Alkylation product separation system, separation method, alkylation process system and method

Abstract

The present invention provides an alkylation product separation system, a separation method, an alkylation process system, and a method. The liquid phase discharge port of the isobutane fractionation unit in the separation system is connected to the feed pipeline of the normal butane fractionation unit via an isobutane bottom pump, and is also connected to a propane compression refrigeration unit including an isobutane top condenser, a throttling expansion valve, a circulating water cooler, a refrigeration compressor, and a refrigerant tank. The isobutane top condenser is located at the top of a low-temperature isobutane distillation tower to cool and reflux its top gas phase. The refrigerant liquid phase inlet of the isobutane top condenser is sequentially connected to the gas phase outlet of the refrigerant tank via a throttling expansion valve, a circulating water cooler, and a refrigeration compressor. The gas phase refrigerant is mixed with part of the liquid phase of the throttling expansion valve via a pipeline and input into the refrigerant tank. The present invention uses a low-temperature isobutane distillation tower with low-temperature heating at the bottom of the tower and a high-efficiency compression refrigeration system at the top of the tower to provide cooling, effectively reducing separation difficulty and improving energy utilization, saving separation energy consumption and process costs.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, and in particular to an alkylation product separation system, a separation method, and an alkylation process system and method. Background Art

[0002] Alkylation product separation is a key process step in the production of alkylate oil. It is mainly used to remove isobutane and n-butane from the alkylation reaction products, recover isobutane and return it to the alkylation reaction unit, and separate alkylate oil that meets the requirements.

[0003] The separation of conventional alkylation products is a significant energy-consuming step in the entire alkylation process. This is particularly true for low-temperature isobutane distillation towers, which feature large material flows, high operating pressures, and high material temperatures. This results in lower relative volatility of n-butane and isobutane, making separation more difficult. For the same separation accuracy, the reflux ratio increases, significantly increasing the consumption of high-temperature steam in the tower bottom reboiler and raising the production cost of alkylate oil. Furthermore, since the alkylation reaction occurs at low temperatures (0-5°C) while the alkylation product separation occurs at high temperatures (5-50°C and approximately 150°C), Figure 1 The heat exchange system in the existing alkylation process flowsheet shown here results in a mismatched temperature profile across the entire alkylation system. This results in low heat exchange efficiency and underutilized heat and cooling capacity. Furthermore, the reaction products and circulating isobutane experience significant repeated heating and cooling, further increasing energy consumption in the alkylation process. Therefore, technological innovations in separation processes and the entire alkylation process are urgently needed to improve the efficiency of alkylation product separation and the energy efficiency of the alkylation process system, thereby achieving reliable energy conservation and consumption reduction. Summary of the Invention

[0004] The present invention aims to provide an alkylation product separation system. By designing a low-temperature isobutane distillation tower with a bottom heated by waste heat from the plant and a propane compression refrigeration system at the top, the isobutane separated at the top can be directly circulated to the alkylation reaction system without further cooling, and the bottom effluent can be directly fed into the n-butane distillation tower after heat exchange with the bottom effluent of the n-butane distillation tower. This system reduces the refrigeration load of the isobutane tower bottom reboiler and the alkylation reaction system, improves energy utilization efficiency and the separation efficiency of the isobutane tower, and saves process costs.

[0005] In order to achieve the above objectives, it is necessary to provide an alkylation product separation system and method in response to the above technical problems.

[0006] In a first aspect, an embodiment of the present invention provides an alkylation product separation system, comprising an isobutane fractionation unit, and a propane compression refrigeration unit and an n-butane fractionation unit connected to the isobutane fractionation unit; a liquid phase discharge port of the isobutane fractionation unit is connected to a feed pipeline of the n-butane fractionation unit via an isobutane bottom pump;

[0007] The propane compression refrigeration device includes an isobutane tower top condenser, a throttling expansion valve, a circulating water cooler, a refrigeration compressor and a refrigerant tank; the isobutane tower top condenser is arranged at the top of the low-temperature isobutane distillation tower in the isobutane fractionation device, and cools the top gas phase of the low-temperature isobutane distillation tower and then inputs it into the isobutane fractionation device through a pipeline; the gas phase outlet of the refrigerant tank is connected to the refrigerant liquid phase inlet of the isobutane tower top condenser through a pipeline in sequence through the refrigeration compressor, the circulating water cooler and the throttling expansion valve; the gas phase refrigerant of the isobutane tower top condenser is mixed with part of the liquid phase refrigerant of the throttling expansion valve through a pipeline and input into the refrigerant tank.

[0008] Furthermore, the isobutane fractionation device includes a low-temperature isobutane distillation tower, an isobutane tower top reflux tank, an isobutane tower bottom low-temperature reboiler, and an isobutane tower bottom pump;

[0009] The feed port of the low-temperature isobutane distillation tower is connected to the alkylation reaction product pipeline; the gas phase outlet of the low-temperature isobutane distillation tower is connected to the feed port of the isobutane tower top reflux tank via the isobutane tower top condenser; the outlet pipeline of the isobutane tower top reflux tank is divided into two, one condensate is connected to the liquid phase reflux port at the top of the low-temperature isobutane distillation tower, and the other condensate is connected to the circulating isobutane feed port of the alkylation reaction system; the liquid phase inlet and gas phase outlet of the low-temperature reboiler at the bottom of the isobutane tower are respectively connected to the bottom and tower body of the low-temperature isobutane distillation tower through pipelines; the liquid phase discharge port at the bottom of the low-temperature isobutane distillation tower is connected to the feed pipeline of the n-butane fractionation device via the isobutane tower bottom pump.

[0010] Furthermore, the heat source inlet of the low-temperature reboiler at the bottom of the isobutane tower is connected to the outlet of an external low-temperature heat source; the temperature of the external low-temperature heat source is 70°C-90°C.

[0011] Furthermore, the n-butane fractionation device includes a n-butane bottoms effluent heat exchanger, a n-butane rectification tower, a n-butane top condenser, a n-butane top reflux tank, a n-butane bottoms reboiler, an alkali wash liquid heat exchanger, and a n-butane bottoms effluent cooler;

[0012] The feed inlet of the n-butane distillation tower is connected to the bottom liquid phase discharge port of the low-temperature isobutane distillation tower via a pipeline, sequentially passing through the n-butane tower bottom flow heat exchanger and the isobutane tower bottom pump; the vapor phase outlet of the n-butane distillation tower is connected to the feed inlet of the n-butane tower top reflux tank via the n-butane tower top condenser; the liquid phase outlet of the n-butane tower top reflux tank is connected to the reflux inlet of the n-butane distillation tower; the liquid phase inlet and vapor phase outlet of the n-butane tower bottom reboiler are connected to the bottom and tower body of the n-butane distillation tower, respectively, via pipelines; and the bottom liquid phase discharge port of the n-butane distillation tower is connected to the feed pipeline of the alkylate oil storage tank via the n-butane tower bottom flow heat exchanger, the alkali wash liquid heat exchanger, and the n-butane tower bottom flow cooler.

[0013] In a second aspect, an embodiment of the present invention provides an alkylation product separation method, which is applied to any of the above-mentioned alkylation product separation systems, and the method comprises the following steps:

[0014] The alkylation reaction product is fed into an isobutane fractionation unit for low-temperature isobutane fractionation; the temperature of the bottom reboiler of the low-temperature isobutane fractionation tower is 70°C-90°C;

[0015] The refrigerant is pressurized by a refrigeration compressor and then fed into a circulating water cooler for condensation. A portion of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane column top condenser. The top gas phase of the low-temperature isobutane distillation column is cooled and partially extracted and fed into a circulating isobutane feed port of the alkylation reaction system. The bottom liquid phase of the low-temperature isobutane distillation column is pressurized and then fed into the n-butane fractionation unit for alkylate oil fractionation. The vaporization temperature corresponding to the lowest pressure of the refrigerant is not higher than the condensation temperature of the stream in the top of the low-temperature isobutane distillation column.

[0016] The gas phase refrigerant of the isobutane tower top condenser and part of the liquid phase refrigerant of the throttling expansion valve are collected through a refrigerant tank for circulation.

[0017] In a third aspect, an embodiment of the present invention provides an alkylation process system, comprising an alkylation reaction system and a corresponding compression refrigeration system and effluent refining system, and the alkylation product separation system described in any one of the above items; the isobutane fractionation unit in the alkylation product separation system further comprises a pre-cooling heat exchanger;

[0018] The feed pipeline of the alkylation reaction system is divided into two routes, one of which is connected to the circulating isobutane discharge port of the alkylation product separation system, and the other is connected to the pretreatment material pipeline and the supplementary isobutane pipeline through the reaction system feed heat exchanger; the alkylation reaction product outlet of the alkylation reaction system is connected to the feed port of the effluent refining system through a pipeline sequentially passing through the compression refrigeration system, the reaction system feed heat exchanger and the pre-cooling heat exchanger before the tower; the discharge port of the effluent refining system is connected to the feed port of the low-temperature isobutane distillation tower through a pipeline through the pre-cooling heat exchanger before the tower; the circulating material gas phase outlet of the alkylation reaction system is connected to the flash tank in the compression refrigeration system.

[0019] Furthermore, the system also includes an optimization control subsystem; the optimization control subsystem includes an optimization controller and a low-temperature isobutane distillation tower top pressure control loop, an isobutane tower top condenser refrigerant pressure control loop, a refrigeration compressor outlet pressure control loop, a second refrigeration compressor outlet pressure control loop and a flash tank pressure control loop connected to the optimization controller; the optimization controller outputs a thermal coupling optimal control strategy in real time based on a preset control optimization model; the thermal coupling optimal control strategy includes the isobutane distillation tower top pressure, the refrigeration compressor inlet pressure, the refrigeration compressor outlet pressure, the second refrigeration compressor inlet pressure and the second refrigeration compressor outlet pressure.

[0020] Furthermore, the preset control optimization model is constructed by taking minimization of the unit alkylate oil separation energy consumption cost as the optimization objective under preset control constraints; the preset control constraints include a constraint on the amount of heat absorbed by the refrigerant at the top of the isobutane tower, a constraint on the reduction in refrigeration load of the compression refrigeration system, a constraint on the temperature phase change pressure of propane, a constraint on the condensation temperature at the top of the isobutane tower, a constraint on the temperature phase change pressure of the mixture working fluid in the compression refrigeration system, and a constraint on the compressor inlet temperature of the compression refrigeration system.

[0021] Furthermore, the objective function of the preset control optimization model is expressed as:

[0022]

[0023] Where,

[0024]

[0025] B i =F nbs α

[0026]

[0027]

[0028] Among them, A i 、Bi and C i F represents the refrigeration cost of the low-temperature isobutane distillation tower top, the steam heat source cost of the n-butane tower bottom reboiler, and the refrigeration cost saved by the compression refrigeration system; nbit represents the alkylate oil flow rate; k and Z represent the gas isentropic coefficient and gas compressibility coefficient respectively; R represents 8314 / working fluid molecular weight; T1, p1, p2 and η1 represent the inlet temperature, inlet pressure, outlet pressure and refrigeration mechanical efficiency of the refrigeration compressor respectively; represents the propane flow rate of the refrigeration compressor; γ represents the electricity cost; η2 represents the refrigeration mechanical efficiency of the second refrigeration compressor; F nbs and α represent the steam flow rate and heat source steam cost of the n-butane tower bottom reboiler respectively; p3, p4, p5 and p6 represent the inlet original pressure, outlet original pressure, inlet current pressure and outlet current pressure of the second refrigeration compressor respectively; Indicates the refrigerant flow rate of the second refrigeration compressor; F nbit represents the alkylate oil flow rate; q nbs represents the unit steam phase change heat of the heat source of the n-butane tower bottom reboiler; ω nbs It indicates the heat consumption of reboiler heat source steam per unit effluent volume of n-butane distillation tower.

[0029] In a fourth aspect, an embodiment of the present invention provides an alkylation process method, which is applied to any of the above-mentioned alkylation process systems, and the method comprises the following steps:

[0030] The alkylation reaction product of the alkylation reaction system is cooled by a compression refrigeration system and fed into a feed heat exchanger of the reaction system. After being heated by heat exchange with an upstream material of the alkylation reaction system in the feed heat exchanger, the product is fed into a pre-cooling heat exchanger in front of the tower and cooled by heat exchange with a refined effluent of an effluent refining system. The product is then fed into the effluent refining system for refining treatment. The refined effluent after heat exchange and cooling is fed into a low-temperature isobutane distillation tower for low-temperature isobutane fractionation. The bottom reboiler temperature of the low-temperature isobutane distillation tower is 70° C. to 90° C.

[0031] The refrigerant is pressurized by a refrigeration compressor and then fed into a circulating water cooler for condensation. A portion of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane tower top condenser. The top gas phase of the low-temperature isobutane distillation tower is cooled and partially extracted and fed into a circulating isobutane feed port of the alkylation reaction system. The bottom liquid phase of the low-temperature isobutane distillation tower is pressurized and then fed into the n-butane fractionation unit for alkylate oil fractionation. The gas phase refrigerant of the isobutane tower top condenser and a portion of the liquid phase refrigerant of the throttling expansion valve are combined through a refrigerant tank for recycling.

[0032] Compared with the prior art, the alkylation product separation system, separation method, alkylation process system and method provided by the present invention have the following beneficial effects:

[0033] 1) By using a low-temperature isobutane distillation column to separate isobutane, the overall temperature of the isobutane fractionator can be lowered. High-pressure steam is no longer required to heat the bottom of the column, and low-temperature waste heat from the plant can be used for heating, effectively saving a large amount of energy. The top of the column uses a highly energy-efficient propane compression refrigeration system for cooling, further improving energy efficiency and saving costs. Furthermore, lowering the operating pressure of the isobutane distillation column also helps increase the relative volatility of n-butane and isobutane, making separation easier and further reducing energy consumption.

[0034] 2) By innovatively adopting a low-temperature isobutane distillation process that uses a propane compression refrigeration system at the top of the isobutane fractionation tower for cooling and low-temperature waste heat from the plant for heating at the bottom of the tower, combined with a process design in which the alkylation reaction product feed is heat-exchanged with the isobutane fractionation tower overhead liquid before entering the isobutane fractionation tower, the temperature rise of the feed stream entering the alkylation product separation system is reduced. Furthermore, the isobutane separated at the top of the low-temperature isobutane fractionation tower can be directly recycled to the reaction system without further cooling, effectively solving the problem of severe energy waste caused by repeated heating and cooling of the alkylation product and the recycled isobutane.

[0035] 3) By designing an alkylation thermal coupling system without changing the required tower diameter, combined with a given isobutane fractionator bottom reboiler heat source temperature, an optimization control subsystem is deployed to adaptively control the isobutane fractionator top pressure, the pressure before and after the propane compression refrigeration system, and the pressure before and after the original compression refrigeration system, with the optimization goal of minimizing the unit alkylate oil separation energy consumption cost. This not only effectively saves a large amount of equipment investment costs, but also reduces energy consumption and improves energy utilization efficiency from a global perspective through effective heat integration among multiple systems, thereby reducing unit production costs and increasing production capacity, and ensuring the continuous optimal operation of the alkylation process system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of the existing alkylation process system in an embodiment of the present invention;

[0037] Figure 2 Schematic diagram of the structure of the alkylation product separation system in an embodiment of the present invention;

[0038] Figure 3 1 is a schematic flow diagram of a method for separating an alkylation product according to an embodiment of the present invention;

[0039] Figure 4 Schematic diagram of the structure of an alkylation process system integrated with an alkylation product separation system according to an embodiment of the present invention;

[0040] Figure 5 Schematic diagram of optimization control of the alkylation process system in an embodiment of the present invention;

[0041] Figure 6 Schematic diagram of the structure of the effluent refining system in an embodiment of the present invention;

[0042] Figure 7 Schematic diagram of the alkylation process according to an embodiment of the present invention.

[0043] Reference numerals:

[0044] 1- pre-cooling heat exchanger before the tower, 2- low-temperature isobutane distillation tower, 3- isobutane tower top condenser, 4- isobutane tower top reflux tank, 5- isobutane tower bottom low-temperature reboiler, 6- isobutane tower bottom pump, 7- normal-butane tower bottom effluent heat exchanger, 8- normal-butane distillation tower, 9- normal-butane tower top condenser, 10- normal-butane tower top reflux tank, 11- normal-butane tower bottom reboiler, 12- alkali wash liquid heat exchanger, 13- normal-butane tower bottom effluent cooler, 14- throttling expansion valve, 15- circulating water cooler, 16- refrigeration compressor, 17- refrigerant tank, 18- flash tank, 19- second refrigeration compressor, 20- condenser, 21- second refrigerant Tank, 22-refrigerant cooler, 23-energy-saving tank, 24-flash tank flash side pump, 25-flash tank suction side pump, 26-low-temperature isobutane distillation tower top pressure control circuit, 27-isobutane tower top condenser refrigerant pressure control circuit, 28-refrigerant tank pressure control circuit, 29-refrigeration compressor outlet pressure control circuit, 30-second refrigeration compressor outlet pressure control circuit, 31-flash tank pressure control circuit, 32-second refrigerant tank pressure control circuit, 33-reaction system feed heat exchanger, 34-optimization controller, 100-isobutane fractionation unit, 200-propane compression refrigeration unit, 300-n-butane fractionation unit. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and beneficial effects of this application more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described below are part of the embodiments of the present invention and are only used to illustrate the present invention, but are not used to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0046] The alkylation product separation system provided by the present invention can be independently constructed according to the application requirements of the enterprise to improve separation efficiency, enhance the energy utilization efficiency of the separation system, and reduce separation energy consumption. It can also be integrated with the existing alkylation reaction system, the corresponding compression refrigeration system, and the effluent refining system based on the thermal coupling requirements of the alkylation process system to achieve better energy saving and consumption reduction effects from a global perspective.

[0047] In one embodiment, Figure 2 As shown, an alkylation product separation system is provided, which includes an isobutane fractionation device 100, and a propane compression refrigeration device 200 and an n-butane fractionation device 300 connected to the isobutane fractionation device 100; the liquid phase outlet of the isobutane fractionation device 100 is connected to the feed pipeline of the n-butane fractionation device 300 via an isobutane bottom pump 6;

[0048] The propane compression refrigeration device 200 includes an isobutane tower top condenser 3, a throttling expansion valve 14, a circulating water cooler 15, a refrigeration compressor 16 and a refrigerant tank 17; the isobutane tower top condenser 3 is arranged at the top of the low-temperature isobutane distillation tower 2 in the isobutane fractionation device 100, and the top gas phase of the low-temperature isobutane distillation tower 2 is cooled and then input into the isobutane fractionation device 100 through a pipeline; the gas phase outlet of the refrigerant tank 17 is connected to the refrigerant liquid phase inlet of the isobutane tower top condenser 3 through a pipeline in sequence through the refrigeration compressor 16, the circulating water cooler 15 and the throttling expansion valve 14; the gas phase refrigerant of the isobutane tower top condenser 3 is mixed with part of the liquid phase refrigerant of the throttling expansion valve 14 through a pipeline and input into the refrigerant tank 17. The propane compression refrigeration device 200 adopts compression refrigeration. The gas phase outlet of the refrigeration compressor 16 is connected to the shell side of the circulating water cooler 15. The liquid phase outlet of the throttling expansion valve 14 is connected to the liquid phase inlet of the isobutane tower top condenser 3 (relative to the low-temperature isobutane distillation tower 2, it is a condenser, and relative to the compressed refrigerant, it is a refrigerant evaporator 3. For the sake of convenience, this article uniformly collects the isobutane tower top condenser 3 to describe). That is, it goes through the shell side of the isobutane tower top condenser 3; the refrigerant in the refrigerant tank 17 enters the refrigeration compressor 16 for pressurization, enters the circulating water cooler 15 for condensation, and then passes through the After the throttling expansion valve cools down and reduces the pressure to an appropriate temperature, it enters the isobutane tower top condenser 3 (relative to the low-temperature isobutane distillation tower 2, it is a condenser, and relative to the compressed refrigerant, it is a refrigerant evaporator 3. For the sake of convenience, this article uniformly collects the isobutane tower top condenser 3 for description), and provides cooling capacity to the low-temperature isobutane distillation tower 2 through the isobutane tower top condenser; at the same time, the vaporization temperature corresponding to the lowest pressure of the refrigerant is not higher than the condensation temperature of the logistics in the top of the low-temperature isobutane distillation tower 2, and the compressor outlet pressure corresponding to the refrigerant entering the refrigeration compressor 16 for pressurization can be adjusted according to demand.

[0049] The isobutane fractionation device 100 can be understood as a device for separating isobutane by setting a low-temperature distillation tower. In this embodiment, the isobutane fractionation device preferably includes a low-temperature isobutane distillation tower 2, an isobutane tower top reflux tank 4, an isobutane tower bottom low-temperature reboiler 5, and an isobutane tower bottom pump 6; wherein, the feed inlet (the upper middle part of the tower) of the low-temperature isobutane distillation tower 2 is connected to the alkylation reaction product pipeline (the alkylation reaction product treated by the effluent refining system); the gas phase outlet of the low-temperature isobutane distillation tower 2 is connected to the isobutane tower top reflux tank 4 through the isobutane tower top condenser 3. The outlet pipeline of the isobutane tower top reflux tank 4 is divided into two, one condensate is connected to the liquid phase reflux port at the top of the low-temperature isobutane distillation tower 2, and the other condensate is connected to the circulating isobutane feed port of the alkylation reaction system (not shown in the figure); the liquid phase inlet and gas phase outlet of the low-temperature reboiler 5 at the bottom of the isobutane tower are respectively connected to the bottom and tower body of the low-temperature isobutane distillation tower 2 through pipelines; the liquid phase discharge port at the bottom of the low-temperature isobutane distillation tower 2 is connected to the feed pipeline of the n-butane fractionation device 300 through the isobutane tower bottom pump 6.

[0050] In practical applications, the alkylation reaction effluent from the upstream effluent refinement is first cooled and decompressed to a pressure suitable for the low-temperature isobutane distillation tower 2 through a pressure reducing valve, and then enters the low-temperature isobutane distillation tower 2 from the middle and upper part of the tower. The top of the low-temperature isobutane distillation tower adopts a propane compression refrigeration device 200 for cooling. The gaseous refrigerant first enters the refrigeration compressor 16 to increase the pressure and then enters the circulating water cooler 15 to reduce the temperature. After the refrigerant undergoes phase change to liquid phase, it enters the throttling expansion valve 14 to cool and decompress to a specified temperature and then enters the isobutane tower top condenser 3 for evaporation. The cooling is provided so that the gas phase at the top of the low-temperature isobutane distillation tower 2 is cooled by the isobutane tower top condenser 3 and then enters the isobutane tower top reflux tank 4, where part of it is refluxed and part of it is pumped out by the isobutane tower top pump and circulated to the alkylation reaction system. At the same time, the liquid phase at the bottom of the low-temperature isobutane distillation tower 2 is heated by the isobutane tower bottom low-temperature hot reboiler 5 based on the low-temperature waste heat in the plant, and the vapor phase re-enters the bottom of the distillation tower. The liquid phase of the bottom effluent enters the isobutane tower bottom pump 6 to increase the pressure and then enters the n-butane fractionation device 300 for separation of n-butane and alkylate oil.

[0051] In this embodiment, the low operating pressure setting of the low-temperature isobutane distillation tower 2 in the isobutane fractionation unit 100 can significantly reduce the temperature of the entire tower. When the tower top temperature drops below room temperature, the propane compression refrigeration unit 200 can be used for cooling. When the tower bottom temperature drops below the boiling point of atmospheric pressure water vapor, low-temperature waste heat from the plant can be used instead of high-pressure steam as a heat source. The tower top operating pressure range can be adjusted according to the temperature range of the low-temperature waste heat provided by the tower bottom. The lower the low-temperature waste heat temperature, the lower the operating pressure of the isobutane distillation tower, the lower the tower top condensation temperature, and the lower the refrigeration energy consumption. Based on this, in this embodiment, the heat source inlet of the low-temperature reboiler at the bottom of the isobutane tower is preferably connected to the outlet of an external low-temperature heat source; the temperature of the external low-temperature heat source is 70°C-90°C. It should be noted that due to the lower condensation temperature at the top of the low-temperature isobutane distillation tower 2, the temperature of the circulating isobutane at the top is also reduced, and the amount of cold carried by it when entering the alkylation reaction system is increased, thereby effectively reducing the refrigeration energy consumption of the original compression refrigeration system corresponding to the alkylation reaction system.

[0052] The n-butane distillation in this embodiment adopts conventional operation, that is, the tower pressure is kept within the conventional pressure range (0.5Mpa-0.7Mpa), and the n-butane fractionation device 300 is preferably provided, including a n-butane bottom flow heat exchanger 7, a n-butane distillation tower 8, a n-butane top condenser 9, a n-butane top reflux tank 10, a n-butane bottom reboiler 11, an alkali wash liquid heat exchanger 12 and a n-butane bottom flow cooler 13. Among them, the feed port (lower middle part of the tower body) of the n-butane distillation tower 8 is connected to the bottom liquid phase discharge port of the low-temperature isobutane distillation tower 2 through a pipeline in sequence through the n-butane bottom flow heat exchanger 7 and the isobutane bottom pump 6; the gas phase outlet of the n-butane distillation tower 8 is connected to the feed port of the n-butane top reflux tank 10 through the n-butane top condenser 9; the liquid phase outlet of the n-butane top reflux tank 10 is connected to the n-butane bottom reflux tank 10 through the n-butane bottom condenser 9; The reflux inlet of the butane distillation tower 8 is connected; the liquid phase inlet and gas phase outlet of the n-butane tower bottom reboiler 11 are connected to the bottom and tower body of the n-butane distillation tower 8 respectively through pipelines; the bottom liquid phase discharge port of the n-butane distillation tower 8 is connected to the feed pipeline of the alkylate oil storage tank (not shown) through the n-butane tower bottom effluent heat exchanger 7, the alkali wash liquid heat exchanger 12 and the n-butane tower bottom effluent cooler 13 in sequence.

[0053] In actual practice, the liquid phase of the bottoms stream from the low-temperature isobutane distillation tower 2 enters the isobutane bottom pump 6 to increase its pressure, and then is preheated by the n-butane bottoms heat exchanger 7. The preheated material then enters the n-butane distillation tower 8 from the middle and lower portion for separation and processing. The n-butane overhead condenser 9 and the n-butane bottom reboiler 11 of the n-butane distillation tower 8 both utilize conventional circulating water for cooling and heating. It should be noted that the separation process in the n-butane fractionation unit 300 utilizes existing technology. The overhead gas phase (n-butane) from the n-butane distillation tower 8 is cooled by the n-butane overhead condenser 9, partially refluxed into the n-butane overhead reflux tank 10, and partially discharged from the system. The bottoms stream alkylate oil undergoes heat exchange in sequence through the n-butane bottoms heat exchanger 7, the caustic wash heat exchanger 12, and the n-butane bottoms cooler 13 before being discharged from the system. This will not be described in detail here.

[0054] The alkylation product separation system provided in this embodiment uses a low-temperature isobutane distillation tower to separate isobutane, thereby reducing the overall temperature of the isobutane fractionation tower. High-pressure steam is no longer required to heat the tower bottom, and low-temperature waste heat from the plant can be used for heating, effectively saving a large amount of energy. A highly energy-efficient propane compression refrigeration system is used at the tower top for cooling, further improving energy utilization efficiency and saving costs. Furthermore, lowering the operating pressure of the isobutane distillation tower also helps increase the relative volatility of n-butane and isobutane, making separation easier and further reducing energy consumption.

[0055] In one embodiment, Figure 3 As shown, a method for separating an alkylation product is provided, which is applied to the alkylation product separation system described in any of the above embodiments, and the method comprises the following steps:

[0056] S11, inputting the alkylation reaction product into an isobutane fractionation unit for low-temperature isobutane fractionation; the temperature of the bottom reboiler of the low-temperature isobutane distillation tower is 70° C.-90° C.;

[0057] S12. The refrigerant is pressurized by a refrigeration compressor and then fed into a circulating water cooler for condensation. A portion of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane column overhead condenser. The overhead gas phase of the low-temperature isobutane distillation column is cooled and partially extracted and fed into a circulating isobutane feed port of the alkylation reaction system. The bottom liquid phase of the low-temperature isobutane distillation column is pressurized and then fed into the n-butane fractionation unit for alkylate oil fractionation. The vaporization temperature corresponding to the lowest pressure of the refrigerant is not higher than the condensation temperature of the stream in the overhead of the low-temperature isobutane distillation column.

[0058] S13. The gas-phase refrigerant of the isobutane tower top condenser and part of the liquid-phase refrigerant of the throttling expansion valve are collected through a refrigerant tank for recycling.

[0059] It should be noted that the specific definitions of the alkylation product separation method can be found in the above-mentioned definitions of the alkylation product separation system. The corresponding technical effects can be achieved equivalently and will not be elaborated here. Furthermore, although the steps in the above-mentioned flow chart are shown sequentially as indicated by the arrows, these steps are not necessarily performed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps may be performed; these steps may be performed in any other order.

[0060] In one embodiment, Figure 4 As shown, an alkylation process system is provided, which is applied to the alkylation product separation system described in any of the above embodiments, and the system includes an alkylation reaction system 400 and a corresponding compression refrigeration system 500 and an effluent refining system 600, as well as any of the above alkylation product separation systems; the isobutane fractionation unit 100 in the alkylation product separation system further includes a pre-cooling heat exchanger 1;

[0061] The feed pipeline of the alkylation reaction system 400 is divided into two routes, one of which is connected to the circulating isobutane outlet of the alkylation product separation system, and the other is connected to the pretreatment material pipeline and the supplementary isobutane pipeline through the reaction system feed heat exchanger 33; the alkylation reaction product outlet of the alkylation reaction system 400 is connected to the feed port of the effluent refining system 600 through a pipeline sequentially passing through the compression refrigeration system 500, the reaction system feed heat exchanger 33, and the pre-tower pre-cooling heat exchanger 1; the outlet of the effluent refining system 600 is connected to the feed port of the low-temperature isobutane distillation tower 2 through a pipeline through the pre-tower pre-cooling heat exchanger 1; the circulating material gas phase outlet of the alkylation reaction system 400 is connected to the flash tank in the compression refrigeration system 500. It should be noted that since the temperature of the circulating isobutane produced by the alkylation product separation system is very low, when the total amount of the effluent circulating flow of the alkylation reaction system 400 remains unchanged, the refrigeration temperature can be increased accordingly to reduce the refrigeration severity, thereby achieving the purpose of saving refrigeration power.

[0062] The alkylation process system proposed in this embodiment adopts the existing technology in addition to the alkylation product separation system adopting the separation system proposed in the above embodiment of the present invention, including the isobutane fractionation device 100, the propane compression refrigeration device 200 connected to the isobutane fractionation device 100, and the n-butane fractionation device 300. Figure 5As shown, the system includes a flash tank 18, a second refrigeration compressor 19, a condenser 20, a second refrigerant tank 21, a refrigerant cooler 22, an energy-saving tank 23, a flash tank flash side pump 24, and a flash tank suction side pump 25. In actual application, the effluent of the alkylation reaction system 400 enters the suction side (left side) of the flash tank 18 through the flash tank suction side pump 25. The gaseous phase enters the second refrigeration compressor 19 to increase the pressure to a set value (the set value is related to the refrigeration temperature), then enters the condenser 20 to condense into a liquid phase, and then enters the second refrigerant tank 21. In addition, some excess propane and other non-condensable vapors can be extracted from the upper part of the second refrigerant tank 21. The liquid phase at the lower part enters the refrigerant cooler 22 to be adjusted to an appropriate temperature, and then enters the energy-saving tank 23 to reduce the pressure to the set value. Part of the stream is vaporized (mainly composed of propane). The remaining liquid phase enters the flash tank flash side pump 24 to enter the vapor side (right side) of the flash tank 18 to further reduce the pressure. Part of the stream is vaporized to remove heat, thereby achieving a cooling effect. That is, the compression refrigeration system 500 has two groups of effluents, one of which is sent to downstream processing as a product, and the other group is used as a circulating flow as a compressed refrigerant for heat exchange between the alkylation reaction system 400 and the compression refrigeration system 500 and returned to the alkylation reaction system 400 to provide cooling capacity.

[0063] Effluent refining system 600 Figure 6 The figure shows an acid wash tank, an alkali wash tank and a water wash tank, the main purpose of which is to remove acid esters. In actual application, the alkylation reaction effluent after heat exchange is mixed with acid in the acid wash mixer and then enters the acid wash tank to remove most of the acid esters, and the hydrocarbons and acid in the effluent are separated in the acid wash tank. The effluent after acid wash is mixed with the new alkali solution heated by heat exchange in the n-butane tower bottom effluent heat exchanger 12 and the effluent extracted from the alkali wash tank and the water wash tank by a pump in the alkali solution mixer and then enters the alkali wash tank to remove trace acid, and then enters the water wash tank for water washing treatment, heat exchange and input into the isobutane fractionation device 100 for isobutane separation treatment.

[0064] In practical applications, the recycled isobutane flowing out of the isobutane fractionation unit 100, due to its relatively low temperature, can be directly mixed with the supplemental isobutane after heat exchange and the upstream feed from pretreatment before entering the alkylation reaction system 400. The product flowing out of the alkylation reaction system 400 enters the compression refrigeration system 500 to obtain cooling. Part of the product is returned to the alkylation reaction system 400 to maintain the reaction temperature, and part of the product flows downstream as effluent. Before entering the effluent refining system 600, the product exchanges heat with the supplemental isobutane and the upstream feed from pretreatment through the reaction system feed heat exchanger 33, thereby precooling a portion of the stream entering the alkylation reaction system 400. The product then enters the precooling heat exchanger 1 of the low-temperature isobutane fractionation column 2 of the isobutane fractionation unit 100, thereby precooling the stream entering the isobutane fractionation column of the isobutane fractionation unit 100. The product stream of the alkylation reaction system 400 first exchanges heat with part of the feed of the alkylation reaction system 400 through the reaction system feed heat exchanger 33 to pre-cool the stream entering the alkylation reaction system 400, and then exchanges heat with the product of the effluent refining system 600 through the pre-tower pre-cooling heat exchanger 1 to reduce the temperature of the stream entering the isobutane fractionation unit 100.

[0065] The alkylation process system provided in this embodiment is a fully thermally coupled system. The temperature of the circulating isobutane in the isobutane fractionation unit is significantly lower than that of the circulating isobutane produced by the conventional isobutane fractionation unit, effectively avoiding the need for cooling treatment before entering the alkylation reaction system. Due to the large flow rate of the circulating isobutane stream, the refrigeration load of the original refrigeration system (compression refrigeration system) corresponding to the alkylation reaction system can be significantly reduced. At the same time, considering that the temperature of the stream flowing downstream from the original refrigeration system is very low, and the temperature of the effluent refining part must be raised to a higher level due to process requirements, and then it must be heated again before entering the isobutane fractionation unit, Cooling down to reduce the newly added compression refrigeration load at the top of the tower will result in a characteristic of first heating up and then cooling down. By adding a pre-cooling heat exchanger before the tower after the original reaction feed heat exchanger, the cold contained in the effluent of the original refrigeration system is further recovered. This realizes effective heat integration among the alkylation reaction system, compression refrigeration system, effluent refining system and isobutane fractionation unit, so that the temperature rise of the feed stream entering the alkylation product separation system is reduced, thereby effectively solving the problem of serious energy waste caused by repeated heating and cooling of the alkylation product and circulating isobutane, and greatly reducing energy load demand and production costs.

[0066] Furthermore, considering that the specific settings of the isobutane distillation tower top pressure, the inlet pressure and outlet pressure of the refrigeration compressor in the isobutane fractionation unit in an actual alkylation process system, and the inlet and outlet pressures of the refrigeration compressor in the compression refrigeration system corresponding to the alkylation reaction system directly affect the alkylation product separation efficiency and heat utilization efficiency within the alkylation process system, in order to enable the aforementioned process control items to be accurately adapted to the actual operating conditions of the alkylation process system and thereby ensure the continuous optimal operation of the alkylation process system, this embodiment preferably provides an optimization control subsystem within the alkylation process system for real-time adaptive control of various process control items. By performing real-time loop control of the isobutane distillation tower top pressure, the pressure before and after the newly added compression refrigeration system, and the pressure before and after the original compression refrigeration system under a given isobutane distillation tower bottom reboiler heat source temperature, the overall system energy consumption is further reduced.

[0067] Specifically, such as Figure 5 As shown, the system further includes an optimization control subsystem; the optimization control subsystem includes an optimization controller 34 and a low-temperature isobutane distillation tower top pressure control loop 26 (provided with a valve), an isobutane tower top condenser refrigerant pressure control loop 27 (provided with a valve), a refrigeration compressor outlet pressure control loop 29 (provided with a valve), a second refrigeration compressor outlet pressure control loop 30, and a flash tank pressure control loop 31 (provided with a valve) connected to the optimization controller 34. The optimization controller 34 outputs a thermal coupling optimal control strategy in real time based on a preset control optimization model. That is, the optimization controller 34 can be understood as a programmable controller including a processor, a memory, and a transceiver connected via a bus. The memory stores an alkylation process optimization control program written based on the preset control optimization model. The processor executes the alkylation process optimization control program based on the operating data of the alkylation process system obtained in real time by the transceiver to generate a thermal coupling optimal control strategy, and accordingly generates corresponding control instructions for real-time regulation of each of the above control loops. The thermal coupling optimal control strategy includes the isobutane distillation tower top pressure, the refrigeration compressor inlet pressure, the refrigeration compressor outlet pressure, the second refrigeration compressor inlet pressure, and the second refrigeration compressor outlet pressure.

[0068] To ensure that both the energy-saving and consumption-reducing goals of improving the alkylation product separation efficiency and the heat utilization efficiency within the system are achieved, this embodiment preferably designs a preset control optimization model with minimizing the sum of the heat load cost of the n-butane distillation tower bottom reboiler and the refrigeration system consumption cost as the optimal control objective of the optimization control subsystem. Specifically, the preset control optimization model is constructed with minimizing the unit alkylate oil separation energy consumption cost as the optimization objective under preset control constraints. The corresponding objective function can be expressed as:

[0069]

[0070] Where,

[0071]

[0072] B i =F nbs α

[0073]

[0074]

[0075] Among them, A i 、B i and C i F represents the refrigeration cost of the low-temperature isobutane distillation tower top, the steam heat source cost of the n-butane tower bottom reboiler, and the refrigeration cost saved by the compression refrigeration system; nbit represents the alkylate oil flow rate; k and Z represent the gas isentropic coefficient and gas compressibility coefficient respectively; R represents 8314 / working fluid molecular weight; T1, p1, p2 and η1 represent the inlet temperature, inlet pressure, outlet pressure and refrigeration mechanical efficiency of the refrigeration compressor respectively; represents the propane flow rate of the refrigeration compressor; γ represents the electricity cost; η2 represents the refrigeration mechanical efficiency of the second refrigeration compressor; F nbs and α represent the steam flow rate and heat source steam cost of the n-butane tower bottom reboiler respectively; p3, p4, p5 and p6 represent the inlet original pressure, outlet original pressure, inlet current pressure and outlet current pressure of the second refrigeration compressor respectively; Indicates the refrigerant flow rate of the second refrigeration compressor; F nbit represents the alkylate oil flow rate; q nbs represents the unit steam phase change heat of the heat source of the n-butane tower bottom reboiler; ω nbs It indicates the heat consumption of reboiler heat source steam per unit effluent volume of n-butane distillation tower.

[0076] In order to ensure that the optimal control strategy obtained based on the above objective function meets the actual solvent regeneration scenario requirements, this embodiment preferably sets preset control constraints including the isobutane tower top refrigerant absorption heat constraint, the compression refrigeration system refrigeration load reduction constraint, the propane temperature phase change pressure constraint, the isobutane tower top condensation temperature constraint, the mixture working fluid temperature phase change pressure constraint in the compression refrigeration system, and the compression refrigeration system compressor inlet temperature constraint, which are expressed as:

[0077] 1) The heat absorption constraint for the refrigerant at the top of the isobutane tower can be understood as the calculation constraint for the heat absorption by the working fluid in the newly added refrigeration system (propane compression refrigeration unit) in the isobutane distillation tower:

[0078]

[0079] Where Q m Indicates the heat absorbed by the propane working fluid in the propane compression refrigeration unit in the isobutane distillation tower, the unit is MJ; Q v It indicates the heat absorbed by the propane working fluid when it changes from liquid phase to vapor phase, and the unit is MJ / t; Indicates the propane refrigerant flow rate in the propane compression refrigeration device, kg / s;

[0080] 2) The constraint on the reduction in refrigeration load of the compression refrigeration system can be understood as a conservation constraint that the reduction in refrigeration load of the original compression refrigeration system is equal to the absolute value of the difference in refrigeration capacity contained in the circulating isobutane in the cryogenic distillation process relative to the traditional process:

[0081] ΔQ cold =C q1 F cr (T3-T4)

[0082] ΔQ re =C q2 F ibr (T5-T6)

[0083] ΔQ cold =ΔQ re

[0084] Where ΔQ cold Indicates the reduction in refrigeration load of the original compression refrigeration system, in MJ; ΔQ re It represents the absolute value of the heat difference between the old and new distillation processes of circulating isobutane, in MJ; C q1 Indicates the specific heat of the working fluid in the original compression refrigeration system, the unit is J / (kg.K); C q2 Indicates the specific heat of circulating isobutane, in J / (kg.K); F cr It indicates the flow rate of the material flow to the alkylation reaction system after compression refrigeration and cooling, in t / h; F ibr Indicates the circulating isobutane flow rate, in t / h;

[0085] 3) Propane temperature phase change pressure constraint, which can be understood as the relationship constraint between the inlet temperature and inlet pressure of the refrigeration compressor in the propane compression refrigeration device, and the constraint between the temperature of the working fluid after being cooled by the circulating water and the outlet pressure of the refrigeration compressor:

[0086] f(T1)=p1

[0087] f(T7)=p2

[0088] Where f(·) represents the phase change pressure relationship of propane at different temperatures, which can be obtained through experimental testing; T1 represents the inlet temperature of the refrigeration compressor in the propane compression refrigeration device, in K; T7 represents the temperature of the compressed working fluid after being cooled by circulating water in the propane compression refrigeration device, in K; p1 and p2 represent the inlet pressure and outlet pressure of the refrigeration compressor in the propane compression refrigeration device, respectively, in kPa;

[0089] 4) Isobutane tower top condensation temperature constraint represents the relationship between the isobutane distillation tower top condensation temperature and the propane working fluid temperature before entering the compressor:

[0090] T8≥T1

[0091] Wherein, T1 represents the inlet temperature of the refrigeration compressor in the propane compression refrigeration device, unit is K; T8 represents the condensing temperature at the top of the isobutane distillation tower, unit is K;

[0092] 5) The temperature phase change pressure constraint of the mixture working fluid in the compression refrigeration system can be understood as the phase change pressure constraint corresponding to the mixture working fluid at different temperatures in the original compression refrigeration system:

[0093] g(T2)=p5

[0094] g(T9)=p6

[0095] Where g(·) represents the phase change pressure relationship of the refrigerant at different temperatures, which can be obtained through experimental testing; T2 represents the inlet temperature of the refrigeration compressor in the compression refrigeration system, in K; T9 represents the temperature of the mixed refrigerant after being cooled by the circulating water in the compression refrigeration system, in K; p5 and p6 represent the inlet and outlet pressures of the refrigeration compressor in the compression refrigeration system, respectively, in kPa;

[0096] 6) The compression refrigeration system compressor inlet temperature constraint can be understood as the relationship between the original process flow temperature after compression refrigeration to the alkylation reaction system and the original refrigeration system compressor inlet temperature constraint:

[0097] T4≥T2

[0098] Wherein, T2 represents the inlet temperature of the compressor of the compression refrigeration system, and the unit is K; T4 represents the flow temperature from the original compression refrigeration process to the alkylation reaction system, which is a constant, and the unit is K.

[0099] By combining the objective function and constraints of the preset control optimization model in the optimization control subsystem, the optimized isobutane distillation tower top pressure, refrigeration compressor inlet pressure, refrigeration compressor outlet pressure, second refrigeration compressor inlet pressure and second refrigeration compressor outlet pressure are calculated in real time. At the same time, the optimization results are used as the control set values of the corresponding variables in the optimization control subsystem and combined with the control valves to regulate the corresponding control loops. It should be noted that in order to ensure the comprehensiveness of the alkylation process system control, such as Figure 5 As shown, the optimization control subsystem also includes a refrigerant tank pressure control loop 28 (equipped with a valve) and a second refrigerant tank pressure control loop 32 (equipped with a valve). The corresponding control loops can be implemented by referring to relevant control technologies in the alkylation process system or integrated into the aforementioned preset control optimization model for coordinated optimization. PC in the figure represents pressure control. To facilitate understanding of the control flow of the optimization control subsystem, the following detailed description is based on an actual alkylation process flow:

[0100] The product flowing out of the alkylation reaction system 400 is heated by the reaction system feed heat exchanger 33 before being sent to the effluent refining system 600. It then enters the pre-cooling heat exchanger 1 of the alkylation product separation system for heat exchange and cooling. After heat exchange and cooling, it enters the low-temperature isobutane distillation tower 2. The overhead gas phase of the low-temperature isobutane distillation tower 2 is cooled by the isobutane tower overhead condenser 3 and enters the isobutane tower overhead reflux tank 4. Part of the liquid phase in the reflux tank flows out of the device as recycled isobutane to enter the alkylation reaction system 400, and part returns to the low-temperature isobutane distillation tower 2 as reflux. A pressure control loop and valve 26 are installed at the top of the tower, which is controlled by the liquid phase flow valve of the newly added propane compression refrigeration unit 200. The set value is determined by the calculation results of the above-mentioned preset control optimization model. The propane compression refrigeration device 200 has a circulation loop. The refrigerant first enters the refrigeration compressor 16 from the inlet of the refrigeration compressor 16, is pressurized and enters the circulating water cooler 15 to be completely condensed, and then is reduced to a reasonable pressure through the throttling expansion valve 14, and then releases the cold energy through the isobutane tower top condenser 3. A loop that does not pass through the isobutane tower top condenser is provided here to control the heat exchange of the isobutane tower top condenser 3, thereby controlling the operating pressure of the low-temperature isobutane distillation tower 2, and the compressor outlet pressure and the isobutane tower top condenser refrigerant pressure are given by the calculation results of the optimization model. The evaporated refrigerant enters the refrigerant tank 17, and the pressure of the refrigerant tank 17 is controlled by the flow control loop and the valve 28. An isobutane tower bottom low-temperature reboiler 5 is provided at the bottom of the low-temperature isobutane distillation tower 2. The heat source of the isobutane tower bottom low-temperature reboiler comes from the low-temperature waste heat supplied from the outside. The bottom discharge is pressurized by the isobutane tower bottom pump 6 and sent to the normal butane tower bottom effluent heat exchanger 7 for heat exchange and temperature increase before entering the normal butane distillation tower 8.

[0101] After the material enters the n-butane distillation tower 8, the overhead vapor phase is cooled by the n-butane overhead condenser 9 before entering the n-butane overhead reflux drum 10. The reflux drum's overhead vapor phase is discharged, while the reflux drum's bottom liquid phase returns to the n-butane distillation tower 8 as reflux. An n-butane bottom reboiler 11 is installed at the bottom of the tower to provide heat for the distillation tower. The bottoms effluent is cooled by the n-butane bottoms effluent heat exchanger 7 before entering the alkaline wash liquid heat exchanger 12 for further heat exchange and cooling. Finally, it is cooled to an appropriate temperature by the n-butane bottoms effluent cooler 13 before entering the alkylate oil storage tank.

[0102] It should be noted that the above-mentioned optimization control subsystem is connected to the device in the system to read the temperature parameters of the low-temperature heat source at the bottom of the isobutane distillation tower in real time, and uses it as the input of the preset control optimization model in the optimization controller, so that it can minimize the energy cost per unit product volume. Through optimization calculation and solution, the optimal isobutane distillation tower pressure, the original compressor inlet and outlet pressures, and the newly added compressor inlet and outlet pressures are given, and used as the set values of the corresponding control system to achieve optimal operation and stable operation of the process system.

[0103] The embodiment of the present application proposes an alkylation heat coupling system design that thermally couples an alkylation product separation system using cryogenic distillation of isobutane with an alkylation reaction system and a corresponding compression refrigeration system and an effluent refining system. By innovatively adopting a low-temperature isobutane distillation process in which the top of the isobutane fractionation tower is cooled by a propane compression refrigeration system and the bottom of the tower is heated by low-temperature waste heat from the plant, combined with a process design in which the alkylation reaction product feed is heat-exchanged with the top liquid of the isobutane fractionation tower before entering the isobutane fractionation tower, the temperature rise of the feed stream entering the alkylation product separation system is reduced, and the isobutane separated from the top of the low-temperature distillation tower of the isobutane tower can be directly circulated to the reaction system without further cooling, thereby effectively solving the problem of the above problems. The problem of serious energy waste caused by repeated heating and cooling of the alkylation product and the circulating isobutane is solved. At the same time, by designing an alkylation heat coupling system without changing the tower diameter requirements, combined with the given isobutane fractionator bottom reboiler heat source temperature condition, the optimization control subsystem is deployed with the optimization goal of minimizing the unit alkylate oil separation energy consumption cost. The adaptive control of the isobutane fractionator top pressure, the pressure before and after the propane compression refrigeration system, and the pressure before and after the original compression refrigeration system can not only effectively save a large amount of equipment investment costs, but also reduce energy consumption from a global perspective through effective heat integration among multiple systems, improve energy utilization efficiency, reduce unit production costs and increase production capacity, and ensure the continuous optimal operation of the alkylation process system.

[0104] To verify the practical application of the alkylation process system provided by the present invention, this example also uses an experiment to obtain an isobutane with a purity of not less than 86.0 mol%, an n-butane with a purity of not less than 87.0 mol%, and an alkylation product separation experiment that meets the requirements as an example. The chemical process simulation software Aspen HYSYS V12 is used to conduct simulation verification, and the advantages and disadvantages of the existing process and the process of the present invention are compared and analyzed.

[0105] Assuming a low-temperature hot stream temperature of 85-90°C at the bottom of the isobutane fractionator, the operating pressure of the isobutane fractionator is 0.18-0.19 MPa, and the operating pressure of the n-butane fractionator is 0.5-0.7 MPa. The operating pressure of the refrigerant at the top of the isobutane fractionator is 0.3-0.5 MPa, and the compressor outlet pressure is 1.0-1.3 MPa. Simulation results show the energy consumption of a conventional high-temperature distillation system and the cryogenic distillation system (alkylation product separation system) of the present invention, as shown in Tables 1 and 2. This comparison shows that, under the same separation requirements, the present invention significantly improves overall system energy utilization efficiency and reduces energy loss compared to existing mainstream conventional processes.

[0106] Table 1 Energy consumption of high temperature distillation system

[0107] Energy consumption location Energy consumption (104kcal / h) Logistics temperature (℃) Energy supply method Isobutane distillation tower top 855 59 Circulating water cooling Isobutane distillation tower bottoms 1217 150 Steam heating n-Butane distillation tower top 69 59 Circulating water cooling n-Butane distillation tower bottom 55 152 Steam heating

[0108] Table 2 Energy consumption of cryogenic distillation system

[0109] Energy consumption location Energy consumption (104kcal / h) Logistics temperature (℃) Energy supply method Isobutane fractionation tower top 862 6 Compression refrigeration Isobutane fractionation tower bottoms 847 74 Low temperature waste heat n-Butane fractionation tower top 47 59 Circulating water cooling n-Butane fractionation tower bottoms 150 152 Steam heating New cooling power consumption 2.1MW (electric drive compression refrigeration) 0～3 Chilled brine / cold water Original refrigeration saves electricity -0.11MW (electric drive compression refrigeration) - Chilled brine / cold water

[0110] In one embodiment, Figure 7 As shown, an alkylation process method is provided, which can be applied to the alkylation process system described in any of the above embodiments, and the method includes the following steps:

[0111] S21, cooling the alkylation reaction product of the alkylation reaction system through a compression refrigeration system and feeding it into a reaction system feed heat exchanger; heating it through heat exchange with an upstream material of the alkylation reaction system through the reaction system feed heat exchanger; then feeding it into a pre-cooling heat exchanger before the tower to heat exchange and cool it with the refined effluent of the effluent refining system; and feeding it into the effluent refining system for refining treatment; and feeding the refined effluent after heat exchange and cooling into a low-temperature isobutane distillation tower for low-temperature isobutane fractionation; the bottom reboiler temperature of the low-temperature isobutane distillation tower is 70° C.-90° C.;

[0112] S22. The refrigerant is pressurized by a refrigeration compressor and then fed into a circulating water cooler for condensation. A portion of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane tower top condenser. The gas phase at the top of the low-temperature isobutane distillation tower is cooled and partially extracted and fed into a circulating isobutane feed port of the alkylation reaction system. The liquid phase at the bottom of the low-temperature isobutane distillation tower is pressurized and then fed into the n-butane fractionation unit for alkylate oil fractionation. The gas phase refrigerant from the isobutane tower top condenser and a portion of the liquid phase refrigerant from the throttling expansion valve are combined into a refrigerant tank for recycling.

[0113] For specific definitions of the alkylation process, please refer to the above-mentioned definitions of the alkylation process system. The corresponding technical effects can be achieved equivalently and are not further elaborated here. Furthermore, although the steps in the above flow chart are shown sequentially as indicated by the arrows, these steps are not necessarily performed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps may be performed; the steps may be performed in any other order.

[0114] In summary, the embodiments of the present invention provide an alkylation product separation system, separation method, alkylation process system and method, which have the beneficial effects of at least one of the following:

[0115] 1) By using a low-temperature isobutane distillation column to separate isobutane, the overall temperature of the isobutane fractionator can be lowered. High-pressure steam is no longer required to heat the bottom of the column, and low-temperature waste heat from the plant can be used for heating, effectively saving a large amount of energy. The top of the column uses a highly energy-efficient propane compression refrigeration system for cooling, further improving energy efficiency and saving costs. Furthermore, lowering the operating pressure of the isobutane distillation column also helps increase the relative volatility of n-butane and isobutane, making separation easier and further reducing energy consumption.

[0116] 2) By innovatively adopting a low-temperature isobutane distillation process that uses a propane compression refrigeration system at the top of the isobutane fractionation tower for cooling and low-temperature waste heat from the plant for heating at the bottom of the tower, combined with a process design in which the alkylation reaction product feed is heat-exchanged with the isobutane fractionation tower overhead liquid before entering the isobutane fractionation tower, the temperature rise of the feed stream entering the alkylation product separation system is reduced. Furthermore, the isobutane separated at the top of the low-temperature isobutane fractionation tower can be directly recycled to the reaction system without further cooling, effectively solving the problem of severe energy waste caused by repeated heating and cooling of the alkylation product and the recycled isobutane.

[0117] 3) By designing an alkylation thermal coupling system without changing the required tower diameter, combined with a given isobutane fractionator bottom reboiler heat source temperature, an optimization control subsystem is deployed to adaptively control the isobutane fractionator top pressure, the pressure before and after the propane compression refrigeration system, and the pressure before and after the original compression refrigeration system, with the optimization goal of minimizing the unit alkylate oil separation energy consumption cost. This not only effectively saves a large amount of equipment investment costs, but also reduces energy consumption and improves energy utilization efficiency from a global perspective through effective heat integration among multiple systems, thereby reducing unit production costs and increasing production capacity, and ensuring the continuous optimal operation of the alkylation process system.

[0118] Each embodiment in this specification is described in a progressive manner, and the same or similar parts of each embodiment can be directly referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. It should be noted that the various technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The above-described embodiments merely represent several preferred implementations of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make several improvements and substitutions without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be based on the scope of protection of the claims.

Claims

1. An alkylation process system, characterized in that: The system includes an alkylation reaction system and a corresponding compression refrigeration system and effluent refining system, as well as an alkylation product separation system; The alkylation product separation system includes an isobutane fractionation device, and a propane compression refrigeration device and an n-butane fractionation device connected to the isobutane fractionation device; the liquid phase discharge port of the isobutane fractionation device is connected to the feed pipeline of the n-butane fractionation device via an isobutane bottom pump; the isobutane fractionation device also includes a pre-cooling heat exchanger before the tower; The propane compression refrigeration device includes an isobutane tower top condenser, a throttling expansion valve, a circulating water cooler, a refrigeration compressor and a refrigerant tank; the isobutane tower top condenser is arranged at the top of the low-temperature isobutane distillation tower in the isobutane fractionation device, and cools the top gas phase of the low-temperature isobutane distillation tower and then inputs it into the isobutane fractionation device through a pipeline; the gas phase outlet of the refrigerant tank is connected to the refrigerant liquid phase inlet of the isobutane tower top condenser through a pipeline in sequence through the refrigeration compressor, the circulating water cooler and the throttling expansion valve; the gas phase refrigerant of the isobutane tower top condenser is mixed with part of the liquid phase refrigerant of the throttling expansion valve through a pipeline and input into the refrigerant tank; The feed pipeline of the alkylation reaction system is divided into two routes, one of which is connected to the circulating isobutane discharge port of the alkylation product separation system, and the other is connected to the pretreatment material pipeline and the supplementary isobutane pipeline through the reaction system feed heat exchanger; the alkylation reaction product outlet of the alkylation reaction system is connected to the feed port of the effluent refining system through a pipeline sequentially passing through the compression refrigeration system, the reaction system feed heat exchanger and the pre-cooling heat exchanger before the tower; the discharge port of the effluent refining system is connected to the feed port of the low-temperature isobutane distillation tower through a pipeline through the pre-cooling heat exchanger before the tower; the circulating material gas phase outlet of the alkylation reaction system is connected to the flash tank in the compression refrigeration system.

2. The alkylation process system according to claim 1, wherein: The isobutane fractionation device comprises a low-temperature isobutane distillation tower, an isobutane tower top reflux tank, an isobutane tower bottom low-temperature reboiler and an isobutane tower bottom pump; The feed inlet of the low-temperature isobutane distillation tower is connected to the alkylation reaction product pipeline; the gas phase outlet of the low-temperature isobutane distillation tower is connected to the feed inlet of the isobutane tower top reflux tank via the isobutane tower top condenser; the outlet pipeline of the isobutane tower top reflux tank is divided into two, one condensate is connected to the liquid phase reflux port at the top of the low-temperature isobutane distillation tower, and the other condensate is connected to the circulating isobutane feed inlet of the alkylation reaction system; The liquid phase inlet and gas phase outlet of the low-temperature reboiler at the bottom of the isobutane tower are respectively connected to the bottom and tower body of the low-temperature isobutane distillation tower through pipelines; the liquid phase discharge port at the bottom of the low-temperature isobutane distillation tower is connected to the feed pipeline of the normal butane fractionation device through the isobutane tower bottom pump.

3. The alkylation process system according to claim 2, wherein: The heat source inlet of the low-temperature reboiler at the bottom of the isobutane tower is connected to the outlet of an external low-temperature heat source; the temperature of the external low-temperature heat source is 70°C-90°C.

4. The alkylation process system according to claim 1, wherein: The n-butane fractionation device comprises a n-butane tower bottom effluent heat exchanger, a n-butane rectifying tower, a n-butane tower top condenser, a n-butane tower top reflux tank, a n-butane tower bottom reboiler, an alkali wash liquid heat exchanger and a n-butane tower bottom effluent cooler; The feed inlet of the n-butane distillation tower is connected to the bottom liquid phase discharge port of the low-temperature isobutane distillation tower via a pipeline, sequentially passing through the n-butane tower bottom flow heat exchanger and the isobutane tower bottom pump; the vapor phase outlet of the n-butane distillation tower is connected to the feed inlet of the n-butane tower top reflux tank via the n-butane tower top condenser; the liquid phase outlet of the n-butane tower top reflux tank is connected to the reflux inlet of the n-butane distillation tower; the liquid phase inlet and vapor phase outlet of the n-butane tower bottom reboiler are connected to the bottom and tower body of the n-butane distillation tower, respectively, via pipelines; and the bottom liquid phase discharge port of the n-butane distillation tower is connected to the feed pipeline of the alkylate oil storage tank via the n-butane tower bottom flow heat exchanger, the alkali wash liquid heat exchanger, and the n-butane tower bottom flow cooler.

5. The alkylation process system according to claim 1, wherein: The separation method of the alkylation product separation system comprises the following steps: The alkylation reaction product is fed into an isobutane fractionation unit for low-temperature isobutane fractionation; the temperature of the bottom reboiler of the low-temperature isobutane fractionation tower is 70°C-90°C; The refrigerant is pressurized by a refrigeration compressor and then fed into a circulating water cooler for condensation. A portion of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane column top condenser. The top gas phase of the low-temperature isobutane distillation column is cooled and partially extracted and fed into a circulating isobutane feed port of the alkylation reaction system. The bottom liquid phase of the low-temperature isobutane distillation column is pressurized and then fed into the n-butane fractionation unit for alkylate oil fractionation. The vaporization temperature corresponding to the lowest pressure of the refrigerant is not higher than the condensation temperature of the stream in the top of the low-temperature isobutane distillation column. The gas phase refrigerant of the isobutane tower top condenser and part of the liquid phase refrigerant of the throttling expansion valve are collected through a refrigerant tank for circulation.

6. The alkylation process system according to claim 1, wherein: The system also includes an optimization control subsystem; the optimization control subsystem includes an optimization controller and a low-temperature isobutane distillation tower top pressure control loop, an isobutane tower top condenser refrigerant pressure control loop, a refrigeration compressor outlet pressure control loop, a second refrigeration compressor outlet pressure control loop and a flash tank pressure control loop connected to the optimization controller; the optimization controller outputs a thermal coupling optimal control strategy in real time based on a preset control optimization model; the thermal coupling optimal control strategy includes the isobutane distillation tower top pressure, the refrigeration compressor inlet pressure, the refrigeration compressor outlet pressure, the second refrigeration compressor inlet pressure and the second refrigeration compressor outlet pressure.

7. The alkylation process system according to claim 6, wherein: The preset control optimization model is constructed by minimizing the unit alkylate oil separation energy consumption cost under preset control constraints. The preset control constraints include a constraint on the amount of heat absorbed by the refrigerant at the top of the isobutane tower, a constraint on the reduction in refrigeration load of the compression refrigeration system, a constraint on the temperature phase change pressure of the propane, a constraint on the condensation temperature at the top of the isobutane tower, a constraint on the temperature phase change pressure of the mixture working fluid in the compression refrigeration system, and a constraint on the compressor inlet temperature of the compression refrigeration system.

8. The alkylation process system according to claim 7, wherein: The objective function of the preset control optimization model is expressed as: Where, in, 、 and They represent the refrigeration cost of the low-temperature isobutane distillation tower top, the steam heat source cost of the n-butane tower bottom reboiler, and the refrigeration cost saved by the compression refrigeration system; represents the alkylate oil flow rate; and represent the gas isentropic coefficient and gas compressibility coefficient respectively; Indicates 8314 / molecular weight of working fluid; 、 、 and Respectively represent the inlet temperature, inlet pressure, outlet pressure and refrigeration mechanical efficiency of the refrigeration compressor; Indicates the propane working fluid flow rate of the refrigeration compressor; represents the cost of electricity; Indicates the refrigeration mechanical efficiency of the second refrigeration compressor; and denote the steam flow rate and heat source steam cost of the n-butane tower bottom reboiler respectively; 、 、 and Respectively represent the inlet original pressure, outlet original pressure, inlet current pressure and outlet current pressure of the second refrigeration compressor; Indicates the refrigerant flow rate of the second refrigeration compressor; represents the alkylate oil flow rate; It represents the unit steam phase change heat of the heat source of the n-butane tower bottom reboiler; It indicates the heat consumption of reboiler heat source steam per unit effluent volume of n-butane distillation tower.

9. An alkylation process method, applied to the alkylation process system according to any one of claims 1 to 8, the method comprising the following steps: The alkylation reaction product of the alkylation reaction system is cooled by a compression refrigeration system and fed into a feed heat exchanger of the reaction system. After being heated by heat exchange with an upstream material of the alkylation reaction system in the feed heat exchanger, the product is fed into a pre-cooling heat exchanger in front of the tower and cooled by heat exchange with a refined effluent of an effluent refining system. The product is then fed into the effluent refining system for refining treatment. The refined effluent after heat exchange and cooling is fed into a low-temperature isobutane distillation tower for low-temperature isobutane fractionation. The bottom reboiler temperature of the low-temperature isobutane distillation tower is 70° C. to 90° C. The refrigerant is pressurized by a refrigeration compressor and then fed into a circulating water cooler for condensation. A portion of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane tower top condenser. The top gas phase of the low-temperature isobutane distillation tower is cooled and partially extracted and fed into a circulating isobutane feed port of the alkylation reaction system. The bottom liquid phase of the low-temperature isobutane distillation tower is pressurized and then fed into the n-butane fractionation unit for alkylate oil fractionation. The gas phase refrigerant of the isobutane tower top condenser and a portion of the liquid phase refrigerant of the throttling expansion valve are combined through a refrigerant tank for recycling.

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