Description:TECHNICAL FIELD
[0001] The present disclosure pertains to the technical field of catalytic cracking. In particular, the present disclosure relates to a dual stage apparatus for catalytic cracking of hydrocarbons. Disclosure also relates to a method for production of olefins by catalytic cracking of hydrocarbons in said dual stage apparatus.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Oil refineries are experiencing a decline in their revenue owing to the reducing demand for automotive fuels. Up to year 2010, the demand for automotive fuels was insatiable and crude oil production and refining were in full swing. However, the requirement for automotive fuel in the energy market is now predicted to decline sharply by the year 2030. This reduction in demand can be attributed to the advent of fuel-efficient engines, increased impetus towards sustainable technologies, viable alternate sources of energy, and increasingly stringent environmental emission regulations.
[0004] Meanwhile, the demand for polymers, niche chemicals, and intermediates is continuously rising. The petrochemical sector has ample scope for innovation and development. Refiners have predicted this and are modifying their refinery configurations to install petrochemical complexes in order to secure their profit and their relevance in the future. A conventional refinery generates a minor quantity of petrochemical feedstock in the form of light olefins (ethylene, propylene) from the Fluidized bed cracker (FCC) unit and aromatics (benzene, toluene, xylenes) from Naphtha reforming. FCCs operating at higher severity to intentionally manufacture light olefins; in particular propylene are commercially operational but they are subject to reaction constraints and selectivity issues due to higher saturated gas yield.
[0005] In a conventional method, the heavy oil is injected in the form of a fine mist in the bottom of a long tubular reactor, termed as ‘Riser’. Here it encounters the catalyst in a fluidized state. The catalyst possesses a considerable amount of heat which is utilized in vaporizing the atomized feed and supplying the necessary endothermic heat of the reaction vital for the cracking to occur. Due to the vaporization of feed and the cracking reaction, the volume of the gas-catalyst mixture expands and it ascends up the riser and enters into the disengager through a riser termination device. The reaction mixture is at a maximum temperature in the bottommost portion of the primary reaction zone, thereafter the temperature drops during the upward ascent of the cracked product due to the endothermic nature of the cracking reactions occurring along the length of the riser. Due to such high temperatures, a portion of the feed gets converted into coke and gets deposited on the pores of the catalyst surface. This coke can be the result of improper vaporization of the heavy oil, asphaltene content of heavy oil, or the result of successive over-cracking of heavy oil. Some portion of the product also re-cracks into light-saturated gasses hereafter termed as dry gases. Excess formation of coke and dry gas is undesirable since it translates to a loss in the conversion of feed and inferior selectivity towards desired products. Further, extended residence time within the riser leads to undesirable reactions such as hydrogen transfer which reduce the net light olefin yield and promotes higher yields of dry gas and aromatics. Hence, the yield of light olefins also suffers.
[0006] In yet another alternative conventional method, the heavy oil contacts the catalyst at the top of a tubular reactor. This is called a downer configuration. The reaction mixture descends down the downer, wherein the velocity of the catalyst is higher (in this configuration as compared to riser configuration); hence, its residence time is significantly lower, resulting in reduced hydrogen transfer reactions, lower back-mixing, and thereby reduced coke make. Such configuration is better suited for higher temperature and catalyst circulation, which produces greater amounts of gasoline, but the yield of light olefin is still commercially unsustainable. Considerable steam is injected in both the riser and downer configuration in order to reduce the hydrocarbon partial pressure in the reaction zone. A lower hydrocarbon partial pressure will shift the reaction equilibrium towards higher light olefin yield by promoting paraffin cracking and inhibiting hydrogen transfer. Although the residence time in the downer configuration reduces coke production, the heavy oil contacts the catalyst at a very high temperature; much higher than that in the riser configuration. This contributes to higher coke production. Another shortcoming of the downer configuration is its residence time itself. Production of light olefins requires high severity conditions for a longer residence time.
[0007] There is, therefore, a need in the art to find a suitable apparatus and a method for catalytic cracking of hydrocarbon feed for the production of light olefins, which may overcome the limitations associated with the conventional apparatus and methods, which increases the overall yield and purity of light olefins. The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the state-of-art.

OBJECTS
[0008] It is an object of the present disclosure to provide an apparatus and a method for catalytic cracking of hydrocarbons that overcomes one or more disadvantages associated with the conventional apparatuses and methods.
[0009] Another object of the present disclosure is to provide an apparatus for catalytic cracking of hydrocarbons that is economical and industrially viable.
[0010] Another object of the present disclosure is to provide an apparatus that enables higher yield of light olefins, such as ethylene, propylene and butylene.
[0011] Another object of the present disclosure is to provide a method for production of olefins by catalytic cracking of hydrocarbons.
[0012] Another object of the present disclosure is to provide a method that affords higher yield of light olefins, such as ethylene, propylene and butylene.
[0013] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the exemplary embodiments of the invention.

SUMMARY
[0014] The present disclosure pertains to the technical field of catalytic cracking. In particular, the present disclosure relates to a dual stage apparatus for catalytic cracking of hydrocarbons. Disclosure also relates to a method for production of olefins by catalytic cracking of hydrocarbons in said dual stage apparatus.
[0015] An aspect of the present disclosure relates to a dual stage apparatus 100 for catalytic cracking of hydrocarbons, said apparatus comprising: a riser reactor 10 defining a primary reaction zone A for catalytic cracking of the hydrocarbons in presence of a catalyst to produce partially cracked hydrocarbons, said riser reactor 10 defining a catalyst inlet 6, a hydrocarbon inlet 4 and a partially cracked hydrocarbon outlet 9; a disengager assembly 20, in fluid communication with the partially cracked hydrocarbon outlet 9, to separate the partially cracked hydrocarbons from the spent catalyst, said disengager assembly 20 comprising a plenum 22 for discharging partially cracked hydrocarbons, and a spent catalyst outlet 23; a regenerator 30 to regenerate the spent catalyst, said regenerator 30 defining a spent catalyst inlet 31 and a regenerated catalyst outlet 32; and a secondary reactor 40 defining a secondary reaction zone B for catalytic cracking of the partially cracked hydrocarbons in presence of a regenerated catalyst, said reactor defining a partially cracked hydrocarbons inlet 41, a regenerated catalyst inlet 42, a cracked hydrocarbon outlet 43 and a partially spent catalyst outlet 44. In an embodiment, the secondary reactor 40 is defined atop the disengager 20, said plenum 22 being extending to interior volume of said secondary reactor 40.
[0016] In an embodiment, the apparatus comprises a downer (52), in fluid communication with the partially spent catalyst outlet 44, to recycle the partially spent catalyst to the riser reactor 10. In an embodiment, the riser reactor 10 is located exterior to the disengager assembly 20, and wherein the disengager assembly 20 comprises a vortex 11, a single stage cyclone 12a, 12b and a stripper 13. In an embodiment, the apparatus defines a single vessel 102 comprising a riser reactor 10 and the disengager assembly 20, and wherein the disengager assembly 20 comprises a two-stage cyclone 18.
[0017] Another aspect of the present disclosure relates to a method for production of olefins by catalytic cracking of hydrocarbons in a dual stage apparatus 100, said method comprising the steps of: feeding a hydrocarbon stream 1, a catalyst 5 and a dispersion steam 7 to a riser reactor 10 to bring the hydrocarbons in contact with the catalyst in a primary reaction zone A to produce a stream a comprising a mixture of partially cracked hydrocarbons and spent catalyst; separating the partially cracked hydrocarbons from the spent catalyst in a disengager 10 to obtain a stream of partially cracked hydrocarbons b and a spent catalyst c; feeding the spent catalyst c to a regenerator 30 to obtain a regenerated catalyst d; feeding the stream of partially cracked hydrocarbons b and the regenerated catalyst d to a secondary reactor 40 to bring the partially cracked hydrocarbons in contact with the regenerated catalyst d in a secondary reaction zone B to produce cracked hydrocarbons stream e and a partially spent catalyst f; and recycling the partially spent catalyst f to the riser reactor 10.
[0018] In an embodiment, the cracked hydrocarbons stream e comprises olefinic hydrocarbons in an amount ranging from 30 to 40 wt%. In an embodiment, the riser reactor 10 has a ratio of the catalyst and the hydrocarbon stream ranging from 5 to 12 wt% and has a temperature ranging from 500°C to 550°C. In an embodiment, the secondary reactor 40 has a ratio of the regenerated catalyst d and the partially cracked hydrocarbon stream b ranging from 9 to 25 wt% and has a temperature ranging from 550°C to 620°C.
[0019] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0021] FIG. 1 illustrates a schematic representation of a dual stage catalytic cracking apparatus 100 for catalytic cracking of hydrocarbons, in accordance with an embodiment of the present disclosure.
[0022] FIG. 2A illustrates an exemplary schematic showing a dual stage catalytic cracking apparatus 100 wherein the riser reactor 10 is located exterior to the disengager assembly 20, in accordance with an embodiment of the present disclosure.
[0023] FIG. 2B illustrates an exemplary schematic defining a single vessel 102 comprising the riser reactor 10 and the disengager assembly 20, in accordance with an embodiment of the present disclosure.
[0024] FIG. 3 illustrates the schematic representation of a secondary reactor 40 of the apparatus, in accordance with an embodiment of the present disclosure.
[0025] FIG. 4 illustrates a schematic representation of a dual stage catalytic cracking apparatus integrated with a separation assembly, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0026] The following is a detailed description of embodiments of the present invention. The embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
[0027] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0028] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.
[0029] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0030] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0031] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0032] As used in the description herein, the terms ‘hydrocarbon feed’ and “heavy oil”, as used interchangeably and synonymously throughout the present disclosure, refers to hydrocarbons such as a vacuum gas oil obtained from the vacuum distillation tower having a boiling range between 350°C and 550°C; a straight run gas oil from the atmospheric tower; a hydrocracker bottoms; naphtha from various distillation towers boiling between 36°C and 220°C; residual streams from atmospheric and vacuum distillation towers having a boiling range between 315°C and 700°C; deasphalted oil; desalted crude oil; shale oil and combinations thereof.
[0033] As used in the description herein, the term ‘light olefins’ refers to unsaturated gaseous hydrocarbon products having four or less than four carbon atoms such as ethylene, propylene, butylene and mixtures thereof.
[0034] As used in the description herein, the term ‘catalyst’ refers to the particulate solids that aids in the cracking reactions. Catalysts useful for hydrocarbon cracking (e.g. for converting hydrocarbons into light olefins) are widely known in the art. Exemplary catalysts that may be used in the present disclosure may comprise intricate silica-alumina based structures. .
[0035] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0036] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[0037] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0038] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0039] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0040] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0041] The present disclosure pertains to the technical field of catalytic cracking. In particular, the present disclosure relates to a dual stage apparatus for catalytic cracking of hydrocarbons. Disclosure also relates to a method for production of olefins by catalytic cracking of hydrocarbons in said dual stage apparatus.
[0042] An aspect of the present disclosure relates to a dual stage apparatus 100 for catalytic cracking of hydrocarbons, said apparatus comprising: a riser reactor 10 defining a primary reaction zone A for catalytic cracking of the hydrocarbons in presence of a catalyst to produce partially cracked hydrocarbons, said riser reactor 10 defining a catalyst inlet 6, a hydrocarbon inlet 4 and a partially cracked hydrocarbon outlet 9; a disengager assembly 20, in fluid communication with the partially cracked hydrocarbon outlet 9, to separate the partially cracked hydrocarbons from the spent catalyst, said disengager assembly 20 comprising a plenum 22 for discharging partially cracked hydrocarbons and a spent catalyst outlet 23; a regenerator 30 to regenerate the spent catalyst, said regenerator 30 defining a spent catalyst inlet 31 and a regenerated catalyst outlet 32; and a secondary reactor 40 defining a secondary reaction zone B for catalytic cracking of the partially cracked hydrocarbons in presence of a regenerated catalyst, said reactor defining a partially cracked hydrocarbons inlet 41, a regenerated catalyst inlet 42, a cracked hydrocarbon outlet 43 and a partially spent catalyst outlet 44. In an embodiment, the secondary reactor 40 is defined atop the disengager 20, said plenum 22 being extending to interior volume of said secondary reactor 40.
[0043] In an embodiment, the apparatus comprises a downer 52, in fluid communication with the partially spent catalyst outlet 44, to recycle the partially spent catalyst to the riser reactor 10. In an embodiment, the riser reactor 10 is located exterior to the disengager assembly 20, wherein the disengager assembly 20 comprises a vortex 11, a single stage cyclone 12a, 12b and a stripper 13. In an embodiment, the apparatus defines a single vessel 102 comprising a riser reactor 10 and the disengager assembly 20, wherein the disengager assembly 20 comprises a two-stage cyclone 18.
[0044] FIG. 1 illustrates an exemplary schematic representation of a dual stage catalytic cracking apparatus 100 for catalytic cracking of hydrocarbons. Components of the dual stage catalytic cracking apparatus 100 are detailed below in reference to FIG. 1:
[0045] RISER REACTOR
[0046] A riser reactor 10 defines a primary reaction zone A for catalytic cracking of the hydrocarbons in presence of a catalyst to produce partially cracked hydrocarbons. The riser reactor 10 defines a hydrocarbon inlet 4, a catalyst inlet 6, a steam inlet 8 and a partially cracked hydrocarbon outlet 9. The hydrocarbon stream 1 is fed to the riser reactor 10 via inlet 4, the catalyst 5 is fed to the riser reactor 10 via catalyst inlet 6 and a dispersion steam 7 is fed to the riser reactor 10 via steam inlet 8 to bring the hydrocarbons in contact with the catalyst in the primary reaction zone (A) to produce a stream a comprising a mixture having partially cracked hydrocarbons and spent catalyst.
[0047] DISENGAGER ASSEMBLY
[0048] A disengager assembly 20, in fluid communication with the partially cracked hydrocarbon outlet 9, aids in separating the partially cracked hydrocarbons from the spent catalyst. The disengager assembly 20 includes a plenum 22 for discharging partially cracked hydrocarbons, and a spent catalyst outlet 23.
[0049] In some embodiments, the riser reactor 10 is located exterior to the disengager assembly 20. The disengager assembly 20 comprises a vortex 11, a single stage cyclone 12a, 12b and a stripper 13. The vortex 11 defines two outlets 14 and 15, wherein, outlet 14 connects the vortex 11 with stripper 13, and the outlet 15 connects the vortex 11 to the single stage cyclone 12a, 12b. The single stage cyclone 12a, 12b defines outlets 16a and 16b and outlets 17a and 17b.
[0050] In some embodiments, the apparatus 100 defines a single vessel 102 comprising a riser reactor 10 and the disengager assembly 20 (i.e. a configuration with internal riser reactor). In this configuration, it is advantageous that the disengager assembly 20 has a two-stage cyclone 18. The two-stage cyclone 18 defines two outlets 19a and 19b. The stripper 13 has a plurality of plates 21a, 21b and the likes.
[0051] REGENERATOR
[0052] A regenerator 30 aids in regenerating the spent catalyst. The regenerator defines a spent catalyst inlet 31, a regenerated catalyst outlet 32, a heated high pressure air-oxygen inlet 33 and a flue gas outlet 34. In an embodiment, the regenerator 30 defines a conduit 35 having a valve 36. The secondary reactor 40 includes an oxygen enriched air source 26, blower 27 and heating device 28.
[0053] SECONDARY REACTOR
[0054] A secondary reactor 40 defines a secondary reaction zone B for catalytic cracking of the partially cracked hydrocarbons in presence of a regenerated catalyst. The secondary reactor 40 defines a partially cracked hydrocarbons inlet 41, a regenerated catalyst inlet 42, a cracked hydrocarbon outlet 43 and a partially spent catalyst outlet 44. In an embodiment, the secondary reactor 40 defines a partially cracked hydrocarbons vapour distributer 45 and a catalyst distributer 46. The secondary reactor 40 includes a two stage cyclone 47 with outlets 48, 49a and 49b.
[0055] Another aspect of the present disclosure relates to a method for production of olefins by catalytic cracking of hydrocarbons in a dual stage apparatus 100. The method includes the steps of: feeding a hydrocarbon stream 1, a catalyst 5 and a dispersion steam 7 to a riser reactor 10 to bring the hydrocarbons in contact with the catalyst in a primary reaction zone A to produce a stream a comprising a mixture of partially cracked hydrocarbons and spent catalyst; separating the partially cracked hydrocarbons from the spent catalyst in a disengager 10 to obtain a stream of partially cracked hydrocarbons b and a spent catalyst c; feeding the spent catalyst c to a regenerator 30 to obtain a regenerated catalyst d; feeding the stream of partially cracked hydrocarbons b and the regenerated catalyst d to a secondary reactor 40 to bring the partially cracked hydrocarbons in contact with the regenerated catalyst in a secondary reaction zone B to produce cracked hydrocarbons stream e and a partially spent catalyst f; and recycling the partially spent catalyst f to the riser reactor 10.
[0056] In an embodiment, the cracked hydrocarbons stream e comprises olefinic hydrocarbons in an amount ranging from 30 to 40 wt%. In an embodiment, the riser reactor 10 has a ratio of the catalyst and the hydrocarbon stream ranging from 5 to 12 wt% and has a temperature ranging from 500°C to 550°C. In an embodiment, the secondary reactor 40 has a ratio of the regenerated catalyst d and the partially cracked hydrocarbon stream b ranging from 9 to 25 wt% and has a temperature ranging from 550°C to 620°C.
[0057] For production of olefins by catalytic cracking of hydrocarbons in a dual stage apparatus (100) of the present disclosure, a hydrocarbon stream 1 may be heated in a furnace 2 (or a preheated hydrocarbon feed from a distillation side draws or residue) and fed to a riser reactor 10 via a hydrocarbon inlet 4. The hydrocarbon stream 1 is atomized and sprayed via nozzle(s) 3a, 3b uniformly across the riser reactor 10 through a plurality of perforations (not shown in Fig). The furnace 2 can be any conventional furnace known to a person skilled in the art. The hydrocarbon stream may be pre-subjected to one or more forms of hydro-treatments to enhance the end product yield and to prolong the life of the catalyst.
[0058] In the primary reaction zone A (defined by the riser reactor 10) the hydrocarbons (hydrocarbon stream 1) is catalytically cracked in presence of a catalyst 5 to produce partially cracked hydrocarbons b. The riser reactor 10 defines a hydrocarbon inlet 4, a catalyst inlet 6, a steam inlet 8 and a partially cracked hydrocarbon outlet 9. The hydrocarbon stream 1 is fed to the riser reactor 10 via inlet 4, the catalyst stream 5 is fed to the riser reactor 10 via catalyst inlet 6 and a dispersion steam 7 is fed to the riser reactor 10 via dispersion steam inlet 8 to bring the hydrocarbons in contact with the catalyst in the primary reaction zone A to produce a stream a comprising a mixture of partially cracked hydrocarbons and spent catalyst. The hydrocarbons upon cracking undergoes rapid expansion and start rising in the riser reactor 10 as a stream a comprising a mixture of partially cracked hydrocarbons and spent catalyst and enter into the disengager 20 via a partially cracked hydrocarbon outlet 9. The catalyst stream 5 enters into riser reactor 10 via catalyst inlet 6 through a wye junction to accelerate the entry of catalyst stream 5 into the riser reactor 10 maintaining uniform distribution thereof.
[0059] The catalyst 5 is a partially spent catalyst. The partially spent catalyst has a lower coke deposited on its pores and possesses sufficient activity to crack the hydrocarbons into primarily gasoline, and has optimum selectivity to limit excess coke and dry gas. In an embodiment, the catalyst possesses adequate coke selectivity to sustain heat balance, metal tolerance to crack feeds, and limit access to dry gas to maximize the formation of light gasoline range molecules in the riser reactor 10 that are precursors to light olefins. The shorter residence time in riser reactor 10 works in favour of lower coke/gas generation and improvement in selectivity towards the formation of gasoline in riser reactor 10. In the conventional apparatuses, the riser reactor tends to be as high as 50 meters depending on the residence time required. This is besides the fact that 70% of all the desired cracking reactions are concluded in the initial 1/3rd portion of the riser reactor. Hence, to serve the objective of partial cracking of the hydrocarbon feed in the primary reaction zone A, height of riser reactor 10 in the present disclosure is lesser than that of the conventional riser reactor. In an embodiment, the hydrocarbon is in contact with the catalyst in a primary reaction zone A for a limited time, minimizing the extent of hydrogen transfer and saturation reactions. In an embodiment, the riser reactor 10 has a ratio of the catalyst 5 and the hydrocarbon stream 1 ranging from 5 to 12 wt% and has a temperature ranging from 500°C to 550°C. The cracking in the riser reactor 10 possesses sufficient heat for cracking of hydrocarbons into fraction majorly comprises of gasoline.
[0060] Disengager assembly 20 separates the stream a comprising a mixture of partially cracked hydrocarbons and spent catalyst into a stream of partially cracked hydrocarbons b and a spent catalyst c. As can be seen in FIG. 2A and FIG. 2B, the apparatus may have different configurations with regards positioning of the riser reactor 10 relative to the disengager assembly 20, for example, the riser reactor 10 may be located exterior to the disengager assembly 20 (as shown in FIG. 2A), alternatively, the riser reactor 10 may be located interiorly to the disengager assembly 20 i.e. the apparatus may define a single vessel 102 comprising or housing both - the riser reactor 10 and the disengager assembly 20 (as shown in FIG. 2B).
[0061] FIG. 2A illustrates a schematic representation of the apparatus, wherein the riser reactor 10 is located exterior to the disengager assembly 20. As can be seen in FIG. 2A, stream a comprising a mixture of partially cracked hydrocarbons and spent catalyst enters the vortex 11 of the disengager 20 via partially cracked hydrocarbon outlet 9 from the riser reactor 10. The vortex 11 separates the stream a into a stream of partially cracked hydrocarbons b and a spent catalyst c by centrifugal forces. In an embodiment, the vortex 11 separates the mixture of partially cracked hydrocarbons and spent catalyst with up to 95% efficiency. In an embodiment, partially cracked hydrocarbons b majorly includes gasoline and light cycle oil (LCO) fractions. The partially cracked hydrocarbons vapours b from vortex 11 is received by single stage cyclone 12a, 12b via outlet 15 and the spent catalyst c enters the stripper 13 via outlet 14 of the vortex 11. Any spent catalyst left in the partially cracked hydrocarbons vapours b is further removed by the single stage cyclone 12a, 12b, and fed to the stripper 13 via outlets 17a, 17b of the single stage cyclone 12a, 12b. In an embodiment, the cumulative efficiency of the vortex 11 and single stage cyclone 12a, 12b is about 99%. The partially cracked hydrocarbons vapours b from the single stage cyclone 12a, 12b enter the plenum 22 via outlet 16a, 16b.
[0062] FIG. 2B illustrates a schematic representation of apparatus 100 that defines a single vessel 102 comprising a riser reactor 10 and the disengager assembly 20. As can be seen from FIG. 2B, the stream a comprising a mixture of partially cracked hydrocarbons and spent catalyst enters the two-stage cyclone 18 of the disengager 20. In an embodiment, the two-stage cyclone 18 separates the stream a into a stream of partially cracked hydrocarbons b and spent catalyst c. The partially cracked hydrocarbons b in vapour form enters the plenum 22 via outlet 19a and the spent catalyst b enters the stripper 13 via outlet 19b of the two-stage cyclone 18.
[0063] In an embodiment, the spent catalyst b from the stripper 13 passes through a plurality of plates 21a, 21b and the likes. In an embodiment, any remnant hydrocarbons adsorbed on the pores of the spent catalyst b are displaced using a superheated steam in the stripper 13. The stripper 13 may include different types of plates, depending upon the nature of hydrocarbon stream, stripping time and the stripper’s design pressure drop. In an embodiment, the plates are annular plates, doughnut plates and the likes. However, any other types of plates, as known to or appreciated by a person skilled in the art, can be used to serve the intended purpose. In the case of internal riser reactor (as shown in FIG. 2B), the plates may be annular (doughnut plates). In an embodiment, the spent catalyst b is substantially devoid of any catalytic activity on account of carbonaceous deposits formed on the surface of the catalyst during catalytic cracking in the riser reactor 10.
[0064] The spent catalyst b after being stripped, leave the disengager assembly 20 via a spent catalyst outlet 23 through a conduit 24 having a valve 25, and enters the regenerator 30 for regeneration via a spent catalyst inlet 31. An oxygen enriched air from source 26 is pressurized using blower 27 and heated to a high temperature using a heating device 28 (such as a fuel gas fired furnace or a heat exchanger or any such conventional device known to a person skilled in the art) to obtain a heated high pressure air-oxygen mixture 29. The heated high pressure air-oxygen mixture 29 enters the regenerator 30 via a heated high pressure air-oxygen inlet 33 and comes in contact with the spent catalyst b that has entered the regenerator 30 via the spent catalyst inlet 31 to form a flue gas and a regenerated catalyst d. In an embodiment, when the spent catalyst b comes in contact with the heated high pressure air-oxygen mixture 29 in the regenerator 30, it burns the coke deposited on the surface of the spent catalyst b and regenerate it to form a regenerated catalyst d. In an embodiment, the spent catalyst b is heated in the regenerator 30 at a temperature ranging from 500°C to 750°C, preferably at 600°C to 750°C. In an embodiment, higher regeneration temperature is counteracted by lowering the catalyst circulation rate. If the catalyst circulation is not reduced, the excessively high cracking temperature may negatively affect the product selectivity and catalyst life. Operating a regenerator in full combustion mode while processing resid yields may increase the cracking temperature and cause more coke to form leading to equipment damage and loss of yield. Consequently, in existing art, resid processing unit operates in a partial burn mode. In partial burn mode, the flue gasses resulting from the coke combustion contain a substantial concentration of carbon monoxide. This necessitates the requirement of CO boiler to convert CO to CO2 and recover the heat. In addition, the superior metallurgy is required to withstand the afterburning temperature. Another limitation of partial burn regenerators is a higher Continuous Catalytic reforming (CCR) due to limited air being supplied for combustion. This lowers the activity of the catalyst and negatively affects the yield. A trade-off exists between loss of selectivity due to higher cracking temperature and low activity due to higher CCR while deciding upon a complete or partial burn regenerator. An additional benefit of adopting the instant design is that the unit can process resid feed whilst operating a full combustion regenerator. Since the catalyst at high temperature is used to crack low CCR feed prior to resid feed, excessive coking is prevented.
[0065] The flue gas escapes the regenerator 30 via a flue gas outlet 34. The regenerated catalyst d exits the regenerator 30 via a regenerated catalyst outlet 32, pass through a conduit 35 having a valve 36 and enter into the secondary reactor 40 via a regenerated catalyst inlet 42.
[0066] FIG. 3 illustrates a schematic representation of a secondary reactor of the apparatus 100. As can be seen from FIG. 3, a stream of partially cracked hydrocarbons b from the plenum 22 enters the secondary reactor 40 via partially cracked hydrocarbons inlet 41. The regenerated catalyst d enters the secondary reactor 40 via a regenerated catalyst inlet 42. The stream of partially cracked hydrocarbons b, via partially cracked hydrocarbons vapour distributer 45, and regenerated catalyst d, via catalyst distributer 46, are brought in contact with each other in a secondary reaction zone B to produce a reaction mixture comprising cracked hydrocarbons and a partially spent catalyst. In an embodiment, the secondary reactor 10 operates at a higher temperature and higher catalyst activity as compared to those in the riser reactor 10. Also, the hydrocarbon partial pressure is reduced by excess volume of steam. In an embodiment, space in the secondary reactor is sufficient for optimal mixing of regenerated catalyst d and vapours of partially cracked hydrocarbon b. The reaction mixture enters the two-stage cyclone 47 of the secondary reactor 40, wherein two-stage cyclone 47 separates the reaction mixture into a cracked hydrocarbons stream e and a partially spent catalyst f. The cracked hydrocarbons stream e exits the two-stage cyclone 47 via outlet 48, and finally leaves the secondary reactor 40 via cracked hydrocarbon outlet 43. The partially spent catalyst f exits from the two-stage cyclone 47 via outlet 49a, 49b and leaves the secondary reactor 40 via spent catalyst outlet 44 and enters into the downer 52. In an embodiment, the secondary reactor 40 has a ratio of regenerated catalyst d and the partially cracked hydrocarbon stream b ranging from 5 to 25 wt%, preferably, ranging from 9 to 25 wt% and has a temperature ranging from 550°C to 620°C. In an embodiment, secondary reactor 40 operates at higher temperature than that in the riser reactor 10. Since, the reactant hydrocarbons (i.e. the partially cracked hydrocarbons b stream) in the secondary reactor 40 majorly includes gasoline and light cycle oil (LCO) fractions, the coke formation on the regenerated catalyst d is quite low even at high cracking temperature in the secondary reactor 40. With high catalyst activity and lower hydrocarbon partial pressure, the reaction equilibrium favors higher olefin formation in the secondary reactor 40. Further, the bimolecular hydrogen transfer reactions that consume olefins to produce aromatics are also limited.
[0067] The partially spent catalyst f from the secondary reactor 40 enters into the degasser 50 and recycled into the riser reactor 10 via downer 52 having a valve 51. The degasser acts as temporary storage during which any entrained hydrocarbons on the catalyst’s pores are stripped off. The degassed catalyst is recycled to the riser reactor 10 via the downer 22 where it encounters fresh feedstock (hydrocarbon stream 1). The catalyst circulation rate in the entire apparatus is controlled by the valve 51, present downstream from the degasser 50. Valve 51 also contributes to maintaining the unit’s heat balance by regulating the catalyst flow and thereby controlling the amount of coke deposited on the partially spent catalyst f. In an embodiment, the partially spent catalyst f is not a completely deactivated catalyst owning to its reaction with partially cracked hydrocarbons b in the secondary reactor 40, and hence, after recycling, the same catalyst is recycled and used as catalyst 5 in riser reactor 10.
[0068] FIG. 4 illustrates a schematic representation of a dual stage catalytic cracking apparatus integrated with a separation assembly. As can be seen from FIG. 4, the vaporised cracked hydrocarbons stream e exits the secondary reactor 40 via cracked hydrocarbon outlet 43; and product gasses g leaving the degasser 50 enters into a fractional column 53. The fractional column 53 fractionates the cracked hydrocarbons stream e and the product gasses g into four streams, namely: an upper gas stream 54 consisting majorly of light olefins, two side streams 55 and 56, and one bottoms stream 72, wherein side stream 55 comprises light cycle oil (LCO) with a boiling range between 195-340°C, and side stream 56 comprises heavy cycle oil (HCO) boiling between 340-420°C. Upper gas stream 54 consisting majorly of light olefins is sent to an overhead condenser 57. The overhead condenser 57 separates the stream 54 into an upper gas stream 58 that enters into the ethylene recovery setup 60; and the bottom stream 59 that enters into a debutanizer 61. The ethylene recovery setup 60 separates the upper gas stream 58 into an ethylene stream 62 and a sponge gas 63. The debutanizer 61 separates the bottom stream 59 into an upper gas stream 64 and a lower stream 65, wherein the upper gas stream 64 is sent to a propylene and butylene recovery unit 66 to obtain propylene and butylene fractions as 67 and LPG as 68. The lower stream 65 is an unstable gasoline, which may be recycled to the secondary reactor 40 or withdrawn as product gasoline 69 after stabilization by any conventional method. Side streams 55 and 56 from the fraction column 53 are sent to a low severity hydro-treater 70 to saturate the aromatic molecules of LCO/HCO and thereby extract more light olefins from the LCO/HCO streams. The bottom streams 71 and 72 from the hydro-treater 70 and fraction column 53 are sent to the riser reactor 10 for re-cracking; managing hydrocarbon CCR to maintain heat balance or to quench cracking reactions. While, in the present embodiment, a specific separation assembly is described as being integrated with the advantageous apparatus and process of the present disclosure, it is to be appreciated that any other separation assembly, as known to or appreciated by the skilled person, can also be integrated to separate/segregate olefins from the cracked hydrocarbons stream e.
EXAMPLES
[0069] Laboratory scale experiments were conducted to determine the potential yield improvement by employing a dual-stage approach to heavy oil cracking. All the experiments were conducted in a commercially available lab-scale fixed fluidized bed reactor setup. A partially deactivated catalyst (coke 0.3 to 1.2 wt %) was used to crack heavy oil at lower severity. The gaseous products were collected in a wet gas collection system and analyzed by chromatographic methods. The liquid product was condensed, analyzed, and collected for secondary cracking. To simulate the second stage cracking, the collected liquid products were re-cracked using a regenerated catalyst with negligible coke content at high severity. The gaseous and liquid products obtained were analyzed.

Table 1: Characterization of feed fed to the primary and secondary cracking reaction zones
Properties Primary feed Secondary feed
Density (g/ml) 0.8743 0.8075
Distillation (wt %)
IBP to 192°C 5% 50%
192°C to 360°C 10% 35%
360°C to 425°C 40% 15%
425°C + 45% 0%
[0070] The primary feed (hydrocarbon stream 1) was denser and mostly consists of a hydrocarbon gas oil having boiling point above 360°C. The liquid product condensed from the primary feed cracking reactions was termed as secondary feed. The secondary feed was lighter and contains unsaturated compounds having boiling points below 360°C. The hydrocarbons in the secondary feed are mostly in the gasoline and light diesel range. Table 2 herein-below shows the properties of the catalyst used in the riser reactor and secondary reactor.
Table 1 Catalyst properties
Gasoline maximizing Catalyst
Properties First Stage Second Stage
Surface Area (m2/g) 124 159
Pore volume (ml/g) 0.12 0.15
Carbon wt% 1.51 0.44
LPG maximizing Catalyst
Surface Area (m2/g) 216 230
Pore volume (ml/g) 0.15 0.18
Carbon wt% 1.87 0.41
[0071] Gasoline maximizing catalyst was used in Example 1 that increases the number of gaseous products. Although the catalyst used in both stages is the same, however, the catalyst in the first stage has some coke deposits, which lower the total surface area available for the catalytic reaction. This was done purposely to simulate the catalyst in the primary reaction zone of the present disclosure. The catalyst used in the secondary reaction zone was completely regenerated, and therefore, had negligible coke and higher cracking activity.
[0072] EXAMPLE 1
[0073] Example 1 illustrates a comparison between the product yields of a single-stage FCC and that of the present disclosure. It further illustrates the effect of reaction temperature (cracking temperature or riser outlet temperature, ROT) on the product yields. It also illustrates the effect of increasing catalyst circulation in the second stage on the product yield. The catalyst used in Example 1 was a gasoline maximizing catalyst sourced from commercially operating FCC unit.
[0074] In the instant example, the first stage reaction was carried out at a 515°C with a 5% w/w catalyst to feed ratio. This reaction condition was found to be the most optimal for the maximum production of gasoline. The second stage reaction was carried out at varying conditions (ROT 550-570°C and CTO 9 and 12 w/w) since the optimum was unknown for the feed-in question. It could be observed that the gasoline yield increases with an increase in reaction temperature and catalyst to feed ratio. The temperature was limited to 570°C since it is the upper limit for conventional FCC operation. Despite increasing the temperature up to 570°C, the propylene yield was fairly constant, since the catalyst was more selective towards gasoline.
Table 2: Comparison between the products yield of a single stage FCC and that of present disclosure using gasoline maximizing catalyst
First Stage Second Stage
ROT (°C) 515 550 560 570 550 560 570
CTO (w/w) 5 9 9 9 12 12 12
Conversion (%wt) 60.43 63.67 61.37 63.72 67.08 68.58 68.06
Coke + dry gas (%wt) 7.584 10.674 10.706 11.262 11.93 13.507 13.965
Gasoline (%wt) 39.855 41.187 41.309 41.627 42.414 42.598 42.925
LPG (%wt) 12.989 6.913 7.167 7.136 11.738 12.479 13.173
C3= (%wt) 3.753 3.650 3.121 3.531 3.402 3.630 3.922
Total Gasoline (%wt) 33.457 33.484 35.484 36.458 38.484 38.544
Total LPG (%wt) 19.90 20.156 20.12 24.73 25.468 26.162
Total C3= (%wt) 7.403 6.874 7.284 7.155 7.383 7.675
Conversion 1+2 (%wt) 69.32 69.32 71.18 73.85 74.63 75.05
[0075] EXAMPLE 2
[0076] Example 2 illustrates the comparison between the product yields of a single-stage FCC and that of the present disclosure. It further illustrates the effect of reaction temperature (cracking temperature or riser outlet temperature, ROT) on the product yields. It also illustrates the effect of increasing catalyst circulation in the second stage on the product yield. The catalyst used in Example 1 was a LPG maximizing catalyst sourced from a commercially operating HS-FCC unit.
[0077] In the instant example, the first stage reaction was carried out at 550°C with a 12 w/w catalyst to feed ratio. This reaction condition was found to be the most optimal for maximum production of LPG. The sum total of the liquid product condensed was used as feedstock for the second stage reaction. The second stage reaction was carried out at varying conditions (ROT 570-620°C and CTO 20 and 25 w/w) since the optimum was unknown for the feed-in question. It was observed that the gasoline yield decreases with an increase in reaction temperature and catalyst to feed ratio. This indicates significant gasoline cracking to produce LPG. Gasoline cracking was more pronounced in the second stage cracking. LPG maximizing catalyst used in the instant example is a shape-selective zeolite ZSM-5 that selectively cracks gasoline range hydrocarbons to light olefins and propylene. This effect was enhanced with increasing temperature up to a point after which the formation of coke and dry gas takes precedence.

Table 3: Comparison between the products yield of a single stage FCC and that of present disclosure using LPG maximizing catalyst
First Stage Second Stage
ROT (°C) 550 570 580 590 600 610 620
CTO (w/w) 12 20 20 20 25 25 25
Conversion (%wt) 79.00 74.71 76.40 80.21 75.91 78.69 82.06
Coke + dry gas (%wt) 9.407 10.41 10.08 10.88 12.75 12.96 12.97
Gasoline (%wt) 29.23 44.03 44.57 46.45 41.69 42.34 43.57
LPG (%wt) 40.36 20.27 21.74 23.89 21.02 24.04 25.54
C3= (%wt) 15.1 10.13 10.74 11.56 10.65 12.42 13.34
Total Gasoline (%wt) 22.12 22.39 23.33 20.94 21.69 21.89
Total LPG (%wt) 50.54 51.28 52.36 50.92 52.44 53.19
Total C3= (%wt) 25.23 25.84 26.66 25.75 27.52 28.44
Conversion 1+2 (%wt) 87.29 88.14 90.06 87.90 89.30 90.99
[0078] In both examples, the gaseous product from the first stage cracking could not be recycled to the second stage due to laboratory scale unit’s limitation. However, in commercial practice, the entirety of the first stage products from the primary reactor will be fed to the secondary reactor. The gaseous product contains hydrocarbon molecules that can still crack and produce light olefins. Therefore, the total propylene yield will be much higher than what is reported herein-above.
[0079] Further, in case of multi-staged fluid bed, greater catalyst density can be used with substantially constant catalyst to heavy oil ratio throughout the bed. As a result, higher conversions and olefins production, higher catalytic cracking and less gas make can be achieved. In addition, in accordance to the scheme of the present disclosure, there are smaller temperature changes in fluid bed due to lesser back mixing of catalyst and more catalyst inventory. Further highest temperatures coupled with low hydrocarbon partial pressure in fluid bed system are at the exit. As a result, thermodynamically favourable olefins selectivity is achieved.
[0080] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES
[0081] The present disclosure provides an apparatus and a method for catalytic cracking of hydrocarbons that overcome the one or more disadvantages associated with the conventional apparatuses and methods
[0082] The present disclosure provides an apparatus for catalytic cracking of hydrocarbons that is economical and industrially viable.
[0083] The present disclosure provides an apparatus that enables higher yield of light olefins, such as ethylene, propylene and butylene.
[0084] The present disclosure provides a method for production of olefins by catalytic cracking of hydrocarbons.
[0085] The present disclosure provides method that affords higher yield of light olefins, such as ethylene, propylene and butylene.

, Claims:1. A dual stage apparatus (100) for catalytic cracking of hydrocarbons, said apparatus comprising:
a riser reactor (10) defining a primary reaction zone (A) for catalytic cracking of the hydrocarbons in presence of a catalyst to produce partially cracked hydrocarbons, said riser reactor (10) defining a catalyst inlet (6), a hydrocarbon inlet (4) and a partially cracked hydrocarbon outlet (9);
a disengager assembly (20), in fluid communication with the partially cracked hydrocarbon outlet (9), to separate the partially cracked hydrocarbons from the spent catalyst, said disengager assembly (20) comprising a plenum (22) for discharging partially cracked hydrocarbons and a spent catalyst outlet (23);
a regenerator (30) to regenerate the spent catalyst, said regenerator (30) defining a spent catalyst inlet (31) and a regenerated catalyst outlet (32); and
a secondary reactor (40) defining a secondary reaction zone (B) for catalytic cracking of the partially cracked hydrocarbons in presence of a regenerated catalyst, said reactor defining a partially cracked hydrocarbons inlet (41), a regenerated catalyst inlet (42), a cracked hydrocarbon outlet (43) and a partially spent catalyst outlet (44).

2. The apparatus (100) as claimed in claim 1, wherein the secondary reactor (40) is defined atop the disengager (20), said plenum (22) being extending to interior volume of said secondary reactor (40).

3. The apparatus (100) as claimed in claim 1, wherein the apparatus comprises a downer (52), in fluid communication with the partially spent catalyst outlet (44), to recycle the partially spent catalyst to the riser reactor (10).

4. The apparatus (100) as claimed in claim 1, wherein the riser reactor (10) is located exterior to the disengager assembly (20), and wherein the disengager assembly (20) comprises a vortex (11), a single stage cyclone (12a, 12b) and a stripper (13).
5. The apparatus (100) as claimed in claim 1, wherein the apparatus defines a single vessel (102) comprising a riser reactor (10) and the disengager assembly (20), and wherein the disengager assembly (20) comprises a two-stage cyclone (18).

6. A method for production of olefins by catalytic cracking of hydrocarbons in a dual stage apparatus (100), said method comprising the steps of:
feeding a hydrocarbon stream (1), a catalyst (5) and a dispersion steam (7) to a riser reactor (10) to bring the hydrocarbons in contact with the catalyst in a primary reaction zone (A) to produce a stream (a) comprising a mixture of partially cracked hydrocarbons and spent catalyst;
separating the partially cracked hydrocarbons from the spent catalyst in a disengager (10) to obtain a stream of partially cracked hydrocarbons (b) and a spent catalyst (c);
feeding the spent catalyst (c) to a regenerator (30) to obtain a regenerated catalyst (d);
feeding the stream of partially cracked hydrocarbons (b) and the regenerated catalyst (d) to a secondary reactor (40) to bring the partially cracked hydrocarbons in contact with the regenerated catalyst d in a secondary reaction zone (B) to produce cracked hydrocarbons stream (e) and a partially spent catalyst (f); and recycling the partially spent catalyst f to the riser reactor (10).

7. The method as claimed in claim 6, wherein the cracked hydrocarbons stream (e) comprises olefinic hydrocarbons in an amount ranging from 30 to 40 wt%.

8. The method as claimed in claim 6, wherein the riser reactor (10) has a ratio of the catalyst and the hydrocarbon stream ranging from 5 to 12 wt% and has a temperature ranging from 500°C to 550°C.

9. The method as claimed in claim 6, wherein the secondary reactor (40) has a ratio of the regenerated catalyst (d) and the partially cracked hydrocarbon stream (b) ranging from 9 to 25 wt% and has a temperature ranging from 550°C to 620°C.