EP0874880B1 - Method and device for fluid catalytic cracking of hydrocarbon feedstock - Google Patents

Description

The present invention relates to a method and a catalytic cracker of a charge of hydrocarbons in a descending bed, implementing a improved zone of contact between the load and the catalyst.

We know that, in the petroleum industry, cracking fluid bed catalytic (in English, "Fluid Catalytic Cracking ", or even" FCC "process) has taken an extra place more important in refining because it allows to adapt the constitution of crude oils at the request of markets in refined products.

In these processes, the cracking of the charge is carried out in the absence of hydrogen, in the gas phase; temperature reaction temperature is around 500 ° C and the pressure generally close to atmospheric pressure. During of the cracking reaction, the catalyst is covered with coke and traces of heavy oil and heat resulting from the combustion of this coke, during the operation regeneration in the presence of air or oxygen, allows bring the catalyst to the desired temperature for provide the calories necessary for the cracking reaction, after re-injection of the catalyst into the reactor.

These FCC processes are usually carried out in upward flow reactors, hence the term taken from English for "riser reactor". This operating mode has a number of drawbacks, however: particles of catalyst of the fluidized bed are in equilibrium unstable, because they tend, on the one hand, to rise under the effect of the rise of the gas ensuring fluidization and vaporization of the charge and, on the other hand, to descend from the made of their mass.

It follows that the ratio C / O, between the flow rate C of catalyst and the flow rate O of charge to be treated is limited by a maximum generally between 3 and 7, in the current reactors, and usually close to 5.

Additionally, in upflow reactors occurs an accumulation of particles in the vicinity of the walls of the reactor, resulting in overcracking of the hydrocarbons at this level, which results in the formation of coke, hydrogen, methane and ethane, at location of the desired high octane products, while than at the center of the reactor, where fewer particles are present, an insufficient conversion of the charge.

Finally, if the catalyst grains rise overall in the reactor, some of them can locally go down in the vicinity of the wall, due to the accumulation explained above. This phenomenon, known under the English name of "back-mixing", also results in a local drop in conversion, since the grains which descend are partially disabled and have less effect on the load than the grains that rise. This phenomenon is all the more annoying that the previously mentioned C / O ratio is more low.

In order to overcome the disadvantages of the riser, it was long proposed to use reactors with downward flow of catalyst, or "downer" (see this effect, for example, U.S. Patent No. 2,420,558).

We know, in fact, that the essential difference between these two types of reactors is that the relative position of catalyst and charge remains much the same throughout the downer, since the vapor and solid phases are set in motion under the effect of gravity.

As a result, there is no back mixing, the radial homogeneity of the catalyst in the reactor is preserved and the flow in this reactor is of the type piston. This gives good selectivity to the cracking reaction.

In addition, the reaction times seem to be able to be significantly reduced compared to riser and be significantly less than 1 second, and it seems possible to freely increase the flow of catalyst, which has no of harmful influence on the movement of particles like in the case of the riser.

However, the implementation of a downer presents a lot of difficulties, which means that nobody has really taken the risk yet to pass industrially from upward flow to flow descending.

Indeed, if the downer is supposed to allow access to very short reaction times it is technically very difficult to mix, spray and separation of hydrocarbons and grains of catalyst, when these operations must be carried out in one fraction of a second with speeds of the order of 1500 tonnes / hour of catalyst and 300 tonnes / hour of high boiling point hydrocarbons.

The downer has, in particular, a related drawback to the initial mixture between catalyst and charge: in fact, the catalyst tends to fall off immediately without reflux or recirculation, which has a negative effect on the initial mass and heat transfer with the load.

If the catalyst and feed inlet flows were perfectly regular, this effect would be minor. However, this is not the case, and that is why, in a reactor of cracking, the solid-gas mixture consists of a alternation of zones rich in catalyst, then poor in catalyst.

In a downer, there is no mechanism allowing the burden of moving from one area to another. Therefore, the fraction of hydrocarbons that is in contact with an area at low solids density, will remain there throughout the reactor and will be subject to thermal cracking insufficient, due to premature deactivation of the catalyst. On the other hand, the hydrocarbons present in a high solids area, are susceptible to overcracking.

In order to optimize both the charge-catalyst mixture and the quantity of cracking reactions proper, the patent American No. 5,468,369 proposes a device in which the charge is sprayed, brought into contact with the catalyst and then partially cracked in an upward flow. Then the direction of the flow is reversed and the cracking is completed in a downward flow.

However, this device appears difficult to achieve on a plan mechanical and it does not allow a very efficient mixing in the case high catalyst flow rates. Indeed, when the direction of flow of the charge-catalyst mixture is reversed, the catalyst tends to agglomerate in the vicinity of the walls of the device and is therefore found isolated from the vaporized charge.

The object of the invention is therefore to reconcile the advantages of the flow ascending, namely a satisfactory mixture between large flow rates of charge and catalyst, and downflow, ie good selectivity of the actual cracking reactions.

As part of its work, the Applicant discovered that a particular geometrical conformation of the setting area contact between the catalyst and the charge, optimizes both the quality of the mixture and of the cracking reactions.

• d'une chambre de mélange de section maximale S₂, mise en communication avec les moyens d'alimentation en catalyseur régénéré par un orifice supérieur définissant une section de passage du catalyseur S₁,
• et d'une zone réactionnelle de section maximale S₄ mise en communication avec la chambre de mélange par un orifice intermédiaire de section S₃, et en ce que les rapports S₂/S₁ et S₂/S₃ sont compris entre 1,5 et 8, et de préférence compris entre 2,5 et 6.

The present invention therefore relates to a catalytic hydrocarbon cracking device, comprising a downflow cracking reactor, means for supplying said reactor under pressure with a hydrocarbon charge and with particles of a regenerated cracking catalyst. , a means for separating the products of the cracked charge and the particles of deactivated catalyst, at least one means of stripping by at least one fluid of the particles of deactivated catalyst, at least one unit for regenerating said catalyst by combustion of coke carried by the catalyst, and means for recycling the regenerated catalyst to said supply means,
this device being characterized in that it comprises a specific contacting zone between the hydrocarbons and the catalyst, constituted

• a mixing chamber of maximum section S ₂ , placed in communication with the means for supplying regenerated catalyst by an upper orifice defining a section for passage of the catalyst S ₁ ,
• and a reaction zone of maximum section S ₄ placed in communication with the mixing chamber by an intermediate orifice of section S ₃ , and in that the ratios S ₂ / S ₁ and S ₂ / S ₃ are between 1, 5 and 8, and preferably between 2.5 and 6.

The contacting zone according to the invention makes it possible to achieve the above objectives. Its geometry is particularly applicable to short time insofar as it allows a complete and rapid spraying of the load.

It allows indeed a homogeneous mixture within the mixing chamber. There reigns in this type of flow perfectly agitated, because the upper and intermediate section openings restricted, constitute necks allowing reflux and recirculation of catalyst within the chamber. So, and although the flow is descending, the mixture is generally comparable to that carried out in the mixing zone of a flow reactor ascending.

EP-A-0 209 442 discloses a cracking device catalytic of hydrocarbons, including the contact zone between the catalyst and hydrocarbon consists only of one area elongated reaction vessel (see claim 6, column 3, rows 21 to 24), that is to say of a single part.

In addition, we know from EP-A-0 344 032 a bed reactor entrained fluidized, usable in particular for catalytic cracking hydrocarbons. This reactor, substantially vertical and shaped elongated, has a particle flow regulator solids comprising a fixed part projecting inside the reactor as well as a mobile part which slides by means of a rod (cf. claim 1). This "regulatory body" is a system analogous to a piston, and its function is to regulate the flow of particles catalysts entering the contact zone between the catalyst and hydrocarbons (see column 11, lines 5 to 10).

It differs from the subject of the present invention in that it does not no separate mixing chamber, geometry special.

According to a characteristic of the invention, the ratio S ₁ / S ₃ , between the section S ₁ of passage of the catalyst through the annular orifice and the section S ₃ of the intermediate orifice, is between 0.8 and 1, 25 and preferably between 0.9 and 1.1, in order to allow optimal mixing within the mixing chamber.

Advantageously, the hydrocarbons are injected at counter-current of the downward flow of catalyst particles, according to an angle to the horizontal, between 2 ° and 45 °, and preferably between 5 and 35 °. In this way, the mixture between the charge and the catalyst is optimized, because this direction of injection allows the charge to break down the mass of descending catalyst as well as possible.

According to an additional characteristic of the invention, the reaction zone widens from the intermediate orifice at an angle with the vertical of between 1 and 20 °, and preferably 2 and 15 °, until it reaches its cross section. maximum S ₄ .

This flare allows to gradually transform perfectly agitated flow, prevailing within the mixture, in a piston type flow in the reaction zone. Since such a flow is particularly favorable to the selectivity of cracking reactions, the process of the invention combines so also the specific advantages of the downflow reactor usual.

Advantageously, the ratio S ₄ / S ₃ between the maximum section S ₄ of the reaction zone and the section S ₃ of the intermediate orifice has a value between 1.5 and 8 and, preferably, between 2, 5 and 6.

According to an additional characteristic of the invention, the ratio S ₂ / S ₄ between the maximum section S ₄ of the reaction zone, is between 0.8 and 1.25 and, preferably, between 0.9 and 1.1 .

The invention also relates to a process for the catalytic cracking of hydrocarbons, comprising a phase of contacting the hydrocarbons and particles of a catalyst, a cracking reaction phase in a descending bed, a separation phase of the deactivated catalyst. and effluent hydrocarbons, at least one phase of stripping of the deactivated catalyst, then a phase of regeneration of said catalyst under conditions of combustion of the coke carried by the catalyst and, finally, a phase of recycling of the regenerated catalyst in the supply zone ,
this process being characterized in that a substantial part of the hydrocarbons is sprayed and brought into contact with the catalyst in a specific contacting zone of the catalytic cracking device defined above.

• la figure 1 est une vue schématique d'un ensemble de conversion conforme à l'invention ;
• la figure 2 est une vue plus détaillée de la zone conforme à l'invention de mise en contact entre la charge et le catalyseur.

Other characteristics and advantages of the invention will appear on reading the description which follows of a particular embodiment, with reference to the accompanying drawings, in which:

• Figure 1 is a schematic view of a conversion assembly according to the invention;
• Figure 2 is a more detailed view of the zone according to the invention of contact between the charge and the catalyst.

The device shown comprises a tubular flow reactor 1 descending, or "downer", fed at its upper part, from an enclosure 2, which is coaxial to it, made of catalyst particles regenerated. A valve 3, intended to regulate the mass ratio of catalyst to the mass of feedstock to be treated in the reactor, is interposed between reactor 1 and enclosure 2. Below this valve opens a line 4 for supplying reactor 1 with the load of hydrocarbons to be treated, preheated so known per se. This charge is sprayed into fines droplets, by injectors, at the top of the brought into contact 5, to mix with the particles of catalyst, in contact with which the reaction of cracking. The direction of charge injection, as well that the geometry of the contact area, will be detailed below. The catalyst particles and the charge to process therefore flow from top to bottom in reactor 1.

At the base of it, the spent catalyst particles pour into a stripping chamber 6, provided at its base of a diffuser 7, supplied with water vapor by a line 8.

Also at the base of reactor 1, above enclosure 6, leads to a line 9, through which the cracked products and hydrocarbons from strippers are evacuated to a separation column 10. Before reaching this column 10, the gases evacuated by the line 9 can optionally be soaked with a hydrocarbon or water vapor, introduced through a line 11 in row 9.

The stripped catalyst particles are removed by gravity of the enclosure 6, by an inclined conduit 22, towards a ascending column 12, in which they are routed to the top, towards a regenerator 13, using a carrier gas, disseminated at 14 at the base of column 12, from the line 15.

Column 12 opens into regenerator 13 below a ballistic separator 16, which ensures the separation of catalyst particles and carrier gas. The catalyst particles are then regenerated, so known per se, in the regenerator, by combustion of coke which settled on their surface and oil remaining, using a stream of air or oxygen supplied by line 17 to diffuser 18.

The regenerated catalyst particles are removed by gravity through the conduit 19 in the direction of the enclosure 2, without heat losses.

At the top of the regenerator 13, the gases from combustion are discharged to cyclones 23, which separate the fines, recycled through line 20 to the regenerator, and the gases, evacuated by line 21.

Figure 2 shows the area more precisely contact 5 object of the invention.

The contacting zone 5 is formed by a mixture 24 and a reaction zone 25 arranged immediately below it.

The mixing chamber 24 is supplied at its upper part with hot regenerated catalyst by the cylindrical conduit 26, of section S _C , which is in communication with the enclosure 2 described in FIG. 1 (but not shown in FIG. 2) . A bulkhead 28, known per se, is disposed at the lower end of the conduit 26, thereby defining an upper annular orifice 30 of the mixing chamber 24, through which the catalyst pours into it. This orifice 30 thus delimits a section S ₁ for passage of the catalyst, which is less than the section S _c of the conduit 26.

The mixing chamber 24 widens from its upper orifice 30 along a frustoconical portion 32 with an angle at the apex A, until it reaches its maximum cross section S ₂ . The angle A, for example equal to 40 °, can be between 10 and 60 °, while the section S ₂ is for example equal to 5 S ₁ , but can be between 1.5 and 8 S ₁ .

The periphery 34 of the mixing chamber 24, at the level of the maximum section of the latter, is provided with a series of injectors 36, allowing the charge to be injected after atomization thereof outside the device.

The injectors 36 are oriented so as to direct the charge droplets countercurrent to the downward flow of catalyst particles, at an angle B with respect to the horizontal equal for example to 15 °, but which can be between 2 ° and 45 °. The number of injectors will be such that the entire descending catalyst can be reached by the load droplets.

The mixing chamber 24 then narrows from its maximum section S ₂ along a frustoconical portion 38, until it reaches its lower end of cross section S ₃ . The tapered portion 38 has an apex angle C, which is for example equal to 30 °, but may be between 10 and 50 °, while the section S ₃ is for example equal to S _2/4, but can be understood between 2 S _2/3 and S _2/8.

This mixing chamber, which consists of two cone portions 32, 38 widening then narrowing, is shaped so that there is a type flow perfectly agitated, allowing reflux and recirculation of catalyst necessary for a good mixture of the latter with the vaporized charge.

Downstream of the mixing chamber 24, in the direction of flow of the charge, extends the reaction zone 25, which is in communication with the mixing chamber through the lower end of the latter, which constitutes an orifice intermediate 40 of section S ₃ .

The reaction zone 25 widens from the intermediate orifice in a frustoconical portion 42 of angle at the apex D, until it reaches its maximum cross section S ₄ . The angle D is for example equal to 6 °, but can be between 1 and 15 °, while the section S ₄ is for example equal to 5 S ₃ , but can be between 1.5 and 8 S ₃ .

This flare allows a progressive modification of the nature of the flow of the charge-catalyst mixture. In effect, the agitated flow within the mixing chamber, is transformed in this way into a piston type flow in the reaction zone, which is perfectly suited for ensure good selectivity of the cracking reactions which occur there.

Downstream of this frustoconical portion 42, in the direction of flow of the charge, the reaction zone is constituted by a cylindrical extension 44 and has a substantially constant section, close to S ₄ , so as to best conserve the flow of piston type which was established during the passage of the load in the frustoconical section 42.

This description refers only to dimensional relationships between the different parts of the contacting area object of the invention. Those skilled in the art will dimension this entire area in function of the respective charge and catalyst flow rates and of the charge's adequate residence time in the mixture and in the reaction zone.

The section S ₁ of passage of the catalyst through the upper orifice 30, and the section S ₃ of the intermediate orifice 40 are for example equal to 65 cm ² , but can be between 10 and 500 cm2.

The maximum section S ₂ of the mixing chamber 24, and the maximum section S ₄ of the reaction zone 25 are for example equal to 300 cm ² , but can be between 30 and 2000 cm ² .

This description refers to an area of contact which consists of a series of surfaces of revolution, namely cylindrical portions or frustoconical whose cross section is circular. However, the present invention also relates to any area of contact for which there are certain reports between the sections of its constituent parts, that these sections are either polygonal, ovoid or shaped any.

In addition, the contact area according to the invention finds its application to any cracking device catalytic whose reactor is downflow from charge, whatever the means of stripping and regeneration of the deactivated catalyst.

The example below, which is not limiting, is intended to illustrate the implementation of the invention and the advantages of it.

EXAMPLE

• densité à 15°C : 0,925,
• point 50% de distillation : 470°C,
• viscosité à 100°C : 12,5. 10-6 m2/s (12,5 cst),
• résidu de carbone Conradson : 1,7% en poids,
• teneur en nickel : 0,1 ppm en poids,
• teneur en azote : 390 ppm en poids,
• teneur en vanadium : 1 ppm en poids.

An oil charge has the following properties:

• density at 15 ° C: 0.925,
• 50% distillation point: 470 ° C,
• viscosity at 100 ° C: 12.5. 10-6 m2 / s (12.5 cst),
• Conradson carbon residue: 1.7% by weight,
• nickel content: 0.1 ppm by weight,
• nitrogen content: 390 ppm by weight,
• vanadium content: 1 ppm by weight.

• catalyseur : de type zéolithique commercialisé par Akzo,
• rapport massique catalyseur / charge : 5,
• température de réaction : 520°C,
• nombre d'injecteurs : 8,
• temps de séjour dans la zone réactionnelle : 2 secondes.

This charge is introduced into a catalytic cracker with upward flow under the following operating conditions:

• catalyst: zeolitic type marketed by Akzo,
• catalyst / charge mass ratio: 5,
• reaction temperature: 520 ° C.,
• number of injectors: 8,
• residence time in the reaction zone: 2 seconds.

• catalyseur : de type zéolithique commercialisé par Akzo,
• rapport massique catalyseur / charge : 8,
• température de réaction : 545°C,
• nombre d'injecteurs : 8,
• temps de séjour dans la zone réactionnelle : 350 ms.

This same charge is then introduced into a descending catalytic cracker provided with a contacting zone in accordance with the invention, according to the following operating conditions:

• catalyst: zeolitic type marketed by Akzo,
• catalyst / charge mass ratio: 8,
• reaction temperature: 545 ° C,
• number of injectors: 8,
• residence time in the reaction zone: 350 ms.

The yields obtained during these two cracking operations are shown in the following comparative table: Yield in% by weight Classic cracker Cracker according to the invention Hydrogen, methane and ethane 3.2 2.3 C ₃ paraffins 1.0 1.2 C ₃ olefins 3.3 5.9 C ₄ paraffins 1.9 2.6 C ₄ olefins 4.7 7.8 C ₅ - (boiling point <160 ° C) 31.8 34.8 Gasoline (boiling point 160-220 ° C) 11.7 11.5 OCH (boiling point 220 - 360 ° C) 19.1 17.2 Slurry (boiling point> 360 ° C) 18.8 11.9 Coke 4.4 4.8

• une réduction très significative de la production de gaz secs (environ -30%);
• une augmentation du rendement en GPL (gaz de pétrole liquéfié) et en essence totale ;
• une augmentation de la conversion en général, puisque le pourcentage de la fraction bouillant au-dessous de 360°C passe de 57,7% pour le procédé de l'art antérieur, à 66,1% pour le procédé conforme à l'invention.

The example shows that the use of the catalytic cracking process according to the invention allows:

• a very significant reduction in dry gas production (around -30%);
• an increase in the yield of LPG (liquefied petroleum gas) and of total petrol;
• an increase in the conversion in general, since the percentage of the fraction boiling below 360 ° C goes from 57.7% for the process of the prior art, to 66.1% for the process according to the invention .

• de 6 points pour le RON ("Research Octane Number" ou "Indice d'octane recherche") de l'essence lourde (fraction bouillant entre 160 et 220°C)
• de 4 points pour le MON ("Motor Octane Number" ou "Indice d'octane moteur") de l'essence lourde
• de 2 points pour le RON de l'essence légère (fraction bouillant entre 0 et 160°C)
• de 1 point pour le MON de l'essence légère

In addition, the quality of the gasoline produced is improved since there is, compared with the prior art, an increase in the octane number:

• 6 points for the RON ("Research Octane Number") for heavy fuel (fraction boiling between 160 and 220 ° C)
• 4 points for the MON ("Motor Octane Number") of heavy fuel
• 2 points for the RON of light petrol (fraction boiling between 0 and 160 ° C)
• 1 point for the MON for light gasoline

The process according to the invention therefore makes it possible to increase the selectivity of cracking by authorizing a mass ratio catalyst / charge higher than in the prior art (and therefore a lower Δcoke, i.e. a lower difference between the quantities of coke present on the catalyst at the entrance to the regeneration zone and at the exit from it).

The process according to the invention also allows, when we are targeting a given conversion, to process more difficult, especially denser and the percentage of Conradson carbon residue is higher.

Claims (9)

1. An apparatus for the catalytic cracking of hydrocarbons comprising a downflow cracking reactor (1), means for feeding said reactor under pressure with a hydrocarbon feedstock and with particles of a regenerated cracking catalyst, a means for separating cracked feedstock products and deactivated catalyst particles, at least one means (6) for stripping the deactivated catalyst particles by at least one fluid, at least one unit (13) for regenerating said catalyst by combustion of the coke provided by the catalyst, and means (19; 2; 3) for recirculating the regenerated catalyst to said feed means,
   said apparatus being characterised in that it comprises a specific zone (5) for contacting the hydrocarbons and the catalyst consisting of

   a mixing chamber (24) of maximum section S₂, placed in communication with the regenerated catalyst feed means by an upper opening (30) which defines a catalyst passage section S₁,

   and a reaction zone (25) of maximum section S₄ placed in communication with the mixing chamber (24) by an intermediate opening (40) of section S₃,

   and in that the ratios S₂:S₁ and S₂:S₃ are between 1.5 and 8 and preferably between 2.5 and 6.
2. An apparatus according to claim 1, characterised in that the ratio S₁:S₃ between the catalyst passage section S₁ via the upper opening (30) and the section S₃ of the intermediate opening (40) is between 0.8 and 1.25 and preferably between 0.9 and 1.1.
3. An apparatus according to claim 1 or 2, characterised in that the reaction zone (25) flares out from the intermediate opening (40) at an angle relative to the vertical of between 1 and 20° and preferably of between 2 and 15°, until it reaches its maximum cross-section S₄.
4. An apparatus according to claim 3, characterised in that the ratio S₄:S₃ has a value of between 1.5 and 8.
5. An apparatus according to claim 3 or 4, characterised in that the ratio S₂:S₄ between the maximum section S₂ of the mixing chamber (24) and the maximum section S₄ of the reaction zone (25) is between 0.8 and 1.25 and preferably between 0.9 and 1.1.
6. An apparatus according to any one of claims 1 to 5, characterised in that the catalyst passage section S₁ via the upper opening (30) and the section S₃ of the intermediate opening (40) are between 10 and 500 cm².
7. An apparatus according to any one of claims 1 to 6, characterised in that the maximum section S₂ of the mixing chamber (24) and the maximum section S₄ of the reaction zone (25) are between 30 and 2000 cm².
8. A process for the catalytic cracking of hydrocarbons comprising a phase for contacting the hydrocarbons and the particles of a catalyst, a phase for performing the cracking reaction in a descending bed, a phase for separating the deactivated catalyst and the outflowing hydrocarbons, at least one phase for stripping the deactivated catalyst, then a phase for regenerating said catalyst under combustion conditions of the coke provided by the catalyst and, finally, a phase for recirculating the regenerated catalyst into the feed zone,
   said process being characterised in that a substantial proportion of the hydrocarbons is atomised and contacted with the catalyst in a specific contacting zone such as that defined in any one of claims 1 to 7.
9. A cracking process according to claim 8, characterised in that the hydrocarbons are injected into the mixing chamber countercurrently relative to the downwardly flowing catalyst particles at an angle relative to the horizontal of between 2° and 45° and preferably of between 5° and 35°.

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