Investigation of a high temperature electrostatic precipitator system to avoid particle deposition on a solar reactor window = Untersuchung eines elektrostatischen Hochtemperatur-Abscheidesystems zur Vermeidung von Partikelablagerungen auf einem Solarreaktor-Fenster

Kurzfassung

To curb the current climate crisis, new technologies are needed to enable industrial processes to be carried out using renewable energy systems. There are already systems with a high technology readiness level such as photovoltaic, hydro- and wind turbines, concentrated solar power, among others, which have been developed mainly to produce green electricity. However, to make the energy transition process a reality, the development and improvement of other systems to produce heat or chemical carriers is essential. The high temperatures achieved in concentrated solar systems can be applied to drive high-temperature thermochemical processes. Solar calcination of limestone is a good example of a thermochemical process with various end uses. The solid product of this reaction is calcium oxide, which can be used to store energy, capture carbon dioxide from other industrial processes (a process known as calcium looping cycle), or produce cement, which is one of the most important materials in the construction industry. For the solar calcination process, direct irradiated solar reactors are preferred, as in these reactor designs the concentrated solar radiation heats the solid material directly, which not only allows higher temperatures for the process, but also avoids the additional heat transfer mechanisms that take place in the case of indirectly irradiated solar reactors. However, in order to i) control the atmosphere conditions inside the solar reactor, ii) reduce thermal losses, and iii) allow solar radiation to pass into the reaction chamber, directly heated reactors require a light-transmissive window. This component is clearly the bottleneck of these reactor designs due to the deposition of material on its surface, which causes overheating and failure of the window. The most studied systems to overcome the window problem have been developed based on aerodynamic protection methods such as air curtains or vortex flows. However, the high amount of gas required by these systems considerably reduces the efficiency of the reactor, and in several cases the window could not be completely protected from particle deposition. This study investigates a hitherto unexplored method to avoid the window problem in a solar reactor. The novel system developed uses electrostatic precipitation of particles (ESP) to prevent the migration of solid particles to the window. The application of ESP in a solar reactor is analysed in detail and an experimental setup is developed to demonstrate and evaluate the performance of the system at high temperature conditions (933 K). The developed ESP window protection system is able to protect the window from particle contamination when using particles of limestone and cement raw meal. The system showed its best performance using positive corona discharge, which in comparison with negative discharge is characterised by lower current densities, allowing a wider operation range with more stable corona discharge, and lower energy consumption. The results of this study show the high potential of the ESP protection system to mitigate the window problem in solar reactors, and paves the way for further application of ESP technology in solar processes taking place under high temperature conditions.