A pretreatment system suitable for on-line analyzers of maleic anhydride plants

Abstract

The utility model discloses a pretreatment system suitable for malonic acid device on -line analysis appearance, including sampling subassembly and with the intercommunication of integrated heat tracing pipeline's pretreatment subassembly, sampling subassembly includes sampling probe, process sampling primary valve and probe sampling cut -out valve of sequential intercommunication, and sampling probe inserts sampling pipeline, the pretreatment subassembly includes heat preservation box and sets up in its inside liquid inlet treatment pipeline and liquid outlet treatment pipeline, and heat preservation box is equipped with electric heater, makes the temperature in the box reach 120 DEG C, and the liquid inlet treatment pipeline and liquid outlet treatment pipeline in the pretreatment subassembly all are communicated with on -line analysis appearance through heat tracing pipeline. The utility model can guarantee that instrument system integration long -term stable operation, through high temperature control, effectively avoided the solidification of sample, guaranteed that the measured value is not disturbed, guaranteed that sample is not distortion and satisfies the process demand, provides more accurate data for the process, reduces the maintenance frequency of personnel, reduces the workload of maintenance personnel.

Description

Technical Field

[0001] This utility model relates to the field of petrochemical online analyzer technology, specifically to a pretreatment system suitable for maleic anhydride unit online analyzers. Background Technology

[0002] Currently, maleic anhydride production plants are generally divided into four routes based on the raw material feedstock: benzene oxidation, n-butane oxidation, C4 olefins, and phthalic anhydride by-product. Due to the very limited resources of benzene, the n-butane oxidation and C4 olefins methods for producing maleic anhydride have developed rapidly in recent years. Among them, the n-butane oxidation process can completely eliminate benzene pollution to the environment and has advantages such as high maleic anhydride yield, low solvent loss rate, low energy consumption, high external steam output, and long stable operation cycle. At the same time, it effectively solves the wastewater treatment problem that is common in the maleic anhydride industry. Under the operating conditions of the maleic anhydride reactor in the n-butane process (inlet pressure approximately 0.17 MPa, catalyst bed temperature typically 440-470℃, molten salt temperature 400-420℃), the hot reaction gas is cooled by a gas cooler and then sent to the absorption process. It is often cooled to around 200℃ by an exchanger for sampling by online analytical instruments. Because the product contains maleic anhydride, acetic acid, and other components, these components solidify at low temperatures and have high dew points (up to 110℃), making many UV analyzers unsuitable for field applications. Currently, many system integrators use a "high-temperature sampling + water washing" solution. After water washing, no desolvation is performed, and measurements are taken with a room-temperature UV analyzer. Because no desolvation is performed after washing, saturated water vapor can lower the maleic anhydride content in the sample or cause the loss of heavy components after cooling, affecting the accuracy of the measurement results. Furthermore, the water washing device generally uses stagnant water, requiring regular replacement. Due to the excessively high sample temperature, downstream pipeline blockages are frequent, requiring frequent maintenance by operators, which does not conform to the original design principles of process application and analytical instrument system integration.

[0003] The C4 olefin method uses active components such as n-butene and butadiene from a mixed C4 fraction as raw materials. These components react with air (or oxygen) in the presence of a V₂O₅-P₂O₃ catalyst in the gas phase to produce maleic anhydride. During the reaction, n-butene first undergoes dehydrogenation to form butadiene, which is then oxidized to maleic anhydride. In addition to the main products, the reaction produces byproducts such as carbon monoxide, carbon dioxide, water, and small amounts of acetaldehyde, acetic acid, acrolein, and furan. These byproducts easily solidify at low temperatures, making them unmeasurable and prone to clogging the tubing. Currently, water washing and removal are commonly used as pretreatment to remove maleic anhydride, acetic acid, and other components to prevent tubing blockage. However, using ambient temperature analytical instruments requires frequent water changes and cleaning of the preceding and following tubing. Similarly, excessively high sample temperatures lead to supersaturated water vapor after washing, severely affecting instrument measurements. Furthermore, some processes require additional water measurements, failing to meet process requirements. The method is also highly dependent on the technical skill of on-site maintenance personnel, often resulting in frequent downtime and maintenance. Utility Model Content

[0004] The purpose of this invention is to address the shortcomings of existing analyzers in the prior art, which cannot meet the analytical requirements of products after the reaction of n-butane oxidation and C4 olefins, and to provide a pretreatment system suitable for online analyzers in maleic anhydride units.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows: A pretreatment system for an online analyzer in a maleic anhydride unit includes a sampling component and a pretreatment component connected to it via an integrated heat tracing pipeline. The sampling component includes a sampling probe, a process sampling primary valve, and a probe sampling shut-off valve connected in sequence, wherein the sampling probe is inserted into the sampling pipeline. The pretreatment component includes an insulated box and an inlet and outlet processing pipeline disposed inside the insulated box. The inlet processing pipeline includes a sample inlet shut-off valve, a backflush three-way solenoid valve, a coalescing filter, a three-way switching valve, and an inlet flow meter connected in sequence. The backflush three-way solenoid valve is connected to a nitrogen backflush line and is equipped with a heating coil. The outlet processing pipeline includes a check valve and a sample return shut-off valve connected in sequence. Both the inlet and outlet processing pipelines in the pretreatment component are connected to the online analyzer via heat tracing pipelines.

[0006] Furthermore, the sampling probe in the sampling assembly is inserted into the sampling pipeline at 1 / 3 to 1 / 2 D.

[0007] Furthermore, the integrated heat tracing pipeline is an integrated electric heat tracing cable with constant power, a sample temperature of 220℃, a 3 / 8” OD pipe diameter, and a length of 10–15 meters.

[0008] Furthermore, the pretreatment component includes a double-layered insulated box with a wall thickness of over 50mm, equipped with an electric heater, which enables the internal temperature of the box to reach 120℃.

[0009] Furthermore, the outlet end of the coalescing filter in the liquid inlet treatment pipeline is connected to an automatic drain tank, which is placed inside the aforementioned insulated box.

[0010] The backflush three-way solenoid valve in the liquid inlet treatment pipeline is connected to the PLC control system and purges for 30 seconds every 30 minutes.

[0011] The liquid inlet treatment pipeline has a three-way switching valve that connects to a standard gas pipeline installed externally.

[0012] Furthermore, an atmospheric venting pipeline is connected to the pipeline between the one-way valve and the sample return shut-off valve in the liquid effluent treatment pipeline, and an atmospheric venting shut-off valve is installed on it; the end of the atmospheric venting pipeline is connected to the gas emission pipeline of the online analyzer, and an atmospheric venting drain valve and a rainproof flame arrestor are installed at the outlet end of the gas emission pipeline.

[0013] Furthermore, the end of the liquid treatment pipeline in the pretreatment component is connected to a tail gas recovery system. The tail gas recovery system is housed in a stainless steel casing and includes a waste gas shut-off valve, a gas supply precision pressure regulating valve, a drive gas pipeline, a flare shut-off valve, and a flare pipeline connected to the waste gas pipeline. The drive gas pipeline includes a drive gas shut-off valve, a pressure reducing valve, an ejector drive gas pressure indicator, an ejector, and an ejector pressure indicator, which are connected sequentially from the nitrogen inlet. The ejector is also connected to the connecting pipeline after the waste gas shut-off valve through a venting flow loop.

[0014] Furthermore, the exhaust gas recovery system is equipped with an electric heater.

[0015] Furthermore, the sample, after being processed by the exhaust gas recovery system, is reinjected into the sampling pipeline, which is equipped with a sample return process valve.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. Usage Cycle: The original solution had a normal usage cycle of one week. This utility model can achieve remote and automatic purging, ensuring long-term stable operation of the instrument system. Only routine inspections and monthly checks are required. The inspection content is to first confirm the sample flow rate. If it meets the requirements, no maintenance is needed. If the flow rate does not meet the requirements, simply switch manually to backflushing. If the sample flow rate is too low, the filter element needs to be cleaned.

[0017] 2. Labor Consumption: The original solution required frequent maintenance by personnel, demanding high skill levels and easily leading to instrument and system malfunctions. This invention enables automatic or remote operation, eliminating the need for on-site personnel, reducing maintenance frequency, and lowering the workload of maintenance staff.

[0018] 3. Accuracy: By controlling and measuring high temperatures, sample solidification is effectively avoided, ensuring that the measured values ​​are not disturbed and the samples are not distorted, thus providing more accurate data for the process.

[0019] 4. Practicality: High-temperature solutions can be developed based on the properties of the samples, and stable operation can be achieved after multiple adjustments and tests. Attached Figure Description

[0020] Figure 1 This is the overall process flow diagram (P&ID diagram (piping and instrumentation diagram) of this utility model); Figure 2This is a schematic diagram of the exhaust gas recovery system in this utility model; In the diagram: 1. Sampling probe; 2. Process sampling primary valve; 3. Probe sampling shut-off valve; 4. Integrated electric heating cable; 5. Sample inlet shut-off valve; 6. Backflush three-way solenoid valve; 7. Coalescing filter; 8. Automatic drain tank; 9. Three-way switching valve; 10. Inlet flow meter; 11. Check valve; 12. Sample return shut-off valve; 13. Vent shut-off valve; 14. Heating coil; 15. Tail gas recovery system; 16. Sample return process valve; 17. Nitrogen purging shut-off valve; 18. Nitrogen filter pressure reducing valve; 19. Nitrogen flow rate. 20. Instrument air shut-off valve, 21. Air filter pressure reducing valve, 22. Electric heater, 23. Atmospheric venting drain valve, 24. Rainproof flame arrestor cap, 25. PLC control system, 26. Ultraviolet analyzer, 27. Chassis cooler, 28. Drive air shut-off valve, 29. Pressure reducing valve, 30. Ejector drive air pressure indicator, 31. Ejector, 32. Ejector pressure indicator, 33. Make-up air precision pressure regulating valve, 34. Exhaust gas main pipe pressure indicator, 35. Venting flow rate, 36. Exhaust gas shut-off valve, 37. Flare shut-off valve. Detailed Implementation

[0021] It should be noted that, in the description of this utility model, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," "link," etc., 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 direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0022] The specific embodiments of this utility model will be further described in detail below with reference to the accompanying drawings: like Figure 1 As shown, a pretreatment system suitable for an online analyzer in a maleic anhydride unit includes a sampling component, a pretreatment component, and an online analyzer. The sampling component is used to sample from a sampling pipeline and is connected to the pretreatment component via an integrated heat tracing pipeline. The sampling component includes a sampling probe 1, a process sampling primary valve 2, and a probe sampling shut-off valve 3 connected in sequence. The sampling probe 1 is a clamp-type probe inserted into the sampling pipeline at 1 / 3 to 1 / 2 D to ensure sample representativeness. The integrated heat tracing pipeline is an integrated electric heat tracing cable 4 with constant power to maintain the sample temperature at 220°C. It has a 3 / 8” OD diameter and a length of 10-15 meters to ensure that the online analyzer cabinet can be installed nearby to avoid temperature fluctuations. The analyzer cabinet is equipped with an electric heater 22 and a temperature detector for heat preservation and tracing. The integrated electric heat tracing cable 4 is connected to the inlet end of the pretreatment component.

[0023] The pretreatment assembly includes an insulated box and inlet and outlet liquid treatment pipelines installed inside the insulated box. The inlet liquid treatment pipeline includes a sample inlet shut-off valve 5, a backflush three-way solenoid valve 6, a coalescing filter 7, a three-way switching valve 9, and an inlet flow meter 10, all connected sequentially via pipelines. The backflush three-way solenoid valve 6 is also connected to a nitrogen backflush pipeline for automatically backflushing the sampling assembly pipeline. This pipeline is equipped with a heating coil 14 for nitrogen preheating to prevent the backflush sample from solidifying within the pipeline. Simultaneously, the backflush three-way solenoid valve 6 is connected to a PLC control system 25, which controls the frequency of nitrogen backflush and sets... A timed backflushing process is implemented, purging for 30 seconds every 30 minutes. Data is retained for 2 minutes during this period via PLC to prevent process misjudgment. It can also be used for automatic or manual backflushing and maintenance via DCS remote control, avoiding frequent manual intervention. To ensure that heavy components in the sample cannot be vaporized, an automatic drainage tank 8 is connected to the outlet of the coalescing filter 7 to automatically discharge the condensate of heavy components. The three-way switching valve 9 is also connected to a standard gas pipeline (standard gas refers to a specially prepared and tested gas with known composition and content) for calibrating online analytical instruments. The liquid discharge treatment pipeline includes a one-way valve 11 and a sample return shut-off valve 12 connected sequentially from inlet to outlet. An atmospheric venting pipeline is connected to the pipeline between the two, with an atmospheric venting shut-off valve 13 installed on it. The other end is connected to the gas discharge pipeline of the online analyzer. The atmospheric venting shut-off valve 13 is used for operation and maintenance under abnormal conditions. The insulated box adopts a double-layer insulated box body with a wall thickness of more than 50mm, and is equipped with an electric heater 22. The electric heater 22 is a 2000W explosion-proof electric heater, which can make the temperature inside the box reach 120℃. At the same time, the insulated box is also equipped with a temperature detector that can monitor the temperature inside the box in real time, so as to work with the electric heater 22 to achieve stable control of the internal temperature of the insulated box. In addition, the box body is made of sandwiched material to ensure that the internal temperature of the box will not change suddenly when the door of the pre-treated insulated box is opened.

[0024] In the aforementioned pretreatment components, both the inlet and outlet liquid treatment pipelines are connected to the online analyzer via heated pipelines to prevent cold spots during operation. The online analyzer is a high-temperature ultraviolet analyzer 26, whose measuring cell temperature can reach 120℃. Simultaneously, since the online analyzer operates under high temperature and heated conditions, a cooling component is also provided to prevent excessively high temperatures within the analyzer cabinet. This cooling component includes an instrument air shut-off valve 20, an air filter pressure reducing valve 21, and a chassis cooler 27, sequentially connected from the instrument air inlet. The chassis cooler 27 is connected to the online analyzer and is used to cool the electronic components on both sides of the instrument, ensuring the instrument's normal operating temperature requirements. Due to the instrument's measurement requirements, the online analyzer is also equipped with a nitrogen purging component. This nitrogen purging component includes a nitrogen purging shut-off valve 17, a nitrogen filter pressure reducing valve 18, and a nitrogen flow meter 19, sequentially connected from the nitrogen inlet. These valves control the pressure and flow rate of the purging nitrogen to meet the instrument's measurement requirements.

[0025] The outlet end of the gas emission pipeline of the above-mentioned online analyzer is equipped with an atmospheric venting and drainage valve 23 and a rainproof and flame-retardant cap 24 to achieve drainage and gas emission.

[0026] The liquid outlet of the liquid treatment pipeline in the above-mentioned pretreatment component is connected to a tail gas recovery system 15, combined with Figure 2 As shown, the exhaust gas recovery system 15 is housed in a stainless steel casing and includes an exhaust gas shut-off valve 36, a gas supply precision pressure regulating valve 33, a drive gas pipeline, a flare shut-off valve 37, and a flare pipeline, all connected to the aforementioned liquid treatment pipeline (exhaust gas pipeline). The drive gas pipeline includes a drive gas shut-off valve 28, a pressure reducing valve 29, an ejector drive gas pressure indicator 30, an ejector 31, and an ejector pressure indicator 32, sequentially connected from the nitrogen inlet. The ejector 31 is also connected to a connecting pipeline after the exhaust gas shut-off valve 36 via a vent flow circuit 35, where an exhaust gas main pressure indicator 34 is also installed. The exhaust gas recovery system 15 is also equipped with an electric heater 22. The sample processed by the exhaust gas recovery system 15 is re-injected into the sampling pipeline, with a sample return process valve 16 connected to the injection end.

[0027] The pretreatment system in the above technical solution can effectively avoid the characteristic that samples after the maleic anhydride reactor are prone to solidification below 60°C. It is equipped with high-temperature sampling and delivery throughout the process, with no cold spots. The specific application principle is as follows: After the above sampling probe 1 clamps the sample, it is transmitted into the pretreatment component through the integrated electric heating cable 4. The sample is then controlled by the sample inlet shut-off valve 5 and the flow rate of the coalescing filter 7 is adjusted before entering the online analyzer for measurement. The returned sample is returned to the original process sampling pipeline via the exhaust gas recovery system 15. The analyzed waste gas is first collected in the waste gas pipe of the exhaust gas recovery system 15. The flow of waste gas is controlled by the waste gas shut-off valve 36 (before commissioning, the waste gas shut-off valve 36 needs to be closed, the drive gas shut-off valve 28 needs to be opened and the pressure reducing valve 29 needs to be adjusted to ensure that the ejector drive gas pressure indicator 30 is 18-20 psig. At this time, the ejector 31 will be activated to perform suction. Adjust the venting flow rate 35 to 2L / min. The entire exhaust gas recovery system 15 will be automatically adjusted and balanced through the gas replenishment precision pressure regulating valve 33 to ensure that the exhaust gas main pipe pressure indicator 34 is about 1" WC. At this time, the system reaches mechanical balance and can operate automatically). Opening the waste gas shut-off valve 36 achieves normal operation with a back pressure of 1.5 bar. The sample enters the flare pipeline through the flare shut-off valve 37. After the exhaust gas recovery is completed, the sample is reinjected into the sampling pipeline via the sample return process valve 16.

[0028] In the above embodiments, the integrated sample heating pipeline, the high-temperature heating of the pretreatment components, and the instrument inlet and return pipelines of the online analyzer can also be steam-heated.

[0029] Of course, the above description is not intended to limit the present utility model, and the present utility model is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present utility model should also fall within the protection scope of the present utility model.

Claims

1. A pretreatment system suitable for an online analyzer in a maleic anhydride unit, characterized in that: The system includes a sampling assembly and a pretreatment assembly connected to it via an integrated heated pipeline. The sampling assembly includes a sampling probe, a process sampling primary valve, and a probe sampling shut-off valve connected in sequence, wherein the sampling probe is inserted into the sampling pipeline. The pretreatment assembly includes an insulated box and inlet and outlet liquid treatment pipelines located inside the insulated box. The inlet liquid treatment pipeline includes a sample inlet shut-off valve, a backflush three-way solenoid valve, a coalescing filter, a three-way switching valve, and an inlet flow meter connected in sequence. The backflush three-way solenoid valve is connected to a nitrogen backflush line and is equipped with a heating coil. The outlet liquid treatment pipeline includes a check valve and a sample return shut-off valve connected in sequence. Both the inlet and outlet liquid treatment pipelines in the pretreatment assembly are connected to an online analyzer via heated pipelines.

2. The pretreatment system for an online analyzer of maleic anhydride unit according to claim 1, characterized in that: The sampling probe in the sampling assembly is inserted into the sampling pipeline at 1 / 3 to 1 / 2 D.

3. The pretreatment system for an online analyzer of maleic anhydride unit according to claim 1, characterized in that: The integrated heat tracing pipeline uses an integrated electric heat tracing cable with constant power, a sample temperature of 220℃, a 3 / 8” OD pipe diameter, and a length of 10–15 meters.

4. The pretreatment system for an online analyzer of maleic anhydride unit according to claim 1, characterized in that: The pretreatment component uses a double-layered insulated box with a wall thickness of over 50mm and is equipped with an electric heater to achieve a temperature of 120℃ inside the box.

5. A pretreatment system for an online analyzer of maleic anhydride unit according to claim 1, characterized in that: The outlet end of the coalescing filter in the liquid inlet treatment pipeline is connected to an automatic drain tank, which is placed inside the aforementioned insulated box. The backflush three-way solenoid valve in the liquid inlet treatment pipeline is connected to the PLC control system and purges for 30 seconds every 30 minutes. The liquid inlet treatment pipeline has a three-way switching valve that connects to a standard gas pipeline installed externally.

6. A pretreatment system for an online analyzer of maleic anhydride unit according to claim 1, characterized in that: An atmospheric venting pipeline is connected to the pipeline between the one-way valve and the sample return shut-off valve in the liquid effluent treatment pipeline, and an atmospheric venting shut-off valve is installed on it; the end of the atmospheric venting pipeline is connected to the gas emission pipeline of the online analyzer, and an atmospheric venting drain valve and a rainproof flame arrestor are installed at the outlet end of the gas emission pipeline.

7. A pretreatment system for an online analyzer of maleic anhydride unit according to claim 1, characterized in that: The pretreatment component has an exhaust gas recovery system installed at the end of the liquid treatment pipeline. The exhaust gas recovery system is housed in a stainless steel casing and includes an exhaust gas shut-off valve, a gas supply precision pressure regulating valve, a drive gas pipeline, a flare shut-off valve, and a flare pipeline connected to the exhaust gas pipeline. The drive gas pipeline includes a drive gas shut-off valve, a pressure reducing valve, an ejector drive gas pressure indicator, an ejector, and an ejector pressure indicator, which are connected sequentially from the nitrogen inlet. The ejector is also connected to the connecting pipeline after the exhaust gas shut-off valve through a venting flow loop.

8. A pretreatment system for an online analyzer of maleic anhydride unit according to claim 7, characterized in that: The exhaust gas recovery system is equipped with an electric heater.

9. A pretreatment system for an online analyzer of maleic anhydride unit according to claim 7, characterized in that: The sample, after being processed by the exhaust gas recovery system, is reinjected into the sampling pipeline, which is connected to a sample return process valve.

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