Air supply device for maleic anhydride off-gas recovery, preparation system using the same and method of operation thereof

Abstract

The application provides an air supply device for maleic anhydride reaction tail gas recovery, which comprises: an axial flow air compressor provided with an anti-surge valve; an air inlet pipeline, an air inlet end of the air inlet pipeline being in fluid communication with an air source, and an air outlet end being in fluid communication with an air inlet pipeline of the air compressor; a tail gas recovery pipeline, an air inlet end of the tail gas recovery pipeline being in fluid communication with a downstream of a maleic anhydride reactor, and an air outlet end being in fluid communication with the air inlet pipeline of the air compressor; and an anti-surge valve air release backflow pipeline, an air inlet end of the anti-surge valve air release backflow pipeline being in fluid communication with an exhaust port of the anti-surge valve, and an air outlet end being in fluid communication with the air inlet pipeline of the air compressor, and the air compressor has a shaft end sealing structure. The application can realize that maleic anhydride tail gas and air are mixed and fed through the same air compressor.

Description

Technical Field

[0001] This invention relates to the field of maleic anhydride production, and more specifically, to an air supply device for recovering tail gas from maleic anhydride reaction, a preparation system using the same, and a method for operating the same. Background Technology

[0002] Maleic anhydride is an important basic organic chemical raw material, widely used in the production of various chemicals. Currently, the main industrial production methods for maleic anhydride include the benzene process and the n-butane process. The benzene process uses a mixture of benzene and air as raw material, oxidizing benzene to maleic anhydride in the presence of a catalyst. The n-butane process uses a mixture of n-butane and air as raw material, oxidizing n-butane to maleic anhydride in the presence of a catalyst. Previously, my country mainly used the benzene process to produce maleic anhydride, but due to the advantages of the n-butane process in terms of raw materials, environmental protection, efficiency, and cost, my country's production capacity for maleic anhydride using the n-butane process has been continuously increasing in recent years.

[0003] Both the benzene process and the n-butane process use air as one of the raw materials. In maleic anhydride plants, an air compressor is used to pressurize the air and send it to the maleic anhydride reactor for the oxidation reaction.

[0004] In both the benzene and n-butane processes, the most widely used maleic anhydride reactor is the axial-tube fixed-bed reactor. This reactor consists of numerous tubes and uses molten salt for heat exchange. Because the maleic anhydride formation reaction is highly sensitive to changes in reaction conditions, the smooth progress of maleic anhydride production and product quality are heavily dependent on the radial homogeneity of the material and temperature within the reactor. However, as the reactor diameter increases, controlling the radial homogeneity of the material and temperature within the reactor becomes increasingly difficult. Therefore, to ensure smooth reaction progress and the quality of maleic anhydride, the diameter of the maleic anhydride reactor is limited and cannot be further increased.

[0005] Because the maximum diameter of a single maleic anhydride reactor is limited, the surface area of ​​the fluid flowing through the reactor is also limited, which in turn places higher demands on the catalyst bed height. Industrial maleic anhydride reactors have a large height-to-diameter ratio of the catalyst bed, resulting in a high pressure drop as the reaction fluid flows through the catalyst bed, thus requiring higher air compressor outlet pressures. Due to this high sensitivity, the air supply (also known as air delivery) from the air compressor must maintain both high pressure and very stable operation; otherwise, it may lead to abnormal reactions or even termination of the reaction. These air supply requirements place high demands on the air supply system used in maleic anhydride reactors.

[0006] Downstream of the maleic anhydride reactor, tail gas from the maleic anhydride preparation process is obtained, containing a certain amount of feedstock materials, such as benzene or n-butane. Typically, the tail gas originates from the top of an absorber downstream of the maleic anhydride reactor. The feedstock materials in the tail gas can be recovered and reused as feed to the reactor.

[0007] There is still a need to improve the methods for recovering and reusing the tail gas from maleic anhydride reactors. Summary of the Invention

[0008] In one aspect, the present invention provides an air supply device for recovering tail gas from maleic anhydride reactions, the air supply device comprising:

[0009] Axial flow air compressors are equipped with anti-surge valves;

[0010] An air intake duct, wherein the air intake end of the air intake duct is fluidly connected to an air source, and the air outlet end is fluidly connected to the air intake duct of the air compressor;

[0011] An exhaust gas recovery pipe, wherein the inlet end of the exhaust gas recovery pipe is fluidly connected to the downstream of the maleic anhydride reactor, and the outlet end is fluidly connected to the inlet pipe of the air compressor; and

[0012] The anti-surge valve vent return pipe has its inlet end connected to the exhaust port of the anti-surge valve in fluid communication, and its outlet end connected to the inlet pipe of the air compressor in fluid communication.

[0013] Furthermore, the air compressor has a shaft end sealing structure.

[0014] Optionally, the shaft end sealing structure adopts a combination of carbon ring seal and Labier seal.

[0015] Optionally, at least some of the blade surfaces of the air compressor are treated with acid resistance.

[0016] In another aspect, the present invention provides a maleic anhydride preparation system, the maleic anhydride preparation system comprising:

[0017] Maleic anhydride reactor, and

[0018] The aforementioned air supply device.

[0019] Optionally, the maleic anhydride preparation system further includes:

[0020] In the absorption tower downstream of the maleic anhydride reactor,

[0021] The inlet end of the exhaust gas recovery pipe is in fluid communication with the top of the absorption tower.

[0022] Optionally, the maleic anhydride preparation system includes multiple reactors, and the axial flow air compressor is equipped with stationary blades.

[0023] The air supply device includes:

[0024] A stator vane controller that controls the stator vane angle based on target exhaust pressure and / or flow feedback;

[0025] An anti-surge valve controller, which controls the opening degree of the anti-surge valve based on the anti-surge line feedback of the air compressor; and

[0026] The feedforward performance controller is configured to initiate emergency trip control upon receiving a trip signal from the maleic anhydride reactor, and to terminate the emergency trip control after the anti-surge valve is closed.

[0027] The emergency control for vehicle scrambling includes: feedforward control of the opening of the anti-surge valve, and changing the target exhaust pressure and / or flow rate of the stationary vane controller.

[0028] In another aspect, the present invention provides a method for operating the above-mentioned maleic anhydride preparation system comprising multiple reactors, the method comprising:

[0029] The tail gas, including benzene or n-butane, originating from the maleic anhydride reactor, is passed through the tail gas recovery pipe and the air compressor's inlet pipe before entering the air compressor.

[0030] The vented air from the anti-surge valve enters the air compressor through the anti-surge valve vent return pipe.

[0031] Optionally, the maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including a feedforward performance controller described above, and the method further includes:

[0032] When the plurality of maleic anhydride reactors are running, the stationary vane controller controls the stationary vane angle based on the target exhaust pressure and / or flow rate and feedback from the measured value, and the anti-surge valve controller controls the anti-surge valve opening based on the anti-surge line of the air compressor and feedback from the measured value.

[0033] When at least one of the plurality of maleic anhydride reactors trips, the feedforward performance controller initiates the trip emergency control upon receiving a trip signal from the maleic anhydride reactor, and terminates the trip emergency control after the anti-surge valve closes, wherein the trip emergency control includes:

[0034] i) Based on the number of remaining operating maleic anhydride reactors, quickly open the anti-surge valve to the first opening degree and change the target exhaust pressure and / or flow rate of the stationary vane controller;

[0035] ii) Reduce the anti-surge valve opening from the first degree, and then wait for the stationary vane angle to stabilize;

[0036] iii) Repeat step ii) until the anti-surge valve is closed. Attached Figure Description

[0037] Figure 1 A schematic diagram of an air supply device including an exhaust gas recovery duct is shown as an embodiment of the present invention.

[0038] Figure 2 The combination of Laberling seal and carbon ring seal is shown.

[0039] Figure 3 A typical anti-surge diagram for an air compressor is shown.

[0040] Figure 4 A schematic diagram of the feedforward control connection principle according to an embodiment of the present invention is shown. Detailed Implementation Plan

[0041] The air supply device for recovering tail gas from the maleic anhydride reaction of the present invention can realize the recirculation of tail gas in the maleic anhydride preparation process.

[0042] Downstream of the maleic anhydride reactor, tail gas from the maleic anhydride preparation process is obtained, containing a certain amount of raw materials, such as benzene or n-butane. Typically, the tail gas originates from the top of an absorber downstream of the maleic anhydride reactor. The raw materials in the tail gas can be recovered and reused as feed to the reactor. The inventors have found that directly utilizing the tail gas is cost-effective compared to separating and purifying the raw materials in the tail gas before recycling it into the feed stream. Furthermore, it is cost-effective to introduce the tail gas into the reactor along with air feedstock compared to setting up a separate tail gas feed line for the reactor. The location for introducing the tail gas into the air feedstock can be chosen upstream of the air compressor in the air supply unit or between the air compressor and the reactor. The inventors have found that introducing the tail gas into the air feedstock downstream of the air compressor causes instability in the inlet flow rate and pressure of the maleic anhydride reactor, which is detrimental to the preparation of maleic anhydride.

[0043] Therefore, the exhaust gas from the maleic anhydride preparation process is returned upstream of the air compressor and mixed with fresh air before being sent to the reactor by the air compressor, thus achieving the recycling of raw materials in the exhaust gas. However, the inventors discovered in practice that simply connecting the recycled exhaust gas directly upstream of the air compressor of this invention cannot ensure the safe operation of the maleic anhydride reactor system.

[0044] When an axial-flow air compressor encounters anti-surge control, the anti-surge valve opens, releasing a portion of the feed air into the environment. This is not a problem for feed air that is not mixed with exhaust gas. However, when the feed air contains exhaust gas, the opening of the anti-surge valve will allow flammable, explosive, and toxic benzene or n-butane from the exhaust gas to leak into the environment without treatment, which should be avoided.

[0045] To recycle the tail gas from the maleic anhydride preparation process, this invention provides an air supply device for recovering the tail gas from the maleic anhydride reaction, the air supply device comprising:

[0046] Axial flow air compressors are equipped with anti-surge valves;

[0047] An air intake duct, wherein the air intake end of the air intake duct is fluidly connected to an air source, and the air outlet end is fluidly connected to the air intake duct of the air compressor;

[0048] An exhaust gas recovery pipe, wherein the inlet end of the exhaust gas recovery pipe is fluidly connected to the downstream of the maleic anhydride reactor, and the outlet end is fluidly connected to the inlet pipe of the air compressor; and

[0049] The anti-surge valve vent return pipe has its inlet end connected to the exhaust port of the anti-surge valve in fluid communication, and its outlet end connected to the inlet pipe of the air compressor in fluid communication.

[0050] Furthermore, the air compressor has a shaft end sealing structure.

[0051] The air supply device of the present invention includes an axial flow air compressor as its basic component. The axial flow air compressor is equipped with an anti-surge valve.

[0052] Anti-surge valves can be installed on the air compressor's exhaust pipe, such as on a branch line extending from the exhaust pipe. They can be fully open or partially opened to release air from the exhaust pipe and reduce its pressure. Anti-surge valves are classified according to their adjustment methods, including equal percentage adjustment and linear adjustment. The opening degree at different flow rates can be found through the valve's inherent characteristic curve. Typically, the anti-surge valve is required to open rapidly within 1.5 seconds and fully open (0% to 100%) within 3 seconds. During normal operation of the air compressor, the anti-surge valve is in the closed state.

[0053] The air compressor's intake duct is connected to both an air intake duct and an exhaust gas recovery duct. These two ducts are connected to an air source and the downstream of the reactor, respectively. This allows the air compressor to simultaneously obtain raw air from the air source and recovered exhaust gas from the downstream of the reactor. For example, the exhaust gas recovery duct can be connected to the top of the absorption tower downstream of the maleic anhydride reactor.

[0054] The air compressor's intake pipe is also connected to the anti-surge valve's vent return pipe. That is, in this invention, when the anti-surge valve is open, all the gas it discharges does not enter the ambient air, but returns to the upstream of the air compressor and re-enters the air compressor along with the air and exhaust gas.

[0055] This invention returns the gas discharged from the anti-surge valve back to the air compressor inlet to avoid its adverse environmental impact. The inventors have found that guiding the gas upstream of the air compressor to achieve a closed-loop circulation is significantly more cost-effective and technologically advantageous than treating the exhaust gas from the anti-surge valve to render it harmless and ultimately releasing it into the ambient air.

[0056] Introducing the exhaust gas from the anti-surge valve into the air feed will not adversely affect the inlet pressure and flow rate of the subsequent maleic anhydride reactor. Although the pressurized gas discharged from the anti-surge valve enters the air compressor's inlet pipe and may change the pressure of the air compressor's inlet mixture to some extent, the pressure change of the feed gas reaching the air compressor can be mitigated by feedback control of the stationary vanes, thus maintaining control over the air compressor's exhaust flow rate and pressure.

[0057] In this way, the problem of harmful gas leakage from the anti-surge valve was solved by adding a venting return pipe for the anti-surge valve.

[0058] Besides the possibility of leakage at the anti-surge valve, the air compressor itself may also leak. Therefore, the axial flow air compressor of the present invention also has a shaft end sealing structure to prevent exhaust gas leakage from the shaft end. The air supply device of the present invention can thus supply exhaust gas while simultaneously supplying air to multiple maleic anhydride reactors, without causing environmental pollution.

[0059] Figure 1 A schematic diagram of an air supply device including an exhaust gas recovery pipe according to one embodiment of the present invention is shown. In the figure, 1 is an air compressor, 2 is an air filter, 3 is an anti-surge valve, 4 is a return filter, 5 is an outlet check valve, 6 is a flow meter, 7 is an outlet air supply valve, 8 is a start-up venting regulating valve, 9 is an exhaust gas inlet regulating valve, 10 is a venting silencer, and 11 is an air compressor shaft end seal. Exhaust gas and vent gas from the anti-surge valve enter the air compressor together with the air feedstock, avoiding environmental pollution. The start-up venting regulating valve can be used for venting regulation when there is no exhaust gas input during start-up. However, when the air compressor intake contains exhaust gas, the start-up venting regulating valve is closed to ensure no exhaust gas leakage.

[0060] In one implementation, the method of operating the air supply device may include:

[0061] 1) During the start-up phase of the air compressor unit, since there is no exhaust gas in the downstream system, the tail inlet regulating valve 9 is closed, the outlet check valve 5 is closed, the outlet air supply valve 7 is closed, the anti-surge valve 3 is closed, and the start-up vent regulating valve 8 is open. The air compressor starts up, and air enters the air compressor unit 1 through the air filter 2 for compression. The air compressor is gradually loaded by adjusting the angle of the air compressor stator vanes. The process flow is switched by the start-up vent regulating valve 8 and the outlet air supply valve 7. Finally, the start-up vent regulating valve 8 is fully closed, and the outlet air supply valve 7 and the outlet check valve 5 are fully open.

[0062] 2) During the normal operation of the air compressor, the circulating exhaust gas from the process system is sent to the air compressor inlet. The exhaust gas inlet regulating valve 9 is slowly opened and fed into the air compressor inlet. The flow rate is adjusted according to the system requirements. After mixing with air, it enters the air compressor 1 for compression. The mixed gas is sent to the subsequent process system after passing through the outlet check valve 5, outlet flow meter 6, and outlet air supply valve 7 configured at the outlet. At this time, the start-up vent regulating valve 8 is manually closed, the unit system anti-surge valve 3 is closed, and automatic control is put into operation.

[0063] 3) When the air compressor unit experiences surge, the anti-surge valve 3 opens, and the mixed gas is cooled to the set temperature by the anti-surge return cooler 4 and then returned to the air compressor inlet to maintain the stable operation of the air compressor unit.

[0064] 4) When the air compressor unit is in reverse flow condition, the anti-surge valve 3 is fully open, the outlet check valve 5 is closed, and the outlet air supply valve 7 is closed. The mixed gas is cooled to the set temperature by the anti-surge backflow cooler 4 and then returns to the air compressor inlet. The air compressor stationary blade angle is reduced to 22°, and the unit maintains a safe operating state.

[0065] In a preferred embodiment, the shaft end seal structure employs a combination of a carbon ring seal and a Labellem seal. The Labellem seal is located on the inner side, and the carbon ring seal is located on the outer side. The carbon ring has an inlet. Since the gas entering the air compressor includes both air and exhaust gas, and the substance that needs to be prevented from leaking is only a portion of the exhaust gas, the combination of the Labellem seal and the carbon ring seal provides sufficient sealing performance at a reasonable cost. Figure 2 The diagram illustrates a combination of Labellin seal and carbon ring seal. The left side of the diagram represents the process medium side, and the right side represents the atmospheric side. A Labellin seal 1 is installed around the end of the air compressor main shaft 3, and in addition to the Labellin seal, a carbon ring seal 2 is also installed, with a carbon ring seal inlet 4. This combined sealing method ensures adequate sealing of harmful substances in the maleic anhydride recovery exhaust gas at the air compressor end.

[0066] In a preferred embodiment, at least a portion of the blade surfaces of the air compressor are treated with an acid-resistant coating. The exhaust gas from the downstream absorber of the maleic anhydride reactor contains, in addition to the main gases such as benzene / n-butane, carbon monoxide, and carbon dioxide, a small amount of maleic anhydride. These substances are not corrosive to metals in the absence of an acidic solution. Therefore, theoretically, the air compressor blade surfaces do not require special treatment to cope with these substances.

[0067] However, the inventors unexpectedly discovered that when maleic anhydride mixes with intake air, it may combine with moisture in the air to form maleic acid. This is especially noticeable in the early stages of compression, such as the first three or four stages of the air compressor, where moisture in the air may precipitate and readily combine with carbon dioxide and maleic anhydride to form an acidic liquid. This is particularly evident in maleic anhydride plants in humid regions. This can cause corrosion to the air compressor blades, affecting their strength. Therefore, this invention provides acid-resistant treatment for the compressor blades. However, as the feed gas passes through the air compressor, the temperature rises significantly during the compression process. The water vapor in the air is in a superheated state, and no more water is precipitated during compression. Therefore, this invention can perform acid-resistant treatment only on the moving and stationary blades in the first few stages of the compressor (e.g., the first three or four stages).

[0068] In other words, the inventors discovered that, unlike pure air feed, the present invention involves a mixture of maleic anhydride and air with a certain humidity. During compression in the air compressor, if water from the air is released, an acidic liquid will be generated, damaging the air compressor blades. Therefore, at least some of the air compressor blades are treated with an acid-resistant coating. Preferably, the first three stages of the air compressor's moving and stationary blades are treated with an acid-resistant coating. Or preferably, the first four stages of the air compressor's moving and stationary blades are treated with an acid-resistant coating. After a certain period of compression, the temperature of the mixed gas continues to rise, the water vapor is in a superheated state, no more water is released, and no more acidic liquid is formed. Therefore, subsequent blades and pipes do not require an acid-resistant coating.

[0069] Acid-resistant treatment can be an acid-resistant coating treatment, that is, forming an acid-resistant layer on the surface requiring acid resistance. Suitable methods such as coating, deposition, and electroplating can be used to form the acid-resistant layer. It should be noted that the acid-resistant layer cannot be a coating that can react with the raw material benzene or cyclobutane. Surface modification methods can also be used to directly treat the surface with acid resistance. This invention does not impose any special limitations on this.

[0070] Through the above methods, the air supply device of the present invention can safely achieve the recirculation of tail gas in the maleic anhydride preparation process.

[0071] In one embodiment, the present invention provides a maleic anhydride preparation system, the maleic anhydride preparation system comprising:

[0072] Maleic anhydride reactor, and

[0073] The air supply device of the present invention.

[0074] Such a maleic anhydride preparation system can reuse exhaust gas and avoid environmental pollution.

[0075] Preferably, the maleic anhydride preparation system further includes:

[0076] In the absorption tower downstream of the maleic anhydride reactor,

[0077] The inlet end of the exhaust gas recovery pipe is in fluid communication with the top of the absorption tower.

[0078] The downstream absorber of the maleic anhydride reactor is well-known in the field of maleic anhydride preparation. The gas at the top of the absorber is enriched with unreacted raw materials and contains few harmful impurities, making it suitable for use as tail gas in an air compressor for reuse. Therefore, it is preferable to connect the inlet of the tail gas recovery pipe to the top of the absorber in fluid communication.

[0079] The air supply device of the present invention is particularly suitable for a maleic anhydride preparation system comprising multiple reactors, the maleic anhydride preparation system comprising multiple reactors being configured to handle abnormal reactor tripping conditions by means of anti-surge valves in conjunction with stationary vanes.

[0080] In one embodiment, the maleic anhydride preparation system includes multiple reactors, and the axial flow air compressor is equipped with stationary vanes.

[0081] The air supply device includes:

[0082] A stator vane controller that controls the stator vane angle based on target exhaust pressure and / or flow feedback;

[0083] An anti-surge valve controller, which controls the opening degree of the anti-surge valve based on the anti-surge line feedback of the air compressor; and

[0084] The feedforward performance controller is configured to initiate emergency trip control upon receiving a trip signal from the maleic anhydride reactor, and to terminate the emergency trip control after the anti-surge valve is closed.

[0085] The emergency control for vehicle scrambling includes: feedforward control of the opening of the anti-surge valve, and changing the target exhaust pressure and / or flow rate of the stationary vane controller.

[0086] With continuous improvements and developments in air compressors regarding delivery pressure and stability, it has become possible to simultaneously supply air to multiple maleic anhydride reactors using a single air compressor. However, the inventors have discovered in practice that directly connecting the exhaust port of the air compressor to the air inlet of two or more parallel maleic anhydride reactors makes it difficult to achieve safe production operation of maleic anhydride preparation systems containing multiple reactors.

[0087] A key characteristic of maleic anhydride reactors is that the stability of the incoming air supply is crucial for their smooth operation. In essence, a stable airflow from the air compressor is a prerequisite for the stable operation of the maleic anhydride reactor. Therefore, the air compressor used in maleic anhydride reactors not only needs to provide sufficiently high pressure and flow rate, but also needs to maintain a stable air supply to each normally operating maleic anhydride reactor under various complex operating conditions. Otherwise, it is difficult to successfully implement a design where multiple maleic anhydride reactors share a single air compressor.

[0088] When using a single air compressor to supply pressurized air to multiple maleic anhydride reactors, the air inlet pipes of each reactor are directly connected to the exhaust port of the same air compressor, thus connecting multiple reactors in parallel downstream of the same compressor. However, the inventors unexpectedly discovered in practice that such direct pipe connections downstream of a conventional air compressor are insufficient for practical applications. While this connection method can provide stable air supply to each reactor when all reactors are operating normally, sudden abnormal conditions in some reactors can adversely affect other reactors in the system, even causing unexplained interlocking trips. This renders the aforementioned device impractical. Without relying on any theory, the inventors discovered that these results are caused by the lag in the feedback control of the stator vanes and anti-surge valve, which prevents timely stabilization of exhaust pressure and flow.

[0089] One type of sudden abnormal operation in a maleic anhydride reactor is an unnatural shutdown (also known as a trip) caused by unexpected circumstances. In this case, to avoid damaging the reactor, the feed gas pipeline to that reactor will be shut off as soon as possible to stop receiving air. For a design with multiple independent maleic anhydride reactors, this is not a problem because as the feed gas pipeline is shut down, the air compressor supplying air to the corresponding reactor will also stop or open its vent valve. However, for multiple maleic anhydride reactors connected in parallel sharing the same air compressor, if the air compressor is shut down or vented because one reactor trips, the air supply to all maleic anhydride reactors will be stopped, forcing even reactors that haven't tripped to shut down. This is highly uneconomical from a practical production perspective. Therefore, it is desirable for the air compressor to continue supplying air to the remaining reactors even if one reactor suddenly trips.

[0090] After a reactor trips, the maleic anhydride reactor gradually stops receiving air to avoid damaging it. For example, the inlet flow control valve in the reactor inlet pipe leading to the tripped reactor is closed. One operating mode is to close the corresponding inlet flow control valve when a reactor trips, allowing the air compressor to continue operating to supply air to the remaining reactors. However, the inventors discovered through practice that in a maleic anhydride system operating in this way, the air supply to the remaining reactors is affected, leading to operational instability and potentially interlocking trips. Without relying on any theory, the inventors found the following reason: The total air supply required by the maleic anhydride preparation system is related to the number of operating reactors. Therefore, when one or more of the maleic anhydride reactors suddenly trip, the air supply flow requirement of the air compressor will change dramatically, i.e., a large reduction in air volume will occur suddenly within a short period of time. However, the performance regulation (maintaining air supply pressure / flow) of conventional axial air compressors is mainly accomplished by the stator vanes, which cannot quickly and effectively regulate the air supply volume at the compressor outlet when there are sudden and large fluctuations in the downstream system. Therefore, the air compressor cannot immediately switch to a low airflow rate state suitable for a smaller number of reactors, but instead maintains a relatively high airflow rate. In this situation, when the pressure in the air compressor's air duct rises sharply due to the incompatibility between the high airflow rate and the low airflow demand, it will affect the compressor's operating point, triggering the anti-surge system. The anti-surge system also requires a considerable amount of time to adjust and stabilize its operating point, and cannot quickly stabilize the compressor's outlet pressure, thus affecting the airflow to the operating reactors. In other words, conventional feedback performance regulation and feedback anti-surge regulation are insufficient to quickly adjust the airflow and pressure to a low airflow rate state. Furthermore, the compressor's anti-surge valve will fully open in the event of a sudden and sharp increase in pressure (i.e., a large disturbance), causing a sudden drop in airflow pressure. Although the compressor is protected, the airflow to the maleic anhydride reactor will become insufficient. As mentioned earlier, the maleic anhydride reactor has very high requirements for airflow stability. Therefore, if the air compressor does not make relevant adjustments in advance but continues to make feedback adjustments, the air supply volume may be continuously too high, continuously insufficient, or fluctuate drastically. These situations will quickly affect the operation of the remaining maleic anhydride reactor. At best, it will cause fluctuations in product quality; at worst, it will cause the reactor to stop working, causing interlocking trips and significantly reducing production efficiency.

[0091] Therefore, simply connecting multiple maleic anhydride reactors in parallel downstream of a conventional air compressor cannot adequately handle the aforementioned reactor tripping abnormalities, making it difficult to realize a practical maleic anhydride preparation system that includes multiple reactors.

[0092] To address the above problems, this invention proposes an air supply device for a maleic anhydride preparation system comprising multiple reactors, wherein the air supply device includes:

[0093] Axial flow air compressor, which is equipped with stator vanes and anti-surge valve;

[0094] A stator vane controller that controls the stator vane angle based on target exhaust pressure and / or flow feedback;

[0095] An anti-surge valve controller, which controls the opening degree of the anti-surge valve based on the anti-surge line feedback of the air compressor; and

[0096] The feedforward performance controller is configured to initiate emergency trip control upon receiving a reactor trip signal, and to terminate the emergency trip control after the anti-surge valve closes.

[0097] The emergency control for vehicle scrambling includes: feedforward control of the opening of the anti-surge valve, and changing the target exhaust pressure and / or flow rate of the stationary vane controller.

[0098] The air supply device of this invention includes an axial flow air compressor as its basic component. The axial flow air compressor needs to provide a stable air supply to at least two maleic anhydride reactors simultaneously. A suitable air compressor can be selected based on the required air supply pressure and flow rate of the maleic anhydride reactors and the number of reactors. In one embodiment, the operating pressure of a single maleic anhydride reactor is between 0.29 and 0.35 MPa, and the required air flow rate is between 1000 and 4000 Nm³. 3 / min.

[0099] Axial flow air compressors are equipped with stator vanes and anti-surge valves. These components can all be standard parts found in axial flow air compressors.

[0100] The stator vane angle is adjustable, thus changing the air intake flow rate of the air compressor. The stator vane angle adjustment range for conventional air compressors is from 22° to 79°.

[0101] Anti-surge valves can be installed on the air compressor's exhaust pipe, such as on a branch line extending from the exhaust pipe. They can be fully open or partially opened to release air from the exhaust pipe and reduce its pressure. Anti-surge valves are classified according to their adjustment methods, including equal percentage adjustment and linear adjustment. The opening degree at different flow rates can be found through the valve's inherent characteristic curve. Typically, the anti-surge valve is required to open rapidly within 1.5 seconds and fully open (0% to 100%) within 3 seconds. During normal operation of the air compressor, the anti-surge valve is in the closed state.

[0102] The air supply device of the present invention further includes a vane controller for changing the vane angle. The vane controller may be connected to or include a vane angle adjustment mechanism. The vane controller is a controller with feedback control functionality, which achieves feedback control based on the difference between a setpoint and a current value (measured value). For example, the vane controller may be a controller employing a proportional-integral-derivative (PID) control algorithm. This type of controller has a setpoint (SV) receiver and a current value (PV) receiver. The setpoint for the air compressor exhaust pressure and / or flow rate is input to the controller via the SV receiver, and the measured value of the air compressor exhaust pressure and / or flow rate is input to the controller as the current value via the PV receiver. After calculation by the PID algorithm, a control signal to increase or decrease the vane angle is sent to the vane angle adjustment mechanism via the output (OUT) terminal. In this way, the vane controller can perform feedback control of the vane angle based on the deviation between the current value and the setpoint of the air compressor exhaust pressure and / or flow rate, thereby maintaining the exhaust pressure and / or flow rate near the setpoint. This ensures a stable air supply to the downstream maleic anhydride reactor. It should be noted that this type of feedback control in the stationary vane controller is slow to take effect and does not have sufficient ability to respond to sudden and drastic fluctuations in pressure or flow.

[0103] The air supply device of the present invention also includes an anti-surge valve controller. The anti-surge valve controller is used to control the anti-surge valve and is also a controller with feedback control function. The anti-surge valve feedback control is based on the anti-surge line. By comparing the relative position of the operating point with the anti-surge line, the operating point is adjusted by controlling the opening degree of the anti-surge valve. Similarly, the anti-surge valve controller can also be, for example, a controller employing a PID algorithm. The SV receiver of the anti-surge valve controller receives anti-surge line information, the PV receiver receives the air compressor operating point measurement result, and the OUT outputs the anti-surge valve control signal. When the operating point crosses the anti-surge line and approaches the surge line, based on the operating point measurement result, the anti-surge valve is opened at an appropriate angle, thereby reducing the pressure and returning the operating point to the normal operating range, preventing the air compressor from experiencing surge. It should be noted that this feedback control of the anti-surge valve controller is relatively slow to take effect and its ability to respond to sudden and drastic fluctuations in pressure or flow is not very strong.

[0104] Operating point, surge line, and anti-surge line are well-known concepts in the air compressor industry. For example, state point, surge line, and anti-surge line can be plotted on an anti-surge diagram with the throat differential pressure of the air compressor on the horizontal axis and the exhaust pressure of the air compressor on the vertical axis. Figure 3A typical anti-surge diagram for an air compressor is shown, including surge line 1 and anti-surge line 2. In the anti-surge diagram, each point corresponds to a state point representing the throat differential pressure and exhaust pressure of the air compressor. Based on actual surge tests of the air compressor in the field, surge points at different stator vane angles can be measured. Connecting these surge points yields the actual surge line of the air compressor. State points in the area below and to the right of this surge line (larger throat differential pressure, lower exhaust pressure) do not experience surge. Surge will occur on the surge line and above and to the left of it (too small throat differential pressure, too high exhaust pressure). Therefore, a certain safety margin (e.g., 10%) is reserved below and to the right of the surge line as an anti-surge line. When the air compressor's exhaust pressure increases, causing the operating point to cross the anti-surge line, the air compressor can reduce the exhaust pressure by opening the anti-surge valve to a certain degree, thus moving the operating point away from the surge line and preventing surge. As the operating conditions causing surge gradually fluctuate, the anti-surge valve gradually closes. This process can be achieved through feedback control by an anti-surge valve controller. In one implementation, the throat differential pressure, after temperature and pressure compensation calculations and calculations based on a piecewise linear function within the control system, becomes the setpoint SV of the anti-surge valve controller. The measured exhaust pressure of the air compressor becomes the current value PV of the anti-surge valve controller. The required opening degree of the anti-surge valve is calculated (e.g., using a PID algorithm), and the opening degree of the anti-surge valve is controlled accordingly to prevent surge. It is understood that other suitable feedback algorithms can also be used besides the PID algorithm.

[0105] Feedback control of the anti-surge valve is suitable for situations with small disturbances, i.e., when the operating point slowly and slightly crosses the anti-surge line. In this case, the operating point can be adjusted by gradually opening the anti-surge valve. However, when the pressure rises rapidly or the disturbance is large, the operating point may quickly cross the safety margin between the anti-surge line and the surge line to reach the surge zone. The lag in the above feedback control will make it difficult to guarantee that surge will not occur. Therefore, when a large disturbance causes the operating point to potentially or already enter the surge zone, conventional air compressors, in order to simply protect the air compressor, immediately open the anti-surge valve to its maximum opening (i.e., fully open) to release air, thereby rapidly reducing the exhaust pressure, causing the operating point to leave the surge zone, and eliminating the surge phenomenon. As mentioned above, the inventors found that this seriously affects the stability of the air supply to the remaining maleic anhydride reactor, and in severe cases, the reactor may trip due to excessively low air flow.

[0106] This invention incorporates a feedforward performance controller in the air supply unit to appropriately handle reactor tripping conditions. More specifically, in the event of a reactor trip, this invention utilizes the feedforward performance controller to coordinate the adjustment of the anti-surge valve and the stationary vane to control the air compressor's exhaust pressure and flow rate.

[0107] The feedforward performance controller is configured to initiate trip emergency control upon receiving a trip signal from the maleic anhydride reactor, and terminate the trip emergency control after the anti-surge valve is closed. The trip emergency control includes: feedforward control of the opening degree of the anti-surge valve, and changing the target exhaust pressure and / or flow rate of the stationary vane controller.

[0108] In other words, this invention addresses the issue of some maleic anhydride reactors suddenly tripping in a maleic anhydride preparation system containing multiple reactors by specifically incorporating a feedforward performance controller in the air supply unit for emergency handling of such trips.

[0109] The feedforward performance controller does not operate in the maleic anhydride preparation system unless a trip occurs in the multiple reactors. When each reactor is operating normally, the air compressor's exhaust pressure is controlled by feedback from the stator vane controller and anti-surge valve controller. This feedforward performance controller only participates in the control of the air supply system in the event of a trip, an abnormal operating condition. Even if the air compressor's exhaust pressure suddenly rises for other reasons, this feedforward performance controller will not operate.

[0110] Figure 4 A schematic diagram of the feedforward control connection principle according to an embodiment of the present invention is shown.

[0111] As shown in the figure, when the reactor does not trip, the stationary vane controller controls the stationary vane angle through feedback from the output terminal OUT based on the set value at the SV1 terminal and the measured or actual value at the PV terminal. When the air compressor operating point crosses the anti-surge line, the anti-surge valve controller controls the opening of the anti-surge valve through feedback from the output terminal OUT based on the anti-surge line input from SV1 and the actual operating point position output from PV to eliminate possible surge phenomena.

[0112] The maleic anhydride preparation system can generate and send a trip signal when the maleic anhydride reactor trips. The system can send various reactor operating status signals, or simply operating status signals, with the trip signal being one of them. The operating status signal can be a digital dry contact signal. This signal can be automatically generated by the reactor's control system (e.g., a distributed control system, DCS). The control system measures reactor parameters to determine if the reactor is operating normally. If the control system determines that the reactor is operating normally, it outputs a dry contact signal indicating normal operation as the normal operating status signal, such as a closed signal. When the reactor trips due to a malfunction or other factors, it outputs a trip operating status signal, such as an open signal. Alternatively, a trip signal can be actively issued by the system operator upon detecting a trip.

[0113] The feedforward performance controller is configured to receive a trip signal from the maleic anhydride reactor and, in response to this signal, initiate emergency trip control. For example... Figure 4As shown, the feedforward performance controller can receive trip signals from reactors 1, 2, and 3. The emergency control system of this invention, based on the air volume loss after a reactor trip, coordinates and controls the anti-surge valve and the air compressor stator vanes in advance, ensuring stable air supply to the remaining reactors while preventing air compressor surge. Figure 4 As shown, the feedforward performance controller controls operation through output terminals OUT1 and OUT2.

[0114] Emergency control includes feedforward control of the anti-surge valve opening. As mentioned above, when controlled by the anti-surge valve controller, the anti-surge valve gradually opens under small disturbances and fully opens under large disturbances based on the increased exhaust pressure measurement. In contrast, the feedforward performance controller of this invention responds to a trip signal and controls the anti-surge valve in advance. That is, instead of feedback control after the pressure rise due to the trip and subsequent closure of the reactor's inlet flow regulating valve, control is initiated in advance based on the air supply needs after the trip. The number of tripped reactors can be determined from the trip signal, thus allowing for advance prediction of the required reduction in air supply for the corresponding operating condition and the air supply required for the remaining reactors to continue operating. For example, in a three-reactor system, when the feedforward performance controller receives a trip signal, it indicates that one reactor has tripped while the other two reactors are still operating. The feedforward performance controller can calculate an appropriate anti-surge valve opening based on the required air supply and the anti-surge valve's performance curve. The feedforward performance controller directly opens (or quickly opens) the anti-surge valve to this opening degree. At this valve opening, the venting from the anti-surge valve is not a gradual feedback opening, nor is it a fully open flow, but rather a controlled, rapid opening. Venting through the anti-surge valve ensures that the gas flow rate adapts to the needs of the remaining maleic anhydride reactor, thus maintaining minimal fluctuations in the air flow to the remaining reactor. During this process, the air compressor's operating point does not reach the surge line, and surge does not occur.

[0115] The feedforward performance controller can control the opening of the anti-surge valve through the anti-surge valve controller. That is, the feedforward performance controller sends a control signal to the anti-surge valve controller, which then controls the anti-surge valve through the signal output from the OUT terminal of the anti-surge valve controller. For example... Figure 4 As shown, the anti-surge valve controller controls the opening degree of the anti-surge valve based on the anti-surge line received from the SV1 terminal and the operating point position received from the PV terminal under normal conditions. However, when the feedforward performance controller is in operation, it receives the feedforward signal output from the OUT1 output terminal of the feedforward performance controller from the SELSV2 terminal.

[0116] Simultaneously, the feedforward performance controller calculates the required exhaust pressure and flow rate of the air compressor at the anti-surge valve opening based on the known required air volume, and sends these required values ​​as target exhaust pressure and / or flow rate to the stationary vane controller. For example... Figure 4 As shown, the output is sent from the OUT2 output terminal of the feedforward performance controller to the SEL SV2 terminal of the stator vane controller. The stator vane controller receives the changed target exhaust pressure and / or flow rate from the feedforward performance controller, replacing the previously received setpoint from the SV1 terminal. This changed target exhaust pressure and / or flow rate applies to the operation of the remaining reactor under the aforementioned anti-surge valve opening. Based on this changed target exhaust pressure and / or flow rate, the stator vane controller still controls the stator vane angle based on the test value received from the PV terminal, so that the actual exhaust pressure and / or flow rate remain substantially stable.

[0117] By using a feedforward controller to control the opening of the anti-surge valve and, in conjunction with the feedback control of the stationary vane angle, stable exhaust pressure and flow rate are obtained, ensuring that the remaining reactors can still operate normally.

[0118] However, considering the stability of the system's normal operation, the anti-surge valve cannot remain open for an extended period, as this would cause a large amount of unnecessary compressed air to be discharged from the valve, wasting energy. Therefore, the feedforward performance controller continues to operate, gradually closing the anti-surge valve in small increments. For example, in one implementation, the opening is initially reduced by a certain amount, such as 2%-5%. As the anti-surge valve opening decreases slightly, the discharge pressure and flow rate change accordingly, but not drastically. However, since the stator vane controller is still performing feedback control, the change in the stator vane angle coordinates and stabilizes the compressor's discharge pressure and flow rate.

[0119] Once the exhaust pressure stabilizes, i.e., the stator vane angle remains essentially constant, the feedforward performance controller continues to reduce the opening and repeats the above operation. By gradually and slowly reducing the anti-surge valve opening in this way, the surge valve will eventually close completely. Throughout this process, a stable air supply can be maintained to the remaining maleic anhydride reactors, allowing them to operate normally.

[0120] Once the surge valve is fully closed, the multi-reactor maleic anhydride preparation system has safely recovered from the sudden shutdown and reached a new steady-state operation compared to before, in which the number of operating reactors has decreased, and the target exhaust pressure and / or flow rate have changed accordingly. At this point, the stator vane angle decreases, resulting in a lower intake flow rate and a lower throat differential pressure, and the air compressor will operate at a new operating point. Accordingly, the emergency shutdown control of the feedforward performance control ends.

[0121] As described above, in one embodiment, the stator controller may have another setpoint receiver to receive signals from the feedforward performance controller. The original setpoint receiver is SV1, and the new setpoint receiver is SEL SV2. SEL SV2 is connected to a signal output terminal OUT2 of the feedforward performance controller. When the SEL SV2 receiver receives the changed target exhaust pressure and / or flow rate from the feedforward performance controller, the original target exhaust pressure and / or flow rate input values ​​of SV1 become invalid.

[0122] As described above, in one embodiment, the anti-surge valve controller may also have another setpoint receiver, SELSV2, connected to another signal output, OUT1, of the feedforward performance controller. When the SELSV2 receiver of the anti-surge valve controller receives a control signal from the feedforward performance controller, it will directly change the opening degree of the anti-surge valve through the OUT terminal. The advantage of the feedforward performance controller controlling the anti-surge valve through the anti-surge valve controller is that all control signals for the anti-surge valve are issued by the anti-surge valve controller, avoiding control conflicts. When the feedforward performance controller performs emergency control, the feedback control of the anti-surge valve controller temporarily fails because the feedforward performance controller has already ensured that surge does not occur.

[0123] The feedforward performance controller uses the receipt of a trip signal from the maleic anhydride reactor as a prerequisite for initiating its emergency trip control and determines the corresponding feedforward control strategy. Based on the number of received reactor trip signals, the number of reactors still operating can be determined, along with the required airflow to maintain their normal operation. For example, in a three-reactor system, receiving one trip signal indicates that two reactors still need to remain operational. The feedforward performance controller can provide the necessary control strategy and corresponding control signals based on the number of trip signals.

[0124] Continuing with the example of a reactor tripping in a three-reactor system, when a reactor trips, it immediately sends a trip signal to the feedforward performance controller. The feedforward performance controller then determines that the maleic anhydride system should subsequently be operated in two-reactor mode. The feedforward performance controller calculates the required airflow for both reactors. Based on the inherent characteristic curve of the anti-surge valve, and according to this airflow requirement, the feedforward performance controller sends an opening control signal to the anti-surge valve controller, causing the anti-surge valve to quickly open to the predetermined opening.

[0125] The principle for selecting the predetermined opening degree of the anti-surge valve is to first ensure that the exhaust pressure is in the non-surge zone of the anti-surge diagram under the current throat differential pressure, preferably in the safe zone below the right of the anti-surge line; secondly, to ensure that the air flow and pressure to the maleic anhydride reactor that has not tripped remain basically unchanged under this opening degree, for example, the fluctuation does not exceed 20%, more preferably 10%, more preferably 5%, and more preferably 2%.

[0126] The ultimate goal of emergency control is to achieve the required supply air pressure and flow rate for both reactors to operate. To this end, the feedforward performance controller inputs the target exhaust pressure and / or flow rate into the stator controller, replacing its original exhaust pressure / flow rate setpoints. In other words, after the feedforward performance controller initiates emergency control, the stator controller's exhaust pressure and / or flow rate setpoints are changed to values ​​applicable to both reactors. Subsequently, based on these new setpoints, the stator controller adjusts the stator blades to stabilize the supply air pressure and flow rate, thereby ensuring the basic stable operation of the remaining reactors.

[0127] At this point, the anti-surge valve is still open to its predetermined degree and needs to be gradually closed to return to normal operation and continue its anti-surge function. To this end, the performance controller continues to send feedforward control signals to the anti-surge valve controller. This control signal causes the anti-surge valve to gradually close. In a preferred embodiment, the control signal can be to reduce the opening of the anti-surge valve by 2%-5% at a time. After the opening is reduced, the feedback control of the stator vane controller adjusts the stator vanes to restore stable exhaust pressure and flow. A 2%-5% reduction range strikes a good balance between quickly closing the anti-surge valve and waiting for the stator vanes to adjust in time. After the stator vanes stabilize, the anti-surge valve opening is reduced again. This process is repeated until the anti-surge valve is completely closed. At this point, the feedforward performance controller terminates emergency control.

[0128] Therefore, upon receiving a reactor trip signal, the feedforward performance controller, in conjunction with the anti-surge valve and stator vane control, preemptively adjusts the air compressor's intake and exhaust, regulating the outlet pressure and flow rate (i.e., anti-surge valve performance control activation) to obtain the required air supply. Because it is a feedforward control responding to the trip signal, unlike feedback control, it can effectively intervene in the air supply system before changes in the downstream piping network significantly impact compressor regulation. This process avoids damage to the air compressor and does not affect the operation of the remaining reactors. Through the control of the feedforward performance controller, fluctuations caused by reactor trips are effectively controlled through the coordinated regulation of the stator vanes and anti-surge valve, reducing the risk and probability of system interlock shutdowns.

[0129] The air supply device of the present invention combines the anti-surge control and regulation of the air compressor, the static vane control and regulation, and the operating status signal of the maleic anhydride reactor, and together with the added feedforward performance controller, forms a brand-new air compressor air supply regulation system, thereby ensuring the stability of the air supply to the remaining reactor.

[0130] In a multi-reactor maleic anhydride preparation system, the exhaust gas produced by each reactor can be returned to the air compressor.

[0131] Furthermore, in such a maleic anhydride preparation system, when a reactor trip occurs, the emergency control mechanism of this invention will rapidly open the anti-surge valve to a certain degree and then gradually close it. During this process, unlike the brief, small-scale venting of the anti-surge valve during typical anti-surge processes, the system of this invention continuously releases a large amount of exhaust gas into the environment. This results in a considerable amount of flammable, explosive, and toxic benzene or n-butane being released into the environment without treatment, which must be avoided. The exhaust gas recovery design of this invention is particularly suitable for maleic anhydride preparation systems implementing the aforementioned emergency control.

[0132] Therefore, the air supply device for recovering maleic anhydride reaction tail gas of the present invention is particularly suitable for emergency control of the above-mentioned multi-reactor maleic anhydride preparation system, and can safely and efficiently achieve the operation of the reactor maleic anhydride preparation system.

[0133] The present invention will be described in more detail below through examples.

[0134] Example 1

[0135] Production is carried out using a maleic anhydride preparation system that supplies air to one maleic anhydride reactor via an air compressor. The reactant is n-butane.

[0136] A tail gas recovery pipe connected to the top of the absorber downstream of the maleic anhydride reactor is in fluid communication with the air compressor's inlet pipe. The air supply unit also includes a surge vent return pipe, which connects the anti-surge valve's exhaust port to the air compressor's inlet pipe. The air compressor uses a combination of carbon ring and Labellenn seals as its shaft end seal structure. The Labellenn seal is located on the inner side, and the carbon ring seal is located on the outer side. The carbon ring has an inflation port.

[0137] The maleic anhydride preparation system was run and the air in the air compressor environment was tested; no n-butane was detected.

[0138] However, after 1,000 hours of operation, corrosion was observed on the surface of the air compressor blades.

[0139] Example 2

[0140] The test was conducted in the same manner as in Example 1, except that the surfaces of the first three stages of the air compressor blades were treated with acid resistance.

[0141] After 1000 hours of operation, the surface of the air compressor blades was inspected and no corrosion was observed.

[0142] Example 3

[0143] Production is carried out using a maleic anhydride preparation system that supplies air to one maleic anhydride reactor via an air compressor. The reactant is benzene.

[0144] A tail gas recovery pipe connected to the top of the absorber downstream of the maleic anhydride reactor is in fluid communication with the air compressor's inlet pipe. The air supply unit also includes a surge vent return pipe, which connects the anti-surge valve's exhaust port to the air compressor's inlet pipe. The air compressor uses a combination of carbon ring and Labellenn seals as its shaft end seal structure. The Labellenn seal is located on the inner side, and the carbon ring seal is located on the outer side. The carbon ring has an inflation port.

[0145] The maleic anhydride preparation system was run, and the air in the air compressor environment was tested; no benzene was detected.

[0146] After 1000 hours of operation, corrosion was observed on the surface of the air compressor blades.

[0147] Example 4

[0148] The test was conducted in the same manner as in Example 3, except that the surfaces of the first three stages of the air compressor blades were treated with acid resistance.

[0149] After 1000 hours of operation, the surface of the air compressor blades was inspected and no corrosion was observed.

[0150] Example 5

[0151] Production is carried out using a maleic anhydride preparation system that simultaneously supplies air to three maleic anhydride reactors connected in parallel using a single air compressor. The three maleic anhydride reactors are designated Reactor 1, Reactor 2, and Reactor 3. The reactant is n-butane. Each reactor has its own tail gas recovery pipeline.

[0152] A stator vane controller with an embedded PID algorithm is installed. Its output terminal OUT is connected to the stator vane adjustment mechanism to control the stator vane angle. Its first setpoint receiver SV1 obtains the target exhaust pressure setpoint for normal reactor operation from the control system. Its current value receiver PV receives the real-time exhaust pressure measurement value from the exhaust pressure sensor.

[0153] An anti-surge controller with an embedded PID algorithm is installed. Its output terminal OUT is connected to the anti-surge valve to control the valve opening. Its first setpoint receiver SV1 obtains the anti-surge graph, including the surge line and the anti-surge line, from the control system. Its current value receiver PV receives real-time operating point parameters from the exhaust pressure sensor and the throat differential pressure sensor.

[0154] A feedforward performance controller is installed, with three signal input terminals receiving operating signals from reactors 1-3. Its second output terminal OUT1 is connected to the second setpoint receiver SEL SV2 of the anti-surge valve controller. Its first output terminal OUT2 is connected to the second setpoint receiver SEL SV2 of the stationary vane controller.

[0155] like Figure 4As shown, the reactor, anti-surge controller, anti-surge valve, stationary vane controller, stationary vane, and feedforward performance controller are connected together.

[0156] First, reactors 1-3 are operated under normal conditions. At this time, the feedforward performance controller is not operational. The stator vane controller, based on the target exhaust pressure setpoint obtained from SV1, performs feedback control on the stator vane angle according to the measured value obtained from PV. The anti-surge valve controller, based on the anti-surge line obtained from SV1, performs feedback control on the anti-surge valve opening according to the operating point parameters obtained from PV.

[0157] To simulate a reactor trip, reactor 1 was shut down, and the airflow control valve leading to reactor 1 was immediately closed, while a trip signal was sent to the feedforward performance controller.

[0158] The trip signal of reactor No. 1 triggered the feedforward performance controller, initiating emergency trip control. Based on the single trip signal, the expected gas flow rate would decrease to two-thirds of its original value, while the pressure remained unchanged. Therefore, the feedforward performance controller sent a feedforward signal to the anti-surge valve's SEL SV2, rapidly opening the valve to its first opening degree (not fully open), releasing gas. At this first opening degree, under the current stator vane angle and compressor operating conditions, the exhaust air flow rate downstream is two-thirds of its previous value, while the pressure remains unchanged. This operating point is located to the lower right of the anti-surge line, preventing surge from occurring.

[0159] Simultaneously, the feedforward performance controller sends this target exhaust pressure and / or flow rate to the stator vane controller's SELSV2. The stator vane controller then performs feedback control based on the changed target exhaust pressure and / or flow rate. Since the flow rate and pressure are now approximately at the target values, the stator vane controller only makes fine adjustments to the stator vane angle based on the measured feedback.

[0160] Subsequently, the feedforward performance controller reduces the anti-surge valve opening by 2%. At this point, both the exhaust pressure and flow rate increase. The stator controller receives the increased pressure / flow rate measurements and performs feedback control on the stator, reducing the stator angle so that the exhaust pressure and flow rate drop back to the target values.

[0161] Once the exhaust pressure and flow rate stabilize around the target value (i.e., the stator angle no longer decreases), the feedforward performance controller reduces the anti-surge valve opening by 2% again. Repeat the above process until the anti-surge valve is completely closed.

[0162] After the anti-surge valve is fully closed, the feedforward performance controller shuts down, ending the emergency trip control. The anti-surge valve controller then takes over the feedback control of the anti-surge valve.

[0163] During this process, the air inlet pressure and flow rate in reactors 2 and 3 were monitored, and the operating status of the reactors was checked. The results showed that the air inlet pressure and flow rate in reactors 2 and 3 fluctuated little, the reactors operated smoothly, and the product yield and quality remained stable, unaffected by the trip of reactor 1.

[0164] Furthermore, although the anti-surge valve was open for an extended period during the emergency control process, no n-butane was detected in the air surrounding the air compressor.

[0165] Example 6

[0166] The test was conducted in the same manner as in Example 5, except that reactors 1 and 2 of the three reactors underwent a simulated trip.

[0167] Accordingly, the feedforward performance controller quickly opens the anti-surge valve and sends a modified target exhaust flow rate to the stator controller, which is one-third of the previous rate, while the pressure remains unchanged. Due to the larger opening, the reduction in the anti-surge valve opening is increased to 5% each time during feedforward control.

[0168] During this process, the air inlet pressure and flow rate in reactor No. 3 were monitored, and the reactor's operating status was checked. The results showed that the air inlet pressure and flow rate in reactor No. 3 fluctuated only slightly. The reactor operated smoothly, with stable product yield and quality, unaffected by the shutdowns of reactors No. 1 and No. 2.

[0169] Furthermore, although the anti-surge valve was open for an extended period during the emergency control process, no n-butane was detected in the air surrounding the air compressor.

[0170] Comparative Example 1:

[0171] Except for the absence of a feedforward controller, the maleic anhydride reactor is supplied with air using the same apparatus as in Example 5.

[0172] After the simulated reactor No. 1 tripped, the exhaust pressure measurement rose rapidly, triggering the feedback control of the anti-surge controller, and the anti-surge valve opened fully. Shortly after the anti-surge valve opened fully, reactors No. 2 and No. 3 tripped due to insufficient gas supply and stopped operating.

[0173] Comparative Example 2:

[0174] Except for the absence of a feedforward controller, the maleic anhydride reactor is supplied with air using the same apparatus as in Example 6.

[0175] After reactors 1 and 2 tripped, the exhaust pressure readings rose rapidly, triggering the feedback control of the anti-surge controller, which fully opened the anti-surge valve. Once the anti-surge valve was fully open, reactor 3 quickly tripped due to insufficient gas supply and stopped operating.

[0176] Therefore, when one or more of the maleic anhydride reactors suddenly stop, it is possible to ensure that the air compressor is not damaged due to surge, while also ensuring that the remaining reactors do not experience abnormal operation or interlock shutdown due to a sudden reduction in air supply.

[0177] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An air supply device for recovering tail gas from maleic anhydride reaction, characterized in that, The air supply device includes: Axial flow air compressor, which is equipped with anti-surge valve and stationary vane; An air intake duct, wherein the air intake end of the air intake duct is fluidly connected to an air source, and the air outlet end is fluidly connected to the air intake duct of the air compressor; An exhaust gas recovery pipe, wherein the inlet end of the exhaust gas recovery pipe is fluidly connected to the downstream of the maleic anhydride reactor, and the outlet end is fluidly connected to the inlet pipe of the air compressor; and The anti-surge valve vent return pipe has its inlet end connected to the exhaust port of the anti-surge valve in fluid communication, and its outlet end connected to the inlet pipe of the air compressor in fluid communication. Furthermore, the air compressor has a shaft end sealing structure. The air supply device further includes: A stator vane controller that controls the stator vane angle based on target exhaust pressure and / or flow feedback; An anti-surge valve controller, which controls the opening degree of the anti-surge valve based on the anti-surge line feedback of the air compressor; and The feedforward performance controller is configured to initiate emergency trip control upon receiving a trip signal from the maleic anhydride reactor, and to terminate the emergency trip control after the anti-surge valve is closed. The emergency control for vehicle scrambling includes: feedforward control of the opening of the anti-surge valve, and changing the target exhaust pressure and / or flow rate of the stationary vane controller.

2. The air supply device according to claim 1, characterized in that, The shaft end sealing structure adopts a combination of carbon ring seal and Labier seal.

3. The air supply device according to claim 1, characterized in that, At least some of the blade surfaces of the air compressor are treated with acid resistance.

4. A system for preparing maleic anhydride, characterized in that, The maleic anhydride preparation system includes: Maleic anhydride reactor, and The air supply device according to any one of claims 1-3.

5. The maleic anhydride preparation system according to claim 4, characterized in that, The maleic anhydride preparation system also includes: In the absorption tower downstream of the maleic anhydride reactor, The inlet end of the exhaust gas recovery pipe is in fluid communication with the top of the absorption tower.

6. The maleic anhydride preparation system according to claim 4, characterized in that, The maleic anhydride preparation system includes multiple reactors.

7. A method for operating a maleic anhydride preparation system according to any one of claims 4-6, characterized in that, The operating method includes: The tail gas, including benzene or n-butane, originating from the maleic anhydride reactor, is passed through the tail gas recovery pipe and the air compressor's inlet pipe before entering the air compressor. The vented air from the anti-surge valve enters the air compressor through the anti-surge valve vent return pipe.

8. The method according to claim 7, characterized in that, The maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors according to claim 6, and the method further includes: When multiple maleic anhydride reactors are running, the stationary vane controller controls the stationary vane angle based on the target exhaust pressure and / or flow rate and feedback from the measured values, and the anti-surge valve controller controls the anti-surge valve opening based on the anti-surge line of the air compressor and feedback from the measured values. When at least one of the plurality of maleic anhydride reactors trips, the feedforward performance controller initiates the trip emergency control upon receiving a trip signal from the maleic anhydride reactor, and terminates the trip emergency control after the anti-surge valve closes, wherein the trip emergency control includes: i) Based on the number of remaining operating maleic anhydride reactors, quickly open the anti-surge valve to the first opening degree and change the target exhaust pressure and / or flow rate of the stationary vane controller; ii) Reduce the anti-surge valve opening from the first degree, and then wait for the stationary vane angle to stabilize; iii) Repeat step ii) until the anti-surge valve is closed.

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