Energy-saving multi-effect ammonia distillation system and control method thereof

Abstract

The invention relates to the technical field of ammonia separation in an ethanolamine production process, in particular to an energy-saving multi-effect ammonia distillation system and a control method thereof.The energy-saving multi-effect ammonia distillation system comprises an ammonia distillation tower, the tower top of the ammonia distillation tower is connected with an air cooler, the ammonia distillation tower comprises a flash section and a rectifying section, the flash section is connected with a tower feeding pipeline and a first steam pipeline, and the system further comprises a first flash tank and a preheater; the first flash tank is connected with the bottom of the flash section, the top of the first flash tank is connected with cold air, the bottom of the first flash tank is connected with the preheater and then is connected back to the rectifying section, and the top of the rectifying section is connected with the air cooler. Meanwhile, the risk of ammonia corrosion of the tower plate is reduced; 2, the heat waste of steam condensate is reduced, the steam consumption is reduced, and greater economic benefits are brought; and 3, the system is simple to control and mainly adopts automatic control, so that the production stability is improved.

Description

Technical Field

[0001] The invention relates to the technical field of ammonia separation in an ethanolamine production process, and in particular to an energy-saving multi-effect ammonia distillation system and a control method thereof. Background Art

[0002] The ethanolamine production process mainly uses ethylene oxide and excess liquid ammonia as raw materials, and water as a catalyst to produce monoethanolamine, diethanolamine and triethanolamine products. The production process usually includes a reaction process, an ammonia evaporation and dehydration process, and a product refining process. The mixed materials after the reaction include water, liquid ammonia, monoethanolamine, diethanolamine and triethanolamine, of which the ammonia content is about 52-75%, and the steam consumed by ammonia removal accounts for more than 54% of the steam consumption of the entire production process. In addition, due to the property that ammonia is highly soluble in water, there is a problem of incomplete ammonia evaporation in the ammonia evaporation process. In the ammonia evaporation tower kettle at a temperature close to 180°C, if the residual ammonia concentration is too high, it will cause ammonia corrosion of the tower plate, which will eventually cause the ammonia evaporation efficiency of the ammonia evaporation tower to decrease, and ammonia corrosion will become more and more serious.

[0003] In summary, providing a new ammonia distillation system to reduce ammonia corrosion and steam consumption in the ammonia distillation process is of great significance to the ethanolamine production process. Summary of the invention

[0004] The object of the present invention is to provide an energy-saving multi-effect ammonia distillation system and a control method thereof, which has the characteristics of low energy consumption and good ammonia removal effect.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions: an energy-saving multi-effect ammonia distillation system, comprising an ammonia distillation tower, the top of which is connected to an air cooler, the ammonia distillation tower comprising a flash section and a distillation section, the flash section is connected to a tower feed pipeline and a steam pipeline, and also comprises a flash tank and a preheater, the flash tank is connected to the bottom of the flash section, the top of the flash tank is connected to cold air, the bottom is connected to the preheater and then connected back to the distillation section, and the top of the distillation section is connected to the air cooler.

[0006] Preferably, a demister and a heater are provided above and below the flash section, the feed port of the flash section is located between the demister and the heater, and a feed distributor is provided at the feed port, the demister is a two-layer wire mesh demister, and the heater is a shell-and-tube heater.

[0007] Preferably, the flash section and the distillation section are separated by an arched partition, and the arched partition is connected to the air cooler through a pipeline to transport the ammonia in the distillation section to the air cooler.

[0008] Preferably, a second feed distributor is provided at the feed inlet of the distillation section, and tower plates are provided in the distillation section. The tower plates are floating valve tower plates, the number of tower plates is 10-30 layers, and the tower plates are made of duplex steel.

[0009] Preferably, a reboiler and a second flash tank are further included, wherein the condensate outlet of the reboiler is connected to the second flash tank, and the condensate outlet of the second flash tank is connected to a preheater for preheating the liquid phase discharge from the first flash tank.

[0010] Preferably, the condensate outlet of the heater is connected to the second flash tank.

[0011] A control method for an energy-saving multiple-effect ammonia distillation system comprises the following steps:

[0012] Step 1: Ammonia, water, and ethanolamine mixed products are transported to the flash stage as feed, part of the ammonia is flash vaporized, and the remaining materials are heated by the built-in tube-in-tube heater to further remove part of the ammonia. The ammonia gas is condensed into liquid ammonia by the air cooler, and part of the non-condensable steam is transported to the post-processing system;

[0013] Step 2: The material at the bottom of the flash section enters the flash tank 1 for flash evaporation again, and the flashed ammonia vapor enters the air cooler for condensation. The remaining material in the flash tank 1 is transported to the preheater, heated with 150°C condensate, and then transported to the upper part of the distillation section. The material is further removed of ammonia through flash evaporation and heating;

[0014] Step 3: The material after the treatment in the above steps 1 and 2 enters the distillation section to further remove ammonia. The distillation section removes the remaining ammonia in the material by circulating heating the material. The ammonia gas leaving the distillation section enters the air cooler to condense the ammonia gas into liquid ammonia.

[0015] Preferably, the feed rate of the mixed product of ammonia, water and ethanolamine in step 1 is 32.5-34 t / h, the pressure is 4.5-6.2 MPa, the feed temperature is 93-95°C, the pressure of the ammonia distillation tower is controlled to be 1.2-1.6 MPa, the temperature of the material at the bottom of the flash section is controlled to be 86-118°C, and the operating temperature of the top of the ammonia distillation tower is 86.3-102.8°C.

[0016] Preferably, the pressure of the material from the flash tank 1 to the preheater in step 2 is controlled at 1.3-1.66 MPa, and the preheater is heated by condensate at 150°C.

[0017] Preferably, the temperature control range of the bottom of the distillation section in step 3 is 190-204°C.

[0018] In summary, the present invention has the following beneficial effects:

[0019] 1. After two flash evaporations, heating and one distillation, the ammonia in the material is separated by multiple effects, and the ammonia in the treated material is reduced to the minimum as much as possible. The ammonia concentration can be controlled between 1.4-6.5%, which reduces the difficulty of subsequent product refining and reduces the risk of ammonia corrosion on the tower plate;

[0020] 2. The low-pressure steam produced as a by-product of flash evaporation of high-pressure steam condensate is provided to downstream users. At the same time, the steam condensate is fully utilized to heat materials, reducing the heat waste of steam condensate and steam consumption, thus bringing greater economic benefits.

[0021] 3. The system control is simple and mostly adopts automatic control to improve production stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a comparative process flow chart;

[0023] Figure 2 It is the process flow chart of Example 1 and Example 2.

[0024] In the figure, 1, tower feed pipeline; 2, steam pipeline 1; 3, condensate pipeline 1; 4, liquid outlet pipeline; 5, steam pipeline 2; 6, condensate pipeline 2; 7, condensate pipeline 3; 8, steam pipeline 3; 9, tower bottom circulation pipeline; 10, tower bottom outlet pipeline; 11, tower top gas phase pipeline; 12, flash tank gas phase pipeline; 13, flash tank feed pipeline; 14, flash tank outlet pipeline; 15, distillation gas phase pipeline; 16, liquid ammonia pipeline; 21, ammonia distillation tower; 22, air cooler; 23, flash tank 1 ; 24. Preheater; 25. Booster pump; 26. Circulation pump; 27. Reboiler; 28. Flash tank 2; 29. ​​Condensate transfer pump; 31. Flash section; 32. Distillation section; 33. Defoamer; 34. Heater; 35. Feed distributor 1; 36. Feed distributor 2; 41. Pressure regulating valve; 42. Temperature regulating valve 1; 43. Liquid level regulating valve 1; 44. Temperature regulating valve 2; 45. Liquid level regulating valve 2; 46. Liquid level regulating valve 3; 51. Tower plate; 52. Arched partition. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0026] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0027] Comparative Example:

[0028] like Figure 1As shown, the system of this comparative example includes an ammonia evaporation tower 21, and the ammonia evaporation tower 21 includes an upper flash section 31 and a lower distillation section 32. The flash section 31 connects the tower feed pipeline 1 and the steam pipeline 2. The steam pipeline 2 is used to pass 1.2MPa steam. The top of the ammonia evaporation tower 21 is connected to the air cooler 22 through the top gas phase pipeline 11. The air cooler 22 is connected to the liquid ammonia pipeline 16. The tower bottom of the ammonia evaporation tower 21 is connected to the tower bottom discharge pipeline 10 and the tower bottom circulation pipeline 9. The tower bottom circulation pipeline 9 is connected to the circulation pump 26 and the reboiler 27 in sequence, and then returns to the distillation section 32. The reboiler 27 is connected to the steam pipeline 25 and the condensate pipeline 26. The steam pipeline 25 is used to input 2.5MPa steam to the reboiler, and the condensate pipeline 26 is used to output the condensate.

[0029] In this comparative example, the ammonia evaporation tower 21 contains 52.5% ammonia, 11.7% water, 17.0% monoethanolamine, 12.5% ​​diethanolamine, and 6.3% triethanolamine. The feed rate is 34 tons per hour, the product pressure is 6.2 MPa, and the feed temperature is 95°C. The pressure of the ammonia evaporation tower 21 is set to 1.2 MPa, the bottom operating temperature of the flash section 31 is 118°C, the top operating temperature of the ammonia evaporation tower 21 is 102.8°C, and the bottom operating temperature of the rectifying section 32 is 204°C. The bottom material of the flash section 31 is directly transported to the rectifying section 32.

[0030] Under this operation, the steam consumption at 1.2MPa is 11959kg / h, and the steam consumption at 2.5MPa is 5912kg / h. According to the analysis, the ammonia content in the bottom of the ammonia distillation tower 21 is 16.3%.

[0031] Embodiment 1:

[0032] like Figure 2 As shown, it includes an ammonia distillation tower 21, an air cooler 22, a flash tank 1 23, a preheater 24, a booster pump 25, a circulation pump 26, a reboiler 27, a flash tank 2 28 and a condensate transfer pump 29.

[0033] The top of the ammonia still 21 is connected to the air cooler 22 via the top gas phase pipeline 11, and the bottom of the air cooler 22 is connected to the liquid ammonia pipeline 16. The gas phase discharge pipeline of the air cooler 22 is provided with a pressure regulating valve 41 for regulating the pressure of the ammonia still 21.

[0034] The ammonia distillation tower 21 includes an upper flash section 31 and a lower distillation section 32, and the flash section 31 and the distillation section are separated by an arched partition 52. The flash section 31 includes a demister 33 and a heater 34 arranged above and below. The demister 33 is a two-layer metal wire mesh demister, and the heater 34 is a tube-in-tube heater. A feed port is arranged between the heater 34 and the demister 33, and a feed distributor 35 is arranged at the feed port. The feed port is connected to the tower feed pipeline 1, and the mixed material enters the flash section 31 through the tower feed pipeline 1. The heater 34 is connected to the steam pipeline 2 for passing 1.2MPa steam. A temperature regulating valve 42 is arranged on the steam pipeline 2 for adjusting the temperature of the material at the bottom of the flash section 31. The heater 34 is connected to the condensate pipeline 3. A distillation gas phase pipeline 15 connected to the distillation section 32 is arranged on the top of the arched partition 52, and the distillation gas phase pipeline 15 is connected to the air cooler 22.

[0035] A flash tank feed pipeline 13 is connected between the bottom of the flash section 31 and the flash tank 23, which is used to transport the material to the flash tank 23 through the static pressure difference. The top of the flash tank 23 is connected to the tower top gas phase pipeline 11 through the flash tank gas phase pipeline 12. The bottom of the flash tank 23 is connected to the booster pump 25 through the flash tank discharge pipeline 14, and then connected to the preheater 24 through the pipeline, and finally returned to the distillation section 32 through the pipeline. The outlet pressure of the booster pump 25 is controlled between 1.3-1.66MPa. A liquid level regulating valve 43 for adjusting the liquid level of the flash tank 23 is provided between the booster pump 25 and the preheater 24. The preheater 24 is connected to the condensate pipeline 37 for liquid inlet and the liquid outlet pipeline 4 for liquid outlet. The liquid outlet pipeline 4 outputs 120℃ condensate.

[0036] The distillation section 32 is provided with a feed distributor 2 36 and 10 layers of tower plates 51. The number of tower plates 51 in this embodiment is 10. The tower plates 51 are valve tower plates, and the material of the tower plates 51 is duplex steel.

[0037] The bottom of the ammonia distillation tower 21 is provided with a tower kettle discharge pipeline 10 and a tower kettle circulation pipeline 9. The tower kettle discharge pipeline 10 is provided with a liquid level regulating valve 245 for adjusting the tower kettle liquid level. The tower kettle circulation pipeline 9 is connected to the circulation pump 26 and the reboiler 27 in sequence, and then returns to the ammonia distillation tower 21. The reboiler 27 is connected to the steam pipeline 25 and the condensate pipeline 26. The steam pipeline 25 is used to pass 2.5MPa steam. The steam pipeline 25 is provided with a temperature regulating valve 244 for adjusting the tower kettle temperature of the distillation section 32, and the tower kettle temperature range of the distillation section 32 is 209.3℃.

[0038] The top of the flash tank 28 is connected to the condensate pipeline 13 and the condensate pipeline 26. The bottom of the flash tank 28 is connected to the condensate pipeline 37, and the top is connected to the steam pipeline 38. The condensate pipeline 37 is used to output 150°C condensate. The steam pipeline 38 is used to output 0.4MPa steam. The condensate pipeline 37 is provided with a condensate delivery pump 29 and a liquid level regulating valve 245 for controlling the liquid level of the flash tank 28, and the condensate is delivered to the preheater 24 through the condensate delivery pump 29.

[0039] The operation method includes the following steps:

[0040] Step 1: The mixed product of ammonia, water and ethanolamine is transported to the flash section 31 of the ammonia evaporation tower 21 through the tower feed pipeline 1. The feed of the ammonia evaporation tower 21 contains 52.5% ammonia, 11.7% water, 17.0% monoethanolamine, 12.5% ​​diethanolamine, and 6.3% triethanolamine. The feed rate is 34 tons per hour, the product pressure is 6.2MPa, and the feed temperature is 95°C. The pressure of the ammonia evaporation tower 21 is automatically controlled by the pressure regulating valve 41, and the pressure is 1.2MPa. The temperature of the material at the bottom of the flash section 31 of the ammonia evaporation tower 21 is automatically controlled by the temperature regulating valve 42, and the temperature is 118°C. The operating temperature of the top of the ammonia evaporation tower 21 is 102.8°C. Part of the ammonia flash vaporizes, and the remaining material is heated by the built-in shell-and-tube heater 34 to further remove part of the ammonia. The ammonia gas is condensed into liquid ammonia through the air cooler 22, and part of the non-condensable steam is transported to the post-system for treatment.

[0041] Step 2: The material at the bottom of the flash section 31 enters the flash tank 23 for flashing again, and the flashed ammonia vapor enters the air cooler 22 for condensation. The remaining material in the flash tank 23 is transported to the preheater 24 through the booster pump 25, and is heated with 150°C condensate before being transported to the upper part of the distillation section 32. The material is further deammonified by flashing and heating. The liquid level of the flash tank 23 is automatically controlled by the liquid level regulating valve 43, the outlet pressure of the booster pump 25 is controlled to 1.3MPa, and the preheater 24 is heated with 150°C condensate.

[0042] Step 3: The material after the treatment of the above steps 1 and 2 enters the distillation section 32 to further remove ammonia. The distillation section 32 is provided with a tower bottom circulation pipeline 9 and a reboiler 27. The remaining ammonia in the material is removed by circulating the material and heating. The ammonia gas out of the distillation tower enters the air cooler 22 to condense the ammonia gas into liquid ammonia. The temperature of the tower bottom of the distillation section 32 is automatically controlled by the temperature regulating valve 244, and the temperature is controlled to 204°C. The tower bottom discharge pipeline 10 is provided with a regulating valve to automatically control the tower bottom liquid level.

[0043] Under this operation, the steam consumption at 1.2MPa is 9358kg / h, and the steam consumption at 2.5MPa is 3963kg / h. According to the analysis, the ammonia content in the bottom material of the ammonia distillation tower 21 is 6.19%.

[0044] Embodiment 2:

[0045] The system used in this embodiment is the same as that in Embodiment 1, and the pressure of each steam pipeline and the temperature of each condensate pipeline are also the same as those in Embodiment 1. The difference is that:

[0046] The number of plates 51 used in this example is 30 layers, and the feed of the ammonia evaporation tower 21 contains 52.5% ammonia, 11.7% water, 17.0% monoethanolamine, 12.5% ​​diethanolamine, and 6.3% triethanolamine. The feed rate is 32.5 tons per hour, the product pressure is 4.5MPa, the feed temperature is 93°C, the pressure of the ammonia evaporation tower 21 is set to 1.6MPa, the bottom operating temperature of the flash section 31 is 86°C, the top operating temperature is 86.3°C, and the bottom operating temperature of the distillation section 32 is 190°C. The material in the flash section 31 enters the flash tank 23 for flash evaporation again, and the flashed ammonia vapor enters the air cooler 22 for condensation. The remaining material in the flash tank 23 is transported to the preheater 24 by the booster pump 25. The outlet pressure of the booster pump 25 is controlled to 1.66MPa and is heated with 150°C condensate before being transported to the upper part of the distillation section 32. The material is further heated to remove ammonia by flash evaporation.

[0047] Under this operation, the steam consumption at 1.2MPa is 8565kg / h, and the steam consumption at 2.5MPa is 3844kg / h. According to the analysis, the ammonia content in the bottom material of the ammonia distillation tower 21 is 1.47%.

[0048] The steam dosage and ammonia content of the bottom material in the comparative example, embodiment 1 and embodiment 2 are as follows:

[0049] 1.2MPa steam consumption 2.5MPa steam consumption Ammonia content of tower bottom material Comparative Example 11959kg / h 5912kg / h 16.3％ Example 1 9358kg / h 3963kg / h 6.19％ Example 2 8565kg / h 3844kg / h 1.47％

[0050] By comparison, the material in the flash section 31 is flashed in the flash tank 23 and heated in the preheater 24 before entering the distillation section 32 of the ammonia tower 21. Compared with the material in the flash section 31 of the ammonia tower directly entering the distillation section 32, it has obvious deamination and energy-saving effects. The total steam consumption is reduced by about 30.6%, and the ammonia content in the material after deamination is reduced by about 91.0%.

Claims

1. An energy-saving multi-effect ammonia distillation system, comprising an ammonia distillation tower, the top of which is connected to an air cooler, the ammonia distillation tower comprising a flash section and a distillation section, the flash section being connected to a tower feed pipeline and a steam pipeline, characterized in that: It also includes a flash tank and a preheater. The flash tank is connected to the bottom of the flash section, the top of the flash tank is connected to cold air, the bottom is connected to the preheater and then connected back to the distillation section, and the top of the distillation section is connected to the air cooler.

2. The energy-saving multiple-effect ammonia distillation system according to claim 1, characterized in that: The flash section is provided with demisters and heaters above and below. The feed inlet of the flash section is located between the demisters and the heater, and a feed distributor 1 is provided at the feed inlet. The demister is a two-layer metal wire mesh demister, and the heater is a shell-and-tube heater.

3. The energy-saving multiple-effect ammonia distillation system according to claim 1, characterized in that: The flash section and the distillation section are separated by an arched partition, and the arched partition is connected to the air cooler through a pipeline to transport the ammonia in the distillation section to the air cooler.

4. The energy-saving multiple-effect ammonia distillation system according to claim 1, characterized in that: A second feed distributor is arranged at the feed inlet of the distillation section, and a tower plate is arranged in the distillation section. The tower plate is a floating valve tower plate, the number of the tower plates is 10-30 layers, and the tower plate material is duplex steel.

5. The energy-saving multiple-effect ammonia distillation system according to claim 1, characterized in that: It also includes a reboiler and a second flash tank. The condensate outlet of the reboiler is connected to the second flash tank. The condensate outlet of the second flash tank is connected to a preheater for preheating the liquid phase discharge of the first flash tank.

6. The energy-saving multiple-effect ammonia distillation system according to claim 5, characterized in that: The condensate outlet of the heater is connected to the second flash tank.

7. The control method of the system according to claim 6, characterized in that: The following steps are involved: Step 1: Ammonia, water, and ethanolamine mixed products are transported to the flash stage as feed, part of the ammonia is flash vaporized, and the remaining materials are heated by the built-in tube-in-tube heater to further remove part of the ammonia. The ammonia gas is condensed into liquid ammonia by the air cooler, and part of the non-condensable steam is transported to the post-processing system; Step 2: The material at the bottom of the flash section enters the flash tank 1 for flash evaporation again, and the flashed ammonia vapor enters the air cooler for condensation. The remaining material in the flash tank 1 is transported to the preheater, heated with 150°C condensate, and then transported to the upper part of the distillation section. The material is further removed of ammonia through flash evaporation and heating; Step 3: The material after the treatment in the above steps 1 and 2 enters the distillation section to further remove ammonia. The distillation section removes the remaining ammonia in the material by circulating heating the material. The ammonia gas leaving the distillation section enters the air cooler to condense the ammonia gas into liquid ammonia.

8. The control method of the system according to claim 7, characterized in that: The feed rate of the mixed product of ammonia, water and ethanolamine described in step 1 is 32.5-34 t / h, the pressure is 4.5-6.2 MPa, the feed temperature is 93-95°C, the pressure of the ammonia distillation tower is controlled to be 1.2-1.6 MPa, the temperature of the material at the bottom of the flash section is controlled to be 86-118°C, and the operating temperature of the top of the ammonia distillation tower is 86.3-102.8°C.

9. The control method of the system according to claim 7, characterized in that: In step 2, the pressure of the material from the flash tank 1 to the preheater is controlled at 1.3-1.66 MPa, and the preheater is heated by 150°C condensate.

10. The control method of the system according to claim 7, characterized in that: The temperature control range of the distillation section bottom tower described in step 3 is 190-204°C.

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