Method and device for granulating molten material

Abstract

For a method for granulating molten material, in particular slags, in which the molten material is introduced into a granulating chamber in which water is held as a cooling liquid, wherein the molten material is preferably quenched and granulated with evaporation of the water, an acid is added to the water.

Claims

1-22. (canceled)

23. A method for granulating molten material comprising a slag having, as its main constituents, CaO: >30% by weight, SiO2: >30% by weight, and Al.sub.2O.sub.3: >6% by weight, in particular blast furnace slag, the method comprising introducing the molten material into a granulating chamber, wherein the granulating chamber includes water as a cooling liquid, quenching and granulating the molten material to obtain latent hydraulical particles, adding an acid to the water, wherein the water is in a water bath or the granulating chamber includes a sump and the molten material is introduced into either the water bath brought to boiling temperature or introduced above the water in the sump brought to boiling temperature, and subjecting the molten material in the granulating chamber to a mechanical disintegration by means of a disintegrator.

24. The method according to claim 23, wherein the acid comprises a mineral acid, an organic acid or a mixtures thereof.

25. The method according to claim 23, wherein the method further comprises measuring pH value of the water and regulating the feed of the acid to the water to maintain a predetermined pH value of the water.

26. The method according to claim 23, wherein the mechanical disintegration is performed by means of a rotor.

27. The method according to claim 23, wherein the disintegrator is arranged at least partially in the water bath or adjoining the sump.

28. The method according to claim 26, wherein the rotor has an axis, and either the rotor has axial perforations and water is conducted through axial perforations of the rotor or the rotor has at least one channel extending in the radial direction from the axis of the rotor and water is conducted through the at least one channel of the rotor.

29. The method according to claim 23, wherein in the method water is evaporated while the molten material is quenched and granulated, and the method further comprises condensing the evaporated water, recirculating the thus condensed water to the granulating chamber and bring the water to boiling temperature after being returned to the granulating chamber.

30. The method according to claim 23, wherein the granulating chamber is configured as a grinding mill and the molten material is quenched with metallic grinding media of the grinding mill and the solidified material particles are ground by the action of the grinding media.

31. The method according to claim 24, wherein the inorganic acid comprises sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid; and the organic acid comprises formic acid, acetic acid, stearic acid or ligninsulfonic acid.

32. The method according to claim 31, wherein the method comprises introducing carbon and/or carbon-containing compounds into the granulating chamber for effecting a water gas reaction in the granulating chamber.

33. A device for performing the method according to claim 23, said device comprising a granulating chamber having a water basin for receiving a water bath and/or a sump for water, a feeding device for feeding the molten material into the granulating chamber, a water feed opening into the water basin and/or the sump, a feed for the acid and a discharge opening for the granulated material, wherein a disintegrator, in particular a rotor, is arranged in the granulating chamber in a region where the molten material is fed into the granulating chamber.

34. The device according to claim 33, wherein the device further comprises a sensor for determining the pH value of the water in the granulating chamber, which, together with regulating the quantity of the acid feed to the water, is for maintaining the pH value of the water at a predetermined value.

35. The device according to claim 33, wherein the feeding device for the molten material comprises a dip tube protruding into the granulating chamber.

36. The device according to claim 33, wherein the disintegrator comprises the rotor, and the rotor is arranged in the water bath or adjacent to the sump.

37. The device according to claim 36, wherein the rotor has a vertical axis, and the rotor has axial perforations or at least one channel extending in the radial direction from the vertical axis for the passage of water.

38. The device according to claim 37, wherein the rotor has a channel, which opens out preferably into the region where the molten material is fed into the granulating chamber, for the introduction of reactive gases and/or water vapor.

39. The device according to claim 33, wherein the granulating chamber is configured as a grinding mill filled with metallic grinding media.

40. The device according to claim 39, wherein the grinding mill has a housing formed by a rotatably drivable drum and is configured as a ball mill, fall mill, drum mill, tube mill or sieve drum mill.

41. The device according to claim 39, wherein the grinding media comprise metal balls, the diameter of which is at least 15 mm.

42. The device according to claim 39, wherein the grinding mill has an inner jacket which delimits the grinding space and is provided with perforations, and an outer jacket, wherein the inner and outer jackets delimit an annular space which configures the water basin and is connected to the water feed.

Description

[0075] The invention is explained in more detail below with reference to exemplary embodiments shown schematically in the drawing.

[0076] In these, FIG. 1 shows a first embodiment of a granulating device for performing the method according to the invention,

[0077] FIG. 2 shows a second embodiment of a granulating device,

[0078] FIG. 3 a cross section of a granulating device configured as a ball mill,

[0079] FIG. 4 a longitudinal section of the device according to FIG. 3 and

[0080] FIG. 5 is an enlarged detail view of the device according to FIGS. 3 and 4.

[0081] FIG. 1 shows a granulating device 1 which has a feeding device for molten material 3 configured as a dip tube 2. In the interior of the granulating device 1, a granulating chamber 4 is configured, in which a water bath with a water surface 5 is accommodated. A water feed 6 opens into the water bath. The granulated material is discharged via a discharge opening 7.

[0082] The dip tube 2 immerses into the water bath to just above a disintegrator configured as a rotor 8, so that the melt jet 3 introduced through the dip tube 2 impacts directly on the rotor 8 or only a small water layer passes through, but it evaporates abruptly. The rotor 8 is rotatably mounted about a rotational axis 9 and is driven for rotation according to the arrow 10. The slag jet 3 is preferably introduced centrally, as shown in FIG. 1, i.e., in the region of the rotational axis 9 of the rotor 8. In the center 11 of the rotor 8, the latter has a rounded or convex region, on which the melt jet 3 impacts and is thrown outwards therefrom on account of the rotation. The rotor 8 is arranged essentially at the bottom of the granulating chamber 4. In a radially inner, central partial region of the rotor 8, a sump or a mixing chamber 12, however, is configured below the rotor 8, which forms a recessed region of the granulating chamber 4 and is filled with water. The rotor 8 has axial perforations 13, through which the water is sucked out of the mixing chamber 12.

[0083] The rotor 8 has guide surfaces 14, which act as a cavitator, radially outside the axial perforations 13. The granulating water is provided at a temperature such that it vaporizes abruptly in the region of the introduction of the melt jet 3 or in the region of the rotor 8 due to the thermal energy introduced with the melt. The expanding steam together with the mechanical forces caused by the rotor 8, in particular shearing forces, cause a grinding effect on the solidifying melt particles, so that an extremely fine-grained granulate is formed. At the guide surfaces 14, the expanding steam, in conjunction with the said forces, leads in the micro region to steam explosions, followed by implosions, i.e., to cavitation, whereby an extremely intensive comminution of the forming granules particles is achieved.

[0084] For cooling the central region 11 of the rotor 8, a feed channel 15 is provided which runs inside the shaft 16 of the rotor 8 and is radially deflected in the central region 11 for the formation of radial channels 17. Water or steam can be supplied for cooling the central region 11 of the rotor 8 via the feed channel 15 and the radial channels 17, for example. Reactive gases such as, for example, O.sub.2, air, Cl.sub.2, SO.sub.2, CH.sub.4 and/or coal dust or hydrocarbons can further be introduced together with air/O.sub.2 or water via the feed channel 15 and the radial channels 17.

[0085] The solidified melt particles 18 leave the rotor 8 in the radially outer region thereof and rise due to their low density in the preferably boiling water bath. In this case, a guide apparatus 25 can be provided, which comprises, for example, blade bodies. At the bath surface 5, the solidified melt particles 18 are discharged together with the granulating water via the discharge opening 7 configured as an overflow.

[0086] The gaseous constituents are removed via a reaction gas withdrawal system, which is shown schematically at 21, wherein it is water vapor and, for example, HF, CO, H.sub.2 and SO.sub.2.

[0087] An acid, in particular sulfuric acid, is now added to the water bath. The acid is added via the water feed 6. The acid is added to the water to be fed into the mixing chamber 12 at 19. The quantity control of the acid admixture is effected as a function of measured values of a pH sensor 20 in such a way that a predetermined pH value of the water bath is achieved or maintained or as a function of the chemical composition of the melt and of the melt flow rate.

[0088] The water supply is fed by return water, which is extracted from the discharge opening 7. The granulate brine withdrawn via the discharge opening is subjected for this purpose to at least one separating step in which the granules obtained are separated off. The return water obtained in this way is recycled via line 22. To compensate for evaporated water, the water recycled is mixed with 23 additional water.

[0089] A portion of the water at 24 can be discharged for the separation of components contained in the return water, in particular dissolved therein, like, for example, FeSO.sub.4, Na.sub.2SO.sub.4 and various heavy metals.

[0090] In the modified embodiment according to FIG. 2, the granulating water is presented as a sump only in the chamber 12 below the rotor 8. The water is introduced into the granulating chamber via line 6 at a temperature below the boiling temperature. Carbon and/or hydrocarbons can be introduced into the sump via the line 26 in order to effect a water gas reaction in the granulating chamber 4 in addition to the granulation (with the aid of the water evaporating from the chamber 12). In this embodiment, the solidified melt particles are withdrawn together with the water vapor and the forming water gas via the discharge opening 7, and the melt granules 18 are separated in the cyclone separator 27 from the reaction gases (CO/H.sub.2) and from the H.sub.2O vapor. Pressurized water can be introduced via the channel 15.

[0091] In the embodiment according to FIG. 2, the acid addition can take place directly into the granulating chamber, i.e., without prior admixture into the water 6. The acid is preferably fed via channels running in the rotor 8 which open at a distance from the axis of rotation on the surface of the rotor, i.e., at a point at which a temperature below the decomposition temperature of the acid prevails. The addition of the acid is indicated at 19. Alternatively or additionally, the acid can also be introduced via nozzles 19, by means of which the acid is injected into the granulating chamber in counter current flow to the granulate in the radially inward direction.

[0092] FIGS. 3 and 4 show a granulating device configured as a ball mill. FIG. 3 shows a ball mill 28 in cross section, the cylindrical drum 29 of which is rotatably mounted about the axis of rotation 30. In operation, the drum 29 is driven to rotate in the direction of the arrow 31. The drum 29 has an outer jacket 32 and an inner jacket 34 delimiting the grinding space 33. Between the outer jacket 32 and the inner jacket 33, an annular cavity 35 is formed, which is connected to the grinding space 33 via a plurality of preferably slot-shaped perforations 36 distributed regularly over the circumference of the grinding space 33.

[0093] A slag inlet 37 opens into the grinding space 33 coaxially with the axis of rotation 30, wherein the slag inlet has a slag tundish 38 arranged centrally in the interior of the grinding space 33, the slit-shaped inlet opening 39 of which extends in the axial direction of the drum 29 and is arranged eccentrically within the grinding space 6.

[0094] On the side opposite the slag inlet 37, the drum 29 has a discharge opening 40 coaxial with the axis of rotation 30, to which a discharge line 41 is connected (FIG. 4).

[0095] Instead of the inner jacket 34 provided with perforations, or in addition to this, a spraying bar 42 extending in the axial direction of the drum 29 is arranged in the interior of the grinding space 33, the spray openings of which are directed downwards.

[0096] A metal ball bed 43 is provided in the interior of the grinding space 33, the metal balls, in particular steel balls, forming the grinding media of the ball mill 28. In the operation of the ball mill 28, the metal balls are carried upwards (arrow 44) by the drum 29 rotating in the direction of the arrow 31, as shown in FIG. 3, and fall down again after reaching a critical height due to gravity (arrow 45).

[0097] In the operation of the ball mill 28, as indicated at 46, water is passed into a water feed annular chamber 20 arranged in the drum 29, which is separated from the grinding space 33 by a diaphragm 48. The diaphragm 48 is configured so as to be liquid-permeable only in the region of the water feed annular chamber 47 so that the water feed annular chamber 47 feeds a water bath 49 configured in the grinding space 33 and which is always located in the bottom region of the drum 29. In particular, the water of the water bath 49 fills the annular cavity 35 between the outer jacket 32 and the inner jacket 34 of the drum 29. As can be seen in the detailed view according to FIG. 5, the annular cavity 35 has a plurality of partition walls 50 running in the axial direction of the drum 29 so that a plurality of chambers 51 adjoining one another in the circumferential direction are configured in the annular cavity 35. Each chamber 51 is thereby connected to the grinding space 33 via a slot-shaped perforation 36, wherein the slot-shaped perforations 36 have walls 52 converging towards the grinding space 33, so that there is a nozzle effect.

[0098] When the drum 39 is rotating, blast furnace slag 53 is introduced into the grinding space 33 having a temperature of 1300-1600 C. via the slag tundish 38, wherein the blast furnace slag 53 reaches the ball bed 43, which has a temperature of at most 400-600. The slag is cooled abruptly on the surface of the metal balls of the ball bed 16. At the same time, due to the movement of the balls, the slag is broken down into solidifying particles. The solidifying particles are further comminuted by the grinding effect of the ball bed 43 until they have a minimum upper grain limit of, for example, 60 m, in order to be able to be discharged from the ball mill 28. The particles are cooled in the ball mill 28 to the extent that they have a temperature of 600-800 C. or lower at discharge. The ball mill 28 can be configured in such a way that it has at least two grinding spaces adjoining each other in the axial direction and which are connected to each other by a screening device and grinding media of which are dimensioned such that a higher grinding fineness is achieved in each grinding space. Alternatively, a mill cascade is also conceivable. The longer the residence time of the particles in the mill, the further the ground particles are cooled, so that the exergetic utilization can be further improved.

[0099] Simultaneously with the cooling of the slag at the spherical surfaces, a continual cooling of the metal balls is effected by the action of the water bath 49. The water is evaporated by the heat introduced with the slag, wherein evaporation heat is required, which is withdrawn from the metal balls for the purpose of cooling them. The evaporating water escapes in this case from the chambers 51 via the perforations 36 configured as slot nozzles due to the abrupt volume increase, wherein the nozzle effect leads to an axial uniformization of the outflowing steam quantity due to the pressure gradient. The steam flowing out of the chambers 51 leads to an additional mechanical effect on the balls of the ball bed 43, so that they are excited to vibrations, which improves the grinding effect.

[0100] A mixture of hot steam and the dust of the ground slag particles forms in the interior of the grinding space. The hot steam/dust mixture is discharged via the discharge opening 40 and the discharge line 41.