Conceptual design of a procedure for density monitoring of pulverized fuels in pneumatic conveying systems with microwaves (8–12 GHz)

In this contribution, a novel density measuring concept for gas/coal particle compositions in pneumatic conveying systems is discussed. The proposed monitoring system uses horn antennas to perform complex transmittance measurements through the cross section of the conveying tube. The phase of the complex transmittance contains information about the effective permittivity, which is connected to the volume fraction of the coal. Electromagnetic field simulations have been performed for the evaluation of the concept and the performance of the designed setup. A test stand for measurements on coal dust under reproducible conditions and with well-defined particle concentrations has been developed and implemented. Coal particles with a diameter between 20 μm and 100 μm have been dispersed inside the test tube with a diameter of 200 mm and a length of 400 mm by injecting nitrogen. In the implemented setup the transmission measurements are performed with a calibrated vector network analyzer. Results of the evaluation of the concept by measurements with different concentrations of coal particles are presented and discussed in detail.