GB1574593A - Ore agglomeration - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO ORE AGGLOMERATION (71) We, DELATTRE-LEVIVIER, a French Corporate Body of 16 Boulevard Malesherbes, 75008 Paris, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a process and to an installation for cooling agglomerate in an ore agglomeration installation.

For charging blast furnaces, agglomerated ore is generally used, which has been produced from a mineral mixture which contains a defined proportion of fuel and has been roasted, most commonly on a belt consisting of carriages of which the bottoms form grids through which air which maintains the roasting is drawn. The mixture first passes under an igniting hood and the combustion of the fuel starts at the surface.

Combustion continues by virtue of the air, which passes downwards through the mixture, and the incondescent zone referred to as the flame front descends until it reaches the bottom of the carriages. The roasting operation is finished at that stage and the cake is then cooled in a especial zone of the installation, which can either be a separate cooling zone or a part of the belt itself if such a part is provided for the purpose.

The cake of agglomerate must be crushed on leaving the belt. If the cooling zone is separate from the roasting zone, crushing takes place whilst the material is hot and the crushed ore is poured onto cooling means, which is frequently circular, through which the cooling air is drawn.

If the cooling is carried out on the belt, cracks form in the cake and the cooling air passes through these, but it sometimes happens that the flame front does not descend uniformly over the entire width of the belt as a result of non-uniform permeability of the layer or as a result of segregation of the solid fuel, defining zones which have a higher carbon concentration and are consequently hotter.

As a result, small scorified zones of low permeability are formed, which can still be at a high temperature when they ]eave the cooling zone unless the length of the cooling zone has been calculated accordingly, and in that case it is the coarsest lumps which remain at a high temperature as a result of their locally more compact structure. It is thus necessary to lengthen the cooling zone to achieve complete cooling of theagglomerate.

Equally, if the cooling means is separate and the crushing is carried out hot, the size of the cooling means depends on the size of the largest lumps.

According to one aspect of the invention there is provided a process for cooling agglomerated ore in an agglomeration installation comprising a roasting zone and a zone for cooling the agglomerate, said process comprising: regulating the cooling condition of said cooling zone in such a way as to cool sufficiently, in the cooling zone, only those lumps of agglomerate of a size below a preset limit, separating larger lumps of agglomerate of a size exceeding said preset limit from the sufficiently cooled remainder of the agglomerate as the agglomerate leaves said cooling zone, subjecting said separated agglomerate to a supplementary cooling, and adding said cooled separated agglomerate to said remainder of the agglomerate.

According to another aspect of the invention there is provided an installation for use in cooling agglomerated ore in an agglomerin cooling agglomerated ore in an agglomeation installation comprising a roasting zone and a cooling zone and means for screening the agglomerate, which agglomerate contains a certain proportion of large lumps, the cooling conditions in said cooling zone being such that, on leaving the said cooling zone, only the lumps of a size less than a preset limit are completely cooled, said installation comprising means for separating large lumps from the remainder of the aggomerate from the cooling zone, and means for supplementary cooling of the separated large lumps.

The supplementary cooling means may comprise a double-bottom vibratory conveyor, the upper bottom being permeable and supporting the lumps of agglomerate to be cooled, and the lower bottom collecting the fines, the whole being placed in a chamber connected to a cooling air circulation circcit.

Alternatively, the supplementary cooling means may comprise a hopper equipped at its upper part with an inlet for the large lumps separated from the agglomerate and at its lower part with an outlet for the said large lumps after cooling, and having a shape which allows air to circulate through the lups of aggomerate in the hopper and the Iups of agglomerate in the hopper and which are in the process of cooling.

The invention will be more fully understood from the following description of two embodiments thereof, given by way of example only, with reference to the accompanying drawing.

In the drawing: Figure 1 schematically represents a first embodiment according to the invention and comprising a vibratory conveyor; Figure 2 schematically represents a second embodiment according to the invention and comprising a hopper.

Both the Figures show the end of the belt 1 on which roasting, followed by cooling of the agglomerate, has been carried out. At the end of the belt, the agglomerate is discharged into a hopper 2 inside which is placed a crushing member called a ragwheel, which most frequently consists of a roller equipped with teeth which engage between the bars of a grid.

The cooling conditions, that is to say, in particular the length of the cooling zone and the flow rate of the cooling air, are selected in such a way that only lumps of a size smaller than a certain limit size are sufficiently cooled, whilst the larger lumps are still hot at the end of the cooling zone.

On leaving the hopper 2, the agglomerate is transported onto a screen 3 of mesh size equal to the above limit, for example 50 or 60 mm. The material passing through the screen is conveyed, by means of a belt converyor 4, to the screening station whilst the part retained by the screen is passed to supplementary cooling apparatus.

In the embodiment of Figure 1 the supplementary cooling apparatus comprises a double-bottom metallic vibratory conveyor 5 which is provided with a hood 53. The upper bottom 51, onto which the agglomerate retained by the screen 3 is poured, is performated with holes which allow air to pass through the layer of agglomerate. The lower bottom 52 is intended to collect the fines which become detached by the vibratory movement of the conveyor and which pass through the bottom 51. The whole is placed inside the hood 53 which is connected by a pipeline 54 to the principal suction pipeline of the cooling circuit or of an extractor fan. In this way, the air is drawn from below the upper bottom through orifices formed in the hood and passes through this upper bottom, thereby cooling the large lumps.The induced air flow rate is regulated by a butterfly valve (not shown) in the pipeline 54 which connects the hood 53 to the fume extraction pipeline and is regulated in accordance with the temperature of the air leaving the apparatus.

The vibratory conveyor need not be of the double bottom type. If it is not, the fines are collected by a belt conveyor placed under the vibrating bottom, which makes it necessary slightly to increase the height of the vibrating bottom relative to the conveyor 4.

The residence time in the supplementary cooling apparatus and the volume of air drawn through it are regulated so as to ensure adequate cooling of the hot lumps which, at the end of the conveyor 5, are mixed with the part of the agglomerate which passed through the screen 3 and is present on the conveyor 4.

If there is no objection to further increasing the vertical size of the installation, it is possible to use a static supplementary cooling means as shown in Figure 2. In effect, the large lumps retained by the screen 3 are poured into a cooling apparatus which is in the shape of a hopper 6 closed by a hood 60 and connected by a pipeline 61 to the cooling air suction circuit or to an extractor fan, the bottom 62 of the hopper being designed to allow cooling air to pass through it.

The volume of the hopper is calculated so that the large lumps are cooled sufficiently during their passage through the hopper by the air which circulates at a low speed. At the outlet of the hopper, the cooled agglomerate is poured onto the conveyor 4 where it becomes mixed with the lumps of average size which have already been cooled and have passed through the screen 3.

The agglomerate is removed from the hopper by an extractor 63 which is regulated so as to maintain thehopper at a constant level in order to give the agglomerate the maximum passible time to cool. The air flow rate is again controlled by a butterfly valve (not shown) which is regulated in hopper outlet.

Thus, because of the special supplementary cooling of the largest lumps which take longest to cool, it is possible to avoid having to make the primary cooling surface excessively large.

This supplementary cooling is particularly useful where cooling is effected in such agglomeration belt itself because, in such installations, the length of the cooling zone depends on the position of the roasting point.

If the latter is moved downstream, cooling of the large lumps may be insufficient if the belt is not long enough. As a result of use as above described of a supplementary cooling device, it is possible to determine the size of lumps above which cooling is insufficient and to separate the lumps which are larger than this size at the screen 3 so as to subject these larger lumps to supplementary cooling.

Of course the invention is not limited to the details of the embodiments which have been shown but also encompasses other variants and especially those which would employ equivalent means.

Thus, while in the embodiments described above cooling is brought about by drawing air through the agglomerate, the air can alternatively be blown through the agglomerate by separate and appropriately designed fans, as in certain conventional installations.

Furthermore, depending on the size and proportion of the large lumps to be cooled, it may be considered useful to crush them and to provide corresponding material circuits.

WHAT WE CLAIM IS:- 1. A process for cooling agglomerated ore in an agglomeration installation comprising a roasting zone and a zone for cooling the agglomerate, said process comprising: regulating the cooling condition of said cooling zone in such a way as to cool sufficiently, in the cooling zone, only those lumps of agglomerate of a size below a preset limit, separating larger lumps of agglomerate of a size exceeding said preset limit from the sufficiently cooled remainder of the agglomerate as the agglomerate leaves said cooling zone, subjecting said separated agglomerate to a supplementary cooling, and adding said cooled separated agglomerate to said remainder of the agglomerate.

2. An installation for use in cooling agglomerated ore in an agglomeration installation comprising a roasting zone and a cooling zone and means for screening the agglomerate, which agglomerate contains a certain proportion of large lumps, the cooling conditions in said cooling zone being such that, on leaving the said cooling zone, only the lumps of a size less than a preset limit are completely cooled, said installation comprising means for separating large lumps from the remainder of the aggomerate from the cooling zone, and means for supplementary cooling of the separated large lumps.

3. An installation according to claim 2, wherein said means for separating the large lumps comprises a screen, first outlet means for directing material passing through said screen to apparatus for transporting the agglomerate and a secondoutlet means for directing the material retained on said screen to said supplementary cooling means.

4. An installation according to claim 3, wherein said screen has a mesh size of about 50 mm.

5. An installation according to any one of claims 2 to 4, wherein said supplementary cooling means comprises a vibratory conveyor having an upper bottom and a lower bottom, said upper bottom being permeable and supporting the large lumps to be cooled, said lower bottom being arranged to collect fines passing through said upper bottom, and means for circulating cooling air through said upper bottoms.

6. An installation according to any one of claims 2 to 4, wherein said supplementary cooling means comprises a chamber having a lower end in the form of a hopper, provided at an upper part with an inlet for the separated large lumps and at a lower part with an outlet for the large lumps after they have been cooled, and means for circulating cooling air through said hopper, at least one part of the wall of the hopper being perforated for the passage of cooling air therethrough.

7. An installation according to either claim 5 or claim 6, wherein cooling takes place by forced passage of air through the agglomerate and said means for circulating cooling air is connected downstream of said supplementary cooling means to the main air circulation circuit of the agglomeration installation.

8. An installation for use in cooling agglomerated ore substantially as herein described with reference to the accompanying drawing.

9. An agglomeration installation for agglomerating ore and including an installation for use in cooling the agglomerated ore according to any one of the preceding

Claims (1)

1. claims.