EP2379682B1 - Method for producing pressed articles containing coal particles - Google Patents

Description

The invention relates to a process for the production of pellets containing pellets, the pellets obtained thereby and the use of the pellets in processes for producing pig iron in a fixed bed or in processes for the preparation of carbon carriers for processes for producing pig iron in a fixed bed.

In processes for pig iron production in a fixed bed, for example in melter gasifiers, or in processes for the production of carbon carriers for processes for pig iron production in a fixed bed, for example coke production for blast furnaces, containing carbon particles containing pellets, such as briquettes, after the discharge from the press have a certain Have fall and crush resistance. The drop resistance is required so that the original size of the compacts in the course of charging in a process without prejudice to inevitable falls, for example when transferring from one to another conveyor belt or when charging in a material bunker, as much as possible. Compressive strength is required to maintain the original size of the compacts after being charged into a material bunker or fixed bed reactor, despite pressure exerted by superposed layers of material.
These strength requirements are also summarized under the term green strength.
In addition to the green strength, the hot strength of compacts - especially when used in thermal processes - is a criterion for their suitability for use. In the particular case of using fine particles containing carbon particles in pig iron production processes, such as in a melter gasifier or blast furnace, the term hot strength refers to a) the strength of the semi-coke or coke particles remaining after pyrolysis of the pellets in a high-temperature zone, and b) a strength of these semi-coke or coke particles after chemical attack by a hot, CO ₂ -containing gas. A minimum level of hot strength allows the size of these particles, which is present after the conversion of the compacts by pyrolysis in semicoke or coke particles, to be largely retained. In pig iron production processes in a fixed bed, the development of undersized particles from compacts or coke particles prior to charging into a fixed bed or within a fixed bed is undesirable because this results in the permeability of the product Fixed bed is deteriorated. In the particular case of a process for the production of pig iron this concerns both the gas permeability and the drainage behavior of the fixed bed with respect to the molten pig iron and the slag. If the permeability of the fixed bed deteriorates, adverse effects on its productivity, its specific energy requirement and its product quality are to be expected.

Out WO 02 / 50219A1 It is known to produce compacts with sufficient green strength from fine-grained carbon particles by means of a binder system of quicklime and molasses. Here, fine-grained coal particles of fine coal and quicklime are mixed, the mixture for the purpose of progressing the quenching reaction with moisture from the coal particles rest, then added molasses, kneaded the resulting mixture and finally pressed from her pellets.

• auf die Generierung von unbenetztem Porenvolumen durch Trocknung verzichtet werden, oder
• um so viel mehr Melasse zugesetzt werden, wie von dem Porenvolumen aufgenommen wird und daher nicht zur Bindung der auf der Oberfläche der Kohlepartikel zur Verfügung steht.

There are coals which show an extraordinarily high water absorption capacity, in particular characterized by a high inherent moisture content. For use in pig iron production, however, the moisture content of the compacts should not be too high, ie at a maximum of 7% by weight. This is because this moisture is energetically stressful when using the pellets for pig iron production or for the production of carbon carriers for processes for pig iron production, since the moisture content of the pellets significantly increases the specific consumption of carbon carriers. Therefore, coals whose moisture is higher must be dried before processing into compacts. In addition to the unwetted pore volume already present in the undried coal, the expulsion of water from cavities during drying produces additional pore volume. The unwetted pore volume can absorb a corresponding amount of water or aqueous media. Of course, the additional pore volume can again absorb water or aqueous medium. Moreover, certain coals also tend to generate additional pore volume due to grain damage, especially during intense drying. When drying a coal with a high water absorption capacity to an acceptable moisture level before applying the in WO 02 / 50219A1 described method for the production of compacts, a large additional pore volume is generated. Therefore, a dried carbon particle sucks a significant portion of the molasses needed to form a bond on the particle surface, which is to be understood as an aqueous solution, into its pores. Therefore, for such coals is common used molasses additives of ≤ 10% by weight, based on the weight of the coal to be processed, to obtain sufficient strength for the compacts. However, in order to produce compacts with sufficient strength based on molasses binder, must

• to dispense with the generation of unwetted pore volume by drying, or
• the more molasses is added, as is absorbed by the pore volume and therefore not available for binding to the surface of the carbon particles.

However, these measures are undesirable for reasons of process economy.

Even with naturally less moist coals, which do not have to be dried to achieve a moisture content of the compacts of at most 7% by weight, some of the molasses is absorbed into the pores of the carbon particles. However, molasses contains components that act catalytically with respect to a reaction of carbon with hot, CO ₂ -containing gases, whereby, especially in the hot zones of a production of pig iron serving fixed bed at temperatures> 800-1000 ° C, depending on the pressure, the extent a conversion of solid carbon with CO _{2 increases} according to Boudouard reaction. As a result, the hot strength of molasses-treated compacts is relieved by pyrolysis-derived, semi-coke or coke particles.

In the WO9901583A1 The proposed use of bitumen as a binder does not pose such problems associated with molasses. However, the production of pellets with bitumen is associated with very high binder costs.

The in the AT005765U1 The proposed use of an aqueous bitumen emulsion as a binder system reduces bitumen consumption by more than 50%. In practice, however, it has been found that the feed carbons must have humidities of substantially more than 5% by weight in order to produce stable compacts when using such bitumen emulsions. There is also the problem that pores present in the carbon particles can absorb aqueous bitumen emulsion or deprive the emulsion of water and thus destabilize it due to droplet coalescence, before a substantially uniform distribution of the emulsion within the material to be processed into compacts and, correspondingly, uniform wetting of the Particle surface can be done by the emulsion. This reduces the effectiveness of the emulsion as a binder.

In the US2310095A describes the treatment of coal particles with bitumen emulsion and subsequent addition of asphalt as a binder to seal the pores of the carbon particles. An influence of such a treatment on the CO ₂ reactivity of the resulting after pyrolysis of the compacts in a melter carburetor or the cokes obtained from compacts is not explained.

The object of the present invention is to provide a process for the production of compacts, in which these disadvantages of the prior art are overcome, and compacts with sufficient green and hot strength even with the use of carbon particles, which must be pre-dried, using a known Lesser amount of a water-containing binder system can be produced.

• Bindemittelsystem enthaltend Melasse sowie Branntkalk oder Kalkhydrat,
• Bindemittelsystem enthaltend eine Emulsion von Bitumen in Wasser, vermischt werden und die dabei erhaltene Mischung durch Pressung zu Presslingen weiterverarbeitet wird,

dadurch gekennzeichnet,
dass vor dem Vermischen mit dem Wasser enthaltenden Bindemittelsystem die Kohlepartikel einem Imprägnierungsschritt unterworfen werden, in welchem sie mit einer flüssigen wasserunlöslichen und/oder wasserabstoßenden Substanz imprägniert werden,
wobei die Untergrenze der Menge von im Imprägnierungsschritt zugesetzter wasserunlöslicher und/oder wasserabstoßender Substanz 0,5 Gewichts%, bevorzugt 1 Gewichts%, bezogen auf das Gewicht des zu Presslingen zu verarbeitenden Gutes Kohlepartikel, beträgt.This object is achieved by a method for producing a carbon particle-containing compact, wherein the carbon particles with a binder system containing water
from the group

• Binder system containing molasses and quick lime or hydrated lime,
• Binder system containing an emulsion of bitumen in water, are mixed and the resulting mixture is further processed by pressing into pellets,

characterized,
in that before mixing with the water-containing binder system, the carbon particles are subjected to an impregnation step in which they are impregnated with a liquid water-insoluble and / or water-repellent substance,
wherein the lower limit of the amount of water-insoluble and / or water-repellent substance added in the impregnation step is 0.5% by weight, preferably 1% by weight, based on the weight of the carbon particle to be processed into compacts.

During the impregnation, the substance either penetrates into the pores of the carbon particles and accordingly prevents the penetration of components of the aqueous binder system by filling in the pore space. Or the substance settles in the exit points of the pores on the carbon particle surface, also called pore necks, and prevents by this clogging of the pore necks penetration of components of the aqueous binder system in the pores.
In this way it is prevented that aqueous binder system, which is needed on the coal particle surface for binding purposes, can no longer fulfill these binding purposes after penetration into the pores. Accordingly, as compared with a method in which aqueous binder system can penetrate the pores, the amount of aqueous binder system required is reduced.

The aqueous binder system may contain one or more other components besides water.

The impregnation step can consist of steaming the carbon particles with the substance, spraying the carbon particles with the substance, mixing the substance into a moving bed of carbon particles, or mixing the substance into a fluidized bed of the carbon particles.

The substance with which the carbon particles are impregnated in the impregnation step is a water-insoluble and / or water-repellent substance.
If the pores are filled with such a substance in the impregnation step and the pore walls are coated with such substances, the tendency of the pores to absorb components of the aqueous binder system decreases. If the exit points of the pores on the carbon particle surface are closed by such substances, components of the aqueous binder system can no longer penetrate into the pores. As a result, previously sucked into pores and thus ineffective for the binding of the compacts components can make a contribution to the binding of the compacts.

The water-insoluble and / or water-repellent substance belongs to the group of substances consisting of waxes, organic coking or refinery products, as well as plastics or plastic waste. It may be also to deal with waste oil. These substances are usually available in large quantities at low cost.

In this case, the impregnation step takes place at a temperature at which the water-insoluble and / or water-repellent substance is liquid, in particular viscous. As viscous in this sense, liquids are considered whose viscosity is at least 1 Pas, and a maximum of 100 Pas, for example, 10 Pas. In these conditions, the substance spreads on the surface of the carbon particles and penetrates into the exit points of the pores but hardly into the interior of the pores. As a result, the consumption of the water-insoluble and / or water-repellent substance in the impregnation step is kept low. Advantageously, the water-insoluble and / or water-repellent substance solidifies on cooling in the exit points of the pores on the coal particle surface.

When entering the pores, the carbonaceous substances are deposited in thin layers on the pore surface. During pyrolysis, carbon films are formed from these thin layers. These reduce the reactivity of the compact to hot CO ₂ -containing gases compared to an embodiment in which no thin layers of the substances are deposited in the pores. This is because the carbon layers resulting from the substances contain few or no catalytically active substances with respect to reaction with hot CO ₂ -containing gases. In contrast, contain the carbon particles or the material to be processed into compacts, catalytically active compounds, such as iron or alkalis. Accordingly, the reactivity of a compact whose surface and pores are covered with a carbon layer resulting from the substances is lower than that of a compact without such a carbon layer.

When coal particles are used, which require pre-drying before processing into compacts, it is advantageous for economic reasons not to advance the drying substantially below 5% by weight of moisture, ie to a maximum of 4% by weight of moisture. As a result, the formation of additional pore volume is limited as a result of drying and taken accordingly less substance in the impregnation step of pores. Accordingly, less substance is consumed in the impregnation step. In addition, less equipment and energy expense must be operated for drying.

The lower limit of the amount of substance added in the impregnation step, called impregnating agent, is 0.5% by weight, preferably 1% by weight, the upper limit is 5% by weight, preferably 3% by weight, more preferably 2% by weight, based on the weight of the compacts to be processed good, so the Carbon particles. Addition of more than 5% by weight of impregnating agent does not make economic sense. If less than 0.5% by weight of impregnating agent is added, impregnation is no longer effective.

According to the process of the invention, the binder system contains molasses as well as quicklime or hydrated lime. It can also consist of these components.

According to other embodiments, the binder system contains molasses in combination with strong inorganic acids, such as phosphoric acid, sulfuric acid, nitric acid.

According to the method of the invention, the binder system contains an emulsion of bitumen in water. It can also consist of such an emulsion.

According to further embodiments, the binder system contains products from waste liquors of pulp production, starches, cellulose, beet pulp, waste paper pulp, groundwood, or long-chain polyelectrolytes such as carboxymethylcellulose.

According to one embodiment of the method according to the invention also iron or iron oxide-containing particles are processed in a mixture with the carbon particles.

According to a particular embodiment of the inventive method, the compacts are subjected to a heat treatment after the pressing.

The heat treatment is carried out at a temperature higher than the pressure. The heat treatment causes a drying and / or hardening of the compacts. The heat treatment can be carried out at temperatures of preferably ≥ 250 ° C and ≤ 350 ° C at which irreversible chemical processes can convert binder components. For example, water-soluble binder components can be converted to water-insoluble compounds.

The compounds formed in such conversions can contribute to the strength of the compacts.

In the case of a molasses-containing binder system, for example, a conversion of molasses by caramelization.

According to a particular embodiment of the inventive method, the carbon particles are subjected to a heat treatment after the impregnation step prior to mixing with the water-containing binder system.

The heat treatment causes a drying. In the event that solutions or emulsions are present in the pores, the heat treatment additionally causes a concentration of the solutions, suspensions or emulsions and, correspondingly, a coating of the pore walls with dissolved, suspended or emulsified components. These may, in addition to the aqueous binder system added thereafter, contribute to increased hot strength and green strength of the compacts.

Furthermore, the heat treatment can effect the conversion of the coating of the pore walls initially formed as a result of the heat treatment into water-insoluble compounds, or compounds which reduce the reactivity of the carbon particles with respect to hot CO ₂ -containing gases. The maximum temperature of the heat treatment is limited by the pyrolysis of the carbon particles and is at 350 ° C. The lower limit for the temperature in this heat treatment is 150 ° C.

Overall, therefore, less water-containing binder system is required for the production of the compacts as in a production without impregnation step.

The processing into compacts after the impregnation step can be carried out by known methods, for example as in WO 02 / 50219A1 or in AT005765U1 described, or by any suitable for processing coal particles with a water-containing binder system to compacts suitable methods.

An inventive according to the invention after the impregnation step with a water-insoluble and / or water-repellent substance addition of water-containing binder systems in the production of compacts reduces the process costs compared to conventional methods such as according to WO02 / 50219A1 , The avoidance of carbon uptake during the manufacture of briquettes with binder systems containing water, on the one hand, reduces specific coal consumption in pig iron production processes using the briquettes or coke obtained therefrom, since less water from the binder system is present in the briquette and correspondingly less energy must be spent for its evaporation. On the other hand, occurring in conventional processes for the production of compacts due to the absorption of water from the binder system need for post-drying of the compacts when using the method can be omitted, or the drying effort can be reduced, resulting in an energy saving results. There Accordingly, it can be dispensed with the establishment or operation of devices for post-drying, or the dimensions of the devices and the cost of their operation can be reduced, this is equivalent to operating costs and investment cost reduction.

As an additional advantageous effect of the impregnation step, depending on the nature of the substance used for the impregnation, a reduction in the CO ₂ reactivity of the resulting after pyrolysis of the compacts in a melter carburetor or the cokes obtained from compacts result. Low CO ₂ reactivity is desired in the operation of a melter gasifier so that the semi-coke in the fixed bed of the melter gasifier or the coke in the fixed bed of a blast furnace remain stable from the charge on the bed surface until reaching the immediate gasification zone in the area of the oxygen nozzles or the tuyeres and thereby promote the permeability of the fixed bed with respect to the gassing and the drainage of molten phases. The reduction of the CO ₂ reactivity of the coke or the coke is achieved in that the inner surface of the pores of the carbon particles in the compact can no longer be coated by the impregnation of a binder which contains reactivity-promoting substances. For example, the binder component molasses contains alkalis as reactivity-promoting substances. Is-containing substances by impregnation, such as bitumens or waxes avoided that molasses coats the inner surface of the pores, the CO ₂ reactivity is thus over by a method reduced without the impregnation step recovered char or coke.

A minor fraction of undersized coke is often added to the feed coal in the COREX® or FINEX® process for producing pig iron in a fixed bed of a melter gasifier in order to improve the permeability of the fixed bed. When using compacts according to the invention, or made from such coke, a softening of the coke or coke particles is inhibited by hot CO ₂ and thus counteracts a disintegration of the particles. With a fixed bed packed from pyrolysis-derived semicarbons packed in accordance with the invention, a significantly better gas permeability and a better drainage behavior of the fixed bed are made possible than in the prior art. The improvement of the reactive properties of the semi-coke therefore makes it possible Reduction or even avoidance of coke addition to COREX® or FINEX® charcoal

In the field of coking technology, the quality of the coke produced therefrom is known to be improved by increasing the bulk density of the feed coal. The use of many carburets for the production of metallurgical coke is even possible by a compression of the feed coal. In addition to stamped coking plants, process variants were developed for coking plants in bulk operation, which provided for briquetting or partial briquetting of the feed coal. From today's perspective, however, briquetting with bituminous binders for economic reasons, hot briquetting or briquetting with coal tar-based binder for health reasons, and briquetting with molasses or similar binders because of the entry of undesirable substances in the coke problematic.

The inventive method for the production of compacts makes it possible to reduce the consumption of binder or to curb the harmful effects of reactant-promoting binder components even in the production of coke using compacts of the starting materials.

The compacts may be, for example, briquettes or slugs from a compaction.

The compacts contain up to 97% by weight of carbon particles, and up to 12% by weight of binder system components, as well as carbon particles, water-insoluble and / or water-repellent substances, or solids having water repellency, in an amount based on the weight of the article to be processed whose lower limit is 0.5% by weight, preferably 1% by weight, and whose upper limit is 5% by weight, preferably 3% by weight, particularly preferably 2% by weight

According to one embodiment, the compact also contains iron or iron oxide-containing particles. Such particles can originate, for example, from dusts or sludges produced in the production of pig iron or steel.

• Figur 1 zeigt ein herkömmliches Verfahren zur Herstellung von Presslingen ohne Imprägnierungsschritt.
• Figur 2 zeigt ein erfindungsgemäßes Verfahren zur Herstellung von Presslingen mit Imprägnierungsschritt.
• Figur 3 zeigt ein erfindungsgemäßes Verfahren zur Herstellung von Presslingen mit einer dem Imprägnierungsschritt vorgelagerten Wärmebehandlung.

In the following, the method according to the invention will be described with reference to FIGS FIGS. 1 to 3 outlined block diagrams.

• FIG. 1 shows a conventional method for producing compacts without impregnation step.
• FIG. 2 shows a process according to the invention for the production of compacts with impregnation step.
• FIG. 3 shows a process according to the invention for the production of compacts with a heat treatment upstream of the impregnation step.

According to FIG. 1 For example, the coal 1 to be processed into compacts, in this case briquettes, is subjected to drying 2 and then brought to a desired grain size by granulation 3. The carbon particles thus obtained are then followed by the addition of a water-containing binder system 4, in this case molasses, optionally with the addition of solid, finely divided binder components such as hydrated lime or quicklime, with mixing 5, wherein the mixing 5 may be one or more stages. The mixture thus obtained is subjected to kneading 6 and a mixture 7. The product obtained after curing 7 is the briquette.

The inventive method according to FIG. 2 is different from the one in FIG. 1 in that prior to mixing 5 with the binder system 4 containing the water, the carbon particles are subjected to an impregnation step 10 in which they are impregnated with a substance 11, the impregnating agent. Only after this impregnation step 10 is the mixing with the water-containing binder system 4 and the further processing of the resulting mixture accordingly FIG. 1 ,

In FIG. 3 is a variant of the method FIG. 2 in which after the impregnation step 10, before mixing with the water-containing binder system 4, a heat treatment 12 is performed.

LIST OF REFERENCE NUMBERS

1

coal

2

desiccation

3

roughen

4

Water-containing binder system

5

Mix

6

kneading

7

squeeze

8th

hardening

9

product

10

impregnation step

11

Substance (impregnating agent)

12

heat treatment

Claims (7)

1. Method for producing a pressed article containing coal particles in which the coal particles are mixed with a water-containing binder system from the group comprising

   - a binder system containing molasses as well as quicklime or hydrated lime,

   - a binder system containing an emulsion of bitumen in water, and the mixture thereby obtained is further processed into pressed articles by pressing

   characterized in that,
   before the mixing with the water-containing binder system, the coal particles are subjected to an impregnating step in which they are impregnated with a liquid water-insoluble and/or water-repellent substance, wherein the water-insoluble and/or water-repellent substance belongs to the group of substances comprising waxes, organic coking-plant or refinery products, plastics or plastics scrap, and used oil, and wherein the lower limit of the amount of water-insoluble and/or water-repellent substance added in the impregnating step is 0.5% by weight, preferably 1% by weight, with respect to the weight of the material to be processed into pressed articles, the coal particles.
2. Method according to Claim 1, characterized in that the impregnating step comprises damping the coal particles with the water-insoluble and/or water-repellent substance, spraying the coal particles with the water-insoluble and/or water-repellent substance, mixing the water-insoluble and/or water-repellent substance into a moving packed bed of the coal particles, or mixing the water-insoluble and/or water-repellent substance into a fluidized bed of the coal particles.
3. Method according to one of the preceding claims, characterized in that the upper limit of the amount of water-insoluble and/or water-repellent substance added in the impregnating step is 5% by weight, preferably 3% by weight, particularly preferably 2% by weight, with respect to the weight of the material to be processed into pressed articles, the coal particles.
4. Method according to one of the preceding claims, characterized in that iron- or iron-oxide-containing particles are also processed in a mixture with the coal particles.
5. Method according to one of the preceding claims, characterized in that the pressed article is subjected to a heat treatment after the pressing.
6. Method according to one of the preceding claims, characterized in that the coal particles are subjected to a heat treatment after the impregnating step, before mixing with the water-containing binder system.
7. Use of a pressed article obtained by a method according to one of Claims 1 to 6 in a process for producing pig iron in a fixed bed as a carbon carrier or in a process for producing carbon carriers for a process for producing pig iron in a fixed bed.

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