DE10336676B4 - Process and plant for the reduction of iron oxide-containing solids - Google Patents

Abstract

method for the reduction of iron oxide-containing solids, in particular iron ore, in the fine-grained Solids in a preheating and / or calcination stage (2, 9) heated and at least partially calcined in one of the preheating and / or calcining step (2, 9) downstream of the first reactor (14) prereduced with fluidized bed and reduced in a second reactor (16) with fluidized bed and in a second reactor (16) downstream Brikettierungsstufe (20) at a temperature of over 500 ° C briquetted be characterized in that the preheating and / or calcination (2, 9) together with the iron oxide-containing solids magnesite is added, which in the preheating and / or calcination (2, 9) at least partially calcined to magnesium oxide, wherein more than 50% of the iron oxide-containing solids the preheating and / or calcination stage (2, 9) added magnesite a grain size between 1.25 mm and 3 mm.

Description

The The present invention relates to a method and a plant for Reduction of iron oxide-containing solids, especially iron ore, in the fine-grained Solids in a preheating and / or calcining stage heated and at least partially calcined in one of the preheating and / or Calcination stage downstream first reactor with fluidized bed pre-reduced and reduced in a second reactor with fluidized bed and in a second reactor downstream Brikettierungsstufe at a temperature of over 500 ° C briquetted become.

From the DE 44 10 093 C1 is such a method for the direct reduction of iron ore to sponge iron (DRI) is known in which in a first reactor with circulating fluidized bed prereduction takes place at temperatures between 550 and 650 ° C. In a downstream second reactor with a classical fluidized bed, in which as a reducing agent heated, hydrogen-containing gas is introduced for fluidization, the solids are further reduced, so that the product, for example, has a degree of metallization of over 90%.

At the Transport of sponge iron (DRI) is it for security reasons, eg. because of the fire danger, and because of the better handling (dust development) usual that the iron is briquetted. This briquetting takes place afterwards to the reduction of the iron, whereby the still hot iron sponge during the Supply to the briquetting plant mostly cools. To increase the strength of Briquettes it is desirable that the briquetting if possible high temperatures of, for example, about 700 ° C takes place. At this temperature points the fine-grained Sponge iron, however, has a very poor flow behavior, causing the Briquetting is difficult. To the flow behavior of sponge iron to improve and to ensure a good processability, For example, about 0.5% by weight of magnesium oxide is added to the sponge iron prior to briquetting (MgO) through a pressure lock upstream of the briquetting plant added. Magnesium oxide has no measurable negative impact on the strength or stability the iron sponge briquettes, but it is because of elaborate treatment steps expensive, so that also increase the cost of iron sponge briquettes. moreover Magnesium oxide is hygroscopic and very fine-grained, usually with a particle size below 100 microns, so that it is difficult to store and use.

A process for the production of sponge iron from oxidic iron ores is also known from DE-OS 1 458 756 known, in which the reduction is to take place at the highest possible temperatures. In order to avoid an effect known at such high temperatures during the reduction, known as "bogging" or "fouling", in which the solids stick together or weld into agglomerates, so that the fluidized bed settles in the reduction reactor, the addition of about 0, 05 wt .-% very finely ground oxides or carbonates of magnesium proposed. These additives should be as fine-grained and preferably have a particle size of significantly less than 297 microns, especially less than 44 microns. However, this also causes the problems described above in the storage or use of the additives. In addition, it is necessary in this method to add the additives to the iron ore, for example via a pressure lock before the reduction stage. This increases the investment costs for a system for carrying out the method. Due to the lower temperatures in the reduction stage, a comparatively poor calcination is achieved in this known method, when the addition of magnesium carbonates in the reduction stage takes place. This can be compensated only by longer residence times, which are also undesirable. On the other hand, these problems do not occur when magnesium oxide is added to the reduction stage instead of magnesium magnesium. However, this is associated with the above-mentioned disadvantages of the high cost and poor handleability of the magnesium oxide.

task The present invention is therefore a method and a To provide a plant for the reduction of iron oxide-containing solids, which is characterized by an improved flow behavior of the product and a lower energy consumption.

This object is achieved by a method of the type mentioned, in which the preheating and / or calcination is added together with the iron oxide solids magnesite (MgCO ₃ ), which is at least partially calcined in the preheating and / or calcination to magnesium oxide , Magnesite is much cheaper available compared to magnesium oxide, so that the costs for the production of briquettes from sponge iron can be reduced. Since the magnesite is at least partially calcined to magnesium oxide, the flowability of the sponge iron prior to briquetting is improved. The briquetting can therefore also take place at high temperatures, where usually the flow behavior of the sponge iron is deteriorated. By this hot briquetting is opposite cold briquetting at lower temperatures increases the strength of the briquettes. According to the invention, more than 50% of the magnesite added together with the iron oxide-containing solids of the preheating and / or calcining stage has a particle size of between 1.25 mm and 3 mm. The storage and the handling of the magnesite is thereby improved, without the fluidity of the sponge iron is deteriorated. During the course of the process, the relatively coarse-grained magnesite or magnesium oxide is comminuted in the preheating and / or calcining stage or in the downstream reactors. As a result, the ability to use the Magne is siumoxids increased in the briquetting without deteriorating the handling of the additives.

There the magnesite together with the iron oxide-containing solids in the preheating and / or calcining stage heated is, the heat must be in the two reactors for the reduction of the iron oxide-containing solids no over a strong heating of the reducing agent, for example hydrogen, be ensured. The energy efficiency of the endothermic reduction process can therefore be increased by the fact that the iron oxide-containing Solids and the magnesite already in the preheating and / or calcination stage are heated to the temperature required for the reduction.

By the common supply of iron oxide solids and magnesite into the preheating and / or calcination, it is not necessary additional Magnesium oxide in front of a pressure lock upstream of the reactors add to the solids. This also eliminates the investment costs for the previously common separate supply of magnesium oxide. Often in the magnesite impurities, such as iron oxide and / or limestone, present the further processing do not bother, but for the further processing of iron are sometimes even desirable.

The Energy efficiency of the method according to the invention can thereby be further increased, that the magnesite together with the iron oxide-containing Solids in the preheating and / or calcination at temperatures of 400 to 1250 ° C, in particular at 540 to 1000 ° C is calcined. According to the invention of Temperature range in the calcination also between 1000 and about 1250 ° C lie. Due to the particularly high compared to the known methods Temperatures in the preheating and / or calcination stage needs the heat input for the endothermic reduction of iron oxide with hydrogen does not have a strong heating usually Hydrogen used as a reducing agent.

To a preferred embodiment of Invention have more than 50%, preferably about 90%, of the common with the iron oxide-containing solids of the preheating and / or calcination stage added magnesite a grain size between 300 microns and 3 mm, in particular between 400 microns and 1 mm up. For the method according to the invention is suitable also magnesite with a grain size between 1.25 and 3 mm.

One improved flow behavior and a good processability of sponge iron, especially in the Brikettierungsstufe, is achieved according to the invention, if the iron oxide-containing Solids before and / or during the supply in the preheating and / or Calcination stage between 0.1 and 5 wt .-%, in particular about 0.5 Wt .-%, Magnesite is added. The from the second reactor of Fed Brikettierungsstufe For example, solids contain between 0.1 and 5% by weight, in particular approximately 0.5 wt .-%, magnesium oxide, which by the calcination of magnesite in the preheating and / or Calcining stage has emerged. To the processability of in the second reactor reduced solids in the briquetting stage can continue to improve this together with the magnesium oxide in one of the Brikettierungsstufe upstream heat stage to a temperature of over 600 ° C, in particular about 700 ° C, heated and hot in the Briquetting be introduced. The for the forming in the briquetting step required energy can be further reduced.

Around the formation of agglomerates in the reactors during the reduction largely To inhibit, the iron oxide-containing solids in the first and second reactor, preferably at temperatures below 700 ° C, in particular at about 630 ° C, reduced. At these temperatures, the state of the art known "bogging" - effect not on. That the Preheating and / or calcination stage supplied Magnesite is therefore not already in the reduction stage for Requires formation of magnesium oxide, but provides the fluidity of sponge during the supply to a briquetting plant safely. The degree of fluidization the iron oxide-containing solids in the first and second reactors is therefore during The reduction is particularly high, allowing a good heat exchange and a good reaction with the reducing agent can take place. The iron oxide-containing solids are in the first and the second reactor to metallic iron with a degree of metallization from above 75%, in particular of over 90% reduced.

According to the invention, magnesite having a grain size of between 1.25 mm and 3 mm is used as an aggregate which, in a process for the production of iron sponge briquettes, is used together with iron oxide-containing solids to increase the flowability of hot sponge iron during the feed from a reduction stage to a briquetting stage.

The The problem underlying the invention is further with a plant for the reduction of iron oxide-containing solids with a preheating and / or Calcination, a first and a second, each as a fluidized bed reactor trained reactor and a Brikettierungsstufe thereby solved that the preheating and / or calcining step means for simultaneous continuous or discontinuous introduction of iron oxide-containing solids and magnesite, and that the briquetting step is a heating step upstream. By the joint introduction of iron oxide-containing Solids and magnesite are these in the preheat and / or Heated calcining stage, so that for the subsequent endothermic reduction of the iron oxide required Heat does not have a strong Heating of the reducing agent must be ensured. The the Brikettierungsstufe upstream heat stage allows it In addition, that taken from the reduction reactors sponge iron together with magnesium oxide obtained from magnesite on a for the Briquetting optimum temperature of, for example, about 700 ° C are heated can. The reduction can be done at comparatively low temperatures so that the tendency of the iron oxide to form agglomerates is largely prevented.

The two reactors connected in series, in which the reduction takes place, for example Be fluidized bed reactors with a stationary fluidized bed. Around improved heat and mass transfer conditions during to allow the reduction However, it is preferred if at least one of the two reactors a fluidized bed reactor with a circulating fluidized bed or an annular fluidized bed.

To a preferred embodiment of Invention, the first and / or the second reactor, a plurality of nozzles or inlets for supplying a heated, gaseous Reducing agent, such as hydrogen, on. The reducing agent can at the same time for the fluidization of the reduced in the reactors Be used solids.

The Energy efficiency of the system according to the invention can be improved that the preheating and / or calcining a first preheating, for example. A Venturi preheating, with a downstream first cyclone and a second preheating (calcination stage) having a downstream second cyclone, wherein the first and / or the second cyclone for recycling from dust separated dust over a conduit is connected to the first venturi preheater. The in the preheating and / or calcining heated-up dust is thus used to preheat the iron oxide-containing solids and magnesite used.

Further developments, Advantages and applications The invention will become apparent from the following description an embodiment and the drawing. All are described and / or illustrated illustrated features for itself or in any combination the subject matter of the invention, independently from their summary in the claims or their dependency.

The single FIGURE shows a process diagram of a method and a plant according to an embodiment of the present invention. In the process shown in the figure for the reduction of iron oxide-containing solids is via a supply line 1 For example, wet iron ore together with Magne sit (MgCO ₃ ) in a Venturi preheater 2 brought in. In this, the iron oxide-containing solids and the magnesite are dried and heated. About a line 3 The iron oxide-containing solids together with the magnesite in a cyclone 4 in which the dust-laden exhaust gases are separated from solids.

About a line 5 the dust-laden exhaust gases become a filter 6 , For example, an electrostatic filter, fed, from which the dust via a line 7 is returned to the preheating.

The one in the cyclone 4 solids separated from the exhaust gas are sent via a conduit 8th a calcination stage 9 or a second preheater (Preheater) supplied, which is a burner 9a is assigned, with which the process a main part of the energy is supplied. In the calcination stage 9 For example, the solids and magnesite are preheated to a temperature of, for example, about 850 ° C. Due to this high temperature in the calcination stage 9 The magnesite is calcined to magnesium oxide, which together with the iron oxide-containing solids via a line 10 a second cyclone 11 is supplied. In this, the solids are separated from dust-laden exhaust gas, which via a pipe 12 the first venturi preheater 2 will be directed. The iron oxide-containing solids and the magnesite are thus in the venturi preheater 2 through the exhaust gases of the second cyclone 11 heated and dried.

The one in the second cyclone 11 separated solids are passed through a conduit 13 with pressure lock a first reactor 14 supplied, which, for example, has a circulating fluidized bed. By supplying hydrogen, the heated egg ore containing ore in the first reactor 14 pre-reduced and via a line 15 in a second reactor 16 introduced, which may be a stationary fluidized bed reactor. Also in the second reactor 16 heated hydrogen is introduced as a reducing agent, so that the iron oxide in the second reactor 16 is reduced.

From the second reactor 16 For example, sponge iron with a high degree of metallization is taken together with magnesia and through a pipe 17 in a heat level 18 introduced, in which the solids heated to a temperature of about 700 ° C and via a conduit 19 hot in a briquetting stage 20 be introduced.

The reactors 14 and 16 In this case recycling cyclones can be connected downstream, in which dust-like solids are separated from the gases leaving the reactors. In an exhaust treatment stage 21 These exhaust gases can be cleaned and stored in a reheater 22 be heated before entering the reactors 14 . 16 to be led back.

Example (reduction of iron ore)

In one of the figure corresponding plant were the Venturi preheater 2 over the line 1 61.2 t / h wet iron ore with 7.8% moisture and 300 kg / h of magnesite with a grain size of less than 1 mm fed. The iron ore was mixed with the magnesite in the venturi preheater 2 dried and heated and over the cyclone 4 to the calcination stage 9 in which the iron ore and the magnesite were heated to a temperature of 850 ° C.

From those in the cyclone 4 separated dust-laden exhaust gases were in the filter 6 Separated 2.6 t / h of dust, which contained 25 kg / h of magnesium oxide. This dust was over the line 7 returned to the preheating.

54.2 t / h of in the preheater 9 Iron ores heated to 850 ° C were passed through the line at 150 kg / h to magnesium oxide calcined magnesites 13 with pressure lock in the reactor 14 and the downstream of this reactor 16 brought in. By the reduction in the reactors 14 and 16 at a temperature of about 630 ° C 37 t / h of product with a degree of metallization of 91%. About the line 17 For example, the product containing about 34 t / h of metallic iron and 150 kg / h of magnesium oxide was in the further heat stage 18 brought. In this, the metallic iron and the magnesium oxide were heated to 700 ° C and over the line 19 hot in the briquetting stage 20 brought in.

1

management

2

(First) Venturi preheater

3

management

4

(First) cyclone

5

management

6

filter

7

management

8th

management

9

calciner (second preheater)

9a

burner

10

management

11

(Second) cyclone

12

management

13

management with pressure lock

14

(First) reactor

15

management

16

(Second) reactor

17

management

18

warmth rate

19

management

20

Brikettierungsstufe

21

Exhaust gas treatment stage

22

reheater

Claims (11)

Process for the reduction of iron oxide-containing solids, in particular iron ore, in which fine-grained solids in a preheating and / or calcination stage ( 2 . 9 ) and at least partially calcined, in one of the preheating and / or calcination stage ( 2 . 9 ) downstream first reactor ( 14 ) pre-reduced with fluidized bed and in a second reactor ( 16 ) is reduced with fluidized bed and in a second reactor ( 16 ) downstream briquetting stage ( 20 ) are briquetted at a temperature above 500 ° C, characterized in that the preheating and / or calcination stage ( 2 . 9 ) is added together with the iron oxide-containing solids magnesite, which in the preheating and / or calcination ( 2 . 9 ) is at least partially calcined to form magnesium oxide, wherein more than 50% of the preheating and / or calcination stage (together with the iron oxide-containing solids) ( 2 . 9 ) added magnesite has a particle size between 1.25 mm and 3 mm. A method according to claim 1, characterized in that the magnesite together with the iron oxide-containing solids in the preheating and / or calcination ( 2 . 9 ) is calcined at temperatures of 400 to 1250 ° C. Method according to one of the preceding claims, characterized in that the iron oxide-containing solids before and / or during the supply to the preheating and / or calcining ( 2 . 9 ) between 0.1 and 5 wt .-% magnesite zugege ben. Method according to one of the preceding claims, characterized in that the from the second reactor ( 16 ) of the briquetting stage ( 20 ) contained solids between 0.1 and 5 wt .-% magnesium oxide. Method according to one of the preceding claims, characterized in that in the second reactor ( 16 ) reduced solids together with the magnesium oxide in one of the Brikettierungsstufe ( 20 ) upstream heat stage ( 18 heated to a temperature above 600 ° C and hot in the Brikettierungsstufe ( 20 ) are introduced. Method according to one of the preceding claims, characterized in that the iron oxide-containing solids in the first and second reactor ( 14 . 16 ) at temperatures below 700 ° C to metallic iron with a degree of metallization of over 75% can be reduced. Use of magnesite with a grain size between 1.25 mm and 3 mm as an aggregate, which in a process for the production of sponge iron briquettes, in particular after a of the preceding claims, is abandoned together with iron oxide solids to the fluidity of hot Sponge iron during the feed from a reduction stage to a briquetting stage to increase. Plant for the reduction of iron oxide-containing solids, in particular for carrying out a process according to one of Claims 1 to 6, with a preheating and / or calcination stage ( 2 . 9 ), a first and a second reactor each formed as a fluidized bed reactor ( 14 . 16 ) and a briquetting stage ( 20 ), characterized in that the preheating and / or calcination stage ( 2 . 9 ) Medium ( 1 ) for the simultaneous continuous or discontinuous introduction of iron oxide-containing solids and magnesite, and that the Brikettierungsstufe ( 20 ) a heat level ( 18 ) is connected upstream. Plant according to claim 8, characterized in that at least one of the two reactors ( 14 . 16 ) is a fluidized bed reactor with a circulating fluidized bed and / or an annular fluidized bed. Plant according to claim 9, characterized in that the first and the second reactor ( 14 . 16 ) have a plurality of nozzles or inlet openings for the supply of a heated, gaseous reducing agent, such as hydrogen. Installation according to one of claims 8 to 10, characterized in that the preheating and / or calcination ( 2 . 9 ) a first venturi preheater ( 2 ) with a downstream first cyclone ( 4 ) and a second preheater ( 9 ) with a downstream second cyclone ( 11 ), wherein the first and / or the second cyclone ( 4 . 11 ) for returning dust separated from exhaust gas via a line ( 5 . 7 ) with the first venturi preheater ( 2 ) are connected.