CN107837556B - Operation control method of dividing wall rectifying tower - Google Patents

Operation control method of dividing wall rectifying tower Download PDF

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CN107837556B
CN107837556B CN201610831436.4A CN201610831436A CN107837556B CN 107837556 B CN107837556 B CN 107837556B CN 201610831436 A CN201610831436 A CN 201610831436A CN 107837556 B CN107837556 B CN 107837556B
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tower
product
liquid level
dividing wall
control
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CN107837556A (en
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郭艳姿
陈亮
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China Petroleum and Chemical Corp
Sinopec Shanghai Research Institute of Petrochemical Technology
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China Petroleum and Chemical Corp
Sinopec Shanghai Research Institute of Petrochemical Technology
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14Fractional distillation or use of a fractionation or rectification column
    • B01D3/141Fractional distillation or use of a fractionation or rectification column where at least one distillation column contains at least one dividing wall
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14Fractional distillation or use of a fractionation or rectification column
    • B01D3/143Fractional distillation or use of a fractionation or rectification column by two or more of a fractionation, separation or rectification step
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14Fractional distillation or use of a fractionation or rectification column
    • B01D3/32Other features of fractionating columns ; Constructional details of fractionating columns not provided for in groups B01D3/16 - B01D3/30
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14Fractional distillation or use of a fractionation or rectification column
    • B01D3/32Other features of fractionating columns ; Constructional details of fractionating columns not provided for in groups B01D3/16 - B01D3/30
    • B01D3/322Reboiler specifications
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/42Regulation; Control
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/42Regulation; Control
    • B01D3/4205Reflux ratio control splitter
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/42Regulation; Control
    • B01D3/4211Regulation; Control of columns
    • B01D3/4255Head-, side-, bottom- and feed stream

Abstract

The invention relates to an operation control method of a dividing wall rectifying tower, which mainly solves the technical problems that the operation control of the conventional dividing wall rectifying tower is difficult, the stability is poor and the product quality and the yield are difficult to control. The invention adopts five control areas of the dividing wall rectifying tower: the technical scheme of controlling the temperature, flow and liquid level in the raw material feeding control area, the tower top reflux and extraction control area, the liquid collection and distribution control area, the side extraction control area and the tower bottom extraction control area better solves the technical problems and can be used in the industrial production of the dividing wall rectifying tower.

Description

Operation control method of dividing wall rectifying tower
Technical Field
The invention relates to an operation control method of a dividing wall rectifying tower, which can be used in the industrial production of the dividing wall rectifying tower.
Background
Rectification is the most mature and widely applied separation technology in petrochemical production, but the energy consumption in the rectification process is huge, and it is estimated that 40-70% of the energy consumption in the chemical process is used for separation, and the rectification energy consumption accounts for 95% of the energy consumption. In order to reduce the energy consumption in the rectification process, researchers at home and abroad carry out extensive research, and the dividing wall rectification tower is widely concerned as a typical rectification energy-saving device or a process strengthening energy-saving technology.
The dividing wall rectifying tower is characterized in that one or more vertical partition plates with certain length or partition plates with inclined angles are arranged in one rectifying tower, and a set of vaporization and condensation system is adopted to simultaneously separate three or more products. Because only one set of vaporization and condensation system is provided and the remixing of the intermediate components is avoided when multi-tower rectification is adopted, the investment is saved by 20-30% and the energy consumption is reduced by 20-40% in the dividing wall rectification technology compared with the traditional rectification technology.
Actually, in 1930, Eeic w.lustrer (US1915681) proposed the concept of the dividing wall rectifying tower for the separation of cracked gas, but the first dividing wall rectifying tower (BASF) was not put into industrial production until 1985, and only 200 or more dividing wall rectifying towers were used in industrial application, so far, and it was difficult to widely popularize, and the fundamental reason among them is that the dividing wall rectifying tower has a great difficulty in operation and control, besides the lack of reliable structural design, which is a crucial point that is not neglected.
Taking the most common dividing wall rectifying tower for three-component separation as an example, the partition is arranged along the axial direction of the tower, and the dividing wall rectifying tower is divided into a public rectifying section above the partition, a public stripping section below the partition and a dividing wall section where the partition is located, wherein the dividing wall section is divided into a feeding side and a product side according to different feeding and intermediate component extraction. Therefore, compared with the conventional rectifying tower, the dividing wall rectifying tower has more freedom degrees due to the structural particularity, and besides the same process parameters as the conventional rectifying tower, such as operating pressure, cold and heat load, reflux ratio, product extraction amount and the like, the dividing wall rectifying tower also comprises the extraction of a side product and the distribution of gas phase and liquid phase at two sides of the clapboard, moreover, the high coupling among the above process parameters, the change of any one of them will bring direct influence on the operation of other parameters, for example, the change of the amount of the overhead reflux liquid not only affects the quality of the overhead product, but also directly changes the total amount of the bottom distillate liquid of the public rectification section, under the condition of fixing the liquid phase distribution ratio at two sides, the liquid distribution amounts at two sides of the partition plate are directly influenced, and the pre-separation effect at the feed side of the partition wall section and the lateral line product quality at the product side are directly influenced by the change of the liquid distribution amounts at two sides; if the amount of liquid distributed on the two sides is fixed, the change of the amount of reflux liquid on the top of the tower directly destroys the material balance in the tower and affects the processes of mass transfer, heat transfer and gas-liquid balance, so the high coupling and chain reaction among the process parameters in the dividing wall rectifying tower can obviously affect the product quality and stable operation control of the dividing wall rectifying tower, which is the direct reason that the dividing wall rectifying tower is difficult to realize stable control, and is a research key point and difficulty in the development process of the dividing wall rectifying tower.
At present, the Operation control of the dividing wall rectifying tower is disclosed in less patent publications, and CN102631791A discloses a control method of the dividing wall rectifying tower, which is mainly to add a control loop on the basis of three-point control method (Operation integrated route-product (petlyuk) distillation columns, e.a.wolff, s.skogestad, ind.eng.chem.res.,1995,34(6): 2094-2103) of e.a.wolff et al, i.e. to control the purity of the overhead product by adjusting the amount of the reflux overhead, to control the purity of the sidedraw product by adjusting the amount of the sidedraw, and to control the purity of the bottom product by adjusting the amount of the vapor in the bottom, to control the content of the heavy component in the ascending vapor phase at the top of the feeding side by adjusting the liquid phase distribution ratio at both sides of the dividing wall rectifying tower. Although the product quality is correspondingly controlled, the discharge amount of products at the top of the tower and the bottom of the tower are not controlled, the yield of each product including a side product cannot be ensured, and meanwhile, the liquid levels of a plurality of areas in the tower, such as a tower top reflux area, a public rectification section bottom liquid collection and distribution area and a tower bottom area are not controlled, so that the material balance and stable control of the dividing wall rectification tower are difficult to ensure.
Obviously, the control method in the prior art cannot ensure the product quality and the product yield at the same time, and cannot realize stable operation, so that a more effective operation control method needs to be developed to comprehensively control a plurality of process parameters or operation variables of the dividing wall rectifying tower, realize the stable operation of the dividing wall rectifying tower, and simultaneously ensure the quality and the yield of each product.
Disclosure of Invention
The invention aims to solve the technical problems that the operation control of the dividing wall rectifying tower is difficult, the stability is poor and the product quality and yield are difficult to control in the prior art. The invention provides an operation control method of a dividing wall rectifying tower, which realizes the comprehensive control of the dividing wall rectifying tower by controlling the temperature, the flow and the liquid level of different areas in the dividing wall rectifying tower, ensures the product quality and the product yield, realizes the stable control and can be used in the industrial production of the dividing wall rectifying tower.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the dividing wall rectifying tower comprises 5 control areas which are respectively: the system comprises a raw material feeding control area, a tower top reflux and extraction control area, a liquid collecting and distributing control area, a side extraction control area and a tower kettle extraction control area, wherein the control method of each control area comprises the following steps:
(1) raw material feeding control area: controlling the raw material feeding amount by adopting a flow controller and controlling the raw material feeding temperature by adopting a temperature controller;
(2) the tower top reflux and extraction control area: controlling the amount of reflux liquid at the top of the tower by adopting a temperature controller, controlling the extraction amount of products at the top of the tower by adopting a flow controller, and controlling the heat of a reboiler at the bottom of the tower by adopting a liquid level controller;
(3) liquid collection and distribution control area: controlling the flow of the distillate at the bottom of the public distillation section by adopting a liquid level controller and controlling the distribution liquid amount at the product side of the dividing wall section by adopting a temperature controller;
(4) side draw control zone: controlling the side product extraction amount by adopting a flow controller;
(5) the extraction control area of the tower kettle: and controlling the product extraction amount of the tower kettle by adopting a liquid level controller.
In the technical scheme, the flow controller in the raw material feeding control area controls the raw material feeding amount, and the actual raw material feeding amount is automatically adjusted according to the set raw material feeding amount. The specific control process is as follows: and (3) leading the measured actual raw material feeding quantity signal into a flow controller, outputting a signal to a raw material feeding regulating valve by the flow controller according to the size relation between the actual measured value and the set value of the raw material feeding quantity, and correspondingly regulating the opening degree by the regulating valve until the actual measured value is basically the same as the set value.
In the technical scheme, the temperature controller in the raw material feeding control area controls the temperature of the sensitive plate at the feeding side of the dividing wall section of the dividing wall rectifying tower, and the raw material feeding temperature is automatically adjusted according to the temperature of the sensitive plate. The main function of the feed side is to realize the pre-separation of the raw materials, namely, part of middle components enter the public rectification section along with light components, and the rest of middle components enter the public stripping section along with heavy components, so that the temperature control of the sensitive plate at the feed side of the bulkhead section is realized by adjusting the feed temperature of the raw materials, the pre-separation effect can be ensured, and the heavy components are effectively prevented from entering the public rectification section from the upper part of the partition plate and then entering the product side in a liquid phase mode to influence the quality of side line products. Usually, the sensitive plate on the feeding side of the wall segment of the dividing wall rectifying tower is positioned at the top or in the middle-upper part of the feeding side. The specific control process is as follows: and (3) leading the temperature signal of the sensitive plate at the feeding side, which is actually measured, into a temperature controller, outputting a signal to a raw material preheater by the temperature controller according to the magnitude relation between the actual measured value and the set value of the temperature, and correspondingly adjusting the preheating temperature of the raw material by the raw material preheater until the measured value of the temperature of the sensitive plate at the feeding side is basically the same as the set value.
In the technical scheme, the temperature of a sensitive plate of a public rectifying section of the dividing wall rectifying tower is controlled by a temperature controller in the tower top reflux and extraction control area, and the flow of tower top reflux liquid is automatically adjusted according to the temperature of the sensitive plate. Due to the corresponding relation between the temperature and the composition, the temperature control of the sensitive plate of the public rectification section is realized by adjusting the reflux liquid amount of the tower top, and the product quality of the tower top can be ensured. Typically, the common rectification section sensitive plate is located at the top or middle upper part of the common rectification section. The specific control process is as follows: and (3) leading actually measured temperature signals of the sensitive plates of the public rectification section into a temperature controller, outputting signals to a reflux adjusting valve at the top of the tower by the temperature controller according to the size relation between the actually measured temperature value and the set value, and correspondingly adjusting the opening of the reflux adjusting valve until the measured temperature value of the sensitive plates of the public rectification section is basically the same as the set value.
In the technical scheme, the flow controller in the tower top reflux and extraction control area controls the extraction amount of the tower top product, the flow is set according to the feeding amount of the raw material and the percentage content of the corresponding light component in the feeding composition, and the actual extraction amount of the tower top product is automatically adjusted according to the set product extraction amount, so that the yield of the tower top product is ensured. The specific control process is as follows: and (3) introducing the actually measured signal of the extraction amount of the tower top product into a flow controller, outputting a signal to a tower top product extraction regulating valve by the flow controller according to the size relation between the actually measured value of the flow and the set value, and correspondingly regulating the opening by the regulating valve until the actually measured value of the extraction amount of the tower top product is basically the same as the set value.
In the technical scheme, the liquid level controller in the tower top reflux and extraction control area controls the liquid level of the tower top reflux tank, and the heat of a reboiler of the tower kettle is automatically adjusted according to the liquid level to ensure the ascending vapor amount of the tower kettle. Because the reflux and the extraction at the top of the tower are correspondingly controlled, the liquid level of the reflux tank at the top of the tower is stable, the stable operation of the reflux and the extraction areas at the top of the tower is equal to that of the reflux and the extraction areas at the top of the tower, and the material balance of light components in the dividing-wall rectifying tower is ensured. The specific control process is as follows: and (3) guiding the actually measured liquid level signal of the tower top reflux tank into a liquid level controller, outputting a signal to a tower kettle reboiler by the liquid level controller according to the size relation between the actually measured liquid level value and the set value, and correspondingly adjusting the heating power or the flow of the heating medium by the tower kettle reboiler until the measured liquid level value of the tower top reflux tank is basically the same as the set value.
In the technical scheme, the liquid level controller in the liquid collection and distribution control area controls the liquid level of the liquid collection area at the bottom of the public rectifying section of the dividing wall rectifying tower, and the total flow of bottom distillate liquid is automatically adjusted according to the liquid level. Because the liquid distribution on the two sides of the partition plate directly influences the separation result of the dividing wall rectifying tower, and the distributed liquid comes from the liquid in the liquid collecting area at the bottom of the public rectifying section, the liquid level control is carried out on the area, thereby being beneficial to avoiding the material leakage of a gas phase or the overflow of a liquid phase and simultaneously ensuring the liquid distribution effect on the side of the partition plate and the stable operation of the dividing wall rectifying tower. The specific control process is as follows: and (3) introducing a liquid level signal of the liquid collection area which is actually measured into a liquid level controller, outputting a signal to a distillate liquid regulating valve by the liquid level controller according to the size relation between the actual measured value of the liquid level and the set value, and correspondingly regulating the opening of the regulating valve until the measured value of the liquid level of the collection area is basically the same as the set value.
In the technical scheme, the temperature controller in the liquid collection and distribution control area controls the temperature of the sensitive plate at the product side of the dividing wall section of the dividing wall rectifying tower, and the distribution liquid amount at the product side is automatically adjusted according to the temperature of the sensitive plate. The temperature of the sensitive plate at the product side of the partition wall section directly influences the quality of a lateral line product, so that the temperature of the product side is controlled, and the quality of the lateral line product is ensured; meanwhile, the adjustment of the liquid distribution amount on the product side is equal to the adjustment of the reflux ratio which is a key process parameter on the product side, and the lateral line product quality can be better controlled. Usually, the sensitive plate on the product side of the wall segment of the dividing wall rectifying tower is positioned at the bottom or the middle-lower part of the product side. The specific control process is as follows: and (3) leading actually measured temperature signals of the sensitive plate at the product side of the partition wall section into a temperature controller, outputting the signals to a liquid regulating valve at the product side by the temperature controller according to the size relation between the actually measured temperature value and the set value, and correspondingly regulating the opening by the regulating valve until the measured temperature value of the sensitive plate at the product side is basically the same as the set value.
In the technical scheme, the flow controller in the side draw control area controls the side draw amount of the side product, the flow rate of the side product is set according to the feeding amount of the raw material and the percentage content of the corresponding intermediate component in the feeding composition, and the actual side draw amount of the side product is automatically adjusted according to the set product draw amount, so that the yield of the side product is ensured. The specific control process is as follows: and (3) introducing the actually measured lateral product extraction quantity signal into a flow controller, outputting a signal to a lateral product extraction regulating valve by the flow controller according to the size relation between the actually measured flow value and the set value, and correspondingly regulating the opening degree by the regulating valve until the actually measured lateral product extraction quantity value is basically the same as the set value.
In the technical scheme, the liquid level controller in the tower kettle extraction control area controls the liquid level of the tower kettle of the dividing wall rectifying tower, and the product extraction amount of the tower kettle is automatically adjusted according to the liquid level. Obviously, the liquid level of the tower kettle is controlled, so that the ascending vapor amount in the tower is favorably ensured, and the stable operation of the dividing wall rectifying tower is realized; meanwhile, on the basis of effectively controlling the extraction amount of products at the top and at the side line of the tower, the yield of products at the bottom of the tower is ensured, and the material balance of the whole tower is realized. The specific control process is as follows: and (3) introducing the actually measured liquid level signal of the tower kettle into a liquid level controller, outputting a signal to a product extraction regulating valve of the tower kettle by the liquid level controller according to the size relation between the actually measured liquid level value and the set value, and correspondingly regulating the opening by the regulating valve until the measured liquid level value of the tower kettle is basically the same as the set value.
In summary, based on the corresponding relationship between the temperature and the composition in the rectifying tower, the temperature of the sensitive plates in the common rectifying section directly affects the quality of the product at the top of the tower, and the temperature of the sensitive plates on the feed side and the product side directly affects the contents of the heavy component falling from the top of the product side and the heavy component rising from the bottom of the product side, i.e. directly affects the quality of the side product, so the quality of the products at the top of the tower and the side product can be ensured by controlling the appropriate temperature of the sensitive plates. According to the invention, the temperature of the common rectifying section sensitive plate is controlled by adjusting the flow of reflux liquid in the tower top reflux and extraction control area, so that the quality of a tower top product is ensured; the temperature control of sensitive plates at the feed side and the product side is respectively realized by adjusting the feed temperature of the raw materials in the raw material feed control area and the liquid distribution amount of the product side in the liquid collection and distribution control area, so that the control of impurities at the product side, particularly the content of heavy components is realized, and the quality of side line products is ensured; meanwhile, on the premise of ensuring the product quality, the invention respectively realizes the control of the raw material feeding amount, the tower top and side line product extraction amount through three flow controllers in the raw material feeding control area, the tower top reflux and extraction control area and the side line extraction control area, thereby ensuring the yield of the tower top and side line products; in addition, based on the stable operation of the dividing wall rectifying tower and the influence of the steam amount or the gas-liquid flow in the tower on the product extraction amount, the invention respectively realizes the control of the liquid level of the tower kettle and the liquid level of the condensing tank at the top of the tower by adjusting the tower kettle extraction amount and the heat of a reboiler in the tower kettle extraction control area, and realizes the liquid level control of the area by adjusting the total amount of bottom distillate liquid in the liquid collection and distribution control area, thereby ensuring the gas-liquid flow in the tower and the material balance of the whole tower on the one hand, ensuring the product quality and the yield of the tower kettle under the condition that the product quality and the yield of the top of the tower and the side line are effectively controlled on the other hand, ensuring the stable operation of each area of the whole tower and realizing the stable operation of the whole dividing wall rectifying tower; therefore, the temperature, the flow and the liquid level of the five control areas, namely the raw material feeding control area, the tower top reflux and extraction control area, the liquid collection and distribution control area, the side extraction control area and the tower kettle extraction control area are respectively controlled, so that the quality and the yield of products at the tower top, the side line and the tower kettle can be ensured, the stable operation of each area including the tower top, the tower kettle, the bottom of a public rectification section and the like in the dividing wall rectification tower can be ensured, and the stable operation of the whole tower is finally realized. Therefore, the technology disclosed by the invention can better solve the technical problems that the operation control of the conventional dividing wall rectifying tower is difficult, the stability is poor and the product quality and yield are difficult to control.
Drawings
FIG. 1 is a schematic view of a method for controlling the operation of a divided wall distillation column according to the present invention;
FIG. 2 is a schematic view of a method for controlling a divided wall rectifying column according to comparative example 1;
FIG. 3 is a schematic view of a method for controlling the divided wall rectifying column described in comparative example 2.
In fig. 1, C101 is a dividing wall rectifying tower, E101 is an overhead condenser, E102 is a tower kettle reboiler, and E103 is a raw material preheater; TIC is a temperature controller, FIC is a flow controller, and LIC is a liquid level controller; the partition plate is arranged along the middle part of the tower to divide the dividing wall rectifying tower into 4 parts, wherein I is a public rectifying section, II is a public stripping section, III is a feeding side of the dividing wall section, and IV is a product side of the dividing wall section; n1 is a public rectification section sensitive plate, N2 is a bulkhead section feed side sensitive plate, and N3 is a bulkhead section product side sensitive plate; the material flow (101) is raw material, the material flow (102) is top product, the material flow (103) is side product, the material flow (104) is bottom product, the material flow (105) is top reflux liquid, the material flow (106) is bottom distillate of the public rectification section, the material flow (107) is distribution liquid at the feeding side of the dividing wall section, and the material flow (108) is distribution liquid at the product side of the dividing wall section.
In FIG. 1, the raw material feeding area adopts a flow controller to control the opening of a raw material feeding valve and adopts the temperature of a sensitive plate N2 on the feeding side of a dividing wall section to control the raw material feeding temperature; tower top reflux, adopting the temperature of a public rectification section sensitive plate N1 to control the tower top reflux liquid quantity in an area, adopting a flow controller to control the opening degree of a tower top product extraction regulating valve, and adopting the tower top reflux tank liquid level to control the heating power or the heating medium flow of a tower kettle reboiler E102; the liquid collecting and distributing area adopts the liquid level of the liquid collecting area at the bottom of the public rectifying section to control the total flow of the bottom distillate liquid and adopts the temperature of a product side sensitive plate N3 to control a regulating valve of the product side distributing liquid; the opening degree of a lateral line product extraction regulating valve is controlled by a flow controller in the lateral line extraction area; the tower kettle extraction area adopts the tower kettle liquid level to control the opening degree of a tower kettle product extraction regulating valve.
In fig. 2, the equipment and material flows of the dividing wall rectifying tower except the raw material preheater are the same as those in fig. 1, and the control scheme is as follows: the liquid amount of the reflux at the top of the tower is controlled by the composition of the product at the top of the tower, the output amount of the side product is controlled by the composition of the side product, the heat load of a reboiler at the bottom of the tower is controlled by the composition of the product at the bottom of the tower, and the proportion of the liquid distributed at the two sides of the partition plate is controlled by the content of the heavy component in the gas phase at the top of the.
In fig. 3, the equipment and material flows of the dividing wall rectifying tower are the same as those in fig. 1, and the control scheme is as follows: the method comprises the steps of controlling the amount of tower top reflux liquid through the temperature of a sensitive plate at the top of the product side of a partition section, controlling the amount of tower top product extracted through the liquid level of a tower top condenser, controlling the amount of distribution liquid at the feed side of the partition section through the liquid level of a liquid collection region at the bottom of a public rectification section, controlling the proportion between the amounts of distribution liquid at two sides of a partition plate through a proportion controller, controlling the amount of side line product extracted through the temperature of the sensitive plate at the bottom of the product side of the partition section, and controlling the.
The invention is further illustrated by the following examples.
Detailed Description
[ example 1 ]
The benzene/toluene/mixed xylene material is used as a raw material, and the composition of the benzene/toluene/mixed xylene material is 12.80 percent of benzene, 70.69 percent of toluene and 16.51 percent of mixed xylene by weight percentage. Taking the feeding flow rate of 80g/min as a reference, separating according to the operation control method of the dividing wall rectifying tower shown in figure 1, obtaining a benzene product at the tower top, obtaining a toluene product at the side line, and obtaining a mixed xylene product at the tower bottom. The total theoretical plate number of the dividing wall rectifying tower is 70, the theoretical plate number of the public rectifying section is 15, the theoretical plate number of the feeding side and the product side of the dividing wall section is 35, raw materials enter from the 23 rd theoretical plate of the feeding side I of the dividing wall section from top to bottom, methylbenzene is extracted from the 17 th theoretical plate of the product side III of the dividing wall section from top to bottom, the operation pressure is normal pressure, the control temperatures of sensitive plates N1, N2 and N3 are 79.7 ℃, 108.4 ℃ and 110.9 ℃, the extraction amounts of the tower top and the side line are respectively controlled to be 10.2g/min and 56.5g/min, the liquid levels of a tower top condensing tank, a liquid collecting region and a tower kettle are respectively controlled to be 50%, 60% and 80%, and the control results are shown in Table 1. It can be seen that the purity of the benzene, toluene and mixed xylene products reaches more than 99.9%, the yield of the benzene and toluene also reaches more than 99.9%, meanwhile, the stabilization time of the whole tower is shorter, about 2-3 hr, and the separation effect and the stabilization time are obviously superior to those of a comparative example, which shows that the operation control method provided by the invention realizes the ideal control effect of the dividing wall rectifying tower.
[ example 2 ]
The benzene/toluene/mixed xylene material is used as a raw material, and the composition of the benzene/toluene/mixed xylene material is 33.85 percent of benzene, 54.61 percent of toluene and 11.54 percent of mixed xylene by weight percentage. Taking a feeding flow of 80g/min as a reference, separating according to an operation control method of the dividing wall rectifying tower shown in figure 1, wherein the total number of theoretical plates of the dividing wall rectifying tower is 70, the number of theoretical plates of a common rectifying section is 20, and the number of theoretical plates of a feeding side and a product side of the dividing wall rectifying tower is 30, raw materials enter from a 17 th theoretical plate of a feeding side I of the dividing wall section from top to bottom, methylbenzene is extracted from a 15 th theoretical plate of a product side III of the dividing wall section from top to bottom, the operation pressure is normal pressure, the control temperatures of sensitive plates N1, N2 and N3 are respectively 80 ℃, 108.6 ℃ and 111.3 ℃, the extraction amounts of a tower top and a side line are respectively controlled to be 27.1g/min and 43.6g/min, the liquid levels of a condensing tank, a liquid collecting region and a tower bottom are respectively controlled to be 60%, 60% and 75%, and the control results are shown in table 1. It can be seen that the operation control method related by the invention also achieves the ideal control effect after the raw material composition and the structural parameters of the dividing wall rectifying tower are replaced.
[ example 3 ]
The ethanol/isobutanol/n-pentanol mixture is used as a raw material, and the composition of the ethanol/isobutanol/n-pentanol mixture is 12.80 percent of ethanol, 70.69 percent of isobutanol and 16.51 percent of n-pentanol in percentage by weight. Taking the feeding flow rate of 80g/min as a reference, separating according to the operation control method of the dividing wall rectifying tower shown in figure 1, obtaining an ethanol product at the tower top, obtaining an isobutanol product at the side line, and obtaining an n-pentanol product at the tower bottom. The structural parameters of the dividing-wall rectifying tower are the same as those of the embodiment 1, the operation pressure is normal pressure, the control temperatures of the sensitive plates N1, N2 and N3 are 77.5 ℃, 105.8 ℃ and 108.2 ℃, the extraction amounts of the top and the side line are respectively controlled to be 10.2g/min and 56.5g/min, the liquid levels of the condensation tank at the top of the tower, the liquid collecting region and the tower kettle are respectively controlled to be 60%, 60% and 80%, and the control results are shown in table 1. It can be seen that the operation control method according to the present invention can still achieve a desired control effect after the replacement of the separator system.
TABLE 1 control Effect
Example 1 Example 2 Example 3
Quality of the product
Benzene product concentration wt% 99.99 99.96 99.95
Concentration wt% of toluene product 99.96 99.95 99.95
Concentration wt% of mixed xylene product 99.92 99.90 99.97
Product yield
Yield of benzene product wt% 100.00 99.97 99.96
Yield of toluene product wt% 99.98 99.96 99.95
The yield of the mixed dimethylbenzene product is wt% 99.83 99.80 99.86
Steady state
Stabilization time hr 2~3 ≈3 2~3
Comparative example 1
The same dividing wall column and the same composition of the raw material as in example 1 were used to carry out the separation in accordance with the control method shown in FIG. 2, and the control results are shown in Table 2. It can be seen that, under the control method, in order to ensure that the product purity of the benzene and the toluene is not less than 99.9%, the purity and the yield of the mixed xylene in the tower bottom are difficult to ensure and are only 99.78%, and meanwhile, the stabilization time of the whole tower is longer and exceeds 10 hr; if the heat load of the reboiler of the tower kettle is further increased, the purity of the mixed xylene in the tower kettle can be improved to 99.9 percent, but the pressure difference below the public stripping section and the partition plate is obviously increased at the moment and is increased from 0.5KPa to 3KPa, so that the stable operation of the dividing wall rectifying tower is damaged.
Comparative example 2
The same dividing wall column and the same composition of the raw material as in example 1 were used to conduct the separation in accordance with the control method shown in FIG. 3, and the control results are shown in Table 2. It can be seen that under the control method, the purity of benzene and toluene products is obviously lower, especially benzene, because only the temperature of the tower plate at the top of the product side and the liquid phase distribution at the two sides of the partition wall section are controlled, the content of impurity benzene and xylene in the side line products can be effectively controlled, namely the product quality of the side line toluene is controlled, but the product quality of the tower top benzene and the tower bottom xylene cannot be ensured; meanwhile, in the control scheme, because the evaporation capacity or the gas-liquid flow in the tower is not correspondingly controlled, the product yield cannot be effectively controlled, for example, the yield of mixed xylene in the tower kettle is obviously lower, and the stabilization time of the dividing wall rectifying tower is relatively longer.
TABLE 2 control Effect of different control schemes
Example 1 Comparative example 1 Comparative example 2
Quality of the product
Benzene product concentration wt% 99.99 99.96 99.85
Concentration wt% of toluene product 99.96 99.95 99.92
Concentration wt% of mixed xylene product 99.92 99.78 99.62
Product yield
Yield of benzene product wt% 100.00 99.97 100.00
Yield of toluene product wt% 99.98 99.94 99.88
The yield of the mixed dimethylbenzene product is wt% 99.83 99.81 99.65
Steady state
Stabilization time hr 2~3 ≥10 ≥5

Claims (6)

1. The operation control method of the dividing wall rectifying tower comprises the following five control areas:
(1) raw material feeding control area: the flow controller is adopted to control the feeding amount of raw materials, the temperature controller is adopted to control the temperature of a sensitive plate at the feeding side of the bulkhead section of the bulkhead rectifying tower, and the feeding temperature of the raw materials is automatically adjusted according to the temperature of the sensitive plate;
(2) the tower top reflux and extraction control area: controlling the temperature of a sensitive plate of a public rectifying section of the dividing wall rectifying tower by adopting a temperature controller, automatically adjusting the flow of reflux liquid at the top of the tower according to the temperature of the sensitive plate, controlling the extraction amount of products at the top of the tower by adopting a flow controller, and controlling the heat of a reboiler at a tower kettle by adopting a liquid level controller;
the liquid level controller controls the liquid level of the tower top reflux tank, and the heat of a reboiler of the tower kettle is automatically adjusted according to the liquid level;
(3) liquid collection and distribution control area: controlling the flow of the distillate at the bottom of the public distillation section by adopting a liquid level controller, controlling the temperature of a sensitive plate at the product side of the bulkhead distillation tower bulkhead section by adopting a temperature controller, and automatically adjusting the liquid distribution amount at the product side according to the temperature of the sensitive plate;
(4) side draw control zone: controlling the side product extraction amount by adopting a flow controller;
(5) the extraction control area of the tower kettle: and controlling the product extraction amount of the tower kettle by adopting a liquid level controller.
2. The method of claim 1, wherein the flow controller in the material feed control area controls the material feed amount, and the actual material feed amount is automatically adjusted according to the set material feed amount.
3. The method of claim 1, wherein the flow controller in the top reflux and recovery control zone controls the amount of top product recovered, the flow rate of which is set according to the amount of raw material fed and the percentage of the corresponding light fraction in the feed composition, and the actual amount of top product recovered is automatically adjusted according to the set amount of top product recovered.
4. The method of claim 1, wherein the liquid level controller in the liquid collection and distribution control section controls a liquid level in a bottom liquid collection section of the common rectifying section of the divided wall rectifying column, and the total flow rate of the bottom distillate liquid is automatically adjusted according to the liquid level.
5. The method of claim 1, wherein the side draw is controlled by a flow controller in the side draw control zone, wherein the flow rate is set according to the feed rate of the feedstock and the percentage of the corresponding intermediate component in the feed composition, and the actual side draw is automatically adjusted according to the set product draw.
6. The method for controlling the operation of a dividing wall rectifying tower according to claim 1, wherein the liquid level controller in the tower bottom extraction control area controls the liquid level of the tower bottom of the dividing wall rectifying tower, and the extraction amount of the tower bottom product is automatically adjusted according to the liquid level.
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