A method and system for the production of light olefins and aromatics by catalytic cracking of a hydrocarbon feed

Abstract

The application provides a method for producing low-carbon olefins and aromatic hydrocarbons through vortex catalytic cracking, which comprises: in a down-flow bed reactor, carrying out catalytic cracking reaction on a reaction material containing a fluidizing medium, a catalyst and a raw oil in a vortex and down-flow state, then carrying out gas-solid separation and stripping to obtain spent catalyst and reaction product oil gas, and returning the spent catalyst to the catalytic cracking reaction after regeneration. The application also provides a system for producing low-carbon olefins and aromatic hydrocarbons through vortex catalytic cracking. Through the technical scheme, the application strengthens the gas-solid contact between the raw oil and the catalyst through a vortex, thereby effectively improving the conversion rate and selectivity of catalytic cracking for producing low-carbon olefins and aromatic hydrocarbons.

Description

Technical Field

[0001] The present invention relates to the field of petrochemical industry, in particular to a method for producing light olefins and aromatics by eddy current catalytic cracking and a system for producing light olefins and aromatics by eddy current catalytic cracking. Background Art

[0002] Catalytically cracked diesel (LCO) is rich in aromatics and is a potential ideal feedstock for aromatics production. Monocyclic aromatics are crackable and can be directly catalytically cracked to produce aromatics. Polycyclic aromatics are easily saturated to monocyclic aromatics after hydrotreatment. Therefore, hydrotreating LCO and combining it with catalytic cracking processes has the potential to increase aromatics production capacity.

[0003] US6656346B2 discloses a catalytic cracking process which uses a downer reactor to carry out a catalytic cracking reaction at high severity to produce propylene.

[0004] However, the conversion rate and selectivity of existing catalytic cracking methods still need to be further improved. Summary of the Invention

[0005] The purpose of the present invention is to further improve the conversion rate and selectivity of catalytic cracking to produce light olefins and aromatics.

[0006] In order to achieve the above-mentioned object, the present invention provides a method for producing light olefins and aromatics by eddy catalytic cracking, which comprises: in a down-flowing bed reactor, allowing a reaction material containing a fluidized medium, a catalyst and a feedstock oil to undergo a catalytic cracking reaction in a eddy and downwardly flowing state, then performing gas-solid separation and steam stripping to obtain a spent catalyst and reaction product oil and gas, and then regenerating the spent catalyst and returning it to the catalytic cracking reaction.

[0007] The present invention also provides a system for producing light olefins and aromatics by vortex catalytic cracking, the system comprising a down-flow bed reactor, a gas-solid rapid separation device, a stripper and a regenerator connected in sequence, the discharge port of the regenerator being connected to the catalyst inlet of the fluidized bed reactor; wherein a vortex device is provided at the inlet of the down-flow bed reactor.

[0008] Through the above technical solution, the present invention strengthens the gas-solid contact between the feed oil and the catalyst through eddy currents, thereby effectively improving the conversion rate and selectivity of catalytic cracking to produce light olefins and aromatics.

[0009] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0011] Figure 1 This is a schematic diagram of the system structure in a preferred embodiment of the present invention.

[0012] Figure 2 This is a schematic structural diagram of an eddy current distribution plate in a preferred embodiment of the present invention.

[0013] Figure 3 for Figure 2 Schematic diagram of the operation of the eddy current distribution plate.

[0014] Description of Reference Numerals

[0015] Figure 1 In the figure, 1 is the fluidizing medium; 2 is the inlet distributor; 3 is the slide valve to be regenerated; 4 is the vortex distribution plate; 5 is the fluidizing air inlet; 6 is the oil inlet nozzle; 7 is the downer reaction section; 8 is the product oil and gas discharge pipeline; 9 is the cyclone separator; 10 is the gas-solid rapid separator; 11 is the stripping oil and gas pipeline; 12 is the catalyst pipeline; 13 is the stripping steam; 14 is the stripper; 15 is the regeneration slide valve; 16 is the regeneration medium; 17 is the riser regenerator; 18 is the riser outlet cyclone separator; 19 is the settler; 20 is the settler cyclone separator; 21 is the flue gas outlet pipeline. DETAILED DESCRIPTION

[0016] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0017] The present invention provides a method for producing light olefins and aromatics by eddy catalytic cracking, which comprises: in a down-flow bed reactor, allowing reaction materials containing a fluidized medium, a catalyst and a feedstock oil to undergo a catalytic cracking reaction in a eddy-flow and downward-flowing state, then performing gas-solid separation and steam stripping to obtain a spent catalyst and reaction product oil and gas, and then regenerating the spent catalyst and returning it to perform the catalytic cracking reaction.

[0018] The inventors of the present invention have discovered that stringent reaction conditions and high gas-solid contact efficiency are beneficial for improving the conversion and selectivity of light olefins and aromatics produced through catalytic cracking reactions. However, existing downer reactors suffer from low bed particle concentrations and weak backmixing, resulting in low gas-solid contact efficiency, which in turn affects the conversion and selectivity of the catalytic cracking reaction. The inventors of the present invention have further discovered that conducting the catalytic cracking reaction in a vortex state in a downer reactor effectively enhances the gas-solid contact efficiency, allowing for the use of more stringent reaction conditions (higher temperatures and greater catalyst-to-oil ratios) and extending the gas-solid residence time, thereby improving the reaction conversion and selectivity, and thus increasing the yield of olefin and aromatic products.

[0019] Various vortex flow devices can be used to cause the fluidized medium to rotate. According to a preferred embodiment of the present invention, the fluidized medium is caused to rotate by a monocline tube or a vortex distribution plate, thereby driving the catalyst and the feedstock oil into a vortex and downward flow state. Specifically, the fluidized medium flows from the inlet of the downer reactor through the vortex distribution plate into the downer reactor, and the catalytic cracking catalyst from the regenerator enters the downer reactor through the central through-hole of the vortex distribution plate. After passing through the vortex distribution plate, the fluidized medium can mix with the catalyst flowing out of the catalyst delivery pipe. Under the influence of the vortex fluidization field formed by the fluidized medium, the catalyst also forms a vortex and downward flow state. After being preheated, the feedstock oil enters the inlet of the downer reactor through a nozzle to mix and contact with the catalyst. Carried by the vortex and downward flow of the fluidized medium, the feedstock oil and catalyst also reach a vortex and downward flow state, and undergo a catalytic cracking reaction in the downer reactor. The catalyst then moves to the outlet of the downer reactor and enters the gas-solid rapid separator for rapid gas-solid separation.

[0020] The inclination angle of the monoclinic tube may be 5°-85°, preferably 20°-70°.

[0021] The eddy current distribution plate may have various structures suitable for the method of the present invention. Figure 2 and Figure 3As a preferred embodiment, the vortex distribution plate includes an outer ring and an inner ring arranged concentrically, the diameter of the outer ring is 0.01-0.9 times, preferably 0.1-0.8 times, the inner diameter of the down-flow reactor; the diameter of the inner ring is 0.01-0.5 times, preferably 0.1-0.4 times the diameter of the outer ring; a fixed connection is provided between the outer ring and the inner wall of the tubular fluidized bed reactor, the inner ring is connected to the catalyst input pipe, and the catalyst enters the down-flow reactor through the inner ring; a plurality of propeller-shaped distribution blades are radially spaced between the outer ring and the inner ring, the plurality of distribution blades have the same inclination direction and an inclination angle of 5°-85°, preferably 20°-70°; the gap between two adjacent distribution blades is used to allow the fluidized medium to pass obliquely and flow along the inner wall of the down-flow tube reactor to generate rotation. In this preferred embodiment, the vortex distribution plate has the advantages of large operating load and strong stability, can be adapted to different operating gas velocities, and can achieve uniform distribution of vortex fields in different fluidization states.

[0022] Typically, the linear velocity of the gas in the vortex can be 0.1-10 m / s, preferably 1-5 m / s, and the angular velocity of the gas in the vortex can be 0.01-10 s -1 , preferably 0.1-5 s -1 The angular velocity of the vortex gas can be adjusted by the tilt direction of the distribution blades, the linear velocity of the gas, the inner diameter of the downer reactor, etc.

[0023] Optionally, the downer reactor has a length-to-diameter ratio of 2-50:1, preferably 5-20:1.

[0024] Optionally, the catalytic cracking conditions include: reaction temperature of 500-800°C, preferably 550-650°C; reaction pressure of 0.1-2.0 MPa, preferably 0.3-1 MPa; catalyst-oil weight ratio of 10-150, preferably 15-50; residence time of 0.2-10 seconds, preferably 0.5-5 seconds.

[0025] Optionally, the catalyst regeneration conditions may include: a regeneration temperature of 550-850° C., and air as the regeneration medium.

[0026] Optionally, the fluidizing medium is at least one of water vapor and dry gas.

[0027] Optionally, the catalyst contains 10-60wt% of a molecular sieve, 1-40wt% of a binder and 1-90wt% of a carrier; the molecular sieve is a modified Y-type molecular sieve and / or an unmodified Y-type molecular sieve; the binder is a silica binder and / or an alumina binder; the carrier can be selected from one or more of silica, kaolin, montmorillonite, diatomaceous earth, halloysite, saponite, rectorite, sepiolite, attapulgite, hydrotalcite and bentonite.

[0028] The method of the present invention is highly adaptable to feedstocks and is applicable not only to light catalytic cracking feedstocks such as hydrogenated LCO, but also to deep catalytic cracking of low-quality heavy feedstocks with high density and low hydrogen content. Optionally, the feedstock oil is at least one of unhydrogenated LCO, hydrogenated LCO, straight-run diesel, coker diesel, and hydrorefined straight-run diesel.

[0029] Optionally, in the modified Y-type molecular sieve, calculated as oxide, the rare earth element content is 3-15wt%, the sodium element content is 0.01-0.8wt%, and the zinc element content is 0.2-4.5wt%; the rare earth element may be, but is not limited to, one or more of La, Ce, Pr and Nd.

[0030] On the other hand, reference Figure 1 The present invention also provides a system for producing light olefins and aromatics by vortex catalytic cracking. The system comprises a downer reactor, a gas-solid rapid separation device, a stripper, and a regenerator connected in sequence, wherein the regenerator outlet is connected to the catalyst inlet of the fluidized bed reactor; a vortex device is provided at the inlet of the downer reactor. This system is particularly suitable for use in the method of the present invention for producing light olefins and aromatics by catalytic cracking.

[0031] Preferably, the vortex device is a mono-oblique tube or a vortex distribution plate.

[0032] Wherein, the inclination angle of the monoclinic tube is 5°-85°, preferably 20°-70°.

[0033] Wherein, the eddy current distribution plate can have various structures suitable for the method of the present invention. As a preferred embodiment, refer to Figure 2 and Figure 3The swirl distribution plate includes an outer ring and an inner ring arranged concentrically, the diameter of the outer ring is 0.01-0.9 times, preferably 0.1-0.8 times, the diameter of the down-flow bed reactor; the diameter of the inner ring is 0.01-0.5 times, preferably 0.1-0.4 times, the diameter of the outer ring; a fixed connection is provided between the outer ring and the inner wall of the down-flow bed reactor, the inner ring is connected to the catalyst input pipe, and a plurality of propeller-shaped distribution blades are radially spaced between the outer ring and the inner ring. The inclination direction of the plurality of distribution blades is the same, and the inclination angle is 5°-85°, preferably 20°-70°; the gap between two adjacent distribution blades is used to allow the fluidized medium to pass obliquely and flow along the inner wall of the down-flow bed reactor to generate rotation.

[0034] The system also includes a cyclone separator, the feed inlet of the cyclone separator is connected to the side discharge port of the gas-solid rapid separation device, the solid phase discharge port of the cyclone separator is connected to the stripper, and the stripping outlet of the stripper is connected to the feed inlet of the cyclone separator.

[0035] Optionally, the downer reactor has a length-to-diameter ratio of 2-50:1, preferably 5-20:1.

[0036] According to a particularly preferred embodiment of the present invention, Figure 1-3 The catalyst enters the down-bed reactor 7 through the slide valve 3 and the inlet distributor 2. The fluidized medium 1 enters the top of the down-bed reactor 7 through the fluidizing air inlet 5. After passing through the vortex distributor 4 to generate a rotating airflow, the fluidized medium 1 drives the catalyst to swirl and move downward. After being preheated, the raw oil enters the down-bed reactor 7 through the oil inlet nozzle 6 to mix and contact with the catalyst. The raw oil gas and catalyst swirl and flow downward to carry out catalytic cracking reaction. The reaction product oil gas and catalyst are separated at the bottom of the down-bed reactor 7 by the gas-solid rapid separation device 10. The separated side materials enter the cyclone separator 9 for further separation. The separated product oil gas enters the fractionation unit through the product oil gas discharge pipeline 8. The catalyst separated by the cyclone separator 9 enters the stripper 14 through the catalyst pipeline 12 and is stripped by the stripping steam 13. After the catalyst is stripped, the stripped oil gas enters the cyclone separator through the stripping oil gas pipeline 11. The stripped catalyst enters the riser regenerator 17 through the regeneration slide valve 15 for char regeneration. The catalyst is separated in the riser outlet cyclone 18 and settles in the settler 19. The flue gas generated by the regeneration is separated in the settler cyclone 20 and discharged through the flue gas outlet pipeline 21. The regenerated catalyst enters the reactor through the waiting slide valve 3 for the next cycle.

[0037] The present invention is further described in detail below by way of examples. Unless otherwise specified, the raw materials used in the examples can be obtained from commercial sources.

[0038] The properties of the raw material hydrogenated LCO used in the examples and comparative examples are shown in Table 1.

[0039] Table 1

[0040]

[0041] The catalyst SLA used in the examples and comparative examples is the same, and the catalyst properties are listed in Table 2. The preparation method is as follows: (1) NaY molecular sieve is ion exchanged with a rare earth salt solution (cerium nitrate) at a temperature of 40°C for 100 minutes. The mass ratio of the NaY molecular sieve, rare earth salt, and solvent water is 1:0.1:10; the masses of the NaY molecular sieve and rare earth salt are calculated on a dry basis and rare earth oxide basis, respectively. (2) The molecular sieve after ion exchange is calcined at a temperature of 400°C in an atmosphere with a water vapor content of 40% by volume for 6 hours. (3) The calcined molecular sieve is reacted with silicon tetrachloride at a temperature of 500°C for 3 hours. The mass ratio of the silicon tetrachloride to the calcined molecular sieve is 0.5:1. The mass of the calcined molecular sieve is calculated on a dry basis. (4) The molecular sieve was impregnated with a zinc salt solution (zinc nitrate), and the impregnated molecular sieve was calcined at an impregnation temperature of 40°C, a calcination temperature of 500°C, and a calcination time of 3 hours to obtain a modified Y molecular sieve having a rare earth element (Ce) content of 9 wt%, a sodium element content of 0.5 wt%, and a zinc element content of 2 wt%. (5) 15 wt% of the modified Y molecular sieve, 10 wt% of a binder (silicon oxide binder), 70 wt% of a carrier (kaolin), and water were formed into a slurry (solid content of 40 wt%) and spray-dried to obtain the catalyst.

[0042] Table 2

[0043]

[0044] Example 1

[0045] This embodiment follows Figure 1 The device and process were tested in a small down-flow reactor. The hydrogenated LCO listed in Table 1 was used as the feed oil. The test was conducted on a down-flow reactor using SLA-10 catalyst with an activity of 75. The catalyst properties are listed in Table 2. The reaction and regeneration process conditions were: hydrogenated LCO preheat temperature of 200°C, reaction outlet temperature of 600°C, reaction pressure of 0.2 MPa, catalyst-to-oil ratio of 20, residence time of 1.0 second, vortex gas linear velocity of 4 m / s, and gas angular velocity of 2 s -1, the regenerator outlet temperature is 700℃, the regenerator pressure is 0.6MPa, the regenerator medium is air, and the weight ratio of water vapor to total raw materials is 0.15.

[0046] The catalyst enters the downer reactor through a waiting slide valve. The fluidized medium passes through a monocline tube and then tangentially enters the top of the downer reactor. The fluidized medium generates a swirling airflow, which drives the catalyst downward in a vortex. After preheating, the crude oil enters the top of the downer reactor through an oil inlet nozzle, mixing with the catalyst. The crude oil gas and catalyst swirl and flow downward into the downer reactor section for catalytic cracking. The reaction products, oil gas and catalyst, are separated at the bottom of the downer by a gas-solid rapid separation device. The separated side materials enter a cyclone separator for further separation. The separated product oil gas enters the fractionation unit through a product oil gas discharge line. The catalyst separated by the cyclone separator enters a stripper, where it is stripped with stripping gas. After the catalyst is stripped, the stripped oil gas enters the cyclone separator through a stripping oil gas pipeline. The stripped catalyst enters the riser regenerator through the regeneration slide valve for char regeneration. The catalyst is separated in a cyclone at the riser outlet and settles in a settler. The flue gas generated by regeneration is separated in the settler cyclone and discharged through the flue gas outlet pipeline. The regenerated catalyst enters the reactor through the regeneration slide valve for the next cycle. The operating conditions and products are listed in Table 3.

[0047] Example 2

[0048] Catalytic cracking was carried out according to the method of Example 1, except that the mono-oblique tube was changed to Figure 2 and Figure 3 The vortex distribution plate shown causes the fluidized medium to rotate through the vortex distribution plate, which in turn drives the catalyst and the feedstock oil to form a vortex and flow downward. The oil and gas residence time is 1.5 seconds. The operating conditions and products are listed in Table 3.

[0049] Comparative Example 1

[0050] This comparative example employed a conventional riser catalytic cracking process, conducted in a small riser reactor, operating in a non-hydrogenation mode. The catalyst and feedstock were the same as in Example 1. The reaction and regeneration conditions were as follows: hydrogenated LCO preheat temperature of 200°C, reactor outlet temperature of 550°C, reaction pressure of 0.2 MPa, catalyst-to-oil ratio of 10, residence time of 3.5 seconds, fluidizing gas linear velocity of 4 m / s, regenerator outlet temperature of 700°C, regenerator pressure of 0.6 MPa, air as the regeneration medium, and a steam-to-total feedstock weight ratio of 0.15. The operating conditions and product distribution are listed in Table 3.

[0051] Comparative Example 2

[0052] This comparative example employed a conventional downer catalytic cracking process in a small downer reactor, operating in a non-hydrogenation mode. The catalyst and feedstock were identical to those in Example 1, and catalytic cracking was performed according to the method of Example 1. However, the vortex device was omitted, the fluidizing medium did not rotate, and the oil and gas residence time was 0.8 s. The operating conditions and products are listed in Table 3.

[0053] As can be seen in Table 3, Examples 1 and 2 exhibit higher triene and BTX yields than Comparative Examples 1 and 2. These results demonstrate that the use of a high-temperature, high-drug-to-oil ratio eddy-flow downer reactor achieves higher yields of light olefins and aromatics. By enhancing gas-solid contact efficiency and leveraging the advantages of high severity, product selectivity is increased.

[0054] Table 3

[0055]

[0056] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0057] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0058] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for producing light olefins and aromatics by eddy current catalytic cracking, characterized in that: The method comprises: in a down-flow reactor, allowing a reaction material containing a fluidized medium, a catalyst and a feedstock oil to undergo a catalytic cracking reaction in a vortex-flowing and downwardly flowing state, then performing gas-solid separation and steam stripping to obtain a spent catalyst and reaction product oil and gas, and then regenerating the spent catalyst and returning it to the catalytic cracking reaction; The fluidized medium is caused to rotate by passing through a vortex distribution plate, thereby driving the catalyst and the feedstock oil to form a vortex and flow downward; The vortex distribution plate includes an outer ring and an inner ring arranged concentrically. The outer ring is fixedly connected to the inner wall of the downer reactor. The inner ring is connected to the catalyst input pipe, and the catalyst enters the downer reactor through the inner ring. A plurality of propeller-shaped distribution blades are radially spaced between the outer ring and the inner ring, and the inclination directions of the plurality of distribution blades are the same. The gap between two adjacent distribution blades is used to allow the fluidized medium to pass obliquely and flow along the inner wall of the downer reactor to generate rotation. The diameter of the outer ring is 0.01-0.9 times the inner diameter of the downer reactor, and the diameter of the inner ring is 0.01-0.5 times the diameter of the outer ring. The inclination angles of the plurality of distribution blades are 5°-85°.

2. The method according to claim 1, wherein The inclination angle of the plurality of distribution blades is 20°-70°.

3. The method according to claim 1, wherein The linear velocity of the gas in the vortex is 0.1-10 m / s; the angular velocity of the gas in the vortex is 0.01-10 s -1 .

4. The method according to claim 3, wherein: The linear velocity of the gas in the vortex is 1-5 m / s; the angular velocity of the gas in the vortex is 0.1-5 s -1 .

5. The method according to claim 1, wherein The downer reactor has an aspect ratio of 2-50:1; The catalytic cracking conditions include: reaction temperature of 500-800° C.; reaction pressure of 0.1-2.0 MPa; catalyst-oil weight ratio of 10-150; and residence time of 0.2-10 seconds.

6. The method according to claim 5, wherein: The downer reactor has an aspect ratio of 5-20:1; The catalytic cracking conditions include: reaction temperature of 550-650° C.; reaction pressure of 0.3-1 MPa; catalyst-to-oil weight ratio of 15-50; and residence time of 0.5-5 seconds.

7. The method according to claim 1, wherein The fluidizing medium is steam and / or dry gas; The catalyst contains 10-60 wt% of a molecular sieve, 1-40 wt% of a binder, and 1-90 wt% of a carrier; the molecular sieve is a modified Y-type molecular sieve and / or an unmodified Y-type molecular sieve; the binder is selected from a silica binder and / or an alumina binder; and the carrier is selected from at least one of silica, kaolin, montmorillonite, diatomaceous earth, halloysite, saponite, rectorite, sepiolite, attapulgite, hydrotalcite, and bentonite; The raw oil is at least one of unhydrogenated LCO, hydrogenated LCO, straight-run diesel, coker diesel and hydrorefined diesel.

8. The method according to claim 7, wherein: In the modified Y-type molecular sieve, the rare earth element content, calculated as oxide, is 3-15wt%, the sodium element content is 0.01-0.8wt%, and the zinc element content is 0.2-4.5wt%; the rare earth element is one or more of La, Ce, Pr and Nd.

9. A system for the method for producing light olefins and aromatics by eddy current catalytic cracking according to claim 1, characterized in that: The system comprises a downer reactor, a gas-solid rapid separation device, a stripper and a regenerator connected in sequence, wherein the discharge port of the regenerator is connected to the catalyst inlet of the downer reactor; wherein a vortex device is provided at the inlet of the downer reactor; The eddy current device is an eddy current distribution plate; The vortex distribution plate includes an outer ring and an inner ring arranged concentrically. The outer ring is fixedly connected to the inner wall of the down-flow bed reactor. The inner ring is connected to the catalyst input pipe. A plurality of propeller-shaped distribution blades are radially spaced between the outer ring and the inner ring. The inclination directions of the plurality of distribution blades are the same. The gap between two adjacent distribution blades is used to allow the fluidized medium to pass obliquely and flow along the inner wall of the down-flow bed reactor to generate rotation. The diameter of the outer ring is 0.01-0.9 times the inner diameter of the down-flow bed reactor, the diameter of the inner ring is 0.01-0.5 times the diameter of the outer ring, and the inclination angles of the plurality of distribution blades are 5°-85°.

10. The system according to claim 9, wherein: The inclination angle of the plurality of distribution blades is 20°-70°.

11. The system according to claim 9 or 10, wherein: The system also includes a cyclone separator, the feed inlet of the cyclone separator is connected to the side discharge port of the gas-solid rapid separation device, the solid phase discharge port of the cyclone separator is connected to the stripper, and the stripping outlet of the stripper is connected to the feed inlet of the cyclone separator.

12. The system according to claim 9 or 10, wherein: The downer reactor has a length-to-diameter ratio of 2-50:

1.

13. The system according to claim 12, wherein: The downer reactor has a length-to-diameter ratio of 5-20:1.

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