Coal-to-methanol VOCs recovery control system based on reciprocating compressor and multi-section cooling separation

Abstract

The invention provides a coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-section cooling separation, and relates to the technical field of chemical engineering, the coal-to-methanol VOCs recovery control system comprises a central control unit used for controlling the opening and closing of an emergency cut-off valve based on oxygen concentration monitoring data and controlling the opening and closing of an emergency cut-off valve based on pressure sensor monitoring data; determining a minimum circular region containing all the pressure data points through calculation, and identifying a pressure abnormal range through boundary features of the minimum circular region to obtain an identification result; and the compressor operation frequency and the backflow pipeline adjusting valve opening degree are cooperatively controlled based on the recognition result, and the compressor inlet pressure is kept stable within the set range. According to the method, the double tail gas treatment systems are matched with different gas sources, oxygen concentration monitoring and explosion prevention are combined, the stable pressure is cooperatively regulated and controlled through recognition of the minimum pressure circular area, the frequency of the compressor and the reflux valve, and safe and stable recovery of the VOCs from the coal-to-methanol is achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation. Background Technology

[0002] In the coal-to-methanol industry, the treatment of volatile organic compounds (VOCs) generated from storage tank areas and distillation units has been a major concern. Currently, common treatment methods include activated carbon adsorption, regenerative thermal oxidizer (RTO / RCO), and compression recovery. These methods each have their own characteristics in terms of applicable conditions, energy efficiency, and operational stability, but they also present some noteworthy operational challenges.

[0003] Taking the compression recovery process as an example, this method recovers useful components in waste gas by pressurizing, which has certain resource utilization advantages. However, in actual operation, due to the fluctuation of the gas volume emitted by the storage tank, the compressor inlet pressure is prone to instability. Existing control methods mostly adopt conventional pressure regulation strategies, which have certain limitations in the accuracy of pressure fluctuation identification and response efficiency. This may lead to a decrease in efficiency or unstable operation of the system when the operating conditions change, affecting the continuity and energy efficiency of the overall recovery process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation, so as to improve the overall system operating efficiency.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: The VOCs recovery control system for coal-to-methanol based on reciprocating compressors and multi-stage cooling separation includes: The methanol exhaust gas treatment system is used to treat the exhaust gas from the breather valve at the top of the methanol storage tank. The crude methanol and pre-distillation tower non-condensable gas tail gas treatment system is used to treat the exhaust gas from the breather valve at the top of the crude methanol storage tank and the non-condensable gas from the pre-distillation tower; The central control unit is used to control the opening and closing of the emergency shut-off valve based on oxygen concentration monitoring data, and to calculate and determine the smallest circular area containing all pressure data points based on pressure sensor monitoring data. The boundary features of the smallest circular area are used to identify the pressure anomaly range and obtain the identification result. Based on the identification result, the compressor operating frequency and the opening of the return pipeline regulating valve are coordinated and controlled to keep the compressor inlet pressure stable within the set range.

[0006] The above-described solution of the present invention has at least the following beneficial effects: To address issues such as unstable compressor inlet pressure and decreased system efficiency caused by fluctuations in the storage tank's breathing exhaust volume during the compression recovery process, the central control unit uses a minimum circular area algorithm to identify abnormal pressure ranges. Combined with coordinated control of the compressor operating frequency and the opening of the return pipeline regulating valve, this stabilizes the compressor inlet pressure within a set range, preventing compressor surge and equipment damage caused by pressure fluctuations. Simultaneously, it ensures the continuity of the recovery process and improves overall system operating efficiency. The system retains and integrates an online oxygen content monitoring and emergency shut-off valve linkage mechanism. Combined with the real-time data response from the central control unit, this dynamically prevents excessively high oxygen concentrations. The system mitigates the risk of VOCs gas explosions. Both the refined and crude methanol tail gas treatment systems are equipped with buffer tanks, safety valves, and emergency flare lines, forming a multi-layered safety protection system and addressing the issue of lagging safety control during the treatment process. After treatment, the gas phase of the refined methanol tail gas can be recycled as nitrogen to the cryogenic methanol washing unit, while the liquid phase is sent back to the pre-distillation tower. The non-condensable gas phases from the crude methanol and pre-tower can be sent to the boiler for co-firing, and the liquid phase is returned to the corresponding storage tank as needed, maximizing the recovery of methanol and nitrogen, solving the problem of wasted process resources, and considering economic feasibility. The system requires no additional external exhaust outlets and does not involve the emission of harmful gases, avoiding the environmental shortcomings of technologies such as activated carbon adsorption and absorption. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of a coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation, provided by an embodiment of the present invention.

[0008] Explanation of reference numerals in the attached figures: 1. First online oxygen content analyzer; 2. First mixed gas buffer tank; 3. First reciprocating compressor; 4. First stage cooler; 5. First inlet buffer tank; 6. First outlet buffer tank; 7. First compressor outlet cooler; 8. First gas-liquid separator; 9. Second online oxygen content analyzer; 10. Second mixed gas buffer tank; 11. Second reciprocating compressor; 12. Second stage cooler; 13. Second inlet buffer tank; 14. Second outlet buffer tank; 15. Second compressor outlet cooler; 16. Second gas-liquid separator. Detailed Implementation

[0009] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0010] like Figure 1As shown, embodiments of the present invention propose a coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation, comprising: The methanol exhaust gas treatment system is used to treat the exhaust gas from the breather valve at the top of the methanol storage tank. The crude methanol and pre-distillation tower non-condensable gas tail gas treatment system is used to treat the exhaust gas from the breather valve at the top of the crude methanol storage tank and the non-condensable gas from the pre-distillation tower; The central control unit is used to control the opening and closing of the emergency shut-off valve based on oxygen concentration monitoring data, and to calculate and determine the smallest circular area containing all pressure data points based on pressure sensor monitoring data. The boundary features of the smallest circular area are used to identify the pressure anomaly range and obtain the identification result. Based on the identification result, the compressor operating frequency and the opening of the return pipeline regulating valve are coordinated and controlled to keep the compressor inlet pressure stable within the set range.

[0011] In this embodiment of the invention, to address issues such as unstable compressor inlet pressure and decreased system efficiency caused by fluctuations in the storage tank's exhaust volume during the compression recovery process, the central control unit identifies abnormal pressure ranges using a minimum circular area algorithm. Combined with the coordinated control of the compressor operating frequency and the opening of the return pipeline regulating valve, the compressor inlet pressure can be stabilized within a set range, preventing compressor surge and equipment damage caused by pressure fluctuations. Simultaneously, it ensures the continuity of the recovery process and improves overall system operating efficiency. The system retains and integrates an online oxygen content monitoring and emergency shut-off valve linkage mechanism, which, in conjunction with the real-time data response of the central control unit, can dynamically avoid oxygen... The system mitigates the risk of VOC gas explosions caused by excessively high concentrations. Both the refined and crude methanol tail gas treatment systems are equipped with buffer tanks, safety valves, and emergency flare lines, forming a multi-layered safety protection system and addressing the issue of lagging safety control during the treatment process. After treatment, the gas phase of the refined methanol tail gas can be recycled as nitrogen in a cryogenic methanol washing unit, while the liquid phase is returned to the pre-distillation tower. The non-condensable gas phases from the crude methanol and pre-tower can be sent to the boiler for co-firing, and the liquid phase is returned to the corresponding storage tank as needed, maximizing the recovery of methanol and nitrogen, solving the problem of wasted process resources, and considering economic feasibility. The system requires no additional external exhaust outlets and does not involve the emission of harmful gases, avoiding the environmental shortcomings of technologies such as activated carbon adsorption and absorption.

[0012] In a preferred embodiment of the present invention, the exhaust gas treatment system for refined armor includes: The first online oxygen content analyzer 1 is installed on the tail gas outlet pipeline of the refined car body to monitor the oxygen concentration in real time; The first mixed gas buffer tank 2 is connected to the first online oxygen content analyzer 1 and is used to buffer gas pressure fluctuations. The first reciprocating compressor 3 is connected to the outlet of the first mixed gas buffer tank 2 and is used for multi-stage compression of gas. The first-stage cooler 4 is connected to one outlet of the first reciprocating compressor 3 and is used to cool the compressed gas. The first inlet buffer tank 5 is connected to the outlet of the first stage cooler 4 and is used to stabilize the gas pressure entering the second stage of the first reciprocating compressor 3. The first outlet buffer tank 6 is connected to the second outlet of the first reciprocating compressor 3 and is used to buffer the gas pressure after compression. The first compressor outlet cooler 7 is connected to the outlet of the first outlet buffer tank 6 and is used to further cool the gas. The first gas-liquid separator 8 is connected to the outlet of the first compressor outlet cooler 7 and is used to separate the gas phase and the liquid phase. The separated gas phase is sent to the hydrogen sulfide concentration tower of the low-temperature methanol washing unit for nitrogen stripping, while the liquid phase is sent to the pre-distillation tower for recycling.

[0013] In this embodiment of the invention, the exhaust gas discharged from the breather valve at the top of the refined methanol storage tank first enters the initial safety screening stage. The exhaust gas flows through the first online oxygen content analyzer 1 installed on the outlet pipeline. This analyzer monitors the oxygen concentration in the exhaust gas in real time. Its safety control standard (i.e., safety threshold) is an oxygen concentration of 0.5%. If the monitoring data shows that the oxygen concentration is ≥0.5%, the first online oxygen content analyzer 1 will immediately link with the emergency shut-off valve, triggering the emergency shut-off valve to automatically close. On the one hand, it stops the exhaust gas from being transported to the subsequent treatment system, and on the other hand, it guides the exhaust gas into the accident flare pipeline through the preset emergency pipeline, where it is incinerated to eliminate safety hazards and avoid the risk of VOCs gas explosion caused by excessive oxygen concentration from the source. If the oxygen concentration is detected to be <0.5%, it is determined that the exhaust gas meets the safety treatment conditions and enters the next stage of pressure buffering and stabilization.

[0014] The exhaust gas that passes the safety screening then enters the first mixed gas buffer tank 2. Since the exhaust volume of the storage tank is easily affected by factors such as the temperature difference between day and night and changes in the liquid level of the storage tank, there are obvious pressure fluctuations. The subsequent first reciprocating compressor 3 has high requirements for inlet pressure stability. Sudden pressure changes can easily lead to compressor surge or a decrease in operating efficiency. Combined with the initial pressure condition (0.1MPa) of the exhaust gas from the breather valve at the top of the refined methanol storage tank, the core function of the first mixed gas buffer tank 2 is to absorb the pressure fluctuations of the exhaust gas. Through the buffering and regulation of the airflow in the internal space, the exhaust gas pressure is finally stabilized within the range of 0.1MPa that is suitable for the inlet of the first reciprocating compressor 3.

[0015] After pressure buffering and stabilization, the exhaust gas enters the first reciprocating compressor 3. The system employs a segmented compression and intermediate cooling process design to achieve efficient compression. First, the exhaust gas undergoes initial compression in the first stage of the first reciprocating compressor 3. During compression, the gas temperature rises synchronously. If it directly enters the second stage compression, it will not only increase energy consumption, but the high-temperature gas may also damage subsequent equipment. Therefore, the gas after initial compression must be immediately sent to the first-stage cooler 4. The first-stage cooler 4 reduces the gas temperature through heat exchange, which reduces the energy consumption requirement of the subsequent second-stage compression and avoids damage to the first inlet buffer tank 5 and the second-stage components of the first reciprocating compressor 3 from the high-temperature gas. Finally, the gas is cooled to 40℃ (suitable temperature) for the second-stage compression conditions. The 0℃ gas phase then enters the first inlet buffer tank 5, which further fine-tunes and stabilizes the gas pressure to ensure that the inlet pressure of the second stage of the first reciprocating compressor 3 is always maintained at 0.25MPa (set range). This pressure value matches the gas pressure after the first stage compression, which can effectively prevent wear and failure of internal components of the second stage compressor due to pressure fluctuations or liquid carryover in the gas. The gas with a stable pressure of 0.25MPa enters the second stage of the first reciprocating compressor 3 for secondary compression. After reaching 0.5MPa (target pressure), it is sent to the first outlet buffer tank 6. The first outlet buffer tank 6 is used to buffer the pressure fluctuations of the gas after the second stage compression to avoid the pulsed airflow from impacting the downstream first compressor outlet cooler 7 and the first gas-liquid separator 8.

[0016] After being pressurized by the first outlet buffer tank 6, the gas enters the deep cooling and gas-liquid separation stage. The gas first flows through the first compressor outlet cooler 7, where deep cooling promotes the liquefaction of condensable components (mainly methanol) in the gas. The cooled gas-liquid mixture enters the first gas-liquid separator 8, where gravity settling and airflow rectification achieve efficient separation of the gas and liquid phases. The separated gas phase (mainly nitrogen containing trace amounts of methanol) is transported to the hydrogen sulfide concentration tower of the low-temperature methanol washing unit, where it is recycled as stripped nitrogen to replace the low-pressure nitrogen in the traditional process. The separated liquid phase (mainly liquid methanol) is pumped to the existing pre-distillation tower in the plant area and reintegrated into the distillation process for recycling, thus realizing the recovery of methanol resources.

[0017] This embodiment, through the linkage design of the first online oxygen content analyzer and the emergency shut-off valve, can intercept unsafe exhaust gas with excessive oxygen concentration in real time. Combined with the emergency response mechanism of the accident flare, it avoids the risk of explosion caused by excessive oxygen in VOCs gas at the source, ensuring the safe operation of the entire system. Through multi-stage pressure buffering of the first mixed gas buffer tank, the first inlet buffer tank, and the first outlet buffer tank 6, and the staged cooling of the first stage cooler and the first compressor outlet cooler, it effectively solves the problems of compressor surge and equipment damage caused by exhaust gas pressure fluctuations and excessive temperature. The system avoids problems such as malfunctions, ensuring the long-term stable operation of the compressor and downstream equipment, reducing maintenance costs and downtime losses. After gas-liquid separation, the gas phase is used as stripped nitrogen for reuse, and the liquid phase is returned to the pre-distillation tower as methanol, converting the originally emitted tail gas into resources for production and avoiding the waste of methanol and nitrogen. The entire treatment process has no new external discharge outlets, and the VOCs (methanol) in the tail gas are recovered to achieve zero emissions, avoiding the secondary pollution that may be caused by traditional VOCs treatment technologies, such as the secondary treatment of adsorbents in activated carbon adsorption and the NOx emissions of RTO / RCO methods.

[0018] In a preferred embodiment of the present invention, the first online oxygen content analyzer 1 is linked with the emergency shut-off valve. When the oxygen content is ≥0.5%, the emergency shut-off valve closes, stops the gas supply, and introduces the gas into the emergency flare pipeline.

[0019] In this embodiment of the invention, the first online oxygen content analyzer 1 is fixedly installed on the tail gas outlet pipeline of the breather valve at the top of the refined methanol storage tank. After the tail gas is discharged from the storage tank, it must first flow through this analyzer. Its core function is to continuously and in real time collect oxygen concentration data in the tail gas to ensure uninterrupted monitoring of the dynamic changes in the tail gas oxygen content. The system presets an oxygen concentration safety threshold of 0.5% (based on the VOCs gas explosion-proof safety standard in the coal-to-methanol industry). The first online oxygen content analyzer 1 will automatically compare the real-time monitored oxygen concentration data with this threshold. When the monitoring data shows that the oxygen content is ≥0.5%, it is determined that the tail gas is in an unsafe state. At this time, the oxygen concentration in the tail gas has reached the explosion risk threshold of VOCs (mainly methanol). If it enters the subsequent compression and recovery system, it may cause an explosion due to a small spark or pressure change during equipment operation. When the monitoring data shows that the oxygen content is <0.5%, it is determined that the tail gas is in an unsafe state. When the oxygen content is ≥0.5%, the exhaust gas is deemed to meet safe treatment conditions, and no emergency measures need to be triggered. Based on the above judgment, the first online oxygen content analyzer 1 and the emergency shut-off valve on the pipeline form an electrical linkage control. If the condition is determined to be unsafe (oxygen content ≥0.5%), the analyzer immediately sends a shut-off signal to the emergency shut-off valve. The emergency shut-off valve closes rapidly in a short time, directly blocking the exhaust gas from being transported to the subsequent first mixed gas buffer tank 2 and the compressor system. At the same time, the emergency pipeline valve linked to the emergency shut-off valve opens synchronously, guiding the exhaust gas in the unsafe state into the emergency flare pipeline. The VOCs in the exhaust gas are eliminated by flare combustion, preventing direct emission or retention that could cause a safety accident. If the condition is determined to be safe (oxygen content <0.5%), the emergency shut-off valve remains open, and the exhaust gas can smoothly enter the first mixed gas buffer tank 2 to start the subsequent pressure buffering and compression treatment process.

[0020] This embodiment, through the linkage of real-time monitoring and automatic cut-off, can instantly block the entry of exhaust gas with excessive oxygen content into subsequent systems. This prevents explosions caused by equipment friction and pressure changes during compression, cooling, and other process stages after the high-oxygen-concentration exhaust gas mixes with VOCs. This linkage mechanism is fully automated, eliminating the need for manual inspection and judgment. Compared to manual monitoring, it shortens emergency response time and avoids the expansion of safety hazards due to delays caused by manual operation. If high-oxygen-concentration exhaust gas enters subsequent equipment such as the first reciprocating compressor and buffer tank, it may not only cause an explosion but also cause equipment corrosion and component wear due to the chemical reaction between oxygen, methanol, and metal parts of the equipment. By cutting off the excessive exhaust gas in advance, the linkage mechanism can reduce safety losses in downstream equipment and lower the frequency and cost of equipment maintenance and replacement.

[0021] In a preferred embodiment of the present invention, a return pipeline is provided between the outlet of the first stage cooler 4 and the inlet of the first inlet buffer tank 5 to regulate the gas volume and prevent compressor surge.

[0022] In this embodiment of the invention, the first reciprocating compressor 3 adopts a segmented compression process, which consists of a first-stage compression, cooling, and a second-stage compression. The first-stage compression requires raising the exhaust gas pressure to 0.25 MPa. After being cooled to 40°C by the first-stage cooler 4, the gas enters the first inlet buffer tank 5. The buffer tank's set pressure range is 0.25 MPa. Its function is to provide a stable intake pressure and gas volume for the second stage of the first reciprocating compressor 3, ensuring the second-stage compression efficiency and equipment safety. If the gas volume entering the second stage after the first-stage compression is excessive (e.g., a sudden increase in the exhaust gas volume from the storage tank causes the first-stage output gas volume to exceed the limit), or If the pressure of the first inlet buffer tank 5 exceeds the set range of 0.25MPa, it will disrupt the matching balance between the output gas volume of the first stage and the processing capacity of the second stage, causing pulsation, backflow, and sudden pressure changes in the airflow inside the compressor. In severe cases, it will damage the compressor piston, valves and other core components. The return pipeline connects the outlet of the first stage cooler 4 (the gas flow path after the first stage compression and cooling to 40°C) and the inlet of the first inlet buffer tank 5 (the flow path before the second stage intake). Essentially, it is to construct a gas volume regulation channel for the gas from the first stage outlet to the first stage inlet, which is used to balance the gas volume and pressure in the system.

[0023] Under normal operating conditions (stable exhaust gas volume in the storage tank and matching compressor load), the 40°C gas cooled by the first stage cooler 4 will enter the first inlet buffer tank 5 in full. After buffering, it will maintain a set pressure of 0.25MPa and then smoothly enter the second stage of the first reciprocating compressor 3. At this time, the regulating valve on the return pipeline is closed or slightly open, maintaining only a small amount of airflow circulation to cope with sudden fluctuations and ensure that the airflow flows to the second stage to guarantee compression efficiency. When the system experiences abnormal operating conditions (for example, the pressure sensor detects that the pressure of the first inlet buffer tank 5 exceeds the set range of 0.25MPa, or the compressor current fluctuates and shows that the airflow is unstable), the central control unit will immediately send a signal to open the regulating valve on the return pipeline. At this time, part of the 40°C gas cooled by the first stage cooler 4 will be transported back to the inlet of the first mixed gas buffer tank 2 through the return pipeline, mixed with fresh refined exhaust gas, and then re-enter the first stage of the first reciprocating compressor 3 for secondary compression. This process directly reduces the amount of gas entering the first inlet buffer tank 5, allowing the output gas volume of the first stage to be rematched with the processing capacity of the second stage based on the 0.25MPa set pressure, eliminating the airflow pulsation and pressure over-limit problems at the inlet of the second stage, and preventing surge from the root cause; once the system returns to stability (the pressure sensor detects that the pressure of the first inlet buffer tank 5 has returned to the 0.25MPa set range, and the compressor current tends to be stable), the central control unit will gradually close the regulating valve on the return pipeline, allowing the gas from the outlet of the first stage cooler 4 to re-enter the first inlet buffer tank 5 in full, and the system returns to normal operation.

[0024] This embodiment, by dynamically adjusting the gas volume entering the second stage, can directly eliminate the core cause of surge—gas volume mismatch—and avoid problems such as internal component wear and seal failure caused by compressor surge, thus extending the service life of the first reciprocating compressor 3. There is no need for temporary shutdowns for adjustment due to gas volume fluctuations; the return pipeline can be dynamically adjusted in real time, ensuring the continuous and stable operation of equipment such as the first reciprocating compressor 3 and the first inlet buffer tank 5. This avoids interruptions in VOCs recovery due to shutdowns, ensuring the continuity of the overall treatment system. Compared to shutdown depressurization and manual gas volume adjustment, this return pipeline is automatically adjusted, requiring no manual intervention. This reduces manual operation costs and avoids additional energy consumption due to shutdown restarts. The tail gas volume of the refined gas is easily affected by tank breathing and changes in production load; the return pipeline can quickly adapt to these fluctuations through gas volume circulation, eliminating the need for frequent adjustments to the overall compressor operating parameters and improving the system's adaptability to changes in operating conditions.

[0025] In a preferred embodiment of the present invention, two paths are provided between the outlet of the first outlet buffer tank 6 and the inlet of the first compressor outlet cooler 7. One path directly enters the first compressor outlet cooler 7, and the other path is equipped with a safety valve for opening the emergency flare under emergency conditions.

[0026] In this embodiment of the invention, the two-path configuration and core parameters are first clarified. The two paths between the outlet of the first outlet buffer tank 6 and the inlet of the first compressor outlet cooler 7 are designed in parallel. The first path is the conventional processing path, which directly connects the two and is used to transport gas under normal operating conditions. The second path is the emergency pressure relief path, which is equipped with a safety valve (the safety valve's opening pressure is preset to be slightly higher than the target pressure of the second stage compression by 0.55 MPa, based on the system pressure safety redundancy design). The end is connected to the emergency flare pipeline for pressure relief and gas treatment in case of abnormal overpressure. Under normal operating conditions, the gas after the second stage compression of the first reciprocating compressor 3 (pressure stabilized at 0.5 MPa) enters the first outlet buffer tank 6. After buffering, the pressure inside the tank is maintained within the set range of 0.5 MPa. At this time, the first conventional path remains unobstructed, and the gas mainly enters the first compressor outlet cooler 7 directly through this path for subsequent deep cooling and gas-liquid separation. The safety valve on the second emergency path remains closed because the system pressure has not reached the opening value, ensuring that all gas flows to the conventional processing flow and ensuring the continuity of VOCs recovery.

[0027] In emergency situations, such as a blockage inside the first compressor outlet cooler 7 causing a sudden increase in downstream resistance, poor exhaust from the gas-liquid separator 8, or a sudden increase in the intake of the first outlet buffer tank 6 exceeding its buffering capacity, the pressure inside the first outlet buffer tank 6 will rapidly rise and exceed the safety valve's 0.55MPa trigger pressure. At this point, the safety valve will automatically open, activating the second emergency path: the overpressurized gas in the first outlet buffer tank 6 will enter the emergency flare pipeline through this path, where it will be incinerated by the flare to eliminate the risk of VOCs pollution. Simultaneously, the pressure inside the first outlet buffer tank 6 will be rapidly reduced to prevent the buffer tank, compressor second-stage outlet components, or conventional pipelines from deforming, leaking, or even rupturing due to overpressure. Once the system pressure returns to the normal range of 0.5MPa, the safety valve will automatically close, the second emergency path will stop working, and the gas will re-enter the subsequent processing stage through the first conventional path.

[0028] This embodiment, through the combination of a safety valve and an emergency access path, can quickly relieve pressure in the event of system overpressure, preventing structural damage to the first outlet buffer tank, the second-stage outlet of the first reciprocating compressor, and conventional pipelines due to long-term overpressure, thus extending the service life of core equipment such as compressors and buffer tanks. The emergency access path is connected to an emergency flare, allowing overpressured gas to be discharged after incineration, preventing direct leakage of VOCs such as methanol due to equipment overpressure rupture. This complies with environmental regulations for VOCs treatment and eliminates safety hazards such as explosions and poisoning caused by leaked gas. Under normal operating conditions, the first access path stably delivers gas, ensuring uninterrupted treatment of the refined gas tail gas. In emergency situations, the second access path responds quickly, eliminating the need to temporarily shut down the entire system due to overpressure; normal operation can be restored simply by local pressure relief, reducing recovery efficiency losses due to downtime. This design can quickly intervene to handle sudden anomalies such as cooler blockage and gas volume fluctuations, preventing a single access path failure from causing a complete process paralysis, and giving the system a stronger adaptability and response capability to complex production conditions.

[0029] In a preferred embodiment of the present invention, the crude alumina and pre-tower non-condensable gas tail gas treatment system includes: The second online oxygen content analyzer 9 is installed on the non-condensable gas outlet pipeline of the crude alumina and pre-tower for real-time monitoring of oxygen concentration; The second mixed gas buffer tank 10 is connected to the second online oxygen content analyzer and is used to buffer gas pressure fluctuations. The second reciprocating compressor 11 is connected to the outlet of the second mixed gas buffer tank 10 and is used to perform multi-stage compression of the gas. The second-stage cooler 12 is connected to one outlet of the second reciprocating compressor 11 and is used to cool the compressed gas. The second inlet buffer tank 13 is connected to the outlet of the second stage cooler 12 and is used to stabilize the gas pressure entering the second stage of the second reciprocating compressor 11. The second outlet buffer tank 14 is connected to the second outlet of the second reciprocating compressor 11 and is used to buffer the gas pressure after compression. The second compressor outlet cooler 15 is connected to the outlet of the second outlet buffer tank 14 and is used to further cool the gas. The second gas-liquid separator 16 is connected to the outlet of the second compressor outlet cooler 15 and is used to separate the gas phase and the liquid phase. The separated gas phase is sent to a boiler for co-firing or an emergency flare, while the liquid phase is sent to a crude methanol tank or an isobutyl oil tank based on the test results.

[0030] In this embodiment of the invention, the gas discharged from the breather valve at the top of the crude methanol storage tank is first mixed with the non-condensable gas generated by the pre-distillation tower, and then enters the first step of the treatment process, safety screening. That is, the mixed tail gas first flows through the second online oxygen content analyzer 9 installed on the outlet pipeline. This analyzer monitors the oxygen concentration in the tail gas in real time. The system's preset safety threshold is 0.5% (set according to the explosion-proof standard of crude methanol VOCs gas). If the monitoring result shows that the oxygen concentration is ≥0.5%, the second online oxygen content analyzer 9 will immediately link with the emergency shut-off valve on the pipeline, triggering the emergency shut-off valve to automatically close and stop the supply of tail gas to the subsequent system. At the same time, the valve of the emergency pipeline will open synchronously, introducing the tail gas with excessive oxygen into the emergency flare pipeline, eliminating the risk through incineration, and avoiding an explosion caused by the mixing of oxygen with methanol and CO in the tail gas. Conversely, if the oxygen concentration is detected to be <0.5%, it is determined that the tail gas meets the safety treatment conditions and enters the next stage.

[0031] The exhaust gas, having passed safety screening, enters the second mixed gas buffer tank 10. Because the exhaust volume of the crude gas tank is easily affected by changes in the tank level, and the non-condensable gas volume in the pre-tower fluctuates with the operating load, the pressure of the mixed exhaust gas becomes unstable. The subsequent second reciprocating compressor 11 has high requirements for inlet pressure stability; sudden pressure increases or decreases can easily cause compressor surge. Therefore, the second mixed gas buffer tank 10 uses its internal space to buffer and regulate the airflow, stabilizing the exhaust gas pressure within the range of 0.1 MPa suitable for the compressor inlet. After pressure stabilization, the exhaust gas enters the second reciprocating compressor 11, and the system adopts... The process of segmented compression and intercooling is adapted to meet the compression requirements of the crude exhaust gas. In the segmented compression stage, the exhaust gas first enters the first stage of the second reciprocating compressor 11 and is compressed to 0.25MPa. Since the gas temperature will rise synchronously during the compression process, it is easy to increase the energy consumption of the subsequent two-stage compression and may also damage the equipment. Therefore, the compressed gas needs to be sent to the second-stage cooler 12 immediately. The second-stage cooler 12 reduces the gas temperature to 40℃ through heat exchange, which reduces the energy consumption of the subsequent two-stage compression and avoids the high-temperature gas from damaging the second inlet buffer tank 13 and the second-stage compressor components.

[0032] After the gas is cooled to 40°C, it enters the second inlet buffer tank 13. The function of this buffer tank is to further stabilize the gas pressure at 0.25 MPa, ensuring that the inlet pressure of the second stage of the second reciprocating compressor 11 remains constant. This prevents wear or malfunction of internal components of the second stage compressor due to pressure fluctuations or liquid carryover. The stabilized gas then enters the second stage of the second reciprocating compressor 11 and is compressed to 0.45 MPa (this pressure is the target pressure for co-firing the crude gas in the boiler). After compression, the gas is sent to the second outlet buffer tank 14. The core of the second outlet buffer tank 14... The core function is to buffer the pulse pressure fluctuations generated by the gas after the second stage compression, so as to avoid the airflow impact on the downstream second compressor outlet cooler 15 and the second gas-liquid separator 16, and ensure the stable operation of the downstream equipment. The gas after being stabilized by the second outlet buffer tank 14 will enter the second compressor outlet cooler 15 and be cooled to 30°C through deep heat exchange. This temperature can fully liquefy the condensable components (mainly methanol) in the exhaust gas. The cooled gas-liquid mixture enters the second gas-liquid separator 16, and through the synergistic effect of gravity settling and airflow rectification, the gas phase and liquid phase are accurately separated.

[0033] The separated gas phase, containing small amounts of methanol and CO and possessing a certain calorific value, will be preferentially sent to the boiler for co-firing as fuel supplementation. If the boiler operates abnormally or the system is in an emergency, it can also be switched to the emergency flare line for processing. The separated liquid phase needs to be analyzed for composition. If the test results show that the methanol purity is high, it will be sent to the crude methanol tank to participate in the distillation process again. If the test results show that the content of fusel oil (such as isobutyl alcohol) is high, it will be sent to the isobutyl oil tank for recovery, ultimately achieving precise diversion and utilization of different components.

[0034] This embodiment, through the linkage design of the second online oxygen content analyzer and the emergency shut-off valve, can intercept unsafe exhaust gas with excessive oxygen levels in real time. Combined with the emergency flare for backup, it eliminates the explosion risk of the oxygen, methanol, and CO mixture system at the source. At the same time, the multi-stage buffer tank can avoid compressor surge caused by pressure fluctuations, providing double protection for the safety of the entire system process. The segmented compression and intermediate cooling process design can avoid damage to compressor components by high-temperature gas. The buffering effect of the second outlet buffer tank on pulse pressure can reduce the impact loss of downstream coolers and separators. The overall process has no drastic changes in operating conditions, which can extend the service life of core equipment such as the second reciprocating compressor and coolers, and reduce the frequency and cost of downtime maintenance. The gas phase is used as boiler co-fuel, replacing part of the purchased energy and reducing the company's fuel costs. The liquid phase is accurately diverted and recovered according to its composition, avoiding the waste of methanol and fusel oil resources caused by emissions.

[0035] In a preferred embodiment of the present invention, the second online oxygen content analyzer 9 is linked with the emergency shut-off valve. When the oxygen content is ≥0.5%, the emergency shut-off valve closes, stops the gas supply, and introduces the gas into the emergency flare pipeline.

[0036] In this embodiment of the invention, the second online oxygen content analyzer 9 is fixedly installed on the mixing outlet pipeline of the exhaust gas from the breather valve at the top of the crude methanol storage tank and the non-condensable gas from the pre-distillation tower. The mixed tail gas, after being discharged from the production end, must preferentially flow through this analyzer. Its core function is to continuously and in real-time collect oxygen concentration data in the tail gas, accurately capturing dynamic changes in oxygen content. Based on the explosion-proof safety standards for crude methanol VOCs gas and the system's operational requirements, a preset oxygen concentration safety threshold of 0.5% is established. The second online oxygen content analyzer 9 automatically compares the real-time monitored oxygen concentration data with this threshold. When the monitoring data shows an oxygen content ≥ 0.5%, the tail gas is determined to be in an explosive risk state. At this point, the oxygen concentration has reached the critical explosion condition for the methanol and CO mixture. If it enters subsequent closed equipment such as compressors or buffer tanks, it may cause an explosion due to minor sparks or pressure changes during equipment operation. When the monitoring data shows an oxygen content < 0.5%, the tail gas is considered to be in an explosive risk state. If the exhaust gas is determined to meet safe treatment conditions and no emergency measures need to be triggered, the second online oxygen content analyzer 9 and the emergency shut-off valve on the pipeline will form an electrical linkage control. If the condition is determined to be explosive (oxygen content ≥ 0.5%), the analyzer will immediately send a shut-off signal to the emergency shut-off valve. The emergency shut-off valve will close rapidly in a short time, directly blocking the transmission path of the risky exhaust gas to the subsequent second mixed gas buffer tank 10 and compressor system. At the same time, the emergency pipeline valve linked to the emergency shut-off valve will open synchronously, introducing the risky exhaust gas into the accident flare pipeline. The flare will eliminate flammable components such as methanol and CO in the exhaust gas through combustion, preventing the risky exhaust gas from stagnating or being directly emitted and causing a safety accident. If the condition is determined to be safe (oxygen content < 0.5%), the emergency shut-off valve will remain open, and the exhaust gas can smoothly enter the second mixed gas buffer tank 10 to start the subsequent pressure buffering and compression treatment process.

[0037] This embodiment, through real-time monitoring and automatic cut-off, can intercept dangerous exhaust gas the moment the oxygen content exceeds the standard, fundamentally avoiding explosion accidents caused by high oxygen concentration exhaust gas mixing with methanol and CO in subsequent compression and buffering stages, thus laying a solid safety foundation for the entire process of treating crude methanol and pre-tower non-condensable gas. The linkage mechanism is fully automated, eliminating the need for manual inspection and judgment, shortening emergency response time compared to manual monitoring, and avoiding the risk expansion caused by delays due to manual operation. If high oxygen concentration exhaust gas enters equipment such as the second reciprocating compressor 11 and the second mixed gas buffer tank 10, it may not only cause an explosion, but also cause equipment corrosion and component wear due to the chemical reaction between oxygen and methanol and equipment metal parts. By cutting off dangerous exhaust gas in advance, the linkage mechanism can reduce safety losses of downstream equipment and reduce the frequency and cost of maintenance and replacement.

[0038] In a preferred embodiment of the present invention, a return pipeline is provided between the outlet of the second stage cooler 12 and the inlet of the second inlet buffer tank 13 to regulate the gas volume and prevent compressor surge.

[0039] In this embodiment of the invention, the second reciprocating compressor 11 adopts a segmented compression process, specifically consisting of a first-stage compression, cooling, and a second-stage compression. In this process, the intake volume and pressure of the second stage must be precisely matched with the output capacity of the first stage and its own processing load. However, the volume of crude alumina and non-condensable gas in the pre-tower is easily affected by changes in the crude alumina storage tank level and fluctuations in the pre-tower operating load, making it unstable. If the volume of gas entering the second stage after the first stage compression is excessive (e.g., a sudden increase in tail gas volume causing the first stage output to exceed the limit), or if the pressure of the second inlet buffer tank 13 exceeds the set range of 0.25 MPa, the compressor may fail to deliver the required amount of gas. If the flow is disrupted, it will break the balance between the output of the first stage and the reception of the second stage, which will cause pulsation, backflow, and sudden pressure changes in the airflow inside the compressor, resulting in a surge phenomenon. In severe cases, it will damage the compressor piston, seals and other core components. The return pipeline connects the outlet of the second stage cooler 12 (the gas flow path after the first stage compression and cooled to 40°C) and the inlet of the second inlet buffer tank 13 (the flow path before the second stage intake). Its essence is to build a gas volume regulation channel for the gas from the first stage outlet to the first stage inlet. By allowing the excess gas volume to circulate back, the intake demand of the second stage is balanced.

[0040] When the system is running stably (the tail gas volume of the crude gas tank is stable and the pre-tower load is stable), the 40°C gas (pressure 0.25MPa) cooled by the second stage cooler 12 will enter the second inlet buffer tank 13 in full. After buffering, the set pressure of 0.25MPa will be maintained, and then the gas will smoothly enter the second stage of the second reciprocating compressor 11. At this time, the regulating valve on the return pipeline is controlled by the central control unit and is in a closed or slightly open state, maintaining only a small amount of airflow circulation (for rapid response to sudden fluctuations) to ensure that the gas flows to the second stage in full, ensuring the compression efficiency and the continuity of the subsequent processing flow. When the system detects an abnormal signal (for example, the pressure sensor detects that the pressure of the second inlet buffer tank 13 is >0.25MPa, or the compressor current fluctuation shows that the airflow is unstable), the central control unit will immediately send a command to open the regulating valve on the return pipeline. At this time, some of the 40°C gas cooled by the second stage cooler 12 will be reversed through the return pipeline to the inlet of the second mixed gas buffer tank 10. After mixing with fresh crude methanol and pre-tower non-condensable gas, it will re-enter the first stage of the second reciprocating compressor 11 for secondary compression. This process can directly reduce the amount of gas entering the second inlet buffer tank 13, so that the gas output of the first stage is rematched with the processing capacity of the second stage based on the 0.25MPa set pressure, eliminating the airflow pulsation and pressure over-limit problem at the inlet of the second stage, and preventing surge from the root cause. After the pressure sensor detects that the pressure of the second inlet buffer tank 13 returns to the 0.25MPa set range, and the compressor current and exhaust gas volume tend to be stable, the central control unit will gradually close the regulating valve on the return pipeline, allowing the gas from the outlet of the second stage cooler 12 to re-enter the second inlet buffer tank 13 in full, and the system will return to normal operation.

[0041] This embodiment, by dynamically adjusting the two-stage air intake, can directly eliminate the core cause of surge—air volume mismatch—avoiding problems such as internal component wear and seal failure in the second reciprocating compressor due to surge, extending the compressor's service life, and reducing equipment maintenance and replacement costs and downtime. It eliminates the need to temporarily shut down the entire treatment system due to air volume fluctuations; the return pipeline can adapt to load changes through real-time dynamic adjustment, ensuring the continuous and stable operation of equipment such as the second reciprocating compressor and the second inlet buffer tank. This avoids interruptions in the recovery of crude methanol and pre-tower non-condensable gas due to shutdowns, ensuring the continuity of VOCs treatment and resource recovery. The adjustment process of this pipeline is automatically executed by the central control unit based on monitoring data, eliminating the need for manual inspection and adjustment. This reduces manual operation costs and avoids energy waste caused by delayed manual response, meeting the requirements of automated system operation. The air volume of crude methanol and pre-tower non-condensable gas is easily affected by tank levels and pre-tower load, and the return pipeline can quickly adapt to these dynamic changes without frequent adjustments to the overall compressor operating parameters, improving the system's adaptability to complex production conditions and ensuring process stability.

[0042] In a preferred embodiment of the present invention, two paths are provided between the outlet of the second outlet buffer tank 14 and the inlet of the compressor outlet cooler 15. One path directly enters the second compressor outlet cooler 15, and the other path is equipped with a safety valve for opening the emergency flare under emergency conditions.

[0043] In this embodiment of the invention, the two-path configuration and core parameters are first clarified. The outlet of the second outlet buffer tank 14 and the inlet of the second compressor outlet cooler 15 adopt a parallel two-path design. The first path is a conventional processing path, which directly connects the two. Its core function is to transport the gas after two-stage compression under normal operating conditions to ensure the continuity of the subsequent deep cooling (requiring a temperature drop to 30°C) and gas-liquid separation process without interrupting VOCs recovery. The second path is an emergency pressure relief path. A safety valve (with a preset opening pressure of 0.5MPa) is specially installed on the pipeline. This pressure value is a safety redundancy designed based on the target pressure of 0.45MPa for two-stage compression. It can avoid accidental triggering of the safety valve due to small pressure fluctuations. At the same time, the end of the path is connected to the emergency flare pipeline for rapid pressure relief and handling of hazardous gases when the system is overpressured.

[0044] Under normal operating conditions, the airflow direction is highly matched with the equipment status. The gas after two-stage compression by the second reciprocating compressor 11 (pressure stabilized at 0.45MPa) enters the second outlet buffer tank 14. After buffering, the pressure inside the tank is always maintained within the normal range of 0.45MPa. At this time, the first conventional processing path remains unobstructed, and the gas preferentially enters the second compressor outlet cooler 15 directly through this path to carry out subsequent processing according to the established process. Meanwhile, the safety valve on the second emergency path remains closed because the system pressure has not reached the 0.5MPa threshold. This design ensures that all gas flows to the conventional recovery process, guaranteeing the continuity and efficiency of the recovery of crude alumina and pre-tower non-condensable gas.

[0045] When a system malfunction causes a sudden pressure surge, the emergency circuit will be quickly triggered and play a protective role. For example, if the internal pipes of the second compressor outlet cooler 15 are blocked, the exhaust valve of the second gas-liquid separator 16 malfunctions, or the intake volume of the second outlet buffer tank 14 suddenly increases beyond its buffering capacity, the pressure inside the tank will rapidly exceed the normal range of 0.45 MPa, until it reaches the safety valve's 0.5 MPa trigger pressure. At this time, the safety valve will automatically open, and the second emergency circuit will be activated: the overpressure gas (containing flammable components such as methanol and CO) in the second outlet buffer tank 14 will be quickly introduced into the emergency flare pipeline through the emergency circuit. After being incinerated by the flare, the pollution risk of direct VOC emissions can be eliminated, and the explosion hazard caused by the accumulation of flammable gases can be avoided. At the same time, the pressure relief process will quickly reduce the pressure inside the tank, preventing the pressure from continuing to rise and causing deformation, leakage, or even rupture of the second outlet buffer tank 14, the second reciprocating compressor 11's second-stage outlet components, and the conventional pipeline.

[0046] Once the abnormal issues are resolved, the system will gradually stabilize and reset. For example, after the cooler blockage is cleared and the separator exhaust valve is repaired, the pressure in the second outlet buffer tank 14 will gradually drop back to the normal range of 0.45MPa. At this time, the safety valve will automatically close, and the second emergency passage will stop working. The gas will then re-enter the second compressor outlet cooler 15 through the first conventional processing passage, and the entire crude alumina and pre-tower non-condensable gas treatment system will resume its normal recovery process.

[0047] This embodiment, through the combination of a safety valve and an emergency access circuit, can rapidly release pressure in the event of overpressure, preventing structural damage to the second outlet buffer tank, the second reciprocating compressor's second-stage outlet, and conventional pipelines caused by prolonged overpressure. This extends the service life of high-value core equipment such as compressors and buffer tanks, reducing maintenance and replacement costs and downtime due to equipment damage. The emergency access circuit is connected to an emergency flare, where overpressure gas is incinerated and discharged harmlessly, completely preventing the direct leakage of VOCs such as methanol and CO into the atmosphere due to equipment overpressure rupture. This not only meets current environmental regulations for VOC emissions but also eliminates the risk of workshop poisoning and environmental explosions caused by leaked gas. Safety hazards such as explosions are eliminated; under normal operating conditions, the conventional pathway stably delivers gas, ensuring uninterrupted cooling, separation, and recovery of non-condensable gases in the crude alumina and pre-tower; in emergency situations, the emergency pathway responds quickly, eliminating the need to temporarily shut down the entire processing system due to overpressure issues, and normal operation can be restored simply by local depressurization, reducing VOCs recovery efficiency loss and energy waste caused by downtime; for sudden anomalies such as cooler blockage, valve failure, and sudden gas volume increases, this design can quickly intervene and handle them, avoiding the paralysis of the entire process due to a single pathway failure, making the system more adaptable and capable of responding to complex operating conditions such as crude alumina tank level fluctuations and pre-tower operating load changes, ensuring process stability.

[0048] In a preferred embodiment of the present invention, the opening and closing of the emergency shut-off valve is controlled based on oxygen concentration monitoring data, and the smallest circular region containing all pressure data points is calculated based on pressure sensor monitoring data. The boundary features of the smallest circular region are used to identify the pressure anomaly range, and the identification result is obtained. Based on the identification result, the compressor operating frequency and the opening of the return pipeline regulating valve are coordinated and controlled to keep the compressor inlet pressure stable within the set range, including: Based on the real-time monitoring of oxygen concentration data by the first online oxygen content analyzer 1 and the second online oxygen content analyzer 9, it is determined whether the oxygen concentration exceeds the safety threshold of 0.5%. When the oxygen concentration exceeds the safety threshold, the corresponding emergency shut-off valve is closed to prevent the exhaust gas from entering the first mixed gas buffer tank 2 or the second mixed gas buffer tank 10. When the oxygen concentration is less than or equal to the safety threshold, the system is kept running normally so that the exhaust gas can enter the subsequent treatment process. Based on the pressure sensor monitoring data set at the inlet of the first reciprocating compressor 3 and the second reciprocating compressor 11, a pressure data point set is obtained. By calculating the distance between each point in the pressure data point set, the two points with the largest distance are selected as the initial diameter endpoints. The midpoint of the two points is taken as the initial circle center, and the initial radius is set to half the distance between the two points. It is checked whether all pressure data points are inside the circle. If there are pressure data points outside the circle, the circle center position and radius are adjusted, and the circle containing all pressure data points is reconstructed until the smallest circular area that can contain all pressure data points is found. The center coordinates and radius parameters of the smallest circular area are obtained. Based on the radius parameter and variation trend of the smallest circular region, the range and degree of abnormal pressure fluctuations are identified, and pressure anomaly identification results are generated. Based on the pressure anomaly identification results, a pressure distribution feature matrix is ​​established. By solving the eigenvalues ​​and eigenvectors of the pressure distribution feature matrix, the adjustment parameters of the operating frequency of the first reciprocating compressor 3 and the second reciprocating compressor 11 are determined. Based on the pressure anomaly identification results, the pressure data point set is projected onto the feature space. By calculating the distance distribution of each pressure data point to the origin of the feature space, the opening control parameters of the return pipeline regulating valve set at the outlet of the first stage cooler 4 and the second stage cooler 12 are generated. Based on the compressor operating frequency adjustment parameters and the return pipeline regulating valve opening control parameters, the operating frequencies of the first reciprocating compressor 3 and the second reciprocating compressor 11, as well as the opening of the corresponding return pipeline regulating valve, are coordinated and controlled to keep the compressor inlet pressure stable within the set range.

[0049] In this embodiment of the invention, the first step is oxygen concentration monitoring and emergency shut-off valve control, which is a prerequisite for ensuring system safety. This step addresses the explosion-proof requirements of two types of tail gases: refined methanol tail gas, crude methanol tail gas, and pre-tower non-condensable gas. Real-time control is achieved through two oxygen content analyzers. In terms of data acquisition and threshold judgment, the first online oxygen content analyzer 1 continuously monitors the oxygen concentration of the exhaust gas from the breather valve of the refined methanol storage tank, and the second online oxygen content analyzer 9 continuously monitors the oxygen concentration after the exhaust gas from the breather valve of the crude methanol storage tank is mixed with the pre-tower non-condensable gas. Both use 0.5% as the safety threshold, which is the explosion-proof critical value for VOCs gas in coal-to-methanol. Regarding valve linkage execution, if any analyzer detects an oxygen concentration greater than 0.5%, such as the oxygen content of refined methanol tail gas rising to 0.6%, or the oxygen content of crude methanol mixed tail gas rising to 0.55%, the central control unit will immediately send a closing command to the emergency shut-off valve of the corresponding channel. The valve corresponding to the first online oxygen content analyzer 1 will close, blocking the refined methanol tail gas from entering the first mixed gas buffer tank 2; the valve corresponding to the second online oxygen content analyzer 9 will close, blocking the crude methanol mixed tail gas from entering the second mixed gas buffer tank 10. At the same time, the emergency pipeline valve will open synchronously, guiding the tail gas with excessive oxygen into the accident flare pipeline for incineration, completely eliminating the risk of explosion caused by the mixture of oxygen and methanol / CO. If the detected oxygen concentration is less than or equal to 0.5%, it is determined that the tail gas meets the safety standard, the emergency shut-off valve remains open, and the tail gas smoothly enters the corresponding mixed gas buffer tank, initiating the subsequent compression and recovery process.

[0050] The second step is pressure data acquisition and minimum circular region calculation, which is the foundation for pressure anomaly identification. This step addresses the issue of compressor inlet pressure fluctuations easily causing surge. The minimum circular region algorithm quantifies the pressure fluctuation range, providing data support for subsequent anomaly identification. For pressure data acquisition, pressure sensors are installed at the inlet 3 of the first reciprocating compressor and the inlet 11 of the second reciprocating compressor. These sensors continuously collect real-time pressure data, for example, one data point per second, forming a pressure data set containing 100 to 200 points. This data set reflects pressure changes over a certain period. In constructing the minimum circular region, the distance between all points in the pressure data set is first calculated, and the two points with the greatest distance are selected, such as point A at 0.09 MPa and point B at 0.11 MPa. These two points are then used as the initial... The initial center of the circle is the midpoint of the line connecting the two points (e.g., at 0.10 MPa), and the initial radius is set to half the distance between the two points, such as 0.01 MPa. Next, check whether all points in the pressure data set are inside the initial circle. For example, if a point C is at 0.085 MPa, it exceeds the range of the initial circle radius of 0.01 MPa. If there are points outside the circle, adjust the center position to include all points, for example, move it towards point C to 0.0975 MPa, and adjust the radius size, for example, increase it to 0.0125 MPa, and reconstruct the circular area. Finally, repeat the verification and adjustment steps until the smallest circular area that can include all pressure data points is found. Finally, obtain the center coordinates of the circle (e.g., 0.098 MPa, which reflects the average pressure) and the radius parameter (e.g., 0.013 MPa, which reflects the pressure fluctuation range).

[0051] The next step is the identification of the pressure anomaly range and severity. This step, based on the core parameter (radius) and change trend of the smallest circular area, determines whether the pressure is abnormal and the severity of the anomaly. For anomaly range identification, combined with the process requirements of the compressor inlet pressure setpoint (0.1 MPa), a preset allowable radius threshold for pressure fluctuation is 0.02 MPa. This threshold is a reasonable range determined based on the compressor's anti-surge capability and the stability requirements of subsequent processes. If the radius of the smallest circular area is ≤0.02 MPa, it indicates that the pressure fluctuation has not exceeded the tolerance range of the equipment and process, and is judged as being within the normal range. If the radius is >0.02 MPa, for example, a calculated radius of 0.025 MPa, it is directly identified as an excessive pressure fluctuation range. The corresponding anomaly range can be precisely described as the current pressure deviating from the average pressure ±0.025 MPa, clearly defining the specific interval of the pressure fluctuation. For anomaly severity identification, a radius change rate threshold needs to be preset (with a standard monitoring cycle of 5 minutes, combined with the compressor's response characteristics, a radius change >0.008 MPa within 5 minutes is considered a relatively fast rate). A change of <0.003 MPa is considered slow. Further judgment is made by tracking the real-time trend of the radius parameter. If the radius increases from 0.015 MPa to 0.025 MPa within 5 minutes, the calculated change within 5 minutes is 0.01 MPa, exceeding the rate threshold of 0.008 MPa. This is considered an aggravated abnormality, indicating that pressure fluctuations are rapidly expanding and requiring immediate increased adjustment. If the radius remains stable at 0.022 MPa, the change within 5 minutes is only 0.002 MPa, below the rate threshold of 0.003 MPa. The threshold is determined to be a mild anomaly, indicating that although the pressure fluctuation exceeds the standard, it tends to stabilize and can be controlled with small adjustments. Finally, the system will integrate the above information to generate a pressure anomaly identification result that includes the range of the anomaly, the degree of the anomaly, the trend of change, and the basis for judgment. For example, the pressure fluctuation range of the first compressor inlet is ±0.025MPa (exceeding the allowable radius of 0.02MPa), and the radius increases from 0.015MPa to 0.025MPa within 5 minutes (change amount of 0.01MPa, exceeding the rate threshold), indicating that the degree of anomaly is aggravated and shows an expanding trend.

[0052] Next is the generation of compressor frequency and return valve opening control parameters. This step, combined with the pressure anomaly identification results, calculates the specific control parameters for compressor operating frequency and return pipeline regulating valve opening. For compressor operating frequency parameter generation, a pressure distribution feature matrix is ​​first constructed based on the pressure data point set. Using the pressure data point set collected by the pressure sensor (e.g., pressure values ​​containing 100 monitoring times) as a basis, a two-dimensional pressure distribution feature matrix is ​​built. In this matrix, rows correspond to each monitoring time (e.g., second 1, second 2… second 100), and columns are fixed as compressor inlet pressure values. Each element represents the deviation between the pressure value at that moment and the pressure at the center of the smallest circular area (i.e., the average pressure). For example, if the average pressure is calculated to be 0.098 MPa, and the actual pressure detected in the first second is 0.10 MPa, the corresponding matrix element is 0.002 MPa (0.10 MPa - 0.098 MPa); if the actual pressure drops to 0.095 MPa in the fifth second, the corresponding matrix element is -0.003 MPa (0.095 MPa - 0.098 MPa). This matrix can intuitively show the distribution pattern of pressure fluctuations at different times.

[0053] After constructing the pressure distribution feature matrix, the dispersed pressure monitoring data needs to be transformed into a pressure deviation matrix. Then, through a continuous process of data transformation, covariance calculation, feature solving, and result verification, combined with linear algebra principles and simplified examples, the eigenvalues ​​and eigenvectors are finally obtained. These two parameters are the core of transforming abstract pressure data into understandable fluctuation patterns. The specific process is as follows: First, a specific pressure deviation matrix is ​​constructed. Taking the compressor inlet pressure monitoring of the Jingjia system as an example, three consecutive monitoring times are selected (this can be expanded to more times as needed, the logic is completely consistent). Basic data is obtained first. Assuming that, based on previous calculations, the average pressure of the compressor inlet (i.e., the pressure at the center of the smallest circular area) is 0.1 MPa, the actual pressures at the three monitoring times are 10.102 MPa, 20.097 MPa, and 30.101 MPa, respectively. Next, the pressure deviation at each time is calculated by subtracting the average pressure from the actual pressure, resulting in a deviation of 0.002 MPa (0.102 - 0.1) at time 1 and -0.003 MPa at time 2. (0.097-0.1), Time 3 deviation 0.001MPa (0.101-0.1); Finally, according to the monitoring time sequence, these three deviation values ​​are arranged into a 3x1 pressure deviation matrix (denoted as matrix A), with elements of 0.002MPa, -0.003MPa, and 0.001MPa respectively. This matrix is ​​a non-square matrix. It needs to be transformed into a computable covariance matrix because the solution for eigenvalues ​​and eigenvectors must be a square matrix (number of rows equals number of columns), and pressure deviation matrix A is 3x1. Since the data is not a square matrix, it needs to be converted into a covariance matrix (denoted as matrix C). The covariance matrix of single-dimensional data is a square matrix with 1 row and 1 column. The calculation process is as follows: First, calculate the mean of the deviations. Add the three deviation values ​​together and divide by the number of monitoring times (3), that is, (0.002 - 0.003 + 0.001) ÷ 3 = 0 MPa. In this example, the positive and negative deviations cancel each other out. In actual scenarios, if the mean is not zero, the calculation logic remains the same. Then, calculate the square of each deviation and the mean. Subtract the mean (0 in this example) from each deviation value and square it to get the square value of time 1. Time 2 squared value Time 3 square value Then, calculate the covariance, add the three squared values ​​together, and divide by (the number of monitoring times minus 1), which is 2. This is to avoid errors caused by an excessively small sample size; in statistics, this is called degrees of freedom correction. That is, (0.000004 + 0.000009 + 0.000001) ÷ 2 = 0.000007 MPa 2 Finally, the covariance matrix C is formed, which is a 1x1 square matrix, and the unique element in the matrix is ​​0.000007 MPa. 2 .

[0054] Then we move on to the core eigenvalue and eigenvector solving stage, which requires the mathematical definition of a square matrix. According to the definition of linear algebra, for a square matrix C, if there exists a constant λ (eigenvalue) and a non-zero vector x (eigenvector) satisfying Cx = λx, then λ and x are the required eigenvalue and eigenvector. For a 1x1 covariance matrix C, the calculation is much simpler. When solving for the eigenvalue λ, since C is a first-order square matrix, after substituting into the definition, the equation holds regardless of the non-zero value of the vector x (which must be consistent with the dimensions of the pressure deviation matrix, i.e., 3x1). At this point, the value of the eigenvalue λ is equal to the unique element in the covariance matrix C, i.e., λ = 0.000007 MPa. 2 When solving for the eigenvector x, x must be a non-zero vector with 3 rows and 1 column, and the positive and negative trends of the elements in the vector must be consistent with the deviation trend of the pressure deviation matrix (so as to reflect the true direction of pressure fluctuation). In this example, the absolute value of the negative deviation at time 2 is the largest (-0.003MPa), which is the main direction of fluctuation. Therefore, the elements of the eigenvector x are taken as time 1=0.5, time 2=-1, and time 3=0.3. The absolute value of the negative element is the largest, which matches the deviation trend. The specific numerical ratio does not affect the direction judgment, as long as the positive and negative trends are correct.

[0055] After the solution is completed, it is necessary to verify the accuracy of the results and ensure that the calculation is error-free. The obtained eigenvalue λ = 0.000007 MPa 2 The eigenvectors x (with elements of 0.5, -1, and 0.3) are substituted into the definition Cx = λx for verification. First, calculate Cx on the left side: a 1x1 matrix C multiplied by a 3x1 vector x. The result is a 3x1 vector, where each element equals an element of C multiplied by the corresponding element of x. Then calculate λx on the right side: the eigenvalue λ multiplied by the vector x. The result is also a 3x1 vector, where each element equals λ multiplied by the corresponding element of x. The results on both sides are completely consistent, indicating that the calculation of the eigenvalue and eigenvector is accurate and effective. From the perspective of the eigenvalue, it reflects the intensity of pressure fluctuations in a certain fixed direction. The larger the eigenvalue, the more significant the fluctuation in that direction, and the greater the impact on the stability of compressor operation. For example, if the calculated eigenvalue is 0.0006 MPa... 2 (much greater than 0.000007 MPa in this example) 2This indicates that the current pressure is fluctuating significantly and frequently in a certain direction (e.g., below the average pressure), which is considered a violent fluctuation and needs to be suppressed primarily by adjusting the compressor frequency. From the perspective of the eigenvector, it reflects the main direction of pressure fluctuation. If the elements in the eigenvector are predominantly positive (e.g., all elements are 0.6, 0.8, 0.7), it means that the pressure fluctuation is mainly biased towards the direction above the average pressure (the pressure is higher than the average pressure most of the time). If the elements are predominantly negative (e.g., eigenvector elements are 0.5, -1, 0.3, with the negative elements having the largest absolute values), it means that the pressure is mainly biased towards the direction below the average pressure. For example, when the eigenvalue is 0.0006 MPa... 2 When the eigenvector is -0.8 (representing drastic fluctuations) and the overall value is negative, it becomes clear that the core pattern of the current pressure fluctuation is mainly drastic fluctuations below the average pressure.

[0056] Next, the frequency adjustment amplitude and direction are determined. Combining the characteristic parameters with the pressure anomaly identification results generated earlier, a matching standard for characteristic value-adjustment amplitude and characteristic vector-adjustment direction is preset in advance (this standard is based on a comprehensive setting of the compressor's load adjustment capability and the degree of pressure anomaly, ensuring that the adjustment is effective without damaging the equipment). Regarding the adjustment amplitude, if the characteristic value is 0.0006 MPa... 2 (In cases where the abnormality worsens), the frequency of the first reciprocating compressor 3 needs to be reduced by 1.5Hz; if the characteristic value is 0.0003MPa 2 (For mild anomalies), the frequency is reduced by 0.8Hz. Simply put, the larger the eigenvalue, the larger the adjustment range. The purpose is to quickly suppress severe pressure fluctuations. In terms of adjustment direction, the sign of the eigenvector determines the direction. If the eigenvector is negative (pressure fluctuations tend to be lower than the average pressure), it means that the current overall pressure is too low, and the frequency needs to be increased to increase the compressor's air intake, thereby increasing the pressure. If the eigenvector is negative (for example, the pressure anomaly range is ±0.025MPa, the average pressure is 0.098MPa, and the current pressure is mostly above 1.003MPa, meaning the fluctuations tend to be higher than the average pressure), the frequency needs to be reduced to decrease the air intake and lower the pressure.

[0057] Finally, the final frequency parameters are generated. By combining the adjustment amplitude and direction, the specific compressor operating frequency adjustment parameters can be obtained. For example, when the characteristic value is 0.0006 MPa... 2 When the eigenvector is negative and the pressure anomaly intensifies, a command will eventually be generated to adjust the frequency of the first reciprocating compressor 3 from 50Hz to 48.5Hz. This parameter can quickly alleviate the problem of high pressure and violent fluctuations by reducing the compressor's intake rate.

[0058] The generation of the opening parameters for the reflux line regulating valve involves projecting a feature space, calculating the deviation distance, and matching the opening. This logic transforms pressure fluctuations into reflux valve opening adjustment commands, using reflux air volume regulation to assist in stabilizing the pressure. The specific steps are as follows: The first step is to project the pressure data point set onto the feature space. That is, to project the pressure data point set onto a pressure fluctuation feature space with the pressure fluctuation feature vector as the coordinate axis. This process can be understood as rearranging the pressure data points, which were originally scattered at different times, according to the main direction of the fluctuation, transforming them into coordinate points in the feature space. The value of each coordinate point represents the degree of deviation of the pressure fluctuation in the main direction at that moment. For example, the first... After projecting the pressure data points from the 1st to the 100th second, we obtain coordinate points such as (0.02MPa), (0.015MPa)...(0.025MPa). This visually presents the core trend of pressure deviation from steady state at different times, avoiding interference from secondary fluctuations. The second step is to calculate the distance distribution from the coordinate points to the origin. In the pressure fluctuation characteristic space, the origin represents the complete steady state of pressure (i.e., the ideal state without fluctuations), while the distance from the coordinate point to the origin directly reflects the severity of the pressure deviation from steady state at that moment. The larger the distance, the more severe the deviation, and the greater the amount of return gas that needs to be adjusted; the smaller the distance, the less severe the deviation, and the smaller the adjustment range. For example, a certain coordinate... A distance of 0.03 MPa from the origin indicates a significant deviation of the pressure from steady state, requiring substantial adjustment of the reflux valve. A distance of 0.015 MPa indicates a relatively minor deviation, necessitating only a small adjustment. The third step is to determine the reflux valve opening. Based on the reflux pipeline's airflow adjustment capacity and pressure deviation, a pre-defined distance-opening matching standard is established. If the distance from the origin is 0.03 MPa (corresponding to severe deviation from steady state), the reflux valve opening at the outlet of the first-stage cooler (outlet 4) is set to 30%. This increases the reflux airflow, reducing the actual airflow entering the compressor and quickly alleviating the high pressure problem. If the distance is 0.015 MPa (corresponding to mild deviation), the reflux valve opening is adjusted accordingly. (If the pressure deviates from steady state), the opening is set to 15%. Only a small adjustment of the return air volume is needed to avoid a sudden drop in pressure due to over-adjustment. The fourth step is to generate the final opening parameters. That is, by combining the distance distribution of coordinate points and the pressure anomaly range, specific return valve opening adjustment parameters can be generated. For example, for a pressure anomaly range of ±0.025MPa, and for a situation where the distance from the coordinate point to the origin is more than 0.025MPa most of the time, the final command will be generated to adjust the opening of the return valve at the outlet of the first stage cooler 4 from 10% to 30%. This adjustment action can be coordinated with the compressor frequency adjustment to further reduce the actual amount of gas entering the compressor by increasing the return air volume, thus helping to stabilize the pressure.

[0059] Through the above quantitative calculations, the combined control parameters of compressor frequency and return valve opening are finally obtained. These combined parameters can accurately match abnormal pressure conditions and achieve the effect of dual regulation and coordinated pressure control. For example, the combination of the first compressor frequency of 48.5Hz and return valve opening of 30% can reduce the compressor intake rate by lowering the frequency and reduce the actual intake volume by increasing the return gas volume. The two can work together to quickly suppress drastic pressure fluctuations and ensure that the compressor inlet pressure gradually stabilizes within the set range of 0.1MPa.

[0060] Finally, the central control unit coordinates the execution of control measures and maintains stable pressure. Based on the parameters calculated above, it synchronously executes coordinated control operations to ensure that the compressor inlet pressure remains stable within the set range. The compressor inlet pressure for both the fine and coarse alumina systems is set to 0.1 MPa. For the first reciprocating compressor 3, the operating frequency is adjusted according to the frequency regulation parameters (e.g., 48.5 Hz), and simultaneously, the return valve regulating valve at the outlet of the first stage cooler 4 is opened according to the return valve opening parameters (e.g., 30%). Through the dual effects of reducing the compressor intake rate and increasing the return gas volume, the amount of exhaust gas entering the compressor is reduced. To alleviate pressure fluctuations, the same applies to the second reciprocating compressor 11. Adjustments are made according to the corresponding frequency parameters (e.g., 49Hz) and return valve opening parameters (e.g., 25%) to maintain its inlet pressure at a stable 0.1MPa. During the control process, the system will provide real-time feedback on pressure data. If the pressure returns to the normal range of 0.1MPa±0.02MPa, the previous adjustment parameters will be gradually adjusted back. For example, the frequency of the first reciprocating compressor 3 will be adjusted from 48.5Hz to 49.5Hz, and the opening of the return valve at the outlet of the first stage cooler 4 will be adjusted from 30% to 15% to avoid over-adjustment.

[0061] This embodiment, through real-time oxygen concentration monitoring and linkage with the emergency shut-off valve, blocks high-oxygen-concentration exhaust gas from entering the system at the source, completely avoiding the explosion risk caused by methanol / CO and high oxygen levels. Simultaneously, it controls pressure fluctuations, preventing compressor surge due to sudden pressure changes, reducing wear on core components such as pistons and seals, and extending equipment lifespan. Compared to pressure control methods with single threshold alarms, the minimum circular area algorithm can accurately identify the range and trend of pressure fluctuations. Combined with parameter calculations based on feature matrices and spatial projections, it can achieve on-demand adjustment, stabilizing the compressor inlet pressure within the allowable range of ±0.02MPa, avoiding a decrease in recovery efficiency due to pressure instability. The coordinated control logic requires no manual intervention, automating the entire process from data acquisition and anomaly identification to parameter adjustment, reducing manual inspection and operating costs. Furthermore, by adjusting the frequency and opening degree, it avoids energy waste caused by compressor idleness or excessive opening of the return valve, improving system energy utilization efficiency.

[0062] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A VOCs recovery control system for coal-to-methanol based on a reciprocating compressor and multi-stage cooling separation, characterized in that, include: The methanol exhaust gas treatment system is used to treat the exhaust gas from the breather valve at the top of the methanol storage tank. The crude methanol and pre-distillation tower non-condensable gas tail gas treatment system is used to treat the exhaust gas from the breather valve at the top of the crude methanol storage tank and the non-condensable gas from the pre-distillation tower; The central control unit controls the opening and closing of the emergency shut-off valve based on oxygen concentration monitoring data. Based on pressure sensor monitoring data, it calculates and determines the smallest circular area containing all pressure data points, identifies the pressure anomaly range based on the boundary features of the smallest circular area, and obtains the identification result. Based on the identification result, it coordinates and controls the compressor operating frequency and the opening of the return pipeline regulating valve to keep the compressor inlet pressure stable within the set range.

2. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation as described in claim 1, characterized in that, The exhaust gas treatment system for the precision-engineered aircraft includes: The first online oxygen content analyzer (1) is installed on the tail gas outlet pipeline of the refined car body to monitor the oxygen concentration in real time. The first mixed gas buffer tank (2) is connected to the first online oxygen content analyzer (1) and is used to buffer gas pressure fluctuations; The first reciprocating compressor (3) is connected to the outlet of the first mixed gas buffer tank (2) and is used to compress the gas in multiple stages. The first stage cooler (4) is connected to one outlet of the first reciprocating compressor (3) and is used to cool the compressed gas. The first inlet buffer tank (5) is connected to the outlet of the first stage cooler (4) to stabilize the gas pressure entering the second stage of the first reciprocating compressor (3); The first outlet buffer tank (6) is connected to the second outlet of the first reciprocating compressor (3) and is used to buffer the gas pressure after compression. The first compressor outlet cooler (7) is connected to the outlet of the first outlet buffer tank (6) for further cooling of the gas; The first gas-liquid separator (8) is connected to the outlet of the first compressor outlet cooler (7) and is used to separate the gas phase and the liquid phase. The separated gas phase is sent to the hydrogen sulfide concentration tower of the low-temperature methanol washing unit for nitrogen stripping, while the liquid phase is sent to the pre-distillation tower for recycling.

3. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation as described in claim 2, characterized in that, The first online oxygen content analyzer (1) is linked with the emergency shut-off valve. When the oxygen content is ≥0.5%, the emergency shut-off valve closes, stops the gas supply, and introduces the gas into the emergency flare pipeline.

4. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation according to claim 3, characterized in that, A return pipeline is provided between the outlet of the first stage cooler (4) and the inlet of the first inlet buffer tank (5) to regulate the gas volume and prevent compressor surge.

5. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation according to claim 4, characterized in that, Two paths are provided between the outlet of the first outlet buffer tank (6) and the inlet of the first compressor outlet cooler (7). One path goes directly into the first compressor outlet cooler (7), and the other path is equipped with a safety valve, which is used to open the emergency flare in emergency conditions.

6. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation according to claim 5, characterized in that, The crude alumina and pre-tower non-condensable gas tail gas treatment system includes: The second online oxygen content analyzer (9) is installed on the non-condensable gas outlet pipeline of the crude alumina and pre-tower for real-time monitoring of oxygen concentration. The second mixed gas buffer tank (10) is connected to the second online oxygen content analyzer and is used to buffer gas pressure fluctuations; The second reciprocating compressor (11) is connected to the outlet of the second mixed gas buffer tank (10) and is used to compress the gas in multiple stages. The second-stage cooler (12) is connected to one outlet of the second reciprocating compressor (11) and is used to cool the compressed gas. The second inlet buffer tank (13) is connected to the outlet of the second stage cooler (12) and is used to stabilize the gas pressure entering the second stage of the second reciprocating compressor (11); The second outlet buffer tank (14) is connected to the second outlet of the second reciprocating compressor (11) and is used to buffer the gas pressure after compression. The second compressor outlet cooler (15) is connected to the outlet of the second outlet buffer tank (14) for further cooling of the gas; The second gas-liquid separator (16) is connected to the outlet of the second compressor outlet cooler (15) and is used to separate the gas phase and the liquid phase. The separated gas phase is sent to a boiler for co-firing or an emergency flare, while the liquid phase is sent to a crude methanol tank or an isobutyl oil tank based on the test results.

7. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation according to claim 6, characterized in that, The second online oxygen content analyzer (9) is linked with the emergency shut-off valve. When the oxygen content is ≥0.5%, the emergency shut-off valve closes, stops the gas supply, and introduces the gas into the emergency flare pipeline.

8. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation according to claim 7, characterized in that, A return pipeline is provided between the outlet of the second stage cooler (12) and the inlet of the second inlet buffer tank (13) to regulate the gas volume and prevent compressor surge.

9. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation as described in claim 8, characterized in that, The outlet of the second outlet buffer tank (14) and the inlet of the compressor outlet cooler (15) are provided with two paths. One path goes directly into the second compressor outlet cooler (15), and the other path is equipped with a safety valve, which is used to open the emergency flare in emergency conditions.

10. The coal-to-methanol VOCs recovery control system based on a reciprocating compressor and multi-stage cooling separation according to claim 9, characterized in that, The opening and closing of the emergency shut-off valve is controlled based on oxygen concentration monitoring data, and the smallest circular area containing all pressure data points is determined by calculation based on pressure sensor monitoring data. The boundary features of the smallest circular area are used to identify the pressure anomaly range and obtain the identification result. Based on the identification results, coordinate and control the compressor operating frequency and the opening of the return line regulating valve to maintain the compressor inlet pressure stable within the set range, including: Based on the real-time monitoring of oxygen concentration data by the first online oxygen content analyzer (1) and the second online oxygen content analyzer (9), it is determined whether the oxygen concentration exceeds the safety threshold of 0.5%. When the oxygen concentration exceeds the safety threshold, the corresponding emergency shut-off valve is closed to block the tail gas from entering the first mixed gas buffer tank (2) or the second mixed gas buffer tank (10). When the oxygen concentration is less than or equal to the safety threshold, the system is kept running normally so that the tail gas can enter the subsequent treatment process. Based on the pressure sensor monitoring data set at the inlet of the first reciprocating compressor (3) and the second reciprocating compressor (11), a pressure data point set is obtained. By calculating the distance between each point in the pressure data point set, the two points with the largest distance are selected as the initial diameter endpoints. The midpoint of the two points is taken as the initial circle center, and the initial radius is set to half the distance between the two points. Check whether all pressure data points are inside the circle. If there are pressure data points outside the circle, adjust the circle center position and radius size, and reconstruct a circle containing all pressure data points until the smallest circular area that can contain all pressure data points is found. The center coordinates and radius parameters of the smallest circular area are obtained. Based on the radius parameter and variation trend of the smallest circular region, the range and degree of abnormal pressure fluctuations are identified, and pressure anomaly identification results are generated. Based on the pressure anomaly identification results, a pressure distribution feature matrix is ​​established. By solving the eigenvalues ​​and eigenvectors of the pressure distribution feature matrix, the adjustment parameters of the operating frequency of the first reciprocating compressor (3) and the second reciprocating compressor (11) are determined. Based on the pressure anomaly identification results, the pressure data point set is projected onto the feature space. By calculating the distance distribution of each pressure data point to the origin of the feature space, the opening control parameters of the return pipeline regulating valve set at the outlet of the first stage cooler (4) and the second stage cooler (12) are generated. Based on the compressor operating frequency adjustment parameters and the return pipeline regulating valve opening control parameters, the operating frequencies of the first reciprocating compressor (3) and the second reciprocating compressor (11), as well as the opening of the corresponding return pipeline regulating valve, are coordinated and controlled to keep the compressor inlet pressure stable within the set range.

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