System for reducing C4 content in acetonitrile recovery tower

Abstract

The utility model discloses a system for reducing C4 content in an acetonitrile recovery tower, which comprises a flash evaporation device used for receiving nitrile-containing washing water from a heat exchanger of a recovery tower kettle and flashing C4 components in the nitrile-containing washing water into a gas phase to be discharged by reducing the pressure in the flash evaporation device so as to obtain a residual liquid phase; and the acetonitrile recovery tower is used for receiving the liquid phase from the flash evaporation device and recovering the liquid phase to obtain acetonitrile. According to the utility model, C4 components in the nitrile-containing washing water are discharged in advance through pressure reduction, so that the C4 components are prevented from being brought into the acetonitrile recovery tower, the stable operation of the acetonitrile recovery tower is ensured, the acetonitrile content in the circulating washing water is reduced, and the stable operation time of a butadiene device is effectively prolonged.

Description

Technical Field

[0001] The utility model relates to the technical field of extracting butadiene from cracked C4 by acetonitrile method, in particular to a system for reducing the C4 content in an acetonitrile recovery column. Background Technique

[0002] The nitrile-containing washing water discharged from the butadiene water washing column, the raffinate C4 water washing column, and the alkyne water washing column is heat-exchanged with the hot water discharged from the bottom of the acetonitrile recovery column in the bottom heat exchanger of the recovery column, and then enters the acetonitrile recovery column. After sufficient mass transfer and heat transfer in the column, a gas phase with an acetonitrile-water azeotropic composition is obtained at the top of the column, which flows into the condenser of the acetonitrile recovery column and enters the reflux drum of the acetonitrile recovery column after condensation. The recovered acetonitrile in the reflux drum of the acetonitrile recovery column is pumped out by the acetonitrile recovery column reflux pump. Part of it is sent to the top of the acetonitrile recovery column as reflux after flow adjustment; the other part is sent to the second extraction and rectification upper column of the second extraction and rectification unit after being adjusted by the liquid level control and flow control of the reflux drum. Due to the complex source of the nitrile-containing washing water, which carries saturated C4 components, during the rectification process of the acetonitrile recovery column, the boiling point of the C4 components is much lower than that of acetonitrile, so non-condensable gases are formed at the top of the acetonitrile recovery column, resulting in a gradual increase in the pressure during the operation of the acetonitrile recovery column and unable to ensure its stable operation. Currently, it mainly relies on setting a vent at the top of the reflux drum of the acetonitrile recovery column to continuously discharge the non-condensable C4 gas to the flare to reduce the operating pressure of the acetonitrile recovery column. However, continuous flaring of the reflux drum of the acetonitrile recovery column will cause acetonitrile to be discharged together to the flare, resulting in a large loss of raw material acetonitrile. At the same time, during the continuous discharge process, the adjustment of the valve is involved. Whether the valve is adjusted larger or smaller will affect the discharge speed, thereby causing changes in the top pressure, and then causing fluctuations in the bottom temperature. Often, due to the unstable operation of the acetonitrile recovery column, the acetonitrile in the circulating washing water exceeds the standard, resulting in acetonitrile loss, and the acetonitrile carried in the raffinate C4 will cause poisoning of the catalyst in the olefin conversion reactor. Content of the Utility Model

[0003] To solve the defects of the existing technology, the main purpose of the utility model is to provide a system for reducing the C4 content in an acetonitrile recovery column, so as to reduce the C4 components in the nitrile-containing washing water, ensure the stable operation of the acetonitrile recovery column, and reduce the acetonitrile content in the circulating washing water.

[0004] To achieve the above-mentioned utility model purpose, the utility model provides a system for reducing the C4 content in an acetonitrile recovery column, including:

[0005] A flash evaporation device for receiving the nitrile-containing washing water from the bottom heat exchanger of the recovery column, and flashing the C4 components in the nitrile-containing washing water into a gas phase and discharging them by reducing the pressure in the flash evaporation device to obtain the remaining liquid phase;

[0006] An acetonitrile recovery column for receiving the liquid phase from the flash evaporation device and recovering acetonitrile.

[0007] Further, the flash evaporation device is provided with a feed inlet for receiving the nitrile-containing washing water, an exhaust outlet for discharging the gas phase, and a discharge outlet for discharging the liquid phase.

[0008] Further, the exhaust outlet of the flash evaporation device is communicated with an external flash evaporation gas exhaust pipe, and an exhaust control valve is arranged on the pipeline of the flash evaporation gas exhaust pipe.

[0009] Further, the flash evaporation device is further provided with an air inlet for receiving nitrogen, the air inlet is communicated with an external nitrogen pipeline, and a nitrogen control valve is arranged on the nitrogen pipeline.

[0010] Further, the flash evaporation device is further provided with a pressure detector for detecting the internal pressure of the flash evaporation device.

[0011] Further, the system further includes a pressure control system communicated with the pressure detector, which is used for receiving the pressure information of the pressure detector and controlling the opening degree of the exhaust control valve and the nitrogen control valve according to the pressure information.

[0012] Further, the flash evaporation pressure of the flash evaporation device is equal to the feed pressure of the acetonitrile recovery column.

[0013] Further, the flash evaporation device is further provided with a pressure relief port.

[0014] Further, a temperature detector is arranged inside the flash evaporation device.

[0015] Further, the discharge outlet is communicated with an external discharge pipe, the discharge pipe is communicated with the acetonitrile recovery column, and a discharge control valve is arranged on the pipeline of the discharge pipe.

[0016] Further, the flash evaporation device is further provided with a liquid level detector for detecting the internal liquid level of the flash evaporation device.

[0017] Further, the system further includes a liquid level control system communicated with the liquid level detector, which is used for receiving the liquid level information of the liquid level detector and adjusting the opening degree of the discharge control valve according to the liquid level information.

[0018] Compared with the prior art, the present utility model has the following advantages:

[0019] The present utility model adds a flash evaporation device at the outlet of the tube side of the recovery tower kettle heat exchanger. The nitrile-containing washing water entering the tower is first sent into the flash evaporation device. By reducing the pressure inside the flash evaporation device, the C4 components are flashed into the gas phase and discharged, reducing the C4 component content in the nitrile-containing washing water; the remaining liquid phase enters the acetonitrile recovery column to recover acetonitrile. Therefore, the present utility model discharges the C4 components in the nitrile-containing washing water in advance by reducing the pressure, avoiding the C4 components from entering the acetonitrile recovery column, ensuring the stable operation of the acetonitrile recovery column, reducing the acetonitrile content in the circulating washing water, and effectively increasing the stable operation time of the butadiene device.

[0020] Other features and advantages of the present utility model will be described in detail in the following specific embodiments. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present utility model, the accompanying drawings required for the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0022] Figure 1 It is a schematic structural diagram of a system for reducing the C4 content in an acetonitrile recovery column provided for an embodiment of the present utility model.

[0023] Marking description: 1 - Feed pipe, 2 - Flash tank, 3 - Discharge pipe, 4 - Liquid level detector, 5 - Liquid level control system, 6 - Discharge control valve, 7 - Flash gas exhaust pipe, 8 - Pressure detector, 9 - Pressure detection system, 10 - Flash gas exhaust regulating valve, 11 - Nitrogen inlet regulating valve, 12 - Nitrogen inlet pipe, 13 - Safety relief facility, 14 - Temperature detector. Specific Embodiments

[0024] The following details the specific embodiments of the present utility model. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present utility model, and are not used to limit the present utility model.

[0025] In the description of the present utility model, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present utility model. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions.

[0026] Unless otherwise clearly specified and defined, the terms "installed", "connected", "connected", "fixed" should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0027] The present utility model aims at the unstable operation of the pressure and temperature of the acetonitrile recovery column; the continuous discharge of the torch at the top of the reflux drum behind the column causes the loss of raw material acetonitrile. A system for reducing the content of C4 in the acetonitrile recovery column is provided, including:

[0028] A flash evaporation device for receiving the nitrile-containing washing water from the heat exchanger at the bottom of the recovery column, and flashing the C4 components in the nitrile-containing washing water into a gas phase by reducing the pressure in the flash evaporation device and discharging the gas phase, and obtaining the remaining liquid phase;

[0029] An acetonitrile recovery column for receiving the liquid phase from the flash evaporation device and recovering acetonitrile.

[0030] In the system of the present utility model, the nitrile-containing washing water entering the acetonitrile recovery column is first flash-evaporated, and the C4 components in the water are reduced to the concentration of the solubility content at the lowest pressure required for entering the column, and then sent to the acetonitrile recovery column by pressure; specifically, the present utility model reduces the pressure in the flash tank, and then flashes the C4 components into a gas phase to reduce the content of C4 components in the nitrile-containing washing water.

[0031] Preferably, the flash evaporation pressure of the flash evaporation device is designed to be the feed pressure of the acetonitrile recovery column, so that the material in the flash evaporation device can be pressed into the acetonitrile recovery column without the need to additionally increase a pressurizing device, achieving the effect of energy saving and efficiency improvement.

[0032] In some embodiments, the flash evaporation device is provided with a feed inlet for receiving the nitrile-containing washing water, an exhaust port for discharging the gas phase, and a discharge port for discharging the liquid phase. Preferably, the feed inlet and the exhaust port are separately arranged at the top of the flash evaporation device, and the discharge port is arranged at the bottom of the flash evaporation device.

[0033] In some embodiments, the exhaust port of the flash evaporation device is communicated with an external flash gas exhaust pipe, and an exhaust control valve is arranged on the pipeline of the flash gas exhaust pipe.

[0034] In some embodiments, the pressure in the flash tank is reduced by opening the exhaust control valve.

[0035] In some embodiments, the flash evaporation device is further provided with an air inlet for receiving nitrogen, the air inlet is communicated with an external nitrogen pipeline through a nitrogen inlet pipe, and a nitrogen control valve is arranged on the nitrogen pipeline. Preferably, the nitrogen air inlet is arranged at the top of the flash evaporation device.

[0036] In the system of the present utility model, the nitrogen pipeline is used for pressing materials, and when the pressure of the flash evaporation device does not meet the feed pressure requirement of the acetonitrile recovery column, nitrogen can be supplemented to make the pressure of the flash evaporation device reach the feed pressure requirement, so as not to waste raw materials and save production costs.

[0037] In some embodiments, the flash evaporation device is further provided with a pressure detector for detecting the internal pressure of the flash evaporation device.

[0038] In some embodiments, the system further includes a pressure control system communicated with the pressure detector, which is configured to receive the pressure information from the pressure detector and control the opening degrees of the exhaust regulating valve and the nitrogen regulating valve according to the pressure information.

[0039] In the system of the present utility model, the flash evaporation device is provided with a pressure detection interlock to control the intake valve, so as to control the pressure of the flash evaporation device, thereby ensuring that the liquid phase remaining in the flash evaporation device can be smoothly pumped into the acetonitrile recovery column.

[0040] In some embodiments, the flash evaporation device is further provided with a pressure relief port and a safety pressure relief facility to prevent safety accidents caused by overpressure in the storage tank. Preferably, the pressure relief port is arranged at the top of the flash evaporation device.

[0041] In some embodiments, a temperature detector is arranged inside the flash evaporation device.

[0042] In some embodiments, the discharge port is communicated with an external discharge pipe, the discharge pipe is communicated with the acetonitrile recovery column, and a discharge control valve is arranged on the pipeline of the discharge pipe.

[0043] In some embodiments, the flash evaporation device is further provided with a liquid level detector for detecting the internal liquid level of the flash evaporation device. Controlling the liquid level of the flash evaporation device to be 50% ± 10% can achieve the maximum flash evaporation area.

[0044] In some embodiments, the system further includes a liquid level control system communicated with the liquid level detector, which is configured to receive the liquid level information from the liquid level detector and adjust the opening degree of the discharge control valve according to the liquid level information.

[0045] In the system of the present utility model, the flash evaporation device is provided with liquid level detection, and the discharge control valve is interlocked to control the liquid level of the flash evaporation device to prevent the flash evaporation device from being empty or full.

[0046] For other structures of the acetonitrile recovery column and the flash evaporation device of the present utility model that are not detailed, as well as the pressure, temperature, liquid level detectors and control systems, valves, etc., reference is made to the existing technical structures and will not be elaborated here.

[0047] For the convenience of those skilled in the art to understand, the present utility model will be clearly and completely described below with reference to the accompanying drawings.

[0048] Specifically, please refer to Figure 1, A system for reducing the content of C4 in the acetonitrile recovery system. A flash tank (i.e., a flash device) is added at the outlet of the tube side of the heat exchanger at the bottom of the recovery column. The top of the flash tank is separately provided with a feed inlet, an exhaust port, a nitrogen inlet, and a pressure relief port. The bottom of the flash tank device is provided with a discharge port. The top of the flash tank is connected to a pressure detector, the side of the flash tank is connected to a liquid level detector, and a temperature detector is arranged inside the flash tank. The working process is as follows: The nitrile-containing washing water (0.4 MPaG) from the heat exchanger at the bottom of the recovery column is injected into the flash tank 2 through the feed pipe 1 for flashing. The flashing pressure is 0.15 MPaG. The flashed C4 vapor is discharged into the flare system through the flash vapor exhaust pipe 7 and the flash vapor exhaust control valve 10. The flash vapor exhaust control valve 10 is controlled by the pressure detector 8 through the pressure control system 9, and the control pressure is 0.15 MPaG. The nitrile-containing washing water after removing C4 is sent to the acetonitrile recovery column through the discharge pipe 3 and the discharge control valve 6. The discharge control valve 6 is controlled by the liquid level detector 4 through the liquid level control system 5, and the control liquid level is 50% ± 10%. Nitrogen is injected into the flash tank 2 for pressing materials through the nitrogen inlet control valve 11 and the nitrogen inlet pipe 12. The nitrogen inlet control valve 11 is controlled by the pressure detector 8 through the pressure control system 9. A pressure relief port and a safety pressure relief facility 13 are arranged at the top of the flash tank for process safety control, and a temperature detector 14 is arranged inside the flash tank for temperature monitoring. In this system, the stable operation of the acetonitrile recovery column is ensured, and the content of acetonitrile in the circulating washing water is reduced.

[0049] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to enumerate all the implementation manners here. All obvious changes or variations derived from the technical solutions of the present invention are within the spirit scope covered by the present invention.

Claims

1. A system for reducing the carbon four content in an acetonitrile recovery tower, characterized in that: include: A flash evaporation device is used to receive the nitrile-containing washing water from the recovery tower bottom heat exchanger, and flash the carbon four components in the nitrile-containing washing water into a gas phase and discharge it by reducing the pressure in the flash evaporation device to obtain the remaining liquid phase; The acetonitrile recovery tower is used to receive the liquid phase from the flash evaporation device and recover acetonitrile.

2. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 1, characterized in that: The flash evaporation device is provided with a feed inlet for receiving nitrile-containing washing water, the flash evaporation device is provided with an exhaust port for discharging a gas phase, and the flash evaporation device is provided with a discharge port for discharging a liquid phase.

3. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 2, characterized in that: The exhaust port of the flash evaporation device is communicated with an external flash gas exhaust pipe, and an exhaust regulating valve is arranged on the pipeline of the flash gas exhaust pipe.

4. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 1, characterized in that: The flash evaporation device is also provided with an air inlet for receiving nitrogen, the air inlet is communicated with an external nitrogen pipeline, and a nitrogen regulating valve is provided on the nitrogen pipeline.

5. The system for reducing the carbon four content in the acetonitrile recovery tower according to any one of claims 1 to 4, characterized in that: The flash evaporation device is also provided with a pressure detector for detecting the internal pressure of the flash evaporation device.

6. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 5, characterized in that: The system also includes a pressure control system communicated with the pressure detector, which is used to receive pressure information from the pressure detector and control the opening degree of the exhaust regulating valve and the nitrogen regulating valve according to the pressure information.

7. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 1, characterized in that: The flash pressure of the flash evaporation device is equal to the feed pressure of the acetonitrile recovery tower; The flash evaporation device is also provided with a pressure relief port; A temperature detector is arranged inside the flash evaporation device.

8. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 2, characterized in that: The discharge port is communicated with an external discharge pipe, the discharge pipe is communicated with an acetonitrile recovery tower, and a discharge control valve is arranged on the pipeline of the discharge pipe.

9. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 8, characterized in that: The flash evaporation device is also provided with a liquid level detector for detecting the liquid level inside the flash evaporation device.

10. The system for reducing the carbon four content in the acetonitrile recovery tower according to claim 9, characterized in that: The system also includes a liquid level control system communicated with the liquid level detector, which is used to receive liquid level information from the liquid level detector and adjust the opening degree of the discharge control valve according to the liquid level information.

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