DMT dilution tank with double liquid level detection device
By designing a dual-level detection device, combining a bubbling type and a dual-flange level gauge, the reliability and clogging issues of level detection in DMT dilution tanks were solved, enabling stable and efficient operation in high-viscosity environments and improving the continuity and economy of the PET recycling process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- ZHEJIANG JINGGONG SCI & TECH
- Filing Date
- 2025-05-22
- Publication Date
- 2026-06-16
AI Technical Summary
Existing DMT dilution tank level detection solutions suffer from insufficient reliability, susceptibility to clogging, and high costs. They are also difficult to operate stably in high-viscosity, highly turbulent environments, affecting the continuity and economy of PET recycling processes.
A dual-level detection device is adopted, combining a bubble level gauge and a dual-flange level gauge. The gas bubbling principle reduces the risk of blockage by high-viscosity materials, and the pressure is transmitted through the flange diaphragm for stable measurement. A closed-loop control system is constructed, which, combined with a heat tracing system and a differential pressure measurement system, achieves redundant detection and anti-interference capabilities.
It improves the accuracy and stability of liquid level detection, reduces maintenance frequency, ensures the efficient operation of DMT dilution process and system safety, and adapts to complex industrial environments.
Smart Images
Figure CN224358353U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of PET recycling equipment technology, and in particular to a DMT dilution tank with a dual liquid level detection device. Background Technology
[0002] With the deepening of global low-carbon and environmental protection concepts, PET (polyethylene terephthalate) recycling technology has attracted much attention due to its alignment with sustainable development needs. In the industrial production of PET recycling, the centrifugal separation section is a crucial link, and the level detection accuracy of its core equipment, the DMT dilution tank, directly affects material proportioning control, separation efficiency, and process stability. Because the PET recycling technology system is complex, involving numerous types of instruments with extremely high accuracy requirements, the selection and application of level gauges have become a significant factor restricting the stable operation of the section.
[0003] Currently, the liquid level detection and control of DMT dilution tanks generally adopts a single liquid level gauge detection scheme. This scheme has the following significant defects: (1) Insufficient reliability. If a single liquid level gauge experiences a measurement failure or data transmission delay, the lack of a redundant detection mechanism can easily lead to the failure of the entire process control logic, or even production stoppage; (2) Prone to clogging. The stirring conditions during the operation of the DMT dilution tank and the high viscosity DMT material in the tank can cause the liquid level gauge detection parts (such as probes and sensor interfaces) to become clogged due to material adhesion or deposition, resulting in distorted or invalid detection data; (3) Contradiction between cost and environmental adaptability. Although some high-precision liquid level gauges can meet the detection requirements, they have problems such as high equipment costs and sensitivity to environmental conditions such as temperature, humidity and corrosivity, making it difficult to operate stably for a long time in complex industrial environments.
[0004] The aforementioned problems result in drawbacks for existing testing solutions when faced with high-viscosity, highly turbulent DMT dilution processes, such as decreased testing accuracy, high maintenance frequency, and weak system fault tolerance, which seriously affect the continuity and economy of PET recycling processes.
[0005] Therefore, there is an urgent need to design a liquid level detection device that can adapt to high-viscosity material environments and has redundant detection functions to solve the reliability defects of single detection schemes, improve the accuracy and stability of liquid level detection in DMT dilution tanks, and ensure the efficient operation of PET recycling processes. This invention, by constructing a dual liquid level detection device and a matching control system, aims to achieve redundant backup of liquid level detection, enhanced anti-interference capabilities, and long-term stable operation, effectively overcoming the shortcomings of existing technologies. Utility Model Content
[0006] In the DMT dilution process, the medium in the dilution tank contains DMT (dimethyl terephthalate) and MET (methanol). Due to the agitation, the high-viscosity DMT easily adheres to the instrument detection area, leading to a decrease in the detection accuracy of traditional single level gauges. To address this technical challenge, this solution constructs a composite detection system that organically combines the advantages of a bubble level gauge and a dual-flange level gauge: the bubble level gauge reduces direct contact between high-viscosity materials and the detection component through the gas bubbling principle, lowering the risk of adhesion and blockage; the dual-flange level gauge utilizes flange diaphragms to transmit pressure, adapting to stable level measurement under strong agitation conditions. The two work together to comprehensively capture level change information. After the detection data is processed by the control system, the valve opening, agitator speed, and delivery pump power are precisely adjusted to form a closed-loop control, effectively solving the detection error problem in high-viscosity media environments and ensuring the stable and efficient operation of the DMT dilution process.
[0007] To achieve the above objectives, the technical solution of this utility model is implemented as follows:
[0008] A DMT dilution tank with dual level detection devices includes a DMT dilution tank, a dilution tank agitator, a dual-flange level gauge, a bubbling level gauge, and a DMT slurry delivery pump. The dilution tank agitator is located inside the DMT dilution tank, the dual-flange level gauge is installed on the side of the DMT dilution tank, the bubbling level gauge extends into the DMT dilution tank from the top, and the DMT slurry delivery pump is connected to the DMT dilution tank.
[0009] In a structure that optimizes the aforementioned solution, a regulating valve is also included, which is located at the top of the DMT dilution tank. The regulating valve and the dual liquid level detection device form a closed-loop control system, dynamically adjusting the input flow rate of the medium (such as MET methanol) at the top of the dilution tank based on real-time data from the liquid level gauges, ensuring the accuracy of the DMT to MET ratio; at the same time, it can respond quickly in case of abnormal liquid level, such as quickly cutting off the feed when the level exceeds the limit, and working in conjunction with the agitator and the delivery pump to achieve coordinated control of process parameters, improving the system's automation level and safety.
[0010] In a structure that optimizes the aforementioned solution, the dual-flange level gauge is connected to the side of the DMT dilution tank via a PN25DN80 flange. Addressing the problem that high-viscosity material agitation easily clogs the detection area of traditional level gauges and that a single level gauge cannot adapt to medium- and high-pressure conditions, this design uses a PN25DN80 flange to connect the dual-flange level gauge to the side of the DMT dilution tank. This achieves pressure-bearing capacity matching, standardized connection, and disturbance-resistant measurement: the PN25 (nominal pressure 2.5MPa) flange meets the requirements of medium- and high-pressure environments under agitation conditions, ensuring the sealing and structural strength of the flange connection; the DN80 nominal diameter is compatible with the piping system, facilitating precise docking with the tank side interface to reduce installation errors; the dual-flange level gauge isolates the material inside the tank through a diaphragm, preventing the high-viscosity DMT from directly contacting the detection probe. Combined with the stable installation of the PN25 flange, stable transmission of level and pressure signals can be achieved under strong agitation conditions, effectively solving the applicability problems of traditional detection solutions.
[0011] In a structure that optimizes the aforementioned scheme, the bubbling level gauge includes a sleeve, a positive pressure needle, and a transmitter. The sleeve is connected to the inner top wall of the DMT dilution tank, the positive pressure needle extends into the sleeve, the transmitter is connected to the positive pressure needle through an air passage, and an external air blowing device is connected to the transmitter. To address the issues of clogging caused by adhesion of high-viscosity DMT at the detection site and the insufficient reliability of single detection methods, a technical improvement is achieved through the anti-clogging mechanism of the bubble level gauge and a composite detection mode. A sleeve is used as an isolation chamber to physically separate the positive pressure pin from the material inside the tank. An external blowing device continuously introduces inert nitrogen gas into the sleeve, creating a bubbling effect. The gas pressure prevents high-viscosity material from adhering to the pin. Simultaneously, the transmitter indirectly calculates the liquid level by monitoring the pressure at the pin tip via the gas path, avoiding direct contact between the detection component and the material. This structurally solves the clogging problem of traditional level gauges. Furthermore, the bubble level gauge works in conjunction with a dual-flange level gauge to form a composite detection mode of "pressure difference measurement + bubble indirect measurement," covering the detection needs of different liquid level ranges. Data complementarity improves the completeness of liquid level detection data, effectively compensating for the reliability deficiencies of single detection methods.
[0012] In a structure that optimizes the aforementioned solution, a heat transfer medium pipe and a heat transfer medium tracing port are also included. The heat transfer medium pipe is installed on a sleeve inside the DMT dilution tank, and the heat transfer medium tracing port is located outside the DMT dilution tank and connected to the heat transfer medium pipe. Addressing the issue that DMT's tendency to solidify at low temperatures may lead to blockage of the gas path inside the sleeve or reduced material flowability, this solution installs a heat transfer medium pipe on the sleeve and a heat transfer medium tracing port outside the tank. External heat transfer medium (such as steam or heat transfer oil) is introduced into the heat transfer medium pipe through the tracing port to provide constant temperature heating for the sleeve and internal pins. This achieves a dual anti-blocking function: firstly, it heats the introduced nitrogen gas to prevent blockage of the positive pressure side port due to low-temperature condensation, ensuring unobstructed gas flow in the bubble level gauge; secondly, when improper operation causes DMT material to backflow into the positive pressure side pipeline, the heat transfer medium tracing system can continuously heat the backflowing DMT material, keeping it in a liquid state and allowing it to flow back into the dilution tank, effectively preventing the material from solidifying and sticking due to excessively low temperatures. The above design can keep the DMT material inside the sleeve in a liquid state at all times, ensuring that the bubble level gauge can operate stably for a long time under low temperature conditions.
[0013] In a structure that optimizes the aforementioned solution, the sleeve and the DMT dilution tank are connected via a PN16DN100 flange. Addressing the need for the top detection device to balance sealing performance with ease of installation and prevent connection failure due to agitation vibration, the use of a PN16DN100 flange to connect the sleeve and the DMT dilution tank achieves pressure rating adaptation and pipe diameter optimization: the PN16 (nominal pressure 1.6MPa) flange meets the requirements of atmospheric to low-pressure conditions at the top of the dilution tank, balancing safety and cost while ensuring connection sealing; the DN100 nominal diameter provides sufficient inner diameter space for easy installation and maintenance of positive and negative pressure pins, while ensuring smooth gas flow within the sleeve and reducing pressure drop loss, thereby achieving stable installation and reliable operation of the detection device under complex vibration conditions.
[0014] In a structure that optimizes the aforementioned scheme, a negative pressure needle is also included. The negative pressure needle extends into the DMT dilution tank through a sleeve, and the transmitter is connected to the negative pressure needle through a gas path. By adding a negative pressure needle to construct a differential pressure measurement system, a positive pressure needle is placed at the bottom of the tank to detect the liquid phase pressure to reflect the actual liquid level, and a negative pressure needle is placed at the top of the tank to detect the gas phase pressure as a reference zero point for differential pressure calculation. The transmitter calculates the pressure difference between the two in real time, effectively eliminating the interference of gas pressure fluctuations in the tank on liquid level measurement, and realizing a dual calibration mechanism of "static pressure method + differential pressure method". This significantly improves the accuracy and reliability of liquid level detection under complex working conditions such as liquid surface sloshing caused by stirring and the influence of foam layers.
[0015] In a structure that optimizes the aforementioned solution, a backflush valve is also included. Air passage A, connecting to an external blowing device, is located on both the air passage between the transmitter and the positive pressure needle and the air passage between the transmitter and the negative pressure needle. A backflush valve is installed on air passage A. To address the problem of bubbling level gauge failure due to blockage of the gas passage by material particles or condensate during long-term operation, a backflush valve is installed on air passage A between the transmitter and the positive / negative pressure needles, establishing an automatic maintenance mechanism. High-pressure gas (such as compressed nitrogen) is periodically or as needed introduced into air passage A via the backflush valve to backflush the positive / negative pressure needles and the inside of the sleeve, effectively removing attached material residue or impurities, preventing detection failure due to passage blockage, thereby extending the maintenance-free cycle of the level gauge, reducing the frequency of manual maintenance, and ensuring the long-term reliable operation of the bubbling level gauge.
[0016] In a structure that optimizes the aforementioned scheme, the negative pressure needle is positioned at the top of the DMT dilution tank, while the positive pressure needle is positioned at the bottom. By placing the positive pressure needle at the bottom of the tank to detect the pressure at the bottom of the liquid phase and reflect the actual liquid level in real time, and simultaneously placing the negative pressure needle at the top of the tank to detect the gas phase pressure and use it as the reference zero point for differential pressure calculation, the two work together to construct a full-range detection system from the bottom to the top of the tank. This system can accurately capture critical signals when the liquid level is extremely low (close to the pump inlet) or extremely high (close to the safety upper limit), providing complete and continuous liquid level data for the control system. This effectively avoids process accidents such as pump dry running and tank overpressure caused by detection blind spots, significantly improving the safety and reliability of DMT dilution tank operation.
[0017] Compared to existing technologies, the DMT dilution tank with a dual level detection device described in this utility model solves the problems mentioned in the prior art through the synergistic effect of a bubbling level gauge and a dual-flange level gauge. The specific beneficial effects are as follows:
[0018] This invention utilizes a combined bubbling level gauge and a dual-flange level gauge to construct a composite detection mode, achieving dual detection and avoiding control failures caused by single faults. This ensures the integrity and accuracy of level detection under high viscosity and strong stirring conditions. The bubbling level gauge uses a sleeve isolation and gas bubbling to prevent material blockage, and combined with the backflush valve for automatic maintenance, it extends the maintenance-free period. The dual-flange level gauge uses diaphragm isolation and a PN25DN80 flange for stable installation, improving its anti-disturbance measurement performance under medium and high pressure environments. The top regulating valve, linked to the dual level detection device, dynamically regulates the material ratio, forming a "detection-control-execution" closed-loop system, optimizing process automation and ratio accuracy. The heat tracing system for the heating medium solves the problem of solidification of low-temperature materials, and the PN16DN100 flange balances top sealing and installation convenience. Positive / negative pressure pins construct a differential pressure measurement system to achieve full-range detection, eliminating interference from stirring and air pressure, and preventing safety accidents. Overall, through structural and mechanism innovation, this invention significantly improves the accuracy, reliability, and environmental adaptability of DMT dilution tank level detection, reduces maintenance costs, and provides key support for PET recycling processes. Attached Figure Description
[0019] The accompanying drawings, which form part of this utility model, are used to provide a further understanding of the utility model. The illustrative embodiments of the utility model and their descriptions are used to explain the utility model and do not constitute an undue limitation of the utility model. In the drawings:
[0020] Figure 1 This is a schematic diagram of the structure of the DMT dilution tank with dual liquid level detection device described in this utility model.
[0021] Figure 2 This is a schematic diagram of the structure of the bubble level gauge described in this utility model.
[0022] Figure 3 This is a flowchart illustrating the operation of the DMT dilution tank with dual liquid level detection device described in this utility model.
[0023] Explanation of reference numerals in the attached figures:
[0024] 1. DMT dilution tank; 2. Dilution tank agitator; 3. Double flange level gauge; 4. Bubble level gauge; 5. DMT slurry transfer pump; 6. Control valve; 7. Methanol transfer pump.
[0025] 41. Sleeve; 42. Positive pressure needle; 43. Transmitter; 44. Heat medium tracing port; 45. Negative pressure needle; 46. Backflush valve; 47. Gas line A. Detailed Implementation
[0026] It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.
[0027] In the description of this utility model, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.
[0028] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.
[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0030] like Figure 1-2As shown, a specific implementation structure of a DMT dilution tank with a dual liquid level detection device is as follows: The vertical cylindrical container DMT dilution tank 1 has an internal stirring shaft that vertically penetrates the top of the tank and extends to the bottom. The stirring blades of the dilution tank 2 have an anchor-type structure and are used to mix high-viscosity DMT and MET media. A dual-flange liquid level gauge 3 is vertically installed in the middle section of the side of the tank via a PN25DN80 flange with a raised RF sealing surface. Its diaphragm-type detection element contacts the medium inside the tank to monitor the liquid level and static pressure. The sleeve 41 of the bubble level gauge 4 is connected to the flange hole on the top of the tank via a PN16DN100 flange, extending into the tank from the top. The DMT slurry delivery pump 5 is connected to the discharge port at the bottom of the tank. The sleeve 41 of the bubble level gauge 4 is a hollow cylindrical tube, with its lower end communicating with the top wall of the tank to form an isolation cavity. The positive pressure needle 42 is vertically inserted from the top of the sleeve to a position 50mm from the bottom of the tank to detect the liquid phase pressure, and the negative pressure needle 45 is inserted at an angle from the side of the sleeve into the gas phase space at the top of the tank to detect the gas phase pressure. The external blowing device is connected to the pins via two independent air lines, including a backflush valve 46 and an air line A47. The external blowing device, via transmitter 43, introduces nitrogen into the positive pressure pin 42 and negative pressure pin 45 through the air lines to create a bubbling effect. During maintenance, the backflush valve 46 is opened, allowing compressed air to purge the pins and the inside of the sleeve 41 in the reverse direction. The heat medium pipe wound around the outside of the sleeve 41 is connected to the external heat medium circulation system through the heat medium tracing port 44 on the tank top, maintaining the heat medium temperature at 60±5℃ to ensure the material inside the sleeve remains liquid. The positive and negative pressure pins form a differential pressure measurement loop via the transmitter. Combined with the static pressure data from the dual-flange level gauge, the system undergoes dual calibration via the DCS system to eliminate interference from agitation and air pressure. The regulating valve 6 on the top of the tank is connected to the DCS system via a 4-20mA signal. When the liquid level is below the lower limit, the regulating valve automatically opens, starting the methanol transfer pump 7 to increase the MET feed rate. When the level is above the upper limit, the valve closes and an alarm sounds. Simultaneously, the agitator speed and the transfer pump power are dynamically adjusted according to the liquid level, achieving coordinated control of process parameters.
[0031] The DCS system is the control core, responsible for compiling the liquid level information transmitted by the level gauge and outputting control commands to the regulating valve 6, conveying device, and stirring device to execute corresponding actions. Internally, it divides the information into four segments according to the liquid level: low-low limit (LL), low limit (L), high limit (H), and high-high limit (HH), and outputs different control commands for each segment. The conveying device includes a DMT slurry conveying pump 5 and a methanol conveying pump 7. The DMT slurry conveying pump 5 is used to convey the diluted DMT material in the DMT dilution tank 1 to the next stage device, and the methanol conveying pump 7 is used to convey methanol to the DMT dilution tank 1. Both are started or stopped according to signal commands. The DMT dilution tank stirrer 2 is used to stir the material in the tank, and stirring is started or stopped according to signal commands. The regulating valve 6 is located on the pipeline between the methanol conveying pump 7 and the DMT dilution tank 1, and its opening is adjusted according to signal commands.
[0032] Specific examples Figure 3As shown, when the DMT dilution section is running smoothly, the material condition is stable, and the in-tank agitator and transfer pump start up smoothly and uniformly mix the material, the dual-flange level gauge 3 and the bubble level gauge 4 accurately capture the liquid level changes and transmit the data to the DCS system in real time. The DCS system carefully compares and analyzes the two liquid level information. After confirming that the values are both within the preset error range, it issues an instruction based on the result: when the liquid level touches the low-low limit (LL), the DCS quickly sends a shutdown instruction to the DMT slurry transfer pump 5 to ensure safety; if the liquid level drops to the low limit (L), it instructs the dilution tank agitator 2 to stop working to prevent over-mixing. When the liquid level rises to the high limit (H), an alarm mechanism is immediately triggered, and an alarm signal is displayed on the control panel to remind the operator. When the liquid level reaches the high-high limit (HH), the DCS sends a command to stop the methanol transfer pump 7. If the methanol transfer pump 7 has been stopped but the liquid level continues to be at the high-high limit (HH), a closing command is sent to the regulating valve 6 to effectively control the liquid level. In addition, a calibration function is implemented in conjunction with the DCS system. When there is a large deviation in the data detected by the two liquid level gauges, the control panel will display an error signal in real time, which will help the operator to quickly locate and solve the problem, ensuring the stable operation of the DMT dilution section.
[0033] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.
Claims
1. A DMT dilution tank with dual liquid level detection means, characterized by: The device comprises a DMT dilution tank (1), a dilution tank agitator (2), a double-flange liquid level meter (3), a bubbling liquid level meter (4), and a DMT slurry delivery pump (5).
2. The DMT dilution tank with dual liquid level detection device according to claim 1, characterized in that: The device further comprises an adjusting valve (6) arranged on the top of the DMT dilution tank (1).
3. The DMT dilution tank with dual liquid level detection device according to claim 1, characterized in that: The double-flange liquid level meter (3) is connected to the side of the DMT dilution tank (1) through a PN25 DN80 flange.
4. The DMT dilution tank with dual liquid level detection device according to claim 1, characterized in that: The bubbling liquid level meter (4) comprises a sleeve (41), a positive pressure insertion needle (42), and a transmitter (43).
5. The DMT dilution tank with dual liquid level detection device according to claim 4, characterized in that: The sleeve (41) is in communication with the inner top wall of the DMT dilution tank (1), the positive pressure insertion needle (42) extends into the sleeve (41), and the transmitter (43) is in communication with the positive pressure insertion needle (42) through an air path.
6. The DMT dilution tank with dual liquid level detection device according to claim 4, characterized in that: The device further comprises a heat medium pipe and a heat medium heating port (44).
7. The DMT dilution tank with dual liquid level detection device according to claim 4, characterized in that: The heat medium pipe is arranged on the sleeve (41) inside the DMT dilution tank (1), and the heat medium heating port (44) is arranged outside the DMT dilution tank (1) and in communication with the heat medium pipe.
8. The DMT dilution tank with dual liquid level detection device according to claim 7, characterized in that: The sleeve (41) is connected to the DMT dilution tank (1) through a PN16 DN100 flange.
9. The DMT dilution tank with dual liquid level detection device according to claim 7, characterized in that: The device further comprises a negative pressure insertion needle (45) extending into the DMT dilution tank (1) through the sleeve (41), and the transmitter (43) is in communication with the negative pressure insertion needle (45) through an air path. The device further comprises a back-blowing valve (46) arranged on the air path between the transmitter (43) and the positive pressure insertion needle (42) and on the air path between the transmitter (43) and the negative pressure insertion needle (45). The end of the negative pressure insertion needle (45) is located at the top of the DMT dilution tank (1), and the end of the positive pressure insertion needle (42) is located at the bottom of the DMT dilution tank (1).