Device for distributing fluid in a downflow reactor

Abstract

The present subject matter relates to an apparatus (120) for distributing a multiphase fluid mixture to a catalyst bed in a downflow reactor (100). The apparatus (120) includes a distribution tray (140) having a plurality of distribution units (150). A distribution unit (150) includes an inner tube (210), an outer tube (220) disposed outside and concentrically with the inner tube (210), a cover (346), a cover plate (350), and a gas inlet (358). The inner tube includes a first aperture (314) that allows liquid to enter the inner tube (210) and a solid insert (326) that forms a narrow channel (330). The outer tube (220) includes a slot (338) to allow liquid to enter an annulus (342) from the distribution tray (140).

Description

TECHNICAL FIELD

[0001] The present subject matter relates generally to downflow reactors and, in particular, to an apparatus for distributing a multiphase fluid mixture to a catalyst bed in a downflow reactor. BACKGROUND

[0002] Reactor used in chemical, petroleum refining and other industries typically have a fluid flowing through a catalyst bed to perform various types of treatment such as cracking, hydrotreating, etc. The fluid can be a multiphase mixture of gas and liquid. In a downflow reactor, the gas and liquid flow in a co-current manner from the top of the reactor to the bottom of the reactor. To ensure complete and efficient utilization of the catalyst, it is necessary to distribute the mixture of gas and liquid across the catalyst bed. Typically, the distribution of the fluid in the reactor is achieved by using a distribution plate or a distribution tray. These distributors can be plates with orifices, wherein the distribution plate is disposed above the catalyst bed such that the fluid flows through the distribution plate before entering the catalyst bed. BRIEF DESCRIPTION OF DRAWINGS

[0003] The detailed description is described with reference to the accompanying figures. In the figures, the left-most (or bottom-most) digit / numeric character of each reference numeral refers to the figure in which that reference numeral first appears. Where possible, the same reference numerals are used in the different figures to refer to similar or related items.

[0004] Figure 1 An exemplary downflow reactor including an exemplary apparatus for distributing a multiphase liquid mixture according to an embodiment of the present subject matter is shown.

[0005] Figure 2 A top view of a cross-section of an exemplary distribution tray including a plurality of distribution units according to an embodiment of the present subject matter is shown.

[0006] FIG. 3(a) shows a cross-section of an exemplary distribution unit according to an embodiment of the present subject matter.

[0007] FIG. 3(b) shows a top view of a cross-section of the exemplary distribution unit shown in FIG. 3(a) along line A-A according to an embodiment of the present subject matter.

[0008] FIG. 3(c) shows a top view of a cross-section of the exemplary distribution unit shown in FIG. 3(a) along line B-B according to an embodiment of the present subject matter.

[0009] FIG. 3(d) shows an enlarged view of an exemplary dispersion section 374 according to an embodiment of the present subject matter.

[0010] FIG. 3(e) shows a top view of a cross-section of the exemplary distribution unit shown in FIG. 3(d) along line C-C according to an embodiment of the present subject matter.

[0011] Figure 3(f) illustrates a top view of a cross-section of the exemplary distribution unit shown in Figure 3(d) along line D-D, according to an embodiment of the present subject matter.

[0012] Figure 4(a) illustrates another exemplary distribution unit comprising a solid insert attached to the cover plate, according to an embodiment of the present subject matter.

[0013] Figure 4(b) illustrates a top view of a cross-section of the exemplary distribution unit shown in Figure 4(a) along line A-A, and Figure 4(c) illustrates a top view of a cross-section of the exemplary distribution unit shown in Figure 4(a) along line B-B, according to an embodiment of the present subject matter.

[0014] Figure 4(d) illustrates another exemplary distribution unit comprising a static mixer, according to an embodiment of the present subject matter.

[0015] Figure 5(a) illustrates a cross-sectional view of another embodiment of a distribution unit comprising one tube, according to an embodiment of the present subject matter.

[0016] Figure 5(b) illustrates a top view of a cross-section of the exemplary distribution unit shown in Figure 5(a) along line A-A, according to an embodiment of the present subject matter.

[0017] Figure 6 Figure 6 illustrates the variation of sensitivity with superficial velocity for Example 2, according to an embodiment of the present subject matter. DETAILED DESCRIPTION

[0018] The present subject matter relates generally to downflow reactors, and in particular to an apparatus for distributing a multiphase fluid mixture to a catalyst bed in a downflow reactor.

[0019] In a downflow reactor, a fluid having reactants enters from the top of the reactor and products are removed from the bottom of the reactor. The fluid can be multiphase and include at least one liquid phase reactant and one gaseous phase reactant. The gas and liquid reactants are mixed and passed through a catalyst bed to perform a number of processes such as hydrotreating, cracking, desulfurization, etc. It is important that the gas-liquid mixture be uniformly distributed across the catalyst bed as the mixture passes through the catalyst to ensure efficient use of the catalyst. Efficient use of the catalyst is important to ensure uniform reaction rates, increase productivity and yield. This can also allow for increased use of the catalyst before regeneration or replenishment. Further, in a hydrotreating reactor involving exothermic reactions, non-uniform distribution of the liquid or gas can result in certain areas releasing more heat than others. The high temperatures further accelerate the reaction rates, resulting in hot spots in the reactor, shortening the life of the overall catalyst.

[0020] Generally, the distribution of gas and liquid over a catalyst bed is achieved using distribution plates or distribution trays. Typically, sieve plate distribution plates and chimney distributors are used to distribute the gas and liquid reactants over the catalyst bed. Sieve tray distribution plates can be plates with orifices that are disposed horizontally above the catalyst bed. Conventional sieve tray distribution plates have orifices in the plate through which the liquid and gas flow. The gas and liquid flow through the orifices and into the catalyst bed. Since the orifices are spread out over the plate, distribution of the gas-liquid mixture is facilitated. However, if the plate is not perfectly level, then the distribution of fluid through these plates is also uniform. Over time, the plate can become out of level, i.e., the plate can become tilted such that one side of the plate can be at a slightly lower level than the other side. In this case, more fluid flows through the portion of the plate that is at the lower level than the portion of the plate that is at the higher level. In other words, the plate is very sensitive to out-of-levelness. Conventional chimney distributors include a tube (called a downcomer) that passes through an orifice in the distribution plate. Gas enters the downcomer near the top end of the downcomer and flows down the tube. Liquid collects above the tray and enters the downcomer through small holes on the side of the downcomer and then flows down with the gas. The minimum size of these holes on the side of the downcomer is about 6 mm. When the liquid is muddy, cloudy, or has scale, these holes can easily become clogged, requiring the distribution plate to be removed and cleaned. This increases reactor downtime and increases operating costs.

[0021] Furthermore, conventional distributors require a large number of orifices and specific designs to ensure uniform distribution. If the distribution plate becomes out of level, then some areas of the catalyst bed receive more gas-liquid mixture than other areas, resulting in uneven distribution of fluid over the catalyst bed. In exothermic reactions, if the distribution plate is unable to provide uniform fluid distribution to the catalyst bed (e.g., due to the distribution plate being out of level), then poor heat exchange occurs, which results in hot spots forming in the catalyst bed. This reduces reaction rates and reduces product yield.

[0022] The present subject matter overcomes these and other problems associated with current distributors in downflow reactors. The present subject matter relates to an apparatus for distributing a multiphase fluid mixture over a catalyst bed in a downflow reactor. The apparatus includes a distribution disc that includes a plurality of distribution units.

[0023] In one embodiment, the distribution unit includes an inner tube disposed over an orifice in the distribution tray. The inner tube includes a first orifice disposed on a side of the inner tube to allow liquid to enter the inner tube. A solid insert is disposed in a top of the inner tube, the solid insert having an outer diameter that is less than an inner diameter of the inner tube. The solid insert causes a narrow channel to be formed in the top of the inner tube around the solid insert to allow gas to pass through. An outer tube is disposed concentrically with the inner tube, forming an annulus between the inner tube and the outer tube. The outer tube includes a slot disposed on a bottom of the outer tube. The slot allows liquid to enter the annulus between the inner tube and the outer tube from the distribution tray. A ring-shaped cover is disposed on the top of the inner tube inside the outer tube to close the annulus at the top while leaving the top end of the inner tube open to allow gas to enter. A support structure is disposed on the outer tube at the top of the outer tube to extend above the outer tube, and a gas inlet is disposed on the support structure to allow gas to enter the distribution unit. A top end of the support structure is covered by a cover plate disposed on the support structure. Thus, gas enters the inner tube through the support structure and mixes with liquid that enters the inner tube through the first orifice. In an example, a venturi insert can be disposed within the inner tube below the first orifice to further promote mixing of the liquid and gas.

[0024] Compared to conventional distribution trays, the device of the present subject matter allows for improved distribution of liquid-gas mixture to the catalyst bed. During operation, gas flows at high velocity through the narrow channel in the inner tube, causing a pressure drop. This allows liquid that enters through the slot in the outer tube to rise in the annular region. Thus, since the liquid flow depends on the gas flow, the device of the present subject matter is less sensitive to the degree of level deviation of the distribution tray. Thus, even if the distribution tray is not level, the flow to the catalyst bed is uniform. The device can be used for a wide range of fluid flow conditions by varying the size of the solid insert in the inner tube. For example, under low gas flow conditions, the narrow channel can be made narrower than under high gas flow conditions to increase the gas velocity and thus provide a greater pressure drop, which increases the amount of liquid that enters through the slot in the outer tube and the height of the liquid rise in the annulus. This increases the dependence of the liquid flow on the gas flow even under low gas flow conditions. This is advantageous under low gas flow conditions because the use of the solid insert can create a low pressure in the annulus, so that the sensitivity to level deviation is low. As will be appreciated, the low gas flow conditions and the high gas flow conditions can correspond to different gas flow rates used in the reactor, which can depend on the reactor configuration and processing parameters.

[0025] When the liquid first enters the slot in the outer tube and then enters the first hole or the second hole (disposed above the first hole) in the inner tube, solid particles present in the liquid will be deposited on the distribution tray, wherein the first hole and the second hole are disposed 90° from the slot on the circumference of the inner tube. This prevents clogging of the holes compared to conventional distributors, allowing the distribution tray to be used for a longer time between maintenance. This reduces reactor downtime and allows for lower operating costs. A venturi insert disposed in the inner tube allows for further mixing of the gas and liquid before the mixture enters the catalyst bed. In an example, a static mixer can be disposed near the outlet of the inner tube, which further improves mixing. The enhanced mixing increases the reaction rate, thereby increasing product yield. Furthermore, the device allows for uniform flow of the liquid out of the inner tube even if the liquid to the distribution plate is uneven or pulsed.

[0026] In another embodiment, the distribution unit includes a tube disposed on the distribution tray. A first hole is disposed on a lower portion of the tube proximate to the distribution tray to allow the liquid to enter the distribution unit. A solid insert is disposed within the tube such that a lower portion of the solid insert is adjacent to the first hole. The lower portion of the solid insert has a corrugated edge and an upper portion of the solid insert has a rounded edge. A cover plate is disposed on a support structure disposed on the tube and a gas inlet is disposed on the support structure to allow the gas to enter the distribution unit.

[0027] Aspects of the present subject matter are further described in conjunction with the appended figures. It is to be noted that the description and figures merely illustrate principles of the present subject matter. It will thus be appreciated that various arrangements, although not explicitly described or shown herein, can embody the principles of the present subject matter and are included within the scope of the present subject matter. Furthermore, all statements herein reciting principles, aspects, and embodiments of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0028] Figure 1An exemplary downflow reactor according to embodiments of the present subject matter is shown, which includes exemplary apparatus for distributing a multiphase liquid mixture. The downflow reactor 100 includes a fluid inlet 110. The fluid can include a mixture of gas and liquid. The fluid flows through an apparatus 120 for distributing the mixture and into a catalyst bed 130 where catalytic hydrotreating reactions (such as hydrotreating, cracking, etc.) take place. The apparatus 120 can be a distribution tray 140, which includes a plurality of distribution units 150. In an example, after the reactions are completed, the resulting product can flow through a second apparatus 160 for distributing the product mixture to a second catalyst bed 170. The second apparatus 160 can be the same as the apparatus 120, or can be a conventional distributor. Product gas and liquid can be removed from the bottom of the reactor from a gas outlet 180 and a liquid outlet 190.

[0029] Figure 2 A top view of a cross-section of an exemplary distribution tray according to embodiments of the present subject matter is shown, which includes a plurality of distribution units. The distribution tray 140 includes a plurality of distribution units 150 (referred to individually as distribution unit 150). The plurality of distribution units 150 can be arranged in any layout on the distribution tray 140 depending on the desired flow characteristics. In an example, the plurality of distribution units 150 can be arranged in a triangular pitch. The distribution unit 150 includes an inner tube 210 and an outer tube 220, which is concentric with the inner tube.

[0030] FIG. 3(a) shows a cross-section of an exemplary distribution unit according to embodiments of the present subject matter. The distribution unit 150 includes an inner tube 210, which is vertically disposed on an aperture 310 of the distribution tray 140. The inner tube 210 includes a first hole 314 disposed on a side of the inner tube 210 at a predetermined height above the distribution tray 140 to allow liquid to enter the inner tube 210. In another example, the inner tube 210 can include two first holes 314 disposed at 180° from each other on the circumference of the inner tube 210 at the same height. In an example, a second hole 318 can be disposed on a side of the inner tube 210 above the first hole 314. In another example, the inner tube 210 can include two second holes 318 disposed at 180° from each other on the circumference of the inner tube 210. In various examples, the first hole 314 and the second hole 318 can have a circular cross-section or a cross-section of other shapes. The size of the holes 314 and 318 can be set to provide the required resistance to liquid flow depending on the operating characteristics of the reactor 100.

[0031] A venturi insert 322 can be disposed within the inner tube 210 below the first holes 314. In another example, a static mixer (not shown) can be disposed below the venturi insert 322. In an example, the static mixer can include twisted ribbons. The inlet of the venturi insert 322 is disposed such that liquid entering the inner tube 210 from the first holes 314 enters the venturi insert 322 and is further mixed with incoming gas from the top of the inner tube 210.

[0032] A solid insert 326 can be disposed coaxially with the inner tube 210 and at the top of the inner tube 210. In an example, the solid insert 326 can be shaped as a cylinder with a hemispherical top and a smooth edge at the bottom. The solid insert 326 forms a narrow channel 330 in the inner tube 210 around the solid insert 326, in which gas flows at high speed and thus creates a reduced pressure. The solid insert 326 can be held in place using support rods 328 that attach the solid insert 326 to the top end of the inner tube 210. The support rods 328 can pass through the inner tube 210 and the solid insert 326 to securely hold the solid insert 326. In an example, multiple support rods 328 can be disposed at multiple locations around the solid insert 326 with spacing between the multiple support rods 328 to allow gas to flow in. The solid insert 326 can be disposed such that the solid insert 326 is adjacent to an inner groove 334 on the inner tube 210. The inner groove 334 can be fluidly connected to the narrow channel 330. In an example, there can be two inner grooves 334 that are diametrically opposite each other. The inner grooves 334 are sized such that they provide low resistance to fluid flow.

[0033] The outer tube 220 can be disposed concentrically with the inner tube 210 on the distribution tray 140, forming an annular section 342 between the outer tube 220 and the inner tube 210. The outer tube 220 includes slots 338 disposed on the bottom of the outer tube 220 and in contact with the distribution tray 140. The slots 338 allow liquid to enter the outer tube 220 from the distribution tray 140 and into the annular section 342 between the outer tube 220 and the inner tube 210. In an example, two slots 338 can be disposed 180° apart from each other on the circumference of the outer tube 210. In another example, the slots 338 can be disposed 90° from the first holes 314 and the second holes 318. As the liquid travels upward in the annular section 342 and horizontally (e.g., at 90°) around the circumference of the inner tube 210 in the annular region, most undesirable particles or scale deposits on the distribution tray 140. This prevents clogging of the first holes 314 or the second holes 318. Depending on the capacity of the reactor 100, the size of the slots 338 and the size of the diameter of the outer tube 220 can be set to provide a calculated resistance for the liquid to flow through the annular section 342.

[0034] A lid 346 can be provided on top of the inner tube 210 within the outer tube 220 to cover the annular section 342 while keeping the top end of the inner tube 210 open. The lid 346 can be, for example, ring shaped. In an example, a solid insert 326 can be attached to the lid 346. A cover plate 350 can be provided on a support structure 354 which is provided on the outer tube 220. The cover plate 350 covers the dispensing unit 150 on top. In an example, the support structure 354 can be a welded metal rod or bar to hold the cover plate 350 in position above the outer tube 220. A gas inlet 358 can be provided on the support structure 354 to allow gas to enter the dispensing unit as shown by the arrow 358.

[0035] During operation, liquid accumulates on the dispensing tray 140, forming a liquid level 362. Gas enters the dispensing unit 150 via the gas inlet 358 and enters the inner tube 210 via the narrow channel 330 (shown by the multiple dotted arrows in Figure 3(a)). As the gas is less dense, the gas path volume is reduced to create a pressure drop which can cause the liquid in the annular section 342 to rise. This is achieved using the solid insert 326 in the upper region of the inner tube by creating the narrow channel 330. As a result, the liquid level within the annular section 342 is increased compared to the liquid level on the dispensing tray 140. Because the high velocity in the narrow channel 330 causes a low pressure in the narrow channel 330, the gas does not flow into the annular section 342, the low pressure is transmitted to the annular section 342 as the inner channel 334 is in fluid communication with the annular section 342 and the narrow channel 330, and causes the liquid in the annular section 342 to rise to an annular liquid level 366. The liquid in the annular section 342 enters the inner tube 210 via the first hole 314 (liquid flow is shown by the multiple solid arrows in Figure 3(a)). The presence of the venturi insert 322 increases the mixing between the gas and the liquid. In an example, if the annular liquid level 366 is high, liquid can also enter the inner tube 210 via the second hole 318. If the annular liquid level 366 rises further, liquid can enter the inner tube 210 via a third hole (not shown in the figure). Any shape, any number of holes can be provided on the inner tube 210 to allow liquid to enter. It is preferable that the holes are immersed in the liquid, otherwise it can not be possible to maintain a low pressure in the annular section 342 (compared to the pressure in the inner tube 210). For higher liquid flow rates, it is preferable that the liquid flows past the lower end of the inner channel 334. However, at the lower end of the inner channel 334, because the inner channel is close to the narrow channel 330, the low pressure in the annular section 342 is not greatly affected even if they are not immersed in the liquid. The position of the solid insert 326 allows a low pressure region to be formed just at the inner channel 334 and for the low pressure to enter the annular section 342. This ensures that the low pressure is directly imparted to the annular section 342 without reducing the gas path too much, which is particularly advantageous for relatively low gas flow rates.

[0036] For low liquid flow rates, the size of the hole in conventional dispensers is very small, which results in clogging of the liquid hole for slurry liquid. However, in the present subject matter, as the first orifice 314 is provided on the inner tube 210 which is inside the outer tube 220, the chances of clogging of the hole are reduced as the particles settle on the tray rather than entering the inner tube 210.

[0037] In an example, a tube structure 370 can be provided below the first orifice 314 and the venturi insert 322. The tube is held in position by a hole plate 371. The tube structure 370 can be provided on the bottom of the inner tube 210 above the orifice 310. The tube structure 370 further reduces the cross sectional area of the fluid flow. The shape of the tube structure 370 can be any shape which provides a constriction in the fluid flow path in the inner tube 210. The size of the tube structure 370 is provided to provide a calculated flow resistance and the shape of the tube structure 370 is provided to provide a constriction in the fluid flow path. The presence of this flow resistance increases the liquid level in the annular portion 342 of the dispensing unit 150. This resistance to liquid flow acts in series with the resistance caused by the liquid flow through the first orifice 314. The shape of the outlet of the tube structure 370 is provided to splash the gas-liquid mixture on the portion below. In conventional dispensers, the minimum size of the hole for liquid flow in the downflow tube (for example, in chimney type dispensers) is about 6 mm. In case of low liquid flow, it is not advisable to further reduce the size of the hole to increase the resistance to liquid flow as it results in clogging of the hole. In the present subject matter, due to the above reasons, with the flow resistance in the inner tube 210, by proper adjustment of the size of the tube structure 370, the required flow resistance is provided without clogging. Additionally, some resistance to liquid flow can also be provided by the slots 338.

[0038] The liquid level in the annular portion 342 is more stable as compared to the liquid level outside the outer tube 220 due to control by the gas flow rate. As the outer tube 220 helps to dampen the liquid waves on the tray plate, the amount of liquid entering the inner tube 210 is more uniform without much pulsation or uneven flow. This results in uniform flow of liquid through the first orifice 314 into the inner tube 210.

[0039] Since there is no pressure differential between the inner tube 210 and the annular portion 342 (as there is no gas flow through the inner channel 334 or minimal gas flow through the inner channel 334), the flow of liquid from the annular portion 342 to the inner tube 210 is only due to the liquid head in the annular portion 342 and not due to the low pressure in the inner tube 210. As a result, the liquid flow is only due to the liquid head, which reduces the liquid flow through the second hole 318 (disposed above the first hole 314). Since there is no significant deviation when the liquid level passes above the first hole 314 or the second hole 318, the device 120 can operate through only the first hole 314 or through both the first hole 314 and the second hole 318, which increases the operating range of the dispensing unit 150.

[0040] Since the liquid level depends on the gas flow through the narrow channel 330 and the resistance provided by the tubular structure 370, when the dispensing tray 140 is tilted from the horizontal, the liquid flow through the dispensing unit 150 that is lower than the other dispensing units 150 increases due to the same pressure drop across the dispensing units 150 on the dispensing tray 140. As a result, the gas flow through the narrow channel 330 is lower. Due to the presence of flow resistance caused by the tubular structure 370, when the dispensing tray 140 is tilted from the horizontal, the total pressure drop across the dispensing units 150 is equal, and hence the lower dispensing units 150 deliver more liquid, resulting in lower gas flow. This results in less gas flowing into the lower dispensing units 150, which results in a lower accumulation of liquid level in the annular portion 342, resulting in less liquid flow. Thus, the dispensing tray 140 is less sensitive to the deviation in the level of horizontality.

[0041] Figure 3(b) illustrates a top view of a cross-section of the exemplary dispensing unit shown in Figure 3(a) along line A-A, according to an embodiment of the present subject matter. The outer tube 220 is disposed concentrically with the inner tube 210 and is disposed outside the inner tube 210 to form the annular region 342. The solid insert 326 is disposed in the inner tube 210 to form the narrow channel 330 in the inner tube 210. The inner tube 210 has two inner channels 334 that open into the annular region 342.

[0042] Figure 3(c) illustrates a top view of a cross-section of the exemplary dispensing unit shown in Figure 3(a) along line B-B, according to an embodiment of the present subject matter. The first hole 314 is disposed on the inner tube 210. Two slots 338 are disposed on the outer tube 220 such that the two slots 338 are disposed 180° apart from each other on the circumference of the outer tube 220 and are disposed 90° apart from the first hole 314.

[0043] Figure 3(d) illustrates an enlarged cross-sectional view of an example dispersion section 374, in accordance with an embodiment of the present subject matter. In an example, the dispersion section 374 can be disposed below the outlet of the inner tube 210. The dispersion section 374 allows the exiting gas-liquid mixture to be dispersed before entering the catalyst bed. The dispersion section 374 can include a plurality of dispersion slots 378. The plurality of dispersion slots 378 can be disposed at the outlet of the inner tube 210. In one example, the width of the plurality of dispersion slots 378 can be equal to the spacing between them. An upper screen plate 382 can be attached below the dispersion slots 378 such that there is a height h between the upper screen plate 382 and the dispersion slots 378. A splash guard 384 can be disposed on the upper screen plate 382 such that the top of the splash guard 384 is at the same height h above the top of the upper screen plate 382.

[0044] A pipe fitting structure 370 can be shaped to direct the fluid onto the splash guard 384. The pipe fitting structure 370 is intended to be used with the splash guard 384. When the fluid mixture is directed by the pipe fitting structure 370, the fluid hits the splash guard 384, thereby dispersing the liquid through the dispersion slots 378. A portion of the liquid is dispersed and passes through the dispersion slots 378. Another portion of the liquid passes through the upper screen plate 382 and is dispersed over the larger diameter lower screen plate 320, where the liquid is dispersed even more widely. The lower screen plate 320 has a screen plate wall 323 that is on the edge with screen plate slots 324. This allows an amount of liquid to remain on the lower screen plate 320, thereby allowing the liquid to flow uninterrupted.

[0045] Figure 3(e) illustrates a top view of a cross-section of the example distribution unit shown in Figure 3(d) along line C-C, in accordance with an embodiment of the present subject matter. The splash guard 384 is disposed on the upper screen plate 382 that includes the screen holes 325.

[0046] Figure 3(f) illustrates a top view of a cross-section of the example distribution unit shown in Figure 3(d) along line D-D, in accordance with an embodiment of the present subject matter. The lower screen plate 320 includes the screen plate slots 324 and the lower screen holes 321. The lower screen plate 320 allows the fluid to have more diffusion before entering the catalyst bed.

[0047] Figure 4(a) illustrates another example distribution unit that includes a solid insert attached to a cover plate, in accordance with an embodiment of the present subject matter. A solid insert 326b is disposed within the inner tube 210. The top of the solid insert 326b can be detachably (e.g., using bolts) attached to the cover plate 350. This allows the solid insert to be replaced as needed for processes or reactors that require different gas flow rates. For example, for low gas flow rates, a solid insert 326b with a larger diameter can be used. A dispersion section 374 can be disposed below the outlet of the inner tube 210.

[0048] Figure 4(b) illustrates a top view of a cross-section of the exemplary distribution unit shown in Figure 4(a) along line A-A, and Figure 4(c) illustrates a top view of a cross-section of the exemplary distribution unit shown in Figure 4(a) along line B-B, according to an embodiment of the present subject matter. With reference to Figure 4(b), the solid insert 326b can be provided within the inner tube 210. The inner tube 210 has two inner slots 334. The outer tube 220 is provided concentrically with the inner tube 210 and outside the inner tube 210. With reference to Figure 4(c), the first hole 314 is provided on the inner tube 210. Two slots 338 are provided on the outer tube 220 such that the two slots 338 are provided 180° apart from each other on the circumference of the outer tube 220 and 90° apart from the first hole 314.

[0049] Figure 4(d) illustrates another exemplary distribution unit including a static mixer, according to an embodiment of the present subject matter. In another example, a tube structure 370 can be provided below the first hole 314 and the static mixer 322b. In an example, the static mixer 322b can include twisted ribbons. Any other static mixer known in the art can be used. The inlet of the static mixer 322b is provided such that the liquid enters each opening of the static mixer 322b from the first hole 314 and mixes with the incoming gas in a series of rotations. The thickness of the ribbons of the static mixer 322b can be varied such that there is no significant pressure loss due to the static mixer 322b. The static mixer 322b can be provided close to the outlet of the inner tube 210 to cause the gas-liquid mixture exiting the inner tube 210 to have a swirling motion.

[0050] The tube structure 370 can be provided on the bottom of the inner tube 210 above the orifice 310. The tube structure 370 reduces the cross-sectional area of the fluid flow. The shape of the tube structure 370 can be any shape that provides a constriction in the fluid flow path in the inner tube 210. The dimensions of the tube structure 370 are provided to provide a calculated flow resistance and the shape of the tube structure 370 is provided to provide a constriction in the fluid flow path. The presence of this flow resistance increases the liquid level in the annular portion 342 of the distribution unit 150. This resistance to liquid flow is in series with the resistance caused by the first hole 314 through which the liquid flows. The shape of the outlet of the tube structure 370 is provided to cause the gas-liquid mixture to splash onto the portion below. In a conventional distributor downcomer (for example, in a chimney type distributor), the minimum size of the hole for liquid flow is about 6 mm. In case of low liquid flow, it is not advisable to further reduce the hole size to increase the resistance to liquid flow as this can cause clogging of the hole. The required flow resistance in the present subject matter is provided by utilizing the flow resistance in the inner tube 210 by appropriately determining the dimensions of the tube structure 370. Further, the required resistance to liquid flow can also be imparted by the slots 338.

[0051] FIG. 5(a) illustrates a cross-sectional view of another embodiment of a distribution unit comprising a tube, according to an embodiment of the present subject matter. In another embodiment, the distribution unit 500 comprises a tube 510 disposed over an orifice 514 on the distribution tray 140. A first hole 518 can be disposed on the lower portion of the tube 510 proximate to the distribution tray 140 to allow liquid to enter the distribution unit 500. In an example, there can be two first holes 518 disposed at the same height on the circumference of the tube 510, 180° apart from each other. A solid insert 522 can be disposed within the tube 510 such that the lower portion of the solid insert 522 is adjacent to the first hole 518. The lower portion of the solid insert 522 can have a corrugated edge 526 and the upper portion of the solid insert 522 can be hemispherical or can have a circular arc edge 530. The solid insert 522 can be held in place using a support rod 528 that attaches the insert to the tube 510. The support rod 528 can pass through the tube 510 and the solid insert 522 to securely hold the insert 522. The support rod 528 can exist at multiple locations around the solid insert 522 while leaving enough space to allow gas and liquid flow. A cover plate 534 can be disposed on a support structure 538 disposed on the tube 510. A gas inlet 542 can be disposed on the support structure 538 to allow gas to enter the distribution unit 500. The distribution unit 500 can comprise a second hole 546 disposed on the portion of the tube 510 above the first hole 518. The second hole 546 allows liquid to enter the tube 510. A top slot 550 can be disposed proximate to the top of the tube 510 to allow liquid to enter the tube in case the liquid level 554 on the distribution tray 140 becomes high or the flow conditions increase.

[0052] In an example, the first hole 518 can be disposed 1 inch to 4 inches above the distribution tray 140. The size of the first hole 518 and the second hole 546 can be set to provide the required resistance to liquid flow, depending on the operating characteristics of the reactor. The solid insert 522 effectively reduces the flow path and creates a channel 562 between the solid insert 522 and the tube 510. The supplied gas flows through the channel 562 at high velocity, creating a low pressure region in this area. The liquid from the distribution tray 140 is drawn towards this low pressure region and the corrugated edge 526 increases the mixing of the liquid with the gas.

[0053] An orifice insert 558 can be provided at the outlet of the tube 510, which reduces the flow area, thereby enhancing the mixing of gas and liquid. In an example, the orifice insert 558 can be provided 1-3 inches below the solid insert 522. In one example, the orifice 514 can be part of the orifice insert 558, and in this case, the orifice 514 can be provided higher or lower in the tube 510, and can be different from the tray orifice, which is the location at which the tube 510 is attached to the tray 140. In another example, a venturi insert can be provided below the first orifice 518. In an example, the dispersion section 374 as described above can be provided below the outlet of the tube 510. A distribution tray 140 comprising a plurality of distribution units 500 can be used to distribute the gas-liquid mixture in a reactor.

[0054] Figure 5(b) shows a top view of the cross-section of the example distribution unit shown in Figure 5(a) along line A-A, according to an embodiment of the present subject matter. The solid insert 522 is adjacent to two first orifices 518, which are provided 180° apart on the circumference of the tube 510.

[0055] During operation, the low pressure in the channel 562 causes liquid to be pulled into the tube 510 via the first orifice 518. As a result, the driving force of the liquid flow is increased, which increases the gas velocity, compared to the liquid head above the tray 140. This helps to place lower requirements on the height of the distribution unit 500, with the same sensitivity to level deviations.

[0056] The volumetric liquid flow rate is

[0057] Q L = f(H 0.5 ) + g(Q G )

[0058] where H = liquid height above the lowest orifice,

[0059] Q L = volumetric liquid flow rate

[0060] Q G = volumetric gas flow rate

[0061] f(H 0.5 ) is a function of h 0.5

[0062] g(Q L ) is a function of Q L ​Another function of the tray 140 is that when the tray 140 is off level, the lower distribution units pass more liquid due to the increased height. This causes less gas to flow through that particular distribution unit because the pressure drop is reduced due to the lower gas flow, which in turn reduces the amount of liquid that flows through the distribution unit. Thus, the distribution device has a lower sensitivity to level deviation because the liquid flow depends on the increased gas velocity.

[0063] Examples

[0064] The present disclosure will now be demonstrated with operational examples, which are intended to demonstrate the operation of the present disclosure and are not intended to limit the scope of the present disclosure in any way. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods and to the described experimental conditions, as these can vary.

[0065] Example 1

[0066] The advantages of using a solid insert 326 in the distribution unit 150 (including inner tube 210 and outer tube 220) will be demonstrated below. This is compared to a conventional distribution tray without a chimney-type distribution unit. The distribution tray is off level with respect to the horizontal plane such that the higher distributors are 1 cm above the lower distributors. The sensitivity that results from a 1 cm level deviation is defined as:

[0067]

[0068] Q L = f(H 0.5 ) + g(Q G )

[0069] where Q low is the volumetric liquid flow rate through the lower distribution units and Q high is the volumetric liquid flow rate through the higher distribution units.

[0070] Table 1 shows a comparison of the sensitivity of the distribution device of the present subject matter and a conventional device to level deviation. The distribution unit of the present subject matter has the least sensitivity to level deviation at both high and low flow rates. Increasing the solid insert 326 and additional resistance (such as the venturi insert 370) further reduces the sensitivity.

[0071] Table 1: Comparison of sensitivity of different distribution devices to level deviation.

[0072]

[0073] Example 2

[0074] The following is to illustrate the different benefits of the distribution unit 150 (with inner tube 210 and outer tube 220) compared to a traditional chimney-type distributor. The distribution tray is offset from horizontal such that the higher distributors are located 1 cm above the lower distributors. The sensitivity resulting from the 1 cm levelness deviation is defined as

[0075]

[0076] where Q low is the volumetric liquid flow rate through the lower distribution unit, Q high is the volumetric liquid flow rate through the higher distribution unit. A low value of sensitivity indicates better performance in case of liquid depth non-uniformity on the tray.

[0077] Figure 6 The sensitivity of Example 2 according to embodiments of the present subject matter is shown as a function of superficial velocity. The range of operating superficial velocities of liquid in a typical hydroprocessing reactor is between 0.3 cm / s and 1.2 cm / s. The solid line 610 is for the distribution unit 150 of the present subject matter, and the dashed line 620 is for a standard chimney-type distributor with slot openings. The dash-dot line 630 shows the sensitivity of a conventional chimney-type distributor with two holes. This figure shows that the sensitivity of the distribution unit 150 is less than the 20% limit (which is better than the 20% acceptable limit) for velocities above 0.3 cm / s. This is achieved due to the combined effect of using the solid insert 326 and the additional inserts such as the Venturi insert 322 and the pipe fitting structure 370 in order to account for the flow resistance in the inner tube 210. In contrast, the conventional distributor cannot achieve a sensitivity below 20% at any flow rate, and the distributor with two holes can achieve a sensitivity below 20% only at high flow rates above about 0.7 cm / s.

[0078] Example 3

[0079] A comparison of two distributors is made to illustrate the advantage that the liquid flow rate depends on the gas velocity in addition to the static liquid head. Table 2 shows a comparison of the sensitivity values and the liquid level height values for a conventional chimney-type distributor and for a distribution unit 500 including the pipe 510. At equal sensitivity, it can be seen that the distribution unit 500 of the present disclosure has a liquid level height of 3 cm compared to the conventional chimney-type distributor. The additional height can be used for catalyst bed.

[0080] Q L = f(H 0.5 ) + g(QG

[0081] Table 2: Comparison of sensitivity to level deviation for conventional dispensers and dispensers of the present disclosure (with one tube).

[0082]

[0083] While the embodiments of the subject matter have been described in terms of specific languages of structural features, it is to be understood that these specific features and methods are as illustrative examples only.​

Claims

1. An apparatus for distributing a multiphase fluid mixture to a catalyst bed in a downflow reactor, the apparatus comprising a distribution tray, the distribution tray comprising a plurality of distribution units, wherein, The allocation unit includes: An inner tube, the inner tube being disposed on an opening in the dispensing tray, wherein the inner tube comprises: A first orifice, provided on a portion of the inner tube, allows liquid to enter the inner tube; and A solid insert is disposed at the top of the inner tube, wherein the solid insert forms a narrow channel in the top of the inner tube to allow gas to pass through; An outer tube, concentric with the inner tube and disposed on the dispensing tray, wherein the outer tube comprises: A slot is provided on the bottom of the outer tube, wherein the slot allows liquid to enter from the dispensing tray into the annular portion between the inner tube and the outer tube; A cover, which is disposed on the top of the inner tube inside the outer tube, to close the annular portion on the top; A cover plate, the cover plate being disposed on a supporting structure, the supporting structure being disposed on the outer tube; and A gas inlet is provided in the support structure to allow gas to enter the distribution unit.

2. The apparatus according to claim 1, wherein, The inner tube includes a second hole, which is disposed on the portion of the inner tube above the first hole.

3. The device according to claim 1, comprising two first holes, wherein, The two first holes are arranged at 180° to each other on the circumference of the inner tube.

4. The device according to claim 2, comprising two second holes, wherein, The two second holes are arranged at 180° to each other on the circumference of the inner tube.

5. The device according to claim 1, comprising two slots arranged at 180° to each other on the circumference of the outer tube.

6. The apparatus according to claim 2, wherein, The slot is set at a 90° angle to the first hole and the second hole.

7. The apparatus according to claim 1, wherein, The bottom of the inner tube above the orifice includes a Venturi insert, wherein the Venturi insert reduces the cross-sectional area for fluid flow.

8. The apparatus of claim 7, comprising a tubular structure disposed below the venturi insert.

9. The apparatus according to claim 1, wherein, The inner tube includes an inner groove that fluidly connects the narrow channel and the annular portion located between the inner tube and the outer tube.

10. The apparatus according to claim 9, wherein, The inner tube includes two inner grooves that are opposite each other in diameter.

11. The apparatus according to claim 1, comprising a dispersing section disposed at the outlet of the inner tube.

12. The apparatus according to claim 11, wherein, The dispersion section includes a dispersion tank, an upper sieve plate, and a splash guard.

13. A reactor comprising the apparatus of claim 1.

14. An apparatus for dispensing a multiphase fluid mixture to a catalyst bed, the apparatus comprising a dispensing tray, the dispensing tray comprising a plurality of dispensing units, wherein, The allocation unit includes: The tube is disposed on an opening in the dispensing tray; A first hole is provided on the lower part of the tube near the dispensing tray to allow liquid to enter the dispensing unit; A solid insert is disposed within the tube such that its lower portion is adjacent to the first hole, wherein... The lower portion of the solid insert has a corrugated edge, and The upper part of the solid insert has an arc-shaped edge; A cover plate, the cover plate being disposed on a supporting structure, the supporting structure being disposed on the pipe; and A gas inlet is provided on the support structure to allow gas to enter the distribution unit.

15. The apparatus of claim 14, further comprising a second hole disposed on the portion of the tube above the first hole, wherein, The second hole allows liquid to enter the tube.

16. The apparatus of claim 14, further comprising a top groove disposed near the top of the tube to allow liquid to enter the tube.

17. The apparatus according to claim 14, wherein, The first hole is located 1 to 4 inches above the dispensing tray.

18. The apparatus of claim 14, further comprising a venturi insert disposed near the outlet of the tube.

19. The device of claim 14, comprising two first holes arranged at 180° to each other on the circumference of the tube.

20. A reactor comprising the apparatus of claim 14.

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