Patent Application
20150027038
The present invention relates to a process for producing a briquette containing carbon carriers, wherein the carbon carriers together with a binder system are subjected to mixing with the introduction of steam and the mixture obtained is subjected to pressing to form briquettes.
Previously, hard coal briquetting was primarily used to produce lumpy carbon carriers from fine coal for use as domestic coal or in industrial grate firing. As a result, numerous processes for hard coal briquetting are known. Hard coal briquetting is of great importance for the COREX®/FINEX® processes for the production of liquid pig iron since these processes are based on a fixed bed process in which the fixed bed is created by lumpy carbon.
During this process, which is also known by the technical term melt-reduction process, lumpy carbon carriers are charged together with pre-reduced iron carriers and admixtures onto the fixed-bed surface of a so-called melt-down gasifier. In the melt-down gasifier, the pre-reduced iron carriers are completely reduced and a molten pig iron and molten slag produced, which are obtained from time to time from the run-off. The heat for the melting process is provided by gasification of the lumpy carbon carriers by means of oxygen. The hot gases that form hereby penetrate the fixed bed with the emission of heat and leave the fixed bed at the fixed-bed surface. In countercurrent to the hot gases, molten pig iron and molten slag percolate the fixed bed and accumulate in its lowermost region, the so-called sump tank. These processes require sufficient permeability of the fixed bed which is determined by the granulation of the lumpy carbon carriers during charging onto the fixed-bed surface and the particle stability of the lumpy carbon carriers under the conditions prevailing on the fixed-bed surface or in the fixed bed. Therefore, during charging onto the fixed-bed surface, the granulation of the lumpy carbon carriers should have a sufficiently high coarse particle content and a limited content of undersized particles. Suitable granulation for the charged lumpy carbon carriers established from the raw material for the carbon carriers by screening must not be substantially destroyed during the handling up to the charging onto the fixed-bed surface due to mechanical stresses. In addition, the granulation of the lumpy carbon carriers under the conditions prevailing on the fixed-bed surface or in the fixed bed must ensure a sufficiently large particle content and a limited content of undersized particles. The ability of a lumpy carbon carrier to resist destruction of its granulation during handling up to the charging onto the fixed-bed surface is referred to as strength at low temperatures, the ability of a lumpy carbon carrier to resist destruction of its granulation under the conditions prevailing on or in the fixed bed is known as high-temperature resistance.
During the COREX®/FINEX® process for the production of liquid pig iron, it is usual to use hard coal as the carbon carrier. Commercially available hard coal usually only contains 30-70% coarse particles which can be charged directly as lumpy carbon carriers. Briquetting is a suitable method to enable undersized particles also to be used in lumpy carbon carriers. Unlike the case with pieces of hard coal with which low-temperature resistance and high-temperature resistance are naturally occurring properties, during briquetting, the low-temperature resistance and high-temperature resistance of the briquettes containing lumpy carbon carriers can be influenced by the nature of the process used and the features of the way it is performed.
U.S. Pat. No. 6,332,911, W0200250219, WO2004020555, WO2005071119, WO9901583 and WO2010081620 describe hard-coal briquetting processes in conjunction with COREX®/FINEX®. These documents name a plurality of possible binder systems for this purpose, also including starch and polymers. In the embodiments named, in each case binders in liquid form are with mixed with the coal to be briquetted. However, starch and polymers—in particular PVA—, which are present in solid-granular to powdery consistency, have to be mixed with high proportions of water—1 part of dry binder with at least 10 parts water or more—to produce a manipulable liquid binder. If insufficient water is added, it is difficult to achieve a uniform distribution of the binder in the coal. Slight agglomerations form. This reduces the binder's binding power which then has to be compensated by the use of additional binder. However, this is not desirable for reasons of cost. Although, if the proportion of water in the binder is increased for this reason, the binder is better distributed in the coal, this results in a very wet mixture which cannot be easily briquetted since, due to its adhesiveness, the wet mixture in the briquette press feed has a greater tendency toward bridging and the briquettes therefore often stick in the molds of the press.
However, the use of the briquettes in COREX®/FINEX® processes for the production of liquid pig iron requires that a briquetting process be controlled not only with respect to optimizing the strength of the briquettes but also with respect to restricting the moisture in the briquettes before use for the production of liquid pig iron.
U.S. Pat. No. 1,121,325 also describes the mixing of starch in powder form with coal with the simultaneous use of steam. However, the steam first has to be produced in an expensive way which impairs the economic efficiency of the process.
U.S. Pat. No. 3,018,227A, U.S. Pat. No. 4,557,733A, U.S. Pat. No. 1,871,104A describe steam in the context of briquette production, but no waste steam from other steps of the process is added during the step to mix carbon carriers and binder system.
It is the object of the present invention to provide a process and an apparatus for the production of briquettes which also enables the process to be performed economically when steam is used for mixing carbon carriers and binder systems.
This object is achieved by a process for the production of a briquette containing carbon carriers, wherein the carbon carriers together with a binder system are subject to mixing with the introduction of steam and the mixture obtained is subjected to pressing to form briquettes.
The process according to the invention is characterized in that at least one of the steps from the group consisting of
The carbon carriers are preferably carbon carriers with a particle size of less than 4 mm, determined by sieve analysis. In this application, carbon carriers of this kind are also called fine coal.
Preferably, the carbon carriers comprise coal, particularly preferably hard coal, quite particularly preferably the carbon carriers are hard coal. The carbon carriers can also comprise coke, petroleum coke, carbonaceous dusts, carbonaceous sludges or consist thereof. It is possible to use a single type of carbon carrier, for example a single type of coal or hard coal, or mixtures of different types of carbon carriers, for example different types of coal or hard coal. Here, one type of carbon carrier means, for example, carbon carriers from one point of origin or carbon carriers of one rank or, for example, only metallurgical coal or only thermal coal. Here, different types of carbon carrier should, for example, be understood to mean carbon carriers from different points of origin or carbon carriers with different ranks or, for example, metallurgical coal and thermal coal.
With the process according to the invention, carbon carriers are processed to form briquettes in that the carbon carriers are mixed with a binder system with the introduction of steam and the mixture obtained is pressed to form briquettes.
Due to the use of steam, much higher strengths of the briquettes are obtained with the same binder system consumption compared to processes which do not use steam.
The steam—or its properties, which means its quality—added during mixing influences the properties of the briquettes obtained—for example by means of the quantity of the water introduced into the mixture or by means of the quantity of energy introduced. The quality of the steam with respect to energy content and water content per quantity unit of steam can, for example, be set by means of the extent of superheating in superheated steam or by means of the extent of condensation in wet steam. To this end, it is possible to mix steams of different quality. The mixing can also be set with respect to optimizing the briquette quality by means of the quantity of the steam added and/or the duration of the addition.
The binder system comprises at least one binder and optionally further substances, for example solvents for the binder. In this context, a binder is a substance by means of which solids with a fine degree of dispersion, for example powders, are bonded to one another.
In one embodiment, the binders are poorly water-soluble substances; a poorly water-soluble substance should be understood to be a substance which requires a weight percentage ratio of water to binder of equal to or greater than 5 to 1 for complete dissolution at 20° C.
Binders are for example starch or polyvinyl acetate, PVA. It is, for example, possible to use starch dissolved in water as the binder system.
With the process according to the invention, at least one of the steps from the group of steps consisting of
If the carbon carriers contain too much moisture to produce briquettes with acceptable moisture, according to the invention they are dried before mixing with the binder system takes place. Preferably, the moisture has a water content less than or equal to 7 percent by mass, particularly preferably the moisture has a water content of less than or equal to 5 percent by mass.
Setting the temperature of the carbon carriers to be mixed with the binder system enables the strength properties of the briquettes to be influenced. Therefore, according to the invention, optionally before mixing, the temperature of the carbon carriers to be mixed with the binder system is set in a predefined—selected with respect to the desired strength properties—temperature range.
The temperature of the carbon carriers initially determines the quantity of heat which has to be supplied with the steam in order to set the desired temperature for mixing the binder system with the carbon carriers. Depending upon how much energy is withdrawn from the steam by heating the carbon carriers, condensation takes place to varying degrees. If the moisture of the mixture, which is, for example, changed by this condensation, is in an adequate ratio to the quantity of binder system used, the strength of the briquettes is influenced favorably.
According to the invention, optionally a heat treatment—for example heating up—which can take place in one or more stages—of the briquettes is performed after pressing. The heat treatment can influence the strength properties of the briquettes in the sense of hardening.
According to the invention, at least one of the process steps
In the case of direct interaction, the superheated steam and the carbon carriers or briquette are in physical contact, wherein heat transmission takes place.
In the case of indirect interaction, the superheated steam and the carbon carriers or briquette are not in physical contact; heat transmission takes place through a wall, for example. After completion one more of the tasks
The mixing can be performed with batchwise material feed or continuous material feed.
Heat treatment should be understood to mean heat input, that is heating, but not heat removal, that is cooling.
According to the invention, waste steam that occurs during direct or indirect interaction is used as at least part of the steam introduced during mixing. All or a part of the waste steam that occurs can be used in this way. This increases the economic efficiency of the process since the waste steam is used energetically and materially for heating and as a solvent for the binder system during mixing.
According to a preferred embodiment, with the process according to the invention, the binder system is mixed with the carbon carriers in solid state, preferably dry. This enables the binder system to be mixed more effectively with the carbon carriers than would be the case if, for example, a viscous binder system were used.
According to a further embodiment, the binder system is mixed with the carbon carriers in liquid state; this is in particular the case with liquid binder systems.
According to a further embodiment, the binder system is mixed with the carbon carriers in a first mixing step to form a premix and the premix is subjected to a second mixing step with the introduction of the steam. The steam then arrives at an already extensively homogenized mixture of carbon carriers and binder system.
In this case, according to a further embodiment, the inlet temperature of the premix is set in a predefined temperature range on entry into the second mixing step. This again enables the properties of the briquettes obtained to be influenced, as already discussed above.
In this case, according to a further embodiment the inlet temperature of the premix is set by setting the temperature of the carbon carriers supplied to the first mixing step in a predefined temperature interval. Then, the premix does not have to be additionally heated in the mixing apparatus in which it is produced thus resulting in reduced complexity of the equipment.
According to a further embodiment, the second mixing step is regulated and/or controlled by changing at least one of the parameters from the group consisting of the members
If, with batchwise operation, the quantity of the added steam based on the quantity of the carbon carriers in the second mixing step is regulated for the duration of the addition of the steam, this obviously requires the prevailing steam mass flow in this time to be known.
According to a further embodiment, with at least one member of the group consisting of the members
According to a further embodiment, waste steam that occurs during this interaction is used as at least part of the steam introduced during mixing. This has the advantage that it is returned materially and energetically to the process.
Advantageously, the binder system contains starch. Starch is cheap and easily available and not harmful to the environment. According to a further embodiment, the binder system contains at least one component from the group consisting of the members
Synthetic polymers should, for example, be understood to mean:
The binder system preferably contains polyvinyl acetate. Polyvinyl acetate is easily obtained and available in large quantities and, for example as claimed in claim 12, can be produced during the course of a process for the production of pig iron.
According to a further embodiment, components that increase the heat resistance of briquettes are added to the carbon carriers in a quantity of 1 to up to 10 percent by mass, based on the mass of the supplied for mixing. This can, for example, involve bitumens in granular form or as spray droplets, dusts/sludge from metallurgical processes or coal with a higher heat resistance than the carbon carriers.
According to a further embodiment of the process according to the invention before being subject to pressing to form briquettes, the mixture is subjected to pre-agglomeration. The pressing of the pre-agglomerated mixture achieves advantages with respect to the properties of the briquettes, especially a higher density, resulting in more solid briquettes.
A further subject matter of the present application is the use of briquettes produced using the process according to the invention in a process for the production of pig iron with gasification of the carbon carriers. Preferably, waste heat that occurs during the process for the production of pig iron with gasification of the carbon carriers is used to produce at least part of a steam used in the process according to the invention.
A further subject matter of the present application is a process with which the binder system contains polyvinyl acetate, wherein the polyvinyl acetate is at least partially produced from monomers, which are obtained by means of a synthesis gas, which is based on export gas that occurs during the process according to the invention for the production of pig iron with gasification of the carbon carriers, with conversion of CO of the synthesis gas via acetic acid into vinyl acetate.
A further subject matter of the present application is an apparatus,
suitable for carrying out a process according to the invention with a mixing mechanism for mixing carbon carriers with a binder system
and with a pressing mechanism for pressing briquettes on the basis of a mixture obtained from the mixing mechanism,
wherein the mixing mechanism comprises a steam supply conduit for supplying steam,
characterized in
that at least one member of the group consisting of
If in
For example, pressure-equalizing locks are installed for the briquettes if the pressure in the heat treatment apparatus for heat treatment of the briquettes is higher than that of the environment.
The mixing mechanism can be operated batchwise or continuously.
The apparatus for changing the temperature of the carbon carriers before entry into the mixing mechanism can, for example, be embodied as a heatable chamber.
According to a preferred embodiment, the dryer is the apparatus for changing the temperature of the carbon carriers before entry into the mixing mechanism. This reduces the complexity of the equipment, the amount of maintenance and capital expenditure and operating costs.
The heat treatment apparatus for heat treatment of the briquettes can, for example, be embodied as a heatable chamber.
In one embodiment, a carbon-carrier store is provided from which a carbon-carrier output conduit opens into the dryer. Preferably, the carbon-carrier store is provided with an apparatus for changing the temperature of carbon carriers in the carbon-carrier store. This means that no extra unit is required for changing the temperature of the carbon carriers.
Preferably, the mixing mechanism comprises
Preferably, the premixing unit comprises an apparatus for changing the temperature of premix in the premixing unit; for example heating elements through which steam or thermal oil flow or electrical heating elements.
Preferably, an apparatus for regulating and/or controlling the quantity of steam
per time unit
and/or
per quantity unit of material to be briquetted to be introduced into the final mixing unit is provided. This can increase the efficiency of the process according to the invention in that the treatment conditions are optimized to the mixture to be briquetted.
Preferably, at least one member of the group consisting of the members
In some embodiments, the waste-steam conduit opens into the steam supply conduit and/or in the mixing mechanism. According to a further embodiment, the waste-steam conduit opens into the final mixing unit.
In some embodiments, the premixing unit and final mixing unit are combined in one piece of equipment in the mixing mechanism. This reduces the complexity of the equipment, the amount of maintenance and capital expenditure and operating costs.
According to a further embodiment, the apparatus according to the invention also comprises an apparatus for the pre-agglomeration of the mixture produced in the mixing mechanism. This is then connected via a mixture feed conduit to the mixing mechanism and to pre-agglomerate discharge conduit with the pressing mechanism for pressing briquettes. Optionally, the mixture produced in the mixing mechanism is kneaded before being introduced into the apparatus for pre-agglomeration in an optionally provided kneader. This improves the consistency of the mixture for the briquetting process compared to the state following the mixing mechanism.
For the purposes of the present application, the word steam always means water vapor.
In the following, the present invention is described with reference to some exemplary schematic figures.
The dryer 6 is an apparatus for indirect interaction with steam and the heat treatment apparatus 7 for heat treatment of the briquettes is an apparatus for direct interaction with steam; a steam-feeder conduit 8a, 8b for feeding steam opens into both apparatuses and a waste-steam conduit 9a, 9b leads from both apparatuses, wherein the waste-steam conduit 9a opens into the steam supply conduit 5 and the waste-steam conduit 9b opens into the mixing mechanism 1.
The carbon carriers 2, in this case a mixture of fine coals of different origin and different granulation, are subjected to mixing with the introduction of steam in the mixing mechanism 1 with a binder system 3, in this case starch powder. The mixture obtained thereby is then subjected to pressing to form briquettes in the pressing mechanism 4. The drying in the dryer 6 is performed to a water content of less than or equal to 7 percent by mass. The drying of the carbon carriers before mixing and the heat treatment of the briquettes after pressing is performed by means of superheated steam supplied via steam feeder conduits 8a, 8b. The waste steam that occurs thereby is introduced into the steam supply conduit 5 via the waste-steam conduit 9a and into the mixing mechanism 1 via the waste-steam conduit 9b where it is a part of the steam introduced during mixing.
The mixing mechanism 1 comprises a premixing unit 10 for carrying out a first mixing step, and a final mixing unit 11 for carrying out a second mixing step. In the mixing mechanism 1, premixing unit 10 and final mixing unit 11 are combined in one piece of equipment. A binder supply conduit 12 for the addition of the binder system 3 to the premixing unit 10 opens into the premixing unit 10. A carbon-carrier supply conduit 13 for supplying carbon carriers 3 from the dryer 6 to the premixing unit 10 also opens into the premixing unit 10. The steam supply conduit 5 opens into the final mixing unit 11. In a first mixing step, the binder system 3 is mixed with the carbon carriers 2 in the premixing unit 10 to form a premix and the premix is subjected to a second mixing step in the final mixing unit 11 with the introduction of the steam via the steam supply conduit 5. The steam supply conduit 5 contains an apparatus 14 for regulating and/or controlling the quantity of steam to be introduced into the final mixing unit per time unit and/or per quantity unit of material to be briquetted. This enables the regulation and/or control of the second mixing step by changing at least one of the parameters from the group consisting of the members
Apparatuses of this kind for regulation and/or control are also provided in the waste-steam conduits 9a, 9b, but these are not shown for reasons of clarity.
The dryer 6 is simultaneously an apparatus for changing the temperature of the carbon carriers before entry into the mixing mechanism. This dryer 6 can be used to set the inlet temperature of the premix on entry into the second mixing step in a predefined temperature range by setting the temperature of the carbon carriers 3 supplied to the first mixing step in a predefined temperature interval. In addition thereto, the inlet temperature of the premix on entry into the second mixing step can be set in a predefined temperature range by an apparatus 15 belonging to the premixing unit for changing the temperature of premix in the premixing unit. The settings of the inlet temperature of the premix on entry into the second mixing step are performed by means of indirect interaction with steam. Waste steam that occurs during an interaction of this kind can be used as a component of the steam supplied to the final mixing unit 11, although, this and a steam feeder conduit for feeding steam to the apparatus 15 is not shown additionally reasons of clarity.
The carbon carriers 2 are conducted from a carbon-carrier store 16, in which they are stored prior to being supplied to the mixer 6 into the dryer via a carbon-carrier output conduit 17. The carbon-carrier store 16 is provided with an apparatus 18 for changing the temperature of carbon carriers 2 in the carbon-carrier store. This apparatus 18 is also an apparatus for indirect interaction with steam, into which a steam feeder conduit, which is not additionally shown for reasons of clarity, for feeding steam opens.
Before pressing briquettes, pre-agglomeration can be performed by means of an apparatus 28 for pre-agglomeration of the mixture in the mixing mechanism 1. Optionally, before introduction into the apparatus 28 for pre-agglomeration, the mixture produced in the mixing mechanism 1 is kneaded in an optionally provided kneader 29.
The briquettes produced according to the invention are used in a process for the production of pig iron with gasification of the carbon carriers;
Although the invention has been illustrated and described in greater detail by the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variations can be derived herefrom by the person skilled in the art without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12163533.8 | Apr 2012 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/056648 | 3/28/2013 | WO | 00 |
