Design of Electrified Calciner for Direct Capture of CO2 from Cement Raw Meal

Abstract

The main focus in this thesis is on designing an electrified calciner for direct CO2 capture from cement raw meal, investigating various operating conditions using CPFD simulations. The calciner, a binary fluidized bed reactor with several immersed electrically heated cylinders, includes the raw meal (fine powder <200µm) and coarse lime particles (400µm-800µm). The electrically heated cylinders immersed in the bed provide energy both for heating up the raw meal to calcination temperature and for the endothermic calcination reaction. The design has been made using mass and energy balance as well as fluidized bed calculations. The reactor performance is deeply investigated in different operating conditions using CPFD simulations. Key findings show that efficient spreading the raw meal over the heat source (hot cylinders) and preheating the meal can improve the calcination degree in the reactor. Also, the hotter the cylinders (up to 1150℃) the higher the calcination degree. The designed reactor showed a performance of 90% calcination degree for a preheated meal to 720℃ and a hot cylinder temperature of 1150℃. Also, for a 20℃ cold meal, having 1150℃ wall temperature of hot cylinders can lead to almost 70% calcination in the reactor. It should be noted that the more calcination the more gas production and higher particle entrainment. Another investigated factor was the fluidization velocity which has been calculated between 0.2 m/s-0.8 m/s. Simulation results showed that 0.3 m/s works best in terms of mixing and fluidization efficiency and 0.8m/s shall be avoided as it makes even coarse particles escape the bed very quickly. The results of this study also showed that the fluidization velocity has the most effect on the residence time of particles. Having 0.2 m/s fluidization velocity leads to almost 30 s average residence time of fine particles, for the case with 0.3 m/s it is decreased to 24 s while for the case with 0.8 m/s fluidization velocity, the average residence time is only 5 seconds!