METHOD AND SYSTEM FOR THE PRODUCTION OF POROUS IRON

Abstract

Described are a method and a system for producing porous iron by means of a direct reduction process. In said method and system, a reducing gas is introduced into a DRI reduction device, and the direct reduction process is carried out therein. Coke oven gas and/or natural gas is/are reformed by adding gas, which contains steam and carbon dioxide and which is top gas from a DRI reduction device, and oxygen in a COG reformer so as to obtain reducing gas.

Claims

1. Method for the production of porous iron via a direct reduction process in which the reducing gas is introduced into the DRI reduction device and in which the direct reduction process is carried out, identified by the coke oven gas and/or natural gas by the addition of water vapor and carbon dioxide gas, which is top gas from a DRI reduction device (5), and from the oxygen in a COG reformer (1) is reformed to the reducing gas.

2. Method according to claim 1, characterized in that the reducing gas is partially produced in the COG reformer (1) from the coke oven gas and/or natural gas and partly from the top gas of the same DRI reduction device (5).

3. Method according to claim 2, characterized in that the reducing gas is produced in approximately equal parts from the outlet gas of the COG reformer (1) and from the top gas of the reduction device (5).

4. Method according to one of the preceding claims, characterized in that the coke oven gas and/or natural gas is mixed with water vapor and carbon dioxide containing gas and the resulting gas mixture and oxygen are introduced into the COG reformer (1).

5. Method according to claim 4, characterized in that the obtained gas mixture and oxygen in the lower region of the COG reformer (1) and a subset of the oxygen in the central region of the COG reformer (1) are introduced.

6. Method according to one of the preceding claims, characterized in that the outlet gas of the COG reformer (1) is supplied to a subset of coke oven gas and/or natural gas.

7. Method according to one of claims 4 to 6, characterized in that the gas mixture of coke oven gas and/or natural gas, the water vapor and carbon dioxide containing gas is heated prior to introduction into the COG reformer (1), wherein its temperature becomes adjusted depending on the methane content.

8. Method according to one of the preceding claims, characterized in that at least one double lance (10) is used to introduce the gas mixture from the coke oven gas and/or natural gas as well as the water vapor, the carbon dioxide gas and oxygen, wherein the oxygen via the inner lance tube and the space between the inner tube and outer tube, the gas mixture in the COG reformer (1) are introduced.

9. System for the production of porous iron, in particular for carrying out the process according to one of claims 1 to 8, with a DRI reduction device, characterized in that it further comprises a COG reformer (1) in which the coke oven gas and/or the natural gas, water vapor and carbon dioxide-containing gas, which is top gas from a DRI reduction device (5) and oxygen is reformed to the reducing gas, is provided.

10. System according to claim 9, characterized in that in comprises a device for discharging and processing the top gas of the DRI reduction device (5) to the reducing gas and for supplying the same reduction device together with the reducing gas from the COG reformer.(1).

11. System according to claims 9 to 10, characterized in that it comprises means for mixing the coke oven gas and the natural gas with the water vapor and carbon dioxide containing gas prior to introduction into the COG reformer (1).

12. System according to claim 11, characterized in that it comprises the means for introducing the obtained gas mixture and oxygen into the lower region of the COG reformer (1) and the means for introducing oxygen into the middle part of the COG reformer (1).

13. System according to one of claims 9 to 12, characterized in that it comprises the means for supplying a subset of coke oven gas and/or natural gas to the outlet gas of the COG reformer (1).

14. System according to one of claims 9 to 13, characterized in that it has a device for heating the water vapor and the carbon containing gas, prior to introduction into the COG reformer (1).

15. System according to one of claims 12 to 14, characterized in that it comprises at least one double lance (10) for introducing the gas mixture and oxygen in the COG reformer (1).

16. System according to claim 15, characterized in that the double lance (10) designed as a double tube has a water-cooled inner tube enveloped by a protective tube.

Description

[0034] The invention will be explained below with a reference to an implementation in conjunction with the detailed drawings. The single FIGURE shows a schematic representation of the structure of a system for the production of porous iron with a DRI reduction device and a COG reformer.

[0035] In the lower region of the COG reformer 1 is a mixture of coke oven gas and/or natural gasintroduced by a line 7water vapor and carbon dioxide containing gas from a top gas scrubber 6introduced via a line 8preheated in a heat exchanger 2 and injected via a line 9 and double lances 10 in the lower region of COG reformer 1 and converted by blowing the bulk of oxygen via double lances 10introduced via a line 11to the reducing gas. The blowing of the oxygen through the inner tube and the supply of the preheated mixed gas over the space between the inner and outer tube of the double lance 10. A smaller amount of oxygensupplied through the common oxygen line 11is injected through a simple, radially on the circumference of the COG reformer 1 mounted oxygen lances 12 into the central region of the COG reformer 1. The oxygen that is injected by oxygen lances 12 into the middle region of the COG reformer 1, serves in regulating the dome temperature of the COG reformer 1 and at the same time to mix the gas rising from the lower region of the COG reformer. The reducing gas produced in the COG reformer 1is led out via a line 14is added via a line 13 coke oven gas and/or natural gas to adjust the methane content of the reducing gas for the reduction device 5. The top gas led out of the reduction device 5 is washed and cooled in a gas scrubber 6, the water vapor formed in the reduction device 5 is condensing out. Most of the washed top gas is supplied via line 15 of a carbon dioxide precipitation system 3. The hydrogen and carbon monoxide-containing product gas is introduced via a line 16 to a reduction heater 4, heated to about 900 C. and is introduced via a line 17 to the reducing gas produced in the COG reformer 1, admixed via line 13, the reduction device 5 and introduced for producing porous iron, which is then discharged at the lower end or the reduction device 5. The carbon dioxide containing exhaust gas (tail gas), which is passed out via a line 18 from the carbon dioxide precipitation system 3, a smaller amount of the top gas from the gas scrubber 6 is added via a line 19 and fed to the reducing gas heater 4 as the heating medium.

[0036] The DRI system with a COG reformer 1 is a simple reformer in which the reducing gas is produced by reforming of the coke oven gas and/or the natural gas and by supplying an oxidizing agent and then it is supplied to the reduction device 5 via the line 13. The water vapor formed in the reduction device 5 is discharged in a gas scrubber 6 and the carbon dioxide that is formed, in a carbon dioxide precipitation system 3. The thus prepared reducing gas is heated in a heat exchanger 4 to the required temperature, mixed with the hot reducing gas from the COG reformer 1, supplied to the reduction device 5 and used for the production of porous iron. The amount of the water vapor and the carbon dioxide-containing gas supplied to the coke oven gas and/or the natural gas and the temperature to which the mixed gas is preheated before being blown into the COG reformer 1, are adjusted depending on the methane content of the mixed gas. A higher preheating temperature of the mixed gas leads to a lower oxygen consumption and a higher reduction potential of the produced reducing gas. A too high preheating temperature should, however, be avoided in order for the carbon precipitation to be kept low and for the sooting by thermal decomposition of methane in the heat exchanger 2 and in the COG reformer 1 low as well.

[0037] Since the steam is a much stronger medium against sooting than carbon dioxide, gas scrubbing 6 is operated at a higher methane content of the mixed gas with a higher feed water temperature, whereby more water vapor via line 8 is introduced with the coke oven gas and/or natural gasintroduced via line 7into the preheater 2 is supplied, whereby the gas mixture in the preheater 2 can be heated to a higher temperature. At a very high methane content of the reducing gas also steam can be supplied to this subset of the top gas from the gas scrubber 6.

[0038] In order to mix the oxidizing agent and the preheated mixed gas as well as possible and to bring oxygen and methane to the reaction, both mediums are injected via radially circumferentially mounted double lances 10 in the lower region of the COG reformer 1, the oxygen over the inner tube and the preheated gas mixture are introduced through the space between the inner and outer tube of the double lances 10.

[0039] A smaller portion of the oxygen is blown through a plurality of oxygen lances 12 arranged on the circumference of the COG reformer at a higher speed into the middle region of the COG reformer 1 in order to better mix the gas components of the rising gas from the lower region of the COG reformer 1 and to increase the efficiency of it. The amount of oxygen supplied to the central region of the COG reformer 1 simultaneously serves to regulate the dome temperature of the COG reformer 1.

[0040] In order to ensure the fine adjustment of the methane content of the reducing gas for the reduction device 5, the outlet gas from the COG reformer 1 is supplied with a corresponding amount of coke oven gas or natural gas. The basic adjustment of the methane content is carried out by adjusting the ratio of the preheated mixed gas/oxygen, which are supplied via double lances 10 of the lower region of the COG reformer 1.

[0041] The adjustment of the temperature of the reducing gas mixture from the COG reformer 1 and from the carbon dioxide precipitation system 3 or from the gas heater 4, which is supplied to the reduction device 5, is done via the temperature of the reducing gas produced in the COG reformer 1.

[0042] In the operating DRI systems, in which the natural gas prices have become too high and the operation of the systems has become uneconomical, by converting the systems of catalytic reformers to COG reformers 1, a part of the catalytic reformer and the entire recuperation system can be put into further use. The use of the entire catalytic reformer is no longer necessary, since the heat requirement for heating the reducing gas from the carbon dioxide precipitation system to the required temperature, is not as high as for the decomposition of methane by water vapor and carbon dioxide in a catalytic reformer. It makes sense to use only a part of the catalytic reformer, including the catalytic tubes for heating the reducing gas from the carbon dioxide precipitation system to about 900 C. and the feed gas recuperating system from preheating the gas mixture for the COG reformer 1. However, small adjustments of the amount of the fuel gas, the ratio of air/fuel gas and the height of the temperatures of the combustion gas are required.

[0043] The inner tube of the double lance 10 designed as a double tube is furnished with a protection tube and can be made of highly heat-resistant steel or be designed as a water-cooled lance.

[0044] When converting a conventional DRI system based on natural gas, of coke oven gas and/or other gases, the catalyst reformer is replaced by a COG reformer 1, the catalytic reformer and recuperation of an operational system are rebuilt so that only one part of the catalytic reformer is maintained. The catalyst is thereby emptied, and the catalytic tubes are used for heating the reducing gas from the carbon dioxide precipitation system 3 and the feed gas preheater for preheating the mixed gas for the COG reformer 1.