RU2811916C1 - Device for separating vapors and catalyst at outlet of riser of catalytic cracking unit - Google Patents

Abstract

FIELD: oil refining.

SUBSTANCE: devices for separating vaporous cracking products and catalyst particles suspended in them at the outlet of the riser of a catalytic cracking unit. Device (1) for separating vapors and catalyst at the outlet of the riser of a catalytic cracking unit, including a straight inlet pipe (3) connected by means of a rotary connecting pipe (4) with a receiving chamber (5), a drain pipe (6) with the possibility of outlet spent catalyst and gas outlet pipe (7), wherein the rotary connecting pipe (4) includes a sequentially located main section (8) and a transition section (9) with a smooth narrowing of the passage, the outlet of which is connected to the inlet of the receiving chamber (5); the receiving chamber (5) is equipped with first and second outlets, with the first outlet connected to the drain pipe (b), and the second outlet is a gas collection pipe (10), equipped with a slot (11) and adjacent to the rotary connecting pipe (4) in the transition area from the main section (8) to the transition section (9), while the gas collection pipe (10) is connected to the gas outlet pipe (7) and is made cylindrical, with a diameter d and an axis parallel to the surface of the rotary connecting pipe (4), and the length of the transition section (9) with a smooth narrowing of the passage lies in the range from 0.8d to l.5d, and the smooth narrowing of the passage of the transition section (9) is no more than 20%.

EFFECT: increase in the separation properties of the device while simultaneously reducing the erosive effect on its structural elements.

1 cl, 1 tbl, 2 dwg

Description

The invention relates to the field of oil refining, in particular to devices for separating vaporous cracking products and catalyst particles suspended in them at the outlet of the riser reactor of a catalytic cracking unit.

From the prior art, a device is known for separating gas and solid particles suspended in it, disclosed in patent RU 2115460, published on July 20, 1998. The known device is intended for separating gas and solid particles suspended in it at the outlet of a pneumatic conveying line and includes a receiving chamber connected to nozzle at the end of the pneumatic conveying line. The outlet section of the pipe is bent by 45-180° with a radius of 1.0-7.0 of the minimum transverse dimensions of the pipe. The receiving chamber is also connected to the solids collection chamber. The device is equipped with a gas exhaust chamber connected to means for gas purification. The number of receiving chambers, gas exhaust chambers and pipes is provided from 1 to 8. A vortex chamber is attached to each receiving chamber, the longitudinal surface of which is curved by 60-360° with a radius of 0.8-6.0 of the minimum transverse dimensions of the pipe, connected to the gas exhaust chamber and the collection particle chamber. The gas exhaust chamber is installed inside the vortex chamber, and the axis of the longitudinal surface of the vortex chamber is parallel to the longitudinal surface of the gas exhaust chamber. The flow area at the entrance to the vortex chamber is 40-95% of the cross-section of the outlet section of the pipe at the end of the pneumatic transport line.

The disadvantage of this device is that the entrance to the additional vortex chamber of the device is connected to the receiving chamber, and the inlet pipe of the receiving chamber connecting it to the pneumatic transport line is not adjacent to the gas exhaust chamber, as a result of which the dusty flow of gas suspension may partially enter the gas exhaust chamber. before it has made a full revolution in the curved part of the nozzle, which significantly reduces the efficiency of particle separation. The vortex chamber is located inside the receiving chamber and its transverse size is smaller than the size of the receiving chamber by the size of the curved part of the inlet pipe, which significantly shortens the path from the entrance to the vortex chamber to the entrance to the gas exhaust chamber, which also significantly reduces the efficiency of separating particles from gas at the second stage of separation. An increased flow rate of a gas suspension in a vortex chamber can lead to increased erosive wear of device elements, including the vortex and gas exhaust chambers.

Also known from the prior art is a device disclosed in US Patent No. 6,113,777, published on September 5, 2000. The known device includes at least one chamber containing a zone with a rectangular or square cross-section for passing the mixture circulating in the reactor, and a rotary zone that turns the mixture to be separated in a vertical plane at an angle of no more than 360°. The rotating zone has an outer wall that specifies a rotation through an angle from 70 to 225°, and an inner wall that rotates coaxially with the outer wall at an angle of at least 30° and no more than the angle at which the outer wall rotates plus 90°. The device is equipped with a gas outlet pipe, which is coaxial with the rotating zone, and an outlet for separated particles.

The known device separates the flow of the steam-catalyst mixture in one stage due to the influence of centrifugal forces when turning the flow. However, a rotation of 70-225° alone is not enough to completely separate the vapors and the catalyst. In addition, if the internal wall of the turning zone is not long enough, catalyst particles will be drawn into the gas outlet pipe, which will provoke further undesirable thermal reactions in the mixture, and will also require additional measures for high-quality separation of the mixture.

The technical problem to be solved by the present invention is to create a device for separating vapors and catalyst at the outlet of the riser reactor of a catalytic cracking unit, which has high efficiency and reliability with a short separation time.

The technical result achieved when using the claimed invention is to increase the separation properties of the device while simultaneously reducing the erosive effect on its structural elements.

The technical problem is solved, and the technical result is achieved due to the fact that the device for separating vapors and catalyst at the outlet of the lift reactor of the catalytic cracking unit includes a straight inlet pipe connected by means of a rotary connecting pipe to the receiving chamber, a drain pipe with the possibility of removing the spent catalyst , and gas outlet pipe. The rotary connecting pipe includes a sequentially located main section and a transition section with a smooth narrowing of the passage, the outlet of which is connected to the inlet of the receiving chamber. The receiving chamber is equipped with first and second outlets, the first outlet being connected to the drain pipe, and the second outlet being a gas collection pipe provided with a slot and adjacent to the rotary connecting pipe in the area of transition from the main section to the transition section. The gas collection pipe is connected to the gas outlet pipe.

A sharp turn in the flow at the entrance to the device from the lift reactor can negatively affect the uniformity of flow distribution in the device, increasing flow turbulence and increasing local resistance.

It is well known that the main reason for reducing the efficiency of phase separation in separation devices is the intensity of turbulence of the incoming two-phase flow and its turbulization inside the device. Since the magnitude of efficiency depends on the scale of turbulence and the amount of energy lost by the flow in the apparatus due to hydraulic resistance, it is advisable to reduce these two factors by all means.

The presence of a straight inlet pipe helps to reduce the intensity of turbulence at the entrance to the rotary connecting pipe and reduce local resistance, which makes it possible to increase the efficiency of separation of vaporous cracking products and catalyst particles suspended in them.

The implementation of the claimed device with two zones of rotation of the separated flow makes it possible to increase the efficiency of separation of the flow of the steam-catalyst mixture. Upon entering the straight inlet pipe, the flow is leveled, after which the mixture flow is rotated, during which, due to centrifugal forces, the first stage of separating the catalyst from the vapor occurs. At the end of the turning section, the flow section begins to gradually narrow to increase the flow rate of the separated flow. In this case, slower catalyst particles move near the outer wall of the rotary connecting pipe, and faster vapors move closer to the axis of rotation of the rotary connecting pipe. Thus, an additional separation of the mixture by movement speed is ensured, which, at the end of the transition section of the rotary connecting pipe, due to the ballistic effect, allows for the second stage of separating the remaining catalyst particles from the vapor. In addition, the presence of a transition section makes it possible to move the separated catalyst away from the slot of the gas collection pipe and reduce the likelihood of re-entrainment of this catalyst by vapors, which allows minimizing the drawing of catalyst particles into the gas outlet pipe.

The technical problem is solved, and the technical result is also achieved in the following particular embodiments of the device.

The gas collection pipe is made cylindrical with a diameter d and an axis parallel to the surface of the rotary connecting pipe, and the length of the transition section with a smooth narrowing of the passage lies in the range from 0.8d to l.5d.

The smooth narrowing of the passage of the transition section is preferably no more than 20%.

Such values are due to the need to ensure free passage of the catalyst separated at the first stage of separation and to reduce erosive wear of the inner wall of the transition pipe adjacent to the gas collection pipe.

The claimed device is illustrated by drawings. Figure 1 schematically shows an example of one of the embodiments of a device for separating vapors and a catalyst at the outlet of the riser reactor of a catalytic cracking unit. Figure 2 also shows one embodiment of the device.

A device for separating vapors and catalyst at the outlet of the riser reactor of a catalytic cracking unit (see Figs. 1 and 2) is designed for quick and effective separation of vapors of cracking products from the coked catalyst at the outlet of the riser reactor of a catalytic cracking unit in order to significantly reduce the share secondary thermal cracking reactions on a coked catalyst, leading to the decomposition of the target products, reducing their yield and increasing the yield of dry gas and coke. For clarity, the movement of vapors and the catalyst is shown by arrows, vapors of cracking products are shown by black arrows, and the coked catalyst is shown by white arrows. The device (1) is located directly at the outlet of the lift reactor (2) of the catalytic cracking unit and is connected to it by an inlet straight pipe (3), connected by means of a rotary connecting pipe (4) to the receiving chamber (5). The rotary connecting pipe (4) includes a sequentially located main section (8) and a transition section (9) with a smooth narrowing of the passage, the outlet of which is connected to the inlet of the receiving chamber (5). The receiving chamber (5) is equipped with first and second terminals. The first outlet is connected to the drain pipe (b), and the second outlet is a gas collection pipe (10) equipped with a slot (11). In this case, the gas collection pipe (10) is adjacent to the rotary connecting pipe (4) in the area of transition from the main section (8) to the transition section (9), in other words, in the area where the narrowing of the rotary connecting pipe (4) begins. The gas collection pipe (10) is connected to the gas outlet pipe (7).

The gas collection pipe (10) can be made cylindrical with a diameter d and an axis parallel to the surface of the rotary connecting pipe (4), and the length of the transition section (9) with a smooth narrowing of the passage preferably lies in the range from 0.8d to l.5d. The specified range of sizes determines the distance from the area (12) of the exit of the dusty gas flow from the rotary connecting pipe (4) to the slot (11) of the gas collection pipe (10), necessary for the effective separation of vapors from catalyst particles when the vapor flow of cracking products flows around the wall of the transition section ( 9) a rotating connecting pipe (4) and eliminating the re-capture of the separated catalyst from the receiving chamber (5). The preferred length is determined by the space required to completely rotate the separated flow around the wall of the transition section (9) and separate the remaining catalyst particles from the cracking product vapors before the latter enters the slot (11).

Preferably, the smooth narrowing of the passage of the transition section (9) is no more than 20%, which also makes it possible to significantly reduce the erosive wear of the device elements, including the transition section (9) of the rotary connecting pipe (4) and the receiving chamber (5), and also provides better quality separation of the flow when the vapor flow of the cracking products passes around the wall of the transition section (9). The narrowing of the passage, combined with its smoothness, makes it possible to increase the speed of movement of the separated flow before going around the wall of the transition section (9). Due to the fact that the catalyst, heavier than the rest of the mixture being separated, receives less acceleration, such a narrowing of the passage will improve the separation characteristics of the device, and also, when going around the wall of the transition section (9), provide better separation of the remaining catalyst particles from the vapor.

Device (1) operates as follows.

The steam catalyst mixture from the lift reactor (2) enters the straight inlet pipe (3) of the device (1) at a high linear speed. Next, the steam-catalyst mixture enters the rotary connecting pipe (4), where, due to centrifugal forces, it is freed from most of the catalyst. Then the steam-catalyst mixture, partially cleared of the catalyst, flows from the main section (8) of the rotary connecting pipe (4) into the transition section (9) with a smooth narrowing of the passage. The smooth narrowing of the passage increases the speed of movement of the passing mixture, enhancing the centrifugal separation of the catalyst from the vapors carried out in the rotary connecting pipe (4). The vapors, bending around the wall of the transition section (9), enter the gas collection area (marked by hatching in Figs. 1 and 2) of the receiving chamber (5), then into the slot (11) of the gas collection pipe (10) and then into the gas outlet pipe (7), and the remaining part of the catalyst, having a significantly greater inertia than the vapors, separated from the latter, continues to move in a given direction and, together with the catalyst, previously separated due to centrifugal forces at the first stage of separation, enters the receiving chamber (5) and is directed to its first outlet and drain pipe (6), and from there - into the spent catalyst collection tank and/or the stripping zone of the reactor. Vapors from the gas outlet pipe (7) are supplied for further purification and processing.

The internal surfaces of the pipes in the device (1) are equipped with an erosion-resistant coating to reduce wear by a high-speed flow of a concentrated steam catalyst mixture.

Using the described two-stage separation in the proposed device, a degree of vapor purification from the spent catalyst of at least 99% is achieved with a very short residence time and reduced erosive wear of the device elements, due, in particular, to the use of the ballistic principle at the second stage of separation.

Examples.

The advantages of the claimed device (1) for separating vapors and catalyst at the outlet of the lift reactor of a catalytic cracking unit are illustrated by laboratory test data conducted during experiments aimed at simulating the conditions existing in the streams of cracking products and catalyst particles suspended in them at the exit from the lift -reactors of catalytic cracking units, confirming that the maximum efficiency of separating particles of fine cracking catalyst from vapors is achieved when the length of the transition section (9) connecting the rotary connecting pipe (4) with the receiving chamber (5) is from 0.8 to 1.5 times the diameter gas collection pipe (10) for collecting purified gas and with a smooth narrowing of the passage of the specified transition section (9) no more than 20%.

Although the following example illustrates particular embodiments of the claimed device within the framework of the present invention, they are not intended to limit the general scope of the invention presented in the claims.

During the experiments, the efficiency of separation of a gas flow and an equilibrium microspherical cracking catalyst with a particle diameter of more than 20 microns was studied, taking into account the fact that the final purification of vapors from catalyst particles less than 20 microns in the reactor of an industrial catalytic cracking unit is carried out in post-purification cyclones. In each test, a model of a device with a cylindrical gas collection pipe with a diameter of d=110 mm and a number of length values of the tapering transition section of the rotary pipe of the device, formed by external and internal replaceable walls adjacent to the gas collection pipe, was studied. At the same initial value of linear velocity and flow concentration of the catalyst in the flow at the entrance to the straight inlet pipe of the device, the length of the tapering transition section of the rotary pipe was changed by replacing the specified inner wall of the transition pipe. At the same time, the degree of narrowing of the transition section of the rotary pipe at the entrance to the receiving chamber of the device also changed.

The efficiency of separating the catalyst from the gas in the experiments was characterized by the degree of purification, which shows in percentage terms the ratio of the mass of the separated catalyst entering the collection container through the outlet pipe of the device to the mass of the catalyst entering its inlet pipe as part of the gas catalyst flow.

The results of the study are shown in Table 1.

From the above data it follows that outside the declared range of values of the ratio of the length of the transition section of the rotary pipe to the diameter of the gas collection pipe from 0.8 to 1.5 and an increase in the degree of narrowing of the passage of the transition section above the declared maximum value of 20%, the efficiency of separating the catalyst from vapors in the claimed device is significantly reduced.

This is explained by the fact that at smaller values of the ratio of the length of the transition section of the rotary pipe to the diameter of the gas collecting pipe, the gas collection area behind the internal wall of the transition section of the rotary pipe adjacent to the gas collection pipe is insufficiently separated from the space of the rotary pipe, and the gas flow, when not completely bending around the specified the inner wall cannot be adequately freed from the remaining catalyst before entering the slot of the gas collection pipe.

At large values of the ratio of the length of the transition section of the rotary pipe to the diameter of the gas collecting pipe and a greater narrowing of its passage, the inner wall of the transition section of the rotary pipe introduces additional disturbance into the downward flow of the separated catalyst, which leads to an increase in flow turbulence and secondary capture of the already separated catalyst from the inlet into the gas collection area into the receiving chamber of the device.

As a result of the described adverse phenomena, when the specified parameters go beyond the stated ranges of numerical values, the efficiency of vapor separation from catalyst particles is significantly reduced. In addition, in these cases, due to an increase in turbulence and the speed of the suspended flow, the local resistance in the narrowed section of the transition section of the rotary pipe increases, which leads to increased erosive wear of the device elements and a reduction in its service life.

Claims (8)

Device (1) for separating vapors and catalyst at the outlet of the riser reactor of a catalytic cracking unit, including straight inlet pipe (3), connected by means of a rotary connecting pipe (4) to the receiving chamber (5), drain pipe (6), with the possibility of removing spent catalyst, and gas outlet pipe (7), wherein the rotary connecting pipe (4) includes a sequentially located main section (8) and a transition section (9) with a smooth narrowing of the passage, the outlet of which is connected to the inlet of the receiving chamber (5); the receiving chamber (5) is equipped with first and second terminals, wherein the first outlet is connected to the drain pipe (b), and the second outlet is a gas collection pipe (10), equipped with a slot (11) and adjacent to the rotary connecting pipe (4) in the area of transition from the main section (8) to the transition section (9 ), in this case, the gas collection pipe (10) is connected to the gas outlet pipe (7) and is made cylindrical with a diameter d and an axis parallel to the surface of the rotary connecting pipe (4), and the length of the transition section (9) with a smooth narrowing of the passage lies in the range from 0.8d up to l.5d, and the smooth narrowing of the passage of the transition section (9) is no more than 20%.

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