WO2002034394A1

WO2002034394A1 - Beater wheel for an integral-fan mill

Info

Publication number: WO2002034394A1
Application number: PCT/DE2001/003999
Authority: WO
Inventors: Bodo Gehrke; Wolfgang Rieker
Original assignee: Alstom Power Boiler Gmbh
Priority date: 2000-10-28
Filing date: 2001-10-17
Publication date: 2002-05-02
Also published as: DE10053652A1; DE10053652C2; AU2002215825A1

Abstract

The invention relates to a beater wheel for an integral-fan mill, in particular for comminuting coal for the pulverised-coal firing of a steam generator. Said wheel comprises a plurality of struts (5) distributed at uniform intervals around the circumference of the beater wheel and extending between the beater-wheel hub (3) and the beater-wheel ring (4). Each strut is reinforced in the direction of rotation of the beater wheel by several beater plates (9, 8) lying parallel to the beater-wheel axis. Each of the beater plates that lie towards the interior of the radius is provided with a beater strip (7) in the vicinity of its beater edge (17), which is formed by the beater surfaces (12, 16) of said plate. At least one part of the cross-sectional length of the beater strip consists of a highly wear-resistant material, said part of the cross-section forming the border region (15) of the beater strip (7) and said border region delimiting the beater surfaces (12, 16).

Description

description

Schlαgrαd for a Ventilαformühle

The invention relates to a beater wheel for a fan mill, in particular for the comminution of coal for a pulverized coal firing of a steam generator, with a large number of webs distributed uniformly around the circumference of the beater wheel and extending between the beater wheel hub and the beater wheel ring in the direction of rotation of the beater wheel are reinforced by several striking plates lying parallel to the striking wheel axis.

The beater wheel in a coal dust fan mill is used to grind and process coal into coal dust and to convey the coal dust into the coal dust furnaces of steam generators. The raw lignite is comminuted in a coal dust fan mill in such a way that a rotating impact wheel breaks up the coal supplied for it. The beater wheel essentially consists of the beater wheel hub and a beater wheel ring and webs which are inserted between the radially outer part of the beater wheel hub and the beater wheel ring. Striking plates are arranged on the webs, single and multi-part striking plate sets being known. Due to the shredding work and the stress caused by friction, the impact plates are subject to severe wear, which after a relatively short operating time, e.g. 500-5000 hours requires the complete replacement of the striking plates. Due to the intensive wear on the inner edge of the striking plate set, this inner edge is rounded in a very short time and is associated with a loss of the shredding and ventilation performance.

For example, it is known from the publication "Energie, Volume 27, No. 7/8, July / August 1975, page 186" to protect the surfaces against which the millbase is flowing against wear with a welded-on hard metal layer. This process reduces the wear rate in the initial operating time of the impact plates, but it does not prevent the rapid progress of wear after wear of this hard metal layer and the associated decrease in mill performance. An exchange of the impact plates immediately after wear of the welded hard metal layer or a regeneration of the worn build-up weld in the or the dismantled condition of the impact wheels is out of the question because of the high costs and also because of the operational downtimes of the mills.

In order to prolong the service life of the striking plates, it has also become known from the document DE 298 06 686 Ul to increase the thickness of the striking plate of the plate set lying radially on the inside of the striking wheel. This design has the disadvantage that an extension of the total service life of the impact plates is to be expected, but this extended operating time is in the range of greatly reduced mill output.

The object of the invention is now to provide a beater wheel for a fan mill in which the abovementioned disadvantages can be avoided or the wear rate of the beater plate set can be reduced and the power loss of the fan mill can be avoided.

The above object is achieved by the characterizing features of patent claim 1.

Advantageous embodiments of the invention can be found in the subclaims.

The solution according to the invention creates a beater wheel for a fan mill, which has the following advantages:

Constant performance of the fan mill over a long period of operation of the mill and thus investment savings through the use of a smaller mill, reduction of the mill maintenance costs, since only replacement of a blow bar and not a complete set of beater plates per beater wheel web is required and quick removal and installation possible, possibly extending the maintenance intervals for the striking wheels.

Is the striking bar of the respective striking wheel web lying radially on the inside and facing the striking surface on the cross section at least over part of the cross section with a highly wear-resistant material, this part of the cross-section forming the adjoining edge area of the striking surface (the face pointing in the direction of rotation of the striking wheel and the face pointing radially inward) of the striking bar, it is advantageous if the edge area or the highly wear-resistant layer has a thickness or depth of 1 to 50 mm. With such a configuration, a long operating time of the impact wheel can be achieved.

In an advantageous embodiment of the invention, the impact bar of the respective impact wheel webs, which is located radially on the inside and faces the impact surface, is formed from a ductile base material and the edge region is made from a hard metal armor. In a further advantageous embodiment of the invention, this blow bar is formed from a composite material with a ductile metal matrix and hard metal particles embedded therein or from an MMC composite material (Matrix Metal Composite) with ceramic particles embedded therein. Particularly long service life of the blow bars can be achieved with these materials.

In order to protect the highly wear-resistant impact bar of the respective impact wheel webs, which is located radially on the inside and facing the impact surface, against breakage when exposed to foreign bodies, it is advantageous to design the material of these impact plates with still sufficiently ductile properties.

Since the grinding material flow profile is non-uniform over the width of the beater wheel, it is advantageous to design the beater bar of each beater wheel web over the length of this beater bar with an unequal cross-section and / or an uneven hard metal armor layer thickness in accordance with the expected mill material flow profile. With this measure, the particularly affected wear points on the blow bar can be influenced by giving these points a larger cross section or a greater hard metal armor layer thickness than others.

By forming the remaining striking plates of each striking wheel web from a ductile, not highly wear-resistant material - only the radially inner and the The impact bar facing the impact surface consists at least in part of a highly wear-resistant material - material and investment costs can be saved.

The impact bar of the respective impact wheel webs of the impact wheel according to the invention is advantageously designed as a rod and inserted into a recess in the adjacent impact plate. In a further advantageous embodiment, the rod-shaped blow bar has a rectangular cross section. The beater bar designed as a rod can also have an L-shaped or an essentially triangular cross section and can either be embedded in a recess of the adjacent beater plate or rest thereon. The shape and installation position of the rod-shaped beater bar can influence the operating time of the beater wheel, since it can cover the parts of the beater wheel that are most susceptible to wear.

A particularly good wear protection against the adjacent striking plates of the striking bar of the respective striking wheel webs lying radially on the inside and the striking surface is achieved if the latter striking bar advantageously protrudes in steps from the striking surface of the striking plate set of the respective striking wheel web and thus forms a flow shadow for the neighboring striking boards which largely keeps the abrasive regrind away from the neighboring impact plates. It is also advantageous if the striking bar of the respective striking wheel webs, which is located radially on the inside and faces the striking surface, protrudes in steps towards the striking wheel axis towards the neighboring striking plate by a distance t, since here, too, the adjacent striking plate is largely protected from wear by the flow shadow.

It is advantageous that the striking bar of each striking wheel web, which is located radially on the inside and facing the striking surface, can be removed without removing the striking wheel from the fan mill and without dismantling further striking plates. This enables a very quick and inexpensive disassembly and assembly of the inner blow bar. It is also advantageous that the blow bar by removal is only one fastening part αusbαubαr, the fastening part being a section of the striking plate holding strip on the ring disc side.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings and the description.

It shows:

1 is a part of a vertical section through the beater wheel of a fan mill according to the invention,

2 shows a cross section according to section A-A in FIG. 1 of a striking wheel web with a striking plate set,

3 shows a further alternative embodiment to FIG. 2,

4 shows a further alternative embodiment to FIG. 2,

5 shows a further alternative embodiment to FIG. 2.

6 shows a schematic representation of the state of wear over the operating time of a striking wheel with standard striking plates according to a prior art,

7 shows a schematic representation of the state of wear over the operating time of an impact wheel with standard impact plates of greater wall thickness according to a prior art,

8 like FIG. 6, but with a striking wheel fitted with standard striking plates with hard metal armor according to a prior art,

9 shows a schematic representation of the state of wear over the operating time of an impact wheel according to the invention, Fig. 10 diagram: dependence of the mill output of a fan mill on the

Operating time or the state of wear of the impact wheel impact plates. FIG. 1 shows a vertical section of one half of the impact wheel 2 according to the invention of a fan mill 1, not shown. The beater wheel 2 in a coal dust fan mill 1 is used for grinding and processing coal into coal dust and for conveying the coal dust into the coal dust combustion of a steam generator, since the rotating beater wheel 2 also exerts a ventilation effect and thus a promotional effect in addition to the comminution effect. The comminution of the coal, in particular raw lignite in a coal dust fan mill, is carried out in such a way that a beater wheel 2 rotating about the beater wheel axis 14 smashes the coal supplied for it. The striking wheel 2 consists essentially of the striking wheel hub 3 and a striking wheel ring 4 and webs 5 which are inserted between the radially outer part of the striking wheel hub 3 and the striking wheel ring 4. On the webs 5 pointing in the direction of rotation of the striking wheel 2 (see direction of rotation arrow in FIGS. 2 to 9) striking plate sets 6 are arranged, which comprise at least two striking plates 8, 9 and essentially radially from the inside out, ie. H. Striking plate 8 inside and striking plate 9 are arranged radially on the outside, on the web 5. The front, i.e. the surface of the striking plate set 6 pointing in the direction of rotation of the striking wheel 2 forms the striking surface 12 and the surface of the striking plate set 6 pointing radially inward toward the striking wheel axis 14 forms the striking surface 1 6 of the respective striking plates 8, 9 of each striking wheel web 5.

According to the invention, the respective radially inner striking plate 8 is formed in the region of the striking edge 17 formed by its striking surfaces 12, 16 with a striking bar 7, which is formed over the length on the cross-sectional side at least over part of the cross section with a highly wear-resistant material and this part of the cross section forms the edge area 15 of the blow bar 7 delimiting the striking surfaces 12 and 16 (FIGS. 1 to 5). The edge region 15 of the blow bar 7 can preferably have a thickness or depth of 1 to 50 mm, measured from the outer edge of the blow bar 7. In an embodiment of the invention, the striking plates 8, 9 associated with the respective web 5 are formed from a ductile material, since the wear on the radially outer parts of the striking wheel 2 is comparatively lower and the use of costly, highly wear-resistant materials can be saved.

The blow bar 7, as mentioned above, can be formed with a highly wear-resistant material only at the adjacent edge region 15 of the striking surfaces 12 and 16, however, in the embodiment of the invention, it can be completely, i.e. over the full cross section, made of a highly wear-resistant material, for example a composite material with a ductile metal matrix and hard metal particles embedded therein, or an MMC composite material (Matrix Metal Composite) with ceramic particles embedded therein. In a further embodiment of the invention, the blow bar 7 can be formed from a ductile base material with surface hard metal armor on the striking surfaces 12 and 16 or the material of the highly wear-resistant blow bar 7 can be provided with sufficient ductile properties, i.e. be sufficiently insensitive to breakage when exposed to foreign bodies.

The striking bar 7 located radially on the inside can either lie directly against the web 5 or, as shown in FIG. 2, be inserted into a recess 13 in the adjacent striking plate 8 and point towards the striking surface 12 and 16. In a further embodiment of the invention, the striking bar 7 protrudes stepwise from the striking surface 12 of the striking plate 8, 9 by a distance s, so that the less wear-resistant striking plates 8, 9 lie in the flow shadow of the striking bar 7 and are therefore less stressed by the regrind. Furthermore, the striking bar 7 can protrude inwards towards the striking wheel axis 14 opposite the striking surface 16 of the adjacent striking plate 8 - if present in FIG. 2 - by a distance t, as in the striking surface 12, for the less wear-resistant striking plate 8 a flow shadow and to achieve less wear. The distance s or t is preferably 5 to 50 mm. The beating bar 7 can be designed as a rod with a rectangular cross section according to FIGS. 1 and 2 and can be inserted between the beater wheel hub 3 and beater wheel ring 4. However, other cross sections are also possible, for example an L cross section according to FIGS. 3 and 5 or an essentially triangular cross section according to FIG. 4. A blow bar 7 designed in this way can either be inserted into a recess 13 in the adjacent blow plate 8 (FIGS. 3 and 4). or placed on top of it (Figure 5).

In an embodiment of the invention, the blow bars 7 can be removed and installed very easily and quickly by the impact wheel 2 without removing the complete set of blow plates 6. This can take place even when the impact wheel 2 is still warm. For this purpose, a striking plate fastening part 11 is provided separately on the striking wheel ring 4, which is usually a section of the striking plate holding strip 10 on the ring disk side and which only locks and fixes the striking strip 7 on the striking wheel 2. After removal of this fastening part 11, the impact bar 7, which is held on the hub side of the impact wheel 2 by a plug connection, can be pulled axially out of the plug connection of the hub 3 and then exchanged or replaced or prepared for further use. The remaining striking plates 8, 9 are held separately by the aforementioned holding strip 10 and do not have to be exchanged in most cases when the striking strip 7 is replaced.

Since the millbase flow profile is usually not uniform over the width of the beater wheel 2, the beater bar 7 can be designed over its length either with an unequal cross-section or an unequal hard metal armor layer thickness in accordance with or in adaptation to the expected millbase flow-through profile. As a result, a larger cross section or a thicker hard metal armor layer can be provided at the points of the blow bar 7 of each impact wheel web that are particularly susceptible to wear, and the operating time of the impact wheel 2 can be increased.

From Figures 6 to 10 are different designs of impact wheel impact plates as well as their degree of wear and the mill performance depending on this Wear reasons or the Schlαgplαtten operating time can be seen. Figure 6 shows a Stαndαrd-Schlαgplαtte or Schlαgplαttensαtz according to the prior art with a thickness m and different degrees of wear I, II and III. In FIG. 10, the curve with degrees of wear I, II and III shows the course of the mill output as a function of the operating time and the state of wear of this set of striking plates. With degree of wear I the corner of the striking plate is slightly worn, with II up to the rear corner on the web and with III the thickness m of the plate is already severely attacked or reduced. At this stage, the plate must also be replaced. If a thicker impact plate (FIG. 7) is used, a longer operating time can be achieved up to the point IN 'according to the curve mentioned above. It can be seen from FIG. 10 that the fan mill with impact plates according to FIGS. 6 and 7 already loses a great deal of power from the state of wear I.

FIG. 8 also shows a known prior art, in which case the standard striking plate or the striking plate set has hard metal armor on the striking surface 12 and 16. The course of the curve with the degrees of wear I *, II * and III * showing the dependency of the mill output in relation to the beater wheel operating time and the wear state of the beater plates according to FIG. 8 is again recorded in FIG. 10, it being evident that the Mill output can be kept high much longer. Only after the hard metal armor has worn down on the inner edge of the impact plate - for example from wear level I * - does the mill's performance drop sharply. The service life of these impact plates has been reached at point III *. The striking plates must then be replaced.

FIG. 9 shows the degree of wear and the operating time of the impact plates of an impact wheel according to the invention, which is dependent on this. From curve "C" it can be seen that the mill output can be kept very high over a considerably longer operating time and drops only insignificantly over the operating time. The striking plate set 6 according to FIG Striking plate 8 protrudes stepwise and their entire cross section consists of highly wear-resistant material. With degree of wear I **, the radially inner edge 17 of the blow bar 7 facing the striking surface 12 is worn off. However, since the performance of the impact wheel 2 has hardly decreased, the fan mill can continue to be operated. Only when the degree of wear of the blow bar 7 has reached the state of curve II **, ie the blow bar 7 is worn to the outer contour of the striking surfaces 12 and 16 of the striking plate 8, and when the striking wheel 2 is used again the adjacent and less wear-resistant striking plates 8, 9 attacked by the regrind, an exchange of the blow bar 7 is provided. Thus, the beater bar 7 of a beater plate set 6 or all of the beater bars 7 of a beater wheel 2 are replaced when the degree of wear II ** is reached and replaced by new ones. From this point in time, the fan mill again has its full grinding and ventilation capacity, as can be seen in FIG. 10. It can also be seen from FIG. 10 that in this example the operating time of the impact wheel 2 according to the invention is somewhat shorter than that of the impact wheels with the impact plates according to FIGS. 6 to 8, but the mill output remains approximately the same over the entire operating time. This represents a significant improvement over the known state of the art and not inconsiderably increases the efficiency of the mill and thus also of the overall system.

LIST OF REFERENCE NUMBERS

1 valve gate mill

2 Schlαgrαd

3 Schlαgrαdnαbe

4 Schlαgrαdring

5 bridge

6 Schlαgplαttensαtz

7 racket

8 Schlαgplαtte

9 Schlαgplαtte

10 Schlαgplαtten holding strip

1 1 Schlαgplαtten fastening part

12 striking surface

13 recess

14 beater wheel axis

15 edge area

1 6 face

1 7 striking edge

1 8

19

20

21

22

Claims

claims

1 . Impact wheel for a fan mill, in particular for the comminution of coal for a pulverized coal firing of a steam generator, with a large number of webs distributed uniformly around the circumference of the impact wheel and extending between the impact wheel hub and the impact wheel ring, each in the direction of rotation of the impact wheel by several parallel to the impact wheel axis horizontal striking plates are reinforced, characterized in that in each case the radially inner striking plate (8) is formed in the region of the striking edge (1, 7) formed by its striking surfaces (12, 16) with a striking bar (7) which at least over the length of the cross-section side is formed over a part of the cross section with a highly wear-resistant material and this part of the cross section forms the edge region (15) of the blow bar (7) which delimits the striking surfaces (12, 16).

2. Impact wheel according to claim 1, characterized in that the edge region (15) of the blow bar (7) has a thickness or depth of 1 to 50 mm.

3. Impact wheel according to claim 1 or 2, characterized in that the edge region (15) of the blow bar (7) from a hard metal armor and the remaining cross section of the blow bar (7) is formed from a ductile material.

4. Impact wheel according to claim 1, characterized in that the blow bar (7) is formed over its entire cross-section from a composite material with a ductile metal matrix and hard metal particles embedded therein.

5. Impact wheel according to claim 1, characterized in that the blow bar (7) is formed over its entire cross-section from an MMC composite material (matrix metal composite) with ceramic particles embedded therein.

6. Schlαgrαd according to one of the preceding claims, characterized in that the material of the highly wear-resistant blow bar (7) is formed with sufficient ductile properties.

7. Impact wheel according to one of the preceding claims, characterized in that the blow bar (7) is designed to match the expected grist flow profile over the width of the impact wheel over its length with an unequal cross section and / or an unequal hard metal armor layer thickness.

8. impact wheel according to one of the preceding claims, characterized in that the respective web (5) associated impact plates (8, 9) are formed from a ductile material.

9. beater wheel according to one of the preceding claims, characterized in that the beater bar (7) is designed as a rod and is inserted into a recess (13) of the adjacent beater plate (8).

10. Impact wheel according to one of claims 1 to 8, characterized in that the impact bar (7) is designed as a rod and is placed on the adjacent impact plate (8).

1 1. Impact wheel according to one of the preceding claims, characterized in that the impact strip (7) has a rectangular or an essentially triangular or an L-shaped cross section.

12. Impact wheel according to one of the preceding claims, characterized in that the impact bar (7) with respect to the impact surface (12) of the adjacent impact plate (8, 9) protrudes step-by-step (s).

13. Impact wheel according to one of the preceding claims, characterized in that the impact bar (7) inwards to the impact wheel axis (14) opposite the Striking surface (16) of the adjacent striking plate (8) protrudes step-by-step by a distance (t).

14. Impact wheel according to one of the preceding claims, characterized in that the blow bar (7) can be removed from the fan mill (1) without dismantling the impact wheel (2) and without dismantling impact plates (8, 9).

15. Impact wheel according to claim 14, characterized in that the blow bar (7) can be removed by removing a fastening part (1 1), the fastening part (1 1) being a section of the washer-side striking plate holding bar (10).