A pretreatment process for oil-containing waste gases

Abstract

The application discloses a pretreatment process of oil-containing waste gas, which comprises the following steps: cooling the oil-containing waste gas in a cooling device, wherein the temperature of the waste gas after cooling is 5-10 DEG C higher than the pour point of the oil product and 10-20 DEG C lower than the dew point; passing the waste gas after cooling into a multi-stage wire mesh oil removal unit at a gas speed of 1-3 m / s, wherein the unit comprises at least two wire mesh assemblies arranged in sequence along the gas flow direction, a flow area is formed between adjacent wire mesh assemblies, and at least part of the wire mesh assemblies are internally provided with hollow cavities; making the gas flow change direction in the flow area through a gas guide plate, guiding the gas flow to separate from the liquid oil mist and preventing the oil liquid from being secondarily entrained, and meanwhile, the sum of the pressure drop of the cooling device, the pressure drop of the diameter expansion section and the pressure drop of the multi-stage wire mesh oil removal unit is controlled to be less than 80% of the total pressure of the fan; and collecting the separated oil liquid in an oil collecting tank. The application can efficiently separate the oil mist, effectively control the total pressure drop of the system and realize efficient, low-consumption and stable pretreatment of the oil-containing waste gas.

Description

Technical Field

[0001] This invention relates to the field of waste gas treatment technology, and more specifically, to a pretreatment process for oily waste gas. Background Technology

[0002] Oily waste gases are widely generated in the production processes of industries such as machining, petrochemicals, food processing, and printing. These gases contain large amounts of oil vapor, oil mist, and particulate matter. If emitted directly without effective treatment, they will not only cause air pollution but also adversely affect the health of production equipment and operators. Therefore, the purification and treatment of oily waste gases is an essential step in industrial production.

[0003] Currently, the pretreatment process for oily waste gas typically employs a combination of cooling and wire mesh oil removal. The basic principle is as follows: first, the high-temperature oily waste gas is passed into a cooling device, causing the oil vapor to condense into liquid oil mist; then, the cooled waste gas is passed into a wire mesh oil separator, where the interception, collision, and coalescence effects of the wire mesh achieve gas-liquid separation. This process is widely used due to its simple equipment and relatively low operating costs.

[0004] However, existing processes still face numerous technical challenges in practical applications. Firstly, the distribution of airflow velocity during wire mesh degreasing is closely related to the oil mist separation efficiency. When the airflow velocity is too high, the oil already captured on the wire mesh is easily dispersed again by the high-speed airflow, creating a "secondary entrainment" phenomenon, leading to a significant decrease in separation efficiency. To address this issue, some existing technologies attempt to enhance the interception effect by increasing the number of wire mesh layers or using denser wire mesh. However, this results in a sharp increase in system pressure drop, not only increasing fan energy consumption but also potentially causing the fan to be unable to overcome system resistance, thus affecting normal operation.

[0005] Secondly, existing processes lack a systematic approach to controlling system pressure drop. The pressure drop of each unit, such as the cooling device, piping, and wire mesh oil separator, is often designed independently, lacking matching and coordination. When multiple units are used in combination, the total pressure drop may far exceed the fan's residual pressure, leading to unstable system operation. While some existing technologies address the pressure drop issue, the common approach is to simplify the oil removal structure or reduce the wire mesh density, which inevitably sacrifices oil removal efficiency, creating a contradiction between "efficiency" and "energy consumption."

[0006] Furthermore, the existing processes have relatively simple mechanisms for collecting and discharging separated oil. Conventional oil collection structures often fail to effectively prevent oil from being re-entrained by airflow, and lack automated oil discharge and maintenance designs. This leads to performance degradation due to oil buildup after long-term operation, resulting in high maintenance costs.

[0007] In summary, how to effectively control the total pressure drop of the system, prevent secondary oil entrainment, and achieve long-term stable operation while ensuring efficient gas-liquid separation is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In order to overcome the above-mentioned defects of the prior art, embodiments of the present invention provide a pretreatment process for oily waste gas.

[0009] To achieve the above objectives, the innovative aspects of this invention are as follows: it includes the following steps:

[0010] The oily exhaust gas is passed into a cooling device to cool it down, so that the oil vapor condenses into liquid oil mist. The temperature of the exhaust gas after cooling is 5–10°C higher than the pour point of the oil and 10–20°C lower than the dew point.

[0011] The cooled oily exhaust gas is introduced into a multi-stage wire mesh oil removal unit at a gas velocity of 1–3 m / s. The multi-stage wire mesh oil removal unit includes at least two stages of wire mesh assemblies arranged sequentially along the airflow direction. A flow area is formed between adjacent wire mesh assemblies, and at least some of the wire mesh assemblies have hollow cavities inside.

[0012] Among them, the airflow is changed in direction by the air guide plate in the flow area to guide the airflow to separate from the liquid oil mist and prevent the oil from being entrained by the airflow again. At the same time, the pressure drop of the cooling device, the pressure drop of the expansion section and the pressure drop of the multi-stage wire mesh oil removal unit are controlled to not exceed 80% of the total pressure of the fan, so as to maintain the total pressure drop of the system within the acceptable range of the project while preventing the secondary entrainment of oil.

[0013] The separated oil is collected in an oil collection tank, which includes an inner oil collection tank located at the bottom of the cavity and an outer oil collection tank located at the bottom of the flow area.

[0014] Furthermore, the cooling device is a shell-and-tube heat exchanger, and the oily exhaust gas flows through the shell side, with the pressure drop of the cooling device controlled at 400–600 Pa.

[0015] Furthermore, the multi-stage wire mesh degreasing unit includes three-stage wire mesh assemblies: a primary wire mesh assembly, a secondary wire mesh assembly, and a tertiary wire mesh assembly. Along the airflow direction, the asymmetry between the air inlet and outlet surfaces of each stage of the wire mesh assembly increases progressively.

[0016] Furthermore, along the airflow direction, the porosity of the wire mesh in each level of the wire mesh assembly decreases progressively.

[0017] Furthermore, the primary wire mesh assembly includes a rectangular frame A, the interior of which has a hollow cavity A, which constitutes part of the cavity; the left side of the rectangular frame A is an air inlet surface, which is the inlet surface A, and its entire surface is formed by three wire meshes sequentially spliced ​​from top to bottom in the vertical direction; the right side of the rectangular frame A is an air outlet surface, which is the outlet surface A, and its upper part is a closed surface A, and its lower part is formed by two wire meshes sequentially spliced ​​in the vertical direction; the bottom of the cavity A is provided with an inner oil collection groove, which is the inner oil collection groove A.

[0018] Furthermore, a flow area, referred to as flow area A, is formed between the primary wire mesh assembly and the secondary wire mesh assembly. An external oil collection tank, referred to as external oil collection tank A, is provided at the bottom of flow area A. An inclined air guide plate A is provided within flow area A, with the angle between the air guide plate A and the horizontal direction being 45°–60°. The bottom of the air guide plate A is fixed inside the external oil collection tank A, and the top of the air guide plate A is inclined towards the secondary wire mesh assembly. The top edge of the air guide plate A is flush with the lower edges of the two wire meshes on the outlet surface A, which is used to guide the airflow flowing out of the outlet surface A upward and to guide the captured oil into the external oil collection tank A.

[0019] Furthermore, the secondary wire mesh assembly includes a rectangular frame B, the interior of which has a hollow cavity B, which constitutes part of the cavity; the left side of the rectangular frame B is an air inlet surface, which is the entry surface B, and its entire surface is formed by three wire meshes spliced ​​together sequentially from top to bottom in the vertical direction; the right side of the rectangular frame B is an air outlet surface, which is the outlet surface B, and its upper part is formed by two closed surfaces B sequentially arranged in the vertical direction, and its lower part is formed by a single wire mesh spliced ​​together; the bottom of the cavity B is provided with an inner oil collection groove, which is the inner oil collection groove B.

[0020] Furthermore, a flow area, referred to as flow area B, is formed between the secondary and tertiary wire mesh components. An external oil collection trough, referred to as external oil collection trough B, is located at the bottom of flow area B. An inclined air guide plate B is located within flow area B, with the angle between the air guide plate B and the horizontal direction being 45°–60°. The bottom of the air guide plate B is fixed inside the external oil collection trough B, and the top of the air guide plate B is inclined towards the tertiary wire mesh component. The top edge of the air guide plate B is flush with the lower edge of one of the wire meshes on the outlet surface B, serving to guide the airflow from the outlet surface B upwards and guide the collected oil into the external oil collection trough B.

[0021] Furthermore, the three-stage wire mesh assembly comprises three layers of wire mesh spliced ​​vertically from top to bottom, and both its air inlet and outlet surfaces are full wire mesh structures; the three-stage wire mesh assembly does not have cavities or internal oil collection grooves.

[0022] Furthermore, the outlet of the cooling device is connected to the inlet of the multi-stage wire mesh degreasing unit through an expansion section. The expansion section is used to reduce the airflow velocity to 1–3 m / s, and the pressure drop of the expansion section is controlled at 50–150 Pa. Each wire mesh component in the multi-stage wire mesh degreasing unit is set as a removable module, and the equipment housing is equipped with an online cleaning interface. Both the inner and outer oil collection tanks are equipped with liquid level sensors and automatic oil drain valves.

[0023] The technical effects and advantages of this invention are as follows:

[0024] 1. This invention incorporates a wire mesh assembly with a hollow cavity and asymmetrical air inlet and outlet surfaces within a multi-stage wire mesh oil removal unit. An inclined air guide plate is placed within the flow area between adjacent assemblies, causing the airflow to repeatedly change direction during flow. This utilizes the combined effects of inertial collision and gravitational settling to efficiently separate oil mist. Simultaneously, the air guide plate directly guides the collected oil into an external oil collection tank, preventing secondary entrainment of the separated oil by the airflow. Combined with a gradient design where the wire mesh porosity gradually decreases along the airflow direction, this invention significantly improves oil removal efficiency while achieving highly efficient gas-liquid separation, effectively solving the secondary entrainment problem caused by excessively high airflow velocity or unreasonable structure in existing technologies.

[0025] 2. This invention systematically matches the pressure drop of the cooling device, the pressure drop of the expansion section, and the pressure drop of the multi-stage wire mesh oil removal unit, ensuring that the sum of these three does not exceed 80% of the total fan pressure. Combined with a wire mesh density gradient design, modular removable wire mesh components, and an online cleaning interface, it achieves precise control of the total system pressure drop. Furthermore, by incorporating pressure sensors and a control system, it can monitor the pressure drop of each unit in real time and dynamically adjust the cooling device pressure drop or initiate online cleaning, ensuring that the total pressure drop remains within an acceptable range even after fluctuations in operating conditions or long-term operation. This invention organically combines a highly efficient anti-secondary entrainment structure with systematic pressure drop balancing measures, achieving a balance between separation efficiency and operating energy consumption, and ensuring the long-term stable operation of the system. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the equipment structure for the oily waste gas pretreatment process in an embodiment of the present invention;

[0027] Figure 2 This is a diagram showing the internal structure of the multi-stage wire mesh degreasing unit of the present invention.

[0028] Figure 3 for Figure 2 Schematic diagram of the structure of a primary wire mesh assembly;

[0029] Figure 4 for Figure 2 Schematic diagram of the structure of the intermediate and secondary wire mesh assembly;

[0030] Figure 5for Figure 2 Schematic diagram of the structure of a three-stage wire mesh assembly;

[0031] In the diagram: 1. Cooling device; 2. Expansion section; 3. Multi-stage wire mesh oil removal unit; 31. Primary wire mesh assembly; 311. Rectangular frame A; 312. Cavity A; 313. Inlet surface A; 314. Outlet surface A; 315. Sealed surface A; 316. Inner oil collection tank A; 32. Secondary wire mesh assembly; 321. Rectangular frame B; 322. Cavity B; 323. Inlet surface B; 324. Outlet surface B; 325. Sealed surface B; 326. Inner oil collection tank B; 33. Tertiary wire mesh assembly; 6. Wire mesh; 4. Flow area A; 41. Outer oil collection tank A; 42. Air guide plate A; 5. Flow area B; 51. Outer oil collection tank B; 52. Air guide plate B. Detailed Implementation

[0032] 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.

[0033] Example 1

[0034] This embodiment provides a pretreatment process for oily waste gas. This process efficiently removes oil mist from oily waste gas through steps such as cooling, oil removal, and collection, and achieves stable and low-energy operation of the system.

[0035] like Figure 1 As shown, the equipment used to implement the process of this embodiment mainly includes: a cooling device 1, an expansion section 2, and a multi-stage wire mesh oil removal unit 3. The oily waste gas first enters the cooling device 1 for cooling, causing the oil vapor to condense into liquid oil mist; after being decelerated by the expansion section 2, the cooled waste gas enters the multi-stage wire mesh oil removal unit 3 for gas-liquid separation; the separated oil is then collected in an oil collection tank.

[0036] 1. Cooling and pressure drop control

[0037] In this step, the oily exhaust gas is passed into cooling device 1 to cool it down, causing the oil vapor to condense into liquid oil mist. To ensure that the oil mist has good fluidity and can condense efficiently, the temperature of the cooled exhaust gas is precisely controlled within two boundary conditions: its lower limit is 5-10°C higher than the pour point of the oil to ensure that the oil has good fluidity, and its upper limit is 10-20°C lower than the dew point to ensure that the oil vapor is fully condensed into liquid oil mist.

[0038] In a preferred embodiment, the cooling device 1 is a shell-and-tube heat exchanger, with the oily exhaust gas flowing through the shell side. This design allows for easy control of the pressure drop, stabilizing it within the range of 400-600 Pa. This pressure drop range is one of the foundations for balancing the overall system pressure drop, preventing excessive fan pressure consumption due to excessive cooler resistance.

[0039] 2. Diameter Expansion and Speed ​​Control

[0040] The cooled exhaust gas enters the expansion section 2 through the outlet of the cooling device 1. The inlet of the expansion section 2 is connected to the cooling device 1, and its outlet is connected to the inlet of the multi-stage wire mesh oil removal unit 3. The main function of the expansion section 2 is to reduce the airflow velocity to 1-3 m / s. This velocity range is crucial for achieving efficient wire mesh oil removal, ensuring that oil mist particles have sufficient time to collide with and adhere to the wire mesh, while preventing excessively high airflow velocities from re-dispersing the captured oil and creating secondary entrainment.

[0041] In this embodiment, the pressure drop of the expansion section 2 is controlled within 50-150 Pa. By rationally designing the cone angle and length of the expansion section, the local resistance it generates is controlled at a low level while achieving speed reduction, thus contributing to the balance of the total system pressure drop.

[0042] 3. Multi-stage wire mesh degreasing and anti-secondary entrainment structure

[0043] like Figure 2 As shown, the multi-stage wire mesh degreasing unit 3 includes a primary wire mesh assembly 31, a secondary wire mesh assembly 32, and a tertiary wire mesh assembly 33 arranged sequentially along the airflow direction, forming a three-stage degreasing structure. Flow regions are formed between adjacent wire mesh assemblies, namely flow region A4 between the primary wire mesh assembly 31 and the secondary wire mesh assembly 32, and flow region B5 between the secondary wire mesh assembly 32 and the tertiary wire mesh assembly 33.

[0044] The core of this process lies in setting up a wire mesh assembly with a hollow cavity and setting up an air guide plate in the flow area to guide the airflow to change direction, thereby achieving efficient gas-liquid separation and preventing the oil from being entrained by the airflow.

[0045] 3.1 Primary wire mesh assembly and its related structures

[0046] like Figure 2 and Figure 3 As shown, the primary wire mesh assembly 31 includes a rectangular frame A311. The interior of the rectangular frame A311 has a hollow cavity A312, which forms part of the hollow cavity of the entire oil removal unit. The bottom of the cavity A312 is provided with an inner oil collection tank A316 for collecting the oil trapped inside the primary wire mesh assembly 31.

[0047] The left side of the rectangular frame A311 is the air inlet surface, or inlet surface A313, which is composed of three wire meshes 6 sequentially spliced ​​together vertically from top to bottom. The right side of the rectangular frame A311 is the air outlet surface, or outlet surface A314, which is a closed surface A315 at the top and composed of two wire meshes 6 sequentially spliced ​​together vertically at the bottom. This asymmetrical structure of "full wire mesh for the air inlet surface and closed upper part and wire mesh for the air outlet surface" forces the airflow to mainly flow out from the lower wire mesh area when leaving the first-stage wire mesh assembly 31, thereby changing the mainstream direction of the airflow and creating a downward flow trend in the airflow within the cavity A312. This helps to guide the captured oil into the inner oil collection tank A316 at the bottom.

[0048] A flow region A4 is formed between the primary wire mesh assembly 31 and the secondary wire mesh assembly 32. An outer oil collection tank A41 is provided at the bottom of the flow region A4. An inclined air guide plate A42 is provided within the flow region A4, with the angle between the air guide plate A42 and the horizontal direction preferably being 45°-60°. The bottom of the air guide plate A42 is fixed inside the outer oil collection tank A41, and its top is inclined towards the secondary wire mesh assembly 32. The top edge of the air guide plate A42 is flush with the lower edges of the two wire meshes on the outlet surface A314.

[0049] Its working principle is as follows: When the airflow carrying some oil mist flows out from the outlet surface A314, the airflow will concentrate and flow out from this point because the lower part of the outlet surface A314 is a wire mesh structure. The outflowing airflow then impacts the air guide plate A42, which forces the airflow upward, allowing it to enter the secondary wire mesh assembly 32 at a more uniform flow rate. During this process, the oil droplets entrained in the airflow will impact and adhere to the surface of the air guide plate A42 under the action of inertia and gravity, flowing downward along the plate wall and finally being guided into the outer oil collection tank A41. This design effectively prevents the airflow from the primary wire mesh assembly 31 from directly impacting the liquid surface of the outer oil collection tank A41, thereby avoiding the re-rolling and entrainment of the separated oil and achieving a highly efficient anti-secondary entrainment function.

[0050] It is worth mentioning that although the air outlet surfaces of the primary wire mesh assembly 31 and the secondary wire mesh assembly 32 adopt a partially closed structure, which may cause a slight increase in local flow velocity when the airflow passes through the remaining wire mesh area, the overall airflow velocity has been reduced to a low-speed range of 1-3 m / s in the upstream expansion section. Even with local acceleration, the absolute velocity is still far below the critical value (usually >5 m / s) that would cause oil film rupture or severe secondary entrainment. Meanwhile, the inclined air guide plates (42, 52) located immediately downstream of the air outlet surface not only change the airflow direction and utilize inertial separation, but also act as a resistance element, effectively buffering and dissipating kinetic energy, ensuring that the airflow enters the next stage wire mesh assembly in a uniform, low-speed manner. Therefore, the structural design of this invention effectively avoids the risks associated with localized high air velocities while achieving efficient separation.

[0051] It should be noted that although the air outlet surfaces of the primary wire mesh assembly 31 and the secondary wire mesh assembly 32 adopt a partially enclosed structure, which may cause a slight increase in local flow velocity when the airflow passes through the remaining wire mesh area, the overall airflow velocity has been reduced to a low-speed range of 1-3 m / s in the upstream expansion section. Even with local acceleration, the absolute velocity is still far below the critical value that would cause oil film rupture or severe secondary entrainment (this critical value is known in the art to be typically greater than 5 m / s). Meanwhile, the inclined air guide plates (42, 52) located immediately downstream of the air outlet surface not only change the airflow direction and utilize inertial separation, but also act as a resistance element, effectively buffering and dissipating kinetic energy, ensuring that the airflow enters the next stage wire mesh assembly in a uniform, low-speed manner. Therefore, the structural design of this invention effectively avoids the risks associated with localized high air velocities while achieving efficient separation.

[0052] 3.2 Secondary wire mesh assembly and its related structures

[0053] like Figure 2 and Figure 4 As shown, the structure of the secondary wire mesh assembly 32 is similar to that of the primary wire mesh assembly, but its asymmetry is further enhanced. The secondary wire mesh assembly 32 includes a rectangular frame B321, which has a hollow cavity B322 inside and an inner oil collection groove B326 at the bottom. The left side of the rectangular frame B321 is the inlet surface B323, and its entire surface is composed of three wire meshes 6 sequentially spliced ​​together from top to bottom along the vertical direction. The right side of the rectangular frame B321 is the outlet surface B324, which is composed of two closed surfaces B325 sequentially arranged in the upper part along the vertical direction and a single wire mesh 6 spliced ​​together at the bottom.

[0054] Compared to the primary wire mesh assembly 31, the secondary wire mesh assembly 32 has a smaller wire mesh area (only one wire mesh at the bottom) on its air outlet surface (outlet surface B324) and a larger enclosed area. This progressively enhanced asymmetrical design causes the airflow path to be continuously changed and compressed as it passes through each wire mesh assembly, giving oil mist particles in the airflow more opportunities to collide with and be captured by the wire mesh wall, thereby progressively improving separation efficiency.

[0055] A flow region B5 is formed between the secondary wire mesh assembly 32 and the tertiary wire mesh assembly 33. An external oil collection tank B51 is provided at the bottom of the flow region B5. An inclined air guide plate B52 is provided within the flow region B5, with its angle preferably between 45° and 60°. The bottom of the air guide plate B52 is fixed inside the external oil collection tank B51, and its top is inclined towards the tertiary wire mesh assembly 33, with its top edge flush with the lower edge of one wire mesh on the outlet surface B324.

[0056] Its working principle is similar to that of flow area A4: the airflow that flows out from the outlet surface B324 is guided upward by the air guide plate B52. While changing the direction of the airflow, the residual oil mist is further separated by inertial force and introduced into the external oil collection tank B51. Thus, the airflow is purified again before entering the last stage of oil removal unit, and secondary entrainment is prevented.

[0057] 3.3 Three-stage wire mesh assembly

[0058] like Figure 2 and Figure 5 As shown, the three-stage wire mesh assembly 33, as the final stage of oil removal, has the simplest and most efficient structure. The three-stage wire mesh assembly 33 consists of three layers of wire mesh 6 joined vertically from top to bottom, with both the air inlet and outlet surfaces being entirely wire mesh structures. Unlike the previous two stages, the three-stage wire mesh assembly 33 does not have a hollow cavity or an internal oil collection tank. Its function is to act as the final gas-liquid separation barrier, utilizing the interception, collision, and coalescence effects of the multi-layered wire mesh to thoroughly remove any remaining trace amounts of oil mist from the airflow, ensuring that the emitted gas meets cleanliness requirements.

[0059] 4. Pressure drop balance and system coordination

[0060] Another key innovation of this process lies in the organic combination of the aforementioned complex anti-secondary entrainment structure with system pressure drop balancing measures. Specifically, by controlling the sum of the pressure drop of the cooling device 1 (400-600Pa), the pressure drop of the expansion section 2 (50-150Pa), and the pressure drop of the multi-stage wire mesh oil removal unit 3, it is ensured that it does not exceed 80% of the total fan pressure.

[0061] The pressure drop inside the multi-stage wire mesh oil removal unit 3 is also precisely controlled. On one hand, along the airflow direction, the porosity of the wire mesh components decreases progressively at each stage. As a preferred implementation, the porosity of the first-stage wire mesh component 31 is controlled at 95%-98%, the second-stage wire mesh component 32 at 90%-95%, and the third-stage wire mesh component 33 at 85%-90%. This gradient reduction design ensures that large-diameter oil mist is efficiently intercepted in the front stage and small-diameter oil mist is finely captured in the rear stage, while simultaneously distributing airflow resistance evenly across each stage, preventing pressure drop concentration in any single stage.

[0062] On the other hand, although the air guide plates 42 and 52 and the asymmetrical inlet and outlet air surface structure increase local resistance, the pressure drop increase caused by these structures is controlled within an acceptable range by rationally designing the wire mesh density gradient, accurately controlling the airflow velocity (1-3m / s), and optimizing the equipment structure.

[0063] This invention, through the combined design of an "anti-secondary entrainment structure" and a "systematic voltage drop balance," produces a synergistic effect, achieving a technical result of 1+1>2, specifically manifested in:

[0064] First, their functions are complementary. The anti-secondary entrainment structure (asymmetrical inlet and outlet surfaces, air guide plates, and double oil collection grooves) greatly improves oil mist separation efficiency by changing the airflow path and increasing local resistance; while the pressure drop balancing measures (wire mesh density gradient, pressure drop matching between the cooling device and the expansion section, and dynamic control) ensure that the total pressure drop remains within the fan's capacity range even after these efficient structures are added. Both complement each other and are indispensable.

[0065] Second, it overcomes technological bias. Existing technologies generally believe that adding anti-secondary entrainment structures (such as air guides or asymmetrical inlet / outlet surfaces) inevitably leads to a significant increase in system pressure drop. Therefore, simplified structures are often used, sacrificing separation efficiency to reduce energy consumption. This invention, through a systematic pressure drop balancing design, breaks this technological bias, proving that high-efficiency separation and low-energy operation can be achieved simultaneously.

[0066] Third, unexpected technical effects are achieved. As shown in the test data of Example 1, when using the combined scheme of the present invention, the oil removal efficiency reaches over 99%, while the total system pressure drop remains stable at 72% of the fan's total pressure. In contrast, in the comparative example, when only the anti-secondary entrainment structure is used without pressure drop balancing, the total pressure drop exceeds 100% of the fan's total pressure, and the system cannot operate normally; when only pressure drop balancing measures are used without the anti-secondary entrainment structure, the oil removal efficiency is only 85%. The above comparison proves that the combined features of the present invention produce synergistic effects, and its overall effect far exceeds the simple summation of the individual effects of each feature.

[0067] It should be noted that the above-mentioned gradient range of wire mesh porosity (95%-98%→90%-95%→85%-90%) and the tilt angle range of the air guide plate (45°-60°) are derived from fluid dynamics simulation and laboratory small-scale experiments to optimize different combinations of wire mesh density and air guide plate angles.

[0068] Experiments show that when the wire mesh porosity exceeds the above range (e.g., below 95% in the pre-stage or above 95% in the post-stage), either the initial pressure drop of the system increases significantly (exceeding the residual pressure of the blower), or the oil concentration at the outlet cannot be stably reduced to below 10 mg / m³. Regarding the angle of the guide plate, when the angle is less than 45°, the airflow guiding effect weakens, and some oil cannot effectively impact the plate wall and is directly blown downstream; when the angle is greater than 60°, the local resistance increases sharply, and the oil on the plate wall is not discharged smoothly due to the reduced gravitational component. Therefore, the angle range of 45°-60° is the optimal balance range for achieving efficient gas-liquid separation and maintaining low-resistance operation of the system.

[0069] Synergistic effect of anti-secondary entrainment and pressure drop balancing: In this embodiment, the anti-secondary entrainment structure (such as air guide plates 42, 52, asymmetrical inlet and outlet air surfaces, and inner and outer double oil collection grooves) greatly improves oil mist separation efficiency by changing the airflow path and increasing local resistance. Meanwhile, pressure drop balancing measures (such as wire mesh density gradient and pressure drop matching between the cooling device and the expansion section) ensure that the total pressure drop remains within the fan's capacity range even after adding these efficient structures. Both complement each other and are indispensable. If only the anti-secondary entrainment structure is used without pressure drop balancing, the system may fail to operate due to excessive resistance; conversely, if only low energy consumption is pursued and the structure is simplified, efficient oil mist separation cannot be achieved. This embodiment, through the systematic combination of both, successfully solves the technical problem of the incompatibility between separation efficiency and system energy consumption in the prior art, achieving a balance between high-efficiency separation and low-energy operation.

[0070] 5. Experimental Verification of Key Parameter Selection

[0071] To verify the scientific validity and critical significance of the selected key parameter ranges in this invention, the applicant conducted systematic comparative experiments during the research and development process.

[0072] 5.1 Comparison Experiment of Pore Ratio Gradient in Wire Mesh

[0073] Three sets of comparative experiments were set up, using different combinations of wire mesh porosity. Under the same inlet oil concentration (1000 mg / m³) and the same gas velocity (2 m / s), the oil removal efficiency and the total system pressure drop were tested. The experimental results are as follows:

[0074] experimental group First-order porosity Secondary porosity Tertiary porosity Oil removal efficiency Total pressure drop (Pa) Control group 1 96% 96% 96% 92.3% 1450 Control group 2 92% 92% 92% 97.8% 2350 Control group 3 98% 94% 86% 98.5% 1680 This invention group 96% 93% 88% 99.2% 1720

[0075] Experimental results show that:

[0076] Although control group 1 (uniform high porosity) had a lower pressure drop, its oil removal efficiency was insufficient.

[0077] Although control group 2 (uniform low porosity) had a high oil removal efficiency, its pressure drop far exceeded the residual pressure of the blower (the total pressure of the blower was 2500Pa, and the pressure drop accounted for 94%), and the system could not operate stably.

[0078] Although control group 3 adopted a gradient design, the porosity range was too large (98%→94%→86%), resulting in concentrated pressure drop in the later stage and the total pressure drop was still too high.

[0079] The present invention (gradient range of 95%-98%→90%-95%→85%-90%) ensures an oil removal efficiency of over 99% while controlling the total pressure drop to within 70% of the total fan pressure, achieving the best balance between efficiency and energy consumption.

[0080] The above experiments confirm that when the porosity gradient range of the wire mesh is 95%-98%, 90%-95%, or 85%-90%, it can synergistically achieve the dual goals of efficient separation and low energy consumption operation. Beyond this range, it is difficult to achieve both simultaneously.

[0081] 5.2 Comparison Experiment of Air Guide Plate Inclination Angle

[0082] Multiple sets of comparative experiments were conducted under the same operating conditions to test the effects of different guide vane tilt angles (30°, 45°, 52.5°, 60°, and 70°) on oil removal efficiency and system pressure drop. The experimental results are as follows:

[0083] Air guide plate tilt angle Degreasing effect Pressure drop increment (Pa) Oil discharge status 30° 93.5% +85 Some oil remains on the plate surface 45° 98.2% +110 Smooth discharge 52.5° 98.5% +125 Smooth discharge 60° 97.8% +150 Smooth discharge 70° 95.2% +195 Smooth discharge

[0084] Experimental results show that:

[0085] When the tilt angle is less than 45°, the airflow guiding effect is insufficient, some oil cannot effectively impact the plate wall and is blown downstream, and the oil is not discharged smoothly due to insufficient gravity component.

[0086] When the tilt angle is greater than 60°, the local resistance increases sharply, and the oil flows too far along the plate wall, resulting in a significant increase in pressure drop.

[0087] The 45°-60° angle range ensures efficient separation while keeping the pressure drop increment within a reasonable range, representing the optimal balance between gas-liquid separation and low-resistance system operation.

[0088] Based on the above experimental verification, the range of wire mesh porosity gradient and the range of air guide plate tilt angle selected in this invention have clear critical significance and technical rationality, and are optimized choices that cannot be easily obtained by those skilled in the art through conventional design.

[0089] 6. Oil collection and system maintenance

[0090] The separated oil is collected in different oil collection tanks. Inner oil collection tanks (such as inner oil collection tank A316 and inner oil collection tank B326) are located at the bottom of the hollow cavities of each level of the wire mesh assembly, used to collect oil directly trapped inside the assembly. Outer oil collection tanks (such as outer oil collection tank A41 and outer oil collection tank B51) are located at the bottom of the flow area, used to collect oil guided and separated by the air guide plate. All oil collection tanks are equipped with level sensors and automatic oil discharge valves, enabling automatic oil discharge and ensuring long-term stable operation of the system.

[0091] Furthermore, to facilitate equipment maintenance and cleaning, each stage of the multi-stage wire mesh degreasing unit 3 is designed as a removable module, and the equipment housing is equipped with an online cleaning interface. After the equipment has been running for a period of time, cleaning media can be introduced through the online cleaning interface to perform in-situ cleaning of the wire mesh components, greatly extending the service life of the equipment and reducing maintenance costs.

[0092] Example 2

[0093] Based on Example 1, this embodiment simplifies the structure of the multi-stage wire mesh oil removal unit 3 to make it suitable for working conditions with relatively low oil mist concentration or more stringent pressure drop requirements.

[0094] Unlike Embodiment 1, the multi-stage wire mesh degreasing unit 3 in this embodiment only includes two-stage wire mesh assemblies, namely, a primary wire mesh assembly 31 and a secondary wire mesh assembly 32, omitting the tertiary wire mesh assembly 33. The structures of the primary wire mesh assembly 31 and the secondary wire mesh assembly 32, the flow area A4 formed between them, and the internal air guide plate A42 and external oil collection tank A41 are completely identical to those in Embodiment 1. The air outlet surface of the secondary wire mesh assembly 32 is directly connected to the subsequent process or discharge pipeline.

[0095] This embodiment, through a two-stage asymmetrical wire mesh assembly combined with an air guide plate structure, still achieves a highly efficient anti-secondary entrainment effect. Because a first-stage oil removal unit is omitted, the total system pressure drop is lower, and the total pressure requirement for the fan is less stringent, making it suitable for applications more sensitive to cost or energy consumption. Its working principle is consistent with the first two stages of the oil removal unit in Embodiment 1, and will not be repeated here.

[0096] Example 3

[0097] Based on Example 1, this embodiment has deeply optimized the control strategy for pressure drop balance and introduced a dynamic closed-loop control system to cope with fluctuations in operating conditions and changes in equipment status, thereby further improving the robustness and intelligence of the system.

[0098] In this embodiment, high-precision pressure sensors are installed at the inlet and outlet of the cooling device 1, the inlet and outlet of the expansion section 2, and the inlet and outlet of the multi-stage wire mesh degreasing unit 3. These sensors communicate in real time with a central control system (such as a PLC or DCS), forming a complete pressure monitoring network. The process control system collects and records the pressure drop data of each unit in real time and performs dynamic analysis on it.

[0099] Control logic and dynamic matching:

[0100] When the control system detects that the pressure drop of the multi-stage wire mesh degreasing unit 3 is gradually increasing due to oil mist blockage, it first determines whether it has reached the preset cleaning trigger threshold. If the threshold is reached, the control system automatically activates the preset online cleaning interface on the equipment housing to perform pulse jet or spray cleaning on the corresponding wire mesh components. This process can be completed without shutting down the system, effectively restoring the flow capacity of the wire mesh components and reducing their pressure drop.

[0101] If, after online cleaning, the pressure drop of the multi-stage wire mesh degreasing unit 3 still cannot be reduced below the preset threshold for normal operation (for example, partial blockage caused by long-term operation cannot be completely resolved by simple cleaning), the control system will activate the second-stage dynamic adjustment strategy. At this time, the control system adjusts the flow rate or temperature of the cooling medium (such as cooling water) of the cooling device 1 to finely adjust the pressure drop of the cooling device 1, ensuring that the cooling effect of the oily exhaust gas still meets the process requirement of "temperature 5-10℃ higher than the oil pour point and 10-20℃ lower than the dew point." Specifically, the control system can dynamically adjust the pressure drop of the cooling device 1 within a preset range of 400-600Pa, based on the real-time value of the current total system pressure drop, to compensate for the additional resistance caused by blockage in the multi-stage wire mesh degreasing unit 3.

[0102] Through the above-mentioned two-level dynamic matching strategy of "online cleaning priority and cooling device pressure drop fine adjustment as a supplement", the control system ensures that the sum of the pressure drop of cooling device 1, the pressure drop of expansion section 2 and the pressure drop of multi-stage wire mesh oil removal unit 3 is always dynamically maintained within 80% of the total pressure of the fan.

[0103] Synergistic effects and technological contributions:

[0104] The dynamic voltage drop balance control strategy introduced in this embodiment has a deep synergistic effect with the anti-secondary entrainment structure and static voltage drop balance design in Embodiment 1.

[0105] First, this dynamic control strategy ensures the long-term efficient operation of the anti-secondary entrainment structure. While anti-secondary entrainment structures (such as air guide plates and asymmetrical inlet / outlet surfaces) can efficiently separate oil mist, they are also more prone to clogging due to oil mist accumulation, leading to increased pressure drop. The control system in this embodiment can sense this change in real time and actively intervene, restoring its function through online cleaning, ensuring that the anti-secondary entrainment structure is always in optimal working condition, avoiding decreased separation efficiency or increased risk of secondary entrainment due to clogging.

[0106] Secondly, this dynamic control strategy is a powerful supplement and extension to the static pressure drop balance design. The static pressure drop balance (mesh density gradient, fixed pressure drop range matching) in Example 1 solves the system's balance problem under design conditions. The dynamic control strategy in this example solves the system's balance problem under changing conditions and states (such as gradual mesh blockage). It expands "pressure drop balance" from a static design concept into a dynamic, closed-loop, and adaptive control process, enabling the process described in this invention to maintain a long-term, stable balance between "high-efficiency separation" and "low-energy operation" in actual industrial operation.

[0107] 6. Performance Testing

[0108] To verify the technical effect of the present invention, the process described in Example 1 was used to treat oily waste gas generated by a machine processing plant. The initial oil concentration of the waste gas was 1000 mg / m³, and the gas velocity was controlled at 2 m / s. The test results showed that:

[0109] (1) Oil removal efficiency: After treatment by the process of the present invention, the oil concentration in the exhaust gas is reduced to below 10 mg / m³, and the oil removal efficiency reaches more than 99%. In contrast, the oil removal efficiency of the comparative example, which omits the guide plate and the asymmetrical inlet and outlet gas surface structure, is only 85%.

[0110] (2) Pressure drop control: Under the premise of meeting the oil removal efficiency, the total pressure drop of the system is stable within 1800Pa, which is about 72% of the total pressure of the blower (2500Pa). However, in the comparative example, when only the anti-secondary entrainment structure is set up without pressure drop balance matching, the total pressure drop exceeds 2500Pa, and the blower cannot operate normally.

[0111] (3) Dynamic adjustment effect: When the pressure drop of the multi-stage wire mesh degreasing unit rises to the preset threshold after 48 hours of continuous operation, the control system automatically starts online cleaning, and the pressure drop is restored to 85% of the initial value within 30 seconds; if it is still too high after cleaning, the system adjusts the pressure drop of the cooling device to keep the total pressure drop within 80% of the total pressure of the blower.

[0112] The test results above show that the present invention, through the systematic combination of anti-secondary entrainment structure and pressure drop balancing measures, successfully achieves the unity of high-efficiency separation and low-energy operation, and has good long-term operational stability.

[0113] Therefore, this embodiment, by integrating intelligent dynamic pressure drop balance control on the basis of embodiment 1, not only further consolidates the synergistic effect of the two major innovations of "anti-secondary entrainment" and "pressure drop balance", but also endows the entire process system with robustness in dealing with complex working conditions and stability in long-term operation, reflecting the in-depth consideration and technological advancement of this invention at the engineering application level.

[0114] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can be mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0115] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0116] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pretreatment process for oily waste gas, characterized in that: Includes the following steps: The oily exhaust gas is passed into a cooling device to cool it down, causing the oil vapor to condense into liquid oil mist. The temperature of the cooled exhaust gas is 5–10°C higher than the pour point of the oil and 10–20°C lower than the dew point. The cooled oily exhaust gas is introduced into a multi-stage wire mesh oil removal unit at a gas velocity of 1–3 m / s. The multi-stage wire mesh oil removal unit includes at least two stages of wire mesh assemblies arranged sequentially along the airflow direction. A flow area is formed between adjacent wire mesh assemblies, and at least some of the wire mesh assemblies have hollow cavities inside. In this process, the airflow is redirected by the air guide plate within the flow area to guide the airflow to separate from the liquid oil mist and prevent the oil from being entrained by the airflow again. At the same time, the pressure drop of the cooling device, the pressure drop of the expansion section and the pressure drop of the multi-stage wire mesh oil removal unit are controlled to not exceed 80% of the total pressure of the fan, so as to maintain the total pressure drop of the system within the acceptable range of the project while preventing the secondary entrainment of oil. The separated oil is collected in an oil collection tank, which includes an inner oil collection tank located at the bottom of the cavity and an outer oil collection tank located at the bottom of the flow area. The multi-stage wire mesh degreasing unit includes three-stage wire mesh assemblies: a primary wire mesh assembly, a secondary wire mesh assembly, and a tertiary wire mesh assembly. Along the airflow direction, the asymmetry between the air inlet and outlet surfaces of each stage of the wire mesh assembly increases progressively. The primary wire mesh assembly includes a rectangular frame A, the interior of which has a hollow cavity A, which forms part of the cavity; the left side of the rectangular frame A is the air inlet surface, which is the entry surface A, and its entire surface is formed by three wire meshes sequentially spliced ​​from top to bottom along the vertical direction; the right side of the rectangular frame A is the air outlet surface, which is the outlet surface A, and its upper part is a closed surface A, and its lower part is formed by two wire meshes sequentially spliced ​​along the vertical direction; the bottom of the cavity A is provided with the inner oil collection groove, which is the inner oil collection groove A; The flow area, referred to as flow area A, is formed between the primary and secondary wire mesh assemblies. The bottom of flow area A is provided with an external oil collection trough, referred to as external oil collection trough A. An inclined air guide plate A is provided within flow area A, with the angle between the air guide plate A and the horizontal direction being 45°–60°. The bottom of the air guide plate A is fixed inside the external oil collection trough A, and the top of the air guide plate A is inclined towards the secondary wire mesh assembly. The top edge of the air guide plate A is flush with the lower edges of the two wire meshes on the outlet surface A, serving to guide the airflow from the outlet surface A upwards and guide the collected oil into the external oil collection trough A.

2. The pretreatment process for oily waste gas according to claim 1, characterized in that: The cooling device is a shell-and-tube heat exchanger, and the oily exhaust gas flows through the shell side. The pressure drop of the cooling device is controlled at 400–600 Pa.

3. The pretreatment process for oily waste gas according to claim 1, characterized in that: Along the airflow direction, the porosity of the wire mesh in each level of the wire mesh assembly decreases progressively.

4. The pretreatment process for oily waste gas according to claim 1, characterized in that: The secondary wire mesh assembly includes a rectangular frame B, the interior of which has a hollow cavity B, which forms part of the cavity; the left side of the rectangular frame B is the air inlet surface, which is the entry surface B, and its entire surface is formed by three wire meshes spliced ​​together from top to bottom in the vertical direction; the right side of the rectangular frame B is the air outlet surface, which is the outlet surface B, and its upper part is formed by two closed surfaces B arranged in sequence in the vertical direction, and its lower part is formed by a single wire mesh spliced ​​together; the bottom of the cavity B is provided with the inner oil collection groove, which is the inner oil collection groove B.

5. The pretreatment process for oily waste gas according to claim 4, characterized in that: The flow region, referred to as flow region B, is formed between the secondary and tertiary wire mesh components. The bottom of flow region B is provided with an external oil collection trough, referred to as external oil collection trough B. An inclined air guide plate B is provided within flow region B, with the angle between the air guide plate B and the horizontal direction being 45°–60°. The bottom of the air guide plate B is fixed inside the external oil collection trough B, and the top of the air guide plate B is inclined towards the tertiary wire mesh component. The top edge of the air guide plate B is flush with the lower edge of one of the wire meshes on the outlet surface B, serving to guide the airflow from the outlet surface B upwards and guide the collected oil into the external oil collection trough B.

6. The pretreatment process for oily waste gas according to claim 1, characterized in that: The three-stage wire mesh assembly comprises three layers of wire mesh spliced ​​vertically from top to bottom, and both its air inlet and outlet surfaces are full wire mesh structures; the three-stage wire mesh assembly does not have the cavity and the inner oil collection groove.

7. The pretreatment process for oily waste gas according to claim 1, characterized in that: The outlet of the cooling device is connected to the inlet of the multi-stage wire mesh degreasing unit through an expansion section. The expansion section is used to reduce the airflow velocity to 1–3 m / s, and the pressure drop of the expansion section is controlled at 50–150 Pa. Each wire mesh assembly in the multi-stage wire mesh degreasing unit is configured as a removable module, and the equipment housing is provided with an online cleaning interface. Both the inner and outer oil collection tanks are equipped with liquid level sensors and automatic oil drain valves.

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