Measurement of electrical resistivity of Ca-based particles to determine their suitability for electrostatic separation in solar applications

Abstract

The calcination of minerals for the production of cement or lime is a widespread and energy-intensive process. The solarisation of such a process would result in a significant reduction in anthropogenic CO2 production, firstly by replacing the combustion of fossil fuels used to provide the heat for the endothermal reaction with the sustainable use of concentrated solar energy, and secondly by being able to capture the CO2 produced through the stoichiometry of the reaction itself. In order to achieve these two objectives, the solar reactor must be operated in close configuration to extract a pure stream of CO2. Due to the high temperature level required, direct irradiation could increase the system efficiency by reducing the operating temperature, as the maximum temperature is present in the directly absorbing particle bed. To achieve this, the concentrated radiation must pass through a transparent medium (a window), leading to the challenge of keeping the window clean from the processed particles. The integration of an Electrostatic Separation of Particles (ESP) system into a solar reactor could be an option to overcome the problem of particle deposition on its window. ESP is widely used in industrial processes at ambient and low temperatures (typically below 473 K). However, the use of this technology at high temperatures requires extensive and exact characterisation of the electrical properties of the powder, which is rarely available at high temperatures. To this purpose, an experimental setup capable of operating up to 1200 K has been developed and employed to derive the electrical resistivity of various powdered materials, including limestone, cement raw meal and kaolin. The results demonstrate the compatibility of ESP with all the materials analysed. An uncertainty analysis was conducted to identify the main impacting parameters to the electrical resistivity error and to assess the precision of the results.