Process and system for catalytic cracking of hydrocarbon oils

Abstract

A process for catalytic cracking of hydrocarbon oils includes the step of contacting a hydrocarbon oil feedstock with a catalytic cracking catalyst in a reactor comprising a dilute-phase transport fluidized bed and a fast fluidized bed connected in series for reaction. In the fast fluidized bed, the axial solid fraction of the catalyst is controlled within the range of about 0.1 to about 0.2. When used for catalytic cracking of hydrocarbon oil feedstocks, particularly heavy feedstock oils, the process and system show lower yields of dry gas and coke, and good product distribution.

Claims

1. A process for catalytic cracking of hydrocarbon oils, comprising the step of contacting a hydrocarbon oil feedstock with a catalytic cracking catalyst for reaction in a reactor comprising a dilute-phase transport fluidized bed and a fast fluidized bed connected in series, wherein the fast fluidized bed comprises a full dense-phase reaction zone that has an axial solid fraction of the catalyst within a range of about 0.1 to about 0.2 from bottom to top.

2. The process according to claim 1, further comprises the steps of: i) contacting a first feedstock with the catalytic cracking catalyst in the dilute-phase transport fluidized bed to carry out a first catalytic cracking reaction; and ii) subjecting a reaction effluent from step i) and optionally a second feedstock to a second catalytic cracking reaction in the fast fluidized bed, wherein the first feedstock and the second feedstock each comprises a heavy feedstock, or a light feedstock, or both, and the light feedstock is selected from the group consisting of a C4 hydrocarbon fraction, a C5-C6 light gasoline fraction, and combinations thereof, with the proviso that at least one of the first and second feedstocks comprises a heavy feedstock oil.

3. The process according to claim 2, further comprising the steps of: i) contacting the first feedstock with the catalytic cracking catalyst in the dilute-phase transport fluidized bed to carry out the first catalytic cracking reaction; ii) subjecting the reaction effluent from step i) and optionally the second feedstock to the second catalytic cracking reaction in the fast fluidized bed under conditions effective to produce light olefins; iii) separating the reaction effluent from the reactor to obtain a reaction product rich in light olefins and a spent catalyst; iv) regenerating the spent catalyst and recycling at least a portion of the resulting regenerated catalyst to step i) as the catalytic cracking catalyst; and v) optionally, separating the reaction product to obtain dry gas, liquefied petroleum gas, gasoline, diesel oil and slurry.

4. The process according to claim 2, wherein conditions for the first catalytic cracking reaction include: a reaction temperature of about 500-600 C., a reaction time of about 0.05-5 seconds, a catalyst-to-oil weight ratio of about 1:1 to about 50:1, a water-to-oil weight ratio of about 0.03:1 to about 0.5:1, a catalyst density of about 20-100 kg/m.sup.3, a vapor velocity of about 4-18 m/s, a reaction pressure of about 130-450 kPa, and a catalyst mass flow rate G.sub.s of about 180-500 kg/(m.sup.2.Math.s); and conditions for the second catalytic cracking reaction include: a reaction temperature of about 510-650 C., a reaction time of about 1-20 seconds, a catalyst-to-oil weight ratio of about 3:1 to about 50:1, a water-to-oil weight ratio of about 0.03:1 to about 0.8:1, a catalyst density of about 120-290 kg/m.sup.3, a vapor velocity of about 0.8-2.5 m/s, a reaction pressure of about 130-450 kPa, and a catalyst mass flow rate G.sub.s of about 15-150 kg/(m.sup.2.Math.s).

5. The process according to claim 2, wherein the heavy feedstock oil is an inferior heavy oil at least one of properties selected from a density at 20 C. of about 900-1000 kg/m.sup.3, a carbon residue of about 2-10 wt %, a total nickel and vanadium content of about 2-30 ppm, and a characterization factor K of less than about 12.1.

6. The process according to claim 2, wherein the heavy feedstock oil is an inferior heavy oil selected from heavy petroleum hydrocarbons, mineral oils, and combinations thereof; wherein the heavy petroleum hydrocarbons is selected from the group consisting of vacuum residuum, inferior atmospheric residuum, inferior hydrogenated residuum, coker gas oil, deasphalted oil, vacuum gas oil, high acid value crude oil, high metal crude oil, and combinations thereof; and the mineral oils is selected from the group consisting of coal liquefaction oil, oil sand bitumen, shale oil, and combinations thereof.

7. The process according to claim 2, wherein at least one of the first and second feedstocks comprises the light feedstock.

8. The process of claim 7, wherein the first feedstock comprises the light feedstock and the heavy feedstock oil, and at least a portion of the light feedstock is introduced into the dilute-phase transport fluidized bed at an upstream location of where the heavy feedstock oil is introduced into the dilute-phase transport fluidized bed.

9. The process according to claim 2, wherein the fast fluidized bed comprises, from bottom to top, the full dense-phase reaction zone and a transition section, the full dense-phase reaction zone is in a form of an equal-diameter or varied-diameter hollow column with an approximately circular cross-section, an open bottom end and an open top end, the dilute-phase transport fluidized bed is in communication with the bottom end of the full dense-phase reaction zone, the top end of the full dense-phase reaction zone is in communication with an outlet section of the reactor via the transition section, wherein a cross-sectional diameter of the bottom end of the full dense-phase reaction zone is greater than or equal to the diameter of the dilute-phase transport fluidized bed and the cross-sectional diameter of the top end of the full dense-phase reaction zone is greater than the diameter of the outlet section, and the bottom or a side wall of the full dense-phase reaction zone is provided with one or more inlets for supplementary catalyst, each independently disposed at a location within about 0-90% of a total height of the fast fluidized bed.

10. The process according to claim 9, wherein the full dense-phase reaction zone is in the form of an equal-diameter hollow cylinder or a hollow column having a diameter increases continuously or discontinuously from bottom to top.

11. The process according to claim 9, wherein the full dense-phase reaction zone is in the form of an inverted hollow truncated cone, a hollow column having two or more cylinder sections with successively increased diameters, a hollow column having two or more sections of inverted truncated cones with successively increased diameters, or a hollow column having one or more cylinder sections and one or more sections of inverted truncated cones.

12. The process according to claim 1, further comprising: introducing one or more streams of supplementary catalyst into the fast fluidized bed, wherein the one or more streams of supplementary catalyst each independently has a carbon content of about 0-1.0 wt. %, and is each independently a regenerated catalytic cracking catalyst, a semi-regenerated catalytic cracking catalyst, or a spent catalytic cracking catalyst, and a total amount of the one or more streams of supplementary catalyst accounts for about 0-50 wt. % of a catalyst circulation rate of the reactor; and each of the one or more streams of supplementary catalyst is independently introduced at an inlet disposed at a location within about 0-90% of a total height of the fast fluidized bed.

13. The process according to claim 12, wherein a total amount of the one or more streams of supplementary catalyst accounts for about 5-30 wt. % of the catalyst circulation rate of the reactor.

14. The process according to claim 1, wherein the catalytic cracking catalyst comprises, based on a dry weight of the catalytic cracking catalyst, from about 1 wt % to about 50 wt % of a zeolite, from about 5 wt % to about 99 wt % of an inorganic oxide, and from about 0 wt % to about 70 wt % of a clay; the zeolite comprises a mesopore zeolite and optionally a macropore zeolite, wherein the mesopore zeolite is selected from the group consisting of ZSM zeolites, ZRP zeolites, and combinations thereof, and the macropore zeolite selected from the group consisting of rare earth exchanged Y-type zeolites, rare earth exchanged H-Y type zeolites, ultrastable Y-type zeolites, high-silica Y-type zeolites, and combinations thereof.

15. The process according to claim 14, wherein the mesopore zeolite accounts for about 0-20 wt % of a total weight of the zeolite on a dry weight basis.

16. The process according to claim 12, wherein each of the one or more inlets for supplementary catalyst is independently disposed at a location within about 30-75% of the total height of the fast fluidized bed.

17. The process according to claim 1, wherein the catalytic cracking catalyst comprises, based on a dry weight of the catalytic cracking catalyst, from about 10 wt % to about 40 wt % of a zeolite.

18. The process according to claim 1, wherein the catalytic cracking catalyst comprises, based on a dry weight of the catalytic cracking catalyst, from about 20 wt % to about 70 wt % of an inorganic oxide.

19. The process according to claim 1, wherein the catalytic cracking catalyst comprises, based on a dry weight of the catalytic cracking catalyst, from about 10 wt % to about 50 wt % of a clay.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings, forming a part of the present description, are provided to help the understanding of the present application, and should not be considered to be limiting. The present application can be interpreted with reference to the drawings in combination with the Detailed Description hereinbelow. In the drawings:

(2) FIG. 1 is a schematic diagram of a preferred embodiment of the present application; and

(3) FIG. 2 is a schematic diagram of another preferred embodiment of the present application.

(4) TABLE-US-00001 Description of the reference numerals I Dilute-phase transport fluidized bed II Fast fluidized bed 1 Pre-lifting medium pipeline 2 Pre-lifting section 3 Outlet section 4 Disengager 5 Stripper 6 Cyclone 7 Plenum chamber 8 Reactor vapor pipeline 9 Spent catalyst standpipe 10 Regenerator 11 Regenerated catalyst standpipe 12 Flue gas pipeline 13 Air distributor 14 First feed line 15 Complement pipeline 16 Second feed line 17 Full dense-phase reaction zone 18 Transition section

DETAILED DESCRIPTION OF THE INVENTION

(5) The present application will be further described hereinafter in detail with reference to specific embodiments thereof and the accompanying drawings. It should be noted that the specific embodiments of the present application are provided for illustration purpose only, and are not intended to be limiting in any manner.

(6) Any specific numerical value, including the endpoints of a numerical range, described in the context of the present application is not restricted to the exact value thereof, but should be interpreted to further encompass all values close to said exact value, such as all possible values within 5% of the exact value. Moreover, regarding any numerical range described herein, arbitrary combinations can be made between the endpoints of the range, between each endpoint and any specific value within the range, or between any two specific values within the range, to provide one or more new numerical range(s), where said new numerical range(s) should also be deemed to have been specifically described in the present application.

(7) In the present application, the dilute-phase transport fluidized bed and the fast fluidized bed constitute two reaction zones connected in series of the reactor, and may therefore also be referred to as dilute-phase transport fluidized bed reaction zone and fast fluidized bed reaction zone, respectively.

(8) In the present application, the term dilute-phase transport fluidized bed has the same meaning well known to those skilled in the art, and specifically refers to a fluidized bed in which catalyst particles form a dilute phase in suspension in a fluid and will be entrained by the fluid exiting the fluidized bed.

(9) In the present application, the term fast fluidized bed has the same meaning well known to those skilled in the art, and particularly refers to a fluidized bed in which catalyst particles are present in a fast fluidized state. The fast fluidized state is a gas-solid contact fluidized state without bubbles, of which the important characteristic is that solid particles tend to move in clusters. When the catalyst is present in a fast fluidized state, the axial solid fraction of the catalyst in the fluidized bed is generally in the range of about 0.05 to about 0.4. However, in conventional fast fluidized beds, the catalyst is typically distributed in a dilute-to-dense pattern from top to bottom, for example the axial solid fraction of the catalyst in the upper part may be in the range of about 0.05 to about 0.1, and the axial solid fraction of the catalyst in the lower part may be in the range of about 0.3 to about 0.4.

(10) According to the present application, in the fast fluidized bed, when the axial solid fraction of the catalyst is controlled within the range of about 0.1 to about 0.2 from bottom to top (i.e., the axial solid fractions of the catalyst measured in the upper, middle and lower parts of the reaction zone divided equally in the axial direction are each not less than about 0.1 and not greater than about 0.2), the catalyst is distributed in a quasi-uniform full dense-phase pattern throughout the fast fluidized bed. Accordingly, a fast fluidized reaction zone in which the catalyst is distributed in such a full dense-phase pattern may be referred to as a full dense-phase reaction zone.

(11) In the present application, the term water-to-oil weight ratio refers to the ratio of the total weight of steam injected into the reactor to the weight of the feedstock.

(12) In the present application, the terms upstream and downstream are used with reference to the flow direction of the reaction stream. For example, when the reaction stream flows from bottom to top, said upstream refers to a lower position, and said downstream refers to a higher position.

(13) Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art; and if the terms are defined herein and their definitions are different from the ordinary understanding in the art, the definition provided herein shall prevail.

(14) In the context of the present application, in addition to those matters explicitly stated, any matter or matters not mentioned are considered to be the same as those known in the art without any change. Moreover, any of the embodiments described herein can be freely combined with another one or more embodiments described herein, and the technical solutions or ideas thus obtained are considered as part of the original disclosure or original description of the present application, and should not be considered to be a new matter that has not been disclosed or anticipated herein, unless it is clear to those skilled in the art that such a combination is obviously unreasonable.

(15) All of the patent and non-patent documents cited herein, including but not limited to textbooks and journal articles, are hereby incorporated by reference in their entirety.

(16) In a first aspect, the present application provides a process for catalytic cracking of hydrocarbon oils, comprising the step of contacting a hydrocarbon oil feedstock, particularly a heavy feedstock oil, with a catalytic cracking catalyst for reaction in a reactor comprising a dilute-phase transport fluidized bed and a fast fluidized bed connected in series, wherein, in the fast fluidized bed, the axial solid fraction of the catalyst is controlled within the range of about 0.1 to about 0.2.

(17) In a preferred embodiment, the process according to the present application is used for the production of light olefins, such as ethylene and propylene, from heavy feedstock oil, and further comprises the steps of: i) contacting a first feedstock comprising a light feedstock and/or a heavy feedstock oil with a catalytic cracking catalyst in a dilute-phase transport fluidized bed to carry out a first catalytic cracking reaction; and ii) subjecting the reaction effluent from step i) and optionally a second feedstock comprising a light feedstock and/or a heavy feedstock oil to a second catalytic cracking reaction in a fast fluidized bed, wherein the light feedstock is selected from the group consisting of a C4 hydrocarbon fraction, a C5-C6 light gasoline fraction, and combinations thereof, and at least one of the first and second feedstocks comprises the heavy feedstock oil; wherein, in the fast fluidized bed, the axial solid fraction of the catalyst is controlled within the range of about 0.1 to about 0.2.

(18) According to the present application, the axial solid fraction of the catalyst in the fast fluidized bed is controlled within the range of about 0.1 to about 0.2 from bottom to top, so that the catalyst is prevented from being distributed in a dilute-to-dense pattern in the fast fluidized bed from top to bottom, the real catalyst-to-oil ratio is kept consistent in the fast fluidized bed from top to bottom, the yield of dry gas and coke can be reduced, and the yield of the desired product can be improved.

(19) In a further preferred embodiment, the process according to the present application further comprises the steps of: i) contacting the first feedstock with the catalytic cracking catalyst in the dilute-phase transport fluidized bed to carry out the first catalytic cracking reaction; ii) subjecting the reaction effluent from step i) and optionally the second feedstock to the second catalytic cracking reaction in the fast fluidized bed under conditions effective to produce light olefins, wherein the axial solid fraction of the catalyst in the fast fluidized bed is controlled within the range of about 0.1 to about 0.2; iii) separating the reaction effluent from the reactor to obtain a reaction product rich in light olefins and a spent catalyst; iv) regenerating the spent catalyst and recycling at least a portion of the resulting regenerated catalyst to step i) as the catalytic cracking catalyst; and v) optionally, separating the reaction product to obtain dry gas, liquefied petroleum gas, gasoline, diesel oil and slurry.

(20) As used herein, said effective to produce light olefins means at least a portion of the feedstock undergoes effective cracking, e.g., deep catalytic cracking, in the fast fluidized bed to produce light olefin products, such as ethylene and propylene, thereby providing a product mixture rich in light olefins.

(21) As used herein, said rich in light olefins means the total content of light olefins (e.g., ethylene and propylene) in the reaction product or product mixture is greater than about 10 wt %, preferably greater than about 15 wt %, and more preferably greater than about 20 wt %, of the reaction product or product mixture.

(22) In some embodiments, prior to said step i) and/or after said step ii), the process according to the present application may further comprise one or more additional reaction steps, such as catalytic cracking and/or catalytic isomerization, carried out in an additional fluidized bed reaction zone, such as a dilute-phase transport fluidized bed, a dense-phase fluidized bed, a conventional fast fluidized bed, and the like.

(23) In some other embodiments, the process according to the present application does not comprise any additional reaction step prior to said step i) or after said step ii).

(24) In some particularly preferred embodiments, the process according to the present application further comprises the steps of: i) introducing a first feedstock comprising a preheated inferior heavy oil into a lower part of the dilute-phase transport fluidized bed to contact with the catalytic cracking catalyst, and subjecting it to a first catalytic cracking reaction while passing through the dilute-phase transport fluidized bed from bottom to top, to obtain a reaction effluent comprising a first reaction product and a semi-spent catalyst; ii) introducing the reaction effluent from step i) into the bottom of the fast fluidized bed and subjecting it to a second catalytic cracking reaction, together with an optional second feedstock comprising a light feedstock introduced from the bottom of the fast fluidized bed, while passing through the fast fluidized bed from bottom to top, to obtain a reaction effluent comprising a second reaction product and a spent catalyst, wherein the axial solid fraction of the catalyst in the fast fluidized bed is controlled to satisfy: 0.10.2; iii) separating the second reaction product from the spent catalyst in the reaction effluent from step ii); iv) sending the spent catalyst to the regenerator for regeneration by coke burning, and recycling at least a portion of the resulting regenerated catalyst to the step i) as the catalytic cracking catalyst; and v) optionally, separating the resulting second reaction product to obtain dry gas, liquefied petroleum gas, gasoline, diesel oil and slurry.

(25) In some other particularly preferred embodiments, the process according to the present application further comprises the steps of: i) introducing a first feedstock comprising a light feedstock into a lower part of the dilute-phase transport fluidized bed to contact with the catalytic cracking catalyst, and subjecting it to a first catalytic cracking reaction while passing through the dilute-phase transport fluidized bed from bottom to top, to obtain a reaction effluent comprising a first reaction product and a semi-spent catalyst; ii) introducing the reaction effluent from step i) into the bottom of the fast fluidized bed, and subjecting it to a second catalytic cracking reaction, together with a second feedstock comprising a preheated inferior heavy oil introduced from the bottom of the fast fluidized bed, while passing through the fast fluidized bed from bottom to top, to obtain a reaction effluent comprising a second reaction product and a spent catalyst, wherein the axial solid fraction of the catalyst in the fast fluidized bed is controlled to satisfy: 0.10.2; iii) separating the second reaction product from the spent catalyst in the reaction effluent from step ii); iv) sending the spent catalyst to the regenerator for regeneration by coke burning, and recycling at least a portion of the resulting regenerated catalyst to the step i) as the catalytic cracking catalyst; and v) optionally, separating the resulting second reaction product to obtain dry gas, liquefied petroleum gas, gasoline, diesel oil and slurry.

(26) In a preferred embodiment, the process according to the present application further comprises: introducing one or more streams of supplementary catalyst into the fast fluidized bed, and contacting the supplementary catalysts with the material in the fast fluidized bed to carry out a catalytic cracking reaction.

(27) According to the present application, the one or more streams of supplementary catalyst may each independently have a carbon content of about 0-1.0 wt %. For example, the one or more streams of supplementary catalyst may each independently be selected from regenerated catalysts, spent catalysts, and semi-regenerated catalysts, i.e., regenerated, spent, and semi-regenerated catalytic cracking catalysts.

(28) According to the present application, the total amount of the one or more streams of supplementary catalyst may account for about 0-50 wt %, preferably about 5-30 wt %, of the catalyst circulation rate of the reactor.

(29) According to the present application, the one or more streams of supplementary catalyst are each independently introduced at a position with a distance from the bottom of the fast fluidized bed of about 0-90% of the total height thereof. Preferably, the one or more streams of supplementary catalyst are each independently introduced at about 20-80%, more preferably about 30-75%, of the height of the fast fluidized bed. For example, the introduction position may be at the bottom of the fast fluidized bed, or at about of the total height of the fast fluidized bed. The temperature of the supplementary catalyst can be adjusted according to the desired reaction temperature, for example, cold and/or hot regenerated catalyst can be introduced, or cold and/or hot spent catalyst can be introduced.

(30) According to the present application, by the introduction of the supplementary catalyst into the fast fluidized bed, the catalyst-to-oil ratio can be adjusted in a wider range, and more active sites can be provided for the cracking reaction. Meanwhile, by the introduction of the supplementary catalyst, the flexibility of the adjustment of reaction temperature can be enhanced, and the gradient of the temperature and the catalyst activity in the fast fluidized bed can be effectively adjusted. In addition, by the introduction of the supplementary catalyst into the fast fluidized bed, the uniformity of the catalyst density in the fluidized bed can be maintained as much as possible, the distribution of the catalyst density can be effectively adjusted, so that the cracking reaction can be ensured to be fully and effectively carried out, and the selectivity of the desired product can be improved.

(31) According to the present application, the catalyst distribution within the fast fluidized bed can be further adjusted by adjusting the vapor velocity in the fast fluidized bed, and/or providing a catalyst distribution plate in the fast fluidized bed, thereby allowing the catalyst to be distributed in a quasi-uniform full dense-phase pattern.

(32) According to the present application, the hydrocarbon oil feedstock, such as a heavy feedstock oil, particularly an inferior heavy oil, may be introduced into the reactor comprising a dilute-phase transport fluidized bed and a fast fluidized bed at one or more positions. For example, the hydrocarbon oil feedstock may be introduced into the dilute-phase transport fluidized bed entirely at one injection position, or into the fast fluidized bed entirely at one injection position. Optionally, the hydrocarbon oil feedstock may be introduced into the dilute-phase transport fluidized bed and/or the fast fluidized bed at two or more injection positions in the same or different proportions. For example, a portion of the hydrocarbon oil feedstock may be introduced into the dilute-phase transport fluidized bed at one injection position and another portion of the hydrocarbon oil feedstock may be introduced into the fast fluidized bed at another injection position, or the hydrocarbon oil feedstock may be introduced into the dilute-phase transport fluidized bed at two or more injection positions, or the hydrocarbon oil feedstock may be introduced into the fast fluidized bed at two or more injection positions.

(33) According to the present application, the inferior heavy oil refers to a heavy oil that is less useful for catalytic cracking processing than conventional heavy oils. For example, the properties of the inferior heavy oil may satisfy at least one, such as one, two, three, or four, of the following criteria: a density at 20 C. of about 900-1000 kg/m.sup.3, preferably about 910-940 kg/m.sup.3; a carbon residue of about 2-10 wt %, preferably about 3-8 wt %; a total nickel and vanadium content of about 2-30 ppm, preferably about 5-20 ppm; a characterization factor K of less than about 12.1, preferably less than about 12.0. The carbon residue in the inferior heavy oil is measured by the Conradson carbon residue test method according to ASTMD-189.

(34) For example, the inferior heavy oil may be heavy petroleum hydrocarbons and/or other mineral oils; the heavy petroleum hydrocarbon may be selected from the group consisting of vacuum residuum (VR), inferior atmospheric residuum (AR), inferior hydrogenated residuum, coker gas oil, deasphalted oil, vacuum gas oil, high acid value crude oil, high metal crude oil, and combinations thereof; said other mineral oil may be selected from the group consisting of coal liquefaction oil, oil sand bitumen, shale oil, and combinations thereof.

(35) The catalytic cracking catalyst used herein is not particularly limited, and may be, for example, various catalytic cracking catalysts known to those skilled in the art suitable for producing light olefins from hydrocarbon oil feedstocks, such as heavy feedstock oils. In a preferred embodiment, the catalytic cracking catalyst comprises, based on the dry weight of the catalytic cracking catalyst, from about 1% to about 50%, preferably from about 5% to about 45%, more preferably from about 10% to about 40%, by weight of a zeolite, from about 5% to about 99%, preferably from about 10% to about 80%, more preferably from about 20% to about 70%, by weight of an inorganic oxide, and from about 0% to about 70%, preferably from about 5% to about 60%, more preferably from about 10% to about 50%, by weight of a clay; the zeolite, as an active component, may comprise a mesopore zeolite and optionally a macropore zeolite. Preferably, the mesopore zeolite may account for about 0-50 wt %, preferably about 0-20 wt %, of the total weight of the zeolite on a dry weight basis.

(36) In the present application, the mesopore and macropore zeolites are as commonly known in the art, i.e., the mesopore zeolite has an average pore size of about 0.5-0.6 nm and the macropore zeolite has an average pore size of about 0.7-1.0 nm.

(37) For example, the macropore zeolite may be one or more selected from the group consisting of rare earth exchanged Y-type (REY) zeolites, rare earth exchanged HY type (REHY) zeolites, and ultrastable Y-type zeolites and high-silica Y-type zeolites obtained by different methods. The mesopore zeolite may be selected from zeolites having the MFI structure, such as ZSM zeolites and/or ZRP zeolites. Optionally, the mesopore zeolite may be modified with a nonmetallic element such as phosphorus and/or a transition metal element such as iron, cobalt, nickel. A more detailed description of ZRP zeolites can be found in U.S. Pat. No. 5,232,675A. The ZSM zeolite is preferably a mixture of one or more selected from ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other zeolites of similar structure. A more detailed description of ZSM-5 can be founded in U.S. Pat. No. 3,702,886A.

(38) According to the present application, the inorganic oxide, as a binder, is preferably silicon dioxide (SiO.sub.2) and/or aluminum oxide (Al.sub.2O.sub.3). The clay, as a matrix (i.e., carrier), is preferably kaolin and/or halloysite.

(39) The catalytic cracking reaction conditions used herein are not strictly limited, and may be, for example, those well known to those skilled in the art suitable for producing light olefins from hydrocarbon oil feedstocks, such as heavy feedstock oils. In a preferred embodiment, the conditions for the first catalytic cracking reaction may include: a reaction temperature of about 500-600 C., a reaction time of about 0.05-5 seconds, a catalyst-to-oil weight ratio of about 1:1 to about 50:1, a water-to-oil weight ratio of about 0.03:1 to about 0.5:1, a catalyst density of about 20-100 kg/m.sup.3, a vapor velocity of about 4-18 m/s, a reaction pressure of about 130-450 kPa, and a catalyst mass flow rate, G.sub.s, of about 180-500 kg/(m.sup.2.Math.sec). Further preferably, the conditions for the first catalytic cracking reaction may include: a reaction temperature of about 520-580 C., a reaction time of about 1-3 seconds, a catalyst-to-oil weight ratio of about 5:1 to about 25:1, a water-to-oil weight ratio of about 0.05:1 to about 0.3:1.

(40) In a preferred embodiment, the conditions for the second catalytic cracking reaction may include: a reaction temperature of about 510-650 C., a reaction time of about 1-20 seconds, a catalyst-to-oil weight ratio of about 3:1 to about 50:1, a water-to-oil weight ratio of about 0.03:1 to about 0.8:1, a catalyst density of about 120-290 kg/m.sup.3, a vapor velocity of about 0.8-2.5 m/s, a reaction pressure of about 130-450 kPa, and a catalyst mass flow rate, G.sub.s, of about 15-150 kg/(m.sup.2.Math.sec). Further preferably, the conditions for the second catalytic cracking reaction may include: a reaction temperature of about 550-620 C., a reaction time of about 3-15 seconds, a catalyst-to-oil weight ratio of about 10:1 to about 30:1, a water-to-oil weight ratio of about 0.05:1 to about 0.5:1, a catalyst density of about 150-250 kg/m.sup.3, a vapor velocity of about 1-1.8 m/s, a reaction pressure of about 130-450 kPa, and a catalyst mass flow rate, G.sub.s, of about 20-130 kg/(m.sup.2.Math.sec).

(41) According to the present application, the separation of the reaction product from the spent catalyst can be carried out in a manner known to those skilled in the art, for example in a disengager using a cyclone. The manner of further separating the reaction product to obtain dry gas, liquefied petroleum gas, gasoline, diesel oil and slurry is also well known to those skilled in the art. In a preferred embodiment, the dry gas and the liquefied petroleum gas can be further separated by separation means commonly used in the art to obtain a desired product, such as ethylene, propylene, and the like.

(42) In a preferred embodiment, the process according to the present application further comprises: introducing a C4 hydrocarbon fraction and/or a C5-C6 light gasoline fraction as the light feedstock of said first and/or second feedstocks into said fast fluidized bed and/or dilute-phase transport fluidized bed at one or more positions for catalytic cracking reactions. For example, in some preferred embodiments, at least one of the first and second feedstocks comprises a light feedstock selected from the group consisting of a C4 hydrocarbon fraction, a C5-C6 light gasoline fraction, and combinations thereof. In some further preferred embodiments, the first feedstock comprises a light feedstock and a heavy feedstock oil, and at least a portion of the light feedstock is introduced into the dilute-phase transport fluidized bed upstream of the position where the heavy feedstock oil is introduced into the dilute-phase transport fluidized bed. In yet still further preferred embodiments, the first feedstock comprises a heavy feedstock oil, such as an inferior heavy oil, and the second feedstock comprises the light feedstock. In yet still further preferred embodiments, the first feedstock comprises the light feedstock and the second feedstock comprises a heavy feedstock oil, such as an inferior heavy oil.

(43) According to the present application, the C4 hydrocarbon fraction refers to a light hydrocarbon fraction present in a gaseous form at normal temperature and pressure that comprises C4 fraction as a main component, including alkanes, alkenes and alkynes having 4 carbon atoms in molecule. It may include gaseous hydrocarbon products (e.g. liquefied petroleum gas) produced by the process according to the present application enriched in C4 hydrocarbon fractions, or gaseous hydrocarbons produced by other units enriched in C4 fractions, preferably C4 hydrocarbon fractions produced by the process according to the present application. The C4 hydrocarbon fraction is preferably an olefin-rich C4 hydrocarbon fraction, which may have a C4 olefin content of greater than about 50 wt %, preferably greater than about 60 wt %, more preferably above about 70 wt %.

(44) According to the present application, the C5-C6 light gasoline fraction refers to a component of gasoline having a carbon number of C5-C6, which may include a cracking gasoline produced by the process according to the present application and may also include gasoline fractions produced by other units, such as at least one C5-C6 fraction selected from the group consisting of deep catalytic cracking gasoline, catalytic cracking gasoline, straight run gasoline, coker gasoline, thermal cracking gasoline and hydrogenated gasoline.

(45) According to the present application, the spent catalyst may be regenerated by means well known to those skilled in the art, for example regenerated in a regenerator by coke burning. Specifically, an oxygen-containing gas such as air may be introduced into the regenerator to contact with the spent catalyst. Flue gas obtained by regeneration via coke burning can be separated from the catalyst in the regenerator and then sent to a subsequent energy recovery system.

(46) In some preferred embodiments of the present application, the regenerated catalyst obtained after regeneration via coke burning in the regenerator may be cooled to about 600-680 C. by a catalyst cooler before being recycled to the reactor. The recycle of the hot regenerated catalyst to the reactor after being cooled is beneficial to reducing the contact temperature of the oil and the catalyst, improving the contact state of the feedstock oil and the catalyst and further improving the selectivity to dry gas and coke generation.

(47) In some preferred embodiments, the fast fluidized bed comprises a full dense-phase reaction zone and a transition section from bottom to top, the full dense-phase reaction zone is in the form of an equal-diameter or varied-diameter hollow column with a roughly circular cross section, an open bottom end and an open top end, the dilute-phase transport fluidized bed is in communication with the bottom end of the full dense-phase reaction zone, the top end of the full dense-phase reaction zone is in communication with the outlet section of the reactor through the transition section, the bottom of the full dense-phase reaction zone is optionally provided with one or more inlets for feeding the second feedstock, wherein the cross-sectional diameter of the bottom end of the full dense-phase reaction zone is greater than or equal to the diameter of the dilute-phase transport fluidized bed and the cross-sectional diameter of the top end of the full dense-phase reaction zone is greater than the diameter of the outlet section, and the bottom or the side wall of the full dense-phase reaction zone is provided with one or more inlets for supplementary catalyst, each independently disposed at about 0-90%, preferably about 20-80%, more preferably about 30-75%, of the total height of the fast fluidized bed.

(48) According to the present application, the full dense-phase reaction zone can be in the form of an equal-diameter or varied-diameter hollow column with a roughly circular cross section, an open bottom end and an open top end, such as an equal-diameter hollow cylinder or a hollow column having a diameter increases continuously or discontinuously from bottom to top.

(49) According to the present application, by diameter increases continuously is meant that the diameter increases continuously in a linear or non-linear manner. As an example of the hollow column having a diameter increases continuously from bottom to top, an inverted hollow truncated cone can be mentioned.

(50) According to the present application, by diameter increases discontinuously is meant that the diameter increases in a discontinuous manner, for example increases stepwise. As an example of the hollow column having a diameter increases discontinuously from bottom to top, a hollow column constituted by two or more cylinder sections with successively increased diameters can be mentioned.

(51) For example, the full dense-phase reaction zone may be in the form of a hollow cylinder, an inverted hollow truncated cone, a hollow column constituted by two or more cylinder sections with successively increased diameters, a hollow column constituted by two or more sections of inverted truncated cones with successively increased diameters, or a hollow column constituted by one or more cylinder sections and one or more sections of inverted truncated cones.

(52) In some preferred embodiments, the bottom of the full dense-phase reaction zone is provided with a catalyst distribution plate.

(53) In some preferred embodiments, the bottom of the full dense-phase reaction zone is provided with one or more second feedstock inlets, and preferably, a gas distributor is provided at the position of the second feedstock inlet.

(54) In a preferred embodiment, the ratio of the diameter of the maximum cross-section of the full dense-phase reaction zone to the total height of the fast reaction bed is about 0.005:1 to about 1:1, preferably about 0.01:1 to about 0.8:1, more preferably about 0.05:1 to about 0.5:1; the ratio of the height of the full dense-phase reaction zone to the total height of the fast reaction bed is about 0.1:1 to about 0.9:1, preferably about 0.3:1 to about 0.85:1, more preferably about 0.5:1 to about 0.8:1.

(55) In some preferred embodiments, the full dense-phase reaction zone is in the form of an inverted hollow truncated cone with a longitudinal section of an isosceles trapezoid, which has a bottom cross-sectional diameter of about 0.2-10 meters, preferably about 0.5-8 meters, more preferably about 1-5 meters; a ratio of the top cross-sectional diameter to the bottom cross-sectional diameter of from greater than 1 to about 50, preferably from about 1.2 to about 10, more preferably from about 1.5 to about 5; a ratio of the diameter of the maximum cross-section to the total height of the fast reaction bed of about 0.005:1 to about 1:1, preferably about 0.01:1 to about 0.8:1, more preferably about 0.05:1 to about 0.5:1; a ratio of the height of the full dense-phase reaction zone to the total height of the fast reaction bed of about 0.1:1 to about 0.9:1, preferably about 0.3:1 to about 0.85:1, more preferably about 0.5:1 to about 0.8:1.

(56) In some other preferred embodiments, the full dense-phase reaction zone is in the form of a hollow column consisting of a section of an inverted truncated cone and a cylinder section, preferably the truncated cone is located below the cylinder, wherein the truncated cone has a longitudinal section of an isosceles trapezoid, a bottom cross-sectional diameter of about 0.2-10 meters, preferably about 0.5-8 meters, more preferably about 1-5 meters; and a ratio of the top cross-sectional diameter to the bottom cross-sectional diameter of from greater than 1 to about 50, preferably about 1.2 to about 10, more preferably about 1.5 to about 5; the diameter of the cylinder is approximately the same as the diameter of the top cross section of the truncated cone, and the ratio of the height of the hollow cylinder to the height of the truncated cone is about 0.4:1 to about 2.5:1, preferably about 0.8:1 to about 1.5:1; the ratio of the diameter of the maximum cross-section of the full dense-phase reaction zone to the total height of the fast reaction bed is about 0.005:1 to about 1:1, preferably about 0.01:1 to about 0.8:1, more preferably about 0.05:1 to about 0.5:1; the ratio of the height of the full dense-phase reaction zone to the total height of the fast reaction bed is about 0.1:1 to about 0.9:1, preferably about 0.3:1 to about 0.85:1, more preferably about 0.5:1 to about 0.8:1.

(57) In yet other preferred embodiments, the full dense-phase reaction zone is in the form of a hollow cylinder having a diameter of about 0.2-10 meters, preferably about 1-5 meters; the ratio of the diameter of the full dense-phase reaction zone to the total height of the fast reaction bed is about 0.005:1 to about 1:1, preferably about 0.01:1 to about 0.8:1, more preferably about 0.05:1 to about 0.5:1; the ratio of the height of the full dense-phase reaction zone to the total height of the fast reaction bed is about 0.1:1 to about 0.9:1, preferably about 0.3:1 to about 0.85:1, more preferably about 0.5:1 to about 0.8:1.

(58) In a preferred embodiment, the full dense-phase reaction zone has a height of about 2-50 meters, preferably about 5-40 meters, and more preferably about 8-20 meters.

(59) In a preferred embodiment, the ratio of the height of the transition section to the total height of the fast reaction bed is about 0.1:1 to about 0.9:1, preferably about 0.2:1 to about 0.5:1. it is further preferred that the transition section is in the form of a hollow truncated cone with a longitudinal section of an isosceles trapezium with sides having an internal inclination angle of about 25-85, preferably about 30-75.

(60) In some embodiments, the reactor employed in the present application may further comprise one or more additional fluidized bed reaction zones at the upstream of the dilute-phase transport fluidized bed and/or the downstream of the fast fluidized bed, such as a dilute-phase transport fluidized bed, a dense-phase fluidized bed, a conventional fast fluidized bed, and the like.

(61) In some other embodiments, the reactor employed in the present application does not comprise any additional reaction zone at the upstream of the dilute-phase transport fluidized bed or the downstream of the fast fluidized bed.

(62) In some embodiments, the reactor employed in the present application may be arranged coaxially with the disengager, or may be arranged in parallel with the disengager.

(63) In a second aspect, the present application provides a system useful for catalytic cracking of hydrocarbon oils, particularly heavy feedstock oils, comprising a catalytic cracking reactor, a catalyst separation device, an optional reaction product separator, and a regenerator, wherein the catalytic cracking reactor comprises a dilute-phase transport fluidized bed and a fast fluidized bed connected in series, with the dilute-phase transport fluidized bed being in fluid communication with the fast fluidized bed and disposed at the upstream of the fast fluidized bed, along the flow direction of the reaction stream; the dilute-phase transport fluidized bed is provided with a catalyst inlet at the bottom and a first feedstock inlet at the lower part, the fast fluidized bed is provided with an outlet at the top and an optional second feedstock inlet at the bottom, the catalyst separation device is provided with an inlet, a catalyst outlet and a reaction product outlet, the optional reaction product separator is provided with a reaction product inlet, a dry gas outlet, a liquefied petroleum gas outlet, a gasoline outlet, a diesel oil outlet and a slurry outlet, and the regenerator is provided with a catalyst inlet and a catalyst outlet, the catalyst inlet of the dilute-phase transport fluidized bed is in fluid communication with the catalyst outlet of the regenerator, the outlet of the fast fluidized bed is in fluid communication with the inlet of the catalyst separation device, the reaction product outlet of the catalyst separation device is in fluid communication with the reaction product inlet of the optional reaction product separator, and the catalyst outlet of the catalyst separation device is in fluid communication with the catalyst inlet of the regenerator.

(64) In a preferred embodiment, the fast fluidized bed and the dilute-phase transport fluidized bed are coaxially arranged one above the other, and the fast fluidized bed is disposed above the dilute-phase transport fluidized bed.

(65) In some preferred embodiments, the fast fluidized bed is provided with a catalyst distribution plate, which may be disposed at the bottom of the fast fluidized bed, for example at the junction of the dilute-phase transport fluidized bed and the fast fluidized bed.

(66) According to the present application, the catalyst distribution plate may be any type of distribution plate commonly used in the industry, such as one or more of flat, arched, dished, annular, and umbrella-shaped plates. The use of the catalyst distribution plate is beneficial to enabling the catalyst to contact with the feedstock oil at an uniform concentration along the axial direction of the full dense-phase reaction zone for catalytic cracking reaction, thereby reducing the generation of strippable coke and thermal reaction coke caused by an overhigh or overlow concentration of the catalyst.

(67) In some preferred embodiments, the fast fluidized bed is provided with one or more inlets for the second feedstock at the bottom, preferably with a gas distributor at the position of the inlet.

(68) In some preferred embodiments, the fast fluidized bed has a structure as described above, i.e., a structure comprising a full dense-phase reaction zone and a transition section sequentially from bottom to top. The detailed description of the specific arrangement of the full dense-phase reaction zone and the transition section will not be repeated here.

(69) In some embodiments, the catalytic cracking reactor may further comprise one or more additional fluidized bed reaction zones, such as a dilute-phase transport fluidized bed, a dense-phase fluidized bed, a conventional fast fluidized bed, and the like, at the upstream of the dilute-phase transport fluidized bed and/or the downstream of the fast fluidized bed.

(70) In some other embodiments, the catalytic cracking reactor does not comprise any additional reaction zone at the upstream of the dilute-phase transport fluidized bed or the downstream of the fast fluidized bed.

(71) According to the present application, the catalyst separation device and the reaction product separator may be any device known to those skilled in the art. For example, the catalyst separation device may include a cyclone, a disengager, a stripper, and the like, and the reaction product separator may be a fractionator, and the like.

(72) The present application will be further described with reference to preferred embodiments shown in the drawings, but the present application is not limited thereto.

(73) FIG. 1 shows a preferred embodiment of the present application, in which a pre-lifting medium, which may be dry gas, steam or a mixture thereof, is introduced into the bottom of a dilute-phase transport fluidized bed I through the bottom of a pre-lifting section 2 via a pre-lifting medium pipeline 1. A regenerated catalyst from a regenerated catalyst standpipe 11 is introduced into the lower part of the pre-lifting section 2, then into the dilute-phase transport fluidized bed I, and moves upwards under the lifting action of the pre-lifting medium. A first feedstock comprising a C4 hydrocarbon fraction, a C5-C6 light gasoline fraction and/or a hydrocarbon oil feedstock, such as an inferior heavy oil, is injected into the lower part of the dilute-phase transport fluidized bed I through a first feed line 14, mixed and contacted with the catalyst in the dilute-phase transport fluidized bed I for a first catalytic cracking reaction, to obtain a reaction effluent comprising a first reaction product and a semi-spent catalyst. The reaction effluent moves upwards into the bottom of a fast fluidized bed II, is contacted with a supplementary catalyst, which may be a regenerated catalyst or spent catalyst, introduced via a complement pipeline 15 for a second catalytic cracking reaction. The complement pipeline 15 is connected to the fast fluidized bed II at about 0-90%, preferably about 20-80%, more preferably about 30-75%, of the height thereof. Optionally, a second feedstock comprising a C4 hydrocarbon fraction, a C5-C6 light gasoline fraction and/or a hydrocarbon oil feedstock, such as an inferior heavy oil, is passed into the bottom of the fast fluidized bed II via a second feed line 16. The reaction effluent comprising the second reaction product and the deactivated spent catalyst generated by the reaction is passed into a cyclone 6 in a disengager 4 through an outlet section 3, to separate the spent catalyst from the second reaction product. The separated second reaction product is introduced into a plenum chamber 7, and the reaction product in the plenum chamber 7 is passed into a subsequent product separation system (not shown) through a reactor vapor pipeline 8. Fine catalyst powders are returned to the disengager 4 through the dipleg of the cyclone 6, and the spent catalyst in the disengager 4 is passed to a stripper 5. The reaction product stripped from the spent catalyst is passed into the plenum chamber 7 after passing through the cyclone 6. The stripped spent catalyst is passed into a regenerator 10 through a spent catalyst standpipe 9, and air is introduced into the regenerator 10 after distribution through an air distributor 13 to burn off the coke on the spent catalyst in the dense bed at the bottom of the regenerator 10, so that the deactivated spent catalyst is regenerated to obtain a regenerated catalyst. The regenerated catalyst is recycled to the pre-lifting section 2 through the regenerated catalyst standpipe 11, and the flue gas is passed into a subsequent energy recovery system (not shown) through a flue gas pipeline 12.

(74) FIG. 2 shows another preferred embodiment of the present application, which is essentially identical to the embodiment shown in FIG. 1, except that the fast fluidized bed II comprises, from bottom to top, a full dense-phase reaction zone 17 and a transition section 18. The full dense-phase reaction zone 17 is in the form of an inverted hollow truncated cone with a longitudinal section of an isosceles trapezoid. The transition section 18 is in the form of a hollow truncated cone with a longitudinal section of an isosceles trapezium with sides having an internal inclination angle of about 25-85, preferably about 30-75

(75) In some preferred embodiments, the present application provides the following technical solutions: 1. A process for catalytic cracking using a dilute-phase transport fluidized bed and a fast fluidized bed, comprising the steps of: i) introducing a preheated inferior heavy oil into a lower part of the dilute-phase transport fluidized bed to contact with a catalytic cracking catalyst and conduct a first catalytic cracking reaction while moving from bottom to top, to obtain a first reaction product and a semi-spent catalyst; ii) introducing the resulting first reaction product and the semi-spent catalyst into the bottom of the fast fluidized bed to conduct a second catalytic cracking reaction while moving from bottom to top, to obtain a second reaction product and a spent catalyst; wherein the catalyst in the fast fluidized bed is distributed in a full dense-phase pattern, and the distribution of the axial solid fraction in the fast fluidized bed satisfies: 0.10.2; iii) sending the spent catalyst to a regenerator for regeneration by coke burning, and recycling at least a portion of the resulting regenerated catalyst to the bottom of the dilute-phase transport fluidized bed as the catalytic cracking catalyst; and iv) separating the second reaction product to obtain dry gas, liquefied petroleum gas, gasoline, diesel oil and slurry. 2. The process of Item 1, wherein the properties of the inferior heavy oil meet one, two, three, or four of the following criteria: a density at 20 C. of 900-1000 kg/m.sup.3, a carbon residue of 2-10 wt %, a total content of nickel and vanadium of 2-30 ppm, and a characterization factor K value of less than 12.1. 3. The process of Item 1, wherein the properties of the inferior heavy oil meet one, two, three, or four of the following criteria: a density at 20 C. of 910-940 kg/m.sup.3, a carbon residue of 3-8 wt %, a total content of nickel and vanadium of 5-20 ppm, and a characterization factor K value of less than 12.0. 4. The process of Item 1, wherein the inferior heavy oil is heavy petroleum hydrocarbons and/or other mineral oils; the heavy petroleum hydrocarbon is one or more selected from vacuum residuum, inferior atmospheric residuum, inferior hydrogenated residuum, coker gas oil, deasphalted oil, vacuum gas oil, high acid value crude oil and high metal crude oil, and said other mineral oil is one or more selected from coal liquefaction oil, oil sand bitumen and shale oil. 5. The process of Item 1, wherein the catalytic cracking catalyst comprises, based on the dry weight of the catalytic cracking catalyst, 1-50 wt % zeolite, 5-99 wt % inorganic oxide, and 0-70 wt % clay; the zeolite comprises a mesopore zeolite which is a ZSM zeolite and/or a ZRP zeolite and optionally a macropore zeolite which is one or more selected from rare earth exchanged Y, rare earth exchanged H-Y, ultrastable Y and high-silica Y. 6. The process of Item 5, wherein the mesopore zeolite accounts for 0-50 wt % of the total weight of zeolite on a dry weight basis. 7. The process of Item 5, wherein the mesopore zeolite accounts for 0-20 wt % of the total weight of zeolite on a dry weight basis. 8. The process of Item 1, wherein the conditions for the first catalytic cracking reaction include: a reaction temperature of 500-600 C., a reaction time of 0.05-5 seconds, a catalyst-to-oil weight ratio of (1-50):1, a water-to-oil weight ratio of (0.03-0.5):1, a catalyst density of 20-100 kg/m.sup.3, a vapor velocity of 4-18 m/s, a reaction pressure of 130-450 kPa, and a catalyst mass flow rate, G.sub.s, of 180-500 kg/(m.sup.2.Math.sec); the conditions for the second catalytic cracking reaction include: a reaction temperature of 510-650 C., a reaction time of 1-20 seconds, a catalyst-to-oil weight ratio of (3-50):1, a water-to-oil weight ratio of (0.03-0.8):1, a catalyst density of 120-290 kg/m.sup.3, a vapor velocity of 0.8-2.5 m/s, a reaction pressure of 130-450 kPa, and a catalyst mass flow rate, G.sub.s, of 15-150 kg/(m.sup.2.Math.s). 9. The process of Item 1, wherein the conditions for the first catalytic cracking reaction include: a reaction temperature of 520-580 C., a reaction time of 1-3 seconds, a catalyst-to-oil weight ratio of (5-25):1, a water-to-oil weight ratio of (0.05-0.3):1; the conditions for the second catalytic cracking reaction include: a reaction temperature of 550-620 C., a reaction time of 3-15 seconds, a catalyst-to-oil weight ratio of (10-30):1, a water-to-oil weight ratio of (0.05-0.5):1, a catalyst density of 150-250 kg/m.sup.3, a vapor velocity of 1-1.8 m/s, and a catalyst mass flow rate, G.sub.s, of 20-130 kg/(m.sup.2.Math.sec.). 10. The process of Item 1, further comprising: introducing a C4 hydrocarbon fraction and/or a C5-C6 light gasoline fraction into the fast fluidized bed and/or dilute-phase transport fluidized bed for catalytic cracking reaction. 11. The process of Item 10, wherein the C4 hydrocarbon fraction and/or the C5-C6 light gasoline fraction are introduced before the position where the inferior heavy oil is introduced into the dilute-phase transport fluidized bed. 12. The process of Item 1, further comprising: introducing a supplementary catalyst into the fast fluidized bed to conduct the second catalytic cracking reaction together with the first reaction product and the semi-spent catalyst; wherein the carbon content of the supplementary catalyst is 0-1.0 wt. %. 13. The process of Item 12, wherein the supplementary catalyst accounts for 0-50 wt % of the total catalyst circulation rate of the dilute-phase transport fluidized bed and the fast fluidized bed. 14. The process of Item 12, wherein the supplementary catalyst accounts for 5-30 wt % of the total catalyst circulation rate of the dilute-phase transport fluidized bed and the fast fluidized bed. 15. The process of Item 12, wherein the supplementary catalyst is introduced into the bottom of the fast fluidized bed. 16. A catalytic cracking system, comprising a dilute-phase transport fluidized bed, a fast fluidized bed, an catalyst separation device, a reaction product separator and a regenerator; the dilute-phase transport fluidized bed is in fluid communication with the fast fluidized bed and is disposed at the upstream of the fast fluidized bed, along the flow direction of the reaction stream; the dilute-phase transport fluidized bed is provided with a catalyst inlet at the bottom and an inferior heavy oil inlet at the lower part, the fast fluidized bed is provided with an outlet at the top, the catalyst separation device is provided with an inlet, a catalyst outlet and a reaction product outlet, the reaction product separator is provided with a reaction product inlet, a dry gas outlet, a liquefied petroleum gas outlet, a gasoline outlet, a diesel oil outlet and a slurry outlet, and the regenerator is provided with a catalyst inlet and a catalyst outlet; the catalyst inlet of the dilute-phase transport fluidized bed is in fluid communication with the catalyst outlet of the regenerator, the outlet of the fast fluidized bed is in fluid communication with the inlet of the catalyst separation device, the reaction product outlet of the catalyst separation device is in fluid communication with the reaction product inlet of the reaction product separator, and the catalyst outlet of the catalyst separation device is in fluid communication with the catalyst inlet of the regenerator. 17. The system of Item 16, wherein the fast fluidized bed is arranged coaxially with the dilute-phase transport fluidized bed and the fast fluidized bed is disposed above the dilute-phase transport fluidized bed.

(76) The definition and calculation of each parameter in the present application are as follows:
Axial solid fraction of catalyst, =pressure difference between two points in the reaction zone along the axial direction measured by a pressure difference meterdistance between the two points along the axial directioncatalyst particles density;(1) wherein the pressure difference is expressed in kg/m.sup.2, the distance between the two points along the axial direction is expressed in meters (m), and the density of catalyst particles is expressed in kg/m.sup.3.
Density of catalyst particles=framework density/(pore volume of catalystframework density+1), wherein the framework density is expressed in kg/m.sup.3 and the pore volume of catalyst is expressed in m.sup.3, the framework density and the pore volume of catalyst are determined by pycnometer test method and aqueous titration method, respectively.
Reaction time=volume of reaction zone/logarithmic mean volume flow rate of oil vapor;(2) wherein the volume of reaction zone is expressed in m.sup.3, and the logarithmic mean volume flow rate of oil vapor is expressed in m.sup.3/s;
Logarithmic mean volume flow rate of oil vapor=(V.sub.outV.sub.in)/ln(V.sub.out/V.sub.in), wherein V.sub.out and V.sub.in represent the volume flow rates of oil vapor at the outlet and the inlet of the reaction zone, respectively;
Volume flow rate of oil vapor at the outlet of the reaction zone V.sub.out=m/.sub.3;
Volume flow rate of oil vapor at the inlet of the reaction zone V.sub.in=m/.sub.4; wherein m represents the feed rate of feedstock oil and atomizing steam per unit time, expressed in kg/s; .sub.3 represents the density of oil vapor at the outlet of the reaction zone, expressed in kg/m.sup.3; .sub.4 represents the density of oil vapor at the inlet of the reaction zone, expressed in kg/m.sup.3.
Catalyst density in the reaction zone (or an upper, middle or lower part thereof)=pressure difference between two points in the reaction zone (or an upper, middle or lower part thereof) along the axial direction measured by a pressure difference meterdistance between the two points along the axial direction;(3) wherein the pressure difference is expressed in kg/m.sup.2, the reaction zone is divided equally into three parts, i.e. an upper part, a middle part and a lower part, along the axial direction, and the distance between the two points along the axial direction is expressed in meter (m).
Vapor velocity=logarithmic mean volume flow rate of oil vaporcross-sectional area of reaction zone;(4) where the reaction zone is in a non-cylindrical form, the vapor velocity refers to the logarithmic mean value of the vapor velocity at the bottom of the reaction zone and the vapor velocity at the top of the reaction zone.
Catalyst mass flow rate G.sub.s=catalyst circulation rate of reactorcross-sectional area of reaction zone;(5)

(77) where the reaction zone is in a non-cylindrical form, the catalyst mass flow rate, G.sub.s, refers to the logarithmic mean value of G.sub.s at the bottom of the reaction zone and G.sub.s at the top of the reaction zone;

(78) wherein the catalyst circulation rate is expressed in kg/s;
Catalyst circulation rate of reactor=coke generation rate(carbon content of spent catalystcarbon content of regenerated catalyst);

(79) wherein, the coke generation rate is expressed in kg/s, and the carbon content of spent catalyst and the carbon content of regenerated catalyst are both expressed in content by weight;
Coke generation rate=flue gas amount(CO.sub.2%+CO %)VmM;

(80) wherein Vm represents molar volume of gas, which takes the value of 22.410 m.sup.3/mol, and M represents the molar mass of carbon element, which takes the value of 1210.sup.3 kg/mol;
Flue gas amount=(air rate79 vol %)/(1CO.sub.2%CO %O.sub.2%);

(81) wherein the air rate is expressed in m.sup.3/s, the flue gas amount is expressed in m.sup.3/s, and the CO.sub.2%, CO % and O.sub.2% represent the volume percentages of the CO.sub.2, CO and O.sub.2 in the flue gas, respectively.

EXAMPLES

(82) The present application will be further illustrated with reference to the following examples, but the present application is not limited thereto.

(83) The feedstock oils used in the following examples and comparative examples are all hydrogenated residuum, of which the properties are shown in Table 1. The catalyst used is a commercial catalytic cracking catalyst purchased from the Catalyst Branch of Sinopec Co., Ltd., under the trade name of DMMC-2.

(84) TABLE-US-00002 TABLE 1 Properties of the feedstock oil Density (20 C.)/g .Math. cm.sup.3 0.9237 Refractive index/70 C. 1.4914 Basic nitrogen/g .Math. g.sup.1 506 Conradson Carbon residue/wt % 3.11 Characteristic factor K 11.8 Distillation range/ C. 5 vol % 357 10 vol % 387 30 vol % 443 50 vol % 490 70 vol % 550 Metal content/g .Math. g.sup.1 Fe 34.4 Ni 4.4 Ca 7.8 V 4.3 Na 2.0

Example 1

(85) This example was carried out in accordance with the process flow shown in FIG. 1 on a medium-sized apparatus, using the hydrogenated residuum as feedstock oil, the DMMC-2 catalyst as catalyst, a combined reactor comprising a dilute-phase transport fluidized bed and a fast fluidized bed connected in series as the reactor. A preheated feedstock oil was introduced into the dilute-phase transport fluidized bed to contact with the catalyst for a first cracking reaction. The reaction effluent moved upwards into the fast fluidized bed to mix with a supplemented regenerated catalyst for a second catalytic cracking reaction. The carbon content of the supplemented regenerated catalyst was 0.05 wt %, the supplemented catalyst was introduced at of the total height of the fast fluidized bed, and the supplemented catalyst accounted for 5 wt % of the catalyst circulation rate of the reactor. The catalyst in the fast fluidized bed was controlled to be distributed in a full dense-phase pattern by adjusting the vapor velocity and providing an umbrella-shaped catalyst distribution plate at the bottom of the fast fluidized bed, so that the axial solid fraction of the catalyst in the fast fluidized bed was within the range of 0.1-0.2 from bottom to top. The reaction product and the spent catalyst were quickly separated, and the reaction product was further separated in a product separation system according to the distillation range. The spent catalyst was passed into a stripper under gravity, the hydrocarbon vapors adsorbed on the spent catalyst were stripped by steam, the stripped catalyst was directly passed into a regenerator without heat exchange and contacted with air for regeneration by coke burning, and the regenerated catalyst was recycled to the reactor for reuse. The operating conditions used and the product distribution are listed in Table 2.

(86) As can be seen from Table 2, in this example, the ethylene yield is 5.2 wt %, the propylene yield is 18.2 wt %, the light aromatics yield is 11.5 wt %, and the dry gas and coke yields are 10.8 wt % and 8.5 wt %, respectively.

Example 2

(87) This example was carried out in accordance with the process flow shown in FIG. 2 on a medium-sized apparatus, using the hydrogenated residuum as feedstock oil, the DMMC-2 catalyst as catalyst, and a combined reactor comprising a dilute-phase transport fluidized bed and a fast fluidized bed connected in series as the reactor. A preheated feedstock oil was introduced into the bottom of the dilute-phase transport fluidized bed to contact with the catalytic cracking catalyst for a first cracking reaction. The reaction effluent moved upwards into the full dense-phase reaction zone of the fast fluidized bed to mix with a supplemented regenerated catalyst for a second catalytic cracking reaction. The carbon content of the supplemented regenerated catalyst was 0.05 wt %, the supplemented catalyst was introduced at of the total height of the fast fluidized bed, and the supplemented catalyst accounted for 5 wt % of the catalyst circulation rate of the reactor. The catalyst in the full dense-phase reaction zone was controlled to be distributed in a full dense-phase pattern by adjusting the vapor velocity and providing an umbrella-shaped catalyst distribution plate at the bottom of the full dense-phase reaction zone, so that the axial solid fraction of the catalyst in the full dense-phase reaction zone was within the range of 0.1-0.2 from bottom to top. The reaction product and the spent catalyst were quickly separated, and the reaction product was further separated in a product separation system according to the distillation range. The spent catalyst was passed into a stripper under the action of gravity, the hydrocarbon vapors adsorbed on the spent catalyst were stripped by steam, the stripped catalyst was directly passed into a regenerator without heat exchange and contacted with air for regeneration by coke burning, and the regenerated catalyst was recycled to the reactor for reuse. The mixed C4 fraction obtained after the separation of the reaction product was recycled to the bottom of the dilute-phase transport fluidized bed for further reaction. The operating conditions used and the product distribution are listed in Table 2.

(88) As can be seen from Table 2, in this example, the ethylene yield is 5.9 wt %, the propylene yield is 21.1 wt %, the light aromatics yield is 11.8 wt %, and the dry gas and coke yields are 10.7 wt % and 8.4 wt %, respectively.

Comparative Example 1

(89) This comparative example was carried out on a medium-sized apparatus, using the hydrogenated residuum as feedstock oil, the DMMC-2 catalyst as catalyst, and a combined reactor comprising a riser and a fluidized bed connected in series as the reactor. A preheated feedstock oil was introduced into a lower part of the riser to contact with a catalyst for catalytic cracking reaction. The resulting reaction oil vapor, steam and spent catalyst were passed into the dense-phase fluidized bed through the outlet of the riser for further reaction. The reaction effluent was passed into a closed cyclone where the reaction product and the spent catalyst were quickly separated, and the reaction product was further separated in a product separation system according to the distillation range. The spent catalyst was passed into a stripper under the action of gravity, the hydrocarbon vapors adsorbed on the spent catalyst were stripped by steam, the stripped catalyst was directly passed into a regenerator without heat exchange and contacted with air for regeneration by coke burning, and the regenerated catalyst was recycled to the riser for reuse. The operating conditions used and the product distribution are listed in Table 2.

(90) As can be seen from the results of Table 2, in this comparative example, the ethylene yield is 3.7 wt %, the propylene yield is 12.8 wt %, the light aromatics yield is 5.5 wt %, and the dry gas and coke yields are 12.9 wt % and 13.3 wt %, respectively.

Comparative Example 2

(91) This comparative example was substantially the same as Example 1, except that no catalyst distribution plate was provided at the bottom of the fast fluidized bed, and the axial solid fraction of the catalyst in the fast fluidized bed showed a gradient of 0.1.fwdarw.0.2.fwdarw.0.3 from top to bottom. The operating conditions used are the same as in Example 1, and the product distribution is given in Table 2.

(92) TABLE-US-00003 TABLE 2 Comparison of results of Examples 1-2 and Comparative Examples 1-2 Comp. Comp. Ex. 1 Ex. 2 Ex. 1 Ex. 2 Conditions in the riser/dilute-phase transport fluidized bed Temperature at the reactor outlet, C. 565 565 585 565 Reaction time, s 2 2 2 2 Water-to-oil weight ratio 0.25 0.25 0.25 0.25 Catalyst-to-oil weight ratio 15 15 10 15 Catalyst density, kg/m.sup.3 60 60 60 60 Vapor velocity, m/s 8 8 12 8 Reaction pressure, kPa 210 210 210 210 Gs, kg/(m.sup.2 .Math. s) 300 300 300 300 Conditions in the dense-phase/fast fluidized bed Bed/outlet temperature, C. 585 585 565 585 Weight hourly space velocity, hr.sup.1 / / 4 / Reaction time, s 3 3 / 3 Catalyst density in the upper part 195 190 480 120 of the reaction zone, kg/m.sup.3 Catalyst density in the lower part 200 195 480 200 of the reaction zone, kg/m.sup.3 Vapor velocity, m/s 2 2.2 0.6 2 Gs, kg/(m.sup.2 .Math. s) 75 80 / 75 Product distribution, wt % Dry gas 10.8 10.7 12.9 11.9 ethylene 5.2 5.9 3.7 4.2 Liquefied petroleum gas 38 39.3 26.1 32.7 propylene 18.2 21.1 12.8 15.5 C4 fraction 12.5 8.1 10.5 11.1 Gasoline 25.9 25.0 22.9 24.9 BTX 11.5 11.8 5.5 8.8 Diesel oil 11.8 11.6 16.4 13.6 Slurry 5 5.0 8.4 5.8 Coke 8.5 8.4 13.3 11.1 Total 100.0 100.0 100.0 100.0

(93) From the results of the above examples and comparative examples, it can be seen that the process according to the present application shows higher yields of ethylene, propylene and light aromatics, while providing lower yields of dry gas and coke.

(94) Preferred embodiments of the present application have been described in detail above, but the present application is not limited to the details of the above embodiments. Various modifications can be made to the technical solution of the present application within the inventive concept thereof, and those modifications should fall within the scope of the present application.

(95) It should be noted that, various features described in the above-described embodiments may be combined in any suitable manner, where there is no confliction. To avoid unnecessary repetition, those possible combinations are not described in the present application.

(96) In addition, various embodiments of the present application may also be combined arbitrarily, and those combinations should also be considered as a part of the present application, as long as they do not depart from the spirit of the present application.