FI98529C - Method and apparatus for the preparation of light olefins - Google Patents

Description

98529.

Method and apparatus for the preparation of light olefins

The present invention relates to the preparation of light olefins. In particular, the invention relates to a process according to the preamble of claim 1 for the preparation of light olefins, such as propylene, butenes and amylenes, from hydrocarbon feedstocks such as light and heavy gas oil, vacuum gas oil, naphtha, propane, butanes or light condensates. The invention also relates to an apparatus according to the preamble of claim 16 for the production of light olefins from said hydrocarbon feedstocks.

Several commercially available methods for producing propylene, butenes or amylenes from petroleum-based feedstocks are currently known. These methods include thermal cracking, fluid catalytic cracking (FCC) and dehydration. The prior art methods have certain drawbacks, which are as follows:

Thermal cracking: The main product of the thermal cracking process is ethylene. Propylene and heavier olefins are the main by-products but their yields cannot be significantly increased by changing the operating conditions. Other by-products ·. : includes flue gas, aromatic tar and coke which · are harmful to the process and have an economic value ·: ··: little or no energy.

· · · 30 ”. Conventional Lei Jucatalytic Cracking (FCC): The yield of light olefins is low and the quality of the main product component, FCC-gasoline, is poor for future requirements due to low octane number and high concentrations of benzene and heavy olefins. Light olefins 35 ;;; higher temperatures and short residence times are required to increase dosing, which is not practical in current reactors, as will be described below. As the temperature is raised, the endotherm of the reaction increases and the heat /; the vacuum difference between the reactor and the regenerator decreases. Since the temperature of the 2 98529 regenerator cannot be raised without damaging the catalyst, either the catalyst-oil ratio must be increased or some of the energy must be transferred to the reactor in some other way to produce all the energy required.

5

Dehydration: Hydrocarbons are dehydrated at relatively high temperatures. The dehydrogenation reaction is very endothermic, requiring a large, carefully controlled heat input to the reaction zone. This has led to complex and expensive reactor / regenerator structures.

The types of reactors used in hydrocarbon conversion processes can be classified as follows: 1. 1. fixed bed reactors and 2. fluidized bed reactors.

At very high fluidization rates, the surface of the layer is no longer precisely defined, but the layer is in fact a zone where the solids content slowly decreases as it goes up. If the particles are finely divided, this will result in rapid fluidization. wherein the removal of solids from the reaction zone takes place so rapidly that in general such rapidly le- '. the layered layers can only be maintained by recycling the 2β 'removed solid through cyclones. Such a system ··; called the circulating pulp bed (CFB).

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One of the most commonly used reactor systems is the FCC apparatus, the main components of which are a riser operating in the rapid fluidization zone 30, a high volume reactor operating in dilute suspension phases, and a regenerator operating in the fluidized bed region. riser (30 - 40 m) compared to the regenerator, which makes it possible to connect the re-35 · generator to the riser-reactor combination at a point between the top of the reactor and the bottom of the riser.

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98529 3 as to ensure the hydrodynamic operation of the regenerator equipment. This sets the boundary conditions for the process in terms of residence time and hardware design. These limitations are particularly disadvantageous when short residence times and high solids concentrations are required in the reactor. These restrictions on residence time and solids levels make it impossible to achieve very short residence times or high solids levels in the FCC system.

U.S. Patent No. 4,980,053 describes experiments performed using a heavy hydrocarbon fraction, such as vacuum gas oil, under harsher operating conditions than the FCC but under milder conditions than thermal cracking, resulting in higher yields of propylene and butenes than ethylene. This so-called "Deep Catalytic Cracking" process (DCC) has been studied in pilot units and commercial, modified FCC units. A DCC unit is, in effect, an FCC unit-20 unit with different operating parameters and a modified cover.

EP-A-395 345 discloses a process. to light olefins, especially propylene, using a zeolite catalyst and reaction temperatures between 500 and 700 ° C at low hydrocarbon partial pressures. In the examples of said reference, the process has been applied using solid bed reactors. However, the process can be kept short, but the process can also be carried out in fluidized bed systems, and the prior art process is claimed to have lower capital costs and to be more selective for propylene and butenes than conventional thermal cracking.

However, the above-mentioned reactor systems have serious drawbacks which limit their use, especially in processes where short residence times and high solids concentrations in the reactor are required. In such a process, the riser should be low compared to the regenerator. The problem is even worse if at the same time the pressure difference between the re-5 generator and the riser is large. In that state, the regenerator cannot be connected to the riser cyclone.

Instead, complex systems are needed to recycle the catalyst. In practice, the reactor riser should be designed to be impractically high, in which case the velocity of the gas 10 would become too high and the volume fraction of the catalyst in the riser would be too small for optimal process conditions. A limitation of the FCC method is that the volume fraction of the catalyst cannot be freely controlled without affecting other process variables.

The object of the present invention is to obviate the above-mentioned drawbacks of the prior art and to provide a new process and reactor system for the production of light olefins from a hydrocarbonaceous feedstock.

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The invention is based on the idea that the catalytic conversion of hydrocarbons is carried out in a circulating fluidized bed (CFB) reactor using a short residence time. Preferably, the catalyst used is also regenerated in a circulating mass reactor-type regenerator (CFB) and all the thermal energy required for the endothermic conversion reaction is introduced into the reactor by recycled, regenerated catalyst particles.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

»• · ·

The reactor system according to the invention contains hydrocarbons 35 '. for catalytic conversion, at least one circulating unit (reactor) provided with hydrocarbon feedstock supply connections and connections for the recirculation of catalyst particles. The CFB reactor is also equipped with a cyclone or similar separator to separate the spent catalyst from the product stream. The cyclone in question has a product outlet for light olefins and a solids outlet for the separated catalyst particles. In addition, the reactor system includes at least one circulating mass unit for regenerating the catalyst by combustion, which unit is provided with feed connections for the spent catalyst to be regenerated, and a cyclone or similar separator for separating the regenerated catalyst from the combustion process flue gases. The feed connection of the regenerator unit is connected to the solids removal of the reactor cyclone.

More specifically, the reactor system is characterized by what is set forth in the characterizing portion of claim 16.

The invention will now be examined in more detail by means of a detailed description and with reference to the accompanying drawing, which schematically shows a simplified process diagram for a preferred embodiment of the invention.

In the context of the present invention, the terms "spent catalyst 1" and "deactivated catalyst" are used interchangeably 25 'to mean catalyst particles or particles on the surface of which coke or other impurities have accumulated which reduce the catalytic activity of the catalyst.

• »> ·: 'The abbreviation" CFB "is used to denote" circulating mass layer-30 ta ", where the solid is conveyed vertically in a vertical pipe by means of a high-velocity gas flow. The CFB is preferably provided with a cyclone in which solids are separated from the gas stream. Often a return pipe is also connected to the cyclone to recycle the solids. The return tube represents a preferred embodiment of the CFB according to the invention, but the CFB units described below are also operable without the return tube. The superficial gas velocities (superficial gas 98529 6 velocities) in the CFB reactor are usually about 2 to about 10 m / s. The flow capacity of solids (catalyst particles) is very high at these gas velocities, which minimizes the required reactor diameter. The surface velocity of the gases in the 5 CFB regenerator is not critical because the coated lysator can be recycled to achieve the desired residence time for catalyst regeneration.

"Light olefins" means olefins containing from 10 to 6 carbon atoms, preferably ethylene, propylene, butenes and pentenes.

When referring to a feedstock-catalyst contact, the term "short contact" refers to residence times between 0.1 and 3 s.

The process for converting hydrocarbons to light olefins involves conventional steps, i.e. the introduction of hydrocarbons into a reaction zone containing a solid catalyst. In the reaction zone 20, hydrocarbons come into contact with the catalyst under conditions that favor the catalytic conversion of hydrocarbons to light olefins. The light olefins and unreacted starting materials formed are separated from the catalyst particles after the reaction. The spent, deactivated kata-25 ', lysate is recovered and regenerated in a regenerator by burning the coke accumulated in the catalyst particles.

According to the invention, the hydrocarbon feedstock is contacted with Catalyst V in a circulating bed (CFB reactor) with a residence time of 0.1 to 3 seconds. The CFB system of the invention differs from the conventional FCC system in that: 1) a high volume reactor 1) is replaced by a riser with a small out-of-pipe cyclone and the reactions occur only in the riser; 2) the bubbling bed regenerator 35 is replaced by a CFB regenerator. Both of these changes' promote residence time control and provide a better reactor structure.

«I * * · li 7 98529 Until now, circulating mass reactors (CFBRs) have been used primarily for non-catalytic processes. However, a circulating mass reactor (CFB) for the production of maleic anhydride based on the catalytic oxidation of butanes is already known [Pugsley, T. et al., Ind. Eng. Chem. Res.

31 (1992) 2652-2660]. As a disadvantage of the known CFB structure, it should be mentioned that the volume fraction of the catalyst in the reactor cannot be freely controlled without affecting other process variables. In addition, it has not previously been suggested in the art that the same 10 devices could be used for cracking reactions or the production of light olefins.

The catalyst used according to the invention is separated from the products and the hydrocarbon feedstock in an external cyclone connected to a CFB reactor. Preferably, the regenerator is of the same type as the reactor, whereby the regeneration of the spent catalyst can be carried out in a second circulating pulp bed. However, other types of regenerators can also be used.

According to the invention, it is possible to arrange two (or more) reactor units (reactor units) in series using the product stream of the previous reactor as the feed to the next reactor. The reactors of this embodiment can be operated at different temperatures and pressures, allowing adaptations to the most diverse types of hydrocarbon feedstocks.

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According to a particularly preferred embodiment, in which the reactor system comprises a CFB reactor and a CFB regenerator, at least a portion of the separated, deactivated catalyst is passed to the regenerator via a first pipe ("spent catalyst pipe") connected to the bottom of the regenerator. The supply of deactivated catalyst to the regenerator is preferably controlled by a valve connected to the supply nozzle of the pipe in such a way that the pipe contains at least a minimum amount of catalyst to keep the pipe substantially gas-tight. The "plug" formed by the catalyst in the tube 8. 98529 sa prevents the reaction zone gases from entering the regenerator in. This eliminates the risk of explosion.

According to the invention, it is possible to feed all the separated, deak-5-activated catalyst to the regenerator without internal recycling of the catalyst.

The deactivated catalyst is preferably regenerated by burning the coke accumulated on its surface in a second layer of circulating mass at a temperature of 650 to 800 ° C, preferably by introducing hot air and possibly hot flue gas produced by additional fuel into the regenerator. As already mentioned above, it is also possible to use other types of regenerators, such as a conventional bubble bed type regenerator.

An important advantage of this reactor system, which will be described in more detail below, is that the catalyst concentration in the reactor can be kept high, thus ensuring a high catalyst contact surface with the hydrocarbon-20 reactants. The reactor system of the invention is therefore preferably provided with a second tube ("catalyst recycle tube") for circulating the catalyst separated by the cyclone back to the reactor.

25 The flow rate of the spent catalyst to be regenerated and recycled depends on the hydrocarbon feedstock, feed rate, * i.

the catalyst used and the process conditions.

i: »« »(« • * V As in the case of a CFB reactor, part of the catalyst is preferably returned to the CFB regenerator via a return pipe, while the rest of the catalyst, i.e. the non-regenerated part, flows back to the CFB reactor via a catalyst recycle pipe connected to its bottom.

The invention can be used to convert hydrocarbons to light olefins under cracking and dehydration conditions. In the present invention, the hydrocarbon feedstock for catalytic cracking may be light gas oil (LGO), heavy gas oil (HGO), vacuum gas oil (VGO) or naphtha. Steam or other gas can be used as a diluent. The light olefins produced are ethylene, propylene, butenes, amylenes and a high-octane, low-benzene gasoline fraction.

Conventional cracking catalysts and improved cracking catalysts are used as solid catalysts. The process conditions for the catalytic cracking in the reactor assembly of this invention are as follows: temperature: 10,520 to 700 ° C; pressure: 105 - 500 kPa; residence time: 0.1 - 3 s.

According to the invention, air can be fed to the reactor to promote the course of the reaction, the amount of air being 0 to 50%. If additional air is fed to the reactor, it is preferably present in an amount of about 0.1 to about 50% by weight of the hydrocarbons.

The main advantages of the invention over known processes are: The short residence time and the high volume fraction of catalyst can be maintained without the use of complex mechanical or pneumatic transfer systems to transfer the catalyst from one unit to another.

25 All the energy required for the catalytic conversion of hydrocarbons is obtained from the recycled catalyst, which is regenerated in a circulating mass generator, except when air is also injected into the reactor and the oxidation of the starting materials and the reaction products resulting from the air injection are brought in. some heat into the reactor.

The volume fraction of catalyst in the reactor can be set to the desired value by the internal circulation of the catalyst, independent of other process flows.

35.

The pressure levels in the reactor and regenerator can be adjusted independently. This also makes it possible to use one regenerator together with several reactors, each of which operates with its own optimal process parameters and its own raw material.

Compared to conventional cracking processes, the process of this invention provides a good yield of light olefins, a good quality gasoline fraction, high conversion and a simple, inexpensive reactor structure.

Compared to current dehydration processes, the present invention provides a very simple and inexpensive reactor / regenerator solution.

Compared to FCC-type units, the regenerator is small 15 and the amount of catalyst is small. This makes it possible, with appropriate design, to avoid existing heavy, high temperature resistant structures and to use easy-to-maintain, lightweight, simple, economical, externally insulated structures.

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The average cracking temperature in the CFB reactor can be increased without increasing the reactor feed temperature, as a result of which the yield of light olefins increases when air is used as a pre-fluidization gas due to exothermic combustion. This combustion takes place in the reaction zone at the same time as the endothermic cracking.

• «· ·

The accompanying drawing shows a preferred embodiment of the present invention. Short Contact Reactor / Regenerator-3CC *:. the construction is used to achieve the desired process conditions. The basic principle that governs the interaction between two CFB units is described in more detail in Finnish patent application 924438 (Einco Oy, Finland).

35 ": ·.. According to the invention, the hydrocarbon feedstock mixed with the heated catalyst is cracked in a short contact CFB reactor (1)

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98529 11 at temperatures between 520 and 700 ° C. The hydrocarbons are fed through the feed nozzle (24). The reactor operating pressure is 105 to 500 kPa (a) and the residence time is 0.1 to 3 s. The catalyst-oil ratio can vary from 10 to 120. The hydrocarbon-5 feed partial pressure can be reduced by adding steam or other diluting gases, such as circulating gas, from the unit, but the use of a dilution gas is not a prerequisite for the operation of the process. The supply comes from the pipe (17) and the pre-fluidization gas is injected through the pipe (18).

10

After the cracking reaction, the spent catalyst is separated from the products in a cyclone (2) located outside the fluidized bed reactor. The hydrocarbons adsorbed on the spent catalyst either remain in the spent catalyst and burn in the re-15 generator (3) or can be removed by steam in the purification zone (21) below the cyclone, if purification is economically justified. The products exit through the pipe (19). A part of the spent catalyst is controlled from the cyclone (2) to the regenerator (3) via a spent catalyst transfer pipe (16), whereby the flow of catalyst particles can be controlled by a pipe valve (8) near the feed nozzle (8 ') connected to the bottom of the regenerator (3). Some of the spent catalyst can be returned to the reactor as an internal circulation through the control valve (6) via the 25 'catalyst recirculation pipe (12). By adjusting the catalyst recirculation rate with the valve (6), the catalyst status can be ··· *. and the temperature profile in the reactor. To prevent mixing of the reactor and regenerator gases, the valve (8) adjusts the flow of catalyst particles so that the pipe (16) is always full of catalyst. The adjustment of the surface of the catalyst layer is indicated by L.

The regenerator (3) is in principle a circulating mass reactor.

.The regenerator serves two purposes: the thermal energy endo-35. '; · For the thermal cracking reaction is introduced into the reactor via a catalyst heated in the generator, and the coke deposited on the spent catalyst particles is burned off 98529 12. Regeneration of the catalyst takes place at temperatures between 650 and 800 ° C by blowing preheated air through the air supply pipe (22) and injecting additional fuel through the pipe (23) at the lower end of the regenerator.

In the regenerator cyclone (4), the regenerated hot catalyst is separated from the flue gases leaving the exhaust pipe (20), and the regenerated catalyst is returned to the reactor (1) via the regenerated catalyst pipe (15). The catalyst flow is controlled by the control valve (10). The remainder of the regenerated catalyst 10 is returned as internal circulation to the regenerator through the catalyst recycle tube (14).

Under steady state conditions, the catalyst flow rates through tubes (15) and (16) are equal.

The catalyst is added to the system via a valve (5) controlled by the pressure difference between the top and bottom of the regenerator.

The reactor system may comprise more than one reactor in series or more than one reactor may be installed in parallel so that each has its own feed.

The products separated from the catalyst in the reactor cyclone can be further processed into intermediate fractions using the usual 25 '. or a modified FCC process product recovery system.

Exemplary embodiments of the present invention, i.e., results from the conversion of gas oils to olefins in pilot plant experiments, are set forth below.

Example 1

The assembly consisted of one CFB reactor and one CFB-re-35. · Generator. The regenerated catalyst entering the reactor was pre-fluidized with nitrogen. Light gas oil (LGO) was fed to the reactor through a nozzle with a small flow of decomposition air.

98529 13 No internal catalyst recycling was used in this experiment. The main parameters were:

Reactor: 5 height 1.85 m diameter 0.030 m oil mass flow 1.13 g / s external catalyst / oil ratio 27 g / g 10 internal catalyst / oil ratio 0% catalyst volume 2 - 7% pre-fluidization tube height 0.25 m pre-fluidization pipe diameter 0.018 m 15 Regenerator: height 3.1 m diameter 0.08 m Exhaust gas O2 content 4 - 5% 20 catalyst volume fraction 4%

Example 2

The structure and feed of the reactor were the same as in Example 1, except that the internal and external catalyst / oil ratios were both 15. The internal catalyst recycle ratio was just above the oil injection point.

»·« <• · 1 (<- .. Example 3 «· 3 01. ·

The structure and feed of the reactor were the same as in Example 2 except that no air was used to decompose the feed and the proportion of the internal circulation of the catalyst was about 8.

98529 14

Example 4

The structure and feed of the reactor were similar to Example 1 except that air was used for pre-fluidization but not for feed decomposition. The diameter of the riser in this experiment was 0.042 m.

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98529 15

Table 1. Results of the experiments of Examples 1-4

Example 12 3 4

Material balance 5 Feed, g oil 4073 3802 4248 8780 nitrogen 3323 2620 2618 0 air 593 428 0 2962 10 tot. 7989 6850 6866 11742

Products, g gas 5593 4563 4406 7164 condensate 15 2132 1594 2234 3555 coke 407 380 425 1300 tot. 8132 6537 7065 10719 20 Difference -143,313 -199 -277 error relative to input -2% 5% -3% -2%

Process 25 Yields, wt%

Cj. - C4 alkanes 5.8 6.4 5.9 13.8 C2 '- C4 · 26.2 24.2 21.2 26.0 petrol 28.3 30.8 37.1 30.4 fuel oil 23.9 23 , 1 20.3 12.5 30 bases 4.3 4.0 3.7 0.4 coke 10.7 9.9 11.5 14.3 CO2, H2, H2O 0.8 0.8 0.2 2 , 5 tot. 100.0 99.8 99.7 99.9 .35: '·' Conversion, p-%

Reactor temperature, ° C

588 587 585 591

413- Regenerator temperature, ° C

· ;;; 760 755 786 762::: Including catalyst / oil ratio 0 15 8 0

Ext. catalyst / oil ratio 45 27 15 15 22

Dwell time, s 0.25 0.31 0.32 0.83

Claims (16)

A process for catalytic conversion of hydrocarbons to light olefins, according to which process 5 - the hydrocarbon reactor is fed into a reaction zone (1) containing a solid catalyst, the hydrocarbon reactor being contacted with the catalyst, in conditions which promote the catalytic conversion of the hydrocarbons, the reaction products obtained are separated from the reaction zone (1) after the catalytic reaction, the catalyst used is recovered and the deactivated catalyst is regenerated, characterized in that the hydrocarbon reactor is exposed to the catalyst in a circulation reactor (1). 0.1 - 3 sec, and the deactivated catalyst is regenerated in a regenerator (3) containing a circulation bed, wherein at least a portion of the catalyst used is diverted from the circulation reactor (1) and passed to the circulation regenerator (3) for regeneration by combustion. -ning, after which the regenerated ka the talysator is returned to the circulation reactor (1). 25 2. A process according to claim 1, characterized in that in practice all the necessary heat for the catalytic reaction of the hydrocarbon feedstock is obtained from the recovered catalyst regenerated in the circulation generator (3). . • · · • · * 30 3. A process according to claim 1 or 2, characterized in that the catalyst used is separated into: ·; a cyclone (2) outside the circulation reactor (1) and connected to the reactor, and at least part of the catalyst 35 is fed to the regenerator (3) through a transfer tube (16) of the catalyst used, which tube is connected to the lower part of the circulation regenerator (3). 98529 21 4. Process according to claim 3, characterized in that part of the catalyst used is fed to the reactor as an internal circulation. Process according to claim 3, characterized in that the separated catalyst is fed in its entirety to the regenerator (3). 6. A process according to any of claims 3-5, characterized in that the current of the used catalyst to the regenerator (3) via the pipe (16) of the used catalyst is controlled by a valve (8) arranged in the pipe (16). ) for the used catalyst in such a way that the tube (16) of the used catalyst is filled at any moment with catalyst which prevents mixing of the gases in the reactor and the regenerator. Process according to any of claims 3, 4 or 6, characterized in that the concentration in the reactor 20 and the temperature profile of the reactor (1) is controlled by controlling the internal recovery amount of the catalyst through a recovery tube (12) for the catalyst to the reactor. Process according to any of the preceding claims, characterized in that the regenerated catalyst. . . the tower is separated into a cyclone (4) outside the circulation generator (3), part of the catalyst is returned to the circulation. the cooling regenerator (3) through a feed tube (14) for the catalyst, while the remainder of the catalyst is fed to the lower part of the tower (1) through the transfer tube (15) for the regenerated catalyst. 9. A method according to claim 1, characterized in that the hydrocarbon reactor, such as light gas oil, heavy gas oil, vacuum gas oil or industrial gasoline, is processed in the ratio for catalytic cracking without diluted gas or through ·· ·· use of meadow or other gas as diluent for conversion of the hydrocarbon feedstock to light olefins such as propylene, butene, amylene and low octane gasoline with low benzene content. 10. A process according to claim 9, characterized in that a solid catalyst is used, which can be either a conventional cracking catalyst or an improved cracking catalyst. 10 Process according to any of the preceding claims, characterized in that the fume is exposed to the catalyst in the circulation reactor (1) at a temperature of 520 - 700 ° C, at a pressure of 105 - 500 kPa and at a residence time of 0 , 1 - 3.0 pp. 15 Process according to claim 1, characterized in that the hydrocarbon reactor, such as propane, isobutane or light condensate, is treated under dehydration conditions in the presence of a dehydration catalyst for reacting the hydrocarbon reactor to propylene, butene or amylene. Method according to claim 12, characterized in that the fox is subjected to contact with the catalyst in the circulation reactor (1) at a temperature of 580 - 750 25 ° C and a retention time of 0.1 -3.0 s. Process according to any of the preceding claims, characterized in that 0.1 - 50% air calculated by the weight of the hydrocarbon reactor is fed into the reactor (1). • · · • · 1 30 15. A process according to any of the preceding claims, characterized in that the deactivated catalyst is regenerated by combustion of coke deposited on its surface in the circulation regenerator (3) at a temperature of. . 35-800 ° C, by means of hot air and possibly additional fuel. • · 98529 23 Apparatus for catalytic conversion of hydrocarbons to light olefins, characterized in that it comprises at least one circulation reactor (1), 5. nozzles (24) for feeding the hydrocarbon feedstock and an recovered catalyst (61) into the lower part of the circulation reactor. (1), a catalyst separation cyclone (2) disposed adjacent to the sewer pipe in circulation reactor 10 (1), for separating the catalyst used from the reactor's product stream, which cyclone has a sewer pipe for products (19) and a sewer pipe (12). , 16) for the catalyst solid, a circulation regenerator (3) for regeneration of the catalyst, a nozzle (6 ') for the catalyst used for regeneration on the lower part of the second circulation regenerator (3), and a separation cyclone (4) for the catalyst for separating the separated catalyst from the flue gases in the regenerator. • • • • • • • I • I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I »» »