Method and vertical mill for grinding material to be ground

Abstract

A vertical mill for grinding material to be ground and a method for this are claimed, wherein the vertical mill has a grinding table and one or more grinding rollers. A ring duct with blade ring for a transport gas flow ascending around the grinding table is provided. An annular gap distance is present between a downwardly projecting oversize material cone and the upper region of the grinding rollers, through which annular gap distance a proportion of fine particles is also fed back in a recirculating manner to the grinding table. In order to overcome this disadvantage, a barrier gas flow flowing from inside to outwards is provided in the region of the gap distance, whereby the recirculation of grinding particles of a certain size can be prevented.

Claims

1. A vertical mill for grinding material to be ground, comprising a grinding table and a plurality of grinding rolls or grinding rollers arranged so as to rotate thereon, a ring duct surrounding the grinding table to introduce an ascending transport and/or drying gas flow, an oversize material cone, arranged centrally relative to the grinding table, approximately above the grinding rolls or grinding rollers and tapering downwards, for the recirculation of coarse oversize particles onto the grinding table, and an approximately annular gap distance between the lower outlet region of the oversize material cone and the upper region of the grinding rolls or grinding rollers, wherein a feed unit for a gas flow with outward flow direction is provided in the lower region of the oversize material cone to deflect fine particles fed to the annular gap distance into the ascending transport and/or drying gas flow.

2. The vertical mill according to claim 1, wherein the feed unit is designed as a gas duct surrounding the lower region of the oversize material cone.

3. The vertical mill according to claim 2, wherein the gas duct surrounds the lower region of the oversize material cone as a ring duct or with a plurality of ring duct segments around it.

4. The vertical mill according to claim 1, wherein the gas duct of the feed unit is provided for the gas flow, acting as a barrier gas flow, as a bypass line to the main supply line of the vertical mill for transport and/or drying gas.

5. The vertical mill according to claim 1, wherein a barrier gas flow is fed separately to the transport and/or drying gas flow as ambient air or fresh air.

6. The vertical mill according to claim 1, wherein a barrier gas flow has a vertical flow component directed from inside to outside.

7. The vertical mill according to claim 1, wherein the space volume in the vertical mill is evened out for the transport and/or drying gas flow ascending in the region of the grinding rolls respectively grinding rollers and the oversize material cone.

8. A method for grinding material to be ground in a vertical mill, having a grinding table and at least one grinding roll or grinding roller arranged so that it can rotate thereon, wherein an ascending transport and/or drying gas flow is introduced via a ring duct surrounding the grinding table, wherein coarse oversize materials are fed back to the grinding table via an oversize material cone arranged centrally relative to the grinding table, approximately above the grinding roll or grinding roller, and tapering downwards, wherein an approximately annular gap distance is formed between the lower outlet region of the oversize material cone and the upper region of the grinding roll or grinding roller, wherein a barrier gas flow is fed in the lower region of the oversize material cone, with flow direction from inside to outside into and/or via the annular gap distance against an inflow and recirculation of fine particles into the gap distance.

9. The method according to claim 8, wherein the barrier gas flow is branched off from the main gas flow for transport and drying gas produced for the vertical mill.

10. The method according to claim 8, wherein the barrier gas flow is fed as an external gas flow of ambient air or fresh air.

11. The method according to claim 8, wherein the barrier gas flow fed as a partial gas flow is blown in with a vertical flow component and the ascending transport and/or drying gas flow is thus reinforced in terms of volume.

12. The method according to claim 8, wherein the volume and/or temperature of the barrier gas flow is/are regulated as a function of the desired fine particles.

Description

(1) The invention will be explained in more detail below by reference to schematic examples. In the drawing:

(2) FIG. 1 shows, in a highly schematic representation, a vertical section through a vertical mill according to the invention with a bypass line and a barrier gas flow outwards;

(3) FIG. 2 shows the vertical mill according to FIG. 1 with a barrier gas flow with a vertical component; and

(4) FIG. 3 shows a vertical mill according to the prior art in the schematic vertical section with the essential components corresponding to FIG. 1 but with the recirculation flowwhich is problematic and is to be avoidedfor fine particles in an annular gap between the grinding rollers and oversize material cone.

(5) FIGS. 1 to 3 show coinciding components of the vertical mills 1 and 30 with the same reference symbols. This also applies to the gas flows, insofar as these coincide.

(6) The vertical mills shown in FIGS. 1, 2 and 3 have the same structure having regard to the essential components such as grinding table 3, grinding rollers 4, oversize material cone 6 and classifier 9, arranged above, with surrounding mill housing 11.

(7) The problematic recirculation flow 33 (FIG. 3) of upwardly guided fine particles and the deflection thereof inwards into the annular gap 21, also due to the pressure drop in the flow region between the mill housing 11 and the outer contour of the oversize material cone 6, are overcome in a way that is simple in terms of construction and method through the solutions according to FIGS. 1 and 2.

(8) In the example of the vertical mill 1 according to FIG. 1, a partial flow is branched off from the main gas flow 14 via the bypass line 17.

(9) Insofar as the grinding process carried out in the vertical mill is a grindingdrying process, for example for moist raw coal, hot gas is produced in a hot gas generator and is fed as a main gas flow 14 to the vertical mill 1 below the grinding table 3. The branching-off of the partial gas flow via the bypass line 17 hereby takes place below the grinding table 3 or outside of the mill housing 11. This is represented schematically through the arrows 15 as a flow through the ring duct 5 with blade ring.

(10) This flow 15 transports the grinding particles, ground between the grinding rollers 4 and grinding table 3 and fed outwardly into the region of the ring duct 5, extensively vertically upwards. This pneumatic transport function is dependent in particular upon the flow speed and the flow volume of the transport and drying gas.

(11) Also in the example according to FIGS. 1 and 2, there is an annular gap 21 between the lower region of the oversize material cone 6 and the upper region of the grinding rollers 4, through which annular gap 21 already over-ground material can fall back onto the grinding table 3 or is recirculated.

(12) Having regard to ascending fine particles in the flow 15, however, this is prevented by a barrier gas flow 22 being produced, in the lower region of the oversize material cone 6, from inside to outwards to shield the annular gap 21 against an entry of fine particles in this region.

(13) This barrier gas flow 22 has been branched off from the main gas flow 14 as a bypass flow 16 and introduced via the bypass line 17 and the feed unit 18 into a ring duct 19 surrounding the oversize material cone 6 and blown there around the whole periphery of the ring duct 19 as a barrier gas flow 22 with flow direction from inside to outwards into the free space for the transport flow 24.

(14) The bypass line 17 is hereby guided above the grinding rollers 4 approximately horizontally through the mill housing 11 on a short path to the outer surface of the oversize material cone 6 and, in the example shown, over a short stretch on the oversize material cone 6 downwards to the ring duct 19.

(15) The bypass flow 16 can flow through the ring duct 19 in a direction around said ring duct 19.

(16) In order to create approximately identical pressure conditions all around for the outflowing barrier gas flow 22, the ring duct 19 can also have for example two 180 segments, through which flows take place in opposite directions.

(17) It is also possible to provide a plurality of bypass lines with the same angle distance relative to each other. For example, three bypass lines 17, respectively offset by 120, can be connected in terms of flow to a respective one of three ring duct segments 19.

(18) The barrier gas flow 22 in FIG. 1 blocks the annular gap 21 in the upper, inner region against a penetration of fine particles. The barrier gas flow is deflected further outwards upwardly into the vertical transport flow 24 so that an upward flow with a larger volume is available for ground particles.

(19) The barrier gas flow 22 can be controlled in dependence upon output volume, output speed and output angle from the ring duct 19 in such a way that a recirculation of fine particles is prevented from a certain fineness and is fed with the vertical transport flow 24 upwards to the classifier 9.

(20) The barrier gas flow 22 should thus be set so that over-ground but coarser grinding material particles are recirculated through the annular gap 21 back to the grinding table 3. The branching-off of the bypass flow as a barrier gas flow to prevent recirculation of certain particle sizes through the annular gap 21 ultimately leads to an improvement in the energy balance of the vertical mill in comparison with the desired fine particles output.

(21) The example according to FIG. 2 corresponds, apart form the barrier gas flow 25, to the exemplary embodiment according to FIG. 1.

(22) In FIG. 2, the barrier gas flow 25 leaving through the ring duct 19 has above the annular gap 21, besides an outwardly directed flow component, also a vertical flow component.

(23) This allows on the one hand the blocking of an entry of fine particles of a certain fineness into the annular gap 21 and on the other hand a joint flow, favourable in terms of flow, with the ascending transport flow 24 such that a homogenisation but also a reinforcement of the volume of the transport flow 24 are achieved. The fluid flow 26 leaving the classifier upwardly is a fine particles/gas mixture, from which the fine particles are separated in upstream cyclones and/or filters.

(24) The device according to the invention and the method according to the invention thus create a relatively simple possibility of being able to achieve a more efficient operation of such a vertical mill by blocking the recirculation of certain particle sizes.