EP0573316B1 - Process and apparatus for the catalytic cracking in two successive reaction zones - Google Patents

Description

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

We know that the petroleum industry usually uses cracking in which the molecules of hydrocarbons of molecular weight and high boiling points are split into smaller molecules to point lower boiling point.

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

It is therefore necessary to vaporize the charge properly in such processes. Indeed, it would be prejudicial, for obtaining products of cracking with a boiling point lower than that of the charge, than this charge atomized is found in contact with catalyst having already yielded a large part of his warmth. Not only would the reaction yield be affected, but the backward mixing of the catalyst would also cause formation additional coke.

Partly to limit these drawbacks, cracking methods have been designed catalytic in which one operates with a reaction medium in flow descending. The catalyst is then introduced into the upper part of the zone reaction and the atomized hydrocarbon charge is injected into the same part but in 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 then at least in part recycled to the cracking reactor.

These downflow processes are very satisfactory in terms of reactive, but their use poses problems. One drawback is in the solid / gas separation, which, due to the high concentration of catalyst in the reaction medium, requires devices specifically adapted for suitable efficiency. Furthermore, the facilities industrial plants usually have a flow reaction vessel ascending. Important and expensive changes to make to change the direction of flow dissuades industrialists from using these processes efficient.

The applicant proposes a method and a device for using a cracking reactor having a downflow reaction zone followed by an upward flow reaction zone, which allows to cumulate the advantages of an efficient reaction and a solid / gas separation improved. Such a device can also be installed on the units existing with lower costs than those due to changes in direction of the flow.

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

The description of the process will be made from Figure 1 without the invention is 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 introduces, along this axis, the catalyst (2) which comes at least in part from catalyst regeneration reactor (3).

The particle flow rates of the catalyst between the reactor (3) and the first zone reaction (4) are adjusted by a pressure difference caused by 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, being able to go up to 20 m / s more generally up to 5 m / s. The apparent density of the suspended catalyst is then about 50 to 600 kg / m ³ .

The load (5) previously heated to temperatures between 100 and 250 ° C. is then introduced into 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 often obtained from known means atomization.

The hydrocarbon charges to be treated are advantageously made up heavy hydrocarbons, i.e. with final boiling points around 700 ° C, such as vacuum gas oils, but also more heavy such as crude oils and vacuum residues. These charges may, if applicable, have received prior treatment, for example a hydrotreating in the presence of a Co-Mo type catalyst. Light loads can also be processed, which have lower boiling points at 400 ° C.

The preferred fillers for the process according to the invention contain fractions normally boiling up to 700 ° C and above, and may contain high percentages of asphalt products, Conradson carbon content up to 4% and even beyond. These charges may possibly be mixed with lighter hydrocarbon cuts, such as LCOs and HCO.

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

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

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

The reaction medium flows into the second reaction zone so ascending, with speeds generally greater than 2 m / s and capable of going 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 bottom of the second reactor (or near it) of this part, which is equivalent). This fluid can be one or more naphtha 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, one can advantageously introduce into the reaction medium entering the second reaction zone, a hydrocarbon phase (8).

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

The hydrocarbon phase can consist of part of the charge to treat. It can also be a light load, i.e. a load of boiling point below 400 ° C, and most often around 180 ° C at about 380 ° C.

The product obtained at the top 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 a at least part of the particles is recycled to the first reaction zone.

We can now emphasize an essential advantage of the process according to the invention, which consists in that the gas / solid separation is carried out on a mixture more diluted in catalyst. We can for example decrease by 1.5 times to At least 2.0 times the volume content of catalyst in the mixture entering the separator (9), by suitably injecting for example from 20 to 40% in weight of light hydrocarbons (8) relative to the charge introduced in (5), by relative to the catalyst content of the mixture entering the separator if this 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 method of catalytic cracking of hydrocarbon feed according to the process object 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 introducing the catalyst into the upper part of the reactor, of means (24) for the introduction of the atomized charge to be treated in the upper part of the reactor, said means (24) being located below means (21), and said reactor also being provided with an opening arranged at the bottom of the reactor and along its axis, for the evacuation of the product obtained, said device further comprising a second axis reactor (28) substantially vertical, provided at its lower part with an opening for the introduction of the product obtained at the bottom of the first reactor (20) and provided at its upper part with a pipe (29) for the evacuation of the product obtained after treatment in the second reactor, said device also comprising at least one pipe (30) connecting the parts lower of the first and second reactors.

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

The catalyst is introduced by means (21) generally consisting of 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 a means of atomization (26). This pipe opens below the opening through which introduced the catalyst, so as to introduce the charge into the catalyst downward movement.

The product obtained at the lower part (27) of the first reactor is transferred by 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.

The pipe (30) - or the pipes if necessary - must allow a rapid transfer and with a low deposit of solid catalyst.

The angled shape shown in Figure 2 is perfect, we then have a U-shaped device. The curvature and the spacing between the two reactors are then calculated so that the transfer is carried out properly within process conditions.

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

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 (line (42) and / or (32) shown in FIG. 3) or proximity to this part. Preferably, said means are constituted by vents (34) arranged on the pipe (30) so that the direction of the injection follows the movement of the catalyst (injection substantially tangential). This embodiment makes it possible to significantly reduce the deposits.

The means cited can obviously be combined.

The device can also include, at the bottom of the second reactor (28) or nearby, a pipe (33) for the introduction of a fluid training. This fluid may for example be 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 therefrom upper part by a pipe (29) to be directed to a separator gas / solid then to a catalyst regeneration reactor. By a conduct connecting said reactors to the first cracking reactor, at least part of the catalyst is recycled.

Claims (18)

1. A process for cracking a hydrocarbon load, in contact with a catalyst in an entrained or fluidized bed, the particles of catalyst, after reaction, being separated from the gaseous phase, regenerated and at least partly recycled, the said process being characterised in that the cracking reaction takes place in two substantially vertical and successive reaction zones, the load flowing from the top to the bottom of the first zone then at least a part of the product obtained at the discharge from the first zone is introduced into a second reaction zone in which it circulates in an ascending fashion.
2. A process according to claim 1, characterised in that all the product obtained at the discharge from the first zone is introduced into the second reaction zone.
3. A process according to claim 1 or 2, characterised in that the load entering in the top of the first zone consists of heavy hydrocarbons.
4. A process according to claim 1 or 2, characterised in that the load entering in the top of the first zone consists of light hydrocarbons with a boiling point below 400°C.
5. A process according to one of the preceding claims, characterised in that a hydrocarbon phase is introduced into the reaction medium entering the second reaction zone.
6. A process according to claim 5, characterised in that the hydrocarbon phase is identical to the load to be treated.
7. A process according to claim 5, characterised in that the hydrocarbon phase is a light phase with a boiling point below 400°C.
8. A process according to claim 7, characterised in that the hydrocarbon phase is a light phase with a boiling point comprised between 180 and 380°C.
9. A process according to one of claims 5 to 8, characterised in that the quantity of hydrocarbon phase introduced represents 0 to 50% of the volume of the load introduced into the first reaction zone.
10. A process according to claim 9, characterised in that this quantity ranges from 5 to 30% of the volume of the load.
11. A process according to any one of the preceding claims, characterised in that a propellant fluid is introduced into the bottom part of the second reaction zone.
12. A process according to one of the claims 1 to 11, characterised in that the rate of the descending flow comprising the catalyst and the entrained load is comprised between 0,5 m/s and 50 m/s and the rate of the ascending flow of the reaction medium is comprised between 2 m/s and 50 m/s.
13. A process according to one of the claims 1 to 12, characterised in that the rate of the descending flow comprising the catalyst and the entrained load is comprised between 0,5 m/s to 10 m/s.
14. A process according to one of the claims 1 to 13 characterised in that the ascending flow of the reaction medium is comprised between 10 m/s and 30 m/s.
15. An apparatus for catalytic cracking of a hydrocarbon load comprising a first reactor (20) of substantially vertical axis provided with means (21) of introducing catalyst into the upper part of the reactor, means (24) of introducing the atomized load into the upper part of the reactor and situated below the means (21), the said reactor (20) being likewise fitted with an aperture for discharge of the product obtained and disposed in the bottom part of the reactor, on its axis, the said apparatus being characterised in that it comprises also a second reactor (28) of substantially vertical axis provided in its bottom part with an aperture for introduction of the product obtained in the bottom part of the first reactor (20) and provided in its upper part with a duct (29) for discharge of the product obtained after treatment in the said second reactor, the said first and second reactors (20) and (28) being connected in their bottom parts by at least one duct (30).
16. An apparatus according to claim 11, characterised in that it comprises means (32) and/or (42) of introducing a hydrocarbon phase into the reaction medium in the second reactor.
17. An apparatus according to claim 12, characterised in that the means of introducing a hydrocarbon phase consist of at least one duct (32) disposed in the bottom part of the second reactor.
18. An apparatus according to one of the preceding claims, characterised in that it comprises means (33) of introducing a propellant fluid into the bottom part of the second reactor (28).

Images