Circulating fluidized bed boiler air chamber structure with water-cooling slag pipe
By adopting a water-cooled slag tube structure in a circulating fluidized bed boiler, the problem of slag discharge tube expansion under high-temperature conditions was solved, thus achieving stable boiler operation and improved safety.
Patent Information
- Application Number
- CN202423088861.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-14
- Publication Date
- 2025-11-21
- Estimated Expiration
- 2034-12-14
AI Technical Summary
The ash discharge pipes of existing circulating fluidized bed boilers are prone to expansion under high temperature conditions, which can lead to breakage or cracking at the welds, affecting the safety and stability of the boiler. In addition, the traditional expansion joint design has wear and blockage problems.
The slag discharge channel adopts a water-cooled slag pipe structure. The slag discharge channel is composed of a water-cooled membrane wall and wear-resistant castable. The internal temperature of the left and right membrane walls is consistent with that of the furnace air chamber. The whole structure expands and is combined with refractory and wear-resistant castable to prevent wear. The header is tightly welded to the water-cooled air chamber to ensure airtightness.
It effectively prevents wear and deformation of the slag discharge pipe, ensures the stability of boiler operation, avoids slag leakage and blockage, and improves the safety and long-term operating efficiency of the boiler.
Smart Images
Figure CN223579905U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to a kind of wind chamber structure, especially a kind of primary air chamber structure of circulating fluidized bed boiler, belong to circulating fluidized bed boiler technical field. BACKGROUND
[0002] Circulating fluidized bed boiler is usually composed of combustion system, gas-solid separation and return device, tail part convection flue and auxiliary equipment, wherein combustion system is the important component of circulating fluidized bed boiler, and the parameters such as bed temperature, material layer differential pressure, furnace negative pressure, which are mainly operated and monitored, are all embodied in boiler combustion system, and the adjustment of combustion system is related to the safety, economy and environmental protection of the whole boiler operation, and its role is very prominent;Combustion system mainly includes furnace, combustion chamber, air distribution plate, primary air chamber and slagging device.
[0003] The most important component in slagging device is slagging pipe, which continuously or intermittently discharges, so that the solid bed of boiler maintains appropriate height, effectively controls material circulation, and makes material layer differential pressure control within reasonable range, so that combustion reaction is more sufficient, and boiler thermal efficiency is improved. Through slagging work, impurities and harmful substances in bed can also be cleaned regularly, to avoid the occurrence of problems such as blockage, coking and corrosion in bed. Therefore, the normal operation of slagging pipe is crucial for stable combustion of boiler, and the structure of slagging pipe also determines whether the slagging work of boiler can be carried out safely and stably for a long time.
[0004] The existing slagging mode is generally that slagging pipe is arranged at the bottom of furnace of circulating fluidized bed boiler, for discharging slag in furnace, the slagging pipe is arranged to discharge slag after passing through the bottom plate of air chamber, the lower end of slagging pipe is connected with slagging valve after extending out of air chamber. When slagging is needed, slagging valve is opened, so that ash and slag are discharged from the bottom of furnace through slagging pipe. The upper end of slagging pipe is welded and connected with slagging port on air distribution plate at the top of water-cooled air chamber, the lower end of slagging pipe is connected with slag cooler in sequence after passing through water-cooled air chamber and slagging pipe passing hole on the bottom plate of water-cooled air chamber, and the slagging pipe and the passing hole on the bottom plate of water-cooled air chamber are also fixed together by welding, to prevent leakage and spattering of slag at the contact part between the lower part of slagging pipe and the water-cooled wall of primary air chamber. During the operation of boiler, high-temperature slag passes through slagging pipe, and since the temperature of slag is generally above 800℃, it will cause large axial displacement of slagging pipe, so that the expansion amount of slagging pipe is greater than the expansion amount of boiler body. Although this fixed connection mode solves the problems of leakage and spattering of slag, it limits the thermal expansion of slagging pipe. When the expansion force exceeds the stress limit of slagging pipe, cracking will occur at the weak part of pipe, and then the whole slag pipe will be broken. When the expansion stress of slagging pipe cannot be completely released, it will impact the welded part of slagging pipe and water-cooled air chamber, so that the welded part is cracked, which causes the failure of slagging pipe and leakage of water-cooled wall of primary air chamber.
[0005] For this reason, the prior art has made some improvements to the structure of the slag discharge pipe, and a metal expansion joint is designed at the slag discharge pipe: some are designed separately in the primary air chamber, and some are designed separately outside the primary air chamber. Designing a metal expansion joint in the primary air chamber, the expansion joint can effectively absorb the thermal expansion of the slag discharge pipe, solving the problem of cracking and cracking caused by the expansion of the slag discharge pipe. However, the temperature in the primary air chamber is much higher than the ambient temperature, and the long-term high temperature and the ash and slag leaking into the primary air chamber will have a serious impact on the corrugated part of the expansion joint, which is easy to cause residual deformation of the elastic element of the expansion joint, seriously affecting the service life and safety of the expansion joint. Designing a metal expansion joint outside the primary air chamber allows the slag discharge pipe to slide relative to the primary air chamber water cooling wall, which also solves the problem caused by the expansion of the slag discharge pipe. However, the ash and slag leaking into the primary air chamber will accumulate at the sliding contact, causing blockage, making the slag discharge pipe and the primary air chamber water cooling wall relative sliding, and limiting the free expansion of the slag pipe. The expansion stress cannot be fully released, and stress failure phenomenon will still occur, affecting the long-term, efficient and safe operation of the boiler.
[0006] Figure 1 An expansion sealing structure of a fluidized bed boiler slag discharge pipe is shown, the slag discharge pipe 1 is installed in the air chamber of the furnace, the upper end of the slag discharge pipe 1 is connected with the air distribution plate 2 in the furnace, and the air distribution plate 2 has evenly distributed air caps, the lower end of the slag discharge pipe 1 is connected with the slag discharge valve after extending out of the air chamber. When slag needs to be discharged, the slag discharge valve is opened, and the ash and slag are discharged from the bottom of the furnace through the slag discharge pipe 1, the air enters the air chamber through the air inlet, and then enters the furnace through the air cap. The weight of the entire slag discharge pipe 1 is borne by the weld between the upper end of the slag discharge pipe 1 and the air distribution plate 2, the lower end of the slag discharge pipe 1 is sealed with the air chamber bottom plate 3 by using a metal expansion joint 5 at the position where the air chamber bottom plate 3 is penetrated, and the lower end of the slag discharge pipe 1 is not welded with the air chamber bottom plate 3. This structure can meet the expansion sealing requirements in a short time, but when the boiler is operated in an intermittent slag discharge mode, the temperature of the slag discharge pipe 1 also changes periodically and sharply, and the metal expansion joint 5 at the position where the air chamber bottom plate 3 is penetrated is prone to fatigue failure and air leakage, which forms an accident hazard and affects the normal and safe operation of the boiler. SUMMARY
[0007] The utility model discloses a circulating fluidized bed boiler air chamber structure with water-cooled slag pipe to overcome the defects of the prior art.
[0008] The utility model discloses the technical scheme adopted for realizing the above-mentioned purpose is:
[0009] The application discloses a circulating fluidized bed boiler air chamber structure with a water-cooled slag pipe, which comprises an air chamber composed of a membrane water-cooled wall and a slag discharge pipe, the top wall of the air chamber is a wind distribution plate, the upper end of the slag discharge pipe is connected with the wind distribution plate, and the lower end of the slag discharge pipe extends out of the air chamber; the membrane water-cooled wall is an air-tight tube panel formed by connecting multiple large C-shaped pipes in parallel through flat steel, the two ends of each large C-shaped pipe are connected with an upper right header of the air chamber and a lower right header of the air chamber respectively, and the slag discharge pipe is located between two adjacent large C-shaped pipes.
[0010] In the air chamber structure of the circulating fluidized bed boiler with the water-cooled slag pipe, the slag pipe water-cooled membrane wall comprises a left membrane wall and a right membrane wall, the left membrane wall comprises a left flat steel and an inverted C-shaped pipe, the right membrane wall comprises a right flat steel and a C-shaped pipe, the left flat steel connects multiple inverted C-shaped pipes in parallel to form an air-tight tube panel, and the right flat steel connects multiple C-shaped pipes in parallel to form an air-tight tube panel; the inverted C-shaped pipe and the bottom of the C-shaped pipe form the slag discharge channel.
[0011] Further, the air chamber structure further comprises a left lower header of the air chamber and a left upper header of the air chamber, the bottom of the inverted C-shaped pipe is connected through the left flat steel, the two ends of the inverted C-shaped pipe are connected with the left upper header of the air chamber and the left lower header of the air chamber respectively, the bottom of the C-shaped pipe is connected through the right flat steel, the two ends of the C-shaped pipe are connected with the right upper header of the air chamber and the right lower header of the air chamber respectively, and the left flat steel and the right flat steel are connected with each other in a head-to-tail mode.
[0012] By adopting the technical scheme, the left membrane wall and the right membrane wall forming the slag discharge channel of the slag discharge pipe are water-cooled membrane wall structures, and the inner sides are provided with refractory castable materials; the slag discharge channel adopts the water-cooled membrane wall structure, the internal working medium temperature of the left membrane wall and the right membrane wall is consistent with the internal working medium temperature of the membrane wall of the furnace air chamber, so that the slag discharge channel and the furnace air chamber expand downward as a whole, and there is no expansion difference between the two, meanwhile, the membrane wall structure ensures the sealing property, and the ash and slag cannot leak out. The inner sides of the slag discharge channel are provided with the refractory castable materials, which can prevent the left membrane wall and the right membrane wall from being abraded and deformed by the high-temperature ash and slag, and prevent the slag discharge device from being damaged. The left upper header of the air chamber, the left lower header of the air chamber, the left membrane wall and the right membrane wall are embedded in the original water-cooled air chamber structure, are tightly welded with each other, and the sealing property is ensured.
[0013] Further, multiple inverted C-shaped short pipes are arranged between the left upper header of the air chamber, the left lower header of the air chamber and the inverted C-shaped pipes, each inverted C-shaped short pipe is located between two adjacent inverted C-shaped pipes, the bottom of each inverted C-shaped short pipe is connected through flat steel, and the two ends of the inverted C-shaped short pipe are connected with the left upper header of the air chamber and the left lower header of the air chamber respectively.
[0014] By adopting the technical scheme, a plurality of reverse C-shaped short pipes are arranged between the left upper header tank of the air chamber, the left lower header tank of the air chamber and the reverse C-shaped pipe, the open end of the reverse C-shaped pipe can be blocked, and the sealing of the air chamber is ensured.
[0015] In the air chamber structure of the circulating fluidized bed boiler with the water-cooled slag pipe, the upper end of the wear-resistant castable built in the slag discharge passage is connected with the bed surface castable on the air distribution plate.
[0016] By adopting the technical scheme, the upper end of the wear-resistant castable built in the slag discharge passage is connected with the bed surface castable on the air distribution plate, the problem of traditional slag pipe wear is solved, and the operation stability of the boiler is significantly improved.
[0017] In the air chamber structure of the circulating fluidized bed boiler with the water-cooled slag pipe, the lower end of the slag discharge pipe is connected with a slag pipe joint.
[0018] By adopting the technical scheme, the lower end of the slag discharge pipe is connected with the slag pipe joint, and the slag discharge valve and other facilities can be conveniently connected.
[0019] In the air chamber structure of the circulating fluidized bed boiler with the water-cooled slag pipe, the cross section of the slag discharge pipe is circular.
[0020] In the air chamber structure of the circulating fluidized bed boiler with the water-cooled slag pipe, the cross section of the slag discharge pipe is rectangular.
[0021] By adopting the technical scheme, the cross section of the slag discharge pipe can be set as a circular shape, a rectangular shape, a square shape, a waist circular shape and other suitable shapes according to actual needs. Advantages
[0022] The expansion sealing structure of the slag discharge pipe of the fluidized bed boiler of the utility model is arranged between the two large C-shaped pipes constituting the air chamber, the slag discharge pipe comprises a slag pipe water-cooled membrane wall and wear-resistant castable, the slag discharge pipe water-cooled membrane wall forms a slag discharge passage, and the wear-resistant castable is built in the slag discharge passage. Since the left membrane wall and the right membrane wall constituting the slag discharge passage of the slag discharge pipe are water-cooled membrane wall structures, the temperature of the working medium in the left membrane wall and the right membrane wall is consistent with the temperature of the working medium in the membrane wall of the furnace air chamber, the slag discharge passage and the furnace air chamber expand downward as a whole, and there is no expansion difference between the two. Meanwhile, the slag discharge passage composed of the membrane water-cooled wall structure and the refractory castable can effectively ensure the sealing of the slag discharge passage, prevent the leakage of ash and slag, and prevent the left membrane wall and the right membrane wall from being abraded and deformed by high-temperature ash and slag, thereby preventing the slag discharge device from being damaged. The left upper header tank of the air chamber, the left lower header tank of the air chamber, the left membrane wall and the right membrane wall are embedded in the original water-cooled air chamber structure, are tightly welded with each other, and the sealing is ensured. BRIEF DESCRIPTION OF DRAWINGS
[0023] Figure 1It is a structural schematic view of the existing technology fluidized bed boiler slag tapping pipe and air chamber.
[0024] Figure 2 It is a top view schematic diagram of the embodiment one of the utility model.
[0025] Figure 3 It is Figure 2 A-A section view schematic diagram in it.
[0026] Figure 4 It is Figure 2 B-B section view schematic diagram in it.
[0027] Figure 5 It is a top view schematic diagram of the embodiment two of the utility model.
[0028] Figure 6 It is a top view schematic diagram of the embodiment three of the utility model.
[0029] Figure 7 It is a top view schematic diagram of the embodiment four of the utility model.
[0030] In the drawing: 1 is slag tapping pipe, 2 is air distribution plate, 3 is air chamber bottom plate, 4 is big C type pipe, 5 is metal expansion joint, 6 is C type pipe, 7 is reverse C type short pipe, 8 is reverse C type pipe, 9 is air chamber right lower header, 10 is air chamber right upper header, 11 is air chamber left lower header, 12 is air chamber left upper header, 13 is slag pipe joint, 14 is wear-resistant castable, 15 is flat steel, 16 is left flat steel, 17 is right flat steel. Specific implementation
[0031] In order to clearly illustrate the technical features of the scheme, the utility model is further described below through non-limiting examples and in conjunction with the drawings. Embodiment one:
[0032] See Figures 2 to 4 A circulating fluidized bed boiler air chamber structure with water-cooled slag pipe, including the air chamber and slag pipe by membrane water wall, the top wall of the air chamber is air distribution plate, and the air distribution plate is provided with the air cap assembly communicated with the air chamber, which provides combustion-supporting air for the hearth, the upper end of the slag pipe is connected with the air distribution plate, and the lower end of the slag pipe extends out of the air chamber, the membrane water wall is a gas-tight tube panel formed by connecting multiple big C type pipes side by side with flat steel, and the two ends of each big C type pipe are connected with the air chamber right upper header and the air chamber right lower header respectively, in the embodiment, the slag pipe is arranged at the middle position of the air distribution plate and located between the adjacent two big C type pipes, the slag pipe includes slag pipe water-cooled membrane wall and wear-resistant castable, the slag pipe water-cooled membrane wall encloses to form a slag tapping channel, and the wear-resistant castable is built in the slag tapping channel.
[0033] Specifically, the slag pipe water-cooled membrane wall comprises a left membrane wall and a right membrane wall, the left membrane wall comprises a left flat steel and a plurality of reverse C-shaped tubes, and the right membrane wall comprises a right flat steel and a plurality of C-shaped tubes, the left flat steel connects the plurality of reverse C-shaped tubes in parallel to form an airtight tube panel, and the right flat steel connects the plurality of C-shaped tubes in parallel to form an airtight tube panel; the reverse C-shaped tubes and the bottoms of the C-shaped tubes form a slag discharging channel with a rectangular cross section, and the rectangular cross section can be a square or a rectangle.
[0034] The wind chamber structure of the embodiment further comprises a wind chamber lower left header and a wind chamber upper left header; the bottoms of the reverse C-shaped tubes are connected by the left flat steel, and the two ends of the reverse C-shaped tubes are connected with the wind chamber upper left header and the wind chamber lower left header respectively; the bottoms of the C-shaped tubes are connected by the right flat steel, and the two ends of the C-shaped tubes are connected with the wind chamber upper right header and the wind chamber lower right header respectively; the left flat steel and the right flat steel are connected head to tail with each other.
[0035] A plurality of reverse C-shaped short tubes are arranged between the wind chamber upper left header, the wind chamber lower left header and the reverse C-shaped tubes, each reverse C-shaped short tube is located between two reverse C-shaped tubes adjacent to each other, the bottoms of the reverse C-shaped short tubes are connected by the flat steel, and the two ends of the reverse C-shaped short tubes are connected with the wind chamber upper left header and the wind chamber lower left header respectively.
[0036] The upper end of the wear-resistant castable built in the slag discharging channel is connected with the bed surface castable on the air distribution plate. In order to make the wear-resistant castable built in the slag discharging channel more firm, a plurality of V-shaped nails are arranged on the surface of the slag pipe water-cooled membrane wall, the V-shaped vertexes are welded to the surface of the slag pipe water-cooled membrane wall, and the nails can also adopt Y-shaped or other known structures.
[0037] The lower end of the slag discharging pipe is connected with a slag pipe joint, the slag pipe joint is connected with a slag discharging valve, and the lower part of the slag discharging valve is provided with a slag cooler.
[0038] In the embodiment, the wind chamber water-cooled wall is connected with the overall water (steam) circulation system of the boiler through the wind chamber upper right header and the wind chamber lower right header, the slag pipe water-cooled membrane wall is connected with the overall water (steam) circulation system of the boiler through the wind chamber upper right header, the wind chamber lower right header, the wind chamber upper left header and the wind chamber lower left header, and of course, an independent circulation system can also be connected; the specific circulation loop is as follows:
[0039] The wind chamber lower right header 9, the large C-shaped tube 4 and the wind chamber upper right header 10 constitute the main structure of the water-cooled wind chamber.
[0040] The wind chamber lower right header 9, the C-shaped tube 6 and the wind chamber upper right header 10 constitute the right membrane wall structure of the slag pipe water-cooled membrane wall.
[0041] The wind chamber lower left header 11, the reverse C-shaped tube 8 and the wind chamber upper left header 12 constitute the left membrane wall structure of the slag pipe water-cooled membrane wall.
[0042] The left lower header tank 11 of the air chamber, the reverse C-shaped short pipe 7 and the left upper header tank 12 of the air chamber form a structure for complementing the gap on the left side of the air chamber and ensuring the sealing of the whole water-cooled air chamber. Example two:
[0043] See Figure 5 The water-cooled membrane wall of the slag pipe of the circulating fluidized bed boiler air chamber structure comprises a left membrane wall and a right membrane wall, the left membrane wall comprises a left flat steel and a reverse C-shaped pipe, the right membrane wall comprises a right flat steel and a C-shaped pipe, the left flat steel connects a plurality of reverse C-shaped pipes in parallel to form an airtight pipe screen, and the right flat steel connects a plurality of C-shaped pipes in parallel to form an airtight pipe screen. Example three:
[0044] See Figure 6 The water-cooled membrane wall of the slag pipe of the circulating fluidized bed boiler air chamber structure comprises a left membrane wall and a right membrane wall, the left membrane wall comprises a left flat steel and a reverse C-shaped pipe, the right membrane wall comprises a right flat steel and a C-shaped pipe, the left flat steel connects a plurality of reverse C-shaped pipes in parallel to form an airtight pipe screen, and the right flat steel connects a plurality of C-shaped pipes in parallel to form an airtight pipe screen. Example four:
[0045] See Figure 7 The water-cooled membrane wall of the slag pipe of the circulating fluidized bed boiler air chamber structure comprises a left membrane wall and a right membrane wall, the left membrane wall comprises a left flat steel and a reverse C-shaped pipe, the right membrane wall comprises a right flat steel and a C-shaped pipe, the left flat steel connects a plurality of reverse C-shaped pipes in parallel to form an airtight pipe screen, and the right flat steel connects a plurality of C-shaped pipes in parallel to form an airtight pipe screen.
[0046] In the description of the utility model, it is to be explained that, the terms "left", "right", "front", "back", "upper", "lower", "inner", "outer" and the like indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, and the above terms are only for the convenience of describing the utility model and simplifying the description, and are not indicative or suggestive of the devices or elements indicated must have a specific orientation, a specific orientation and operation, and therefore cannot be understood as a limitation on the utility model.
[0047] Unless otherwise clearly indicated and limited, the terms "mounting", "connected", "connecting" should be understood broadly, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection, can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.
[0048] In addition to the technical features described in the specification, they are known to those skilled in the art.
[0049] The above-mentioned embodiments are only for understanding the present application, and are not a limitation on the technical solutions described in the present application. Those skilled in the art can make various changes or modifications on the basis of the technical solutions described in the claims, and all equivalent changes or modifications should be covered within the protection scope of the claims of the present application.
Claims
1. A circulating fluidized bed boiler air chamber structure with a water-cooled slag pipe, comprising an air chamber composed of a membrane water-cooled wall and a slag discharge pipe, wherein the top wall of the air chamber is an air distribution plate, the upper end of the slag discharge pipe is connected to the air distribution plate, and the lower end of the slag discharge pipe extends out of the air chamber; the membrane water-cooled wall is an airtight tube screen formed by connecting multiple large C-shaped tubes side by side with flat steel, and both ends of each large C-shaped tube are respectively connected to the upper right header and the lower right header of the air chamber, characterized in that: The slag discharge pipe is located between two adjacent large C-shaped pipes; the slag discharge pipe includes a water-cooled membrane wall and a wear-resistant castable, the water-cooled membrane wall of the slag pipe encloses to form a slag discharge channel, and the wear-resistant castable is built into the slag discharge channel.
2. The structure of the air chamber of a circulating fluidized bed boiler with a water-cooled slag pipe according to claim 1, characterized in that: The slag pipe water-cooled membrane wall includes a left membrane wall and a right membrane wall. The left membrane wall includes a left flat steel and an inverted C-shaped tube, and the right membrane wall includes a right flat steel and a C-shaped tube. The left flat steel connects multiple inverted C-shaped tubes side by side to form an airtight tube screen, and the right flat steel connects multiple C-shaped tubes side by side to form an airtight tube screen. The bottom of the inverted C-shaped tube and the C-shaped tube enclose each other to form a slag discharge channel.
3. The structure of the air chamber of a circulating fluidized bed boiler with a water-cooled slag pipe according to claim 2, characterized in that: It also includes a lower left header and an upper left header of the air chamber; the bottom of the inverted C-shaped tube is connected by a left flat steel, and the two ends of the inverted C-shaped tube are respectively connected to the upper left header and the lower left header of the air chamber; the bottom of the C-shaped tube is connected by a right flat steel, and the two ends of the C-shaped tube are respectively connected to the upper right header and the lower right header of the air chamber; the left flat steel and the right flat steel are connected end to end to each other.
4. The structure of the air chamber of a circulating fluidized bed boiler with a water-cooled slag pipe according to claim 3, characterized in that: Multiple inverted C-shaped short pipes are installed between the upper left header and the lower left header of the air chamber and the inverted C-shaped pipe. Each inverted C-shaped short pipe is located between two adjacent inverted C-shaped pipes. The bottom of each inverted C-shaped short pipe is connected by a flat steel bar, and the two ends of the inverted C-shaped short pipe are respectively connected to the upper left header and the lower left header of the air chamber.
5. The structure of the air chamber of a circulating fluidized bed boiler with a water-cooled slag pipe according to claim 1, characterized in that: The upper end of the wear-resistant castable lining built in the slag discharge channel is connected to the bed surface castable lining on the air distribution plate.
6. The structure of a circulating fluidized bed boiler air chamber with a water-cooled slag pipe according to claim 1, 2, 3, 4, or 5, characterized in that: The lower end of the slag discharge pipe is connected to a slag pipe joint.
7. The structure of the air chamber of a circulating fluidized bed boiler with a water-cooled slag pipe according to claim 1, 2, 3, 4, or 5, characterized in that: The slag discharge pipe has a circular cross-section.
8. The structure of a circulating fluidized bed boiler air chamber with a water-cooled slag pipe according to claim 1, 2, 3, 4, or 5, characterized in that: The cross-section of the slag discharge pipe is rectangular.