METHOD FOR THE DIRECT REDUCTION OF IRON ORE

Abstract

The invention relates to a process for direct reduction of iron ore to afford direct reduced iron, wherein the iron ore sequentially passes through a reduction zone for reducing the iron ore to direct reduced iron and a cooling zone for cooling the direct reduced iron, wherein in the reduction zone the iron ore is subjected to a flow of a reduction gas and wherein in the cooling zone the direct reduced iron is subjected to a flow of a cooling gas. The cooling gas in the cooling zone comprises H2 and CO2, wherein the ratio of the mole fractions of H2 to CO2 is greater than 1.8 and the mole fraction of CO2 is greater than 20 mol %.

Claims

1. A process for direct reduction of iron ore to afford direct reduced iron, wherein the iron ore sequentially passes through a reduction zone for reducing the iron ore to direct reduced iron and a cooling zone for cooling the direct reduced iron, wherein in the reduction zone the iron ore is subjected to a flow of a reduction gas and wherein in the cooling zone the direct reduced iron is subjected to a flow of a cooling gas, wherein the cooling gas in the cooling zone comprises H2 and CO2, wherein the ratio of the mole fractions of H2 to CO2 is greater than 1.8 and the mole fraction of CO2 is greater than 20 mol %.

2. The process as claimed in claim 1, wherein the cooling gas in the cooling zone comprises less than 5 mol % of hydrocarbons, in particular less than 2 mol % of hydrocarbons.

3. The process as claimed in claim 2 wherein upon entering the cooling zone the direct reduced iron has a temperature in the range from 400° C. to 1100° C.

4. The process as claimed in claim 3 wherein in the cooling zone the cooling gas in the presence of the direct reduced iron as catalyst undergoes a Bosch reaction with the result that carbon is deposited on the direct reduced iron.

5. The process as claimed in claim 4, wherein the deposited carbon reacts with the iron of the direct reduced iron to form Fe3C.

6. The process as claimed in claim 5 wherein the carbon content of the cooled direct reduced iron is in the range from 0.5% by weight to 4.5% by weight.

7. The process as claimed in claim 6 wherein the reduction zone is arranged above the cooling zone in a shaft furnace and the iron ore passes through the shaft furnace in a vertical direction.

8. The process as claimed in claim 7, wherein the cooling gas flows through the cooling zone counter to a direction of motion of the iron ore.

9. The process as claimed in claim 6 wherein the reduction zone comprises one or more fluidized bed reactors and/or the cooling zone comprises one or more fluidized bed reactors.

10. The process as claimed in claim 9 wherein the reduction gas in the reduction zone contains more than 75 mol % of H2.

11. The process as claimed in claim 14 wherein the reduction gas in the reduction zone comprises less than 5 mol % of hydrocarbons.

12. A cooling gas for use in a process as claimed in claim 10 wherein the cooling gas comprises H2 and CO2, wherein the ratio of the mole fractions of H2 to CO2 is greater than 1.8 and the mole fraction of CO2 is greater than 20 mol %.

13. The cooling gas as claimed in claim 12 wherein the cooling gas comprises less than 5 mol % of hydrocarbons.

14. The process as claimed in claim 9 wherein the reduction gas in the reduction zone contains more than 85 mol % of H2.

15. The process as claimed in claim 14 wherein the reduction gas in the reduction zone comprises less than 2 mol % of hydrocarbons.

16. The cooling gas as claimed in claim 12 wherein the cooling gas comprises less than 2 mol % of hydrocarbons.

Description

[0019] The invention is more particularly elucidated with reference to the following exemplary embodiments in conjunction with the figures. In the figures:

[0020] FIG. 1 shows a schematic representation of a shaft furnace;

[0021] FIG. 2 shows a schematic representation of a cascade of fluidized bed reactors.

[0022] FIG. 1 shows the schematic representation of a shaft furnace 11. Arranged in the shaft furnace 11 are a reduction zone 13 and a cooling zone 15. The reduction zone 13 is arranged above the cooling zone 15. The shaft furnace 11 is filled with iron ore from above. The direct reduced iron produced can be removed at the lower end of the shaft furnace 11. Reduction gas is simultaneously introduced into the shaft furnace 11 via the inlet 17. The reduction gas then flows through the iron ore in the reduction zone 13. In this variant the reduction gas is preheated to a temperature of up to 1100° C. but at least 800° C. The reduction gas may alternatively also be partially combusted in the shaft furnace 11 to produce the required temperatures for the reaction. In such a case oxygen is often added to the reaction gas to promote combustion. Unconsumed reduction gas, together with any gaseous reaction products, exits the furnace again at outlet 19. The reduction gas thus flows through the reduction zone 13 counter to a direction of motion of the iron ore. The reduction gas in the reduction zone 15 contains a high hydrogen content such that the reduction of the iron ore to afford direct reduced iron is based substantially on the reaction

Fe2O3+3H2.fwdarw.2Fe+3H2O.

[0023] Due to the high hydrogen content and the low carbon content in the reduction gas the direct reduced iron exits the reduction zone 13 with a very low carbon content of less than 0.25% by weight. After exiting the reduction zone 13 the direct reduced iron enters the cooling zone 15. The direct reduced iron has a temperature in the range from 850° C. to 1000° C. In the cooling zone 15 the direct reduced iron in the cooling gas is subjected to a flow counter to the direction of motion of the direct reduced iron. To this end, the cooling gas enters the shaft furnace 11 through the inlet 21. Unconsumed cooling gas, together with any gaseous reaction products, exits the furnace again at outlet 23. It will be appreciated that a certain proportion of the cooling gas can also enter the reduction zone 13. A certain proportion of the reduction gas can likewise enter the cooling zone 15. Mixtures of cooling gas and reduction gas can therefore occur at the transition between the reduction zone 13 and the cooling zone 15. The cooling gas in the cooling zone 15 comprises H2 and CO2. The mole fraction of CO2 is 30 mol % and the mole fraction of H2 is 60 mol %. The hydrocarbon content of the cooling gas is less than 1 mol %. The cooling gas has a temperature of up to 400° C. upon entering the cooling zone. However, depending on the desired cooling effect, it is also possible to establish a lower temperature down to room temperature (20° C.). In the cooling zone the cooling gas undergoes the Bosch reaction in the presence of the hot direct reduced iron as catalyst. Hydrogen and CO2 in the cooling gas thus react according to the reaction

CO2+2H2.fwdarw.C+2H2O

[0024] to afford water vapor and carbon, wherein the carbon is deposited on the direct reduced iron serving as catalyst. The deposited carbon then diffuses into the interior of the direct reduced iron and forms Fe3C. This effect increases the carbon content of the direct reduced iron to 1.5% by weight to 3.5% by weight. The direct reduced iron carburized and cooled in this way may be removed in the lower region of the shaft furnace 11 and subjected to further processing in the known manner for steel production.

[0025] FIG. 2 shows a schematic representation of a cascade 25 of fluidized bed reactors 27a, 27b, 27c and 27d. The fluidized bed reactors 27a, 27b and 27c form the reduction zone 13 and the fluidized bed reactor 27d forms the cooling zone 15. The iron ore passes through the fluidized bed reactors 27a, 27b and 27c successively and is gradually converted into direct reduced iron. The arrows 29 indicate the material direction of the solids. The conversion of iron ore to direct reduced iron is effected in similar fashion when the iron ore in the respective fluidized bed reactor is subjected to a flow of the reduction gas from below. Reduction gas is introduced through inlet 17 and flows successively through the cascade of fluidized bed reactors in the sequence 27c, 27b, 27a. In this variant the reduction gas is preheated to a temperature of 1100° C. Unconsumed reduction gas, together with any gaseous reaction products, exits the furnace again at outlet 19. The reduction gas in the reduction zone 15 contains a high hydrogen content such that the reduction of the iron ore to afford direct reduced iron is based substantially on the reaction

Fe2O3+3.fwdarw.H2.fwdarw.2Fe+3H2O.

[0026] Due to the high hydrogen content and the low carbon content in the reduction gas the direct reduced iron exits the fluidized bed reactor 27c and thus the reduction zone 13 with a very low carbon content of less than 0.25% by weight. After exiting the reduction zone 13 the direct reduced iron enters the cooling zone 15 in the form of fluidized bed reactor 27d. The direct reduced iron has a temperature in the range from 850° C. to 1100° C. In the fluidized bed reactor 27d the direct reduced iron is subjected to a flow of the cooling gas which enters the fluidized bed reactor 27d via the inlet 21. Unconsumed cooling gas, together with any gaseous reaction products, exits the furnace again at outlet 23. The cooling gas in the cooling zone 15 comprises H2 and CO2. The mole fraction of CO2 is 30 mol % and the mole fraction of H2 is 60 mol %. The hydrocarbon content of the cooling gas is less than 1 mol %. The cooling gas has a temperature of up to 400° C. upon entering the cooling zone. In the cooling zone the cooling gas undergoes the Bosch reaction in the presence of the hot direct reduced iron as catalyst. Hydrogen and CO2 in the cooling gas thus react according to the reaction

CO2+2H2.fwdarw.C+2H2O

[0027] to afford water vapor and carbon, wherein the carbon is deposited on the direct reduced iron serving as catalyst. The deposited carbon then diffuses into the interior of the direct reduced iron and forms Fe3C. This effect increases the carbon content of the direct reduced iron to 1.5% by weight to 3.5% by weight. The direct reduced iron carburized and cooled in this way may be removed from the fluidized bed reactor 27d and subjected to further processing in the known manner for steel production.

[0028] A cascade of three fluidized bed reactors 27a, 27b, 27c for the reduction and one fluidized bed reactor 27d for the cooling and carburizing was elucidated here by way of example. It will be appreciated that depending on the application a different number of fluidized bed reactors may be connected to form a cascade for reduction or cooling and carburizing.