Centrifugal blowing control system and control method for preparing phthalic anhydride through oxidation of o-xylene

Abstract

The invention discloses a centrifugal blowing control system and a control method for preparing phthalic anhydride by oxidizing o-xylene. The centrifugal blowing control system comprises a microcontroller, an oxidation fan arranged on one side of an air inlet of the oxidation reactor, a mass flow meter arranged on one side of a material inlet of the oxidation reactor, a reaction product monitor arranged on one side of a material outlet of the oxidation reactor, and a temperature sensor arranged in the oxidation reactor; the control method comprises the steps that oxidation reaction parameters are detected in real time, and a dynamic interlocking model between the current air outlet volumes of the oxidation fans is established based on the feeding amount and the reaction product concentration; and recalculating the required current air outlet volume according to the dynamic interlocking model, and adjusting the rotation frequency of the oxidation fan according to the current air outlet volume. According to the method, multi-parameter cooperative regulation and control are achieved, accurate air volume adaptation is achieved, manual valve adjustment is reduced, the workload is reduced, meanwhile, the process matching performance is improved, the energy consumption of the system can be effectively reduced, the production cost is reduced, and the phthalic anhydride yield is increased.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical production process control, and particularly relates to a centrifugal blower control system and control method for preparing phthalic anhydride by oxidizing o-xylene. BACKGROUND

[0002] The preparation of phthalic anhydride by gas-phase catalytic oxidation of xylene is the mainstream process for the industrial production of phthalic anhydride. With the improvement of catalyst performance and the large-scale production equipment, the production capacity of phthalic anhydride per unit gradually expands. At present, in the process of preparing phthalic anhydride by oxidizing o-xylene, the centrifugal blower at the inlet of the oxidation reactor is the core oxygen supply equipment, and the gas flow control is directly related to the reaction efficiency and product yield. The centrifugal blower usually operates at a constant speed, and the air volume control in the oxidation reactor mainly relies on the control of the valve, and the amount depends on the manual experience to adjust the air volume, which has great experience and uncertainty. The existing control technology has the following systematic defects:

[0003] (1) The unbalanced process caused by the backward control means, the constant speed operation of the blower, the air volume adjustment relying on the inlet / outlet valve opening, the fixed value or manual adjustment of the inlet / outlet air volume of the oxidation reactor, and the rough control method causing the imbalance of the oxygen / hydrocarbon ratio and the increase of by-products (such as benzoic acid and maleic anhydride); the local temperature of the catalyst bed is overheated, the selectivity is reduced, the valve opening adjustment depends on the operator's experience, lacks quantitative standard, and causes the large fluctuation of the phthalic anhydride yield;

[0004] (2) The single parameter control causes the chain problem, the air volume is adjusted only by the single parameter of the reactor temperature, the dynamic correlation of the raw materials and products is not considered, the air volume and the feed amount are not closed-loop linked, the load change cannot be adapted, and the real-time feedback control of the product composition is lacked

[0005] Based on the above defects, it is urgent to develop a centrifugal blower control system and control method for preparing phthalic anhydride by oxidizing o-xylene, which can fuse the raw material feed amount, product composition and temperature data to establish a dynamic decision model in real time; so as to realize the precise control of the oxygen / hydrocarbon ratio and reduce the generation of by-products. SUMMARY

[0006] The purpose of the present application is to provide a centrifugal blower control system and control method for preparing phthalic anhydride by oxidizing o-xylene, which realizes the precise adaptation of the air volume through the multi-parameter collaborative regulation, realizes the real-time automatic control of the air volume, reduces the manual adjustment of the valve, reduces the workload, improves the process matching, effectively reduces the energy consumption of the system, reduces the production cost, improves the yield of phthalic anhydride, and is suitable for the intelligent upgrading of chemical production. In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] According to one aspect of the present application, the present application provides a centrifugal blast control system for preparing phthalic anhydride by oxidizing o-xylene, which comprises a microcontroller 1, an oxidation fan arranged at one side of an air inlet of an oxidation reactor, a mass flow meter arranged at one side of a material inlet of the oxidation reactor, a reaction product monitor arranged at one side of a material outlet of the oxidation reactor, and a temperature sensor arranged in the oxidation reactor, wherein an air outlet of the oxidation fan is communicated with the one side of the air inlet of the oxidation reactor through an air supply main pipe, and the detection output ends of the mass flow meter, the reaction product monitor, and the temperature sensor are connected with the microcontroller respectively, and the control end of the oxidation fan is connected with the control output end of the microcontroller through a frequency converter.

[0008] Further preferably, the centrifugal blast control system further comprises an air preheater arranged at one side of the air outlet of the oxidation fan, and the air outlet of the oxidation fan is communicated with the air inlet port of the air preheater.

[0009] Further preferably, the centrifugal blast control system further comprises a buffer mixer, which has a material inlet and an air inlet, and the material outlet of the buffer mixer is communicated with the one side of the material inlet of the oxidation reactor through a feeding pipe, and the mass flow meter is arranged on the feeding pipe and at one side close to the material inlet of the oxidation reactor.

[0010] Further preferably, the air supply branch pipe communicated with the air inlet of the buffer mixer is arranged on the air supply main pipe at one side close to the air outlet of the oxidation fan, and an air volume control valve is arranged on the air supply branch pipe and connected with the microcontroller.

[0011] According to another aspect of the present application, the present application provides a control method of a centrifugal blast control system for preparing phthalic anhydride by oxidizing o-xylene, which comprises the following steps:

[0012] Step 1, real-time detection of oxidation reaction parameters, which comprises real-time detection of the feeding amount Q OX of o-xylene into the oxidation reactor, real-time detection of the concentration of reaction products discharged at one side of the material outlet of the oxidation reactor, and real-time detection of the temperature data in the oxidation reactor, and feeding the feeding amount Q OX , the concentration of reaction products C PA , and the temperature data T x into the microcontroller respectively;

[0013] Step 2, establishment of the current air outlet volume V OX of the oxidation fan based on the feeding amount Q PA , the concentration of reaction products C airDynamic interlocking model between them;

[0014] Step 3, based on the current temperature data T of the oxidation reaction x Determine if the temperature is greater than the threshold temperature T o If the temperature exceeds the threshold, the required current air volume V will be recalculated based on the dynamic interlocking model. air According to the current air volume V air Adjust the rotation frequency f of the oxidation blower n This ensures stable operation of the oxidation blower and precise supply of air and oxygen to the oxidation reactor.

[0015] In a further preferred embodiment of the above-described scheme of the present invention, the dynamic interlocking model satisfies:

[0016]

[0017] Wherein, κ1 is the linear coefficient between raw material and air volume, and κ2 is the air volume compensation for the rate of change in reaction product concentration.

[0018] κ3 is the concentration deviation integral adjustment coefficient. The target concentration.

[0019] In a further preferred embodiment of the above-described scheme of the present invention, the air volume V air With rotational frequency f n The relationship satisfies:

[0020]

[0021] k is the number of pole pairs of the drive motor in the oxidation blower, η is the gain coefficient (0.5-2.0), and ΔO2 is the oxygen balance coefficient in the oxidation reactor; whereby ΔO2, the oxygen balance coefficient in the oxidation reactor, satisfies:

[0022]

[0023] A is the theoretical oxygen consumption coefficient, which is the molar ratio of oxygen required for the complete oxidation of a unit of o-xylene.

[0024] In a further preferred embodiment of the above-described scheme of the present invention, the control method further includes preheating the air intake of the oxidation blower and mixing and preheating the o-xylene fed into the feed inlet of the oxidation reactor with hot air.

[0025] In summary, the invention adopts the above-mentioned technical solution and has the following technical effects:

[0026] The control system and control method of the application realize multi-parameter coordinated control to realize accurate air volume matching, can realize real-time automatic control of air volume, reduce manual adjustment of valves, reduce workload, improve the accuracy of air supply, solve the problem of imbalance of oxygen / hydrocarbon ratio, improve process matching, effectively reduce the energy consumption of the system, reduce production cost, improve the yield of phthalic anhydride, and is suitable for intelligent upgrading of chemical production. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a system principle diagram of a first embodiment of a centrifugal blast control system for preparing phthalic anhydride by oxidizing o-xylene according to the application;

[0028] Figure 2 is a system principle diagram of a second embodiment of a centrifugal blast control system for preparing phthalic anhydride by oxidizing o-xylene according to the application;

[0029] Figure 3 is a control method of a centrifugal blast control system for preparing phthalic anhydride by oxidizing o-xylene according to the application;

[0030] In the drawings, microcontroller 1, oxidation fan 3, frequency converter 4, air preheater 5, buffer mixer 6, mass flowmeter 10, reaction product monitor 11, temperature sensor 12, air volume control valve 13. DETAILED DESCRIPTION

[0031] To make the purpose, technical scheme and advantages of the application clearer and more apparent, the application is further described in detail below with reference to the drawings and preferred embodiments. However, it should be noted that many details listed in the description are only to make the reader have a thorough understanding of one or more aspects of the application, and the aspects of the application can be realized even without these specific details.

[0032] In combination Figure 1 , the application provides a centrifugal blast control system for preparing phthalic anhydride by oxidizing o-xylene, which comprises a microcontroller 1, an oxidation fan 3 arranged at the air inlet side of an oxidation reactor 2, a mass flowmeter 10 arranged at the material inlet side of the oxidation reactor, a reaction product monitor 11 arranged at the material outlet side of the oxidation reactor, and a temperature sensor 12 arranged in the oxidation reactor, the air outlet of the oxidation fan 3 is communicated with the air inlet side of the oxidation reactor 2 through a blast main pipe, the detection output end of the mass flowmeter 10, the detection output end of the reaction product monitor 11, and the detection output end of the temperature sensor 12 are connected with the microcontroller 1 respectively, and the control end of the oxidation fan 3 is connected with the control output end of the microcontroller 1 through a frequency converter 4; in the application, the microcontroller 1 adopts a PLC controller, the mass flowmeter 10 is used for detecting the feeding amount Q OXand the detected feed quantity is transmitted to the microcontroller 1; the reaction product monitor is an oxidation product gas chromatograph or an infrared spectrometer, preferably, an online gas chromatograph is arranged at the outlet of the oxidation reactor 2 for monitoring the concentration (C PA ) of phthalic anhydride, the concentration of by-products (maleic anhydride, CO x ); the reaction product monitor 11 (online gas chromatograph) samples once every 1-5 minutes and communicates in real time with the PLC controller through an OPC protocol; the temperature sensor 12 is used to detect the temperature of the oxidation reaction in the oxidation reactor 2; the present application analyzes and processes the real-time monitoring of the raw material feed quantity and the product component concentration and transmits them to the microcontroller 1; according to the analysis and processing results, the microcontroller 1 outputs a variable frequency control instruction and drives the frequency converter 4 to accurately adjust the rotation speed of the oxidation fan (blower); when the reaction temperature is approximately limited by safety, the emergency cooling of the air volume is triggered; when the feed is interrupted, it is automatically switched to the minimum air volume mode (maintaining the activity of the catalyst). Such an intelligent control method can effectively reduce the energy consumption of the system, reduce the production cost, increase the yield of phthalic anhydride, and is suitable for intelligent upgrading of chemical production.

[0033] As another embodiment of the present application, as shown in Figure 2 , the centrifugal blower control system of the present application further comprises an air preheater 5 and a buffer mixer 6; the air preheater 5 is arranged near the air outlet side of the oxidation fan; the air outlet of the oxidation fan 3 communicates with the air inlet port of the air preheater 5; the buffer mixer 6 has a material inlet and an air inlet; the material outlet of the buffer mixer 6 communicates with one side of the material inlet of the oxidation reactor 2 through a feeding pipe; the mass flow meter 10 is arranged on the feeding pipe and near the material inlet of the oxidation reactor 2; a branch air supply pipe that communicates with the air inlet of the buffer mixer 6 is arranged on the air supply main pipe near the air outlet of the air preheater 5; the air volume control valve 13 is arranged on the branch air supply pipe; the air volume control valve 13 is connected with the microcontroller 1; before the oxidation fan 3 sends the oxidation air into the oxidation reactor 2, the air is filtered and heated by the air preheater 5 and then sent into the oxidation reactor 2 for oxidation reaction, preventing the temperature in the oxidation reactor 2 from changing too much; before the o-xylene raw material is sent into the oxidation reactor 2, the air sucked from the outside by the oxidation fan 3 is filtered and preheated by the air preheater 5, and the hot air is sent into the buffer mixer 6 through the air supply main pipe and the branch air supply pipe; the hot air volume sent into the buffer mixer 6 is adjusted by the air volume control valve 13 during the conveying process in the branch air supply pipe, the o-xylene raw material is preheated and mixed, and then sent into the oxidation reactor 2 for high-temperature oxidation reaction, making the reaction more sufficient and reducing the by-products.

[0034] According to another aspect of the present application, as Figure 3As shown, the present invention provides a control method for a centrifugal blower control system for the oxidation of o-xylene to phthalic anhydride, the control method comprising the following steps:

[0035] Step 1: Real-time monitoring of oxidation reaction parameters, including the real-time monitoring of the feed rate Q of o-xylene into the oxidation reactor. OX The concentration of reaction products discharged from the outlet side of the oxidation reactor is monitored in real time, and the temperature data inside the oxidation reactor is monitored in real time. The feed rate Q is also recorded. OX Concentration of reaction products C PA Temperature data T x The data is fed into the microcontroller in real time.

[0036] Step 2, based on the feed rate Q OX Concentration of reaction products C PA Establish the current air volume V of the oxidation fan air The dynamic interlocking model between them; the control logic of air volume demand is based on the main reaction chemical equation in the oxidation process of phthalic anhydride to o-xylene:

[0037] C8H 10 +3O2→C8H4O3+3H2O

[0038] Oxygen makes up approximately 21% of the volume of air, therefore 1 mol of C8H2O... 10 3 mol of O2 requires 14.3 mol of air; theoretically, the volume ratio of air to o-xylene is approximately 14.3, and the mass ratio of air to o-xylene is 3.9.

[0039] Therefore, the dynamic interlocking model satisfies:

[0040]

[0041] Wherein, κ1 is the raw material-air volume linearity coefficient (determined by the stoichiometric ratio of the reaction),

[0042] κ2 is the airflow compensation for the rate of change in the concentration of reaction products, when When the value is negative (increased byproducts), the air volume is reduced by κ2 to inhibit excessive reaction;

[0043] κ3 is the concentration deviation integral adjustment coefficient, ensuring phthalic anhydride yield. Timely optimization of airflow ensures phthalic anhydride yield. When C PA Less than the target phthalic anhydride concentration Triggering the integral term κ3 increases airflow and enhances oxidation.

[0044] The target concentration;

[0045] Based on the feed rate Q of o-xylene OXand the concentration of phthalic anhydride C PA , the correlation between the concentration of phthalic anhydride C air and the wind volume V x , dynamically calculates the optimal wind volume V o ; based on the process requirements, sets a safety dynamic interlock model and makes safety protection actions in time;

[0046] Step 3, based on the temperature data T x of the current oxidation reaction, judges whether it is greater than the threshold temperature T o , if it is greater than the threshold temperature, according to the dynamic interlock model, recalculates the required current air volume V air ; based on the current air volume V air , adjusts the rotation frequency f n of the oxidation fan, so that the oxidation fan runs stably and accurately supplies air and oxygen to the oxidation reactor; the oxidation fan (centrifugal blower) is equipped with a frequency converter 4, which receives instructions from the microcontroller 1 to adjust the speed and accurately control the air volume V air , realizes safety interlock control, based on the oxidation process requirements of o-xylene to phthalic anhydride, the reaction temperature is 400-460℃, when the temperature exceeds 460℃, increase the air volume by 20% to reduce the temperature, which needs to be handled in priority, when the feed is interrupted, automatically switch to the minimum air volume mode (maintain the activity of the catalyst)

[0047] The relationship between the air volume V air and the rotation frequency f n satisfies:

[0048]

[0049] k is the number of pole pairs of the driving motor in the oxidation fan, η is the gain coefficient (0.5-2.0), ΔO2 is the oxygen balance coefficient in the oxidation reactor (the relative deviation between the theoretical oxygen demand and the actual oxygen supply); wherein, the oxygen balance coefficient ΔO2 in the oxidation reactor satisfies:

[0050]

[0051] A is the theoretical oxygen consumption coefficient, the unit is the molar ratio of oxygen required for complete oxidation of o-xylene, and the main reaction chemical equation is:

[0052] The raw material feed quantity Q OX and the product concentration C PA are synchronized into the air volume decision, breaking through the single parameter control limitation, realizing double parameter collaborative control:

[0053] (1) Dynamic compensation mechanism: with the closed loop linkage of raw material feed quantity-blast volume and the dynamic compensation mechanism of product component concentration-air volume, through the differential term and the integral term Early response to the trend of side reaction; when the o-xylene feed is detected to be interrupted, automatically switch to the minimum air volume mode, which is 25-35% of the theoretical oxygen demand;

[0054] (2) Frequency energy-saving coupling: based on the frequency-air volume relationship to realize nonlinear energy-saving regulation, and realize safe dynamic interlocking: when the reaction temperature > 460℃, adjust the air blower to run to the highest speed gear to trigger the air volume to increase by 20% for emergency cooling; when the feed is interrupted, automatically switch to the minimum air volume mode (maintain catalyst activity); use variable frequency direct control instead of valve throttling (reduce energy consumption by 15-20%), and real-time fusion of raw material feed quantity, product components, and temperature data to establish a dynamic decision model, realize the dual safety interlocking of over-temperature large air volume cooling / discontinuous minimum air volume activity preservation, and the purpose of precise control of oxygen / hydrocarbon ratio, improve the yield of phthalic anhydride, and reduce the generation of by-products.

[0055] The present application realizes precise air volume matching through multi-parameter coordinated regulation, can realize real-time automatic control of air volume, reduces manual adjustment of valves, reduces workload while improving the accuracy of air supply, solves the problem of imbalance of oxygen / hydrocarbon ratio, improves process matching, effectively reduces the energy consumption of the system, reduces production cost, improves the yield of phthalic anhydride, and is suitable for intelligent upgrading of chemical production;

[0056] In the present application, as shown in Figure 2 In the air volume and feed control process, the control method further comprises preheating the air entering the air inlet of the oxidation air blower and mixing and preheating the o-xylene on one side of the feed inlet of the oxidation reactor with hot air. Before the oxidation air blower 3 sends the oxidation air into the oxidation reactor 2, the oxidation air sucked by the oxidation air blower 3 is sent to the air preheater 5 for filtration and heating, and the oxidation air sucked by the oxidation air blower 3 is sent to the air preheater 5 to increase the temperature of the compressed air, so as to reach the required temperature for the reaction, and then sent into the oxidation reactor 2 for oxidation reaction, preventing the temperature from changing too much when the air in the oxidation reactor 2 is mixed; before the o-xylene raw material is sent into the oxidation reactor 2, the hot air preheated by the air preheater 5 is sent into the buffer mixer 6 through the oxidation air blower 3 and the air supply branch pipe, and the hot air volume sent into the buffer mixer 6 is adjusted by the air volume control valve 13, and the o-xylene raw material is preheated and mixed, and then sent into the oxidation reactor 2 for high-temperature oxidation reaction, so that the reaction is more sufficient and the by-products are reduced.

[0057] The above only describes the preferred embodiments of the application, and it should be noted that those skilled in the art can make some improvements and refinements without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A centrifugal blast control system for the oxidation of ortho-xylene to phthalic anhydride, characterized by: The centrifugal blast control system comprises a microcontroller 1, an oxidation air blower arranged at the air inlet side of the oxidation reactor, a mass flow meter arranged at the material inlet side of the oxidation reactor, a reaction product monitor arranged at the material outlet side of the oxidation reactor, and a temperature sensor arranged in the oxidation reactor, the air outlet of the oxidation air blower is communicated with the air inlet side of the oxidation reactor through an air supply main pipe, the detection output ends of the mass flow meter, the reaction product monitor and the temperature sensor are connected with the microcontroller, and the control end of the oxidation air blower is connected with the control output end of the microcontroller through a frequency converter.

2. A centrifugal blast control system for the oxidation of o-xylene to phthalic anhydride according to claim 1, characterized in that: The centrifugal blast control system further comprises an air preheater arranged at the air outlet side of the oxidation air blower, and the air outlet of the oxidation air blower is communicated with the air inlet port of the air preheater.

3. A centrifugal blast control system for the oxidation of ortho-xylene to phthalic anhydride according to claim 2, characterized in that: The centrifugal blast control system further comprises a buffer mixer, the buffer mixer has a material inlet and an air inlet, the material outlet of the buffer mixer is communicated with the material inlet side of the oxidation reactor through a feeding pipe, and the mass flow meter is arranged on the feeding pipe and at the material inlet side of the oxidation reactor.

4. A centrifugal blast control system for the oxidation of ortho-xylene to phthalic anhydride according to claim 3, characterized in that: An air supply branch pipe communicated with the air inlet of the buffer mixer is arranged on the air supply main pipe at the air outlet side of the air preheater, and an air volume control valve is arranged on the air supply branch pipe and connected with the microcontroller.

5. A control method for a centrifugal blast control system for the oxidation of o-xylene to phthalic anhydride according to any one of claims 1 to 4, characterized in that: The control method comprises the following steps: Step 1, real-time detection of oxidation reaction parameters, including real-time detection of the amount of o-xylene entering the oxidation reactor as feed Q OX , real-time detection of the concentration of reaction products discharged from the discharge side of the oxidation reactor, and real-time detection of temperature data in the oxidation reactor, and feeding the amount of feed Q OX , the concentration of reaction products C PA , and the temperature data T x into the microcontroller in real time, respectively; Step 2, based on the feed amount Q OX , the reaction product concentration C PA Establish a dynamic interlocking model between the current air output V of the oxidation fan air ​ Step 3, based on the current oxidation reaction temperature data T x Determine whether greater than threshold temperature T o If greater than threshold temperature, recalculate the required current air volume V air According to the current air volume V air Adjust the rotation frequency f n of the oxidation fan, so that the oxidation fan runs stably and accurately supplies oxygen to the oxidation reactor.

6. The control method of the centrifugal blast control system for the oxidation of o-xylene to phthalic anhydride according to claim 5, characterized in that: The dynamic interlocking model satisfies: wherein κ1 is a raw material-air volume linear coefficient, κ2 is an air volume compensation of a reaction product concentration change rate, A is a theoretical oxygen consumption coefficient, and the unit is the molar ratio of oxygen required for complete oxidation of o-xylene. K3 is a concentration deviation integral adjustment coefficient, is the target concentration.

7. The control method of the centrifugal blast control system for the oxidation of o-xylene to phthalic anhydride according to claim 6, characterized in that: The air volume V air The relationship between the rotation frequency f n satisfies: k is the number of pole pairs of the driving motor in the oxidation blower, η is the gain coefficient (0.5-2.0), ΔO2 is the oxygen balance coefficient in the oxidation reactor; wherein, the oxygen balance coefficient ΔO2 in the oxidation reactor satisfies: The control method further comprises preheating the air inlet of the oxidation air blower and mixing and preheating o-xylene with hot air at the material inlet side of the oxidation reactor.

8. The control method of the control system for the oxidation of o-xylene to phthalic anhydride according to claim, characterized in that: ​

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