KR19990077053A - Process for producing sponge iron by direct reduction of iron oxide-containing materials - Google Patents

Abstract

In the process for producing iron-iron-containing material by direct reduction, the synthesis gas is mixed with the top gas formed in the direct reduction of the iron oxide-containing material and used as a CO- and H ₂ -containing reducing gas to directly reduce and The iron oxide containing material is heated to the reduction temperature.

In order to save energy in an economically efficient manner, especially during steelmaking, direct reduction is carried out as follows:

In addition to reducing gases, gases containing carbon-containing gases such as natural gas or high-grade hydrocarbons are used for the reduction,

The iron oxide-containing material is exposed to reducing gas and additionally supplied carbon-containing gas for a predetermined period of time beyond the period necessary for complete reduction,

The CO / CO ₂ ratio in the reducing gas is adjusted in the range of 2 to 5, preferably at least 2.5.

Description

Process for producing sponge iron by direct reduction of iron oxide-containing materials

Processes of this type are known, for example, from USA-A-2,752,234, US-A-5,082,251 and EP-A-0 571 358, WO 96/00304 and DE-B-24 05 898.

EP-A-0 571 358 is not limited to the reduction of spectroscopy through a strong endothermic reaction with H ₂ according to the following formula,

Fe ₂ O ₃ + 3 H ₂ = 2 Fe + 3 H ₂ O-ΔH

It is known to carry out further by endothermic reaction with CO by following Formula.

Fe ₂ O ₃ + 3CO = 2 Fe + 3CO ₂ + ΔH

Thus, the associated operating costs, in particular energy costs, can be significantly reduced.

The sponge iron produced by the direct reduction of the iron oxide-containing material according to the prior art generally has a carbon content of 1 to 1.5%. However, in order to further process the barbed iron, it is desirable to increase the carbon content so that energy can be saved when melting the barbed iron and in the subsequent refining process without adding (carbonizing) additional carbon.

The present invention relates to a process for the production of spongy iron by direct reduction of iron oxide-containing materials, wherein a synthesis gas, preferably a modified natural gas, is mixed with the top gas formed in the direct reduction of iron oxide-containing materials, and It is used as CO- and H ₂ -containing reducing gases for heating the reducing and iron oxide containing materials to the reducing temperature.

1 is a schematic diagram of a plant for carrying out a process according to the invention.

Therefore, it is an object of the present invention to modify the process according to the above-mentioned kind so as to increase the carbon content of sponge iron, preferably to represent 2-4%, in particular 2.5% or more. However, this is likely to result in a slight increase in energy costs-albeit little-and thus incurs a little extra cost compared to the conventional process of producing sponge iron, and the energy savings in the refining process are not compensated, The economic effects of the steel prototype production process are the most complete.

In the present invention, the above object is characterized by:

In addition to reducing gas, carbon-containing gas such as natural gas or gas with high hydrocarbon content is used for the reduction,

The iron oxide containing material is exposed to reducing gas and additionally supplied carbon-containing gas for a predetermined period of time exceeding the period necessary for complete reduction,

The CO / CO ₂ ratio in the reducing gas is achieved by combining what is adjusted to 2 to 5, preferably 2.5 or more, especially 3 or more.

In WO 96/00304 it is known to reduce or prevent "metal dust" by adjusting the specific CO / CO ₂ ratio in the so-called range of 1 to 3, but between 1.5 and 2, which is itself present. It does not help to achieve the object of the invention.

The production of sponge iron having a carbon content of 0.5 to 2.5% is already known from WO-A-93 / 14228; In particular, in this known process, a small amount of natural gas directly blown into the fluidized bed reactor is adopted to adjust carbon. However, this method alone is not so effective because the complete decomposition of natural gas is not certain at the reduction temperature for direct reduction.

In US-A-5,137,566, iron ore is known to be produced from highly concentrated iron carbide by reducing gas and carbonization gas, which is converted to a longer residence time due to time sensitivity in the iron carbide forming process. Increasing the residence time of iron oxide-containing materials in direct reduction significantly reduces productivity, i.e. significantly reduces the output of reducing materials per unit. Thus, this method is expensive and the iron carbide thus produced is only used additionally in the iron making process, while the object to be achieved in the present invention is to increase the carbon content of all the sponges used in iron making, i.e. Spongy iron with high carbon content is not only used additionally in steelmaking but also constitutes the basic material itself.

Processes of this kind are also known from US Pat. No. 5,437,708. Iron carbide is produced by reducing gas in a direct shaft shaft furnace. In addition, it is not desirable to extend the residence time of the iron oxide-containing material in the reduction reactor. The residence time ranges from 9 to 15 hours, which leads to a significant decrease in productivity-as described above.

In US-A-Re-32,247 it is known to convert iron oxide containing material to iron carbide in the first stage and to produce steel directly with iron carbide in the second stage. In this known method, a hydrogen-containing reducing gas is adopted to reduce and form iron carbide with a carbon-containing material. One disadvantage associated with this method is the complete conversion of iron to iron carbide, which also entails high energy costs (the consumption of carbonaceous materials in the direct reduction is significantly higher).

In the present invention, in addition to reducing gas, high hydrocarbons, C ₃ H ₈ and more are further used as direct reducing carbon-containing gases, and hydrocarbons of this type are easily decomposed at relatively low temperatures to increase carbon content. The advantage is that it shows sufficient effect. In the present invention, such a hydrocarbon provided in addition to the reducing gas is sufficient in a small amount.

Preferably, the process according to the invention, wherein the direct reduction takes place in two or more connected fluidized bed reactors and transfers natural gas or high hydrocarbons into the fluidized bed reactors last arranged in the flow direction of the iron oxide containing material, They are passed through the reactor and then through another fluidized bed reactor in the reverse direction of the iron oxide containing material. This is a particularly high-efficiency method performed by combination, so that even if the time for which the iron oxide-containing material is exposed to the reducing gas is increased, there is almost no decrease in productivity.

In a preferred variant, the increase in time to directly reduce the iron oxide containing material results in a direct reduction in at least one fluidized bed reactor in which the bed height of the fluidized bed is adjusted to be higher than the minimum fluidized bed height required to achieve full reduction of the iron oxide containing material. Can be realized in such a way that the substance to be reduced is exposed to the reducing gas and additionally supplied carbon-containing gas in excess of the time necessary for complete reduction, or that the output of direct reduction is the minimum output required for complete reduction of the iron oxide-containing material. Reduction may occur in comparison with.

Another preferred measure of the process according to the invention is characterized in that the reduction is carried out with an increased specific amount of reducing gas as compared to the specific minimum amount of gas required for full reduction of the iron oxide containing material.

An essential process step to increase the carbon content of sponge iron is by changing the ratio of steam to natural gas in the supply of the reformer, suitably in the range of 3 to 4.5, in particular about 3.5, in natural gas in reforming operations. the adjustment of the operating characteristics of a reformer which serves to produce synthesis gas from to adjust the CO / CO ₂ ratio.

The ratio of CO / CO ₂ is adjusted by mixing a portion of the reformed gas supplied to the CO conversion directly with the top gas, i.e. without CO conversion, to increase the H ₂ content after being produced from steam and natural gas in the reformer. It is preferable that the amount of reformed gas mixed directly is variable.

In another preferred embodiment, CO ₂ is removed, preferably CO ₂ is cleaned before using both reformed gas and top gas as reducing gas, and the ratio of CO / CO ₂ reduces at least some volume of the reformed gas to reducing gas. And by mixing directly with to prevent the removal of CO ₂ .

Further, CO / rate of CO ₂ is the reformed gas and the top gas both to remove the CO _2, and preferably be adjusted to clean the CO _2, the ratio of CO / CO ₂ is a reducing gas at least part of the volume of the top gas By direct mixing with to prevent removal of CO ₂ . In addition, the degree of removal of CO _2, may be changed such that remain in the gas to be bar early part of the CO ₂ cleaning.

The residence time of the iron oxide-containing material is preferably extended to 40 to 80 minutes, preferably 40 to 60 minutes.

In order to adjust the specific carbon content of the sponge iron, it is preferable that the H ₂ S content of the reducing gas can also be used.

Next, a process according to the present invention will be described in detail with reference to the drawings showing a process diagram according to a preferred embodiment.

The equipment for carrying out the process according to the invention comprises fluidized bed reactors 1 to 4 connected in series, in which the first fluidized bed reactor 1 is loaded with iron oxide-containing material such as spectroscopy through ore feed pipe 5 It is heated to a reduction temperature (ie, pre-reduction) and then transferred from the fluidized bed reactor to the fluidized bed reactor via transfer tube 6. The completely reduced material (sponge iron) becomes hot briquettes in the briquetting plant 7. If necessary, reduced iron is prevented from reoxidation during briquetting by an inert gas system, not shown.

Prior to charging spectroscopy into the first fluidized bed reactor 1, ore preparations such as drying and sieving, not shown in detail, are made.

The reducing gas is transferred from the fluidized bed reactor 4 to the fluidized bed reactors 3 to 1 in the reverse flow direction of the ore flow, and is discharged as top gas through the top gas discharge pipe 8 in the fluidized bed reactor 1 arranged last in the gas flow direction. Cooled and cleaned in scrubber 9.

The reducing gas is supplied through the pipe 11 and produced by reforming the desulfurized natural gas in the reformer 10 in the desulfurization facility 12. Basically, the gas emitted from the reformer and formed of natural gas and steam is composed of H ₂ , CO, CH ₄ , H ₂ O and CO ₂ . This reformed natural gas is supplied to several heat exchangers 14 through reformed gas pipe 13 where it is cooled to 80 to 150 ° C. to condense the gas into water.

The reformed gas pipe 13 communicates with the top gas discharge pipe 8 after the top gas is compressed by the compressor 15. The mixed gas thus formed passes through the CO ₂ scrubber 16, whereby CO ₂ is removed and H ₂ S is also removed. Instead of a CO ₂ scrubber, different types of CO ₂ removal equipment, for example pressure-swing adsorption equipment, may also be arranged. The mixed gas can be used as the reducing gas. The reducing gas, which has passed through the reducing gas supply pipe 17, is heated to a reducing gas temperature of about 800 ° C. in a gas heater 18 connected downstream of the CO ₂ scrubber, and supplied to the fluidized bed reactor 4 arranged in the gas flow direction at the front, where spectroscopy and Reaction produces iron directly reduced. The fluidized bed reactors 4 to 1 are connected in series, and the reducing gas passes through the connecting tube 19 from the fluidized bed reactor to the fluidized bed reactor, that is, in the countercurrent direction of the iron oxide containing material.

Part of the top gas is sensitized in the gas circulation systems 8, 17 and 19 to prevent the addition of inert gases such as N ₂ . The scoured top gas is supplied to the gas heater 18 which heats the reducing gas through the branch pipe 20 and burned there. Energy that may be lacking is supplemented with natural gas supplied through supply line 21.

The detectable heat of reformed natural gas and reformer combustion gas exiting Reformer 10 is used in a recovery heat exchanger 22 to preheat the natural gas that has passed through the desulfurization plant 12 to generate steam for reforming, And the combustion air supplied to the gas heater 18 through tube 23, if desired, also the reducing gas, is also preheated. The combustion air supplied to the reformer 10 through the tube 24 is also preheated.

As one of the main measures taken to increase the carbon content of the barbed iron, the predetermined CO / CO ₂ ratio is adjusted to a so-called 2 to 5 range, preferably 2 to 3 range. In a first variant according to the invention, this is achieved by varying the ratio of steam to natural gas supplied to Reformer 10, wherein the ratio of steam to natural gas is preferably adjusted to a value in the range of 3-5, in particular 3.5. . Control valves, ie control valves 25 and 26, serve this purpose and can be adjusted or controlled respectively from the measuring station 27 which measures the CO / CO ₂ ratio of the reducing gas.

As is apparent from the figure, the reformed gas, at least part of its volume, is fed to the CO conversion 28 and the H ₂ content is increased before being fed to the CO ₂ scrubber 16. The remaining volume of the reformed gas is directly mixed with the top gas by bypassing the CO conversion 28 via the bypass tube 29. Therefore, it is possible to adjust the CO content to a desired value, whereby the desired CO / CO ₂ ratio can also be adjusted by this treatment, thereby increasing the carbon content.

In addition, the predetermined CO / CO ₂ ratio can be adjusted by directly injecting a portion of the volume of the top gas into the reducing gas supply pipe 17 through the bypass pipe 30 which avoids the CO ₂ scrubber. In addition, a portion of the volume of the reformed gas may also be directly supplied to the reducing gas supply pipe 17 through the bypass pipe 31 branched from the reformed gas pipe 13 bypassing the CO ₂ scrubber 16.

The bypass tubes 29, 30 and 31 are all equipped with adjustments, i.e. control valves 32, 33 and 34, which are controlled according to the measured value of the CO / CO ₂ ratio of the reducing gas taken at the measuring station 27.

The desired CO / CO ₂ ratio of the reducing gas can also be adjusted by passing all of the top gas and both the reforming gas through a CO ₂ scrubber, but adjusting the scrubber to the wash level results in the CO ₂ portion (also H ₂ S portion) being CO _2. It will remain in the gas exiting the scrubber. This has the advantage that auxiliary means such as bypass tubes 29, 30 and 31, including valves 32, 33 and 34, do not have to be disposed of, but the total amount of gas, i.e. both the top gas and the reforming gas, must pass through the CO ₂ scrubber. And thus the scrubber should have a size for this amount.

The top gas from the fluidized bed reactor 1 contains H ₂ S in the range from 40 to 140 ppmV, depending on the sulfur content of the ore. H ₂ S gas is formed while the spectrometer is heated to the reduction temperature or while the spectrometer is preliminarily reduced.

As the H ₂ S content of the reducing gas increases, the carbon content of the sponge iron also increases, so H ₂ S is not completely washed from the top gas by the CO ₂ scrubber, but the desired ratio of H ₂ S for the reducing gas It is especially preferable when attention is paid to the supply of reducing gas from the top gas. In this case, this can be realized by adjustment from the top gas discharge pipe 8 bypassing the CO ₂ scrubber, that is, bypass pipe 30 branching through the control valve 33 to communicate with the reducing gas supply pipe 17. The control valve 33 is adjustable so that the H ₂ S content is present in the reducing gas in the range of 20 to 40 ppmV, preferably about 25 ppmV. In this case, the control valve is preferably operated via the H ₂ S measuring means 35.

The foregoing measures of adjusting the desired CO / CO ₂ ratio of the reducing gas, individually or in combination, several or all of them in such a way that the most desirable process variants can be chosen as a function of the ore component for each operating condition. Can be taken.

In the present invention, the CO / CO ₂ ratio is characterized by the additional supply of carbonaceous gas, such as natural gas or preferably C ₃ H ₈ or higher hydrocarbons, in addition to the reducing gas into the fluidized bed reactor and the iron oxide containing material to the reducing gas during direct reduction. Adjusted in conjunction with the increase in the time of exposure.

The additionally supplied carbon-containing gas may be mixed with the reducing gas prior to feeding it into the fluidized bed reactor last arranged in the direction of flow of the iron oxide containing material, or as shown in the fluidized bed reactor 4 via a separate tube 21. Blown into.

The increase in exposure time to the reducing gas and additionally supplied carbon-containing gas of the iron oxide-containing material may be a function of the desired final carbon content of the sponge iron. In either case, the iron oxide containing material is exposed to the reducing gas as well as the additionally supplied carbon containing gas in excess of the time required for complete reduction.

Example I

Dry spectroscopy is charged 100t per hour in a spectroscopic direct reduction facility as described above, which is designed to produce 70t of spongy iron per hour. The components of the spectroscopy are as follows.

Hematite 94.2%

Gangue 2.2%

Sulfur 0.02%

The top gas formed in the direct reduction is mixed with 79,000 Nm ³ per hour and 54,000 Nm ³ reformed cooling natural gas and passed through a CO ₂ scrubber 16 where CO ₂ and most of the sulfur are removed.

The chemical composition of the reformed natural gas and saw gas is shown in the following table (volume%).

Reformed natural gas Topgas CH ₄ 3.0 31.7 CO 10.5 6.1 CO ₂ 10.0 6.0 H ₂ 63.0 51.8 H ₂ O 13.5 0.70 N ₂ 0.0 3.70 H ₂ S 0.0 78.0 ppmV

The temperature of the reformed natural gas is 120 ° C and the top gas is 100 ° C. The gas mixture exiting the CO ₂ scrubber is fed to a direct cooler 25 and cooled to 68 ° C. The components of the cooled gas mixture are as follows.

CH ₄ 21.8 CO 9.8 CO ₂ 1.3 H ₂ 63.0 H ₂ O 1.7 N ₂ 2.4 H ₂ S 5 ppmV

This gas mixture is mixed with 79,000 Nm ³ of top gas blown into the reducing gas supply pipe 17 via the bypass pipe 26 but not through the CO ₂ scrubber 16. This mixing produces a reducing gas having a temperature of 75 ° C. and having the following components fed to gas heater 18 and subsequently to the fluidized bed reactors 1-4.

Reducing gas CH ₄ 25.2 CO 8.0 CO ₂ 2.9 H ₂ 59.7 H ₂ O 1.4 N ₂ 2.8 H ₂ S 30 ppmV

In addition, 3,400 Nm ³ of natural gas per hour is fed to the fluidized bed reactor 4 via tube 21 '.

The residence time in the bottom fluidized bed reactor 4 is about 40 minutes.

The degree of metallization (Fe _met / Fe _tot ) of sponge iron is about 92%, the carbon content is about 2.5%, and the maximum 5%.

Example II

In the following table, the sponges containing 1.1% carbon produced according to the prior art and the sponges with an increased carbon content of 2.5% are compared.

Ore Component Weight% Product component weight% Reducing gas component volume% 1.1% C 2.5% C 1.1% C 2.5% C Fe _TOTAL 65.57 Fe ₂ O ₃ 93.75 FeO 0 Fe 0 Gangue 1.8 C 0 MgO 0.00 S 0.02 93.41 1.62 9.64 84.79 2.68 1.1 0.15 0.02 89.83 3.26 11.6 80.87 1.6 2.5 0.15 0.02 H ₂ CO H ₂ O CO ₂ CH ₄ N ₂ 63.34 6.81 1.48 3.3821.8 3.19 60.46 6.32 1.4 2.67 25.27 3.9

To produce a sponge iron containing 1.1% carbon without blowing a gas to the fluidized bed reactor 4 as a bottom layer, to produce sponge iron with a 2.5% carbon is blown into the natural gas 3,400Nm ₃ per hour do. The residence time in the lowest fluidized bed reactor 4 is 33 minutes for low carbon content and 37.5 minutes for carbon content with increased carbon content. The ratio of CO / CO ₂ is 2 in the first case and 2.4 in the second case. The chemical composition of natural gas adopted for the production of reducing gas is shown in the following table.

Natural gas volume% CH ₄ C ₂ H ₆ C ₃ H ₈ CO ₂ C ₄ 81.42 7.75 1.9 7.78 1.15

Claims (15)

In the process of producing iron-containing materials by direct reduction, the synthesis gas, preferably modified natural gas, is mixed with the top gas formed in the direct reduction of the iron oxide-containing material, and CO- and H ₂ -containing reduction As a gas, a process of directly reducing and heating the iron oxide-containing material to a reduction temperature, In addition to reducing gas, carbon-containing gas such as natural gas or gas having high-grade hydrocarbons is used for the reduction, The iron oxide-containing material is exposed to reducing gas and additionally supplied carbon-containing gas for a predetermined period of time beyond the period necessary for complete reduction, The CO / CO ₂ ratio in the reducing gas is adjusted in the range of 2-5, preferably 2.5 or more. Sponge iron production process, characterized in that. The process according to claim 1, wherein in addition to the reducing gas, C ₃ H ₈ or higher high quality hydrocarbons are further used for direct reduction. The method of claim 1 or 2, wherein the direct reduction is carried out in two or more sequentially connected fluidized bed reactors, and the natural gas or high-grade hydrocarbons are transferred into a fluidized bed reactor arranged last in the flow direction of the iron oxide containing material. And after passing through the reactor, passing through another fluidized bed reactor in the countercurrent direction of the iron oxide containing material. The method of claim 1, wherein the direct reduction is carried out in at least one fluidized bed reactor in which the bed height of the fluidized bed is adjusted to be higher than the minimum bed height required for full reduction of the iron oxide containing material. And the substance to be exposed to the reducing gas and additionally supplied carbon-containing gas in excess of the time required for complete reduction. The process according to any one of claims 1 to 4, wherein the direct reduction yield is reduced compared to the lowest yield required for full reduction of the iron oxide containing material. The process according to any one of claims 1 to 5, wherein the reduction is performed at a specific reduced gas amount increased compared to a specific minimum gas amount required for full reduction of the iron oxide-containing material. The method according to any one of claims 1 to 6, wherein the CO / CO ₂ ratio is a function of producing the syngas from natural gas in a reforming operation by changing the ratio of steam to natural gas supplied to the reformer 10. And adjusting the movable characteristics of the reformer (10). Process according to claim 7, characterized in that the ratio of steam to natural gas is adjusted to a value in the range from 3 to 4.5, in particular 3.5. The reforming gas according to any one of claims 1 to 8, wherein the CO / CO ₂ ratio is produced from the reforming gas supplied from the vapor and natural gas of the reformer 10 and then fed to the CO conversion to increase the H ₂ content. Wherein a portion of the volume is adjusted by mixing with the top gas directly, i.e. without converting CO, and the amount of reformed gas directly mixed is variable. 10. The process according to any one of claims 1 to 9, wherein both the reformed gas and the top gas are CO ₂ removed, preferably CO ₂ is washed, and CO ₂ ratio of CO ₂ is removed before being used as reducing gas. Wherein the adjustment is made while preventing the removal of CO ₂ by at least some volume of the reformed gas to be mixed directly into the reducing gas. The reformed gas and the saw gas are both CO ₂ removed, preferably CO ₂ washed, and the adjustment of the CO / CO ₂ ratio is directly directed to the reducing gas. At least a portion of the volume of saw gas to be mixed while preventing the removal of CO ₂ . 12. The process according to any one of claims 1 to 11, wherein both the reformed gas and the top gas are CO ₂ removed, preferably CO ₂ washed, and the CO / CO ₂ ratio is reduced before being used as reducing gas. adjustment step, characterized in that removal is carried out by changing the amount of CO ₂ remains in the gas to be cleaned is part of a-called CO _2. The process according to any one of claims 1 to 12, wherein the residence time of the iron oxide-containing material is extended to 40 to 80 minutes, preferably 40 to 60 minutes. The process according to any one of claims 1 to 13, wherein the adjustment of the specific carbon content in the surface iron is carried out by adjusting the H ₂ S content in the reducing gas. The process according to any one of claims 1 to 14, wherein the reducing gas is adjusted to have a CO / CO ₂ ratio of more than 3.