Online monitoring of particle distribution in pneumatic conveying systems via electrical capacitance tomography
Sprache des Titels:
Proceedings of the International Congress on Particle Technology 2019
Steady state conveying of solid particles is a crucial factor for many applications in industry. Although there has been research on this topic for decades there are still areas with little progress up to the present. Especially for dense conveying there were no possibilities to identify the state of a particle flow inside a conveying pipe with high temporal and spatial resolution in a continuous online application. Methods based on laser diffraction are limited to very dilute particle flows but, if applicable, can deliver highly accurate measurements on particle size distribution and mass flow rates. For dense phase conveying the standard instrumentation are pure flow detectors which give a simple yes/no information if there is a particle flow above a certain threshold or not. However, most of these devices do not have sufficient time resolution to identify unstable plug flow conditions. Mass flow information is usually obtained by capacitive measurements on an average basis across the pipe cross section. Hereby the mass fraction is estimated based on the dielectric permittivity distribution. By constantly recalibrating the measurement signals with balance data of the conveyed material, this family of devices can give good estimates on the mass flow rates. However, the quality of the results strongly depends on the state of the particle flow. Unsteady flow conditions will inevitably cause large errors in the mass flow results. A measurement system which overcomes this issue is Electrical Capacitance Tomography (ECT). As ECT uses more than two electrodes it allows to fully reconstruct the spatial material distribution ?? inside a pipe by measuring the permittivity distribution ??. However, the process of reconstruction is not trivial as the soft field nature of the electric field inside the pipe leads to an ill-posed mathematical problem. Thus, post processing of ECT data is time consuming and was not possible online with high sampling rates.