EP0573316A1 - Process and apparatus for the catalytic cracking in two successive reaction zones - Google Patents

Abstract

The invention relates to a catalytic cracking process, and the associated device, in which the cracking reaction takes place in two successive substantially vertical reaction zones, the charge (25) being introduced into the first zone (27) where it flows from the top. downwards, then at least part of the product obtained being introduced into a second reaction zone (28) where it circulates in an ascending manner. An additional hydrocarbon phase (33) is advantageously introduced into the product entering the second zone. The invention is particularly applicable to heavy loads, with a U-shaped device.

Description

The present invention relates to a process and a device for the catalytic cracking of hydrocarbon charges.

It is known that the petroleum industry customarily uses cracking processes in which the molecules of hydrocarbons of high molecular weight and with a high boiling point are split into smaller molecules with a lower boiling point.

In recent catalytic cracking processes, described for example in patent EP-A-291253, the cracking reaction takes place in an elongated enclosure of substantially circular section, the catalyst being admitted to the lower part of the enclosure as well as the hydrocarbon charge previously atomized. The contacting of the charge with the hot catalyst makes it possible to vaporize the hydrocarbons which then entrain the catalyst towards the upper part of the reaction zone, the introduction of a drive fluid helping the upward movement.

It is therefore necessary to vaporize the filler properly in such processes. Indeed, it would be detrimental, for obtaining cracking products with a boiling point lower than that of the feed, if this atomized feed is found in contact with catalyst having already given up a large part of its heat. Not only would the reaction yield be affected, but the back-mixing of the catalyst would also cause additional coke formation.

Partly to limit these drawbacks, catalytic cracking processes have been devised in which the reaction medium is operated in a downward flow. The catalyst is then introduced into the upper part of the reaction zone and the atomized hydrocarbon charge is injected into the same part but into the downward flow of the catalyst (patent documents US-A-4,385,985 and EP-A.254,333).

The reaction product is then subjected to separation, for example in a cyclone, so as to obtain, on the one hand, a gaseous hydrocarbon phase and, on the other hand, the catalyst. The catalyst is regenerated and then at least partially recycled to the cracking reactor.

These downflow processes are entirely satisfactory in terms of reaction, but their use poses problems. A drawback lies in the solid / gas separation, which, due to the high concentration of the catalyst in the reaction medium, requires devices specifically adapted for suitable efficiency. In addition, industrial installations generally include an upward flow reaction enclosure. The significant and expensive modifications to be made to change the direction of flow dissuade manufacturers from using these efficient processes.

The Applicant proposes a method and a device making it possible to use a cracking reactor comprising a reaction zone with downward flow followed by a reaction zone with upward flow, which makes it possible to combine the advantages of an efficient reaction and of separation solid / gas improved. Such a device can also be installed on existing units with costs lower than those due to changes in direction of flow.

More specifically, the subject of the invention is a method for cracking hydrocarbon charges, the cracking reaction taking place in the presence of catalyst in a entrained or fluidized bed, the catalyst particles being, after reaction, separated from the gas phase , regenerated and at least partly recycled, process in which the cracking reaction takes place in two successive substantially vertical reaction zones, the charge being introduced into the upper part of a first reaction zone, then at least part of the product obtained at the lower part of said first zone is introduced into a second reaction zone where it circulates in an ascending manner.

The description of the process will be made from FIG. 1 without the invention being limited to this embodiment.

Figures 2 and 3 show devices associated with said method.

At the top of the tubular reactor (1) with a substantially vertical axis is introduced, along this axis, the catalyst (2) which comes in part at least from the catalyst regeneration reactor (3).

The particle flow rates of the catalyst between the reactor (3) and the first reaction zone (4) are adjusted by a pressure difference caused for example in a valve, or any other suitable means.

The catalyst enters with a speed greater than 0.5 m / s and generally greater than 1 m / s, up to 20 m / s more generally up to 5 m / s. The apparent density of the suspended catalyst is then approximately 50 to 600 kg / m³.

The charge (5) previously heated to temperatures between 100 and 250 ° C. is then introduced in contact with the hot catalyst in a fluidized bed, in the form of fine droplets with a diameter generally between 20 and 300 μm (micrometers), most obtained often from known means of atomization.

The hydrocarbon feedstocks to be treated advantageously consist of heavy hydrocarbons, that is to say having final boiling points of the order of 400 ° C., such as gas oils under vacuum, but also oils more heavy such as crude oils and vacuum residues. These fillers may, if necessary, have received a preliminary treatment, for example a hydrotreatment in the presence of a catalyst of the Co-Mo type. Light fillers can also be treated, which have boiling points below 400 ° C.

The preferred fillers for the process according to the invention contain fractions normally boiling up to 700 ° C. and more, and which may contain high percentages of asphaltic products, the carbon content Conradson up to 4% and even beyond. These charges can optionally be mixed with lighter hydrocarbon fractions, such as LCO and HOO.

Upon contact with the catalyst, the charge vaporizes. It is then entrained by the catalyst current with which it flows in downward co-current in this first reaction zone (4) where cracking takes place in part (the speed of the downward flow in the reactor varies and is most often between 0.5 to 50 m / s and preferably 0.5 to 10 m / s).

The product obtained at the lower part of said first reaction zone (4) is transferred, at least in part and preferably in whole, to the lower part of the second reaction zone (6) located in the reactor (7) with substantially axis vertical.

This transfer must be carried out quickly and changes in the direction of flow must be controlled so as to avoid sedimentation of the catalyst particles. The invention also provides suitable devices described below (U-shaped tubes, inclined ...).

The reaction medium flows in the second reaction zone in an ascending manner, with speeds generally greater than 2 m / s and which can range up to 50 m / s, and preferably between 10 and 30 m / s.

To help this flow, it is possible (but not compulsory) to introduce a drive fluid, at the lower part of the second reactor (or near this part, which is equivalent). This fluid can be a naphtha or more generally a liquid with a boiling point lower than that of the feed, which allows the calories to be removed from the reaction zone. According to the invention, it is advantageously possible to introduce, into the reaction medium entering the second reaction zone, a hydrocarbon phase (8).

This introduction can be done either at the lower part of the second reaction zone in the medium entering this zone, or a little upstream, that is to say in the reaction medium being transferred between the two reaction zones. The amount of hydrocarbon phase introduced relative to the amount of charge introduced into the first reaction zone represents from 0 to 50% by weight, and preferably from 5 to 30%.

The hydrocarbon phase can consist of part of the charge to be treated. It can also be a light charge, that is to say a boiling point charge of less than 400 ° C, and most often from about 180 ° C to about 380 ° C.

The product obtained at the upper part of the reaction zone (6) is transferred to a solid / gas separation means (9) to obtain, on the one hand, the gas phase (10) containing the cracked products, and on the other hand the catalyst.

The separated catalyst particles are transferred to at least one regeneration reactor (3), where the coke is burned in a conventional manner, then at least part of the particles is recycled to the first reaction zone.

An essential advantage of the process according to the invention can now be emphasized, which consists in that the gas / solid separation is carried out on a more dilute mixture of catalyst. For example, the volume content of catalyst in the mixture entering the separator (9) can be reduced from 1.5 times to 2.0 times at least, by suitably injecting, for example, from 20 to 40% by weight of light hydrocarbons (8 ) with respect to the feed introduced in (5), with respect to the catalyst content of the mixture entering the separator if the latter was positioned at the bottom of the first reaction enclosure (1). This provides better separation efficiency.

Another object of the invention is a device for carrying out the process for catalytic cracking of a hydrocarbon feedstock according to the method which is the subject of the invention. The device is described from Figures 2 and 3.

Said device comprises a first reactor (20) with a substantially vertical axis provided with means (21) for the introduction of the catalyst into the upper part of the reactor, means (24) for the introduction of the charge to be treated atomized in the part upper part of the reactor, said means (24) being located below the means (21), and said reactor also being provided with an opening disposed at the lower part of the reactor and along its axis, for the evacuation of the product obtained, said device further comprising a second reactor (28) of substantially vertical axis, provided at its lower part with an opening for the introduction of the product obtained at the lower part of the first reactor (20) and provided at its upper part with '' a pipe (29) for the evacuation of the product obtained at the end of the treatment in the second reactor, said device also comprising at least one pipe (30) connecting the lower parts of the first and second reactor s.

It comprises the two successive reactors (20) and (28) of substantially vertical axis, the lower parts of which are connected by a pipe (30).

The catalyst is introduced by means (21) generally constituted by a pipe (22) provided with a slide valve (23) arranged on the axis of the reactor.

The charge to be treated is introduced, in atomized form, by means (24), generally constituted by a pipe (25) provided with an atomization means (26). This pipe opens below the opening through which the catalyst is introduced, so as to introduce the charge into the downward moving catalyst.

The product obtained at the lower part (27) of the first reactor is transferred via line (30) to the second reactor.

For drawing convenience, the figures show reactors and pipe (30) of almost identical diameter, the invention is not limited to these modes of representation.

Line (30) - or lines if necessary - must allow rapid transfer and with a low deposit of solid catalyst.

The bent shape shown in FIG. 2 is perfectly suitable, there is then a U-shaped device. The curvature and the spacing between the two reactors are then calculated so that the transfer is carried out properly under the conditions of the process.

FIG. 3 represents a pipe (30) inclined towards the second reactor, the transfer takes place by entrainment. This configuration is particularly interesting because it is close to the current configuration of catalytic cracking processes, the charge being injected in recent processes most generally in (32) and / or (42). In these processes according to the prior art, the parts (20) and (30) are then not reaction zones and play a purely functional role in the transport of the catalyst. It is possible to keep in place in the part (28) one or more means (42) of injection-atomization of the hydrocarbon charge, which optionally makes it possible to inject a fraction of hydrocarbons to be converted into the ascending part. .

Said means (42) can be constituted simply by a pipe provided with injection means and arranged for example in the lower part of the second reactor (pipe (42) and / or (32) shown in FIG. 3) or near this part . Preferably, said means are constituted by aerators (34) arranged on the pipe (30) so that the direction of injection follows the movement of the catalyst (substantially tangential injection). This embodiment makes it possible to significantly reduce deposits.

The means mentioned can obviously be combined.

The device can also include, at or near the bottom of the second reactor (28), a pipe (33) for the introduction of a fluid drive. This fluid can be for example a hydrocarbon preferably liquid or gaseous, water or an inert gas such as for example nitrogen.

The reaction medium (35) rises in the reactor (28), is evacuated at the top by a line (29) to be directed to a gas / solid separator and then to a catalyst regeneration reactor. By a line connecting said reactors to the first cracking reactor, at least part of the catalyst is recycled.

Claims (15)

1 - Process for cracking hydrocarbon feedstock, in contact with catalyst in entrained or fluidized bed, the catalyst particles being after reaction separated from the gas phase, regenerated and at least partially recycled, said process being characterized in that the cracking reaction takes place in two successive substantially vertical reaction zones, the charge flowing from the top to the bottom of the first zone, then at least part of the product obtained at the end of said first zone is introduced into a second reaction zone where it circulates in an ascending manner. 2 - Process according to claim 1, characterized in that all of the product obtained at the end of the first zone is introduced into the second reaction zone. 3 - Process according to claim 1 or 2, characterized in that the feed entering the descending reaction zone consists of heavy hydrocarbons. 4 - Process according to claim 1 or 2, characterized in that the charge entering the descending reaction zone consists of light hydrocarbons with a boiling point below 400 ° C. 5 - Method according to one of the preceding claims, characterized in that a hydrocarbon phase is introduced into the reaction medium entering the second reaction zone. 6 - Process according to claim 5, characterized in that the hydrocarbon phase is identical to the feed to be treated. 7 - Process according to claim 5, characterized in that the hydrocarbon phase is a light phase with a boiling point below 400 ° C. 8 - Process according to claim 7, characterized in that the hydrocarbon phase is a light phase with a boiling point between 180 and 380 ° C. 9 - Method according to one of claims 5 to 8, characterized in that the amount of hydrocarbon phase introduced represents 0 to 50% of the volume of the feed introduced into the first reaction zone. 10 - Process according to claim 9, characterized in that this amount ranges from 5 to 30% of the volume of the load. 11 - Method according to any one of the preceding claims, characterized in that a drive fluid is introduced into the lower part of the second reaction zone. 12 - Device for the catalytic cracking of hydrocarbon feeds, comprising a first reactor (20) of substantially vertical axis provided with means (21) for the introduction of the catalyst into the upper part of the reactor, with means (24) for the introduction of the atomized charge into the upper part of the reactor and located below the means (21), said reactor (20) also being provided with an opening for the discharge of the product obtained and disposed at the lower part of the reactor along its axis, said device being characterized in that it further comprises a second reactor (28) of substantially vertical axis, provided at its lower part with an opening for the introduction of the product obtained at the lower part of the first reactor (20) and provided at its upper part with a pipe (29) for discharging the product obtained at the end of the treatment in said second reactor, said first and second reactors (20) and (28) being connected their lower part by at least one pipe (30). 13 - Device according to claim 11, characterized in that it comprises means (32) and / or (42) for the introduction of a hydrocarbon phase in the reaction medium of the second reactor. 14 - Device according to claim 12, characterized in that the means for introducing a hydrocarbon phase are constituted by at least one pipe (32) disposed at the bottom of the second reactor. 15 - Device according to one of the preceding claims, characterized in that it comprises means (33) for the introduction of a drive fluid to the lower part of the second reactor (28).

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