A PROCESS FOR PRODUCING DIRECTLY REDUCED IRON IN A FURNACE

Field of invention:
The present invention relates to a process of producing directly reduced iron (DRI).

Background of the invention:
In iron or steel making industries directly reduced iron (DRI) or sponge iron is produced by reduction of iron oxides source material. There is number of processes available for production of directly reduced iron (DRI) or sponge iron. The conventional processes for producing DRI can be divided into the following three categories:

Gas based process: In this process iron ore pellets/ lump ore is charged into a vertical shaft and a reducing gas normally containing a mixture of carbon monoxide, hydrogen and carbon-dioxide etc is passed through the lower part of the shaft at a temperature in the range of 750oC to 950oC. Due to counter current gas solid reaction the pellets/lump ore gets reduced to DRI. There are number of gas based processes, such as, Midrex, HYL-III etc. In this process normally natural gas is used as a source of reducing gas and energy.

Coal based process: In this process iron ore pellets/lump and coal fines/lumps are charged into an inclined kiln. During decent of the burden the pellet/lump ore gets reduced to DRI. In this process coal is the only sources of reductant and energy.

Rotary hearth process: In this process carbon and iron bearing materials are mixed together and formed composite pellets. These pellets are charged inside a rotary hearth furnace, where the pellets get reduced at a temperature over 1300oC.

All of the above indicated processes involve large capital expenditure and require large amount of energy for reduction of iron ore. Therefore, there exists a need to develop a process which is comparatively cheaper and has lesser energy consumption.

Objects of the Present Invention:
The main object of the present invention is to provide a process for producing directly reduced iron (DRI).
Another object of the present invention is to provide a process for producing directly reduced iron (DRI) which involves lesser capital cost and lesser cost of production.

Summary of the invention:
The present invention provides a process for producing DRI using various iron and carbon bearing wastes in a steel plant. The Applicant has named the DRI produced by the process of the present invention as ‘RG DRI Process’.

Brief description of figures:
Figure 1 illustrates a container and a method for providing a charge according to an aspect of the process of the present invention.
Figure 2 is an exemplary illustration of a furnace for producing a directly reduced iron according an aspect of the process of the present invention.

Detailed description of the invention:
Accordingly, the present invention provides a process for producing a directly reduced iron, said process comprising the steps of providing a charge of iron oxide source material and a carbon source material in a partially closed metallic container and placing the said container in a furnace for a predetermined time at a temperature in the range of 900oC to 1200oC.

In an aspect of the present invention the container is made up of steel.

In another aspect of the present invention the said container is an elongated cylindrical container having an open end and a closed end.

In still another aspect of the present invention said open end of the container is closed with perforated metallic plate and clay.
In yet another aspect of the present invention the charge comprising mixture of iron oxide material and a carbon source material.

In a further aspect of the present invention the charge comprising layers of iron oxide material and a carbon source material.

In a further more aspect of the present invention said charge is tightly packed in the metallic container using a ram and moisture in the range of 5-10% of the total charge mix.

In another aspect of the present invention the container is placed inside the furnace for a time period in the range of 5 to 10 hours.

In still another aspect of the present invention the iron oxide source material is selected from the group comprising iron ore lump and fines, mill scale, de-dusting dust produced in iron and steel making process, tailing generated during beneficiation and sinter fines.

In yet another aspect of the present invention the carbon source material is selected from the group comprising coal, crushed coal, coal fines, coke, coke fines, iron and steel making sludge, blast furnace dust catcher dust, petroleum coke, calcined petroleum coke, tar, charcoal and charcoal fines.

In a further aspect of the present invention the charge comprising dolomite fines.

In a further more aspect of the present invention the ratio of iron oxide source material and carbon source material is in the range of 1:1 to 8:1, preferably 5:1.

An aspect of the present invention provides a process for producing a directly reduced iron, said process comprising the steps of:
(a) providing a charge of iron oxide source material and a carbon source material in plurality of metallic barrels;
(b) sealing each of the said plurality of barrels with clay and perforated metallic plate;
(c) heating the said plurality of metallic barrels at a temperature of 900 to 1200oC for a predetermined time; and
(d) cooling the barrels to a room temperature and removing directly reduced iron by magnetic separation.

In one more aspect of the present invention the said furnace is a pusher-type reheating furnace.

The present invention also provides a furnace for producing a directly reduced iron, the furnace comprising:
(a) a charging end for charging the plurality of said partially closed elongated container provided with the charge of the iron oxide source and carbon source material;
(b) a burner zone located opposite to the charging end and said burner zone comprising one or more burners for heating the containers;
(c) a discharge end located near the burner zone and said discharge end is disposed on the furnace wall adjacent to the charging end and the discharge end;
(d) a furnace base having a slope in the range of 5 to 20 degrees for movement of the plurality of containers due to gravity from the charging end to the discharge end;
(e) a manhole located opposite to the discharge end for pushing the container towards the discharge end.

According to the process of the present invention, a directly reduced iron (DRI) is produced by reduction of iron oxide source material in the presence of a carbon source material in a partially closed container at a temperature of 900 to 1200oC. As it can be clearly understood, when iron oxide source material and carbon source material is hearted at temperature of 900 to 1200oC in absence of oxygen, the iron oxide gets reduced to iron or sponge iron. During this process the CO is generated which reacts with the iron oxide and converts it to a DRI of high degree of metallization. In the reduction process of iron oxide following are the main reactions which take place between 950 -1050oC:

Fe2O3 + 3CO = 2Fe + 3CO2
CO2 + C = 2CO

In the process of the present invention the charge of iron oxide source material and a carbon source material is provided in a partially closed metallic container. Then the container is heated for a temperature in the range of 900oC to 1200oC for a predetermined time which may be in the range of 5 to 10 hours.

In the process of the present invention a variety of raw materials or plant wastes can be used for the production of directly reduced iron DRI. For example charcoal fine, coal fines, coke fines, BF sludge or any steel plant waste which contains carbon may be used as a carbon source material. For better reaction kinetics the carbon carrier should be below 6 mm size. Similarly, Iron ore lumps and fines, mill scale, BOF dust or any steel plant waste which contains iron may be used as iron oxide source material.

In the process of the present invention, the charge comprises iron oxide source material and carbon source material in the ratio from 1:1 to 8:1. Preferably, the charge comprises iron oxide source material and carbon source material in the ratio 5:1.

In an aspect of the present invention Dolomite/limestone fines from any sources can be used along with carbon source material.

In the process of the present invention the container may be made up of any metallic material suitable for sustaining such a higher temperature of 900oC to 1200oC. Preferably, the container is made up of steel. According to an aspect of the present invention the container is an elongated cylinder which has an open end and a closed end. After the charge of iron oxide source material and carbon source material is fed inside the container the open end is sealed with clay and perforated steel plate. The perforated steel plate acts as a passage for releasing the carbon-monoxide (CO) generated during the process. This increases the partial pressure of CO inside the container and improves the kinetics of reduction process.

Figure 1 describes a method of providing a charge according to an aspect of the process of the present invention. As shown in figure 1, the metallic container is of cylindrical shape or having a shape of a barrel. The container or barrel is provided with charge of iron ore and coke with dolomite fines in layered form. The layer of iron ore is sandwiched between the layers of coke with dolomite fines. However, the charge as a mixture of iron ore and coke with dolomite fine may also provided inside the barrel. After providing the charge inside the barrel, all the material is tightly packed using a ram and moisture in the range of 5 to 10% of the total charge mix. The barrel packed with the charge is now subjected to a temperature of 900 to 1200oC for a time period in the range of 5 to 10 hours. After said period lapsed, the barrel is break open and directly reduced iron may be separated magnetically.

For mass production of directly reduced iron by the process of the present invention plurality of barrels packed with charge may be prepared. Said plurality of barrels can be heated in a furnace for producing the directly reduced iron (DRI). One of such arrangement is shown in figure 2. As shown in figure 2, plurality of barrels is placed inside a tunnel furnace. According to the size of the furnace the number of barrels can be decided. As shown in figure 2, the furnace has a charging end and a discharge end. As the barrels gradually moved from charging end towards the discharge end, number of processes, such as, drying, preheating, calcination, reduction, Boudward reaction etc take place. The main reactions takes place between 950 -1050oC are

Fe2O3 + 3CO = 2Fe + 3CO2
CO2 + C = 2CO

By the time the barrels are discharged from the furnace, the iron carrier or iron oxide source material would be metalized in access of 85%. The said DRI analysis is similar to that of coal based DRI analysis and can be used in steel making on a regular basis.

In iron ore ‘iron’ is present in the form of oxides (i.e. iron combined with oxygen). During directly reduced iron (DRI) production it is required to separate the oxygen from the iron. Removal of oxygen or reduction of iron is done by carbon which combines with oxygen at high temperature and forms carbon monoxide. However, it is practically not possible to remove all the oxygen from iron ore. For this reason inside the DRI there would be both metallic iron and iron oxide. Effectiveness of reduction can be indicated by degree of metallization which can be described as follows:

Degree of Metallization = (wt. of Metallic iron in DRI) x 100/ (wt. of total iron in DRI)

By the process of the present invention the degree of metallization of the DRI could be over 85%.

Particularly, figure 2 shows a pusher type reheating furnace. As shown in figure 2, the furnace is provided with oil fired burners placed at one end near the discharge side of the furnace. The furnace is also provided with an exhaust which is placed at the other end i.e. near the charging side of the furnace. The exhaust is through natural draft chimney.

The discharge end or discharge side is designed to be at maximum operating temperature of 1200oC (max). The operating temperature at the discharge end could be varied depending upon the retention time of each barrel inside the furnace and the product quality. As we move from the discharge end towards the charging end, there is a gradual drop of temperature across the furnace. The temperature at the charging end would be a function of number of barrels charged and, of course, the thermal balance of the furnace at that point of time. However, the operating temperature at the charging end should be below 300oC. Furnace shown in figure 2 may be operates with little excess air (oxygen), so that the CO generated during the reduction can be utilized inside the furnace for heat generation.

The furnace doors are designed and constructed in such a way that charging and discharging of the barrels are possible without shutting down the burners. Both charging and discharging end are provided with a pusher facility, which can be operated manually from outside the furnace. Also, the furnace can be provided with number of manholes (which can be opened easily) on the furnace walls, so that, in case of, barrel misalignment it can be taken care of immediately.
As indicated in figure 2, the furnace base is provided with a gradual slope for easy movement of barrels from charging end to discharge end due to the gravity. The slope can be in the range of 5-20 degrees.). Two rails are mounted at the bottom of the furnace for easy friction free movement of the barrels from the charging to discharge end. The furnace can also be provided with side guards (made out of steel with refractory coating) on either side of the furnace walls to avoid misalignment of the barrels.

Once the barrels are discharged from the furnace, it would be cooled to room temperature by natural cooling. Thereafter, the barrel can be broken form removing the treated charge and then the DRI can be separated magnetically.

Example 1:
The Steel barrel is filled with iron ore fines (size below 10 mm) and coke fines (size below 6 mm) in the ratio of 4:1 as indicated in figure-1. About 1.5% of the total charge mix dolomite fine is also added along with coke fines. The steel barrel is place inside the furnace (shown in figure 2) for the time period of about 9 hrs. After discharging from the furnace, the barrel is cooled to room temperature. Thereafter, the material from the barrel is subjected to magnetic separation and thus DRI fine is separated from the non-magnetic materials. The main product, i.e., the directly reduced iord DRI fines would be in clustered or agglomerated form. The non-magnetic materials (i.e., by-product) contain residual carbon, coke ash and calcined dolomite fines.

Example 2:
The Steel barrel is filled with iron ore lumps (size 4mm to 15mm) and coke fines (size below 6mm) in the ration of 5:1 as indicated in figure-1. About 1.5% of the total charge mix dolomite fine is also added along with coke fines. The steel barrel is place inside the furnace (Figure 2) for the time period of about 10 hrs. After discharging from the furnace, the barrel is cooled to room temperature. Thereafter, the material from the barrel is subjected to magnetic separation and thus lumpy DRI is separated from the non-magnetic materials. The main product, i.e., the DRI lumps would be in clustered or agglomerated form. The non-magnetic materials (i.e., by-product) contain residual carbon, coke ash and Calcined dolomite fines.
Some of the advantages of the present invention are as follows:
1. The cost of production of RG DRI by the process of the present invention is substantially less as compared to the conventional used processes. This is because in the process of the present invention amount of carbon source required is much lesser compared to the conventional processes. Additionally, this process uses cheaper plant generated wastes for the production of DRI.
2. Utilization of lesser carbon in production of directly reduced iron (DRI) of the present invention enables the process to qualify for ‘Carbon Credit’ in the international market.
3. Production of RG DRI by the process of the present invention is capable of improving production capacity of any steelmaking or iron making unit.
4. By the process of the present invention In-House production of directly reduced iron (DRI) with very less capital expenditure is possible.
5. The directly reduced iron (DRI) produced by the process of the present invention can be used in any steel making units as a replacement of purchased DRI.
6. The cost of installing a 100 TPD Rotary kiln for the production of coal based DRI is about 20 crores and it requires 18-20 months time to install the facility. Whereas, the process of the present invention can be carried out with much cheaper investment and the furnace can be commissioned within a couple of month’s time.
7. The process of producing directly reduced iron (i.e. RG DRI) of the present invention can be easily integrated with steel making facilities through induction furnace route. Hot charging of DRI into the induction furnace is easily possible, which would substantially reduce the power requirement and thereby the cost of steel production.

We Claim:

1. A process for producing a directly reduced iron, said process comprising the steps of providing a charge of iron oxide source material and a carbon source material in a partially closed metallic container and placing the said container in a furnace for a predetermined time at a temperature in the range of 900oC to 1200oC.

2. A process as claimed in claim 1, wherein the container is made up of steel.

3. A process as claimed in any one of the preceding claims, wherein the said container is an elongated cylindrical container having an open end and a closed end.

4. A process as claimed in claim 3, wherein said open end of the container is closed with perforated metallic plate and clay.

5. A process as claimed in any one of the preceding claims 1 to 4, wherein the charge comprising mixture of iron oxide material and a carbon source material.

6. A process as claimed in any one of the preceding claims 1 to 4, wherein the charge comprising layers of iron oxide material and a carbon source material.

7. A process as claimed in any one of the preceding claims, wherein said charge is tightly packed in the metallic container using a ram and moisture in the range of 5-10% of the total charge.

8. A process as claimed in any one of the preceding claims, wherein the container is placed inside the furnace for a time period in the range of 5 to 10 hours.

9. A process as claimed in any one of the preceding claims, wherein iron oxide source material is selected from the group comprising iron ore lump and fines, mill scale, de-dusting dust produced in iron and steel making process, tailing generated during beneficiation and sinter fines.

10. A process as claimed in any one of the preceding claims, wherein the carbon source material is selected from the group comprising coal, crushed coal, coal fines, coke, coke fines, iron & steel making sludge, blast furnace dust catcher dust, petroleum coke, calcined petroleum coke , tar, charcoal and charcoal fines.

11. A process as claimed in any one of the preceding claims, wherein the charge comprising limestone or dolomite fines.

12. A process as claimed in any one of the preceding claims, wherein the ratio of iron oxide source material and carbon source material is in the range of 1:1 to 8:1, preferably 5:1.

13. A process for producing a directly reduced iron, said process comprising the steps of:
(a) providing a charge of iron oxide source material and a carbon source material in plurality of metallic barrels;
(b) sealing each of the said plurality of barrels with clay and perforated metallic plate;
(c) heating the said plurality of metallic barrels at a temperature of 900oC to 1200oC for a predetermined time in a furnace; and
(d) cooling the barrels to a room temperature and removing directly reduced iron by magnetic separation.

14. A process as claimed in claim 13, wherein the said furnace is a pusher type reheating furnace.

15. A furnace for producing a directly reduced iron by a process as claimed in any of the preceding claims1 to 14, wherein the furnace comprising:
(a) a charging end for charging the plurality of said partially closed elongated container provided with the charge of the iron oxide source and carbon source material;
(b) a burner zone located opposite to the charging end and said burner zone comprising one or more burners for heating the containers;
(c) a discharge end located near the burner zone and said discharge end is disposed on the furnace wall adjacent to the charging end and the discharge end;
(d) a furnace base having a slope in the range of 5 to 20 degrees for movement of the plurality of containers due to gravity from the charging end to the discharge end;
(e) a manhole located opposite to the discharge end for pushing the container towards the discharge end.

16. A process for producing a directly reduced iron substantially as herein described with reference to the accompanying drawings and foregoing examples.