Study on Direct Reduction of Hematite Pellets Using a New TG Setup

Abstract

A new thermogravimetric setup was developed to study direct reduction of iron oxide under well‐controlled experimental conditions. Pure and industrial hematite samples were isothermally reduced by hydrogen and carbon monoxide gaseous mixtures. Influences of gas composition, gas flow rate, and temperature on reduction were investigated. Reduction rates obtained using the new setup were higher compared to conventional thermogravimetric method. This difference was due to the time required to replace the inert gas with the reactant gas in the conventional method, which led to lower reduction rate at the initial stage. Carbon deposited on the surface of the pellets at relatively high gas flow rates and at low temperatures. The presence of pure iron and high carbon potential in the gas phase were the cause for carbon deposition. Study of partially reduced samples illustrated that the outer layer of pellet with high iron content thickened as reduction proceeded inside the pellet. Closure of micro‐pores and formation of dense iron phase in this layer decelerated diffusion of reactant and product gases, and led to decrease of reduction rate at later stages of reaction. At lower temperatures, this effect was coupled with carbon deposition. Therefore, the reduction was seriously hindered.

Effect of Experimental Conditions on Cementite Formation During Reduction of Iron Ore Pellets

“…Similar results were obtained and discussed in the previous work. [11] Carbon deposition during reduction has been reported in other works which used gas mixtures containing H 2 and CO. [1,2,6,7,9] Formation of graphite takes place on the surface of pellets in atmospheres with high carbon potential. Reduced iron acts as a catalyst for carbon deposition; therefore, the amount of deposited carbon is enhanced as reduction proceeds.…”

“…Calculation of the thermodynamic activity of carbon in a gas mixture of H 2 -CO-H 2 O-CO 2 was performed previously by the authors. [11] The results showed that increasing the temperature at a fixed gas composition, and gradual increase of CO 2 (from 0.01 to 10 pct) at a constant temperature decrease the carbon activity in the gas mixture.…”

“…Details of the apparatus and experimental procedure can be found in the previous publication. [11] The experimental procedure is briefly described here. In a typical run, a small basket made of Nikrothal 80 wire was used to hold the sample.…”

“…Reduced iron acts as a catalyst for carbon deposition; therefore, the amount of deposited carbon is enhanced as reduction proceeds. [11] The thickness of the carbon layer increases with time and slows down the diffusion of reducing gases to the pellets. Consequently, at 973 K (700°C), carbon activity inside the solid is lower compared to 1123 K (850°C), and less cementite is formed.…”

Development of Integrated Gas Instrumentation System in Direct Reduction Plant

“…DRI derives its name from the chemical change that iron ore undergoes when it is heated in a furnace at high temperatures. The reducing gas is a mixture, the majority of which is hydrogen (H 2 ) and carbon monoxide (CO) which act as reducing agents [2][3].…”