Polyester esterification water treatment method

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly relates to a polyester esterification water treatment method which comprises the following steps: conveying esterification steam to a steam generator set, and exhausting and emptying the steam generator set by adopting a screw vacuum pump to obtain power generation tail gas and power generation condensation esterification water; the power generation tail gas is conveyed to a 2-MD decomposition tank for decomposition, acetaldehyde-containing gas is discharged from the top of the 2-MD decomposition tank, and ethylene glycol-containing liquid is discharged from the bottom of the 2-MD decomposition tank; the power generation condensation esterification water is conveyed to a stripping tower, is discharged from the bottom of the stripping tower after being subjected to stripping, and is discharged after being subjected to sewage treatment. According to the invention, the COD value of the esterified water before entering the stripping tower can be reduced to about 6000 ppm, the subsequent treatment pressure of the esterified water is greatly reduced, and the environmental protection pressure is relieved; the 2-MD in the power generation tail gas can be decomposed into acetaldehyde and ethylene glycol in the 2-MD decomposition tank, gas-phase acetaldehyde and liquid-phase ethylene glycol are separated, and ethylene glycol can be recycled to a process tower, so that the consumption of raw materials is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a polyester esterification water treatment method. Background Art

[0002] Polyethylene terephthalate (PET for short) is made by first esterifying purified terephthalic acid (PTA) and ethylene glycol (EG) to synthesize dihydroxyethyl terephthalate, and then polycondensing it. It is a crystalline saturated polyester, a milky white or light yellow, highly crystalline polymer with a smooth and shiny surface. It is widely used in textiles, packaging, electronics, electrical appliances, medical equipment, construction and other fields. In the polyester production process, esterification reaction is one of the key steps, and the treatment of esterification water is an indispensable part of the process. Traditional esterification water treatment processes include direct cold air discharge, slurry heat exchange discharge, hot water lithium bromide refrigerator heat exchange, and the current mainstream esterification steam power generation.

[0003] In the esterification steam power generation process, the liquid ring vacuum pump system is used as a means of vacuuming. Under certain conditions, it has high vacuum and high power generation. However, the liquid ring vacuum pump system currently involves several problems: First, it needs cooling water for refrigeration; in practice, it is found that the water temperature of the working fluid of the liquid ring vacuum pump is related to the power generation, so a series of refrigeration equipment should be added to reduce the temperature of the working fluid of the liquid ring vacuum pump. Therefore, its daily operation cost is high and the power generation will decrease significantly in summer. Second, the COD content of the esterified water in the liquid ring vacuum pump system is much higher than the COD content of the esterified water in the condenser, which indicates that a large amount of organic gas enters the esterified water in the liquid ring vacuum pump link. Moreover, the esterified water has a high content of 2-methyl-1,3-dioxolane (2-MD), which decomposes into EG and acetaldehyde, resulting in an increase in the EG content, which brings great pressure to subsequent treatment and may even cause environmental accidents.

[0004] Therefore, it is necessary to optimize the treatment process of esterification water in the polyester production process. Summary of the invention

[0005] The present invention aims to provide a polyester esterification water treatment method to solve the problems of high energy consumption and high COD value in the existing esterification water treatment process.

[0006] In order to achieve the above object, the scheme of the present invention is: a polyester esterification water treatment method, comprising the following steps:

[0007] S1. Steam power generation: The esterification steam is transported to the steam generator set, and the steam generator set is evacuated and emptied by a screw vacuum pump to obtain power generation tail gas and power generation condensed esterification water;

[0008] S2. Power generation tail gas treatment: The power generation tail gas is transported to the 2-MD decomposition tank for decomposition. The top of the 2-MD decomposition tank discharges gas containing acetaldehyde, and the bottom of the 2-MD decomposition tank discharges liquid containing ethylene glycol;

[0009] S3. Treatment of condensed esterified water from power generation: The condensed esterified water from power generation is transported to a stripping tower, and is discharged from the bottom of the stripping tower after stripping, and then discharged after sewage treatment.

[0010] The working principle and beneficial effects of this solution are as follows: In this solution, a screw vacuum pump is used to replace a liquid ring vacuum pump, and the power of the screw vacuum pump is selected to be larger, and a frequency converter is added to adjust the frequency of the screw vacuum pump under different loads to achieve energy saving. Moreover, the screw vacuum pump is little affected by the ambient temperature, which can ensure the power generation of the steam generator set.

[0011] Secondly, in this scheme, esterified water is only produced in the condenser of the steam generator set, and the COD value of the esterified water is only 6000-7000ppm. After treatment in the stripping tower, the COD value can be reduced to about 2000ppm, and then after sewage treatment, the COD value can be reduced to below 50. The COD value of the esterified water under the liquid ring vacuum pump system is 35000ppm before entering the stripping tower, which is reduced to 4000ppm after treatment in the stripping tower, and then reduced to below 50ppm after sewage treatment. It can be seen that this scheme significantly reduces the COD value of esterified water, greatly reduces the pressure of subsequent treatment of esterified water, and thus reduces environmental pressure.

[0012] Furthermore, in this scheme, the power generation tail gas enters the 2-MD decomposition tank for decomposition to obtain ethylene glycol and acetaldehyde, and the separation of ethylene glycol and acetaldehyde is achieved, thereby realizing the recovery of ethylene glycol and acetaldehyde. As one of the raw materials for the esterification reaction, ethylene glycol can be returned to the process tower after slurry preparation, thereby reducing raw material consumption and reducing production costs. In addition, acetaldehyde can directly enter the distillation tower without going through the stripping process. Moreover, in this scheme, the COD value of the esterified water is low, which means that the content of organic matter in the esterified water is low, proving that the recovery efficiency of EG in this scheme is high and the waste rate of EG is low.

[0013] Moreover, in this solution, the power generation tail gas directly enters the 2-MD decomposition tank, while the conventional method is to use solvent to capture the power generation tail gas, and then send the captured solvent into the device for decomposition. The 2-MD decomposition tank used in this solution concentrates the capture and decomposition of the power generation tail gas, and the separation of the gas phase and liquid in the tank, realizing the efficient recycling of 2-MD.

[0014] Optionally, in step S1, chilled water is taken by a refrigeration machine, and the chilled water is used as circulating cooling water for a condenser of a steam generator set.

[0015] In this solution, the traditional water tower structure is abandoned to cool the condenser of the steam generator set by heat exchange, and chilled water is used for heat exchange and cooling, thereby effectively reducing the condenser water temperature and improving the cooling efficiency. In addition, the water tower structure has a large amount of evaporated water and high water consumption. Using a refrigeration mechanism to extract chilled water as circulating cooling water for the condenser can effectively reduce water consumption.

[0016] Optionally, in step S2, the acetaldehyde-containing gas discharged from the top of the 2-MD decomposition tank enters a distillation tower to obtain high-purity acetaldehyde.

[0017] In this scheme, acetaldehyde directly enters the distillation tower to obtain high-purity acetaldehyde without going through a stripping process.

[0018] Optionally, in step S2, the 2-MD decomposition tank includes a tank body, a partition I and a partition II are provided inside the tank body, the partition I and the partition II divide the internal space of the tank body into a decomposition chamber, a separation chamber and a drainage chamber, the tops of the decomposition chamber, the separation chamber and the drainage chamber are connected, a heater for heating the liquid, a temperature sensor I for detecting the temperature of the liquid and a pH sensor for detecting the pH value of the liquid are provided in the decomposition chamber, the decomposition chamber is connected with an air inlet pipe I, a liquid inlet pipe I and a liquid inlet pipe II, one end of the air inlet pipe I located in the decomposition chamber is submerged below the liquid surface, and a first valve is installed on both the liquid inlet pipe I and the liquid inlet pipe II; a stirring shaft is provided in the separation chamber, a stirring blade is fixedly connected to the stirring shaft, a motor for driving the stirring shaft to rotate is provided outside the tank body, a gas discharge pipe is connected to the top of the separation chamber; a drainage pipe is connected to the bottom of the drainage chamber, and a second valve is installed on the drainage pipe.

[0019] In this scheme, liquid (the source of the liquid can be condensed esterified water from power generation or desalted water) is added to the decomposition chamber through the liquid inlet pipe I to ensure that the liquid level in the tank is maintained within a certain range. The power generation tail gas enters the decomposition chamber below the liquid level through the gas inlet pipe I, and the heat carried by the power generation tail gas is absorbed by the liquid, thereby utilizing the heat of the power generation tail gas; in the decomposition chamber, 2-MD in the power generation tail gas undergoes decomposition reaction under decomposition conditions (pH value 1.5-2.5, temperature 85-88°C) to generate ethylene glycol and acetaldehyde; after the liquid enters the separation chamber, it is stirred by the stirring blade, and stirring forms a micro-negative pressure environment in the liquid, so that the acetaldehyde in the liquid can be better separated under stirring, and the acetaldehyde and non-condensable gas are discharged through the gas discharge pipe; the liquid continues to enter the discharge chamber, and the liquid in the discharge chamber is an ethylene glycol aqueous solution, which can be discharged through the discharge pipe. In this way, the capture and decomposition of power generation exhaust gas and the separation of gas and liquid can be concentrated in the tank body, and the pH value of the liquid in the decomposition chamber is detected by a pH sensor, and a pH regulator is added to the decomposition chamber through the liquid inlet pipe II to ensure that the pH value of the liquid in the decomposition chamber is maintained at 1.5-2.5; the temperature of the liquid in the decomposition chamber is detected by a temperature sensor, and the temperature of the liquid is maintained at 85-88°C by a heater to ensure that suitable decomposition conditions of 2-MD are maintained in the tank body.

[0020] Optionally, the gas discharge pipe includes a discharge section I and a discharge section II, a condensation reflux chamber is provided between the discharge section I and the discharge section II, a cooling jacket is provided outside the condensation reflux chamber, the bottom end of the discharge section I is connected to the separation chamber, the top end of the discharge section I has a downward folded portion, and the folded portion at the top end of the discharge section I is connected to the bottom of the condensation reflux chamber, and the discharge section II is connected to the top end of the condensation reflux chamber; the bottom end of the condensation reflux chamber is connected to a reflux pipe, and the end of the reflux pipe away from the condensation reflux chamber is connected to the top of the decomposition chamber.

[0021] When acetaldehyde and non-condensable gas are discharged, they will carry gaseous ethylene glycol and 2-MD. To prevent ethylene glycol and 2-MD from escaping, in this scheme, a condensation reflux chamber is designed between the discharge section I and the discharge section II. The discharged gas is cooled by a cooling jacket to reduce its temperature to 20-30°C, so that the gaseous ethylene glycol and 2-MD are condensed into liquid and refluxed into the decomposition chamber through the reflux pipe. In the above process, the folded portion at the top of the discharge section I can effectively prevent the liquid from flowing into the discharge section I.

[0022] Optionally, a temperature sensor II for detecting temperature is provided on the top of the condensation reflux chamber.

[0023] In this scheme, a temperature sensor is used to detect the temperature at the top of the condensation reflux chamber to ensure that the temperature of the gas has dropped to 20-30°C before entering the discharge section II, thereby ensuring that ethylene glycol and 2-MD will not escape.

[0024] Optionally, a gas collecting hopper is fixedly connected to the bottom end of the gas exhaust pipe, a closed gas collecting cavity is formed between the gas collecting hopper and the top wall of the tank body, a gas exhaust port is opened on the top wall of the tank body, and the gas exhaust port is located within the coverage of the gas collecting hopper.

[0025] In this solution, the design of the gas collecting hopper increases the number of gas discharge ports, thereby increasing the amount of gas in the tank that flows out per unit time.

[0026] Optionally, an explosion-proof fan I is installed on the discharge section II, and a pressure sensor for detecting air pressure is provided in the air collecting hopper.

[0027] In this scheme, the air pressure in the gas collecting hopper is detected by a pressure sensor, and the gas displacement is controlled by explosion-proof fan I, so that the air pressure in the gas collecting hopper is controlled at 1-8 kPa, avoiding untimely condensation in the condensation reflux chamber due to excessive gas displacement.

[0028] Optionally, the tank body is provided with a liquid level meter for detecting the liquid level height in the decomposition chamber.

[0029] In this solution, a liquid level meter is used to detect the liquid level in the decomposition chamber so that the staff can grasp the liquid level in the decomposition chamber and add liquid to the decomposition chamber in time or speed up the discharge of liquid in the drainage chamber to keep the liquid level in the decomposition chamber within an appropriate range.

[0030] Optionally, the decomposition chamber is also connected to an air inlet pipe II, on which an explosion-proof fan II is installed, and one end of the air inlet pipe II located in the decomposition chamber is submerged below the liquid surface.

[0031] In this scheme, the air inlet pipe II can allow other process tail gas containing 2-MD to enter the decomposition chamber for decomposition reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic flow diagram of a polyester esterification water treatment method in Example 1 of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the 2-MD decomposition tank used in Example 1 of the present invention;

[0034] Figure 3 It is a schematic diagram of the process of esterification water treatment based on liquid ring vacuum pump system;

[0035] Figure 4 This is a schematic flow diagram of a polyester esterification water treatment method in Example 2 of the present invention;

[0036] Figure 5 This is a schematic diagram of the structure of the 2-MD decomposition tank used in Example 2 of the present invention. DETAILED DESCRIPTION

[0037] The following is further described in detail through specific implementation methods:

[0038] The marks in the drawings of the specification include: tank body 1, decomposition chamber 101, separation chamber 102, drainage chamber 103, partition I2, partition II3, heater 4, temperature sensor I5, pH sensor 6, liquid level meter 7, air inlet pipe I8, liquid inlet pipe I9, liquid inlet pipe II10, first valve 11, stirring shaft 12, stirring blade 13, motor 14, gas discharge pipe 15, discharge section I151, return portion 15101, discharge section II152, condensation reflux chamber 16, cooling jacket 17, gas collecting hopper 18, gas discharge port 19, reflux pipe 20, temperature sensor II21, drainage pipe 22, second valve 23, flow meter 24, controller 25, explosion-proof fan I26, pressure sensor 27, air inlet pipe II28, explosion-proof fan II29.

[0039] Example 1

[0040] This embodiment provides a polyester esterification water treatment method, the process is basically as follows Figure 1As shown, the processing method includes the following steps:

[0041] 1) Steam power generation: The esterification steam is transported to the steam generator set, and the steam generator set is evacuated and emptied by a screw vacuum pump to obtain power generation tail gas and power generation condensed esterification water. In this step, chilled water is taken by a refrigeration mechanism, and the chilled water is used as circulating cooling water for the condenser of the steam generator set to reduce the temperature of the condenser.

[0042] 2) Treatment of power generation tail gas: The power generation tail gas is transported to the 2-MD decomposition tank for decomposition. The gas containing acetaldehyde is discharged from the top of the 2-MD decomposition tank, and the liquid containing ethylene glycol is discharged from the bottom of the 2-MD decomposition tank. The acetaldehyde-containing gas discharged from the top of the 2-MD decomposition tank enters the distillation tower to obtain high-purity acetaldehyde; the ethylene glycol-containing liquid discharged from the bottom of the 2-MD decomposition tank returns to the process tower after slurry preparation, realizing the recycling of ethylene glycol and reducing raw material consumption.

[0043] 3) Treatment of condensed esterified water from power generation: The condensed esterified water from power generation is transported to a water storage tank for storage, and then transported to a stripping tower. The condensed esterified water from power generation is discharged from the bottom of the stripping tower after stripping, and then discharged after sewage treatment; and the gas phase of the stripping tower is burned and discharged. In this step, the COD value of the condensed esterified water from power generation is 6000-7000ppm.

[0044] The 2-MD decomposition tank used in step 2) above has a structure as follows: Figure 2 As shown, it includes a tank body 1, in which a partition Ⅰ2 and a partition Ⅱ3 are arranged. The partition Ⅰ2 and the partition Ⅱ3 divide the internal space of the tank body 1 into a decomposition chamber 101, a separation chamber 102 and a drainage chamber 103. The tops of the decomposition chamber 101, the separation chamber 102 and the drainage chamber 103 are connected.

[0045] The decomposition chamber 101 is provided with a heater 4 for heating the liquid, a temperature sensor I5 for detecting the temperature of the liquid, and a pH sensor 6 for detecting the pH value of the liquid. The tank body 1 is provided with a liquid level gauge 7 for detecting the height of the liquid level in the decomposition chamber 101. The decomposition chamber 101 is connected with an air inlet pipe I8, a liquid inlet pipe I9, and a liquid inlet pipe II10. One end of the air inlet pipe I8 located in the decomposition chamber 101 is submerged below the liquid surface. In this embodiment, the outlet port of the air inlet pipe I8 is submerged below the liquid surface by 5 cm. The first valve 11 is installed on the liquid inlet pipe I9 and the liquid inlet pipe II10. In this embodiment, the air inlet pipe I8 supplies the power generation tail gas into the decomposition chamber 101, the liquid inlet pipe I9 supplies the deionized water into the decomposition chamber 101, and the liquid inlet pipe II10 supplies the pH regulating liquid (the pH regulating liquid in this embodiment is a phosphoric acid solution) into the decomposition chamber 101. In addition, the heater 4 is an electric heating pipe. In another embodiment, the heater 4 can be selected as a heat exchange pipe, so that the liquid in the decomposition chamber 101 is heated by a heat medium.

[0046] A stirring shaft 12 is provided in the separation chamber 102, and a stirring blade 13 is fixedly connected to the stirring shaft 12, and the stirring blade 13 is in a cross-shaped shape. A motor 14 for driving the stirring shaft 12 to rotate is provided outside the tank body 1. A gas discharge pipe 15 is connected to the top of the separation chamber 102. Specifically, the gas discharge pipe 15 includes a discharge section I 151 and a discharge section II 152. A condensation reflux chamber 16 is provided between the discharge section I 151 and the discharge section II 152. A cooling jacket 17 is provided outside the condensation reflux chamber 16. A gas collecting hopper 18 is welded to the bottom end of the discharge section I 151, and the discharge section I 151 is connected to the inside of the gas collecting hopper 18. A closed gas collecting chamber is formed between the gas collecting hopper 18 and the top wall of the tank body 1. A gas discharge port 19 is provided on the top wall of the tank body 1. The discharge port 19 is located within the coverage of the gas collecting hopper 18; the top of the discharge section Ⅰ151 has a downward bend 15101, and the bend 15101 at the top of the discharge section Ⅰ151 is connected to the bottom of the condensation reflux chamber 16; the discharge section Ⅱ152 is connected to the top of the condensation reflux chamber 16, and the bottom of the condensation reflux chamber 16 is connected to a reflux pipe 20, and the end of the reflux pipe 20 away from the condensation reflux chamber 16 is connected to the top of the decomposition chamber 101; a temperature sensor Ⅱ21 for detecting temperature is provided at the top of the condensation reflux chamber 16.

[0047] The bottom of the liquid discharge chamber 103 is connected with a liquid discharge pipe 22, and a second valve 23 and a flow meter 24 are installed on the liquid discharge pipe 22. A controller 25 is provided outside the tank body 1, and the temperature sensor I5, the pH sensor 6, the liquid level meter 7 and the temperature sensor II21 are all electrically connected to the controller 25. The controller 25 controls the heater 4 to work according to the signal transmitted by the temperature sensor I5, thereby controlling the temperature of the liquid in the decomposition chamber 101 to be 85-88°C; the controller 25 controls the opening of the first valve 11 on the liquid inlet pipe II10 according to the signal transmitted by the pH sensor 6, thereby controlling the pH value of the liquid in the decomposition chamber 101 to be 1.5-2.5; the controller 25 controls the opening of the first valve 11 on the liquid inlet pipe I9 and the second valve 23 on the liquid discharge pipe 22 according to the signal transmitted by the liquid level, thereby controlling the liquid height in the decomposition chamber 101 to be within a suitable range; the controller 25 controls the flow of cooling water in the cooling jacket 17 according to the signal transmitted by the temperature sensor II21, thereby controlling the temperature at the top of the reflux condensation chamber to be 20-30°C. In this embodiment, the controller 25 is a PLC.

[0048] When used specifically, the power generation exhaust gas in step 1) enters the decomposition chamber 101 through the air inlet pipe Ⅰ8 and is fully in contact with the liquid in the decomposition chamber 101. Under the conditions of a temperature of 85 to 88°C and a pH value of 1.5 to 2.5, the 2-MD in the power generation exhaust gas undergoes a decomposition reaction and is decomposed into ethylene glycol and acetaldehyde. Since acetaldehyde has a low boiling point and is in a gaseous state at 85 to 88°C, and the boiling point of ethylene glycol is much higher than 88°C, ethylene glycol remains in the liquid.

[0049] Next, the liquid in the decomposition chamber 101 flows into the separation chamber 102, and the motor 14 is started. The motor 14 drives the stirring shaft 12 to rotate, so that the stirring blade 13 stirs the liquid; under the stirring of the stirring blade 13, the liquid in the separation chamber 102 flows more, so that a micro-negative pressure environment is formed in the liquid, so that the acetaldehyde can be better separated. The acetaldehyde in the tank body 1 enters the gas collecting hopper 18 through the gas discharge port 19 on the top wall of the separation chamber 102, and then is discharged through the discharge section I 151, the condensation reflux chamber 16 and the discharge section II 152. During the gas discharge process, the gas contains volatile ethylene glycol and 2-MD. When the volatile ethylene glycol and 2-MD pass through the condensation reflux chamber 16, they lose heat and condense into liquid. The liquid ethylene glycol and 2-MD flow downward along the inner wall of the condensation reflux chamber 16 and flow into the decomposition chamber 101 through the reflux pipe 20 to prevent the ethylene glycol and 2-MD from escaping, and the unreacted 2-MD is sent back to the decomposition chamber 101 for further reaction. In this process, since the top of the discharge section I 151 has a downward folded portion 15101, the condensate in the condensation reflux chamber 16 will not enter the discharge section I 151. In this way, the gas discharged through the gas discharge pipe 15 is acetaldehyde and non-condensable gas. Finally, the liquid in the separation chamber 102 flows into the drainage chamber 103 and is discharged through the drainage pipe 22. The discharged liquid is an ethylene glycol solution, and its ethylene glycol content is about 40%.

[0050] In the above process, the temperature sensor Ⅰ5 detects the temperature of the liquid in the decomposition chamber 101 in real time. When the temperature is lower than 85°C, the controller 25 controls the heater 4 to work, heats the liquid in the decomposition chamber 101, and makes the temperature of the liquid rise; when the temperature of the liquid is higher than 88°C, the controller 25 controls the heater 4 to stop working, thereby controlling the temperature of the liquid to be maintained at 85-88°C. The pH sensor 6 detects the pH value of the liquid in the decomposition chamber 101 in real time. When the pH value is higher than 2.5, the controller 25 controls the first valve 11 on the liquid inlet pipe Ⅱ10 to open, and the pH regulating liquid (phosphoric acid solution) flows into the decomposition chamber 101, thereby reducing the pH value of the liquid; when the pH value is lower than 1.5, the controller 25 controls the first valve 11 on the liquid inlet pipe Ⅱ10 to close, thereby controlling the pH value of the liquid to be maintained at 1.5-2.5. The liquid level meter 7 detects the liquid level in the decomposition chamber 101 in real time. When the liquid level in the decomposition chamber 101 is too high, the controller 25 controls the first valve 11 on the liquid inlet pipe Ⅰ9 to be closed and / or controls the second valve 23 on the liquid discharge pipe 22 to be opened, so that the liquid level of the liquid decreases; when the liquid level in the decomposition chamber 101 is too low, the controller 25 controls the first valve 11 on the liquid inlet pipe Ⅰ9 to be opened and / or controls the second valve 23 on the liquid discharge pipe 22 to be closed, so that the liquid level of the liquid increases, thereby controlling the liquid level in the decomposition chamber 101 to be within a suitable range. In addition, during this process, the staff can grasp the displacement of the liquid discharge pipe 22 through the flow meter 24 to ensure that the displacement of the liquid discharge pipe 22 is stable within a certain range. The temperature sensor II 21 detects the temperature at the top of the condensation reflux chamber 16 in real time. When the temperature is higher than 30°C, the controller 25 controls the cooling water flow in the cooling jacket 17 to increase, thereby reducing the temperature; when the temperature is lower than 20°C, the controller controls the cooling water flow in the cooling jacket 17 to decrease, thereby controlling the temperature at the top of the condensation reflux chamber 16 to remain at 20-30°C.

[0051] Thus, the power generation tail gas in step 1) enters the decomposition chamber 101 through the air inlet pipe Ⅰ8, and the 2-MD in the power generation tail gas is decomposed into acetaldehyde and ethylene glycol, and the gas containing acetaldehyde is discharged from the gas discharge pipe 15, and the liquid containing ethylene glycol is discharged from the liquid discharge pipe 22. In addition, in this embodiment, the pH regulating liquid used to adjust the pH value of the liquid in the decomposition chamber 101 is a phosphoric acid solution, because phosphoric acid or phosphate ester is added as an auxiliary material in the polyester production process. Therefore, when the ethylene glycol obtained in step 2) is recycled, the amount of auxiliary material added is calculated according to the ethylene glycol recycling flow rate and the content of phosphoric acid in the ethylene glycol, thereby avoiding the use of additional acidic reagents.

[0052] In addition, the process of esterification water treatment based on liquid ring vacuum pump system is basically as follows Figure 3As shown, in this process, the COD value of the esterified water entering the stripping tower is 35000ppm. In this embodiment, the COD value of the esterified water entering the stripping tower is only 6000-7000ppm, which effectively reduces the subsequent treatment pressure of the esterified water, thereby alleviating the environmental pressure.

[0053] Example 2

[0054] The difference between this embodiment and embodiment 1 is that: Figure 4 and Figure 5 As shown, in this embodiment, an explosion-proof fan I26 is installed on the discharge section II152, and a pressure sensor 27 for detecting air pressure is provided in the gas collecting hopper 18. The pressure sensor 27 is electrically connected to the controller 25, and the controller 25 controls the operation of the explosion-proof fan I26 according to the signal transmitted by the pressure sensor 27. In addition, the decomposition chamber 101 is connected to the air inlet pipe II28, and an explosion-proof fan II29 is installed on the air inlet pipe II28. One end of the air inlet pipe II28 located in the decomposition chamber 101 is submerged below the liquid surface. In this embodiment, the outlet port of the air inlet pipe II28 is submerged below the liquid surface by 5 cm.

[0055] In this embodiment, under the air supply of the explosion-proof fan II 29, other process tail gas containing 2-MD generated in the polyester production process can enter the decomposition chamber 101 through the air inlet pipe II 28, so that the 2-MD in the process tail gas can be recycled. In addition, the pressure sensor 27 is used to detect the air pressure in the gas collecting hopper 18 in real time. When the air pressure is lower than 1 kPa, the controller 25 controls the speed of the explosion-proof fan I 26 to decrease, so that the air pressure in the gas collecting hopper 18 increases; when the air pressure in the gas collecting hopper 18 is higher than 8 kPa, the controller 25 controls the speed of the explosion-proof fan I 26 to increase, so that the air pressure in the gas collecting hopper 18 decreases, thereby controlling the air pressure in the gas collecting hopper 18 to maintain at 1 to 8 kPa, thereby controlling the discharge flow of acetaldehyde and non-condensable gas, and maintaining a slight positive pressure in the gas collecting hopper 18.

[0056] The above are only embodiments of the present invention. The invention is not limited to the fields involved in this implementation case. The common sense such as the known specific structures and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field to which the invention belongs before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the present invention. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to explain the content of the claims.

Claims

1. A polyester esterification water treatment method, characterized in that: The following steps are involved: S1. Steam power generation: The esterification steam is transported to the steam generator set, and the steam generator set is evacuated and emptied by a screw vacuum pump to obtain power generation tail gas and power generation condensed esterification water; S2. Power generation tail gas treatment: The power generation tail gas is transported to the 2-MD decomposition tank for decomposition. The top of the 2-MD decomposition tank discharges gas containing acetaldehyde, and the bottom of the 2-MD decomposition tank discharges liquid containing ethylene glycol; S3. Treatment of condensed esterified water from power generation: The condensed esterified water from power generation is transported to a stripping tower, and is discharged from the bottom of the stripping tower after stripping, and then discharged after sewage treatment.

2. The polyester esterification water treatment method according to claim 1, characterized in that: In step S1, chilled water is taken by a refrigeration machine and used as circulating cooling water for a condenser of a steam generator set.

3. The polyester esterification water treatment method according to claim 1, characterized in that: In step S2, the acetaldehyde-containing gas discharged from the top of the 2-MD decomposition tank enters a distillation tower to obtain high-purity acetaldehyde.

4. The polyester esterification water treatment method according to claim 1, characterized in that: In step S2, the 2-MD decomposition tank includes a tank body, a partition I and a partition II are arranged inside the tank body, and the partition I and the partition II divide the internal space of the tank body into a decomposition chamber, a separation chamber and a drainage chamber. The tops of the decomposition chamber, the separation chamber and the drainage chamber are connected. A heater for heating the liquid, a temperature sensor I for detecting the temperature of the liquid and a pH sensor for detecting the pH value of the liquid are arranged in the decomposition chamber. The decomposition chamber is connected with an air inlet pipe I, a liquid inlet pipe I and a liquid inlet pipe II. One end of the air inlet pipe I located in the decomposition chamber is submerged below the liquid surface. The first valve is installed on the liquid inlet pipe I and the liquid inlet pipe II; a stirring shaft is arranged in the separation chamber, and a stirring blade is fixedly connected to the stirring shaft. A motor for driving the stirring shaft to rotate is arranged outside the tank body. The top of the separation chamber is connected with a gas discharge pipe; the bottom of the drainage chamber is connected with a drainage pipe, and the second valve is installed on the drainage pipe.

5. The polyester esterification water treatment method according to claim 4, characterized in that: The gas discharge pipe includes a discharge section I and a discharge section II, a condensation reflux chamber is provided between the discharge section I and the discharge section II, a cooling jacket is provided outside the condensation reflux chamber, the bottom end of the discharge section I is connected to the separation chamber, the top end of the discharge section I has a downward folded portion, and the folded portion at the top end of the discharge section I is connected to the bottom of the condensation reflux chamber, and the discharge section II is connected to the top end of the condensation reflux chamber; the bottom end of the condensation reflux chamber is connected to a reflux pipe, and the end of the reflux pipe away from the condensation reflux chamber is connected to the top of the decomposition chamber.

6. The polyester esterification water treatment method according to claim 5, characterized in that: A temperature sensor II for detecting temperature is provided on the top of the condensation reflux chamber.

7. The polyester esterification water treatment method according to claim 5, characterized in that: The bottom end of the gas discharge pipe is fixedly connected with a gas collecting hopper, and a closed gas collecting cavity is formed between the gas collecting hopper and the top wall of the tank body. The top wall of the tank body is provided with a gas discharge port, and the gas discharge port is located within the coverage of the gas collecting hopper.

8. The polyester esterification water treatment method according to claim 7, characterized in that: An explosion-proof fan I is installed on the discharge section II, and a pressure sensor for detecting air pressure is provided in the air collecting hopper.

9. The polyester esterification water treatment method according to claim 4, characterized in that: The tank body is provided with a liquid level meter for detecting the liquid level height in the decomposition chamber.

10. The polyester esterification water treatment method according to claim 4, characterized in that: The decomposition chamber is also connected with an air inlet pipe II, on which an explosion-proof fan II is installed, and one end of the air inlet pipe II located in the decomposition chamber is submerged below the liquid surface.

Images