Supercritical carbon dioxide collaborative cleaning electronic-grade tank car system and method

Abstract

The invention belongs to the technical field of zero-emission cleaning of electronic-grade chemical storage and transportation equipment, and discloses a zero-liquid and zero-solid emission dry-type cleaning system and method for the interior of a tank car. The zero-liquid and zero-solid emission dry-type cleaning system and method utilize supercritical carbon dioxide to cooperate with plug-in resorption, miniature ultrasonic cavitation, on-line barrel type filtration, a substitution type low-residue entrainer and an original manhole equal-diameter seal. The system sequentially comprises a liquid CO2 storage tank, a pressure and temperature rising unit, a static mixer, a top cover sealing assembly, an insertion type back-suction cleaning head, an on-line barrel type filtering unit, an on-line particle monitor and a PLC (Programmable Logic Controller) along a material flowing direction, the top cover sealing assembly comprises a top cover with the same diameter as the manhole flange, a stainless steel feeding / suction pipe and a quick-opening clamp, and original manhole-level sealing is formed. According to the device, insertion and sealing are completed through an original manhole or an original discharge port, after cleaning, the particle size is smaller than or equal to 10 pcs / mL, the metal impurity size is smaller than or equal to 1 ppt, the CO2 recovery rate is larger than or equal to 99%, the preparation time is smaller than or equal to 15 min, the cost is reduced by 40-70%, and the requirements of ppt-grade cleaning of 12-30 nm electronic-grade chemicals for advanced manufacturing procedures and the GB 39731-2020 national standard are met.

Description

Technical Field

[0001] This invention belongs to the field of zero-emission cleaning technology for electronic-grade chemical storage and transportation equipment. It discloses a dry cleaning system and method for zero liquid and zero solid emissions inside tank trucks, which utilizes supercritical carbon dioxide (SC-CO2) synergistic insertion-type back suction, micro ultrasonic cavitation, online cylindrical filtration, alternative low-residue entrainment agent and original manhole equal-diameter sealing. Background Technology

[0002] Tank trucks are the "mobile storage tanks" of the electronic-grade chemical supply chain, undertaking the "last mile" storage and transportation of ultrapure sulfuric acid, hydrogen peroxide, ammonia, and other chemicals used in 12-30nm advanced processes from the manufacturing plant to the wafer fab. A single 30m³ tank truck can carry 25-28 tons, equivalent to 3-5 days' worth of chemicals for a 12-inch wafer line. Tank trucks directly connect to the wafer fab's storage tanks, whose inner wall cleanliness must be ≤10pcs / mL and metal impurities ≤1ppt. Any micro- or nano-particle or ionic contamination can lead to wafer defects and reduced yield, and is known as the "mobile blood" source of contamination. Therefore, ppt-level dry cleaning of tank trucks has become an indispensable key basic equipment for 12-30nm processes.

[0003] With the promulgation of GB 39731-2020 "Zero Liquid Discharge," special emission limits are being enforced in key regions such as the Yangtze River Delta and the Pearl River Delta. Traditional alkaline spray cleaning of tank trucks generates 0.8-1.2 tons of high-salt wastewater (COD>2000mg / L, total nitrogen>300mg / L) per ton of product. This wastewater cannot be directly recycled and requires evaporation and concentration, resulting in operating costs exceeding 120 yuan / ton, accounting for 15-20% of chemical logistics costs. This has become the last-mile bottleneck for the implementation of "Zero Liquid Discharge." In addition, existing SC-CO2 single cleaning has an inorganic particle removal rate of <40% and lacks engineering solutions such as original manhole-level sealing, no solids collection, and mobile deployment. A secondary rinsing is still required after cleaning, which increases the amount of wastewater and dry sludge generated, failing to meet the ppt-level cleanliness requirements of 12-30nm processes.

[0004] Therefore, developing a dry cleaning system that is zero-liquid, zero-solid, with original manhole seals, mobile, and PPT-level cleanliness is of great practical significance and industrial value for breaking through the bottleneck of "zero liquid discharge" of electronic-grade chemicals, reducing wafer defect rates, and promoting the green upgrading of the semiconductor industry. Summary of the Invention

[0005] This invention relates to a supercritical carbon dioxide synergistic cleaning system and method for dry cleaning the interior of electronic-grade tank trucks. It aims to provide a zero-emission dry cleaning solution that effectively removes PPT-level particles and metallic impurities from ultrapure chemicals such as electronic-grade sulfuric acid, restoring the cleanliness of the tank truck's interior walls, while achieving zero liquid and zero solid emissions. The device employs a three-stage synergistic mechanism of insertion back suction + micro-ultrasound + online cylindrical filtration. The first stage utilizes a 360° annular micro-orifice nozzle to create an upward swirling flow, which, in conjunction with a coaxial back suction port, establishes a forced circulation from bottom to top. The second stage involves integrating a micro-ultrasonic array within the coaxial backflow channel to generate a 120° cavitation cloud, which strips off and disperses wall particles. The third stage utilizes a 20-inch standard cartridge filter for online interception, with continuous LPC monitoring until particles are ≤6pcs / mL, achieving a zero-collection, zero-liquid, ppt-level clean cleaning solution. This meets the GB 39731-2020 standard for ppt-level cleanliness and wastewater discharge of mobile storage and transportation containers in advanced 12-30nm processes. The GB 39731-2020 standard is as follows:

[0006] A system for supercritical carbon dioxide co-cleaning of electronic-grade tank trucks, comprising, in sequence along the material flow direction: The outlet of the liquid CO2 storage tank is connected to the inlet of the pressurization and heating unit via a pipeline; The outlet of the pressurization and heating unit is connected to the main fluid inlet of the static mixer; The static mixer is provided with an entrainer inlet for connecting to an entrainer storage tank; The outlet of the static mixer is connected to the feed pipe of the insertion-type back-suction ultrasonic cleaning head via a high-pressure pipeline; The outlet of the suction tube of the insertable back-suction ultrasonic cleaning head is connected to the inlet of the online cylindrical filter unit; The outlet of the online cartridge filter unit is connected to the inlet of the online particle monitor; The signal output terminal of the online particle monitor is communicatively connected to the PLC controller. The material outlet of the online particle monitor is connected to the reflux port of the liquid CO2 storage tank via a recovery pipeline.

[0007] The pressurization and heating unit consists of a cold pump and an electric heater connected in series; the inlet of the cold pump is connected to the liquid CO2 storage tank, the outlet is connected to the inlet of the electric heater, and the outlet of the electric heater is connected to the static mixer.

[0008] The insertable back suction ultrasonic cleaning head includes a top cover sealing assembly and an insertable back suction cleaning head fixed thereto; the top cover sealing assembly includes a top cover with the same diameter as the manhole flange, a feed / back suction pipe penetrating the top cover, and a quick-release clamp for pressing the top cover onto the manhole flange.

[0009] The insertable back suction cleaning head is axially inserted into the tank truck through the manhole or unloading port on the top of the tank truck, with an insertion depth of 60% to 95% of the total height of the tank truck; the lower end of the insertable back suction cleaning head is provided with a 360° annular arrangement of micro-orifice nozzles and a coaxial back suction port located in the center of the nozzles.

[0010] The orifice diameter of the micro-orifice nozzle is 80-120µm. Its spraying, in conjunction with the suction of the coaxial return suction port, forms a forced circulating flow field with a Reynolds number of Re=3000-5000 inside the tanker, with the flow going from bottom to top.

[0011] The insertable back-suction cleaning head integrates a miniature ultrasonic array, which is arranged within the back-suction channel. This array consists of multiple piezoelectric crystals arranged circumferentially along the channel and operates in pulse mode under PLC control, with a working frequency of 18-30kHz and a power density of 15-25 W·L. -1 .

[0012] The micro-ultrasonic array is arranged coaxially with the coaxial back suction port; each piezoelectric crystal has a polyimide heat insulation layer on its back side and a titanium alloy acoustic window fixed to its front side through an acoustic coupling layer. The titanium alloy acoustic window has a thickness of 1-2 mm and its structure ensures that the ultrasonic radiation angle is ≥120°, so that the cavitation cloud covers the entire back suction channel.

[0013] The online cartridge filter unit is equipped with a replaceable cartridge filter element. The filter element is made of PP or PTFE, with a filtration accuracy of 0.1-0.5 µm and a normal operating pressure drop of ≤0.05 MPa. When the filter element is saturated, it is replaced as a whole without online backflushing regeneration.

[0014] The detection limit of the online particle monitor is 0.2 µm; the PLC controller is configured to automatically determine that the cleaning is qualified and send a signal when the particle concentration reading received from the online particle monitor is ≤10 pcs / mL for 3 consecutive minutes.

[0015] The top cover sealing assembly includes a top cover of the same diameter as the manhole flange, a feed / return pipe, and a quick-opening clamp, forming a seal equivalent to the original manhole level, with a leakage rate ≤1×10⁻⁶. -9 Pa·m 3 ·s -1 .

[0016] In a preferred embodiment, the internal integrated micro-ultrasound array comprises 6-12 PZT-8 piezoelectric crystals, with a frequency of 18-30 kHz and a power density of 15-25 W·L. -1 The pulse mode is on for 3 seconds and off for 1 second, with a duty cycle of 75%, and is used to generate cavitation clouds in the back suction channel to enhance particle stripping and dispersion.

[0017] The micro ultrasonic array is coaxially arranged with the back suction port. A polyimide heat insulation layer is provided on the back of the wafer, and a titanium alloy acoustic window with a thickness of 1-2 mm is provided at the front end. The ultrasonic radiation angle is ≥120° to ensure that the cavitation cloud covers the entire back suction channel.

[0018] The outer diameter of the top cover of the manhole flange is equal to ±2mm of the outer diameter of the manhole flange, the thickness is ≥12mm, and the material is 316L; the lower surface is machined with an annular tenon groove, and a PTFE O-ring is built in, with a sealing pressure ≥3Mpa.

[0019] The feed / reverse suction pipe is welded to the top cover of equal diameter to the manhole flange and the main pipe of the insert-type reverse suction cleaning head as a single unit. Internally, it is divided into two pipelines, one for feeding and one for suction. The feed / reverse suction pipe is made of stainless steel.

[0020] The quick-release clamps consist of 6-8 GB / T 6073 or HG / T 20592-2009 PN10 clamps, which can be installed and removed within 30 seconds without the need for additional drilling or welding. The online cartridge filter unit uses a PP or PTFE filter element with a filter accuracy of 0.1-0.5 µm and a pressure drop ≤0.05 MPa. It is used for simple filtration of reabsorbed waste liquid. The entire filter element is replaced when saturated, with no online backflushing. In the preferred embodiment, the cartridge filter element is a standard 20-inch PP or PTFE filter element with a filter accuracy of 0.2 µm, a pressure drop ≤0.05 MPa, a replacement time ≤2 minutes, and no backflushing.

[0021] The detection limit of the online particle monitor is 0.2 µm. When the reading is ≤10 pcs / mL for 3 consecutive minutes, the PLC determines that the cleaning is qualified. It is interlocked with the PLC (16) to realize automatic determination of the cleaning endpoint; CO2 recovery rate ≥99%.

[0022] In some embodiments, the online particle monitor continuously samples the returned liquid. When the reading is ≤10pcs / mL for 3 consecutive minutes, the PLC sends a cleaning qualified signal, allowing CO2 to be reused.

[0023] The entire system is easy to operate and is suitable for cleaning tank trucks carrying various electronic-grade chemicals (sulfuric acid, phosphoric acid, hydrogen peroxide, ammonia).

[0024] A method for dry cleaning of electronic-grade tank trucks using the system includes the following steps: S1: Pre-emptive purging, using filtered clean air to blow out the tanker truck; S2: Increase pressure and temperature to adjust CO2 to a supercritical state; S3: Inject entrainer, introducing 0.3-0.8 wt% entrainer; S4: Insertion-Back-Suction - Ultrasonic Co-processing Cleaning: The insertion-type back-suction cleaning head is inserted into the tanker truck through the manhole or discharge port to a depth of 60-95%. During operation, supercritical carbon dioxide fluid is ejected at high speed through the annular micro-orifice nozzle at the bottom of the cleaning head, forming a strong upward vortex inside the tanker truck, effectively stripping contaminants from the inner wall surface. Simultaneously, a micro-ultrasonic array integrated into the cleaning head works in a pulsed manner, generating a strong cavitation effect within the back-suction channel, utilizing the instantaneous burst energy of microbubbles to further break down stubborn dirt. The coaxial back-suction port at the center of the cleaning head creates a local negative pressure environment, actively and efficiently drawing the stripped supercritical CO2 fluid carrying contaminant particles to the external treatment unit. This "bottom-in, top-out" fluid organization method creates a forced, closed-loop cleaning cycle inside the tanker truck, ensuring full contact between the cleaning medium and the entire inner surface and rapid removal of contaminants.

[0025] S5: In-line cartridge filtration. The supercritical CO2 fluid containing contaminants drawn back from the coaxial back suction port enters the in-line cartridge filtration unit, where particulate contaminants are trapped by the filter element. S6: Online particle monitoring and endpoint determination: The filtered supercritical CO2 fluid flows through an online particle monitor for real-time monitoring; when the PLC controller determines that the particle concentration is ≤10 pcs / mL for 3 consecutive minutes, it issues a cleaning qualified signal and terminates the cleaning cycle; S7: CO2 storage and recovery: After the cleaning is qualified, the system switches to recovery mode, depressurizes and liquefies the supercritical CO2 in the system, and then transports it back to the liquid CO2 storage tank for reuse. S8: Clean nitrogen purging: Introduce clean nitrogen that has been filtered through a 0.1 µm filter into the system to purge the tank truck and pipelines, removing residual CO2 until the CO2 concentration in the tank truck is <1 ppm.

[0026] In some preferred embodiments, a method for dry cleaning tank trucks using the system includes the following steps: S1 Pre-purging: Purge with 0.2µm filtered clean air for 5 minutes; S2 Pressure and Temperature Increase: Liquid CO2 is pressurized to 8-15MPa by a cold pump and electrically heated to 35-50℃; S3 Injection of entrainer: Introduce 0.3-0.8 wt% of alternative entrainer at the inlet of the static mixer; S4 Insertion-Back Suction-Ultrasonic Synergistic Cleaning: The insertion-type back suction cleaning head is inserted into the interior through the manhole or discharge port to a depth of 60% to 95%. SC-CO2 is ejected through an annular micro-orifice nozzle, forming an upward swirling flow. The micro-ultrasonic array operates synchronously with pulses, generating cavitation clouds within the back suction channel. A local negative pressure is established at the coaxial back suction port, actively drawing back the SC-CO2 containing particles, forming a forced circulation from bottom to top. The synergistic effect of ultrasound and back suction results in a particle stripping rate of ≥96%. S5 Online Cartridge Filtration: Waste liquid is drawn back into a replaceable cartridge filter element (0.2µm precision), where particles are trapped; the entire cartridge is replaced when saturated, with no online backflushing. S6 Online Particle Monitoring: The online particle monitor continuously samples, and when the reading is ≤10pcs / mL for 3 consecutive minutes, the PLC sends a cleaning qualified signal; S7 CO2 Recovery: After filtration, CO2 is liquefied and returned to the liquid CO2 storage tank, with a recovery rate of ≥99%. S8 Clean Nitrogen Purging: The tank truck is purged with N2 filtered through a 0.1µm filter for 3 minutes using an insertable back-suction cleaning head to remove residual CO2 from the inner wall (<1ppm).

[0027] The entrainer is sodium fluorosulfonate (C4-C6 short chain), which has a solubility of ≥6 wt% in CO2 at 35°C and 10 MPa, and a residual concentration on the inner wall of ≤0.005 µg·m³. -2 .

[0028] The method achieves zero liquid and zero solid emissions, CO2 recovery rate ≥99%, cleaning time ≤30 min, and after cleaning, the particles on the inner wall of the tanker are ≤6 pcs / mL, and the metal impurities are ≤1 ppt. Attached Figure Description

[0029] Figure 1 System flowchart.

[0030] Figure 2 Flowchart of the method for cleaning electronic-grade tank trucks.

[0031] Figure 3 A schematic diagram of the insertable back-suction ultrasonic cleaning head.

[0032] Figure 4 Schematic diagram of the sealing assembly between the top cover and the manhole flange.

[0033] Figure 5 Internal diagram of the feed / return suction pipe.

[0034] Figure 6 Schematic diagram of the bottom of the top cover sealing assembly.

[0035] Figure 7 Axial schematic diagram of the bottom-insertion back-suction cleaning head.

[0036] Figure 8 Schematic diagram of an online cartridge filter unit.

[0037] In the diagram: 1 is a liquid CO2 storage tank, 2 is a cold pump, 3 is an electric heater, 4 is a static mixer, 5 is an entrainer storage tank, 6 is an insert-type back-suction ultrasonic cleaning head, 7 is a top cover with the same diameter as the manhole flange, 8 is a feed / back-suction pipe, 9 is a quick-opening clamp, 10 is a lower annular micro-orifice nozzle, 11 is a coaxial back-suction port, 12 is an internally integrated micro ultrasonic array, 13 is an online cartridge filter unit, 14 is a replaceable cartridge filter element, and 15 is a particle monitor. Detailed Implementation

[0038] To better understand the technical means of this invention and to enable its implementation according to the description, the invention is further described below with reference to embodiments. However, it should not be construed that the scope of the invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of this invention should be included within the scope of protection of this invention.

[0039] Example 1: A supercritical carbon dioxide synergistic cleaning method for electronic-grade 30m 3 The system of the sulfuric acid tanker truck, along the material flow direction, includes, in sequence: 30m 3 Sulfuric acid tanker, manhole flange outer diameter Φ660mm, PN10.

[0040] Along the material flow direction, the following are included in sequence: Liquid CO2 storage tank 1; The pressure and temperature boosting unit, consisting of a cold pump 2 and an electric heater 3, is used to adjust CO2 to a supercritical state. Static mixer 4 is equipped with an entrainer inlet; The insertable back suction ultrasonic cleaning head 6 includes a top cover sealing assembly and an insertable back suction cleaning head. The insertable back suction cleaning head is provided with a nozzle 10 and a back suction port 11, and integrates an internal micro ultrasonic array 12.

[0041] The top cover sealing assembly includes a top cover 7 of the same diameter as the manhole flange, a feed / return pipe 8, and quick-opening clamps 9, forming a seal equivalent to the original manhole. The top cover sealing assembly has an outer diameter of 658 mm, a thickness of 15 mm, and is made of 316L stainless steel. After tightening the six quick-opening clamps 9 (GB / T 6073), the leakage rate is 1×10⁻¹⁰ Pa·m³·s. -1 (Helium mass spectrometry leak detection), consistent with the original manhole sealing level. The upper top cover sealing assembly and the bottom insert-type back suction cleaning head are connected by bottom welding, and the internal pipeline extends all the way to the bottom of the cleaning connector.

[0042] Insertion back suction cleaning head reaches a depth of 30m 3 The sulfuric acid tanker has an insertion depth of 2.85m (95%) and integrates a miniature ultrasonic array 12 containing 12 PZT-8 chips, with a frequency of 22 kHz and a power density of 20 W·L. -1 The pulse turns on for 3 seconds and off for 1 second.

[0043] The internally integrated micro-ultrasonic array 12 is coaxially arranged with the back suction port 11. A polyimide heat insulation layer is provided on the back of the wafer, and a 2mm thick titanium alloy acoustic window is provided at the front end. The acoustic impedance of this acoustic window (approximately 27 MRayl) is between that of the piezoelectric wafer (approximately 33 MRayl) and the supercritical CO2 phase (approximately 0.15 MRayl). Its 2mm thickness is designed to be one-quarter wavelength (λ / 4) at the operating frequency to achieve perfect acoustic impedance matching and maximum acoustic energy transmission. The acoustic window ensures an ultrasonic radiation angle of ≥120°, allowing the cavitation cloud to completely cover the back suction channel.

[0044] The lower end of the insertable back-suction cleaning head is equipped with a 360° annular micro-orifice nozzle 10 and a coaxial back-suction port 11, forming a forced circulation flow field with bottom inlet and top outlet. The 360° annular micro-orifice nozzle 10 has an orifice diameter of 100µm and a Reynolds number Re=3000-5000, forming a forced circulation with bottom inlet and top outlet. The coaxial back-suction port 11 has an inner diameter of 40 mm, a local negative pressure of 0.08MPa, and a circulation flow rate of 150kg·min-1. Ultrasonic-back-suction synergy: cavitation cloud covers the entire back-suction flow channel, with a particle stripping rate of 96%. Online cartridge filter unit 13: Replaceable cartridge filter element made of 20-inch standard PTFE filter element, accuracy 0.2µm, pressure drop ≤0.05MPa, no backflushing.

[0045] Example 2 The following process is performed using the apparatus of Example 1, including the following steps: S1 Pre-purging: Purge with 0.2µm filtered clean air for 5 minutes; S2 Pressure and Temperature Increase: Liquid CO2 is pressurized to 8-15MPa by a cold pump and electrically heated to 35-50℃; S3 Entrainer Injection: To enhance the cleaning ability for polar contaminants and fine particles, the system precisely injects 0.5 wt% sodium perfluorobutane sulfonate as an entrainer at the static mixer inlet. This entrainer is a highly efficient fluorinated surfactant, and its role is crucial: 1. Solubilization: It forms reverse micelles in supercritical CO2, encapsulating originally insoluble polar contaminants and metal ions within their polar cores, achieving highly efficient solubilization. 2. Wetting and Stripping: It significantly reduces fluid surface tension, enhances wettability to the tank truck inner wall and contaminants, allowing the fluid to penetrate microscopic gaps and thoroughly strip away dirt. 3. Anti-Redeposition: Adsorbed on the surface of stripped particles, it prevents their re-aggregation and deposition through electrostatic and steric hindrance effects, ensuring thorough removal of contaminants. 4. Synergistic Effect: It works synergistically with ultrasonic cavitation, enhancing cavitation intensity and more efficiently pulverizing stubborn residues.

[0046] S4 Insertion-Back Suction-Ultrasonic Synergistic Cleaning: The insertion-type back suction cleaning head 6 is inserted into the interior through the manhole or discharge port to a depth of 95%. SC-CO2 is ejected through the annular micro-orifice nozzle 10 to form an upward swirling flow. The micro-ultrasonic array 12 operates synchronously with pulses, generating cavitation clouds within the back suction channel. The coaxial back suction port 11 establishes a local negative pressure, actively drawing back the SC-CO2 containing particles, forming a forced circulation from bottom to top. The synergistic effect of ultrasound and back suction results in a particle stripping rate of ≥96%. S5 Online cartridge filtration: Waste liquid is drawn back into the replaceable cartridge filter element 14 (0.2µm precision, the replaceable cartridge filter element 14 is set in the online cartridge filtration unit 13), where particles are trapped; the entire filter element is replaced when it is saturated, without online backflushing; S6 Online Particle Monitoring: The online particle monitor continuously samples for 15 minutes. When the reading is ≤10pcs / mL for 3 consecutive minutes, the PLC sends a cleaning qualified signal. S7 CO2 Recovery: After filtration, CO2 is liquefied and returned to the liquid CO2 storage tank, with a recovery rate of ≥99%. S8 Clean Nitrogen Purging: The tank truck is purged with N2 filtered through a 0.1µm filter for 3 minutes using the insertable back-suction cleaning head 6 to remove residual CO2 from the inner wall (<1ppm).

[0047] 30nm particles: 3800 → 10pcs·mL -1 The wastewater discharge consisted of Fe 0.5ppt, Na 0.3ppt, K 0.5ppt, Ca 0.5ppt, Ni 0.5ppt, As 1ppt, with a total organic carbon content ≤ 10 ppb. CO2 recovery was 99.5%, and the total processing time was 30 minutes, with zero liquid and zero solid discharge. Wastewater discharge complied with GB 39731-2020 standards.

[0048] Comparative Example 1 Without performing the ultrasonic cleaning step in S4, the content of particles with a diameter of 30 nm is 5000-15000 pcs·mL. -1 Fe 800-550ppt, Na 500-350ppt, K 1000-800ppt, Ca 1000-800ppt, Ni 500-350ppt, As 500-350ppt, total organic carbon ≤ 230 ppb.

[0049] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A system for supercritical carbon dioxide synergistic cleaning of electronic-grade tank trucks, characterized in that, The components connected sequentially along the direction of the cleaning medium flow include: The outlet of the liquid CO2 storage tank (1) is connected to the inlet of the pressurization and heating unit via a pipeline; The outlet of the pressurization and heating unit is connected to the main fluid inlet of the static mixer (4); The static mixer (4) is provided with an entrainer inlet for connecting to the entrainer storage tank (5). The outlet of the static mixer (4) is connected to the feed pipe of the insertion-type back suction ultrasonic cleaning head (6) via a high-pressure pipe; The outlet of the back suction tube of the insertable back suction ultrasonic cleaning head (6) is connected to the inlet of the online cylindrical filter unit (13); The outlet of the online cartridge filter unit (13) is connected to the inlet of the online particle monitor (15); The signal output terminal of the online particle monitor (15) is connected to the PLC controller for communication. The material outlet of the online particle monitor (15) is connected to the reflux port of the liquid CO2 storage tank (1) via a recovery pipeline.

2. The system as described in claim 1, characterized in that: The pressure and temperature boosting unit is composed of a cold pump (2) and an electric heater (3) connected in series; the inlet of the cold pump (2) is connected to the liquid CO2 storage tank (1), the outlet is connected to the inlet of the electric heater (3), and the outlet of the electric heater (3) is connected to the static mixer (4).

3. The system as described in claim 1, characterized in that: The insertable back suction ultrasonic cleaning head (6) includes a top cover sealing assembly and an insertable back suction cleaning head fixed thereto; the top cover sealing assembly includes a top cover (7) of the same diameter as the manhole flange, a feed / back suction pipe (8) passing through the top cover (7), and a quick-release clamp (9) for pressing the top cover (7) onto the manhole flange.

4. The system as described in claim 3, characterized in that: The insertable back suction cleaning head is axially inserted into the tank truck through the manhole or unloading port on the top of the tank truck, with an insertion depth of 60% to 95% of the total height of the tank truck; the lower end of the insertable back suction cleaning head is provided with a 360° annular arrangement of micro-hole nozzles (10) and a coaxial back suction port (11) located in the center of the nozzle.

5. The system as described in claim 4, characterized in that: The orifice diameter of the micro-orifice nozzle (10) is 80-120µm. Its spraying is combined with the suction of the coaxial back suction port (11) to form a forced circulation flow field with a Reynolds number of Re=3000-5000 inside the tank car, with the flow going from bottom to top.

6. The system as described in claim 1 or 4, characterized in that: The insertable back suction cleaning head integrates a miniature ultrasonic array (12), which is arranged in the back suction channel and consists of multiple piezoelectric crystals arranged circumferentially along the channel. It operates in pulse mode under PLC control, with a working frequency of 18-30 kHz and a power density of 15-25 W·L. -1 The micro ultrasonic array (12) is arranged coaxially with the coaxial back suction port (11); each piezoelectric crystal has a polyimide heat insulation layer on its back side and a titanium alloy acoustic window fixed to its front end through an acoustic coupling layer. The thickness of the titanium alloy acoustic window is 1-2 mm, and its structure ensures that the ultrasonic radiation angle is ≥120°, so that the cavitation cloud covers the entire back suction channel.

7. The system as described in claim 1, characterized in that: The online cylindrical filter unit (13) is equipped with a replaceable cylindrical filter element (14). The filter element is made of PP or PTFE, with a filtration accuracy of 0.1-0.5 µm and a normal operating pressure drop of ≤0.05 MPa. After the filter element is saturated, it is replaced as a whole without online backflushing regeneration.

8. The system as described in claim 1, characterized in that: The detection limit of the online particle monitor (15) is 0.2µm; the PLC controller is configured to automatically determine that the cleaning is qualified and send a signal when the particle concentration reading received from the online particle monitor (15) is ≤10 pcs / mL for 3 consecutive minutes.

9. A method for dry cleaning of electronic-grade tank trucks using the system described in any one of claims 1-8, characterized in that, Includes the following steps: S1: Pre-emptive purging: Use clean air treated with a 0.2 µm filter to purge the inside of the tanker for 3-10 minutes; S2: Pressure and temperature increase: The liquid CO2 from the liquid CO2 storage tank (1) is pressurized to 8-15 MPa by the cold pump (2), and then heated to 35-50 ℃ by the electric heater (3) to reach the supercritical state; S3: Injecting entrainer: While supercritical CO2 enters the static mixer (4), an entrainer accounting for 0.3-0.8 wt% of the total mass of CO2 is injected through its entrainer inlet to fully mix it with the supercritical CO2; S4: Insertion-back suction-ultrasonic synergistic cleaning: Fix the assembled insertion-back suction ultrasonic cleaning head (6) to the manhole of the tank truck, so that the cleaning head is inserted into the tank truck to a depth of 60% to 95% of the total height of the tank truck; start the system to make the supercritical CO2 fluid mixed with the entrainer spray out at high speed from the bottom annular micro-orifice nozzle (10) to form an upward swirling flow; at the same time, start the micro ultrasonic array (12) to work in pulse mode to generate a cavitation effect in the back suction channel; and open the coaxial back suction port (11) to establish a local negative pressure, actively back suction the supercritical CO2 fluid carrying pollutants, thereby forming a forced circulation cleaning from bottom to top inside the tank truck; S5: Online cartridge filtration: The supercritical CO2 fluid containing contaminants drawn back from the coaxial back suction port (11) enters the online cartridge filtration unit (13), where particulate contaminants are trapped by the filter element; S6: Online particle monitoring and endpoint determination: The filtered supercritical CO2 fluid flows through the online particle monitor (15) for real-time monitoring; when the PLC controller determines that the particle concentration is ≤10 pcs / mL for 3 consecutive minutes, it issues a cleaning qualified signal and terminates the cleaning cycle; S7: CO2 storage and recovery: After the cleaning is qualified, the system switches to recovery mode, and the supercritical CO2 in the system is depressurized and liquefied, and then transported back to the liquid CO2 storage tank (1) for reuse; S8: Clean nitrogen purging: Introduce clean nitrogen that has been filtered through a 0.1 µm filter into the system to purge the tank truck and pipelines, removing residual CO2 until the CO2 concentration in the tank truck is <1 ppm.

10. The method as described in claim 9, characterized in that: The entrainer is a C4-C6 short-chain sodium fluorosulfonate surfactant.

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