A kind of production method and device of acrylonitrile

Abstract

The present invention provides a method and device for producing acrylonitrile, the method comprising the following steps: (1) stripping and separating a rich liquid containing acrylonitrile in a recovery tower, obtaining a gas phase flow containing acrylonitrile at the top of the recovery tower, and obtaining a high-temperature lean liquid substantially free of acrylonitrile at the bottom of the recovery tower; (2) flashing the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower, and using the steam obtained by flashing as a heat source at a heat-requiring end. The method comprises flashing the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower, pressurizing the steam obtained by flashing and using it as a heat source for at least one of a recovery tower, a wastewater evaporator, a decyanation tower, and a finished product tower. The use of the method and device can effectively recover and utilize low-grade heat sources, thereby saving energy and reducing consumption.

Description

Technical Field

[0001] The invention belongs to the technical field of acrylonitrile, and in particular relates to a method and a device for producing acrylonitrile. Background Art

[0002] Acrylonitrile is one of the three major derivatives of propylene and occupies an important position in the fields of synthetic resins, synthetic fibers, synthetic rubber and other materials. In industry, propylene ammoxidation is often used to produce acrylonitrile. The production unit includes a reaction unit, a recovery unit, a refining unit and a wastewater treatment unit. Propylene, ammonia and air are fed into a fluidized bed reactor in proportion. Under the action of a catalyst, acrylonitrile is generated by reaction, and by-products such as acetonitrile, water, acrolein, hydrogen cyanide and acrylic acid are also produced; the gas phase after the reaction is cooled and cooled to remove heavy components and waste catalysts, and unreacted ammonia is neutralized with sulfuric acid, and the sulfur-ammonia liquid is sent to the sulfur-ammonia recovery device; the gas after ammonia removal is sent to the absorption section, and water is used as an absorbent to absorb acrylonitrile, acetonitrile, hydrogen cyanide and other organic matter in the gas. The unabsorbed CO, CO2, N2, O2 and unreacted hydrocarbons are treated by the tail gas treatment system, and the absorption liquid enters the refining section. In the refining section, the acetonitrile in the absorption liquid is first separated by the recovery tower and sent to the acetonitrile device, then the hydrogen cyanide is separated by the decyanation tower and sent to the acetone cyanohydrin device, and finally the crude acrylonitrile enters the finished product tower for refining, and the bottom liquid part of the recovery tower is sent to the wastewater evaporator as wastewater for pretreatment and then sent to sewage treatment, and the other part is returned to the absorption tower as absorbent lean liquid after cooling. Due to the solubility of acrylonitrile in water, the acrylonitrile concentration in the absorbent (water) rich liquid generated after the reaction gas is absorbed by water is about 4-5wt%, and more than 20 tons of water are required for each ton of acrylonitrile to absorb, and low-temperature absorption and high-temperature analysis and recovery cause the absorption tower and the recovery tower to become the energy-intensive area of ​​the acrylonitrile device. In order to save energy, the commonly used method in industry is to use the lean water at the bottom of the recovery tower as a heat source directly as the heat source of the decyanation tower and the finished product tower. Even so, due to the large amount of lean water, the lean water temperature after heat exchange is still high, and there is still a large energy-saving space. Summary of the invention

[0003] In order to improve the deficiencies of the prior art, the object of the present invention is to provide a method and device for producing acrylonitrile, wherein the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of a recovery tower is flashed, and the steam obtained by flashing is pressurized and used as a heat source for a heat-requiring end (e.g., a recovery tower, a wastewater evaporator, a dehydrocyanide tower, and a finished product tower). The use of the method and device can effectively recover and utilize low-grade heat sources, thereby saving energy and reducing consumption.

[0004] The object of the present invention is achieved through the following technical solutions:

[0005] A method for producing acrylonitrile, comprising the following steps:

[0006] (1) stripping and separating the rich liquid containing acrylonitrile in a recovery tower, obtaining a gas phase stream containing acrylonitrile at the top of the recovery tower, and obtaining a high-temperature lean liquid substantially free of acrylonitrile at the bottom of the recovery tower;

[0007] (2) Flash distilling the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower, and using the steam obtained by flash distillation as a heat source at the heat-requiring end.

[0008] According to the present invention, the heat-demanding end includes at least one of a recovery tower, a wastewater evaporator, a decyanation tower, and a finished product tower.

[0009] When the heat-demanding end is a recovery tower, the steam obtained by flash evaporation can enter the bottom of the recovery tower for direct heating, and / or enter the reboiler at the bottom of the recovery tower as a heat source for indirect heating.

[0010] The wastewater evaporator is used for distilling and dehydrating the discharged lean liquid to obtain condensate water and concentrated wastewater. The condensate water is reused and the concentrated wastewater is further processed. The discharged lean liquid comes from the liquid after flash evaporation or from the bottom liquid of the recovery tower.

[0011] The decyanation tower is used to separate and recover the gaseous phase flow containing acrylonitrile from the top of the tower to obtain hydrogen cyanide and crude acrylonitrile. The heat-requiring end is, for example, a reboiler at the bottom of the decyanation tower.

[0012] The finished product tower is used to separate crude acrylonitrile and prepare acrylonitrile products, and the heat-requiring end is, for example, a reboiler at the bottom of the finished product tower.

[0013] According to the present invention, in step (1), the rich liquid containing acrylonitrile is obtained by the following method:

[0014] The gaseous phase flow of the reaction product obtained from the ammoxidation of propylene and / or propane is cooled and sent to a rapid cooling and ammonia removal section. The gaseous phase flow of the reaction product after rapid cooling and ammonia removal is contacted with water in an absorption tower, and a rich liquid containing acrylonitrile is obtained at the bottom of the absorption tower.

[0015] Wherein, the contact temperature is 20-50°C, and the contact pressure is 100-150 kPa.

[0016] The reaction product gas phase material includes acrylonitrile, hydrogen cyanide, acetonitrile, propylene, propane, acrolein, carbon monoxide, carbon dioxide, ammonia, oxygen, nitrogen and argon.

[0017] The temperature of the gas phase flow of the reaction product after the rapid cooling and ammonia removal treatment is 30-70°C and the pressure is 120-150 kPa.

[0018] In step (1), the content of acrylonitrile in the rich liquid containing acrylonitrile is 2-10wt%, such as 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%.

[0019] In step (1), the recovery tower is a recovery tower known in the art.

[0020] In step (1), the pressure of the stripping separation is 100-250 kPa and the temperature is 70-140°C.

[0021] In step (1), the acrylonitrile content in the acrylonitrile-containing gas phase stream obtained at the top of the recovery tower is 70-80 wt %; and the acrylonitrile content in the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower is less than 100 ppm.

[0022] In step (1), the temperature of the gas phase stream containing acrylonitrile obtained at the top of the recovery tower is 50-90°C and the pressure is 110-120 kPa; the temperature of the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower is 90-130°C and the pressure is 110-350 kPa.

[0023] According to the present invention, in step (2), the flash evaporation is performed at least at one pressure level, preferably at least at two pressure levels, for example, at one, two, three, four or more pressure levels.

[0024] In step (2), the gas phase stream obtained by each stage of flash evaporation is pressurized, for example, the gas phase stream obtained by each stage of flash evaporation is pressurized respectively, and the pressurized gas phase stream is used as a heat source at the heat-requiring end.

[0025] For example, the flash evaporation level is level 1, and the gas phase flow after the first-level flash evaporation is pressurized and used as the heat source at the heat-requiring end.

[0026] For example, the flash evaporation level is N, N ≥ 2, and except for the Nth stage, each flash evaporation level is pressurized and used as a heat source at the heat-demanding end; or the pressurized stream is mixed with the gaseous stream to be pressurized in the next flash evaporation level and pressurized together; the gaseous stream obtained in the Nth stage is pressurized and used as a heat source at the heat-demanding end. Exemplarily, when N = 2, the gaseous stream obtained by the first stage flash evaporation is pressurized, mixed with the gaseous stream obtained by the second stage flash evaporation, and pressurized together to serve as a heat source at the heat-demanding end.

[0027] In step (2), the lean liquid obtained after flash evaporation is discharged and / or returned to the absorption tower for reuse.

[0028] For example, the flash evaporation level is level 1, and the lean liquid obtained from the level 1 flash evaporation is discharged and / or returned to the absorption tower for reuse.

[0029] For example, the flash evaporation level is N, N≥2, except for the Nth stage, the lean liquid obtained by the previous flash evaporation is used as the feed of the next flash evaporation; the lean liquid obtained by the Nth flash evaporation is discharged and / or returned to the absorption tower for reuse. Exemplarily, when N=2, the lean liquid obtained by the first flash evaporation is used as the feed of the second flash evaporation, and the lean liquid obtained by the second flash evaporation is discharged and / or returned to the absorption tower for reuse.

[0030] In step (2), the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower is subjected to a primary flash evaporation, wherein the gaseous phase stream obtained by the primary flash evaporation is pressurized and used as a heat source at the heat-requiring end; and the lean liquid obtained by the primary flash evaporation is discharged and / or returned to the absorption tower for reuse.

[0031] In step (2), the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower is subjected to a first-stage flash evaporation and a second-stage flash evaporation, wherein the gaseous phase stream obtained by the first-stage flash evaporation is pressurized and then mixed with the gaseous phase stream obtained by the second-stage flash evaporation, and the two are pressurized together to serve as a heat source for the heat-requiring end; the lean liquid obtained by the first-stage flash evaporation is used as a feed for the second-stage flash evaporation, and the lean liquid obtained by the second-stage flash evaporation is discharged and / or returned to the absorption tower for reuse.

[0032] In step (2), the gaseous phase logistics obtained after the flash evaporation can be pressurized by a centrifugal compressor, a screw compressor, a reciprocating compressor, a Roots blower, or a steam ejector.

[0033] Wherein, the compression ratio of the compressor is 1.1-5.0.

[0034] The present invention also provides an acrylonitrile production device, comprising: a recovery tower, a flash unit and a pressurizing unit; the flash unit is connected to the bottom of the recovery tower; one end of the pressurizing unit is connected to the gas outlet of the flash unit, and the other end is connected to the heat-demanding end;

[0035] The flash unit includes at least one flash evaporator, and the pressurizing unit includes at least one pressurizing device.

[0036] Preferably, the flash unit comprises at least two flash evaporators.

[0037] Preferably, the boosting unit comprises at least two boosting devices.

[0038] Preferably, the number of the flash evaporators is the same as or different from the number of the boosting devices, preferably the same.

[0039] According to the present invention, the flash unit comprises at least two flash evaporators, which are connected in series. Specifically, except for the last stage flash evaporator, the liquid outlet of the previous stage flash evaporator is connected to the material inlet of the next stage flash evaporator; and the liquid outlet of the last stage flash evaporator is connected to an external pipeline.

[0040] According to the present invention, the boosting unit includes at least two boosting devices. Except for the last-stage boosting device, the boosted logistics outlet of the previous-stage boosting device is connected to the heat-requiring end, or is connected to the material inlet of the next-stage boosting device; the boosted logistics outlet of the last-stage boosting device is connected to the heat-requiring end.

[0041] According to the present invention, the gas outlet of the first-stage flash evaporator is connected to the material inlet of the last-stage booster, the gas outlet of the second-stage flash evaporator is connected to the material inlet of the penultimate-stage booster, and so on, the gas outlet of the last-stage flash evaporator is connected to the material inlet of the first-stage booster.

[0042] According to the present invention, the acrylonitrile production device comprises: a recovery tower, a flash unit and a pressurizing unit; the flash unit comprises a first-stage flash evaporator and a second-stage flash evaporator, and the pressurizing unit comprises a first-stage compressor and a second-stage compressor;

[0043] The bottom of the recovery tower is connected to the material inlet of the first-stage flash evaporator, the liquid outlet of the first-stage flash evaporator is connected to the material inlet of the second-stage flash evaporator, and the liquid outlet of the second-stage flash evaporator is connected to an external pipeline;

[0044] The gas outlet of the first-stage flash evaporator is connected to the material inlet of the second-stage compressor, the gas outlet of the second-stage flash evaporator is connected to the material inlet of the first-stage compressor, the pressurized logistics outlet of the first-stage compressor is connected to the heat-demanding end, or is connected to the material inlet of the second-stage compressor, and the pressurized logistics outlet of the second-stage compressor is connected to the heat-demanding end.

[0045] According to the present invention, the acrylonitrile production device comprises: a recovery tower, a flash unit and a pressurizing unit; the flash unit comprises a primary flash evaporator, and the pressurizing unit comprises a primary compressor;

[0046] The bottom of the recovery tower is connected to the material inlet of the first-stage flash evaporator, and the liquid outlet of the first-stage flash evaporator is connected to an external pipeline;

[0047] The gas outlet of the first-stage flash evaporator is connected to the material inlet of the first-stage compressor, and the pressurized logistics outlet of the first-stage compressor is connected to the heat-demanding end.

[0048] According to the present invention, the acrylonitrile production device comprises: a recovery tower, a flash unit and a pressurizing unit; the flash unit comprises a primary flash evaporator, and the pressurizing unit comprises a steam ejector;

[0049] The bottom of the recovery tower is connected to the material inlet of the first-stage flash evaporator, and the liquid outlet of the first-stage flash evaporator is connected to an external pipeline;

[0050] The gas outlet of the first-stage flash evaporator is connected to the material inlet of the steam ejector, and the logistics outlet of the steam ejector is connected to the heat-demanding end.

[0051] According to the present invention, the heat-demanding end includes at least one of a recovery tower, a wastewater evaporator, a decyanation tower, and a finished product tower.

[0052] Wherein, when the heat-demanding end is a recovery tower, the pressurized flash steam can enter the bottom of the recovery tower to directly supply heat, and / or enter the reboiler at the bottom of the recovery tower as a heat source to indirectly supply heat. That is, the recovery tower is connected to a pressurizing unit, such as the bottom of the recovery tower is connected to a pressurizing unit, or the reboiler at the bottom of the recovery tower is connected to a pressurizing unit.

[0053] The wastewater evaporator is connected to the booster unit to discharge the lean liquid for distillation and dehydration to obtain condensate water and concentrated wastewater. The condensate water is reused and the concentrated wastewater is further processed. When the heat-demanding end is the wastewater evaporator, the pressurized flash steam can enter the wastewater evaporator for heating; that is, the wastewater evaporator is connected to the booster unit.

[0054] The decyanation tower is connected to the top of the recovery tower to separate the gas phase stream containing acrylonitrile from the top of the recovery tower to obtain hydrogen cyanide and acrylonitrile crude products. When the heat-demanding end is the decyanation tower, the pressurized flash steam enters the decyanation tower bottom reboiler as a heat source for indirect heating; that is, the decyanation tower bottom reboiler is connected to the pressurizing unit.

[0055] Wherein, the finished product tower is connected to the decyanation tower for separating crude acrylonitrile and preparing acrylonitrile products. When the heat-requiring end is the finished product tower, the pressurized flash steam enters the bottom reboiler of the finished product tower as a heat source for indirect heating; that is, the bottom reboiler of the finished product tower is connected to the pressurizing unit.

[0056] Beneficial effects of the present invention:

[0057] The present invention provides a method and device for producing acrylonitrile. The method comprises the following steps: flashing a high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of a recovery tower, pressurizing the steam obtained by flashing and using it as a heat source for at least one of a recovery tower, a wastewater evaporator, a decyanation tower and a finished product tower. The method and device can effectively recover and utilize low-grade heat sources, thereby saving energy and reducing consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a process flow chart of two-stage flash distillation and pressurization in Example 1 of the present invention;

[0059] Figure 2 This is a process flow chart of flash jet pump pressurization in Example 2 of the present invention;

[0060] Figure 3 This is a process flow chart of single-stage flash distillation and pressurization according to Example 3 of the present invention.

[0061] Figure symbols: A, recovery tower, B, reboiler at the bottom of recovery tower, D, steam ejector, E1, first-stage compressor, E2, second-stage compressor, V, flash evaporator, V1, first-stage flash evaporator, V2, second-stage flash evaporator, 1, rich liquid containing acrylonitrile, 2, reflux liquid, 3, gas phase logistics at the top of recovery tower, 4, high-temperature lean liquid at the bottom of recovery tower, 5, lean liquid after first-stage flash evaporation, 6, first-stage flash steam, 7, lean liquid after second-stage flash evaporation, 8, second-stage flash steam, 9, first-stage compressor inlet, 10, second-stage compressor inlet, 11, first-stage compressor outlet, 13, pressurized flash steam, 14, side line extraction, 15, recovery tower bottom liquid, 16, external steam, 17, flash steam to jet pump, 18, single-stage flash steam to compressor, 19, lean liquid after jet pressurized flash evaporation, 20, jet pump outlet steam, 21, single-stage flash evaporation lean liquid. DETAILED DESCRIPTION

[0062] The present invention will be described in further detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0063] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0064] In the description of the present invention, it should be noted that the terms "first", "second", etc. are only used for descriptive purposes, and do not indicate or imply relative importance.

[0065] Example 1

[0066] like Figure 1The recovery tower A is used to separate acrylonitrile, hydrogen cyanide and acetonitrile. The gas phase flow 3 at the top of the recovery tower contains acrylonitrile, hydrogen cyanide and water. After condensation and stratification, the organic phase (crude acrylonitrile) is sent to the dehydrocyanation tower for dehydrocyanation, and then separated by the finished product tower to obtain acrylonitrile. Reflux 2 is an aqueous phase at about 45°C, which can be a cooled lean liquid. The reboiler B at the bottom of the recovery tower controls the temperature of the bottom of the recovery tower. The fraction containing acetonitrile, water and a small amount of hydrogen cyanide is extracted 14 from the side line of the recovery tower to the acetonitrile tower to obtain crude acetonitrile. The bottom liquid 15 of the recovery tower is extracted and sent to the wastewater evaporator for treatment. The high-temperature lean liquid 4 at the bottom of the recovery tower enters the first-stage flash evaporator V1 for flash evaporation to obtain first-stage flash steam 6 and first-stage flashed lean liquid 5. The first-stage flashed lean liquid 5 enters the first-stage flash evaporator V2 for flash evaporation to obtain second-stage flash steam 8 and second-stage flashed lean liquid 7. The second-stage flash steam 8 enters from the first-stage compressor inlet 9, and after being pressurized, it exits from the first-stage compressor outlet 11 and merges with the first-stage flash steam 6 to enter the second-stage compressor inlet 10. The pressurized flash steam 13 exiting from the second-stage compressor outlet can be used as a heat source for at least one of the recovery tower, the wastewater evaporator, the dehydrogen cyanide tower and the finished product tower.

[0067] Example 2

[0068] like Figure 2 The recovery tower A is used to separate acrylonitrile, hydrogen cyanide and acetonitrile. The gas phase flow 3 at the top of the recovery tower contains acrylonitrile, hydrogen cyanide and water. After condensation and stratification, the organic phase (crude acrylonitrile) is sent to the dehydrocyanide tower for dehydrocyanide, and then separated by the finished product tower to obtain acrylonitrile. Reflux 2 is an aqueous phase of about 45°C, which can be a cooled lean liquid. The reboiler B at the bottom of the recovery tower controls the temperature of the bottom of the recovery tower. The fraction containing acetonitrile, water and a small amount of hydrogen cyanide is extracted 14 from the side line of the recovery tower to the acetonitrile tower to obtain crude acetonitrile. The bottom liquid 15 of the recovery tower is extracted and sent to the wastewater evaporator for treatment. The high-temperature lean liquid 4 at the bottom of the recovery tower enters the flash evaporator V for flash evaporation, and the additional steam 16 passes through the ejector D. The flash steam 17 to the ejector is sucked by the ejector, and the ejector outlet steam 20 can be used as a heat source for at least one of the recovery tower, the wastewater evaporator, the dehydrocyanide tower and the finished product tower.

[0069] Example 3

[0070] like Figure 3The recovery tower A is used to separate acrylonitrile, hydrogen cyanide and acetonitrile. The gas phase flow 3 at the top of the recovery tower contains acrylonitrile, hydrogen cyanide and water. After condensation and stratification, the organic phase (crude acrylonitrile) is sent to the dehydrocyanide tower for dehydrocyanide, and then separated by the finished product tower to obtain acrylonitrile. Reflux 2 is an aqueous phase of about 45°C, which can be a cooled lean liquid. The reboiler B at the bottom of the recovery tower controls the temperature of the bottom of the recovery tower. The fraction containing acetonitrile, water and a small amount of hydrogen cyanide is extracted from the side line of the recovery tower 14, and the acetonitrile tower is removed to obtain crude acetonitrile. The bottom liquid 15 of the recovery tower is extracted and sent to the wastewater evaporator for treatment. The high-temperature lean liquid 4 at the bottom of the recovery tower enters the flash evaporator V for flash evaporation to obtain flash steam 18 to the compressor and lean liquid 21 after flash evaporation. The flash steam 18 to the compressor is compressed by the compressor E to obtain the pressurized flash steam 13, which can be used as a heat source for at least one of the recovery tower, wastewater evaporator, dehydrocyanide tower and finished product tower.

[0071] Example 4

[0072] Take the recovery tower of a 40,000 t / a acrylonitrile unit as an example.

[0073] use Figure 1 The process flow is shown.

[0074] The rich liquid from the absorption tower of 102700kg / h has a temperature of 66℃ after heat exchange, which contains 5.3wt% acrylonitrile, 0.2wt% acetonitrile, 0.6wt% hydrogen cyanide, and 0.4wt% acrolein. It enters from the middle and upper part of the recovery tower. The reboiler uses 0.4MPa steam as a heat source to control the temperature of the recovery tower. The gas phase at the top of the recovery tower is 69℃, the pressure is 110kPa, and the flow rate is 7340kg / h. It contains 80wt% acrylonitrile, 8.3wt% hydrogen cyanide, and 11.7wt% water. It goes to the next step to separate hydrogen cyanide and acrylonitrile. The top reflux is 48℃ 47000kg / h lean liquid. The side line of the recovery tower is 110℃, containing 8.5wt% acetonitrile, 0.3wt% hydrogen cyanide, and 91.2wt% water. The gas phase fraction goes to the acetonitrile tower. The bottom liquid of the tower is extracted with 115℃, 300kPa, 8600kg / h of wastewater to be treated in the wastewater evaporator. The bottom of the tower has a high temperature of 115℃ lean liquid of 134300kg / h, which enters the first-stage flash evaporator for flash evaporation to obtain 120kPa, 105℃ flash steam of 2780kg / h. After the first flash evaporation, the high temperature lean liquid enters the second-stage flash evaporator for secondary flash evaporation to obtain 85kPa, 95℃ secondary flash steam of 2630kg / h. The secondary flash steam enters the inlet of the first-stage compressor for compression, and 120kPa compressed gas is discharged from the outlet of the first-stage compressor, and mixed with the primary flash steam and then enters the inlet of the second-stage compressor. The pressurized flash steam of 5410kg / h is discharged from the outlet of the second-stage compressor, with a pressure of 310kPa and a temperature of 255℃, which can be used as a heat source for at least one of the recovery tower, wastewater evaporator, decyanation tower and finished product tower.

[0075] Save 5410kg / h of steam, and save 811 yuan / h in steam costs; increase compressor power by 475kW, and increase electricity costs by 308 yuan / h; cost savings: 811-308=503 yuan / h.

[0076] Example 5

[0077] The recovery tower feed, tower pressure and tower temperature are the same as those in Example 4. The difference is that the high-temperature lean liquid is treated using Figure 2 Process, 4000kg / h of external steam with a pressure of 500kPa is injected into the jet pump D, 134300kg / h of high-temperature lean liquid enters the flash evaporator V, the vacuum generated by the steam jet pump brings the flash steam into the ejector, and the steam ejector outlet is 6100kg / h of steam at 300kPa, which can be used as a heat source for at least one of the recovery tower, wastewater evaporator, decyanation tower and finished product tower.

[0078] Save 2100kg / h of steam (6100kg / h-4000kg / h), and save steam costs: 315 yuan / h.

[0079] Example 6

[0080] The recovery tower feed, tower pressure and tower temperature are the same as those in Example 4. The difference is that the high-temperature lean liquid is treated using Figure 3 Process, 134300kg / h of lean liquid enters the flash evaporator V, and 5420kg / h of 0.085MPa 95℃ flash steam is obtained. The flash steam enters the compressor and is pressurized to 310kPa. The pressurized steam can be used as a heat source for at least one of the recovery tower, wastewater evaporator, decyanation tower and finished product tower.

[0081] Save 5420kg / h of steam, and save 813 yuan / h in steam costs; increase the compressor power by 550kW, and increase the electricity cost by 357 yuan / h; cost savings: 813-357=456 yuan / h.

[0082] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for producing acrylonitrile, wherein: The method comprises the following steps: (1) stripping and separating the rich liquid containing acrylonitrile in a recovery tower, obtaining a gas phase stream containing acrylonitrile at the top of the recovery tower, and obtaining a high-temperature lean liquid substantially free of acrylonitrile at the bottom of the recovery tower; (2) flashing the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower, and using the steam obtained by flashing as a heat source at the heat-requiring end; the liquid at the bottom of the recovery tower is taken out and sent to a wastewater evaporator for treatment; The flash evaporation level is N, N ≥ 2. Except for the Nth level, the stream after flash evaporation pressurization in each level is mixed with the gas stream to be pressurized in the next level of flash evaporation and pressurized together; the gas stream obtained in the Nth level is used as the heat source at the heat-demanding end after pressurization; Except for the Nth stage, the lean liquid obtained from the previous flash evaporation is used as the feed for the next flash evaporation; the lean liquid obtained from the Nth flash evaporation is discharged and / or returned to the absorption tower for reuse; The gaseous stream obtained after flash evaporation is pressurized by a centrifugal compressor, a screw compressor, a reciprocating compressor, a Roots blower or a steam ejector; The heat demanding end includes a recovery tower.

2. The production method according to claim 1, wherein The heat-demanding end also includes at least one of a wastewater evaporator, a decyanation tower and a finished product tower.

3. The production method according to claim 1, in step (1), the rich liquid containing acrylonitrile is obtained by the following method: The gaseous phase flow of the reaction product obtained from the ammoxidation of propylene and / or propane is cooled and sent to a rapid cooling and ammonia removal section. The gaseous phase flow of the reaction product after rapid cooling and ammonia removal is contacted with water in an absorption tower, and a rich liquid containing acrylonitrile is obtained at the bottom of the absorption tower.

4. The production method according to any one of claims 1 to 3, wherein in step (1), the content of acrylonitrile in the rich liquid containing acrylonitrile is 2-10 wt%.

5. The production method according to any one of claims 1 to 3, wherein in step (1), the temperature of the gas phase stream containing acrylonitrile obtained at the top of the recovery tower is 50-90° C. and the pressure is 110-120 kPa; the high-temperature lean liquid substantially free of acrylonitrile obtained at the bottom of the recovery tower has a temperature of 90-130° C. and a pressure of 110-350 kPa.

6. The production method according to any one of claims 1 to 3, wherein in step (2), N=2, the gaseous phase stream obtained by the first stage flash evaporation is pressurized, mixed with the gaseous phase stream obtained by the second stage flash evaporation, and after being pressurized together, it is used as a heat source for the heat-requiring end; the lean liquid obtained by the first stage flash evaporation is used as feed for the second stage flash evaporation, and the lean liquid obtained by the second stage flash evaporation is discharged and / or returned to the absorption tower for reuse.

7. The production method according to claim 1, wherein the method is implemented in an acrylonitrile production device, the device comprising: A recovery tower, a flash unit and a pressurizing unit; the flash unit is connected to the bottom of the recovery tower; one end of the pressurizing unit is connected to the gas outlet of the flash unit, and the other end is connected to the heat-demanding end; the heat-demanding end includes a recovery tower; The flash unit comprises at least two flash evaporators, and the at least two flash evaporators are connected in series; Except for the last stage flash evaporator, the liquid outlet of the previous stage flash evaporator is connected to the material inlet of the next stage flash evaporator; the liquid outlet of the last stage flash evaporator is connected to the external pipeline; The boosting unit comprises at least two boosting devices; except for the last-stage boosting device, the boosting logistics outlet of the previous-stage boosting device is connected to the heat-requiring end, or is connected to the material inlet of the next-stage boosting device; the boosting logistics outlet of the last-stage boosting device is connected to the heat-requiring end; The gas outlet of the first stage flash evaporator is connected to the material inlet of the last stage booster, the gas outlet of the second stage flash evaporator is connected to the material inlet of the penultimate stage booster, and so on, the gas outlet of the last stage flash evaporator is connected to the material inlet of the first stage booster.

8. The production method according to claim 7, wherein: The acrylonitrile production device comprises: a recovery tower, a flash unit and a pressurizing unit; the flash unit comprises a first-stage flash evaporator and a second-stage flash evaporator, and the pressurizing unit comprises a first-stage compressor and a second-stage compressor; The bottom of the recovery tower is connected to the material inlet of the first-stage flash evaporator, the liquid outlet of the first-stage flash evaporator is connected to the material inlet of the second-stage flash evaporator, and the liquid outlet of the second-stage flash evaporator is connected to an external pipeline; The gas outlet of the first-stage flash evaporator is connected to the material inlet of the second-stage compressor, the gas outlet of the second-stage flash evaporator is connected to the material inlet of the first-stage compressor, the pressurized logistics outlet of the first-stage compressor is connected to the heat-demanding end, or is connected to the material inlet of the second-stage compressor, and the pressurized logistics outlet of the second-stage compressor is connected to the heat-demanding end.

9. The production method according to claim 7 or 8, wherein: The heat-demanding end also includes at least one of a wastewater evaporator, a decyanation tower and a finished product tower.

10. The production method according to claim 7 or 8, wherein: The heat-demanding end is a recovery tower, the bottom of the recovery tower is connected to a pressurizing unit, or the reboiler at the bottom of the recovery tower is connected to a pressurizing unit.

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