Operating method of an air supply device for a maleic anhydride preparation system with combined steam and electric drive

Abstract

The present invention provides an operation method for an air supply device driven by both steam and electricity in a maleic anhydride preparation system. The air supply device includes an air compressor, an electric motor, a steam turbine, a gearbox, and a clutch. The operation method includes: when there is start-up steam, using the start-up steam to drive the steam turbine to drive the air compressor and the electric motor to increase their speeds together, where the steam turbine is in a speed control mode; after the speed of the air compressor reaches the normal speed, the electric motor is connected to the grid for power generation, and the mode of the steam turbine changes to a load control mode; and when there is no start-up steam, with the steam turbine disengaged from the air compressor, using electricity to drive the electric motor to drive the air compressor to operate and carry out the preparation of maleic anhydride; obtaining steam from the preparation of maleic anhydride to drive the steam turbine; and engaging the clutch so that the steam turbine is connected to the air compressor. The present invention can achieve starting the air compressor in a dual mode during the preparation of maleic anhydride.

Description

Technical Field

[0001] The present invention relates to the field of maleic anhydride production, and more particularly, to an operation method of a steam-electric dual-driven air supply device for a maleic anhydride preparation system. 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, maleic anhydride was previously mainly produced by the benzene method. 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 required to pressurize 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 fluid area through which the fluid passes through the reactor is also limited, which in turn places higher requirements on the bed height of the catalyst. The industrial maleic anhydride reactor has a large aspect ratio of the catalyst bed, and the pressure drop when the reaction fluid flows 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 blowing) of the air compressor needs to be very stable while maintaining high pressure, otherwise it may cause 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] The core of the air supply device for supplying air to the maleic anhydride reactor is an air compressor. Usually, the air compressor can be driven by an electric motor or a steam turbine.

[0007] There is also a need for improvement in the air supply device used in the maleic anhydride preparation system. Summary of the Invention

[0008] In one aspect, the present invention provides an operation method for a steam-electric dual-driven air supply device for a maleic anhydride preparation system. The air supply device includes an air compressor, 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.

[0009] The operation method includes:

[0010] When there is start-up steam, use the start-up steam to drive the steam turbine, and drive the air compressor and the electric motor to increase their speeds together, where the steam turbine is in the speed control mode;

[0011] After the speed of the air compressor reaches the normal speed, the electric motor is connected to the grid for power generation, and the mode of the steam turbine changes to the load control mode.

[0012] And

[0013] When there is no start-up steam, with the steam turbine disconnected from the air compressor, use electricity to drive the electric motor to drive the air compressor to operate, and carry out the preparation of maleic anhydride;

[0014] Obtain self-generated steam from the preparation of maleic anhydride to drive the steam turbine;

[0015] Engage the clutch so that the steam turbine is connected to the air compressor.

[0016] Optionally, use the molten salt waste heat of the maleic anhydride reactor to generate the self-generated steam.

[0017] Optionally, use the waste gas incinerator of the maleic anhydride preparation system to generate the self-generated steam.

[0018] Optionally, use the molten salt waste heat of the maleic anhydride reactor to generate the self-generated steam, and use the waste gas incinerator of the maleic anhydride preparation system to further heat the self-generated steam.

[0019] Optionally, the maleic anhydride preparation system is a system including multiple reactors.

[0020] The air compressor is an axial-flow air compressor, which is provided with static blades and an anti-surge valve;

[0021] The air supply device of the air compressor further includes: a static blade controller, which controls the static blade angle based on the target exhaust pressure and / or flow rate feedback.

[0022] A surge prevention valve controller that feedback-controls the opening degree of a surge prevention valve based on the surge prevention line of the air compressor; and

[0023] A feedforward performance controller configured to initiate a trip emergency control when receiving a trip signal of a reactor and end the trip emergency control after the surge prevention valve is closed,

[0024] wherein the trip emergency control includes: feedforward controlling the opening degree of the surge prevention valve and changing the target exhaust pressure and / or flow rate of the stator vane controller,

[0025] The operation method includes:

[0026] 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 values, and the surge prevention valve controller feedback-controls the opening degree of the surge prevention valve based on the surge prevention line of the air compressor and according to the measured values;

[0027] When at least one of the multiple maleic anhydride reactors trips, after the feedforward performance controller receives the trip signal of the maleic anhydride reactor, it initiates the trip emergency control and ends the trip emergency control after the surge prevention valve is closed, wherein the trip emergency control includes:

[0028] i) According to the number of remaining operating maleic anhydride reactors, quickly open the surge prevention valve to a first opening degree and change the target exhaust pressure and / or flow rate of the stator vane controller;

[0029] ii) Reduce the surge prevention valve from the first opening degree, and then wait for the stator vane angle to stabilize;

[0030] iii) Repeat operation ii) until the surge prevention valve is closed. Description of the Drawings

[0031] Figure 1 Shows a schematic diagram of an air compressor unit including an air compressor and a drive source.

[0032] Figure 2 Shows a schematic connection diagram of a steam-electric dual-drive air compressor unit and a reactor in one embodiment.

[0033] Figure 3 Shows a typical air compressor surge prevention diagram.

[0034] Figure 4 Shows a schematic diagram of the feedforward control connection principle according to one embodiment of the present invention. Detailed Embodiments

[0035] In a maleic anhydride factory, to save energy, a steam-electricity dual-drive 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 can 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 factory, such as an exhaust gas incinerator.

[0036] The inventors found that due to differences in power supply modes in different maleic anhydride factories, the specialized air supply device still 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 the 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.

[0037] Therefore, in order to achieve a general 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.

[0038] 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.

[0039] The air supply device of the present invention can be configured to start both with and without startup steam. Thus, based on the existing maleic anhydride preparation systems with different process characteristics, the present invention proposes a dual-mode startup method for the air compressor unit, which solves the problem of starting the air compressor unit under two process conditions of having and not having startup steam for users, without the need to re-design the air compressor unit due to different steam conditions of users. According to different process characteristics, the optimal unit matching method is formulated to reduce the unit cost and greatly improve the economic benefits.

[0040] The present invention provides an operation method for an air supply device for a maleic anhydride preparation system. The air supply device includes an air compressor, 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.

[0041] The operation method includes:

[0042] When there is startup steam, use the startup steam to drive the steam turbine, and drive the air compressor and the electric motor to increase speed together, where the steam turbine is in a speed control mode.

[0043] After the rotational speed of the air compressor reaches the normal rotational speed, the motor is connected to the grid for power generation, and the steam turbine mode changes to the load control mode.

[0044] and

[0045] When there is no start-up steam, with the steam turbine disconnected from the air compressor, electric power is used to drive the motor to drive the air compressor to operate, and maleic anhydride is prepared.

[0046] Self-generated steam is obtained from the preparation of maleic anhydride to drive the steam turbine.

[0047] Engage the clutch so that the steam turbine is connected to the air compressor.

[0048] The air supply device 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.

[0049] The rotating shaft of the motor is coupled to the rotating shaft of the air compressor through the gearbox. The gearbox keeps the air compressor always coupled to the motor and can convert the rotational speed of the motor shaft into a suitable rotational speed of the air compressor shaft.

[0050] 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 presence of start-up 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 motor through the gearbox.

[0051] Correspondingly, the operation method of the present invention includes starting the air compressor in the following manner:

[0052] When there is start-up steam, use the start-up steam to drive the steam turbine to drive the air compressor and the motor to increase their speeds together, where the steam turbine is in the rotational speed control mode.

[0053] After the rotational speed of the air compressor reaches the normal rotational speed, the motor is connected to the grid, and the steam turbine mode changes to the load control mode.

[0054] That is, the start-up steam is used 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 the engaged state. The steam turbine drives the air compressor and the motor to accelerate together through the clutch. The steam turbine is set to the rotational speed control mode. After the main motor of the unit accelerates 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 rotational 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 production unit generates self-produced steam, it is introduced into the steam turbine. The self-produced steam can be used as supplementary steam or main steam.

[0055] The start-up steam source can be the start-up steam initially designed by the user, the maleic anhydride plant waste gas incinerator is designed with a start-up mode, or there are other steam gas sources in the user's plant area, which can provide a certain amount of start-up steam to meet the flow demand for the start-up of the steam turbine. It should be noted that the start-up steam is responsible for starting up and does not require continuous supply throughout the maleic anhydride production process. After successful start-up, additional driving steam can be obtained from maleic anhydride production.

[0056] In this start-up mode, after the steam turbine drives the unit to accelerate, the motor is started. The main motor does not require auxiliary start-up equipment and performs grid connection operation at near the rated rotational speed of the motor, resulting in a small impact on the user's power grid.

[0057] When the maleic anhydride user device is initially designed without start-up steam, the incinerator is designed without a start-up mode, or there are no other steam gas 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.

[0058] 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 motor through a gearbox.

[0059] Correspondingly, the operation method of the present invention includes starting the air compressor in the following manner:

[0060] When there is no start-up steam, with the steam turbine disengaged from the air compressor, the motor is driven by electricity to drive the air compressor to operate, and maleic anhydride is prepared;

[0061] Self-produced steam is obtained from the preparation of the maleic anhydride to drive the steam turbine;

[0062] The clutch is engaged so that the steam turbine is connected to the air compressor.

[0063] That is, when there is no start-up steam in the device, the steam turbine cannot operate before the unit starts. At this time, first use the motor to drive the air compressor to run. 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 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 steam conditions meet the usage requirements, steam can be introduced into the steam turbine. At this time, the steam turbine can be set to the speed control mode and the speed is increased. 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 that of the output end. The engagement of the clutch enables the 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 with the motor.

[0064] By setting the clutch and adopting the start-up method of the present invention, the start-up under different start-up steam conditions is realized by using the same air supply device. In this way, in a maleic anhydride plant where separate start-up steam cannot be provided or the maleic anhydride reactor has not started to operate, a steam-electric dual-drive air supply device can also be set up and safely started.

[0065] In one embodiment, the self-produced steam is generated by using the molten salt waste heat of the maleic anhydride reactor. As Figure 2 shown, the boiler feed water can be passed through the molten salt heat exchanger 14, and the molten salt waste heat is used 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. Using the steam to recover the waste heat from the molten salt used in the maleic anhydride reactor to drive the steam turbine can achieve significant energy saving.

[0066] In one embodiment, the self-produced steam is generated by using 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 that can be carried by steam, and using it to drive the steam turbine can achieve significant energy saving.

[0067] In a preferred embodiment, the self-produced steam is generated by using the molten salt waste heat of the maleic anhydride reactor, and the waste gas incinerator of the maleic anhydride preparation system is used to further heat the self-produced steam. As Figure 2 shown, the steam generated by using the molten salt waste heat can be further passed through the waste gas incinerator, and the heat generated by the incineration tail gas is used to heat and boost 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 a stronger drive for the steam turbine.

[0068] For a maleic anhydride preparation system containing multiple reactors, preferably, the operating method of the present invention can also cooperate with an anti-surge valve and a stator vane to cope with the abnormal condition of reactor trip.

[0069] In one embodiment, the maleic anhydride preparation system is a system containing multiple reactors.

[0070] The air compressor is an axial flow air compressor, which is provided with a stator vane and an anti-surge valve.

[0071] The air supply device of the air compressor further includes:

[0072] A stator vane controller, which feedback-controls the stator vane angle based on the target exhaust pressure and / or flow rate.

[0073] An anti-surge valve controller, which feedback-controls the anti-surge valve opening based on the anti-surge line of the air compressor; and

[0074] A feedforward performance controller, which is configured to start a trip emergency control when receiving a trip signal of the reactor, and end the trip emergency control after the anti-surge valve is closed.

[0075] Wherein, the trip emergency control includes: feedforward controlling the anti-surge valve opening, and changing the target exhaust pressure and / or flow rate of the stator vane controller.

[0076] The operating method includes:

[0077] 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 anti-surge valve controller feedback-controls the anti-surge valve opening based on the anti-surge line of the air compressor and according to the measured value.

[0078] When at least one of the multiple 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:

[0079] i) According to the number of remaining operating maleic anhydride reactors, quickly open the anti-surge valve to a first opening, and change the target exhaust pressure and / or flow rate of the stator vane controller.

[0080] ii) Reduce the anti-surge valve from the first opening, and then wait for the stator vane angle to stabilize.

[0081] iii) Repeat operation ii) until the anti-surge valve is closed.

[0082] 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 makes it difficult to achieve the safe production operation of a maleic anhydride preparation system with multiple reactors.

[0083] The characteristic of a maleic anhydride reactor is that the stability of the inlet air of the air raw material 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 truly succeed in implementing the design of sharing one air compressor by multiple maleic anhydride reactors.

[0084] 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 simply making such a direct pipeline connection downstream of a conventional air compressor cannot 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 inexplicably. This makes the above device mode 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 leads to the inability to stabilize the exhaust pressure and flow rate in a timely manner.

[0085] One sudden abnormal working condition of a maleic anhydride reactor is abnormal shutdown (also known as tripping) caused by some unexpected situations. At this time, to avoid damaging the reactor, the raw gas pipeline leading to this reactor will be closed as soon as possible to stop receiving air. For a design scheme of multiple independent maleic anhydride reactors, this will not cause problems, because as the raw gas pipeline is closed, the air compressor supplying air to the corresponding reactor will also stop or the vent 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 the reactors that have not tripped also having to stop. This is very uneconomical from the perspective of actual production. Therefore, it is desired that when one reactor suddenly trips, the air compressor can still continue to supply air to the remaining reactors.

[0086] 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 volume required by the maleic anhydride preparation system is related to the number of operating reactors. 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 there is a sudden large fluctuation in the subsequent system. 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 adjustment and stabilization of the operating point 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 the conventional feedback type performance regulation and 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 air supply stability. Therefore, if the air compressor does not make relevant adjustments in advance but continues with the feedback type regulation, the air supply volume may continue to be too high, too low 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 least and reactor shutdown at the worst, causing an interlock trip and greatly reducing production efficiency.

[0087] Therefore, the method of simply connecting multiple maleic anhydride reactors in parallel downstream of a conventional air compressor cannot properly handle the above abnormal reactor trip conditions, and it is difficult to realize a practical maleic anhydride preparation system including multiple reactors.

[0088] In view of the above problems, the present invention provides an air supply device and a related operation method for a maleic anhydride production system including multiple reactors. The air supply device includes:

[0089] An axial flow air compressor provided with a stator vane and an anti-surge valve;

[0090] A stator vane controller that feedback-controls the stator vane angle based on the target exhaust pressure and / or flow rate;

[0091] An anti-surge valve controller that feedback-controls the opening degree of the anti-surge valve based on the anti-surge line of the air compressor; and

[0092] A feedforward performance controller configured to start a trip emergency control when receiving a trip signal of the reactor and end the trip emergency control after the anti-surge valve is closed,

[0093] wherein the trip emergency control includes: feedforward controlling the opening degree of the anti-surge valve and changing the target exhaust pressure and / or flow rate of the stator vane controller.

[0094] The air supply device of this embodiment 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.

[0095] The axial flow air compressor is provided with a stator vane and an anti-surge valve. These components can all be conventional components in the axial flow air compressor.

[0096] The stator vane angle is adjustable to change the intake air flow rate of the air compressor. The conventional stator vane angle adjustment range of the air compressor is between 22° and 79°.

[0097] The anti-surge valve can be arranged on the air compressor exhaust pipeline, for example, on a branch pipe separated from the air compressor exhaust pipeline, and can be fully opened or opened to a certain degree to allow the exhaust pipeline to release gas and reduce the air pressure therein. Classified according to the specific adjustment method of the anti-surge valve, there are equal percentage adjustment, linear adjustment, etc. The corresponding opening degree at different flow rates can be obtained through the inherent characteristic curve of the anti-surge valve. Generally, it is required that the anti-surge 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 anti-surge valve is in a closed state.

[0098] The air supply device of this embodiment 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 using 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 exhaust pressure and / or flow rate is input to the controller through the SV receiving end, and the measured value of the air compressor exhaust 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 exhaust pressure and / or flow rate, so as to maintain the exhaust 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.

[0099] The air supply device of this embodiment further includes a surge valve controller. The surge valve controller is used to control the surge valve, and it 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 using, 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 returns 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.

[0100] 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 exhaust pressure of the air compressor. Figure 3Shows a typical anti-surge diagram of an air compressor, 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 on-site actual surge experiment of the air compressor, the surge points of the air compressor at different stator 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 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 (e.g., 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 embodiment, after the throat differential pressure is compensated for temperature and pressure operations inside the control system and then operated according to a piecewise function, it is used as the set value SV of the anti-surge valve controller, and the measured value of the exhaust pressure of the air compressor is used as the current value PV of the anti-surge valve controller. The required opening of the anti-surge valve is calculated (e.g., 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.

[0101] The feedback control of the anti-surge valve is applicable to the situation 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 in other words, 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 be difficult to ensure the avoidance of 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 the 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 interlock and trip due to too low air supply flow rate.

[0102] 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 stator blades to control the exhaust pressure and flow rate of the air compressor.

[0103] 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 static vane controller.

[0104] 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 for emergency handling of trips in the air supply device.

[0105] The feedforward performance controller does not work when the multiple reactors in the maleic anhydride preparation system do not trip. When each reactor is operating normally, the exhaust pressure of the air compressor is feedback-controlled by the static vane controller and the anti-surge valve controller. This feedforward performance controller only participates in the control of the air supply device under abnormal conditions such as trips. Even if the exhaust pressure of the air compressor suddenly rises for other reasons, this feedforward performance controller does not work.

[0106] Figure 4 The schematic diagram of the feedforward control connection principle according to an embodiment of the present invention is shown.

[0107] As shown in the figure, in the case where the reactor does not trip, the static vane controller feedback-controls the static 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.

[0108] 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, for example, it can be a closed signal. When the reactor trips due to factors such as a fault, it outputs a trip operating state signal, for example, it can be an open signal. It can also be that the system operator actively issues a trip signal when discovering the occurrence of a trip.

[0109] The feedforward performance controller is configured to receive the trip signal of the maleic anhydride reactor and initiate a trip emergency control in response to the trip signal. As Figure 4As shown, the feedforward performance controller can receive the trip signals of Reactors 1, 2, and 3. The emergency control of this implementation scheme coordinates and controls the anti-surge valve and the compressor stator vane in advance according to the air volume loss 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 4 shown, the feedforward performance controller conducts operation control through output terminals OUT1 and OUT2.

[0110] 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 vents under large disturbances. In contrast, the feedforward performance controller of this implementation scheme 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 is used to control according to the air supply requirement after the trip in advance. Based on the trip signal, the number of tripped reactors can be known, so the reduced air supply volume required for the corresponding working conditions 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 one 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 venting of the anti-surge valve is not gradually opened by feedback or fully vented, but quickly opened under control. By venting through the anti-surge valve, the gas flow is adapted to the requirements of the remaining maleic anhydride reactors, so that the air flow rate 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.

[0111] 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 4 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.

[0112] 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 vane controller. AsFigure 4 As shown, it is output from the OUT2 output terminal of the feedforward performance controller to the SEL SV2 terminal of the static blade controller. The static blade 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 blade controller still feedback-controls the static blade angle based on the measured value received from the PV terminal, so that the actual exhaust pressure and / or flow rate remains basically stable.

[0113] Through the feedforward control of the anti-surge valve opening by the feedforward controller and the coordinated feedback control of the static blade angle, stable exhaust pressure and flow rate are obtained, ensuring that the remaining reactors can still operate normally.

[0114] 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 a small step forward. 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 a small step, the exhaust pressure and flow rate change slightly accordingly, but not violently. However, since the static blade controller is still performing feedback control, the static blade angle is changed to coordinate and stabilize the exhaust pressure and flow rate of the air compressor.

[0115] After the exhaust pressure is stabilized, that is, when the static blade 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.

[0116] When the surge valve is completely closed, the multi-reactor maleic anhydride preparation system has safely escaped from the sudden shutdown situation and reached a new steady-state operation state compared with before. The number of operating reactors has decreased, and the target exhaust pressure and / or flow rate has changed accordingly. At this time, the static blade angle decreases, causing the intake air flow rate to decrease and the throat differential pressure to decrease. The air compressor will operate at a new operating point. Correspondingly, the feedforward performance control's emergency control for shutdown ends.

[0117] As described above, in one embodiment, in order to be able to receive signals from the feedforward performance controller, the static blade 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 input values of the target exhaust pressure and / or flow rate of the original SV1 become invalid.

[0118] As described above, in one embodiment, the surge valve controller may also have another setpoint receiver SEL SV2 and is 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.

[0119] 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.

[0120] Continuing to take 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 thus determines that the maleic anhydride system should then 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 to quickly open the surge valve to this predetermined opening.

[0121] The principle for selecting the predetermined opening of the surge valve is, first, to ensure 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 and to the right of the surge prevention line; second, to make the air flow rate and pressure flowing to the non-tripped maleic anhydride reactors basically unchanged at this opening, for example, the fluctuation does not exceed 20%, more preferably 10%, more preferably 5%, more preferably 2%.

[0122] The ultimate goal of emergency control is to achieve the required air supply pressure and flow rate during the operation of the two reactors. To this end, the feed-forward 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 feed-forward performance controller starts emergency control, the exhaust pressure and / or flow rate set value of the stator vane controller changes to a value suitable for 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.

[0123] At this time, the anti-surge valve is still in the state of opening a predetermined opening, 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 feed-forward 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 of the anti-surge valve is reduced by 2%-5% at a time. After the opening 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 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 is carried out. Repeat this process until the anti-surge valve is completely closed. At this time, the feed-forward performance controller ends the emergency control.

[0124] Thus, starting from receiving the reactor trip signal, the feed-forward performance controller coordinates the control of the anti-surge valve and the stator vane, 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 feed-forward 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 pipeline network system behind the air compressor has a greater impact on the adjustment of the air compressor. During this process, neither damage to the air compressor nor the operation of the remaining reactor is affected. Through the control of the feed-forward 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.

[0125] The air supply device of this embodiment combines the anti-surge control adjustment of the air compressor, the stator vane control adjustment and the operation state signal of the maleic anhydride reactor, and jointly forms a new air compressor air supply adjustment system with the added feed-forward performance controller, thereby ensuring the stability of the air supply to the remaining reactor.

[0126] The present invention will be described in more detail below through examples.

[0127] Example 1:

[0128] Production is carried out using a maleic anhydride preparation system in which an air compressor of the present invention supplies air to three parallel maleic anhydride reactors simultaneously. The maleic anhydride plant has start-up steam.

[0129] The start-up steam is used to drive the steam turbine, and the steam turbine drives the air compressor and the motor to increase the speed together. The steam turbine is set to the speed control mode. After the speed is increased to the normal speed, the motor is switched on and connected to the grid. Subsequently, 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.

[0130] After the steam of the maleic anhydride reactor, the steam is introduced into the steam turbine as the main driving steam.

[0131] The results show that the air compressor can be started first under the condition of having start-up steam, and then the self-produced steam is used to drive the air compressor.

[0132] Example 2:

[0133] Production is carried out using the maleic anhydride preparation system of Example 1. The maleic anhydride plant has no start-up steam.

[0134] Due to the absence of start-up steam, the maleic anhydride reactor cannot provide the waste heat for generating steam before the air compressor unit starts, and the steam turbine cannot operate. First, the motor is used to drive the air compressor to run. Due to the existence of the clutch, the steam turbine is in the automatic disengagement state. After the motor drives the air compressor to reach the rated speed, the load is gradually increased according to the demand of the downstream reactor. After the steam conditions of the subsequent system meet the use requirements, steam is introduced into the steam turbine to drive the compressor unit to run together.

[0135] The results show that the air compressor can be started first under the condition of no start-up steam, and then the self-produced steam is used to drive the air compressor.

[0136] Example 3

[0137] On the basis of Example 1, production is carried out using a maleic anhydride preparation system in which this air compressor supplies air to three parallel maleic anhydride reactors simultaneously. 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. Each of the three reactors has a steam drum and supplies steam to the steam turbine. When the preparation system operates, the air compressor is driven by the motor and the steam turbine together.

[0138] A stator vane controller is set, and a PID algorithm is embedded. Its output terminal OUT is connected to the stator vane adjustment mechanism to control the stator vane angle. Its first set value receiving terminal SV1 obtains the target exhaust pressure set value when the reactor operates normally from the control system. Its current value receiving terminal PV receives the real-time exhaust pressure measurement value from the exhaust pressure sensor.

[0139] A surge controller is set up, with a PID algorithm embedded. Its output terminal OUT is connected to a surge valve to control the opening degree of the surge valve. Its first set value receiving terminal SV1 obtains a surge map from the control system, including a surge line and a surge prevention line. Its current value receiving terminal PV receives real-time operating point parameters from an exhaust pressure sensor and a throat differential pressure sensor.

[0140] A feedforward performance controller is set up. The three signal input terminals of the feedforward performance controller receive 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 valve controller. Its first output terminal OUT2 is connected to the second set value receiving terminal SEL SV2 of the stator vane controller.

[0141] As Figure 4 shown, the reactor, surge controller, surge valve, stator vane controller, stator vane, and feedforward performance controller are connected together.

[0142] First, make Reactors 1 - 3 operate under normal conditions. At this time, the feedforward performance controller does not work. The stator vane controller performs feedback control on the stator vane angle based on the target exhaust pressure set value obtained by SV1 and the measured value obtained by PV. The surge valve controller performs feedback control on the opening degree of the surge valve based on the surge prevention line obtained by SV1 and the operating point parameters obtained by PV.

[0143] To simulate a reactor trip, stop Reactor 1, immediately close the air inlet flow regulating valve leading to Reactor 1, and at the same time send a trip signal to the feedforward performance controller.

[0144] The trip signal of Reactor 1 causes the feedforward performance controller to start and begin trip emergency control. Since there is 1 trip signal, it is expected that the air supply flow rate 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 valve, quickly opening the opening degree of the surge valve to a first opening degree (not fully open) to discharge gas. At this first opening degree, with the current stator vane angle and the operating state of the air compressor, the exhaust flow rate 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.

[0145] At the same time, the feedforward performance controller sends this target exhaust pressure and / or flow rate to SEL SV2 of the stator vane controller. The stator vane controller then performs feedback control based on the changed target exhaust pressure and / or flow rate. Since the flow rate and pressure are approximately the target values at this time, the stator vane controller only makes fine adjustments to the stator vane angle based on the measurement feedback.

[0146] 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 vane controller will receive the increased pressure / flow rate measurement values and perform feedback control on the stator vanes to reduce the stator vane angle, causing the exhaust pressure and flow rate to drop back to the target values.

[0147] After the exhaust pressure and flow rate are stabilized around the target values (i.e., after the stator vane 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.

[0148] 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.

[0149] During this process, monitor the air inlet pressure and flow rate in Reactors 2 and 3, and check the operating 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.

[0150] Example 4

[0151] The test is carried out in the same manner as in Example 3, except that simulated shutdowns are performed on Reactors 1 and 2 among the three reactors.

[0152] Accordingly, the feedforward performance controller quickly opens the anti-surge valve, and the changed target exhaust flow rate sent to the stator vane 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%.

[0153] During this process, monitor the air inlet pressure and flow rate in Reactor 3, and check the operating 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.

[0154] At the same time, due to the shutdown of Reactors 1 and 2, there are significant changes in the steam supply to the steam turbine. The steam turbine can be temporarily shut down. The speed control mode is used to reduce the speed of the steam turbine, cut the steam turbine out from the air compressor, and shut down the steam turbine after successful cut-out. The air compressor is driven by an electric motor to supply air to the remaining reactors.

[0155] Comparative Example 1:

[0156] Air is supplied to the maleic anhydride reactor with the same device as in Example 3, except that no feedforward controller is set.

[0157] After simulating the tripping of Reactor 1, the measured exhaust pressure rose rapidly, triggering the feedback control of the anti-surge controller, and the anti-surge valve opened fully. Soon after the anti-surge valve opened fully, Reactors 2 and 3 tripped due to insufficient air supply and stopped operating.

[0158] Comparative Example 2:

[0159] Except for not setting up the feedforward controller, air was supplied to the maleic anhydride reactor with the same device as in Example 3.

[0160] After simulating the tripping of Reactors 1 and 2, the measured exhaust pressure rose rapidly, triggering the feedback control of the anti-surge controller, and the anti-surge valve opened fully. After the anti-surge valve opened fully, Reactor 3 soon tripped due to insufficient air supply and stopped operating.

[0161] It can be seen from this that when one or several of multiple maleic anhydride reactors suddenly shut down, the device and method of the present invention can ensure that the air compressor will not be damaged due to surge while also ensuring that the remaining reactors will not malfunction or trip due to a sudden reduction in air supply.

[0162] 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 within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all 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. A method for operating a steam and electric dual-driven air supply device for a maleic anhydride preparation system. The air supply device includes an air compressor, 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. It is characterized in that The operating method includes: When there is start-up steam, use the start-up steam to drive the steam turbine, and drive the air compressor and the electric motor to accelerate together, where the steam turbine is in a speed control mode; After the speed of the air compressor reaches the normal speed, the electric motor is connected to the grid for power generation, and the mode of the steam turbine changes to a 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 electric motor to drive the air compressor to operate, and carry out the preparation of maleic anhydride; Obtain self-generated 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. Wherein, The maleic anhydride preparation system is a system including multiple maleic anhydride reactors. The air compressor is an axial flow air compressor, which is provided with static blades and an anti-surge valve; The air supply device further includes: A static blade controller, which feedback-controls the static blade angle based on the target exhaust pressure and / or flow rate; An anti-surge valve controller, which feedback-controls the opening of the anti-surge valve based on the anti-surge line of the air compressor; and 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 anti-surge valve is closed. Wherein, 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 static blade controller. The operating method further includes: When the multiple maleic anhydride reactors are operating, the static blade controller feedback-controls the static blade angle based on the target exhaust pressure and / or flow rate and according to the measured value, and the anti-surge valve controller feedback-controls the opening of the anti-surge valve based on the anti-surge line of the air compressor and according to the measured value; When at least one of the multiple maleic anhydride reactors trips, the feedforward performance controller starts the trip emergency control after receiving the trip signal of the maleic anhydride reactor, and ends the trip emergency control after the anti-surge valve is closed. Wherein, the trip emergency control includes: i) According to the number of remaining operating maleic anhydride reactors, quickly open the anti-surge valve to a first opening, and change the target exhaust pressure and / or flow rate of the static blade controller; ii) Reduce the anti-surge valve from the first opening, and then wait for the static blade angle to stabilize; iii) Repeat operation ii) until the anti-surge valve is closed.

2. The operating method according to claim 1, characterized in that The self-generated steam is generated by using the molten salt waste heat of the maleic anhydride reactor.

3. The operating method according to claim 1, characterized in that The self-generated steam is generated by using the waste gas incinerator of the maleic anhydride preparation system.

4. The operating method according to claim 1, wherein the self-generated steam is generated by using the waste heat of the molten salt of the maleic anhydride reactor, and the self-generated steam is further heated by using the waste gas incinerator of the maleic anhydride preparation system.

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