WO2002014221A1

WO2002014221A1 - Process and apparatus for post-treatment of iron oxide

Info

Publication number: WO2002014221A1
Application number: PCT/US2001/025533
Authority: WO
Inventors: Edgar J. Robert; Donald F. Kuschel
Original assignee: INTERNATIONAL STEEL SERVICES Inc
Current assignee: INTERNATIONAL STEEL SERVICES Inc
Priority date: 2000-08-15
Filing date: 2001-08-15
Publication date: 2002-02-21
Anticipated expiration: 2003-02-15
Also published as: AU2001286487A1

Abstract

A process for the treatment of iron oxide generated from waste pickle liquor containing free hydrogen chloride. Undesirable large pieces are separated from the iron oxide. The iron oxide is maintained at an elevated temperature for a residence time in a reactor vessel. A fluidization agent is then injected to create a fluid bed with the iron oxide. The level of the fluidized iron oxide is maintained and the iron oxide is then discharged from the reaction vessel. An apparatus for carrying out this process is also disclosed.

Description

PROCESS AND APPARATUS FOR POST-TREATMENT

OF IRON OXIDE

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to processes and apparatus for treating iron oxide, and more particularly to such processes and apparatus, which are used to reduce chlorine concentrations.

Background Information A typical process to produce iron oxide from waste steel pickle liquor is spray roasting. This process produces hydrochloric acid in the off gas stream and particles of iron oxide.

Iron oxide powder produced from waste pickle liquor in conventional steel making operations has residual chloride compounds. The chloride content of the iron oxide may vary from 0.10-0.50%. Some applications require low chloride content. There are several post-treatment processes that are intended to reduce the chloride content of the iron oxide. These processes have various degree of success and the most efficient processes are expensive to operate. Some special operating practices leads to very low chlorides, however, they lead to low surface areas. It is not difficult to obtain 0.08% Cl, but in those cases, the surface area is below 3.4 m²/g, which severely limits its application.

The reduction of chlorides in iron oxide has been attempted by processing the iron oxide through a screw conveyor while the off-gases from a burner are flowing through the screw conveyor. This method requires the installation of costly equipment expensive to maintain and operate. The basis of this process is that the chlorides formed on the surface of the iron oxide can be removed by exposing the particles to high temperature and hot gases loaded with moisture. By this method, it appears that it is possible to achieve chloride levels of 0.12% or lower. Another method is to wash the iron oxide, dry-out and condition the resulting material by grinding. While with this method, it appears to be possible to achieve chloride levels of 0.05%. The capital and operating cost of this procedure are high.

Another process described in the U. S. Patent No. 5,597,547 is based on mixing the iron oxide with about 3-25% by weight of yellow iron oxide containing crystalline water and adding water. The mixture formed is heated up to 800°C above the decomposition temperature of the yellow iron oxide for times up to 10 hours. Another method similar to the above is based on the addition of sulfuric acid followed by drying and calcining.

The above-described methods are relatively elaborate and expensive to operate due to the long processing time. A need still exists to reduce chlorine concentrations in an easier, more cost effective manner.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process to modify the chemistry and physical properties of the iron oxide produced by thermal processes, such as roasting, by injection of various gases in a fluid bed vessel.

This process takes advantage of the heat content of the iron oxide to obtain temperature compounds by controlling the atmosphere surrounding the iron oxide particles during cooling. The process of this invention involves in situ post treatment of the iron oxide to change its chemistry and properties to meet a wide range of specifications. The apparatus used to carry out this method consists of a vertical vessel attached to the primary source of iron oxide, which may be a roaster and which has the means to fluidize the iron oxide, by injection of a gas through a fiuidizing media. The mass of gas injected is small compared to the mass of iron oxide, thus the temperature of the iron oxide is not substantially affected by the injection of the fiuidizing gas.

The fiuidizing gas has also the function of producing chemical changes and/or preventing chemical reactions with the iron oxide. The level of iron oxide in the vessel is set to the desired residence time to achieve the desired properties.

Industrial tests show a substantial reduction of chlorides in the iron oxide obtained by preventing the formation of metallic chlorides at temperatures below 500°C. An additional benefit of the treatment is to maintain physical characteristics at desired levels in spite of substantial residence time in the vessel.

Typically, the chlorine content of the iron oxide before the process will be about 0.15% by weight or greater and, more typically, in the range of about 0.16% by weight to about 0.17% by weight. After the process the chlorine content of the iron oxide will preferably be reduced to about 0.12% by weight or less and typically to a range of from about .012% by weight or less and typically to a range of from about 0.10% by weight to about 0.11% by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the invention, illustrative of the best mode in which applicant contemplated applying the principles, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims.

Fig. 1 is a schematic drawing of a preferred embodiment of the apparatus of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the figure, the apparatus of the present invention includes an iron oxide roaster 10, which is superimposed over a reactor 12. The reactor 12 includes temperature probes 14 and 16. The reactor 12 also includes fluid inlet lines 18 and 20, which are positioned respectively on aeration pads 22 and 24. Iron oxide 26 from the iron oxide roaster 10 is positioned in the reactor 12. Inside the reactor 12 there is a sloped screen 28 interposed between the iron oxide roaster 10 and the iron oxide 26 which separate large pieces of iron oxide. The iron oxide 26 is preferably in a powder having a specific surface area in the range of 4.5m²/g to 5.5m²/g, in the reactor 12. The screen 28 sloped slops downwardly and laterally to a terminal lateral pocket 30. Beneath the reactor 10, there is an outlet rotary valve 32, which unloads treated iron oxide to a final product conveyor 34. The system consists of a reaction vessel 12 that is attached to the iron oxide 26, which is usually a roaster 10. The reaction vessel 12 is thermally insulated to limit heat losses, and maintain the temperature of the iron oxide 26 as high as possible, generally above 450°C. The screen 28 separates large pieces from the iron oxide 26. Large pieces of material, which may be refractory or other undesirable pieces, are separated by the screen 28 from the iron oxide 26 are collected in the pocket 30 and removed from time to time.

The iron oxide 26 is maintained at the desired level in the reactor 12 by controlling the feed rate of the rotary valve 32. The temperature probes 16 and 18 provide the information to control the level of the iron oxide 26 by controlling the feed rate of the rotary valve through a programmable logic controller fluidization/reaction gas through fluid inlet lines 18 and 20, which give rise to the fluid bed. The velocity of the gas in the reaction vessel 12 is maintained above the critical velocity to obtain a fluid bed. The fluidized iron oxide 26 is removed from the bottom of the reaction vessel 12, after a suitable residence time is achieved. The final product, which will preferably have a chlorine content of 12% by weight or less is screened and removed in conveyor 34.

The volume of the reaction vessel as well as the level depends on the objective of the treatment. Typically, the iron oxide being treated will have residence times, up to 60 minutes. The gases that can be used to produce the fluid bed and react with the iron oxide are natural gas, nitrogen, air, ammonia, steam, synthesis gas, combustion gases and other chemical compounds that may suit the application. The temperature of these gases may vary from room temperature up to 590°C, depending upon the specific application. The mechanical effects of the fluid bed will prevent the agglomeration of the iron oxide. This effect leads to powders with desired physical characteristics, such as surface area and particle size. Some applications of this invention are production of iron powder, production of iron carbide, production of iron alloy powder, production of low chloride, high surface area iron oxide powder.

Waste pickle liquor used for roasting has a concentration of FeCI² between 18 and 26%, and a concentration of HCI between 0 and 10%. In general, the process can treat the iron oxide produced from waste pickle liquor with the above concentration.

A number of metallic chlorides will form at temperatures between 200°C and 800°C. The present invention proposes to control the environment surrounding the iron oxide during the cooling phase, preventing the presence of chlorinated gases and consequently the formation of low temperature chlorides.

The following table shows the temperature range at which various metallic chlorides will form.

The above table shows that there is a family of chlorides that will form at low temperature, such as Mn, Ni, Mg and Zn. The present invention prevents the formation of these and similar chlorides. The injection of air as a fiuidizing gas at a rate of 1.2SCF/lb. of iron oxide leads to the formation of a fluid bed. The fluidization of the iron oxide particles will prevent the agglomeration of the iron oxide resulting on a larger specific surface area. Applying this process, a surface area as high as 5.5m²/g may be obtained with a net chloride reduction of 0.06%. Additional reduction in the chloride level may be expected with the injection of steam as a fiuidizing gas.

The following example describes one application of this invention.

Example Reduction of Chloride Content in Spray Roasted Iron Oxide

A quality of iron oxide is produced in a roaster at a rate of 700kg/h to a temperature of 470°C. The iron oxide is in particles having an average major dimension of about 0.52um. Specific surface area is 5.4m²/g. The iron oxide has a chlorine content of 0.16% by weight. The iron oxide is screened to remove particles having a major dimension of 12mm and is removed to a reactor having internal dimensions of 910mmX910mmX760mm. Inside the reactor, the iron oxide is maintained at a temperature of 430°C and a fluid bed is established by injecting air into the base of the reactor at a rate of 2.8Nm³/min. After having a residence time of about 17 minutes in the reactor, the iron oxide is removed from the reactor through a rotary valve at a rate of

28.3kg/min. The final product iron oxide is removed and cooled to a temperature of 130°C over a period of 3 minutes and was found to have a chlorine content of 0.10% by weight.

It will be appreciated that a process and apparatus has been described which afford an effective and cost effective means of reducing chlorine content in iron oxide generated from waste pickle liquor containing free hydrogen chloride. While the present invention has been described in connection with the preferred embodiments of the various elements, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the present described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.

Claims

CLAIMS What is claimed is:

1. A process for the treatment of iron oxide having undesirable large pieces generated from waste pickle liquor and containing free hydrogen chloride, comprising the steps of: separating the undesirable large pieces from the iron oxide; maintaining the iron oxide at an elevated temperature for a residence time in a reactor vessel; injecting a fluidization agent to create a fluid bed having a level with the iron oxide; maintaining the level of the fluid bed with the iron oxide; and discharging the iron oxide from the reaction vessel.

2. The process of claim 1 wherein air is used as the fluidization agent.

3. The process of claim 1 wherein steam is used as the fluidization agent.

4. The process of claim 1 wherein natural gas is used as the fluidization agent.

5. The process of claim 1 wherein the chemical composition of the iron oxide is modified.

6. The process of claim 1 wherein the specific surface area is about 5.5 m²/g or less.

7. The process of claim 6 wherein the iron oxide is a powder having a specific surface area from about 4.5m²/g to about 5.5m²/g.

8. The process of claim 1 wherein the chloride content of the iron oxide is reduced by at least about 0.05%.

9. The process of claim 1 wherein the undesirable large pieces separated from the iron oxide have a major dimension of about 12mm or more.

10. The process of claim 1 wherein the iron oxide is maintained in the 5 reactor at an elevated temperature.

11. The process of claim 2 wherein the air prevents the formation of low temperature metallic chlorides.

10 12. The process of claim 1 wherein the fluid bed prevents the agglomeration of the iron oxide.

13. The process of claim 1 wherein the level of the fluidization oxide is maintained from the top of the reactor.

15

14. The process of claim 1 wherein the reactor has a top and bottom and the iron oxide is introduced into the reaction from the top of the reactor and is discharged form the bottom of the reactor.

20 15. The process of claim 1 wherein the iron oxide has a chlorine content.

16. The process of claim 15 wherein the chlorine content is about 0.15% by weight or more prior to carrying out the process.

25 17. The process of claim 16 wherein the chlorine content is from about 0.16% by weight to about 0.17% by weight prior to carrying out the process.

18. The process of claim 16 wherein the chlorine content is about 0.12% by weight or more after carrying out the process.

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19. The process of claim 17 wherein the chlorine content is from about 0.10% by weight to about 0.11% by weight after the process.

20. The process of claim 1 wherein the iron oxide maintained at an elevated temperature of about 450°C or more for a residence time of about 60 minutes or less.

5

21. The process of claim 1 wherein the ferric oxide is removed from the reactor vessel through a rotary valve.

22. A process for reducing a chlorine content in iron oxide comprising the 10 steps of: introducing the iron oxide to a reaction vessel; and injecting a fluidization agent into the reaction vessel to create a fluid bed and maintaining the iron oxide in said fluid bed for a period of time necessary to reduce said chlorine content. 15

23. A process for the treatment of iron oxide having undesirable large pieces generated from waste pickle liquor and containing free hydrogen chloride, comprising the steps of: separating the undesirable large pieces having a major dimension of 20 about 12mm or more from the iron oxide so that the iron oxide has a specific surface area of about 5.5m²/g or less; maintaining the iron oxide at an elevated temperature of about 450°C or more for a residence time of about 60 minutes or less in a reactor vessel; injecting a fluidization agent selected from the group consisting of 25 natural gas, nitrogen, air, ammonia, steam, synthesis gas and combustion gases to create a fluid bed having a level with the iron oxide; maintaining the level of the fluidized iron oxide; and discharging the iron oxide from the reaction vessel.

30 24. An apparatus for reducing chlorine content in iron oxide comprising: a reaction vessel comprising an upper feed opening and a lower discharge opening and means for introducing a fluidization agent; an iron oxide feed means superimposed over the upper feed opening; and an iron oxide discharge means positioned below the lower discharge opening of the reaction vessel.