Book Description

A laboratory rig has been used to study the gaseous reduction of commercial hematite pellets. Mixtures of CO2, CO, H-2 and H2O were used as reductants. A system was built to produce mixtures at shift equilibrium from initial gas streams of CO2, CO, and H2. In the reduction procedure weight loss was recorded and pellets were subjected to gas mixtures with varying compositions close to those encountered by pellets descending an industrial counter-current shaft. Experiments were made under isothermal and non- isothermal conditions to model industrial plants where gas input temperatures may vary between 1000 and 1200 K. Kinetic results were analyzed and activation parameters derived for the FeO-Fe reduction using the single interface model developed by McKewan. It was shown that this model was not accurate when used to reproduce reduction curves in the later stages of reduction. The rig was also used to examine a complete industrial model of a shaft furnace incorporating full heat and mass balances. Comparison between laboratory measurements and the industrial model showed reasonable agreement in overall reduction times but deviations between experiment and model occurred at intermediate compositions. A simplified model of the shaft was designed using a computer spreadsheet. This was used to predict reduction rates under various conditions and tested against laboratory measurements. It was shown that the reduction rates could be predicted with reasonable accuracy using this empirical spreadsheet model. Equipment was built to study hematite reductions under load so that stickiness and dimensional changes could be examined. Stickiness was influenced by reduction conditions although sticking always occurred above a certain temperature. A review of the relevant literature is included.