Environmental Engineering Reference
In-Depth Information
Figure 3.5. Bestwod BAS-600 system for on-line analysis.
3.4.2.3
Microwave spectroscopy (RF)
Microwave spectroscopy is often referred to as radio frequency spectroscopy (RF) which analyses
the absorption of microwaves. Depending on the moisture content, the microwave pulse will be
subject to different attenuation and time delay. This relationship is represented in a calibration
model that is used for moisture estimation. There is no immediate correlation between the ele-
mentary composition and spectra. Among the error sources in RF measurement of biomass are
fluctuations in density and the concentration of Na and K ions. This technique is described in
detail by Nyström (2006) and Paz (2010).
One advantage of RF spectroscopy is that it might analyze the bulk properties of a material
in larger, closed compartments. The sampling error is reduced because the radio waves travel
through the entire part of the material to be analyzed. This is important for analysis of very
heterogeneous materials, for example. Examples of RF-based equipment are the desktop and
on-line analyzers from the Finnish supplier Senfit and the Bestwood BAS-800 system that is used
for on-line moisture determination of household waste and boiler control.
3.4.2.4
X-ray spectroscopy
X-ray spectroscopy analyses photons emitted when inner shell electrons are excited and replaced
with outer shell atoms. The wavelengths of the photons are characteristic for the respective
elements in the sample. Data about the elemental composition of the sample is used in order to
calculate the moisture content. X-ray spectroscopy can analyze a large part of the bulk in a sample
or material flow.
Figure 3.7 shows a desktop scanner from the Swedish supplier Mantex. It uses photon absorp-
tiometry to register the effective atomic numbers and density of the material analyzed. By
using two different energy levels, this technique may be used to identify different materials.
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