DE102012005454A1 - Process for granulation and / or pelleting of iron-containing solid - Google Patents

Abstract

In the production of hardened granules of iron-containing particles, the iron-containing particles are mixed with at least one binder and water to form a mix, the mix is formed into granules and introduced the granules for curing in a fluidized bed reactor. To reduce the abrasion in downstream processing stages, the granules are still wet at the hottest point of the fluidized bed introduced into the fluidized bed reactor.

Description

The invention relates to the production of hardened granules from iron-containing dusts, wherein the iron-containing dusts are mixed with at least one binder and water to form a mix, the mix is formed into granules, introduced the granules for curing in a fluidized bed reactor and subjected to reduction of the hardened granules become.

In some reduction processes for obtaining metallized iron, the iron-containing material is introduced in the form of fine-grained particles. An example of such a method is the so-called SL / RN method, a combination of the Stelco-Lurgi method and the Republic Steel-National Lead method (RN). The Stelco-Lurgi process is a direct reduction process originally aimed at the production of sponge iron for steel furnaces and the use of iron-rich ores. Also, the Republic Steel National-Lead process is a direct reduction process in which iron ores are decomposed into their components metallic iron and gangue after reduction. Gait is in this context the non-ferrous rocks found in iron ores. By combining the two processes, the SL / RN process was developed in 1964, in which iron oxides are reduced in the rotary kiln with solid reducing agents. In the kiln ores or so-called green pellets are introduced together with coal, especially lignite, in excess as a reducing agent and dolomite for desulfurization. The kiln discharge is indirectly cooled in a tube cooler and then separated by sieving, magnetic separation and coal separation into sponge iron, excess, coal and ash.

The SL / RN process usually uses lumps with a grain size of 5-18 mm or pellets with 9-16 mm. Iron sands or ilmenites of a particle size preferably greater than 106 μm are also used. Particles with a diameter <63 μm are not suitable for use in a SL / RN process, since they lead to sticking and thus formation of deposits in the rotary kiln, which can lead to interruptions in operation.

However, to make smaller particles accessible to this process, there are a number of methods for forming granules of the desired diameter. It is possible by the processing and additives, such as binders, the granules in such a way that the dust during their production remains low (<10 wt .-%).

From the WO 98/49352 A1 is the granulation of fine-grained iron ore fractions known in which as binder material, for example. Bentonite is used. Bentonite is a rock containing a mixture of different clay minerals, the most important constituent (60-80% by weight) being montmorillonite.

The US 6,024,790 describes that it may be useful to activate this binder material bentonite for its uses by ion exchange with the incorporated cations. An activated bentonite usually has a better swelling capacity and a higher thermal resistance. The activation process described in US Pat. No. 6,024,790 must be carried out over a period of several hours to several days in order to ensure sufficient ion exchange.

From the JP 63103851 It is known to add small amounts of sodium hydroxide to the bentonite and thus to activate the clay material.

The DE 25 175 43 discloses a process for agglomerating metallurgical dusts, in which the metallurgical dust is mixed with 2 to 20% by weight of binder and about 0.5 to 5% by weight of silicon-containing material, this mixture is formed into pellets or granules and subsequently hardened. It is also known to add to the binder other additives such as sodium hydroxide, sodium carbonate and sodium bicarbonate in amounts of about 3% by weight.

From the EP 1 290 232 B1 discloses a process for producing metallized iron agglomerates from fine iron-containing particles by means of a binder, using cellulose fibers as the binder. The cellulose fibers act as binders in the formation of the particles, but due to their high carbon content they can also be used simultaneously as reducing agents in the downstream reduction process.

Also the EP 0 916 742 discloses a method in which the reducing agent is already incorporated in the iron-containing granules. For this purpose, the iron oxide-containing raw material is mixed with a carbonaceous material, an organic binder and an inorganic coagulant and then mixed with water. The pellets thus obtained are dried with a dispersing agent and then reduced. Among other things, sodium hydroxide solution can be used as the dispersing agent.

By processing in a rotary kiln, together with the solid reducing agent and comparatively long residence times, however, it comes in the further processing, especially in the SL / RN process, in all of these methods Use of green pellets for increased formation of fine abrasion. High abrasion requires a high workup effort in order to be able to recover these dusts in such a way that valuable products can be produced from them. Otherwise, the material contained in the dusts is lost.

It is therefore an object of the present invention to provide a method and a device to produce granules for further processing, which have such a hardness that it does not come to a significant abrasion in downstream processing steps.

This object is achieved with the features of claim 1. The finest-grained Fe concentrate is fed with a mixing unit and mixed there with at least one binder and water. In addition, even more additives can be added in this mixing unit. The resulting mix is then formed into granules in a micro-granulator. Subsequently, the granules are introduced into a preferably circulating fluidized bed, wherein the introduction takes place at the hottest point of the fluidized bed. This sudden temperature change leads to rapid sintering of the small granules and thus to an evasive strength of the grain for the subsequent reduction in a rotary kiln. In a circulating fluidized bed, the heat exchange due to the high flow rates is particularly good, so that the sintering process is further accelerated.

This method is contrary to the usual procedure, according to which the introduction of the material to be processed in the fluidized bed in a region in which the material is not exposed to high temperature gradient, since in particular larger particles a high temperature difference to stresses in the material and consequent cracks and Can cause deformations. In addition, higher demands are placed on the material of the supply line by the introduction at the hottest point. Even a dosage is more expensive.

The hottest part of the fluidized bed is where the combustion takes place or where the hot gases enter.

It has furthermore proven to be favorable that the iron-containing particles have an iron content of at least 30% by weight, preferably at least 50 to 80% by weight, so that the work-up time remains economical. An advantageous embodiment of the invention provides that the iron particles Concentrate a grain size of max. 5 wt .-% coarser than 100 microns and about 55 to 60 wt .-% has less than 32 microns, since at a larger average diameter direct processing can be economically useful.

The very fine-grained concentrate can be present as a filter cake or as a dry powdered bulk material. The specific surface area of the particles is between 1,600 and 4,000 cm ² / g, depending on the mineralogy or mineral composition of the iron concentrate used. A preprocessing, for example in the form of grinding, can be useful for a more homogeneous grain size.

As binders is best an inorganic binder such. B. bentonite, as this unwanted side reactions in the sudden increase in temperature during curing can be excluded. According to the invention, the amount of addition of this binder should be between 0.25 and 1.5% by weight, depending fundamentally on the mineral composition and the specific surface area of the iron concentrate.

The mix formed into granules in the micro-granulator should desirably have a particle size of between 0.1 and 6 mm, since this particle size ensures that virtually all of the grain is heated homogeneously during its introduction into the hottest stage of the reactor and not within the grain individual particles to significant temperature gradient comes.

Furthermore, a water content of 8 to 14 wt .-% has been found to be particularly favorable, which is fundamentally dependent on the particular mineral composition.

The optimum curing temperature is between 850 and 1050 ° C and also has a dependence on the mineral composition within this range. Experiments have shown that in the process according to the invention during the thermal curing max. About 5% by weight of the granules are produced as abrasion, the abrasion here being defined as the grain fraction <100 μm.

As fuel for the curing process, natural gas or light fuel oil can be burned directly in the fluidized bed reactor or in a hot gas generator. If a hot gas generator is used, the hot gas is fed to the fluidized bed reactor.

Alternatively, coal may be used as a fuel wherein the coal is hydrogenated in a separate reactor at temperatures between 650 and 950 ° C, the carbonization gases are brought as fuel in the curing reactor and the coke hot in downstream process stages, preferably one in a rotary kiln occurring reduction, is registered as a reducing agent.

It has also proved to be favorable to let the curing in an oxidizing atmosphere, preferably with an oxygen content in the circulating fluidized bed between 2 and 10 wt .-%, take place. As a result, iron of oxidation state 2 is oxidized to iron of oxidation state 3 and additional heat energy is released. As a result, the heat input in the reactor can be reduced.

During curing in an oxygen-containing atmosphere, the following reactions take place: 2Fe ₃ O ₄ + ½O ₂ → 3Fe ₂ O ₃ (oxidation of the magnetite to hematite) Fe ₂ O ₃ × H ₂ O → Fe ₂ O ₃ + H ₂ O (splitting off of the Crystal water eg of the goethite).

If there is no oxygen in the atmosphere, only the second reaction, the elimination of the water of crystallization, takes place.

The hardened microgranules are then treated with coal in a rotary kiln reducing, whereby the oxygen of the iron oxide is degraded and the iron passes into the metallic phase. The ratio between carbon and iron (C _fix : Fe) is 0.3-0.7: 1. During the reduction, the following reactions take place: Fe ₂ O ₃ + CO → 2FeO + CO ₂ CO ₂ + C → 2CO FeO + CO → Fe _met + CO ₂

In the technical realization it seems particularly useful to introduce the hardened granules from the fluidized bed reactor without cooling hot in the rotary kiln. As a result, on the one hand saves energy and on the other hand, the furnace volume can be reduced and thus its investment costs are reduced. When hot application of the granules eliminates the otherwise necessary for the necessary warming of the granules in the rotary kiln oven length. The rotary kiln can be made shorter or the throughput can be increased in an existing rotary kiln. In existing rotary kilns, the throughput can be increased by the hot introduction. The hot exhaust gases of the fluidized bed reactor can be used to preheat the necessary process air or for steam generation.

In order to be able to economically use the dusts produced in the fluidized bed and the reduction despite the improved hardening, it has been found to be advantageous to separate these dusts from the fluidized bed and / or the reduction stage by means of a dust separation system and either into the mixing or in attributed to the granulation.

Especially at smaller scales, such. As in laboratory and pilot experiments, it is sensible for safety reasons to cool the Ofenaustrag to a temperature below 30 ° C, this cooling should preferably be carried out under an inert atmosphere, such as a nitrogen atmosphere. The cooled material, which is a mixture of sponge iron, char and ash, is placed in a magnetic separator to separate the sponge iron from char and ash.

The invention further comprises a plant with the features of claim 9, which is suitable for carrying out the method according to the invention. Such a plant has a device for mixing iron-containing particles with at least one binder and water to a mix. This device is followed by a device for granulating the mix to granules. This is followed by a reactor with a circulating fluidized bed to harden the granules. The fluidized bed reactor is designed such that the feed line of the granules opens into the lower region of the fluidized bed reactor and thus the hottest point of the fluidized bed. For this purpose, in particular the material of this supply line and a metering device provided there must be designed so that it can withstand these temperatures permanently.

In a further development of the inventive concept, the fluidized bed is fed with hot gas and the feed line of the granules opens in the region of this inlet line, since at this point the hot gases have not lost any heat energy to the fluidized bed.

It is also advantageous if at least one return line from the fluidized bed reactor and / or a downstream reduction device is provided in the device for mixing and / or the device for micro-granulation.

On the one hand, the advantages of the process according to the invention lie in the fact that hitherto only pellets consisting of magnetite and hematite concentrates and having relatively large diameters (between 9 and 16 mm) can be used with the process according to the invention and other grain sizes are used, without setting uncontrollable dust cycle.

In addition, the microgranules hardened according to the invention have a greater porosity compared to lumps and can be reduced faster and better than Lumps and the classically fired pellets that have been cured at over 1300 ° C.

In addition, the hot discharge from the curing oven can be charged directly into the rotary kiln directly by the combination of the curing reactor according to the invention and a SL / RN oven. This saves heat energy and increases the specific throughput of the rotary kiln.

Finally, the method according to the invention also allows all accumulating dusts, wet or dry, to be returned to the microgranulation process, thereby ensuring a completely closed material cycle.

The invention will be explained in more detail with reference to the drawing and an embodiment. All described and / or illustrated features alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their back reference.

The single figure shows the flow diagram of a plant for carrying out the method according to the invention.

The fine-grained iron ore is placed in a mixing device 1 initiated. In this mixer 1 also opens at least one supply line 2 , over which a mixture consisting at least of binder and water is introduced. Of course, it is also possible to provide separate supply lines for each individual additive.

Via wire 3 is the mixture thus produced from the mixing device 1 in the granulator 4 entered. There are formed from the mix granules with a mean grain diameter of 0.1 to 6 mm (microgranulation), which via line 5 in the fluidized bed reactor 10 be introduced. In the preferably designed as a circulating fluidized bed fluidized bed reactor 10 is over the line 11 Fluidizing gas injected, so that over a rust 13 a circulating fluidized bed 14 formed. Via wire 12 occurs just above the grate 13 hot gas through which the fluidized bed 14 is heated. Instead of supplying the hot gases can in a reactor with internal combustion via line 12 or an additional line, not shown, also fuel in the fluidized bed reactor 10 be introduced. The supply line 5 The granules end in the immediate vicinity of the supply line 12 ,

The hardened, iron oxide-containing granules are via a line 15 a reduction stage, in particular a rotary kiln 16 in which they are reduced, for example, by means of an SL-RN method. Via wire 17 For example, coal as a reducing agent in the rotary kiln 16 brought in.

The in the fluidized bed reactor 10 Dust is generated via a pipe 20 in a cyclone 21 guided, in which it is separated from the gas stream. The solids content is via line 22 into the mixing device 1 and / or in the granulation device 4 returned to be worked up again to granules.

That from the fluidized bed reactor 10 withdrawn gas is via pipe 30 an exhaust aftertreatment 31 fed. The gas can then be cleaned via line 32 vented into the atmosphere and / or used as a process gas.

example

granulation:

A 69 wt.% Iron magnetite concentrate ground to a pelleting fineness (<100 μm) and treated is mixed with 0.5 wt.% Bentonite and the required amount of water, determined by the desired moisture content of the granules, and then granulated. The moisture content of the granules thus obtained should be about 10 wt .-%; the grain size of the granules is 0.1 to 3 mm.

cure:

The resulting granules are then cured in a fluidized bed reactor in continuous operation at about 980 ° C and then cooled to about 30 ° C. The throughput of the system used is about 14 kg / h. During curing, which takes place in an oxygen-containing gas atmosphere, magnetite is oxidized to hematite, which in turn releases heat energy.

Reduction of hardened microgranules in a short drum oven:

60 kg of hardened microgranules and 40 kg of coal are mixed and charged into the oven. The C _fix : Fe _tot ratio is 0.60. The batch was treated at 1,020 to 1,050 ° C for about 4 hours. After cooling under a nitrogen atmosphere, an average sample is taken and fed to a low-field magnetic separator to separate the residual coal and ash. The magnetic product, sponge iron, has the following analysis: Fe _total : 80.0% by weight Fe ²⁺ : 2.6% by weight Fe _Met : 76.8% by weight metallization: 96% by weight

The proportion of particles with a diameter <0.1 mm in the magnetic product was 4.5 wt .-%.

LIST OF REFERENCE NUMBERS

1

mixing device

2, 3

management

4

granulator

5

management

10

Fluidized bed reactor

11, 12

management

13

rust

14

fluidized bed

15

management

16

Reduction stage (rotary kiln)

17

management

20

management

21

cyclone

22

management

30

management

31

Gas treatment

32

management

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 98/49352 A1 [0005]
• US 6024790 [0006]
• JP 63103851 [0007]
• DE 2517543 [0008]
• EP 1290232 B1 [0009]
• EP 0916742 [0010]

Claims (12)

A process for producing hardened granules from iron-containing particles, wherein the iron-containing particles are mixed with at least one binder and water to form a mix, the mix is formed into granules and the granules are introduced into a fluidized bed reactor for curing, characterized in that granules are still moist be introduced at the hottest point of the fluidized bed in the fluidized bed reactor. A method according to claim 1, characterized in that the wet granules are introduced into the lower region of the fluidized bed reactor, in which also hot gases are introduced or in which the combustion of a fuel takes place. A method according to claim 1 or 2, characterized in that the iron-containing particles have an iron content of at least 30 wt .-% and / or a grain size of at most 5 wt .-% coarser than 0.1 mm. Method according to one of the preceding claims, characterized in that the binder is an inorganic binder. Method according to one of the preceding claims, characterized in that the granules have a particle size between 0.1 and 6 mm and / or a water content of 8 to 14 wt .-%. Method according to one of the preceding claims, characterized in that the temperature in the fluidized bed reactor is between 850 and 1050 ° C. Method according to one of the preceding claims, characterized in that the curing takes place in the fluidized bed reactor in an oxidizing atmosphere. Method according to one of the preceding claims, characterized in that the hardened granules are fed directly to a downstream reduction stage. Method according to one of the preceding claims, characterized in that iron-containing dusts which arise in the fluidized-bed reactor and / or a reduction stage downstream of the fluidized-bed reactor are recycled for mixing and / or for granulation. Plant for carrying out a method according to one of the preceding claims with a device ( 1 ) for the mixing of iron-containing particles with at least one binder and water to a mix, a device ( 4 ) for granulation of the mixed material to granules and a fluidized bed reactor ( 10 ) for hardening the granules, characterized in that the supply line ( 5 ) of the granules in the lower region of the fluidized bed reactor ( 10 ) opens. Plant according to claim 10 with a supply line ( 11 ) for hot gases or fuel, characterized in that the supply line ( 5 ) of the granules in the region of the inlet of the supply line ( 11 ) of the hot gases or fuel into the fluidized bed reactor ( 10 ) opens. Plant according to claim 10 or 11, characterized in that at least one return line ( 20 . 22 ) from the fluidized bed reactor ( 10 ) and / or a downstream reduction stage ( 16 ) into the device ( 1 ) for mixing and / or the device ( 4 ) leads to granulation.

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