Non-invasive temperature monitoring in fixed-bed reactors by electrical capacitance tomography

Knowledge of the temperature distribution in fixed-bed reactors is of great importance for process control and optimization in many processes of the chemical industry. The state of the art is defined by invasive measuring methods for temperature measurement in such reactors. However, all invasive methods influence both the structure of the fixed-bed and the flow conditions and thus falsify the measurement results compared to real undisturbed conditions in a fixed-bed, above all with regard to the radial temperature profile. In addition, the temperature distribution in the entire reactor is usually derived from a few discrete measuring points based on a model, which sometimes results in large deviations from reality. In this article, electrical capacitance tomography (ECT) is explored as an alternative, non-invasive measurement method to monitor the temperature distribution inside fixed-bed reactors. The method exploits the temperature dependence of the effective bulk permittivity of the reactor filling. By way of an example, this dependence has been investigated in this work for two different hydrogenation catalysts. A temperature-resistant ECT sensor has been designed to perform measurements under the influence of temperature. The investigations show that, with the aid of ECT, it is possible to detect relative temperature changes in the region of interest with the materials examined.