A composite tray and a plate column including the composite tray

Abstract

The present invention provides a composite tray and a plate column including the composite tray. The composite tray includes an inclined tray and baffles arranged on the inclined tray. The composite tray includes a single-tray composite tray or a double-tray composite tray. The number of layers of the inclined trays is at least two, and the inclination directions of adjacent two layers of inclined trays are opposite. At least two baffles are arranged on each inclined tray, and at least one row of downcomer holes is arranged in front of each baffle on the inclined tray. By arranging the trays inclined and setting multiple baffles, the present invention promotes liquid renewal. The formation of steps makes the liquid layer thinner and the liquid distribution more uniform. By arranging downcomer holes in front of the baffles, the dispersion degree of the liquid is increased, the contact with the vapor phase is more sufficient, the entrainment of liquid droplets is less, and the mass transfer and heat transfer efficiency is improved. The structural design of the composite tray can reduce the pressure drop between the trays, reduce the distance between the trays, and thus reduce the equipment cost and operation cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas-liquid mass transfer equipment, and relates to a composite tray and a plate column including the composite tray. Background Art

[0002] A plate column is an important gas-liquid mass transfer equipment in the petrochemical production process. During the production and operation of the equipment, on the premise of ensuring the product separation effect, a circulating reflux is generally set in the middle section of the column. Its function is to remove the excess heat in the fractionating column and serve as the heat source for other operating units, thereby reducing energy consumption. At the same time, by adopting the middle-section circulating reflux, the column diameter can be reduced under the same processing capacity, or the processing capacity of the column can be increased under the same column diameter.

[0003] Conventional plate columns do not specifically consider the trays in the middle-section reflux section, but use the same trays throughout the column. Currently, the widely used ones are valve trays and baffle trays. Among them, the valve tray consists of an overflow weir, a downcomer, and a liquid receiving tray. The liquid enters the lower liquid receiving tray through the downcomer, then flows horizontally across the tray, and forms a liquid curtain over the overflow weir and enters the downcomer. This tray structure is complex, with small gas-liquid fluxes and slow liquid renewal speed. For the baffle tray, there is no downcomer, and only downcomer holes are opened near the overflow weir. A small part of the liquid flows down through the downcomer holes to form liquid columns, and most of the liquid flows down in the form of a liquid curtain over the overflow weir. The gas passes horizontally from below the tray and contacts the liquid columns and the liquid curtain. Due to the gas impact, liquid will accumulate at the tower wall, forming a thick liquid layer, which is not conducive to liquid renewal and reduces the heat and mass transfer efficiency.

[0004] CN 206063827U discloses a fractionating tray and a fractionating column. The fractionating column includes a fractionating column barrel, a fractionating tray, and riser pipes. The fractionating tray includes a tray and an overflow weir. The tray and the overflow weir are perpendicular, and downcomer holes are provided on the tray. The fractionating tray and the fractionating column barrel form a groove structure, and the fractionating trays are arranged in a staggered manner in the fractionating column barrel. The riser pipes are the cavities formed by the inner wall of the fractionating column barrel and the fractionating trays. The structure of the shunt column changes the paths of the gas and the liquid. The gas rises from the riser pipes, and the liquid flows back in the downcomer. The gas does not need to break through the liquid film resistance, thereby reducing the pressure drop. However, this tray has requirements for the liquid flow rate. If the flow rate is too slow, it is difficult to form a liquid film, and the gas will short-circuit. If the flow rate is too fast, it is not conducive to heat exchange.

[0005] CN 101053700A discloses a baffle tray, including a tray. An overflow weir is provided on the tray. The tray consists of steps that slope downward along the liquid flow direction. Sieve holes are provided on each step. Below the tray, an inclined downward bow-shaped deflector is provided at the top of the arc where the highest step of the tray intersects the tower wall of the tower. The steps on the tray promote the liquid flow and improve the mass transfer effect. However, the appearance of the steps will increase the plate spacing and cause an increase in the cost of the device.

[0006] In summary, for the design of the internal structure of a plate column, especially the improvement of the tray structure, it is necessary to be able to promote the gas-liquid mass transfer rate, strengthen the separation effect, while minimizing the equipment cost as much as possible and improving the processing capacity. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the object of the present invention is to provide a composite tray and a plate column including the composite tray. By setting the inclined trays and baffles on the trays, the liquid can form a stepped shape on the trays, reducing the liquid layer thickness and making the liquid distribution more uniform. The setting of downcomer holes on the trays can increase the gas-liquid contact area and improve the mass transfer and heat transfer efficiency.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] The present invention provides a composite tray, which includes an inclined tray and baffles arranged on the inclined tray. The composite tray includes a single-tray composite tray or a double-tray composite tray. The single-tray composite tray has one inclined tray arranged on the same cross-section of the tower body, and the double-tray composite tray has two symmetrically arranged inclined trays on the same cross-section of the tower body;

[0010] In the single-tray composite tray, the number of layers of the inclined trays is at least two, and the inclination directions of adjacent two layers of inclined trays are opposite. The inclined tray is in a bow shape, and the arc segment edge of the bow coincides with the inner side of the tower body, and there is a gap between the straight segment edge and the tower body;

[0011] In the double-tray composite tray, the inclination directions of the two inclined trays on the same cross-section of the tower body are opposite. The number of layers of the inclined trays is at least two. Among adjacent two layers of inclined trays, one layer inclines inward with the inner walls of both sides of the tower body as the base points, and there is a gap in the middle position, and the other layer inclines toward both sides with the middle position as the base point, and there are gaps near the inner walls of both sides;

[0012] In the composite tray, at least two baffles are provided on each inclined tray, one of which is arranged at the edge of the inclined tray, and at least one row of downcomer holes is provided in front of each baffle on the inclined tray.

[0013] In the present invention, the composite tray is installed inside the tower. By tilting the tray and providing multiple baffles, the renewal of the liquid on the tray can be promoted, the liquid flux and the overflow intensity can be increased. The formation of the steps makes the liquid layer thinner and the liquid distribution more uniform. By providing downcomer holes in front of the baffles, multiple liquid curtains are formed by flowing downward through the downcomer holes, increasing the dispersion of the liquid, making the contact with the vapor flowing horizontally below the tray more sufficient, with less entrainment of mist and foam, and both the mass transfer and heat transfer efficiencies are improved; the setting of the downcomer holes can also reduce the liquid curtain flow at the voids of the tray, reducing the possibility of flooding; at the same time, the vapor rises from the voids, reducing the pressure drop between the trays, thereby reducing the operating cost.

[0014] The following are the preferred technical solutions of the present invention, but not the limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] As a preferred technical solution of the present invention, the inclined tray slopes downward along the liquid flow direction, and the angle with the horizontal direction is 1 to 5 degrees, such as 1 degree, 1.5 degrees, 2 degrees, 2.5 degrees, 3 degrees, 4 degrees or 5 degrees, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] Preferably, in the single-tray composite tray, the distance between the edge of the straight section of the inclined tray and the tower body is 15% to 30% of the tower body diameter, such as 15%, 17.5%, 20%, 22.5%, 25%, 27.5% or 30%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] As a preferred technical solution of the present invention, in the double-tray composite tray, the distance between the edges of the two trays inclined inward is 7.5% to 20% of the tower body diameter, such as 7.5%, 10%, 12.5%, 15%, 17.5% or 20%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] Preferably, in the double-tray composite tray, the distance between the edges of the two trays inclined to both sides and the tower body is independently 5% to 15% of the tower body diameter, such as 5%, 7.5%, 10%, 12.5% or 15%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] In the present invention, in the double-tray composite tray, the two trays on both sides are symmetrically arranged. For the two trays inclined from the middle position to both sides, a fixing component is provided in the middle of the tower body to facilitate fixing the trays.

[0020] As a preferred technical solution of the present invention, the number of baffles on each inclined tray is 3 to 5, such as 3, 4 or 5. The selection of the specific number is related to factors such as the size of the tower body, the type of tray, and the processing capacity.

[0021] Preferably, 1 to 3 rows of downcomer holes are provided in front of each baffle on the inclined tray, such as 1 row, 2 rows or 3 rows, etc. The selection of the number of rows of downcomer holes is related to factors such as the spacing of the downcomer holes and the number of baffles.

[0022] Preferably, two adjacent rows of downcomer holes are staggeredly distributed in front of the baffle.

[0023] Preferably, the spacing of the downcomer holes is 2.5 to 5 times the diameter of the downcomer holes, such as 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times or 5 times, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0024] The present invention also provides a plate column, and the middle section tower body of the plate column adopts the above-mentioned composite tray.

[0025] As a preferred technical solution of the present invention, the middle section tower body of the plate column includes the composite tray, a reflux extraction port, a reflux cooler and a reflux inlet. The reflux extraction port is located below the composite tray, the reflux inlet is located above the composite tray, and the reflux extraction port and the reflux inlet are connected by a reflux cooler outside the plate column.

[0026] In the present invention, the middle section tower body is provided with a reflux extraction port and a reflux inlet for heat extraction, which can timely remove the excess heat in the tower, maintain a suitable operating temperature, reduce energy consumption. At the same time, by adopting the middle section circulation method, the tower diameter can be reduced under the same processing capacity, and the processing capacity of the tower can be improved under the same tower diameter.

[0027] As a preferred technical solution of the present invention, the upper section tower body and the lower section tower body of the plate column adopt ordinary trays, and the trays on the same layer are on the same horizontal plane.

[0028] Preferably, the ordinary tray includes a valve tray or a baffle tray.

[0029] As a preferred technical solution of the present invention, the middle section tower body further includes a gas deflector, and the gas deflector is arranged above the uppermost tray and below the lowermost tray of the composite tray.

[0030] In the present invention, in the middle section tower body, the vapor flows horizontally between the trays to the vapor rising area at the tower edge and generally rises in an S-shaped flow, while in the upper section tower body and the lower section tower body, it mainly breaks through the liquid film and rises vertically. Therefore, when entering and leaving the middle section tower body, a gas deflector needs to be set to guide the flow direction of the gas and facilitate the contact between the gas and liquid phases.

[0031] As a preferred technical solution of the present invention, the middle section tower body further includes a reflux pump, and the reflux pump is arranged on the connecting pipeline outside the plate column between the reflux extraction port and the reflux inlet.

[0032] As a preferred technical solution of the present invention, the plate spacing in the middle section tower body is smaller than that in the upper section tower body and the lower section tower body.

[0033] In the present invention, due to the unique structure in the middle section tower body, the plate spacing can be appropriately reduced compared with the conventional plate spacing. Without increasing the tower height, the number of plates can be increased, thereby improving the vapor-liquid mass transfer and heat transfer efficiency in the reflux section.

[0034] In the present invention, when fractionation is carried out using the plate column, its operation process includes:

[0035] The liquid enters the composite tray through the downcomer of the tray where the middle section reflux port is located, forms a stepped liquid film on the tray, and forms a liquid curtain at the downcomer holes in front of each baffle; the vapor flows upward in the tower, flows horizontally between the trays to the vapor rising area at the tower edge, and generally rises in an S shape. Below each tray, the vapor flows horizontally, and the liquid flows vertically downward through the downcomer holes. The vapor and liquid are perpendicular to each other and intersect, enabling full contact, thereby achieving efficient mass transfer and heat transfer and achieving the purpose of fractionation; from entering the middle section reflux section to leaving the middle section reflux section, the flow pattern of the gas first changes from vertically rising through breaking the liquid film to S-shaped rising and then to vertically rising through breaking the liquid film. Gas deflectors are arranged above the uppermost tray and below the lowermost tray in the middle section reflux section to guide the gas flow direction.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) By arranging the trays obliquely and providing multiple baffles, the composite tray of the present invention can promote the renewal of the liquid on the trays, increase the liquid flux and overflow intensity. The formation of the steps makes the liquid layer thinner and the liquid distribution more uniform;

[0038] (2) The present invention provides downcomer holes in front of the baffles. The liquid flows downward through the downcomer holes to form multiple liquid curtains, increasing the liquid dispersion degree, making the contact with the horizontally flowing vapor more sufficient, having less entrainment of liquid droplets, and improving the mass transfer and heat transfer efficiency;

[0039] (3) The structural design of the composite tray of the present invention can reduce the pressure drop between the trays and narrow the distance between the trays, thereby reducing the equipment cost and operation cost. Description of the Drawings

[0040] Figure 1 It is a partial structural schematic diagram of the plate column provided in Embodiment 3 of the present invention;

[0041] Figure 2 It is a schematic cross-sectional structure diagram of the composite tray provided in Embodiment 3 of the present invention;

[0042] Figure 3 It is a schematic partial structure diagram of the plate column provided in Embodiment 4 of the present invention;

[0043] Figure 4 It is a schematic cross-sectional structure diagram of the composite tray provided in Embodiment 4 of the present invention;

[0044] Wherein, 1 - tower body, 2 - reflux distribution pipe, 3 - reflux inlet, 4 - reflux cooler, 5 - reflux pump, 6 - reflux extraction port, 7 - baffle, 8 - inclined tray, 9 - downcomer hole, 10 - ordinary tray, 11 - downcomer, 12 - gas guide plate. Detailed implementation manners

[0045] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention will be further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of the claimed rights of the present invention. The scope of protection of the present invention is subject to the claims.

[0046] The following are typical but non-limiting embodiments of the present invention:

[0047] Embodiment 1:

[0048] This embodiment provides a composite tray. The composite tray includes an inclined tray 8 and a baffle 7 arranged on the inclined tray 8. The composite tray is a single-tray composite tray, and one inclined tray 8 is arranged on the cross-section of the same tower body 1;

[0049] In the single-tray composite tray, the number of layers of the inclined tray 8 is 2 layers, and the inclination directions of adjacent two layers of inclined trays 8 are opposite. The inclined tray 8 is in an arc shape, and the edge of the arc segment coincides with the inner side of the tower body 1, and there is a gap between the straight segment edge and the tower body 1;

[0050] In the composite tray, 4 baffles 7 are arranged on each inclined tray 8, and one of them is arranged at the edge of the inclined tray 8. There are 2 rows of downcomer holes in front of each baffle on the inclined tray 8; the adjacent two rows of downcomer holes 9 are staggered in front of the baffle 7.

[0051] The inclined tray 8 is inclined downward along the liquid flow direction, and the included angle with the horizontal direction is 2 degrees.

[0052] The distance between the straight segment edge of the inclined tray 8 and the tower body 1 is 20% of the diameter of the tower body 1.

[0053] The spacing of the downcomer holes 9 is 3 times the diameter of the downcomer holes 9.

[0054] Example 2:

[0055] This embodiment provides a composite tray, the composite tray includes an inclined tray 8 and a baffle 7 arranged on the inclined tray 8. The composite tray is a double-tray composite tray, and two symmetrical inclined trays 8 are arranged on the cross-section of the same tower body 1;

[0056] In the double-tray composite tray, the inclination directions of the two inclined trays 8 on the cross-section of the same tower body 1 are opposite. The number of layers of the inclined trays 8 is 4. Among the adjacent two layers of inclined trays 8, one layer inclines inward with the inner walls of the two sides of the tower body 1 as the base points, leaving a gap in the middle position, and the other layer inclines outward with the middle position as the base point, leaving gaps at the positions close to the inner walls on both sides;

[0057] In the composite tray, each inclined tray 8 is provided with 3 baffles 7, one of which is arranged at the edge of the inclined tray 8, and 1 row of downcomer holes is arranged in front of each baffle on the inclined tray 8.

[0058] The inclined tray 8 inclines downward along the liquid flow direction, and the included angle with the horizontal direction is 3 degrees.

[0059] In the double-tray composite tray, the distance between the edges of the two trays inclining inward is 15% of the diameter of the tower body 1, and the distances between the edges of the two trays inclining outward and the tower body 1 are both 12% of the diameter of the tower body 1.

[0060] The spacing of the downcomer holes 9 is 5 times the diameter of the downcomer holes 9.

[0061] Example 3:

[0062] This embodiment provides a plate column. The partial structural schematic diagram of the plate column is as Figure 1 shown. The middle section tower body of the plate column adopts the single-tray composite tray, and the diameter of the plate column is 2000 mm.

[0063] The middle section tower body of the plate column includes the single-tray composite tray, a reflux extraction port 6, a reflux cooler 4 and a reflux inlet 3. The reflux extraction port 6 is located at the lower part of the composite tray, the reflux inlet 3 is located at the upper part of the composite tray, the reflux inlet 3 is connected to a reflux distribution pipe 2, and the reflux distribution pipe 2 is horizontally arranged in the tower body 1 and is located above the topmost tray of the composite tray; the reflux extraction port 6 and the reflux inlet 3 are connected through a reflux cooler 4 outside the plate column.

[0064] The cross-sectional structural schematic diagram of the composite tray is as Figure 2As shown in the figure, it includes an inclined tray 8 and a baffle 7 arranged on the inclined tray 8; the number of layers of the inclined tray 8 is 5, the tray spacing is 400 mm, the inclination directions of adjacent two layers of inclined trays 8 are opposite, inclined downward along the liquid flow direction, and the included angle with the horizontal direction is 1 degree; the inclined tray 8 is in a bow shape, the edge of the arc section of the bow coincides with the inner side of the tower body 1, and there is a gap between the straight edge and the tower body 1, and the width of this gap is 30% of the diameter of the tower body 1.

[0065] There are 4 baffles 7 arranged on each inclined tray 8, one of which is arranged at the edge of the inclined tray 8, the spacing of the baffles 7 is 400 mm, and the height of the baffle 7 is 50 mm; there are 2 rows of downcomer holes in front of each baffle on the inclined tray 8, the aperture of the downcomer hole 9 is 10 mm, the adjacent two rows of downcomer holes 9 are staggered in front of the baffle 7, and the spacing of the downcomer holes 9 is 2.5 times the diameter of the downcomer hole 9.

[0066] The middle section of the tower body also includes gas guide plates 12, there are 2 gas guide plates 12, which are respectively arranged above the topmost tray and below the bottommost tray of the compound tray, and the spacing from the corresponding trays is 200 mm.

[0067] The middle section of the tower body also includes a reflux pump 5, and the reflux pump 5 is arranged on the connecting pipeline outside the plate tower of the reflux extraction port 6 and the reflux inlet 3.

[0068] The upper section and the lower section of the tower body of the plate tower adopt ordinary trays, and the trays on the same layer are on the same horizontal plane; the ordinary trays adopt ordinary trays 10, that is, valve trays, and a downcomer 11 is arranged at the edge of the tray; the distance between the ordinary trays 10 is 600 mm.

[0069] Example 4:

[0070] This example provides a plate tower, and the partial structural schematic diagram of the plate tower is as Figure 3 shown, the middle section of the tower body of the plate tower adopts the double-tray compound tray, and the diameter of the plate tower is 4000 mm.

[0071] The middle section of the tower body of the plate tower includes the double-tray compound tray, a reflux extraction port 6, a reflux cooler 4 and a reflux inlet 3. The reflux extraction port 6 is located at the lower part of the compound tray, the reflux inlet 3 is located at the upper part of the compound tray, the reflux inlet 3 is connected to a reflux distribution pipe 2, the reflux distribution pipe 2 is horizontally arranged in the tower body 1, and the reflux distribution pipe 2 is evenly provided with holes and is located above the topmost tray of the compound tray; the reflux extraction port 6 and the reflux inlet 3 are connected through a reflux cooler 4 outside the plate tower.

[0072] The cross-sectional structural schematic diagram of the compound tray is as Figure 4As shown, it includes an inclined tray 8 and a baffle 7 arranged on the inclined tray 8; the two inclined trays 8 on the same cross-section of the tower body 1 have opposite inclination directions, incline downward along the liquid flow direction, and the angle with the horizontal direction is 4 degrees; the number of layers of the inclined tray 8 is 4 layers, and the tray spacing is 400 mm;

[0073] Among two adjacent layers of inclined trays 8, one layer inclines inward with the inner walls of the two sides of the tower body 1 as the base points, leaving a gap in the middle position, and the width of this gap is 8% of the diameter of the tower body 1. There are 5 baffles 7 arranged on this layer of inclined tray 8, and one of them is arranged at the edge of the inclined tray 8. The spacing between the baffles 7 is 350 mm, and the height of the baffle 7 is 40 mm; the other layer inclines toward both sides with the middle position as the base point, leaving gaps near the inner walls on both sides, and the width of each of the two gaps is 5% of the diameter of the tower body 1. There are 4 baffles 7 arranged on this layer of inclined tray 8, and one of them is arranged at the edge of the inclined tray 8. The spacing between the baffles 7 is 400 mm, and the height of the baffle 7 is 40 mm;

[0074] There is 1 row of downcomer holes in front of each baffle on the inclined tray 8. The aperture of the downcomer hole 9 is 20 mm, and the spacing of the downcomer holes 9 is 4 times the diameter of the downcomer hole 9.

[0075] The middle section of the tower body also includes gas guiding plates 12. There are 2 gas guiding plates 12, which are respectively arranged above the topmost tray and below the bottommost tray of the composite tray, and the spacing from the corresponding trays is 200 mm.

[0076] The middle section of the tower body also includes a reflux pump 5. The reflux pump 5 is arranged on the connecting pipeline outside the plate tower for the reflux extraction port 6 and the reflux inlet 3.

[0077] The upper section and the lower section of the tower body of the plate tower adopt ordinary trays, and the trays on the same layer are on the same horizontal plane; the ordinary trays adopt ordinary trays 10, that is, valve trays, and downcomers 11 are arranged at the edges of the trays; the distance between the ordinary trays 10 is 600 mm.

[0078] When fractionation is carried out using the plate tower in the above-mentioned Embodiments 3 - 4, intermediate reflux heat extraction can be carried out, and its operation process includes:

[0079] The liquid enters the composite tray through the reflux inlet, forms a stepped liquid film on the tray, and forms a liquid curtain at the downcomer holes in front of each baffle; the vapor flows upward in the tower, flows horizontally between the trays to the vapor rising area at the edge of the tower, and generally rises in an S-shaped flow. Below each tray, the vapor flows horizontally, and the liquid flows vertically downward through the downcomer holes. The vapor and liquid are perpendicular to each other and intersect, and can be fully contacted, so as to achieve efficient mass transfer and heat transfer, achieve the purpose of fractionation, and can effectively solve the problems of slow liquid renewal, low heat transfer efficiency, and small processing capacity existing in the intermediate reflux trays of the fractionation tower.

[0080] As can be seen from the above embodiments, in the compound tray of the present invention, by obliquely arranging the tray and providing a plurality of baffles, the renewal of the liquid on the tray can be promoted, the liquid flux and the overflow intensity can be increased, the formation of the steps makes the liquid layer thinner and the liquid distribution more uniform; a downcomer hole is provided in front of the baffle, and a plurality of liquid curtains are formed by flowing downward through the downcomer hole, which increases the dispersion degree of the liquid, makes the contact with the horizontally flowing vapor more sufficient, has less entrainment of mist and foam, and improves the mass transfer and heat transfer efficiency; the structural design of the compound tray can reduce the pressure drop between the trays and narrow the distance between the trays, thereby reducing the equipment cost and the operation cost.

[0081] The applicant declares that the present invention uses the above embodiments to illustrate the detailed device of the present invention, but the present invention is not limited to the above detailed device, that is, it does not mean that the present invention must rely on the above detailed device to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the device of the present invention, the addition of auxiliary devices, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A plate column, characterized in that, the middle section of the plate column body includes a composite tray, a reflux extraction port, a reflux cooler and a reflux inlet. The reflux extraction port is located at the lower part of the composite tray, the reflux inlet is located at the upper part of the composite tray, and the reflux extraction port and the reflux inlet are connected by a reflux cooler outside the plate column; the upper section and the lower section of the plate column body adopt ordinary trays, and the trays on the same layer are on the same horizontal plane; the tray spacing in the middle section of the column body is smaller than the tray spacing in the upper section and the lower section of the column body; the composite tray includes an inclined tray and baffles arranged on the inclined tray. The inclined tray slopes downward along the liquid flow direction, and the included angle with the horizontal direction is 1 to 5 degrees; in the composite tray, at least two baffles are arranged on each inclined tray, one of which is arranged at the edge of the inclined tray, and at least one row of downcomer holes is arranged in front of each baffle on the inclined tray; the composite tray includes a single-tray composite tray or a double-tray composite tray. The single-tray composite tray has one inclined tray arranged on the same cross-section of the column body, and the double-tray composite tray has two symmetrically arranged inclined trays on the same cross-section of the column body; in the single-tray composite tray, the number of layers of the inclined tray is at least two, and the inclination directions of adjacent two layers of inclined trays are opposite. The inclined tray is in a bow shape, and the edge of the arc segment of the bow coincides with the inner side of the column body, and there is a gap between the straight segment edge and the column body; in the double-tray composite tray, the inclination directions of the two inclined trays on the same cross-section of the column body are opposite, the number of layers of the inclined tray is at least two, and in adjacent two layers of inclined trays, one layer inclines inward with the inner walls of both sides of the column body as the base points, leaving a gap in the middle position, and the other layer inclines outward with the middle position as the base point, leaving a gap at the position close to the inner walls of both sides; the middle section of the column body further includes a gas deflector, and the gas deflector is arranged above the uppermost tray and below the lowermost tray of the composite tray; when fractionation is carried out using the plate column, during the operation of the plate column, when the vapor phase enters the middle reflux section and leaves the middle reflux section, the flow mode of the gas first changes from vertically rising through the liquid film to S-shaped rising and then to vertically rising through the liquid film.

2. The plate column according to claim 1, characterized in that, in the single-tray composite tray, the distance between the straight segment edge of the inclined tray and the column body is 15% to 30% of the column body diameter.

3. The plate column according to claim 1, characterized in that, in the double-tray composite tray, the distance between the edges of the two inward-inclined trays is 7.5% to 20% of the column body diameter.

4. The plate column according to claim 1, characterized in that, in the double-tray composite tray, the distances between the edges of the two outward-inclined trays and the column body are independently 5% to 15% of the column body diameter.

5. The plate column according to claim 1, characterized in that, the number of baffles on each inclined tray is 3 to 5.

6. The plate column according to claim 1, characterized in that, 1 to 3 rows of downcomer holes are arranged in front of each baffle on the inclined tray.

7. The plate column according to claim 1, characterized in that, two adjacent rows of downcomer holes are staggeredly distributed in front of the baffle.

8. The plate column according to claim 1, characterized in that, the distance between the downcomer holes is 2.5 to 5 times the diameter of the downcomer holes.

9. The plate column according to claim 1, characterized in that, the ordinary tray includes a valve tray or a baffle tray.

10. The plate column according to claim 1, characterized in that, the middle section of the column body further includes a reflux pump, and the reflux pump is arranged on the connecting pipeline outside the plate column at the reflux extraction port and the reflux inlet.

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