The invention relates to a gas-solids separator, more in particular to a gas-solids separator for use in a catalytic cracking process.

In catalytic cracking processes a hydrocarbon feedstock is brought into contact with a hot cracking catalyst in a riser. The feed is cracked into lower boiling products, such as gas, LPG, gasoline, and cycle oils while coke and non-volatile products deposit on the catalyst resulting in spent catalyst. The riser discharges into a primary separator, which is also called a rough-cut separator or primary cyclone in case the separator is a cyclone, wherein spent catalyst is separated from reaction products. The spent catalyst is subsequently stripped, usually with steam, to remove hydrocarbons from the catalyst. The stripped catalyst is passed to a regenerator in which coke and remaining hydrocarbon materials are combusted and wherein the catalyst is heated to a temperature required for the cracking reactions. Hot regenerated catalyst is returned to the riser reactor. The hydrocarbonaceous products separated from the spent catalyst in the primary separator are generally subjected to a further solids removal step with the help of a second separator.

In so-called uncoupled cyclones, hydrocarbons spend some time in the so-called disengager vessel as they are not, or not directly, treated in a second separator. Nowadays, so-called close-coupled cyclones are used in which gaseous hydrocarbons separated off in the primary separator are discharged directly into the inlet of a second separator, most usually a cyclone. This strongly reduces the time during which the hydrocarbons remain at relatively high temperature. Close-coupled cyclones can prevent over-cracking in operations as currently applied. However, it can be desirable to increase the severity of the conversion in order to maximize olefin yield or to convert heavy residual feedstocks. A higher severity usually comprises a higher temperature, and a higher temperature induces undesirable thermal cracking side- reactions besides the desired catalytic cracking ones. US-A-5, 043, 058 teaches to add quench oil into the hydrocarbon products after the products have exited the primary separator and before they enter a further gas- solids separator in order to reduce over-cracking.

We have now found that over-cracking in a catalytic cracking process can be reduced further by introducing quench fluid with the help of a vortex stabiliser. This makes it possible to add quench fluid at an earlier stage and over-cracking can be reduced more efficiently.

Therefore, the present invention relates to a gas- solids separator for a catalytic cracking process which separator comprises a housing, a gas outlet conduit at one end of the housing, and a solids outlet opening and a vortex stabiliser at the opposite end of said housing and an inlet opening for introducing a gas-solids mixture which inlet opening is executed such that it imparts a swirl to the gas-solids mixture, wherein the vortex stabiliser comprises a conduit for introducing quench fluid into the housing.

Any vortex stabiliser known to someone skilled in the art would be suitable for use in the present invention provided that it can be used for introducing quench fluid. A vortex stabiliser which can be used comprises a pin on a stabilising plate or a cone. The pin on a stabilising plate has been found to be especially advantageous. Such vortex stabiliser has been described in WO-A-2004/009244 and WO-A-2008/145657. If a cone or a pin on a stabilising plate is used as vortex stabiliser, it is preferred that the opening of the conduit for introducing quench fluid is at the top of the cone or pin. Furthermore, it is preferred that the cone or pin is directed towards the gas outlet conduit. This set-up makes that the quench fluid efficiently reduces the temperature of the hydrocarbonaceous products while leaving the spent catalyst substantially unaffected. It is preferred that the quench fluid is injected in the direction of the gas outlet conduit when the gas-solids separator is in use.

The housing for use in the present invention can have any shape known to be suitable to someone skilled in the art. Generally, the housing will be tubular or conical. The gas outlet conduit typically is tubular. It is preferred that the tubular or conical housing and the tubular gas outlet conduit have substantially the same longitudinal axis. Preferably, the housing is a cyclone.

During normal operation, the housing will be positioned such that the gas outlet conduit are at the upper end and the solids outlet opening and the vortex stabiliser are at the lower end of the housing.

The quench fluid can be any fluid known to be suitable to someone skilled in the art. It is preferred that the quench fluid is hydrocarbonaceous. It is preferred to use a hydrocarbon stream which has been previously cracked or otherwise processed to remove the most reactive species so that the quench fluid has limited thermal reactivity. Preferably, the quench fluid is the product of a cracking process. Furthermore, it is preferred that the quench fluid is liquid upon introduction into the housing. Preferably, the quench fluid consists of at least 60% by weight, preferably at least 70% by weight, more preferably at least 80% by weight of hydrocarbons boiling in the range of from 150 to 450 ⁰ C, more preferably of from 200 to 400 ⁰ C. A quench fluid which can be used is so-called cat cracked gasoline, light cycle oil, heavy cycle oil or any combination of these.

The temperature of the quench fluid is preferably at least 10 ⁰ C lower than the temperature of the hydrocarbonaceous products, preferably at least 100 ⁰ C lower .

The conduit for introducing quench fluid preferably comprises a nozzle. The use of a nozzle for introducing quench fluid gives the possibility to direct the quench fluid and to ensure thorough mixing of the quench fluid and hydrocarbonaceous products. The quench fluid is preferably atomized upon introduction into the housing. It is preferred that the quench fluid is introduced into the housing in the form of droplets having a diameter of from 1 micron to 1000 microns, more preferably of from 1 micron to 500 microns, most preferably of from 1 micron to 100 microns. The desired droplet size can be attained by any method known to someone skilled in the art. A method which can be used is adding steam to the hydrocarbonaceous quench fluid, preferably by adding steam to the nozzle through which the quench fluid is introduced. The amount of steam can be of from 0 to 20 %wt based on amount of quench fluid, more specifically of from 0.1 to 15 %wt, more specifically of from 0.1 to 10 %wt, more specifically of from 0.1 to 5 %wt, most specifically of from 0.2 to 5 %wt .

The amount of quench fluid added preferably is of from 2 to 20% by weight, more specifically of from 5 to 15% by weight based on the amount of hydrocarbonaceous products. If steam is present, the steam is not considered to be part of the quench fluid for these weight amounts.

The catalyst for use in the present invention can be any catalytic cracking catalyst known to be suitable for the specific catalytic cracking process. The inlet opening for introducing the gas-solids mixture into the separator imparts a swirl to the gas- solids mixture when the gas-solids mixture enters the housing in order to separate gas from solids. The swirl imparting means can be any means known to be suitable to someone skilled in the art such as vanes or a tangential inlet into the housing. If a tangential inlet is used, the housing generally is tubular where the inlet opens into the housing. The vortex stabiliser is preferably positioned in the part of the housing which is the lower end during normal operation. More specifically, the vortex stabiliser is preferably positioned in the vicinity of the solids outlet opening. As mentioned above, the vortex stabilier preferably is a pin on a stabilising plate with the quench fluid being introduced at the top of the pin. In order to introduce the quench fluid in an efficient way in such set-up, it is preferred that the pin extends to of from 20 to 80% of the axis of the housing, said axis running from the stabiliser plate to the inlet of the gas outlet conduit, preferably of from 25 to 75%, more preferably of from 30 to 70%.

Hydrocarbonaceous products from a riser reactor can be fed directly to the separator according to the present invention or the riser product can have been separated in a primary separator and the gaseous fraction thus obtained is subsequently introduced into a separator according to the present invention which then acts as a second separator. Alternatively, riser product is first treated in a separator according to the present invention and subsequently in a second separator which does not need to be according to the present invention. Therefore, the present invention further relates to a separator according to the present invention wherein the separator further comprises a conduit for guiding gas from the gas outlet conduit to an inlet of another gas-solids separator. The present invention furthermore relates to a separator according to the present invention wherein the separator further comprises a conduit for guiding gas from the outlet of a previous separator to the inlet for introducing the gas-solids mixture. As the present invention is especially suitable for quickly reducing the temperature of hydrocarbonaceous products, it is preferred to use this separator for as primary separator as described above. This makes that the separator would treat the direct product of the riser reactor. Therefore, the separator according to the present invention preferably further comprises a conduit for guiding a gas- solids mixture from a catalytic cracking riser reactor to the separator. The present invention further relates to a catalytic cracking process using a gas-solid separator according to the present invention. Such process comprises

(a) contacting the hydrocarbon feedstock in a riser reactor with a cracking catalyst to yield hydrocarbonaceous products and a spent cracking catalyst;

(b) separating spent cracking catalyst from hydrocarbonaceous products;

(c) stripping spent cracking catalyst in a fluidised stripping zone by introducing a stripping medium into the stripping zone to yield stripped spent catalyst;

(d) regenerating said stripped spent cracking catalyst to yield a regenerated cracking catalyst; and

(e) passing at least a portion of the regenerated catalyst to the riser reactor, in which process in step (b) spent cracking catalyst is separated from hydrocarbonaceous products with the help of a gas-solid separator according to the present invention while adding quench fluid through the conduit. It will be clear that the hydrocarbonaceous products can be a fluid directly coming from the riser reactor or a fluid indirectly coming from the riser reactor such as via a previous gas-solid separator. Preferably, the hydrocarbonaceous products come directly from the riser.

The hydrocarbon feedstock for use in the present invention can be any feedstock known to be suitable to someone skilled in the art. The invention is especially suitable for cracking relatively heavy feedstock such as feedstock having a Conradson Carbon Residue number, as measured by ASTM method D 189, of at least 0.5%, more specifically at least 1 %, more specifically at least 1.5%, most specifically at least 2%.

Further, the present invention can be applied in processes which are known to apply higher severity in order to maximize the yield of olefins such as ethene and propene . Such known processes are the so-called Deep Catalytic Cracking (DCC) process and the Catalytic Pyrolysis Process (CPP) .

The invention will be further illustrated by means of Figure 1.

Figure 1 discloses an embodiment of the present invention wherein the vortex stabiliser comprises a stabilising plate and a pin.

Figure 1 shows a riser reactor 1 wherein feedstock is catalytically cracked in the presence of a cracking catalyst under catalytic cracking conditions to produce a hydrocarbonaceous product. The riser reactor 1 is connected with the gas-solids separator 2 via a conduit 4 for guiding the gas-solids mixture from the riser reactor to the separator 2. The inlet opening of conduit 4 is a tangential inlet which imparts a swirl to the gas-solids mixture upon entering the separator 2.

The swirl imparted on the gas-solids mixture upon introduction into separator 2 separates the mixture into a gaseous fraction and a catalyst fraction. Generally, of from 90 to 99 %wt of the catalyst particles are removed from the mixture in this way. At the bottom part of the separator 2 is a solids outlet opening 11 by which the spent catalyst can be removed to be stripped and regenerated.

At the upper part of the tubular housing is a tubular gas outlet conduit 3 having an opening 5 for receiving gas separated from the gas-solid mixture and a conduit 10 for removing gas from the separator.

The separator further comprises a vortex stabiliser comprising a pin 6 having opening 7, a stabilising plate 8 and conduit 9 for introducing quench fluid into the separator. During operation, quench fluid is injected into separator 2 via conduit 9 and opening 7.