Patent Application
20180029133
The invention relates to equipment used for the granulation of molten material.
Metal granulation in water is a well-established method for rapid solidification of liquid metal into a medium sized product form. The Granshot® process has been developed for the direct production of ready to use material for the steel industry. The known apparatus is disclosed in
U.S. Pat. No. 4,402,884 discloses a method of granulating using a rotating disc. The main part of the granules obtained according to this method has a size of less than 10 mm.
Although the grain sizes obtained by the above mentioned method allow a rapid dissolution of the granular metal in a steel melt there is a drawback in that there are limited possibilities to adjust the mean grain size and the grain size distribution.
EP 522 844 discloses a method of producing metal granules by pouring a metal stream into a liquid cooling bath. U.S. Pat. No. 6,287,362 discloses a method of producing metal lumps having a characteristic dimension of 20-100 mm by introducing a molten metal stream into a stream of water. Drawbacks associated with these methods are long dissolution times for the coarse material and a wide particle size distribution.
The general objective of the present invention is to provide a nozzle and a tundish arrangement for the production of a granulated material having an improved size distribution.
Another object is to provide a method and an apparatus for making a granulated material having an improved size distribution. In particular, it should be possible to obtain granules having a low fraction of fines and at the same time a mean size resulting in a rapid dissolution in the melt. For the same reason it is necessary that coarse granules are completely avoided or that the amount of coarse granules are at least limited.
It is also an object to provide a material having a more narrow size distribution of the granules obtained.
These objects are achieved by the means of the invention as defined in the independent claims.
Further advantageous embodiments of the invention have been specified in the dependent claims.
According to the invention the granulation is performed with a nozzle or a tundish arrangement comprising said nozzle. The granulation of molten material results in a granulated material having a mean size in the range of 10-50 mm, wherein the amount of fines in the granulated material having a size of less than 8 mm is limited to 5%.
The nozzle comprises an upper inlet opening, sidewalls forming a channel, a bottom and at least one outlet opening or at least one row of outlet openings at the lower end of the sidewalls forming the channel, wherein the outlet opening or openings in the channel have a size of at least 5 mm in the smallest dimension and wherein the cross section area of the channel at the inlet (AC) is at least 3 times bigger than the total area of the outlet openings (AT).
In the following, the invention will be described in more detail with reference to the preferred embodiments and the appended drawings.
The present invention will be described in detail with reference to the attached drawings.
The inventive nozzle and tundish arrangement can be used in an apparatus for the production of granulated material as shown in
The nozzle is designed in order to optimize the flow conditions for granulation.
The cross sectional area of the channel at the inlet (AC) is much larger than the total area of the outlets (AT), wherein said total area is calculated from the size of the outlet openings on the inside of the sidewalls, because the outlet openings may be tapered. In order to optimize the flow conditions for granulation the ratio between the cross sectional area of the channel at the inlet and the total area of the outlets AC/AT should be at least 3. Preferably, AC/AT≧6, AC/AT≧12, AC/AT≧16 or even AC/AT≧20.
The vertical channel formed by the sidewalls may have a larger cross sectional area at the inlet (AC) than at the lower end. The vertical channel may be tapered or conical. The diameter at the inlet (d) is then larger than at the lower end of the channel.
The nozzle may be provided with one or more of the following features.
Circular openings may be provided at the lower end of the sidewalls having a diameter of 10-50 mm, 10-30, 20-35 or 12-30 mm. The smallest diameter of said opening can be 10, 11, 12, 13, 14, 15, 16, 17, 18 19 or 20 mm. The largest diameter may be restricted to 50, 45, 40, 35, 32, 30, 28, 26, 24, 22, 20, 18 or 16 mm. The size and number of the openings depend on the design capacity i.e. tonnes per minute.
Elliptical openings may be provided having a height to width ratio (h/w) in the range of from 1:1.2 to 1:10. By adjusting the form of the opening, it is possible to adjust the form of the molten stream leaving the distributor. A wider opening results in a more film-like stream, thereby the size and shape of the granules may be influenced.
One row of openings and, preferably, not more than 4 openings may be provided in said single row. In order to get a good heat dissipation, the number of openings may be 2, 3 or 4. This design is the most simple to produce and the method is easy to control. It is therefore a preferred design.
Openings may be directed 0°-45° upwards, e.g., 5° or 25° upwards, or 15°-20° upwards. By this measure, it is possible to adjust the path and the time in the air before the stream hits the cooling liquid. Also, the spread of the molten stream over the cooling bath is influenced by the parabolic flight.
Openings may be directed 0°-45° downwards. By directing one or more streams downwards, it is possible to shorten the flight distance, reduce the risk of disintegration of the stream before it hits the cooling bath and influences the spread over the cooling bath.
Tapered openings may be provided.
According to a preferred embodiment the tundish has a circular cross section and the pouring nozzle is centrally attached thereto. The pouring nozzle may have 4 circular openings each having a diameter of 10-30 mm, preferably 20-25 mm. The pouring nozzle may have 3 circular openings each having a diameter of 10-35 mm, preferably 22-28 mm. The pouring nozzle may have 2 circular openings each having a diameter of 10-40 mm, preferably 26-35 mm.
The tundish may be provided with a weighing system that automatically controls the level in the tundish in order to maintain a constant liquid head and thereby a constant flow rate through the pouring nozzle. Alternatively, the automatic control system may include optical or electromagnetic sensors.
The granulated material obtained with the inventive method has a narrow size distribution and typically a mean size in the range of 12-50 mm, preferably 16-30 mm and wherein the amount of fines having a size of less than 8 mm may be limited to ≦5% or even to ≦3%. The amount of fines having a size of less than 6 mm may be limited to ≦3% or even to ≦1%. The amount of fines having a size of less than 5 mm may be limited to ≦1%. The upper limit for the mean size may be 45 mm, 40 mm, 35 mm, 32 mm, 30 mm or 25 mm. The lower limit for the mean size may be 12 mm, 14 mm, 16 mm, 18 mm or 20 mm. The upper and lower limits may be freely combined. A ferronickel material comprising more than 2 wt. % C and/or wt. % Si may be disclaimed from this invention.
The amount of coarse granules having a size of >80 mm may be limited to 5% or even completely avoided.
The amount of coarse granules having a size of >60 mm may be limited to 10%, 8%, 5%, 3% or 1%.
The amount of coarse granules having a size of >40 mm may be limited to 15%, 10%, 5%, 3% or 1%.
The amount of coarse granules having a size of >25 mm may be limited to 30%, 25%, 20%, 15%, 10%, 5%, 3% or, as shown in
The limitations with respect to the amount of fines and coarse granules are expressed as % of the total weight.
The invention is not to be seen as limited by the embodiments described above, but can be varied within the scope of the claims, as will be understood by the person skilled in the art.
In the following results obtained according to the invention are compared to results obtained with the known apparatus having a flat spray head. In all examples ferronickel was melted in an induction furnace and supplied to the tundish by use of a tapping spout. Tapping temperature was 1650° C. The melt level in the tundish was manually controlled to be 300-400 mm. The nozzle diameter in the tundish was 72 mm. After completed granulation the granules were removed from the tank, dried, weighted and subjected to screening. Size classes used were <4 mm, 4-8 mm, 8-12 mm, 12-16 mm, 16-25 mm and >25 mm. The results are given in % of the total weight.
In this example the ferronickel contained 32% Ni and 0.1% Si.
The nozzle according to the invention had four holes in one single row. The four openings had a total opening area (AT) of 346 mm2, thus AC≧10AT.
A rotation speed of 3 rpm was used in order to secure an uniform heat dissipation.
The size distribution of the granules obtained according to the invention is disclosed in
The size distribution of the granules obtained with a conventional flat spray head is shown in
It is evident that the inventive apparatus resulted in an improved size distribution in that the amount of fines was reduced, the mean size was increased and the size distribution was improved.
In this example the effect of an increased content of Si on the size distribution was examined.
The ferronickel contained 32% Ni and 0.27% Si. The granulation conditions were the same as for Example 1.
The size distribution of the granules obtained according to the invention is disclosed in
The size distribution of the granules obtained with a conventional flat spray head is shown in
An improved size distribution was achieved in both cases.
The result for the conventional spray head was as expected, since it is known that Si has a positive influence on the size distribution. A comparison between Charge Nr. 115 and Charge Nr. 110 reveals that the increased Si content resulted in less fines and an improved size distribution.
However, the increased content of Si turned out to have a remarkable effect on the size distribution obtained with inventive apparatus. A comparison of Charge Nr. 116 and Charge Nr. 115 reveals that the amount of fines was virtually eliminated and the mean size of the granules was very much increased.
In this experiment the generation of fines during the granulation of a commercial ferronickel grade having nominal content of 32% Ni and <0.5% Si. Nozzles of the type disclosed in
The results are given in the Table 1 below.
The cross section area of the channel at the inlet (AC) was nearly 10 times bigger than the total area of the outlet openings (AT) for all charges. The granules obtained had a low fraction of fines having a size of less than 6 mm. In fact, not more than 3 wt. % fines were generated for any of these charges.
The invention is particular suited for application in the ferroalloy-, iron- and steel-industries.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15155251.0 | Feb 2015 | EP | regional |
This is a National Stage Entry into the United States Patent and Trademark Office from International PCT Patent Application No. PCT/SE2016/050108, having an international filing date of Feb. 12, 2016, and which claims priority to European Patent Application No. 15155251.0, filed Feb. 16, 2015, the entire contents of both of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2016/050108 | 2/12/2016 | WO | 00 |
