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CN-121993280-A - Structure and method for preventing urea of marine engine SCR system from crystallizing

CN121993280ACN 121993280 ACN121993280 ACN 121993280ACN-121993280-A

Abstract

The invention discloses a structure and a method for preventing urea from crystallizing in an SCR system of a marine engine, and relates to the technical field of engines. According to the structure and the method for preventing urea crystallization of the marine engine SCR system, the mixing pipe, the inclined plate, the porous plate and the urea spray gun are arranged on the inner axis of the mixing pipe, the inclined plate is used for exciting turbulence, the porous plate is arranged on the rear side of the inclined plate and used for uniformly distributing flow fields, and the urea spray gun sprays urea into the optimized flow fields. The invention adjusts and controls the flow field through the cooperation of the composite structure, so that the evaporation rate of urea liquid drops is more than or equal to 98%, the wall impact rate is less than or equal to 1%, crystallization is stopped from the source, the rolling and pitching of the ship and the full load fluctuation of the engine are adapted, the NOx conversion efficiency is more than or equal to 90%, the exhaust back pressure is increased by less than or equal to 5kPa, no additional energy consumption is required, the reliability of the SCR system is greatly improved, and the operation and maintenance cost is reduced.

Inventors

  • HUANG LIAN
  • LIU QIYUAN
  • RAO WEI
  • SUN RENJUN
  • ZHOU CHUNYAN
  • CHEN KEFU

Assignees

  • 宜昌船舶柴油机有限公司

Dates

Publication Date
20260508
Application Date
20260302

Claims (10)

  1. 1. A structure for preventing urea from crystallizing in an SCR system of a marine engine, comprising: a mixing tube (1); The inclined plate (2) is arranged on the inner side of the mixing pipe (1), and the inclined plate (2) is positioned on the axis of the mixing pipe (1); The porous plate (3) is arranged on the inner side of the mixing pipe (1), the porous plate (3) is positioned on the axis of the mixing pipe (1), and the porous plate (3) is positioned on the rear side of the inclined plate (2); the urea spray gun (4), urea spray gun (4) peg graft on mixing tube (1).
  2. 2. Structure for preventing urea crystallization of marine engine SCR system according to claim 1, characterized in that the mixing pipe (1) is provided with a front end (11) and a rear end (12), the front end (11) is sleeved outside the sloping plate (2).
  3. 3. The structure for preventing urea crystallization of the marine engine SCR system according to claim 1, wherein a first sleeve member (21) is fixedly connected to the inclined plate (2), a first positioning rod (22) is inserted into the inner side of the first sleeve member (21), the first sleeve member (21) is in interference fit with the first positioning rod (22), and two ends of the first positioning rod (22) are fixedly connected to the inner wall of the front end (11).
  4. 4. Structure for preventing urea crystallization in a marine engine SCR system according to claim 1, characterized in that the perforated plate (3) is located at the side of the mixing pipe (1) near the front end (11), and the perforated plate (3) is provided with dense through holes (31).
  5. 5. The structure for preventing urea crystallization of the marine engine SCR system according to claim 1, wherein a second sleeve member (32) is fixedly connected to the porous plate (3), a second positioning rod (33) is inserted into the inner side of the second sleeve member (32), the second sleeve member (32) and the second positioning rod (33) are in interference fit, and two ends of the second positioning rod (33) are fixedly connected to the inner wall of the mixing pipe (1).
  6. 6. 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) penetrates the mixing pipe (1) to the inside, the output end of the urea spray gun (4) is located at the rear side of the porous plate (3), and the output direction is set towards the rear end (12) of the mixing pipe (1).
  7. 7. A method for preventing urea of a marine engine SCR system from crystallizing is characterized in that, a structure for preventing urea crystallization of a marine engine SCR system according to any one of claims 1-6, comprising the steps of: S1, designing structural parameters of the sloping plate (2) and the porous plate (3), installing the sloping plate (2) and the porous plate (3) in a mixing pipe (1), and inserting a urea spray gun (4) on the mixing pipe (1) to determine initial relative positions of the sloping plate (2) and the porous plate (3); S2, constructing a CFD flow field simulation model, namely constructing a simulation model by adopting ANSYS Fluent, importing structural parameters and setting simulation boundary conditions; s3, multiple groups of parameter simulation calculation, namely adjusting structural parameters and arrangement positions, and performing multiple groups of simulation calculation to obtain simulation data; S4, parameter optimization and solidification, namely judging whether a simulation result meets a preset index, solidifying parameters and positions if the simulation result meets the preset index, and returning to the step S3 for re-simulation if the simulation result does not meet the preset index; s5, the actual assembly and operation are completed according to the curing parameters, and the SCR system is connected to be put into operation.
  8. 8. A method for preventing urea crystallization in a marine engine SCR system according to claim 7, wherein in step S2, the simulation boundary conditions are rated load flue gas flow rate 36kg/S, exhaust temperature 430 ℃, ship roll + -30 DEG, pitch + -15 DEG, initial diameter of urea droplet 50 μm, evaporation model is Rosin-Rammler, turbulence model is Realizable k-epsilon, and the inner wall of the mixing tube (1) is set as standard wall insulation slip-free.
  9. 9. The method for preventing urea from crystallizing in an SCR system of a marine engine as claimed in claim 7, wherein in step S3, the structural parameters include size of the inclined plate (2), inclination angle, size of the porous plate (3), and aperture ratio, and the arrangement position includes a distance between the inclined plate (2) and the porous plate (3), and a distance between the inclined plate (2) and the porous plate (3) and the urea spray gun (4).
  10. 10. The method for preventing urea from crystallizing in an SCR system of a marine engine as set forth in claim 7, wherein in step S4, the preset index is that urea droplets do not collide with walls, no visible crystallization occurs, NOx conversion efficiency is not less than 90%, exhaust back pressure rise is not more than 5kPa, evaporation rate of urea droplets is not less than 98%, and wall impact rate is not more than 1%.

Description

Structure and method for preventing urea of marine engine SCR system from crystallizing Technical Field The invention relates to the technical field of engines, in particular to a structure and a method for preventing urea of an SCR system of a marine engine from crystallizing. Background The marine engine SCR system is core equipment for denitration of marine tail gas, and urea aqueous solution with the mass fraction of 40% is required to be sprayed into high-temperature exhaust gas, so that ammonia gas generated by urea decomposition and nitrogen oxides are subjected to selective reaction under the action of a catalyst and converted into harmless nitrogen gas and water, and the requirements of international ship emission regulations such as IMO TierIII and the like are met. However, the marine operation scene has a plurality of special working condition problems, which are easy to cause insufficient evaporation and mixing of partial urea liquid drops, and the partial urea liquid drops impact the inner wall of a pipeline of the SCR system or the inlet of the catalyst carrier, so that solid urea crystals are formed. The existing urea crystallization prevention technology has obvious defects, and can not fundamentally solve the crystallization problem of marine scenes, namely the problems that the flow field of a marine engine is difficult to adapt to greatly fluctuation and uneven distribution of liquid drops are not solved only by improving the urea injection pressure, the additional heating device is added to improve the evaporation efficiency of the liquid drops, but also increase the energy consumption and the structural complexity of the system and improve the failure rate and the maintenance cost of equipment, and the adoption of a single static mixing structure of a pure sloping plate or a pure porous plate can not achieve the turbulence intensity and the uniformity of the flow field, the pure sloping plate is easy to cause the local too high flow velocity, the probability that the liquid drops impact the wall surface is increased, the pure porous plate can cause insufficient turbulence, and the evaporation and the mixing efficiency of the liquid drops are low. The prior art has no solution from the angles of the composite structure and the matching of the marine flow field, so that the reliability of the SCR system is poor, and the problem of urea crystallization repeatedly occurs. Therefore, development of a urea crystallization prevention structure and method which are suitable for complex working conditions of a ship, compatible with turbulence intensity and flow field uniformity and free of additional energy consumption is needed, so that the problems of collision of urea liquid drops and insufficient evaporation and mixing are avoided from the source, and the running stability of an SCR system is improved. Disclosure of Invention The invention aims to provide a structure and a method for preventing urea crystallization of a marine engine SCR system, which are used for solving the technical defect problems of urea crystallization of the existing marine engine SCR system in the background technology. The technical scheme is that the structure for preventing urea of the marine engine SCR system from crystallizing comprises a mixing pipe, a sloping plate, a porous plate and a urea spray gun, wherein the sloping plate is arranged on the inner side of the mixing pipe, and the sloping plate is positioned on the axis of the mixing pipe. The porous plate is arranged on the inner side of the mixing pipe, is positioned on the axis of the mixing pipe and is positioned on the rear side of the sloping plate. The urea spray gun is inserted on the mixing pipe. Preferably, the mixing tube is provided with a front end and a rear end, and the front end is sleeved on the outer side of the inclined plate. Preferably, the inclined plate is fixedly connected with a first sleeve member, a first positioning rod is inserted into the inner side of the first sleeve member, the first sleeve member is in interference fit with the first positioning rod, and two ends of the first positioning rod are fixedly connected to the inner wall of the front end. Preferably, the porous plate is positioned at one side of the mixing pipe close to the front end, and dense through holes are formed in the porous plate. Preferably, the perforated plate is fixedly connected with a second sleeve member, a second positioning rod is inserted into the inner side of the second sleeve member, the second sleeve member is in interference fit with the second positioning rod, and two ends of the second positioning rod are fixedly connected to the inner wall of the mixing tube. Preferably, the output end of the urea spray gun penetrates through the mixing pipe to the inner side, the output end of the urea spray gun is positioned at the rear side of the porous plate, and the output direction is arranged towards the rear end of the mixing pipe. Preferably,