Abstract
Pressurized fluidized bed processes for the reduction of iron ore fines using CO-rich reducing gas formed by coal gasification are an upcoming ironmaking technology. They operate in a continuous multi-staged countercurrent mode at an absolute pressure of 4 bar.
For process optimization, a laboratory-scale pressurized fluidized bed reactor was built to perform experiments similar to industrial conditions. The reactor is operated as a differential reactor to ensure a constant gas concentration and temperature within the reactor volume.
Three-stage experiments with three different iron ores were carried out at an absolute pressure of 4 bar in batch-wise operation. The reducing gas consisted of a mixture of H2, H2O, CH4, CO2 and CO. The CO-concentration was varied in a range between 30% and 50%, the residence time in pre-reduction between 30 and 60 min and the operating temperature from 400°C to 850°C. In correspondence to the tests, microscopic techniques were applied to determine the importance of morphological properties of the ores on their reduction behavior.
A higher temperature in the pre-reduction stage causes an increase of porosity as well as an increase of the final reduction degree. Comparing different ore types, a significant correlation between the morphology of the employed ores and the final reduction degree was found.
