Settling tray

Abstract

The invention relates to a settling tower tray which comprises a liquid receiving area, a tower tray plate, an overflow weir and a downcomer, and further comprises a gas rising pipe, the gas rising pipe is provided with an upward top end opening at the top end and a downward bottom end opening at the bottom end, and the whole pipe wall, between the top end opening and the bottom end opening, of the gas rising pipe is closed; an opening in the bottom end of the riser is communicated with the tower tray hole in the tower tray plate and is tightly connected or integrally formed with the tower tray plate on the whole circumference; the gas rising cap is designed to shield the whole area of the opening in the top end of the gas rising pipe on the upper portion, and a downward opening communicated with the interior of the gas rising pipe is jointly defined by the gas rising cap and the opening in the top end of the gas rising pipe on at least part of the perimeter of the lower edge of the gas rising cap; and the lower edge of the gas raising cap is not higher than the upper edge of the outlet weir.

Description

Technical Field

[0001] The invention relates to a settling tower tray. Background Art

[0002] In many industries such as petrochemical, coal chemical, chlor-alkali industry, fertilizer industry, etc., tower separation often encounters blockage problems. Some of them are because the gas or liquid materials to be treated contain solid substances such as dust, sediment, coke powder, catalysts, etc., and some high-melting point substances (such as inorganic salts, polymers and other solids) that are prone to scaling or coking are generated during the mass transfer process due to heating or chemical reactions.

[0003] When using a plate tower, these solid substances will be deposited on the tray, downcomer or liquid receiving area, hindering the passage of gas or liquid, blocking the sieve holes, floating valves, fixed valves and other bubbling units, and affecting the mass transfer efficiency and processing capacity of the tray. Scaling and solid particles in the material partially or completely block the gas or liquid channels, which will reduce the separation efficiency of the tray, and in severe cases, even completely lose the separation function, causing the tray to be unable to work, and it has to be frequently stopped for cleaning and put back into use after treatment, which seriously affects normal production.

[0004] In the prior art, some technical solutions have been proposed for extending the usable time of the tower tray by increasing the height of the riser and the overflow weir.

[0005] Chinese utility model CN ​​201394374Y discloses a deep liquid layer anti-blocking tower plate, a rectangular or square tower plate hole is opened on the horizontal tower plate installed in the tower, and each tower plate hole corresponds to an anti-blocking type spray hood, a separation plate for gas-liquid separation is installed on the top of the spray hood, and spray plates with spray holes are installed on the upper parts of both sides of the spray hood, and anti-blocking plates are installed on the lower parts of both sides of the spray hood, and a liquid channel is provided between the spray plate and the anti-blocking plate of the spray hood. The liquid that flows down from the downcomer of the upper tower plate and is higher than the liquid channel enters the spray hood from the channel, and the gas enters the rectangular tower plate hole from the bottom of each tower plate and then enters the spray hood. The gas in the spray hood carries the liquid and sprays out from the spray hole on the spray plate, and the gas and liquid are thus transferred for mass and heat. Then, the gas and liquid are separated at the separation plate, the gas enters the upper tower plate, the liquid falls back to the tower plate, and flows to the lower tower plate through the downcomer. The space below the anti-blocking plate is used to settle the easily blocked substances contained in the liquid.

[0006] Chinese utility model CN ​​203971435 U discloses an anti-blocking type fixed valve tower plate, wherein a number of risers are evenly distributed on the tower plate, the risers are embedded in the tower plate and are higher than the tower plate by a certain height, and each riser is provided with a corresponding shielding structure, the shielding structure includes a horizontal top plate and at least two side plates, the horizontal top plate is located above the riser and has a gap with the upper end of the riser, the side plate is located on the outside of the riser and has a gap with the wall of the riser, the bottom end of the side plate is sealed with the tower plate, and the top end of the side plate is sealed with the horizontal top plate to support the horizontal top plate. Injection holes are provided on the side plates of the shielding structure. After sufficient contact between gas and liquid, the gas and liquid leave the shielding structure through the injection holes or the side of the shielding structure without side plates. Solid matter in the liquid settles in the area at the bottom of the riser without injection holes.

[0007] Chinese utility model CN ​​211755042 U discloses an anti-clogging spray tray, wherein a plurality of through holes are evenly arranged on the tray, and the through holes are fixedly connected to an inverted cap cover through a fixedly connected bracket, and a gap is formed between the lower edge of the cap cover and the tray, and a plurality of air outlets are arranged on the side wall of the cap cover. The bottom (gas) medium enters the cap cover after contraction through the through holes of the tray, and the upper (liquid) medium enters the cover from the gap between the tray and the cap cover, and the bottom medium pulls the upper medium entering the cap cover, and after film pulling, film breaking, and crushing, it hits the top of the cap cover, and after the collision, the gas or liquid returns and sprays out from the air outlet of the cap cover, and the liquid drops fall back to the tray, and the gaseous state rises and enters the upper tray.

[0008] Chinese utility model CN ​​212396755 U discloses an anti-blocking valve tray for tower equipment, wherein a plurality of tray holes are arranged on the tray plate, the tray holes are square or rectangular, and a tray hole shielding device is arranged on the tray plate at the tray holes. The tray hole shielding device comprises a top plate, two liquid blocking plates located at one opposite side of the tray hole, and two side plates located at the other opposite side of the tray hole, wherein the area of ​​the top plate is larger than the tray hole; the two liquid blocking plates are closing inclined plates inclined toward the tray hole, the height of the side plates is higher than the liquid blocking plates, and the heights of the two side plates are flush, the two side edges of the top plate are respectively connected to the two side plates, and the other two side edges of the top plate are respectively provided with baffles, wherein the baffles have an angle inclined downward from the lower edge of the connection of the top plate, and the contour of the lower edge of the baffles is serrated. The valve-fixed tray also comprises a cover plate covering all tray hole shielding devices.

[0009] Chinese utility model CN ​​215137010 U discloses a three-dimensional fixed valve tower plate, wherein the three-dimensional fixed valve is arranged above the tower plate and the bottom opening is connected to the corresponding opening. The three-dimensional fixed valve is multiple and at least two three-dimensional fixed valves have different heights. The three-dimensional fixed valve is provided with a spray hole.

[0010] Chinese utility model CN ​​218359288 U discloses a large flux anti-blocking tower tray, including a tower plate, the tower plate is evenly provided with plate holes, the plate holes are provided with a riser, the top of the riser is higher than the tower plate, and the upper part of the riser is provided with staggered multi-layer baffles.

[0011] Chinese utility model CN ​​219630645 U discloses an umbrella-shaped cap, including a cap body, the top of which is provided with wing plates inclined at a certain angle and arranged on both sides of the side baffles of the cap body, with a gap between the wing plates and the rectangular side baffles of the cap body, and the wing plates are provided with wing plate holes; the upper part of the rectangular side baffles is provided with side baffle holes. The gas phase passes through the wing plate holes, increasing the turbulence of the liquid phase on the wing plate to avoid the deposition of solid particles. The liquid on the tower plate enters the cap from the gap between the tower plate and the rectangular side baffles of the cap, mixes with the rising gas, and the gas-liquid mixture is ejected from the side baffle holes, and then separated by the wing plates, the gas rises, and the liquid falls back onto the tower plate.

[0012] The above-mentioned prior art cannot effectively prevent the settled solid matter from blocking the liquid passage. Summary of the invention

[0013] In view of the above technical problems, the present invention provides a sedimentation tray, which comprises: a liquid receiving area, the liquid receiving area is used to receive liquid; a tray plate, the tray plates are arranged side by side to form a tray plane, and are used to receive liquid from the liquid receiving area, and the tray plate has a plurality of tray holes that penetrate the upper and lower surfaces; an overflow weir, the overflow weir is arranged downstream of the tray plate in the liquid flow direction relative to the liquid receiving area, and is used to control the liquid level height on the tray plate; a downcomer, the downcomer is arranged downstream of the overflow weir, and is used to allow the liquid flowing on the tray plate and overflowing the overflow weir to reach the liquid receiving area of ​​the next tray plane from the downcomer; wherein the sedimentation tray also comprises : A riser, the riser having a top opening opening upward at the top and a bottom opening opening downward at the bottom, the entire tube wall of the riser between the top opening and the bottom opening being closed, the bottom opening of the riser being communicated with the tower plate holes on the tower plate and being tightly connected or integrally formed with the tower plate over the entire circumference; a riser cap, the riser cap being designed to cover the entire area of ​​the top opening of the riser at the top and to form together with the top opening of the riser over at least part of the circumference of the lower edge of the riser cap a downward opening communicated with the interior of the riser, the lower edge of the riser cap being no higher than the height of the upper edge of the outlet weir.

[0014] The gas flows downward through the annular space between the gas lift cap and the gas lift pipe to the top of the tower plate, mixes with the liquid on the tower plate for mass transfer and heat transfer, then flows upward, separates from the liquid and enters the upper tower plate.

[0015] The riser and the riser cap together form a bubbling structure on the tray plate. The gas enters the riser from bottom to top through the tray hole. Since the bottom opening of the riser is tightly connected to the tray hole and preferably has a consistent shape, the gas can only continue to move upward until it is folded back by the riser cap. The riser cap and the riser together form a downward opening connected to the top opening of the riser on at least part of the circumference of the lower edge. This means that a gas channel is formed between the riser cap and the riser. The riser cap is suspended above the top opening of the riser, and the gas can be folded over the top opening of the riser and flow downward at least on at least part of the circumference of the riser cap. The liquid flows horizontally through the tray plate. Since the riser protrudes upward from the tray plate, and the liquid level is limited by the upper edge of the overflow weir, when the lower edge of the riser cap is not higher than the upper edge of the overflow weir, the gas sprayed downward from the riser through the riser cap is violently mixed with the liquid near the lower edge of the riser cap, forming turbulence there, and the gas and liquid achieve heat and mass transfer.

[0016] In the dirty blockage system, solid impurities are mainly deposited on the tower plate and the gas lift cap. When the sedimentation tower plate of the present invention is working, the gas reaches the gas lift cap and then turns back and flows downward to the tower plate on the outside of the gas lift pipe, where it is violently mixed with the liquid near the lower edge of the gas lift cap. This can effectively avoid the deposition of solid impurities in the gas channel. The solid impurities deposited on the tower plate have a sufficient height difference from the lower edge of the gas lift cap, so the deposited solid impurities will not block the gas channel, thereby greatly extending the operating cycle of the sedimentation tower plate.

[0017] In a scaling system with high alkalinity, scaling materials mainly grow along the rough surface, such as around the sieve hole or tongue hole, which will cause the sieve hole or tongue hole to become smaller and smaller, thus affecting the operation cycle. In this structure of the present invention, since the only rough surface in contact with the liquid is the lower edge of the gas lift cap, when scaling occurs, scaling materials usually occur on this rough surface and will not accumulate in the gas passage between the gas lift cap and the gas lift pipe. Therefore, the technical solution of the present invention greatly avoids the blockage of the gas passage of the settling tower plate with a simple structure, and also achieves the extension of the operation cycle.

[0018] According to a preferred embodiment of the settling tray of the present invention, the lower edge of the gas lift cap is at least flush with or lower than the height of the top opening of the gas lift pipe. In this way, when the gas reaches the gas lift cap and turns back and flows downward outside the gas lift pipe, the gas is better guided, mixed more intensely with the liquid near the lower edge of the gas lift cap, and the gas-liquid heat and mass transfer effect is better.

[0019] According to another preferred embodiment of the settling tray of the present invention, the gas lift cap is supported on the gas lift pipe by a plurality of support members spaced apart from each other. There is a space between the top opening of the gas lift pipe and the gas lift cap through which gas can pass. For example, the above structure is realized by a support rod, one end of which is supported on the top opening of the gas lift pipe or on the pipe wall near the pipe, and the other end is supported on the bottom inner wall of the gas lift cap, so that the gas in the gas lift pipe can smoothly pass through the gap between the support members and return to the outside of the pipe wall of the gas lift pipe.

[0020] However, according to another preferred embodiment of the settling tray of the present invention, the gas lift cap can also be directly supported on the tray plate by a plurality of support rods without acting on the gas lift pipe, as long as a space for gas to pass is left between the gas lift cap and the top opening of the gas lift pipe.

[0021] According to a preferred embodiment of the settling tray of the present invention, the gas lift cap has an inclined top and a side portion bent downward from the top, and the end of the side portion forms the lower edge of the gas lift cap. As an alternative or supplement, in another preferred embodiment of the settling tray of the present invention, the gas lift cap has a flat top and a side portion bent downward from the top, and the end of the side portion forms the lower edge of the gas lift cap. It should be understood that the role of the gas lift cap is to block the gas riser from above to prevent the gas in the gas riser from escaping directly upward without being turned back, because if this gas is not fully mixed with the liquid on the tray plate to achieve heat and mass transfer. Therefore, as long as the gas lift cap can leave enough space for gas to pass through, the shape of the top is not limited to the above-mentioned sloping top or flat top, but can be set to any shape.

[0022] According to a preferred embodiment of the settling tray of the present invention, the riser has the same cross-sectional area in the extension direction. As an alternative embodiment, the riser may also have a variable cross-sectional area in the extension direction. For example, the cross-sectional area of ​​the riser continuously narrows from bottom to top or narrows first and then increases. Preferably, the top opening of the riser has a smaller cross-sectional area than the bottom opening of the riser.

[0023] According to a preferred embodiment of the settling tray of the present invention, the tray holes of the tray plate have a horizontal projection that coincides with the lower edge of the gas lift cap on a portion of the circumference. Optionally, the tray holes of the tray plate are surrounded by the lower edge of the gas lift cap at a distance on the entire circumference.

[0024] The cross section of the riser is circular, elliptical, polygonal (including triangle, square, rectangle, etc.), or irregularly curved. The riser cap can also have any shape that can cover the riser.

[0025] Preferably, the lower edge of the air riser cap is 0 to 50 mm lower than the top opening of the air riser. Preferably, the lower edge of the air riser cap is 0 to 100 mm lower than the upper edge of the outlet weir. Preferably, the height of the air riser is 10 to 500 mm. Preferably, the width of the air riser is 25 to 300 mm and the length is 50 to 1500 mm. When the cross-section of the air riser is circular, the diameter of the air riser is 25 to 300 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The technical solution of the present invention is described below in conjunction with the accompanying drawings. In the accompanying drawings:

[0027] Figure 1 A schematic cross-sectional view of a settling tray according to the present invention installed in a container is shown;

[0028] Figure 2A A schematic top view of a settling tray according to an embodiment of the present invention is shown;

[0029] Figure 2B A schematic top view of a settling tray according to an embodiment of the present invention is shown;

[0030] Figure 2C A schematic top view of a settling tray according to an embodiment of the present invention is shown;

[0031] FIG. 3A to FIG. 3C A schematic top view of a group of gas risers and a gas riser cap of a settling tray according to an embodiment of the present invention and two schematic cross-sectional views thereof are respectively shown;

[0032] FIG. 4A to FIG. 4C A schematic top view of a group of gas risers and a gas riser cap of a settling tray according to an embodiment of the present invention and two schematic cross-sectional views thereof are respectively shown;

[0033] FIG. 5A to FIG. 5C A schematic top view of a set of gas risers and gas riser caps of a settling tray according to an embodiment of the present invention and two schematic cross-sectional views thereof are respectively shown; and

[0034] FIG. 6A to FIG. 6C A schematic top view of a group of gas risers and gas riser caps of a settling tray according to an embodiment of the present invention and two schematic cross-sectional views thereof are shown.

[0035] The accompanying drawings are only used to explain the present invention and cannot be understood as limiting the present invention. The same reference numerals represent the same technical features, which are illustrative rather than limiting. DETAILED DESCRIPTION

[0036] Figure 1A schematic cross-sectional view of a settling tray according to the present invention installed in a container is shown. The settling tray 1 is arranged in a container in multiple layers. In a typical container for gas-liquid heat and mass transfer, gas is provided from the lower part of the container and flows from bottom to top. Liquid is provided from the upper part of the container and flows from top to bottom. The settling tray 1 of the same layer includes a liquid receiving area 10, a tray plate 20, an outlet weir 30 and a downcomer 40. The liquid receiving area 10 receives the liquid falling from above. Depending on the size of the container, there may be multiple tray plates 20, which are arranged side by side to form a tray plane for receiving liquid from the liquid receiving area 10. The tray plate 20 has a plurality of tray holes 210 that pass through the upper and lower surfaces. The overflow weir 30 is arranged downstream of the tray plate 20 in the liquid flow direction relative to the liquid receiving area 10, and is used to control the liquid level height on the tray plate 20. The downcomer 40 is arranged downstream of the overflow weir 30 in the liquid flow direction. The liquid flowing from the tray plate 20 and overflowing the overflow weir 30 reaches the liquid receiving area 10 of the next tray plane through the downcomer 40.

[0037] Each tray hole 210 of the tray plate 20 corresponds to one riser 50. The riser 50 has a top opening 510 opening upward at the top and a bottom opening 520 opening downward at the bottom. The entire tube wall of the riser 50 between the top opening 510 and the bottom opening 520 is closed. The bottom opening 520 of the riser 50 is connected to the tray hole 210 on the tray plate 20 and is tightly connected or integrally formed with the tray plate 20 over the entire circumference. In this way, the liquid on the tray plate 20 has no passage to enter the interior of the riser.

[0038] On the contrary, the gas lift cap 60 is designed to cover the entire area of ​​the top opening of the gas lift pipe 50 from above and to enclose together with the top opening 510 of the gas lift pipe 50 on at least part of the circumference of the lower edge 610 of the gas lift cap 60 to form a downward opening connected to the interior of the gas lift pipe 50, and the lower edge 610 of the gas lift cap 60 is not higher than the height of the upper edge of the outlet weir 30. Therefore, the gaseous material entering the interior of the gas lift pipe 50 from the lower layer through the tower plate hole 210 can only turn back and cross the pipe wall of the gas lift pipe 50 after encountering the gas lift cap, and leave the gas lift cap downward through the downward opening enclosed by the upper edge of the gas lift pipe 50 and the lower edge 620 of the gas lift cap 60. At this position of leaving the gas lift cap, intense heat and mass transfer occurs between gas and liquid. Unlike the prior art, the riser pipe has no side wall holes, and the gas in the riser pipe leaves the riser cap downward rather than to the side. In this structure, the rough surface in contact with the liquid (such as the cutting surface during processing) is only the lower edge 610 of the riser cap 60, but the lower edge 610 is not in the gas passage, so the gas passage will not be blocked even if scaling occurs thereon.

[0039] When the gas lift cap 60 is designed so that its lower edge 610 is at least flush with or lower than the height of the top opening 510 of the gas lift pipe 50, the gas can be better guided when it reaches the gas lift cap and turns back and flows downward on the outside of the gas lift pipe, and mixes more intensely with the liquid near the lower edge of the gas lift cap, thereby achieving better heat and mass transfer effects between gas and liquid.

[0040] The riser 50 can be surrounded by the riser cap 60 at intervals over the entire circumference. This, for example, forms an annular gas passage around the upper edge of the riser 50. In fact, it is only necessary to arrange a number of support rods connecting the inner bottom surface of the riser cap 60 and the riser 50 at several points on or near the upper edge of the riser 50. These support rods occupy a very small proportion of the gas passage and are not shown in the figure. However, it is obvious that according to a variant implementation, part of the circumference of the riser 50 can also be directly extended to the riser cap 60 to support the latter, while the remaining part of the circumference is open to the gas passage.

[0041] Of course, the gas lift cap may not be supported on the gas lift pipe, but may be directly supported on the tower plate, for example, by a number of support rods. To save space, this embodiment is not shown here as a preferred embodiment.

[0042] In terms of shape, the riser 50 and the riser cap 60 can be of any shape, as long as the former can be completely covered by the latter in horizontal projection and can properly support the latter and leave a gas passage, because this can play the role of returning the airflow in the riser 50 to flow downward.

[0043] The upper edge of the overflow weir 30 has a higher height than the air lift cap 60, such as Figure 1 As shown. The upper edge of the overflow weir 30 is used to control the liquid level on the tower plate 20, which means that the lower edge of the gas lift cap 60 will be completely inserted below the liquid surface. Combined with the design that the lower edge 610 of the gas lift cap 60 is at least flush with or lower than the upper edge of the gas lift pipe 50, this effectively ensures that the gas is ejected downward from the bubbling device composed of the gas lift pipe 50 and the gas lift cap 60, while avoiding the possibility of liquid backflow into the gas lift pipe 50.

[0044] FIG. 2A to FIG. 2C Schematic top views of settling trays according to different embodiments of the present invention are shown respectively. FIG. 2A to FIG. 2C In the embodiment shown, after the liquid falls into the liquid receiving area 10 on the left side of the figure, it flows to the right through all the bubbling devices on the tower plate 20, that is, the combination of the air riser 50 and the air riser cap 60, and then crosses the overflow weir 30 and falls from the downcomer 40 to the liquid receiving area of ​​the lower layer. Figure 2AThe top view of the middle riser 50 and the riser cap 60 are both rectangular. The riser cap 60 completely surrounds the riser 50 in all circumferential directions and leaves a gap. The riser cap 60 can be, for example, in the shape of an arc dome and is supported on the riser 50 by a support rod not shown. Figure 2B and Figure 2A The difference is that the top view rectangular shape of the riser pipe 50 and the riser cap 60 is Figure 2B and Figure 2A has an orthogonal rectangular orientation. Figure 2C A circular air riser cap 60 and an air riser pipe 50 are shown in FIG.

[0045] Accordingly, FIG. 3A to FIG. 6C The four groups of gas risers and gas riser caps of the settling tray according to the embodiment of the present invention are shown in top view and two cross-sectional views thereof. FIG. 2A to FIG. 2C different, FIG. 3A to FIG. 5C The three groups of riser pipes and riser caps shown are completely closed at two sides of the rectangle (preferably the short sides) to form mutual support, and form gas passages at the other two sides (preferably the long sides). FIG. 6A to FIG. 6C A set of rectangular riser pipes and riser caps separated by intervals inside and outside on all four sides are shown, that is, Figure 2A or Figure 2B The bubbling device in the embodiment shown. FIG. 3A to FIG. 4C Two embodiments of a chimney cap with a sloped top are shown, which differ in that the chimney pipe has a different cross-sectional shape. FIG. 3A to FIG. 3C The riser 50 in the embodiment shown tapers upwards, FIG. 4A to FIG. 4C The riser 50 of the embodiment shown has the same cross-sectional area at the top opening 510 and the bottom opening 520. FIG. 5A to FIG. 5C An embodiment of a flat-topped air riser cap is shown, but it should be understood that the air riser 50 may have the same cross-sectional area at the top opening 510 and the bottom opening 520 as shown in the figure, or may be narrowed upward.

[0046] The preferred embodiments of the present invention are described above, but the spirit and scope of the present invention are not limited to the specific contents disclosed herein. Those skilled in the art can arbitrarily combine and expand the above embodiments according to the teachings of the present invention to make more implementation methods and applications within the spirit and scope of the present invention. The spirit and scope of the present invention are not limited by the specific embodiments, but by the claims.

[0047] Reference numerals list

[0048] 1 Settling tray

[0049] 10 Receiving area

[0050] 20 trays

[0051] 210 tray holes

[0052] 30 Overflow weir

[0053] 40 Downcomer

[0054] 50 liters of air pipe

[0055] 510 Top opening

[0056] 520 bottom opening

[0057] 60L Gas Cap

[0058] 610 bottom edge

Claims

1. A settling tray, comprising: A liquid receiving area, the liquid receiving area is used to receive liquid; A tray plate, the tray plates are arranged side by side to form a tray plane, for receiving the liquid from the liquid receiving area, and the tray plate has a plurality of tray holes penetrating the upper and lower surfaces; An overflow weir, the overflow weir is arranged downstream of the tray plate in the liquid flow direction relative to the liquid receiving area, and is used to control the liquid level height on the tray plate; A downcomer, which is arranged downstream of the overflow weir and is used to allow the liquid flowing on the tray plate and overflowing the overflow weir to reach the liquid receiving area on the plane of the next tray layer from the downcomer; Characterized in that the settling tower tray also includes: A riser, wherein the riser has a top opening opening upward at the top and a bottom opening opening downward at the bottom, the entire tube wall of the riser between the top opening and the bottom opening is closed, the bottom opening of the riser is connected to the tray hole on the tray plate and is tightly connected or integrally formed with the tray plate over the entire circumference; An air riser cap is designed to cover the entire area of ​​the top end opening of the air riser from above and to form together with the top end opening of the air riser on at least a portion of the circumference of the lower edge of the air riser cap to form a downward opening connected to the interior of the air riser, and the lower edge of the air riser cap is not higher than the height of the upper edge of the outlet weir.

2. The settling tray according to claim 1, characterized in that: The lower edge of the air riser cap is at least flush with or lower than the height of the top end opening of the air riser.

3. The settling tray according to claim 1, characterized in that: The air lifting cap has an inclined top and a side portion bent downward from the top, and a terminal end of the side portion forms a lower edge of the air lifting cap.

4. The settling tray according to claim 1, characterized in that: The air lifting cap has a flat top and a side portion bent downward from the top, and a terminal end of the side portion forms a lower edge of the air lifting cap.

5. The settling tray according to claim 1, characterized in that: The riser has the same cross-sectional area from bottom to top.

6. The settling tray according to claim 1, characterized in that: The riser has a cross-sectional area that changes from bottom to top.

7. The settling tray according to claim 1, characterized in that: The cross section of the riser is circular, elliptical, polygonal, or irregularly curved.

8. The settling tray according to claim 2, characterized in that: The lower edge of the air riser cap is 0 to 50 mm lower than the top end opening of the air riser.

9. The settling tray according to claim 1, characterized in that: The lower edge of the air lift cap is 0 to 100 mm lower than the upper edge of the outlet weir.

10. The settling tray according to claim 1, characterized in that: The height of the riser is 10 to 500 mm.

11. The settling tray according to claim 1, characterized in that: The riser has a width of 25 to 300 mm and a length of 50 to 1500 mm.

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