Process for direct reduction of iron oxide

Patent metadata

Field	Value
Publication number	US-9273368-B2
Application number	US-201214235277-A
Country	US
Kind code	B2
Filing date	Jul 16, 2012
Priority date	Jul 26, 2011
Publication date	Mar 1, 2016
Grant date	Mar 1, 2016

Abstract

A process for direct reduction of iron oxide in a shaft furnace. The process includes feeding iron oxide to the furnace, passing the iron oxide successively downwardly through a pre-reduction zone, a transition zone, a metallization zone, and a cooling zone while passing rich fuel gas produced by external partial combustion with a sub-stoichiometric volume of air upwardly through the pre-reduction zone in counter-current flow so as to partially reduce the iron oxide, and passing reducing gas downwardly through the metallization zone in co-current flow so as to substantially complete the reduction of the iron oxide to metallic iron. The reducing gas is first pre-heated in a gas heater and then subjected to partial combustion with oxygen to further increase its temperature. The process includes removing a metallized iron product from the cooling zone.

First claim

The invention claimed is:

1. A process for effecting direct reduction of iron oxide in a shaft furnace having a pre-reduction zone near its uppermost portion, a metallization zone below the pre-reduction zone, an intermediate zone which separates the pre-reduction zone from the metallization zone and which includes a restriction to inhibit rich fuel gas from passing from the pre-reduction zone to the metallization zone, and a cooling zone below the metallization zone at the lowest portion of the shaft furnace, the process comprising feeding an iron oxide burden to the shaft furnace, passing the iron oxide burden successively downwardly through the pre-reduction zone, the intermediate zone, the metallization zone, and the cooling zone of the shaft furnace while passing rich fuel gas produced by external partial combustion with a sub-stoichiometric volume of air upwardly through the pre-reduction zone in counter-current flow so as to partially reduce the iron oxide burden, and passing reducing gas downwardly through the metallization zone in co-current flow so as to substantially complete the reduction of the iron oxide burden to metallic iron, the reducing gas having first been preheated in a gas heater and then subjected to partial combustion with oxygen to further increase its temperature, and removing metallic iron from the cooling zone.

2. The process of claim 1 , wherein the partial combustion of the reducing gas with oxygen increases the temperature of the reducing gas to 700-950° C.

3. The process of claim 1 , wherein the reducing gas is preheated in the gas heater to a temperature of 500-750° C.

4. The process of claim 1 , wherein the oxygen is added to partially combust the reducing gas at a rate of 0-70 Nm 3 /t of iron product.

5. The process of claim 1 , wherein the rich fuel gas is produced at a temperature above 1100-1350° C. before it is passed upwardly through the pre-reduction zone to preheat the iron oxide burden at the lower portion of the pre-reduction zone to about 1000-1300° C.

6. The process of claim 1 , wherein the reducing gas is cycled through the cooling zone to cool the metallic iron to a temperature of about 50-70° C.

7. The process of claim 1 , wherein the reducing gas is cycled through the cooling zone to cool the metallic iron to a temperature of about 700-750° C.

8. The process of claim 1 , wherein combustion air used to produce the rich fuel gas is preheated to a temperature of about 700-750° C. before it is used to produce the rich fuel gas with a temperature above 1100-1350° C. which is passed upwardly through the pre-reduction zone.

9. The process of claim 1 , wherein off-gas from the pre-reduction zone is treated to remove carbon dioxide and nitrogen, then mixed with evacuated rich fuel gas and natural gas and combustion air, and then used to heat the gas heater.

10. The process of claim 1 , wherein off-gas from the pre-reduction zone is treated to remove carbon dioxide and nitrogen, then mixed with recycled off gas from the metallization zone that has been cleaned of CO 2 , additional natural gas and water vapor to form a process reducing gas for the metallization zone and cooling gas for the cooling zone.

11. The process of claim 1 , wherein the reducing gas is introduced into the intermediate zone, with a smaller portion being directed to the pre-reduction zone and a larger portion being directed to the metallization zone.

12. The process of claim 1 , wherein the reducing gas comprises in volume about 20-25% methane, about 40-50% hydrogen, about 20-30% carbon monoxide, water vapor, carbon dioxide and nitrogen.

13. The process of claim 1 , wherein between about 45-55% of the reduction of the iron ore burden occurs in the pre-reduction zone.

14. The process of claim 1 , wherein the iron ore burden comprises iron oxide particles coated with a mineral solution, the mineral solution adapted to inhibit agglomeration of the iron oxide particles when the iron oxide particles are heated to over about 1000-1300° C. and metallized iron is heated to about 750-800° C.

15. The process of claim 1 , wherein the rich fuel gas is formed by burning natural gas in preheated atmospheric air or oxygen enriched air at about 30-50% of the stoichiometric amount required to complete combustion.

16. The process of claim 1 , wherein the formation of the rich fuel gas occurs in a burner or combustion chamber downstream from a combustion air pre heater and upstream from the pre-reduction zone.

17. The process of claim 1 , wherein CO 2 is removed from the reducing gas exiting the furnace before the reducing gas is recycled back to the metallization zone and cooling zone to increase H 2 /CO ratio in the recycled reducing gas.

18. The process of claim 1 , wherein water vapor is added to the reducing gas stream supplied to the metallization zone upstream from the reducing gas pre-heater to provide a sufficient amount of H 2 O for methane in-situ reforming.

19. The process of claim 1 , wherein the flow of reducing gas and cooling gas exits the furnace through openings connected to channels in a refractory gas evacuating device comprising gas flow distributor comprising at least four hollow conduits extending in a generally radial direction at a boundary between the metallization zone and, the cooling zone, and supported by liquid cooled beams located in the cooling zone at a temperature of about 400-700° C.

20. The process of claim 1 , wherein the flow of reducing gas and cooling gas exits the furnace through openings in hollow conduits, and the conduits comprise liquid cooled beams extending, along multiple chords of the furnace at a boundary between cooling and metallization zones.

21. The process of claim 1 , wherein distribution of gas flow in the metallization zone is controlled by openings in the gas flow distributor.

22. The process of claim 1 , wherein the furnace comprises a plurality of cross-members extending across the furnace at different elevations within the furnace to break the iron ore burden descending through the furnace thereby increasing the permeability of the material column in a metallization zone.

23. The process of claim 1 , wherein a number of cross-members provided within the furnace is based on a metallization zone diameter.

Assignees

• Gordon Iakov M
• Hatch Ltd

Inventors

• Gordon Iakov M

Classifications

• C21B11/02

  in low shaft furnaces {or shaft furnaces} · CPC title

• C21B13/0073

  Selection or treatment of the reducing gases · CPC title

• Y02P10/128

  Cross-Sectional Technologies · mapped topic

• Y02P10/122

  by capturing or storing CO2 · CPC title

• C21B13/004

  in a continuous way by reduction from ores · CPC title