US20070006786A1

US20070006786A1 - Roller grate

Info

Publication number: US20070006786A1
Application number: US11/423,187
Authority: US
Inventors: Bernhard Zimmermann
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2005-06-10
Filing date: 2006-06-09
Publication date: 2007-01-11
Also published as: CH697973B1; DE102006024632A1

Abstract

A grate covering for a roller grate of an incineration furnace has a furnace space, the grate covering includes a plurality of metallic grate bars arranged on a carrying structure of the roller grate such that they form an outer surface of the roller grate and are exposed directly to the furnace space. The grate bars have a cavity configured to receive a liquid coolant. In addition, a roller grate having such grate bars is provided.

Description

Priority is claimed to Swiss Patent Application No. CH00987/05, filed on Jun. 10, 2005, the entire disclosure of which is incorporated by reference herein.
The present invention relates to the field of incineration technology. It refers to a roller grate for an incineration plant, in particular for a waste incineration plant.

BACKGROUND

It is known prior art to incinerate waste on an incineration grate, for example a roller grate.
Roller grates consist of a plurality of rollers which are arranged axially parallel directly one behind the other and which rotate slowly and codirectionally. The waste is fed onto the uppermost grate roller and, as a result of the rotation of the grate rollers, is transported and circulated through the drying, ignition, main incineration and burn-out zones. An angle of inclination of the grate rollers of 20°, 25° or 30° to assist the conveying mechanisms is customary. Each roller has a carrying structure consisting essentially of a drivable hollow shaft on which radial holders for carriers are fastened peripherally. The carriers are arranged so as to run parallel to the axis of the roller. This carrying structure is provided with a grate covering which consists of numerous circularly arcuate grate bars fastened to the carriers. These grate bars form the outer surface of the rollers. They are, as a rule, lined up with respect to the circumference in 10 rows. A gap, through which the primary air enters the furnace space, is located in each case between the grate bars. Below the rollers are arranged funnels, into which, on the one hand, the primary air is fed and in which, on the other hand, the grate screenings are intercepted. The primary air entering through the gaps between the grate bars has the additional task of cooling the grate bars adjacent to the gap.
DE 199 52 198 A1 discloses a grate roller for a roller grate of a waste incineration plant, in which all the grate bars of the grate roller are provided with orifices in the head and are pushed, largely free of gaps, onto the carrier with their side faces lying next to one another. The orifices are preferably incorporated as edge recesses into the side faces of the grate bar head. An improved air distribution on the roller grate is thereby achieved.
In air-cooled grates of this type, primary air flows through the grate and in this case is used first for cooling the grate bars and subsequently as a necessary reaction partner for incineration. This system has the following disadvantages:

- The marked fluctuation in the waste quality in terms of calorific value, density, flow resistance, moisture, etc. leads to enormous temperature fluctuations, often to an unacceptable excessive temperature of air-cooled cast grate bars.
- The frequent temperature alternation with pronounced temperature gradients and temperature transients leads to the thermomechanical failure of individual grate bars. The changed flow conditions for the primary air which result from this ultimately cause damage to wide regions of the grate.

The above-described gaps between the individual grate bars may become clogged with unburnt fuel or with ash. The cooling-air stream is consequently interrupted at these locations. Moreover, since high incineration temperatures are present, local overheatings may occur which cause a higher wear of the grate bars.
The use of waste with a high calorific value leads repeatedly to problems. The incineration of such waste generates higher incineration temperatures in the case of stoichiometric incineration. Moreover, this waste, as a rule, requires a shorter drying time until ignition occurs. This results in incineration locally commencing too early on the first roller or even in backfires. In practice, an attempt to counteract this problem is made, inter alia, by reducing the primary air. However, there is consequently no longer sufficient air available for cooling the grate covering, so that the grate structure, but, in particular, the grate bars, heat up adversely in this region. This results in a markedly higher wear for the grate structure and in the latter being put at risk. For this reason, the calorific value of the waste which can be incinerated by means of such a plant has to be limited. Often, however, the plant operators wish, or there is the need, to incinerate waste which possesses a higher calorific value.
Plants with roller grates are usually equipped with additional burners in the combustion chamber which are in operation while the plant is being started up. Above all when the furnace space is designed as a cocurrent furnace, an extremely high thermal load on the roller grate occurs when the plant is being started up. This is manifested, inter alia, in that the expansions of the entire structure which are caused thereby may ultimately lead to the blockage of the rotational movement of the rollers. Since the roller movement must be maintained without fail, blockage can be counteracted by an increased supply of primary air. However, an increased primary air stream makes it more difficult to reach the required minimum temperature in the first pass.
If both requirements cannot be combined, all that remains is to enlarge the gap between the stripper and the roller. However, this measure results adversely in increased grate screenings and a poorer distribution of incineration air.
Furthermore, water coolings of the grate covering are known, which are predominantly used in the case of thrust-type or counterthrust-type grates. DE 699 10 783 T2 discloses a grate device with a grate element and with a rotatable shaft arrangement connected to the latter, the grate element, on the one hand, comprising a carrier device which is connected nonrotatably to the shaft arrangement and, on the other hand, comprising a plate device which is attached to the carrier device and forms a grate region. The grate element has a first system of lines for the circulation of liquid coolant, and the shaft arrangement has a second system of lines for the circulation of liquid coolant, the carrier device containing part of the first system of lines, and this part being connected to the second system of lines. The plate device of the grate element contains the remaining part of the first system of lines for cooling.
WO 96/29544 discloses an incineration grate which is both gas-scavenged and liquid-scavenged completely or partially via a control loop. Although this document mentioned describes the invention in terms of a thrust-type grate, it nevertheless at the same time discloses that it can also be used for other grate designs, for example for a roller grate. This grate is suitable for the incineration of waste with a high, but also with a low calorific value.

SUMMARY OF THE INVENTION

The present invention attempts to avoid one or more disadvantages of the known prior art. An object of the present invention is to develop a grate covering, consisting of a multiplicity of grate bars, for a roller grate and also a roller grate, on which waste with a high calorific value can easily be incinerated and which is distinguished by high wear resistance.
The present invention provides a grate covering for a roller grate having grate bars with a cavity through which a liquid cooling medium, preferably water, can be conducted.
The present invention also provide a roller grate, wherein each roller has, on the side facing away from the roller drive, a rotary lead-in which contains a supply line and a discharge line for the supply and discharge of liquid coolant. Two annular chambers are arranged inside each roller, on the one hand the first annular chamber being connected to the supply line and the second annular chamber being connected to the discharge line of the liquid coolant, and, on the other hand, a plurality of separate and parallel-connected sublines for the coolant being branched off from the first annular chamber and being combined again in the second annular chamber. A subline is assigned in each case two series-connected grate bar rows lying opposite one another. The inflow and the outflow for the coolant is arranged on that roller side on which the rotary lead-in is arranged. A reversal of the flow direction of the coolant with respect to the roller axis is provided on the opposite roller side from the exit from the first grate bar row to the entry into the opposite grate bar row.
The liquid cooling medium absorbs the heat flow from the furnace space to the grate bar and thus lowers the operating temperature of the grate bar, so that a relatively cold surface of the rollers is obtained, the entire grate structure being cooled as a result of radiant exchange with this relatively cold roller surface. Consequently, thermally induced expansions of the grate structure are minimized, and the wear of the grate covering is lowered, even at high incineration temperatures, such as occur, for example, during the incineration of fuel having a high calorific value.
It is expedient if the grate bars are produced as a casting and in each case have an inlet and an outlet for the coolant and a straight, serpentine or spiral cooling duct, and the grate bars are fluidically connected in series in such a way that the coolant outlet of the first grate bar is connected to the coolant inlet of the adjacent grate bar. Effective cooling can thereby be achieved.
It is advantageous, furthermore, if the grate bars have a width such as to achieve a roller spacing system of 500 mm. This spacing amount which is conventional for roller grates ensures the retrofittability of existing grates.
Furthermore, it is expedient if the connection of the coolant outlet of the first grate bar to the coolant inlet of the adjacent grate bar takes place with the aid of a hose connection, the hose connection consisting of two hose halves which are connected centrally via a screw connection. After the two adjacent grate bars have been pushed together, the screw connection is completely encased, and the hose connection is completely covered by means of a protective plate. Thus, advantageously, both the screw connection and the entire hose are completely covered and protected against grate screenings. By a hose being used as a means of connection of two grate bars, grate bar expansions and grate bar movements are advantageously compensated.
Furthermore, it is advantageous if the grate bar is provided on is underside with ribs, because this ensures the necessary strength. Moreover, advantageously, orifices for the supply of primary air, which preferably have a circular cross section, may be arranged in a grate bar. Additional cooling of the grate bars consequently becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is illustrated in the drawings, in which:
FIG. 1 shows a section through a diagrammatically illustrated roller grate of an incineration furnace according to the known prior art;
FIG. 2 shows a cross section through a diagrammatically illustrated grate covering according to the invention for a roller grate;
FIG. 3 shows a longitudinal section through a diagrammatically illustrated grate covering according to the invention for a roller grate;
FIG. 4 shows a cross section through the grate roller according to the invention along the line IV-IV according to FIG. 5; and
FIG. 5 shows a longitudinal section through a roller grate according to the invention.
Only the elements essential for understanding the invention are shown. Identical elements are in each case given the same reference symbols.

DETAILED DESCRIPTION

The invention is explained in more detail below by means of an exemplary embodiment and FIGS. 1 to 4.
FIG. 1 shows a section through a diagrammatically illustrated roller grate according to the known prior art. The roller grate 1 consists of a plurality of rollers 2 which are arranged axially parallel directly one behind the other and which rotate slowly and codirectionally. The waste is fed onto the uppermost grate roller and as a result of the rotation of the rollers 2 is transported and circulated through the drying, ignition, main incineration and burn-out zones of the furnace space 3 of a waste incineration furnace. To assist the conveying mechanisms, the rollers 2 are arranged at a specific angle of inclination, for example 25°. Each roller 2 has a carrying structure 4 consisting essentially of a drivable hollow shaft on which radial holders for carriers are fastened peripherally. The carriers are arranged so as to run parallel to the axis 5 of the roller 2. The carrying structure 4 is provided with a grate covering which consists of numerous circularly arcuate grate bars 6 fastened to the carriers. These grate bars 6 form the outer surface of the rollers 2. They are, as a rule, lined up with respect to the circumference in 10 grate bar rows. Between the grate bars 6 is located in each case a gap through which the primary air enters the furnace space 3. Below the rollers are arranged funnels 7, into which, on the one hand, the primary air is fed and in which, on the other hand, the grate screenings are intercepted. The primary air entering through the gaps between the grate bars 6 have the additional task of cooling the grate bars 6 adjacent to the gap.
FIG. 2 illustrates a sectional illustration (cross section) of an exemplary embodiment of a grate bar 6 according to the invention. FIG. 3 shows a longitudinal section through the grate bar 6 according to the invention. The two figures are advantageously to be referred to simultaneously in order to understand the invention.
The grate bar 6 is a casting which is mounted on the carrying structure 4 of the roller 2, of which only a segment is illustrated in FIG. 2. As can be seen clearly, the grate bar 6 is designed as a hollow body, that is to say it has inside it a cavity 8 (FIG. 2) or a cooling duct 9 (FIG. 3), through which a liquid cooling medium, preferably water, is conducted during the operation of the roller grate 1.
Each grate bar 6 possesses an inlet 10 and an outlet 11 for the cooling medium. The grate bars 6 of a grate bar row are fluidically connected in series, so that in each case the outlet 11 for the coolant from one grate bar 6 is connected to the inlet for the coolant 10 of the adjacent grate bar 6. The cooling duct 9 may be designed differently, for example so as to be straight, serpentine or else spiral. The liquid coolant absorbs the heat flow from the furnace space 3 to the grate bar 6 and thus markedly lowers the operating temperature of the grate bar 6. The grate bars 6 cooled by means of liquid coolant thus give rise to an overall relatively cold surface of the rollers 2. The entire grate structure is cooled by radiant exchange with this relatively cold roller surface. As a result, thermally induced expansions of the grate structure are minimized, and the wear of the grate covering is lowered, even at high incineration temperatures, such as occur, for example, during the incineration of fuel having a high calorific value.
The width of the grate bars 6 is advantageously selected such that a roller spacing of 500 mm is achieved. This conventional spacing amount ensures the retrofittability of existing roller grates.
The connection of two grate bars 6 in terms of the coolant is implemented via a hose connection 12. The advantage of this is that grate bar expansions and grate bar movements can thereby easily be compensated. The hose connection 12 consists of two hose halves which are connected to one another in the middle via a screw connection 13. The grate bar 6 is designed such that the screw connection 13 of the two halves of the connecting hose 12 is completely encased after the two grate bars 6 have been pushed together. The screw connection is thereby protected with respect to the grate screenings.
The hose connection 12 is likewise protected against the grate screenings and consequently from damage in that it is completely covered (FIG. 3) by a protective plate 14 mounted on the underside of the grate bar 6.
To increase the strength of the grate bar 6, the latter is provided with ribs 15 on its underside (FIG. 3).
It is evident, furthermore, from FIG. 2 that orifices 16 of preferably circular cross section, which serve for the supply of primary air, may be arranged additionally in the grate bar 6. An additional cooling action can consequently be achieved. The supply of primary air also takes place through defined gaps 28 (FIG. 3) between two adjacent grate bars 6.
FIGS. 4 and 5 show diagrammatically the rollers 2 according to the invention in a cross section (FIG. 4) and in a longitudinal section (FIG. 5). In this exemplary embodiment, the rollers are equipped circumferentially with 10 grate bar rows.
The coolant is supplied to and discharged from each roller 2 by means of a rotary lead-in 17. The rotary lead-in 17 is arranged on that side of the roller 2 which faces away from the roller drive 18. The rotary lead-in 17 has a supply line 19 and a discharge line 20 for the supply and discharge of a liquid coolant. Two annular chambers 21, 22 are arranged inside each roller 2, on the one hand the first annular chamber 21 being connected to the supply line 19 and the second annular chamber 22 being connected to the discharge line 20 (or exactly conversely) for the liquid coolant, and, on the other hand, a plurality of, specifically in the present exemplary embodiment 5, separate and parallel-connected sublines 23 for a part stream 25 of the coolant being branched off from the first annular chamber 21 and being combined again in the second annular chamber 22. In this case, a subline 23 for a part stream 25 of the coolant is in each case assigned two grate bar rows lying opposite one another. These two grate bar rows are connected in series. The part streams 23 of two adjacent grate bar rows 26 and 27 may be contradirectional (as illustrated in FIG. 4) or codirectional.
The inflow and outflow of the coolant are arranged on that roller side on which the rotary lead-in 17 is arranged. On the opposite side, the cooling stream is conducted from the outlet from the grate bar row to the inlet of the opposite grate bar row, at the same time with a reversal 24 of the flow direction with respect to the roller axis 5. The 5 sublines 23 are combined in the annular chamber 22 downstream of the outlet of the second grate bar row and leave the inside of the rollers 2 in the discharge line 20 by means of the rotary lead-in 17.
The invention, of course, is not restricted to the exemplary embodiments described.

Claims

1. A grate covering for a roller grate of an incineration furnace having a furnace space, the roller grate having a carrying structure, the grate covering comprising:

a plurality of metallic grate bars disposed on the carrying structure so as to form an outer surface of the roller grate and being exposed directly to the furnace space, wherein each of the grate bars has a cavity configured to receive a liquid coolant.

2. The grate covering as recited in claim 1, wherein each grate bar is cast and each cavity includes a coolant inlet, a coolant outlet and a cooling duct, and wherein the grate bars are fluidically connected in series so that the coolant outlet of a first grate bar is connected to the coolant inlet of an adjacent grate bar.

3. The grate covering as recited in claim 2, wherein the cooling duct is one of straight, serpentine and spirally shaped.

4. The grate covering as recited in claim 1, wherein in that the grate bars have a width so as to achieve a roller spacing system of 500 mm.

5. The grate covering as recited in claim 2, further comprising a hose connection for fluidically connecting the coolant outlet of the first grate bar to the coolant inlet of the adjacent grate bar.

6. The grate covering as recited in claim 5, wherein the hose connection includes two hose halves connected centrally via a screw connection.

7. The grate covering as recited in claim 6, wherein the screw connection is completely encased by two adjacent grate bars in an assembled state.

8. The grate covering as recited in claim 5, further comprising a protective plate completely covering the hose connection in an assembled state.

9. The grate covering as recited in claim 1, wherein each grate bar includes ribs on an underside of the grate bar.

10. The grate covering as recited in claim 1, wherein each grate bar includes a plurality of orifices for supply of primary air.

11. The grate covering as recited in claim 10, wherein each orifice has a circular cross section.

12. The grate covering as recited in claim 1, wherein the coolant is water.

13. A roller grate comprising:

a roller drive;

a plurality of rollers each defining an axis and disposed axially parallel behind one another, each roller having a carrying structure and a grate covering having a plurality of metallic grate bars disposed on the carrying structure so as to form an outer surface of the roller grate, wherein each of the grate bars has a cavity configured to receive a liquid coolant;

a rotary lead-in device disposed on a first side of each roller facing away from the roller drive, the rotary lead-in device containing a supply line and a discharge line of the liquid coolant;

a first annular chamber disposed inside each roller and connected to the supply line;

a second annular chamber disposed inside each roller and connected to the discharge line;

a plurality of separate and parallel-connected sublines for the coolant being branched off from the first annular chamber and being combined again in the second annular chamber, wherein at least one of the sublines is assigned to two-series connected grate bar rows disposed opposite one another,

wherein an inflow and an outflow of the coolant is arranged on the first side of each roller, and wherein a flow direction of the coolant relative to the roller axis is reversed on a second side of the roller opposite the first side, the coolant flowing from an outlet of a first grate bar row to an inlet of an opposite grate bar row.