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(11) | EP 3 104 077 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | HEAT-INSULATING CERAMIC TILE WITH LOW THICKNESS FOR A COMBUSTION CHAMBER OF A GAS TURBINE |
| (57) A heat-insulating tile made of ceramic material for a combustion chamber of a gas
turbine includes a first face (10), a second face (11), sides (15) adjacent to the
first face (10) and to the second face (11) and anchorage seats (17) on the sides
(15); the anchorage seats (17) being defined by respective recesses open on the first
face (11) and delimited by respective coupling surfaces (18) sloping from the first
face (10) to a respective one of the sides (15).
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[0001] The present invention relates to a heat-insulating ceramic tile with low thickness, more specifically of a type usable in a combustion chamber of a gas turbine, in particular in an annular combustion chamber of a medium-small sized gas turbine.
[0002] As already known, the combustion chamber of a gas turbine must be internally provided with a heat-insulating coating, because of the high temperatures developed by the machine operation. The heat-insulating coating is generally formed by a plurality of tiles arranged in contiguous rows on the inner walls of the combustion chamber casing to define a substantially continuous surface.
[0003] In large-sized gas turbines producing power higher than 150 MW, the heat-insulating tiles are generally made of a refractory ceramic material. This class of materials has a very low thermal conductivity and is particularly suitable for use in gas turbines. In gas turbines of a smaller size, which provide power e.g. around 70 MW or lower, the reduced size does not allow the use of ceramic tiles. The installation of conventional ceramic tiles, in fact, requires an anchorage system arranged between the tiles and the combustion chamber metal frame, which must be thinned by special processes. The anchorage system is usually engaged in appropriate seats formed on the sides of the ceramic tiles, which accordingly must have a minimum thickness sufficient to ensure an adequately resistant section; this greatly limits the possibility of thinning the ceramic tiles. The conventional anchorage system also provides for the tile disassembly by sliding, which is not practicable in small-sized combustion chambers due to the reduced possibility of movement of the operator.
[0004] Since it is not possible to vary the outside size of the casing (for retrofit requirements) or the inside combustion volume (not to affect the combustion efficiency), in small-sized gas turbines the thinning would be excessive and could jeopardize the supporting structure of the combustion chamber. The necessary machining operations are therefore not compatible and the ceramic tiles cannot be used.
[0005] The combustion chambers of small-sized gas turbines are therefore protected with cooled metal shields, whose size (in particular the thickness) allows their installation without potentially harmful effects on the casing. Metal shields, even if obtained through special casting processes and covered with thin ceramic layers, do not have the same insulating power and must be cooled by an abundant flow of air taken from the compressor outlet. However, the cooling air cannot be conveyed into the burners, thus penalizing the efficiency of the machine both with regard to the thermal power output and with regard to the combustion stability. The metal shields, moreover, suffer most under the overheating and must be replaced more frequently, thus heavily increasing the operating costs and the problems related to the overheating that involve their systematic replacement during maintenance.
[0006] The object of the present invention is therefore to provide a heat-insulating tile that can overcome or at least mitigate the aforesaid limitations and, in particular, can be also used in gas turbines smaller than those where the known heat-insulating ceramic tiles can be employed.
[0008] The present invention will now be described with reference to the accompanying drawings showing a non-limiting embodiment, in which:
- Figure 1 is a perspective view, partially sectioned and with parts removed for clarity's sake, of an annular combustion chamber of a gas turbine according to an embodiment of the present invention;
- Figure 2 is a perspective front view of a heat-insulating tile according to an embodiment of the present invention;
- Figure 3 is a three-quarter perspective view from above of the heat-insulating tile of Figure 2, sectioned along the plane III-III of Figure 2;
- Figure 4 is a three-quarter perspective view from below of the heat-insulating tile of Figure 2;
- Figure 5 shows a pair of heat-insulating tiles according to an embodiment of the present invention juxtaposed in the assembly position;
- Figure 6 is an exploded perspective view of an anchorage device of the combustion chamber of Figure 1; and
- Figure 7 is a perspective view of the assembled anchorage device of Figure 6.
[0009] Figure 1 shows a combustion chamber 1 of a gas turbine (not shown in full). The combustion chamber 1 comprises an annular casing 2 extending about an axis and is provided with a heat-insulating coating 3 which internally coats the casing 2 and delimits a combustion volume 4. Figure 1 also shows burner housings 6, which are not described for the sake of simplicity.
[0010] The heat-insulating coating 3 comprises a plurality of heat-insulating tiles 5 made of refractory material, arranged in adjacent rows along circumferences around the axis of the combustion chamber 1. Optionally, the heat-insulating coating 3 may also include rows of metallic heat-insulating shields 7, particularly in the less hot portions of the combustion chamber adjacent to the outlet.
[0011] The heat-insulating tiles 5 are fastened to the casing 2 by anchorage devices 8. Each anchorage device 8 engages a respective pair of adjacent heat-insulating tiles 5.
[0012] One of the heat-insulating tiles 5 of a specific row of the heat-insulating coating 3 is shown in detail in Figures 2-6. What described below, unless otherwise stated, applies in general not only to all the heat-insulating tiles 5 in the same row, which are all the same, but also to the heat-insulating tiles 5 of other rows of the heat-insulating coating 3.
[0013] The insulating tile 5 has a substantially quadrangular shape. More in detail, the heat-insulating tile 5 has a first face or hot face 10 (Figures 2 and 3) exposed to the combustion volume 4, and a second face or cold face 11 (Figures 3 and 4) opposite to the hot face 10 and oriented towards the casing 2. The hot face 10 and the cold face 11 may be slightly curved, respectively concave and convex, according to the distance from the axis of the combustion chamber 1. The heat-insulating tile 5 also has a first side 12 arranged upstream with respect to a direction of flow of the gases in the combustion chamber 1 and a second side 13 arranged downstream with respect to the first side 12. Sides 15 extend between the hot face 10 and the cold face 11 and between the first side 12 and the second side 13. The sides 15 are slightly converging from the first side 12 to the second side 13, so that the heat-insulating tiles 5 in the same row internally and externally define substantially truncated-conical surfaces. The heat-insulating tile 5 is substantially symmetrical with respect to a middle longitudinal axis A (Figure 2), longitudinal being here understood to indicate the direction that perpendicularly goes from the first side 12 to the second side 13.
[0014] The heat-insulating tile 5 (Figures 2-4) has an anchorage seat 17 on each side 15 for its coupling with respective anchorage devices 8. The anchorage seats 17 are defined by respective recesses, open on the hot face 10 and on the respective side 15. The anchorage seats 17 are delimited at the bottom by the coupling surfaces 18 sloping with respect to the hot face 10 of the heat-insulating tile 5. In one embodiment, the coupling surfaces 18 are substantially flat and sloping from the hot face 10 to the respective side 15 with a constant inclination comprised e.g. between 30° and 60° with respect to the hot face 10. Moreover, the sides 15 have recesses at the respective anchorage seats 17, so that two contiguous tiles in the same row define between them a gap 20, open at the bottom and allowing the passage of a respective anchorage device 8 (in this regard see Figure 5). Because of the slope and of the recesses, the coupling surfaces 18 intercept the respective sides 15 at an intermediate height between the hot face 10 and the cold face 11 (Figure 3).
[0015] With reference to Figures 3 and 4, the cold face 11 of the heat-insulating tile 5 has a recessed portion 21, which is surrounded by a raised portion 22 along the perimeter of the heat-insulating tile 5. An insulating layer 25, for example made of woven heat-insulating fibres, is shaped to correspond to the raised portion 22 of the cold face 11 and applied on it by glue points (not shown). The contact surface between the heat-insulating tile 5 and the casing 2 of the combustion chamber 1 is limited to the insulating layer 25 along the raised portion 22, while the recessed portion 21 is separated from the casing 2. Moreover, the material forming the insulating layer 25 also dampens the transmission of mechanical vibrations from the casing 2 to the heat-insulating tiles 5.
[0016] Figures 6 and 7 show in detail one of the anchorage devices 8, which are structurally identical and may possibly include some size differences to allow the coupling to heat-insulating tiles 5 of different rows. In one embodiment, the anchorage devices 8 of a same row of heat-insulating tiles 5 are identical. Figure 7 shows with dashed lines also portions of a heat-insulating tile 5 coupled to the anchorage device 8 and of the casing 2 of the combustion chamber 1.
[0017] The anchorage device 8 comprises an assembly member 27, a clamping bracket 28, a heat shield member 30 and a screw 31.
[0018] In one embodiment, the assembly member 27 comprises a metal sheet folded so as to define a pair of diverging side walls 32, coupled by a bottom portion 33. In one embodiment, a width of the assembly member 27, defined as the maximum distance between the upper edges 32a of the side walls 32, is less than a length, defined in the direction perpendicular to the width and to the direction of insertion of the screw 31. The assembly member 27 is elastically deformable to dampen the vibrations transmitted by the heat-insulating tiles 5. The side walls 32 slope to mate with the coupling surfaces 18 of the heat-insulating tiles 5 and define between them a pocket 34. For example, the side walls 32 form between them an angle α comprised between 60° and 120°. The assembly member 27 is shaped so as to be housed in the gap 20 between two adjacent heat-insulating tiles 5.
[0019] The bottom portion 33 of the assembly member 27 has openings 35 to allow the supply of cooling air to the clamping bracket 28, and an opening 36 for the through screw 31.
[0020] In one embodiment, the clamping bracket 28 is defined by a metal bar inserted into the pocket 34 between the side walls 32 of the assembly member 27. The width of the bracket member 28 is such that the bracket member 28 comes first in contact with the bottom portion 33 of the assembly member 27 and then with the side walls 32.
[0021] The clamping bracket 28 has through holes 38 in positions corresponding to the openings 35 of the bottom portion of the assembly member 27. Furthermore, a through seat 39 allows the insertion of the screw 31 through the clamping bracket 28 and the opening 36 in the assembly member 27. The clamping force exerted by the screw 31 is transmitted and distributed by the clamping bracket 28 to the assembly member 27, which is then stably held in its seat. The clamping bracket 28, furthermore, exerts pressure on the bottom portion 33 of the assembly member 27, thus transmitting through the side walls 32 a desired force against the coupling surfaces 18 of the anchorage seats 17 of heat-insulating tiles 5.
[0022] The heat shield member 30 comprises a plate of a metal alloy resistant to high temperatures, possibly covered with a heat-insulating layer (not shown in detail) made of refractory material, for example a ceramic material. The heat shield member 30 covers the assembly member 27 and the clamping bracket 28. The clamping bracket 28 is then trapped in the pocket 34 between the assembly member 27 and the heat shield member 30. The heat shield member 30 extends beyond the edges of the side walls 32 and, in particular, is shaped so as to close the gap 20 housing the anchorage device 8. The heat shield member 30 thus forms a substantially continuous surface with the hot faces 10 of adjacent heat-insulating tiles 5, protecting the assembly member 27 and the clamping bracket 28.
[0023] On the side facing the clamping bracket 28, the heat shield member 28 has a seat 40 to house the head 41 of the screw 31. The walls defining the seat 40 are also shaped so as to press the clamping bracket 28 against the bottom wall 33 of the assembly member 27 thanks to the tightening of the screw 31. The screw 31 is coupled to a seat (not shown) in the casing 2.
[0024] The air possibly required for cooling the heat shield member 30 may be fed through the openings 35 of the assembly member 27 and the through holes 38 in the clamping bracket 28.
[0025] The screw 31, which has an axial through channel 42 for cooling, can be reached with a tool through a hole 43 in the heat shield member 30.
[0026] The described heat-insulating tile 5 advantageously has a reduced thickness if compared to conventional ceramic tiles. In fact, the tile is just as thick as necessary to obtain an effective coupling with the anchorage devices 8, thanks to the shape of the anchorage seats 17, whose sloping coupling surfaces 18 extend to the hot face 10. In turn, the reduced thickness allows using the heat-insulating tile 5 in substitution of metal shields in the combustion chambers of medium-small sized gas turbines. In addition to lower production and maintenance costs, the insulating tile 5 does not require any cooling air, which may only be possibly required for the anchorage devices 8. The air tapping from the compressor is then dramatically reduced, to the advantage of the efficiency of the machine. The coupling between the mating sloping surfaces 18 and the elastic side walls 32 of the assembly member 27 of the anchorage device 8 is advantageous because the coupling forces are distributed over a wide area, thus reducing the punctual stresses, particularly close to the chamfered edges.
[0027] The advantages deriving from the anchorage device 8 are related to the fact that the cooling air flow rate is limited and comparable with the flow rate required by the known flame-exposed anchorages, but, at the same time, without the limitations that such anchorages impose on a minimum thickness of the heat-insulating tiles. On the other hand, the known flame-exposed anchorages, that have less stringent limitations on a minimum thickness, require significant amounts of cooling air, thus having an impact on the overall efficiency of the machine.
[0028] The anchorage devices 8 can be frontally coupled and removed with respect to the casing 2 of the combustion chamber 1, thus facilitating the maintenance operations. Moreover, the installation of heat-insulating tiles by the anchorage devices 8 requires only the drilling of the casing 2 for machining the coupling seats (directly or by means of interface plates) of the screws 31. No thinning processing is required which could jeopardise the structural integrity of the combustion chamber 1.
1. A heat-insulating tile of ceramic material for a combustion chamber of a gas turbine,
comprising a first face (10), a second face (11), sides (15) adjacent to the first
face (10) and to the second face (11) and anchorage seats (17) on the sides (15);
the anchorage seats (17) being defined by respective recesses open on the first face
(10) and delimited by respective coupling surfaces (18) sloping from the first face
(10) to a respective one of the sides (15).
2. A tile according to claim 1, wherein the coupling surfaces (18) are flat.
3. A tile according to claim 1 or 2, wherein the coupling surfaces (18) slope with respect
to the first face (10).
4. A tile according to claim 3, wherein the coupling surfaces (18) have an inclination
ranging between 30° and 60° with respect to the first face (10).
5. A tile according to any one of the preceding claims, wherein the coupling surfaces
(18) intercept the respective sides (15) at a height intermediate between the first
face (10) and the second face (11).
6. A tile according to any one of the preceding claims, wherein the second face (11)
has a recessed portion (21) and a raised portion (22).
7. A tile according to claim 6, wherein the raised portion (22) of the second face (11)
contours the recessed portion (21).
8. A tile according to claim 6 or 7, comprising an insulating layer (25) applied to the
raised portion (22) of the second face (11).
9. A tile according to claim 8, wherein the insulating layer (25) is made of woven heat-insulating
fibres and is shaped so as to conform to the raised portion (22) of the second face
(11).
10. A combustion chamber of a gas turbine, comprising a plurality of heat-insulating tiles
(5) according to any one of the preceding claims.
11. A combustion chamber according to claim 10, comprising a casing (2) and a heat-insulating
coating (3) arranged to protect the casing (2); at least a portion of the heat-insulating
coating (3) being defined by the heat-insulating tiles (5).
12. A combustion chamber according to claim 11, comprising a plurality of anchorage devices
(8) connecting respective heat-insulating tiles (5) to the casing (2); the sides (15)
of the heat-insulating tiles (5) having, at the respective anchorage seats (17), recessed
shaped so that two contiguous heat-insulating tiles (5) define between them a gap
(20) configured to receive a respective anchorage device (8).
13. A combustion chamber according to claim 12, wherein each anchorage device (8) comprises
a pair of diverging side walls (32) sloping to match with the coupling surfaces (18)
of respective heat-insulating tiles (5).
14. A combustion chamber according to claim 13, wherein each anchorage device (8) comprises
a heat shield member (30) arranged to close the respective gap (20).
15. A combustion chamber according to claim 14, wherein the heat shield member (30) comprises
a plate made of a temperature-resistant metallic alloy, which forms a substantially
continuous surface with the first faces (10) of the adjacent heat-insulating tiles
(5).
16. A combustion chamber according to claim 11 or 12, wherein the heat-insulating coating
(3) delimits a combustion volume (4), the first face (10) of the heat-insulating tiles
(5) is oriented toward the combustion volume (4) and the second face (11) is oriented
toward the casing (2).