EP0384101B1 - Air classifier for sifting a granular material, and grinding plant employing such a classifier - Google Patents

Abstract

In order to ensure in a recirculating grinding plant having a choke feed roll press (27), tube mill (26) and air classifier (10) with recirculation of the classifier oversizes that as far as possible no energy-consuming problems relating to ventilation and the pressing of material occur in the choke bed in the roll nip of the roll press, it is proposed to build into the recirculating grinding plant an air classifier (10) such as is characterised by at least two mutually separate oversize removal openings, to be precise a removal opening (19, 20) for coarse oversizes and a removal opening (22, 23) separate therefrom for finer oversizes, and to recirculate to the high-pressure roll press (27) only the coarse oversizes, and to the tube mill (26) only the finer oversizes. <IMAGE>

Description

The invention relates to a rotary grinding plant with a tube mill and sifter, the tube mill being preceded by a high-pressure roller press with material bed comminution of the feed material and the sifting size being recirculated.

When operating high-pressure roller presses for compacting or for pressure treatment of granular goods, e.g. B. for the purpose of so-called material bed comminution brittle ground material such. B. cement clinker (EP-PS 0 084 383), the feed material fed to the nip must be gripped by the oppositely driven rollers and drawn into the nip by friction. The individual particles of the ground material drawn into the nip by friction are crushed in a bed of material, that is to say in a bed of material compressed between the two roller surfaces when an extremely high pressure is applied. The feed capacity of the rollers would be improved per se if the feed material was fed in in such an amount that a high load of feed material formed over the nip in the feed shaft.

It is also known to connect such a high-pressure roller press for comminuting granular material to a circulating grinding plant with a tube mill and classifier. The invention is based on such a rotary grinding plant for carrying out the so-called hybrid grinding process (DE-A-37 11 926), namely on the rotary grinding plant known there Tube mill and classifier, the tube mill being preceded by a high-pressure roller press with comminution of the feed material and the classifier sizes being recirculated to the high-pressure roller press and the tube mill. In this known circulating grinding plant, the size of the classifier is divided purely in terms of quantity, and the partial flow of semolina recirculated to the feed shaft of the high-pressure roller press corresponds exactly in grain size distribution and fineness of grain to the partial classifier flow recirculated to the tube mill, i.e. both partial streams contain both fine and coarse classifier grain, while the classifier (Finished product) is withdrawn from the classifier together with the classifying air flow.

The problem on which the invention is based, using DE-A-37 11 926, is that in the known material bed comminution in the nip of the high-pressure roller press in the feed hopper arranged above the roller press, into the fresh material, such as, for. B. cement clinker lumps and recirculated sifting of the classifier are abandoned, there are problems if the gaps between the chunks of the fresh material are completely filled with sifting meal, which includes both fine and coarse sizes. It was previously thought that the feed capacity of the press rolls for the fresh material (e.g. cement clinker) would be improved if as many of the air spaces as possible formed between the chunks or grains of the fresh material in the feed material bed, especially with fine ones, were placed in a high feed hopper Classifying would be filled. Large quantities of sifting in the high feed hopper built up above the nip of the high-pressure roller press can, however, cause the following difficulties: Is the feed in the feed chute of the roller press at least partly very fine-grained by recirculating large amounts of the size of the downstream sifter to the fresh feed can, especially in the case of material feed chutes with high material fill levels and low bulk weights of the feed material fed to the feed shaft, increasingly caused by large amounts of recirculated semolina which are already relatively fine and trapped with air inclusions to the roller press, the problem arises that the air pressed by high pressure from the feed material can no longer escape upwards, which worsens the good intake capacity and the good pressing capacity of the rollers, reduces the throughput of the roller press, leads to uneven operation of the roller press and ultimately leads to the material bed reduction achievable energy savings impaired. In addition, in the case of high feed chutes with high feed batches, which have a significant proportion of fine sifter granules in particular, there are noticeable wall friction resistances of the feed material, which hinder the feed material from flowing into the nip, particularly in the area of the two roller ends or the two edge zones of the nip.

The invention has for its object to improve the generic rotary grinding plant of DE-A-37 11 926 in such a way that the above-described energy-consuming ventilation and material pressing difficulties in the roll gap of the material bed comminution roller press and thus also the specific energy requirement of the entire rotary grinding plant are significantly further are reduced.

This object is achieved according to the invention with the features of the characterizing part of claim 1. Advantageous refinements are specified in the subclaims.

In the rotary grinding plant according to the invention, the classifier, which is a bar basket classifier with a high degree of selectivity, has two separate semolina discharges, namely a semolina discharge for coarse semolina and a separate semolina discharge for the finer semolina. The grain size of the coarse semolina can e.g. B. greater than 0.5 mm and the grain size of the finer semolina z. B. be less than 0.5 mm. If one switches such a rod basket sifter into a circulation grinding plant with a high-pressure roller press and tube mill, then according to the invention the possibility is used to recirculate the coarse size of the sifter only for the good job of the high-pressure roller press and the finer size of the same sifter only for the good job of the tube mill. This will remove the high pressure roller press from the Fine material grit of the classifier is relieved in a targeted manner, as a result of which the ventilation and material pressing difficulties in the roller gap of the roller press are significantly reduced. The operation of the roller press becomes more uniform and the energy saving associated with material bed crushing is not reduced by the difficulties described above. In the rotary grinding plant according to the invention, both the high-pressure roller press with material bed comminution and the tube mill work individually under optimal conditions.

SU-A-975 120 does not know a dynamic rod basket sifter, but a static three-product sifter that produces three differently fine finished products, namely coarse semolina, finer semolina as well as the fine material discharged upwards with the air flow from the sifter, which subsequently follows from Visual air flow must be separated in a separator. None of the three different fine products is recirculated in the known sifter. There was no reason to set the classifier of SU-A-975 120 in the rotary grinding plant of DE-A-37 11 926 instead of the classifier there, where the problem or knowledge according to the invention described above was not known. The specialist would have recirculated the fine grains (e.g. SU-A-975 120) to the feed chute of the roller press in order to operate recirculating grinding plants with high-pressure high-pressure roller presses for the reasons described above, in order to recycle the gaps between the chunks of the to fill in fresh feed as completely as possible, because he just thought that this was the only way to use the material bed shredding technique effectively.

The dynamic rod basket sifter integrated into the circulation grinding system according to the invention advantageously has a sifter housing, in the lower region of which the viewing air inlet opening and the discharge opening for the coarse gravel and in the upper region the rotatably arranged rod basket with turbo elements are arranged, which are surrounded by guide elements distributed over the circumference are. With such a turbo-wind sifter, the preliminary separation of the coarse gravel causes wear on the classifier rotor, on the guide elements and on the other parts of the classifier, because with the rod basket classifier used according to the invention, the coarse grains are removed from the classifier (separately from the finer sizes) before they can come into contact with the classifier internals.

The invention and its further features and advantages are explained in more detail with reference to the exemplary embodiments shown schematically in the figures.

Fig. 1:

eine erfindungsgemäße Umlaufmahlanlage mit Rohrmühle, Sichter und Gutbettzerkleinerungs-Hochdruck-Walzenpresse;

Fig. 2:

eine Umlaufmahlanlage gemäß einer zweiten Ausführungsform der Erfindung;

Fig. 3:

eine Umlaufmahlanlage gemäß einer dritten Ausführungsform der Erfindung, und

Fig. 4:

im Vertikalschnitt den in den Umlaufmahlanlagen der Fig. 1 bis 3 eingesetzten Stabkorbsichter.

It shows:

Fig. 1:

a circulation grinding plant according to the invention with tube mill, sifter and material bed crushing high-pressure roller press;

Fig. 2:

a circulation grinding plant according to a second embodiment of the invention;

Fig. 3:

a circulation grinding plant according to a third embodiment of the invention, and

Fig. 4:

in vertical section the rod basket sifters used in the circulation grinding plants of FIGS. 1 to 3.

4 has a housing (10) which, seen in vertical section, tapers conically downwards in its lower region and conically upwards in its upper region. A pipe (11) is inserted into the lower end of the classifier housing (10), through which the classifying air flow (12), loaded with material to be viewed, is introduced into the classifier from below. The loaded stream of sifting air flows from the bottom upwards through the sifter housing (10), is deflected in its upper region, flows between optionally distributed guide elements (13) distributed over the circumference into the annular channel-shaped viewing zone (14) and in the rotatably arranged in the sifter housing and from above via a shaft (15) driven sifting rotor or rod basket (16) which carries sheet-shaped turbo elements (17) on its circumference and is closed at the bottom by a bottom

The classifier according to FIG. 4 has in its lower area a pre-separation zone for the coarse grains, which also collect as a result of the cross-sectional expansion of the classifier housing (10) in the annular space (18) between the classifier housing and the tube (11) projecting into it from below are discharged via the obliquely downwardly inclined tube (19). The operating conditions of the classifier can be set so that the grain size of the coarse grains discharged (20) z. B. is greater than 0.5 mm. It is understood that the built-in sifter is not stressed by the previously separated coarse gravel (20), whereby the wear of the sifter according to the invention is reduced overall.

After the coarse semolina (20) has been drawn off from the classifier, the finer semolina remaining in the classifying air stream falls into the ring channel Visible space (14) down and they are collected via a cone (21), which adjoins the underside of the guide elements (13) downwards, and via an obliquely downwardly inclined tube (22) as a finer size (23) with a Grain size of z. B. less than 0.5 mm separated from the coarse semolina (20) from the classifier. The fine material is taken along by the sifting air flow and drawn out of the classifier with this via a non-rotating fines discharge housing (24) placed on the rod basket (16), as indicated by arrow (25).

According to FIG. 1, the classifier of FIG. 4 is switched on in a circulation grinding plant with a tube mill (26), which is preceded by a high-pressure roller press (27), the classifier discharge for the coarse grains (20) for good feed of the roll press and the classifier discharge for the finer semolina (23) are returned to the tube mill (26). The high-pressure roller press (27) is the feed material to be shredded (28), e.g. B. not pre-crushed cement clinker with a grain size of up to 100 mm, for example, via a feed shaft (29). The grain size of an essential part of the feed material (28) is larger than the width of the narrowest nip of z. B. 20 mm between the two press rolls, which can have a diameter of, for example, 900 mm. The pressing force of the rollers of the roller press, which presses on the material (28, 20), is more than 2 t / cm roller length, for example 6 to 9 t / cm. The feed material is shredded in the gap between the rollers by a combined single-grain shredder and material bed shredder. To carry out the last-mentioned principle of comminution, the feed material to be comminuted is fed to the nip of the press (27) in such a large amount via the feed chute (29) arranged above the nip that the material to be comminuted and drawn in between the rollers by friction pushes the rollers apart and the Particles of the feed material crush each other in the roller gap in a bed or in the collective or in a bed of material. The cement clinker emerges from the nip crushed and partially agglomerated, i. H. to Schülpen (30) pressed, the proportion of particles already reduced to the desired cement fineness can already be relatively high (approx. 25% less than 90 µm). While the bulk density of the fresh ground material (28) is 1,600 kg / m³, the density of the pressed slug (30) is approx. 2,400 kg / m³.

The fact that in the feed shaft (29) of the roller press (27) only the coarse grains (20) of the classifier (10) are recirculated, but not the finer grains (23), the material pressure and ventilation in the material bed shredding in the area of the narrowest nip of the roller press is not hindered. On the contrary, the addition of only the coarse semolina (20) to the fresh feed material (28) can even improve the feeding conditions for the entire feed material in the nip of the roller press (27) during comminution of the material bed.

The tube mill (26) of FIG. 1 is an airflow mill with a central good inlet opening (31) through one end wall spigot and a central discharge opening (32) through the other end wall spigot. The tube mill has, as usual, a discharge wall (33) in front of its discharge opening (32), the openings of which only allow pre-ground material of a certain grain size to pass through, which is represented by the arrow (34). The discharge (30) of the roller press (27) is introduced into the material discharge of the tube mill (26) through a centrifugal shredding device (not shown) through the central mill discharge opening (32) and through the central opening of the discharge wall (33), in countercurrent to the tube mill discharge material, which together with the roller press discharge deagglomerated in the deagglomerating chamber (35) through peripheral openings of the same discharge wall (33) as material flow (34) via the riser pipe (11), the lower part (11a) of which passes to the central material discharge opening (32 ) connects the tube mill, is transported pneumatically to the classifier (10) with the aid of a conveying air flow (36). The roll press discharge material (30) arriving in the disagglomerating chamber (35) of the tube mill (26) (scraper fragments) is designated by reference number (37a). These Schülpen Fragments (37a) are dissolved autogenously by pure circulation movement.

The classifier (10) sifted the sufficiently fine finished product both from the deagglomerated roller press discharge material (30) and from the grinding product of the tube mill (26), namely as a fine grain fraction, which via the line (25) and dust separator (37), e.g. . B. electrostatic dust collector is withdrawn, from which the fine finished product (38), in the exemplary embodiment the sufficiently finely ground cement is removed. An induced draft fan is indicated with (39). There is also the possibility of recirculating a partial flow of the roller press discharge material (30) via the connection (40) shown in dashed lines into the feed shaft (29) of the roller press (27).

1 using the classifier of FIG. 4, an originally existing tube mill can be used without having to be converted. As the only remodeling or supplementary measure, it can be advantageously used in the tube mill (26) at a distance from the discharge wall (33) already present, a perforated partition (41) is installed, which separates the actual grinding chamber containing the grinding media (42) from the disagglomerating chamber (35) located between the discharge wall (33) and the partition (41). separates, provided the tube mill was not originally a two-chamber mill with a partition. The tube mill can also have a material failure housing with a bucket elevator for transporting the ground material to the classifier.

If the air stream (36) is a hot gas stream, the recirculating grinding system of FIG. 1 can be used as a grinding drying system for grinding and drying moist material, e.g. B. from moist starting material for the production of raw cement meal. Then the riser (11) between the mill (26) and classifier (10) serves as a current dryer. There is the option of branching off a partial flow (44) from the drying gas flow (43) after the induced draft fan (39) and mixing it into the fresh hot gas flow (36) via line (45) and / or via line (46) below into the flow dryer (11). Instead of the tube mill (26), another fine comminution device would also be conceivable.

Fig. 2 shows the flow diagram of a grinding drying plant for grinding and drying moist starting material for the production of raw cement meal. The starting material (28) is fed through the feed shaft (29) of the high-pressure roller press (27) and comminuted there, as in the exemplary embodiment in FIG. 1. The slugs (30) which are formed are introduced via a conveyor device (47) and via a material lock (48) into the material inlet (49) of an impact hammer mill (50) with a closed bottom and are deagglomerated there. A hot gas line (51), shown in dashed lines, is connected to the good inlet (49) of the deagglomerator (50). Exhaust gas from a preheater for cement raw meal from a cement clinker combustion plant, hot exhaust air from a cement clinker cooler and / or hot gas from another hot gas generator can be used as hot gas. Connected to the discharge of the deagglomerator (50) is the riser (11, 12) designed as a current dryer, in which the material is dried and which leads to the classifier (10), the classifier discharge (19) for the coarse grains (20) a conveyor (52) for the feed (29) of the roller press (27) and the sifter discharge (22) for the finer grains (23) for the feed of a tube mill (26). The finer semolina (23) are fed into the tube mill (26) together with a hot gas stream (53), which can be branched off from the hot gas line (51), e.g. B. consists of hot flue gas or hot exhaust gas from a cement clinker combustion plant and in so far Has inert gas property. This is important if the moist feed material (28) to be treated in the mill-drying system according to FIG. 2 are not moist cement raw materials, but rather e.g. B. is wet coal. After the treatment in the tube mill (26), the material is introduced via line (54) into the riser (11, 12) leading to the classifier (10). The fine material discharge line (25) of the classifier (10) leads to the separator (37) such as a filter, separating cyclone or the like, which is conveyed via a conveyor (55), e.g. B. screw conveyor the fines as finished goods (38), z. B. completely dried and ground cement raw meal or also completely dried and ground coal, from the classifying gas stream or drying gas stream (43). After the finished product has been separated off, the exhaust gas line (43) is connected via the branch line (44, 45) to the hot gas line (51) connected to the product inlet (49) of the deagglomerator (50) and / or via a branch line (46) to the product discharge of the deagglomerator (50) connected riser (11, 12) in connection.

While FIGS. 1, 2 and 4 show a classifier to which the feed material is fed together with the classifying air, FIG. 3 shows a classifier (10) to which the classifying material is fed separately from the classifying air. This sifter (10) is also switched into a circulation grinding plant with a tube mill (26) and a high-pressure roller press (27). In this rotary grinding plant, the discharge line (20) of the classifier (10) for the coarse semolina to feed the high-pressure roller press (27) and the discharge line (23) for the finer semolina to the material inlet of the tube mill (26) are recirculated. The mill (26) can be operated in an open pass. The material to be discharged from the mill is fed via line (56) to a spreading disc rotating within the classifier (10). With (12a) the sight air entry into the classifier and with (25) the withdrawal of the fine air-laden sight air flow from the classifier (10) is indicated. The advantages of the invention claimed in the description of FIGS. 1, 2 and 4 also apply to the exemplary embodiment in FIG. 3.

Claims (3)

1. A rotary grinding plant comprising a tube mill (26) and a classifier or sifter (10), a high-pressure roll press (27) with means for comminuting a bed of feed material (28) being disposed downstream of the tube mill (26) and the grit being recirculated after sifting, characterised in that the classifier or sifter (10), which is a rod-cage classifier or sifter comprising a rotatable rod cage (16) provided with turbo-elements (17), has two separate outlets for grit, i.e., an outlet (19, 20) for coarse grit and a separate outlet (22, 23) for finer grit, and that the coarse grit from the outlet (19, 20) is returned only to the high-pressure roll press (27) and the finer grit from the outlet (22, 23) is returned only to the tube mill (26).
2. A rotary grinding plant according to claim 1, characterised in that a de-agglomerating drum (35) is disposed at and rotates with the tube mill (26), with its inlet being connected to the outlet (30) of the high-pressure roll press (27) and its outlet being connected to the classifier or sifter (10) whose outlet line (22, 23) for the finer grit leads to the inlet of the tube mill (26).
3. A rotary grinding plant according to claim 2, characterised in that the tube mill (26) has a perforated partition (41) therein which separates a grinding chamber containing grinding elements from the de-agglomerating chamber (35), which latter chamber does not have grinding elements.

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