AU724165B2

AU724165B2 - Annular shield for a rotating pneumatic dust conveyor

Info

Publication number: AU724165B2
Application number: AU26218/97A
Authority: AU
Inventors: Wolfgang Jaschan; Ralf Peter
Original assignee: VEAG Vereinigte Energiewerke AG
Current assignee: Vattenfall Europe Generation AG and Co KG
Priority date: 1996-06-21
Filing date: 1997-06-23
Publication date: 2000-09-14
Anticipated expiration: 2017-06-23
Also published as: CZ194097A3; PL320654A1; PL182772B1; AU2621897A; CZ292361B6

Description

P/00/01 1 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

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Invention Title: ANNULAR SHIELD FOR PNEUMATIC DUST CONVEYOR A ROTATING The following statement is a full description of this invention, including the best method of performing it known to us: GH REF: P17950-M:RW:RK 2 Annular shield for a rotating pneumatic dust conveyor The invention concerns an annular shield for a rotating pneumatic dust conveyor, in particular a coal dust fan-grinder, wherein the annular shield is provided in the gap between the rotating system and the housing of the dust conveyor and is fastened on an annular shield mounting provided on the housing of the grinder.

i0 The housing of a coal dust fan-grinder has as the closure of the housing in the grinding chamber opening an annular shield made of steel, whose plate-shaped segments are provided on an annular shield mounting on the housing.

At the same time the annular shield represents the wear protection of a rotating dust conveyor between the rotating system and the housing. After a relatively short operating time the annular shield and the grinding chamber door shield will abrade by the abrasive parts of the fuel being prepared, so that repairs for wear or replacements are necessary.

Furthermore, inaccurately rolled annular shield elements, due to welding under stress, lead to cracks in the welding seams and thus to the breakdown of the elements.

e 5 It has been established after numerous and time consuming o investigations that due to the circumferential speed of the crusher wheel of the coal dust fan-grinder a pressure :oo: differential is formed by the rotating crusher wheel between ee the grinding chamber and the grinding chamber door. Based on coo• this pressure differential through the annular gap between the crusher wheel and the annular shield a transverse flow of **solids to the grinding chamber door and an annular flow of oo solids is formed in the annular gap. On this occasion wear S• troughs occur in the annular shield caused by the transverse flow.

J:\Spcci\2O( 299\250 299\29142.doc 3 The object of at least preferred embodiments of the invention is to construct the annular shield of a coal dust fan-grinder in such a manner that the wear will be reduced, the detaching annular shield segments do not damage the grinder and the transverse and annular flows as well as the transport of solids associated with it are considerably reduced.

Summary of the Invention The present invention provides an annular shield for a rotating pneumatic dust conveyor, such as a coal dust fan-grinder, wherein the annular shield is provided between the rotating system and a housing of the dust conveyor and is fastened on an annular shield mounting provided on the housing of the grinder, characterised in that the annular shield includes a plurality of segments each formed from soft-ceramic material, and in that the segments are fitted to the mounting by means of corresponding annular engagement portions formed on the annular shield mounting and the segments respectively, and 20 wherein the mounting has a removable portion arranged to oloeo S"enable assembly and disassembly of the segments from the mounting.

Preferably, the corresponding annular engagement portions include a protrusion formed on the annular shield 25 mounting and a complementary shaped recess formed in the ooo* segments.

In one embodiment, the annular shield has grooves S"which are provided transversely to the direction of rotation of the rotating system.

30 The grooves may be arranged with an equal and/or S"unequal spacing.

\\GHSYDNTl\users\Speci\200- 299\250 299\29142.doc 3a The depth and the width of the grooves may be constructed as a function of the distance of the annular shield from the rotating system.

In one embodiment, the grooves are constructed with a depth equalling the distance and with a width equalling at least the five-fold of the distance.

Advantageously, the protrusion formed on the annular shield mounting is interrupted at a length of the removable portion.

Preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig.l Fig.2 the housing of the grinder with a front view on the annular shield, the schematic illustration of the annular shield and annular shield mounting with the dovetail guide, the schematic illustration of the annular shield and annular shield mounting with the section-shaped guide, the schematic illustration of the arrangement of the annular and grinding chamber door shield on the coal dust fan-grinder, mm C S. C

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S Fig.3 Fig.4 the schematic illustration of the uncoiled annular shield elements in side and top views.

SYDI)N'1t \u.cr-s\Spcci\2 299\250 299\29 I42.doc The grinding chamber housing 7 of the coal dust fan-grinder has a grinding chamber opening 8, an annular shield 6, a pressure ring 9, an annular shield mounting 2 and several annular shield segments 10. The pressure ring 9 to seal the grinding chamber door 12 and a portion of the grinding chamber housing 7 are provided with a removable flap 3. The annular shield segments are constructed as formed parts 1 with a shaped section (Figs.2 and 3) and are made of a soft-ceramic material. The annular shield mounting 2 and the annular shield segments have a dovetail-shaped guide 4 (Fig.2). The annular shield mounting 2 and the formed parts 1 may also be constructed with other'shapes for the guiding 4 (Fig.3). The annular shield 6 consists of individual annular shield segments omoeo g~ The grinding chamber door shield 11 and the annular shield mounting 2-for the annular shield 6 are provided on the grinding chamber housing 7 of the coal dust fan-grinder (Fig.4).

The grinding chamber door 12 has a grinding chamber door shield 11 and is connected with the grinding chamber housing 7 via the sealing system 13. The crusher wheel 14 is arranged in the ~grinding chamber housing 7. The annular gap 15 is formed between the annular shield 6 and the crusher wheel 14. The annular shield 6 consists of individual annular shield segments .i 10 (Fig.5) and is fixed on the annular shield mounting 2. The annular shield segments 10 have grooves 5 and elevations 16 at right angles to the direction of conveying of the dust/air mixture. To increase the resistance to the flow in the annular gapl5 the grooves 5 and the elevations 16 are arranged with an equal and/or unequal spacing. The depth and the width of the grooves 5 are to be chosen as a function the annular gap i.e.-the distance of the annular shield 6 to the crusher wheel 14. For a coal dust fan-grinder having a crusher wheel circumferential speed of 80 m/s the following dimensioning is envisaged: Depth of the grooves distance (annular gap) Width of the grooves at least 5-fold of the distance The annular shield operates in the following manner: The annular shield mounting 2 is welded to the grinding chamber housing 7. It has the guide 4 for the formed parts 1. The guide 4 of the annular shield mounting 2 is interrupted in the region of the removable flap 3 or placed on the flap 3, so that the formed parts 1 can be introduced into the guide 4. When dismantling the crusher wheel 14 of the coal dust fan-grinder only the bottom half of the annular shield elements 10 (formed part 1) is removed through the flap 3 and the top half is locked. During the installation of the crusher wheel 14 the reverse sequence is followed. For that case when the softceramic formed parts 1 protrude into the grinding chamber due to wear phenomena, these are ground off or crushed without stopping the grinder, however, they can be replaced during the next planned shutdown.

By means of the depth and width of the grooves 5 provided the transverse and annular flow is "torn" due to the resistance to flow and small whirlings are formed within the grooves 5. Due to the considerably reduced transport of solids in the annular gap 15 the diminished flows lead to,the reduction of the wear of the annular shield 6 and the grinding chamber door shield 11. As a result of this the service life of the annular shield 6 and of the grinding chamber door shield 11 is increased despite using steel of the RST quality. Thus it is possible to extend the period between repairs for wear and thus reduce the expenses.

eo o \\GI-ISYDNT \uscrs\Spcci\200 299\250 299\2)1I 42.dIoc 5a The following advantages are achieved by the preferred embodiment of the invention: 1. The pre-fabrication of the annular shield segments and their small masses result in the reduction of the assembly cost and thus in shorter shutdowns.

2. The soft-ceramic formed parts falling into the grinder are crushed. No additional disruptions of the grinder occur.

In the claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

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IN I N'I \UCI \S~ci\ ')99\250) 2'99\291I42.doc List of reference numerals 1 Formed part 2 Annular shield mounting 3 Flap 4 Guide Groove 6 Annular shield 7 Grinding chamber housing 8 Grinding chamber opening 9 Pressure ring Annular shield segment 11 Grinding chamber door shield 12 Grinding chamber door 13 Sealing system 14 Crusher wheel 15 Annular gap 16 Elevation

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Claims

3. An annular shield according to claim 1 or 2, characterised in that the annular shield has grooves which are provided transversely to the direction of rotation of sees the rotating system. An annular shield according to claim 3, *o o characterised in that the grooves are arranged with an sees 25 equal and/or unequal spacing. 0: 5. An annular shield according to claims 3 or 4, characterised in that the depth and the width of the grooves are constructed as a function of the distance of the annular shield from the rotating system.
6. An annular shield according to anyone of claims 3 to 5, characterised in that the grooves are constructed with a depth equalling the distance and with a width equalling at least the 5-fold of the distance. J:\Speci\200 299\250 299\29142.doc -8
7. An annular shield as claimed in claim 2 wherein the protrusion formed on the annular shield mounting is interrupted at a length of the removable portion.
8. An annular shield substantially as hereinbefore described with reference to the accompanying drawings. \\GHSYDNTI\users\Speci\200 299\250 299\29142.doc