GB2093070A

GB2093070A - Manufacturing sponge iron

Info

Publication number: GB2093070A
Application number: GB8104132A
Authority: GB
Original assignee: SKF Steel Engineering AB
Current assignee: SKF Steel Engineering AB
Priority date: 1981-02-11
Filing date: 1981-02-11
Publication date: 1982-08-25
Also published as: GB2093070B

Abstract

A method and apparatus for manufacturing sponge iron by the continuous reduction of iron oxides in a shaft utilizing recirculation gases. Reaction gas is removed from the shaft furnace, 1 substantially cleaned of all CO2 and H2O, and then divided into at least two flow portions one of which is passed to a gas generator 11 comprising a gas generating shaft substantially filled with a solid reducing agent and a plasma burner 12 arranged in the lower portion of said shaft. An oxidant is injected into the hot gas from the plasma burner so as to form a gas mixture mainly comprising CO and H2, which gas mixture is then mixed with the other flow portion of the cleaned reaction gas in such a proportion that the temperature of the resulting reduction gas is suitable for the reduction of iron oxides in the shaft furnace. The reduction gas is then injected into the shaft furnace and passed upwardly. <IMAGE>

Description

SPECIFICATION Method and apparatus for manufacturing sponge iron The present invention relates to a method of, and apparatus for, manufacturing sponge iron.

Conventional processes for the manufacture of sponge iron in which a solid reducing agent, such as coke, is used as a reducing agent are primarily the following: a. The rotary furnace method in which pit coal is used together with the ore to be reduced, in an inclined rotary furnace. The difficulty with this method is that, mainly due to kinetic energy, it is necessary to work with relatively high temperatures, preferably 10000 C, which causes considerable problems with clogging and the accumulation of material in the reaction chamber.

b. The use of a shaft furnace combined with equipment for gassification of coal, which is based on partial combustion. The drawback with this known method is primarily the extremely high investment cost for the gassification equipment and also the exceptionally high energy consumption.

c. The method, such as is disclosed in Swedish Patent No. 73 04 332-5, of directly gassifying coal in solid form using a plasma generator The drawbacks of this method are that the supply of coal must be extremely accurately adjusted and for some grades of coal there are problems in handling the ash. Moreover, the gas produced has a hydrogen content which is lower than the ideal for reduction purposes.

It has now been found that the above difficulties and drawbacks with the known processes can be substantially eliminated according to the present invention. This invention is directed to a method and apparatus for manufacturing sponge iron by the continuous reduction of iron oxides in a shaft surface.The method of the present invention comprises the following steps: 1 ) removing reaction gas from a shaft furnace; 2) removing from the reaction gas substantially all CO2 and H2O; 3) dividing the reaction gas into at least two flow portions; 4) passing one of the flow portions to a gas generator comprising a gas generating shaft substantially filled with a solid reducing agent, a plasma burner arranged in the lower portion of said shaft, and means for injecting oxidant, heating the reaction gas with the plasma burner and injecting into the heated gas from the plasma burner an oxidant to form an intermediate gas mixture mainly comprising CO and H2; 5) maintaining the intermediate gas mixture at a temperature such that ash contained within the solid reducing agent forms a slag;; 6) forming a reduction gas by mixing the intermediate gas mixture with at least one of the other flow portions in such a proportion that the temperature of the reduction gas is suitable for the reduction of iron oxides in a shaft furnace; 7) injecting the reduction gas into the lower portion of a shaft furnace and passing the reduction gas upwardly through the shaft furnace to reduce iron oxides contained in the furnace and produce further reaction gas; and 8) removing reduced iron from the furnace.

In the present method, a reduction gas is passed counter-current to the iron oxides and consists primarily of CO and H2, the reduction gas being produced from recirculation gas, i.e. reaction gas leaving the shaft furnace, as well as an extra gas produced from solid reducing agent with the help of a plasma generator. The recirculation or reaction gas is first substantially cleaned CO2 and H2O, whereupon the gas thus cleaned is divided into at least two portions, one of which is passed to a gas or plasma generator. The gas generator comprises a gas generating shaft substantially filled with a solid reducing agent such as coke.A plasma burner is arranged in the lower portion of the generating shaft and an oxidant such as water and/or oxygen gas is injected into the hot gas flow leaving the plasma burner so that the oxidant is caused to react with the reducing agent to form a mixture of primarily CO and H2. The temperature level of the gas produced is kept within such a range that ash included in the solid reducing agent forms a slag. The hot CO-H2 mixture leaving the gas generator is mixed with at least some of the other cleaned recirculation or reaction gas in such a proportion that the temperature of the final gas mixture is suitable for the reduction process.

Preferably, the temperature level of the gas produced in the gas generating shaft, i.e. the intermediate gas mixture, is adjusted to a temperature of 1300-1 5000 C. It is also preferable, before the final gas mixture is provided as reduction gas to the lower part of the shaft furnace, for its temperature to be brought to within the range 700-1 OO00C by mixing it with the second flow portion.

The recirculation or reaction gas is preferably cleaned in a gas wash until its content of CO2 is below 2%.

The present invention also provides an apparatus for the manufacture of sponge iron comprising: 1) a shaft furnace for the reduction of iron oxides by a reduction gas mainly comprising CO and H2; 2) means connected to the upper portion of the shaft furnace for removing reaction gas from the furnace; 3) cleaning means for the removal of CO2 from the reaction gas; 4) means for separating the cleaned reaction gas into at least two flow portions; 5) a gas generator for receiving at least one of the flow portions, said gas generator comprising a gas generating shaft substantially filled with a solid reducing agent, a plasma burner arranged in the lower portion of the gas generating shaft, and means for injecting oxidant into gas heated by the plasma burner thereby to produce an intermediate gas mixture mainly comprising CO and H2;; 6) mixing means for the controlled mixing of the intermediate gas mixture with at least one of the other flow portions of the reaction gas to obtain a reduction gas; and 7) means for injecting the reduction gas into the lower portion of the shaft furnace.

Illustrative embodiments of the present invention will now be described, by way of example, with reference to the single figure of the accompanying drawing which illustrates diagrammaticaily a mode of carrying out the invention.

In the drawing, the reduction of chunks of iron oxide is performed in a reduction shaft furnace 1.

The chunks of iron oxide 2 are fed through a sluice valve 3 into the shaft furnace 1 and treated by a counter-current flow of a hot reduction gas consisting primarily of carbon monoxide and hydrogen gas introduced by blowing means at the lower section 4 of the shaft furnace 1. The sponge iron product is removed through an outlet 5 in the bottom 4 of the shaft furnace 1. The reaction gas, 30% to 50% of which has been reacted, is removed from the upper part of the shaft furnace 1 through an outlet 6.

The gas thus removed from the shaft furnace 1, besides containing from 50% to 70% unreacted CO and H2, also contains the reaction products CO2 and H2O. Since this gas still contains relatively high percentages of CO and H2, it is re-usable in the process. However, to enable it to be re-used as reduction gas, the content of CO2 and H20 should be reduced preferably to less than 5%. This is achieved by allowing the gas to pass through a wash (CO2/H20 wash) 7. When the gas passes through this wash, not only is it freed from the reaction products CO2 and H2O, but the actual washing process enables balancing of the gas quantity so that flaring of the gas can be avoided.

The wash 7 may contain mono-ethanolamine, for instance, as active substance and the content of CO2 in the gas can be suitably reduced to below 2% upon passage through the wash.

After the wash 7 the gas passes a compressor 8 to achieve a desirable pressure increase for the process and is then divided into at least two flow portions 9,10.

The flow portion 9, which is at room temperature, is introduced under control into a gas generator 11 where the necessary extra gas is generated from a solid reducing agent, preferably coke, and an oxidant, preferably water and/or oxygen gas. The gas flow 9 is used as plasma gas in gas generator 11 and the quantity of energy necessary for the gas generating process is supplied in a plasma burner 12. The gas generator 11 is substantially filled with a solid reducing agent, preferably coke. An oxidant, preferably water and/or oxygen gas, is supplied to the gas generator 11 through jets 13 so that it penetrates the hot gas flow leaving the plasma burner 12.

Extra reducing agent may optionally be added, for example in powder form through injector means 1 3a. This additional reducing agent is preferably coal dust having a particle size below 20 mesh and preferably below 100 mesh (U.S. Standard screen sizes). The hot gas flow from the plasma burner is thus caused to act upon the reducing agent and form CO and H2.

The supply of energy in the gas generator 11 is regulated so that the ash existing in the coal dust is melted to a slag 14 which can be removed from the lower part of the gas generator 11 in liquid or solid form via tapping means 1 6. Due to the composition of the ash, the temperature is preferably selected to be within the range 1300-1 5000 C.

The gas produced in the gas generator 11, besides containing CO and H2, may also contain sulphur from the reducing agent. This intermediate gas mixture is therefore caused to pass a sulphur filter 1 5 (e.g. a dolbmite filter) where the sulphur content is reduced to an acceptable level for the sponge iron process, preferably below 75 ppm.

According to an alternative embodiment of the invention, the sulphur filter 1 5 may be built into the gas generator itself, by providing the coke bed with suitable material for the purpose.

The gas leaving the sulphur filter 1 5 is at a temperature substantially in excess of that required for the sponge iron process and the temperature is therefore suitably lowered by using an adjustable mixer to mix in a suitable portion of the cold, untreated cleaned reaction gas in the flow portion 10 to yield a temperature suitable for the process -- e.g. from 7000 C, preferably 75O0C, up to 10000 C, more preferably about 8250C. While separate mixing means can be used to mix the gas from the gas generator and the flow portion 10, it is also possible to introduce part or all of the flow portion 10 into the top of the gas generator 11 such that the gas generator is used as a mixing chamber.

Substantial technical advantages are obtained utilizing the method and apparatus according to the invention. In this regard, the gas generation can take place at a temperature such that the ash forms slag which is easy to handle and which can be tapped off without causing clogging problems in the process. The hydrogen content in the reduction gas can be adjusted to an amount suitable for the reduction process by means of the washing process and subsequent injection of water and/or oxygen gas into the gas generator.

Furthermore the combination of gas washing and gas generation at increased temperatures offers superior possibilities of balancing the quantity of gas in the system and regulating the reduction temperature. At the same time, energy efficiency is achieved since the energy supplied by the gas or plasma generator is substantially completely used in the process (i.e. temperature adjustment is accomplished by adding cooler recycled reduction gas rather than by removing heat from the system).

Should difficulties arise in binding the ash from the solid reducing agent in a slag phase, additives affecting the properties (e.g. melting point, sulphur absorption, etc.) of the slag may be used, such as alkali compounds and chalk. These additives are preferably mixed with the solid reducing agent.

Claims

1. A method of manufacturing sponge iron by continuous reduction of iron oxides in a shaft furnace utilising recirculation furnace gases, which process comprises: 1) removing reaction gas from a shaft furnace; 2) removing from the reaction gas substantially all CO2 and H2O; 3) dividing the reaction gas into at least two flow portions; 4) passing one of the flow portions to a gas generator comprising a gas generating shaft substantially filled with a solid reducing agent, a plasma burner arranged in the lower portion of said shaft, and means for injecting oxidant, heating the reaction gas with the plasma burner and injecting into the heated gas from the plasma burner an oxidant to form an intermediate gas mixture mainly comprising CO and H2;; 5) maintaining the intermediate gas mixture at a temperature such that ash contained within the solid reducing agent forms a slag; 6) forming a reduction gas by mixing the intermediate gas mixture with at least one of the other flow portions in such a proportion that the temperature of the reduction gas is suitable for the reduction of iron oxides in a shaft furnace; 7) injecting the reduction gas into the lower portion of a shaft furnace and passing the reduction gas upwardly through the shaft furnace to reduce iron oxides contained in the furnace and produce further reaction gas; and 8) removing reduced iron from the furnace.

2. A method according to claim 1 wherein the oxidant is water or oxygen.

3. A method according to claim 1 or 2, wherein, in step 5), the intermediate gas mixture is maintained at 13000 to 1 5O00C.

4. A method according to claim 1,2 or 3, wherein, in step 6), the intermediate gas mixture is mixed with at least one other flow portion in such a proportion that the temperature of the resulting reduction gas prior to injection into the shaft furnace is 7000 to 10000C.

5. A method according to claim 4 wherein the temperature of the reduction gas prior to injection into the shaft furnace is approximately 8250C.

6. A method according to any one of the preceding claims, wherein, in step 2), CO2 and H20 is removed from the reaction gas by means of a gas wash until the content of CO2 is less than 2%.

7. A method according to any one of the preceding claims, wherein the reducing agent is coke.

8. A method according to any one of the preceding claims, wherein additional reducing agent is injected into the heated gas from the plasma burner.

9. A method according to claim 8 wherein the additional reducing agent is coal dust having a particle size below 20 mesh.

10. A method according to claim 9 wherein the particle size is below 100 mesh.

11. A method according to any one of the preceding claims, wherein the intermediate gas mixture is passed through a sulphur filter.

12. A method according to claim 1 substantially as hereinbefore described with reference to the Figure of the accompanying drawing.

1 3. Apparatus for the manufacture of sponge iron by the continuous reduction of iron oxides comprising: 1) a shaft furnace for the reduction of iron oxides by a reduction gas mainly comprising CO and H2; 2) means connected to the upper portion of the shaft furnace for removing reaction gas from the furnace; 3) cleaning means for the removal of CO2 from the reaction gas; 4) means for separating the cleaned reaction gas into at least two flow portions;; 5) a gas generator for receiving at least one of the flow portions, said gas generator comprising a gas generating shaft substantially filled with a solid reducing agent, a plasma burner arranged in the lower portion of the gas generating shaft, and means for injecting oxidant into gas heated by the plasma burner thereby to produce an intermediate gas mixture mainly comprising CO and H2; 6) mixing means for the controlled mixing of the intermediate gas mixture with at least one of the other flow portions of the reaction gas to obtain a reduction gas; and 7) means for injecting the reduction gas into the lower portion of the shaft furnace.

14. Apparatus according to claim 13, wherein the cleaning means comprises a CO2 wash.

1 5. Apparatus according to claim 14, wherein the CO2 wash contains mono-ethanolamine as the active agent.

1 6. Apparatus according to claim 13, or 15, including a compressor located between the cleaning means and the means for separating the cleaned reaction gas.

1 7. Apparatus according to any one of claims 1 3 to 16, wherein the gas generator is provided with means for removing slag.

1 8. Apparatus according to any one of claims 13 to 17 including a sulphur filter between the gas generator and the mixing means.

1 9. Apparatus according to any one of claims 13 to 1 7, wherein a sulphur filter is incorporated in the gas generator.

20. Apparatus according to any one of claims 13 to 19, including means for injecting additional solid reducing agent in powder form into the heated gas from the plasma burner.

21. Apparatus according to claim 20, wherein the means for injecting additional solid reducing agent has an injection area immediately in front of the plasma burner.

22. Apparatus according to any one of claims 13 to 21, wherein the means for injecting oxidant has an injection area immediately in front of the plasma burner.

23. Apparatus according to claim 1 3 substantially as hereinbefore described with reference to the Figure of the accompanying drawings.

-24. Sponge iron when manufactured by a method as claimed in any one of claims 1 to 1 2 or in apparatus as claimed in any one of claims 13 to 23.