FR2574422A1 - IMPROVEMENTS IN METHODS AND DEVICES FOR FLUID CATALYTIC CRACKING OF HYDROCARBON FILLERS - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR THE CATALYTIC CRACKING IN A FLUID STATE OF A HYDROCARBON FEED, INCLUDING A PHASE OF CONTACT WITH AN ASCENDING FLOW IN AN ELEVATOR, IN CONDITIONS OF CRACKING, OF THE SAID CHARGE AND OF PARTICLES. '' A CRACKING CATALYST, A PHASE OF SEPARATION OF THE USED CATALYST AND THE CRACKED LOAD, DOWNSTREAM FROM THE UPPER END OF THE SAID ELEVATOR, A FIRST STRIPPING PHASE OF THE CATALYST USED BY A GAS INJECTED IN COUNTER-CURRENT OF THIS CATALYST, A PHASE OF REGENERATION OF THE SAID CATALYST IN CONDITIONS OF COMBUSTION OF THE COKE DEPOSITED ON IT, AND A PHASE OF RECYCLING OF THE CATALYST REGENERATED TO THE SUPPLY OF THE SAID ELEVATOR. ACCORDING TO THE INVENTION, AFTER HAVING UNDERGOED THE FIRST STRIPPING AND BEFORE SUBJECTING TO SUCH REGENERATION, THE SIT CATALYST IS SUBJECTED TO A SECOND STRIPPING PHASE BY A GAS INJECTED IN THE SIT CO-CURRENT CATALYZER THEREOF.

Description

Process Improvements and Devices for Catalytic Cracking

  in the fluid state of hydrocarbon feeds. The present invention relates to the catalytic cracking in the fluid state of hydrocarbon feeds. It more particularly relates to improvements made to the stripping of the spent catalyst of such a process, before regeneration of this catalyst, for use

  "Load elevators" shorter than those of the technical

than earlier.

  The petroleum industry is known to routinely use cracking processes, in which high molecular weight and high boiling hydrocarbon molecules are split into larger molecules.

  small, which can boil in tempera-

  lower temperatures, suitable for the intended use.

  The most commonly used method for this purpose,

  at present, is the so-called catalytic cracking process.

  lytic fluid state (in English, Plain Catalytic Cracking, or FCC method). In this type of process, the hydrocarbon feed is simultaneously vaporized and contacted at high temperature with a cracking catalyst, which is kept in suspension in the fumes of the feedstock. After the desired molecular weight range has been reached by cracking, with a corresponding lowering of the boiling points, the catalyst is

separated from the products obtained.

  In processes of this type, the desired reduction in boiling points results from controlled catalytic and thermal reactions. These reactions occur almost instantaneously when the finely atomized filler is brought into contact with the catalyst. However, it is rapidly deactivated during the short time in which it is in contact with the charge, essentially because of hydrocarbon adsorption.

  and a coke deposit on its active sites. It is necessary

  It is possible to continuously stripper the used catalyst, for example, with steam, to recover the adsorbed hydrocarbons, and to reactivate it, also continuously, without altering

  its characteristics by carrying out a controlled combustion

  coke, in a regeneration section with one or more

  several stages, before recycling the catalyst to the

reaction zone.

  In practice, the catalyst of the FPCC process and the feedstock to be treated are injected under pressure and at a high temperature at the base of a column called "load elevator", which technicians often refer to as "riser". . At the top of the column is

  generally arranged a tank concentric with the eleva-

  tor. In this tank and above the telescope is housed a ballistic separation system, such as a cyclone, in which the spent catalyst is separated from the cracked charge. This is evacuated at the top of said tank,

  after cyclones, to reduce the

  of dust, while the particles of

  recovered gas meet a stripping gas such as water vapor, injected for example annularly to the

  tank, before being evacuated to a reg-

  tor. Combustion air is for example injected annularly at the base of the regenerator, while at the top thereof are provided cyclones for separating the combustion gas from the regenerated catalyst particles. This is evacuated at the bottom of the regenerator and recycled to the base of the elevator or "riser", where the load is usually injected at a temperature between 8000 and 40000 and under a pressure ranging from 0.7105 to 3 5. 105 Pascals relative. The FOC process is naturally implemented

  way that the cracking unit is in thermal equilibrium.

  In other words, the hot catalyst feed regu-

  The reactor must be such that it can meet the various thermal requirements of the reaction section, namely, in particular: - the preheating of the liquid feed; - the vaporization of this charge;

  - the intake of calories required by the reactions involved

  which are generally endothermic; - the heat losses of the unit.

  The amount of coke present on the catalyst, at the

  the regeneration zone and the regeneration

  This will determine the final temperature reached in the regeneration zone, since the calories from the combustion of the coke serve, in addition to the heat losses, to heat the regeneration fluid (air and / or oxygen) and are shared between the flue gas and catalyst particles. In operation, the amount of coke produced in the cracking unit will therefore be substantially constant, if the thermal equilibrium

  is not modified by external constraints.

  This amount of coke is related to the Delta difference

  coke between the amounts of coke present on the catalyst

  at the inlet of the regeneration zone and at the outlet of this zone by the following relation: Coke produced = Acoke x C / 0, where C / 0 denotes the mass ratio of the catalyst and the feedstock supplied

  at his contact at the entrance of the reaction zone.

  On the other hand, the difference between the regeneration temperature, T regeneration and the temperature at the outlet of the reaction section, Tractor, is given by the following relation: Treneneration Tractor x Acoke x AH combustion Cp Catalyst og designates the efficiency of the exchange of heat from

  combustion with the catalyst, AH the heat of com-

  Coke and Cp bombardment the specific heat of the catalyst.

  It is apparent that, if the Acoke believes, it is neces-

  to maintain the amount of coke produced

  to reduce the flow rate of the catalyst in circulation.

  Moreover, the increase in Acoke corresponds to a higher regeneration temperature of the catalyst;

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  which may be desirable for vaporizing heavy loads.

  Thus, the control of Acoke, in a modern cracking unit by the FCC process, where the regeneration temperature is not limited, appears as one of the fundamental basic variables of the process. Currently, with increasingly severe operating conditions of the FCG process, corresponding to heavier and therefore heavier loads, and therefore high boiling point, there is an increased deposition of coke on the catalyst. To a certain extent, this is useful because it results in a temperature

  higher catalyst at the entrance to the reaction zone

  This allows a more complete vaporization of the load, a controlled thermal cracking of the asphaltenes

  and a higher activation energy of the catalyst.

  However, it is desirable to be able to control and limit the regeneration temperature of the catalyst, in order to preserve its thermal stability and to reduce the deleterious effect of certain constituents present in the feed, especially in the untreated residues. In addition, it is sometimes desirable to increase the ratio C - defined above, that is to say the mass ratio of the catalyst in contact with the load at the entrance of the elevator "riser" to improve the contact of the charge and the catalyst and increase the conversion of the charge by putting it in the presence of

  more active sites of the catalyst.

  The Applicant has established that efficient stripping of the hydrocarbons entrained by the catalyst particles

  used, prior to their regeneration, contributes to the ob-

these results.

  The stripping of the spent catalyst, already used in the conventional FCC process, aims at displacing by a gas, usually water vapor, the hydrocarbons entrained in the voids separating the catalyst particles and, to a certain extent, the

2574422.

  The lighter hydrocarbons adsorbed on the surface in the pores of the catalyst. It is known, in fact, that a poorly stripped catalyst before its regeneration has a higher coke and a hydrogen concentration on the deposited coke of greater than 7% by weight. It is further known that the stripping is better at high temperature. In order to obtain a better stripping of the spent catalyst, before regeneration thereof, the present invention provides for a second stripping of the catalyst, in series with The first stripping is carried out concurrently with the flow of catalyst, in order to bring it to the height required for feeding the regenerator (s), which makes it possible to use an elevator. shorter charge than in the prior art, while the first stripping

  usual is made against the current.

  The subject of the present invention is therefore, in a process for the catalytic cracking in the fluid state of a hydrocarbon feedstock, comprising a step of contact with ascending flow in an elevator, in a

  conditions of cracking, of said load and of

  particles of a cracking catalyst, a separation phase of the spent catalyst and the cracked feedstock, downstream of the upper end of said elevator, a first phase of stripping the spent catalyst with an injected-to-gas countercurrent of this catalyst, a regeneration phase of said catalyst under combustion conditions of the coke deposited thereon, and a regenerated catalyst recycling phase to said elevator, the improvement that, after having undergoing said first stripping and before being subjected to said regeneration, said catalyst is subjected to a second stripping phase by a gas injected into said

  catalyst to concantant thereof.

  The gas used for the second stripping step may be steam, but in a preferred embodiment of the invention, the gases from the catalyst regeneration will be used which have the advantage to be at a higher temperature than the stripper catalyst, either alone or in mixture with water vapor. From this second phase of stripping in con-current and at higher temperature, result a number of advantages among which: the stripper is shorter than in the known technique

  - the potential water vapor formed from lthy-

  The amount of moisture contained in the coke thus removed will be separated easily from the beginning of the regeneration phase; she

  will therefore be less likely to affect the reaction

  catalyst activity; a significant part of the metals such as nickel and vanadium which are deposited on the surface of the catalyst can be stripped in the form of volatile compounds that can be removed; the life of the catalyst will be improved; the gas of this second stripping phase will serve as a lift gas for the catalyst from the first stripping, in order to convey the grains from the catalyst to the regenerator, and will be explained in more detail in

  following this description the interest of this

  auxiliary function of the stripping gas.

  The invention also relates to a device for

  catalytic cracking in the fluid state of hydrogen

  carbides, comprising a riser-type column, means disposed at the base of said elevator for supplying it under pressure with a hydrocarbon feedstock and particles of a cracking catalyst, a first means for stripping by a first gas spent catalyst particles in an enclosure disposed at the top of said elevator, concentrically therewith, the first gas

  stripping is injected into this chamber against

  spent catalyst particles, at least one regeneration unit of said catalyst by combustion of the coke deposited thereon, and means for recycling the regenerated catalyst to said supply means, said device being characterized in that comprises, between said first stripping means and said regeneration unit, a second means for stripping a second gas of said catalyst particles, said second

  means of stripping being such that the second stripping gas is

  page is injected under pressure into the particle stream

  of co-current catalyst thereof.

  Said second stripping means will advantageously be disposed in the device at a level lower than that of said regeneration unit, said second stripping gas then also serving as a carrier gas for said particles, which allows the use of a

short lift.

  The second stripping gas may or may not be identical to the first stripping gas. Advantageously, it will be constituted at least in part by the gases coming from

the regeneration unit.

  The use of a second stripping means brings

  to the catalyst particles an additional driving pressure

  to diversify the positioning

  different cracking device units, particularly

  televator and regenerator. It also improves the stripping qualities, especially if the second stripping gas is

  from the regeneration unit, which have a temperature

  it is about 25 ° C and, if possible, about 100 ° C higher than that at which the first stripping is carried out, which makes it possible to appreciably reduce A coke and to limit it to the reaction Acoke, with the result that there is less release of heat to regeneration and a

  catalyst less degraded and more stable. We can thus

  lengthen the elevator and / or handle heavier loads. Finally, it is better to control and regulate the feed of the regenerator to spent catalyst, with the advantage of being able to control its temperature by limiting

  hot spots, which preserves the stability of the catalytic

  Therefore, the ability to reduce the length of the elevator by the invention should be emphasized. It allows, on the one hand, to obtain a better selectivity in cracked products of the type of gasoline and distillates

  light, on the other hand, to raise the temperature of

  without increased gas production and even with a reduction in

  Acoke. This results in a better conversion of the feed, with a better octane number of the resulting products, and heavier and more difficult loads can be processed. A low lift is also suitable for ultra-short residence times

of the charge.

  As will be described hereinafter in more detail, -

  The invention also applies to cracking assemblies comprising two regeneration units in series.

  than those with a single regeneration unit. -

  The accompanying drawings illustrate, in a form

  a known device for catalytic cracking to-

  the fluid state and various embodiments of the invention. In these drawings: FIG. 1I is a diagram of a conventional fluid bed catalytic cracking assembly; FIG. 2 is a similar diagram of an assembly according to the invention comprising a regeneration unit;

single-stage catalyst.

  FIGS. 3 and 4 are diagrams of two sets according to the invention each comprising a unit of

  regeneration of the two-stage catalyst.

  The FCC cracking device represents

  Figure 1 is of a type known per se. It essentially comprises a column t said charge elevator, or "riser", fed at its base, by the line 2, in charge to be treated and, through the conduit 3, in particles -9

a cracking catalyst.

  The column 1 opens at its top in a chamber 4, which is concentric to it and in which take place, on the one hand, the separation of the cracked feedstock and, on the other hand, the stripping of the spent catalyst. The treated charge is separated in a cyclone 5 which is housed in the chamber 4, at the top of which is provided an evacuation line

  6 of the cracked load, while the particles of

  spent stripper are discharged at the base of the chamber 4. A line 7 supplies stripping gas, usually water vapor, injectors 8 regularly disposed at the base of the enclosure 4. The stripping is therefore carried out

  preferably in a dense medium against the current of the cata-

  lyst. The spent catalyst particles thus stripped

  are evacuated at the base of enclosure 4 to a regenerator

  9 in the regenerator 9, the coke deposited on the particles of the catalyst is burned with air, injected at the base of the regenerator

  by a line 12, which supplies injectors 13 regular-

  spaced apart. The particles of the treated catalyst

  The combustion gases are separated by cyclones 14 from which the combustion gas is discharged through a line 15 while the catalyst particles are discharged to the base of the regenerator 9, where they are recycled by

  the duct 3, equipped with a regulating valve 16, to the food

elevation 1.

  The dimensional and operating characteristics of such a device are usually as follows: height of the reaction part of the elevator 1: 5 to 40 meters, temperature of the charge to be cracked 75 to 4500.degree. load elevator I to be treated: 1000 to 10,000 tonnes per day, feed rate of the elevator 1 in catalyst 3 to 50 tonnes per minute,

- 13 -

  - residence time of the charge in the eluate 1: 0.1 to 10 seconds, catalyst regeneration temperature: 650 to

900 C,

  - residence time of the catalyst in the regenerator 9: 5 to 20 min, Figure 2 shows a device according to the invention, wherein the members already described in relation to Figure 1 are designated by the same

  reference numbers assigned index '.

  In this device, the conduit 10t, by which the

  spent catalyst particles are removed from the

  belt 4 'disposed at the upper end of the elevator 1', does not open directly into the regenerator 9 ', but has a vertical portion 101, communicating via a portion 102 with the regenerator 91, and connected

  by a bend at the lower end of the conduit 101.

  The base of the duct 101 is supplied with a second stripping gas by a line 18. In the case of the drawing, this second stripping gas is constituted by a mixture of water vapor, brought to the line 18 by the line 19, and effluent gas from the regenerator 91, derived from line 'to line 18 via line 20, equipped with pump 21. It will be noted that the second stripping of the catalyst particles takes place concurrently in the vertical part 101 and that the stripping gas plays the role of carrier gas

  to raise the particles up to the regenerator.

  It is indeed possible to significantly reduce the residence time of the load to be treated in the elevator 1 'and, therefore, the height of the latter. Under these conditions, the enclosure 4 'will not be at a sufficient height so that the used catalyst particles can, by simple gravity, feed the regenerator 9 and, after regeneration, be recycled to the feed of the elevator 1' . The second stripper gas injected via line 18 into the conduit section. 101 will therefore advantageously exercise a poachee on the particles of

- 11 -

  used catalyst to route them to the regenerator.

  With the additional stripping system according to the invention, the dimensional and

  the stripping device can be modified

  in the following manner: - height of the reaction part of the elevator 1 ': 1 to 30 meters, - residence time of the load in the elevator 11: 0.05 to 5 seconds, - catalyst regeneration temperature : 650 to

900 C,

  residence time of the catalyst in the regenerator 9 ': 1 to 15 minutes, catalyst temperature at the outlet of the enclosure

5 ': 480 to 580 C,

  - temperature of the second stripping gas at the inlet

of the conduit 101: 500 to 900 C.

  Figures 3 and 4 illustrate two other forms of implementation of the catalytic cracking process according to the invention, in which a two-stage regeneration chamber is used. In these figures, the members already described in relation to FIGS. 1 and 2 are designated by the same reference numerals, assigned

indices a and b, respectively.

  In the case of Figure 3, the regenerator 9a

  is upflow and has two stages 91a and 91d.

  The spent catalyst having already undergone a first stripping in the chamber 4a is conveyed via the pipe 10a, the vertical section of the pipe 101a and the horizontal section 102c to the lower stage 91a of the regenerator. A second stripping gas is injected under pressure by the line

  18a at the lower part of the vertical section 101a.

  This stripping gas comprises a mixture of water vapor, brought by the line 19a, and combustion gas from the regeneration chamber, brought by the

line 20a.

  The base of the first stage 91a of combustion is

- 12 -

  supplied with air by the line 12a and the air is distributed by injectors regularly spaced 13a. In this stage, cyclones 14a separate the combustion gas

  partially regenerated catalyst particles.

  The combustion gas is conveyed to the line 20a by a line 115, equipped with a valve 116, making it possible to

  divert a portion of the gas stream to a line 117.

  The particles of the catalyst having undergone a first regeneration treatment are then transferred to the second stage 91b of the regenerator via the central duct

  a, supplied with air by line ll1a.

  The base of the floor 91b is also supplied with air

  by the line 112a and by the injectors 113a. The particles

  the regenerated catalyst are discharged laterally in a buffer chamber 118a and are recycled via the conduit 3a to the feed of the elevator 1a. The flue gases discharged at the top of stage 91b are treated

  in an external cyclone 119a, at the base of which the

  The catalyst particles are returned through line 120a to stage 91a, while the flue gases are discharged via lines 121a and 20a to line 18a. A safety valve 122a is provided on the line 121a and a valve

  123a allows a portion of the gas to be diverted to a line 124a.

  This embodiment of the device according to the invention, equipped with a two-stage upflow regenerator, has the following advantages: - double regeneration of the catalyst, allowing an integral combustion of the coke without altering the catalytic properties, - no limitation the temperature of the second regenerator, which allows the catalyst to acquire the

  temperature required to vaporize and crack the load.

  The embodiment of FIG. 4 also comprises a two-stage regenerator 9b 92a and 92b

downflow.

  The catalyst already stripped in the chamber 4b is conveyed via the pipe 10b, the vertical section 101b

- 13 -

  and the horizontal section 102b to the upper stage 92b.

  A second stripping gas is injected under pressure to the lower part of the vertical duct 101b by a line 18b. This stripping gas consists of a mixture of water vapor, brought by the line 19bet of gas from

  combustion, from the regenerator 9b by the line 20b.

  Air is injected at the base of stage 92b via line 112b and injectors 113b. Cyclones 14b separate the particles in suspension from the flue gas, which is discharged via a line 121b, on which a

  the valve 123b makes it possible to divert part of the combustion gas

to a line 124b.

  The particles treated in the first stage 92b are conveyed by gravity via the conduit 125 to the lower stage 92a of the regenerator, at the base of which air is injected via the line 112b and the injectors 113b. The combustion gas is discharged to an external cyclone 119b, whereby the catalyst particles are returned through line 120b to stage 92a, while the gas is discharged via line 115b to line 20b. A valve 116b makes it possible to divert part of the gas towards a line

auxiliary 117b.

  The regenerated catalyst is removed from the base of stage 92a via line 3b and recycled to the feed of elevator 1b. This embodiment of the cracking device according to the invention, which comprises a downflow two-stage regenerator, has, in addition to the previously described advantages, the following advantages:

  - the two stages of regeneration are done against

  cyclones are external and their supports lower, the regenerator operating at the highest temperature, and therefore the heavier, is at the lower level, which simplifies the construction of the unit.

- 14 -

  The following example is intended to illustrate the invention and

has no limiting character.

EXAMPLE

  Two catalytic cracking tests were carried out from the same hydrocarbon feedstock in a two regenerator unit of the type of that described in Figure 3. In contrast to the first test, the second test was carried out using a device comprising a second co-current stripping phase in accordance with the present

  invention with a short elevator.

  Nature of the filler: Density: 0.903 Sulfur: 0.77% by weight Total nitrogen: 0.19% by weight Vanadium: 4 ppm Nickel: 1 1 ppm Conradson carbon: 4.9% by weight C / H ratio: 12, 4 Non distillable at 6000C = 23% vol. Operating conditions: Test without test with additional stripping and additional stripping and short lift Charge temperature, C 95 95 Temperature Riser, OC 525 525

Final temperature -

  regenerated catalyst, OC 815 782 C / O ratio 4.97 5.60 Coke, wt% 7.45 7.36 Delta coke, wt% 1.50 1.31 It is found that the joint use of a short lift and a second co-current stripping with regeneration gas at 5950C results in a reduction of delta coke,

  causing a decrease in the regeneration temperature.

- 15 -

  This allows an increase in the circulation of

  lyser (C / O 5.6) and improved catalyst stability.

  The most important changes in cracking reactions are the following: - reduction of dry gases, - reduction of fresh catalyst addition by 26% 0 / o, - increase of conversion, - increase of liquid yields, as shown the following table: Test without Test with Stripping Additional additional stripping and short lift Dry gases,% by weight 6.3.5.8 Charge to be alkylated,% by weight 17.6 18.0 Gasoline 42.8 45.2 Thinner 16, 15.7 Heavy Diluent 9.3 8.0 Conversion at 220 C, wt.% 74.2 76.3 Conversion at 3550C, wt.% 90.7 92.0 Liquid Yield,% wt. 86.2 86, 9

- 16 -

Claims (10)

  1. In a process for the fluid catalytic cracking of a hydrocarbon feed, comprising a step of upflowing contact in an elevator, under cracking conditions, of said feedstock and   particles of a cracking catalyst, a separation phase   feeding the spent catalyst and the cracked feed, downstream of the upper end of said elevator, a first phase of stripping the spent catalyst with a gas injected against the current of this catalyst, a regeneration phase of said catalyst; catalyst under coke combustion conditions deposited thereon, and a recycle phase of the regenerated catalyst to the feed of said elevator, the improvement that after undergoing said first stripping and before being subjected to said regeneration, said catalyst is.subated to a second stripping phase by a gas injected into said   co-current catalyst thereof.   2. A process according to claim 1, characterized in that said second stripping gas is constituted at least partially by gases from the regeneration phase of the catalyst and optionally the water vapour.   3. Method according to one of claims 1 and 2,   characterized in that said second stripping gas is at a pressure sufficient to serve as a lift gas, with a view to   to raise the catalyst to the regenerator (s).   4. Method according to one of claims 2 and 3,   characterized in that said second stripping gas is   at a temperature of at least 250 ° C above the temperature   the temperature of the catalyst particles coming from   said first stripping phase.   5. A device for catalytic cracking in the fluid state of hydrocarbon feeds, comprising a column (1 ') of the elevator type, means arranged at the base of said elevator to feed it under pressure with a feedstock. hydrocarbons and particles of a - 17 -   cracking catalyst, a first stripping means (7 ', 8') with a first gas of spent catalyst particles in an enclosure (4 ') disposed at the top of said elevator, concentrically thereto, the first stripping gas being injected into this chamber with countercurrent spent catalyst particles, at least one unit (9 ') for regenerating said catalyst by combustion   coke deposited thereon, and means (3 ') of   cycling the regenerated catalyst to said feed means   said device being characterized in that it comprises, between said first stripping means and said regeneration unit, second means (13t) for stripping a second gas of said catalyst particles, said second stripping means being such that the second stripping gas is injected under pressure into the flow of the co-current catalyst particles thereof. 6.- Device according to claim 5, wherein said regeneration unit (9 ') comprises a single regeneration stage, characterized in that said second stripping gas is injected upstream of said unit in a vertical section (101) of the supply duct in   spent catalyst of said regeneration unit.   7.- Device according to claim 6, characterized in that it comprises a line (18) for supplying   second stripping gas connected to the line (15 ') of   cuation of the combustion gases of the regeneration unit (9t). 8.A device according to claim 5, wherein said regeneration unit (9a, 9b) comprises two upflow (91a, 91b) or downflow (92a, 92b) regeneration stages, characterized in that the second stripping is injected upstream of the upstream stage (91a, 91b) of said unit, into a vertical section (101a, 101b) of the spent catalyst supply duct   of said regeneration unit.   9.- Device according to claim 8, characterized - 18 -   in that it comprises a second stripping gas supply line (18a, 18b) connected to the flue gas discharge line (20a, 20b) of the upstream stage (91a, 92b) and or the downstream stage (91b, 92a) of said regeneration unit.   10.- Device according to one of claims 5 to 9,   characterized in that it comprises an elevator (1 ') of reduced height.