Alkali desulfurization system and method for marine fuel oil

Abstract

The application discloses a marine fuel oil alkali metal desulfurization system and method. The system comprises: an alkali metal desulfurization reaction unit, comprising a mixer and a reactor, respectively used for mixing of marine fuel oil, alkali metal and hydrogen and desulfurization reaction; a liquid-solid separation unit, comprising a cyclone magnetic separator, used for liquid-solid separation of reaction products to obtain desulfurized marine fuel oil, alkali metal sulfide particles and heavy metal particles; a product purification unit, used for removing residual alkali metal and alkali metal sulfide microcrystals in the product; an alkali metal sulfide particle drying unit, used for drying of the alkali metal sulfide particles; and an alkali metal sulfide electrolysis unit. The method of the application not only efficiently completes mixing of the reactants, separation and drying of the alkali metal sulfide particles, but also improves the oil quality, realizes recycling of the alkali metal, dry gas and electrolyte, reduces consumption of resources and energy, and lowers the overall cost of the process.

Description

Technical Field

[0001] This invention belongs to the field of petroleum refining technology and relates to an alkali metal desulfurization system and method for marine fuel oil. Background Technology

[0002] In recent years, the global crude oil market has seen a clear trend towards heavier and lower-quality crude oil. Organic sulfides, heavy metals, and other heteroatom compounds are commonly found in heavy crude oil and affect its usability. Sulfur not only pollutes the air and harms human health, but also deactivates catalysts in crude oil refining and automotive three-way catalytic converters. Heavy metals in crude oil can cause deactivation of desulfurization catalysts in hydrodesulfurization processes.

[0003] The International Maritime Organization (IMO) decided to implement a mandatory requirement in 2020 to reduce the sulfur content of global marine fuel oil from 3.5% to 0.5%. Against this backdrop, demand for high-sulfur marine fuel oil has fallen sharply, while demand for low-sulfur marine fuel oil has increased. Hydrodesulfurization technology removes sulfur from fuel oil by reacting hydrogen with organic sulfur in the oil to form hydrogen sulfide, and is currently the mainstream fuel oil desulfurization technology. However, this technology requires high temperatures of 350-450℃, pressures of 5-15MPa, expensive catalysts, and large amounts of hydrogen, resulting in high energy consumption and high operating costs. Large-scale desulfurization of fuel oil would lead to significant waste of resources and energy. Due to its high energy consumption, high hydrogen consumption, and high operating costs, hydrodesulfurization technology cannot meet the requirements of efficient and low-consumption production.

[0004] Sodium metal desulfurization technology significantly reduces the sulfur and heavy metal content in oil by reacting molten sodium with organic sulfur in the oil to form sodium sulfide, sodium hydrosulfide, and other sulfides and reaction byproducts. This technology mainly includes an alkali metal desulfurization process, a liquid-solid separation process, and an electrolytic regeneration process of sodium. Organic sulfides react with sodium to generate sodium sulfide particles. After centrifugation or filtration and washing, these particles enter the electrolysis unit to regenerate sodium, which is then recycled back into the reactor for desulfurization. Sodium metal desulfurization technology removes sulfur from crude oil while reducing overall hydrogen and energy consumption, and also allows for the recycling of reactants, making it a superior desulfurization technology. However, due to the high cost of sodium metal used in the desulfurization reaction, incomplete reaction in stirred tanks, the difficulty of separating small sodium sulfide particles using conventional separation techniques, high energy consumption in washing and drying processes, and low electrolyte recycling rates, sodium metal desulfurization technology has not achieved large-scale commercial application.

[0005] The engineering application of sodium metal desulfurization technology mainly faces the following three problems:

[0006] (1) Incomplete mixing and reaction of materials during alkali metal reaction desulfurization. The alkali metal reaction desulfurization process requires thorough mixing of three raw materials: marine fuel, molten sodium metal, and hydrogen to enhance the desulfurization effect. Currently, this process is mainly completed through a stirred reactor. However, this equipment has a reaction dead zone, which causes some materials to fail to complete the reaction, reducing the overall desulfurization effect. For example, CN109890944A discloses a method for separating particles containing alkali metal salts from liquid hydrocarbons. This method uses a stirred reactor as a reactor for desulfurization reaction. Due to the high viscosity of marine fuel, the high-viscosity liquid far from the blades remains stationary, making it difficult for the liquid in the stirred equipment to form a circulation flow and creating a reaction dead zone, resulting in incomplete reaction. After desulfurization, the sulfur concentration in the oil product far exceeds the limit of sulfur content in fuel oil.

[0007] (2) Low liquid-solid separation efficiency and insufficient separation precision. The sodium sulfide particles generated by the reaction need to be separated into solid and liquid components to obtain low-sulfur oil and recover metallic sodium. The separation of sodium sulfide particles is mainly carried out by gravity separation, filtration, centrifugation, etc. Filtration separation, as a typical non-thermal separation method, can effectively separate fine particulate matter, but it also has problems such as short operating cycle and high operating cost. Therefore, centrifugal separation is more advantageous, and hydrocyclone separation obviously has greater application potential. Hydrocyclone separation is a widely used method for separating heterogeneous mixtures. The hydrocyclone uses the working principle of centrifugal sedimentation. Due to the particle size difference or density difference between coarse particles or heavy phase and fine particles or light phase, most of the coarse particles or heavy phase spiral down to the bottom under the action of centrifugal force, centripetal force, buoyancy, fluid resistance, etc., and are discharged from the sediment outlet as sediment. Fine particles or light phases form an internal spiral flow at the center and move upwards, then are discharged from the overflow pipe as an overflow, thereby achieving the purpose of separation or classification. For example, CN114437822B discloses a method for producing fuel oil, which separates fuel oil from sodium sulfide using a hydrocyclone separator, realizing the desulfurization process of the oil. However, the hydrocyclone in this method is a traditional hydrocyclone separator, and the presence of the air column reduces the separation efficiency, so that some small particles of sodium sulfide remain in the oil after separation. At the same time, this hydrocyclone separator cannot simultaneously separate the oil from sodium sulfide and heavy metals.

[0008] (3) The washing and phase change drying processes are inefficient and costly. Sodium sulfide particles obtained from the liquid-solid separation process need to be washed with organic solvents to remove residual liquid hydrocarbons on the surface and then dried before entering the electrolytic cell for electrolysis. The particle washing process requires a large amount of organic liquid, and the phase change drying technology used in the drying process also causes high energy consumption of the overall process. For example, CN109890944A discloses a method for separating alkali metal salt particles from liquid hydrocarbons. In this process, the washing process of Na2S particles requires a large amount of organic liquid, and the drying process of Na2S particles and the recovery of organic liquid require high-temperature reaction conditions, which causes waste of resources and energy and is not suitable for large-scale industrial production. Summary of the Invention

[0009] To address the problems of high desulfurization cost in existing hydrodesulfurization processes and low reaction efficiency, low efficiency in cyclone separation and drying processes, and high energy consumption in conventional sodium metal desulfurization processes, this invention provides an alkali metal desulfurization system and method for marine fuel oil. This invention combines a cyclone self-rotation enhanced process with an alkali metal desulfurization process, which not only efficiently completes the mixing of reactants, the separation and drying of alkali metal sulfide particles, but also improves oil quality. Simultaneously, it achieves the recycling of alkali metals, drying gas, and electrolyte, reducing resource and energy consumption and lowering the overall process cost.

[0010] The first aspect of this invention provides a marine fuel oil alkali metal desulfurization system, comprising:

[0011] The alkali metal desulfurization reaction unit includes a mixer and a reactor, which are used for mixing and desulfurization reactions of marine fuel oil, alkali metals and hydrogen, respectively.

[0012] The liquid-solid separation unit includes a cyclone magnetic separator, which separates the reaction products into liquid and solid by the action of centrifugal force and magnetic force in the cyclone magnetic separator, to obtain desulfurized marine fuel oil, alkali metal sulfide particles, and heavy metal particles.

[0013] The product purification unit is used to remove residual alkali metals and alkali metal sulfide microcrystals from desulfurized marine fuel oil, thereby purifying the oil.

[0014] Alkali metal sulfide particle drying unit, used for drying alkali metal sulfide particles.

[0015] An alkali metal sulfide electrolysis unit is used to electrolyze alkali metal sulfide particles to obtain metallic sodium and sulfur.

[0016] Furthermore, in the alkali metal desulfurization reaction unit, a cyclone mixer is preferably used as the mixer. The cyclone mixer is a dual-inlet cyclone mixer, including a liquid phase inlet, a gas phase inlet, and an outlet. The liquid phase inlet is located at one end of the horizontal axis of the cyclone mixer, while the gas phase inlet is located at the bottom. The arrangement of the liquid and gas phase inlets ensures that the liquid and gas phase feeds enter the cyclone mixer perpendicularly. The outlet is located at the other end of the horizontal axis of the cyclone mixer. All components are connected to the cyclone mixer by welding. When marine fuel oil enters the mixer, it is separated into multiple streams with different directions of motion by hydrogen. These streams undergo high-speed rotation and revolution within the cyclone mixer, colliding and merging under centrifugal force, thus achieving thorough mixing of the marine fuel oil, alkali metal, and hydrogen.

[0017] Furthermore, in the alkali metal desulfurization reaction unit, the mixed materials enter the reactor, allowing marine fuel oil to react with molten alkali metal. The reactor can be a suspended bed reactor, a fluidized bed reactor, or a stirred reactor.

[0018] Furthermore, the system also includes an alkali metal sulfide particle maturation unit, which is used to cause the alkali metal sulfide particles in the reaction products obtained from the alkali metal desulfurization reaction unit to agglomerate and grow under the action of small particle seed crystals returned from the liquid-solid separation unit.

[0019] Furthermore, in the liquid-solid separation unit, the cyclone magnetic separator includes a column section, a conical section, and a bottom underflow pipe arranged coaxially from top to bottom. A tangential feed inlet is provided on the top side of the column section, and a first overflow outlet pipe coaxial with the column section is provided at the top of the column section. A second overflow outlet pipe with a coaxial annular gap is provided outside the first overflow outlet pipe. A central magnetic rod is provided at the central axis of the column section, the conical section, and the bottom underflow pipe. A coil is wound around the central magnetic rod, and an underflow port is provided at the lower end of the underflow pipe. The cone angle of the hydrocyclone conical section is 3°, 6°, 12°, or 16°, preferably 6°. The ratio of the hydrocyclone column height to its nominal diameter is 0.8-1.5:1. The size of the annular region between the first and second overflow outlet pipes (i.e., the difference between the radii of the first and second overflow outlet pipes) is 2% to 15% of the nominal diameter of the hydrocyclone magnetic separator column, preferably 6%-9%. The insertion depth of the first overflow outlet pipe is 50%-80% of the nominal diameter of the hydrocyclone column, and the insertion depth of the second overflow outlet pipe is 55%-70% of the insertion depth of the first overflow outlet pipe, preferably 60%-65%. Specifically, the ratio of the diameter of the first overflow outlet pipe to the diameter of the central magnetic rod is 3-6:1, the diameter of the first overflow outlet pipe is 5% to 45% of the nominal diameter of the column, preferably 20%-30%, and the diameter of the underflow pipe is 5% to 35% of the nominal diameter of the column, preferably 5%-15%. The hydraulic diameter of the inlet pipe of the cyclone magnetic separator is 12% to 25% of the nominal diameter of the column section. A baffle and ash hopper are also installed at the bottom of the cyclone magnetic separator to collect heavy metals that fall off after being adsorbed by the magnetic rod. Using a cyclone magnetic separator, the high-speed self-rotation of alkali metal sulfide particles enhances the centrifugal force and increases particle collision and coagulation, reducing the probability of particles escaping from the overflow port and improving separation efficiency. The internal central electromagnetic rod structure can occupy the air column position, making the internal flow field of the cyclone separator more stable and improving particle separation efficiency. The separation and recovery of heavy metal particles can be achieved by controlling the intensity of the electromagnetic field and the ash hopper. Preferably, the magnetic field strength is controlled in the range of 50-80 μT, more preferably 60-70 μT.

[0020] Furthermore, in the alkali metal sulfide particle drying unit, an axial flow cyclone dryer is preferably used. Further, the axial flow cyclone dryer includes a shell, inlet I, inlet II, solid outlet, and bottom outlet. A cyclone chamber is arranged penetrating the shell from top to bottom. The cyclone chamber consists of a first-stage cyclone chamber, a second-stage cyclone chamber, and a third-stage cyclone chamber arranged sequentially from top to bottom. The three-stage cyclone chamber is a sleeve structure coaxial with the shell, with helical blades at the axial inlet. The helical blades guide the flow to form a cyclone. The height of the first-stage cyclone chamber is 50%-80% of the diameter of the dryer shell, the height of the second-stage cyclone chamber is 70%-110% of the height of the first-stage cyclone chamber, and the height of the third-stage cyclone chamber is 70%-90% of the height of the second-stage cyclone chamber. The diameter of the first-stage cyclone chamber is 15%-30% of the dryer shell diameter, the diameter of the second-stage cyclone chamber is 102%-108% of the first-stage cyclone chamber diameter, and the diameter of the third-stage cyclone chamber is 90%-98% of the first-stage cyclone chamber diameter. An axial-flow cyclone dryer is used, with an axial inlet at the top. Alkali metal sulfide particles enter the axial-flow cyclone dryer through the axial inlet and mix with hydrogen. The mixture is guided by helical blades to form a cyclone. The hydrogen-generated gas-phase cyclone field drives the high-speed rotation and revolution of the alkali metal sulfide particles, inducing micro-interface oscillations. Liquid hydrocarbons on the surface and within the pores of the alkali metal sulfide particles are removed due to strong centrifugal force, thus drying the alkali metal sulfide particles, which are then discharged from the bottom solid outlet. The oil-gas mixture obtained at the bottom outlet enters a gas-liquid separator for gas-liquid separation. The separated hydrogen can be returned to the cyclone dryer to continue drying the alkali metal sulfide particles, while the oil can be returned to the stirred reactor as feedstock for further desulfurization.

[0021] Furthermore, the alkali metal sulfide electrolysis unit, used to electrolyze alkali metal sulfide particles to obtain metallic sodium and sulfur, can be implemented using conventional equipment and methods.

[0022] A second aspect of the present invention provides a method for alkali metal desulfurization of marine fuel oil, employing the above-mentioned system, the method comprising the following steps:

[0023] (A) In the presence of hydrogen, sulfur-containing marine fuel oil reacts with molten alkali metal to obtain the product;

[0024] Preferably, (B) seed crystals are added to the product obtained in step (A) to cause the alkali metal sulfide particles in the product to aggregate and grow.

[0025] (C) A cyclone magnetic separator is used to separate the product obtained in step (A) or the material obtained in step (B) into liquid and solid by the action of centrifugal force and magnetic force in the cyclone magnetic separator, so as to obtain desulfurized marine fuel oil, alkali metal sulfide particles and heavy metal particles.

[0026] (D) Add salt-forming substances to the desulfurized marine fuel oil obtained in step (C) to remove residual alkali metals and alkali metal sulfide microcrystals from the oil to obtain marine fuel oil product.

[0027] (E) Dry the alkali metal sulfide particles obtained in step (C);

[0028] (F) The dried alkali metal sulfide particles from step (E) are electrolyzed to obtain alkali metals and sulfur.

[0029] Furthermore, the alkali metal is selected from at least one of lithium, sodium, potassium, etc., preferably sodium.

[0030] Further, step (A) is an alkali metal reaction desulfurization step, which specifically includes: passing marine fuel oil, alkali metal, and hydrogen into a cyclone mixer for cyclone mixing, and then passing the mixture into a stirred reactor to allow the organic sulfides in the molten alkali metal marine fuel oil to react and form alkali metal sulfide particles, while heavy metal ions are reduced to heavy metal particles in a hydrogen environment.

[0031] Further, step (B) is the aging and growth step of alkali metal sulfide particles, which specifically includes: the product of step (A) is fed into an aging reactor, and then seed crystals are added to it to cause the alkali metal sulfide particles in the product to continuously aggregate and grow.

[0032] Further, step (C) is a liquid-solid separation step, which specifically includes: passing the material obtained in step (B) into a cyclone magnetic separator, and using the centrifugal force and magnetic force in the cyclone magnetic separator to separate desulfurized marine fuel oil from alkali metal sulfide particles and heavy metal particles.

[0033] Further, step (D) is a product oil purification step, which specifically includes: adding salt-forming substances to desulfurized marine fuel oil to remove residual alkali metals and alkali metal sulfide microcrystals from the oil, thereby purifying the oil and obtaining marine fuel oil product.

[0034] Further, step (E) is a drying step for alkali metal sulfide particles, specifically including: using an axial flow cyclone dryer to remove residual desulfurized liquid hydrocarbons on the Na2S particles, thereby achieving the drying of the Na2S particles.

[0035] Further, step (F) is an alkali metal sulfide electrolysis step, which specifically includes: after the dried alkali metal sulfide particles enter the electrolytic cell for electrolysis, alkali metal and sulfur are obtained. The alkali metal can be recycled to the alkali metal desulfurization unit for continued use in the desulfurization of fuel oil, thereby realizing the recycling of the desulfurizing agent.

[0036] Further, in step (A), the sulfur content in the marine fuel oil is 0.04%-4.5% by mass, for example 0.04%, 0.1%, 0.5%, 1.2%, 2.4%, 3.5%, 4.0%, 4.5%, preferably 0.5-4.5%. The heavy metals in the marine fuel oil mainly include nickel and vanadium. The heavy metal content in the marine fuel oil, calculated as nickel and vanadium, is 100-300 wppm.

[0037] Further, in step (A), the molar ratio of the amount of alkali metal added to the sulfur content in marine fuel oil, expressed as sulfur, is 0.5-3.5, for example, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, preferably 0.6-2.2.

[0038] Further, in step (A), the swirl mixing time is 20-120 min, preferably 40-90 min.

[0039] Further, in step (A), the amount of hydrogen used is 1-3 moles of hydrogen per mole of sulfur.

[0040] Further, in step (A), the reactor is a suspended bed reactor, a fluidized bed reactor, or a stirred reactor.

[0041] Further, in step (A), the reaction temperature is 150-450°C, for example 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, preferably 200-350°C.

[0042] Further, in step (A), the reaction pressure is 0.4-4 MPa, for example 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, preferably 1.5 MPa-3 MPa.

[0043] Furthermore, in step (A), when a stirred reactor is used, the reaction time is 1-20 min.

[0044] Further, in step (B), the seed crystal is an alkali metal sulfide with a median particle size of 0.8 μm-40 μm. Preferably, the seed crystal is obtained by separating fine particles of alkali metal sulfide from an oil solution using a cyclone magnetic separator, with a fine particle concentration of 2000-6500 mg / L. The ratio of the amount of seed crystal returned to the mass of alkali metal sulfide in the product obtained in step (A) is 1:5-1:8.

[0045] Further, in step (B), the ripening time after adding the seed crystal is 15-120 min, for example 15 min, 30 min, 45 min, 60 min, 75 min, 90 min, 105 min, 120 min, preferably 60-120 min.

[0046] Further, in step (B), the particle size of the alkali metal sulfide particles after seed agglomeration and growth is in the range of 10-200 μm, wherein the concentration of particles with a particle size of less than 50 μm is 10000-50000 mg / L.

[0047] Furthermore, the product obtained in step (A) or the alkali metal sulfide particles obtained in step (B) need to be cooled to below 200°C before being passed into a cyclone magnetic separator for liquid-solid separation.

[0048] Furthermore, in step (C), during the cyclone magnetic separation process, the heavy medium alkali metal sulfide particles move downward in an outward spiral motion along the outer wall of the hydrocyclone due to the centrifugal force generated by their high-speed rotation, while the light medium marine fuel oil moves upward in an inward spiral motion along the central axis of the hydrocyclone, thereby achieving liquid-solid separation. In addition, by controlling the internal electromagnetic field, magnetic heavy metals such as nickel are adsorbed onto the electromagnetic rod. Finally, after the current is turned off, the magnetic field disappears, thereby achieving the separation of heavy metal particles.

[0049] Further, in step (C), the separation process temperature is 20-130°C, for example 20°C, 30°C, 50°C, 70°C, 90°C, 110°C, 130°C, preferably 60-120°C.

[0050] Further, in step (C), the separation process pressure is 0.3-3 MPa, for example 0.3 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, preferably 0.5 MPa-2 MPa.

[0051] Furthermore, in step (C), after the cyclone magnetic separation, the liquid-solid separation efficiency is greater than 93%, and the heavy metal content is reduced to below 10 wppm.

[0052] Further, in step (D), the salt-forming substance is hydrogen sulfide, and the amount of salt-forming substance added is 2-6 times, for example, 2 times, 3 times, 4 times, 5 times, or 6 times the residual alkali metal sodium in marine fuel oil, preferably 2-4 times.

[0053] Further, in step (D), the reaction process temperature is 20-130℃, preferably 60-120℃, the reaction process pressure is 0.2-2MPa, preferably 0.3MPa-1MPa, and the reaction time is 1-20min.

[0054] Furthermore, in step (E), the cyclone drying process uses low-temperature drying technology to dry the alkali metal sulfide particles, with an operating temperature of 20-80℃, such as 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, preferably 30-70℃.

[0055] Further, in step (E), the operating pressure of the cyclone drying process is 0.1-2 MPa, for example 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.9 MPa, 1.5 MPa, 1.7 MPa, 2 MPa, preferably 0.3 MPa-1.5 MPa.

[0056] Furthermore, in step (E), during the cyclone drying process, the rotation speed of the alkali metal sulfide particles is 15,000-60,000 rpm, and the drying time is less than 10 seconds, preferably 1-10 seconds.

[0057] Furthermore, in step (E), hydrogen is introduced to provide a continuous gas-phase field and form a cycle, and the hydrogen is not consumed during the separation process. Moreover, since hydrogen has a very low density, a higher gas-liquid / gas-solid density difference can be obtained, which is beneficial for the separation of alkali metal sulfides.

[0058] Further, in step (F), the electrolysis of the alkali metal sulfide particles can be carried out using conventional methods. The electrolytic cell used has an alkali ion conductive membrane configured to selectively transport alkali ions, which separates the anolyte chamber containing the anode from the catholyte chamber containing the cathode. The electrolysis unit is equipped with a polar solvent tank, which can effectively dissolve the alkali metal sulfides generated in the reaction. The polar solvent includes at least one of the following: N,N-dimethylaniline, quinoline, 2-methyltetrahydrofuran, benzene, tetrahydrofuran, cyclohexanefluorobenzene, trifluorobenzene, toluene, xylene, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, isopropanol, ethylpropionaldehyde, dimethyl carbonate, dimethoxy ether, dimethyl propylene urea, ethanol, ethyl acetate, propylene carbonate, ethylene carbonate, diethyl carbonate, and diethyl carbonate. The alkali metal sulfide obtained in step (E) is mixed with the polar solvent to form an anolyte solution, and the anolyte solution is introduced into the anolyte chamber. The catholyte solution is introduced into the catholyte chamber. The catholy solution comprises alkali metal ions and a catholy solvent. The catholy solvent may include at least one of a variety of non-aqueous solvents, selected from at least one of tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl carbonate, dimethoxy ether, propylene carbonate, ethylene carbonate, and diethyl carbonate. An electric current is applied to the oxidizing sulfides and / or polysulfides in the anolyte chamber of the electrolysis unit to form higher valence polysulfides and oxidize the higher valence polysulfides to elemental sulfur. The current further causes alkali metal ions to pass through an alkali metal conductive membrane from the anolyte chamber to the catholyte chamber, and reduces the alkali metal ions in the catholyte chamber to form elemental alkali metal. The resulting alkali metal can be recycled for step (A) of the method of the present invention.

[0059] Furthermore, in step (F), after the alkali metal sulfide particles are electrolyzed, the resulting sulfur particles containing electrolyte are fed into an axial-flow cyclone dryer to separate the electrolyte from the sulfur. Hydrogen is introduced to provide a continuous gas-phase field and form a cycle; the hydrogen is not consumed during the separation process. The resulting electrolyte can be reused for the electrolysis of alkali metal sulfide particles, with an electrolyte recovery rate exceeding 95%.

[0060] Compared with the prior art, the main advantages of the method and system of the present invention are:

[0061] 1. This invention utilizes cyclone mixing, cyclone magnetic separation, and cyclone non-phase change drying technologies to treat sulfur-containing marine fuel oil, alkali metal sulfide particles, heavy metal particles, and other substances. This improves the reaction efficiency of the raw materials, the separation efficiency of sodium sulfide particles in the oil, and reduces the energy consumption of the particle drying process, achieving the recycling of alkali metals, carrier gas (H2), and electrolyte. The alkali metal desulfurization process optimized using cyclone self-rotation technology yields a high-quality, low-sulfur marine fuel oil with a sulfur content of less than 0.1% and a viscosity of 1 / 100-1 / 1000 that of the feedstock oil.

[0062] 2. Existing filtration or centrifugal separation technologies achieve a separation efficiency of approximately 70% when separating high-concentration alkali metal sulfide particles from oil products. The resulting oil contains sulfur content far exceeding 0.1%, failing to meet the sulfur content standards for marine fuel oil. This invention utilizes a cyclone self-rotation enhanced technology that leverages the density differences between alkali metal sulfide particles, heavy metal particles, and the oil product, as well as the centrifugal force generated by particle rotation, for liquid-solid separation. Electromagnetic fields are used to regulate the separation process of heavy metal particles, and a solid rod structure eliminates the adverse effects of air columns on the separation process. This technology achieves a separation efficiency of over 99% for alkali metal sulfide particles, reducing the heavy metal content in the oil product to below 10 wppm.

[0063] 3. The desulfurization method of this invention has lower reaction temperature, pressure, and hydrogen consumption than conventional hydrodesulfurization reactions, effectively reducing operating costs. Its overall process cost is 1 / 5 to 1 / 3 of that of conventional hydrodesulfurization, making it a green, efficient, and continuous desulfurization method. This desulfurization method saves resources, protects the environment, and aligns with the sustainable development strategy of "low-carbon, environmentally friendly, efficient, and energy-saving." Furthermore, the construction and operation management costs of this process are low, resulting in high economic benefits, making it suitable for industrial production.

[0064] 4. In the desulfurization method of this invention, cyclone drying technology, as a non-phase change drying technology, significantly reduces drying energy consumption compared to conventional phase change drying technologies such as hot air drying and superheated steam drying, since it does not require overcoming the latent heat of vaporization. Its drying energy consumption is 1 / 10 to 1 / 5 of that of conventional phase change drying technologies. Furthermore, because the axial flow cyclone dryer is equipped with multi-stage cyclone chambers, residual hydrogen and electrolyte ejected from the bottom of the secondary cyclone chamber can be drawn back into the secondary cyclone chamber under negative pressure. This results in less hydrogen and electrolyte contained in the solid particles exiting the bottom of the dryer, maximizing the recycling of hydrogen and electrolyte and facilitating subsequent electrolysis processes.

[0065] 5. Compared to traditional hydrocyclones, the cyclone magnetic separator used in this invention features a second overflow outlet in an annular gap coaxial with the overflow pipe. This allows for the classification of coarse and fine sodium sulfide particles, enabling the return and reuse of small, hard-to-separate fine crystal particles. Simultaneously, the fine crystal particles drawn out by the annular gap structure are returned to the alkali metal sulfide crystal ripening unit for further ripening and growth, adding seed crystals to the crystallization reactor. The seed crystals serve two purposes: first, providing a growth site for the solute; and second, acting as an adsorbent to some extent. According to adsorption theory, the adsorption capacity is directly related to the surface area of ​​the seed crystals. Therefore, for a given supersaturation level, there is a critical value for the amount of seed crystals added. Only a sufficient amount of seed crystals can effectively adsorb nucleation components, providing enough growth sites for the supersaturated solute, reducing the supersaturation of the solution phase, especially the solid-liquid interface, to below the critical supersaturation level for spontaneous nucleation, thus preventing explosive nucleation. The returned fine-particle alkali metal sulfide crystals can replace the seed material and sulfur supplement in the aging reactor, promoting crystal growth, improving solid-liquid separation efficiency, increasing sodium recovery rate, and achieving efficient utilization of sodium. Attached Figure Description

[0066] Figure 1 This is a schematic flow diagram of a preferred embodiment of the sodium desulfurization process for marine fuel oil according to the present invention.

[0067] The following are explanations of the reference numerals in the attached drawings: 1-Swirl mixer, 2-Stirred reactor, 3-Cooking reactor, 4-Swirl magnetic separator, 5-Liquid-solid cyclone separator, 6-Liquid-liquid cyclone separator, 7-Screw feeder, 8-Axial flow cyclone dryer, 9-Gas-liquid separator, 10-Gas compressor, 11-Polar solvent tank, 12-Liquid-solid mixer, 13-Electrolytic cell, 14-Axial flow cyclone dryer, 15-Gas-liquid separator;

[0068] Figure 2 This is a schematic diagram of a cyclone mixer according to a preferred embodiment of the present invention;

[0069] The reference numerals in the attached diagram are explained as follows: 21 - Gas phase inlet; 22 - Liquid phase inlet; 23 - Underflow outlet;

[0070] Figure 3 This is a schematic diagram of a traditional cyclone separator.

[0071] The reference numerals in the attached diagram are explained as follows: 31-Overflow port; 32-Inlet; 33-Column section; 34-Underflow pipe;

[0072] Figure 4 This is a schematic diagram of a cyclone magnetic separator according to a preferred embodiment of the present invention;

[0073] The reference numerals in the attached drawings are explained as follows: 41-First overflow outlet pipe; 42-Second overflow outlet pipe; 43-Annular gap; 44-Central magnetic rod; 45-Coil; 46-Underflow pipe; 47-Baffle plate; 48-Ash hopper; 49-Inlet.

[0074] Figure 5 This is a schematic diagram of an axial-flow cyclone dryer according to a preferred embodiment of the present invention;

[0075] The reference numerals in the attached drawings are explained as follows: 52-first stage swirling chamber; 51-spiral blade; 53-shell; 54-second stage swirling chamber; 55-third stage swirling chamber; 56-solid discharge port; 57-feed inlet II; 58-feed inlet I; 59-bottom outlet. Detailed Implementation

[0076] The following detailed description of the alkali metal desulfurization method for marine fuel oil, in conjunction with specific embodiments and accompanying drawings, further illustrates the present invention. The embodiments and accompanying drawings are provided to further understand the present invention and constitute only a part of this specification to further explain the present invention, and do not constitute a limitation on the scope of protection of the present invention.

[0077] The present invention provides a schematic flow diagram of an alkali metal desulfurization method for marine fuel oil, as shown below. Figure 1 As shown, it includes:

[0078] (A) Sulfur-containing marine fuel oil, molten alkali metal, and hydrogen are premixed in cyclone mixer 1. The mixed reactants are then fed into stirred reactor 2 for alkali metal desulfurization reaction to obtain the product.

[0079] (B) The product obtained in step (A) enters the maturation reactor 3, where it is grown by returning small seed crystals.

[0080] (C) The material obtained in step (B) enters the hydrocyclone magnetic separator 4 for liquid-solid separation. The deeply purified oil discharged from the overflow outlet goes to the finished oil purification unit to remove unreacted alkali metals. The fine-particle alkali metal sulfide crystals discharged from the second overflow outlet of the hydrocyclone annulus are returned to the maturation reactor for recrystallization and growth. The coarse-particle alkali metal sulfide crystals discharged from the underflow outlet of the liquid-solid hydrocyclone go to the alkali metal sulfide washing unit. At the same time, by controlling the intensity of the electromagnetic field, the heavy metal particles adsorbed on the magnetic rod fall onto the ash hopper, realizing the separation and recovery of heavy metal particles. The alkali metal sulfide microcrystals obtained at the separation overflow outlet can be returned to the maturation reactor 3 for use as seed crystals.

[0081] (D) The light component marine fuel oil obtained in step (C) is mixed with salt-forming substances and then fed into a liquid-solid hydrocyclone 5 for separation. The heavy component alkali metal salt obtained after separation is discharged from the bottom underflow port of the liquid-solid hydrocyclone 5. The light component salt-forming substances and product oil obtained after separation are discharged from the top overflow port of the liquid-solid hydrocyclone 5 and then enter the liquid-liquid hydrocyclone 6 for separation. The heavy component salt-forming substances obtained after separation are discharged from the bottom underflow port and recycled. The light component marine fuel oil obtained after separation is discharged from the top overflow port of the liquid-liquid hydrocyclone 6 to obtain marine fuel oil product.

[0082] (E) The heavy alkali metal sulfide particles obtained in step (C) are discharged from the bottom underflow port of the cyclone magnetic separator 4 and enter the axial flow cyclone dryer 8 through the screw feeder 7. At the same time, hydrogen enters the axial flow cyclone dryer 8 and then alkali metal sulfide particles are dried. The light component oil-gas mixture obtained from drying is discharged from the top overflow port of the axial flow cyclone dryer 8 and enters the gas-liquid separator 9. The separated gas is circulated by the gas compressor 10 for particle drying, and the separated liquid is returned to the cyclone mixing tank 1 for further reaction. The heavy component Na2S particles obtained from drying are discharged from the bottom underflow port of the axial flow cyclone dryer 8.

[0083] (F) The heavy alkali metal sulfide particles obtained from step (E) drying are mixed with the electrolyte in the liquid-solid mixing tank 12 and then enter the electrolytic cell 13 for electrolysis of the alkali metal sulfide particles. The obtained Na is recycled to the hydrocyclone mixer as a raw material for the alkali metal desulfurization reaction. The obtained electrolyte and sulfur enter the hydrocyclone dryer 14 for drying. The light component electrolyte and residual hydrogen obtained from drying are discharged from the bottom overflow port of the hydrocyclone dryer 14 and then enter the gas-liquid separator 15. The separated hydrogen is recycled through the gas compressor for particle drying. The separated polar solvent is returned to the polar solvent tank 11. The separated heavy component sulfur is processed to obtain product sulfur.

[0084] In this invention, the cyclone mixer (see...) Figure 2The system includes a gas phase inlet 21, a liquid phase inlet 22, and an underflow outlet 23. The gas phase inlet 21 is a tangential inlet, while the liquid phase inlet 22 and the underflow outlet 23 are axially coaxial inlets / outlets. The specific operation process is as follows: sulfur-containing marine fuel oil and molten alkali metal enter the cyclone mixer from the liquid phase inlet 22, and hydrogen enters the cyclone mixer from the gas phase inlet 21. After being mixed evenly by cyclone mixing, they enter the stirred reactor together.

[0085] In this invention, the traditional cyclone separator (see...) Figure 3 The system includes an overflow port 31, an inlet 32, a column section 33, a conical section, and an underflow pipe 34. Inlet 32 ​​is a tangential inlet connected to column section 33, and overflow port 31 and underflow port 34 are axial coaxial outlets. The specific operation process is as follows: The light component marine fuel oil obtained from the liquid-solid separation unit is discharged from the top overflow port of the hydrocyclone magnetic separator 4 and mixed with salt-forming substances before being sent to a conventional hydrocyclone separator for separation. The heavy component alkali metal salt obtained from the separation is discharged from the bottom underflow port 34 of the conventional hydrocyclone separator. The light component salt-forming substances and product oil obtained after separation are discharged from the top overflow port of the conventional hydrocyclone separator and then enter the conventional hydrocyclone separator for liquid-liquid separation. The heavy component salt-forming substances obtained after separation are discharged from the bottom underflow port and continue to be used to react with the light components obtained from the hydrocyclone magnetic separator 4. The light component marine fuel oil obtained from the reaction is discharged from the top overflow port of the conventional hydrocyclone separator 6 to obtain product oil.

[0086] In this invention, the cyclone magnetic separator (see...) Figure 4 The device includes a column section, a conical section, and a bottom underflow pipe arranged coaxially from top to bottom. A tangential feed inlet 49 is provided on the top side of the column section. A first overflow outlet pipe 41, coaxial with the column section, is provided on the top of the column section. A second overflow outlet pipe 42, coaxial with an annular gap 43, is provided on the outside of the first overflow outlet pipe 41. A central magnetic rod 44 is provided at the central axis of the column section, the conical section, and the bottom underflow pipe. A coil 45 is wound around the central magnetic rod. A bottom flow port is provided at the lower end of the underflow pipe 46. A baffle plate 47 and an ash hopper 48 are located below the bottom flow port. The specific operation process is as follows: The material enters the cyclone magnetic separator 4 through the feed inlet 49 for liquid-solid separation and undergoes centrifugal motion within the cyclone field. The deeply purified oil discharged from the first overflow outlet pipe 41 goes to the finished oil purification unit to remove unreacted alkali metals. When the fluid moves to the bottom of the annular structure 43, a portion of the oil containing fine alkali metal sulfide particles is drawn out from the annular outlet through the annular flow channel 43 formed by the first overflow outlet pipe 41 and the second overflow outlet pipe 42, and returned to the maturation reactor for recrystallization and growth. The coarse alkali metal sulfide crystals discharged from the bottom outlet of the liquid-solid cyclone go to the alkali metal sulfide washing unit. At the same time, by controlling the intensity of the electromagnetic field, the heavy metal particles adsorbed on the central magnetic rod 44 fall onto the baffle plate 47 and are collected by the ash hopper 48, realizing the separation and recovery of heavy metal particles.

[0087] In this invention, the axial flow cyclone dryer (see...) Figure 5 The device includes a shell, inlet I 58, inlet II 57, and solid outlet 56. A swirling cavity is provided through the shell 53 from top to bottom. The swirling cavity is provided in three stages from top to bottom: a first-stage swirling cavity 52, a second-stage swirling cavity 54, and a third-stage swirling cavity 55. The three-stage swirling cavity is a sleeve structure coaxial with the shell. A helical blade 51 is provided at the axial inlet of the first-stage swirling cavity 52. ​​The function of the helical blade 51 is to guide the flow so that the feed forms a swirling flow. The specific operation process is as follows: The heavy alkali metal sulfide particles separated by the liquid-solid separation unit are discharged from the bottom outlet of the cyclone magnetic separator 4 and then enter the axial flow cyclone dryer 8 through the screw feeder via the feed port I 58. After mixing with the hydrogen entering through the feed port II 57, they enter the first-stage cyclone chamber 52, the second-stage cyclone chamber 54, and the third-stage cyclone chamber 55 in sequence. The hydrogen forms a gas phase system cyclone field to drive the alkali metal sulfide particles to rotate and revolve at high speed, inducing the micro-interface oscillation of the particles. The liquid hydrocarbons on the particle surface and in the pores are removed due to the strong centrifugal force. The dried particles enter the dryer cavity, i.e., the cavity between the shell 53 and the cyclone chamber, and are led out from the solid discharge port 56 at the bottom of the axial flow cyclone dryer 8 and enter the subsequent electrolysis unit. The residual hydrogen gas ejected from the second-stage cyclone chamber 54, along with the oil phase, enters the chamber 54 again. Under the negative pressure within the chamber, it is drawn back into the gap between the top of the second-stage cyclone chamber 54 and the bottom of the first-stage cyclone chamber 51, achieving the reflux and utilization of the oil and gas phases and increasing the solids content of the discharge from the solid outlet 56. The oil-gas mixture obtained from the bottom outlet enters the gas-liquid separator 9 through the bottom outlet 59 for gas-liquid separation. The separated hydrogen gas is recycled through the gas compressor 10 for particle drying and returned to the cyclone dryer 8 for further drying of alkali metal sulfide particles. The oil can be returned to the cyclone mixer 1 as raw material for further desulfurization reaction.

[0088] The test methods in the following examples, where specific conditions are not specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0089] The cyclone magnetic separator used in this embodiment of the invention is specifically as follows: The cyclone magnetic separator includes a column section, a conical section, and a bottom underflow pipe arranged coaxially from top to bottom. A tangential feed inlet is provided on the top side of the column section. A first overflow outlet pipe, coaxial with the column section, is provided at the top of the column section. A second overflow outlet pipe, coaxial with an annular gap, is provided outside the first overflow outlet pipe. A central magnetic rod is provided at the central axis of the column section, the conical section, and the bottom underflow pipe, and a coil is wound around the central magnetic rod. A bottom flow port is provided at the lower end of the underflow pipe. The nominal diameter of the cyclone separator is 25 mm, the cone angle of the conical section is 6°, the ratio of the column section height to the nominal diameter of the column section is 1.2:1, the diameter of the first overflow outlet pipe is 24% of the nominal diameter of the column section, and the diameter of the underflow pipe is 8% of the nominal diameter of the column section. The hydraulic diameter of the inlet pipe of the cyclone magnetic separator is 19% of the nominal diameter of the column section. The ratio of the annular region size between the first and second overflow outlet pipes (i.e., the difference in radii between the first and second overflow outlet pipes) to the nominal diameter of the cyclone separator column is shown in Table 2. The insertion depth of the first overflow outlet pipe is 70% of the nominal diameter of the cyclone separator column, and the insertion depth of the second overflow outlet pipe is 62% of the insertion depth of the first overflow outlet pipe. The ratio of the diameter of the first overflow outlet pipe to the diameter of the central magnetic rod is 5:1. The control magnetic field strength is 65 μT.

[0090] The conventional cyclone separator used in the comparative examples of this invention (such as...) Figure 3 Specifically, the hydrocyclone separator comprises a column section, a conical section, and a bottom underflow pipe arranged coaxially from top to bottom. A tangential feed inlet is located on the top side of the column section, and an overflow outlet pipe coaxial with the column section is located at the top of the column section. The nominal diameter of the hydrocyclone is 25 mm, the diameter of the overflow outlet pipe is 24% of the nominal diameter of the column section, and the diameter of the underflow pipe is 8% of the nominal diameter of the column section. The hydraulic diameter of the inlet pipe of the hydrocyclone magnetic separator is 19% of the nominal diameter of the column section. The cone angle of the conical section of the hydrocyclone is 6°, the ratio of the height of the hydrocyclone column section to its nominal diameter is 1.2:1, and the insertion depth of the overflow outlet pipe is 70% of the nominal diameter of the hydrocyclone column section.

[0091] The axial-flow cyclone dryer used in this embodiment of the invention is as follows: The axial-flow cyclone dryer includes a shell, inlet I, inlet II, solid outlet, and bottom outlet. A cyclone cavity is provided penetrating the shell from top to bottom. The cyclone cavity consists of a first-stage cyclone cavity, a second-stage cyclone cavity, and a third-stage cyclone cavity arranged sequentially from top to bottom. The three-stage cyclone cavity is a sleeve structure coaxial with the shell, with helical blades at the axial inlet. The dryer shell diameter is 50 mm, and the ratio of the dryer height to the shell diameter is 3.2:1. The ratio of the first-stage cyclone cavity diameter to the dryer shell diameter is shown in Table 2. The second-stage cyclone cavity diameter is 104% of the first-stage cyclone cavity diameter, and the third-stage cyclone cavity diameter is 86% of the first-stage cyclone cavity diameter. The height ratio of the three-stage cyclone cavities is 1.8:1.4:1.

[0092] In the embodiments and comparative examples of this invention, the alkali metal is sodium, and the seed crystal is sodium sulfide.

[0093] Example 1

[0094] Marine fuel oil 1 was used as the feedstock, and its properties are shown in Table 1. [The text abruptly ends here, likely due to an incomplete sentence or missing information.] Figure 1 The process is as follows. Operating conditions are shown in Table 2. The properties of the desulfurized marine fuel products are shown in Table 3. The raw material processing capacity is 10m³. 3 / h.

[0095] Example 2

[0096] Marine fuel oil 2 was used as the feedstock, and its properties are shown in Table 1. [The text abruptly ends here, likely due to an incomplete sentence or missing information.] Figure 1 The process is as follows. Operating conditions are shown in Table 2. The properties of the desulfurized marine fuel products are shown in Table 3. The raw material processing capacity is 10m³. 3 / h.

[0097] Example 3

[0098] Marine fuel oil 3 was used as the feedstock, and its properties are shown in Table 1. [The text abruptly ends here, likely due to an incomplete sentence or missing information.] Figure 1 The process is as follows. Operating conditions are shown in Table 2. The properties of the desulfurized marine fuel products are shown in Table 3. The raw material processing capacity is 10m³. 3 / h.

[0099] Example 4

[0100] Marine fuel oil 3 was used as the feedstock, and its properties are shown in Table 1. [The text abruptly ends here, likely due to an incomplete sentence or missing information.] Figure 1 The process is as follows. Operating conditions are shown in Table 2. The properties of the desulfurized marine fuel products are shown in Table 3. The raw material processing capacity is 10m³. 3 / h.

[0101] Comparative Example 1

[0102] The marine fuel oil is the same as in Example 1.

[0103] Compared with Example 1, the difference is that: the following is used... Figure 3 The conventional hydrocyclone separator is used instead of the hydrocyclone magnetic separator of the present invention for liquid-solid separation, and the separated alkali metal sulfide particles are dried using a hot air dryer.

[0104] The properties of desulfurized marine fuel products are shown in Table 3.

[0105] Comparative Example 2

[0106] The marine fuel oil is the same as in Example 2.

[0107] Compared with Example 2, the difference is that: the following is used... Figure 3The conventional hydrocyclone separator is used instead of the hydrocyclone magnetic separator of the present invention for liquid-solid separation, and the separated alkali metal sulfide particles are dried using a hot air dryer.

[0108] The properties of desulfurized marine fuel products are shown in Table 3.

[0109] Table 1 Properties of Marine Fuel Oil

[0110] Marine fuel oil 1 Marine fuel oil 2 Marine fuel oil 3 API level 10.5 11.0 11.5 <![CDATA[Density at 20°C, kg / m 3 > 990.6 992.0 996.0 Residual carbon, wt% 8.0 8.5 9.4 Sulfur content, wt% 1.77 2.3 3.7 Heavy metal content, wppm 190 195 246 Na, wppm 45 48 52 Viscosity at 50℃, cst 24122 24250 27546

[0111] Table 2 Operating conditions for each embodiment and comparative example

[0112]

[0113]

[0114] Table 3 Properties of marine fuel oil products obtained from each embodiment and comparative example

[0115]

[0116]

[0117] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A marine fuel oil alkali metal desulfurization system, comprising: The alkali metal desulfurization reaction unit includes a mixer and a reactor, which are used for mixing and desulfurization reactions of marine fuel oil, alkali metals and hydrogen, respectively. The liquid-solid separation unit includes a cyclone magnetic separator, which separates the reaction products into liquid and solid by the action of centrifugal force and magnetic force in the cyclone magnetic separator, to obtain desulfurized marine fuel oil, alkali metal sulfide particles, and heavy metal particles. The product purification unit is used to remove residual alkali metals and alkali metal sulfide microcrystals from desulfurized marine fuel oil, thereby purifying the oil. Alkali metal sulfide particle drying unit, used for drying alkali metal sulfide particles. An alkali metal sulfide electrolysis unit is used to electrolyze alkali metal sulfide particles to obtain metallic sodium and sulfur.

2. The system according to claim 1, characterized in that, The system also includes an alkali metal sulfide particle maturation unit, which is used to cause the alkali metal sulfide particles in the reaction products obtained from the alkali metal desulfurization reaction unit to agglomerate and grow under the action of small particle seed crystals returned from the liquid-solid separation unit.

3. The system according to claim 1 or 2, characterized in that, In the alkali metal desulfurization reaction unit, the mixer is a cyclone mixer; the cyclone mixer is a dual-inlet cyclone mixer, including a liquid phase inlet, a gas phase inlet, and an outlet. The liquid phase inlet is located at one end of the horizontal axis of the cyclone mixer, the gas phase inlet is located at the bottom of the cyclone mixer, and the arrangement of the liquid phase inlet and the gas phase inlet allows the liquid phase feed and the gas phase feed to enter the cyclone mixer in a vertical direction. The outlet is located at the other end of the horizontal axis of the cyclone mixer.

4. The system according to claim 1 or 2, characterized in that, The reactor is a suspended bed reactor, a fluidized bed reactor, or a stirred reactor.

5. The system according to claim 1 or 2, characterized in that, The cyclone magnetic separator includes a column section, a conical section, and a bottom underflow pipe arranged coaxially from top to bottom. A tangential feed inlet is provided on the top side of the column section. A first overflow outlet pipe coaxial with the column section is provided at the top of the column section. A second overflow outlet pipe with a coaxial annular gap is provided outside the first overflow outlet pipe. A central magnetic rod is provided at the central axis of the column section, the conical section, and the bottom underflow pipe. A coil is wound around the central magnetic rod. A bottom flow port is provided at the lower end of the underflow pipe. Preferably, the diameter of the first overflow outlet pipe is 5% to 45% of the nominal diameter of the column section, the diameter of the underflow pipe is 5% to 35% of the nominal diameter of the column section, and the hydraulic diameter of the inlet pipe of the cyclone magnetic separator is 12% to 25% of the nominal diameter of the column section. Preferably, the cone angle of the cone segment is 3°, 6°, 12°, or 16°; Preferably, the ratio of column segment height to nominal diameter is 0.8-1.5:1; Preferably, the size of the annular region between the first overflow outlet pipe and the second overflow outlet pipe is 2% to 15% of the nominal diameter of the cyclone magnetic separator column section, preferably 6% to 9%. Preferably, the insertion depth of the first overflow outlet pipe is 50%-80% of the nominal diameter of the column segment, and the insertion depth of the second overflow outlet pipe is 55%-70% of the insertion depth of the first overflow outlet pipe, preferably 60%-65%. Preferably, the ratio of the diameter of the first overflow outlet pipe to the diameter of the central magnetic rod is 3-6:1; Preferably, the magnetic field strength is controlled within the range of 50-80 μT, and more preferably 60-70 μT.

6. The system according to claim 1 or 2, characterized in that, In the alkali metal sulfide particle drying unit, an axial flow cyclone dryer is used. Further, the axial flow cyclone dryer includes a shell, inlet I, inlet II, solid outlet, and bottom outlet. A cyclone cavity is arranged through the shell from top to bottom. The cyclone cavity is arranged sequentially from top to bottom as a first-stage cyclone cavity, a second-stage cyclone cavity, and a third-stage cyclone cavity. The three-stage cyclone cavity is a sleeve structure coaxial with the shell, with helical blades at the axial inlet. The height of the first-stage cyclone cavity is 50%-80% of the dryer shell diameter, the height of the second-stage cyclone cavity is 70%-110% of the first-stage cyclone cavity height, and the height of the third-stage cyclone cavity is 70%-90% of the second-stage cyclone cavity height. The diameter of the first-stage cyclone cavity is 15%-30% of the dryer shell diameter, the diameter of the second-stage cyclone cavity is 102%-108% of the first-stage cyclone cavity diameter, and the diameter of the third-stage cyclone cavity is 90%-98% of the first-stage cyclone cavity diameter.

7. A method for desulfurizing alkali metals from marine fuel oil, characterized in that, Using the system described in any one of claims 1-6, the method comprises the following steps: (A) In the presence of hydrogen, sulfur-containing marine fuel oil reacts with molten alkali metal to obtain the product; Preferably, (B) seed crystals are added to the product obtained in step (A) to cause the alkali metal sulfide particles in the product to aggregate and grow. (C) A cyclone magnetic separator is used to separate the product obtained in step (A) or the material obtained in step (B) into liquid and solid by the action of centrifugal force and magnetic force in the cyclone magnetic separator, so as to obtain desulfurized marine fuel oil, alkali metal sulfide particles and heavy metal particles. (D) Add salt-forming substances to the desulfurized marine fuel oil obtained in step (C) to remove residual alkali metals and alkali metal sulfide microcrystals from the oil to obtain marine fuel oil product. (E) Dry the alkali metal sulfide particles obtained in step (C); (F) The dried alkali metal sulfide particles from step (E) are electrolyzed to obtain alkali metals and sulfur.

8. The method according to claim 7, characterized in that, The alkali metal is selected from at least one of lithium, sodium, and potassium, preferably sodium.

9. The method according to claim 7, characterized in that, Step (A) is the alkali metal reaction desulfurization step, which specifically includes: passing marine fuel oil, alkali metal, and hydrogen into a cyclone mixer for cyclone mixing, and then passing the mixture into a stirred reactor to allow the organic sulfides in the molten alkali metal marine fuel oil to react and form alkali metal sulfide particles. Heavy metal ions are reduced to heavy metal particles in the hydrogen environment. And / or, step (D) includes: adding salting substances to desulfurized marine fuel oil to remove residual alkali metals and alkali metal sulfide microcrystals from the oil, thereby purifying the oil and obtaining marine fuel oil product. Preferably, step (F) includes: the dried alkali metal sulfide particles are electrolyzed in an electrolytic cell to obtain alkali metal and sulfur, and the alkali metal is recycled to the alkali metal desulfurization unit for continued use in the desulfurization of fuel oil.

10. The method according to claim 7, characterized in that, In step (A), the sulfur content in the marine fuel oil is 0.04%-4.5% by mass; the heavy metals in the marine fuel oil include nickel and vanadium, and the heavy metal content in the marine fuel oil, calculated as nickel and vanadium, is 100-300 wppm; Preferably, in step (A), the molar ratio of the amount of alkali metal added to the sulfur content in marine fuel oil, expressed as sulfur, is 0.5-3.5; Preferably, in step (A), the swirl mixing time is 20-120 min, more preferably 40-90 min; Preferably, in step (A), the amount of hydrogen used is 1-3 moles of hydrogen per mole of sulfur; Preferably, in step (A), the reaction temperature is 150-450°C, more preferably 200-350°C; Preferably, in step (A), the reaction pressure is 0.4-4 MPa, more preferably 1.5-3 MPa; Preferably, in step (A), when a stirred reactor is used, the reaction time is 1-20 min.

11. The method according to claim 7, characterized in that, In step (B), the seed crystals are alkali metal sulfides with a median particle size of 0.8 μm-40 μm; Preferably, the seed crystals are obtained by separating fine particles of alkali metal sulfides in the oil using a cyclone magnetic separator; more preferably, the concentration of fine particles in the fine particles of alkali metal sulfides in the oil is 2000-6500 mg / L, and the ratio of the amount of seed crystals returned to the mass of alkali metal sulfides in the product obtained in step (A) is 1:5-1:

8. Preferably, in step (B), the ripening time after adding the seed crystal is 15-120 min, more preferably 60-120 min; Preferably, in step (B), the particle size of the alkali metal sulfide particles after seed crystal aggregation and growth is in the range of 10-200 μm, wherein the concentration of particles with a particle size of less than 50 μm is 10000-50000 mg / L.

12. The method according to claim 7, characterized in that, In step (C), the separation process temperature is 20-130°C, preferably 60-120°C; and / or, the separation process pressure is 0.3-3 MPa, preferably 0.5 MPa-2 MPa; Preferably, in step (C), after the cyclone magnetic separation, the liquid-solid separation efficiency is greater than 93%, and the heavy metal content is reduced to below 10wppm.

13. The method according to claim 7, characterized in that, In step (D), the salt-forming substance is hydrogen sulfide, and the amount of salt-forming substance added is 2-6 times, preferably 2-4 times, the residual alkali metal sodium in marine fuel oil in molar terms. Preferably, in step (D), the reaction process temperature is 20-130℃, more preferably 60-120℃, the reaction process pressure is 0.2-2MPa, more preferably 0.3MPa-1MPa, and the reaction time is 1-20min.

14. The method according to claim 7, characterized in that, In step (E), the cyclone drying conditions are as follows: the operating temperature is 20-80℃, preferably 30-70℃; and / or, the operating pressure is 0.1-2MPa, preferably 0.3MPa-1.5MPa; and / or, the rotation speed of the alkali metal sulfide particles is 15000-60000 rpm; and / or, the drying time is less than 10s, preferably 1s-10s.

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