MXPA99010014A - Method for thermal treatment of granulated iron ore before reduction - Google Patents

Abstract

The wet granulated iron ore is initially conducted through a drying zone. The ore leaves the drying zone at a temperature of 120-400°C. The ore is then heated in direct contact with hot gas to temperatures of 700-1,100°C before being delivered to a reduction zone. The ore coming out of the drying zone is fully or partially guided through a separating device so as to separate the ore into fine and coarse grain fractions. The fine-grained ore fraction is conveyed to a granulating device so as to produce an iron ore granulate which is conducted to the drying zone. The coarse-grained ore fraction is heated to temperatures of 700-1,100°C before it is guided into the reduction zone.

Description

PROCESS FOR THE THERMAL TREATMENT OF GRANULATED IRON MINERAL BEFORE THE REDUCTION DESCRIPTION This invention relates to a process for the thermal treatment of wet granular iron ore, where the ore is passed through a drying zone and where the ore, which comes from the drying zone with a temperature in the range from 120 to 400 ° C, it is heated in direct contact with hot gas at temperatures of 700 to 1100 ° C, before it is loaded into the reduction zone. Such processes are known and described for example in U.S. Patent 5,527,379; 5,560,762; and 5,603,748. In this case, the heat treatment is used to prepare the ore to be loaded into a reduction plant, which operates with one or more fluidized beds. As the fluidized gas, a gas rich in hydrogen is used, which as an additional reducing component can also contain carbon monoxide. It has been found that the components of the ore with a particularly fine grain disturb the reduction process and reduce the quality of the product, because these fine-grained components easily blow out of the fluidized bed. As a result, the dwell time in the reduction zone is reduced in such a way that they are not sufficiently reduced. It is a principal object of the invention to ensure that during the thermal pre-treatment of the iron-containing ore or a concentrated mineral, the mineral introduced into the reduction zone does not contain any disturbing amount of fine grain. According to the invention, this object is solved in the aforementioned process because the ore coming from the drying zone is passed totally or partially through separation means, and a fraction of coarse-grained ore is separated from a fraction of fine-grained ore, because the fraction of fine-grained ore is loaded into granulation media and a granulated iron ore is produced, which is introduced into the drying zone, and because the grain mineral fraction Thickness is heated to temperatures of 700 to 1100 ° C, before being introduced into the reduction zone. The separation means may, for example, be a screen or sieve.

The fine-grained ore, which is undesirable in the reduction plant, is obtained in several ways. On the one hand, fines are formed during drying and heating of the granular ore, and fine grains also form due to the disintegration of coarser grains during heating. In addition, the raw mineral, which is provided for reduction in the fluidized bed, is crushed even before drying to an optimum grain size of approximately 0.1 to 3 mm. Up to this point, the roller press known per se can be used for example, but inevitably mineral with an approximately fine grain size is also produced. The care and granulation of this fine-grained component before drying, as proposed for example in the U.S. 5,560,762, does not completely solve the problem of fine grain, because fine grain is also formed again during drying and thermal pretreatment as a result of abrasion and disintegration. By means of the processes according to the invention, it is efficiently and economically ensured that there are no disturbing quantities of fine grains that can be put into the reduction plant.

It is usually stipulated that the ore coming from the drying zone is introduced into at least 50% separation media, in order to separate the fine-grained ore fraction. In the separation means it should conveniently be ensured that the fraction of separated fine grain ore has grain sizes of no more than 0.2 mm by at least 80% by weight. Preferably, the grains of ore extracted from the granulation means have grain sizes of at least 0.3 mm at least 50% by weight. When a fine-grained fraction hovers from the raw ore before drying, this crude fine mineral can also be loaded into the existing granulation media. The crude fine ore will usually have grain sizes of not more than 0.2 mm at least 80% by weight. The ore charged into the reduction plant will usually consist of grain sizes in the range of 0.1 to 3 mm at least 80% by weight. This is especially recommended when the first stage of reduction is designed as a circulating fluidized bed, as is the case in the known processes of the aforementioned US Patents. In the circulating fluidized bed, relatively high gas velocities of the fluidizing and reducing gases are used, and the rates for emptying the gas conduit are usually in the range of 3 to 10 m / s. This first reduction stage as described above is conveniently followed by a second reduction stage, in which the fluidized bed is maintained in the dense phase state. In this case, the speeds to empty the duct of the fluidizing reduction gases are in the range of 0.3 to 1 m / s. The modalities of the process will now be explained with reference to the drawings, which represent a flowchart of the process. Via line 1, the wet granular iron ore or mineral concentrate is also supplied and loaded into a Venturi dryer 2. The ore usually has an Fe content of at least 60% by weight. The ore, which for example, was first passed through a crushing device not reppressed, and grain size up to no more than 10 mm, preferably no more than 6 mm. Advantageously, at least 80% by weight The ore of line 1 must have grain sizes of no more than 4 mm. The hot gas is supplied to dryer 2 through line 3, so that the ore is transported to the top, dried and loaded inside a dust extractor 4 through line 5. The gas containing water and powder is extracted by means of line 4a and is introduced into a non-represented empirical unit. The dry ore, whose temperature is usually in the range of 120 to 400 ° C, leaves the dust extractor 4 through line 6 and is introduced into the separation means, which in this case are designed as a sieve 7. The coarse-grained fraction leaves the sieve 7 through line 10, and the fine-grained ore fraction is supplied through line 11 to a granulator 12. When not all the dry ore from the powder extractor 4 must be introduced into the sieve 7, a partial amount thereof can be directly mixed with the coarse fraction of the line 10 through the deflection line 14 indicated in dotted lines. If necessary, a binder such as bentonite is supplied to granulator 12 through line 15. In addition, a filter cake can be loaded into the granulator via line 16, whose filter cake originates from a unit of gas cleaning not shown and rich in fine-grained iron ore. The granulator 12 known per se, produces an iron ore granulate, where at least 50% by weight of the granulate has grain sizes of at least 0.3 mm. This granulate is introduced into dryer 2 on path 18. The coarse ore fraction of line 10 is heated to temperatures of 700 to 1100 ° C and almost always to no more than 1000 ° C. For this purpose, a circulating fluidized bed is used, to which reactor 20 a liquid or solid gaseous fuel is supplied through line 21, and air is supplied through line 22. Hot combustion gases transport solids upwards to a dust extractor separator 23, where the gases charged with hot powder are supplied to dryer 2 through line 13. The heated heated ore leaves the dust extractor 23 through line 26, and is partially recirculated to the lower part of chamber 20 through line 27. The remaining mineral, which has hardened as a result of heating, is supplied to the reduction plant through line 28.

The reduction plant schematically illustrated in the drawing comprises a first reduction stage 30, a second reduction stage 31 and a gas processing unit 32. In the first stage 30 a circulating fluidized bed is used, and the second stage of reduction 31 is designed as a stationary fluidized bed. The details of the reduction plant are described in the North American Patents 5,527,379; 5,560,762; and 5,603,748. The hot reduction gas, which in addition to the hydrogen may contain carbon monoxide, is supplied via line 33 and is supplied as a fluidizing gas in part to the first stage 30 and the second stage 31. The gas for expulsion of the second stage 31 is supplied to the first stage 30 through line 34. The expulsion gas containing steam and powder, which leaves The first stage 30 through line 35 is recirculated to plant 32 for processing and partial reuse, in which fresh reduction gas is also produced at the plant. The partially reduced ore in the first stage 30 is supplied via the line 36 to the second stage 31 for further reduction, and the finished product is extracted via line 87 and is usually supplied to a cooling unit and of briquette formation not represented. If it is also desired to process coal during the reduction, the fine-grained coal is charged through line 38 together with the gas containing 02 from line 39 to a coal gasification plant known per se and through oxidation. a product gas that contains H2 and CO is produced. This product gas can likewise be introduced into the first reduction stage 30 through the line 41 indicated in dashed lines. E j empl o In a plant corresponding to the drawing without line 14 and without the reduction plant, a fine haematitic mineral with an Fe content of 68.5% by weight is subjected to a heat treatment. The mineral has a water content of 7% by weight. 100 t / h of this mineral have been loaded into the Venturi 32 dryer, whose ore has been crushed to obtain grain sizes smaller than 3 mm. All quantities refer to dry solids, unless otherwise indicated. Gas of 900 ° C is supplied to dryer 2 through line 3, and 26 t / h of granulated mineral with a water content of 8.5% by weight are supplied to the dryer through line 18. The dried ore extracted through line 5 in an amount of 126 t / h with a temperature of 250 ° C. The air classifier 7 is operated with circulating air, so that there is no gas inlet or outlet. The coarse-grained fraction, which has a lower grain limit of 0.1 mm, is passed through line 10 in an amount of 106.5 t / h, the fine-grained ore is supplied to granulator 12 in an amount of 13 t / h. At the same time, 3100 kg / h of water 104 kg / h of bentonite and 11.7 t / h of a filter cake, are loaded into the granular. The filter cake, which originates from the gas cleaning process, comprises 90% by weight of iron ore and 10% by weight of water. The granulator produces 26 t / h of microgranules with 8.5% by weight of water, a maximum grain size of 3 mm, an average grain size (d50) of 0.4 m, and with a component smaller than 0.1 mm of 5% in weigh. These microgranules are supplied to dryer 2 on path 18. Inside reactor 20, 4536 Nm3 / h of natural gas and 46600 Nm3 / h of air are introduced so that a temperature of 900 ° C exists inside the reactor. In line 28, 106.5 t / h of hardened granular iron ore are provided for the reduction plant.

Claims (8)

1. A process for the thermal treatment of granular, wet iron ore, where the ore is passed through a drying zone, and where the 'Mineral, which comes from the drying zone with a temperature in the range of 120 to 400 ° C, is heated in direct contact with hot gas at temperatures of 700 to 1100 ° C, before being loaded into the zone of reduction, characterized in that the ore coming from the drying zones is completely or partially passed through separation means, and a fraction of the grain mineral is separated from a fraction of fine-grained ore, because the fraction of the Fine-grained mineral is loaded into a granulation medium and .produces a granulate of iron ore, which is introduced into a drying zone, and because the fraction of coarse-grained ore is heated to temperatures of 700 to 1100 ° C, before being introduced into the reduction zone.

2. The process as claimed in claim 1, characterized in that the mineral coming from the drying zone is introduced into the separation means at least 50%.

3. The process as claimed in claim 1 or 2, characterized in that the hot gas for heating the coarse-grained ore fraction is produced through the gaseous, liquid or solid fuel composition.

4. The process as claimed in claim 1, or any of the preceding claims, characterized in that the iron-containing ore is first crushed, before being introduced into the drying zone.

5. The process as claimed in any of claims 1 to 4, characterized in that the fraction of fine-grained ore separated in the separation means has grain sizes of not more than 0.2 mm by at least 80% by weight.

6. The process as claimed in any of claims 1 to 5, characterized in that the mineral granulate extracted from the granulation means has grain sizes of at least 0.3 mm at least 50% by weight.

7. The process as claimed in any of the rei indications 1 to 6, characterized in that the iron-containing mineral, which has grain sizes of no more than 0.2 mm at least 80% by weight, is loaded directly into the granulation media.

8. The process as claimed in claim 1 or any of the above indications, characterized in that the iron ore heated from 700 to 1100 ° C is supplied to a reduction plant, which has at least one fluidized bed with the supply of hot reduction fluidizing gas.