EP0713056A1 - Cooled grate bar - Google Patents

Abstract

The cooled grate block has an upper wall (23), the outer surface of which forms a usage surface (33) on which the rubbish to be processed is placed and transported along it. The upper wall limits a cooling chamber (27) beneath it, through which passes a water feed-in conduit (31) and a water feed-out conduit (40,42). Both conduits end in the cooling chamber and have several outlet apertures and inlet apertures (41). The cooling chamber is formed in a U-shaped block body and is closed laterally by two sidewalls and from beneath by a floor and a foot (26). The foot of one grate block is relatively displaceable to the upper wall of a following grate block. The outlet apertures of the water feed-in conduit are arranged in the area of the foot.

Description

The invention relates to a cooled grate block according to the preamble of claim 1.

In conventional waste incineration plants, the waste is conveyed on a grate through a combustion chamber and is dried and burned in the process. In addition to the transport function, the grate also ensures that the waste is constantly mixed so that new waste surfaces are repeatedly exposed to the thermal treatment in the furnace. For this purpose, a grate track has a plurality of rows of grate blocks arranged one behind the other in a step-like manner, each of which alternately fixed and movable rows of grate blocks follow one another. The waste material on the grate, for example waste, is pushed forward by a pushing movement of the movable rows of grate blocks and mixed at the same time. A row of grate blocks is formed by several, usually 16 to 24 grate blocks, which are hung next to one another on a holding tube and braced together by means of a pull rod. The individual grate blocks are cooled by air flowing through them, which at the same time serves as an oxidizing agent for combustion grates.

Despite the air cooling, the grate blocks are exposed to high thermal stress, which results in high thermal stresses in the material of the grate blocks. Cracks can form in the material, which increases the risk of corrosion. The grate blocks must be made of high-quality material, such as high-alloy steel. Because of the large thermal expansions, the size of the individual grate blocks is limited; it is a relatively large number of grate blocks are required in a row of grate blocks. It is disadvantageous that the gaps between the individual grate blocks, caused by repeated expansion and contraction due to different block temperatures, caused by the combustion process and the start-up and shutdown of the furnace, certain portions of the waste to be burned (non-ferrous metals, dust, etc.) fall through, which then go into the slag unburnt. If two or three grate tracks are used next to one another, brackets for the pull rods and seals for the leakage air must be arranged not only on the outside of such a grate, but also between the grate tracks. The replacement of individual grate blocks is therefore complicated and takes long service times.

The object of the present invention is to reduce the thermal stress on the grate block and to enable a grate to be constructed which is simpler in terms of assembly and maintenance, but which also withstands all requirements better in terms of operation.

This object is achieved according to the invention by the features specified in the characterizing part of claim 1.

The advantages achieved by the invention can be seen in particular in the effective cooling, as a result of which thermal stresses and thermal expansions in the grate block are largely eliminated. Thus, only a few, wider grate blocks - connected to one another in a simple manner - can form a grate block row. This not only simplifies assembly and replacement, but also significantly reduces the amount of rust falling through. The grate block can also be made from less high quality material.

Further particular advantages result from using the grate blocks according to the invention for a pyrolysis grate which is used in the process according to Swiss patent application No. 01510 / 94-8 (A 10364 CH). In this process, no air is forced through the grate as an oxidizing agent; since according to the invention the air as coolant is also eliminated, the grate blocks do not have to have any air openings exposed to the risk of clogging.

The invention will now be explained in more detail with reference to the drawings.

Fig.1

ein Ausführungsbeispiel eines Rostelements als Teil eines Rostes nach dem Stand der Technik;

Fig.2

schematisch dargestellt ein Ausführungsbeispiel eines erfindungsgemässen Rostblocks von unten in Pfeilrichtung P nach Fig.1 gesehen;

Fig.3

eine Seitenansicht des Rostblocks in Pfeilrichtung S nach Fig. 2, teilweise im Schnitt und

Fig.4

einen Schnitt nach Linie IV-IV in Fig.2.

Show it:

Fig. 1

an embodiment of a grate element as part of a grate according to the prior art;

Fig. 2

schematically shown an embodiment of a grate block according to the invention seen from below in the direction of arrow P according to Figure 1;

Fig. 3

a side view of the grate block in the direction of arrow S of FIG. 2, partly in section and

Fig. 4

a section along line IV-IV in Fig.2.

1 shows a grate element 3 as part of a grate for a plant for the thermal treatment of waste. An inclined grating track is composed of several grating elements 3 in length; usually three to five grate elements 3 in a row arranged. In addition, several grate tracks can be attached side by side; Usually one to four grate tracks form the width of the grate. The number of grate elements 3 and the grate tracks depends on the predetermined throughput of the waste and on its calorific value.

Each grate element 3 has several, possibly eight grate block rows 4, 5 arranged one behind the other, with a fixed grate block row 4 being followed by a movable grate block row 5. A plurality of grate blocks 6 are arranged next to one another in each grate block row 4, 5. Up to now it has been customary to place 16 to 24 air-cooled grate blocks 6 ′ in a row of grate blocks 4, 5 next to one another. As shown in FIG. 1, they were hung on a block holder tube 7 and braced by means of tie rods 14 and turnbuckle nuts (not shown). According to the invention, only three to four water-cooled grate blocks 6 of a grate block row 4, 5, which are suspended from a block holding tube 7, are now firmly connected to one another, for example screwed. A side plate 15 is screwed onto the outermost block of each fixed row of blocks.

The block holder tubes 7 of the fixed grate block rows 4 are carried by stationary brackets 8 according to FIG. The block holder tubes 7 of the movable grate block rows 5 are fastened in brackets 9, which are assigned to a movable grate carriage 10. Each grate element 3 is equipped with such a grate carriage 10. The grate carriage 10 is driven by means of two hydraulic cylinders 11 arranged in parallel and thereby moved back and forth on rollers 12 on running surfaces 13. This also moves the movable grate block rows 5, which exert a pushing and shearing effect on the waste material located on the grate track 2, so that new ones are produced again and again Waste surfaces are exposed to thermal treatment in the combustion chamber while the waste material is conveyed forward.

An exemplary embodiment of a grate block 6 according to the invention, provided for a combustion grate, will now be described below with reference to FIGS. 2 to 4.

The grate block 6 has a block body 20 of a U-shaped cross section, the upper wall of which is designated by 23 in FIGS. 3 and 4. The outer surface of the upper wall 23 forms a usable surface 33 on which the waste to be treated comes to rest and along which it is transported. A rear wall 21 of the block body 20 is provided with a hook 22 for hanging on the block holder tube 7 (FIG. 1). There is a corner 25 between the upper wall 23 and a front wall 24. The foot 26 of a grate block 6 is assigned to the upper wall 23 of a subsequent grate block 6; they are relatively mutually displaceable.

An inner cooling space 27 is enclosed by the block body 20, the base 28 and the foot 26, and two side walls 29. A water supply line 30 opens into the cooling space 27. The water supply is designated by an arrow W1 in FIG. 3. A water supply cross line 31 connected to the water supply line 30 extends parallel to the rear wall 21 and is provided with outlet openings 32 at individual locations (three shown in FIG. 2). This water outlet is designated by an arrow W2 in FIG. 3. Several, possibly three, longitudinally arranged water supply branch lines branch from the water supply cross line 31 34, which extend up to the front wall 24 and are angled there in such a way that their outlet opening 35 is located directly in front of the foot 26. The water flowing out of the outlet opening 35 fills the closed cooling space 27 in the direction of an arrow W3 together with the water emerging from the outlet openings 32 (arrow W2), these counteracting both water flows in a certain sense and for good water mixing or for an enhanced cooling effect to care. It is important that the point of the grate block 6, which is particularly highly mechanically stressed, namely the foot 26, is acted upon directly by the cooling water.

The front corner 25 is exposed to the greatest temperatures and therefore the greatest thermal stress (cf. in particular Fig. 1, according to which it is easy to imagine which area of the grate blocks is constantly exposed to direct thermal stress or direct contact with the waste layer) no matter in which relative position there are currently movable and fixed grate block rows 4,5). The lighter, already heated water rises to this point of the cooling space 27 and is additionally heated there. Immediately in this area, inlet openings 41 (FIG. 4) of several, possibly two, water drainage branch lines 40 (see FIG. 2) are provided. The entry of the heated water into the water discharge branch lines 40 is indicated by an arrow W4 in FIG. 4. The water discharge branch lines 40 extend obliquely along the bottom 28 and open into a water discharge cross line 42 which is arranged parallel to the water supply cross line 31 and is offset further from this. From there, the heated water is discharged by means of a discharge line 43 in the direction of an arrow W5 (Fig. 4) led away from the cold room 27.

The appropriate arrangement of the cold water supply (outlet openings 35) and the hot water discharge (inlet openings 41) ensures the optimal cooling flow (it is also avoided, for example, that so-called "water pockets" with non-circulating water form at certain points, or that steam bubbles form in the area of corner 25 arise), protects the mechanically stressed foot 26 and avoids excessive thermal stress in the area of the front corner 25.

The water supply line 30 and the water discharge line 43 are connected in a manner not shown to a cold water low pressure system. A connection to a closed cooling water system with a built-in heat exchanger is preferred.

In the embodiment of the grate block 6 shown in FIGS. 2 to 4, which is intended for a combustion grate, air is distributed from below in the direction of an arrow L1 (FIG. 3) as an oxidizing agent necessary for the combustion by a number of uniformly distributed along the grate block width, between the Bottom 28 and the front wall 24 through the cooling space 27 extending tubes 46. According to FIG. 3, the front wall 24 has a plurality of air outlet openings 47 assigned to the tubes 46, from which the combustion air flows in the direction of an arrow L2. Since the air is only used as a combustion medium, but not as a cooling medium, hitherto fewer air outlet openings 47, which have to be cleaned laboriously because of clogging, are required than was previously the case.

If the water-cooled grate blocks 6 according to the invention are used for a pyrolysis grate in which no air is driven through the grate as an oxidizing agent, the pipes 46 and the air outlet openings 47 which are exposed to the risk of clogging are completely eliminated. Since no air has to be passed through the grate 1, a thicker layer of waste can be applied to the grate 1.

In the case of a combustion grate, the first grate element 3, which is intended for rapid ignition by start-up burners, can also consist of grate blocks 6 without pipes 46 and air outlet openings 47, since the water now provides cooling instead of the air.

In the inventive water cooling of individual grate blocks 6, the average temperature values on the grate can be significantly reduced thanks to the more favorable heat transfer numbers from the water compared to the air. If these values were between 350 ° and 700 ° C for air cooling, they could be reduced to approx. 50 ° to 100 ° C by water cooling. The high thermal stresses and strains in the material, which were common in air-cooled grate blocks 6 ', are eliminated in the water cooling according to the invention. As a result, in contrast to earlier grate designs, fewer (three to four), wider grate blocks 6 can be arranged next to one another in a grate block row 4, 5 and form the width of the grate track 2. The previous bracing by tie rods 14 (Fig. 1) is also superfluous; the grate blocks 6 of a grate block row 4 or 5 can be screwed together in a simple manner. In the case of multi-track gratings, the brackets previously required for the tie rods between the individual tracks are also no longer required. A possible change of grate blocks 6 is thereby considerably simplified and claimed shorter service times. In addition, the change at the earlier, high temperatures was necessary more often, for example every year. An essential advantage according to the invention is that the use of a few grate blocks 6 or the absence of gaps significantly reduces grate diarrhea; the risk of non-ferrous metals or dust falling through the grate and getting into the slag unburnt is significantly lower.

Due to the lower temperatures and the lower thermal stress on the grate block 6, the risk that cracks occur in the material due to thermal stresses which favor the corrosion is largely eliminated. Thus, the use of less high quality material for the grate blocks 6 can be considered.

Both the fixed and the movable grate block rows 4 and 5 are preferably composed of water-cooled grate blocks 6. It would also be possible to combine water and air cooling.

Reference numbers

1

2nd

3rd

Rust element

4th

fixed grate block row

5

movable row of grate blocks

6

Rust block

7

Block holder tube

8th

stationary console

9

Console of 10

10th

Rust wagon

11

Hydraulic cylinder

12th

role

13

career

14

Tie rods

15

16

17th

18th

19th

20th

Block body

21

back wall

22

hook

23

top wall

24th

front wall

25th

corner

26

Foot

27

Cold room

28

ground

29

Side wall

30th

Water supply pipe

31

Cross wire

32

Outlet opening in 31st

33

Usable area

34

Water supply pipe

35

Exit opening of 34

36

37

38

39

40

Water drainage pipe

41

Entrance opening

42

Cross wire

43

Water drainage pipe

44

45

46

pipe

47

Air outlet openings

48

49

50

Claims (12)

Cooled grate block as part of a grate for a plant for the thermal treatment of waste, with an upper wall (23), the outer surface of which forms a usable area (33) on which the waste to be treated comes to lie and along which the waste is transported, thereby characterized in that the upper wall (23) delimits an underlying cooling space (27) which is penetrated by a water supply line (30, 31, 34) and a water discharge line (40, 42, 43), the water supply line (30, 31, 34 ) and the water discharge line (40, 42, 43) end in the cooling chamber (27) and have a plurality of outlet openings (35) or a plurality of inlet openings (41). Cooled grate block according to claim 1, characterized in that the cooling space (27) is formed in a U-shaped block body (20), is closed laterally by two side walls (29) and from below by a bottom (28) and a foot (26) , wherein the foot (26) of a grate block (6) is assigned to the upper wall (23) of a grate block (6) connected downstream. Cooled grate block according to claim 2, characterized in that the outlet openings (35) of the water supply line (30, 31, 34) are arranged in the region of the foot (26). Cooled grate block according to claim 2, characterized in that the inlet openings (41) of the water discharge line (40,42,43) in the area of a Transition of the upper wall (23) to a front wall (24) formed corner (25) are arranged. Cooled grate block according to one of claims 2 to 4, characterized in that the water supply line (30, 31, 34) has a transverse line (31) which is arranged parallel to a rear wall (21) of the block body (20) and to which several, up to branch lines (34) projecting into the front area of the cooling space (27) and provided with the outlet openings (35) are connected. Cooled grate block according to one of claims 2 to 4, characterized in that the water discharge line (40, 42, 43) has a transverse line (42) arranged parallel to a rear wall (21) of the block body (20), to which several, up to branch lines (40) projecting into the front area of the cooling space (27) and provided with the inlet openings (41) are connected. Cooled grate block according to claim 5, characterized in that the transverse line (31) is provided with a plurality of additional water outlet openings (32). Cooled grate block according to one of claims 2 to 7, which forms part of a combustion grate of a waste incineration plant, characterized in that a front wall (24) of the block body (20) is provided with a plurality of air outlet openings (47) which are distributed uniformly over the grate block width and which the air as a means of combustion through appropriate cooling space (27) between the floor (28) and the front wall (24) through tubes (46) is supplied. Cooled grate block according to one of claims 1 to 8, characterized in that the water supply line (30, 31, 34) and the water discharge line (40, 42, 43) are connected to a closed cooling water system provided with a heat exchanger. Grate constructed from cooled grate blocks (6) according to one of claims 1 to 9, wherein a plurality of grate blocks (6) are attached to a block holding tube (7) and connected to one another form a grate block row (4 or 5), characterized in that the grate block row (4 or 5) is formed from a maximum of four rust blocks (6). Grate according to claim 10, characterized in that side walls (29) of the adjacent grate blocks (6) are screwed together. Grate according to one of claims 10 or 11, with a plurality of stationary grate block rows (4) and a plurality of movable grate block rows (5) which are arranged alternately in succession, characterized in that both the fixed grate block rows (4) and the movable grate block rows (5) are formed by the water-cooled grate blocks (6).

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