EP0220681B1 - Device for grinding and milling damp brittle material - Google Patents

Description

The invention relates to a device for comminution and grinding and drying (grinding drying) of moist, brittle regrind, such as starting material for cement raw meal, ore, coal or the like, with an impact hammer mill, at the inlet of which the supply of the moist regrind and a hot gas line and others Good discharge is connected to a riser designed as a current dryer, which leads to a classifier, whose discharge line for the coarse material (grit) is connected to the task of a comminution device.

A so-called "tandem mill drying system" ("Cement Data Book" by Duda, 2nd edition 1977, page 101) developed by the applicant has become known for the grinding and simultaneous drying of moist starting material for the production of cement raw meal, in the case of a tube mill or ball mill is preceded by an impact hammer mill and a hot gas stream flows through both mills. With this known system, raw material of up to 100 mm piece size and up to approx. 12% moisture can be ground and dried very well using raw cement raw meal preheater exhaust gas. However, the energy utilization in the tube mill or ball mill used is very low.

Recently, considerable efforts have been made to increase the low energy utilization in the shredding machines, especially in the tube mills. For example, a two-stage device for comminuting and grinding brittle ground material is known (EP patent 0 084 383), in which the ground material that has not been pre-comminuted, for example cement clinker blocks, initially in a first stage in the nip of a high-pressure roller press under high pressure It is pressed, which partly leads to particle destruction, partly to the creation of cracks in the interior of the particle and is expressed visibly in the formation of agglomerates, which in the second stage can then be deagglomerated or dissolved in a tube mill or ball mill with comparatively little energy expenditure and ground to fineness . The roller press operated with a high pressing force of in particular more than 2 t / cm roller length produces agglomerates (Schülpen) during material pressing, the grindability of which is considerably improved compared to unpressed material, so that the known two-stage size reduction leads overall to a significant reduction in the specific energy requirement . In the roller press, the individual material particles are crushed in a material bed, that is, in a material bed compressed between two surfaces, so that in the first stage one speaks of the so-called material bed comminution.

So far, whenever you have used a bed-crushing high-pressure roller press for the purpose of energy saving, this was a circular grinding with fine grinding machine such. B. tube mill and classifier always upstream (EP patent 0 084 383). However, this is the nip fresh regrind to be fed in a high-pressure roller press, which is the case, for example, with raw material for cement raw meal with an initial moisture content of up to about 15%, there is a risk of the high-pressure roller press running uneasily, which can ultimately lead to the loss of the hoped-for energy savings. This disadvantageous circumstance is exacerbated when the grain size distribution of the feed material is very uneven, which is also the case with raw material for cement raw meal with a fluctuating grain size range from 0 to over 50 mm, which can lead to an uneven load on the high-pressure roller press.

The invention is based on the object of making the energy-saving high-pressure roller press with material bed comminution usable even in the mill drying of moist goods, and of ensuring that the high-pressure roller press used receives a feed material with a reasonably uniform grain size distribution, even if the grain size of the fresh moist one Starting material over a wide range of, for example, 0 to 100 mm and also the humidity fluctuates over a wide range, which is actually the case, for example, with moist starting material for cement raw meal, without as previously at the beginning described grinding drying systems usually have to use a ball mill.

This object is achieved according to the invention with a device characterized in claim 1. advantageous embodiments are given in claims 2 and 3.

In the two-stage mill drying device according to the invention with a high-pressure roller press or roller mill and with an impact hammer mill, both crushing machines being connected via a sifter to form a rotary grinding system, the fresh, moist starting material to be crushed is not fed to the high-pressure roller press, but to the other crushing machine, namely the impact hammer which feed material with a grain size distribution of 0 to approx. 80 mm can be easily shredded and which, seen in the regrind stream, is followed by the high-pressure roller press. In the device according to the invention with an integrated high-pressure roller press, it is therefore proposed for the first time to bypass the high-pressure roller press with the fresh starting material. Since a sifter is switched on between the impact hammer mill and the roller press, which already contains enough fine fraction (for example from the impact discharge of the impact hammer mill) approx. 20 to 30%) as finished material, only high-quality coarse material (grains) with an even grain size and an absolute grain size that is small in comparison to the fresh, moist starting material that is fed to the impact hammer mill are used for the high-pressure roller press. Therefore, in the grinding drying device according to the invention, the high-pressure roller press used can always be operated uniformly with the optimally set roller pressing force of, for example, 6 to 9 t / cm roller length, free of shock loads. Overall, the high-pressure roller press, as it is switched on in the mill-drying device according to the invention, runs very quietly, which also means that the savings in comminution energy which can be achieved with the material bed comminution can actually take full effect when the starting material is moist.

The good discharge of the roller press is connected with the good inlet and / or with the good discharge of the impact hammer mill. If the roller press discharge, which usually consists of agglomerates (Schülpen), together with the fresh starting material is fed to the inlet of the impact gas mill through which hot gas flows, the easily crumbling agglomerates of the roller press are removed from the Impact hammer mill deagglomerated practically without additional operating costs. If the roller press discharge bypasses the impact hammer mill and if it is introduced into its discharge, the crop agglomerates are deagglomerated in the riser arranged between impact hammer mill and sifter and / or in a corresponding crop entry lock such as a tubular screw.

The invention is particularly well applicable in the milling drying of fresh, moist starting material, for example starting material for cement raw meal. In the mill drying system according to the invention, a hot gas line is connected to the inlet of the impact hammer mill equipped with a closed bottom, and the riser arranged between the discharge of the impact hammer mill and the classifier is designed as a current dryer. The coarse sifting material (grit) returned from the sifter to the high-pressure roller press has dried to such an extent that the material bed comminution of this sifting coarse material in the nip of the roller press is not hindered by the low residual moisture which may still be present. A characteristic of the mill-drying plant according to the invention for comminuting and grinding moist material is, above all, that the tube mill or ball mill which has always been used in mill-drying systems and which is characterized by very low energy utilization is no longer present, but rather by the principle of commodity bed comminution operated high-pressure roller press is replaced, which results in a significant reduction in investment costs and, above all, the specific energy requirement of the entire mill drying system. It is also possible without difficulty to convert existing grinding drying systems into the grinding drying system according to the invention after removal of the tube mill or ball mill, in order to take advantage of the extraordinarily high energy savings when operating the grinding drying system according to the invention.

The invention and its further features and advantages are explained with reference to the exemplary embodiments shown schematically in FIGS. 1 and 2.

The exemplary embodiment in FIG. 1 shows the flow diagram of a grinding drying plant according to the invention for grinding and drying moist starting material for the production of raw cement meal. The starting material pre-shredded by a primary crusher is given with a grain size distribution of 0 to about 80 mm and with a moisture of up to about 20% via the feed (10) to the feed end of a belt conveyor (11), weigh feeder or the like and via the discharge end of the conveyor and introduced, for example, via a material lock (12), double pendulum lock into the feed inlet (13) of an impact hammer mill (14) with a closed bottom. A hot gas line (15), which is indicated by a broken line, is connected to the inlet (13) of the mill (14). 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. The hot gas supplied via the line (15) flows through the impact hammer mill (14), in which the starting material is pre-comminuted and pre-dried. Connected to the discharge (16) of the impact hammer mill (14) is a riser (17) designed as a current dryer, in which the material is further dried and which leads to an air flow classifier (18), the discharge line (19) for the coarse material (grit) is connected via a conveyor (20) to the feed shaft (21) of a high-pressure roller press (22). The largely dry sifter coarse material (19), which is uniform in its grain size distribution, is comminuted in the gap between the rollers of the high-pressure roller press (22) by means of material bed comminution. For this purpose, the sifting coarse material (19) is placed above the roller gap arranged vertical shaft (21) in such a large quantity to the nip of the press (22) that the material to be shredded and drawn in between the rollers pushes the rollers apart and the particles of the feed material in the nip in a bed or in a collective or in a bed crush each other. The pressing force of the rollers of the roller press (22) pressing the material is more than 2 t / cm roller length, for example 6 to 9 t / cm. In order to ensure that the feed chute (21) of the roller press (22) is always completely filled with coarse sifter material (19), the feed chute can be arranged on a weighing device such as, for example, on pressure load cells (23) or the like.

The material discharge (24) of the roller press (22) emerges from the nip further comminuted and partially agglomerated, that is to say pressed out into slugs which can be crumbled with the hands and which already reduce a considerable proportion of the fineness of the finished product (finished cement raw meal) Include particles. The discharge material (24) is shown in the drawing as a dotted line. The material to be discharged from the press (24) is connected via line (24a) to the material inlet (13) of the impact hammer mill (14) and / or via line (24b) (conveying member) to the riser (17). If the press material to be discharged (24) reaches the impact hammer mill (14) via line (24a), then this has at least three functions at the same time: it serves to pre-shred the fresh starting material (10), to dry the damp material and to deagglomerate and re-shred the agglomerates of the Press discharge material (24) before it reaches the riser (17) serving as a current dryer. It there is also the possibility of having the roller press discharge (24) open into the riser (17) via the line (24b) via a lock, such as a tube screw (25). The material lock (25) serves on the one hand to deagglomerate the roller press discharge material (24b) and on the other hand to prevent the entry of false air into the riser (17), in which, due to the induced draft fan (26), there is a negative pressure of about 350 to 400 mm water column . There is also the possibility that the material discharge (24) of the roller press (22) is divided into two fractions by a classification screen, not shown, of which the fine fraction (24b) to the riser (17) and the coarse fraction (24a) to the material inlet (13) of the impact hammer mill (14). If the roller press discharge material introduced via the line (24b) directly into the riser (17) designed as a current dryer is not sufficiently deagglomerated when it enters the riser (17), this would be harmless because the larger grains or agglomerates contained in the Riser pipe (17) would initially not be transported pneumatically upwards, fall down and get into the impact hammer mill (14), where they are finally crushed to such an extent that they are suspended in the riser pipe (17) from the drying gas in suspension to Sifters (18) are worn.

The fine material discharge line (27) of the classifier (18) leads to a separator such as a filter (28), separating cyclone or the like, which, via a conveyor (29), for example screw conveyor, the fine material as finished product (30), that is, dried and ground cement raw meal , separates from the sight gas stream or drying gas stream (31). The exhaust pipe (31) after separation of the finished product (30) via a branch line (32) with the hot gas line (15) connected to the product inlet (13) of the impact hammer mill and / or via a branch line (33) with the to the product discharge (16) Impact hammer mill (14) connected riser (17) in connection. Gas quantity throttling elements still shown in the gas-carrying lines of the drawing are not provided with reference numbers.

In the case of a conventional grinding drying system with an upstream impact hammer mill and a downstream ball mill, the specific energy requirement based on the finished product is on average about 1.5 kWh / t for the impact hammer mill and about 12 kWh / t for the ball mill. In comparison to this, the specific energy requirement for the impact hammer mill is approximately 1.5 to 5 kWh / t and for the roller press approximately 6 kWh / t in the grinding drying system according to the invention with an upstream impact hammer mill and a downstream high-pressure roller press. In general, it can be said that in the grinding plant according to the invention, the energy savings in kWh / t are higher the poorer the grindability of the starting material to be ground.

The exemplary embodiment in FIG. 2, in which, in comparison to FIG. 1, the same parts are provided with the same reference numbers, shows the flow diagram of a grinding drying system according to the invention for grinding and drying moist starting material (10), namely coal with a composition of 30% by weight. Anthracite, 70% hard coal and with a moisture content of about 10% for the production of dry coal dust, which as a finished product (30) with a grain size of 92% less than 90 um, than leaves the plant with a finer fineness than cement raw meal. In the exemplary embodiment in FIG. 2, there is the possibility of passing a partial flow of the coarse material coming from the classifier (18), for example via an overflow at the feed shaft past the high-pressure roller press (22) via line (34) together with a hot gas flow ( 35), which can be branched off from the hot gas line (15), for example consists of hot flue gas or hot exhaust gas from a cement clinker combustion plant and in so far has inert gas properties, to be introduced into a tube mill or ball mill (36) and after treatment in this tube mill via line (37) in the riser (17) leading to the sifter (18). The tube mill (36) additionally switched on in the embodiment of FIG. 2 compared to FIG. 1, which is comparatively small in volume, also reduces the material circulation rate passed through the high-pressure roller press (22) and thus relieves the roller press. 2 is given as an example of a throughput:

It goes without saying that the grinding plant according to the invention can also be operated with cooling gas instead of drying gas, provided that the starting material 10 is not moist, but hot and is to be cooled during grinding, for example hot cement clinker, hot blast furnace slag or the like. If the starting material to be ground does not have to be dried or cooled, the grinding plant according to the invention can also be operated without air flow. Then the impact hammer mill 14 must have a sieve grate at the bottom and let the ground material emerge downwards, which must then be transported up to the sifter (18) instead of pneumatically and mechanically, for example via a bucket elevator. Instead of the impact hammer mill, which is open at the bottom, another comminution machine would also be conceivable, for example a cone crusher or the like.

Claims (3)

1. A device for crushing and grinding and drying (grind-drying) wet brittle material (10), such as for example starting material for raw cement powder, ore, coal or the like, having an impact hammer mill (14), to the product inlet (13) of which there is connected the supply line (10) of the wet material and a hot gas line (15), and to the product discharge (16) of which there is connected a rising line (17) formed as a flow drier, said rising line leading to a separator (18), the discharge line (19) of which for coarse product (grit) is in connection with the feed of a crushing device, characterised in that the crushing device is a high-pressure roll press (22), its product discharge (24) being connected only with the product inlet (13) of the impact hammer mill (14) or with the product inlet (13) and with the rising line (17) of the impact hammer mill.
2. A device according to claim 1, characterised in that the product discharge (24) of the high-pressure roll press (22) is subdivided into two grain size fractions, only the fine fraction (24b) of which is guided to the rising line (17), while the coarse fraction (24a) leads to the product inlet (13) of the impact hammer mill (14).
3. A device according to claims 1 or 2, characterised in that a partial flow line (34) is branched off from the feed shaft (21) of the high-pressure roll press (22) or from the grit discharge line (19, 20) of the separator (18), said line (34) leading into the inlet of a tube mill (36) while by-passing the roll press (22), the discharge thereof (said tube mill 36) opening into the rising line (17) (Fig. 2).

Images