Structure and method for preventing urea crystallization of marine engine SCR system

Abstract

The invention discloses a structure and method for preventing urea crystallization of a marine engine SCR system, and relates to the technical field of engines. According to the structure and method for preventing urea crystallization of the marine engine SCR system, a mixing pipe, an inclined plate, a perforated plate and a urea spray gun are included, the inclined plate is arranged at the position of the axis in the mixing pipe and used for exciting turbulent flow, the perforated plate is located on the rear side of the inclined plate and used for evenly distributing a flow field, and the urea spray gun sprays urea into the optimized flow field. According to the method, composite structure parameters are optimized through CFD flow field simulation to adapt to marine working conditions; the flow field is cooperatively regulated through the composite structure, the evaporation rate of urea liquid drops is larger than or equal to 98%, the wall impact rate is smaller than or equal to 1%, crystallization is eradicated from the source, ship rolling and pitching and engine full-load fluctuation are adapted, the NOx conversion efficiency is larger than or equal to 90%, the exhaust back pressure rise is smaller than or equal to 5 kPa, extra energy consumption is not needed, the reliability of an SCR system is greatly improved, and the operation and maintenance cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of engine technology, specifically to a structure and method for preventing urea crystallization in a marine engine's SCR system. Background Technology

[0002] Marine engine SCR systems are the core equipment for denitrification of ship exhaust gases. They require the injection of a 40% urea solution into the high-temperature exhaust gas, allowing the ammonia and nitrogen oxides produced by urea decomposition to selectively react with a catalyst, converting them into harmless nitrogen and water to meet international ship emission regulations such as IMO Tier III. However, marine operating scenarios present numerous unique challenges, which can lead to some urea droplets not fully evaporating and mixing. These droplets can then impact the inner walls of the SCR system pipes or the catalyst carrier inlet, resulting in the formation of solid urea crystals.

[0003] Existing anti-urea crystallization technologies all have significant drawbacks and cannot fundamentally solve the crystallization problem in marine applications: simply increasing the urea injection pressure is insufficient to adapt to the large fluctuations in the flow field of marine engines, and the problem of uneven droplet distribution remains unresolved; adding additional heating devices can improve droplet evaporation efficiency, but it increases system energy consumption and structural complexity, raising equipment failure rates and maintenance costs; using a single static mixing structure with pure inclined plates or pure porous plates cannot simultaneously address the turbulence intensity and uniformity of the flow field. Pure inclined plates are prone to causing excessively high local flow velocities, increasing the probability of droplets impacting the wall, while pure porous plates result in insufficient turbulence, leading to low droplet evaporation and mixing efficiency. Existing technologies do not design solutions from the perspective of composite structure and compatibility with marine flow fields, resulting in poor reliability of SCR systems and recurring urea crystallization problems.

[0004] Therefore, there is an urgent need to develop a structure and method for preventing urea crystallization that is suitable for complex marine operating conditions, takes into account both turbulence intensity and flow field uniformity, and requires no additional energy consumption. This would prevent urea droplets from hitting the walls and from being insufficiently evaporated and mixed, thereby improving the operational stability of the SCR system. Summary of the Invention

[0005] The purpose of this invention is to provide a structure and method for preventing urea crystallization in marine engine SCR systems, thereby solving the technical defects of existing marine engine SCR systems with urea crystallization as mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a structure for preventing urea crystallization in a marine engine SCR system, comprising a mixing pipe, an inclined plate, a perforated plate, and a urea spray gun. The inclined plate is installed inside the mixing pipe and is located on the axis of the mixing pipe. The perforated plate is installed inside the mixing pipe and is located on the axis of the mixing pipe, behind the inclined plate. The urea spray gun is inserted into the mixing pipe.

[0007] Preferably, the mixing tube has a front end and a rear end, with the front end sleeved on the outside of the inclined plate.

[0008] Preferably, a first kit is fixedly connected to the inclined plate, a first positioning rod is inserted into the inner side of the first kit, the first kit and the first positioning rod are interference-fitted, and the two ends of the first positioning rod are fixedly connected to the inner wall of the front end.

[0009] Preferably, the porous plate is located on the side of the mixing tube near the front end, and the porous plate has dense through holes.

[0010] Preferably, a second assembly is fixedly connected to the porous plate, a second positioning rod is inserted into the inner side of the second assembly, the second assembly and the second positioning rod are interference-fitted, and the two ends of the second positioning rod are fixedly connected to the inner wall of the mixing tube.

[0011] Preferably, the output end of the urea spray gun extends through the mixing tube to the inside, the output end of the urea spray gun is located behind the perforated plate, and the output direction is set towards the rear end of the mixing tube.

[0012] Preferably, the structure for preventing urea crystallization in a marine engine SCR system as described in any one of claims 1-6 specifically includes the following steps: S1. Layout of inclined plate and perforated plate structure: Design the structural parameters of the inclined plate and perforated plate, install the inclined plate and perforated plate in the mixing pipe, insert the urea spray gun into the mixing pipe, and determine the initial relative positions of the three. S2. Constructing a CFD flow field simulation model: Use ANSYS Fluent to construct the simulation model, import structural parameters and set simulation boundary conditions; S3. Multi-parameter simulation calculation: Adjust the structural parameters and layout position, perform multiple simulation calculations, and obtain simulation data; S4. Parameter optimization and fixation: Determine whether the simulation results meet the preset indicators. If they do, fix the parameters and positions. If they do not meet the preset indicators, return to step S3 and re-simulate. S5. Actual assembly and operation: Complete the assembly according to the fixed parameters and connect to the SCR system for operation.

[0013] Preferably, in step S2, the simulation boundary conditions are: rated load flue gas velocity 36 kg / s, exhaust temperature 430°, ship roll ±30°, pitch ±15°, initial diameter of urea droplets 50 μm, evaporation model is Rosin-Rammler, turbulence model is Realizable k-ε, and the inner wall of the mixing pipe is set as a standard wall surface with adiabatic and no slippage.

[0014] Preferably, in step S3, the structural parameters include the size and tilt angle of the inclined plate, the size and porosity of the perforated plate; the arrangement position includes the distance between the inclined plate and the perforated plate, and the distance between the inclined plate and the perforated plate and the urea spray gun.

[0015] Preferably, in step S4, the preset indicators are: no urea droplets hitting the wall, no visible crystals, NOx conversion efficiency ≥90%, exhaust back pressure increase ≤5kPa, urea droplet evaporation rate ≥98%, and wall impact rate ≤1%.

[0016] The technical effects and advantages of this invention are as follows: 1. The structure and method for preventing urea crystallization in marine engine SCR systems utilize the synergistic effect of a composite structure of inclined plates and perforated plates. The inclined plates guide the exhaust to form high-intensity turbulence, improving the evaporation efficiency of urea droplets. The perforated plates uniformly distribute the turbulence, avoiding excessively high local flow velocities that could cause droplets to collide with the walls. This results in an urea droplet evaporation rate ≥98% and a wall impact rate ≤1%, fundamentally eliminating the formation of urea crystallization. No additional heating device is required, reducing system energy consumption and structural complexity.

[0017] 2. The structure and method for preventing urea crystallization in marine engine SCR systems, based on a composite structure optimized by CFD flow field simulation, can maintain stable turbulence guidance and uniform flow field distribution under ship roll ±30°, pitch ±15° and full load fluctuations from engine idle speed to rated load. The urea mixing and evaporation effects are not affected by the ship's operating conditions, significantly improving the operational reliability of the SCR system.

[0018] 3. The structure and method for preventing urea crystallization in marine engine SCR systems, with an optimized flow field of composite structure, ensures uniform mixing of urea droplets and exhaust gas, achieving NOx conversion efficiency ≥90% and exhaust back pressure increase ≤5kPa, thus avoiding engine power reduction, ensuring stable denitrification efficiency of the SCR system, meeting the requirements of international marine emission regulations such as IMO Tier III, and eliminating the risks of fines and ship impoundment faced by ships due to excessive emissions.

[0019] 4. The structure and method for preventing urea crystallization in marine engine SCR systems are described. The inclined plate and perforated plate are securely installed through the kit and positioning rod, which has good anti-ship vibration effect and low equipment failure rate. It eliminates the need for frequent disassembly and cleaning of crystals, simplifies equipment maintenance, avoids downtime losses caused by crystallization, extends the service life of the catalyst, and significantly reduces the operating and maintenance costs of the ship.

[0020] 5. The structure and method for preventing urea crystallization in marine engine SCR systems are described. The inclined plate and perforated plate are securely installed through a kit and positioning rod, which has good anti-ship vibration effect and low equipment failure rate. It eliminates the need for frequent disassembly and cleaning of crystals, simplifies equipment maintenance, avoids downtime losses caused by crystallization, extends the service life of the catalyst, and significantly reduces the operating and maintenance costs of the ship. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a top view structural diagram of the present invention. Figure 3 This is a schematic diagram of the inclined plate of the present invention; Figure 4 This is a schematic diagram of the structure of the porous plate of the present invention.

[0023] In the diagram: 1. Mixing tube; 11. Front end; 12. Rear end; 2. Inclined plate; 21. First kit; 22. First positioning rod; 3. Perforated plate; 31. Through hole; 32. Second kit; 33. Second positioning rod; 4. Urea spray gun. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention discloses a turning tool for machining the outer diameter of corrosion-resistant materials, according to the attached... Figure 1 As shown, the system includes a mixing tube 1, an inclined plate 2, a perforated plate 3, and a urea spray gun 4. The inclined plate 2 is installed inside the mixing tube 1 and is located on the axis of the mixing tube 1. The perforated plate 3 is installed inside the mixing tube 1 and is located on the axis of the mixing tube 1, behind the inclined plate 2. The urea spray gun 4 is inserted into the mixing tube 1.

[0026] According to the appendix Figures 1-2 As shown, the mixing tube 1 is further provided with a front end 11 and a rear end 12, with the front end 11 sleeved on the outside of the inclined plate 2.

[0027] According to the appendix Figure 3 As shown, further, a first kit 21 is fixedly connected to the inclined plate 2, and a first positioning rod 22 is inserted into the inner side of the first kit 21. The first kit 21 and the first positioning rod 22 are interference-fitted, and the two ends of the first positioning rod 22 are fixedly connected to the inner wall of the front end 11.

[0028] According to the appendix Figure 4 As shown, the porous plate 3 is located on the side of the mixing tube 1 near the front end 11, and the porous plate 3 is provided with dense through holes 31.

[0029] According to the appendix Figure 4 As shown, a second assembly 32 is fixedly connected to the perforated plate 3, and a second positioning rod 33 is inserted into the inner side of the second assembly 32. The second assembly 32 and the second positioning rod 33 are interference-fitted, and the two ends of the second positioning rod 33 are fixedly connected to the inner wall of the mixing tube 1.

[0030] According to the appendix Figure 1 As shown, the output end of the urea spray gun 4 extends through the mixing tube 1 to the inside, and the output end of the urea spray gun 4 is located behind the perforated plate 3, with the output direction facing the rear end 12 of the mixing tube 1.

[0031] According to the appendix Figures 1-4 As shown, a method for preventing urea crystallization in a marine engine SCR system is specifically disclosed, characterized by comprising the following steps: S1. Layout of the inclined plate and perforated plate structure: Design the structural parameters of the inclined plate 2 and the perforated plate 3, install the inclined plate 2 and the perforated plate 3 inside the mixing pipe 1, and insert the urea spray gun 4 into the mixing pipe 1, determining the initial relative positions of the three. Design the dimensions of the inclined plate 2 to match the inner diameter of the mixing pipe 1, with the initial tilt angle set at 45°. Design the dimensions of the perforated plate 3 to match the inner diameter of the mixing pipe 1, with the initial opening ratio set at 0.65. Weld the inclined plate 2 to the inner side of the front end 11 of the mixing pipe 1 through the first kit 21 and the first positioning rod 22. Weld the perforated plate 3 to the rear side of the inclined plate 2 at 20cm through the second kit 32 and the second positioning rod 33. Insert the urea spray gun 4 into the pipe wall of the mixing pipe 1 at 30cm rear side of the perforated plate 3.

[0032] S2. Constructing the CFD Flow Field Simulation Model: The simulation model was constructed using ANSYS Fluent, importing structural parameters and setting simulation boundary conditions. The structural parameters of mixing pipe 1, inclined plate 2, and perforated plate 3 were imported into the ANSYS Fluent software. Simulation boundary conditions were set as follows: rated load flue gas velocity 36 kg / s, exhaust temperature 430℃, ship roll ±30°, pitch ±15°, initial urea droplet diameter 50 μm, evaporation model Rosin-Rammler, turbulence model Realizable k-ε, and the inner wall of mixing pipe 1 was set as a standard wall with adiabatic and no-slip properties.

[0033] S3. Multi-parameter simulation calculation: Adjusting structural parameters and arrangement positions, multiple simulation calculations were performed to obtain simulation data. The tilt angle of inclined plate 2, the porosity of perforated plate 3, the distance between inclined plate 2 and perforated plate 3, and the distance between perforated plate 3 and urea spray gun 4 were adjusted using a CFD model. A total of 27 sets of structural parameters and arrangement positions were simulated to obtain data such as system pressure drop, ammonia uniformity, droplet collision rate, and droplet evaporation rate for each set. Inclined plate 2 tilt angle: 30°, 45°, 60°. Perforated plate 3 porosity: 0.5, 0.65, 0.8. Distance between inclined plate 2 and perforated plate 3: 15cm, 20cm, 25cm. Distance between perforated plate 3 and urea spray gun 4: 25cm, 30cm, 35cm.

[0034] S4. Parameter Optimization and Consolidation: Determine if the simulation results meet the preset indicators. If they do, consolidate the parameters and positions; otherwise, return to step S3 and re-simulate. The simulation should show no wall collisions or visible crystals in the urea droplets, NOx conversion efficiency ≥90%, exhaust back pressure increase ≤5kPa, urea droplet evaporation rate ≥98%, and wall impact rate ≤1%. Simulation verification shows that when the inclined plate 2 has an inclination angle of 45°, the perforated plate 3 has an opening ratio of 0.65, the distance between the inclined plate 2 and the perforated plate 3 is 20cm, and the distance between the perforated plate 3 and the urea spray gun 4 is 30cm, all simulation results meet the preset indicators. At this point, the urea droplet evaporation rate is 98.7%, the wall impact rate is 0.8%, the NOx conversion efficiency is 92.5%, and the exhaust back pressure increase is 3.2kPa. Consolidate the structural parameters and arrangement positions for this set.

[0035] S5. Actual Assembly and Operation: Complete the assembly according to the cured parameters and connect it to the SCR system for operation. According to the cured parameters, complete the welding and insertion assembly of mixing pipe 1, inclined plate 2, perforated plate 3 and urea spray gun 4, and connect the assembled SCR mixing pipe section to the marine diesel engine SCR system with a rated power of 16500kW for actual operation.

[0036] According to the appendix Figures 1-4As shown, specifically disclosed, in step S2, the simulation boundary conditions are: rated load flue gas velocity 36 kg / s, exhaust temperature 430℃, ship roll ±30°, pitch ±15°, initial diameter of urea droplets 50 μm, evaporation model is Rosin-Rammler, turbulence model is Realizable k-ε, and the inner wall of mixing pipe 1 is set as a standard wall surface with adiabatic and no slippage.

[0037] According to the appendix Figures 1-4 As shown, it is particularly important to emphasize that in step S3, the structural parameters include the size and tilt angle of the inclined plate 2, the size and porosity of the perforated plate 3, and the arrangement position includes the distance between the inclined plate 2 and the perforated plate 3, and the distance between the inclined plate 2 and the perforated plate 3 and the urea spray gun 4.

[0038] According to the appendix Figures 1-4 As shown, it is particularly important to emphasize that in step S4, the preset indicators are: no urea droplets hitting the wall, no visible crystals, NOx conversion efficiency ≥90%, exhaust back pressure increase ≤5kPa, urea droplet evaporation rate ≥98%, and wall impact rate ≤1%.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A structure for preventing urea crystallization in a marine engine SCR system, characterized in that, include: Mixing tube (1); Inclined plate (2), the inclined plate (2) is installed inside the mixing tube (1), the inclined plate (2) is located on the axis of the mixing tube (1); A perforated plate (3) is installed inside the mixing tube (1), the perforated plate (3) is located on the axis of the mixing tube (1), and the perforated plate (3) is located behind the inclined plate (2); Urea spray gun (4), which is inserted into the mixing tube (1).

2. The structure for preventing urea crystallization in a marine engine SCR system according to claim 1, characterized in that, The mixing tube (1) is provided with a front end (11) and a rear end (12), and the front end (11) is sleeved on the outside of the inclined plate (2).

3. The structure for preventing urea crystallization in a marine engine SCR system according to claim 1, characterized in that, A first kit (21) is fixedly connected to the inclined plate (2). A first positioning rod (22) is inserted into the inner side of the first kit (21). The first kit (21) and the first positioning rod (22) are interference-fitted. The two ends of the first positioning rod (22) are fixedly connected to the inner wall of the front end (11).

4. The structure for preventing urea crystallization in a marine engine SCR system according to claim 1, characterized in that, The porous plate (3) is located on the side of the mixing tube (1) near the front end (11), and the porous plate (3) has dense through holes (31).

5. The structure for preventing urea crystallization in a marine engine SCR system according to claim 1, characterized in that, A second kit (32) is fixedly connected to the perforated plate (3). A second positioning rod (33) is inserted into the inner side of the second kit (32). The second kit (32) and the second positioning rod (33) are interference-fitted. The two ends of the second positioning rod (33) are fixedly connected to the inner wall of the mixing tube (1).

6. The structure for preventing urea crystallization in a marine engine SCR system according to claim 1, characterized in that, The output end of the urea spray gun (4) passes through the mixing tube (1) to the inside. The output end of the urea spray gun (4) is located behind the perforated plate (3) and the output direction is set towards the rear end (12) of the mixing tube (1).

7. A method for preventing urea crystallization in a marine engine SCR system, characterized in that, The structure for preventing urea crystallization in a marine engine SCR system as described in any one of claims 1-6 specifically includes the following steps: S1. Layout of inclined plate and perforated plate structure: Design the structural parameters of inclined plate (2) and perforated plate (3), install inclined plate (2) and perforated plate (3) in mixing pipe (1), insert urea spray gun (4) into mixing pipe (1), and determine the initial relative position of the three. S2. Constructing a CFD flow field simulation model: Use ANSYS Fluent to construct the simulation model, import structural parameters and set simulation boundary conditions; S3. Multi-parameter simulation calculation: Adjust the structural parameters and layout position, perform multiple simulation calculations, and obtain simulation data; S4. Parameter optimization and fixation: Determine whether the simulation results meet the preset indicators. If they do, fix the parameters and positions. If they do not meet the preset indicators, return to step S3 and re-simulate. S5. Actual assembly and operation: Complete the assembly according to the fixed parameters and connect to the SCR system for operation.

8. A method for preventing urea crystallization in a marine engine SCR system according to claim 7, characterized in that, In step S2, the simulation boundary conditions are: rated load flue gas velocity 36 kg / s, exhaust temperature 430°, ship roll ±30°, pitch ±15°, initial diameter of urea droplets 50 μm, evaporation model is Rosin-Rammler, turbulence model is Realizable k-ε, and the inner wall of the mixing pipe (1) is set as a standard wall surface with thermal insulation and no slippage.

9. A method for preventing urea crystallization in a marine engine SCR system according to claim 7, characterized in that, In step S3, the structural parameters include the size and tilt angle of the inclined plate (2), the size and porosity of the perforated plate (3); the arrangement position includes the distance between the inclined plate (2) and the perforated plate (3), and the distance between the inclined plate (2) and the perforated plate (3) and the urea spray gun (4).

10. A method for preventing urea crystallization in a marine engine SCR system according to claim 7, characterized in that, In step S4, the preset indicators are: no urea droplets hitting the wall, no visible crystals, NOx conversion efficiency ≥90%, exhaust back pressure increase ≤5kPa, urea droplet evaporation rate ≥98%, and wall impact rate ≤1%.

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