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

Abstract

The invention provides an alkylation product separation system, a separation method, an alkylation process system and a method. A liquid phase discharge port of an isobutane fractionation device in the separation system is connected with a feed pipeline of an n-butane fractionation device through an isobutane tower bottom pump; the propane compression refrigeration device comprises an isobutane overhead condenser, a throttling expansion valve, a circulating water cooler, a refrigeration compressor and a refrigerant tank, the isobutane overhead condenser is arranged at the top of the low-temperature isobutane rectifying tower, and a gas phase at the top of the low-temperature isobutane rectifying tower is cooled and refluxed; a refrigerant liquid phase inlet of the isobutane overhead condenser is connected with a gas phase outlet of the refrigerant tank through the throttling expansion valve, the circulating water cooler and the refrigeration compressor in sequence, and a gas phase refrigerant of the isobutane overhead condenser is mixed with part of liquid phase of the throttling expansion valve through a pipeline and input into the refrigerant tank. The low-temperature isobutane rectifying tower adopting low-temperature heat supply at the tower bottom is combined with a high-energy-efficiency compression refrigeration system for cooling at the tower top, so that the separation difficulty is effectively reduced, the energy utilization rate is improved, and the separation energy consumption and the process cost are saved.

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 existing conventional alkylation product separation is an important energy consumption step in the entire alkylation process, especially the low-temperature isobutane distillation tower, which has the characteristics of large material flow, high operating pressure and high material flow temperature, resulting in a decrease in the relative volatility of n-butane and isobutane, an increase in the difficulty of separation, an increase in the reflux ratio for the same separation accuracy, a significant increase in the high-temperature steam consumption of the tower bottom reboiler, and an increase in the production cost of the alkylate oil; at the same time, since the alkylation reaction is at a low temperature (0-5°C) and the alkylation product separation is at a high temperature (5-50°C and about 150°C), Figure 1 The heat exchange system of the existing alkylation process shown in the figure causes the alkylation process system as a whole to be unable to couple and match in terms of temperature. Not only is there a low heat exchange efficiency and insufficient utilization of heat and cooling capacity, but also the reaction product and circulating isobutane experience a large degree of repeated heating and cooling, further increasing the energy consumption of the alkylation process. Therefore, it is urgent to improve the separation efficiency of alkylation products and the energy utilization efficiency of the alkylation process system through technical innovation of the separation process and the entire alkylation process, so as to achieve reliable energy saving and consumption reduction. Summary of the invention

[0004] The object of the present invention is to provide an alkylation product separation system. By designing a low-temperature low-temperature isobutane distillation tower with a plant waste heat heating at the bottom and a propane compression refrigeration system at the top, the isobutane separated at the top of the tower can be directly circulated to the alkylation reaction system without cooling down again, and the bottom effluent can directly enter the normal butane distillation tower after heat exchange with the bottom effluent of the normal butane distillation tower, thereby achieving a dual reduction in the refrigeration load of the isobutane tower bottom reboiler and the alkylation reaction system, while also improving the energy utilization efficiency and the separation efficiency of the isobutane tower, saving process costs.

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

[0006] In a first aspect, an embodiment of the present invention provides an alkylation product separation system, the system comprising an isobutane fractionation device, and a propane compression refrigeration device and a normal 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 normal butane fractionation device via an isobutane bottom pump;

[0007] The propane compression refrigeration device comprises 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 distillation device, and the top gas phase of the low-temperature isobutane distillation tower is cooled and then input into the isobutane distillation 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 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;

[0009] 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 bottom liquid phase discharge port of the low-temperature isobutane distillation tower is connected to the feed pipeline of the normal 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] Further, the n-butane fractionation device comprises a n-butane tower bottom effluent heat exchanger, a n-butane rectification tower, a n-butane tower top condenser, a n-butane tower top reflux tank, a n-butane tower bottom reboiler, a caustic wash liquid heat exchanger and a n-butane tower bottom 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 through a pipeline in sequence through the n-butane tower bottom flow heat exchanger and the isobutane tower bottom pump; the gas phase outlet of the n-butane distillation tower is connected to the feed inlet of the n-butane tower top reflux tank through 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 gas phase outlet of the n-butane tower bottom reboiler are respectively connected to the tower bottom and tower body of the n-butane distillation tower through pipelines; the bottom liquid phase discharge port of the n-butane distillation tower is connected to the feed pipeline of the alkylate oil storage tank in sequence through 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 input into an isobutane fractionation device 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, and part of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane tower top condenser, so that the tower top gas phase of the low-temperature isobutane distillation tower is cooled and then partially extracted and fed into a circulating isobutane feed port of an alkylation reaction system, and the tower bottom liquid phase of the low-temperature isobutane distillation tower is pressurized and then fed into the n-butane fractionation device for alkylation 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 tower;

[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, the system comprising an alkylation reaction system and a corresponding compression refrigeration system and an effluent refining system, and an alkylation product separation system as described in any one of the above; the isobutane fractionation device in the alkylation product separation system further comprises a pre-tower precooling 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 in sequence through the compression refrigeration system, the reaction system feed heat exchanger and the pre-tower precooling heat exchanger; 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-tower precooling heat exchanger; 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 unit alkylate oil separation energy consumption cost as the optimization target under preset control constraints; the preset control constraints include isobutane tower top refrigerant absorption heat constraint, compression refrigeration system refrigeration load reduction constraint, propane temperature phase change pressure constraint, isobutane tower top condensation temperature constraint, mixture working fluid temperature phase change pressure constraint in the compression refrigeration system, and compression refrigeration system compressor inlet temperature constraint.

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

[0022]

[0023] In the formula,

[0024]

[0025] B i =F nbs α

[0026]

[0027]

[0028] Among them, A i , Bi and C i represents the refrigeration cost of the top of the low-temperature isobutane distillation tower, the steam heat source cost of the reboiler at the bottom of the normal butane tower, and the refrigeration cost saved by the compression refrigeration system; F nbit represents the alkylation oil flow rate; k and Z represent the gas isentropic coefficient and gas compressibility coefficient respectively; R represents 8314 / molecular weight of the working fluid; 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 working fluid 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 It represents the unit steam phase change heat of the heat source of the n-butane tower bottom reboiler; ω nbs It indicates the heat consumed by the reboiler heat source steam per unit effluent volume of the 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 input into a reaction system feed heat exchanger, and after being heated by the reaction system feed heat exchanger and the upstream material of the alkylation reaction system, the product is then input into a precooling heat exchanger in front of the tower and the refined effluent of the effluent refining system for heat exchange and cooling, and then input into the effluent refining system for refining treatment, and the refined effluent after heat exchange and cooling is input into the low-temperature isobutane distillation tower for low-temperature isobutane fractionation; the tower bottom reboiler temperature of the low-temperature isobutane distillation tower is 70° C.-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, so that the tower 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, and the tower bottom liquid phase of the low-temperature isobutane distillation tower is pressurized and then fed into the normal butane fractionation device for alkylation oil fractionation, and the gas phase refrigerant of the isobutane tower top condenser and a portion of the liquid phase refrigerant of the throttling expansion valve are collected 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 tower to separate isobutane, the overall temperature of the isobutane fractionation tower can be reduced. The tower bottom does not need to use high-pressure steam to obtain heat, and the low-temperature waste heat in the factory can be used for heating, which effectively saves a lot of energy. At the same time, the top of the tower uses a highly energy-efficient propane compression refrigeration system for cooling, which can further improve energy utilization efficiency and save costs. In addition, by reducing the operating pressure of the isobutane distillation tower, it is also beneficial to increase the relative volatility of n-butane and isobutane, making the separation difficulty lower and further reducing energy consumption;

[0034] 2) By innovatively adopting a low-temperature isobutane distillation process in which the top of the isobutane distillation tower is cooled by a propane compression refrigeration system and the bottom of the tower is heated by low-temperature waste heat in the plant, combined with a process design in which the alkylation reaction product feed is heat-exchanged with the top liquid of the isobutane distillation tower before entering the isobutane distillation tower, the temperature rise of the feed stream entering the alkylation product separation system is reduced, and the isobutane separated at the top of the isobutane tower low-temperature distillation tower does not need to be cooled again and can be directly circulated to the reaction system, thereby effectively solving the problem of serious energy waste caused by repeated heating and cooling of the alkylation product and the circulating isobutane;

[0035] 3) By designing the alkylation heat coupling system without changing the tower diameter requirement and combining it with the given isobutane fractionation tower bottom reboiler heat source temperature condition, the optimization control subsystem is arranged to adaptively control the isobutane fractionation tower 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 alkylation oil separation energy consumption cost. This can not only effectively save a lot 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of an existing alkylation process system in an embodiment of the present invention;

[0037] Figure 2 is a 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 in an embodiment of the present invention;

[0039] Figure 4 is a schematic structural diagram of an alkylation process system integrated with an alkylation product separation system in an embodiment of the present invention;

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

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

[0042] Figure 7 It is a schematic flow diagram of the alkylation process method in 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 washing 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 loop, 27-isobutane tower top condenser refrigerant pressure control loop, 28-refrigerant tank pressure control loop, 29-refrigeration compressor outlet pressure control loop, 30-second refrigeration compressor outlet pressure control loop, 31-flash tank pressure control loop, 32-second refrigerant tank pressure control loop, 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 scheme and beneficial effects of the present application clearer, the present invention is further described in detail below in conjunction with 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 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 the separation efficiency, improve the energy utilization efficiency of the separation system and reduce the 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-reducing effects from a global perspective.

[0047] In one embodiment, Figure 2 As shown, an alkylation product separation system is provided, the system comprising an isobutane fractionation device 100, and a propane compression refrigeration device 200 and a normal 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 normal butane fractionation device 300 via an isobutane tower 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 distillation device 100, and the top gas phase of the low-temperature isobutane distillation tower 2 is cooled and then input into the isobutane distillation 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, and the liquid phase outlet of the throttling expansion valve 14 is connected to the liquid phase inlet of the isobutane tower top condenser 3 (it is a condenser relative to the low-temperature isobutane distillation tower 2, and it is a refrigerant evaporator 3 relative to the compressed refrigerant. For the convenience of explanation, this article uniformly collects the isobutane tower top condenser 3 for description), 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 and reduces the pressure to a suitable temperature, it enters the isobutane tower top condenser 3 (it is a condenser relative to the low-temperature isobutane distillation tower 2, and it is a refrigerant evaporator 3 relative to the compressed refrigerant. 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 feed port is connected; 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 normal butane fractionation device 300 through the isobutane tower bottom pump 6.

[0050] In practical applications, the alkylation reaction effluent from the upstream effluent refining 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 a phase change to a 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, part of which is refluxed, and part of which is extracted through 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, and the liquid phase of the bottom effluent enters the isobutane tower bottom pump 6 to increase the pressure and then is input into the normal butane fractionation device 300 for separation of normal butane and alkylate oil.

[0051] In this embodiment, the lower operating pressure setting of the low-temperature isobutane distillation tower 2 in the isobutane fractionation device 100 can significantly reduce the temperature of the entire tower. When the top temperature drops below room temperature, the propane compression refrigeration device 200 can be used for cooling. When the bottom temperature drops below the boiling point of normal pressure water vapor, the low-temperature waste heat in the plant can be used instead of high-pressure steam as a heat source, and the top operating pressure range can be regulated according to the low-temperature waste heat temperature range provided at the bottom of the tower. The lower the low-temperature waste heat temperature, the lower the operating pressure of the isobutane distillation tower, the lower the condensation temperature at the top of the tower, and the lower the refrigeration energy consumption; based on this, this embodiment preferably sets the heat source inlet of the low-temperature reboiler at the bottom of the isobutane tower to be connected to the outlet of the 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 reduction in the top condensation temperature of the low-temperature isobutane distillation tower 2, the top circulating isobutane temperature is also reduced accordingly, and the cold capacity carried when it enters the alkylation reaction system increases, 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 unchanged in the conventional pressure range (0.5Mpa-0.7Mpa), and the n-butane fractionation device 300 is preferably provided, including a n-butane bottom effluent 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 effluent cooler 13. Among them, the feed inlet (the 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 effluent 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 inlet 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 effluent heat exchanger 7 and the isobutane bottom pump 6 through the pipeline in sequence ... The reflux inlet of the butane distillation tower 8 is connected; the liquid phase inlet and the gas phase outlet of the n-butane tower bottom reboiler 11 are connected to the bottom and the tower body of the n-butane distillation tower 8 through pipelines respectively; the bottom liquid phase discharge port of the n-butane distillation tower 8 is connected to the feed pipeline of the alkylation oil storage tank (not shown in the figure) 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 practical applications, the bottom effluent liquid phase of the low-temperature isobutane distillation tower 2 enters the isobutane tower bottom pump 6 to increase the pressure and then is preheated and heated by the normal butane tower bottom effluent heat exchanger 7. The preheated material enters the tower from the middle and lower part of the normal butane distillation tower 8 for separation treatment. The normal butane tower top condenser 9 and the normal butane tower bottom reboiler 11 of the normal butane distillation tower 8 are both cooled and heated by conventional circulating water. It should be noted that the separation process in the normal butane fractionation device 300 is implemented by the existing technology. The top gas phase (normal butane) of the normal butane distillation tower 8 is cooled by the normal butane tower top condenser 9 and partially refluxed into the normal butane tower top reflux tank 10, and partially discharged from the system. The bottom effluent alkylation oil is sequentially heat-exchanged by the normal butane tower bottom effluent heat exchanger 7, the alkali wash liquid heat exchanger 12 and the normal butane tower bottom effluent cooler 13 and then discharged from the system, which 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 distillation tower. The tower bottom does not need to use high-pressure steam to obtain heat, and low-temperature waste heat in the plant can be used for heating, which effectively saves a lot of energy. At the same time, the tower top uses a highly energy-efficient propane compression refrigeration system for cooling, which can further improve energy utilization efficiency and save costs. In addition, by reducing the operating pressure of the isobutane distillation tower, it is also beneficial to increase the relative volatility of normal butane and isobutane, thereby reducing the difficulty of separation 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 device for low-temperature isobutane fractionation; the temperature of the bottom reboiler of the low-temperature isobutane fractionation tower is 70° C.-90° C.;

[0057] S12, pressurizing the refrigerant through a refrigeration compressor and then feeding it into a circulating water cooler for condensation, cooling and reducing part of the condensate through a throttling expansion valve and then feeding it into an isobutane tower top condenser, cooling the tower top gas phase of the low-temperature isobutane distillation tower and then partially extracting and feeding it into a circulating isobutane feed port of an alkylation reaction system, and pressurizing the tower bottom liquid phase of the low-temperature isobutane distillation tower and then feeding it into the n-butane fractionation device for alkylation 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 tower;

[0058] S13, collecting the gas phase refrigerant of the isobutane tower top condenser and part of the liquid phase refrigerant of the throttling expansion valve through a refrigerant tank for circulation.

[0059] It should be noted that the specific definition of the alkylation product separation method can refer to the definition of the alkylation product separation system above, and the corresponding technical effects can be obtained equivalently, which will not be repeated here. In addition, although the steps in the above flow chart are displayed in sequence according to the instructions of the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders.

[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, and any of the above alkylation product separation systems; the isobutane fractionation device 100 in the alkylation product separation system also includes a pre-tower precooling 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 discharge port of the alkylation product separation system, and the other is connected to the pre-treated 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 in sequence through the compression refrigeration system 500, the reaction system feed heat exchanger 33 and the pre-cooling heat exchanger 1 before the tower; the discharge port 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-cooling heat exchanger 1 before the tower; 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, so as to achieve the purpose of saving refrigeration power.

[0062] The alkylation process system proposed in this embodiment adopts the alkylation product separation system, which adopts the separation system including the isobutane fractionation device 100, the propane compression refrigeration device 200 and the normal butane fractionation device 300 connected to the isobutane fractionation device 100, and the alkylation reaction system 400 and the corresponding compression refrigeration system 500 and the effluent refining system 600, etc., which are all implemented by existing technologies. Figure 5As shown, it 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 gas 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 to a liquid phase and then enters the second refrigerant tank 21, and part of the 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 a suitable temperature, and then enters the energy-saving tank 23 to reduce the pressure to the set value, part of the logistics is vaporized (mainly composed of propane), and the remaining liquid phase enters the vapor side (right side) of the flash tank 18 through the flash tank flash side pump 24 to further reduce the pressure, and part of the logistics is vaporized to take away heat, thereby achieving a cooling effect. That is, the compression refrigeration system 500 has two groups of effluents, one group enters 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 returns to the alkylation reaction system 400 to provide cooling.

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

[0064] In practical applications, the circulating isobutane flowing out of the isobutane fractionation unit 100 can be directly mixed with the supplementary isobutane after heat exchange and the upstream material from the pretreatment to enter the alkylation reaction system 400 due to its low temperature. The product flowing out of the alkylation reaction system 400 enters the compression refrigeration system 500 to obtain cold capacity, part of which is returned to the alkylation reaction system 400 to maintain the reaction temperature, and part of which flows downstream as the discharge material. Before going to the effluent refining system 600, it exchanges heat with the supplementary isobutane and the upstream material from the pretreatment through the reaction system feed heat exchanger 33 to precool part of the flow entering the alkylation reaction system 400, and then exchanges heat with the tower precooling heat exchanger 1 of the low-temperature isobutane fractionation tower 2 in the isobutane fractionation unit 100 to precool the flow entering the isobutane fractionation tower in the isobutane fractionation unit 100. The product flow 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 flow entering the alkylation reaction system 400, and then exchanges heat with the product of the effluent refining system 600 through the pre-tower precooling heat exchanger 1 to reduce the temperature of the flow entering the isobutane fractionation device 100.

[0065] The alkylation process system provided in this embodiment is a full-process thermal coupling system. The temperature of the circulating isobutane in the isobutane fractionation device is significantly lower than that of the circulating isobutane produced by the traditional isobutane fractionation device, which effectively avoids the cooling treatment before entering the alkylation reaction system. Since the circulating isobutane flow rate is large, 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 flow from the original refrigeration system to the downstream is very low, and the temperature of the effluent refining part must be raised to a higher level due to the process requirements, and then it should be heated again when entering the isobutane fractionation device. Cooling down to reduce the newly added compression refrigeration load on the top of the tower will have the characteristics 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, thereby achieving effective heat integration among the alkylation reaction system, the compression refrigeration system, the effluent refining system and the isobutane fractionation unit, reducing the temperature rise of the feed flow entering the alkylation product separation system, thereby effectively solving the problem of serious energy waste caused by repeated heating and cooling of the alkylation product and the circulating isobutane, and greatly reducing the energy load demand and production costs.

[0066] In addition, considering that the specific settings of the top pressure of the isobutane distillation tower, the inlet pressure and the outlet pressure of the refrigeration compressor in the isobutane fractionation unit in the actual alkylation process system, and the inlet pressure and outlet pressure of the refrigeration compressor in the compression refrigeration system corresponding to the alkylation reaction system will directly affect the alkylation product separation efficiency of the alkylation process system and the heat utilization efficiency in the system, in order to enable the above-mentioned process control items to be accurately adapted according to the operating conditions of the actual alkylation process system, thereby ensuring that the alkylation process system can continue to operate optimally, this embodiment preferably sets an optimization control subsystem for real-time adaptive regulation of various process control items in the alkylation process system, and performs real-time loop control on the top pressure of the isobutane distillation tower, the pressure before and after the newly added compression refrigeration system, and the pressure before and after the original compression refrigeration system under the given isobutane distillation tower bottom reboiler heat source temperature condition, thereby further reducing the overall system energy consumption.

[0067] Specifically, Figure 5 As shown, the system also 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; wherein 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 through a bus, and the memory stores an alkylation process optimization control program written based on the preset control optimization model, and 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 the above-mentioned 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] In order to ensure that the energy-saving and consumption-reducing goals of improving the separation efficiency of alkylation products and the heat utilization efficiency in the system are achieved at the same time, in this embodiment, the preset control optimization model is preferably designed by minimizing the sum of the heat load cost of the reboiler at the bottom of the n-butane fractionation tower and the consumption cost of the refrigeration system as the optimal control target of the optimization control subsystem; specifically, the preset control optimization model is constructed by minimizing the unit alkylation oil separation energy consumption cost under the preset control constraints as the optimization target, and the corresponding objective function can be expressed as:

[0069]

[0070] In the formula,

[0071]

[0072] B i =F nbs α

[0073]

[0074]

[0075] Among them, A i , B i and C i represents the refrigeration cost of the top of the low-temperature isobutane distillation tower, the steam heat source cost of the reboiler at the bottom of the normal butane tower, and the refrigeration cost saved by the compression refrigeration system; F nbit represents the alkylation oil flow rate; k and Z represent the gas isentropic coefficient and gas compressibility coefficient respectively; R represents 8314 / molecular weight of the working fluid; 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 working fluid 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 It represents the unit steam phase change heat of the heat source of the n-butane tower bottom reboiler; ω nbs It indicates the heat consumed by the reboiler heat source steam per unit effluent volume of the 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, the present embodiment preferably sets preset control constraints including isobutane tower top refrigerant absorption heat constraint, compression refrigeration system refrigeration load reduction constraint, propane temperature phase change pressure constraint, isobutane tower top condensation temperature constraint, mixture working fluid temperature phase change pressure constraint in compression refrigeration system, and compression refrigeration system compressor inlet temperature constraint, which are expressed as:

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

[0078]

[0079] In the formula, Q m It 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, in MJ / t; Indicates the propane refrigerant flow rate in the propane compression refrigeration device, kg / s;

[0080] 2) The constraint on the reduction of the refrigeration load of the compression refrigeration system can be understood as a conservation constraint that the reduction of the refrigeration load of the original compression refrigeration system is equal to the absolute value of the difference in the cooling 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] Among them, ΔQ cold Indicates the reduction in refrigeration load of the original compression refrigeration system, in MJ; ΔQ re It indicates the absolute value of the heat difference between the new and old distillation processes of circulating isobutane, in MJ; C q1 Indicates the specific heat of the working fluid in the original compression refrigeration system, in 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 It represents the circulating isobutane flow rate in t / h;

[0085] 3) Propane temperature phase change pressure constraint 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] In the formula, f(·) represents the phase change pressure relationship of the refrigerant propane at different temperatures, which can be obtained through experimental tests; 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 constraint between the isobutane distillation tower top condensation temperature and the temperature before the propane working fluid enters the compressor:

[0090] T8 ≥ T1

[0091] Wherein, T1 represents the inlet temperature of the refrigeration compressor in the propane compression refrigeration device, in K; T8 represents the condensation temperature at the top of the isobutane distillation tower, in 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] In the formula, g(·) represents the phase change pressure relationship of the refrigerant at different temperatures, which can be obtained through experimental tests; 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 circulating water in the compression refrigeration system, in K; p5 and p6 represent the inlet current pressure and outlet current pressure of the refrigeration compressor in the compression refrigeration system, respectively, in kPa;

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

[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 logistics temperature from the original compression refrigeration to the alkylation reaction system, which is a constant, and the unit is K.

[0099] By combining the objective function and constraint conditions of the preset control optimization model in the optimization control subsystem, the optimal 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, and the optimization results are used as the control set values ​​of the corresponding variables in the optimization control subsystem in combination with the control valve to regulate the corresponding control loop. 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 (with a valve) and a second refrigerant tank pressure control loop 32 (with a valve). The corresponding control loops can be implemented by referring to the relevant control technology in the alkylation process system or integrated into the above-mentioned preset control optimization model for coordinated optimization. PC in the figure represents pressure control. In order to facilitate the understanding of the control flow of the optimization control subsystem, the following is a detailed description in combination with the actual alkylation process flow:

[0100] The product flowing out from the alkylation reaction system 400 is heated by the reaction system feed heat exchanger 33 before going to the effluent refining system 600, and then enters the pre-cooling heat exchanger 1 in 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 top gas phase of the low-temperature isobutane distillation tower 2 is cooled by the isobutane tower top condenser 3 and enters the isobutane tower top reflux tank 4. Part of the liquid phase of the reflux tank flows out of the device as circulating isobutane to enter the alkylation reaction system 400, and part of it returns to the low-temperature isobutane distillation tower 2 as reflux. The pressure control loop and valve 26 are set at the top of the tower, which are controlled by the liquid phase flow valve of the newly added propane compression refrigeration device 200, and the set value is given by the calculation result of the above-mentioned preset control optimization model. The propane compression refrigeration device 200 has a circulation loop, and the refrigerant first enters the refrigeration compressor 16 from the inlet of the refrigeration compressor 16, enters the circulating water cooler 15 after being pressurized and is completely condensed, and then is reduced to a reasonable pressure through the throttling expansion valve 14, and then releases the cold 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 top gas phase is cooled by the n-butane tower top condenser 9 and then enters the n-butane tower top reflux tank 10. The top gas phase of the reflux tank is discharged from the device, and the bottom liquid phase of the reflux tank is returned to the n-butane distillation tower 8 as reflux. The bottom of the tower is provided with an n-butane tower bottom reboiler 11 to supply heat to the distillation tower. The bottom effluent is cooled by the n-butane tower bottom effluent heat exchanger 7, and then enters the alkali wash liquid heat exchanger 12 for heat exchange and cooling again. Finally, it is cooled to an appropriate temperature by the n-butane tower bottom effluent cooler 13 and then enters the alkylation 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 amount. Through optimization calculation and solution, the optimal isobutane distillation tower pressure, the original compressor inlet and outlet pressures, and the new 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. The design innovatively adopts a low-temperature isobutane distillation process in which the top of the isobutane distillation tower is cooled by a propane compression refrigeration system and the bottom of the tower is heated by low-temperature waste heat in the plant. Combined with the process design in which the alkylation reaction product feed is heat-exchanged with the top liquid of the isobutane distillation tower and then enters the isobutane distillation tower, the temperature rise of the feed stream entering the alkylation product separation system is reduced, and the isobutane separated at the top of the low-temperature distillation tower of the isobutane tower can be directly circulated to the reaction system without cooling again, thereby effectively solving the problem. The problem of serious energy waste caused by repeated heating and cooling of alkylation products and circulating isobutane; at the same time, by designing an alkylation heat coupling system without changing the tower diameter requirement and combining it with a given isobutane fractionation tower bottom reboiler heat source temperature, the optimization control subsystem is arranged to adaptively control the isobutane fractionation tower top pressure, the propane compression refrigeration system front and rear pressures, and the original compression refrigeration system front and rear pressures with the optimization goal of minimizing the unit alkylation oil separation energy consumption cost. This can not only effectively save a lot 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] In order to verify the practical application effect of the alkylation process system provided by the present invention, this embodiment also takes the separation experiment of isobutane with a purity of not less than 86.0 mol%, normal butane with a purity of not less than 87.0 mol%, and alkylation oil that meets the requirements as an example, uses chemical process simulation software Aspen HYSYS V12 to perform simulation verification, and compares and analyzes the advantages and disadvantages of the existing process with the process of the present invention.

[0105] Assuming that the temperature of the low-temperature hot flow in the reboiler at the bottom of the isobutane distillation tower is 85-90°C, the operating pressure of the isobutane distillation tower is 0.18-0.19MPa, and the operating pressure of the normal butane distillation tower is 0.5-0.7MPa; the operating pressure of the refrigerant at the top of the isobutane distillation tower is 0.3-0.5MPa, and the compressor outlet pressure is 1.0-1.3MPa. Through simulation, the energy consumption of the traditional high-temperature distillation system and the low-temperature distillation system (alkylation product separation system) of the present invention as shown in Table 1 and Table 2 is obtained. By comparison, it can be seen that under the same separation requirements, the process of the present invention can greatly improve the overall energy utilization efficiency of the system and reduce energy loss compared with the existing mainstream conventional process.

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

[0107] Energy consumption location Energy consumption (104kcal / h) Logistics temperature (℃) Energy supply 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 Isobutane Fractionation Tower Top 862 6 Compression refrigeration Isobutane Fractionator Bottoms 847 74 Low temperature waste heat n-Butane Fractionator Top 47 59 Circulating water cooling n-Butane fractionation tower bottom 150 152 Steam Heating Additional 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 comprises the following steps:

[0111] S21, cooling the alkylation reaction product of the alkylation reaction system through a compression refrigeration system and inputting it into a reaction system feed heat exchanger, and then inputting it into a pre-cooling heat exchanger in front of the tower and the refined effluent of the effluent refining system for heat exchange and cooling, and then inputting it into the effluent refining system for refining treatment, and inputting the refined effluent after heat exchange and cooling into the low-temperature isobutane distillation tower for isobutane low-temperature fractionation; the tower bottom reboiler temperature of the low-temperature isobutane distillation tower is 70°C-90°C;

[0112] S22, pressurizing the refrigerant through a refrigeration compressor and then inputting it into a circulating water cooler for condensation, cooling and reducing the pressure of part of the condensate through a throttling expansion valve and then inputting it into an isobutane tower top condenser, cooling the tower top gas phase of the low-temperature isobutane distillation tower and then partially extracting and inputting it into a circulating isobutane feed port of the alkylation reaction system, pressurizing the tower bottom liquid phase of the low-temperature isobutane distillation tower and then inputting it into the normal butane fractionation device for alkylation oil fractionation, and collecting the gas phase refrigerant of the isobutane tower top condenser and part of the liquid phase refrigerant of the throttling expansion valve through a refrigerant tank for recycling.

[0113] For the specific definition of the alkylation process method, please refer to the definition of the alkylation process system above, and the corresponding technical effects can be obtained equivalently, which will not be repeated here. In addition, although the steps in the above flow chart are shown in sequence according to the arrows, these steps are not necessarily performed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be performed in other orders.

[0114] In summary, the alkylation product separation system, separation method, alkylation process system and method provided by the embodiments of the present invention have the following beneficial effects:

[0115] 1) By using a low-temperature isobutane distillation tower to separate isobutane, the overall temperature of the isobutane fractionation tower can be reduced. The tower bottom does not need to use high-pressure steam to obtain heat, and the low-temperature waste heat in the factory can be used for heating, which effectively saves a lot of energy. At the same time, the top of the tower uses a highly energy-efficient propane compression refrigeration system for cooling, which can further improve energy utilization efficiency and save costs. In addition, by reducing the operating pressure of the isobutane distillation tower, it is also beneficial to increase the relative volatility of n-butane and isobutane, making the separation difficulty lower and further reducing energy consumption;

[0116] 2) By innovatively adopting a low-temperature isobutane distillation process in which the top of the isobutane distillation tower is cooled by a propane compression refrigeration system and the bottom of the tower is heated by low-temperature waste heat in the plant, combined with a process design in which the alkylation reaction product feed is heat-exchanged with the top liquid of the isobutane distillation tower before entering the isobutane distillation tower, the temperature rise of the feed stream entering the alkylation product separation system is reduced, and the isobutane separated at the top of the isobutane tower low-temperature distillation tower does not need to be cooled again and can be directly circulated to the reaction system, thereby effectively solving the problem of serious energy waste caused by repeated heating and cooling of the alkylation product and the circulating isobutane;

[0117] 3) By designing the alkylation heat coupling system without changing the tower diameter requirement and combining it with the given isobutane fractionation tower bottom reboiler heat source temperature condition, the optimization control subsystem is arranged to adaptively control the isobutane fractionation tower 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 alkylation oil separation energy consumption cost. This can not only effectively save a lot 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.

[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 technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not 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-mentioned embodiments only express several preferred implementation modes of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in the technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be based on the protection scope of the claims.

Claims

1. An alkylation product separation system, characterized in that: The system comprises an isobutane fractionation device, and a propane compression refrigeration device and a normal 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 normal butane fractionation device via an isobutane tower bottom pump; The propane compression refrigeration device comprises 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 distillation device, and the top gas phase of the low-temperature isobutane distillation tower is cooled and then input into the isobutane distillation 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.

2. The alkylation product separation system according to claim 1, characterized in that: The isobutane fractionation device comprises a low-temperature isobutane rectification 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 the 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 product separation system according to claim 2, characterized in that: 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 product separation system according to claim 1, characterized in that: The n-butane fractionation device comprises a n-butane tower bottom effluent heat exchanger, a n-butane rectification 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 through a pipeline in sequence through the n-butane tower bottom flow heat exchanger and the isobutane tower bottom pump; the gas phase outlet of the n-butane distillation tower is connected to the feed inlet of the n-butane tower top reflux tank through 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 gas phase outlet of the n-butane tower bottom reboiler are respectively connected to the tower bottom and tower body of the n-butane distillation tower through pipelines; the bottom liquid phase discharge port of the n-butane distillation tower is connected to the feed pipeline of the alkylate oil storage tank in sequence through the n-butane tower bottom flow heat exchanger, the alkali wash liquid heat exchanger and the n-butane tower bottom flow cooler.

5. A method for separating an alkylation product, characterized in that: Applied to the alkylation product separation system according to any one of claims 1 to 4, the method comprises the following steps: The alkylation reaction product is input into an isobutane fractionation device 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, and part of the condensate is cooled and reduced in pressure by a throttling expansion valve and then fed into an isobutane tower top condenser, so that the tower top gas phase of the low-temperature isobutane distillation tower is cooled and then partially extracted and fed into a circulating isobutane feed port of an alkylation reaction system, and the tower bottom liquid phase of the low-temperature isobutane distillation tower is pressurized and then fed into the n-butane fractionation device for alkylation 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 tower; 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. An alkylation process system, characterized in that: The system comprises an alkylation reaction system and a corresponding compression refrigeration system and an effluent refining system, and an alkylation product separation system as claimed in any one of claims 1 to 4; the isobutane fractionation device in the alkylation product separation system further comprises a pre-cooling heat exchanger before the tower; 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 in sequence through the compression refrigeration system, the reaction system feed heat exchanger and the pre-tower precooling heat exchanger; 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-tower precooling heat exchanger; the circulating material gas phase outlet of the alkylation reaction system is connected to the flash tank in the compression refrigeration system.

7. The alkylation process system according to claim 5, characterized in that: 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.

8. The alkylation process system according to claim 7, characterized in that: The preset control optimization model is constructed by taking the minimization of the unit alkylate oil separation energy consumption cost as the optimization goal under the preset control constraints; the preset control constraints include 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.

9. The alkylation process system according to claim 8, characterized in that: The objective function of the preset control optimization model is expressed as: In the formula, Among them, A i , B i and C i represents the refrigeration cost of the top of the low-temperature isobutane distillation tower, the steam heat source cost of the reboiler at the bottom of the normal butane tower, and the refrigeration cost saved by the compression refrigeration system; F nbit represents the alkylation oil flow rate; k and Z represent the gas isentropic coefficient and gas compressibility coefficient respectively; R represents 8314 / molecular weight of the working fluid; 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 working fluid 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 It represents the unit steam phase change heat of the heat source of the n-butane tower bottom reboiler; ω nbs It indicates the heat consumed by the reboiler heat source steam per unit effluent volume of the n-butane distillation tower.

10. An alkylation process method, applied to the alkylation process system according to any one of claims 6 to 9, the method comprising the following steps: The alkylation reaction product of the alkylation reaction system is cooled by a compression refrigeration system and input into a reaction system feed heat exchanger, and after being heated by the reaction system feed heat exchanger and the upstream material of the alkylation reaction system, the product is then input into a precooling heat exchanger in front of the tower and the refined effluent of the effluent refining system for heat exchange and cooling, and then input into the effluent refining system for refining treatment, and the refined effluent after heat exchange and cooling is input into the low-temperature isobutane distillation tower for low-temperature isobutane fractionation; the tower bottom reboiler temperature of the low-temperature isobutane distillation 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 tower top condenser, so that the tower 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, and the tower bottom liquid phase of the low-temperature isobutane distillation tower is pressurized and then fed into the normal butane fractionation device for alkylation oil fractionation, and the gas phase refrigerant of the isobutane tower top condenser and a portion of the liquid phase refrigerant of the throttling expansion valve are collected through a refrigerant tank for recycling.

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