical particle counter was combined with a differential mobility particle sizer the detection limit of which amounts to 15 nm. Thus, a size range from 15 nm up to 15 pm is covered by the combination of the different devices. The main problem with this combined system is a uniform calibration. As the scattered light intensity depends on both the bulk material and particle shape the optical particle counter had to be calibrated carefully. For spherical particles experimental results, e.g. for polystyrene latices and glycerine droplets, were confirmed by Mie-calculations (Sachweh, 1991). For nonspherical particles such as quartz dust aerodynamic calibration methods were applied (Biittner, 1983; Heidenreich et.al., 1995). Non-sphericity of particles severely affects the shape of the calibration curve. Figure 1 shows two empirical calibration curves for nonspherical quartz dust in comparison to a theoretical calibration curve under the assumption of spherical quartz particles. The scattered light intensity is increased by the irregular particle shape. In order to specify effects of particle shape, electrostatically classified fractions of nonspherical particles were analyzed, which also lead to the relation between the mobility diameter and the equivalent volume diameter. s433

Abstracts of the 5 t h I n t e r n a t i o n a l

$434

Aerosol

Conference

1998

In order to verify the counting and sizing system simultaneous measurements were carded out with the combination of optical particle counter on the one hand and a common cascade impactor on the other hand. Results for both measurements in the laboratory and in industry will be presented.

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This project is funded by the Deutsche Forschungsgemeinschaft (DFG). References

Btittner, H. (1983) Messung von Partikelgr613enverteilungen im gasgetragenen Zustand mit einem optischen Partikelz~aler, Chem. Ing. Tech. 55,733. Heidenreich, S., Btittner, H., Ebert, F., (1995) Investigations on the behaviour of an aerodynamic particle sizer and its applicability to calibrate an optical particle counter, Part. Part. Syst. Charact. 12, 304-308. Sachweh, B., (1991) Erweiterung des Me6bereichs eines Optischen Partikelziihlers durch moderne, digitale Signalverarbeitungstechniken, Dissertation, Fachbereich Maschinenwesen, Universit~t Kaiserslautern. Umhauer, H., (1983) Particle size distribution analysis by scattered light measurements using an optically defined measuring volume, J. Aerosol Sci. 14, 765-770.