GB1567102A

GB1567102A - Apparatus and method for cooling particulate slag

Info

Publication number: GB1567102A
Application number: GB514/78A
Authority: GB
Original assignee: IHI Corp; Sumitomo Metal Industries Ltd
Current assignee: IHI Corp; Nippon Steel Corp
Priority date: 1977-01-07
Filing date: 1978-01-06
Publication date: 1980-05-08
Also published as: DE2759205B2; JPS5385794A; DE2759205A1; FR2377012A1; FR2377012B1; JPS5624857B2

Description

(54) APPARATUS AND METHOD FOR COOLING PARTICULATE SLAG (71) We, ISHIKAWAJIMA-HARIMA JUKOGOYO KABUSHIKI KAISHA, a Company organised under the Laws of Japan, of No. 2-1, 2-chome, Ote-machi, (,hiyoda-ku, Tokyo-to, Japan, and SUMIT OMO METAL INDUSTRIES LTD, a Company organised under the laws of Japan, of No. 15, Kitahama 5-chome, Higashi-ku, Osaka-fu, Japan, 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:- This invention relates to a method and an apparatus for cooling particulate slag.High temperature slag is obtained from furnaces in the refining of iron and other metals, and the slag can be formed into particles which are useful in themselves. for example, as a concrete aggregate.

An object of the present invention is to provide a particularly efficient method and apparatus for obtaining such particulate slag.

According to one aspect of the present invention, apparatus for cooling particulate slag comprises a fluidised bed arranged to receive the slag and containing powder and a supply of gas for fluidising the powder, and having an outlet leading to a classifying passage with means arranged to drive gas to flow along the classifying passage against the flow of particles from the bed, and then into the bed.

It is already known how to form the slag into particules for example, by use of a rotating drum, and by arranging in accordance with the invention for the slag particles to be received in a fluidised bed, they can be cooled without significant mechanical or thermal shocks, and satisfactory cooled particles can be obtained without any tendancy for them to stick together.

The use of the fluidised bed enables the particles to be received without mechanical shocks, and because the fluidised bed has a much greater thermal capacity than the slag particles, the temperature can be maintained at a substantially constant predetermined temperature for the avoidance of thermal shocks.

Thermal shocks occur if the slag particles are merely directed into a cold water bath, and the thermal shocks make the particles powdery so that they are of little use as a concrete aggregate. That disadvantage can be avoided by directing the hot slag particles into heated oil, or heated molten salt, but then subsequent treatment is required for removing oil or salt from the particles.

If instead of using oil or molten salt the particles are cooled in a stream of cooling gas. control is very difficult where the particles are not of uniform size, and it is also difficult to control the temperature because of low heat conduction between the gas and the particles. Large volumes of cooling gas are necessary.

If the slag particles are directed into a bodv of solid particles acting as a cushion against mechanical impact, then after cooling the particles have to be mechanically separated from each other, because the bed of solid particles acts as a thermal insulator so that the temperature around the slag particles rises, and they tend ;o oticTi together.

The apparatus of the present invention avoids thermal and mechanical shocks, and also is well adapted for separating the cooled slag particles from the powder in the bed by flowing against incoming gas if the powder is arranged to be substantially smaller than the slag particles.

Moreover the gas used to fluidised the bed can have its heat collected from it in a heat exchanger so that there is little loss.

The invention includes a method for manufacturing particulate slag in which hot slag particles are supplied to a fluidised bed uherr 71ère they are cooled and from which they pass to a classifying passage along which they flow against the flow of gas which separates powder from the fluidised bed from the slag particles and returns the powder to the fluidised bed.

The invention may be carried into practice in various ways and one preferred embodiment thereof will be described by way of example with reference to the accompanying drawing in which the single figure is a diagram of an apparatus for cooling slag granules.

A rotary drum 2 which is disposed immediately below the nozzle of a tundish 1 is rotated by a motor in the direction indicated by the arrow so that slag granules being formed at the drum surface 2 are charged into a fluidised bed type cooler 3 through its opening adjacent to the periphery of the rotary drum 2. A perforated gas distributor 15 is inclined downwardly at an angle between about 5 and 10 degrees from the side adjacent to the rotary drum 2 to a classifying pipe 8. A heat-exchanger coil 4 is disposed within the cooler 3 and above the gas distributor 15 so that heat exchange occurs between a cooling medium flowing through the coil 4 and a fluidised bed 3a which consists of semi-molten slag granules from the rotary drum 2, pulverised solid particles of silica sand, graphite, alumina, lime stone, or the like, and gas from the distributor 15.

The cooler 3 is connected through the classifying pipe 8 to a moving bed type heatexchanger 9 with an inverted cone-shaped gas distributor 16. The heat-exchanger 9 is connected through a slag granule discharge pipe 10 to a slag granule store 11.

A blower 5 which is disposed below the cooler 3 is connected through a duct 17 to feed gas into the fluidised bed 3a. Disposed above the cooler 3 is a cyclone 13 for separating the slag granules and silica sand from the gas discharged from the cooler 3 through a duct 19, and the slag particles and silica sand separated therein are returned through a return duct 20 into the cooler 3.

Gas from the cyclone 13 is drawn by a blower 14 through a duct 21, a heat exchanger 12 for recovering waste heat from the gas, and a duct 22.

A blower 6 feeds gas into the moving bed of the heat exchanger 9 through a duct 18, and thence from the upper zone of the heatexchanger 9 through a bypass duct 7 into the duct 19.

In operation, molten slag in the tundish 1 is discharged through the nozzles to impinge against the rotary drum 2, becomes granulated as it rebounds from the drum surface, and is fed into the fluidised bed 3a through the opening of the cooler 3. The gas which is introduced through the duct 17 from the blower 5 flows through the perforations of the gas distributor 15 to establish the fluidised bed.

The slag granules fall into the fluidised bed 3a without encountering any mechanical shock and are quickly cooled by the gas and the pulverised solid particles of the fluidised bed 3a to a temperature nearly equal to the temperature of the bed, and the fluidised bed is correspondingly heated.

Some slag granules and other particles are carried by the gas discharged from the cooler 3 through the duct 19 into the cyclone 13. They are separated from the gas in the cyclone 13 and returned through the duct 20 into the cooler 3 while the gas flows from the cyclone 13 through the duct 21 into the heat exchanger 12. The gas which has been cooled in the heat exchanger 12 is discharged through the duct 22 and the blower 14 into the surrounding atmosphere.

The remaining slag granules move toward the classifying pipe 8 along the inclined gas distributor 15 in company with solid particles of the fluidised bed 3a.

Gas is forced by the blower 6 through the duct 18 and the gas distributor 16 into the moving bed in the heat-exchanger 9 and flows upward through the slag granules into the classifying pipe 8 and then into the cooler 3. In the classifying pipe 8, the upward flowing gas is arranged to flow faster than the gas from the fluidised bed 3a; also the size of the solid particles of the bed is less than about one half of the size of the slag granules. As a result, aerodynamical classification occurs at the inlet to the classifiying pipe 8 to separate slag granules from bed particles so that only slag granules continue to fall through the classifying pipe 8 into the heat-exchanger 9 while being cooled by the upwardly flowing gas from the heat-exchanger 9. The slag granules thus cooled are discharged through the discharge pipe 10 into the storage 11.

The adjustment of the particle size classification of slag granules is made by adjusting the degree of opening of a damper (not shown) in the bypass duct 7 to adjust the flow rate of gas in that duct.

The temperature of the fluidised bed 3a is set by the characteristics of the heat-exchange coil 4, the volume of gas bypassed through the duct 7 from the heat-exchanger 9 to the duct 19, and the volume of the gas discharged from the blower 5 into the cooler 3. The apparatus is set so that slag granules are not broken by thermal impacts and do not melt and coalesce.

In the fluidised bed 3a the gas from the heat exchanger 9 through the classifying pipe 8 is mixed with the gas from the blower 5. and then flows into the cyclone 13 through the duct 19, gets separated therein from the slag granules and other particles, and flows into the heat exchanger 12 and is cooled and discharged through the duct 22 and the blower 14 into the surrounding atmosphere in the manner described above.

The gas which has passed through the duct 7 is treated in the same manner.

In the preferred embodiment of the present invention, the rotary drum 2 is used to granulate the molten slag, but it is to be understood that any other suitable means may be employed.

The advantages of the apparatus for cooling slag particles in accordance with the present invention may be summarised as follows: 1. While coverting high temperature slag into a useful granular substance which may be used an an aggreagate, the slat heat is effectively recovered.

2. The cooling gas may be selected dependent upon the characteristics and properties of slag to be treated, and recirculation is possible. As a result the amount of gas discharged is low and poisonous gas and dust pollution is avoided.

3. The fluidised bed prevents the slag particles from being subjected to mechanical, impact, and as the heat capacity of a fluidised bed is several hundred times as high as the heat capacity of slag particles or of the cooling gas, the temperature variation in the fluidised bed due to the variation in the feed of slag particles and cooling gas is mininised and the fluidised bed can be continously maintained at a temperature that will prevent break-up of slag granules due to thermal shock.

4. As the effective thermal conductivity of slag particles within the fluidised bed is of the order of several hundred Kcal/m'hroC, even when slag particles are received in the fluidised bed, in a molten or semi-molten condition, their surface is quickly solidified to prevent mutual coalescence.

5. Because of the active movements of particles in the fluidised bed, the fluidised bed may be maintained throughout at almost uniform optimum intermediate temperature, which satisfies simultaneously the two apparently contradictory conditions, one to avoid thermal impact and the other to cause quick solidification of the surfaces of slag particles.

WHAT WE CLAIM IS: 1. Apparatus for cooling particulate slag comprising a fluidised bed arranged to receive the slag and containing powder and a supply of gas for fluidising the powder, and having an outlet leading to a classifying passage with means arranged to drive gas to flow along the classifying passage, against the flow of particles from the bed, and then into the bed.

2. Apparatus as claimed in Claim 1 in which the passage leads to a cooler in which the gas flows first to cool slag particles in the cooler, and then to classify particles in the classifying passage.

3. Apparatus as claimed in Claim 1 or Claim 2 including a receptacle for particulate slag which has passed through the passage agains the flow of gas.

4. Apparatus as claimed in any of the preceding claims including a collector of gas from the fluidised bed leading to a separator for separating gas from slag particles and bed powder which have been entrained in the gas and returning them to the bed.

5. Apparatus as claimed in Claim 4 and either of Claims 2 and 3 in which gas from the cooler is also fed to the separator.

6. Apparatus as claimed in Claim 4 or Claim 5 including a heat exchanger arranged to extract heat from gas separated by the separator.

7. Apparatus as claimed in any of the preceding claims including heat exchange coils in the fluidised bed.

8. Apparatus as claimed in any of the preceding claims including a rotary drum for providing the slag particles and disposed to feed the particles to the fluidised bed.

9. Apparatus for cooling particulate slag constructed and arranged substantially as herein specifically described with reference to the accompanying drawing.

10. A method of manufacturing particulate slag in which hot slag particles are supplied to a fluidised bed where they are cooled and from which they pass to a classifying passage through which they flow against the flow of gas which separates powder from the fluidised bed from the slag particles and returns the powder to the fluidised bed.

11. A method as claimed in Claim 10 in which gas from the fluidised bed is passed through a separator which separates powder from the bed and particulate slag from the gas and returns the powder and slag to the bed and passes the gas to a heat exchanger for recovery of the heat in it.

12. A method of manufacturing particulate slag performed substantially as herein specifically described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. cooled and discharged through the duct 22 and the blower 14 into the surrounding atmosphere in the manner described above. The gas which has passed through the duct 7 is treated in the same manner. In the preferred embodiment of the present invention, the rotary drum 2 is used to granulate the molten slag, but it is to be understood that any other suitable means may be employed. The advantages of the apparatus for cooling slag particles in accordance with the present invention may be summarised as follows: 1. While coverting high temperature slag into a useful granular substance which may be used an an aggreagate, the slat heat is effectively recovered. 2. The cooling gas may be selected dependent upon the characteristics and properties of slag to be treated, and recirculation is possible. As a result the amount of gas discharged is low and poisonous gas and dust pollution is avoided. 3. The fluidised bed prevents the slag particles from being subjected to mechanical, impact, and as the heat capacity of a fluidised bed is several hundred times as high as the heat capacity of slag particles or of the cooling gas, the temperature variation in the fluidised bed due to the variation in the feed of slag particles and cooling gas is mininised and the fluidised bed can be continously maintained at a temperature that will prevent break-up of slag granules due to thermal shock. 4. As the effective thermal conductivity of slag particles within the fluidised bed is of the order of several hundred Kcal/m'hroC, even when slag particles are received in the fluidised bed, in a molten or semi-molten condition, their surface is quickly solidified to prevent mutual coalescence. 5. Because of the active movements of particles in the fluidised bed, the fluidised bed may be maintained throughout at almost uniform optimum intermediate temperature, which satisfies simultaneously the two apparently contradictory conditions, one to avoid thermal impact and the other to cause quick solidification of the surfaces of slag particles. WHAT WE CLAIM IS:

1. Apparatus for cooling particulate slag comprising a fluidised bed arranged to receive the slag and containing powder and a supply of gas for fluidising the powder, and having an outlet leading to a classifying passage with means arranged to drive gas to flow along the classifying passage, against the flow of particles from the bed, and then into the bed.