System and method for separating ammonia, ethanolamine and water

Abstract

The invention discloses a system and a method for separating ammonia, ethanolamine and water, which belong to the technical field of ammonia still separation, and are characterized in that a shell-and-tube heater is arranged in a flash tank, a reactor a and a reactor b are respectively arranged on two sides of the flash tank, the reactor a is communicated with the flash tank through a pipeline a, the reactor b is communicated with the flash tank through a pipeline b, and the reactor b is communicated with the flash tank through a pipeline b. The problems that separation is difficult, the separation cost is high and the operation period is short are solved, the problems that an existing plate tower is low in separation efficiency and high in energy consumption, silk screen filler is prone to corrosion and the operation period is short are solved, and the device is mainly applied to separation of ammonia, ethanolamine and water.

Description

Technical Field

[0001] The patent of this invention belongs to the field of ammonia distillation tower separation technology, and specifically relates to a separation system and method for ammonia, ethanolamine and water. Background Art

[0002] The main products of ethanolamine (EOA) devices are monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA). Its application areas include medical, emulsification, cement and other industries. Therefore, the market for ethanolamine is relatively good.

[0003] At present, foreign companies engaged in the production of ethanolamine mainly adopt the anhydrous ammonia production process route with a kettle reactor loaded with a catalyst; domestic companies engaged in the production of ethanolamine are numerous, and most of them adopt the aqueous ammonia production process route with a tubular reactor.

[0004] The reaction mechanisms of the two production processes are the same, namely, ethylene oxide and ammonia undergo three main reactions under liquid phase conditions. The reaction equations are as follows:

[0005] ①NH3+C2H4O—NH2CH2CH2OH+26.1kca l / mo l(MEA)

[0006] ②MEA+C2H4O—HN(CH2CH2OH)2+28.3kca l / mol(DEA)

[0007] ③DEA+C2H4O—N(CH2CH2OH)3+24.7kca l / mo l(TEA)

[0008] From the reaction equation, we can see that there are two factors that determine the reaction: ① reactant concentration; ② reaction heat.

[0009] ① Reactant concentration. Industrial production is mostly controlled by the ratio of ammonia to alkyl. The ratio of NH3 to EO (NH3 / EO molar ratio, ammonia to alkyl) in intrinsic safety design is usually selected in the range of 3.0-10.0, so ammonia is always in excess to ensure that EO reacts completely and is outside the explosion limit of 3.0-100%. Therefore, the excess ammonia needs to be separated, recycled and reused. In terms of separation technology, foreign companies producing ethanolamine all use the method of vacuum flash evaporation + wire mesh packing tower separation; domestic companies producing ethanolamine all use the method of vacuum flash evaporation + multi-layer plate tower separation.

[0010] ② Reaction heat. For exothermic reactions, heat control mainly includes the reaction start temperature and the reaction process temperature. The reaction start temperature needs to be heated by an external heat source to maintain it above 50°C, while the reaction process temperature needs to be removed by an external cold source to maintain the temperature below 120°C during the entire reaction process.

[0011] The existing plate tower has low separation efficiency and high energy consumption. The wire mesh packing of foreign enterprises is easy to corrode and has a short operation cycle. Therefore, our company proposes a separation system and method for ammonia, ethanolamine and water. Summary of the invention

[0012] Purpose of the invention: To solve the problems of low separation efficiency, high energy consumption, easy corrosion of wire mesh packing and short operation cycle of the existing plate tower mentioned in the background technology.

[0013] To achieve the above object, the present invention adopts the following technical solution:

[0014] A system for separating ammonia, ethanolamine and water comprises an ammonia still, a rectifying tank, a flash tank, a pump, a reboiler, a tower top cooler and an ammonia tank, wherein the ammonia still comprises a rectifying tank and a flash tank, and a flash tank is arranged on the rectifying tank, and the system is characterized in that a shell and tube heater is arranged inside the flash tank, a reactor a and a reactor b are arranged on both sides of the flash tank, the reactor a is connected to the flash tank through a pipeline a, the reactor b is connected to the flash tank through a pipeline b, and a steam heating pipeline is connected to the shell and tube heater;

[0015] A wire mesh packing and a plate-type tower plate are arranged inside the distillation tank. The bottom of the distillation tank is connected to the dehydration tower through a pipeline c. The side of the distillation tank is connected to the pump through a pipeline d. The pump and the reboiler are connected through a pipeline e. The reboiler is connected to the distillation tank through a distillation section reflux pipe. The horizontal level of the distillation section reflux pipe is lower than the horizontal level of the wire mesh packing. The tower top cooler is connected to the distillation tank and the flash tank respectively through a tee pipe. The tower top cooler is connected to the ammonia tank through a pipeline f.

[0016] An entrainment discharge pipe is arranged on the bottom side of the flash tank, a liquid phase feed pipe is arranged on the top side of the distillation tank, the entrainment discharge pipe and the liquid phase feed pipe are connected through an n-type pipe, and a return air pipe is arranged above the n-type pipe to be connected with the three-way pipe.

[0017] A method for separating ammonia, ethanolamine and water, characterized in that it comprises the following steps:

[0018] Step 1: The mixed product of ammonia, water and ethanolamine passes through reactor a, is decompressed and enters the flash tank of the ammonia distillation tower to achieve reduced pressure flash evaporation. The mixed product of ammonia, water and ethanolamine passes through reactor b, is decompressed and enters the flash tank of the ammonia distillation tower to achieve reduced pressure flash evaporation.

[0019] Step 2: The mixed stream after the reduced pressure flash is further heated by low-pressure steam for thermal separation through the heater in the flash tank at the top of the ammonia tower. In this step, the flash tank heater is kept in a liquid-sealed state through the design of the entrainment discharge pipe, n-type pipe, and liquid phase feed pipe to reduce heat loss and ensure that the dry pipe of the heater is not damaged by dry burning.

[0020] Step 3: The gas-liquid separation is achieved simultaneously through the entrainment discharge pipe, n-type pipe, and liquid phase feed pipe. The gas phase goes out from the top of the n-type pipe, and the liquid phase flows downstream to the lower distillation tank of the ammonia distillation tower.

[0021] Step 4: The distillation tank adopts a tower internals method of combining tower plates and wire mesh packing layers to realize the gas-liquid heat exchange space of the distillation, which not only increases the gas-liquid exchange area, but also improves the corrosion resistance of the tower internals, reduces energy consumption, and ensures the long-term operation of the tower.

[0022] Step 5: A bottom reboiler is set in the lower distillation tank of the ammonia distillation tower. Under the action of the wire mesh packing of the internal parts of the ammonia distillation tower, ammonia separation is quickly achieved and quickly passes through the tower plate. The gas phase at the top of the ammonia distillation tower goes out to the ammonia tank through a three-way pipe, reducing the entrainment caused by the wall flow and achieving the separation of the remaining ammonia.

[0023] Step 6: The 3% ammonia concentration mixture at the bottom of the separation tower enters the dehydration tower through pipeline c, and proceeds to the next unit to achieve distillation separation of water and ethanolamine products.

[0024] The present invention has the following beneficial effects:

[0025] The present invention selects a tower structure of reduced pressure flash evaporation plus composite segmentation, which not only reduces the amount of steam consumed for separating ammonia, but also prolongs the service life of the equipment and fully guarantees the separation efficiency.

[0026] By changing the structure of the ammonia evaporation tower, the ammonia separation technology is improved, energy-saving steam is saved, and the equipment life cycle is extended. First, the ammonia evaporation tower is divided into two sections: a flash tank and a distillation tank. The flash tank makes full use of high pressure to flash to remove 75% of the ammonia, and then enters the distillation tank. The distillation tank replaces the original full-body plate type with an upper plate type and a combination of lower wire mesh fillers to increase the gas-liquid contact area, thereby improving the separation efficiency and the equipment life cycle. Because the ammonia content in the upper section of the distillation tank is relatively high, a bidirectional steel plate structure is used, which plays a role in corrosion resistance. The ammonia content in the lower section of the distillation tank is relatively low, and a wire mesh filler is used to improve the separation efficiency and avoid entrainment. The test method in the present invention is simple and efficient, and has good economic effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow chart of the present invention.

[0028] In the figure; 1. distillation tank; 2. flash tank; 3. reactor a; 4. reactor b; 5. pump; 6. reboiler; 7. top cooler; 8. ammonia tank; 9. shell and tube heater; 10. plate tower; 11. wire mesh packing; 12. steam heating pipeline; 13. pipeline a; 14. pipeline b; 15. return air pipe; 16. n-type pipe; 17. tee pipe; 18. entrainment discharge pipe; 19. liquid phase feed pipe; 20. distillation section reflux pipe; 21. pipeline d; 22. pipeline c; 23. dehydration tower; 24. pipeline e; 25. pipeline f. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0030] By modifying the structure of the ammonia evaporation tower, the separation efficiency of the ammonia evaporation tower was improved, the ammonia content of the ammonia evaporation tower was reduced from 5% to 3%, the steam consumption was reduced, and the failure rate of the tower plate float valve was reduced.

[0031] 1. Before the transformation of the ammonia distillation tower:

[0032] Stream description: Stream a before the change: Reactor a3 is depressurized from 6.5MPa(G) to 1.5MPa(G) and enters flash tank 2 for flash evaporation;

[0033] Before the change, stream b: Reactor b4 is depressurized from 6.5MPa(G) to 1.5MPa(G) and enters flash tank 2 for flash evaporation;

[0034] Stream c before the change: the circulation volume from the bottom of the distillation tank 1 to the reboiler 6;

[0035] Stream d before the change: the gas phase from the top of the flash tank 2 to the top cooler 7;

[0036] Stream e before the change: the circulation volume of the distillation tank 1 from the bottom of the tower to the reboiler 6;

[0037] Change the front stream f to discharge the bottom of the distillation tank 1 to the dehydration tower 23.

[0038]

[0039]

[0040] 2. After the transformation of the ammonia distillation tower:

[0041] Stream description: Stream a after modification: reactor a3 is depressurized from 6.5 MPa (G) to 1.5 MPa (G) for flash evaporation; Stream b after modification: reactor b4 is depressurized from 6.5 MPa (G) to 1.5 MPa (G) for flash evaporation;

[0042] New stream: the gas-liquid two-phase flow of the flash tank 2 in the upper section of the ammonia distillation tower passes through the entrainment discharge pipe 18, the n-type pipe 16 and the liquid phase feed pipe 19, the gas phase is discharged upward through the return pipe 15, and the liquid phase flows into the distillation tank 1;

[0043] Rectification tank stream: the gas phase from the top of the rectification tank 12 to the top cooler 7;

[0044] The modified stream d: the gas phase from the top of the flash tank 2 to the top cooler 7;

[0045] Stream e after modification: circulation volume from the bottom of the distillation tank 1 to the reboiler 6;

[0046] Reflux: the circulation volume from reboiler 6 to distillation tank 1;

[0047] The modified stream f is the bottom discharge from the distillation tank 1 to the dehydration tower 23.

[0048]

[0049] A system for separating ammonia, ethanolamine and water comprises an ammonia still, a rectifying tank 1, a flash tank 2, a pump 5, a reboiler 6, a tower top cooler 7 and an ammonia tank 8, wherein the ammonia still comprises a rectifying tank 1 and a flash tank 2, the flash tank 2 is arranged on the rectifying tank 1, and the system is characterized in that: a shell and tube heater 9 is arranged inside the flash tank 2, a reactor a3 and a reactor b4 are arranged on both sides of the flash tank 2, the reactor a3 is connected to the flash tank 2 through a pipeline a13, the reactor b4 is connected to the flash tank 2 through a pipeline b14, and a steam heating pipeline 12 is connected to the shell and tube heater 9;

[0050] A wire mesh filler 11 and a plate tray 10 are arranged inside the distillation tank 1. The bottom of the distillation tank 1 is connected to the dehydration tower 23 through a pipeline c22. The side of the distillation tank 1 is connected to the pump 5 through a pipeline d21. The pump 5 is connected to the reboiler 6 through a pipeline e24. The reboiler 6 is connected to the distillation tank 1 through a distillation section reflux pipe 20. The horizontal position of the distillation section reflux pipe 20 is lower than the horizontal position of the wire mesh filler 11. The tower top cooler 7 is connected to the distillation tank 1 and the flash tank 2 respectively through a tee pipe 17. The tower top cooler 7 is connected to the ammonia tank 8 through a pipeline f25.

[0051] An entrainment discharge pipe 18 is provided on the bottom side of the flash tank 2, and a liquid phase feed pipe 19 is provided on the top side of the distillation tank 1. The entrainment discharge pipe 18 and the liquid phase feed pipe 19 are connected through an n-type pipe 16. A return gas pipe 15 is provided above the n-type pipe 16 to connect with a three-way pipe 17.

[0052] By changing the structure of the ammonia evaporation tower, the ammonia separation technology is improved, energy-saving steam is saved, and the equipment life cycle is extended. First, the ammonia evaporation tower is divided into two sections: distillation tank 1 and flash tank 2. Flash tank 2 makes full use of high pressure to flash to remove 75% of ammonia, and then enters distillation tank 1. The distillation tank 1 replaces the original full-body plate type with a plate tower plate 10 and a combination of wire mesh fillers 11 at the lower end to increase the gas-liquid contact area, thereby improving the separation efficiency and the equipment life cycle. Because the ammonia content in the upper section of the distillation tank 1 is relatively high, a bidirectional steel plate structure is used to play a role in corrosion resistance. The ammonia content in the lower section of the distillation tank 1 is relatively low, and a wire mesh filler 11 is used to improve the separation efficiency and avoid entrainment.

[0053] Stream a enters the ammonia evaporation tower through pipeline a13, stream b enters the ammonia evaporation tower through pipeline b14, and then passes through flash tank 2 to separate about 75% of the ammonia, stream c passes through entrainment discharge pipe 18, n-type tube 16, and liquid phase feed pipe 19 and then enters distillation tank 1 to separate the remaining 25% of the ammonia and is discharged to dehydration tower 23 through stream d through pipeline c22.

[0054] The ammonia distillation tower is divided into two sections: a flash tank 2 and a distillation tank 1. The cylinder of the flash tank 2 is equipped with a shell and tube heater 9. The material flows through the tube side and the low-pressure steam flows through the shell side, which is used to heat the material coming from the reactor a3. After the material coming out of the reactor a3 and the reactor b4 enters the ammonia distillation tower, it passes through a high pressure drop and enters the flash tank 2 at the upper end of the ammonia distillation tower to flash off about 75% of the unreacted ammonia. The remaining 25% of the ammonia enters the distillation tank 1 at the lower end of the ammonia distillation tower, is heated by steam from the reboiler 6, and a gas-liquid exchange is formed on the tower plate 10 and the wire mesh filler 11 to achieve separation, thereby controlling the ammonia component in the material of the ammonia distillation tower to about 3%.

[0055] Step 1: The mixed product of ammonia, water and ethanolamine passes through the reactor a3 and enters the flash tank 2 of the ammonia distillation tower under reduced pressure to achieve reduced pressure flash evaporation. The mixed product of ammonia, water and ethanolamine passes through the reactor b4 and enters the flash tank 2 of the ammonia distillation tower under reduced pressure to achieve reduced pressure flash evaporation.

[0056] Step 2: The mixed stream after the reduced pressure flash is further heated by low-pressure steam for thermal separation by the heater 9 in the flash tank 2 at the top of the ammonia distillation tower. In this step, the heater 9 of the flash tank 2 is kept in a liquid-sealed state through the design of the entrainment discharge pipe 18, the n-type pipe 16, and the liquid phase feed pipe 19 to reduce heat loss and ensure that the dry pipe of the heater 9 is not burned dry to damage the heater 9;

[0057] Step 3: gas-liquid separation is simultaneously achieved through the entrainment discharge pipe 18, the n-type pipe 16, and the liquid phase feed pipe 19, the gas phase goes out from the top of the n-type pipe 16, and the liquid phase flows downstream to the lower distillation tank 1 of the ammonia distillation tower;

[0058] Step 4: The distillation tank 1 adopts a tower internals method of combining a tower plate 10 and a wire mesh filler 11 layers to realize the gas-liquid heat exchange space of the distillation, which not only increases the gas-liquid exchange area, but also improves the corrosion resistance of the tower internals, reduces energy consumption, and ensures the long-term operation of the tower;

[0059] Step 5: The bottom reboiler 6 is provided in the lower distillation tank 1 of the ammonia distillation tower. Under the action of the wire mesh packing 11 of the internal parts of the ammonia distillation tower, ammonia separation is achieved quickly and quickly passes through the tower plate 10. The gas phase at the top of the ammonia distillation tower is discharged to the ammonia tank 8 through the three-way pipe 17, reducing the entrainment caused by the wall flow and achieving the separation of the remaining ammonia;

[0060] Step 6: The 3% ammonia concentration mixture at the bottom of the separation tower enters the dehydration tower 23 through pipeline c22, and proceeds to the next unit to achieve distillation separation of water and ethanolamine products.

[0061] By modifying the structure of the ammonia evaporation tower, the separation efficiency of the ammonia evaporation tower was improved, the ammonia content of the ammonia evaporation tower was reduced from 5% to 3%, the steam consumption was reduced, and the failure rate of the tower plate float valve was reduced.

[0062] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A system for separating ammonia, ethanolamine and water, comprising an ammonia still, a rectifying tank, a flash tank, a pump, a reboiler, a tower top cooler and an ammonia tank, wherein the ammonia still comprises a rectifying tank and a flash tank, and a flash tank is arranged on the rectifying tank, characterized in that: A shell and tube heater is arranged inside the flash tank, reactor a and reactor b are arranged on both sides of the flash tank respectively, reactor a is connected with the flash tank through pipeline a, reactor b is connected with the flash tank through pipeline b, and the steam heating pipeline is connected with the shell and tube heater; A wire mesh packing and a plate-type tower plate are arranged inside the distillation tank. The bottom of the distillation tank is connected to the dehydration tower through a pipeline c. The side of the distillation tank is connected to the pump through a pipeline d. The pump and the reboiler are connected through a pipeline e. The reboiler is connected to the distillation tank through a distillation section reflux pipe. The horizontal level of the distillation section reflux pipe is lower than the horizontal level of the wire mesh packing. The tower top cooler is connected to the distillation tank and the flash tank respectively through a tee pipe. The tower top cooler is connected to the ammonia tank through a pipeline f. An entrainment discharge pipe is arranged on the bottom side of the flash tank, a liquid phase feed pipe is arranged on the top side of the distillation tank, the entrainment discharge pipe and the liquid phase feed pipe are connected through an n-type pipe, and a return air pipe is arranged above the n-type pipe to be connected with the three-way pipe.

2. A method for separating ammonia, ethanolamine and water according to claim 1, characterized in that: The following steps are involved: Step 1: The mixed product of ammonia, water and ethanolamine passes through reactor a, is decompressed and enters the flash tank of the ammonia distillation tower to achieve reduced pressure flash evaporation; the mixed product of ammonia, water and ethanolamine passes through reactor b, is decompressed and enters the flash tank of the ammonia distillation tower to achieve reduced pressure flash evaporation; Step 2: The mixed stream after the reduced pressure flash is further heated by low-pressure steam for thermal separation through the heater in the flash tank at the top of the ammonia tower. In this step, the flash tank heater is kept in a liquid-sealed state through the design of the entrainment discharge pipe, n-type pipe, and liquid phase feed pipe to reduce heat loss and ensure that the dry pipe of the heater is not damaged by dry burning; Step 3: The gas-liquid separation is realized simultaneously through the entrainment discharge pipe, the n-type pipe, and the liquid phase feed pipe. The gas phase goes out from the top of the n-type pipe, and the liquid phase flows downstream to the lower distillation tank of the ammonia distillation tower; Step 4: The distillation tank adopts a tower internals method of combining tower plates and wire mesh packing layers to realize the gas-liquid heat exchange space of the distillation, which not only increases the gas-liquid exchange area, but also improves the corrosion resistance of the tower internals, reduces energy consumption, and ensures the long-term operation of the tower; Step 5: A bottom reboiler is provided in the lower distillation tank of the ammonia distillation tower. Under the action of the wire mesh packing of the internal parts of the ammonia distillation tower, ammonia separation is achieved quickly and passes through the tower plate quickly. The gas phase at the top of the ammonia distillation tower is discharged to the ammonia tank through a three-way pipe, reducing the entrainment caused by the wall flow and achieving the separation of the remaining ammonia. Step 6: The 3% ammonia concentration mixture at the bottom of the separation tower enters the dehydration tower through pipeline c, and proceeds to the next unit to achieve distillation separation of water and ethanolamine products.

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