CN115779802A - Air supply device for maleic anhydride production system including multiple reactors, production system using the same, and method for operating the same - Google Patents

Abstract

The present invention provides an air supply apparatus for a maleic anhydride production system including a multi-reactor, including a feedforward performance controller configured to start a trip emergency control upon receiving a trip signal of a reactor, and to end the trip emergency control after an anti-surge valve is closed. The invention also provides a maleic anhydride preparation system comprising multiple reactors and a method for operating the same. The invention can realize the supply of air for a plurality of maleic anhydride reactors by using a single air compressor.

Description

Air supply device for maleic anhydride production system including multiple reactors, production system using the same, and method for operating the same

Technical Field

The present invention relates to the field of maleic anhydride production, and more particularly, to an air supply apparatus of a maleic anhydride production system including a multi-reactor, a production system using the same, and an operation method thereof.

Background

Maleic anhydride is an important basic organic chemical raw material and is widely applied to the production of various chemicals. Currently, the main industrial production methods of maleic anhydride include a benzene method and an n-butane method. The benzene method takes a mixed gas of benzene and air as a raw material, and benzene is oxidized and converted into maleic anhydride under the action of a catalyst. The n-butane method uses a mixed gas of n-butane and air as a raw material, and oxidizes and converts n-butane into maleic anhydride under the action of a catalyst. Maleic anhydride is mainly produced by adopting a benzene method in China, but due to the advantages of the n-butane method in the aspects of raw materials, environmental protection, efficiency, cost and the like, the capacity of producing maleic anhydride by the n-butane method in China is continuously increased in recent years.

Both the benzene process and the n-butane process use air as one of the raw materials. In a maleic anhydride plant, air is pressurized by an air compressor and then blown into a maleic anhydride reactor for oxidation.

The most widely used maleic anhydride reactor, whether in the benzene process or in the n-butane process, is an axial tubular fixed bed reactor. The axial tube array type fixed bed reactor consists of a large number of tube arrays, and heat exchange is realized by using molten salt. Since the maleic anhydride-forming reaction is a reaction having high sensitivity to a change in reaction conditions, the smooth progress of maleic anhydride production and the product quality depend greatly on the radial uniformity of the material and temperature in the reactor. However, as the diameter of the reactor increases, the difficulty of controlling the uniformity of the material and the temperature in the radial direction of the reactor increases. Therefore, in order to ensure smooth progress of the reaction and quality of maleic anhydride, the diameter of the maleic anhydride reactor is limited, and further expansion is difficult.

Since the maximum diameter of a single maleic anhydride reactor is limited, the flow area of the fluid through the reactor is also limited, which in turn places higher demands on the bed height of the catalyst. The catalyst bed of commercial maleic anhydride reactors have a large aspect ratio and the pressure drop of the reaction fluid through the catalyst bed is high, requiring a higher outlet pressure of the air compressor. Due to the high sensitivity, the air supply (also called blowing) of the air compressor needs to be kept very stable while keeping the high pressure, otherwise it may cause the reaction to be abnormal or even terminated. The above air supply requirements put high demands on the air supply apparatus for the maleic anhydride reactor.

Furthermore, also due to the limited maximum diameter of a single maleic anhydride reactor, in a maleic anhydride plant, multiple maleic anhydride reactors must typically be built in order to achieve the design throughput. In the current maleic anhydride plant project design, in order to ensure the high-pressure air supply stability, an air compressor is independently equipped for each maleic anhydride reactor to supply air. In the design, the connection relationship between the air compressor and the maleic anhydride reactor is single, and the operation strategy is simple. The exhaust port of the air compressor is directly connected with the air inlet of the maleic anhydride reactor. In production, the air compressor keeps stable air supply under normal working conditions, and when sudden abnormal working conditions are met, the air compressor can quickly reduce air supply pressure or completely shut down to avoid accidents.

With the continuous development of air compressor technology, air compressors which have higher air supply pressure and can still maintain the air supply stability appear. The inventors of the present invention have realized that air compressors have air blowing capability for simultaneously feeding two or even more maleic anhydride reactors. Therefore, from the viewpoint of reducing the cost of the apparatus, two or more maleic anhydride reactors can share the same air compressor.

In order to realize the air supply of a plurality of maleic anhydride reactors by using a single air compressor in actual production, the structure and the operation method of an air supply device need to be improved.

Disclosure of Invention

In one aspect, the present invention provides an air supply apparatus for a maleic anhydride production system including a multi-reactor, the air supply apparatus including:

an axial-flow type air compressor provided with a stationary blade and an anti-surge valve;

a stationary vane controller that controls a stationary vane angle based on a target exhaust pressure and/or flow feedback;

an anti-surge valve controller that controls an opening of an anti-surge valve based on an anti-surge line feedback of the air compressor; and

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

wherein, the jump car emergency control includes: feedforward controlling the anti-surge valve opening, and changing the target exhaust pressure and/or flow rate of the static vane controller.

Optionally, the skip emergency control further comprises feedforward controlling the vane angle.

Optionally, the air supply device further comprises:

an exhaust pressure sensor;

a throat differential pressure sensor; and

an optional exhaust gas flow sensor is provided,

wherein the stationary blade controller performs its feedback control based on a measurement value of the exhaust pressure sensor or the exhaust flow sensor,

the anti-surge valve controller performs feedback control thereof based on the measured values of the exhaust pressure sensor and the throat differential pressure sensor,

the static vane controller and the anti-surge valve controller are controllers embedded with PID algorithm.

In another aspect, the present invention provides a maleic anhydride production system comprising multiple reactors, the maleic anhydride production system comprising multiple reactors comprising:

a plurality of maleic anhydride reactors, and

in the above air supply device, the air compressor outlet conduit of the air supply device is in fluid communication with the reactor inlet conduits of the plurality of maleic anhydride reactors, such that the plurality of maleic anhydride reactors are connected in parallel downstream of the air compressor.

In yet another aspect, the present invention provides a method of operating a maleic anhydride production system comprising a plurality of reactors as described above, the method of operating comprising:

when the plurality of maleic anhydride reactors are operated, the vane controller feedback-controls a vane angle based on a target exhaust pressure and/or flow rate and according to a measurement value, and the anti-surge valve controller feedback-controls an anti-surge valve opening based on an anti-surge line of the air compressor and according to a measurement value;

when at least one of the plurality of maleic anhydride reactors skips the vehicle, the feedforward performance controller starts the vehicle skipping emergency control after receiving a vehicle skipping signal of the maleic anhydride reactor, and ends the vehicle skipping emergency control after the anti-surge valve is closed, wherein the vehicle skipping emergency control comprises:

i) According to the number of the maleic anhydride reactors which are in residual operation, quickly opening the anti-surge valve to a first opening degree, and changing the target exhaust pressure and/or flow of the static vane controller;

ii) reducing the anti-surge valve from the first opening angle, and then waiting for the vane angle to stabilize;

iii) Repeating operation ii) until the anti-surge valve closes.

Optionally, in operation ii), the opening degree of the anti-surge valve is reduced by 2% -5% each time.

Optionally, the operating method comprises:

the vane is quickly closed to a first angle while the anti-surge valve is quickly opened.

In yet another aspect, the invention provides the use of an air supply arrangement as described above for a preparation system comprising a plurality of reactors, the feed forward performance controller being configured to initiate a jump emergency control upon receipt of a jump signal from the reactors.

Drawings

Fig. 1 shows a typical anti-surge diagram of an air compressor.

FIG. 2 shows a schematic diagram of a feedforward control linkage principle according to an embodiment of the present invention.

Detailed description of the preferred embodiments

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

A feature of maleic anhydride reactors is that the stability of the air feed is of paramount importance for its smooth operation. The stability of the air supply quantity of the air compressor is a precondition for the stable operation of the maleic anhydride reactor. Therefore, the air compressor for the maleic anhydride reactor needs to provide enough pressure and flow, and also needs to keep stable air supply for each maleic anhydride reactor which normally works as much as possible under various complicated working conditions which are actually faced, otherwise, the design that a plurality of maleic anhydride reactors share one air compressor is difficult to be successfully and truly realized.

When one air compressor is used for providing pressurized air for a plurality of maleic anhydride reactors, the air inlet pipeline of each maleic anhydride reactor is directly communicated with the exhaust port of the same air compressor, so that the plurality of maleic anhydride reactors are connected in parallel at the downstream of the same air compressor. However, the inventors have unexpectedly found in practice that: the direct pipeline connection only at the downstream of the conventional air compressor is difficult to meet the practical application requirement. In this connection, although air can be stably supplied to each of the maleic anhydride reactors when all the maleic anhydride reactors are in normal operation, when sudden abnormal conditions occur in some of the maleic anhydride reactors, other maleic anhydride reactors in the system are adversely affected, and even interlocking and tripping can occur for unknown reasons. This results in the device being impractical. Without being bound to any theory, the inventors discovered that the reason for these results is the inability to stabilize discharge pressure and flow in time due to the hysteresis of the vane and anti-surge valve feedback controls.

One sudden abnormal condition of a maleic anhydride reactor is an abnormal shut down (also known as a trip) due to some unexpected condition. At this point, the feed gas line to the reactor would be shut down as soon as possible to stop receiving air in order to avoid damage to the reactor. This does not cause problems for a plurality of maleic anhydride reactor designs which are independent of one another, since with the feed gas line closed, the air compressor which supplies the respective reactor is also shut down or the blow valve is opened. However, for a plurality of maleic anhydride reactors connected in parallel which share the same air compressor, if the air compressor is shut down or vented because one of the reactors trips, the air supply to all the maleic anhydride reactors will be stopped, resulting in that the reactor which does not trip also has to be shut down. This is very uneconomical from a practical production point of view. Therefore, it is desirable that when a sudden trip occurs in one reactor, the air compressor can continue to supply air to the remaining reactors.

The maleic anhydride reactor after a trip will gradually stop receiving air to avoid damage to the reactor. For example, the inlet flow control valve in the reactor inlet line to the skip car reactor is closed. One mode of operation may be to close the corresponding intake flow control valve when the reactor trips, allowing the air compressor to continue to operate to supply air to the remaining reactors. However, the inventors have found in practice that in a maleic anhydride system kept in operation in this way, the air intake of the remaining reactor can be affected, leading to unstable operation and also possible occurrence of a jump in interlock. Without being bound to any theory, the inventors found the following reasons. The total air supply required by the maleic anhydride preparation system is related to the number of the working reactors, so when one or more of a plurality of maleic anhydride reactors suddenly jumps, the requirement on the air supply flow of the air compressor is greatly changed suddenly, namely, the air supply is suddenly reduced in a short time. However, the performance adjustment (maintaining the blowing pressure/flow rate) of the conventional axial-flow air compressor is mainly performed by the stationary blades, which cannot rapidly and effectively perform the adjustment of the outlet blowing amount of the air compressor when the rear system suddenly fluctuates greatly. Therefore, the operating state of the air compressor cannot be immediately switched to the low air supply amount state required to accommodate the smaller number of reactors, but is maintained in the relatively high air supply amount state. In this case, when the pressure in the air supply duct of the air compressor rises sharply due to the uncooperative nature of the high air supply amount state and the low air supply amount demand, the operating point of the air compressor is affected, and the response of the anti-surge system of the air compressor is further caused. The anti-surge system of the air compressor also needs a long time to complete the adjustment and stabilization of the working point, and cannot quickly stabilize the outlet pressure of the air compressor, thereby influencing the air intake of the running reactor. In other words, both conventional feedback-type performance regulation and feedback-type anti-surge regulation have difficulty quickly regulating the supply air flow and pressure to a low supply air condition. Moreover, the anti-surge valve of the air compressor performs a full-open air discharge operation in the case where the pressure suddenly increases sharply (i.e., a large disturbance), which causes a sudden drop in the supply air pressure. Although the air compressor is protected, the maleic anhydride reactor air feed will become insufficient. As mentioned above, maleic anhydride reactors have high requirements for blast stability. Therefore, if the air compressor is not adjusted in advance and feedback adjustment is carried out continuously, the air supply amount is possibly continuously too high, continuously insufficient or fluctuated severely, the operation of the residual maleic anhydride reactor is influenced rapidly under the conditions, the product quality is fluctuated slightly, the reactor stops working seriously, the interlocking vehicle jumping is caused, and the production efficiency is greatly reduced.

Therefore, the method of simply connecting a plurality of maleic anhydride reactors in parallel at the downstream of the conventional air compressor cannot properly cope with the abnormal jumping condition of the reactors, and is difficult to realize a practical maleic anhydride preparation system comprising a plurality of reactors.

In view of the above problems, the present invention provides an air supply apparatus for a maleic anhydride production system including a plurality of reactors, wherein the air supply apparatus includes:

an axial-flow type air compressor provided with a stationary blade and an anti-surge valve;

a stationary vane controller that controls a stationary vane angle based on a target exhaust pressure and/or flow feedback;

an anti-surge valve controller that controls an opening of an anti-surge valve based on an anti-surge line feedback of the air compressor; and

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

wherein, the jump emergency control includes: feedforward controlling the anti-surge valve opening, and changing the target exhaust pressure and/or flow rate of the static vane controller.

The air supply device of the invention comprises an axial flow type air compressor as a basic component. The axial flow air compressor needs to provide a stable supply of air to at least two maleic anhydride reactors simultaneously. The appropriate air compressor can be selected according to the air supply pressure and flow required by the maleic anhydride reactor and the number of the reactors. In one embodiment, the operating pressure of the single maleic anhydride reactor is between 0.29 and 0.35MPaA, and the required air flow is between 1000 and 4000Nm ³ /min。

The axial-flow type air compressor is provided with a stationary blade and an anti-surge valve. These components may be conventional components in axial flow air compressors.

The angle of the stationary blade is adjustable, so that the air inlet flow of the air compressor is changed. The angle adjusting range of the static blade of the conventional air compressor is 22-79 degrees.

The anti-surge valve can be arranged on an air compressor exhaust pipeline, for example, a branch pipeline branched from the air compressor exhaust pipeline, and can be fully opened or opened by a certain opening degree, so that the air exhaust pipeline is deflated, and the air pressure in the air exhaust pipeline is reduced. The anti-surge valve is classified according to the specific adjusting mode of the anti-surge valve, and comprises equal percentage adjustment, linear adjustment and the like. The corresponding opening degree under different flow rates can be found through the inherent characteristic curve of the anti-surge valve. Typically, the anti-surge valve is required to open quickly within 1.5 seconds and from fully closed to fully open (0% to 100%) within 3 seconds. When the air compressor normally operates, the anti-surge valve is in a closed state.

The air supply apparatus of the present invention further includes a vane controller for changing a vane angle. The vane controller may be connected to or include a vane angle adjustment mechanism. The stationary blade controller is a controller having a feedback control function that implements feedback control based on a difference between a set value and a current value (measured value). For example, the stationary vane controller may be a controller that employs a Proportional Integral Derivative (PID) control algorithm. The controller has a Set Value (SV) receiver and a current value (PV) receiver. And inputting a set value of the air compressor exhaust pressure and/or flow to the controller through the SV receiving end, and inputting a measured value of the air compressor exhaust pressure and/or flow to the controller through the PV receiving end as a current value. After the calculation of the PID algorithm, a control signal for increasing the angle of the stator blade or decreasing the angle of the stator blade is sent to the stator blade angle adjusting mechanism through an Output (OUT) end. In this way, the stationary vane controller can perform feedback control on the stationary vane angle based on the deviation of the current value and the set value of the exhaust pressure and/or flow rate of the air compressor, so that the exhaust pressure and/or flow rate is maintained to be close to the set value. This ensures a stable air supply to the maleic anhydride reactor downstream. It should be noted that this feedback control of the static vane controller is slow to take effect and does not have sufficient reactive regulatory capability to sudden and severe fluctuations in pressure or flow.

The air supply apparatus of the present invention further comprises an anti-surge valve controller. An anti-surge valve controller is used to control an anti-surge valve, which is also a controller having a feedback control function. The anti-surge valve feedback control is based on an anti-surge line. The relative position of the operating point and the anti-surge line is compared, and the operating point is adjusted by controlling the opening of the anti-surge valve. Likewise, the antisurge valve controller may also be a controller that employs, for example, a PID algorithm. And an SV receiving end of the anti-surge valve controller receives anti-surge line information, a PV receiving end receives a working point measuring result of the air compressor, and OUT outputs an anti-surge valve control signal. When the working point crosses the anti-surge line and is close to the surge line, the anti-surge valve is opened at a proper angle based on the measuring result of the working point, so that the pressure is reduced, the working point returns to a normal working area, and the phenomenon of surge of the air compressor is prevented. It should be noted that such feedback control of an anti-surge valve controller is also relatively slow to effect and is not very responsive to sudden and dramatic fluctuations in pressure or flow.

Operating points, surge lines and surge protection lines are well known in the art of air compressors. For example, the state points, surge lines, and anti-surge lines may be plotted in an anti-surge map with the abscissa representing the throat differential pressure of the air compressor and the ordinate representing the discharge pressure of the air compressor. Fig. 1 shows a typical air compressor surge prevention diagram, in which a surge line 1 and a surge prevention line 2 are shown. In the anti-surge map, each point corresponds to a state point indicating the throat differential pressure and the discharge pressure of the air compressor. According to the field actual surge experiment of the air compressor, the surge point of the air compressor under different stationary blade angles can be measured. And connecting the surge points to obtain an actual surge line of the air compressor. At a point in the region below and to the right of this surge line (greater throat differential pressure, lower discharge pressure), the air compressor does not surge. At the surge line and above the surge line (too small a differential pressure at the throat and too high an exhaust pressure), the air compressor will surge. Furthermore, a certain safety margin (e.g., 10%) is reserved for the surge line at the lower right of the surge line. When the air compressor exhaust pressure increases to cause the working point to cross the anti-surge line, the air compressor can reduce the exhaust pressure by opening the anti-surge valve by a certain opening degree, so that the working point is far away from the surge line to avoid surge. As the operating conditions causing surge fluctuate gradually, the anti-surge valve closes gradually. This process can be achieved by the anti-surge valve controller through feedback control. In one embodiment, the throat differential pressure is calculated by temperature and pressure compensation in the control system and a broken line function, then the throat differential pressure is used as a set value SV of the anti-surge valve controller, the exhaust pressure measured value of the air compressor is used as a current value PV of the anti-surge valve controller, the required opening degree of the anti-surge valve is calculated (for example, by using PID algorithm), and the opening degree of the anti-surge valve is controlled correspondingly to avoid surge. It will be appreciated that other suitable feedback algorithms besides the PID algorithm may be used.

The feedback control of the anti-surge valve is suitable for the condition that the disturbance is small, namely the working point crosses the anti-surge line at a slow speed and a small amplitude. In this case, the operating point can be adjusted by gradually opening the anti-surge valve. However, when the pressure rises rapidly and greatly or the disturbance is large, the operating point may rapidly pass through the safety margin region between the surge prevention line and the surge line to reach the surge region, and the hysteresis of the feedback control described above will be difficult to ensure that surge is avoided. Therefore, in the case where a large disturbance causes an operating point which may or may have entered a surge region, the conventional air compressor adopts an operation of immediately opening the anti-surge valve to the maximum (i.e., fully open) to discharge air in order to simply protect the air compressor, so as to rapidly reduce the discharge pressure, so that the operating point is separated from the surge region, thereby eliminating the surge phenomenon. As described above, the inventors have found that this seriously affects the stability of the air supply to the remaining maleic anhydride reactor, and in severe cases, the reactor is interlocked and tripped due to the excessively low air supply flow rate.

The invention sets a feedforward performance controller in the air supply device and properly deals with the trip condition of the reactor. More specifically, the invention utilizes a feed forward performance controller to cooperatively regulate an anti-surge valve and stationary vanes to control air compressor discharge pressure and flow in the event of reactor trip.

The feedforward performance controller is configured to initiate a trip emergency control upon receiving a trip signal from the maleic anhydride reactor and to terminate the trip emergency control upon closing of the anti-surge valve, the trip emergency control comprising: feedforward controlling the anti-surge valve opening, and changing the target exhaust pressure and/or flow rate of the vane controller.

In other words, the invention aims at the situation that part of maleic anhydride reactors suddenly jump in a maleic anhydride preparation system comprising a plurality of reactors, and a feedforward performance controller for emergency treatment of jumping is specially arranged in an air supply device.

The feedforward performance controller does not work when the multiple reactors in the maleic anhydride preparation system do not jump. When each reactor works normally, the exhaust pressure of the air compressor is controlled by the feedback of the static vane controller and the anti-surge valve controller. The feedforward performance controller participates in the control of the air supply device only when an abnormal condition of vehicle jumping occurs. Even if the discharge pressure of the air compressor suddenly rises for other reasons, the feed-forward performance controller does not operate.

FIG. 2 shows a schematic diagram of a feed forward control connection principle according to an embodiment of the invention.

As shown in the figure, in case of no trip of the reactor, the vane controller feedback-controls the vane angle through the output terminal OUT according to the set value of the SV1 terminal and the measured value or actual value of the PV terminal, and the surge-proof valve controller feedback-controls the opening of the surge-proof valve through the output terminal OUT according to the surge-proof line inputted from the SV1 and the actual operating point position of the PV output when the operating point of the air compressor crosses the surge-proof line to eliminate a possible surge phenomenon.

The maleic anhydride production system may generate and send a trip signal when the maleic anhydride reactor trips. The maleic anhydride preparation system can send various reactor running state signals or running state signals for short, and the trip signal is one of the running state signals. The signal type of the operation status signal may be a digital dry contact signal. The operating state signal may be automatically generated by a control system of the reactor (e.g. a decentralized control system, DCS). The control system of the reactor judges whether the reactor is normally operated by measuring the parameters of the reactor. If the control system determines that the reactor is operating normally, it outputs a dry contact signal indicative of normal operation as the normal operating status signal, which may be, for example, a close signal. When the reactor jumps due to a fault and the like, the reactor outputs a jumping operation state signal, such as a disconnection signal. And the system operator can actively send out a vehicle-jumping signal when finding the occurrence of vehicle-jumping.

The feed forward performance controller is configured to receive a trip signal from the maleic anhydride reactor and initiate a trip emergency control in response to the trip signal. As shown in fig. 2, the feedforward performance controller may receive trip signals of reactors No. 1, 2 and 3. The emergency control of the invention coordinates and controls the anti-surge valve and the air compressor stationary blade in advance according to the air volume lost after the reactor jumps, thereby ensuring the stability of air supply to the residual reactor without jumping while ensuring that the air compressor does not surge. As shown in fig. 2, the feedforward performance controller performs operation control through the output terminals OUT1 and OUT 2.

The emergency control includes feedforward control of the opening of the anti-surge valve. As described above, when feedback controlled by the anti-surge valve controller, the anti-surge valve opens gradually under small disturbances and opens fully under large disturbances based on the increased discharge air pressure measurement. In contrast, the feed forward performance controller of the present invention is activated in response to a trip signal and controls the anti-surge valve in advance. That is, instead of performing feedback control after a pressure rise due to a trip and subsequent closing of the reactor's intake air flow rate regulating valve, control is performed in advance according to the air supply requirement after the trip using a feedforward performance controller. According to the signal of jumping the bus, can learn the reactor quantity of jumping the bus, consequently can learn the required air output of the air output that corresponding operating mode need reduce and the required air output of surplus reactor continuation operation in advance. For example, in a three reactor system, when the feedforward performance controller receives a trip signal, it is known that one reactor is tripping and the other two reactors are still running. The feedforward performance controller may calculate an appropriate opening of the anti-surge valve based on the desired amount of air delivered and based on the performance curve of the anti-surge valve. The feed forward performance controller opens the anti-surge valve directly (or shortly) to this opening. At this anti-surge valve opening, the bleed air from the anti-surge valve is not fed back to open gradually, nor is it fully open to bleed air, but is controlled to open quickly. The gas flow is adapted to the requirements of the remaining maleic anhydride reactor by means of an anti-surge valve bleed, so that the air flow to the remaining reactor does not fluctuate substantially. In the process, the working point of the air compressor does not reach a surge line, and no surge occurs.

The control of the opening of the anti-surge valve by the feedforward performance controller may be performed by an anti-surge valve controller. That is, the feedforward performance controller transmits a control signal to the anti-surge valve controller, and further controls the anti-surge valve through a signal output from the OUT terminal of the anti-surge valve controller. As shown in fig. 2, the anti-surge valve controller feedback-controls the anti-surge valve opening degree according to the anti-surge line received from the SV1 terminal and the operating point position received from the PV terminal in the normal state, but receives the feedforward signal output from the OUT1 output terminal of the feedforward performance controller from the SEL SV2 terminal when the feedforward performance controller is active.

Meanwhile, the feedforward performance controller also calculates the exhaust pressure and flow rate required by the air compressor when the anti-surge valve is under the opening degree according to the known required air supply amount, and sends the required values to the static vane controller as the target exhaust pressure and/or flow rate. As shown in fig. 2, the signal is output to the SEL SV2 terminal of the static vane controller through the OUT2 output terminal of the feedforward performance controller. The static vane controller derives the modified target exhaust pressure and/or flow from the feed forward performance controller in place of the set point previously received from the SV1 side. The modified target discharge pressure and/or flow rate is suitable for operation of the residual reactor at the aforementioned anti-surge valve opening. The vane controller feedback controls the vane angle based on the changed target exhaust pressure and/or flow, still based on the test value received from the PV tip, such that the actual exhaust pressure and/or flow remains substantially stable.

Through the feedforward control of the feedforward controller on the opening of the anti-surge valve and the feedback control matched with the feedforward controller on the angle of the static blade, stable exhaust pressure and flow are obtained, and the normal operation of the rest reactors is guaranteed.

However, the state in which the anti-surge valve is kept open cannot be continued for a long time in consideration of the stability of the normal operation of the system, and this state also causes a large amount of unnecessary compressed air to be discharged from the anti-surge valve, wasting energy. Thus, the feedforward performance controller continues to operate, feedforward progressively closing the anti-surge valve at small amplitudes. For example, in one embodiment, the opening is first reduced to some extent, such as by 2% to 5%. When the opening of the anti-surge valve is reduced by a small amount, the exhaust pressure and the flow rate are slightly changed correspondingly, but not drastically. However, since the stationary vane controller is still performing feedback control, the air compressor discharge pressure and flow rate are coordinated and stabilized by the variation of the stationary vane angle.

After the exhaust pressure is stabilized, i.e., the stationary blade angle is substantially maintained, the feedforward performance controller continues to decrease the opening and repeats the above operations. By thus slowly reducing the antisurge valve opening in steps, eventually the surge valve will be fully closed. In the process, a steady air supply to the remaining maleic anhydride reactors can be maintained at all times so that they can function properly.

After the surge valve is completely closed, the multi-reactor maleic anhydride production system is safely freed from sudden vehicle jumps and, in contrast thereto, a new steady-state operating state is reached in which the number of operating reactors is reduced and the target exhaust pressure and/or flow is correspondingly changed. At this time, the angle of the stationary blade is reduced, so that the intake flow is reduced, the differential pressure of the throat is reduced, and the air compressor is operated at a new working point. Accordingly, the skip emergency control by the feed forward performance control is ended.

As described above, in one embodiment, the static vane controller may have another setpoint receiver in order to be able to receive a signal from the feedforward performance controller. The original set value receiving terminal is SV1, and the new set value receiving terminal is SEL SV2.SEL SV2 is connected to a signal output terminal OUT2 of the feedforward performance controller. When the SEL SV2 receiving end receives the changed target exhaust pressure and/or flow from the feedforward performance controller, the original target exhaust pressure and/or flow input value of SV1 is invalid.

As described above, in one embodiment, the anti-surge valve controller may also have another set point receiver SEL SV2 and be connected to another signal output OUT1 of the feedforward performance controller. When the SEL SV2 receiving terminal of the anti-surge valve controller receives the control signal from the feedforward performance controller, it will change the anti-surge valve opening directly through the OUT terminal. The advantage of the feedforward performance controller controlling the anti-surge valve via the anti-surge valve controller is that all control signals to the anti-surge valve are sent by the anti-surge valve controller, avoiding conflicts in control. In emergency control by the feedforward performance controller, the feedback control of the antisurge valve controller is temporarily disabled because the feedforward performance controller can already ensure that surge does not occur.

The feedforward performance controller takes the received trip signal of the maleic anhydride reactor as a precondition for starting the trip emergency control, and determines a corresponding feedforward control strategy. According to the number of the received reactor trip signals, the number of the reactors which are still in operation can be known, and the air supply quantity required for keeping normal operation can be obtained correspondingly. For example, for a three reactor system, if a trip signal is received, it indicates that two reactors are still in need of remaining in operation. And aiming at the number of the skip signals, the feedforward performance controller can give out a required control strategy and corresponding control signals.

The description continues with the example of one reactor jumping in a three reactor system. When a reactor trips, it immediately sends a trip signal to the feed forward performance controller. The feed forward performance controller thus determines that the maleic anhydride system should then be operated in the two reactor mode. The feedforward performance controller calculates the amount of air supply required by the operation of the two reactors. Based on the intrinsic characteristic curve of the anti-surge valve, the feedforward performance controller sends an opening degree control signal to the anti-surge valve controller according to the air supply amount, so that the anti-surge valve is opened to the preset opening degree quickly.

The selection principle of the preset opening of the anti-surge valve is that firstly, the exhaust pressure is ensured to be in a non-surge area in an anti-surge diagram under the current throat differential pressure, and preferably in a safety area below the right of an anti-surge line; secondly, at this opening, the flow rate and pressure of air flowing to the maleic anhydride reactor which is not skipped are made substantially constant, for example, fluctuating by no more than 20%, more preferably 10%, more preferably 5%, more preferably 2%.

The ultimate goal of emergency control is to achieve the required supply air pressure and flow rate for the two reactors to operate. To this end, the feed forward performance controller inputs a target discharge pressure and/or flow to the stationary vane controller, replacing its original discharge pressure/flow set point. In other words, after the feedforward performance controller initiates the emergency control, the exhaust pressure and/or flow set point of the vane control is changed to a value suitable for both reactors. Subsequently, the stationary blade controller stabilizes the supply air pressure and flow rate by adjusting the stationary blades based on the new set value, thereby ensuring a substantially stable operation of the remaining reactors.

At this time, the anti-surge valve is still in a state of being opened by a predetermined opening degree, and it is necessary to gradually close the valve to return to a normal operation state to continue the anti-surge function. To do so, the performance controller continues to send a feed forward control signal to the anti-surge valve controller. The control signal causes the anti-surge valve to progressively close. In a preferred embodiment, the control signal may be to decrease the opening of the anti-surge valve by 2% -5% at a time. After the opening degree is reduced, the feedback control of the static blade controller enables the air exhaust pressure and flow to be recovered and stabilized through adjusting the static blades. The step range of opening reduction of 2% -5% allows a good balance between closing the anti-surge valve as soon as possible and waiting for the stator blades to adjust in time. And after the static blade is stabilized, reducing the opening of the anti-surge valve for the next time. This is repeated until the anti-surge valve is fully closed. At this time, the feedforward performance controller ends the emergency control.

Therefore, from the moment of receiving a reactor trip signal, the feedforward performance controller adjusts the air inlet and the air outlet of the air compressor in advance by matching the anti-surge valve with the stationary blade control, and adjusts the outlet pressure and the flow (namely, the anti-surge valve-performance control input) to obtain the required air supply. Because the air supply device is the feedforward control responding to the vehicle jumping signal, different from the feedback control, the air supply device can be effectively intervened in advance before the change of a system pipe network behind the air compressor has greater influence on the adjustment of the air compressor. In the process, the air compressor is not damaged, and the work of the rest reactors is not influenced. Through the control of the feedforward performance controller, the fluctuation caused by the reactor tripping is effectively controlled under the cooperative regulation of the stationary blade and the anti-surge valve, and the risk and the probability of the interlocking shutdown of the device are reduced.

The air supply device combines the anti-surge control and regulation of the air compressor, the stationary blade control and regulation and the running state signal of the maleic anhydride reactor, and forms a brand new air supply regulation system of the air compressor together with the additional feedforward performance controller, thereby ensuring the stability of air supply to the rest reactors.

In one embodiment, the skip emergency control further comprises feed forward controlling the vane angle.

In order to complete the emergency control of vehicle jumping more quickly, the angle of the stator blade can be quickly reduced by an angle at the same time of quickly opening the anti-surge valve. Compared with the method of simply performing feedback control on the angle of the static blade, the method of feedforward reducing the angle of the static blade can enable the initial opening degree of the anti-surge valve to be smaller, and therefore the vehicle jumping emergency control can be completed more quickly in the follow-up process.

Preferably, the air supply device further comprises:

an exhaust pressure sensor;

a throat differential pressure sensor; and

an optional exhaust gas flow sensor is provided,

wherein the stationary blade controller performs feedback control thereof based on a measurement value of the exhaust pressure sensor or the exhaust flow sensor,

the anti-surge valve controller performs feedback control thereof based on the measured values of the exhaust pressure sensor and the throat differential pressure sensor,

the static vane controller and the anti-surge valve controller are controllers embedded with PID algorithm.

In one embodiment, the air supply apparatus of the present invention comprises an exhaust pressure sensor. An exhaust pressure sensor may be coupled to the anti-surge valve controller to provide an exhaust pressure measurement as a feedback value to the anti-surge valve controller. The exhaust pressure sensor may be connected to the PV input of the anti-surge valve controller of the PID algorithm. An exhaust pressure sensor may also be coupled to the vane control to provide an exhaust pressure measurement as a feedback to the vane control. The exhaust pressure sensor may be connected to the PV input of the stationary vane controller of the PID algorithm.

In one embodiment, the air supply device of the present invention comprises a throat differential pressure sensor. The throat differential pressure sensor may be coupled to the anti-surge valve controller to provide a throat differential pressure measurement to the anti-surge valve controller as a set point. The throat differential pressure sensor may be connected to the PV input of the anti-surge valve controller of the PID algorithm.

In one embodiment, the air supply apparatus of the present invention comprises an exhaust flow sensor. An exhaust flow sensor may be coupled to the vane controller to provide a measured exhaust flow value as a feedback value to the vane controller. The exhaust flow sensor may be connected to the PV input of the stationary vane controller of the PID algorithm.

By monitoring parameters such as exhaust pressure, throat differential pressure, exhaust flow and the like, the static vane controller and the anti-surge valve controller can realize feedback control.

The air supply device of the present invention may also contain other parameter measuring instruments such as thermometers and the like. Measurement of other parameters such as temperature may also participate in feedback control of the anti-surge valve or vane.

The air supply apparatus for a maleic anhydride production system comprising a multiple reactor of the present invention can realize a practical maleic anhydride production system.

In one embodiment, the present disclosure provides a maleic anhydride production system comprising multiple reactors, wherein the maleic anhydride production system comprising multiple reactors comprises:

a plurality of maleic anhydride reactors, and

the air supply device mentioned above, wherein the air compressor outlet conduit of the air supply device is in fluid communication with the reactor inlet conduits of the plurality of maleic anhydride reactors, such that the plurality of maleic anhydride reactors are connected in parallel downstream of the air compressor.

As described above, the maleic anhydride preparation system can realize that one air compressor drives a plurality of maleic anhydride reactors, and can properly cope with abnormal conditions of reactor jumping.

The inventor of the invention provides a relative operation method while inventing a maleic anhydride preparation system comprising a plurality of reactors, and can appropriately cope with the jumping working condition of the reactors under the condition that one air compressor drives a plurality of maleic anhydride reactors.

The maleic anhydride preparation system comprising the multiple reactors comprises the feedforward performance controller, and the emergency control of vehicle jumping can be realized.

In one embodiment, the present invention provides a method of operating the above maleic anhydride production system comprising multiple reactors, wherein the method of operating comprises:

when the plurality of maleic anhydride reactors are operated, the vane controller feedback-controls a vane angle based on a target exhaust pressure and/or flow rate and according to a measurement value, and the anti-surge valve controller feedback-controls an anti-surge valve opening based on an anti-surge line of the air compressor and according to a measurement value;

when at least one of the plurality of maleic anhydride reactors skips the vehicle, the feedforward performance controller starts the vehicle skipping emergency control after receiving a vehicle skipping signal of the maleic anhydride reactor, and ends the vehicle skipping emergency control after the anti-surge valve is closed, wherein the vehicle skipping emergency control comprises:

i) According to the number of the maleic anhydride reactors which are in residual operation, quickly opening the anti-surge valve to a first opening degree, and changing the target exhaust pressure and/or flow of the static vane controller;

ii) reducing the anti-surge valve from the first opening angle, and then waiting for the vane angle to stabilize;

iii) Repeating operation ii) until the anti-surge valve closes.

As described above, in the operation i), the first opening degree at which the anti-surge valve is quickly opened in the trip emergency control is calculated based on the number of maleic anhydride reactors remaining to be operated. And calculating a proper first opening degree of the anti-surge valve according to the required air supply quantity and the performance curve of the anti-surge valve. At this anti-surge valve opening, the bleed air from the anti-surge valve is not gradually opened, nor is the air fully opened, but is controlled to open quickly. The gas flow is adapted to the requirements of the remaining maleic anhydride reactor by means of an anti-surge valve bleed, so that the air flow to the remaining reactor does not fluctuate substantially.

Meanwhile, the vehicle-skipping emergency control also calculates the required target exhaust pressure and/or flow according to the number of the residual operating maleic anhydride reactors, and correspondingly changes the target exhaust pressure and/or flow of the static vane controller.

On the basis of which the operations ii), iii) are carried out, the opening of the anti-surge valve can be gradually reduced in a feed-forward manner until it is closed, and the static vane controller can always stabilize the exhaust pressure and the flow rate to the extent required by the remaining operating maleic anhydride reactor by means of feedback control. Therefore, the air supply is basically stable after the reactor jumps, so that the rest of the reactor is operated, and the interlocking jump is avoided.

Preferably, in operation ii), the anti-surge valve is reduced by 2% -5% from said first opening degree. As described above, this can be a good balance between closing the antisurge valve as quickly as possible and waiting for the vanes to adjust in time.

In one embodiment, in operation i), the vanes are quickly closed to a first angle while the anti-surge valve is quickly opened. Can be directed against different reactor numbers of jumping a car, set up appropriate initial first aperture and first angle, both cooperations guarantee the stability of air supply pressure and flow. Such efficiency is higher than controlling the vane angle only in feedback.

Although the present invention has been made based on the air supply apparatus for a maleic anhydride production system comprising a plurality of reactors, the inventors have found that the air supply apparatus of the present invention can be used for other reaction systems having the same characteristics as those of maleic anhydride production. That is, each reactor needs to be supplied with air, but each reactor is limited in scale, so that a single air compressor can be used to supply air to a plurality of reactors. At the same time, the reactors are sensitive to flow and pressure fluctuations of the feed gas, possibly due to a reactor trip and interlocked shutdown. For such a reaction system, the air supply device of the present invention can also be used.

In one embodiment, the invention provides the use of an air supply arrangement of the invention for a production system comprising a plurality of reactors, wherein the feed forward performance controller is configured to initiate a trip emergency control upon receiving a trip signal from the reactor.

At the moment, the starting of the feedforward performance controller is triggered by a corresponding reactor trip signal instead. This extends the range of applications of the air supply device of the present invention.

The present invention will be described in more detail below with reference to examples.

Example 1:

the production is carried out by using a maleic anhydride preparation system which uses one air compressor to simultaneously supply air for three maleic anhydride reactors connected in parallel. The three maleic anhydride reactors are referred to as reactor No. 1, reactor No. 2 and reactor No. 3, respectively. The reaction raw material is n-butane.

And (4) setting a static blade controller and embedding a PID algorithm. The output end OUT of the stator blade adjusting mechanism is connected with the stator blade adjusting mechanism to control the angle of the stator blade. The first set value receiving end SV1 obtains a target exhaust pressure set value when the reactor works normally from a control system. Its current value receiving terminal PV receives real-time exhaust pressure measurements from the exhaust pressure sensor.

And an anti-surge controller is arranged, and a PID algorithm is embedded. The output end OUT of the anti-surge valve is connected with the anti-surge valve to control the opening of the anti-surge valve. The first set point receiving end SV1 obtains an anti-surge map from a control system, and the anti-surge map comprises a surge line and an anti-surge line. Its current value receiving terminal PV receives real-time operating point parameters derived from the exhaust pressure sensor and the throat differential pressure sensor.

The device is provided with a feedforward performance controller, and three signal input ends of the feedforward performance controller receive operation signals from reactors 1-3. And a second output end OUT1 of the anti-surge valve controller is connected with a second set value receiving end SEL SV2 of the anti-surge valve controller. And a first output end OUT2 of the static blade controller is connected with a second set value receiving end SEL SV2 of the static blade controller.

As shown in FIG. 2, the reactor, anti-surge controller, anti-surge valve, vane controller, vanes, and feed forward performance controller are connected together.

Reactors No. 1-3 were first run under normal conditions. At this time, the feedforward performance controller does not operate. And the stationary blade controller performs feedback control on the stationary blade angle according to the measured value obtained by the PV on the basis of the target exhaust pressure set value obtained by the SV 1. And the anti-surge valve controller performs feedback control on the opening of the anti-surge valve according to the working point parameter obtained by PV based on the anti-surge line obtained by SV 1.

In order to simulate the reactor trip, the No. 1 reactor is stopped, an air inlet flow regulating valve leading to the No. 1 reactor is closed immediately, and a trip signal is sent to the feedforward performance controller.

The trip signal from reactor No. 1 causes the feedforward performance controller to start and begin a trip emergency control. According to the 1 skip signal, the expected air supply flow is changed into two thirds of the original flow, and the pressure is unchanged. To this end, the feedforward performance controller transmits a feedforward signal to SEL SV2 of the anti-surge valve, and opens the opening degree of the anti-surge valve to a first opening degree (non-full opening) to discharge the gas. At this first opening, the exhaust flow rate of the air to the downstream is two thirds of the former, and the pressure is unchanged, at the current vane angle and the operating state of the air compressor. The working point is positioned at the lower right part of the anti-surge line, so that the surge can be avoided.

At the same time, the feed forward performance controller sends this target exhaust pressure and/or flow to the SEL SV2 of the vane controller. The vane controller is thus feedback controlled based on the changed target exhaust pressure and/or flow rate. Since the flow rate and pressure are at this time approximately at the target values, the vane controller finely adjusts the vane angle only based on the measured value feedback.

The feed forward performance controller then reduces the anti-surge valve opening by 2%. At this point, the exhaust pressure and flow rate are both increased, the vane controller will receive the increased pressure/flow rate measurements and perform feedback control on the vanes to reduce the vane angle so that the exhaust pressure and flow rate drop back to the target values.

After the exhaust pressure and flow stabilize around the target values (i.e., after the stationary blade angle no longer continues to decrease), the feedforward performance controller decreases the anti-surge valve opening by 2% again. The above process is repeated until the anti-surge valve is fully closed.

And after the anti-surge valve is completely closed, the feedforward performance controller is closed, and the vehicle-jumping emergency control is finished. The anti-surge valve controller takes over the feedback control of the anti-surge valve.

In this process, the air intake pressure and flow rate in the reactors No. 2 and No. 3 were monitored, and the operating state of the reactors was checked. As a result, the fluctuation of the air inlet pressure and the air inlet flow of the reactors 2 and 3 is not large, the reactors work smoothly, and the product yield and the product quality are stable and are not influenced by the jumping of the reactor 1.

Example 2

The test was performed in the same manner as in example 1 except that No. 1 and No. 2 of the three reactors were subjected to simulated skip.

Accordingly, the feed forward performance controller quickly opens the anti-surge valve and the changed target exhaust flow sent to the vane controller is one third of the previous, constant pressure. Due to the larger opening, the anti-surge valve opening per reduction increases to 5% during feed forward control.

In the process, the air intake pressure and flow in reactor No. 3 were monitored, and the operating state of the reactor was checked. As a result, it was found that the fluctuation of the air intake pressure and flow rate of the reactor No. 3 was not large. The reactor works stably, the product yield and the product quality are stable, and the influence of the jumping of the No. 1 and No. 2 reactors is avoided.

Comparative example 1:

the maleic anhydride reactor was supplied with air in the same apparatus as in example 1, except that no feed forward controller was provided.

After the simulated No. 1 reactor is tripped, the exhaust pressure measurement value rises quickly, the feedback control of the anti-surge controller is triggered, and the anti-surge valve is fully opened. And the No. 2 and No. 3 reactors jump due to insufficient air supply shortly after the anti-surge valve is fully opened, and stop running.

Comparative example 2:

the maleic anhydride reactor was supplied with air in the same apparatus as in example 2, except that no feed forward controller was provided.

After the simulation of the reactor 1 and the reactor 2, the exhaust pressure measurement value rises quickly, the feedback control of the anti-surge controller is triggered, and the anti-surge valve is fully opened. After the anti-surge valve is fully opened, the No. 3 reactor quickly jumps due to insufficient air supply and stops running.

Therefore, when one or more of the maleic anhydride reactors is or are suddenly shut down, the device and the method ensure that the air compressor is not damaged due to surge and simultaneously ensure that the rest reactors are not abnormally operated or shut down in an interlocking manner due to sudden air supply reduction.

In addition, the above experiment was also conducted on the system for producing maleic anhydride by the benzene process, and similar experimental results were obtained.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. An air supply apparatus for a maleic anhydride production system comprising a plurality of reactors, the air supply apparatus comprising:

an axial-flow type air compressor provided with a stationary blade and an anti-surge valve;

a stationary vane controller that controls a stationary vane angle based on a target exhaust pressure and/or flow feedback;

an anti-surge valve controller that controls an opening of an anti-surge valve based on an anti-surge line feedback of the air compressor; and

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

wherein, the jump emergency control includes: feedforward controlling the anti-surge valve opening, and changing the target exhaust pressure and/or flow rate of the vane controller.

2. The air supply apparatus of claim 1, wherein the skip emergency control further comprises feed forward control of the vane angle.

3. The air supply device according to claim 1, further comprising:

an exhaust pressure sensor;

a throat differential pressure sensor; and

an optional exhaust gas flow sensor is provided and,

wherein the stationary blade controller performs its feedback control based on a measurement value of the exhaust pressure sensor or the exhaust flow sensor,

the anti-surge valve controller performs feedback control thereof based on the measured values of the exhaust pressure sensor and the throat differential pressure sensor,

the static vane controller and the anti-surge valve controller are controllers embedded with PID algorithm.

4. A maleic anhydride production system comprising multiple reactors, wherein the maleic anhydride production system comprising multiple reactors comprises:

a plurality of maleic anhydride reactors, and

the air supply device according to any one of claims 1-3, an air compressor outlet conduit of the air supply device being in fluid communication with the reactor inlet conduits of the plurality of maleic anhydride reactors, such that the plurality of maleic anhydride reactors are connected in parallel downstream of the air compressor.

5. A method of operating a maleic anhydride production system comprising multiple reactors according to claim 4, wherein the method of operating comprises:

when the plurality of maleic anhydride reactors are operated, the vane controller feedback-controls a vane angle based on a target exhaust pressure and/or flow rate and according to a measurement value, and the anti-surge valve controller feedback-controls an anti-surge valve opening based on an anti-surge line of the air compressor and according to a measurement value;

when at least one of the plurality of maleic anhydride reactors skips the vehicle, the feedforward performance controller starts the vehicle skipping emergency control after receiving a vehicle skipping signal of the maleic anhydride reactor, and ends the vehicle skipping emergency control after the anti-surge valve is closed, wherein the vehicle skipping emergency control comprises:

i) According to the number of the maleic anhydride reactors which are in residual operation, quickly opening the anti-surge valve to a first opening degree, and changing the target exhaust pressure and/or flow of the static vane controller;

ii) reducing the anti-surge valve from the first opening angle, then waiting for the vane angle to stabilize;

iii) Repeating operation ii) until the anti-surge valve closes.

6. The operating method according to claim 5, characterized in that in operation ii) the opening degree of the antisurge valve is reduced by 2% -5% each time.

7. The method of operation of claim 5, comprising:

the vane is quickly closed to a first angle while the anti-surge valve is quickly opened.

8. Use of an air supply device according to one of the claims 1 to 3 for a production system comprising multiple reactors,

the feed-forward performance controller is configured to initiate a trip emergency control upon receiving a trip signal from the reactor.

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