AU2008200366B2

AU2008200366B2 - Grinding device for a power plant

Info

Publication number: AU2008200366B2
Application number: AU2008200366A
Authority: AU
Inventors: Peter Helmut Breuhaus; Jaroslaw Szwedowicz
Original assignee: General Electric Technology GmbH
Current assignee: General Electric Technology GmbH
Priority date: 2007-02-08
Filing date: 2008-01-24
Publication date: 2012-02-23
Anticipated expiration: 2028-01-24
Also published as: PL1955772T3; EP1955772B1; AU2008200366A1; EP1955772A3; DK1955772T3; EP1955772A2

Abstract

Abstract of the Disclosure 5 The present invention relates to a grinding device (1) for a power plant, in particular to a beater wheel mill for a coal-fired power station, with a rotating grinding tool (2) and with a grinding housing (3) surrounding the latter. In this case, the rotating grinding tool (2) has beating/impacting elements (4) which experience wear when the grinding device (1) is in operation and in which at least one cavity (5) is provided, which can be 10 acted upon with internal pressure and which is arranged at a distance from a wear-exposed side (6) of the beating/impacting element (4), specifically in such a way that, in the case of a defined degree of wear, an opening of the cavity (5) takes place. In this case, the at least one cavity (5) is connected communicatingly with a checking device (9) detecting at least the pressure in the cavity (5). (Fig. 2) Fig. 2 5' h3

Description

AUSTRALIA FB RICE & CO Patent and Trade Mark Attorneys Patents Act 1990 ALSTOM TECHNOLOGY LTD COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Grinding device for a power plant The following statement is a full description of this invention including the best method of performing it known to us:- IA Grinding device for a power plant Technical Field 5 The invention relates to a grinding device for a power plant, in particular a beater wheel mill for a coal-fired power station. The invention relates, moreover, to a method for producing a plurality of cavities and at least one connection cavity connecting these cavities in a grinding device. The invention relates, moreover, to a power plant equipped with a grinding device according to the invention. 10 Prior Art So that firing in a coal-fired power station can be carried out uniformly and, in particular, more effectively, the coal used for firing is usually ground. For this purpose, 15 beater wheel mills, as they are known, are used, which have a grinding tool rotating at up to 1500 revolutions per minute. The coal is in this case comminuted by virtue of the beating and impacting action within the rotating beating or grinding tool in the often armor-plated grinding housing. The fuel comminuted by the beater wheel mill is often fed to a furnace space at the power station via a solids blower which, furthermore, 20 brings about an additional drying of the fuel. Since, in particular, the rotating grinding tools are naturally exposed to severe wear, they have to be exchanged as a function of a degree of wear or in rotation. An exchange of the grinding tool is in this context always equivalent to a stoppage time of the 25 grinding device and is consequently associated with high outage costs. For the efficiency of the grinding device, it is useful, in particular, to know how long the grinding tool can be used and when the time point for exchange is reached. To be precise, if this time point is overshot, either the grinding action of the grinding device diminishes or the grinding device is damaged. 30 Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each 35 claim of this application.

2 Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 5 Presentation of the Invention In a first aspect, there is provided a grinding device for a power plant with a rotating grinding tool and with a grinding housing surrounding the latter, 10 - the rotating grinding tool having beating/impacting elements which experience wear when the grinding device is in operation, - in at least one beating and impacting element, at least one cavity being provided, which can be acted upon with internal pressure and which is arranged at a distance from a wear-exposed side of the beating/impacting element, in such a way that, in the 15 case of a defined degree of wear, an opening of the cavity takes place, - the at least one cavity being connected communicatingly with a checking device detecting at least the pressure in the cavity. In a second aspect, there is provided a method for producing a plurality of cavities and 20 at least one connection cavity connecting these cavities in a grinding device as defined in the first aspect above, in which first the connection cavity and then at least two cavities intersecting the connection cavity are introduced into the beating/impacting element, the cavities ending at a distance from a wear-exposed side of the beating/impacting element, and in which the cavities are then closed such that they 25 communicate with one another and with the checking device solely via the at least one connection cavity. The present disclosure relates to the general idea of providing a checking device which can monitor a degree of wear of the grinding tool and, as required, can generate 30 corresponding signals. Embodiments of the grinding device disclosed herein have a rotating grinding tool and a grinding housing surrounding the latter, beating/impacting elements which experience wear during the operation of the grinding device being arranged on the grinding tool. In at least one of these beating/impacting elements, at least one cavity is provided, which can be acted upon with internal pressure and which 35 is arranged at a distance from a wear-exposed side of the beating/impacting element, 2A specifically in such a way that, in the case of a defined degree of wear, an opening of the cavity takes place. In this case, the cavity is connected communicatingly to a checking device detecting at least the pressure in the cavity. In the normal operating state, the cavity and the checking device form a closed pressure-loadable system which 3 is opened only as a result of a corresponding wear of the beating/impacting elements. If stripping on the beating/impacting elements has progressed so far that the cavity on the wear-exposed side is opened, then the pressure in the cavity falls, which can be detected by the checking device. The pressure drop may in this case, for example, 5 trigger a first warning signal, since a related degree of wear is reached with the opening of the cavity. Embodiments of the presently disclosed grinding device afford the great advantage that the grinding tool can be operated up to the opening of the at least one cavity, without the need to fear that material-induced failures may occur. If the at least one cavity is opened due to a corresponding stripping of material, the degree of wear of 10 the beating/impacting elements has reached a specific value at which, for example, an exchange of the relevant beating/impacting element must be carried out. Owing to the distance between the wear-exposed side or surface and the cavity arranged in the beating/impacting element, an operating period can be at least approximately fixed. A further great advantage is that embodiments of the presently disclosed grinding device 15 make it possible to check the degree of wear independently of the grinding stock, so that, for example, different sand fractions in the coal no longer have to be taken into account by running times of different length of the grinding device, but, instead, the grinding device can always be operated up to the pressure drop detected by the checking device. Since, in particular, the beating/impacting elements are also costly in 20 terms of exchange and material costs, they can be used particularly efficiently by virtue of the checking device as disclosed herein. According to an embodiment, a plurality of cavities with different distances from a wear-exposed side of the beating/impacting element are provided in at least one 25 beating/impacting element. What can be achieved thereby is that, in the case of a progressive degree of wear, the cavities are opened in succession and a stepped checking system is thereby provided. If, for example, three cavities, in each case with a different distance from the wear-exposed side of the beating/impacting element, are provided, then, in the case of a specific degree of wear, first only that cavity, of which 30 the distance from the wear-exposed side of the beating/impacting element is the shortest, is opened. If, during further operation, the second cavity is then opened, this is an unequivocal indicator of an imminent exchange of the beating/impacting elements. If, finally, the third cavity is opened as a result of the progressive wear, then this may, for example, be equivalent to the situation where a maximum permissible degree of 35 wear is reached and the corresponding beating/impacting element then has to be 4 exchanged. Owing to the successive opening of the different cavities, the checking device detects a stepped pressure drop or a stepped-rising mass/volume flow from the pressure-loaded cavity outward, with the result that the in each case accompanying degree of wear can be detected simply and nevertheless very exactly. The cavities thus 5 formed and arranged therefore constitute, together with the checking device, a simple and accurately operating early warning system, with the result that maintenance work and the associated stoppage times of the grinding device can be controlled more effectively and therefore more economically. 10 According to a further particularly advantageous embodiment, the at least one cavity is acted upon with a gas, in particular with air, or with a liquid, in particular with water pressure. It is important, in this case, merely that a pressure drop can be detected during the opening of the cavity. Thus, it is therefore conceivable that, particularly in a beater wheel mill for a coal-fired power station, a liquid, in particular water, is used, since, if 15 an oxidizer, for example air, is used, an increase in the risk of explosion may occur, which need not be feared when water is used. The example shows, however, that the pressure medium within the cavities can be adapted individually to the respective requirements. 20 Further important features and advantages of embodiments of the grinding device according to the present disclosure may be gathered from the subclaims, from the drawings and from the accompanying figure description with reference to the drawings. Brief Description of the Drawings 25 Preferred exemplary embodiments are illustrated in the drawings and are explained in more detail in the following description, the same reference symbols referring to identical or similar or functionally identical components. 30 In the drawings, in each case diagrammatically, fig. I shows a grinding device according to the present disclosure for a power plant with an extracted rotatable grinding tool, 5 fig. 2 shows a view of a beating/impacting element according to the present disclosure with internal cavities, fig. 3a to 3c show individual method steps for producing the cavities within the 5 beating/impacting element. According to fig. 1, a grinding device I according to the invention for a power plant, not shown, which may be designed, for example, as a beater wheel mill for a coal-fire power station, has a rotating grinding tool 2 and a grinding housing 3 surrounding the 10 latter. In this case, both the grinding tool 2 and the grinding housing 3 consist of a highly abrasion-proof or resistant material and may, in particular, have an armor-plated design, since when the grinding device 1 is in operation, considerable wearing forces act on the grinding tool 2. In the grinding device 1, for example, coal is finely ground, in order to improve subsequent combustion in the power station. The comminuting 15 action is in this case generated by beating/impacting elements 4, as they are known, which are arranged on the rotating grinding tool 2 and which, when the grinding device 1 is in operation, experience wear to an appreciable extent. The degree of wear in this case depends, in particular, on the fraction of foreign constituents in the coal, such as, for example, sand, so that, depending on the composition of the coal to be ground, the 20 life expectancy of, in particular, the beating and impacting elements 4 may be different. This presents the problem that a maintenance or exchange interval of the beating/impacting elements 4 can be forecast only with difficulty. So that such a forecast of the lifetime or of the maintenance and/or exchange interval 25 can be made reliably, in at least one beating/impacting element 4, at least one cavity 5 (cf. fig. 2) is provided, which can be acted upon with an internal pressure and which is arranged at a distance from a wear-exposed side 6 of the beating/impacting element 4. If, when the grinding device 1 is in operation, the wear-exposed side 6 of the beating/impacting element 4 is exposed to increasing stripping/wear, the wear reaches 30 the cavity 5 sometime and opens the latter, a degree of wear being capable of being exactly forecast or defined by means of the exactly fixed distance between the side 6 and the cavity 5. During the opening of the cavity 5, an escape of the pressure stored in the latter takes place, this being detected by a checking device 9, not shown, which is connected communicatingly to the at least one cavity 5. 35 6 According to the beating/impacting element 4 from fig. 2, a total of three cavities 5, 5', 5" are provided, which, in the exemplary embodiment shown in fig. 2, run parallel and extend in the wear direction 7. In this case, the cavities 5, 5', 5" are connected communicatingly to one another via a connection cavity 8 which is itself connected 5 communicatingly to the checking device 9. In the exemplary embodiment shown in fig. 2, the cavities 5, 5', 5" are in each case at a different distance from the wear-exposed side 6. In this case, a distance between the side 6 and the connection cavity 8 is designated by L, and the respective longitudinal 10 extent of the individual cavities 5", 5' and 5 is designated by hl, h 2 and h 3 . Consequently, the distance between the cavity 5 and the wear-exposed side 6 amounts to L-h 3 while a distance between the wear-exposed side 6 and the cavity 5"amounts to L-hi. Since h, is markedly shorter than h 3 , the distance L-h 3 is markedly shorter than the distance L-hi. 15 By virtue of the arrangement of a plurality of cavities 5, 5', 5" with different distances from the wear-exposed side 6, a grading of the beating/impacting elements 4 which is dependent on the degree of wear can take place, and, during stripping in the stripping direction 7, first the cavity 5, then the cavity 5' and, usually, lastly the cavity 5" are 20 opened. By virtue of this step-like early warning system, even a pressure drop during the opening of the cavity 5 can be detected, stripping in this stage already having reached a certain amount, but not yet giving cause for maintenance or exchange of the beating/impacting element 4. If, during the further operation of the grinding device 1, the cavity 5' is then opened, stripping or wear in the wear direction 7 has already 25 progressed markedly further, so that an early exchange of the beating/impacting element 4 must be expected. Normally, the opening of the cavity 5" signals such a far advance of the degree of wear that an exchange of the beating/impacting element 4 then has to take place, if damage to the grinding device 1 is to be avoided. Thus, by virtue of the arrangement of the cavities 5, 5', 5", an early warning system independent of the 30 substance to be ground is afforded, which, independently of the composition of the grinding stock, always give objective information on how high the wear of the beating/impacting elements 4 is. This has not been possible in previous grinding tools 2, in which there has always been the risk that, in the case of a high sand fraction in the coal to be ground, a markedly higher wear of the grinding tool 2 occurs than in the case 35 of a lower sand fraction. However, since the composition of the grinding stock has not 7 always been known, the grinding tool 2 has therefore had to be maintained or exchanged in rotation, often even far too early, with the result that high maintenance or exchange costs have been incurred. If, by contrast, a less abrasive grinding stock has been assumed, there has been the possibility of overestimating the service life of the 5 beating/impacting elements 4, with the result that the overall grinding tool has been damaged. Of course, the arrangement or number of the cavities 5, 5', 5" according to fig. 2 and 3 is to be understood purely by way of example, and therefore another arrangement or 10 number of the cavities is also to be covered by the invention. Expediently, the checking device 9 is designed for monitoring a mass flow and/or a volume flow and/or a pressure drop which is established as a result of a cavity 5, 5', 5" opened due to a corresponding degree of wear. In this case, it is clear that, in the case of 15 an open cavity 5, the pressure drop or a leakage stream is markedly lower than in the case of likewise opened cavities 5, 5', 5". The degree of wear of the beating/impacting elements 4 can thus be determined via the size of the leakage stream. It may likewise be gathered from fig. 2 that the connection cavity 8 connecting the cavities 5, 5', 5" to one another runs orthogonally with respect to the cavities 5, 5', 5". 20 As mentioned initially, the presently disclosure provides for acting with pressure upon the cavities 5, 5', 5" and upon the connection cavity 8, in which case the pressure medium provided may be, for example, a gas, in particular air, or a liquid, in particular water. In the case of a beater wheel mill used for coal grinding, the preferred pressure 25 medium is, for example, water, since air is an oxidizer and increases a latent explosion risk. Of course, it is in this case conceivable that the pressure medium is coordinated individually with the respectively prevailing requirements in the grinding device 1. Fig. 3a to 3c illustrate a method according to the invention for producing at least one 30 cavity 5 and at least one connection cavity 8 in a grinding device 1 according to the invention. First, for this purpose, the connection cavity 8 is introduced, in particular lasered or drilled, into the beating/impacting element 4. In the example illustrated in fig. 3a, the connection cavity 8 extends essentially parallel to the wear-exposed side 6. Subsequently, the at least one cavity 5 is introduced, likewise again lasered or drilled, 35 into the beating/impacting element 4 in such a way that it intersects the connection 8 cavity 8. Of course, even further cavities, not shown, may be introduced into the respective beating/impacting element 4. According to the present disclosure, in this case, the cavity 5 ends at a distance from the wear-exposed side 6 of the beating/impacting element 4. In a further method step, the cavity 5 and, likewise, 5 further cavities, if present, are then closed such that they communicate with one another and/or with the checking device 9 solely via the at least one connection cavity 8. In this case, the closure of the cavity 5 or of further cavities, not shown, is introduced on a side 10 of the beating/impacting element 4 which faces away from the wear, as shown in fig. 3c. 10 It will be appreciated that the illustrated grinding device provides that a degree of wear of the grinding tool can be detected and evaluated and an exchange of the grinding tool or of the beating/impacting elements arranged on it can thereby be carried out, as required.

8A List of Reference Symbols 1 Grinding device 2 Grinding tool 5 3 Grinding housing 4 Beating/impacting element 5 Cavity 6 Wear-exposed side of the beating/impacting element 4 7 Wear direction 10 8 Connection cavity 9 Checking device 10 Side of the beating/impacting element 4 which faces away from the wear

Claims

1. A grinding device for a power plant, with a rotating grinding tool and with a grinding housing surrounding the latter, - the rotating grinding tool having beating/impacting elements which experience wear when the grinding device is in operation, - in at least one beating and impacting element, at least one cavity being provided, which can be acted upon with internal pressure and which is arranged at a distance from a wear-exposed side of the beating/impacting element, in such a way that, in the case of a defined degree of wear, an opening of the cavity takes place, - the at least one cavity being connected communicatingly with a checking device detecting at least the pressure in the cavity.

2. The grinding device as claimed in claim 1, wherein the at least one cavity runs in the wear direction of the beating/impacting element.

3. The grinding device as claimed in claim 1 or 2, wherein, in at least one beating and impacting element, a plurality of cavities are provided at different distances from a wear-exposed side of the beating/impacting element.

4. The grinding device as claimed in any one of claims 1 to 3, wherein at least two cavities are connected communicatingly to one another via a connection cavity which is connected communicatingly to the checking device.

5. The grinding device as claimed in any one of claims 1 to 4, wherein the checking device is designed for monitoring a mass flow and/or a volume flow and/or a pressure drop which is established as a result of a cavity opened due to a corresponding degree of wear.

6. The grinding device as claimed in any one of claims I to 5, wherein at least two cavities run essentially parallel to one another, while the connection cavity connecting the cavities to one another runs orthogonally with respect to these.

7. The grinding device as claimed in any one of claims 1 to 6, wherein the at least one cavity is acted upon with pressure by a gas or by a liquid.

8. The grinding device as claimed in claim 7, wherein the gas is air. 10

9. The grinding device as claimed in claim 7, wherein the liquid is water.

10. A method for producing a plurality of cavities and at least one connection cavity connecting these cavities in a grinding device as claimed in any one of claims 1 to 9, in which first the connection cavity and then at least two cavities intersecting the connection cavity are introduced into the beating/impacting element, the cavities ending at a distance from a wear-exposed side of the beating/impacting element, and in which the cavities are then closed such that they communicate with one another and with the checking device solely via the at least one connection cavity.

11. The method as claimed in claim 10, wherein at least one cavity and/or at least one connection cavity is drilled or lasered.

12. A power plant, with a grinding device as claimed in any one of claims I to 9.

13. A power plant as claimed in claim 12, being a coal-fired power station.

14. A grinding device for a power plant, said grinding device substantially as hereinbefore described with reference to the accompanying drawings.

15. A method for producing a plurality of cavities and at least one connection cavity connecting these cavities in a grinding device, said method substantially as hereinbefore described with reference to the accompanying drawings.