EP1886066A1

EP1886066A1 - A stepped grate for a waste incineration plant

Info

Publication number: EP1886066A1
Application number: EP06722943A
Authority: EP
Inventors: Bertram Holst; Søren Christian JENSEN
Original assignee: Babcock and Wilcox Volund AS
Current assignee: Babcock and Wilcox Volund AS
Priority date: 2005-05-13
Filing date: 2006-05-15
Publication date: 2008-02-13
Also published as: KR20080093855A; CN101198823A; WO2006119777A1; TW200706808A; JP2008540991A

Abstract

Grate bar (6) for use in a stepped grate for a waste incineration plant, said stepped grated consisting of grate blocks (1 ) placed in adjacent rows and in succession in the advancing, direction of the waste and resting on parallel grate beams (2) in which every second row of grate blocks (1) are adapted to make a reciprocating movement while the intermediate rows of grate blocks (1) are stationary, each grate block, comprising: two stringers (3, 4) mutually connected by two (half blocks) or four transverse steel rods (5) and each grate block (1) being filled up with loose, vertically hanging cast grate bars (6) resting on said steel rods (5), said grate bars (6) comprising indentations along their abutting sides forming openings for admitting primary air for the combustion, said primary air also providing the necessary cooling of the grate bars (6).The indentations along the abutting sides are formed as one single elongate indentation positioned centrally on at least one side of each grate bar (6). This provides a grate bar of simple construction at a reduced price.

Description

A STEPPED GRATE FOR A WASTE INCINERATION PLANT

TECHNICAL FIELD

The present invention relates to a stepped grate for a waste incineration plant of the kind set forth in the preamble of claim 1.

BACKGROUND ART

GB 1566382 shows a grate system with replaceable wear elements in which only part of the upper surface in contact with the burning material is replaceable and said wear elements are fixed to the grate system by means of relatively complex fixation means, comprising sliding grooves and bolts which are subjected to wear and contamination by grate screenings, such wear and contamination impeding the efficient function of the fixation means.

From EP 1036986 it is known to provide a stepped grate of this kind in which the grate bars and grate block stringers have indentations along the abutting sides dimensioned and positioned to provide several holes in the longitudinal direction of the grate bar with an average distance of 30-70 mm and a hole size of more than 70 mm², preferable approximately 100 mm². These grate bars are provided in a number of different widths exemplified by the width 25 mm and 30 mm, respectively. One disadvantage, which can be seen in this construction, is the number of grate bars to be positioned in each grate block and the relatively complex formation of the several indentations along the sides of said grate bars.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a stepped grate of the kind referred to above, with which it is possible to provide a simple fixation of the grate bars. According the present invention this is achieved with a stepped grate of said kind, which comprises the features set forth in the characterising part of claim 1. In this way, it is possible to install the grate bars in the grate blocks in a more efficient way. Furthermore, the provision of the primary air opening as one single elongate opening provides the advantage that the tendency _of ashes falling down througrusaid-opening is. reduced due to_a higher .air velocity up through the opening. Advantageous embodiments of the invention, the nature of which will be evident of the following detailed description of the invention, are revealed in the subordinate claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed part of the present description, the invention will be explained in more details with reference to the exemplary embodiment of a grate bar according to the invention shown in the drawings, in which

Fig. 1 shows a vertical section through three succeeding stepped grates of an incineration plant,

Fig 2. shows a grate block in perspective,

Fig 3. shows a grate bar seen from the side,

Fig 4. shows a grate bar of Fig. 3 seen from above, Fig 5. shows a grate bar of Fig. 3 and 4 seen in cross section along the line V-V, and

Fig. 6 shows a grate bar for use in the upper row of a grate section.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The stepped grate for a waste incineration plant shown in fig. 1 consists of three sections, each section comprising stationery and reciprocating grate girders. Each girder consists of a grate beam (2), on which grate blocks (1) are fixed. Every second grate girder is adapted to make reciprocating movements while the intermediate girders are stationary. Each grate block, as shown in fig. 2, consists of two cast stringers (3, 4) mutually connected by two or four transverse steel rods (5). The grate block (1) is filled up with cast grate bars (6) which are resting on the steel rods (5). The grate bars are as shown in figs. 3-5, provided with suitable bearing elements for supporting the grate bars on the transverse steel rods (5).

The fixation of the grate bars is provided by suitably forming the bearing elements with indentations at the bottom side of the grate bars, such that the insertion of the grate bars is made in an inclined direction onto the transverse steel rods (5). The next upper row of the grate bars provides a locking of the grate bars when inserted. The inclined insertion is provided by an angle γ between a line through the transverse steel rods (5) and the insertion indentations, as indicated in Fig. 3, said angle preferably being between 80 ° and 45 °. The primary air for the combustion, which enters into the furnace from below as seen in fig. 1 and through the stepped grate, passes along the sides of the grate bars, these sides being provided with indentations as shown in figs 3-5. The indentations in adjacent grate bars are positioned to provide an elongate opening, typically having a longitudinal dimension of 100 mm and a width of typically 3-5 mm. As shown in figs 3-5, the openings in the grate bars have an opening slope α down along the longitudinal sides, which in the preferred embodiment is approx. 14 °. Correspondingly the openings in the grate bars have an opening slope β down along the narrow end side, which in the preferred embodiment is approx. 14 °.

In accordance with the invention the grate bars (6) are provided with indentations providing elongate openings and the grate block stringers (3, 4) have indentations which together can be optimised in order to provide a suitable level of cooling of the grate bar and a suitable pressure drop across the grate bars in order to avoid the tendency of ashes blocking the openings.

Preferably the width of the grate bars is within the range 45-70 mm. and in the preferred embodiments shown in the drawings the width is 60 mm, other preferred widths are 55 mm, 55,5 mm and 60,5 mm. By providing these relatively broad grate bars the costs for covering a certain area of stepped grates with grate bars can be reduced, compared to the typical dimensions of prior art grate bars having dimensions in the order of 20-30 mm. The broader grate bars provide a reduction in total weight of cast steel in the grate blocks of 15-20% whereby the cost price is reduced correspondingly.

Furthermore, a further advantage is seen in that wear on the grate bars (6) is reduced. This is believed to be a consequence of that wear on the sides of the grate bars (6) will not influence the total side ways dimension of the combined grate bars in a grate block (1) to the same extent as if narrower and more grate bars (6) were provided in each grate block (1), thus resulting in a longer service life.

With grate block stringers (3, 4) and grate bars (6) in accordance with the invention, the intrinsic pressure drop over the grate in typical use condition is between 75 and 300 Pa. This relatively high pressure drop over the grate corresponds to a relatively high air velocity, whereby the primary air openings are kept open and free of ashes and waste material. The grate in accordance with the invention is suited to be used in connection with furnaces and grates which are designed to be used for incinerating waste for supplying heat to steam boilers with or without steam turbines for electric power generation.

As shown in Fig. 6, the upper row of grate bars are provided with an upstanding lip (8) providing an airtight connection to the transition plate to the next grate section or the inlet section of the waste incineration plant.

The grate bars are mounted on the grate section starting from the lower end thereof and each subsequently mounted grate bar above a previously mounted grate bar locks the preceding grate bar in position due to the formation of the engagement means.

The upper row of grate bars (6) on a grate beam (2) is inserted by tilting the grate beam (2), e.g. using a crow bar to lift the lower end of the grate beam (2) or by using a pulley tackle. The tilting of the grate beam (2) provides sufficient room for inserting the upper grate bars (1) in the inclined direction underneath the transition plate, and when the grate beam (2) is moved back to its mounting position the upper row of grate bars (1) are locked in position by engagement between the upstanding lip (8) and the transition plate.

Claims

PATENT CLAIMS

1. Stepped grate for a waste incineration plant, said stepped grated consisting of grate blocks (1) placed in adjacent rows and in succession in the advancing direction of the waste and resting on parallel grate beams (2) in which every second row of grate blocks (1) are adapted to make a reciprocating movement while the intermediate rows of grate blocks (1) are stationary, each grate block, comprising:

two stringers (3, 4) mutually connected by two (half blocks) or four transverse steel rods (5) and each grate block (1) being filled up with loose, vertically hanging cast grate bars (6) resting on said steel rods (5), said grate bars (6) comprising indentations along their abutting sides forming openings for admitting primary air for the combustion, said primary air also providing the necessary cooling of the grate bars (6), said indentations along the abutting sides being formed as one single elongate indentation positioned centrally on at least one side of each grate bar (6), characterised by the fixation of the grate bars (6) to the steel rods (5) is provided by a suitable formation of the bearing elements as indentations at the bottom side of the grate bars (6) such that the grate bars may be inserted on the transverse steel rods (5) in an inclined direction and locked in place by the next following higher positioned row of grate bars (6).

2. Stepped grate in accordance with claim 1 , characterised by the bearing elements being formed with halfcircular bearing surfaces.

3. Stepped grate in accordance with claim 1 or 2, characterised by the angle γ between a line through the steel rods (5) and the direction of the insertion indentations being between 80 and 45 °.

4. Stepped grate in accordance with any of the preceding claims, characterised by said elongate indentations being provided on both sides of said grate bar (6).

5. Stepped grate in accordance with any of the preceding claims, characterised by the area of the openings for primary air amounting to between 3 and 7 % of the total upper surface area of the grate bar (6).

6. Stepped grate in- accordance with any of the preceding. claims,, characterised, by said grate bar (6) having a width of 45-70 mm, preferably 55-60 mm.

7. Stepped grate in accordance with any of the preceding claims, characterised by the primary air openings having a longitudinal dimension of approximately 100 mm and a width of approximately 3-5 mm.

8. Stepped grate in accordance with any of the preceding claims, characterised by the openings for admitting primary air having an opening slope (α) down along the longitudinal sides of more than 10 ° preferably approximately 14 °.

9. Stepped grate in accordance with any of the preceding claims, characterised by the openings for admitting primary air having an opening slope (β) down along the narrow end sides of more than 6 ° preferably approximately 14 °.

10. Stepped grate in accordance with any of the preceding claims, characterised by the pressure drop across the primary air openings being in the range 75-300 Pa, preferably 150-250 Pa.