High-temperature flue gas heat exchanger

Abstract

The utility model discloses a high-temperature flue gas heat exchanger, and relates to the technical field of flue gas heat exchanger equipment. The high-temperature flue gas heat exchanger comprises a shell and a heat exchange area. A flue gas inlet and a flue gas outlet are formed in the two sides of the shell in the first direction respectively; the heat exchange area is located in the middle of the shell and comprises a plurality of heat exchange plates arranged at intervals in the second direction, each heat exchange plate is provided with a water cooling medium inlet and a water cooling medium outlet, and the water cooling medium inlets and the water cooling medium outlets are used for being communicated with small water pipes. The water-cooling medium inlet and the water-cooling medium outlet are located in the same side of the heat exchange plate in the third direction and arranged at the interval of 840 mm to 2340 mm in the first direction. By adopting the technology provided by the utility model, the problem that the shell of the heat exchanger is easy to crack due to tension caused by high-temperature flue gas in the prior art can be effectively avoided.

Description

Technical Field

[0001] The utility model relates to the technical field of flue gas heat exchanger equipment, in particular to a high-temperature flue gas heat exchanger. Background Art

[0002] Various forms of flue gas are easily generated during industrial processing, and a large amount of industrial flue gas (such as flue gas from power plants, smelting, chemical plants, etc.) is high-temperature flue gas. These flue gases are not conducive to environmental protection and usually need to be cooled or further desulfurized and denitrified before they can be discharged.

[0003] At present, the flue gas cooling treatment generally uses a flue gas heat exchanger for heat exchange. However, due to the high temperature of the flue gas, ordinary flue gas heat exchangers have fast heat transfer and fast reaction time to temperature changes, which makes it easy to cause cracking due to thermal expansion and contraction. Specifically, the flue gas heat exchanger uses the cooling water inside the heat exchange plate to exchange heat with the flue gas outside the heat exchange plate, resulting in different temperatures for the shell in contact with the flue gas and the heat exchange plate in contact with the cooling water, which in turn produces different expansion amounts. Since the temperature difference between the high-temperature flue gas and the cooling water is several hundred degrees (for example, more than 600 degrees), different temperatures will produce different expansion amounts, which will cause the welding of the inlet and outlet water pipes on the heat exchange plate group to crack. Since the inlet and outlet water pipes on the heat exchange plate group are fixed on the heat exchanger shell plate, and the entire heat exchange plate group is fixed, the shell expands a lot while the cooling water inside the heat exchange plate expands a little. When the difference in expansion is large (for example, greater than 5mm), there will be a risk of cracking of the heat exchanger shell. Utility Model Content

[0004] The utility model provides a high-temperature flue gas heat exchanger to solve the problem in the prior art that the flue gas heat exchanger is easily torn due to thermal expansion and contraction.

[0005] In order to solve the above technical problems, the technical solution adopted by the utility model is to provide a high-temperature flue gas heat exchanger, which includes: a shell and a heat exchange area.

[0006] The shell is provided with a smoke inlet and a smoke outlet on both sides along the first direction respectively; the heat exchange area is located in the middle of the shell, and includes a plurality of heat exchange plates arranged at intervals along the second direction, the heat exchange plate has a water-cooling medium inlet and a water-cooling medium outlet, the water-cooling medium inlet and the water-cooling medium outlet are used to communicate with the water tube, wherein the water-cooling medium inlet and the water-cooling medium outlet are located on the same side of the heat exchange plate along the third direction, and are arranged at a spacing of 840 mm to 2340 mm along the first direction.

[0007] Compared with the prior art, the technical solution provided by the utility model has the following beneficial effects:

[0008] By setting the water-cooling medium inlet and water-cooling medium outlet of the heat exchange plate on the same side of the heat exchange plate and making the distance between them shorter, that is, the distance range is between 840mm and 2340mm, the water pipes connected to the water-cooling medium inlet and water-cooling medium outlet are not easy to cause the shell to crack due to the large temperature difference between the inside and outside of the pipe. Among them, the water pipe in the heat exchanger refers to the connecting pipe between multiple heat exchange plates and the header. As a key component of heat exchange, it is fixed inside the shell of the heat exchanger and is used to transmit water-cooling medium (heat medium). It can be a straight pipe, a spiral pipe or other shapes.

[0009] In some application scenarios, the inside of the small water tube is cooling water and the outside is high-temperature flue gas. The high-temperature flue gas will cause different expansion amounts between one side of the heat exchanger plate inside the heat exchanger and the inner wall of the shell. Based on the thermal expansion and contraction formula, the volume expansion amount is related to the temperature, expansion coefficient, etc. When the water-cooling medium inlet and the water-cooling medium outlet of the heat exchanger plate are close to each other, the small water tubes connected thereto will also be close to each other, thereby reducing the difference in expansion amount between one side of the heat exchanger plate and the inner wall of the shell, thereby effectively avoiding the difference in expansion amount exceeding the limit value of the heat exchanger without adding redundant structure.

[0010] In some embodiments, the high-temperature flue gas heat exchanger is also provided with a water-cooling medium circulation module, and the water-cooling medium circulation module includes a water-cooling medium total outlet and a water-cooling medium total inlet, wherein the water-cooling medium total outlet and the water-cooling medium total inlet are respectively connected to the small water tubes, and are arranged at intervals on one side of the shell along the first direction.

[0011] By adopting the above technical solution, a water-cooling medium circulation module is arranged to be connected with the internal water pipes to realize the circulation of the water-cooling medium and distribute the water-cooling medium to each heat exchange plate.

[0012] In some embodiments, the heat exchange plate is a cold-rolled plate, wherein the Ra value of the heat exchange plate is 100 microns to 200 microns.

[0013] Using the above technical solution, the cold-rolled plate refers to a steel plate made by a cold rolling process, and the finish of the heat exchange plate is level 1 to level 2, that is, its surface is smooth and not easy to adhere to dust or solid particles mixed in the high-temperature flue gas, and is beneficial to improving heat exchange efficiency and reducing fluid resistance.

[0014] In some embodiments, the shell is provided with a smoke inlet area and a smoke outlet area in sequence along the first direction, and the smoke inlet area and the smoke outlet area are symmetrically arranged along the first direction; wherein the smoke inlet area and the smoke outlet area are trumpet-shaped, and a smoke inlet is provided on a side with a small opening of the smoke inlet area, and a side with a large opening faces an inlet of the heat exchange area; a smoke outlet is provided on a side with a small opening of the smoke outlet area, and a side with a large opening faces an outlet of the heat exchange area.

[0015] By adopting the above technical solution, the smoke inlet and the smoke outlet are set to be trumpet-shaped, which is convenient for improving the flow characteristics of the smoke, so that it can flow evenly between the heat exchange plates in the heat exchange area and evenly flow out from the smoke outlet after fully contacting the heat exchange plates.

[0016] In some embodiments, a drain trough and a drain port are provided at the bottom of the shell along the third direction, and the drain port is located in the middle of the drain trough, wherein the drain trough is connected to the heat exchange area of ​​the shell.

[0017] By adopting the above technical solution, a drain trough is set at the bottom of the heat exchange area, so that the dirt that is not easy to adhere to the heat exchange plate can be located in the drain trough under the action of gravity and discharged along the drain outlet.

[0018] In some embodiments, the drain tank is located in the middle of the shell along the first direction, and the water-cooling medium main inlet and the water-cooling medium main outlet are located on one side of the shell along the first direction.

[0019] By adopting the above technical solution, since the internal water pipes, i.e. the water-cooling medium inlet and the water-cooling medium outlet, are located on the same side and are close to each other, the water-cooling medium total outlet and the water-cooling medium total inlet are correspondingly set at similar locations, which can reduce the length required for the internal pipeline layout.

[0020] In some embodiments, the shell is further provided with lifting ears at the top along the third direction, and the lifting ears are arranged at intervals on both sides of the heat exchange area of ​​the shell along the first direction.

[0021] By adopting the above technical solution, the lifting ears are arranged to facilitate the lifting and positioning of the equipment during transportation and installation. Among them, since the heat exchange area is the center of gravity of the heat exchanger, it is more stable to arrange the lifting ears on both sides of the heat exchange area.

[0022] In some embodiments, the heat exchange area is further provided with a cleaning door, which is located at the top of the shell along the third direction and is connected to the heat exchange area of ​​the shell, wherein the cleaning door is located between two adjacent lifting ears along the first direction.

[0023] By adopting the above technical solution, a cleaning door that can be opened and closed is added to facilitate cleaning of the heat exchange area, such as cleaning sediments and other impurities inside the heat exchanger, thereby maintaining efficient operation and heat exchange efficiency of the heat exchanger.

[0024] In some embodiments, the smoke inlet and / or the smoke outlet is a circular duct opening.

[0025] By adopting the above technical solution, the smoke inlet and the smoke outlet are set as circular pipe openings to facilitate direct connection with the external smoke pipe, wherein the trumpet shape of the smoke inlet area can effectively guide the smoke entering from the circular pipe opening.

[0026] In some embodiments, a plurality of reinforcing ribs are provided on both sides of the shell along the second direction, and the plurality of reinforcing ribs are staggered along the first direction and the third direction, wherein ear seats are further provided at the intersections of the plurality of reinforcing ribs.

[0027] By adopting the above technical solution, the strength of the shell is strengthened as a whole by the reinforcing ribs, wherein the ear seats are arranged at the connection of the reinforcing ribs, which is conducive to the firm installation of the heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work, among which:

[0029] Figure 1 This is a schematic diagram of the internal structure of an embodiment of a high-temperature flue gas heat exchanger provided by the utility model;

[0030] Figure 2 This is a three-dimensional structural schematic diagram of an embodiment of a heat exchange plate of a high-temperature flue gas heat exchanger provided by the utility model;

[0031] Figure 3 yes Figure 1 A partial enlarged view of part A;

[0032] Figure 4 This is a three-dimensional structural diagram of an embodiment of a high-temperature flue gas heat exchanger provided by the utility model. Figure 1 ;

[0033] Figure 5 This is a three-dimensional structural diagram of an embodiment of a high-temperature flue gas heat exchanger provided by the utility model. Figure 2 ;

[0034] Figure 6 It is a side view of an embodiment of a high-temperature flue gas heat exchanger provided by the utility model.

[0035] In the figure:

[0036] Shell—10; smoke inlet—11; smoke outlet—12; smoke inlet area—13; smoke outlet area—14; sewage trough—15; sewage outlet—16; lifting ear—17; cleaning door—18; reinforcing rib—19; ear seat—190;

[0037] Heat exchange area—20; heat exchange plate—21; water-cooling medium inlet—210; water-cooling medium outlet—211; small water pipe—22; water-cooling medium circulation module—30; water-cooling medium total outlet—31; water-cooling medium total inlet—32. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, rather than all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the utility model.

[0039] In order to facilitate the subsequent description, before describing the specific structure of the high-temperature flue gas heat exchanger, this application first combines Figure 4 A first direction (X), a second direction (Z), and a third direction (Y) are defined. The first direction is the length direction of the high-temperature flue gas heat exchanger when it is normally placed, such as the X direction; the second direction is the height direction of the high-temperature flue gas heat exchanger when it is normally placed, such as the Z direction; and the third direction is the width direction of the high-temperature flue gas heat exchanger when it is normally placed, such as the Y direction. In this application, the first direction (X), the second direction (Z), and the third direction (Y) are perpendicular to each other.

[0040] It can be understood that the mutual perpendicularity in the present application is not absolute perpendicularity, and the approximate perpendicularity caused by processing errors and assembly errors (for example, the angle between two structural features is 89.9°) is also within the range of mutual perpendicularity in the present application.

[0041] See also Figures 1 to 3 As shown, Figure 1 A schematic diagram of the internal structure of an embodiment of a high-temperature flue gas heat exchanger provided by the present application is shown; Figure 2 A schematic diagram of the three-dimensional structure of an embodiment of a heat exchange plate 21 of a high-temperature flue gas heat exchanger provided by the present application is shown; Figure 3 Shows Figure 1 A partial enlarged view of part A.

[0042] In order to solve the above technical problems, the technical solution adopted by the present invention is to provide a high-temperature flue gas heat exchanger, which includes: a shell 10 and a heat exchange area 20.

[0043] A smoke inlet 11 and a smoke outlet 12 are respectively provided on both sides of the shell 10 along the first direction; the heat exchange area 20 is located in the middle of the shell 10, and includes a plurality of heat exchange plates 21 arranged at intervals along the second direction, the heat exchange plate 21 has a water-cooling medium inlet 210 and a water-cooling medium outlet 211, and the water-cooling medium inlet 210 and the water-cooling medium outlet 211 are used to communicate with the water tube 22, wherein the water-cooling medium inlet 210 and the water-cooling medium outlet 211 are located on the same side of the heat exchange plate 21 along the third direction, and are arranged at a spacing of 840 mm to 2340 mm along the first direction.

[0044] In the present application embodiment, combined Figure 2 As shown, by arranging the water-cooling medium inlet 210 and the water-cooling medium outlet 211 of the heat exchange plate 21 on the same side of the heat exchange plate 21 and making the distance between them shorter, that is, the distance range is between 840mm and 2340mm, so that the water pipe 22 connected to the water-cooling medium inlet 210 and the water-cooling medium outlet 211 is not easy to cause the shell 10 to be torn due to the large temperature difference between the inside and outside of the pipe. Among them, the water pipe 22 in the heat exchanger refers to the connecting pipe between the multiple heat exchange plates 21 and the header 33. As a key component of heat exchange, it is fixed inside the shell 10 of the heat exchanger and is used to transmit the water-cooling medium (heat medium). It can be a straight pipe, a spiral pipe or other shapes.

[0045] In some application scenarios, cooling water flows inside the water tube 22 and high-temperature flue gas flows outside. Due to thermal expansion and contraction, the water tube 22 will shrink on the side close to the heat exchange plate 21 and expand on the side close to the inner wall of the shell 10, so that there is a difference in expansion between the two. When the difference in expansion is greater than 3 mm or 5 mm (that is, it reaches the limit value of the heat exchanger shell 10 according to different materials of the heat exchanger), there is a risk of cracking of the heat exchanger shell 10.

[0046] For example, when the distance between the water-cooling medium inlet 210 and the water-cooling medium outlet 211 of the heat exchange plate 21 is relatively close, Figure 3 As shown, the small water tube 22 connected thereto will also be closer, so that the temperature difference between the hot water and the cold water inside the small water tube 22 is smaller, and the difference in expansion between the side of the small water tube 22 close to the heat exchange plate 21 and the side close to the inner wall of the shell 10 is smaller, and thus, without adding redundant structures (such as adding expansion joints), the difference in expansion can be effectively avoided from exceeding the limit value of the heat exchanger, and the cracking of the heat exchanger shell 10 can be avoided at a very low cost.

[0047] In some embodiments, the heat exchange plate 21 is a cold-rolled plate, wherein the Ra value of the heat exchange plate 21 is 100 microns to 200 microns.

[0048] In the embodiment of the present application, the cold-rolled plate refers to a steel plate made by a cold rolling process, and the finish of the heat exchange plate 21 is level 1 to level 2, that is, its surface is smooth, dust or solid particles mixed in the high-temperature flue gas are not easily adhered, and it is beneficial to improve the heat exchange efficiency and reduce the fluid resistance. Exemplarily, when the distance between the water-cooling medium outlet 211 and the water-cooling medium inlet 210 of the heat exchange plate 21 is between 840 mm and 2340 mm, the length of the heat exchange plate 21 is 1 m to 2 m.

[0049] In some embodiments, a drain trough 15 and a drain port 16 are provided at the bottom of the shell 10 along the third direction, and the drain port 16 is located in the middle of the drain trough 15 , wherein the drain trough 15 is connected to the heat exchange area 20 of the shell 10 .

[0050] In the present application embodiment, combined Figure 1 As shown, a drain trough 15 is provided at the bottom of the heat exchange area 20 , so that dirt that is not easily adhered to the heat exchange plates 21 can be located in the drain trough 15 under the action of gravity and discharged along the drain outlet 16 .

[0051] In some embodiments, the drain tank 15 is located in the middle of the shell 10 along the first direction, and the water-cooling medium main inlet 31 and the water-cooling medium main outlet 32 ​​are located on one side of the shell 10 along the first direction.

[0052] Since the internal water pipe 22, i.e. the water-cooling medium inlet 210 and the water-cooling medium outlet 211 are located on the same side and are close to each other, the water-cooling medium main outlet 32 ​​and the water-cooling medium main inlet 31 are correspondingly arranged at a close location, which can reduce the length required for the internal pipeline layout.

[0053] See also Figure 4 As shown, Figure 4 The three-dimensional structure diagram of an embodiment of a high-temperature flue gas heat exchanger provided by the present application is shown in FIG. Figure 1 .

[0054] In some embodiments, the high-temperature flue gas heat exchanger is also provided with a water-cooling medium circulation module 30, which includes a water-cooling medium total outlet 32 ​​and a water-cooling medium total inlet 31, wherein the water-cooling medium total outlet 32 ​​and the water-cooling medium total inlet 31 are respectively connected to the small water tube 22, and are arranged at intervals on one side of the shell 10 along the first direction.

[0055] In the present application embodiment, combined Figure 3 to Figure 4As shown, a water-cooling medium circulation module 30 is provided to communicate with the internal water pipe 22 to realize the circulation of the water-cooling medium and distribute the water-cooling medium to each heat exchange plate 21. Specifically, the water-cooling medium total outlet 32 ​​and the water-cooling medium total inlet 31 are also connected to the header 33. When the water-cooling medium (such as cooling water, waste water) flows into the header 33 through the water-cooling medium total inlet 31, it is distributed to the inside of each heat exchange plate 21 by the header 33, and then integrated into the water-cooling medium total outlet 32 ​​by another header 33 to realize the heat recovery of the flue gas.

[0056] See also Figure 5 and Figure 6 As shown, Figure 5 The three-dimensional structure diagram of an embodiment of a high-temperature flue gas heat exchanger provided by the present application is shown in FIG. Figure 2 ; Figure 6 A side view of an embodiment of a high-temperature flue gas heat exchanger provided in the present application is shown.

[0057] In some embodiments, the shell 10 is sequentially provided with a smoke inlet area 13 and a smoke outlet area 14 along a first direction, and the smoke inlet area 13 and the smoke outlet area 14 are symmetrically arranged along the first direction; wherein, the smoke inlet area 13 and the smoke outlet area 14 are trumpet-shaped, and a smoke inlet 11 is provided on a side with a smaller opening of the smoke inlet area 13, and a side with a larger opening faces an entrance to the heat exchange area 20; a smoke outlet 12 is provided on a side with a smaller opening of the smoke outlet area 14, and a side with a larger opening faces the exit to the heat exchange area 20.

[0058] In the embodiment of the present application, the smoke inlet 11 and the smoke outlet 12 are set to be trumpet-shaped, so as to improve the flow characteristics of the smoke, so that the smoke can flow evenly between the heat exchange plates 21 of the heat exchange area 20, and after fully contacting the heat exchange plates 21, flow out evenly from the smoke outlet 12.

[0059] Exemplarily, the smoke inlet 11 and / or the smoke outlet 12 are circular duct openings to facilitate direct connection with an external smoke duct, wherein the trumpet shape of the smoke inlet area 13 can effectively guide the smoke entering from the circular duct opening.

[0060] In some embodiments, the top of the shell 10 along the third direction is further provided with a lifting lug 17 , and the lifting lug 17 is spaced apart on both sides of the heat exchange area 20 of the shell 10 along the first direction.

[0061] In the embodiment of the present application, the lifting lugs 17 are provided to facilitate lifting and positioning of the equipment during transportation and installation. Since the heat exchange area 20 serves as the center of gravity of the heat exchanger, it is more stable to provide the lifting lugs 17 on both sides of the heat exchange area 20.

[0062] In some embodiments, the heat exchange area 20 is further provided with a cleaning door 18, which is located at the top of the shell 10 along the third direction and is connected to the heat exchange area 20 of the shell 10, wherein the cleaning door 18 is located between two adjacent lifting ears 17 along the first direction.

[0063] In the embodiment of the present application, a cleaning door 18 that can be opened and closed is additionally provided to facilitate cleaning of the heat exchange area 20, such as cleaning sediments and other impurities inside the heat exchanger, thereby maintaining efficient operation and heat exchange efficiency of the heat exchanger.

[0064] In some embodiments, a plurality of reinforcing ribs 19 are provided on both sides of the housing 10 along the second direction, and the plurality of reinforcing ribs 19 are staggered along the first direction and the third direction, wherein ear seats 190 are further provided at the intersections of the plurality of reinforcing ribs 19. The strength of the housing 10 is strengthened as a whole by the reinforcing ribs 19, wherein the ear seats 190 are provided at the connection of the reinforcing ribs 19, which is conducive to the firm installation of the heat exchanger.

[0065] The above description is only an implementation method of the present utility model, and does not limit the patent scope of the present utility model. Any equivalent structure or equivalent process transformation made using the contents of the specification and drawings of the present utility model, or directly or indirectly used in other related technical fields, should be included in the protection scope of the present utility model.

Claims

1. A high-temperature flue gas heat exchanger, characterized in that: include: A shell, wherein two sides of the shell along a first direction are respectively provided with a smoke inlet and a smoke outlet; A heat exchange area, the heat exchange area is located in the middle of the shell, and includes a plurality of heat exchange plates spaced apart along the second direction, the heat exchange plates having a water-cooling medium inlet and a water-cooling medium outlet, the water-cooling medium inlet and the water-cooling medium outlet are used to communicate with a small water tube, wherein the water-cooling medium inlet and the water-cooling medium outlet are located on the same side of the heat exchange plate along the third direction, and are spaced apart from each other by 840 mm to 2340 mm along the first direction.

2. The high-temperature flue gas heat exchanger according to claim 1, characterized in that: The high-temperature flue gas heat exchanger is also provided with a water-cooling medium circulation module, which includes a water-cooling medium total outlet and a water-cooling medium total inlet, wherein the water-cooling medium total outlet and the water-cooling medium total inlet are respectively connected to the small water tubes and are arranged at intervals on one side of the shell along the first direction.

3. The high-temperature flue gas heat exchanger according to claim 1, characterized in that: The heat exchange plate is a cold-rolled plate, wherein the Ra value of the heat exchange plate is 100 microns to 200 microns.

4. The high-temperature flue gas heat exchanger according to claim 1, characterized in that: The shell is sequentially provided with a smoke inlet area and a smoke outlet area along the first direction, and the smoke inlet area and the smoke outlet area are symmetrically arranged along the first direction; wherein the smoke inlet area and the smoke outlet area are trumpet-shaped, and a smoke inlet is provided on a side with a small opening of the smoke inlet area, and a side with a large opening faces an inlet of the heat exchange area; a smoke outlet is provided on a side with a small opening of the smoke outlet area, and a side with a large opening faces an outlet of the heat exchange area.

5. The high-temperature flue gas heat exchanger according to claim 1, characterized in that: The shell is provided with a drain groove and a drain port at the bottom along the third direction, wherein the drain port is located in the middle of the drain groove, wherein the drain groove is connected to the heat exchange area of ​​the shell.

6. The high-temperature flue gas heat exchanger according to claim 2 or 5, characterized in that: The sewage drain is located in the middle of the shell along the first direction, and the water-cooling medium total inlet and the water-cooling medium total outlet are located on one side of the shell along the first direction.

7. The high-temperature flue gas heat exchanger according to claim 1, characterized in that: The top of the shell along the third direction is further provided with lifting ears, and the lifting ears are arranged at intervals on both sides of the heat exchange area of ​​the shell along the first direction.

8. The high-temperature flue gas heat exchanger according to claim 7, characterized in that: The heat exchange area is also provided with a cleaning door, which is located at the top of the shell along the third direction and communicates with the heat exchange area of ​​the shell, wherein the cleaning door is located between two adjacent lifting ears along the first direction.

9. The high-temperature flue gas heat exchanger according to claim 1, characterized in that: The smoke inlet and / or smoke outlet is a circular pipe opening.

10. The high-temperature flue gas heat exchanger according to claim 1, characterized in that: The shell is provided with a plurality of reinforcing ribs on both sides along the second direction, and the plurality of reinforcing ribs are staggered along the first direction and the third direction, wherein ear seats are further provided at the intersections of the plurality of reinforcing ribs.

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