STEAM CONDENSATION SYSTEM FOR A GRANULATION INSTALLATION

Abstract

The present invention concerns a granulation installation for granulating molten material produced in a metallurgical plant, the installation includes a water injection device, for injecting granulation water into a flow of molten material and thereby granulating the molten material; a granulation tank for collecting the granulation water and the granulated material; and a steam condensation system including a steam collecting hood located above the granulation tank, for collecting steam generated in the granulation tank, a gas conduit arranged between the steam collecting hood and a water column, and a gas compressor arranged within said gas conduit for compressing the steam before feeding it into the water column.

Claims

1. A granulation installation for granulating molten material produced in a metallurgical plant, said installation comprising: a water injection device, for injecting granulation water into a flow of molten material and thereby granulating the molten material; a granulation tank for collecting the granulation water and the granulated material; characterized by a steam condensation system comprising: a steam collecting hood located above said granulation tank, for collecting steam generated in said granulation tank, a water column configured to dissolve and condensate gas therein, a gas conduit arranged between said steam collecting hood and said water column, a gas compressor arranged within said gas conduit for compressing said steam from the steam collecting hood before feeding it through said water column.

2. The granulation installation as claimed in claim 1, further comprising a dewatering unit, in particular a dewatering unit with a rotary filtering drum, having a water recovery tank, characterized in that said water column to which said gas conduit is connected is said water recovery tank of said dewatering unit.

3. The granulation installation as claimed in claim 1, further comprising a cooling system, in particular a cooling tower, having a water recovery tank, characterized in that said water column to which said gas conduit is connected via branch is said water recovery tank of said cooling system.

4. The granulation installation as claimed in claim 1, characterized in that said water column to which said gas conduit 484 is connected is a dedicated water reservoir.

5. The granulation installation as claimed in claim 1, further comprising deviation plates arranged in said water column, so as to deviate incoming steam for longer residence time within the water column.

6. The granulation installation as claimed in claim 1, wherein said gas conduit is connected to a distribution tube arranged within said water column, said distribution tube comprising a number of perforations for distributing said steam into said water column at different locations.

7. The granulation installation as claimed in claim 2, further comprising a further steam collecting hood located above said dewatering unit, for collecting steam generated in said dewatering unit, a further gas compressor arranged within a gas conduit connecting to said gas conduit.

8. The granulation installation as claimed in claim 1, wherein said gas compressor is connected to a controller for controlling said gas compressor.

9. The granulation installation as claimed in claim 1, wherein said gas compressor has a volume flow of at least 20.000 Nm.sup.3/h, preferably at least 40.000 Nm.sup.3/h.

10. The granulation installation as claimed in claim 1, wherein said further gas compressor has a volume flow of between 5.000 Nm.sup.3/h and 10.000 Nm.sup.3/h.

11. A method for condensing steam generated in a granulation installation, said granulation installation comprising a steam condensation system with a steam collecting hood located above a granulation tank and a gas conduit comprising a gas compressor connected between said steam collecting hood and a water column; wherein said method comprises: collecting steam generated in said granulation tank via said steam collecting hood; compressing said steam within said gas conduit; and feeding said steam into said water column, dissolving and condensing said steam within said water column.

12. The method according to claim 11, wherein said steam is fed to a water recovery tank of a dewatering unit and/or to a water recovery tank of a cooling system and/or to a dedicated water reservoir.

13. The method according to claim 11, comprising the further steps of: collecting steam generated in a dewatering unit via a further steam collecting hood; compressing said steam within said gas conduit by means of a further gas compressor; and feeding said steam into said water column and condensing said steam within said water column.

14. A blast furnace plant comprising a granulation installation as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further details and advantages of the present invention will be apparent from the following detailed description of a not limiting embodiment with reference to the attached drawings, wherein:

[0029] FIG. 1 is a block schematic diagram of an embodiment of a granulation installation equipped with a steam condensation system according to the invention;

[0030] FIG. 2 illustrates a known granulation installation according to prior art.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] For illustrating an embodiment of the present invention, FIG. 1 shows a diagrammatic view of a granulation installation 10 designed for slag granulation in a blast furnace plant (the plant not being shown). Generally speaking, the installation 10 thus serves to granulate a flow of molten blast furnace slag 14 by quenching it with one or more jets 12 of comparatively cold granulation water. As seen in FIG. 1, a flow of molten slag 14, inevitably tapped with the pig iron from a blast furnace, falls from a hot melt runner tip 16 into a granulation tank 18. During operation, jets of granulation water 12, which are produced by a water injection device 20 (often also called a blowing box) supplied by a supply conduit 22, preferably comprising one or more parallel high-pressure pump(s) (not shown), impinge onto the molten slag 14 falling from the hot runner tip 16. A suitable configuration of a water injection device 20 is e.g. described in patent application WO 2004/048617. In older granulation installations (not shown, but encompassed), molten slag falls from a hot runner onto a cold runner, with jets of granulation water from a similar water injection device entraining the flow on the cold runner towards a granulation tank. Irrespective of the design, granulation is achieved when the granulation water jets 12 impinge on the flow of molten slag 14.

[0032] By virtue of quenching, the molten slag 14 breaks up into grain-sized granules, which fall into a large water volume maintained in the granulation tank 18. These slag granules completely solidify into slag sand by heat exchange with water. It may be noted that the jets of granulation water 12 are directed towards the water surface in the granulation tank 18, thereby promoting turbulence that accelerates cooling of the slag.

[0033] As is well known, quenching of an initially hot melt (>1000 C.) such as molten slag results in important quantities of steam (i.e. water vapor). This steam is usually contaminated, among others, with gaseous sulfur compounds. In order to reduce atmospheric pollution, steam released in the granulation tank 18 is collected in a steam collection hood 24 (hereinafter in short hood 24) that is located vertically above the granulation tank 18. As seen in FIG. 1, the hood 24 is a small edifice compared to a traditional condensation tower as shown in FIG. 2. The hood 24 has an external shell, which is typically but not necessarily a welded steel plate construction. The hood 24 has a certain height and diameter dimensioned for a volume of emitted steam/min. The hood 24 does not contain any water-spraying devices to condensate the steam as in a conventional condensation tower. During operation, steam rises from the granulation tank 18 into the hood 24.

[0034] As seen in FIG. 1, at the bottom of the granulation tank 18, solidified slag sand mixed with granulation water is evacuated via a drainage conduit 26. The mixture (slurry) is fed to a dewatering unit 28. The purpose of this dewatering unit 28 is to separate granulated material (i.e. slag sand) from water, i.e. to enable separate recovery of slag sand and process water. A suitable general configuration of a dewatering unit 28 is well known from existing INBA installations or described e.g. in US Pat. No. 4,204,855 and thus not further detailed here. Such a dewatering unit comprises a rotary filtering drum 30, e.g. as described in more detail in US Pat. No. 5,248,420. Any other static or dynamic device for dewatering fine solidified melt granules may also be used. As further shown in FIG. 1, a granulation water recovery tank 32 (often called a hot water tank) is associated with the dewatering unit 28 for collecting water that is separated from the granulated slag sand. In most cases, this water recovery tank 32 is conceived as a settling tank with a settling compartment and a clean water compartment (not shown), into which the largely sand-free (clean) water overflows. The water from the water recovery tank 32 is feed through conduit 34 to a cooling system 36 that has one or more cooling towers.

[0035] Cooled process water from the cooling system 36 may be evacuated via an evacuation conduit 42 for disposal or for use elsewhere. Preferably, the evacuation conduit 42 is connected to the supply conduit 22 of the water injection device 20 via a recirculation conduit (not shown), thus forming a closed-circuit configuration for process water.

[0036] According to an important aspect of the present invention, the hood 24 is connected to a gas conduit 38 comprising an evacuation device 40 for extracting steam and gas from the hood 24. The evacuation device 40, as schematically illustrated in FIG. 1, is preferably a gas compressor compressing the steam and gas collected from the hood 24 and feeding the compressed gas down the gas conduit 38.

[0037] The gas conduit 38 is connected to a lower portion of the water recovery tank 32 of the dewatering unit 28 at a pressure superior to the pressure reigning in the water recovery tank 32. Upon entering the water recovery tank 32, the compressed steam and gas expands and bubbles up through the water in the water recovery tank 32 while interacting therewith.

[0038] According to the present invention, condensation of the steam is not carried out in a large condensation tower. Instead, condensation of the steam is effected in a water column, preferably in a water column that is already present in the granulation installation 10 anyway. The water recovery tank 32 of the dewatering unit 28 is a good candidate for providing the water column needed for condensation of the steam. The pressure created by the gas compressor should be sufficient to overcome the pressure of the water column and said gas mix should then rise as bubbles inside the water volume. For the water recovery tank 32 (below dewatering drum), the normal working pressure usually ranges from 0.05 to 1.0 bar(g), preferably from 0.1 to 0.5 bar(g). This movement creates a significant surface for efficient condensation and sulphur dissolution. The condensation does thus no longer take place in a separate condensation tower but it is switched to an already existing water tank, thus resulting in lower investment costs and potentially better results due to an increased surface for efficient condensation.

[0039] Deviation plates (not shown) may be arranged in the lower part of the water recovery tank 32 in the area where the gaseous mixture is injected in order to deviate the gases and thus create a longer residence time inside the liquid surroundings.

[0040] A distribution tube (not shown) connected to the gas conduit may be arranged within the water column. Such a distribution tube may comprise a number of perforations arranged so as to distribute the steam into the water column at different locations. This may further improve the repartition of the steam in the water column.

[0041] A further gas compressor 40 may be used to extract steam and gas from the dewatering unit 28 via a further steam collection hood 48 above the rotary filtering drum 30. The gas compressor 40 may be installed so as to suck off steam and gas from the dewatering unit 28 and/or from the steam collection hood 48. This configuration has the benefit of properly evacuating steam and gas from the dewatering unit 28 and condensing the steam and thus reducing visibility problems in the surroundings of the dewatering unit 28 and the installation 10 in general.

[0042] Alternatively or additionally, the granulation installation may comprise a cooling system 36, in particular a cooling tower 36, having a water recovery tank 32 with a water column. The compressed gas from either or both of the compressors 40, 40 can be fed to the bottom of the water column in said water recovery tank 32 via gas conduits 38, 38. For the water recovery tank 32 (below cooling tower), the normal working pressure range usually is from 0.05 to 2.0 bar(g), preferably between 0.1 and 1.0 bar(g).

[0043] Preferably, the gas compressor(s) 40, 40 is (are) connected to a controller, which can be integrated into the process control system of the entire plant. The gas compressors are preferably controlled by frequency converters and an adjustable flow rate valve for keeping the same pressure at differing flow rates. The flow rate adjustment may be based on a pressure measurement inside the steam collecting hood, in particular the steam collecting hood 24.

[0044] In conclusion, it will be appreciated that the present invention not only enables an important increase in operational safety of a water-based granulation installation 10, especially for blast furnace slag. In addition, the invention permits reliable operation at lower capital and operating expenditure.

LEGEND

[0045] 10 granulation installation 30 rotary filtering drum [0046] 12 water jets 32 water recovery tank (of 28) [0047] 14 melt flow 32 water recovery tank (of 36) [0048] 16 hot runner tip 34 conduit [0049] 18 granulation tank 36 cooling system (cooling tower) [0050] 20 water injection device 38, 38 gas conduit [0051] 22 supply conduit (of 20) 40 gas compressor [0052] 24 steam collecting hood 40 further gas compressor [0053] 26 drainage conduit 42 evacuation conduit [0054] 28 dewatering unit 48 further steam collecting hood