Stable automatic control method of multi-section rectification thermal coupling rectifying tower

Abstract

The invention discloses a stable automatic control method of a multi-section rectification thermal coupling rectification tower, which comprises the following steps: under a set tower top pressure, calculating to obtain the reflux quantity of a medium-pressure optimal dimethyl tower and a medium-pressure optimal trimethyl tower by taking the sum of 105% of the designed reflux quantity of a light separation tower and the energy consumption required by the designed reflux quantity of an azeotropic tower as a reference; then, the flow of the tower top of the high-pressure optimal dimethyl tower sent to the tower kettle of the medium-pressure optimal dimethyl tower and the tower kettle of the trimethyl tower is calculated, the sum of the flow of the tower kettle of the medium-pressure optimal dimethyl tower and the flow of the tower kettle of the trimethyl tower is the reflux quantity of the high-pressure optimal dimethyl tower, the use amount of 0.5 MPa steam is calculated according to the reflux quantity of the high-pressure optimal dimethyl tower, and the heat balance of the whole rectification coupling system can be determined. On the basis of heat balance of the system, material balance and gas-liquid balance of the whole rectification coupling system are adjusted by utilizing reflux quantity adjustment, pressure adjustment, liquid level adjustment and other matched regulation and control methods. The control method adopted by the invention is advanced in technology, and the goal of energy conservation and optimization can be achieved on the premise of ensuring that product indexes and operation parameters of each tower are normal.

Description

Technical Field

[0001] The invention belongs to the technical field of organosilicon production technology, and in particular relates to a stable automatic control method of a multi-stage rectification heat-coupled distillation tower. Background Art

[0002] The multi-stage distillation heat-coupled distillation tower is a kind of tower that divides the entire distillation process into multiple towers with different energy levels. The top steam of the higher temperature tower is used to heat the reboiler of the lower temperature tower, and the steam is condensed at the same time. In the multi-effect distillation, only the kettle of the first tower needs high-pressure steam to provide heat, and the top steam of the last tower is condensed with cooling medium. The remaining towers no longer need to be heated and cooled by the outside world, which has obvious energy-saving effects. The specific coupling method is the top gas phase of the high-pressure excellent dimethyl tower 1 The material is used as the heat source of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 5. At the same time, the gaseous material at the top of the tertiary tower 5 is used as a heat source to heat the azeotropic tower 4, and the gaseous material at the top of the medium-pressure excellent dimethyl tower 2 is used as a heat source for the light fraction tower 3. The process design requirements of the above towers are as follows: the feed of the high-pressure excellent dimethyl tower 1 and the medium-pressure excellent dimethyl tower 2 is both greater than 99%wt of dimethyldichlorosilane, and after tower separation to remove alkanes, olefins and other high-boiling impurities, it is discharged from the tower kettle to the storage tank, and the high-purity dimethyldichlorosilane product is sent from the top of the tower to the product tank; the light fraction tower 3 is used as the heat source of the medium-pressure excellent dimethyl tower 1 and the medium-pressure excellent dimethyl tower 2. The feed of the sub-tower 3 is a mixture of trimethylchlorosilane, monomethyldichlorosilane, silicon tetrachloride, trichlorosilane, tetramethylsilane, a small amount of monomethyltrichlorosilane and other high and low boiling impurities. After separation in the light fraction tower 3, the sum of trimethylsilane and silicon tetrachloride is less than 0.3%wt of the low-boiling products of monomethyl hydrogen and tetramethylsilane obtained at the top of the tower, which are sent to the next tower for treatment. The mixture of trimethylsilane, silicon tetrachloride, a small amount of monomethyl and other impurities with a monomethyl hydrogen content of less than 0.5%wt is obtained in the bottom of the tower and is sent to the azeotropic tower 4; the mixture from the bottom of the light fraction tower 3 is After separation in azeotropic tower 4, an azeotrope consisting of 52%wt of trimethylchlorosilane and 48%wt of silicon tetrachloride is obtained at the top of the tower and is sent out of the system, and trimethylchlorosilane containing a small amount of monomethyldichlorosilane and other impurities with a content of less than 0.05%wt of silicon tetrachloride is obtained in the bottom of the tower and is sent to trimethyl tower 5; the mixture from the bottom of azeotropic tower 4 is purified in trimethyl tower 5, and a trimethylchlorosilane product with a content of more than 99.5%wt is obtained at the top of the tower and is sent to a product tank, and monomethyldichlorosilane containing a small amount of impurities is obtained in the bottom of the tower and is returned to the system.The control method adopted for the stable operation of the above system is as follows: the steam flow of the tower kettle reboiler of the high-pressure excellent dimethyl tower 1, the main heat supply, is controlled by the tower pressure difference; the top material of the high-pressure excellent dimethyl tower 1 is automatically controlled by the valve to be diverted to the reboilers of the medium-pressure excellent dimethyl tower 2 and the three-methane tower 5 according to the designed flow; the top pressure of each tower system is automatically controlled by the corresponding tower top condenser outlet lower liquid valve; the reflux volume of each tower system is automatically controlled by its own reflux regulating valve; the liquid level of the top reflux tank of each tower system is cascade controlled with the tower top production flow, and the tower kettle liquid level is cascade controlled with the tower kettle production flow The above design conditions and control methods are based on the fact that the components of high-pressure dimethyl tower 1 and medium-pressure dimethyl tower 2, azeotropic tower 4, and trimethyl tower 5 are relatively stable, and the fluctuation of components is not large, so the control adjustment is not frequent, and the overall control requirements are not high. However, in the actual operation, this control method still has the following problems: First, the complexity of the organic reaction of the monomer fluidized bed in the upstream process leads to the fluctuation of the chlorosilane component in the light fraction tower 3, azeotropic tower 4, and trimethyl tower 5, and several alkane and olefin impurities are generated, which react with dimethyl dichloride. Silane and trimethylchlorosilane are easy to form azeotropes and are very difficult to separate. There are two impurity peaks in trimethylchlorosilane, with contents of 3-18%wt and 0.5-3.5%wt respectively. If not well controlled, it will lead to unqualified trimethylchlorosilane products, which will eventually affect the purity of the product. At the same time, the system needs to focus on regulating the light fraction tower 3 and the azeotropic tower 4. These two towers are at the end of the coupling and are far away from the heater. When adjusting, the medium-pressure dimethyl tower 2 and the trimethyl tower 5 in the middle section of the coupling need to be changed first before they can be transferred to the high-pressure dimethyl tower for heating. 1. The whole process has many variables, long reaction time and large hysteresis, which can easily lead to large fluctuations in product quality; second, when the system is running, affected by the region, when there is a large temperature difference between day and night, heavy rain, changes in the composition of distillation raw materials, and load adjustment, the pressure, temperature, flow rate, and liquid level of the tower fluctuate greatly, which can easily destroy the heat balance, material balance, and gas-liquid balance of the entire coupled distillation system. If the entire multi-stage distillation heat-coupled distillation tower system cannot be stably controlled and adjusted in time, it will not only have a great impact on product quality, but also increase energy and material consumption. Therefore, it is an objective need to develop a stable automatic control method for a multi-stage distillation heat-coupled distillation tower with advanced control methods, easy operation, good energy-saving effect, which can effectively improve the production quality of products and improve the stability of system operation. Summary of the invention

[0003] In order to solve the technical problems of large fluctuations in product quality and poor system operation stability existing in the background technology, the purpose of the present invention is to provide a multi-stage distillation heat-coupled distillation tower with advanced control method, easy operation, good energy-saving effect, which can effectively improve the production quality of products and improve the system operation stability.

[0004] The invention discloses a stable automatic control method for a multi-stage distillation heat-coupled distillation tower, characterized in that: under a set tower top pressure, firstly, based on the sum of the energy consumption required for 105% of the light fraction tower design reflux of 65,000 kg / h and the azeotropic tower design reflux of 15,000 to 17,000 kg / h, the reflux amounts of the medium-pressure superior dimethyl tower and the trimethyl tower are calculated, and then the flow rates of the high-pressure superior dimethyl tower top sent to the tower kettles of the medium-pressure superior dimethyl tower and the trimethyl tower are calculated, and the sum of the flow rates of the tower kettles of the medium-pressure superior dimethyl tower and the trimethyl tower is the reflux amount of the high-pressure superior dimethyl tower. The 0.5 MPa steam consumption is calculated based on the reflux amount of the high-pressure superior dimethyl tower, and the heat balance of the entire distillation coupling system can be determined. On the basis of the heat balance of the system, the material balance and gas-liquid balance of the entire distillation coupling system are adjusted by a combination of reflux amount regulation, pressure regulation, liquid level regulation and temperature regulation.

[0005] The method for regulating the reflux flow rate is as follows: the steam supplied from the 0.5MPa steam main pipe is automatically controlled by the regulating valve G1 to provide sufficient heat to meet the reflux flow rate of the high-pressure excellent dimethyl tower to reach 40000-80000kg / h; the flow rate from the top of the high-pressure excellent dimethyl tower to the medium-pressure excellent dimethyl tower is automatically controlled by the regulating valve Z1 to control the reflux flow rate of the medium-pressure excellent dimethyl tower to reach 35000-75000kg / h; the flow rate from the top of the high-pressure excellent dimethyl tower to the tertiary tower is automatically controlled by the regulating valve S1 to ensure that the reflux flow rate of the tertiary tower reaches 15000-30000kg / h; the heat from the top of the medium-pressure excellent dimethyl tower is all supplied to the light fraction tower, and the heat from the top of the tertiary tower is all supplied to the azeotropic tower to control the reflux flow rate of the light fraction tower. The flow rate reaches 40000-65000kg / h, the reflux rate of the azeotropic tower reaches 15000-25000kg / h, the reflux rates of the high-pressure dimethyl tower, the trimethyl tower and the azeotropic tower are automatically controlled by regulating valve G5, regulating valve S3 and regulating valve F3 respectively, and the minimum reflux rate protection values ​​of the high-pressure dimethyl tower, the trimethyl tower and the azeotropic tower are set, which are 38000kg / h for the high-pressure dimethyl tower, 14000kg / h for the trimethyl tower and 12000kg / h for the azeotropic tower respectively. When the reflux rates of the high-pressure dimethyl tower, the trimethyl tower and the azeotropic tower reach the set minimum reflux rate protection value, the valve position openings of the locking regulating valves G5, S3 and F3 are no longer adjusted downward to ensure the separation effect of the tower.

[0006] The pressure regulation method is: the high-pressure dimethyl tower, medium-pressure dimethyl tower, light fraction tower, tertiary tower and azeotropic tower all use the tower top pressure to automatically control through the corresponding condenser outlet regulating valve G3, regulating valve Z3, regulating valve Q2, regulating valve S2 and regulating valve F1 respectively. The top pressure of the high-pressure dimethyl tower is required to be controlled at 0.19-0.25MPa, the top pressure of the medium-pressure dimethyl tower is controlled at 0.1-0.12MPa, the top pressure of the light fraction tower is controlled at 0.06-0.12MPa, the top pressure of the tertiary tower is controlled at 0.1-0.13MPa, and the top pressure of the azeotropic tower is controlled at 0.03-0.04MPa. When the pressure of each tower increases, the valve opening is opened wider, and when the pressure of each tower decreases, the valve opening is reduced to stabilize the pressure of each tower within the index requirements.

[0007] The method of liquid level regulation is: the liquid level of the kettle of the high-pressure dimethyl tower is automatically controlled by the regulating valve G1-1 on the 0.5MPa steam main pipe to control the liquid level of the high-pressure dimethyl tower kettle to be stable between 40% and 65%. At the same time, the cascade control of the liquid level of the kettle of the medium-pressure dimethyl tower and the coupled reboiler regulating valve Z1-1 is increased to control the liquid level of the kettle of the medium-pressure dimethyl tower to be stable between 40% and 65%. In addition to the coupled reboiler, the kettle of the tertiary tower is also equipped with an auxiliary reboiler. The automatic control of the kettle level of the tertiary tower and the steam flow of the auxiliary reboiler is increased through the regulating valve S5 to control the liquid level of the kettle of the tertiary tower to be stable between 40% and 65%.

[0008] The temperature regulation method is: a: Select the sensitive plate temperature of the distillation section of the light fraction tower as the main controlled variable. The temperature of the distillation section of the light fraction tower and the reflux flow are cascade controlled through the regulating valve Q3. The temperature control range of the distillation section of the light fraction tower is 55-58°C, and the set value is 56.5°C. When the distillation temperature of the light fraction tower is lower than the set value, the reflux flow is reduced. When the distillation temperature of the light fraction tower is higher than the set value, the reflux flow is increased. b: Select the top temperature of the azeotropic tower and the sensitive plate temperature of the distillation section of the azeotropic tower to calculate the temperature difference. The temperature difference is used as the main variable. The temperature difference and the reflux flow are cascade controlled through the regulating valve F3-1. The temperature difference control range is 3 to 6 ° C, and the set value is 4.5 ° C. When the temperature difference decreases, the reflux flow increases, and when the temperature difference increases, the reflux flow decreases; c: The temperature of the kettle of the three-layer tower is selected as the main variable. The kettle temperature of the three-layer tower and the reflux volume are cascade-controlled through the regulating valve S6. The control range of the kettle temperature of the three-layer tower is 91-94°C, and the set value is 92.5°C. When the kettle temperature of the three-layer tower is lower than the set value, the kettle extraction is reduced. When the kettle temperature of the three-layer tower (5) is higher than the set value, the kettle extraction is increased.

[0009] Furthermore, on the basis of the reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, an automatic load control model is added. This automatic load control model is mainly based on the steady-state process model, supplemented by PID calculus regulation and dynamic process regulation; the steady-state process model is used for material and energy balance, the PID model is used to adjust the action trend and frequency, and the dynamic process model is used to monitor the signal transmission between production load changes. When the load is adjusted, the program is started on the premise of meeting the load and index requirements of the light-dimethyl tower, and the high-pressure dimethyl tower, medium-pressure dimethyl tower, light-dimethyl tower, tertiary tower and azeotropic tower are coupled in series. The entire coupling system is centered on the light-dimethyl tower. The reflux flow of the light-dimethyl tower is controlled at 40,000-65,000 kg / h through the feed load of the light-dimethyl tower, and then the reflux flow of the medium-pressure dimethyl tower is controlled at 35,000-75,000 kg / h and the reflux flow of the high-pressure dimethyl tower is controlled at 40000-75000 kg / h. 0~80000kg / h, the reflux volume of the high-pressure preferred dimethyl tower is used to control the steam change in the tower kettle, and then the compensation value of the steam change is used to control the coupled steam heat source of the tertiary tower (5). At the same time, the tertiary tower assists in coupling the reboiler steam volume and the tower kettle liquid level automatic control. The top pressure of the tertiary tower is used as the temperature difference of the azeotropic tower to control the compensation value of the reflux volume of the azeotropic tower through the regulating valve F3-2. When the temperature difference adjustment deviates from 2℃ / minute or the pressure deviation of the tertiary tower is greater than 5KPa / minute, the pressure of the tertiary tower assists in controlling the reflux volume of the azeotropic tower, and the extraction volume of the light fraction tower kettle assists in controlling the change of the azeotropic tower liquid level. In this way, the change of the 5 coupled towers is comprehensively adjusted during the lifting and lowering load period based on the feed load of the light fraction tower. After the lifting and lowering load is over, the tower control of the entire distillation coupling system is mainly controlled by reflux volume balance adjustment, pressure balance adjustment, liquid level balance adjustment and temperature balance adjustment, supplemented by the lifting and lowering load automatic control model, and jointly controlled.

[0010] Furthermore, on the basis of the coordinated regulation of reflux flow rate regulation, pressure regulation, liquid level regulation and temperature regulation, the ratio of the feed flow rate of the high-pressure excellent dimethyl tower to the bottom withdrawal flow rate is calculated, and the ratio of the feed flow rate of the medium-pressure excellent dimethyl tower to the bottom withdrawal flow rate is calculated, the ratio = feed amount × (0.01 ~ 0.05), the ratio is selected as the main variable, the ratio calculated by the high-pressure excellent dimethyl tower and the bottom withdrawal flow rate are cascade controlled through the regulating valve G6-1, the ratio calculated by the medium-pressure excellent dimethyl tower and the bottom withdrawal flow rate are cascade controlled through the regulating valve Z6-1, the ratio = feed amount × (0.01 ~ 0.05), the control interval of 0.01 ~ 0.05 is selected and adjusted according to the high boiling point impurity content in the sampling analysis results, when the high boiling point impurity content is high, it is adjusted towards a high value, under the same load, the ratio increases, the bottom withdrawal flow rate increases, when the high boiling point impurity content is low, it is adjusted towards a low value, under the same load, the ratio decreases, and the bottom withdrawal flow rate decreases.

[0011] Furthermore, on the basis of the coordinated regulation of reflux volume balance regulation, pressure balance regulation, liquid level balance regulation and temperature balance regulation, the liquid level of the top reflux tank of the light fraction tower and the top production flow are cascade controlled through the regulating valve Q4, the liquid level of the bottom of the light fraction tower and the production flow of the bottom are cascade controlled through the regulating valve Q5, and the liquid level of the bottom of the azeotropic tower and the production flow of the bottom are cascade controlled through the regulating valve F4. The liquid level of each tower is selected as the main variable. When the liquid level of each tower rises, the production flow increases, and when the liquid level decreases, the production flow decreases.

[0012] Compared with the original control method: the advantages of the present invention are: First, compared with the traditional single-loop control of the top extraction volume and the reflux tank liquid level, the cascade control of the reboiler flow valve position and the heat and the tower kettle liquid level, the single-loop control of the reflux volume and the temperature of the sensitive plate in the tower, and the single-loop control system of the top pressure and the top cooling volume, the present invention adopts the balance of inlet and outlet materials, the control variable selects 2 to 3 temperature components in the tower to control the upper and lower limits of the first, second and third intervals, the manipulated variable selects the heat source flow and the tower reflux flow, and the interference variable selects the feed flow and part of the auxiliary heat source flow. In the case of a long heat transfer line in the coupling system, the control system can also achieve the purpose of energy self-balance, recover excess heat, and achieve better energy-saving effects; Secondly, compared with the traditional single-tower control method of a distillation tower, the present invention connects the feed rate, reflux rate, liquid level, temperature, temperature difference and pressure balance of the front and rear tower systems in series. Under the condition of stable regulation of a single tower, the front and rear related coupling systems are taken into consideration together to form a control logic of a central control segment. By adjusting the control of the associated towers through the core point, both the self-regulation of the core tower and the single tower and the mutual coupling relationship between the front and rear towers are taken into consideration, so that the system with a complex coupling relationship that is difficult to control and has many variables is simplified to a single variable system. Such a control method can not only fundamentally solve the problems of many variables, long reaction time, large hysteresis and other problems that may lead to large fluctuations in product quality during the system distillation process, but also realize dual control of independence and integration between systems, reduce the interference caused by fluctuations at the front or back end of the system, improve the stability of system operation, and ensure the heat balance, material balance and gas-liquid balance of the entire coupled distillation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of the present invention; In the figure: 1-high pressure excellent dimethyl tower, 2-medium pressure excellent dimethyl tower, 3-light fraction tower, 4-azeotropic tower, 5-tertiary tower, 6-steam main pipe, 7-regulating valve G1, 8-regulating valve Z1, 9-regulating valve S1, 10-regulating valve G3, 11-regulating valve Z3, 12-regulating valve Q2, 13-regulating valve S2, 14-regulating valve F1, 15-regulating valve G1-1, 16-reboiler, 17-regulating Valve Z1-1, 18-regulating valve Q3, 19-regulating valve F3-1, 20-regulating valve S6, 21-regulating valve F3-2, 22-regulating valve G5, 23-regulating valve S3, 24-regulating valve F3, 25-auxiliary reboiler, 26-regulating valve S5, 27-regulating valve G6-1, 28-tower top reflux tank, 29-regulating valve Q4, 30-regulating valve Q5, 31-regulating valve F4. DETAILED DESCRIPTION

[0014] The present invention is further described below in conjunction with the embodiments and accompanying drawings, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention belong to the protection scope of the present invention. Example 1

[0015] The stable automatic control method of the multi-stage distillation heat-coupled distillation tower described in Example 1, the multi-stage distillation heat-coupled distillation tower mainly includes a high-pressure excellent dimethyl tower 1, a medium-pressure excellent dimethyl tower 2, a light fraction tower 3, an azeotropic tower 4 and a tertiary tower 5. The connection structure and process principle of each tower are the existing technology. Under the set tower top pressure, the reflux rate of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 5 are calculated based on the sum of the energy consumption of 105% of the design reflux rate of 50000kg / h of the light fraction tower 3 and the design reflux rate of 15000kg / h of the azeotropic tower 4. The flow rate is calculated, and then the flow rates from the top of the high-pressure excellent dimethyl tower 1 to the kettles of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 2 are calculated. The sum of the flow rates of the kettles of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 5 is the reflux rate of the high-pressure excellent dimethyl tower 1. The 0.5MPa steam consumption is calculated according to the reflux rate of the high-pressure excellent dimethyl tower 1, and the heat balance of the whole distillation coupling system can be determined. On the basis of the heat balance of the system, the material balance and gas-liquid balance of the whole distillation coupling system are adjusted by using the combination of reflux rate regulation, pressure regulation, liquid level regulation and temperature regulation.

[0016] The method for regulating the reflux flow rate is as follows: the steam supplied from the 0.5MPa steam main pipe 6 is automatically controlled by the regulating valve G17 to provide sufficient heat to meet the reflux flow rate of the high-pressure excellent dimethyl tower 1 to reach 50000kg / h, the flow rate from the top of the high-pressure excellent dimethyl tower 1 to the medium-pressure excellent dimethyl tower 2 is stably automatically controlled by the regulating valve Z18 to ensure that the reflux flow rate of the medium-pressure excellent dimethyl tower 2 reaches 45000kg / h, the flow rate from the top of the high-pressure excellent dimethyl tower 1 to the tertiary tower 5 is automatically controlled by the regulating valve S19 to ensure that the reflux flow rate of the tertiary tower 5 reaches 15000kg / h, the heat from the top of the medium-pressure excellent dimethyl tower 2 is all supplied to the light fraction tower 3, and the heat from the top of the tertiary tower 5 is all supplied to the azeotropic tower 4, and no adjustment is required, but the reflux flow rate of the light fraction tower 3 must be ensured to reach The reflux rate of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 reaches 50000kg / h, and the reflux rate of the azeotropic tower 4 reaches 15000kg / h. During the adjustment process, the reflux rates of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 are automatically controlled by the regulating valve G522, the regulating valve S323 and the regulating valve F324, respectively, and the minimum reflux rate protection values ​​of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 are set, which are 38000kg / h for the high-pressure dimethyl tower, 14000kg / h for the trimethyl tower and 12000kg / h for the azeotropic tower, respectively. When the reflux rates of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 reach the set minimum reflux rate, the valve positions of the regulating valves G522, the regulating valves S323 and the regulating valves F324 are locked and no longer adjusted downward to ensure the separation effect of the towers. The pressure regulation method is: the high-pressure dimethyl tower 1, the medium-pressure dimethyl tower 2, the light fraction tower 3, the tertiary tower 5, and the azeotropic tower 4 are all automatically controlled by the tower top pressure through the corresponding condenser outlet regulating valve G310, regulating valve Z311, regulating valve Q212, regulating valve S213, and regulating valve F114. When the pressure of each tower increases, the valve opening is opened wide, and when the pressure of each tower decreases, the valve opening is reduced to stabilize the pressure of each tower within the index requirements. Preferably, the tower top pressure of the high-pressure dimethyl tower 1 is controlled at 0.19MPa, the tower top pressure of the medium-pressure dimethyl tower 2 is controlled at 0.1MPa, the tower top pressure of the light fraction tower 3 is controlled at 0.07MPa, the tower top pressure of the tertiary tower 5 is controlled at 0.1MPa, and the tower top pressure of the azeotropic tower 4 is controlled at 0.03MPa. The method of liquid level regulation is: the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 is automatically controlled by the regulating valve G1-115 on the 0.5MPa steam main pipe 6. When the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 increases, the steam flow of the 0.5MPa steam main pipe 6 is increased, and when the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 decreases, the steam flow of the 0.5MPa steam main pipe 6 is reduced, so that the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 is stabilized between 40% and 65%. At the same time, the cascade control of the liquid level of the bottom of the medium-pressure excellent dimethyl tower 2 and the material regulating valve Z1-117 of the coupling reboiler 16 is increased, and the liquid level of the bottom of the medium-pressure excellent dimethyl tower 2 is controlled. When the level rises, the material steam flow rate increases. When the liquid level of the tower kettle of the medium-pressure superior dimethyl tower 2 decreases, the steam flow rate decreases, so that the liquid level of the tower kettle of the medium-pressure superior dimethyl tower 2 is stabilized between 40% and 65%. When designed, in addition to the coupling reboiler 16, the tower kettle of the three-methyl tower 5 is also equipped with an auxiliary reboiler 25 to increase the automatic control of the tower kettle liquid level of the three-methyl tower 5 and the steam flow of the auxiliary reboiler 25 through the regulating valve S526. When the liquid level of the three-methyl tower 5 rises, the steam valve opening is increased. When the liquid level of the three-methyl tower 5 decreases, the steam flow rate is reduced, so that the liquid level of the three-methyl tower 5 kettle is stabilized between 40% and 65%; The temperature regulation method is: The sensitive plate temperature of the distillation section of the light fraction tower 3 is selected as the main controlled variable. The temperature of the distillation section of the light fraction tower 3 and the reflux flow are cascade controlled through the regulating valve Q318. The temperature control range of the distillation section of the light fraction tower 3 is 55-56°C, and the set value is 55.5°C. When the distillation temperature of the light fraction tower 3 is lower than the set value, the reflux flow is reduced. When the distillation temperature of the light fraction tower 3 is higher than the set value, the reflux flow is increased. Select the top temperature of azeotropic tower 4 and the sensitive plate temperature of the distillation section of azeotropic tower 4 to calculate the temperature difference. The temperature difference is used as the main variable and is cascade controlled with the reflux flow through the regulating valve F3-119. The temperature difference control range is 3-4°C, and the set value is 3.5°C. When the temperature difference decreases, the reflux flow increases, and when the temperature difference increases, the reflux flow decreases. The temperature of the kettle of the third tower 5 is selected as the main variable. The temperature of the kettle of the third tower 5 and the reflux volume are cascade-controlled through the regulating valve S620. The control range of the temperature of the kettle of the third tower 5 is 91-92°C, and the set value is 91.5°C. When the temperature of the kettle of the third tower 5 is lower than the set value, the kettle extraction is reduced. When the temperature of the kettle of the third tower 5 is higher than the set value, the kettle extraction is increased. Furthermore, on the basis of the reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, an automatic load control model is added. The automatic load control model is mainly based on the steady-state process model, supplemented by PID calculus regulation and dynamic process regulation; the steady-state process model is used for material and energy balance, the PID model is used to adjust the action trend and frequency, and the dynamic process model is used to monitor the signal transmission between production load changes. When the load is adjusted, the program is started on the premise of meeting the load and index requirements of the light fraction tower 3, and the high pressure The excellent dimethyl tower 1, the medium-pressure excellent dimethyl tower 2, the light fraction tower 3, the tertiary tower 5, and the azeotropic tower 4 are coupled in series. The entire coupling system is centered on the light fraction tower 3. The reflux rate of the light fraction tower 3 is controlled at 40,000 to 50,000 kg / h by the feed load of the light fraction tower 3. Then, the reflux rate of the medium-pressure excellent dimethyl tower 2 is controlled at 35,000 to 45,000 kg / h and the reflux rate of the high-pressure excellent dimethyl tower 1 is controlled at 40,000 to 50,000 kg / h. The reflux rate of the high-pressure excellent dimethyl tower 1 is used to control the steam change in the tower kettle, and then the compensation value of the steam change controls the three The coupled steam heat source of the A tower 5 and the auxiliary coupled reboiler 16 of the tertiary tower 5 are automatically controlled for steam volume and tower bottom liquid level. The top pressure of the tertiary tower 5 is used as the compensation value of the reflux volume of the azeotropic tower 4 through the regulating valve F3-221 as the temperature difference of the azeotropic tower 4. When the temperature difference adjustment deviates by 2°C / minute or the pressure deviation of the tertiary tower 5 is greater than 5KPa / minute, the pressure of the tertiary tower 5 assists in controlling the reflux volume of the azeotropic tower 4, and the extraction volume of the kettle of the light fraction tower 3 assists in controlling the liquid level change of the azeotropic tower 4. In this way, the changes of the 5 coupled towers are based on the feed load of the light fraction tower 3. Comprehensive adjustment is carried out during the load lifting period. When the load lifting is finished, the coupled series tower control is mainly based on ① to ④, supplemented by the load lifting automatic control model, and jointly controlled. The present invention takes into account the interference of the system during the load lifting process. The coupled series tower control is mainly based on the cascade, temperature and pressure of each tower on the DCS interface, supplemented by the load lifting automatic control model. The combination of the two makes the control of the entire system more stable, greatly reduces human interference, saves labor costs, reduces losses caused by misjudgment during human operation, and reduces operational risks; Furthermore, on the basis of the coordination and control of reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, the ratio of the feed flow of high-pressure excellent dimethyl tower 1 to the tower bottom output flow is calculated, and the ratio of the feed flow of medium-pressure excellent dimethyl tower 2 to the tower bottom output flow is calculated. The ratio = feed amount × (0.01~0.05). The ratio is selected as the main variable. The ratio calculated by high-pressure excellent dimethyl tower 1 and the tower bottom output flow are cascade controlled through regulating valve G6-127, and the ratio calculated by medium-pressure excellent dimethyl tower 2 is The ratio and the bottom extraction flow rate are controlled in cascade through the regulating valve Z6-128. The ratio = feed amount × (0.01~0.05). The control range of 0.01~0.05 is selected and adjusted according to the high boiling point impurity content in the sampling analysis results. When the high boiling point impurity content is high, it is adjusted to a high value. Under the same load, the ratio increases and the bottom extraction flow rate increases. When the high boiling point impurity content is low, it is adjusted to a low value. Under the same load, the ratio decreases and the bottom extraction flow rate decreases.

[0017] Furthermore, on the basis of the coordinated regulation of reflux volume regulation, pressure regulation, liquid level regulation and temperature regulation, the liquid level of the top reflux tank of the light fraction tower 3 and the top production flow are controlled in cascade through the regulating valve Q4, the liquid level of the bottom of the light fraction tower 3 and the bottom production flow are controlled in cascade through the regulating valve Q530, the liquid level of the bottom of the azeotropic tower 4 and the bottom production flow are controlled in cascade through the regulating valve F431, the liquid level of each tower is selected as the main variable, the production flow is increased when the liquid level of each tower rises, and the production flow is reduced when the liquid level decreases.

[0018] This embodiment 1 thoroughly solves the problems of system lag and large fluctuation by adjusting and matching the pressure, temperature, liquid level, flow rate, etc. of each tower in the system, and can effectively improve the effect of product distillation separation. The control method adopted by the present invention is advanced in technology and easy to control. On the premise of ensuring that the product indicators and the operating parameters of each tower are normal, the goal of energy saving and optimization can be achieved. Compared with the traditional control method, the impurity content of butene-based impurities in the product is reduced by about 200ppmwt, which reduces the quality fluctuation of downstream products, and can save 0.3 to 0.5t / h of steam consumption, saving about 430,000 yuan / year in economic value. Example 2

[0019] The stable automatic control method of the multi-stage distillation heat-coupled distillation tower described in Example 2, the multi-stage distillation heat-coupled distillation tower mainly includes a high-pressure excellent dimethyl tower 1, a medium-pressure excellent dimethyl tower 2, a light fraction tower 3, an azeotropic tower 4 and a tertiary tower 5. The connection structure and process principle of each tower are the existing technology. Under the set tower top pressure, the top of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 5 are calculated based on the sum of the energy consumption of 105% of the design reflux flow of 55000kg / h of the light fraction tower 3 and the design reflux flow of 16000kg / h of the azeotropic tower 4. The reflux rate is calculated, and then the flow rates from the top of the high-pressure excellent dimethyl tower 1 to the kettles of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 2 are calculated. The sum of the flow rates of the kettles of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 5 is the reflux rate of the high-pressure excellent dimethyl tower 1. The 0.5MPa steam consumption is calculated according to the reflux rate of the high-pressure excellent dimethyl tower 1, and the heat balance of the entire distillation coupling system can be determined. On the basis of the heat balance of the system, the material balance and gas-liquid balance of the entire distillation coupling system are adjusted by using the combination of reflux rate regulation, pressure regulation, liquid level regulation and temperature regulation.

[0020] The method for regulating the reflux flow rate is as follows: the steam supplied from the 0.5MPa steam main pipe 6 is automatically controlled by the regulating valve G17 to provide sufficient heat to meet the reflux flow rate of the high-pressure excellent dimethyl tower 1 to reach 55000kg / h, the flow rate from the top of the high-pressure excellent dimethyl tower 1 to the medium-pressure excellent dimethyl tower 2 is stably automatically controlled by the regulating valve Z18 to ensure that the reflux flow rate of the medium-pressure excellent dimethyl tower 2 reaches 50000kg / h, the flow rate from the top of the high-pressure excellent dimethyl tower 1 to the tertiary tower 5 is automatically controlled by the regulating valve S19 to ensure that the reflux flow rate of the tertiary tower 5 reaches 20000kg / h, the heat from the top of the medium-pressure excellent dimethyl tower 2 is all supplied to the light fraction tower 3, and the heat from the top of the tertiary tower 5 is all supplied to the azeotropic tower 4, and no adjustment is required, but the reflux flow rate of the light fraction tower 3 must be ensured to reach The reflux rate of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 reaches 55000kg / h, and the reflux rate of the azeotropic tower 4 reaches 16000kg / h. During the adjustment process, the reflux rates of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 are automatically controlled by the regulating valve G522, the regulating valve S323 and the regulating valve F324, respectively, and the minimum reflux rate protection values ​​of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 are set, which are 38000kg / h for the high-pressure dimethyl tower, 14000kg / h for the trimethyl tower and 12000kg / h for the azeotropic tower, respectively. When the reflux rates of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 reach the set minimum reflux rate, the valve positions of the regulating valves G522, the regulating valves S323 and the regulating valves F324 are locked and no longer adjusted downward to ensure the separation effect of the towers. The pressure regulation method is: the high-pressure dimethyl tower 1, the medium-pressure dimethyl tower 2, the light fraction tower 3, the tertiary tower 5, and the azeotropic tower 4 are all automatically controlled by the tower top pressure through the corresponding condenser outlet regulating valve G310, regulating valve Z311, regulating valve Q212, regulating valve S213, and regulating valve F114. When the pressure of each tower increases, the valve opening is opened wide, and when the pressure of each tower decreases, the valve opening is reduced to stabilize the pressure of each tower within the index requirements. Preferably, the tower top pressure of the high-pressure dimethyl tower 1 is controlled at 0.2MPa, the tower top pressure of the medium-pressure dimethyl tower 2 is controlled at 0.11MPa, the tower top pressure of the light fraction tower 3 is controlled at 0.072MPa, the tower top pressure of the tertiary tower 5 is controlled at 0.11MPa, and the tower top pressure of the azeotropic tower 4 is controlled at 0.035MPa. The method of liquid level regulation is: the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 is automatically controlled by the regulating valve G1-115 on the 0.5MPa steam main pipe 6. When the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 increases, the steam flow of the 0.5MPa steam main pipe 6 is increased, and when the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 decreases, the steam flow of the 0.5MPa steam main pipe 6 is reduced, so that the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 is stabilized between 40% and 65%. At the same time, the cascade control of the liquid level of the bottom of the medium-pressure excellent dimethyl tower 2 and the material regulating valve Z1-117 of the coupling reboiler 16 is increased, and the liquid level of the bottom of the medium-pressure excellent dimethyl tower 2 is controlled. When the level rises, the material steam flow rate increases. When the liquid level of the tower kettle of the medium-pressure superior dimethyl tower 2 decreases, the steam flow rate decreases, so that the liquid level of the tower kettle of the medium-pressure superior dimethyl tower 2 is stabilized between 40% and 65%. When designed, in addition to the coupling reboiler 16, the tower kettle of the three-methyl tower 5 is also equipped with an auxiliary reboiler 25 to increase the automatic control of the tower kettle liquid level of the three-methyl tower 5 and the steam flow of the auxiliary reboiler 25 through the regulating valve S526. When the liquid level of the three-methyl tower 5 rises, the steam valve opening is increased. When the liquid level of the three-methyl tower 5 decreases, the steam flow rate is reduced, so that the liquid level of the three-methyl tower 5 kettle is stabilized between 40% and 65%; The temperature regulation method is: a: Select the sensitive plate temperature of the distillation section of the light fraction tower 3 as the main controlled variable. The temperature of the distillation section of the light fraction tower 3 and the reflux flow are cascade controlled through the regulating valve Q318. The temperature control range of the distillation section of the light fraction tower 3 is 56-57°C, and the set value is 56.5°C. When the distillation temperature of the light fraction tower 3 is lower than the set value, the reflux flow is reduced. When the distillation temperature of the light fraction tower 3 is higher than the set value, the reflux flow is increased; b: Select the top temperature of azeotropic tower 4 and the sensitive plate temperature of the distillation section of azeotropic tower 4 to calculate the temperature difference. The temperature difference is used as the main variable and is cascade controlled with the reflux flow through the regulating valve F3-119. The temperature difference control range is 4-5℃, and the set value is 4.5℃. When the temperature difference decreases, the reflux flow increases, and when the temperature difference increases, the reflux flow decreases; c: Select the kettle temperature of the 5th tower of the three-methyl tower as the main variable. The kettle temperature of the 5th tower of the three-methyl tower and the reflux volume are cascade-controlled through the regulating valve S620. The control range of the kettle temperature of the 5th tower of the three-methyl tower is 92-93°C, and the set value is 92.5°C. When the kettle temperature of the 5th tower of the three-methyl tower is lower than the set value, the kettle extraction is reduced. When the kettle temperature of the 5th tower of the three-methyl tower is higher than the set value, the kettle extraction is increased. Furthermore, on the basis of the reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, an automatic load control model is added. The automatic load control model is mainly based on the steady-state process model, supplemented by PID calculus regulation and dynamic process regulation; the steady-state process model is used for material and energy balance, the PID model is used to adjust the action trend and frequency, and the dynamic process model is used to monitor the signal transmission between production load changes. When the load is adjusted, the program is started on the premise of meeting the load and index requirements of the light fraction tower 3, and the high pressure The excellent dimethyl tower 1, the medium-pressure excellent dimethyl tower 2, the light fraction tower 3, the tertiary tower 5, and the azeotropic tower 4 are coupled in series. The entire coupling system is centered on the light fraction tower 3. The reflux rate of the light fraction tower 3 is controlled at 50,000 to 55,000 kg / h by the feed load of the light fraction tower 3. Then, the reflux rate of the medium-pressure excellent dimethyl tower 2 is controlled at 45,000 to 50,000 kg / h and the reflux rate of the high-pressure excellent dimethyl tower 1 is controlled at 50,000 to 55,000 kg / h in turn. The reflux rate of the high-pressure excellent dimethyl tower 1 is used to control the steam change in the tower kettle, and then the compensation value of the steam change controls the three The coupled steam heat source of the A tower 5 and the auxiliary coupled reboiler 16 of the tertiary tower 5 are automatically controlled for steam volume and tower bottom liquid level. The top pressure of the tertiary tower 5 is used as the compensation value of the reflux volume of the azeotropic tower 4 through the regulating valve F3-221 as the temperature difference of the azeotropic tower 4. When the temperature difference adjustment deviates by 2°C / minute or the pressure deviation of the tertiary tower 5 is greater than 5KPa / minute, the pressure of the tertiary tower 5 assists in controlling the reflux volume of the azeotropic tower 4, and the extraction volume of the kettle of the light fraction tower 3 assists in controlling the liquid level change of the azeotropic tower 4. In this way, the changes of the 5 coupled towers are based on the feed load of the light fraction tower 3. Comprehensive adjustments are made during the load lifting period. When the load lifting is completed, the coupled series tower control is mainly based on ① to ④, supplemented by the load lifting automatic control model, and they are controlled together. The present invention takes into account the interference of the system during the load lifting process. The coupled series tower control is mainly based on the cascade, temperature and pressure of each tower on the DCS interface, supplemented by the load lifting automatic control model. The combination of the two makes the control of the entire system more stable, greatly reduces human interference, saves labor costs, reduces losses caused by misjudgment during human operation, and reduces operational risks.

[0021] Furthermore, on the basis of the coordination and control of reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, the ratio of the feed flow of high-pressure excellent dimethyl tower 1 to the tower bottom output flow is calculated, and the ratio of the feed flow of medium-pressure excellent dimethyl tower 2 to the tower bottom output flow is calculated. The ratio = feed amount × (0.01~0.05). The ratio is selected as the main variable. The ratio calculated by high-pressure excellent dimethyl tower 1 and the tower bottom output flow are cascade controlled through regulating valve G6-127, and the ratio calculated by medium-pressure excellent dimethyl tower 2 is The ratio and the bottom extraction flow rate are controlled in cascade through the regulating valve Z6-128. The ratio = feed amount × (0.01~0.05). The control range of 0.01~0.05 is selected and adjusted according to the high boiling point impurity content in the sampling analysis results. When the high boiling point impurity content is high, it is adjusted to a high value. Under the same load, the ratio increases and the bottom extraction flow rate increases. When the high boiling point impurity content is low, it is adjusted to a low value. Under the same load, the ratio decreases and the bottom extraction flow rate decreases.

[0022] Furthermore, on the basis of the coordinated regulation of reflux volume regulation, pressure regulation, liquid level regulation and temperature regulation, the liquid level of the top reflux tank of the light fraction tower 3 and the top production flow are controlled in cascade through the regulating valve Q4, the liquid level of the bottom of the light fraction tower 3 and the bottom production flow are controlled in cascade through the regulating valve Q530, the liquid level of the bottom of the azeotropic tower 4 and the bottom production flow are controlled in cascade through the regulating valve F431, the liquid level of each tower is selected as the main variable, the production flow is increased when the liquid level of each tower rises, and the production flow is reduced when the liquid level decreases.

[0023] This embodiment 2 can effectively improve the effect of product distillation separation by adjusting the pressure, temperature, liquid level, flow rate, etc. of each tower in the system, thoroughly solving the problems of system lag and large fluctuations. The control method adopted by the present invention is advanced in technology and easy to control. Under the premise of ensuring that the product indicators and the operating parameters of each tower are normal, the goal of energy saving and optimization can be achieved. Compared with the traditional control method, the impurity content of butene-based products in the product is reduced by about 280ppmwt, which reduces the quality fluctuation of downstream products, saves steam consumption by 0.4-0.8t / h, and saves economic value of about 800,000 yuan / year. Example 3

[0024] The stable automatic control method of the multi-stage distillation heat-coupled distillation tower described in Example 3, the multi-stage distillation heat-coupled distillation tower mainly includes a high-pressure excellent dimethyl tower 1, a medium-pressure excellent dimethyl tower 2, a light fraction tower 3, an azeotropic tower 4 and a tertiary tower 5. The connection structure and process principle of each tower are the existing technology. Under the set tower top pressure, the top of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 5 are calculated based on the sum of the energy consumption of 105% of the design reflux flow of 60000kg / h of the light fraction tower 3 and the design reflux flow of 17000kg / h of the azeotropic tower 4. The reflux rate is calculated, and then the flow rates from the top of the high-pressure excellent dimethyl tower 1 to the kettles of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 2 are calculated. The sum of the flow rates of the kettles of the medium-pressure excellent dimethyl tower 2 and the tertiary tower 5 is the reflux rate of the high-pressure excellent dimethyl tower 1. The 0.5MPa steam consumption is calculated according to the reflux rate of the high-pressure excellent dimethyl tower 1, and the heat balance of the entire distillation coupling system can be determined. On the basis of the heat balance of the system, the material balance and gas-liquid balance of the entire distillation coupling system are adjusted by using the combination of reflux rate regulation, pressure regulation, liquid level regulation and temperature regulation.

[0025] The method for regulating the reflux flow rate is as follows: the steam supplied from the 0.5MPa steam main pipe 6 is automatically controlled by the regulating valve G17 to provide sufficient heat to meet the reflux flow rate of the high-pressure excellent dimethyl tower 1 to reach 60000kg / h, the flow rate from the top of the high-pressure excellent dimethyl tower 1 to the medium-pressure excellent dimethyl tower 2 is stably automatically controlled by the regulating valve Z18 to ensure that the reflux flow rate of the medium-pressure excellent dimethyl tower 2 reaches 55000kg / h, the flow rate from the top of the high-pressure excellent dimethyl tower 1 to the tertiary tower 5 is automatically controlled by the regulating valve S19 to ensure that the reflux flow rate of the tertiary tower 5 reaches 23000kg / h, the heat from the top of the medium-pressure excellent dimethyl tower 2 is all supplied to the light fraction tower 3, and the heat from the top of the tertiary tower 5 is all supplied to the azeotropic tower 4, and no adjustment is required, but the reflux flow rate of the light fraction tower 3 must be ensured to reach The reflux rate of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 reaches 60000kg / h, and the reflux rate of the azeotropic tower 4 reaches 17000kg / h. During the adjustment process, the reflux rates of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 are automatically controlled by the regulating valve G522, the regulating valve S323 and the regulating valve F324, respectively, and the minimum reflux rate protection values ​​of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 are set, which are 38000kg / h for the high-pressure dimethyl tower, 14000kg / h for the trimethyl tower and 12000kg / h for the azeotropic tower, respectively. When the reflux rates of the high-pressure dimethyl tower 1, the trimethyl tower 5 and the azeotropic tower 4 reach the set minimum reflux rate, the valve positions of the regulating valves G522, the regulating valves S323 and the regulating valves F324 are locked and no longer adjusted downward to ensure the separation effect of the towers. The pressure regulation method is: the high-pressure dimethyl tower 1, the medium-pressure dimethyl tower 2, the light fraction tower 3, the tertiary tower 5, and the azeotropic tower 4 are all automatically controlled by the tower top pressure through the corresponding condenser outlet regulating valve G310, regulating valve Z311, regulating valve Q212, regulating valve S213, and regulating valve F114. When the pressure of each tower increases, the valve opening is opened wide, and when the pressure of each tower decreases, the valve opening is reduced to stabilize the pressure of each tower within the index requirements. Preferably, the tower top pressure of the high-pressure dimethyl tower 1 is controlled at 0.21MPa, the tower top pressure of the medium-pressure dimethyl tower 2 is controlled at 0.12MPa, the tower top pressure of the light fraction tower 3 is controlled at 0.075MPa, the tower top pressure of the tertiary tower 5 is controlled at 0.12MPa, and the tower top pressure of the azeotropic tower 4 is controlled at 0.038MPa. The method of liquid level regulation is: the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 is automatically controlled by the regulating valve G1-115 on the 0.5MPa steam main pipe 6. When the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 increases, the steam flow of the 0.5MPa steam main pipe 6 is increased, and when the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 decreases, the steam flow of the 0.5MPa steam main pipe 6 is reduced, so that the liquid level of the bottom of the high-pressure excellent dimethyl tower 1 is stabilized between 40% and 65%. At the same time, the cascade control of the liquid level of the bottom of the medium-pressure excellent dimethyl tower 2 and the material regulating valve Z1-117 of the coupling reboiler 16 is increased, and the liquid level of the bottom of the medium-pressure excellent dimethyl tower 2 is controlled. When the level rises, the material steam flow rate increases. When the liquid level of the tower kettle of the medium-pressure superior dimethyl tower 2 decreases, the steam flow rate decreases, so that the liquid level of the tower kettle of the medium-pressure superior dimethyl tower 2 is stabilized between 40% and 65%. When designed, in addition to the coupling reboiler 16, the tower kettle of the three-methyl tower 5 is also equipped with an auxiliary reboiler 25 to increase the automatic control of the tower kettle liquid level of the three-methyl tower 5 and the steam flow of the auxiliary reboiler 25 through the regulating valve S526. When the liquid level of the three-methyl tower 5 rises, the steam valve opening is increased. When the liquid level of the three-methyl tower 5 decreases, the steam flow rate is reduced, so that the liquid level of the three-methyl tower 5 kettle is stabilized between 40% and 65%; The temperature regulation method is: a: Select the sensitive plate temperature of the distillation section of the light fraction tower 3 as the main controlled variable. The temperature of the distillation section of the light fraction tower 3 and the reflux flow are cascade controlled through the regulating valve Q318. The temperature control range of the distillation section of the light fraction tower 3 is 57-58°C, and the set value is 57.5°C. When the distillation temperature of the light fraction tower 3 is lower than the set value, the reflux flow is reduced. When the distillation temperature of the light fraction tower 3 is higher than the set value, the reflux flow is increased. b: Select the top temperature of azeotropic tower 4 and the sensitive plate temperature of the distillation section of azeotropic tower 4 to calculate the temperature difference. The temperature difference is used as the main variable and is cascade controlled with the reflux flow through the regulating valve F3-119. The temperature difference control range is 5-6℃, and the set value is 5.5℃. When the temperature difference decreases, the reflux flow increases, and when the temperature difference increases, the reflux flow decreases; c: Select the temperature of the kettle of the Trimethyl Tower 5 as the main variable. The kettle temperature of the Trimethyl Tower 5 and the reflux volume are cascade controlled through the regulating valve S620. The control range of the kettle temperature of the Trimethyl Tower 5 is 93-94°C, and the set value is 93.5°C. When the kettle temperature of the Trimethyl Tower 5 is lower than the set value, the kettle extraction is reduced. When the kettle temperature of the Trimethyl Tower 5 is higher than the set value, the kettle extraction is increased. Furthermore, on the basis of the reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, an automatic load control model is added. The automatic load control model is mainly based on the steady-state process model, supplemented by PID calculus regulation and dynamic process regulation; the steady-state process model is used for material and energy balance, the PID model is used to adjust the action trend and frequency, and the dynamic process model is used to monitor the signal transmission between production load changes. When the load is adjusted, the program is started on the premise of meeting the load and index requirements of the light fraction tower 3, and the load is adjusted. The high-pressure excellent dimethyl tower 1, the medium-pressure excellent dimethyl tower 2, the light fraction tower 3, the tertiary tower 5, and the azeotropic tower 4 are coupled in series. The entire coupling system is centered on the light fraction tower 3. The reflux rate of the light fraction tower 3 is controlled at 55,000 to 65,000 kg / h through the feed load of the light fraction tower 3. Then, the reflux rate of the medium-pressure excellent dimethyl tower 2 is controlled at 60,000 to 75,000 kg / h and the reflux rate of the high-pressure excellent dimethyl tower 1 is controlled at 55,000 to 80,000 kg / h. The reflux rate of the high-pressure excellent dimethyl tower 1 is used to control the steam variation in the tower kettle, and then the steam variation is compensated. The value controls the coupled steam heat source of the triple tower 5. At the same time, the steam volume of the auxiliary coupled reboiler 16 of the triple tower 5 and the liquid level of the tower are automatically controlled. The top pressure of the triple tower 5 is used as the temperature difference of the azeotropic tower 4 to control the compensation value of the reflux volume of the azeotropic tower 4 through the regulating valve F3-221. When the temperature difference adjustment deviation or the pressure deviation of the triple tower 5 is greater than 5KPa / minute, the pressure of the triple tower 5 assists in controlling the reflux volume of the azeotropic tower 4, and the extraction volume of the kettle of the light fraction tower 3 assists in controlling the change of the liquid level of the azeotropic tower 4. In this way, the changes of the five coupled towers are based on the feed load of the light fraction tower 3. The present invention takes into account the interference of the system in the process of load lifting. The control of the coupled series towers is mainly based on the cascade, temperature and pressure of each tower on the DCS interface, supplemented by the automatic control model. The combination of the two makes the control of the entire system more stable, greatly reduces human interference, saves labor costs, reduces losses caused by misjudgment during human operation, and reduces operational risks.

[0026] Furthermore, on the basis of the coordination and control of reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, the ratio of the feed flow of high-pressure excellent dimethyl tower 1 to the tower bottom output flow is calculated, and the ratio of the feed flow of medium-pressure excellent dimethyl tower 2 to the tower bottom output flow is calculated. The ratio = feed amount × (0.01~0.05). The ratio is selected as the main variable. The ratio calculated by high-pressure excellent dimethyl tower 1 and the tower bottom output flow are cascade controlled through regulating valve G6-127, and the ratio calculated by medium-pressure excellent dimethyl tower 2 is The ratio and the bottom extraction flow rate are controlled in cascade through the regulating valve Z6-128. The ratio = feed amount × (0.01~0.05). The control range of 0.01~0.05 is selected and adjusted according to the high boiling point impurity content in the sampling analysis results. When the high boiling point impurity content is high, it is adjusted to a high value. Under the same load, the ratio increases and the bottom extraction flow rate increases. When the high boiling point impurity content is low, it is adjusted to a low value. Under the same load, the ratio decreases and the bottom extraction flow rate decreases.

[0027] Furthermore, on the basis of the coordinated regulation of reflux volume regulation, pressure regulation, liquid level regulation and temperature regulation, the liquid level of the top reflux tank of the light fraction tower 3 and the top production flow are controlled in cascade through the regulating valve Q4, the liquid level of the bottom of the light fraction tower 3 and the bottom production flow are controlled in cascade through the regulating valve Q530, the liquid level of the bottom of the azeotropic tower 4 and the bottom production flow are controlled in cascade through the regulating valve F431, the liquid level of each tower is selected as the main variable, the production flow is increased when the liquid level of each tower rises, and the production flow is reduced when the liquid level decreases.

[0028] This embodiment 3 can effectively improve the effect of product distillation separation by adjusting and controlling the pressure, temperature, liquid level, flow rate, etc. of each tower in the system, thoroughly solving the problems of system lag and large fluctuations. The control method adopted by the present invention is advanced in technology and easy to control. Under the premise of ensuring that the product indicators and the operating parameters of each tower are normal, the goal of energy saving and optimization can be achieved. Compared with the traditional control method, the impurity content of butene-based products in the product is reduced by about 300ppmwt, which reduces the quality fluctuation of downstream products, saves steam consumption by 0.5-0.8t / h, and saves economic value of about 1 million yuan / year.

Claims

1. A stable automatic control method for a multi-stage distillation heat-coupled distillation tower, characterized in that: Under the set tower top pressure, the reflux rates of the medium-pressure excellent dimethyl tower (2) and the tertiary tower (5) are calculated based on the sum of the energy consumption of 105% of the design reflux rate of 52000 kg / h of the light fraction tower (3) and the design reflux rate of 15000-17000 kg / h of the azeotropic tower (4) as the basis, and then the flow rates sent from the tower top of the high-pressure excellent dimethyl tower (1) to the tower bottoms of the medium-pressure excellent dimethyl tower (2) and the tertiary tower (2) are calculated. The sum of the flow rates of the tower bottoms of the medium-pressure excellent dimethyl tower (2) and the tertiary tower (5) is the reflux rate of the high-pressure excellent dimethyl tower (1). The 0.5 MPa steam consumption is calculated based on the reflux rate of the high-pressure excellent dimethyl tower (1), and the heat balance of the entire distillation coupling system can be determined. On the basis of the system heat balance, the material balance and gas-liquid balance of the entire distillation coupling system are adjusted by using the combination of reflux rate regulation, pressure regulation, liquid level regulation and temperature regulation.

2. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 1, characterized in that: The method for regulating the reflux flow rate is as follows: the steam supplied from the 0.5MPa steam main pipe (6) is automatically controlled by the regulating valve G1 (7) to provide sufficient heat to meet the reflux flow rate of the high-pressure excellent dimethyl tower (1) to reach 40,000 to 80,000 kg / h; the flow rate supplied from the top of the high-pressure excellent dimethyl tower (1) to the medium-pressure excellent dimethyl tower (2) is automatically controlled by the regulating valve Z1 (8) to control the reflux flow rate of the medium-pressure excellent dimethyl tower (2) to reach 35,000 to 75,000 kg / h; and the high-pressure excellent dimethyl tower The flow rate supplied from the top of the tower (1) to the tertiary column (5) is automatically controlled by a regulating valve S1 (9) to ensure that the reflux rate of the tertiary column (5) reaches 15,000 to 30,000 kg / h. The heat from the top of the medium-pressure dimethyl column (2) is all supplied to the light fraction column (3). The heat from the top of the tertiary column (5) is all supplied to the azeotropic column (4). The reflux rate of the light fraction column (3) is controlled to reach 40,000 to 65,000 kg / h, and the reflux rate of the azeotropic column (4) is controlled to reach 15,000 to 25,000 kg / h.

3. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 2, characterized in that: The reflux rates of the high-pressure dimethyl tower (1), the trimethyl tower (5) and the azeotropic tower (4) are automatically controlled by the regulating valve G5 (22), the regulating valve S3 (23) and the regulating valve F3 (24) respectively, and the minimum reflux rate protection values ​​of the high-pressure dimethyl tower (1), the trimethyl tower (5) and the azeotropic tower (4) are set, which are 38000 kg / h for the high-pressure dimethyl tower, 14000 kg / h for the trimethyl tower and 12000 kg / h for the azeotropic tower, respectively. When the reflux rates of the high-pressure dimethyl tower (1), the trimethyl tower (5) and the azeotropic tower (4) reach the set minimum reflux rate protection values, the valve positions of the regulating valves G5 (22), the regulating valves S3 (23) and the regulating valves F3 (24) are locked and are no longer adjusted downward, thereby ensuring the separation effect of the towers.

4. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 1, characterized in that: The pressure regulation method is as follows: the high-pressure dimethyl column (1), the medium-pressure dimethyl column (2), the light fraction column (3), the tertiary column (5), and the azeotropic column (4) are all automatically controlled by using the tower top pressure through the corresponding condenser outlet regulating valve G3 (10), regulating valve Z3 (11), regulating valve Q2 (12), regulating valve S2 (13), and regulating valve F1 (14), respectively. The tower top pressure of the high-pressure dimethyl column (1) is required to be controlled within 0.19-0.25 MPa, the tower top pressure of the medium-pressure dimethyl column (2) is required to be controlled within 0.1-0.12 MPa, the tower top pressure of the light fraction column (3) is required to be controlled within 0.06-0.12 MPa, the tower top pressure of the tertiary column (5) is required to be controlled within 0.1-0.13 MPa, and the tower top pressure of the azeotropic column (4) is required to be controlled within 0.03-0.04 MPa. When the pressure of each tower increases, the valve opening is increased, and when the pressure of each tower decreases, the valve opening is reduced to stabilize the pressure of each tower within the index requirement.

5. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 1, characterized in that: The liquid level regulation method is as follows: the liquid level of the bottom of the high-pressure dimethyl tower (1) is automatically controlled by the regulating valve G1-1 (15) on the 0.5MPa steam main pipe (6), so that the liquid level of the bottom of the high-pressure dimethyl tower (1) is controlled to be stable between 40% and 65%. At the same time, the liquid level of the bottom of the medium-pressure dimethyl tower (2) and the regulating valve Z1-1 (17) of the coupling reboiler (16) are cascade-controlled to control the liquid level of the bottom of the medium-pressure dimethyl tower (2) to be stable between 40% and 65%. In addition to the coupling reboiler (16), the bottom of the three-methane tower (5) is also provided with an auxiliary reboiler (25). The liquid level of the bottom of the three-methane tower (5) and the steam flow of the auxiliary reboiler (25) are automatically controlled by the regulating valve S5 (26), so that the liquid level of the bottom of the three-methane tower (5) is controlled to be stable between 40% and 65%.

6. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 1, characterized in that: The temperature regulation method is: The sensitive plate temperature of the distillation section of the light fraction tower (3) is selected as the main controlled variable. The sensitive plate temperature of the distillation section of the light fraction tower (3) and the reflux flow rate are cascade controlled through the regulating valve Q3 (18). The sensitive plate temperature control range of the distillation section of the light fraction tower (3) is 55-57° C., and the set value is 56° C. When the sensitive plate temperature of the distillation section of the light fraction tower (3) is lower than the set value, the reflux flow rate is reduced. When the sensitive plate temperature of the distillation section of the light fraction tower (3) is higher than the set value, the reflux flow rate is increased. The top temperature of the azeotropic tower (4) and the sensitive plate temperature of the distillation section of the azeotropic tower (4) are selected to calculate the temperature difference. The temperature difference is used as the main variable. The temperature difference and the reflux flow are cascade controlled through the regulating valve F3-1 (19). The temperature difference control range is 3 to 4°C, and the set value is 3.5°C. When the temperature difference decreases, the reflux flow increases, and when the temperature difference increases, the reflux flow decreases. The temperature of the kettle of the three-layer tower (5) is selected as the main variable. The temperature of the kettle of the three-layer tower (5) and the reflux amount are cascade-controlled through the regulating valve S6 (20). The control range of the temperature of the kettle of the three-layer tower (5) is 91-93°C, and the set value is 92°C. When the temperature of the kettle of the three-layer tower (5) is lower than the set value, the kettle extraction is reduced. When the temperature of the kettle of the three-layer tower (5) is higher than the set value, the kettle extraction is increased.

7. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 1, characterized in that: On the basis of the reflux flow rate regulation, pressure regulation, liquid level regulation and temperature regulation, an automatic load lifting control model is added. When the load is adjusted, the program is started on the premise of meeting the load and index requirements of the light fraction tower (3), and the high-pressure excellent dimethyl tower (1), the medium-pressure excellent dimethyl tower (2), the light fraction tower (3), the tertiary tower (5) and the azeotropic tower (4) are coupled in series. The entire coupling system is centered on the light fraction tower (3). The reflux flow of the light fraction tower (3) is controlled to be between 40,000 and 65,000 kg / h through the feed load of the light fraction tower (3), and then the reflux flow of the medium-pressure excellent dimethyl tower (2) is controlled to be between 35,000 and 75,000 kg / h and the reflux flow of the high-pressure excellent dimethyl tower (1) is controlled to be between 40,000 and 80,000 kg / h in turn. The reflux flow of the high-pressure excellent dimethyl tower (1) is used to control the steam change in the tower kettle, and then the compensation value of the steam change is used to control the tertiary tower ( 5), and the steam volume and the tower bottom liquid level of the auxiliary coupling reboiler (16) of the three-column tower (5) are automatically controlled. The top pressure of the three-column tower (5) is used as the compensation value of the reflux volume of the azeotropic tower (4) through the regulating valve F3-2 (21) as the temperature difference of the azeotropic tower (4). When the temperature difference adjustment deviates by 2°C / minute or the pressure deviation of the three-column tower (5) is greater than 5KPa / minute, the pressure of the three-column tower (5) assists in controlling the reflux volume of the azeotropic tower (4), and the extraction volume of the kettle of the light fraction tower (3) assists in controlling the change of the azeotropic tower (4) liquid level. In this way, the change of the five coupled towers is comprehensively adjusted during the lifting and lowering load period based on the feed load of the light fraction tower (3). After the lifting and lowering load is completed, the tower control of the entire distillation coupling system is mainly controlled by the reflux volume balance adjustment, pressure balance adjustment, liquid level balance adjustment and temperature balance adjustment, and the lifting and lowering load automatic control model is used as a supplement for joint control.

8. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 1, characterized in that: On the basis of the coordination and control of reflux flow regulation, pressure regulation, liquid level regulation and temperature regulation, the ratio of the feed flow of the high-pressure excellent dimethyl tower (1) to the tower bottom output flow is calculated, and the ratio of the feed flow of the medium-pressure excellent dimethyl tower (2) to the tower bottom output flow is calculated. The ratio = feed amount × (0.01-0.05). The ratio is selected as the main variable. The ratio calculated by the high-pressure excellent dimethyl tower (1) and the tower bottom output flow are cascade controlled through the regulating valve G6-1 (27). The medium-pressure excellent dimethyl tower (2) The calculated ratio and the bottom extraction flow rate are controlled in cascade via regulating valve Z6-1 (28). Ratio = feed amount × (0.01 to 0.05). The control interval of 0.01 to 0.05 is selected and adjusted based on the high boiling point impurity content in the sampling analysis results. When the high boiling point impurity content is high, the ratio is adjusted to a higher value. Under the same load, the bottom extraction flow rate increases when the ratio increases. When the high boiling point impurity content is low, the ratio is adjusted to a lower value. Under the same load, the bottom extraction flow rate decreases.

9. The stable automatic control method of a multi-stage distillation heat-coupled distillation tower according to claim 1, characterized in that: On the basis of the coordinated regulation of reflux volume balance regulation, pressure balance regulation, liquid level balance regulation and temperature balance regulation, the liquid level of the top reflux tank of the light fraction tower (3) and the top extraction flow rate are controlled in series through the regulating valve Q4 (39), the liquid level of the bottom of the light fraction tower (3) and the bottom extraction flow rate are controlled in series through the regulating valve Q5 (30), and the liquid level of the bottom of the azeotropic tower (4) and the bottom extraction flow rate are controlled in series through the regulating valve F4 (31). The liquid level of each tower is selected as the main variable. When the liquid level of each tower rises, the extraction flow rate increases, and when the liquid level decreases, the extraction flow rate decreases.

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