METHOD FOR PRODUCING PRESSED ARTICLES CONTAINING COAL PARTICLES
In a method for producing pressed articles containing coal particles, before being mixed with a binder system containing water, at least a subset of the coal particles is subjected to at least two impregnation steps in which it is impregnated with at least one substance. The pressed articles may be used, for example, in methods of pig iron production in a packed bed or in methods for producing carbon carriers for methods of pig iron production in a packed bed.
This application is a U.S. National Stage Application of International Application No. PCT/EP2011/061619 filed Jul. 8, 2011, which designates the United States of America, and claims priority to AT Patent Application No. A 1179/2010 filed Jul. 12, 2010. The contents of which are hereby incorporated by reference in their entirety.
TECHNICAL FIELDThe disclosure relates to a method for manufacturing pressed articles containing coal particles, to the pressed articles thus obtained and also to the use of the pressed articles in methods of pig iron production in a packed bed or in methods for manufacturing carbon carriers for methods of pig iron production in a packed bed.
BACKGROUNDPressed articles containing coal particles, for example briquettes, used in methods of pig iron production in a packed bed, for example in melter gasifiers, or in methods for manufacturing carbon carriers for methods of pig iron production in a packed bed, for example coke generation for blast furnaces, must exhibit a certain drop resistance and crush strength after removal from the press. Drop resistance is required so that the original size of the pressed articles when being loaded into a process is largely maintained undamaged by unavoidable shocks, for example on transfer from one conveyer to another or during loading into a material bunker. The crush strength is required so that the original size of the pressed articles after loading into a material bunker or a packed bed reactor is maintained despite pressure exerted by layers above.
These resistance requirements are also summed up by the term green strength.
As well as the green strength, the hot strength of pressed articles—especially when used in thermal processes—is a criterion for their suitability for use. In the particular case of the use of fine-grain pressed articles containing coal particles in methods of pig iron production, such as in a melter gasifier or blast furnace for example, the term hot strength relates a) to a strength of the semicoke or coke particles remaining after pyrolysis of the pressed articles in a high-temperature zone, and b) to a strength of the semicoke or coke particles after they have been attacked chemically by a hot gas containing CO2. A minimum degree of hot strength makes it possible for the available size of these particles to be largely maintained after the conversion of the pressed articles by pyrolysis into semicoke or coke particles.
In methods of pig iron production in a packed bed the development of undersized grains from pressed articles or coke particles before loading into a packed bed or within a packed bed is therefore undesirable, since the permeability of the packed bed is adversely affected by this. In the particular case of a method of pig iron production, this relates both to the gas permeability and also to the drainage behavior in slag. If the permeability of the packed bed worsens, the expected results can be adverse effects on its productivity, its specific energy requirement, and also its product quality.
It is known from WO 02/50219A1 to produce pressed articles with sufficient green strength from fine-grained coal particles by means of a binder system of quicklime and molasses. This involves mixing fine-grained coal particles of fine coal and quicklime, leaving the mixture to rest, for the purpose of progressing the slaking reaction with moisture from the coal particles, then mixing in molasses, kneading the mixture thereby obtained and finally pressing pressed articles from it.
There are coals that exhibit extremely high absorptive capacity for water, particularly characterized by a high inherent moisture content. For use in the production of pig iron, however, the moisture content of the pressed articles should not be too high, that is to say at most 7% by weight. This is because, when using the pressed articles to produce pig iron or to produce carbon carriers for methods of producing pig iron, this moisture is a drain on energy, since the specific consumption of carbon carriers increases significantly with the moisture content of the pressed articles. Therefore, coals with a higher moisture content must be dried before being processed into pressed articles. In addition to the unwetted pore volume that already exists in the undried coal, additional pore volume is produced by driving out water from cavities during drying. The unwetted pore volume can absorb a corresponding amount of water or aqueous media. The additional pore volume can of course also once again absorb water or aqueous medium. Moreover, certain coals also have a tendency—particularly during intensive drying—to generate additional pore volume as a result of grain damage. When drying a coal with a high absorptive capacity for water to an acceptable moisture content before application of the method described in WO 02/50219A1 for producing pressed articles, a large additional pore volume is generated. Therefore, a dried coal particle sucks into its pores a considerable part of the molasses that are required for producing a bond on the particle surface and can be regarded as an aqueous solution. Therefore, for such coals with conventionally used additions of molasses of ≧10% by weight, with respect to the weight of the coal to be processed, sufficient strength of the pressed articles cannot be achieved. In order to allow pressed articles with sufficient strength nevertheless to be produced on the basis of a molasses binder, it is necessary:
to dispense with the generation of unwetted pore volume by drying, or
to add as much additional molasses as the pore volume takes up, which is therefore not available for binding on the surface of the coal particles.
These measures are undesired, however, for reasons of process economy.
Also in the case of coals that are naturally less moist, which do not have to be dried to achieve a moisture content of the pressed articles of at most 7% by weight, part of the molasses is sucked into pores of the coal particles. However, molasses contain components which act catalytically with regard to a reaction of carbon with hot, CO2-containing gases, whereby the extent of a reaction of solid carbon with CO2 according to the Boudouard reaction increases, particularly in the hot zones of a fixed bed serving for producing pig iron at temperatures >800-1000° C., dependent on the pressure. As a result of this, the hot strength of semicoke or coke particles obtained by pyrolysis from pressed articles treated with molasses decreases.
The use of bitumen as a binder, proposed in WO9901583A1, does not give rise to such problems associated with molasses.
However, production of pressed articles with bitumen entails very high binder costs.
The use of an aqueous bitumen emulsion as a binder system, proposed in AT005765U1, lowers the bitumen consumption by up to more than 50%. In practice, however, it has been found that the charging coals must have moisture contents of much more than 5% by weight in order for stable pressed articles to be obtained when using such bitumen emulsions. Moreover, there is the problem that pores present in the coal particles can absorb aqueous bitumen emulsion, or extract water from the emulsion and destabilize the latter as a result of droplet coalescence, before a largely uniform distribution of the emulsion within the material to be processed into pressed articles, and correspondingly uniform wetting of the particle surface by the emulsion, can take place. As a result, the effectiveness of the emulsion as a binder is reduced.
A pre-treatment of fine coal with moist or dry sludge or dust, followed by quicklime, before the addition of an aqueous binder, is described in WO-A-2004/020555
EP-A-0368041 discloses an aqueous strong suspension as binder in combination with a silicon dispersion, wherein the ability of the coal briquette to take up water is to be reduced.
U.S. Pat. No. 1,551,966 discloses an impregnation of coal with non-aqueous binders such as fuel oil or asphalt, for the purpose of increasing the calorific value.
U.S. Pat. No. 2,310,095 discloses a method of sealing pores by aqueous asphalt emulsion in lignite from which water has been removed. Non-aqueous binder agents such as asphalt or coal tar are used as binders, i.e., not aqueous binding agent systems as in the method disclosed herein.
SUMMARYIn one embodiment, a method is provided for producing a pressed article containing coal particles, in which the coal particles are mixed with a binder system containing water and the mixture obtained in this way is further processed by being pressed into pressed articles, wherein before being mixed with the binder system containing water, at least a subset of the coal particles is subjected to at least two impregnation steps, in which it is impregnated with at least one substance, wherein the substance is used as a liquid or by means of a liquid respectively for impregnation, and the lower limit of the amount of substance added in the at least two impregnation steps amounts to 0.5% by weight, for example 1% by weight, in relation to the weight of the coal particle material to be processed into pressed articles.
In a further embodiment, an impregnation step includes wetting the coal particles with the substance, spraying the coal particles with the substance, mixing the substance into a moving packed bed of the coal particles or mixing the substance into a fluid bed of the coal particles.
In a further embodiment, the substance with which the coal particles are impregnated is water.
In a further embodiment, the substance with which the coal particles are impregnated is a water-insoluble and or water-repellent substance.
In a further embodiment, the substance with which the coal particles are impregnated is an aqueous solution of a substance or a substance mixture.
In a further embodiment, the substance with which the coal particles are impregnated is an aqueous suspension of solid colloids, the solid substance having water-repelling properties.
In a further embodiment, the substance with which coal particles are impregnated is an emulsion, containing water on the one hand and carbon-containing substances on the other hand.
In a further embodiment, the upper limit of the quantity of the substance added in the at least two impregnation steps amounts to 5% by weight, for example 3% by weight, especially for example 2% by weight in relation to the weight of the coal particles material to be processed into pressed articles.
In a further embodiment, the binder system contains molasses and also quicklime or hydrated lime.
In a further embodiment, the binder system contains an emulsion of bitumen in water.
In a further embodiment, particles containing iron or iron oxide are also processed in the mixture with the coal particles.
In a further embodiment, the pressed article is subjected to heat treatment after being pressed.
In a further embodiment, the coal particles are subjected to a heat treatment after the impregnation step before being mixed with the binder system containing water.
An exemplary embodiment of a method is provided for producing a pressed article containing coal particles is shown in the single FIGURE.
Some embodiments provide a method for producing pressed articles that overcome certain disadvantages of conventional methods, and/or for producing pressed articles with sufficient green strength and hot strength even when using coal particles that have to be pre-dried, using an amount of a water-containing binder system that is less by comparison with certain known methods.
Fro example, some embodiment provide a method for producing a pressed article containing coal particles in which the coal particles are mixed with a water-containing binder system and the mixture thereby obtained is further processed into pressed articles by pressing, wherein before the mixing with the water-containing binder system, the coal particles are subjected to an impregnating step in which they are impregnated with at least one substance.
During the impregnation, the substance either penetrates into the pores of the coal particles and, by filling the pore space, correspondingly prevents penetration of components of the aqueous binder system. Or the substance becomes deposited in the outlets of the pores on the coal particle surface, also known as pore necks and, by this plugging of the pore necks, prevents penetration of components of the aqueous binder system into the pores.
In this way, aqueous binder system that is required on the coal particle surface for binding purposes is prevented from performing these binding purposes after penetration into the pores. Correspondingly, the amount of aqueous binder system that is required is reduced by comparison with a method in which aqueous binder system can penetrate into the pores.
The coal particles to be processed into pressed articles, or at least a subset thereof, can be subjected before the impregnation step to drying to a moisture level of less than 8% by volume, for example to a moisture level of less than 7% by volume. A moisture level in a range of greater than/equal to 4% weight by volume to less than 8% weight by volume is especially preferred, a moisture level in a range or greater than/equal to 5% weight by volume to less than 7% weight by volume is especially preferred.
Apart from water, the aqueous binder system may contain one or more further components.
The impregnating step may comprise sputtering the coal particles with the substance, spraying the coal particles with the substance, mixing the substance into a moving packed bed of the coal particles, or mixing the substance into a fluidized bed of the coal particles.
A subset or the entire amount of coal particles to be processed into pressed articles can be subjected to at least two impregnation steps. There can also be three, four, five, six, seven, eight, nine, ten or more impregnation steps.
If the total amount of coal particles to be processed into pressed articles is subjected to at least two impregnation steps, the effects of the impregnation described above will occur for the total amount of coal particles to be processed into pressed articles.
If a subset of the amount of coal particles to be processed into pressed articles is subjected to at least two impregnation steps, less impregnation agent is used than for the impregnation of total amount of coal particles to be processed into pressed articles. The effects of the impregnation described above occur for the subset and thus contribute to an improvement of the properties of the pressed article.
A first impregnation can improve the efficiency and/or the durability of a subsequent impregnation. With only one impregnation step the result can be a weakening of the effect brought about by the impregnation as the age of the pressed articles increases - for example such that the briquettes behave in a brittle manner after a certain time. A weakening of the effect brought about by the impregnation can have been caused for example by incomplete closing-off of the pores by the impregnation means or by the impregnation means coming away from the pore walls, for example as a result of cooling down and/or contraction.
If two impregnation steps are carried out, such effects can be reduced or prevented respectively. In such cases it is especially advantageous for different impregnation means to be used for the first and second impregnation step. In the second impregnation step for example, a penetration and as a result closing off of the pores which were not completely closed off or were not closed off after the first impregnation step can take place—because the impregnation means in the second impregnation step for example has a different viscosity and/or other user properties in relation to the coal particles.
It can be advantageous for a subset or the total amount of coal particles to be processed into pressed articles to be subjected to more than two impregnation steps. Remaining unclosed or unwetted pores after a preceding impregnation step can be impregnated or wetted or closed off respectively in one of the subsequent impregnation steps.
The coal particles can be impregnated with the same substance in all impregnation steps. Different substances can also be used in different impregnation steps.
The substance used for impregnation may be used for impregnation as a liquid or by means of a liquid respectively. Substances which are liquid at the temperature obtaining during the impregnation step are used as the liquid. Impregnation by means of a liquid refers for example to impregnation with substances which, although they are not liquid under the conditions obtaining during the impregnation step, they are however emulsified or suspended in a liquid. Compared to a used of solid substances, this improves the penetration into pores of the blocking of pore necks or even makes it possible at all.
In order to guarantee that a substance used during the impregnation step remains liquid during the impregnation step, the coal particles to be impregnated may be heated up to a temperature at which the substance is liquid.
According to one embodiment, the substance with which the coal particles are impregnated in at least one impregnation step is water.
Then, in the impregnating step, water is sucked into the pores, which as a result no longer show any tendency to absorb components of the aqueous binder system fed to the coal particles after the impregnating step. As a result, components which, in the case of previous methods, were sucked into the pores, and consequently became ineffective for the binding of the pressed articles, can make a contribution to the binding of the pressed articles.
By limiting the proportion of pressed articles impregnated with water in a charging mixture for a pig iron production process in combination with carbon carriers which have a lower moisture content than these pressed articles, the amount of water introduced into the pig iron production process can be limited to an acceptable amount.
According to another embodiment, the substance with which the coal particles are impregnated in the impregnating step is a water-insoluble and or water-repellent substance. If, in the impregnating step, the pores are filled with such a substance, and the pore walls are thereby coated with such substances, the tendency of the pores to absorb components of the aqueous binder system decreases. If the outlets of the pores on the coal particle surface are closed by such substances, no components of the aqueous binder system can penetrate any longer into the pores. As a result, components which were previously sucked into the pores, and consequently became ineffective for the binding of the pressed articles, can make a contribution to the binding of pressed articles.
The water-insoluble and/or water-repellent substance may belong to the group of substances comprising waxes, organic coking-plant or refinery products, as well as plastics or plastics scrap. It may also be used oil. The substances are usually available in large amounts at low cost.
In this case, the impregnating step advantageously takes place at a temperature at which the water-insoluble and/or water-repellent substance is liquid, particularly viscous. The liquids are regarded as viscous in this sense if their viscosity is at least 1 Pas, and at most 100 Pas, for example 10 Pas. Under these conditions, the substance is dispersed on the surface of the coal particle and penetrates into the outlets of the pores but scarcely into the interior of the pores. As a result, the consumption of the water-insoluble and/or water-repellent substance in the impregnating step is kept low. The water-insoluble and/or water-repellent substance advantageously solidifies in the outlets of the pores on the coal particle surface during cooling.
According to another embodiment, the substance with which the coal particles are impregnated in the impregnating step is an aqueous solution of a substance or a substance mixture. For example, it comprises molasses, an aqueous solution of a mixture of carbohydrates and other natural substances.
In principle, dissolved substances of all kinds that improve the hot strength and green strength of the pressed articles may be used, for example starch or lignin lyes from spent liquors of pulp production.
It is preferred to use solutions of substances or substance mixtures which are transformed into water-insoluble substances by heat treatment and/or reaction with the coal particles.
This achieves the result that the effects induced by these substances or substance mixtures are not lessened by them dissolving in the water of the water-containing binder system and being washed out from the pores.
According to another embodiment, the substance with which the coal particles are impregnated in the impregnating step is an aqueous suspension of solid colloids, the solid substance having water-repelling properties. An example of this are suspensions of colloidal talc, of graphite or of waxes in water. If the solid substances are deposited in the pores or in the pore necks, it is made more difficult for water-containing binder systems to enter on account of the high surface tension of the water-repelling solid substances.
According to another embodiment, the substance with which the coal particles are impregnated in the impregnating step is an emulsion containing water on the one hand and carbon-containing substances on the other hand, such as for example bitumens, crude tars obtained from hard coal, pitches, waxes or oils.
When such emulsions penetrate into the pores, the carbon-containing substances are deposited in thin layers on the pore surface. During pyrolysis, carbon layers are produced from these thin layers. These reduce the reactivity of the pressed article with respect to hot CO2-containing gases by comparison with an embodiment in which no thin layers of the substances are deposited in the pores. Such an effect also occurs if the substance with which the subset of the coal particles is impregnated in the impregnation step is not an emulsion, for example if the substance is bitumen.
The reason for this is that the carbon layers produced from the substances contain little or no substances that act catalytically with respect to the reaction with hot CO2-containing gases. By contrast, the coal particles or the material that is to be processed into pressed articles contain(s) catalytically acting compounds, for example iron or alkalis. Correspondingly, the reactivity of a pressed article of which the surface and pores are covered with a carbon layer created from the substances is less than that of a pressed article without such a carbon layer.
When using coal particles which require pre-drying before being processed into pressed articles, it is of advantage for commercial reasons not to pursue the drying to a moisture content much below 5% by weight, that is to say to a moisture content of at most 4% by weight. As a result, the creation of additional pore volume as a consequence of the drying is limited and correspondingly less substance is taken up by pores in the impregnating step. Correspondingly, less substance is used in the impregnating step. Moreover, less expenditure in terms of equipment and energy is required for the drying.
The lower limit of the amount of substance added in the impregnating step, known as impregnating agent, is 0.5% by weight, for example 1% by weight; the upper limit is 5% by weight, for example 3% by weight, particularly for example 2% by weight, with respect to the weight of the material to be processed into pressed articles, that is to say the coal particles. Adding more than 5% by weight of impregnating agent is not economically advisable. Adding less than 0.5% by weight of impregnating agent means that impregnation is no longer effective.
According to one embodiment of the method, the binder system contains molasses and quicklime or hydrated lime. It may also consist of these components.
According to another embodiment, the binder system contains molasses in combination with strong inorganic acids, such as for example phosphoric acid, sulfuric acid or nitric acid.
According to one embodiment of the method, the binder system contains an emulsion of bitumen in water. It may also consist of such an emulsion.
According to further embodiments, the binder system contains products from spent liquors of pulp production, starches, cellulose, beet chips, waste paper pulp, wood pulp or other long-chained polyelectrolytes such as for example carboxy methylcellulose.
Since binder systems containing quicklime or hydrated lime have the disadvantage that quicklime CaO and hydrated lime Ca(OH)2 increase the reactivity of the pressed articles with respect to hot CO2-containing gases as a result of catalytic effectiveness, the embodiments without quicklime or hydrated lime have the advantage of providing pressed articles with comparatively lower reactivity.
According to one embodiment of the method, iron- or iron-oxide-containing particles are also processed in a mixture with the coal particles.
According to one particular refinement of the method, the pressed articles are subjected to a heat treatment after the pressing.
The heat treatment takes place at a temperature that is increased by comparison with the pressing. The heat treatment brings about a drying and/or hardening of the pressed articles. The heat treatment may take place at temperatures of for example ≧250° C. and ≦350° C., at which irreversible chemical processes can transform binder components. For example, water-soluble binder components may be transformed into water-insoluble compounds.
The compounds produced in such transformations may make a contribution to the strength of the pressed articles. In the case of a binder system containing molasses, for example, the transformation of molasses takes place by caramelization.
According to one particular refinement of the method, the coal particles are subjected to a heat treatment after the impregnating step, before mixing with the water-containing binder system.
The heat treatment brings about a drying. For the case where there are solutions or emulsions in the pores, the heat treatment additionally brings about a concentration of the solutions, suspensions or emulsions, and correspondingly a coating of the pore walls with dissolved, suspended or emulsified components. In addition to the aqueous binder system then to be added, these may make a contribution to increased hot strength and green strength of the pressed articles.
Furthermore, the heat treatment may bring about the transformation of the coating of the pore walls, initially produced as a result of the heat treatment, into water-insoluble compounds, or into compounds lowering the reactivity of the coal particles with respect to hot CO2-containing gases. The maximum temperature of the heat treatment is restricted by the pyrolysis of the coal particles and is at 350° C. The lower limit for the temperature in this heat treatment is at 150° C.
If the same water-containing emulsion is used for the impregnation as is used as the water-containing binder system, the amount added in the impregnating step is less than the amount of water-containing binder system added in the subsequent mixing. For example when using a bitumen-in-water emulsion in the impregnating step and as the binder system, in the impregnating step an addition of 2-3% by weight is made, while 7-10% by weight are added later as the binder system. The same applies if the same aqueous solution of a substance or a substance mixture is used for the impregnation as that used as the water-containing binder system. For example when using molasses in the impregnating step and as the binder system, in the impregnating step an addition of 3 to 5% by weight is made, while 6 to 8% by weight are added later as the binder system.
In this case, the limits of the specified ranges are also included. In these cases, a heat treatment is necessary after the addition in the impregnating step, in order to remove the water, as the carrier liquid, to the extent that the emulsified substances or the dissolved substances settle in the pores or the pore necks. As a result, the pores are covered or the pore necks are plugged. Altogether, therefore, less water-containing binder system is required for producing the pressed articles than in the case of production without an impregnating step.
The processing into pressed articles after the impregnating step can be performed by known methods, for example as described in WO 02/50219A1 or AT005765U1, or by any method suitable for processing coal particles with a water-containing binder system into pressed articles.
An addition of water-containing binder systems which, according to the present disclosure, only takes place after the impregnating step with a water-insoluble and/or water-repellent substance, in the production of pressed articles reduces the costs of the method by comparison with conventional methods, such as for instance according to WO02/50219A1. The avoidance of water absorption by the coal during the production of pressed articles with water-containing binder systems on the one hand reduces the specific coal consumption in pig iron production methods in which the pressed articles or coke obtained from them are used, since less water from the binder system is present in the pressed article and correspondingly less energy has to be expended for vaporizing said water. On the other hand, when the disclosed method is used, it is possible to dispense with a necessity that occurs in conventional methods for producing pressed articles for afterdrying the pressed articles as a result of the water absorption from the binder system, or it is possible to reduce the drying effort, resulting in an energy saving. Since it is correspondingly possible to dispense with the setting up or operation of devices for afterdrying, or it is possible to reduce the dimensions of the devices and the effort involved in their operation, this is synonymous with a reduction in operating costs and a reduction in investment costs.
Depending on the type of substance used for the impregnation, a lessening of the CO2 reactivity of the semicoke produced after pyrolysis of the pressed articles in a melter gasifier, or of the coke obtained from pressed articles, may be obtained as an additional advantageous effect of the impregnating step. A low CO2 reactivity is desired when operating a melter gasifier, in order that the semicoke in the fixed bed of the melter gasifier or the coke in the fixed bed of a blast furnace remains stable from the charging onto the bed surface to the reaching of the direct gasification zone in the region of the oxygen nozzles or the air-blast tuyeres and, as a result, promotes the permeability of the fixed bed with respect to the gas distribution and drainage of molten phases. The lessening of the CO2 reactivity of the semicoke or the coke is achieved by the inner surface of the pores of the coal particles in the pressed article no longer being able to be coated by the impregnation with a binder which contains reactivity-promoting substances. For example, the molasses as a binder component contains alkalis as reactivity-promoting substances. If coating of the inner surface of the pores with molasses is avoided by the impregnation, for example with substances containing bitumens or waxes, the CO2 reactivity is therefore lowered by comparison with semicoke or coke obtained by means of a method without an impregnating step.
A lower proportion of undersized coke is often added to the charging coal in the COREX® or FINEX® process for pig iron production in a packed bed of a melter gasifier in order to improve the permeability of the packed bed. When using pressed articles produced according to various embodiments, or coke produced in this way, softening of the semicoke or coke particles is inhibited by hot CO2, and consequently a disintegration of the particles is counteracted. With inventively produced pressed articles an improved thermo-mechanical stability compared to pressed articles produced in the conventional manner is namely to be seen. Thermo-mechanical stability thus relates to the aspect of the hot strength which concerns a strength of the semicoke or coke particles remaining after pyrolysis of the pressed articles in a high-temperature zone. Thermo-mechanical stability relates to a test method in which the pressed articles are subjected to a thermoshock procedure, and the semicoke obtained in this procedure is subjected to drum agitation. The improved thermo-mechanical stability manifests itself in that the portion of coarse grain of the drum-agitated semicoke is increased by the disclosed impregnation compared to conventionally produced pressed articles.
With a packed bed packed with semicoke obtained from inventively produced pressed articles through pyrolysis a considerably better gas permeability and a better drainage behavior of the packed bed is made possible than in certain conventional methods. The improvement of the reactive properties of the semicoke thus makes it possible to reduce or even avoid the addition of coke to COREX® or FINEX® charging coal.
In the area of coking plant technology, it is known to improve the quality of the coke produced from the charging coal by increasing its bulk density. The use of many charging coals for producing metallurgical coke is made possible in the first place by compacting of the charging coal. Apart from tamping coking plants, therefore, method variants for coking plants in loose-fill operation were developed, providing briquetting or partial briquetting of the charging coals. From today's viewpoint, however, briquetting with a bituminous binder is problematic for commercial reasons, hot briquetting or briquetting with binders originating from hard coal tar is problematic for health reasons, and briquetting with molasses or comparable binders is problematic because of the introduction of undesired substances into the coke.
The method according to various embodiments for producing pressed articles makes it possible to reduce binder consumption, or to mitigate the harmful effects of reactivity-promoting binder components, even when producing coke using articles pressed from the charge materials.
The pressed articles may be, for example, briquettes or compressed strips from compacting.
Pressed articles contain up to 97% by weight of coal particles, and up to 15% by weight of components of a binder system, as well as, with respect to the weight of the coal particles as the material to be processed into pressed articles, water-insoluble and/or water-repellent substances, or solid substances with water-repelling properties, in an amount of which the lower limit is 0.5% by weight, for example 1% by weight, and the upper limit is 5% by weight, for example 3% by weight, particularly for example 2% by weight.
In this case the 15% by weight of components of a binder system is to be understood as water not being included as a component of the binder system—the 15% by weight thus relates to the non-aqueous components of the binder system.
According to one embodiment, the pressed article also contains iron- or iron-oxide-containing particles. Such particles may, for example, originate from dusts or slurries occurring in the production of pig iron or steel.
Table 1 shows the evaluation of trials for producing pressed articles in respect of the drop resistance (SF) and the crush strength (PDF) of the pressed articles within the context of a series of example trials. In these trials the pressed articles were produced in accordance with the disclosed method with impregnation of a subset of the coal particles with two impregnation steps, or with one impregnation step respectively. The pressed articles involve briquettes.
A system including molasses and quicklime has been used as the water-containing binder system. The molasses itself had a water content of 20% by volume.
The following commercially available molasses were used in the binder system:
Sugarcane molasses made by Tate & Lyle with an overall sugar content of 51%.
White fine lime quicklime from Walhalla Kalk was used as quicklime in the binder system.
For impregnation bitumen and commercially-available hydraulic oil was used as the impregnation means. Mexphalte 55 from Shell was used as the bitumen. The commercially-available hydraulic oil used was of lower viscosity than the bitumen under the usage conditions.
The bitumen impregnation agent was mixed in a Lodige Type FM130D ploughshare mixer, the other mixtures were produced in an Eirich Type R08 W sample mixer.
The Koppern kneading machine used for the kneading consisted of a vertical cylindrical container through which an essentially rotating shaft with kneading arms is guided.
The production of the green pressed articles was carried out by means of a Koppern Type 52/10 trial roller press. The selected pillow-shaped format for the green pressed articles and has a nominal volume of 20 cm3. The material to be pressed is loaded by means of gravity distributors. In this case bands consisting of a number of green pressed articles were produced by the trial roller press. In these bands green pressed articles were located both in the edge area of the bands and also in the central area of the bands.
In order to obtain the drop resistance or crush strength respectively of individual green pressed articles or individual pressed articles for the determination, the bands were broken down along the separation wires between the individual green pressed articles. As a rule the bands break on ejection from the trial roller press into individual green pressed articles.
After the kneading process in the kneading mechanism the kneaded mixtures were subjected as material to be pressed to pressing in the trial roller press, in order to produce green pressed articles.
The green pressed articles obtained in such cases are still soft—a fact which is indicated by the use of the word “green” in technical jargon—and are subjected to hardening in order to obtain finished pressed articles. This hardening can for example be undertaken by at least part drying by storage in the air and/or by a thermal treatment.
After the pressing, individual green pressed articles were each immediately examined, in the green state in technical jargon, for drop resistance (SF) and crush strength (PDF). The results of these examinations are shown in the columns labeled “immediate” for PDF and SF.
The measurements of drop resistance and crush strength were repeated in each case after one hour hardening in air and after 24 hours hardening in air. The results of these investigations are shown in the columns labeled “1 h” and “24 h”.
In the drop resistance test (related to ASTM D440) for ascertaining the drop resistance, a sample of green pressed articles weighing 2 kg of pressed articles hardened by drying in air or by thermal drying were dropped four times down a pipe from a height of 5 m into a collection container of which the base is embodied in the form of a massive steel plate. The pipe has a diameter of 200 mm and the collection container has a diameter of 260 mm. The thickness of the steel plate is 12 mm. The evaluation of the drop resistance tests by sieve analysis is undertaken after the second and fourth drop. The numerical values for drop resistance SF in Table 1 each give the proportion of grain fraction >20 mm after four drops.
For determining the crush strength a Type 469 test machine made by ERICHSEN was used. In this test method individual green pressed articles or pressed articles hardened by drying in air or by thermal drying were clamped between two supports of which the lower is coupled to a force sensor and the upper support is continuously adjusted by means of a spindle drive to apply a creeping, increasing compressive force. The lower support is formed by a round plate of diameter 80 mm and the upper support by a horizontal round iron of diameter 10 mm. The speed of advance for the upper support amounts to 8 mm/min. The crush strength PDF is registered as the maximum load able to be accepted by a green or by a hardened pressed article before it breaks—the entries in Table 1 specify the average crush strength for a break as a result of crush strength load in Newton. Six green pressed articles or pressed articles respectively from the central area and six green pressed articles or pressed articles respectively from the edge area of the bands obtained in the trial roller press were examined. Average values were computed for the data obtained in these examinations, wherein the minimum and maximum values were excluded from the considerations. The average values are specified in Table 1.
In trial 1 a mixture of 70% by weight Ensham coal with an average particle size d50 of 0.95 mm together with 30% by weight Ensham coal with an average particle size d50 of 0.57 mm was used as the coal particle material to be processed into pressed articles. This material to be processed into pressed articles was processed with one impregnation step into pressed articles, by the coal to be processed being subjected to a drying and thereafter being brought to a desired grain sized by granularization. The coal particles obtained in this process are subjected to an impregnation step with the addition of bitumen. A binder system containing water is added to the coal particles obtained in this way, in this case molasses with the addition of the solid fine-particle binder component quicklime, with mixing, wherein the mixing can be single stage or multi-stage. The mixture obtained in this case is subjected to kneading and pressing. The product obtained after hardening is the briquette.
Ensham coal comes from Ensham Resources from Queensland, Australia.
The binder system containing molasses in water was used in a quantity of 8% by weight, in relation to the weight of the material to be processed into pressed articles. The molasses itself contained a proportion of 20% water by weight. The binder system containing water, in addition to molasses, also included 2% by weight of quicklime, in relation to the weight of the material to be processed into pressed articles, Ensham coal.
Compression strength and drop resistance at different points in time are specified in Table 1, in the first column of data.
In trial 2 in accordance with the disclosed method the same material to be processed into pressed articles was used. All of the Ensham coal used was impregnated with commercially-available hydraulic oil and left to stand overnight. The quantity of oil used amounted to 2% by volume in relation to the weight of the Ensham coal material to be processed into pressed articles. Then the entire Ensham coal used already impregnated with oil was impregnated with bitumen. Shell Mexphalte 50/70 with a softening point of around 50° C. was used as the bitumen. The quantity of bitumen used amounted to 2% by weight in relation to the weight of the material to be processed into pressed articles. After the impregnation with bitumen the processing in accordance with trial 1 was undertaken after its single impregnation step. The temperature of the coal treated with oil and bitumen was 53° C. before the addition of molasses.
It is evident that a two-stage impregnation leads to pressed articles which, by comparison with pressed articles produced with a single-stage impregnation, have a higher drop resistance and after 24 hours have a higher compression strength.
Part of a subset can also be impregnated in one or two stages, while the other part is not impregnated or is only impregnated in one stage.
In accordance with
In general, in the production of pressed articles in accordance with the present disclosure, the addition of the molasses/quicklime binder system containing water to the material to be processed into pressed articles can be undertaken such that molasses and quicklime are added at the same time or such that quicklime and molasses are added one after another.
In this case it is preferred in the use of impregnation agents such as bitumen for example that first of all a subset of the molasses intended for the production of the pressed articles is added, then mixing takes place and then quicklime is added. After the mixture obtained in this process has been left to stand, the remaining quantity of the molasses intended for the production of the pressed articles is added. Part quantity and remaining quantity in total amount to the molasses intended for the production of the pressed articles. The advantage of this procedure is that a kneading of the quicklime into soft impregnation agent can be avoided, or reduced during the mixing of the material to be processed into pressed articles with the binder system containing water.
In the case of the impregnation it can occur that the moisture needed for the dissolving reaction of the quicklime is not available in sufficient quantities—in non-impregnated coals this moisture can be obtained by the quicklime from the coal particles. In this case it is necessary to wet the impregnated coals with moisture. This can be done with water or with a part of the aqueous molasses of the binder system. Up to a half, for example up to a third of the molasses can be used for this purpose.
LIST OF REFERENCE CHARACTERS
- 1 Coal
- 2 Drying
- 3 Grains
- 4 Coal particles
- 5 First impregnation agent
- 6 First impregnation step
- 7 Product of the first impregnation step
- 8 Second impregnation step
- 9 Second impregnation agent
- 10 Product of the second impregnation step
- 11 Binder system containing water
- 12 Mixing
- 13 Mixture
- 14 Kneading
- 15 Pressing
- 16 Hardening
- 17 Product obtained after hardening
- WO02/50219A1
- WO9901583A1
- AT005765U1
Claims
1-17. (canceled)
18. A method for producing a pressed article containing coal particles, comprising:
- mixing the coal particles with a binder system containing water,
- further processing the mixture by pressing the mixture into pressed articles,
- before mixing the coal particles with the binder system containing water, subjecting at least a subset of the coal particles to at least two impregnation steps to impregnate the subset of the coal particles with a substance,
- wherein the substance is used as or by a liquid for the impregnation, and
- wherein a ratio of the substance added during the at least two impregnation steps in relation to a weight of the coal particle material processed into pressed articles is at least 0.5% by weight.
19. The method of claim 18, wherein one of the impregnation steps comprises at least one of: wetting the coal particles with the substance, spraying the coal particles with the substance, mixing the substance into a moving packed bed of the coal particles, and mixing the substance into a fluid bed of the coal particles.
20. The method of claim 18, wherein the substance with which the coal particles are impregnated is water.
21. The method of claim 18, wherein the substance with which the coal particles are impregnated is a water-insoluble and or water-repellent substance.
22. The method of claim 18, wherein the substance with which the coal particles are impregnated is an aqueous solution of a substance or a substance mixture.
23. The method of claim 18, wherein the substance with which the coal particles are impregnated is an aqueous suspension of solid colloids, the solid substance having water-repelling properties.
24. The method of claim 18, wherein the substance with which coal particles are impregnated is an emulsion comprising water and carbon-containing substances.
25. The method of claim 18, wherein the ratio of the substance added during the at least two impregnation steps in relation to a weight of the coal particle material processed into pressed articles is at most 5% by weight.
26. The method of claim 18, wherein the binder system contains molasses and also quicklime or hydrated lime.
27. The method of claim 18, wherein the binder system contains an emulsion of bitumen in water.
28. The method of claim 18, wherein particles containing iron or iron oxide are also processed in the mixture with the coal particles.
29. The method of claim 18, further comprising subjecting the pressed article to heat treatment after being pressed.
30. The method of claim 18, further comprising subjecting the coal particles to a heat treatment after the impregnation step before being mixed with the binder system containing water.
31. The method of claim 18, wherein the ratio of the substance added during the at least two impregnation steps in relation to a weight of the coal particle material processed into pressed articles is at least 1% by weight.
32. The method of claim 18, wherein the ratio of the substance added during the at least two impregnation steps in relation to a weight of the coal particle material processed into pressed articles is at between 1% and 3% by weight.
33. The method of claim 18, wherein the substance includes multiple component substances.
Type: Application
Filed: Jul 8, 2011
Publication Date: Jul 11, 2013
Inventors: Hado Heckmann (Linz), Josef Stockinger (Luftenberg)
Application Number: 13/809,968
International Classification: C10L 5/06 (20060101);
