Ship dual-fuel engine flue gas oxidative demethanation system and method

Abstract

The present application discloses a system and method for oxidative demethanation of flue gas from a marine dual-fuel engine. The system includes an oxidation tower, an oxidizing solution recovery device, and a liquid replenishing device. The oxidation tower includes a tower body; a first reactor disposed inside the tower body and connected to a flue gas input pipe; a second reactor disposed inside the tower body and sleeved on the outer periphery of the first reactor. The top of the second reactor is connected to a flue gas output pipe, and a flue gas inlet pipe is further provided on the side wall of the second reactor; a first spraying assembly for delivering an oxidizing solution to the inside of the first reactor; a second spraying assembly for delivering an oxidizing solution to the outside of the second reactor; the oxidizing solution recovery device includes a liquid inlet end and a liquid outlet end, and the liquid inlet end is connected to the outlet at the bottom of the tower body, and the liquid outlet end is connected to the first spraying assembly and the second spraying assembly; the liquid replenishing device is used to supplement the oxidizing solution. The system and method for oxidative demethanation of flue gas from a marine dual-fuel engine can efficiently decompose the escaped methane in the flue gas.

Description

Technical Field

[0001] The present application relates to the field of flue gas treatment technology, and in particular to a system and method for oxidative demethanization of flue gas from a dual-fuel engine for a ship. Background Art

[0002] With increasingly stringent environmental regulations and adjustments to energy mix, the shipping industry is increasingly adopting dual-fuel engines, such as blending liquefied natural gas (LNG) with traditional fuels, to reduce greenhouse gas emissions. While dual-fuel engines significantly reduce carbon dioxide and nitrogen oxide emissions during operation, a certain amount of escaped methane (CH4) remains in the flue gas. This is a potent greenhouse gas with a global warming potential (GWP) far greater than that of carbon dioxide.

[0003] Therefore, how to efficiently decompose escaped methane in flue gas has become a technical problem that needs to be solved urgently in the shipping industry. Summary of the Invention

[0004] The technical problem actually solved by the technical solution of this application is how to efficiently decompose escaped methane in flue gas.

[0005] In order to solve the above technical problems, the technical solution of the present application provides a flue gas oxidation demethanization system for a dual-fuel engine of a ship, comprising: an oxidation tower, an oxidizing solution recovery device and a liquid replenishing device; wherein: the oxidation tower is used to input flue gas and oxidizing solution, and output treated flue gas and unreacted oxidizing solution, and the oxidation tower comprises: a tower body with an outlet at the bottom, a flue gas input pipe, and a flue gas output pipe; a first reactor is arranged in the tower body and is connected to the flue gas input pipe, and has a first output end at the bottom; a second reactor is arranged in the tower body and is sleeved on the outer periphery of the first reactor, and has a second output end at the bottom , wherein the first output end extends out of the second output end, the top of the second reactor is connected to the flue gas output pipe, and the side wall of the second reactor is also provided with a flue gas inlet pipe; a first spray assembly is used to transport the oxidizing solution to the interior of the first reactor; a second spray assembly is used to transport the oxidizing solution to the outside of the second reactor; the oxidizing solution recovery device includes a liquid inlet end and a liquid outlet end, and the liquid inlet end is connected to the outlet at the bottom of the tower body, and the liquid outlet end is connected to the first spray assembly and the second spray assembly; the liquid replenishing device is connected to the tower body for replenishing the oxidizing solution.

[0006] In some embodiments, the first output end includes at least two air ducts, and the air outlets at the ends of each of the air ducts are bent in a clockwise or counterclockwise direction.

[0007] In some embodiments, the number of the flue gas input pipes and the number of the flue gas inlet pipes are both two. Among them, the two flue gas input pipes are symmetrically arranged with respect to the axis center of the first reactor, and the two flue gas inlet pipes are symmetrically arranged with respect to the axis center of the second reactor.

[0008] In some embodiments, the oxidation tower further includes: a heat exchange coil pipe, which is arranged inside the tower body, sleeved on the outer periphery of the second reactor, and located below the flue gas inlet pipe.

[0009] In some embodiments, the oxidation tower further includes: a first catalyst packing layer, which is arranged inside the tower body, located on the outer periphery of the second reactor, and located below the flue gas inlet pipe.

[0010] In some embodiments, the ship dual-fuel engine flue gas oxidation and demethanation system further includes an oxidation and dehydration device, and the oxidation and dehydration device includes: an oxidation and dehydration cavity, whose side wall is provided with a smoke inlet, the top is provided with a smoke outlet, and the bottom is provided with a liquid outlet. Among them, the smoke inlet is communicated with the flue gas output pipe, the smoke outlet is used for outputting clean flue gas, and the liquid outlet is communicated with the liquid outlet end of the oxidizing solution recovery device; a second catalyst packing layer, which is arranged inside the oxidation and dehydration cavity and located above the smoke inlet; a fourth spraying assembly, which is used for spraying oxidizing solution above the second catalyst packing layer; a demisting assembly, which is arranged inside the oxidation and dehydration cavity and close to the smoke outlet.

[0011] In some embodiments, the ship dual-fuel engine flue gas oxidation and demethanation system further includes: a first heat exchange device, one end of which is communicated with the flue gas output pipe, the other end is communicated with the smoke inlet, and is used for cooling the flue gas transported to the inside of the oxidation and dehydration cavity to a first target temperature; a second heat exchange device, one end of which is communicated with the liquid outlet end of the oxidizing solution recovery device, the other end is communicated with the fourth spraying assembly, and is used for cooling the oxidizing solution transported to the fourth spraying assembly to a second target temperature.

[0012] In some embodiments, the oxidizing solution is acidic hydrogen peroxide, and the mass concentration of the acidic hydrogen peroxide is 20% - 30%, and the pH is 5 - 6;

[0013] The first catalyst packing layer and / or the second catalyst packing layer includes a graphene composite material, and the graphene composite material includes: a graphene matrix and rare earth oxides attached to the graphene matrix. Among them, the mass of the rare earth oxides accounts for 50% - 70% of the total mass of the graphene composite material, and the rare earth oxides include rhenium oxide, neodymium oxide and cerium dioxide with a mass ratio of 1:1:1.

[0014] In some embodiments, the flue gas oxidative demethanation system of the marine dual-fuel engine further includes a pH detection device for monitoring the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device.

[0015] The present application also provides a method for flue gas oxidative demethanation of a marine dual-fuel engine, which uses the flue gas oxidative demethanation system described in any one of the above, and the method includes: inputting flue gas and an oxidizing solution into an oxidation tower, and the oxidation tower outputs the treated flue gas and the unreacted oxidizing solution, wherein the heat of the flue gas vaporizes the oxidizing solution into oxidizing steam, and an oxidation reaction occurs between the flue gas and the oxidizing steam; recovering the unreacted oxidizing solution through an oxidizing solution recovery device and transporting it to the oxidation tower; when it is detected that the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device increases, then discharging the oxidizing solution in the oxidation tower and the oxidizing solution recovery device, and supplementing the oxidizing solution into the oxidation tower through a liquid supplementing device.

[0016] Compared with the prior art, the flue gas oxidative demethanation system and method of the technical solution of the present application have the following beneficial effects:

[0017] The flue gas oxidative demethanation system and method of the present application can achieve gas-vapor contact between the flue gas and the oxide. Compared with the gas-liquid contact method of the traditional scrubbing tower, it can greatly increase the contact probability between the flue gas and the oxide, thereby significantly improving the oxidation and decomposition efficiency of the flue gas, and can also reduce the consumption of the oxidizing solution, so as to achieve efficient decomposition of the escaped methane in the flue gas. At the same time, the waste heat of the flue gas can directly vaporize the oxidizing solution without an external heat source, which can not only avoid the energy consumption of external heating, but also reduce the manufacturing cost and maintenance difficulty of the equipment.

[0018] Furthermore, the first output end of the first reactor includes at least two air ducts, and the air outlets at the ends of each air duct are bent in the same direction, either clockwise or counterclockwise, which can form a swirling wind field at the bottom of the tower body. Thus, it can not only increase the mixing and contact probability between the flue gas and the oxidizing solution, but also increase the residence time of the flue gas in the tower body, further improving the oxidation efficiency.

[0019] Furthermore, the flue gas input pipe is symmetrically arranged with respect to the axis center of the first reactor, which can make the input flue gas form a swirling wind field in the first reactor, facilitating the downward swirling of the flue gas and the oxidizing steam in the first reactor. The flue gas inlet pipe is symmetrically arranged with respect to the axis center of the second reactor, making the flue gas entering the second reactor form a swirling wind field, improving the gas-liquid separation effect.

[0020] Furthermore, making the first catalyst packing layer and / or the second catalyst packing layer include a specific graphene composite material can significantly improve the methane removal rate. When the flue gas temperature is above 245°C, the methane removal rate can reach over 92.1%. Particularly, when the flue gas temperature is 411°C, the methane removal rate reaches 100%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following drawings detail the exemplary embodiments disclosed in the present application. Wherein the same reference numerals represent similar structures in several views of the drawings. Those of ordinary skill in the art will understand that these embodiments are non-limiting, exemplary embodiments, and the drawings are only for illustrative and descriptive purposes and are not intended to limit the scope of the present application. Embodiments in other ways may also achieve the inventive intent in the present application. It should be understood that the drawings are not drawn to scale. Among them:

[0022] Figure 1 is a schematic structural diagram of a ship dual-fuel engine flue gas oxidative methane removal system according to an embodiment of the present application;

[0023] Figure 2 is a schematic structural diagram of an oxidation tower according to an embodiment of the present application;

[0024] Figure 3 is a schematic structural diagram of the first reactor and the second reactor of the oxidation tower according to an embodiment of the present application;

[0025] Figure 4 is a schematic top view structural diagram of the oxidation tower according to an embodiment of the present application;

[0026] Figure 5 is a schematic structural diagram of an air duct according to an embodiment of the present application;

[0027] Figure 6 is a schematic cross-sectional view of the first catalyst packing layer according to an embodiment of the present application;

[0028] Figure 7 is a schematic structural diagram of another ship dual-fuel engine flue gas oxidative methane removal system according to an embodiment of the present application;

[0029] The meanings of the reference numerals are as follows:

[0030] 1 - oxidation tower; 2 - oxidizing solution recovery device; 3 - liquid supplement device; 4 - oxidation dehydration device; 5 - first heat exchange device; 6 - second heat exchange device; 7 - pH detection device; 8 - circulation pump; 9 - supplement pump; 10 - tower body; 11 - flue gas input pipe; 12 - flue gas output pipe; 13 - flue gas inlet pipe;

[0031] 41 - oxidation dehydration cavity; 42 - second catalyst packing layer; 43 - fourth spraying assembly; 44 - demisting assembly;

[0032] 100 - First reactor; 101 - First cylindrical section; 102 - First conical section; 103 - Second cylindrical section; 104 - Air duct

[0033] 200 - Second reactor; 201 - Third cylindrical section, 202 - Second conical section; 203 - Fourth cylindrical section

[0034] 300 - First spray assembly; 301 - First spray head; 302 - First spray head pipeline

[0035] 400 - Second spray assembly; 401 - Second spray head pipeline; 402 - Second spray head

[0036] 500 - First catalyst packing layer; 600 - Heat exchange coil

[0037] 700 - Third spray assembly; 701 - Third spray head; 702 - Third spray head pipeline Detailed implementation mode

[0038] The following description provides specific application scenarios and requirements of the present application, aiming to enable those skilled in the art to manufacture and use the content of the present application. For those skilled in the art, various partial modifications to the disclosed embodiments are obvious, and the general principles defined here can be applied to other embodiments and applications without departing from the spirit and scope of the present application. Therefore, the present application is not limited to the illustrated embodiments, but has the broadest scope consistent with the claims. The oxidation tower of the embodiment of the present application will be described in detail below with reference to the accompanying drawings.

[0039] The embodiment of the present application provides a ship dual - fuel engine flue gas oxidation and demethanation system, which can oxidize the input gas and can be applied to the demethanation treatment of the flue gas of a ship LNG dual - fuel engine.

[0040] Reference Figure 1 , the ship dual - fuel engine flue gas oxidation and demethanation system of the embodiment of the present application includes: an oxidation tower 1, an oxidizing solution recovery device 2 and a liquid supplement device 3. Among them, the oxidation tower 1 is used to input flue gas and oxidizing solution, and output the treated flue gas and the unreacted oxidizing solution. The oxidizing solution recovery device 2 is used to recover the unreacted oxidizing solution and transport the unreacted oxidizing solution to the oxidation tower 1 to complete the recycling of the oxidizing solution. The liquid supplement device 3 is used to supplement the oxidizing solution into the oxidation tower 1.

[0041] Combined with Figure 2 and Figure 3, the oxidation tower includes a tower body 10 with an outlet at the bottom, a flue gas inlet pipe 11, a flue gas outlet pipe 12, a first reactor 100, a second reactor 200, a first spray assembly 300, and a second spray assembly 400.

[0042] The first reactor 100 is disposed inside the tower body 10, communicates with the flue gas inlet pipe 11, and has a first output end at the bottom. The flue gas inlet pipe 11 is used to convey flue gas into the first reactor 100. In some embodiments, the flue gas inlet pipe 11 may be disposed on the side wall of the first reactor 100, the first end of the flue gas inlet pipe 11 communicates with the first reactor 100, and the second end of the flue gas inlet pipe 11 extends out of the tower body 10.

[0043] The number of the flue gas inlet pipes 11 is at least one. In some preferred embodiments, the number of the flue gas inlet pipes 11 is at least two, and the two flue gas inlet pipes 11 are configured such that the input flue gas can form a swirling wind field inside the first reactor 100, and this swirling wind field can make the flue gas, oxidizing steam, and unvaporized oxidizing solution continuously swirl towards the bottom of the first reactor 100 and flow out from the first output end. In some specific embodiments, as Figure 4 shown, the number of the flue gas inlet pipes 11 is two, and the two flue gas inlet pipes 11 are symmetrically arranged with respect to the axis center of the first reactor 100.

[0044] The first spray assembly 300 is used to convey an oxidizing solution into the interior of the first reactor 100. Since the temperature of the flue gas is usually relatively high and higher than the vaporization temperature of the oxidizing solution, this causes the oxidizing solution to vaporize into oxidizing steam, thereby realizing an oxidation method of gas-vapor contact. Compared with the traditional oxidation method of gas-liquid contact, the contact probability between the flue gas and the oxidizing steam is greatly increased, thereby significantly improving the oxidation decomposition efficiency of methane.

[0045] In some specific embodiments, the first spray assembly 300 includes: a first spray head 301 and a first spray head pipe 302, wherein the first spray head 301 is disposed at the top of the first reactor 100, the first end of the first spray head pipe 302 communicates with the first spray head 301, and the second end of the first spray head pipe 302 extends out of the tower body 10. The flue gas inlet pipe 11 is disposed close to the first spray head 301 to increase the contact probability between the flue gas and the oxidizing solution, thereby improving the vaporization efficiency of the oxidizing solution and the oxidation decomposition efficiency of the flue gas.

[0046] In some embodiments, the first output end of the first reactor 100 includes at least two air ducts 104 and is configured to form a swirling wind field at the bottom of the tower body 10 for the output flue gas and oxidizing steam. On the one hand, this swirling wind field can increase the probability of mixing and contact between the flue gas and the oxidizing solution, thereby improving the oxidation decomposition efficiency; on the other hand, this swirling wind field can improve the horizontal flow of the flue gas, thereby increasing the residence time of the flue gas in the tower body 10, thus improving the oxidation decomposition efficiency.

[0047] In some embodiments, the air outlets at the ends of each air duct 104 are bent together in a clockwise or counterclockwise direction to form a swirling wind field. In some specific embodiments, as Figure 5 shown, the number of the air ducts 104 is four, and the air outlets at the ends of each air duct 104 are bent together in a clockwise or counterclockwise direction. More specifically, two adjacent air ducts 104 are perpendicularly distributed, and the air outlets at the ends of each air duct 104 are bent 90 degrees counterclockwise together.

[0048] In some specific embodiments, the first reactor 100 includes a first cylindrical section 101, a first conical section 102, and a second cylindrical section 103, which are smoothly connected in sequence along the top-to-bottom direction of the first reactor 100, wherein the inner diameter of the first cylindrical section 101 is larger than the inner diameter of the second cylindrical section 103.

[0049] The second reactor 200 is disposed in the tower body 10 and sleeved on the outer periphery of the first reactor 100, and has a second output end at the bottom, wherein the first output end at the bottom of the first reactor 100 extends out of the second output end at the bottom of the second reactor 200 to prevent the flue gas and oxidizing steam output from the first reactor 100 from rising into the second reactor 200. The top of the second reactor 200 is connected to the flue gas output pipe 12, and a flue gas inlet pipe 13 is further provided on the side wall of the second reactor 200.

[0050] In some specific embodiments, the first end of the flue gas output pipe 12 communicates with the top of the second reactor 200, and the second end of the flue gas output pipe 12 extends out of the tower body 10 for outputting the flue gas outside the tower body 10. The first end of the flue gas inlet pipe 13 communicates with the side wall of the second reactor 200, and the second end of the flue gas inlet pipe 13 communicates with the inside of the tower body 10 and is used for conveying the flue gas after oxidation decomposition in the tower body 10 into the second reactor 200. Since the oxidation decomposition products of methane in the flue gas are carbon dioxide and water, the flue gas after oxidation decomposition is a gas-liquid mixture. This gas-liquid mixture enters the second reactor 200 through the flue gas inlet pipe 13 for gas-liquid separation. The separated gas phase will be output from the tower body 10 through the flue gas output pipe 12, and the separated liquid phase flows out from the second output end at the bottom of the second reactor 200.

[0051] The number of the flue gas inlet pipes 13 is at least one. In some preferred embodiments, the number of the flue gas inlet pipes 13 is at least two and is configured such that the input flue gas after oxidation decomposition forms a swirling wind field in the second reactor 200 to improve the gas-liquid separation effect. In some specific embodiments, as Figure 4 shown, the number of the flue gas inlet pipes 13 is two and is symmetrically arranged with respect to the axis center of the second reactor 200.

[0052] In some specific embodiments, the second reactor 200 includes a third cylindrical section 201, a second conical section 202, and a fourth cylindrical section 203, which are smoothly connected in sequence along the direction from the top to the bottom of the second reactor 200, wherein the inner diameter of the third cylindrical section 201 is larger than the inner diameter of the fourth cylindrical section 203.

[0053] The second spraying assembly 400 is used for conveying an oxidizing solution to the outside of the second reactor 200. The waste heat of the flue gas output from the first output end of the first reactor 100 can vaporize the oxidizing solution, increasing the concentration of the oxidizing steam and further improving the oxidation decomposition efficiency of methane.

[0054] In some specific embodiments, the second spraying assembly 400 includes: at least one second spray head pipe 401, and the second spray head pipe 401 includes: an annular pipe section surrounding the outer periphery of the second reactor 200, and a plurality of second spray heads 402 are uniformly arranged on the annular pipe section, wherein the input end of the second spray head pipe 401 extends out of the tower body 10.

[0055] To accelerate the oxidative decomposition of flue gas and achieve more complete decomposition of escaped methane, a first catalyst packing layer 500 may be provided within the tower body 10. The first catalyst packing layer 500 is located on the periphery of the second reactor 200 and below the flue gas inlet pipe 13. In some embodiments, the first catalyst packing layer 500 is located between the flue gas inlet pipe 13 and the second spray assembly 400. Figure 6 FIG2 shows a cross-sectional view of a first catalyst filler layer 500. The first catalyst filler layer 500 may include conventional catalyst fillers as long as they can play a catalytic role. As an example, the catalyst filler is an oxide filler of a metal such as manganese, copper, or titanium.

[0056] In some embodiments, reference Figure 2 The oxidation tower further includes a heat exchange coil 600, which is disposed in the tower body 10 and is sleeved on the outer periphery of the second reactor 200 and located below the flue gas inlet pipe 13. In some embodiments, the heat exchange coil 600 is also located below the first catalyst packing layer 500. The heat exchange coil 600 is used to absorb the waste heat of the flue gas and the oxidizing steam, wherein the oxidizing steam will produce a temperature drop after absorbing heat, and then precipitate small droplets, which will fall to the bottom of the tower body 10. When the heat exchange coil 600 is in operation, a waste heat recovery medium such as cold water is input to the input end of the heat exchange coil 600. The waste heat recovery medium flows in the heat exchange coil 600, absorbs the waste heat to form hot water or steam, and is discharged from the tower body 10 at the output end of the heat exchange coil 600.

[0057] In some embodiments, reference Figure 2 and Figure 3 The oxidation tower also includes: a third spray assembly 700, which is used to transport an oxidizing solution into the second reactor 200, and can oxidize the flue gas input into the second reactor 200, thereby improving the oxidation treatment effect of the oxidation tower.

[0058] In some specific embodiments, the third spray assembly 700 includes a third spray head 701 and a third spray head pipe 702, wherein the third spray head 701 is disposed on the inner sidewall of the second reactor 200 and above the flue gas inlet pipe 13. A first end of the third spray head pipe 702 is connected to the third spray head 701, and a second end of the third spray head pipe 702 extends out of the tower body 10.

[0059] In some specific embodiments, the input ends of the first nozzle pipe 302 of the first spray assembly 300, the second nozzle pipe 401 of the second spray assembly 400, and the third nozzle pipe 702 of the third spray assembly 700 are connected to the oxidizing liquid delivery pipe outside the tower body 10.

[0060] Combine Figure 1 、 Figure 2 and Figure 7 The oxidizing solution recovery device 2 includes a liquid inlet and a liquid outlet. The liquid inlet is connected to the outlet at the bottom of the tower body 10, and the liquid outlet is connected to the first spray assembly 300 and the second spray assembly 400. Specifically, the liquid outlet is connected to the first spray head pipe 302 of the first spray assembly 300 and the second spray head pipe 401 of the second spray assembly 400.

[0061] In some embodiments, the marine dual-fuel engine flue gas oxidation demethanization system further includes an oxidation dehydration device 4 for oxidizing and dehydrating the treated flue gas output from the oxidation tower 1. The oxidation dehydration device 4 may include an oxidation dehydration chamber 41, a second catalyst packing layer 42, a fourth spray assembly 43, and a demisting assembly 44.

[0062] The side wall of the oxidation and dehydration chamber 41 is provided with a smoke inlet, the top is provided with a smoke outlet, and the bottom is provided with a liquid outlet, wherein the smoke inlet is connected to the smoke output pipe 12, and is used to input treated smoke into the interior of the oxidation and dehydration chamber 41, and the smoke outlet is used to output clean smoke, that is, demethanized smoke, and the liquid outlet is connected to the liquid outlet end of the oxidizing solution recovery device 2, and is used to output the liquid output by the oxidation and dehydration device 4 to the liquid outlet end of the oxidizing solution recovery device 2.

[0063] The second catalyst packing layer 42 is disposed within the oxidative dehydration chamber 41 and above the smoke inlet. The second catalyst packing layer 42 can comprise a conventional catalyst packing, which can be the same or different from the material of the first catalyst packing layer 500, as long as it can provide a catalytic effect. For example, the catalyst packing is an oxide filler of a metal such as manganese, copper, or titanium. The structure of the second catalyst packing layer 42 can refer to the structure of the first catalyst packing layer 500.

[0064] The fourth spray assembly 43 is used to spray the oxidizing solution above the second catalyst packing layer 42. The fourth spray assembly 43 may include a fourth nozzle pipe and a fourth nozzle, wherein a first end of the fourth nozzle pipe is connected to the liquid outlet of the oxidizing solution recovery device 2, and a second end of the fourth nozzle pipe is connected to the fourth nozzle.

[0065] The demisting component 44 is arranged inside the oxidation and dehydration cavity 41 and near the smoke outlet, and is used for dehydrating the flue gas. The specific structure of the demisting component 44 is not required, as long as it can play a role in dehydration.

[0066] After the processed flue gas is transported into the oxidation and dehydration cavity 41, it enters the second catalyst packing layer 42. At the same time, the oxidizing solution is sprayed into the second catalyst packing layer 42 through the fourth spraying component 43. The flue gas and the oxidizing solution are in countercurrent contact in the second catalyst packing layer 42, and the oxidizing solution can catalytically oxidize the remaining methane to improve the methane removal rate of the flue gas.

[0067] The unreacted oxidizing solution in the oxidation and dehydration cavity 41 will be output to the liquid outlet end of the oxidizing solution recovery device 2 through the liquid outlet of the oxidation and dehydration cavity 41. After converging with the unreacted oxidizing solution output from the liquid outlet end of the oxidizing solution recovery device 2, it is transported to the first spraying component 300, the second spraying component 400, the third spraying component 700, and the fourth spraying component 43 to realize the recycling of the oxidizing solution.

[0068] In some embodiments, the marine dual-fuel engine flue gas oxidation and demethanation system further includes a first heat exchange device 5 and a second heat exchange device 6. The first end of the first heat exchange device 5 is communicated with the flue gas output pipe 12, and the second end is communicated with the smoke inlet of the oxidation and dehydration cavity 41, and is used for cooling the flue gas transported into the oxidation and dehydration cavity 41 to a first target temperature. The first end of the second heat exchange device 6 is communicated with the liquid outlet end of the oxidizing solution recovery device 2, the second end is communicated with the fourth spraying component 43, and is used for cooling the oxidizing solution transported to the fourth spraying component 43 to a second target temperature. As an example, the first target temperature and the second target temperature are 25-35°C.

[0069] In some specific embodiments, both the first heat exchange device 5 and the second heat exchange device 6 are seawater heat exchangers. Low-temperature seawater is transported into the first heat exchange device 5 and the second heat exchange device 6 through a seawater pump to absorb heat, and the formed high-temperature seawater will be discharged.

[0070] The liquid replenishing device 3 is connected to the tower body 10 and is used to replenish the oxidizing solution into the tower body 10. In some embodiments, when it is detected that the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device 2 increases, it represents that the oxidizing property of the oxidizing solution in the system decreases, and new oxidizing solution needs to be replenished into the tower body 10 through the liquid replenishing device 3. In some embodiments, the ship dual-fuel engine flue gas oxidation and demethanation system further includes a pH detection device 7, which is used to monitor the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device 2.

[0071] In some specific embodiments, a circulation pump 8 is further provided at the liquid outlet end of the oxidizing solution recovery device 2, and the circulation pump 8 is used to transport the unreacted oxidizing solution. The liquid replenishing device 3 is connected to the tower body 10 through a replenishing pump 9, and the replenishing pump 9 is used to input the oxidizing solution in the liquid replenishing device 3 into the tower body 10.

[0072] The following combines Figure 2 and Figure 7 to further illustrate the overall operation process of the ship dual-fuel engine flue gas oxidation and demethanation system according to the embodiments of the present application.

[0073] The flue gas is input into the first reactor 100 through the flue gas input pipe 11, and an oxidizing solution is transported into the first reactor 100 through the first spraying assembly 300. The high temperature carried by the flue gas causes the oxidizing solution to vaporize and undergo an oxidation reaction. The formed gas-liquid vapor is output through the first output end of the first reactor 100. The liquid phase drips to the bottom of the tower body 10 and is output to the oxidizing solution recovery device 2. The gas phase contacts the oxidizing solution sprayed by the second spraying assembly 400, causing it to vaporize and undergo an oxidation reaction. The liquid phase generated in this process drips to the bottom of the tower body 10 and is output to the oxidizing solution recovery device 2. The concentration of the oxidizing vapor in the flue gas is further increased and enters the first catalyst packing layer 500 to undergo a catalytic oxidation reaction, oxidizing and decomposing methane in the flue gas. The output gas-liquid mixture enters the second reactor 200 through the flue gas inlet pipe 13 for gas-liquid separation. An oxidizing solution is transported into the second reactor 200 through the third spraying assembly 700 to oxidize the flue gas again. The separated liquid phase is output through the second output end of the second reactor 200, drips to the bottom of the tower body 10, and is output to the oxidizing solution recovery device 2. The separated gas phase is discharged out of the tower body 10 through the flue gas output pipe 12. After being cooled to the first target temperature by the first heat exchange device 5, it enters the oxidation and dehydration cavity 41 for oxidation treatment and dehydration treatment, outputting methane-removed flue gas, thereby realizing the methane removal treatment of the flue gas of the ship's LNG dual-fuel engine. The liquid generated by oxidation and dehydration is output to the liquid outlet end of the oxidizing solution recovery device 2. After converging with the unreacted oxidizing solution output from the liquid outlet end of the oxidizing solution recovery device 2, it is transported to the first spraying assembly 300, the second spraying assembly 400, the third spraying assembly 700, and the fourth spraying assembly 43. Before being transported to the fourth spraying assembly 43, it is cooled to the second target temperature by the second heat exchange device 6 to realize the recycling of the oxidizing solution. During the above oxidation treatment process, the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device 2 is monitored by the pH detection device 7. When it is detected that the pH value increases, new oxidizing solution is supplemented into the tower body 10 through the liquid supplement device 3.

[0074] Currently, when the traditional ship dual-fuel engine uses the catalytic oxidation method to decompose the escaped methane in the flue gas, the catalyst used is easily contaminated by impurities in the flue gas, resulting in catalyst failure and the unstable operation of the catalytic oxidation equipment. The traditional purification absorption tower usually uses chemicals to absorb pollutants in the flue gas, such as using alkaline solution or weakly alkaline seawater to absorb SO2, amine solution to absorb CO2, etc. However, CH4 is insoluble in acids, bases, and organic solvents. Therefore, this application uses a water-soluble strong oxidant to react with the escaped CH4 in the flue gas to eliminate the greenhouse effect of CH4 on the earth.

[0075] In some preferred embodiments, the oxidizing solution is acidic hydrogen peroxide, and the mass concentration of the acidic hydrogen peroxide is 20% - 30%, and the pH is 5 - 6.

[0076] In some preferred embodiments, the catalyst packing of the first catalyst packing layer 500 and / or the second catalyst packing layer 42 comprises a graphene composite material, and the graphene composite material comprises: a graphene matrix and rare earth oxides attached to the graphene matrix, wherein the mass of the rare earth oxides accounts for 50% - 70% of the total mass of the graphene composite material, and the rare earth oxides comprise rhenium oxide, neodymium oxide and cerium dioxide with a mass ratio of 1:1:1. Graphene is composed of layers of neatly arranged carbon atoms, and each carbon atom forms covalent bonds with three surrounding carbon atoms to form a hexagonal structure. The structure of graphene is similar to a honeycomb-like grid, making graphene have extremely high strength and stability. At the same time, the grid structure can accommodate more metal oxides, increasing the attachment amount of the effective catalytic material, thereby improving the catalytic efficiency.

[0077] In some preferred embodiments, the preparation method of the graphene composite material comprises:

[0078] (1) Providing graphene particles with a size of 25 nm - 50 nm and rare earth oxides.

[0079] The preparation method of the graphene particles may comprise: spray-drying the graphene material in a nitrogen atmosphere at 100 °C to form dry graphene particles, and screening graphene particles with a size of 25 nm - 50 nm.

[0080] The rare earth oxides comprise a mixture of rhenium oxide, neodymium oxide and cerium dioxide with a mass ratio of 1:1:1.

[0081] (2) Mixing and depositing the graphene particles and the rare earth oxides by chemical vapor deposition to obtain a graphene composite material, wherein the mass fraction of the rare earth oxides is 5% - 70%.

[0082] The chemical vapor deposition method is to instantaneously evaporate the rare earth oxides at extremely high temperature by an electric arc, and then rapidly introduce graphene particles at -35 °C, and the rare earth oxides crystallize in the graphene particles. Through chemical vapor deposition, a larger attachment amount of the effective catalytic material can be obtained, thereby increasing the contact area between the substance to be catalyzed and the catalyst, and further improving the catalytic efficiency.

[0083] In some specific embodiments, the graphene composite material is made into particles with a diameter of 10 mm by a granulator for filling the catalyst bed of the actual equipment (1 Nm 3 flue gas requires 0.011 m 3 catalyst).

[0084] Adopt Figure 7 The methane removal system for the flue gas of a marine dual-fuel engine shown in the figure is used to remove methane from the flue gas. The oxidizing solution is acidic hydrogen peroxide with a pH of 6 and a mass concentration of 25%. The methane removal rates of different catalyst packings are compared. Methane removal rate = (C 初始甲烷 - C 处理后甲烷 ) / C 初始甲烷 × 100%, where C 初始甲烷 represents the concentration of methane in the initial flue gas, and C 处理后甲烷 represents the concentration of methane in the flue gas after oxidation treatment. These two concentration values can be measured at the corresponding positions using a concentration meter. In the catalyst packing layer, the total mass ratio of the oxides loaded on the graphene particles is 60%. The difference between different catalyst packings lies only in the types of oxides loaded on the graphene matrix. The results are shown in Table 1.

[0085] Table 1 Methane removal rate results of different catalyst packings

[0086] Flue gas temperature Oxide composition Mass ratio Methane removal rate 411℃ Rhenium oxide + neodymium oxide + cerium dioxide 1:1:1 100% Manganese dioxide + titanium dioxide 1:1 71.3% 245℃ Rhenium oxide + neodymium oxide + cerium dioxide 1:1:1 92.1% Manganese dioxide + titanium dioxide 1:1 38.9% 51℃ Rhenium oxide + neodymium oxide + cerium dioxide 1:1:1 42.2% Manganese dioxide + titanium dioxide 1:1 11.3%

[0087] As can be seen from Table 1, when the catalyst packing is the same, as the temperature of the input flue gas increases, the methane removal rate shows an upward trend. This is because as the temperature of the flue gas increases, more acidic hydrogen peroxide vaporizes, and the oxidation efficiency is improved. When the temperature of the input flue gas is the same, when the composition of the loaded oxides is a mixture of rhenium oxide, neodymium oxide, and cerium dioxide with a mass ratio of 1:1:1, the methane removal rate is significantly increased. In particular, when the temperature of the input flue gas is 411 °C and the loaded oxides with this specific composition are used, the methane removal rate is as high as 100%, achieving complete removal of the escaped methane in the flue gas.

[0088] The embodiment of the present application also provides a method for methane oxidation and removal from the flue gas of a marine dual-fuel engine. The above-mentioned methane oxidation and removal system for the flue gas of a marine dual-fuel engine is adopted, and this method includes the following steps:

[0089] S1: Input flue gas and an oxidizing solution into the oxidation tower. The oxidation tower outputs the treated flue gas and the unreacted oxidizing solution. The heat of the flue gas vaporizes the oxidizing solution into an oxidizing vapor, and the flue gas and the oxidizing vapor undergo an oxidation reaction;

[0090] S2: Recover the unreacted oxidizing solution through an oxidizing solution recovery device and transport it to the oxidation tower;

[0091] S3: When it is detected that the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device increases, then discharge the oxidizing solution in the oxidation tower and the oxidizing solution recovery device, and supplement the oxidizing solution to the oxidation tower through a liquid supplement device.

[0092] In some embodiments, the method for oxidatively removing methane from the flue gas of a marine dual-fuel engine further includes step S1-2: subjecting the treated flue gas output from the oxidation tower to oxidation treatment and dehydration treatment using an oxidation dehydration device, and outputting methane-removed flue gas and liquid, wherein the liquid is output to the liquid outlet end of the oxidizing solution recovery device, and after converging with the unreacted oxidizing solution output from the oxidizing solution recovery device, is sent to the first spraying assembly, the second spraying assembly, the third spraying assembly, and the fourth spraying assembly to realize the recycling and reuse of the oxidizing solution.

[0093] It should be noted that the beneficial effects that may be produced by different embodiments are different. In different embodiments, the beneficial effects that may be produced may be any one or several combinations of the above, or any other beneficial effects that may be obtained.

[0094] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only an example and does not constitute a limitation to this specification. Although not explicitly stated here, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are proposed in this specification, so such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of this application.

[0095] It should be noted that in the description of this application, unless otherwise clearly specified and limited, the terms "installation", "connection", "connection", "connection", "fixation" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be a rotational connection or a sliding connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood in combination with specific situations.

[0096] In addition, when terms such as "first", "second", "third", etc. are used in the description of this application to describe various features, these terms are only used to distinguish these features and cannot be understood as indicating or implying the relevance, relative importance, or implicitly indicating the quantity of the indicated features.

[0097] In addition, the specification of the present application describes exemplary embodiments by referring to idealized exemplary cross-sectional views and / or plan views and / or three-dimensional views. Therefore, differences from the shapes shown in the figures are foreseeable due to, for example, manufacturing techniques and / or tolerances. Accordingly, the exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but should include deviations in the shapes caused by, for example, manufacturing. Thus, the regions shown in the figures are substantially schematic, and their shapes are not intended to show the actual shape of the regions of the device nor to limit the scope of the exemplary embodiments.

[0098] Meanwhile, the present application uses specific terms to describe the embodiments of this specification. Terms such as "one embodiment", "an embodiment", and / or "some embodiments" mean a certain feature, structure, or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that the "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more at different positions in the present application does not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the present application can be combined appropriately.

[0099] Similarly, it should be noted that, in order to simplify the presentation of the disclosure of the present application and thus help the understanding of one or more inventive embodiments, in the foregoing description of the embodiments of the present application, sometimes multiple features are grouped into one embodiment, drawing, or description thereof. However, this method of disclosure does not mean that the features required by the subject matter of the present application are more than those mentioned in the claims. In fact, the features of the embodiments are fewer than all the features of the single embodiments disclosed above.

[0100] Finally, it should be understood that the embodiments described in the present application are only used to illustrate the principles of the embodiments of the present application. Other variations may also fall within the scope of the present application. Therefore, by way of example and not limitation, alternative configurations of the embodiments of the present application can be considered to be consistent with the teachings of the present application. Accordingly, the embodiments of the present application are not limited to the embodiments explicitly introduced and described in the present application.

Claims

1. A dual-fuel engine flue gas oxidative demethanation system for ships, characterized in that, Comprising: An oxidation tower (1), an oxidizing solution recovery device (2), and a liquid replenishing device (3); wherein: The oxidation tower (1) is used to input flue gas and an oxidizing solution, and output the treated flue gas and the unreacted oxidizing solution, and the oxidation tower (1) includes: A tower body (10) with an outlet at the bottom, a flue gas input pipe (11), and a flue gas output pipe (12); A first reactor (100), disposed inside the tower body (10), communicated with the flue gas input pipe (11), and having a first output end at the bottom; wherein the flue gas input pipe (11) is disposed on the side wall of the first reactor (100), and the number of the flue gas input pipes (11) is at least two and is configured such that the input flue gas forms a swirling wind field inside the first reactor (100); the first output end includes at least two air guide pipes (104) and is configured to cause the output flue gas and oxidizing steam to form a swirling wind field at the bottom of the tower body (10); A second reactor (200), disposed inside the tower body (10), sleeved on the outer periphery of the first reactor (100), and having a second output end at the bottom, wherein the first output end extends out of the second output end, the top of the second reactor (200) is communicated with the flue gas output pipe (12), and a flue gas inlet pipe (13) is further provided on the side wall of the second reactor; A first catalyst packing layer (500), disposed inside the tower body (10), located on the outer periphery of the second reactor (200), and below the flue gas inlet pipe (13); the first catalyst packing layer (500) includes a graphene composite material, and the graphene composite material includes: a graphene matrix and rare earth oxides attached to the graphene matrix, wherein the rare earth oxides include rhenium oxide, neodymium oxide, and cerium dioxide; A first spraying assembly (300), used to convey the oxidizing solution into the interior of the first reactor (100); A second spraying assembly (400), used to convey the oxidizing solution to the outside of the second reactor (200); A third spraying assembly (700), used to convey the oxidizing solution into the second reactor (200); The oxidizing solution recovery device (2) includes a liquid inlet end and a liquid outlet end, and the liquid inlet end is communicated with the outlet at the bottom of the tower body (10), and the liquid outlet end is communicated with the first spraying assembly (300) and the second spraying assembly (400); The liquid replenishing device (3) is communicated with the tower body (10) and is used to replenish the oxidizing solution into the tower body (10) when the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device (2) increases.

2. The ship dual-fuel engine flue gas oxidative demethanation system according to claim 1, characterized in that The air outlet at the end of each air guide pipe (104) is bent clockwise or counterclockwise together.

3. The ship dual-fuel engine flue gas oxidative demethanation system according to claim 1, characterized in that, The number of the flue gas input pipes (11) and the flue gas inlet pipes (13) is both two, wherein the two flue gas input pipes (11) are symmetrically arranged with respect to the axis center of the first reactor (100), and the two flue gas inlet pipes (13) are symmetrically arranged with respect to the axis center of the second reactor (200).

4. The ship dual-fuel engine flue gas oxidative demethanation system according to claim 1, characterized in that, The oxidation tower further includes: a heat exchange coil (600), which is arranged inside the tower body (10), sleeved on the outer periphery of the second reactor (200), and located below the flue gas inlet pipe (13).

5. The ship dual-fuel engine flue gas oxidative demethanation system according to claim 1, characterized in that The ship dual-fuel engine flue gas oxidation and demethanation system further includes an oxidation and dehydration device (4), and the oxidation and dehydration device (4) includes: An oxidation and dehydration cavity (41), with a flue gas inlet provided on its side wall, a clean flue gas outlet provided on its top, and a liquid outlet provided on its bottom. The flue gas inlet is communicated with the flue gas output pipe (12), the clean flue gas outlet is used for outputting clean flue gas, and the liquid outlet is communicated with the liquid outlet end of the oxidizing solution recovery device (2); A second catalyst packing layer (42), which is arranged inside the oxidation and dehydration cavity (41) and located above the flue gas inlet; A fourth spraying assembly (43), which is used for spraying the oxidizing solution above the second catalyst packing layer (42); A demisting assembly (44), which is arranged inside the oxidation and dehydration cavity (41) and close to the clean flue gas outlet.

6. The ship dual-fuel engine flue gas oxidative demethanation system according to claim 5, characterized in that, The ship dual-fuel engine flue gas oxidation and demethanation system further includes: A first heat exchange device (5), one end of which is communicated with the flue gas output pipe (12), the other end of which is communicated with the flue gas inlet, and which is used for cooling the flue gas transported to the inside of the oxidation and dehydration cavity (41) to a first target temperature; A second heat exchange device (6), one end of which is communicated with the liquid outlet end of the oxidizing solution recovery device (2), the other end of which is communicated with the fourth spraying assembly (43), and which is used for cooling the oxidizing solution transported to the fourth spraying assembly (43) to a second target temperature.

7. The ship dual-fuel engine flue gas oxidative demethanation system according to claim 5, characterized in that, The oxidizing solution is acidic hydrogen peroxide, and the mass concentration of the acidic hydrogen peroxide is 20% - 30%, and the pH is 5 - 6; The second catalyst packing layer (42) includes a graphene composite material, and the graphene composite material includes: a graphene matrix and rare earth oxides attached to the graphene matrix, wherein the mass of the rare earth oxides accounts for 50% - 70% of the total mass of the graphene composite material, and the rare earth oxides include rhenium oxide, neodymium oxide and cerium dioxide with a mass ratio of 1:1:

1.

8. The ship dual-fuel engine flue gas oxidative demethanation system according to claim 1, characterized in that The ship dual-fuel engine flue gas oxidation and demethanation system further includes a pH detection device (7), which is used for monitoring the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device (2).

9. A method for oxidative demethanation of flue gas from a marine dual-fuel engine, characterized in that, Using the ship dual-fuel engine flue gas oxidation and demethanation system according to any one of claims 1 to 8, and the method includes: Inputting flue gas and an oxidizing solution into the oxidation tower (1), and the oxidation tower (1) outputs the treated flue gas and the unreacted oxidizing solution. The heat of the flue gas vaporizes the oxidizing solution into oxidizing steam, and the flue gas and the oxidizing steam undergo an oxidation reaction; Recycling the unreacted oxidizing solution through the oxidizing solution recovery device (2) and transporting it to the oxidation tower (1); When the pH value of the oxidizing solution at the liquid outlet end of the oxidizing solution recovery device (2) is detected to increase, the oxidizing solution in the oxidation tower (1) and the oxidizing solution recovery device (2) is discharged, and the oxidizing solution is replenished into the oxidation tower (1) through the liquid replenishing device (3).

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