Air supply device for maleic anhydride preparation system including multiple reactors, preparation system using the same, and operation method thereof

Abstract

The present invention provides an air supply device for a maleic anhydride preparation system comprising multiple reactors, which includes a feedforward performance controller and a feedforward countercurrent protection controller. The feedforward performance controller is configured to initiate a trip emergency control when receiving a trip signal of a maleic anhydride reactor, and end the trip emergency control after the anti-surge valve is closed. The feedforward countercurrent protection controller is configured to start detecting countercurrent when receiving an overpressure signal of the maleic anhydride reactor, and cause the air compressor to perform a safe operation action when countercurrent is detected. The present invention also provides a maleic anhydride preparation system comprising multiple reactors and an operation method thereof. The present invention can achieve supplying air to multiple maleic anhydride reactors with a single air compressor.

Description

Technical Field

[0001] The present invention relates to the field of maleic anhydride production, and more particularly, to an air supply device for a maleic anhydride preparation system including multiple reactors, a preparation system using the same, and an operation method thereof. Background Art

[0002] Maleic anhydride is an important basic organic chemical raw material and is widely used in the production of various chemicals. At present, the main industrial production methods of maleic anhydride include the benzene method and the n-butane method. The benzene method uses a mixed gas of benzene and air as raw materials, and oxidizes and converts benzene into maleic anhydride under the action of a catalyst. The n-butane method uses a mixed gas of n-butane and air as raw materials, and oxidizes and converts n-butane into maleic anhydride under the action of a catalyst. In China, the benzene method was mainly used for maleic anhydride production before. However, due to the advantages of the n-butane method in terms of raw materials, environmental protection, efficiency, and cost, the production capacity of maleic anhydride by the n-butane method in China has been increasing in recent years.

[0003] Both the benzene method and the n-butane method use air as one of the raw materials. In a maleic anhydride factory, an air compressor is needed to pressurize the air and supply it to the maleic anhydride reactor for the oxidation reaction.

[0004] Whether in the benzene method or the n-butane method, the most widely used maleic anhydride reactor is an axial tube-sheet fixed-bed reactor. The axial tube-sheet fixed-bed reactor consists of a large number of tubes and uses molten salt for heat exchange. Since the maleic anhydride formation reaction is a reaction highly sensitive to changes in reaction conditions, the smooth progress of maleic anhydride production and product quality highly depend on the radial uniformity of the materials and temperature in the reactor. However, as the diameter of the reactor increases, the difficulty of controlling the material uniformity and temperature uniformity in the radial direction of the reactor continuously rises. Therefore, in order to ensure the smooth progress of the reaction and the quality of maleic anhydride, the diameter of the maleic anhydride reactor is limited and it is difficult to further expand.

[0005] Since the maximum diameter of a single maleic anhydride reactor is limited, the flow area of the fluid passing through the reactor is also limited, which further puts higher requirements on the bed height of the catalyst. The industrial maleic anhydride reactor has a large aspect ratio of the catalyst bed height to diameter, and the pressure drop of the reaction fluid flowing through the catalyst bed is high, thus requiring a higher outlet pressure of the air compressor. Due to the above-mentioned high sensitivity, the air supply (also called air delivery) of the air compressor needs to be very stable while maintaining high pressure, otherwise it may lead to abnormal reactions or even termination. The above-mentioned air supply requirements pose high requirements on the air supply device for the maleic anhydride reactor.

[0006] In addition, due to the limitation of the maximum diameter of a single maleic anhydride reactor, in a maleic anhydride plant, in order to achieve a higher design production capacity, it may be necessary to construct multiple maleic anhydride reactors. In the previous design of maleic anhydride plant projects, in order to ensure the stability of high-pressure air supply, an air compressor is provided separately for each maleic anhydride reactor for air supply. In such a design, the connection relationship between the air compressor and the maleic anhydride reactor is single, and the operation strategy is simple. The air outlet of the air compressor is directly connected to the air inlet of the maleic anhydride reactor. During production, under normal operating conditions, the air compressor maintains stable air supply, while when encountering sudden abnormal operating conditions, the air compressor can quickly reduce the air supply pressure or completely stop to avoid accidents.

[0007] With the continuous development of air compressor technology, air compressors with higher air supply pressure and still maintaining air supply stability have emerged. The inventor of the present invention has realized that the air compressor already has the air supply capacity to supply air to two or even more maleic anhydride reactors simultaneously. Therefore, from the perspective of reducing equipment costs, two or even more maleic anhydride reactors can share the same air compressor.

[0008] In order to realize the air supply to multiple maleic anhydride reactors with a single air compressor in actual production, it is necessary to improve the structure and operation method of the air supply device. Summary of the Invention

[0009] In one aspect, the present invention provides an air supply device for a maleic anhydride preparation system including multiple reactors, the air supply device comprising:

[0010] An axial-flow air compressor provided with stator blades, a surge relief valve and a check valve;

[0011] A stator blade controller for feedback controlling the stator blade angle based on a target exhaust pressure and / or flow rate;

[0012] A surge relief valve controller for feedback controlling the opening of the surge relief valve based on the surge line of the air compressor;

[0013] A feedforward performance controller configured to start a trip emergency control when receiving a trip signal of the maleic anhydride reactor, and end the trip emergency control after the surge relief valve is closed; and

[0014] A feedforward reverse flow protection controller configured to start detecting reverse flow when receiving an overpressure signal of the maleic anhydride reactor, and cause the air compressor to perform a safe operation action when reverse flow is detected,

[0015] wherein the trip emergency control includes: feedforward controlling the opening of the surge relief valve, and changing the target exhaust pressure and / or flow rate of the stator blade controller,

[0016] The safe operation actions include: reducing the angle of the stationary blade, increasing the opening of the anti-surge valve, and assisting in closing the check valve.

[0017] Optionally, the air supply device further includes:

[0018] An exhaust pressure sensor;

[0019] A throat differential pressure sensor; and

[0020] An optional exhaust gas flow sensor,

[0021] wherein, the stationary blade controller performs its feedback control according to the measured value of the exhaust pressure sensor or the exhaust gas flow sensor,

[0022] The anti-surge valve controller performs its feedback control according to the measured values of the exhaust pressure sensor and the throat differential pressure sensor,

[0023] The stationary blade controller and the anti-surge valve controller are controllers embedded with the PID algorithm.

[0024] Optionally, the air supply device further includes:

[0025] An air intake pipeline, the intake end of the air intake pipeline is in fluid communication with an air source, and the outlet end is in fluid communication with the intake pipeline of the air compressor;

[0026] A tail gas recovery pipeline, the intake end of the tail gas recovery pipeline is in fluid communication downstream of the maleic anhydride reactor, and the outlet end is in fluid communication with the intake pipeline of the air compressor; and

[0027] An anti-surge valve bleed-back pipeline, the intake end of the anti-surge valve bleed-back pipeline is in fluid communication with the exhaust port of the anti-surge valve, and the outlet end is in fluid communication with the intake pipeline of the air compressor,

[0028] And the air compressor has a shaft end sealing structure.

[0029] Optionally, the air supply device further includes a motor, a steam turbine, a gearbox and a clutch, the rotating shaft of the motor is coupled to the rotating shaft of the air compressor through the gearbox, and the rotating shaft of the steam turbine is detachably coupled to the rotating shaft of the air compressor through the clutch.

[0030] In another aspect, the present invention provides a maleic anhydride preparation system including multiple reactors, the maleic anhydride preparation system including multiple reactors comprises:

[0031] Multiple maleic anhydride reactors, and

[0032] The above air supply device, the outlet pipe of the air compressor of the air supply device is in fluid communication with the reactor inlet pipes of the plurality of maleic anhydride reactors, such that the plurality of maleic anhydride reactors are connected in parallel downstream of the air compressor.

[0033] Optionally, the air supply device is the above air supply device including an exhaust gas recovery pipe.

[0034] Further optionally, the maleic anhydride preparation system including multiple reactors includes an absorption tower downstream of the maleic anhydride reactors,

[0035] wherein, the inlet end of the exhaust gas recovery pipe is in fluid communication with the top of the absorption tower.

[0036] Optionally, the air supply device is the above air supply device including a steam turbine, and

[0037] the maleic anhydride preparation system including multiple reactors includes a steam generation device,

[0038] wherein, the steam generation device is configured to supply steam to the steam turbine.

[0039] In yet another aspect, the present invention provides an operating method for the above maleic anhydride preparation system including multiple reactors, the operating method comprising:

[0040] When the plurality of maleic anhydride reactors are operating, the stator blade controller controls the stator blade angle based on the target exhaust pressure and / or flow rate and feedback according to the measured values, and the anti-surge valve controller controls the opening of the anti-surge valve based on the anti-surge line of the air compressor and feedback according to the measured values;

[0041] When at least one of the plurality of maleic anhydride reactors trips, after the feedforward performance controller receives the trip signal of the maleic anhydride reactor, it starts the trip emergency control and ends the trip emergency control after the anti-surge valve is closed, wherein, the trip emergency control includes:

[0042] i) According to the number of remaining operating maleic anhydride reactors, quickly open the anti-surge valve to a first opening degree, and change the target exhaust pressure and / or flow rate of the stator blade controller;

[0043] ii) Reduce the anti-surge valve from the first opening degree, and then wait for the stator blade angle to stabilize;

[0044] iii) Repeat operation ii) until the anti-surge valve is closed,

[0045] And, the operating method further includes:

[0046] When at least one of the multiple maleic anhydride reactors is overpressured, after receiving the overpressure signal of the maleic anhydride reactor, the feedforward countercurrent protection controller starts to detect countercurrent, checks whether countercurrent occurs, and performs the following actions according to the situation:

[0047] When countercurrent does not occur, continue to detect; and

[0048] When countercurrent occurs, perform the safe operation action, and detect again whether countercurrent occurs. If countercurrent still occurs, stop the air compressor.

[0049] Optionally, the maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors and a steam generating device as described above, where the power of the motor is insufficient to drive the air compressor load when all maleic anhydride reactors are operating; and

[0050] The operation method further includes:

[0051] a) When the air compressor sheds load, perform the safe operation action and interlock the steam turbine to stop;

[0052] b) When the motor is running but the steam turbine stops, detect the static blade angle when the steam turbine stops; if the air compressor load corresponding to the static blade angle can be driven by the motor alone, the motor continues to drive the air compressor; if the air compressor load corresponding to the static blade angle cannot be driven by the motor alone, the air compressor performs the safe operation action, and after performing the safe operation action, detect the anti-surge valve opening and the motor current; if the anti-surge valve is not fully open and the motor current exceeds the rated value, stop the air compressor;

[0053] c) When an interlock signal appears in the air compressor or the motor, stop the steam turbine.

[0054] Optionally, the maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors and a steam turbine as described above, and

[0055] The operation method further includes:

[0056] Reduce the steam turbine speed using the speed control mode, judge whether the cut-out is successful by detecting the clutch engagement switch holding time and the motor power, and if the cut-out is successful, close the steam turbine; and

[0057] Increase the steam turbine speed using the speed control mode, judge whether the engagement is successful by detecting the clutch engagement switch holding time and the motor power, and if the engagement is successful, change the speed control mode to the load loading control mode.

[0058] Optionally, the maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors and a steam generation device as described above, and

[0059] The operation method further includes:

[0060] When starting steam exists, use the starting steam to drive the steam turbine, driving the air compressor and the motor to increase speed together, where the steam turbine is in a speed control mode;

[0061] After the speed of the air compressor reaches the normal speed, the motor is connected to the grid, and the mode of the steam turbine changes to a load control mode,

[0062] and

[0063] When starting steam does not exist, with the steam turbine disconnected from the air compressor, use electricity to drive the motor to drive the air compressor to operate, and prepare maleic anhydride;

[0064] Obtain the steam from the preparation of maleic anhydride to drive the steam turbine;

[0065] Engage the clutch so that the steam turbine is connected to the air compressor. Description of the Drawings

[0066] Figure 1 Shows a typical anti-surge diagram of an air compressor.

[0067] Figure 2 Shows a schematic diagram of the feedforward control connection principle according to an embodiment of the present invention.

[0068] Figure 3 Shows a schematic diagram of an air supply device including an exhaust gas recovery pipeline according to an embodiment of the present invention.

[0069] Figure 4 Shows a combination method of labyrinth seal and carbon ring seal.

[0070] Figure 5 Shows a schematic diagram of an air compressor unit including an air compressor and a drive source.

[0071] Figure 6 Shows a schematic diagram of the connection between a steam-electric dual-drive air compressor unit and a reactor in an embodiment.

[0072] Figure 7 Shows a safety operation strategy of an embodiment of the method of the present invention when the air compressor undergoes load rejection.

[0073] Figure 8 Shows the judgment logic of an interlock shutdown program.

[0074] Figure 9 Shows the operation mode during interlock shutdown in one embodiment of the present invention.

[0075] Figure 10 Shows the operation mode when performing turbine interlock shutdown in one embodiment of the present invention. Specific embodiments

[0076] With the continuous improvement and development of air compressors in terms of air supply pressure and stability, it has become possible to use a single air compressor to supply air to multiple maleic anhydride reactors simultaneously. However, the inventors have found in practice that directly connecting the exhaust port of the air compressor to the air inlets of two or more parallel maleic anhydride reactors is difficult to achieve the safe production operation of a maleic anhydride preparation system including multiple reactors.

[0077] The characteristic of a maleic anhydride reactor is that the stability of the air raw material inlet is extremely important for its smooth operation. It can be said that the stability of the air supply volume of the air compressor is a prerequisite for the smooth operation of the maleic anhydride reactor. Therefore, the air compressor used for the maleic anhydride reactor not only needs to provide a sufficiently large pressure and flow rate, but also needs to maintain a stable air supply to each normally operating maleic anhydride reactor as much as possible under various complex working conditions actually faced. Otherwise, it is difficult to successfully and truly implement the design of sharing one air compressor among multiple maleic anhydride reactors.

[0078] When using one air compressor to supply pressurized air to multiple maleic anhydride reactors, the air inlet pipes of each maleic anhydride reactor are directly connected to the exhaust port of the same air compressor, so that multiple maleic anhydride reactors are connected in parallel downstream of the same air compressor. However, the inventors have unexpectedly found in practice that such a direct pipeline connection only downstream of a conventional air compressor is difficult to meet the actual application requirements. In this connection mode, although stable air supply can be provided to each reactor when all maleic anhydride reactors are operating normally, when some of the multiple maleic anhydride reactors present sudden abnormal working conditions, the other maleic anhydride reactors in the system will be adversely affected, and even trip due to unknown reasons. This results in the above device mode being not very practical. Without relying on any theory, the inventors have found that the reason for these results is the lag of the feedback control of the stator blades and the anti-surge valve, which causes the exhaust pressure and flow rate to not be stabilized in time.

[0079] An unexpected abnormal condition of a maleic anhydride reactor is an abnormal shutdown (also known as a trip) caused by some unexpected situations. At this time, to avoid damaging the reactor, the raw material gas pipeline leading to the reactor will be closed as soon as possible to stop receiving air. For multiple independent design schemes of maleic anhydride reactors, this will not cause problems because as the raw material gas pipeline is closed, the air compressor supplying gas to the corresponding reactor will also stop or the relief valve will be opened. However, for multiple parallel maleic anhydride reactors sharing the same air compressor, if the air compressor is stopped or vented because one of the reactors trips, the air supply to all maleic anhydride reactors will be stopped, resulting in reactors that have not tripped also having to shut down. This is very uneconomical from the perspective of actual production. Therefore, it is hoped that when one reactor suddenly trips, the air compressor can still continue to supply air to the remaining reactors.

[0080] After a reactor trip, the maleic anhydride reactor will gradually stop receiving air to avoid damaging the reactor. For example, the air inlet flow regulating valve in the reactor inlet pipe leading to the tripped reactor is closed. One operating mode can be to close the corresponding air inlet flow regulating valve when the reactor trips and let the air compressor continue to operate to supply air to the remaining reactors. However, through practice, the inventor found that in the maleic anhydride system operating in this way, the air inlet volume of the remaining reactors will be affected, resulting in unstable operation and possible interlock trips. Without relying on any theory, the inventor found the reasons as follows. The total air supply required by the maleic anhydride preparation system is related to the number of reactors in operation. Therefore, when one or several of several maleic anhydride reactors trip suddenly, there will be a large mutation in the requirement for the air supply flow of the air compressor, that is, a large amount of air volume will suddenly decrease in a short time. However, the performance regulation (maintaining the air supply pressure / flow) of a conventional axial flow air compressor is mainly completed by the stator blades, and it cannot quickly and effectively complete the regulation of the air supply volume at the outlet of the air compressor when the subsequent system fluctuates greatly suddenly. Therefore, the operating state of the air compressor cannot be immediately switched to the low air supply volume state required for a smaller number of reactors, but still remains in a relatively high air supply volume state. In this case, when the pressure in the air supply pipe of the air compressor rises sharply due to the incoordination between the high air supply volume state and the low air supply volume demand, it will affect the operating point of the air compressor, and then trigger the response of the anti-surge system of the air compressor. The anti-surge system of the air compressor also takes a long time to complete the operating point regulation and stabilization, and cannot quickly stabilize the outlet pressure of the air compressor, thus affecting the air inlet volume of the reactors in operation. In other words, it is difficult for both the conventional feedback type performance regulation and the feedback type anti-surge regulation to quickly adjust the air supply flow and pressure to the low air supply volume state. Moreover, the anti-surge valve of the air compressor will perform a full-open air release action when the pressure suddenly rises sharply (i.e., a large disturbance), which causes the air supply pressure to drop suddenly. Although the air compressor is protected, the air supply to the maleic anhydride reactor will become insufficient. As mentioned above, the maleic anhydride reactor has high requirements for the stability of the air supply. Therefore, if the air compressor does not make relevant adjustments in advance but continues with the feedback type regulation, the air supply volume may be continuously too high, continuously insufficient, or fluctuate violently, and all these situations will quickly affect the operation of the remaining maleic anhydride reactors, resulting in fluctuations in product quality at the lightest, or causing the reactor to stop working at the heaviest, resulting in an interlock trip and greatly reducing the production efficiency.

[0081] Another sudden abnormal condition of the maleic anhydride reactor is reactor overpressure. When there is reactor overpressure, the air compressor initially exhibits the same effect as when there is a reactor trip, that is, the air compressor outlet pressure increases. However, the high pressure in the trip condition is caused by the reduction of the reactor gas demand but the air compressor still maintains a large amount of gas supply, while the high pressure in the overpressure condition is caused by the increase in the pressure of the downstream reactor. Therefore, the overpressure condition may cause the medium to flow back to the air compressor. In the case of a single reactor, in order to prevent the backflow from damaging the air compressor, a check valve is usually required, and the air compressor is shut down in time when the backflow continues. However, in the case of multiple reactors, it is not desirable that the air compressor shut down once the reactor is overpressured, thereby causing other reactors to trip in an interlock, because this is disadvantageous from a cost point of view. In addition, unlike the immediate shutdown of the aforementioned tripped reactor, the overpressured reactor will not shut down immediately. Therefore, if the overpressure is short-lived and can be eliminated, it is not desirable to shut down the temporarily overpressured maleic anhydride reactor to eliminate the overpressure.

[0082] Therefore, simply connecting multiple maleic anhydride reactors in parallel downstream of a conventional air compressor cannot properly deal with the above-mentioned reactor jump and overpressure abnormal conditions, and cannot realize a practical maleic anhydride preparation system including multiple reactors.

[0083] In view of the above problems, the present invention provides an air supply device for a maleic anhydride preparation system comprising multiple reactors, wherein the air supply device comprises:

[0084] An axial flow air compressor is provided with stationary blades, an anti-surge valve and a check valve;

[0085] a stator vane controller that controls the stator vane angle based on target exhaust pressure and / or flow rate feedback;

[0086] An anti-surge valve controller, which controls the opening of the anti-surge valve based on the anti-surge line feedback of the air compressor;

[0087] a feedforward performance controller configured to start the trip emergency control upon receiving a trip signal of the maleic anhydride reactor and to end the trip emergency control after the anti-surge valve is closed; and

[0088] A feedforward backflow protection controller is configured to start detecting backflow upon receiving an overpressure signal from the maleic anhydride reactor, and to cause the air compressor to perform a safe operation action when backflow is detected.

[0089] The vehicle trip emergency control includes: feedforward control of the anti-surge valve opening, and changing the target exhaust pressure and / or flow of the stationary blade controller.

[0090] The safe operation actions include: reducing the stationary blade angle, increasing the anti-surge valve opening, and assisting in closing the check valve.

[0091] When an abnormal condition suddenly occurs in one of the maleic anhydride reactors in a maleic anhydride preparation system containing multiple reactors, the air supply device of the present invention can, while ensuring that the air compressor does not enter a surge or reverse flow state to protect the air compressor itself, maintain the air supply stability in the air supply pipe network of the air compressor as much as possible, so that the remaining maleic anhydride reactors without abnormal conditions can continue to operate and avoid interlock shutdown.

[0092] The air supply device of the present invention includes an axial flow air compressor as its basic component. The axial flow air compressor needs to provide a stable air supply for at least two maleic anhydride reactors at the same time. An appropriate air compressor can be selected according to the air supply pressure and flow rate required by the maleic anhydride reactor and the number of reactors. In one embodiment, the working pressure of a single maleic anhydride reactor is between 0.29 and 0.35 MPaA, and the required air supply flow rate is between 1000 and 4000 Nm 3 / min.

[0093] The axial flow air compressor is provided with stator blades, a surge prevention valve and a check valve. These components can all adopt conventional components in the axial flow air compressor.

[0094] The angle of the stator blades is adjustable, thereby changing the intake air flow rate of the air compressor. The adjustment range of the stator blade angle of a conventional air compressor is between 22° and 79°.

[0095] The surge prevention valve can be arranged on the exhaust pipeline of the air compressor, for example, on a branch line branched from the exhaust pipeline of the air compressor, and can be fully opened or opened by a certain degree to allow the exhaust pipeline to vent gas and reduce the air pressure therein. Classified according to the specific adjustment method of the surge prevention valve, there are equal percentage adjustment, linear adjustment, etc. The corresponding opening degree at different flow rates can be obtained by referring to the inherent characteristic curve of the surge prevention valve. Generally, it is required that the surge prevention valve can be quickly opened within 1.5 seconds and can be fully opened (from 0% to 100%) within 3 seconds. When the air compressor is operating normally, the surge prevention valve is in a closed state.

[0096] The check valve can be arranged on the exhaust pipeline of the air compressor, for example, downstream of the branch point of the branch line where the surge prevention valve is located. In the normal state, it allows the medium to flow unidirectionally from the air compressor to the reactor and prevents reverse flow, and enters an accident state when receiving an accident signal and can quickly close to cut off the pipeline.

[0097] The air supply device of the present invention further includes a stator vane controller for changing the stator vane angle. The stator vane controller can be connected to or include a stator vane angle adjustment mechanism. The stator vane controller is a controller with feedback control function, which realizes feedback control based on the difference between the set value and the current value (measured value). For example, the stator vane controller can be a controller adopting proportional integral derivative (PID) control algorithm. This type of controller has a set value (SV) receiving end and a current value (PV) receiving end. The set value of the air compressor discharge pressure and / or flow rate is input to the controller through the SV receiving end, and the measured value of the air compressor discharge pressure and / or flow rate is input to the controller through the PV receiving end as the current value. After calculation by the PID algorithm, a control signal for increasing or decreasing the stator vane angle is sent to the stator vane angle adjustment mechanism through the output (OUT) end. In this way, the stator vane controller can perform feedback control on the stator vane angle based on the deviation between the current value and the set value of the air compressor discharge pressure and / or flow rate, so as to maintain the discharge pressure and / or flow rate near the set value. This can ensure stable air supply to the downstream maleic anhydride reactor. It should be noted that the feedback control of the stator vane controller takes effect slowly and does not have sufficient reaction adjustment ability for sudden severe fluctuations in pressure or flow rate.

[0098] The air supply device of the present invention further includes a surge valve controller for controlling the surge valve, which is also a controller with feedback control function. The surge valve feedback control is based on the surge line. By comparing the relative positions of the operating point and the surge line, the opening degree of the surge valve is controlled to adjust the operating point. Similarly, the surge valve controller can also be a controller adopting, for example, the PID algorithm. The SV receiving end of the surge valve controller receives the surge line information, the PV receiving end receives the measurement result of the air compressor operating point, and the OUT outputs the surge valve control signal. When the operating point crosses the surge line and approaches the surge line, based on the measurement result of the operating point, the surge valve is selected to open at an appropriate angle, so that the pressure drops and the operating point retreats to the normal operating area, preventing the air compressor from surging. It should be noted that the feedback control of the surge valve controller also takes effect relatively slowly and its reaction adjustment ability for sudden severe fluctuations in pressure or flow rate is not very strong.

[0099] The operating point, surge line and surge prevention line are well-known in the field of air compressors. For example, the state point, surge line and surge prevention line can be plotted in a surge prevention diagram with the abscissa being the throat differential pressure of the air compressor and the ordinate being the discharge pressure of the air compressor. Figure 1A typical anti-surge diagram of an air compressor is shown, in which the surge line 1 and the anti-surge line 2 are shown. In the anti-surge diagram, each point corresponds to a state point representing the throat differential pressure and the exhaust pressure of the air compressor. According to the actual on-site surge experiment of the air compressor, the surge points of the air compressor at different static blade angles can be measured. Connecting these surge points gives the actual surge line of the air compressor. For the state points in the area below and to the right of this surge line (where the throat differential pressure is greater and the exhaust pressure is lower), the air compressor does not surge. Above the surge line and to its upper left (where the throat differential pressure is too small and the exhaust pressure is too high), the air compressor will surge. Further, a certain safety margin (such as 10%) is reserved below and to the right of the surge line as the anti-surge line. When the exhaust pressure of the air compressor increases and causes the operating point to cross the anti-surge line, the air compressor can open the anti-surge valve by a certain opening to reduce the exhaust pressure, so that the operating point moves away from the surge line and avoids surging. As the operating conditions causing surging gradually change, the anti-surge valve gradually closes. This process can be achieved by the anti-surge valve controller through feedback control. In one implementation, after the throat differential pressure undergoes temperature and pressure compensation operations and is calculated according to a piecewise function within the control system, it serves as the set value SV of the anti-surge valve controller, and the measured value of the exhaust pressure of the air compressor serves as the current value PV of the anti-surge valve controller. The required opening of the anti-surge valve is calculated (such as using the PID algorithm), and the opening of the anti-surge valve is controlled accordingly to avoid surging. It can be understood that in addition to the PID algorithm, other suitable feedback algorithms can also be used.

[0100] The feedback control of the anti-surge valve is applicable to situations where the disturbance is small, that is, 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 and significantly, or the disturbance is large, the operating point may quickly pass through the safety margin area between the anti-surge line and the surge line and reach the surge area. The lag of the above feedback control will make it difficult to ensure avoiding surging. Therefore, in the case where large disturbances cause the operating point to possibly or already enter the surge area, in order to simply protect the air compressor, conventional air compressors take the operation of immediately opening the anti-surge valve to its maximum (i.e., fully open) for bleeding, so as to quickly reduce the exhaust pressure and make the operating point leave the surge area and eliminate the surging phenomenon. As described above, the inventors found that this seriously affects the stability of the air supply to the remaining maleic anhydride reactors, and in severe cases, the reactor will trip due to too low air supply flow rate.

[0101] The present invention sets a feedforward performance controller in the air supply device and appropriately disposes of the tripping conditions of the reactor. More specifically, the present invention uses the feedforward performance controller in the case of reactor tripping to cooperate and adjust the anti-surge valve and the static blade to control the exhaust pressure and flow rate of the air compressor.

[0102] The feedforward performance controller is configured to initiate a trip emergency control when receiving a trip signal of the maleic anhydride reactor, and end the trip emergency control after the anti-surge valve is closed. The trip emergency control includes: feedforward controlling the opening of the anti-surge valve, and changing the target exhaust pressure and / or flow rate of the stator vane controller.

[0103] In other words, in view of the situation where some maleic anhydride reactors in the maleic anhydride preparation system with multiple reactors suddenly trip, the present invention specifically provides a feedforward performance controller in the air supply device for emergency handling of trips.

[0104] The feedforward performance controller does not work when there is no trip in the multiple reactors of the maleic anhydride preparation system. When each reactor is operating normally, the exhaust pressure of the air compressor is feedback-controlled by the stator vane controller and the anti-surge valve controller. This feedforward performance controller only participates in the control of the air supply device when an abnormal condition of a trip occurs. Even if the exhaust pressure of the air compressor suddenly rises for other reasons, this feedforward performance controller does not work.

[0105] Figure 2 The schematic diagram of the feedforward control connection principle according to an embodiment of the present invention is shown.

[0106] As shown in the figure, in the case where there is no trip in the reactor, the stator vane controller feedback-controls the stator vane angle through the output terminal OUT according to the set value at the SV1 terminal and the measured value or actual value at the PV terminal, and when the operating point of the air compressor crosses the anti-surge line, the anti-surge valve controller feedback-controls the opening of the anti-surge valve through the output terminal OUT according to the anti-surge line input from SV1 and the actual operating point position output from PV to eliminate possible surge phenomena.

[0107] The maleic anhydride preparation system can generate and send a trip signal when the maleic anhydride reactor trips. The maleic anhydride preparation system can send various reactor operating state signals or simply referred to as operating state signals, and the trip signal is one of them. The signal type of the operating state signal can be a digital dry contact signal. The operating state signal can be automatically generated by the control system of the reactor (such as a distributed control system, DCS). The control system of the reactor measures the parameters of the reactor to judge whether the reactor is operating normally. If the control system judges that the reactor is operating normally, it outputs a dry contact signal indicating normal operation as the normal operating state signal, which can be a closed signal for example. When the reactor trips due to factors such as a fault, it outputs a trip operating state signal, which can be an open signal for example. It can also be that when the system operator discovers the occurrence of a trip, the trip signal is actively sent.

[0108] The feedforward performance controller is configured to be able to receive the trip signal of the maleic anhydride reactor, and initiate a trip emergency control in response to the trip signal. As Figure 2As shown, the feedforward performance controller can receive the trip signals of Reactors 1, 2, and 3. The emergency control of the present invention coordinates and controls the anti-surge valve and the compressor stator blades in advance according to the air volume lost after the reactor trips, ensuring the stability of the air supply to the remaining non-tripped reactors while preventing the compressor from surging. As Figure 2 shown, the feedforward performance controller performs operation control through output terminals OUT1 and OUT2.

[0109] The emergency control includes feedforward control of the opening degree of the anti-surge valve. As described above, when feedback-controlled by the anti-surge valve controller, the anti-surge valve gradually opens under small disturbances based on the increased exhaust pressure measurement value and fully opens for exhaust under large disturbances. In contrast, the feedforward performance controller of the present invention is activated in response to the trip signal and controls the anti-surge valve in advance. That is, instead of performing feedback control after the pressure increases due to the trip and subsequent closing of the inlet flow regulating valve of the reactor, the feedforward performance controller of the present invention controls according to the air supply requirement after the trip. According to the trip signal, the number of tripped reactors can be known, so the reduced air supply volume required for the corresponding working condition and the air supply volume required for the remaining reactors to continue operating can be predicted in advance. For example, in a three-reactor system, when the feedforward performance controller receives a trip signal, it can be known that one reactor has tripped and the other two reactors are still operating. The feedforward performance controller can calculate an appropriate opening degree of the anti-surge valve according to the required air supply volume and the performance curve of the anti-surge valve. The feedforward performance controller directly opens (or quickly opens) the anti-surge valve to this opening degree. At this opening degree of the anti-surge valve, the exhaust from the anti-surge valve is not gradually opened by feedback or fully opened for exhaust, but is quickly opened under control. By exhausting through the anti-surge valve, the gas flow is adapted to the requirements of the remaining maleic anhydride reactors, so that the air flow flowing to the remaining reactors basically does not fluctuate. During this process, the operating point of the air compressor does not reach the surge line and no surging occurs.

[0110] The feedforward performance controller can control the opening degree 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, and then controls the anti-surge valve through the signal output from the OUT terminal of the anti-surge valve controller. As Figure 2 shown, the anti-surge valve controller normally feedback-controls the opening degree of the anti-surge valve according to the anti-surge line received from the SV1 terminal and the working point position received from the PV terminal, but receives the feedforward signal output from the OUT1 output terminal of the feedforward performance controller from the SELSV2 terminal when the feedforward performance controller is in effect.

[0111] At the same time, the feedforward performance controller also calculates the required exhaust pressure and flow rate that the air compressor needs to provide at this opening degree of the anti-surge valve according to the known required air supply volume, and sends these required values as the target exhaust pressure and / or flow rate to the stator blade controller. AsFigure 2 As shown, it is output from the OUT2 output terminal of the feedforward performance controller to the SEL SV2 terminal of the static vane controller. The static vane controller obtains the changed target exhaust pressure and / or flow rate from the feedforward performance controller, replacing the set value previously received from the SV1 terminal. The changed target exhaust pressure and / or flow rate is applicable to the operation of the remaining reactors under the aforementioned anti-surge valve opening. Based on the changed target exhaust pressure and / or flow rate, the static vane controller still feedback-controls the static vane angle based on the measured value received from the PV terminal, so that the actual exhaust pressure and / or flow rate remains basically stable.

[0112] Through the feedforward control of the anti-surge valve opening by the feedforward controller and the coordinated feedback control of the static vane angle, stable exhaust pressure and flow rate are obtained, ensuring that the remaining reactors can still operate normally.

[0113] However, considering the stability of the normal operation of the system, the anti-surge valve cannot be kept open for a long time, and this state also causes a large amount of unnecessary compressed air to be discharged from the anti-surge valve, wasting energy. Therefore, the feedforward performance controller continues to work and gradually closes the anti-surge valve in small steps in a feedforward manner. For example, in one embodiment, the opening is first reduced by a certain degree, such as 2% - 5%. When the opening of the anti-surge valve is reduced in small steps, the exhaust pressure and flow rate change slightly accordingly, but not drastically. However, since the static vane controller is still performing feedback control, the static vane angle is changed to coordinate and stabilize the exhaust pressure and flow rate of the air compressor.

[0114] After the exhaust pressure is stabilized, that is, when the static vane angle remains basically unchanged, the feedforward performance controller continues to reduce the opening and repeats the above operation. By gradually and slowly reducing the opening of the anti-surge valve in this way, the surge valve will eventually be completely closed. During this process, a stable air supply to the remaining maleic anhydride reactors can always be maintained, enabling them to operate normally.

[0115] When the surge valve is completely closed, the multi-reactor maleic anhydride production system has safely escaped from the sudden trip situation and reached a new steady-state operation state compared with before, where the number of operating reactors has decreased and the target exhaust pressure and / or flow rate has changed accordingly. At this time, the static vane angle is reduced, resulting in a decrease in the intake air flow rate and the throat differential pressure, and the air compressor will operate at a new operating point. Correspondingly, the trip emergency control of the feedforward performance control ends.

[0116] As described above, in one embodiment, in order to be able to receive signals from the feedforward performance controller, the stator vane controller may have another setpoint receiver. 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 target exhaust pressure and / or flow rate input value of the original SV1 becomes invalid.

[0117] As described above, in one embodiment, the surge valve controller may also have another setpoint receiver SEL SV2 and be connected to another signal output terminal OUT1 of the feedforward performance controller. When the SEL SV2 receiver of the surge valve controller receives a control signal from the feedforward performance controller, it will directly change the opening of the surge valve through the OUT terminal. The advantage of the feedforward performance controller controlling the surge valve through the surge valve controller is that all control signals for the surge valve are issued by the surge valve controller, avoiding control conflicts. When the feedforward performance controller performs emergency control, the feedback control of the surge valve controller is temporarily invalid because the feedforward performance controller can already ensure that surging does not occur.

[0118] The feedforward performance controller takes receiving the trip signal of the maleic anhydride reactor as a prerequisite for starting the trip emergency control and determines the corresponding feedforward control strategy. According to the number of reactor trip signals received, the number of remaining reactors still in operation can be known, and accordingly the air supply volume required for them to operate normally can be obtained. For example, for a three-reactor system, if one trip signal is received, it means that two reactors still need to remain in operation. For the number of trip signals, the feedforward performance controller can give the required control strategy and corresponding control signals.

[0119] Continuing with the example of one reactor trip in a three-reactor system for illustration. When one 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 operate in a two-reactor mode. The feedforward performance controller calculates the air supply volume required for the two-reactor operation. Based on the inherent characteristic curve of the surge valve, according to this air supply volume, the feedforward performance controller sends an opening control signal to the surge valve controller, causing the surge valve to quickly open to the predetermined opening.

[0120] The principle for selecting the predetermined opening of the surge valve is that, first, it is ensured that the exhaust pressure is in the non-surge zone in the surge prevention diagram under the current throat differential pressure, preferably in the safe zone below the right of the surge prevention line; second, at this opening, the air flow rate and pressure flowing to the non-tripped maleic anhydride reactors are basically unchanged, for example, the fluctuation does not exceed 20%, more preferably 10%, more preferably 5%, more preferably 2%.

[0121] The ultimate goal of the emergency control is to achieve the air supply pressure and flow rate required during the operation of the two reactors. To this end, the feedforward performance controller inputs the target exhaust pressure and / or flow rate into the stator vane controller, replacing its original exhaust pressure / flow rate set value. In other words, after the feedforward performance controller activates the emergency control, the exhaust pressure and / or flow rate set value of the stator vane controller changes to a value applicable to the two reactors. Subsequently, based on this new set value, the stator vane controller stabilizes the air supply pressure and flow rate by adjusting the stator vane, thereby ensuring the basic stable operation of the remaining reactor.

[0122] At this time, the anti-surge valve is still in the state of being opened at a predetermined opening degree, and it is necessary to gradually close it to return to the normal operating state so as to continue to play the role of anti-surge. To this end, the performance controller continues to send a feedforward control signal 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 such that the opening degree of the anti-surge valve is reduced by 2% - 5% at a time. After the opening degree is reduced, the feedback control of the stator vane controller makes the exhaust pressure and flow rate stable again by adjusting the stator vane. The opening degree reduction step range of 2% - 5% can achieve a good balance between closing the anti-surge valve as soon as possible and waiting for the stator vane to adjust in time. After the stator vane is stable, the next reduction of the anti-surge valve opening degree is carried out. Repeat this process until the anti-surge valve is completely closed. At this time, the feedforward performance controller ends the emergency control.

[0123] Thus, starting from receiving the reactor trip signal, the feedforward performance controller coordinates the anti-surge valve and stator vane controls, adjusts the air intake and exhaust of the air compressor in advance, and adjusts the outlet pressure and flow rate (i.e., the anti-surge valve - performance control is put into operation) to obtain the required air supply. Since it is a feedforward control in response to the trip signal, different from the feedback control, it can effectively intervene in the air supply device in advance before the change of the air compressor post-system pipe network has a greater impact on the air compressor regulation. During this process, neither damage to the air compressor nor the operation of the remaining reactors is affected. Through the control of the feedforward performance controller, the fluctuations caused by the reactor trip are effectively controlled under the collaborative adjustment of the stator vane and the anti-surge valve, reducing the risk and probability of the device interlocking and shutting down.

[0124] The air supply device of the present invention combines the anti-surge control regulation of the air compressor, the stator vane control regulation, and the operation state signal of the maleic anhydride reactor, and jointly forms a brand-new air compressor air supply regulation system with the added feedforward performance controller, thereby ensuring the stability of the air supply to the remaining reactors.

[0125] The present invention also provides a feedforward countercurrent controller in the air supply device and can appropriately handle the overpressure condition of the reactor. More specifically, when there is an overpressure in the reactor, the present invention uses the feedforward countercurrent controller to cooperate and adjust the anti-surge valve, the stator blades, and the check valve to minimize the impact on the system. The role of the feedforward countercurrent controller is also to effectively intervene in the air supply device in advance before the abnormal condition of the reactor causes a greater impact on the entire preparation system.

[0126] The feedforward countercurrent controller is configured to start detecting countercurrent after receiving the overpressure signal of the maleic anhydride reactor, and when detecting countercurrent, cause the air compressor to perform a safe operation action. The safe operation actions include: reducing the stator blade angle, increasing the opening of the anti-surge valve, and assisting in closing the check valve.

[0127] By actively reducing the stator blade angle and increasing the opening of the anti-surge valve, the load of the air compressor can be quickly reduced, and the pressure in the subsequent downstream pipe network can be rapidly decreased. By assisting in closing the check valve, the actual occurrence of countercurrent can be prevented as soon as possible. The safe operation actions enable the air compressor to remain in operation, avoiding the reactor from tripping due to its shutdown.

[0128] Specifically, when at least one of the plurality of maleic anhydride reactors is overpressured, after the feedforward countercurrent protection controller receives the overpressure signal of the maleic anhydride reactor, it starts to detect countercurrent, checks whether countercurrent occurs, and performs the following actions according to the situation:

[0129] When countercurrent does not occur, continue the detection; and

[0130] When countercurrent occurs, perform the safe operation actions, and detect again whether countercurrent occurs. If countercurrent still occurs, stop the air compressor.

[0131] When there is a reactor in an overpressure state, the feedforward countercurrent protection controller starts to work and checks whether medium countercurrent has occurred.

[0132] If there is no medium countercurrent despite the pressure increase, the air supply device can rely on its anti-surge valve controller to open the anti-surge valve to discharge part of the gas to reduce the pressure in the exhaust pipe, thereby preventing the countercurrent caused by the pressure increase. At this time, the feedforward countercurrent protection controller continues the detection but does not perform any actions.

[0133] If the pressure increase speed caused by overpressure is very fast, and the feedback opening of the anti-surge valve and the slow feedback reaction of the stator blades are not sufficient to offset it, countercurrent may occur. At this time, the feedforward countercurrent protection controller of the present invention will intervene in the control in advance to prevent continuous countercurrent of the air compressor. However, the feedforward countercurrent protection controller does not stop the air compressor but first actively performs the safe operation actions.

[0134] During the safe operation action, the stationary blades and anti-surge valves are feedforward controlled. In this way, the air compressor can enter the safe operation state in time. In this state, the air compressor inhales the minimum amount of air due to the active reduction of the stationary blade angle, and the high-pressure gas can be discharged through the anti-surge valve with an actively increased opening. At the same time, the check valve is also assisted to close to reduce the occurrence of backflow. The check valve can be quickly assisted to close by sending an accident signal to the check valve to put it into an accident state. Performing the safe operation action can keep the air compressor running and avoid the downstream maleic anhydride reactor from being interlocked and shut down due to the air compressor shutdown.

[0135] If the overpressure is too great, even in safe operation, there may still be reverse flow through the check valve and internal leakage. At this time, the air compressor must be shut down to protect the air compressor itself. However, this only happens when the overpressure is so severe that it still causes continuous reverse flow in safe operation. Before this, if the overpressure condition of the overpressure reactor is alleviated or disappears, the working point of the air compressor can gradually return to normal.

[0136] The feedforward reverse flow protection controller is a controller that can perform the above functions well and can be integrated into the air compressor unit control system.

[0137] Therefore, by providing a feedforward backflow protection controller capable of executing safe operation actions, the air supply device of the present invention can reasonably deal with the abnormal operating condition of overpressure in some reactors in the maleic anhydride preparation system comprising multiple reactors, and avoid premature shutdown of the air compressor and interlock jump of the reactor as much as possible.

[0138] The conditions of maleic anhydride reactor tripping and overpressure both lead to an increase in the exhaust pressure of the air compressor, and cause the same feedback control in a conventional air supply device. The air supply device of the present invention is provided with a feedforward performance controller and a feedforward backflow protection controller for the two conditions. The present invention can solve the interlock tripping problem caused by the tripping of some reactors or overpressure, and improves the practicality of the maleic anhydride preparation system including multiple reactors.

[0139] In one embodiment, the vehicle trip emergency control further comprises feed-forward controlling the stationary blade angle.

[0140] In order to complete the car jumping emergency control more quickly, the stator blade angle can be quickly reduced by an angle while the anti-surge valve is opened quickly. Compared with simply feedback control of the stator blade angle, reducing the stator blade angle in a feedforward manner can make the initial opening of the anti-surge valve smaller, so that the car jumping emergency control can be completed more quickly later.

[0141] Preferably, the air supply device further comprises:

[0142] Exhaust pressure sensor;

[0143] Laryngeal differential pressure sensor; and

[0144] An optional exhaust gas flow sensor,

[0145] wherein, the stator vane controller performs its feedback control according to the measured value of the exhaust gas pressure sensor or the exhaust gas flow sensor,

[0146] the surge valve controller performs its feedback control according to the measured values of the exhaust gas pressure sensor and the laryngeal differential pressure sensor,

[0147] the stator vane controller and the surge valve controller are controllers embedded with a PID algorithm.

[0148] In one embodiment, the air supply device of the present invention includes an exhaust gas pressure sensor. The exhaust gas pressure sensor can be connected to the surge valve controller to provide the measured exhaust gas pressure value to the surge valve controller as a feedback value. The exhaust gas pressure sensor can be connected to the PV input terminal of the surge valve controller with a PID algorithm. The exhaust gas pressure sensor can also be connected to the stator vane controller to provide the measured exhaust gas pressure value to the stator vane controller as a feedback value. The exhaust gas pressure sensor can be connected to the PV input terminal of the stator vane controller with a PID algorithm.

[0149] In one embodiment, the air supply device of the present invention includes a laryngeal differential pressure sensor. The laryngeal differential pressure sensor can be connected to the surge valve controller to provide the measured laryngeal differential pressure value to the surge valve controller as a set value. The laryngeal differential pressure sensor can be connected to the PV input terminal of the surge valve controller with a PID algorithm.

[0150] In one embodiment, the air supply device of the present invention includes an exhaust gas flow sensor. The exhaust gas flow sensor can be connected to the stator vane controller to provide the measured exhaust gas flow value to the stator vane controller as a feedback value. The exhaust gas flow sensor can be connected to the PV input terminal of the stator vane controller with a PID algorithm.

[0151] By monitoring parameters such as exhaust gas pressure, laryngeal differential pressure, and exhaust gas flow, the stator vane controller and the surge valve controller can achieve feedback control.

[0152] The air supply device of the present invention can also include other parameter measuring instruments, such as a thermometer, etc. The measurement of other parameters such as temperature can also participate in the feedback control of the surge valve or the stator vane.

[0153] In addition to being able to handle abnormal conditions such as reactor trip, the air supply device of the present invention for a maleic anhydride preparation system including multiple reactors can also achieve the tail gas recirculation in the maleic anhydride preparation process.

[0154] Downstream of the maleic anhydride reactor, tail gas of the maleic anhydride preparation process can be obtained, which contains a certain amount of raw materials, such as benzene or n-butane. Typically, the tail gas comes from the top of the absorption tower downstream of the maleic anhydride reactor. The raw materials in the tail gas can be recovered and reused as the feed of the reactor. The inventor found that directly using the tail gas is cost-effective compared to separating and purifying the raw materials in the tail gas and incorporating them into the raw material stream for recycling. Furthermore, compared with setting a separate tail gas feed line for the reactor, it is cost-effective to make the tail gas enter the reactor with the air raw material. The tail gas can be incorporated into the air raw material position in the air supply device. The air compressor upstream or between the air compressor and the reactor. The inventor found that incorporating the tail gas into the air raw material downstream of the air compressor will make the intake flow and pressure of the maleic anhydride reactor unstable, which is unfavorable for the preparation of maleic anhydride.

[0155] Therefore, the tail gas of the maleic anhydride preparation process is sent back to the upstream of the air compressor, and after being mixed with fresh air, it is sent to the reactor by the air compressor to realize the recycling of raw materials in the tail gas. However, the inventors have found in practice that only directly connecting the recycled tail gas to the upstream of the air compressor of the present invention cannot realize the safe production operation of the maleic anhydride reactor system. In the maleic anhydride preparation system of the present invention, when encountering the reactor jump condition, the emergency control of the present invention will quickly open the anti-surge valve to a certain opening and gradually close it; and when encountering the reactor overpressure condition, if the safe operation action is entered, the anti-surge valve will also continue to remain open. In these two processes, unlike the short-term small amount of exhaust of the anti-surge valve in the general anti-surge process, the system of the present invention continuously discharges a large amount of tail gas to the environment. This will cause a considerable amount of flammable, explosive, toxic and harmful benzene or n-butane to be discharged into the environment without treatment, which must be avoided.

[0156] In order to make the air supply device of the present invention also suitable for recycling the tail gas of the maleic anhydride preparation process, in one embodiment, the air supply device further comprises:

[0157] An air intake duct, wherein the air intake end of the air intake duct is in fluid communication with an air source, and the air outlet end of the air intake duct is in fluid communication with the air intake duct of the air compressor;

[0158] A tail gas recovery pipeline, wherein the air inlet end of the tail gas recovery pipeline is in fluid communication with the downstream fluid of the maleic anhydride reactor, and the air outlet end of the tail gas recovery pipeline is in fluid communication with the air inlet pipeline of the air compressor; and

[0159] The anti-surge valve venting return pipe has an air inlet end in fluid communication with the exhaust port of the anti-surge valve, and an air outlet end in fluid communication with the air inlet pipe of the air compressor.

[0160] Furthermore, the air compressor has a shaft end sealing structure.

[0161] The intake pipe of the air compressor is simultaneously connected to the air intake pipe and the tail gas recovery pipe. The air intake pipe and the tail gas recovery pipe are respectively connected to the air source and the downstream of the reactor, so that the air compressor can obtain air raw materials from the air source and the recovered tail gas from the downstream of the reactor at the same time. For example, the tail gas recovery pipe can be connected to the top of the absorption tower downstream of the maleic anhydride reactor.

[0162] The intake pipe of the air compressor is also connected to the anti-surge valve bleed return pipe. That is, in the present invention, when the anti-surge valve is opened, all the discharged gas does not enter the ambient air, but returns upstream of the air compressor and re-enters the air compressor together with the air and the tail gas.

[0163] The present invention returns the gas discharged from the anti-surge valve to the air compressor inlet again to avoid its adverse impact on the environment. The inventors have found that compared with the harmless treatment of the exhaust gas of the anti-surge valve and finally discharging it into the ambient air, guiding it upstream of the air compressor to achieve a closed-loop cycle is significantly beneficial both in terms of cost and process.

[0164] Introducing the exhaust gas of the anti-surge valve into the air feed will not have an adverse impact on the intake pressure and flow rate of the subsequent maleic anhydride reactor. Although the gas with a certain pressure discharged from the anti-surge valve enters the intake pipe of the air compressor and may change the pressure of the air intake mixture of the air compressor to a certain extent, since the exhaust gas flow rate and pressure of the air compressor can be adjusted by the stator blades, the pressure change of the feed gas reaching the air compressor can be eliminated by feedback controlling the stator blades, so as to maintain the control of the exhaust gas flow rate and pressure of the air compressor.

[0165] In this way, the problem of a large amount of harmful gas leakage that may be caused during the long-term tripping emergency control and safe operation of the anti-surge valve is solved by adding an anti-surge valve bleed return pipe.

[0166] In addition to the possible leakage at the anti-surge valve, the air compressor itself may also leak air. Therefore, the axial flow air compressor of the present invention also has a shaft end seal structure to avoid tail gas leakage from the shaft end. The air supply device of the present invention can thus supply tail gas while supplying air to multiple maleic anhydride reactors without polluting the environment.

[0167] Figure 3Schematic diagram of an air supply device including an exhaust gas recovery pipeline according to an 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 reflux filter, 5 is an outlet check valve, 6 is a flowmeter, 7 is an outlet air supply valve, 8 is a start-up vent regulating valve, 9 is an exhaust gas inlet regulating valve, 10 is a vent silencer, and 11 is a shaft end seal of the air compressor. Both the exhaust gas and the bleed air from the anti-surge valve enter the air compressor together with the air raw material, avoiding environmental pollution. The start-up vent regulating valve can be used for vent regulation when there is no exhaust gas input during start-up. However, when the intake air of the air compressor contains exhaust gas, the start-up vent regulating valve is closed to ensure no exhaust gas leakage.

[0168] In one embodiment, the operating method of the air supply device may include:

[0169] 1) During the start-up stage of the air compressor unit, since there is no exhaust gas in the subsequent system, the exhaust gas 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 opened. The air compressor is started, and the air enters the air compressor unit 1 through the air filter 2 for compression. The static blade angle of the air compressor is adjusted to gradually load, and the process flow is switched through 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 opened;

[0170] 2) During the normal operation stage of the air compressor, the recycled exhaust gas from the process system is sent to the air compressor inlet. By controlling the slow opening of the exhaust gas inlet regulating valve 9, it is incorporated into the air compressor inlet, and the flow rate is adjusted according to the system requirements. After mixing with the air, it enters the air compressor 1 for compression. The mixed gas is sent to the subsequent process system through the outlet check valve 5, the outlet flowmeter 6, and the outlet air supply valve 7 configured at the outlet. At this time, the start-up vent regulating valve 8 is manually in the closed state, the anti-surge valve 3 of the unit system is closed, and the automatic control is put into use;

[0171] 3) When the air compressor unit shows a surge phenomenon, the anti-surge valve 3 acts to open, and the mixed gas is cooled to the set temperature by the anti-surge reflux cooler 4 and then returns to the air compressor inlet to maintain the stable operation of the air compressor unit;

[0172] 4) When the air compressor unit shows a reverse flow condition, the anti-surge valve 3 is fully opened, 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 reflux cooler 4 and then returns to the air compressor inlet. The static blade angle of the air compressor is closed to 22°, and the unit maintains a safe operating state.

[0173] In a preferred embodiment, the shaft end sealing structure adopts a combined seal of carbon ring seal and Labyrinth seal. The Labyrinth seal is located on the inner side, and the carbon ring seal is located on the outer side. The carbon ring is provided with an inflation port. Since the gas entering the air compressor includes air and tail gas, and the substance that needs to be prevented from leaking only accounts for a part of the tail gas, the selection of the combination of Labyrinth seal and carbon ring seal can provide sufficient sealing performance at an appropriate cost. Figure 4 The combined mode of the Labyrinth seal and the carbon ring seal is shown. The left side in the figure is the process medium side, and the right side is the atmosphere side. A Labyrinth seal 1 is arranged around the end of the main shaft 3 of the air compressor, and in addition to the Labyrinth seal, a carbon ring seal 2 is also arranged. A carbon ring seal inflation port 4 is arranged in the carbon ring seal. Such a combined sealing mode can ensure the full sealing of harmful substances in the tail gas of maleic anhydride recovery at the end of the air compressor.

[0174] In a preferred embodiment, at least part of the blade surface of the air compressor is acid-resistant treated. In the tail gas discharged from the absorption tower downstream of the maleic anhydride reactor, in addition to the main gases such as benzene / n-butane, carbon monoxide, and carbon dioxide, there is also a small amount of maleic anhydride. These substances are not corrosive to metals without generating acidic solutions. Therefore, theoretically, the blade surface of the air compressor does not need to be specially treated to deal with these substances.

[0175] However, the inventors surprisingly found that when maleic anhydride is mixed with air intake, it may combine with water vapor in the air to form maleic acid. Especially in the initial stage of compression, such as the first three or four stages of the air compressor, water vapor in the air may precipitate and is prone to form acidic liquids with carbon dioxide, maleic anhydride, etc. This is particularly obvious in maleic anhydride factories in humid air areas. This will cause certain corrosion to the blades of the air compressor and affect the strength of the blades. Therefore, the blades of the compressor in the present invention are acid-resistant treated. However, when the feed gas is compressed by the air compressor, the temperature will increase significantly with the compression process. The water vapor in the air is in a superheated state, and no more water will precipitate during the compression process. Therefore, the present invention can only perform acid-resistant treatment on the moving and static blades of the first few stages (such as the first three or four stages) of the compressor.

[0176] In other words, the inventors found that different from pure air feed, after the air feed mixed with maleic anhydride and having a certain humidity in the present invention passes through the compression process of the air compressor, if water in the air precipitates, acidic liquids will be generated, which will damage the blades of the air compressor. For this reason, at least part of the blade surface of the air compressor is acid-resistant treated. Preferably, the moving and static blades of the first three stages of the air compressor are acid-resistant treated. Or preferably, the moving and static blades of the first four stages of the air compressor are acid-resistant treated. After a certain amount of compression, the temperature of the mixed gas continues to rise, the water vapor is in a superheated state, no more water precipitates, and no more acidic liquids are formed. Therefore, the subsequent blades and pipelines do not need acid-resistant coatings.

[0177] The acid-resistant treatment may be an acid-resistant coating treatment, i.e., forming an acid-resistant layer on the surface that needs to be acid-resistant. Suitable coating, deposition, electroplating and other methods 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 raw material benzene or cyclobutane. Surface modification and other methods can also be used to directly perform acid-resistant treatment on the surface. The present invention does not make special limitations in this regard.

[0178] In the above manner, the air supply device of the present invention can safely achieve the tail gas recirculation in the maleic anhydride preparation process.

[0179] The axial flow air compressor in the present invention can be driven by an electric motor, or can be driven by both an electric motor and a steam turbine in a combined electric and steam drive mode.

[0180] In a maleic anhydride plant, in order to save energy, a combined electric and steam driven air compressor can be used, which is jointly driven by an electric motor and a steam turbine. Among them, the steam used to drive the steam turbine can be obtained from the heat recovered from the maleic anhydride reactor or the heat from other sources. For example, the maleic anhydride preparation system may include a steam drum for recovering heat from the maleic anhydride reactor. The steam can also be obtained from other sources in the maleic anhydride plant, such as an exhaust gas incinerator.

[0181] In one embodiment, the air supply device further comprises an electric motor, a steam turbine, a gearbox and a clutch. The rotating shaft of the electric motor is coupled to the rotating shaft of the air compressor through the gearbox, and the rotating shaft of the steam turbine is detachably coupled to the rotating shaft of the air compressor through the clutch.

[0182] The rotating shaft of the electric motor is coupled to the rotating shaft of the air compressor through the gearbox. The gearbox enables the air compressor to be always coupled to the electric motor and can convert the rotational speed of the electric motor shaft into a suitable rotational speed of the air compressor shaft.

[0183] The input shaft of the clutch is connected to the steam turbine, and the output shaft is connected to the air compressor. The clutch performs engagement and disengagement actions by comparing the rotational speed of the input shaft with that of the output shaft. When the rotational speed of the clutch input shaft is greater than that of the output shaft, i.e., when the rotational speed of the rotating shaft of the steam turbine is greater than that of the rotating shaft of the air compressor, the clutch automatically engages, and the steam turbine can be put into operation to drive the air compressor. When the rotational speed of the clutch input shaft is less than that of the output shaft, i.e., when the rotational speed of the rotating shaft of the steam turbine is less than that of the rotating shaft of the air compressor, the clutch automatically disengages, and the steam turbine can be cut out.

[0184] Figure 5 The schematic diagram of an air compressor unit including an air compressor and a drive source is shown. Among them, the rotating shaft of the electric motor 2 is coupled to the rotating shaft of the air compressor 1 through the gearbox 4, and the rotating shaft of the steam turbine 3 is detachably coupled to the rotating shaft of the air compressor 1 through the clutch 5.

[0185] Figure 6The figure shows a schematic connection diagram of a steam-electric dual-drive air compressor unit and a reactor in an embodiment. In the figure, the components corresponding to each numerical label are: air compressor 1, electric motor 2, steam turbine 3, gearbox 4, clutch 5, air filter 6, vent silencer 7, anti-surge valve 8, check valve 9, flowmeter 10, air supply valve 11, mixer 12, maleic anhydride reactor 13, molten salt heat exchanger 14, steam drum 15, incinerator 16. Boiler feed water enters the molten salt heat exchanger, and after being heated, it passes through the steam drum. The generated steam is further heated in the incinerator and used to drive the steam turbine. The steam turbine can be disengaged from the air compressor through the clutch.

[0186] By setting a clutch between the steam turbine and the air compressor and a gearbox between the electric motor and the air compressor, the present invention can achieve a flexible combination of electric motor drive and steam turbine drive. Combined with the specific operations in the operation method, the steam turbine and the electric motor can be flexibly combined to drive the air compressor according to different working conditions, thereby keeping the air supply to the maleic anhydride reactor stable.

[0187] In an embodiment, the power of the electric motor is not sufficient to drive the air compressor load when all maleic anhydride reactors are operating.

[0188] In current maleic anhydride plants, one air compressor supplies air to one reactor. For such an air compressor, the steam turbine in the steam-electric dual-drive is a beneficial supplement to the electric motor. That is, the power of the electric motor can drive the air compressor alone to the maximum operating load. When the reactor is operating, the steam turbine operates, so that the electric motor can operate at a lower power to save electrical energy.

[0189] However, the inventors found that in a maleic anhydride preparation system containing multiple reactors, each maleic anhydride reactor requires a relatively high air supply pressure, which requires a high total power of the air compressor. Using a single large-power electric motor has high requirements for equipment. However, the maleic anhydride preparation system can generate a relatively large amount of available waste heat. Therefore, in an embodiment, the power of the electric motor of the present invention is selected such that it cannot drive the air compressor alone to the maximum operating load, but can only drive the air compressor to operate at a partial load. In other words, when the maleic anhydride preparation system is operating normally, the steam turbine and the electric motor are required to jointly drive the air compressor. This can avoid using a single large-power electric motor and make full use of the waste heat in the plant to save energy. However, it is necessary to find an appropriate operation method at the same time to ensure the safe operation of the air supply device under various working conditions. For such a system, the online input and cut-out operations of the steam turbine are particularly necessary.

[0190] The air supply device for a maleic anhydride preparation system containing multiple reactors of the present invention can realize a practical maleic anhydride preparation system.

[0191] In one embodiment, the present invention provides a maleic anhydride preparation system comprising multiple reactors, wherein the maleic anhydride preparation system comprising multiple reactors comprises:

[0192] a plurality of maleic anhydride reactors, and

[0193] the above-mentioned air supply device, the outlet pipe of the air compressor of the air supply device is in fluid communication with the reactor inlet pipes of the plurality of maleic anhydride reactors, such that the plurality of maleic anhydride reactors are connected in parallel downstream of the air compressor.

[0194] As described above, such a maleic anhydride preparation system can enable one air compressor to drive multiple maleic anhydride reactors and can appropriately cope with abnormal conditions such as reactor trip and overpressure.

[0195] In one embodiment, the air supply device is the above-mentioned air supply device comprising an exhaust gas recovery pipe, and

[0196] the maleic anhydride preparation system comprising multiple reactors includes an absorption tower downstream of the maleic anhydride reactor,

[0197] wherein, the inlet end of the exhaust gas recovery pipe is in fluid communication with the top of the absorption tower.

[0198] The absorption tower downstream of the maleic anhydride reactor is well-known in the field of maleic anhydride preparation. The gas at the top of the absorption tower is enriched with unreacted raw materials and has few harmful impurities, and is suitable for being introduced into the air compressor as exhaust gas for reuse. Therefore, it is preferred that the inlet end of the exhaust gas recovery pipe is in fluid communication with the top of the absorption tower.

[0199] In one embodiment, the air supply device is the air supply device having the above-mentioned steam turbine, and

[0200] the maleic anhydride preparation system comprising multiple reactors includes a steam generation device,

[0201] wherein, the steam generation device is configured to supply steam to the steam turbine.

[0202] When the maleic anhydride preparation system of the present invention includes a steam generation device and can drive a steam turbine, the thermal energy can be fully utilized to be converted into the driving force of the air compressor. The steam generation device can be a device that utilizes the heat release of the reactor, a device that utilizes the heat release of the waste gas incinerator, an additional separate steam generation device, etc. The steam generation device can be, for example, a steam drum.

[0203] The inventor of the present invention proposed a related operation method while inventing the maleic anhydride preparation system comprising multiple reactors, which can appropriately cope with various abnormal reactor conditions when one air compressor drives multiple maleic anhydride reactors.

[0204] The maleic anhydride preparation system including multiple reactors according to the present invention includes a feedforward performance controller and a feedforward countercurrent protection controller, which can achieve emergency trip control and safe operation actions under overpressure conditions.

[0205] In one embodiment, the present invention provides an operation method for the above-mentioned maleic anhydride preparation system including multiple reactors, wherein the operation method includes:

[0206] When the multiple maleic anhydride reactors are operating, the stator vane controller feedback-controls the stator vane angle based on the target exhaust pressure and / or flow rate and according to the measured value, and the surge valve controller feedback-controls the opening of the surge valve based on the surge line of the air compressor and according to the measured value;

[0207] When at least one of the multiple maleic anhydride reactors trips, after receiving the trip signal of the maleic anhydride reactor, the feedforward performance controller starts the emergency trip control and ends the emergency trip control after the surge valve is closed, wherein the emergency trip control includes:

[0208] i) According to the number of remaining operating maleic anhydride reactors, quickly open the surge valve to a first opening degree, and change the target exhaust pressure and / or flow rate of the stator vane controller;

[0209] ii) Reduce the surge valve from the first opening degree, and then wait for the stator vane angle to stabilize;

[0210] iii) Repeat operation ii) until the surge valve is closed.

[0211] And the operation method further includes:

[0212] When at least one of the multiple maleic anhydride reactors is overpressured, after receiving the overpressure signal of the maleic anhydride reactor, the feedforward countercurrent protection controller starts to detect countercurrent, detects whether countercurrent occurs, and performs the following actions according to the situation:

[0213] When no countercurrent occurs, keep detecting; and

[0214] When countercurrent occurs, perform the safe operation action, and detect again whether countercurrent occurs. If countercurrent still occurs, stop the air compressor.

[0215] As described above, in operation i), the first opening of the anti-surge valve for quick opening in the emergency control of the vehicle tripping is calculated according to the number of the remaining maleic anhydride reactors in operation. According to the required air supply volume and the performance curve of the anti-surge valve, the appropriate first opening of the anti-surge valve is calculated. Under this opening of the anti-surge valve, the venting from the anti-surge valve is not gradually opened, nor is it fully opened, but is controlled to open quickly. By venting the anti-surge valve, the gas flow rate is adapted to the needs of the remaining maleic anhydride reactors, so that the air flow rate flowing to the remaining reactors does not fluctuate substantially.

[0216] At the same time, the jump emergency control also calculates the required target exhaust pressure and / or flow rate according to the number of remaining maleic anhydride reactors in operation, and changes the target exhaust pressure and / or flow rate of the stationary blade controller accordingly.

[0217] On this basis, operations ii) and iii) can be performed to gradually reduce the anti-surge valve opening until it is closed by feedforward, and the stationary vane controller can always stabilize the exhaust pressure and flow rate at the required level of the remaining maleic anhydride reactor through feedback control. In this way, the air supply is basically stable after the reactor trips, so that the remaining reactors can operate without interlock tripping.

[0218] Furthermore, as has been stated, the operating method using the feedforward backflow protection controller can avoid premature shutdown of the air compressor and interlock tripping of the reactor as much as possible when the reactor is over-pressurized.

[0219] Preferably, in operation ii), the anti-surge valve is reduced from the first opening by 2%-5%. As described above, this can achieve a good balance between closing the anti-surge valve as soon as possible and waiting for the stationary vanes to be adjusted in time.

[0220] In one embodiment, in operation i), the anti-surge valve is opened quickly and the stationary vane is closed quickly to the first angle. According to the number of different tripped reactors, an appropriate initial first opening and first angle can be set, and the two cooperate to ensure the stability of the gas supply pressure and flow rate. Such efficiency is higher than that of controlling the stationary vane angle only by feedback.

[0221] In one embodiment, the operation method of the present invention can not only handle abnormal operating conditions of the reactor such as jumping or overpressure, but also handle some abnormal operating conditions of the air supply device itself. In particular, for the aforementioned air compressor that is powered by both steam and electricity and the electric motor is not sufficient to drive multiple maleic anhydride displays alone, the operation method of the present invention proposes special operations to deal with abnormal operating conditions.

[0222] An abnormal operating condition of the air compressor is that the air compressor itself unloads. In some emergencies, the air compressor will unload. At this time, the air compressor controller sends a safety operation action control command to the air compressor. The safety operation action here is the same as the foregoing. In other words, after receiving this command, the air compressor closes the static blades to the minimum, quickly opens the anti-surge valve, and at the same time allows the check valve to quickly close. The quick opening of the anti-surge valve can be achieved by de-energizing the solenoid valve of the anti-surge valve. The quick assisted closing of the check valve can be achieved by de-energizing the solenoid valve of the check valve.

[0223] By performing the above actions, the intake air volume of the air compressor becomes smaller, the exhaust gas is discharged through the anti-surge valve, and the check valve becomes effective to prevent gas backflow, and the air compressor is in a safe operating state.

[0224] When the air compressor in the state of steam-electric double drive enters the safe operating state, the control system needs to send an interlock shutdown command to the steam turbine. At this time, the steam turbine will quickly close the quick shutdown valve and cut off the steam inlet by de-energizing the shutdown solenoid valve.

[0225] That is, in one embodiment, the maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors and a steam generation device as described above, and the power of the motor is not sufficient to drive the load of the air compressor when all maleic anhydride reactors are operating, and the operation method further includes:

[0226] a) When the air compressor unloads, perform the safety operation action and interlock the steam turbine to shut down.

[0227] Figure 7 Shows the safety operation strategy of an embodiment of the method of the present invention when the air compressor unloads. After issuing the safety operation instruction, the check valve quickly closes, the anti-surge valve quickly opens, the static blades are closed to the minimum angle and locked. The quick assisted closing of the check valve and the quick opening of the anti-surge valve can both be achieved by de-energizing the respective solenoid valves. At the same time, the safety operation instruction sets the control system memory. In addition, the safety operation instruction is sent to the interlock shutdown program for subsequent judgment and operation.

[0228] Figure 8 Gives the judgment logic of an interlock shutdown program. After receiving the air compressor safety operation signal, first judge whether the system is in the steam-electric double drive state. If the steam turbine is not operating, no instruction is issued to the steam turbine. If the steam turbine is in the operating state, the system issues an interlock shutdown instruction to the steam turbine and alarms. The interlock shutdown instruction to the steam turbine can de-energize the shutdown solenoid valve of the steam turbine, and the quick shutdown valve of the steam turbine quickly closes to cut off the steam inlet.

[0229] In some cases, the steam turbine will trip due to some emergencies in the maleic anhydride preparation system. For example, a failure in one of the multiple maleic anhydride reactors may cause the steam turbine to trip. At this time, since the motor is not selected according to the ability to drive the air compressor to the maximum load alone during the design and selection, when the steam turbine suddenly trips, if the operating condition of the air compressor is at a relatively large load, the normal operation of the air compressor cannot be maintained only by the output power of the motor. Therefore, if no protection is provided in the internal program after the steam turbine trips, it is possible that the motor current exceeds the rated value, which will damage the motor. Moreover, the motor will trigger a protection action for the current exceeding the rated value, which may directly cause a trip. Such a shutdown method is not desired by the user.

[0230] Therefore, the operation method further includes:

[0231] b) When the steam turbine trips, detect the static blade angle at the time of the steam turbine trip; if the static blade angle corresponding to the air compressor load can be driven by the motor alone, the motor continues to drive the air compressor to operate; if the load corresponding to the static blade angle cannot be driven by the motor alone, the air compressor performs the safe operation action, and after performing the safe operation action, detect the anti-surge valve opening and the motor current; if the anti-surge valve is not fully open and the motor current exceeds the rated value, stop the air compressor.

[0232] That is, in order to meet the operating state of the air compressor unit of this type of steam-electric double-drive unit, further judgment needs to be combined with the static blade angle of the unit. First, detect the static blade angle value of the air compressor at the moment when the steam turbine trips. If the static blade angle of the air compressor is less than a certain limit value (the specific limit value is confirmed according to the allowable load of the main motor corresponding to the load at different static blade angles of the air compressor) at this time, the air compressor unit continues to operate driven by the motor. If the static blade angle of the air compressor is greater than a certain limit value at this time, the air compressor unit performs the safe operation action, that is, the air compressor unloads and vents, and at the same time the static blade closes to the minimum to reduce the load of the air compressor to the minimum. After a delay of 3 seconds, after 3 seconds, detect the opening of the anti-surge valve and the real-time current of the main motor. If the anti-surge valve is not fully open and the main motor exceeds the rated current, the entire unit performs the shutdown action.

[0233] In other words, it is necessary to determine whether a single motor can drive the air compressor after the turbine is shut down. If it is possible to drive, continue to run. If it cannot be dragged, perform the aforementioned safe operation action. After the safe operation action, the stationary blade angle has been closed to the minimum and the anti-surge valve has been opened, which correspondingly reduces the load of the air compressor to the minimum. Give the safe operation action a running time of 3 seconds, and then check the opening of the anti-surge valve and the motor current. If the opening of the anti-surge valve is not fully open, it means that the air compressor is still running at the working point on the right side of the surge line. At this time, if the motor current is overloaded, it means that the air compressor driven only by the motor is still unable to maintain the system in a stable working state, so the air compressor has to be shut down.

[0234] Through the above-mentioned step-by-step judgment method, the possibility of the air compressor continuing to operate is maintained as much as possible, and unless the air compressor is completely unable to match the load state, the air compressor will not be shut down, thereby reducing the probability of the air compressor shutting down and providing convenience for users.

[0235] Figure 9 The figure shows the operation mode of the interlock shutdown in one embodiment of the present invention. The serial numbers in the figure represent the relevant valves or sensors, etc.

[0236] In addition, when the air compressor itself sends an interlocking signal or the motor experiences a load shedding condition, the steam turbine will perform an interlocking shutdown action.

[0237] When the air compressor or motor has an interlock signal, the entire unit must be interlocked and shut down. Because when the air compressor itself has a fault, the unit is prohibited from continuing to operate. When the motor has a fault, because the steam turbine has the risk of overspeed, and the motor also needs to be shut down for inspection, the steam turbine is not allowed to run alone to drag the air compressor and the motor tow net.

[0238] That is, the operating method of the present invention also includes:

[0239] c) When an interlocking signal appears in the air compressor or the electric motor, the steam turbine is shut down.

[0240] Figure 10 The figure shows the action mode of the steam turbine interlock shutdown in one embodiment of the present invention. The serial numbers in the figure represent the relevant valves or sensors, etc. It can be seen that when the air compressor or the motor has an interlock signal, the steam turbine interlock shutdown can be caused.

[0241] In the operation method of the present invention, by controlling the abnormal operating conditions of the air compressor unit as described above, the entire maleic anhydride preparation system is prevented from stopping working as much as possible while maintaining system safety.

[0242] In actual operation, the power and load conditions of the air compressor are constantly changing. In some cases, the steam provided by the maleic anhydride plant may be unstable. For example, problems may occur in the steam system. In addition, the steam turbine may malfunction and cannot operate normally. If the air supply to the maleic anhydride reactor by the air compressor fluctuates greatly due to the abnormal operation of the steam turbine, the reaction result of maleic anhydride, which is highly sensitive to the stability of the air supply, will deteriorate. Therefore, during the operation of the air compressor, the steam turbine needs to be able to arbitrarily perform on-line input and cut-out operations to prevent the steam turbine failure from affecting the stable air supply to the maleic anhydride reactor.

[0243] In one embodiment, during the operation of the air compressor, due to the instability of the steam conditions, the operation of the steam turbine requires on-line commissioning and cut-out operations.

[0244] In the air supply device of the present invention, in order not to affect the normal operation of the motor-driven unit when problems occur in the steam system or the steam turbine cannot operate normally, a clutch coupling the steam turbine and the air compressor is used.

[0245] As described above, the clutch can perform meshing and disengaging actions by comparing the rotational speed of the input shaft with that of the output shaft. However, the above situation is only an ideal state. In actual operation, it is necessary to ensure that the action is completed and the air compressor is subsequently in the correct working state. For this purpose, in one embodiment, the operation method of the present invention performs special detection operations to achieve input and cut-out.

[0246] During the cut-out operation, the holding time of the engagement switch of the clutch is detected and combined with the change in the motor power to determine whether the steam turbine has been successfully cut out. If the holding time of the engagement switch is within the limit and the motor power increases significantly, it indicates that the cut-out is successful. If the holding time of the engagement switch exceeds the limit or the motor power does not increase significantly, it indicates that the cut-out is not successful. If the cut-out is successful, the steam turbine enters the shutdown operation. The above judgment and control can be automatically executed through a set program.

[0247] During the input operation, the holding time of the engagement switch of the clutch is detected and combined with the change in the motor power to determine whether the steam turbine has been successfully input. If the holding time of the engagement switch is within the limit and the motor power decreases significantly, it indicates that the input is successful. If the holding time of the engagement switch exceeds the limit or the motor power does not increase significantly, it indicates that the input is not successful. If the input is successful, the steam turbine changes from the rotational speed control mode before input to the load loading control mode. The above judgment and control can be automatically executed through a set program.

[0248] Correspondingly, the operation method of the present invention includes:

[0249] Reduce the speed of the steam turbine by using the speed control mode, and determine whether the cut-out is successful by detecting the holding time of the clutch engagement switch and the motor power. If the cut-out is successful, the steam turbine is shut down; and

[0250] Increase the speed of the steam turbine by using the speed control mode, and determine whether the engagement is successful by detecting the holding time of the clutch engagement switch and the motor power. If the engagement is successful, change the speed control mode to the load loading control mode.

[0251] The above judgment can be automatically executed by the control program.

[0252] In other words, in one embodiment, the online engagement and cut-out operations of the steam turbine include:

[0253] 1. When the steam-electric dual-drive unit is operating normally, if a fault occurs in the steam turbine or the steam system and the steam turbine needs to be shut down, but the unit needs to operate normally, the speed of the steam turbine can be reduced to be lower than the speed of the air compressor. At this time, the rotational speed of the input shaft of the clutch is lower than that of the output shaft, and the clutch automatically disengages. The steam turbine can then be cut out from the unit's operating shaft system and can be stopped separately, while the unit operates solely under electric drive.

[0254] 2. Before the steam turbine is cut out, the speed of the steam turbine is reduced. Based on the disengagement holding time of the clutch engagement switch and the change in the main motor power, the control program automatically determines whether the steam turbine has been successfully cut out. After automatically determining that the steam turbine has been successfully disengaged, the steam turbine automatically enters the shutdown operation.

[0255] 3. When the motor drives the air compressor unit to operate normally, if it is necessary to engage the steam turbine, the speed of the steam turbine can be increased to be higher than the speed of the air compressor. At this time, the rotational speed of the input shaft of the clutch is greater than that of the output shaft, and the clutch automatically engages. The steam turbine can then be engaged into the unit's shaft system, and the unit operates in steam-electric dual-drive mode.

[0256] 4. For the engagement of the steam turbine, mainly based on the engagement holding time of the clutch engagement switch and the change in the main motor power, the control program automatically determines whether the steam turbine has been successfully engaged. At the same time, after determining that the steam turbine has completed the online engagement, the control mode of the steam turbine changes from the speed control mode before engagement to the load loading control mode after engagement.

[0257] By setting the clutch and providing the above operation method, when there is a problem with the maleic anhydride steam system or the steam turbine cannot operate normally in the air supply device of the present invention, it does not affect the normal operation of the motor-driven unit, does not cause a great impact on the user's process device or cause the reactor to shut down, and improves the startup rate.

[0258] The inventors also found that due to differences in power supply modes in different maleic anhydride factories, the specialized air supply device needs to be further specialized according to the specific conditions of different maleic anhydride factories. This results in an increase in the cost of the air compressor. Moreover, when the power supply mode of a maleic anhydride factory changes, for example, due to industrial upgrading or transformation, it may be necessary to replace the drive components of the air supply device, causing cost waste.

[0259] Therefore, in order to achieve a universal air supply device applicable to maleic anhydride production lines with different power supply modes, it is necessary to improve the structure and operation strategy of the air compressor.

[0260] Specifically, in some maleic anhydride factories, steam power can be continuously provided, while in other maleic anhydride factories, steam power can only be provided after the maleic anhydride reactor starts running. At startup, whether steam can be provided for the steam turbine driving the air compressor will result in different startup methods for the air compressor.

[0261] The air supply device of the present invention can be configured to start both with and without startup steam. As described above, the clutch is arranged between the rotating shaft of the air compressor and the rotating shaft of the steam turbine. In the case of having startup steam, the clutch is engaged and locked, the rotating shafts of the air compressor and the steam turbine are coaxial, and are coupled to the electric motor through a gearbox.

[0262] Correspondingly, the operation method of the present invention includes starting the air compressor in the following manner:

[0263] When there is startup steam, use the startup steam to drive the steam turbine, driving the air compressor and the electric motor to increase speed together, where the steam turbine is in a speed control mode;

[0264] After the rotational speed of the air compressor reaches the normal rotational speed, the electric motor is connected to the grid, and the mode of the steam turbine changes to a load control mode.

[0265] That is, use the startup steam to drive the steam turbine. The steam turbine starts first. The rotational speed of the input end of the clutch is higher than that of the output end, and the clutch is in an engaged state. The steam turbine drives the air compressor and the electric motor to increase speed together through the clutch. The steam turbine is set to the speed control mode. After the main motor of the unit increases speed to near the normal rotational speed (for example, more than 90% of the rated rotational speed), the motor is switched on and connected to the grid. The control of the steam turbine is switched from the speed control mode to the load control mode, and the steam turbine gradually increases the load according to the unit load and steam conditions to reach the normal operating condition. After that, after the maleic anhydride preparation device generates self-produced steam, introduce it into the steam turbine. The self-produced steam can be used as supplementary steam or main steam.

[0266] The start-up steam source can be the start-up steam initially designed by the user, the waste gas incinerator of the maleic anhydride plant is designed with a start-up mode, or there are other steam sources in the user's plant area, which can provide a certain amount of start-up steam to meet the flow requirements for the start-up of the steam turbine. It should be noted that the start-up steam is responsible for starting up and is not required to be provided throughout the maleic anhydride preparation process. After successful start-up, additional driving steam can be obtained from the maleic anhydride preparation.

[0267] In this start-up mode, after the steam turbine drives the unit to increase the speed, the motor is then started. The main motor does not require auxiliary starting equipment and performs grid connection operation at a speed close to the rated speed of the motor, with little impact on the user's power grid.

[0268] When the initial design of the maleic anhydride user device has no start-up steam, the incinerator design has no start-up mode, or there are no other steam sources in the user's plant area, and the conditions for starting the steam turbine are not met, it belongs to the situation of no start-up steam.

[0269] In the case of no start-up steam, the clutch is disengaged, the rotating shaft of the air compressor is disengaged from the rotating shaft of the steam turbine and coupled to the electric motor through a gearbox.

[0270] Correspondingly, the operation method of the present invention includes starting the air compressor in the following manner:

[0271] When there is no start-up steam, with the steam turbine disengaged from the air compressor, the electric motor is used to drive the electric motor to drive the air compressor to operate and prepare maleic anhydride;

[0272] Self-produced steam is obtained from the preparation of the maleic anhydride to drive the steam turbine;

[0273] Engage the clutch so that the steam turbine is connected to the air compressor.

[0274] That is, when there is no start-up steam in the device, the steam turbine cannot operate before the unit starts. At this time, the electric motor is first used to drive the air compressor to operate. Due to the existence of the clutch, the rotational speed of the input end of the clutch is lower than that of the output end, and the steam turbine is in an automatically disengaged state. After the electric motor drives the air compressor to reach the rated speed, the load is gradually increased according to the device requirements, and the maleic anhydride reactor starts to operate and generate self-produced steam. After the system's self-produced steam conditions are met for use, self-produced steam can be introduced into the steam turbine. At this time, the steam turbine can be set to the speed control mode to increase the speed. When the rotational speed of the steam turbine rises to the specified value and exceeds the rotational speed of the air compressor side driven by the motor, the clutch automatically engages due to the higher rotational speed of the input end than the output end. The engagement of the clutch enables the electric motor and the steam engine to jointly drive the air compressor unit to operate. At this time, the steam turbine can be switched from the speed control mode to the load control mode and jointly drive the air compressor unit to operate with the motor.

[0275] By setting the clutch and adopting the starting method of the present invention, starting under different start-up steam conditions with the same air supply device is achieved. In this way, in a maleic anhydride plant where separate start-up steam cannot yet be provided or the maleic anhydride reactor has not yet started operating, an air supply device with both steam and electricity drive can also be set up and started safely.

[0276] The inventors found that the following components in the maleic anhydride preparation system are particularly suitable for providing stable and sufficient self-generated steam drive for the steam turbine of the air compressor during production.

[0277] In one embodiment, the self-generated steam is generated by utilizing the molten salt waste heat of the maleic anhydride reactor. As Figure 6 shown, boiler feed water can be passed through the molten salt heat exchanger 14 to utilize the molten salt waste heat to heat the water and generate steam in the steam drum. The molten salt of the maleic anhydride reactor can provide a large amount of heat that can convert water into steam. Utilizing the waste heat recovered from the molten salt used in the maleic anhydride reactor by steam to drive the steam turbine can achieve significant energy savings.

[0278] In one embodiment, the self-generated steam is generated by utilizing the waste gas incinerator of the maleic anhydride preparation system. The waste gas incinerator of the maleic anhydride reactor can provide a large amount of energy carried by steam, and utilizing it to drive the steam turbine can achieve significant energy savings.

[0279] In a preferred embodiment, the self-generated steam is generated by utilizing the molten salt waste heat of the maleic anhydride reactor, and the self-generated steam is further heated by utilizing the waste gas incinerator of the maleic anhydride preparation system. As Figure 6 shown, the steam generated by utilizing the molten salt waste heat can further pass through the waste gas incinerator, and the heat generated by the incineration tail gas is used to heat and boost the pressure of the steam. This can make full use of the heat in the molten salt that dissipates heat for the reactor, and at the same time make full use of the combustion heat contained in the waste gas, so as to provide stronger drive for the steam turbine.

[0280] The present invention will be described in more detail below through examples.

[0281] Example 1:

[0282] Production is carried out using a maleic anhydride preparation system that supplies air to three parallel maleic anhydride reactors with one air compressor. The three maleic anhydride reactors are respectively called Reactor No. 1, Reactor No. 2, and Reactor No. 3. The reaction raw material is n-butane.

[0283] A stator blade controller is set up, with a PID algorithm embedded. Its output terminal OUT is connected to the stator blade adjustment mechanism to control the stator blade angle. Its first set value receiving terminal SV1 obtains the target exhaust pressure set value when the reactor is operating normally from the control system. Its current value receiving terminal PV receives the real-time exhaust pressure measurement value from the exhaust pressure sensor.

[0284] A surge prevention controller is set, with a PID algorithm embedded. Its output terminal OUT is connected to the surge prevention valve to control the opening degree of the surge prevention valve. Its first set value receiving terminal SV1 obtains the surge prevention map from the control system, including the surge line and the surge prevention line. Its current value receiving terminal PV receives the real-time operating point parameters from the exhaust pressure sensor and the throat differential pressure sensor.

[0285] A feedforward performance controller is set. The three signal input terminals of the feedforward performance controller receive the operating signals from Reactors 1 - 3. Its second output terminal OUT1 is connected to the second set value receiving terminal SEL SV2 of the surge prevention valve controller. Its first output terminal OUT2 is connected to the second set value receiving terminal SEL SV2 of the stator blade controller.

[0286] As Figure 2 shown, the reactor, the surge prevention controller, the surge prevention valve, the stator blade controller, the stator blade, and the feedforward performance controller are connected together.

[0287] First, make Reactors 1 - 3 operate in a normal state. At this time, the feedforward performance controller does not work. The stator blade controller performs feedback control on the stator blade angle based on the target exhaust pressure set value obtained by SV1 and the measured value obtained by PV. The surge prevention valve controller performs feedback control on the opening degree of the surge prevention valve based on the surge prevention line obtained by SV1 and the operating point parameters obtained by PV.

[0288] To simulate the tripping of the reactor, stop Reactor 1, and immediately close the air inlet flow regulating valve leading to Reactor 1. At the same time, send a tripping signal to the feedforward performance controller.

[0289] The tripping signal of Reactor 1 causes the feedforward performance controller to start and begin the tripping emergency control. According to the fact that there is 1 tripping signal, it is expected that the air supply flow will become two-thirds of the original, and the pressure remains unchanged. For this reason, the feedforward performance controller sends a feedforward signal to SEL SV2 of the surge prevention valve, quickly opening the opening degree of the surge prevention valve to the first opening degree (not fully open) to discharge the gas. At this first opening degree, under the current stator blade angle and the operating state of the air compressor, the exhaust flow of the air leading to the downstream is two-thirds of the previous value, and the pressure remains unchanged. This operating point is located below the right of the surge prevention line, which can avoid surge occurrence.

[0290] At the same time, the feedforward performance controller sends this target exhaust pressure and / or flow to SEL SV2 of the stator blade controller. The stator blade controller then performs feedback control based on the changed target exhaust pressure and / or flow. Since the flow and pressure are approximately the target values at this time, the stator blade controller only performs fine adjustment on the stator blade angle according to the feedback of the measured value.

[0291] Subsequently, the feedforward performance controller reduces the opening of the anti-surge valve by 2%. At this time, both the exhaust pressure and flow rate increase. The stator blade controller will receive the increased pressure / flow rate measurement values and perform feedback control on the stator blades, reducing the stator blade angle so that the exhaust pressure and flow rate drop back to the target values.

[0292] After the exhaust pressure and flow rate are stabilized around the target values (i.e., after the stator blade angle no longer continues to decrease), the feedforward performance controller reduces the opening of the anti-surge valve by 2% again. Repeat the above process until the anti-surge valve is fully closed.

[0293] After the anti-surge valve is fully closed, the feedforward performance controller is turned off, ending the emergency shutdown control. The anti-surge valve controller takes over the feedback control of the anti-surge valve.

[0294] During this process, monitor the air inlet pressure and flow rate in Reactors 2 and 3, and check the working status of the reactors. It is found that the fluctuations of the air inlet pressure and flow rate in Reactors 2 and 3 are not significant, the reactors operate stably, the product yield and quality are stable, and they are not affected by the shutdown of Reactor 1.

[0295] Example 2

[0296] The test is carried out in the same manner as in Example 1, except that simulated shutdowns are performed on Reactors 1 and 2 among the three reactors.

[0297] Accordingly, the feedforward performance controller quickly opens the anti-surge valve, and the changed target exhaust flow rate sent to the stator blade controller is one-third of the previous value, with the pressure remaining unchanged. Due to the larger opening, during the feedforward control, the reduction in the opening of the anti-surge valve each time is increased to 5%.

[0298] During this process, monitor the air inlet pressure and flow rate in Reactor 3, and check the working status of the reactor. It is found that the fluctuations of the air inlet pressure and flow rate in Reactor 3 are not significant. The reactor operates stably, the product yield and quality are stable, and it is not affected by the shutdowns of Reactors 1 and 2.

[0299] Comparative Example 1:

[0300] Except for not setting the feedforward controller, air is supplied to the maleic anhydride reactor using the same device as in Example 1.

[0301] After simulating the shutdown of Reactor 1, the measured exhaust pressure quickly rises and triggers the feedback control of the anti-surge controller, and the anti-surge valve is fully opened. Shortly after the anti-surge valve is fully opened, Reactors 2 and 3 trip due to insufficient air supply and stop operating.

[0302] Comparative Example 2:

[0303] Except for not setting up the feedforward controller, air is supplied to the maleic anhydride reactor with the same device as in Example 2.

[0304] After simulating the trip of Reactors No. 1 and No. 2, the measured exhaust pressure rose rapidly, triggering the feedback control of the anti-surge controller, and the anti-surge valve was fully opened. After the anti-surge valve was fully opened, Reactor No. 3 quickly tripped due to insufficient air supply and stopped operating.

[0305] It can be seen that when one or several of the multiple maleic anhydride reactors of the device and method of the present invention suddenly shut down, while ensuring that the air compressor will not be damaged due to surge, it also ensures that the remaining reactors will not malfunction or trip due to a sudden reduction in air supply.

[0306] Example 3

[0307] A feedforward countercurrent protection controller is set up in the maleic anhydride preparation system of Example 1.

[0308] The condition of overpressure in Reactor No. 1 was simulated and actually tested according to the operation method of the present invention.

[0309] The results show that the air compressor enters the safe operation mode, and Reactors No. 2 and No. 3 do not trip due to the shutdown of the air compressor.

[0310] Comparative Example 3

[0311] Except for not setting up the feedforward controller, air is supplied to the maleic anhydride reactor with the same device as in Example 3, and the condition of overpressure in Reactor No. 1 was simulated and actually tested.

[0312] The results show that the air compressor quickly shuts down due to overpressure, causing Reactors No. 2 and No. 3 to trip.

[0313] Example 4

[0314] Production is carried out using a maleic anhydride preparation system in which one air compressor supplies air to three parallel maleic anhydride reactors simultaneously. The reaction raw material is n-butane.

[0315] The tail gas recovery pipeline connected to the top of the absorption tower downstream of the maleic anhydride reactor is in fluid communication with the intake pipeline of the air compressor. The air supply device also includes an anti-surge valve bleed-back pipeline, which fluidly connects the exhaust port of the anti-surge valve to the intake pipeline of the air compressor. The air compressor uses a combined seal of a carbon ring seal and a Labyrinth seal as the shaft end seal structure. The Labyrinth seal is located on the inner side, and the carbon ring seal is located on the outer side. The carbon ring is provided with an inflation port.

[0316] The maleic anhydride preparation system is operated, and the air in the air compressor environment is detected during the trip test as in Examples 1 and 2, and no n-butane is found.

[0317] After running for 1000 hours, the surface of the air compressor blades was inspected, and corrosion was observed.

[0318] Example 5

[0319] The test was carried out in the same manner as in Example 4, except that the surfaces of the first three stages of the air compressor blades were acid-resistant treated.

[0320] After running for 1000 hours, the surface of the air compressor blades was inspected, and no corrosion was observed.

[0321] Example 6

[0322] Production was carried out using a maleic anhydride preparation system in which one air compressor of the present invention supplies air to three parallel maleic anhydride reactors simultaneously. The reaction raw material is n-butane. The system includes a steam drum for recovering heat from the maleic anhydride reactor, which supplies steam to a steam turbine.

[0323] The air compressor is configured with both steam and electricity drive. The rotating shaft of the air compressor is coupled to an electric motor through a gearbox and coupled to a steam turbine through a clutch. The power of the electric motor is not sufficient to drive the three maleic anhydride reactors.

[0324] According to the operation method of the present invention, simulations and actual tests were carried out on working conditions such as the air compressor shedding load, the steam turbine interlocking and shutting down, and the electric motor shutting down. The test results show that all components of the air compressor unit are safe under various working conditions and will not damage the maleic anhydride reactor. In addition, if the above abnormal working conditions can be eliminated in time, the maleic anhydride preparation system can operate without shutting down.

[0325] Example 7

[0326] Production was carried out using a maleic anhydride preparation system in which one air compressor of the present invention supplies air to three parallel maleic anhydride reactors simultaneously. The reaction raw material is n-butane.

[0327] Tests were carried out on starting the air compressor with / without starting steam and on putting into / cutting out the steam turbine during the operation of the preparation system according to the operation method of the present invention. The test results show that the air compressor unit can be started and operated normally.

[0328] In addition, the above experiments were also carried out on the system for producing maleic anhydride by the benzene method, and similar experimental results were obtained.

[0329] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, and all should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An air supply device for a maleic anhydride preparation system including multiple reactors, characterized in that, The air supply device includes: An axial flow air compressor, which is provided with stator blades, a surge valve and a check valve; A stator blade controller, which feedback-controls the stator blade angle based on the target exhaust pressure and / or flow rate; A surge valve controller, which feedback-controls the opening degree of the surge valve based on the surge line of the air compressor; A feedforward performance controller, which is configured to start a trip emergency control when receiving a trip signal of the maleic anhydride reactor, and end the trip emergency control after the surge valve is closed; and A feedforward reverse flow protection controller, which is configured to start detecting reverse flow when receiving an overpressure signal of the maleic anhydride reactor, and cause the air compressor to perform a safe operation action when reverse flow is detected, wherein, the trip emergency control includes: feedforward controlling the opening degree of the surge valve, and changing the target exhaust pressure and / or flow rate of the stator blade controller, The safe operation action includes: reducing the stator blade angle, increasing the opening degree of the surge valve, and assisting in closing the check valve.

2. The air supply device according to claim 1, characterized in that, The air supply device further includes: An exhaust pressure sensor; A throat differential pressure sensor; and An optional exhaust flow sensor, wherein, the stator blade controller performs its feedback control according to the measured value of the exhaust pressure sensor or the exhaust flow sensor, The surge valve controller performs its feedback control according to the measured values of the exhaust pressure sensor and the throat differential pressure sensor, The stator blade controller and the surge valve controller are controllers embedded with a PID algorithm.

3. The air supply device according to claim 1, characterized in that, The air supply device further includes: An air inlet pipeline, the inlet end of the air inlet pipeline is in fluid communication with an air source, and the outlet end is in fluid communication with the inlet pipeline of the air compressor; A tail gas recovery pipeline, the inlet end of the tail gas recovery pipeline is in fluid communication with the downstream of the maleic anhydride reactor, and the outlet end is in fluid communication with the inlet pipeline of the air compressor; and A surge valve bleed return pipeline, the inlet end of the surge valve bleed return pipeline is in fluid communication with the exhaust port of the surge valve, and the outlet end is in fluid communication with the inlet pipeline of the air compressor, and the air compressor has a shaft end seal structure.

4. The air supply device according to claim 1, characterized in that The air supply device further includes a motor, a steam turbine, a gearbox and a clutch. The rotating shaft of the motor is coupled to the rotating shaft of the air compressor through the gearbox, and the rotating shaft of the steam turbine is detachably coupled to the rotating shaft of the air compressor through the clutch.

5. A maleic anhydride preparation system comprising multiple reactors, characterized in that, The maleic anhydride preparation system including multiple reactors includes: Multiple maleic anhydride reactors, and The air supply device according to any one of claims 1-4, the outlet pipeline of the air compressor of the air supply device is in fluid communication with the reactor inlet pipelines of the multiple maleic anhydride reactors, so that the multiple maleic anhydride reactors are connected in parallel downstream of the air compressor.

6. The maleic anhydride preparation system including multiple reactors according to claim 5, wherein, The air supply device is the air supply device according to claim 3, and The maleic anhydride preparation system including multiple reactors includes an absorption tower downstream of the maleic anhydride reactor, wherein, the inlet end of the tail gas recovery pipeline is in fluid communication with the top of the absorption tower.

7. The maleic anhydride preparation system including multiple reactors according to claim 5, characterized in that, the air supply device is the air supply device according to claim 4, and the maleic anhydride preparation system including multiple reactors includes a steam generating device, wherein, the steam generating device is configured to supply steam to the steam turbine.

8. A method for operating a maleic anhydride production system comprising multiple reactors according to any one of claims 5-7, characterized in that, The operation method includes: when the multiple maleic anhydride reactors are operating, the stator vane controller feedback-controls the stator vane angle based on the target exhaust pressure and / or flow rate and according to the measured value, and the surge control valve controller feedback-controls the opening of the surge control valve based on the surge line of the air compressor and according to the measured value; when at least one of the multiple maleic anhydride reactors trips, after receiving the trip signal of the maleic anhydride reactor, the feedforward performance controller starts the trip emergency control and ends the trip emergency control after the surge control valve is closed, wherein, the trip emergency control includes: i) according to the number of remaining operating maleic anhydride reactors, quickly open the surge control valve to a first opening degree, and change the target exhaust pressure and / or flow rate of the stator vane controller; ii) reduce the surge control valve from the first opening degree, and then wait for the stator vane angle to stabilize; iii) repeat operation ii) until the surge control valve is closed, and, the operation method further includes: when at least one of the multiple maleic anhydride reactors is overpressured, after receiving the overpressure signal of the maleic anhydride reactor, the feedforward countercurrent protection controller starts to detect countercurrent, detects whether countercurrent occurs, and performs the following actions according to the situation: when countercurrent does not occur, keep detecting; and when countercurrent occurs, perform the safe operation action, and detect again whether countercurrent occurs. If countercurrent still occurs, stop the air compressor.

9. The operation method according to claim 8, characterized in that, the maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors according to claim 7, wherein the power of the motor is not sufficient to drive the air compressor load when all maleic anhydride reactors are operating; and the operation method further includes: a) when the air compressor sheds load, perform the safe operation action and interlock the steam turbine to stop; b) when the motor is operating but the steam turbine stops, detect the stator vane angle when the steam turbine stops; if the stator vane angle corresponding to the air compressor load can be driven by the motor alone, the motor continues to drive the air compressor to operate; if the stator vane angle corresponding to the air compressor load cannot be driven by the motor alone, the air compressor performs the safe operation action, and after performing the safe operation action, detect the opening of the surge control valve and the motor current; if the surge control valve is not fully open and the motor current exceeds the rated value, stop the air compressor; c) when an interlock signal appears in the air compressor or the motor, stop the steam turbine.

10. The operating method according to claim 8, characterized in that The maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors according to claim 7, and the operation method further includes: Reduce the speed of the steam turbine by adopting the speed control mode, and judge whether the cut-out is successful by detecting the holding time of the clutch engagement switch and the motor power. If the cut-out is successful, shut down the steam turbine; and Increase the speed of the steam turbine by adopting the speed control mode, and judge whether the input is successful by detecting the holding time of the clutch engagement switch and the motor power. If the input is successful, change the speed control mode to the load loading control mode.

11. The operating method according to claim 8, characterized in that, The maleic anhydride preparation system including multiple reactors is the maleic anhydride preparation system including multiple reactors according to claim 7, and The operation method further includes: When there is start-up steam, use the start-up steam to drive the steam turbine, drive the air compressor and the motor to increase speed together, where the steam turbine is in the speed control mode; After the speed of the air compressor reaches the normal speed, the motor is connected to the grid, and the steam turbine mode changes to the load control mode, and When there is no start-up steam, with the steam turbine disconnected from the air compressor, use electricity to drive the motor to drive the air compressor to operate and carry out the preparation of maleic anhydride; Obtain the steam from the preparation of maleic anhydride to drive the steam turbine; Engage the clutch so that the steam turbine is connected to the air compressor.

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