CN103725311A - Catalyst regeneration method used for reducing carbon dioxide release and improving selectivity - Google Patents

Abstract

A catalyst regeneration method that reduces carbon dioxide emissions and improves selectivity. The carbon-coated catalyst is partially regenerated with pure oxygen in the first regenerator, and then enters the second regenerator through a U-shaped delivery pipe to burn the remaining coke with pure oxygen. The flue gas from the first regenerator is divided into three parts, of which the first part of the flue gas is recycled to the bottom of the second regenerator; the second part sends the semi-regenerated catalyst from the first regenerator to the second regenerator; the third part Enter the flue gas energy recovery system; the flue gas from the second regenerator merges with the flue gas from the first regenerator from the flue gas energy recovery system and then enters the carbon dioxide separation system, where carbon dioxide is separated and captured, and the regenerated catalyst is cooled by the catalyst , After activation, enter the reactor for recycling. This method can not only completely regenerate the catalyst, but also distribute the activity of the catalyst more uniformly, thereby reducing the yield of coke and dry gas, the by-products of catalytic cracking; it can also greatly reduce carbon emissions, and even achieve zero carbon emissions.

Description

A Catalyst Regeneration Method That Reduces Carbon Dioxide Emissions and Improves Selectivity

technical field

The invention relates to a method for regenerating carbon-containing catalysts in hydrocarbon processing. More specifically, the present invention relates to a catalyst regeneration method for reducing carbon dioxide emissions and improving catalyst selectivity in the heavy oil catalytic cracking process.

Background technique

Today, the development of the global oil refining industry is facing many challenges such as fluctuations in oil prices, worsening trend of crude oil quality, improved oil product quality specifications, stricter requirements for energy conservation and emission reduction, and rapid development of biofuels. Reducing carbon dioxide emissions and mitigating climate change have become the key factors for the oil refining industry to transform the economy. The way of growth and the only way to maintain sustainable development. In October 2009, the country announced the action goal of controlling greenhouse gas emissions, that is, by 2020, _CO2 emissions per unit of GDP in the country will be reduced by 40% to 45% compared with 2005, and it is clearly stated that during the "Twelfth Five-Year Plan" period, the unit GDP Carbon dioxide emissions will be reduced by 17%. At the same time, the country may levy a "carbon tax" in due course during the "Twelfth Five-Year Plan" period. Therefore, it is particularly important to effectively reduce carbon emissions in the process of petroleum refining and chemical production. Capturing, storing and managing CO ₂ will become an important task for refineries in the future. Carbon emissions in heavy oil processing are mainly carbon emissions from catalytic cracking coking, hydrogen production, and energy consumption in the process. The catalytic cracking unit is the core production unit of a refinery, and it is one of the main sources of _CO2 emissions due to catalyst burnt.

US2011/0155642A1 discloses a catalytic cracking process for reducing carbon dioxide emissions, which uses burnt tube series dense-phase bed regeneration devices, pure oxygen, and regeneration technology that supplements oxygen at multiple points in the burnt tube. A tank is added to the standby line, in which the tank of the regeneration line uses nitrogen to degas the regenerated catalyst, and the tank of the standby line introduces the mixture of the spent catalyst and the regenerated catalyst to increase the temperature of the spent catalyst before regeneration to improve the coking efficiency. However, the introduction of nitrogen in the regeneration line will eventually inevitably lead to nitrogen flowing back into the flue gas through the regenerator, which obviously loses the advantages of pure oxygen regeneration, but the coking efficiency has improved, but the recovery of carbon dioxide has increased difficulties.

US4542114 discloses an integrated process for recovering flue gas components such as carbon dioxide, which can realize the production of hydrogen and carbon dioxide products during the coking process, and completely eliminate the emission of sulfur and nitrogen oxides in the air. It uses carbon dioxide to dilute The pure oxygen mixture gas is used to burn the catalyst to produce carbon dioxide-rich flue gas. However, in order to achieve no additional heat extraction equipment in the regenerator, this process emphasizes that the oxygen concentration in the mixed gas is 60-21% and preferably 30-24%, thus partially losing the advantages of using pure oxygen for regeneration, such as greatly improving the coking efficiency, Reduce regenerator size and more.

US5565089 discloses a catalytic cracking catalyst regeneration process, which is to first use air to enter the regenerator to burn the catalyst, then recover the carbon dioxide in the regeneration flue gas, recycle the carbon dioxide and gradually merge it into the oxygen-containing gas flow until the temperature in the regenerator is normal , and finally only oxygen and carbon dioxide are injected to burn the catalyst. This regeneration process method only focuses on the improvement of the intake system and the treatment of the flue gas during the regeneration process, without considering the structure of the regenerator or the specific regeneration process and the circulation of the catalytic cracking catalyst.

CN1600431A discloses an incompletely regenerated flue gas combustion technology, which adopts the method of supplementing air in the incompletely regenerated flue gas between the catalyst regenerator and the inlet of the hood, so that the CO in the incompletely regenerated flue gas continues to burn, As a result, the temperature of the flue gas is raised to 660-760°C, and finally the inlet temperature of the hood reaches 640-700°C, which improves the recovery efficiency of the hood and maximizes the recovery of the pressure energy of the flue gas to reduce the energy consumption of the device. Adopting the present invention, according to the scale of the device and the concentration of CO and/or entrained hydrocarbons, the supplementary air volume is 20-300Nm ³ /min, which can effectively increase the temperature of the flue gas by 20-80°C and improve the efficiency of the smoke machine. For single-stage incomplete regeneration, supplementing air in the flue can also fully burn the hydrocarbons entrained in the flue gas and eliminate its impact on the smoke machine, but it cannot effectively reduce carbon dioxide emissions.

Since the conventional regeneration method of catalyst burnt is to inject air or oxygen-containing gas into the fluidized bed for regeneration, and the air is mainly composed of _O2 and _N2 , the regeneration flue gas generated after catalyst burnt regeneration contains a large amount of N ₂ , CO ₂ and a small amount of O ₂ and CO. However, due to the low concentration of _CO2 , the flue gas of this composition is difficult and costly to separate _CO2 , and it cannot be separated and collected. It can only be discharged directly after entering the energy recovery system, thereby causing the greenhouse effect.

In addition, from the perspective of the development of catalytic cracking regeneration technology, it has been pursuing to achieve the maximum recovery of the activity of the regenerated catalyst, so as to achieve the maximum conversion capacity of hydrocarbons. However, the activity of the catalyst is a conceptual expression of a macroscopic conversion rate, which does not reflect the pursuit of the selectivity of the target product. For example, the highest activity recovery of the regenerated catalyst can be achieved during regeneration, but when the regenerated catalyst participates in the reaction, it may cause high coke and dry gas yields due to its high activity, which is undesirable. Therefore, it is necessary to pursue a uniform recovery of catalyst activity during regeneration, or to achieve a uniform distribution of acidity on the regenerated catalyst, so as to achieve low coke and dry gas yields and high target product selectivity. Therefore, it is necessary to develop a catalyst regeneration method that reduces carbon dioxide emissions and improves selectivity.

Contents of the invention

The purpose of the present invention is to provide a catalyst regeneration method for reducing carbon dioxide emission and improving selectivity on the basis of the prior art.

The catalyst regeneration method (1) for reducing carbon dioxide emissions and improving selectivity provided by the present invention adopts a parallel two-device regeneration device type, the first regenerator and the second regenerator are arranged side by side, and the first regenerator and the second regenerator are arranged in parallel. Connected by a U-shaped catalyst conveying pipe, the first regenerator operates as a turbulent bed, and the second regenerator operates as a bubbling bed. The method includes:

(1) The carbon catalyst from the stripping section of the catalytic cracking unit is first regenerated with pure oxygen gas in the first regenerator, and coke combustion reaction occurs, and the charred ratio of the first regenerator is 55-65%;

(2) The semi-regenerated catalyst from the lower part of the first regenerator enters the second regenerator through the U-shaped catalyst delivery pipe, and further supplements pure oxygen gas at the bottom of the second regenerator, so that the incompletely regenerated catalyst is in the dense phase bed Further scorched, fully regenerated, the scorched ratio of the second regenerator is 35-45%;

(3) The flue gas from the first regenerator is divided into three parts, of which the first part of the flue gas is recycled to the bottom of the second regenerator; the second part is used as a transport medium to send the semi-regenerated catalyst from the first regenerator to the second regenerator The third part enters the flue gas energy recovery system, and the flue gas circulation needs to keep the oxygen concentration in the second regenerator not lower than 30%, preferably not lower than 40%;

(4) The flue gas from the second regenerator merges with the flue gas from the first regenerator from the flue gas energy recovery system and enters the carbon dioxide separation system, where carbon dioxide is separated and captured;

(5) A catalyst activation system is installed in the regeneration inclined pipe, which includes a catalyst cooler and an activator. The regenerated catalyst from the regenerator passes through the catalyst activation system and then enters the reactor for recycling.

The operating conditions of the first regenerator are: the temperature is 550-700°C, the average residence time of the catalyst is 1.0-4.0 minutes, preferably 1.0-3.0 minutes, and the gas superficial linear velocity of the first regenerator is preferably 0.6-1.0m/s It is 0.7-0.9m/s. The first regenerator may or may not be provided with an internal heat extractor, depending on whether the temperature of the scorched tank exceeds 750°C.

The operating conditions of the second regenerator are: the temperature is 580-700°C, the average residence time of the catalyst is 1.0-5.0 minutes, preferably 1.0-4.0 minutes, and the gas superficial linear velocity is 0.4-0.8m/s, preferably 0.4-0.6m /s. The second regenerator is provided with a heat collector to control the temperature of the dense-phase bed in the second regenerator not to exceed 750°C, preferably not to exceed 720°C. The heat extractor provided by the second regenerator is an internal heat extractor or/and an external heat extractor, and there are one or more heat extractors.

The operating conditions of the catalyst activation system are as follows: the structure of the catalyst cooler in the activation system is similar to that of an external heat collector, wherein the catalyst operates in a dense phase with a density of 300-700kg/m ³ , and the cooling medium can be water or other media. The cooler needs to ensure that the temperature of the regenerated catalyst after cooling is 550-640°C, preferably 560-630°C. The activator is a fluidized bed device, the fluidized medium is medium pressure superheated steam, the pressure is 3.0-3.5MPa, and the temperature is 400-450°C. The catalyst is operated in dense phase in the activator, the density is 300-500kg/m ³ , and the residence time of the catalyst in it is 2-8 minutes, preferably 3-6 minutes.

The catalyst includes zeolite, inorganic oxide and optional clay, and each component accounts for the total weight of the catalyst respectively: zeolite 1 wt%-50 wt%, inorganic oxide 5 wt%-99 wt%, clay 0 wt% -70% by weight. Wherein the zeolite is the active component, selected from medium-pore zeolite and/or optional large-pore zeolite, the medium-pore zeolite accounts for 10%-100% by weight of the total weight of the zeolite, preferably 20%-80% by weight, and the large-pore zeolite It accounts for 0% to 90% by weight of the total weight of the zeolite, preferably 20% to 80% by weight. Medium pore zeolites are selected from one or more mixtures of ZSM series zeolites and/or ZRP zeolites, and the above medium pore zeolites can also be modified with non-metallic elements such as phosphorus and/or transition metal elements such as iron, cobalt, and nickel . The large-pore zeolite is selected from one or more mixtures of zeolites in the group consisting of rare earth Y (REY), rare earth hydrogen Y (REHY), ultrastable Y obtained by different methods, and high silicon Y.

The inorganic oxide is used as the catalyst carrier and is selected from silicon dioxide and/or aluminum oxide or a mixture of the two.

Clay is used as a binder, and is selected from one or more of kaolin, montmorillonite, diatomite, saponite, rectorite, sepiolite, hydrotalcite and bentonite.

Compared with existing regeneration methods, the main advantages of the present invention lie in the following two aspects:

1. This method can not only fully regenerate the catalyst, but also greatly reduce carbon emissions, even zero carbon emissions, and reduce the greenhouse effect.

2. This method can greatly reduce the catalyst inventory of the device, especially the regenerator inventory, greatly reduce the size of static equipment and dynamic equipment, reduce investment, and reduce floor space.

3. Due to the high concentration of pure oxygen in the regeneration system, the coking efficiency is greatly improved, the regeneration time is shortened, the breakage and wear of the catalyst are reduced, and the use efficiency of the catalyst is improved.

4. The method can realize the uniform distribution of the activity of the regenerated catalyst, thereby reducing the yield of coke and dry gas in the catalytic cracking product.

Description of drawings

The accompanying drawing is a schematic flowchart of a catalyst regeneration method for reducing carbon dioxide emissions and improving selectivity provided by the present invention.

Detailed ways

The method provided by the present invention will be further described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

The accompanying drawing is a schematic flowchart of a catalyst regeneration method for reducing carbon dioxide emissions and improving selectivity provided by the present invention.

The descriptions of each number in the accompanying drawings are as follows:

1, 3, 4, 7, 8, 9, 10, 11, 12, 17, 18, 23, 27, 28, 29 all represent pipelines; 2 is the first regenerator; 16 is the second regenerator; 6 is U 13, 14 and 22 are cyclone separation systems; 15 is flue gas energy recovery system; 26 is carbon dioxide separation system; 19 is riser reactor; 20 is stripping section; 21 is settler; 24 is Oil-gas separation system; 25 is an external heat extractor; 30 is a catalyst cooler; 31 is an activator.

As shown in the figure, the spent catalyst enters the first regenerator 2 through the spent inclined pipe 1, and the pure oxygen gas also enters the first regenerator 2 through the pipeline 3, where it contacts the spent catalyst and undergoes coke combustion reaction. The incompletely regenerated catalyst is lifted from the bottom of the first regenerator 2 to the second regenerator 16 through the U-shaped catalyst delivery pipe 6 and the circulating flue gas from the first regenerator through the pipeline 12 . After the flue gas from the first regenerator comes out of the cyclone separation system 13 and the pipeline 7, at least part of it enters the flue gas energy recovery system 15 through the pipeline 9 to recover energy, and the other part is divided into two paths, one path goes to the pipeline 12 as the lifting medium, and the other path It enters the second regenerator 16 through the pipeline 4 to assist in coking, and at the same time, the concentration of carbon dioxide in the flue gas entering the carbon dioxide separation system 26 can be increased. Pure oxygen gas also enters the bottom of the second regenerator 16 through the pipeline 8 for further charring. The second regenerator is provided with an external heat extractor 25 to control the temperature of the second regenerator. The flue gas from the second regenerator 16 leaves the second regenerator through the cyclone separation system 14 and enters the carbon dioxide separation system 26 after being merged with the flue gas from the first regenerator coming out of the flue gas energy recovery system 15 through the pipeline 10 to realize the separation of carbon dioxide. Separation and capture. The regenerated catalyst that comes out from the second regenerator 16 enters the catalyst cooler 30 through the regenerating inclined pipe 11, and enters the activator 31 by the inclined pipe 27 after the catalyst is cooled, and superheated steam also enters the activator 31 through the pipeline 29, and the regeneration after activation The catalyst enters the bottom of the riser reactor 19 through the inclined pipe 28, the pre-lift medium enters the bottom of the riser reactor through the pipeline 17 to lift the regenerated catalyst upward, and the feedstock oil enters the riser reactor through the pipeline 18 to contact the regenerated catalyst and perform catalytic cracking reaction. The reacted oil and gas enter the oil and gas separation system 24 through the settler 21, the cyclone separation system 22 and the oil and gas pipeline 23 to obtain various products. After being stripped by the stripping section 20, the standby catalyst enters the standby inclined tube 1 and returns to the first regenerator 2 for regeneration, thereby realizing recycling.

The following examples will further illustrate the present invention, but do not limit the present invention thereby. The raw material oil used in Examples and Comparative Examples is vacuum residue, and its properties are listed in Table 1. The catalyst was produced by Qilu Catalyst Factory of Sinopec Catalyst Branch Company, the product number is MLC-500, and its properties are listed in Table 2.

Example

The embodiment is carried out on a catalytic cracking demonstration unit, as shown in the accompanying drawing. The demonstration plant does not have a flue gas energy recovery system and a carbon dioxide separation system. The inner diameter of the dense-phase bed of the first regenerator is 50 cm, and the inner diameter of the dense-phase bed of the second regenerator is 40 cm. The catalyst is regenerated according to the regeneration method proposed by the present invention, and pure oxygen gas is introduced into the dense-phase beds of the first regenerator and the second regenerator respectively, and at the same time, part of the flue gas from the cyclone separation system of the first regenerator is returned to the second regenerator. At the bottom of the dense-phase bed of the second regenerator, the other part is used as a lifting medium to transport the incompletely regenerated catalyst to the second regenerator, and the last part is combined with the flue gas from the second regenerator before exiting the demonstration device. The bed temperature of the first regenerator is 660°C, and the dense-phase bed temperature of the second regenerator is 670°C. The residence time of the catalyst in the dense-phase bed of the first regenerator is 2 minutes, and the average residence time in the dense-phase bed of the second regenerator is 3 minutes. The superficial linear velocity of gas in the first regenerator is 0.82m/s, and the superficial linear velocity of gas in the second regenerator is 0.54m/s. The catalyst density of the catalyst cooler in the activation system is 550kg/m ³ , and the temperature of the catalyst after cooling is 620°C. The medium pressure superheated steamer in the activation system has a pressure of 3.4MPa, a temperature of 425°C, a catalyst density of 350kg/m ³ in the activator, and a residence time of the catalyst in the activator of 3 minutes. The catalyst after coming out of the activation system enters the reactor, contacts with the raw material oil listed in Table 1, and carries out the catalytic cracking reaction. The flue gas composition in Table 3 is the composition after the flue gas from the first regenerator and the second regenerator are combined.

comparative example

The comparison example is also carried out on a catalytic cracking demonstration unit with the same structure, without flue gas energy recovery system, carbon dioxide separation system and catalyst activation system. But the inner diameter of the dense-phase bed of the first regenerator and the second regenerator is different from the embodiment, the inner diameter of the dense-phase bed of the first regenerator is 200 centimeters, the inner diameter of the dense-phase bed of the second regenerator is 160 centimeters, other structures Dimensions and examples are exactly the same. According to the conventional regeneration method, the spent catalyst identical to the embodiment is regenerated. The dense-phase beds of the first regenerator and the second regenerator are fed with air respectively. The bed temperature of the first regenerator is 670 ° C, and the second regeneration The temperature of the dense-phase bed is 710°C. The residence time of the catalyst in the dense-phase bed of the first regenerator is 9 minutes, and the average residence time in the dense-phase bed of the second regenerator is 12 minutes. The superficial linear velocity of gas in the first regenerator is 0.8m/s, and the superficial linear velocity of gas in the second regenerator is 0.5m/s. The regenerated catalyst enters the reactor, contacts with the feedstock oil listed in Table 1, and undergoes catalytic cracking reaction. The regeneration conditions, reaction conditions, carbon content of the regenerated catalyst, flue gas composition, and product distribution are all listed in Table 3. The flue gas composition in Table 3 is the composition after the flue gas from the first regenerator and the second regenerator are combined.

From the comparison of the operating conditions and the results in Table 3, it can be seen that compared with the comparative example, the size of the burnt pot and the size of the regenerated dense phase bed are greatly reduced, the total storage capacity of the device is greatly reduced, and the air consumption index is significantly reduced. Under the premise of using the regeneration method proposed by the present invention, the carbon content on the regenerated catalyst is greatly reduced. In addition, the flue gas generated by the catalyst regeneration method does not contain CO and N ₂ , and the carbon dioxide concentration is as high as 56.2%, which is conducive to the reduction of carbon dioxide. Separation and capture. In addition, due to the use of the catalyst activation system in the embodiment, compared with the comparative example, the dry gas yield decreased by 0.7 percentage points, the coke yield decreased by 0.9 percentage points, the gasoline and diesel yield increased, and the total liquid yield (liquefied gas, gasoline, diesel yield) sum) increased by 1.5 percentage points.

Table 1

Raw oil name Vacuum residue Density (20℃), kg/ ^m3 920.9 Kinematic viscosity, ^mm2 /s 100°C 114.4 Carbon residue value, wt% 8.2 freezing point, ℃ 25 Total nitrogen, weight % 0.33 Sulfur, wt% 0.21 Carbon, weight % 86.91 Hydrogen, weight % 12.55 Metal content, ppm nickel 8.8 vanadium 0.1 iron 1.8 copper <0.1 sodium 3.0 Distillation range, ℃ HK (initial boiling point) 415 10% 545 30% / 50% / 70% / KK (end boiling point) /

Table 2

Catalyst Product Number MLC-500 Chemical composition, wt% Aluminum oxide 50.2 sodium oxide 0.321 Apparent density, kg/m ³ 700 Pore volume, mL/g 0.38 Specific surface area, m ² /g 229 Wear index, weight % ^-1 1.9 Sieve composition, wt% 0～40 microns 17.3 40～80 microns 49.3 >80 microns 33.4

table 3

Example comparative example Total storage capacity of catalyst in the device, tons 1.2 6 Hydrocarbon cracking reaction unit Riser outlet temperature, ℃ 500 500 Catalyst/raw material weight ratio 6 6 Response time, seconds 3 3 Water vapor/raw material weight ratio 0.05 0.05 Product distribution, weight % dry gas 2.9 3.6 liquefied gas 14.2 14.8 gasoline 39.7 38.4 diesel fuel 28.0 27.2 heavy oil 6.7 6.6 coke 8.5 9.4 regeneration unit Inner diameter of the first regenerator dense bed, cm 50 200 Inner diameter of the second regenerator dense bed, cm 40 160 Air consumption index, Nm ³ /kg 3.7 16.8 Carbon content on the regenerated catalyst, weight % 0.01 0.06 Composition of regeneration flue gas, % N ₂ 0 78.62 CO ₂ 57.58 13.76 CO 0 5.73 O ₂ 42.42 1.89

Claims (12)

1. A catalyst regeneration method that reduces carbon dioxide emissions and improves selectivity, is characterized in that the method adopts a parallel two-device regeneration device type, the first regenerator and the second regenerator are arranged side by side, and the first regenerator and the second regenerator The regenerators are connected by a U-shaped catalyst delivery pipe, the first regenerator operates in a turbulent bed, and the second regenerator operates in a bubbling bed. The method includes: (1) The carbon catalyst from the stripping section of the catalytic cracking unit is first regenerated with pure oxygen gas in the first regenerator, and coke combustion reaction occurs, and the charred ratio of the first regenerator is 55-65%; (2) The semi-regenerated catalyst from the lower part of the first regenerator enters the second regenerator through the U-shaped catalyst delivery pipe, and further supplements pure oxygen gas at the bottom of the second regenerator, so that the incompletely regenerated catalyst is in the dense phase bed Further scorched, fully regenerated, the scorched ratio of the second regenerator is 35-45%; (3) The flue gas from the first regenerator is divided into three parts, of which the first part of the flue gas is recycled to the bottom of the second regenerator; the second part is used as a transport medium to send the semi-regenerated catalyst from the first regenerator to the second regenerator The third part enters the flue gas energy recovery system, and the flue gas circulation needs to keep the oxygen concentration in the second regenerator not lower than 30%, preferably not lower than 40%; (4) The flue gas from the second regenerator merges with the flue gas from the first regenerator from the flue gas energy recovery system and enters the carbon dioxide separation system, where carbon dioxide is separated and captured; (5) A catalyst activation system is installed in the regeneration inclined pipe, which includes a catalyst cooler and an activator. The regenerated catalyst from the regenerator passes through the catalyst activation system and then enters the reactor for recycling. 2. according to the method for claim 1, it is characterized in that the operating condition of described first regenerator is: temperature 550-700 ℃, catalyst average residence time is 1.0-4.0 minute, and gas superficial linear velocity is 0.4-0.8m/ s. 3. According to the method of claim 2, it is characterized in that the operating conditions of the first regenerator are: the catalyst average residence time is 1.0-3.0 minutes, and the gas superficial linear velocity is 0.7-0.9m/s. 4. according to the method for claim 1, it is characterized in that the operation condition of described second regenerator is: temperature 580-700 ℃, catalyst average residence time is 1.0-5.0 minute, and gas superficial linear velocity is 0.4-0.8m/ s. 5. According to the method of claim 4, it is characterized in that the operating conditions of the second regenerator are: the average residence time of the catalyst is 1.0-4.0 minutes, and the superficial linear velocity of the gas is 0.4-0.6m/s. 6. According to the method of claim 1, it is characterized in that the second regenerator is provided with a heat extractor to control the temperature of the second regenerator dense-phase bed not to exceed 750 ° C, and the heat extractor is an internal heat extractor or/ and an external heat extractor, one or more heat extractors. 7. The method according to claim 6, characterized in that the temperature of the dense-phase bed in the second regenerator is controlled not to exceed 720°C. 8. According to the method of claim 1, it is characterized in that the oxygen concentration in the flue gas described in step (3) is not less than 40%. 9. Process according to claim 1, characterized in that the catalyst is operated in dense phase in said catalyst cooler with a density of 300-700 kg/ ^m3 . 10. According to the method of claim 1, it is characterized in that the catalyst is operated in dense phase in the activator, the density is 300-500kg/m ³ , the residence time of the catalyst therein is 2-8 minutes; the fluidized medium is medium pressure The pressure of superheated steam is 3.0-3.5MPa, and the temperature is 400-450℃. 11. Process according to claim 10, characterized in that the residence time of the catalyst in said activator is 3-6 minutes. 12. according to the method for claim 1, it is characterized in that described catalyzer comprises zeolite, inorganic oxide and optional clay, and each component accounts for catalyst gross weight respectively and is: zeolite 1 weight %-50 weight %, inorganic oxide 5 wt%-99 wt%, clay 0 wt%-70 wt%.

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