Vacuum system for a ptc intermittent production plant

Abstract

The utility model discloses a kind of vacuum systems of PCTG intermittent production device, including sequentially connected polycondensation condenser, cyclone separator, cold trap, vertical sprayer and vacuum pump group;Process steam enters polycondensation condenser, the upper air inlet of cyclone separator is connected with the top outlet of polycondensation condenser, and its top exhaust port is connected with cold trap inlet;The liquid discharge of polycondensation condenser, cyclone separator enters condensate collection tank, and cold trap shell side is connected with refrigeration or heating medium;The upper air inlet of vertical sprayer is connected with the top outlet of cold trap, and its inside is equipped with spraying inner cylinder and two-stage spraying EG nozzle, and its bottom outlet is connected with condensate receiving groove;The overflow of condensate receiving groove is connected with vertical sprayer EG nozzle through condensate pump, plate heat exchanger and EG spraying pipe, and constitutes circulation loop;The inlet of vacuum pump group is connected with the exhaust port of vertical sprayer.This system can ensure that vacuum pump operates stably, maintain product index stability, reduce waste liquid generation and reduce energy consumption.

Description

Technical Field

[0001] This utility model relates to a PCTG production device, and more particularly to a vacuum system for a PCTG intermittent production device, belonging to the field of vacuum equipment technology. Background Technology

[0002] PCTG is a transparent plastic, an amorphous copolyester, officially named polyethylene terephthalate-1,4-cyclohexanediethanol ester. The commonly used comonomer for PCTG is 1,4-cyclohexanediethanol (CHDM). Current PCTG technology uses terephthalic acid (PTA) or isophthalic acid (IPA), neopentyl glycol (NPG) (or CHDM), and ethylene glycol (EG) as raw materials, with antimony compounds or titanium-based catalysts, and is produced through direct esterification followed by polycondensation. PCTG exhibits good viscosity, transparency, color, chemical resistance, and stress whitening resistance. It can be quickly thermoformed or extruded and blow-molded, and its viscosity is better than that of acrylic.

[0003] Conventional PCTG production lines typically use terephthalic acid (PTA), 1,4-cyclohexanediethanol (CHDM), and ethylene glycol (EG) as raw materials. The vacuum system employs a polycondensation condenser, a cyclone separator, and a three-stage jet pump + liquid ring pump configuration. This three-stage jet pump + liquid ring pump vacuum system can create a vacuum environment of 50 Pa(A). Under these conditions, the majority of the process vapor from the reactor condenses into a mixed liquid of 1,4-cyclohexanediethanol (CHDM) and ethylene glycol (EG) in the polycondensation condenser and cyclone separator; trace amounts of 1,4-cyclohexanediethanol (CHDM) enter the three-stage jet pump system and mix with the ethylene glycol (EG) working fluid, all of which is then collected.

[0004] Due to the high price of CHDM monomers, product costs are very high, and the supply of raw materials has long been restricted by foreign suppliers, limiting its application scope and cost-effectiveness, and inhibiting the development of the industry. Against this backdrop, people have been seeking cheaper monomers to replace CHDM. Neopentyl glycol (NPG) is a white crystalline solid, odorless, and highly hygroscopic; its melting point is 124~130℃, and its boiling point is 210℃. It is easily soluble in water, alcohols, ketones, and other solvents. Currently, its market price is 1 / 3 to 1 / 4 that of CHDM. The raw material is readily available, non-toxic, and environmentally friendly, making it extremely cost-effective. Although it cannot meet the needs of high-end medical and baby product sectors, it has a trend of replacing CHDM in industries such as food packaging and machinery.

[0005] When the vacuum level is ≤5 kPa, neopentyl glycol will vaporize directly upon heating to 130°C, no longer remaining in a liquid state. Due to the characteristics of neopentyl glycol, traditional PCTG vacuum systems are unsuitable for PCTG production using neopentyl glycol as the main reactant, with the following problems: First, vaporized neopentyl glycol will crystallize in the polycondensation condenser and cyclone separator, clogging the system and preventing the reaction from proceeding. Second, a large amount of neopentyl glycol will enter the three-stage jet pump system and dissolve into the ethylene glycol working fluid. As the neopentyl glycol content in ethylene glycol increases, exceeding 5%, the vacuum level of the vacuum system will decrease, failing to meet the vacuum requirements of the reaction. Similarly, if a large amount of ethylene glycol is introduced for displacement, the mixed solution of neopentyl glycol and ethylene glycol cannot be separated by conventional operations, greatly increasing waste liquid production and energy consumption. Utility Model Content

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, and such simplifications or omissions should not be construed as limiting the scope of the present invention.

[0007] In view of the problems existing in the above and / or prior art, this utility model is proposed.

[0008] The purpose of this invention is to overcome the problems existing in the prior art and provide a vacuum system for a PCTG batch production device. Under the premise of meeting the vacuum level of the reactor, it collects neopentyl glycol, water and low-boiling substances in the gas phase, prevents solid particles from entering the vacuum pump, ensures the stable operation of the vacuum pump, maintains the stability of product indicators, reduces waste liquid generation and reduces energy consumption.

[0009] To solve the above technical problems, the present invention provides a vacuum system for a PCTG intermittent production device, comprising a polycondensation condenser, a cyclone separator, a cold trap, a vertical sprayer, and a vacuum pump unit connected in sequence along the process steam flow direction. The inlet of the polycondensation condenser is used to connect to the process steam discharge pipe, and its bottom drain port is connected to the condensate collection tank. The upper side wall of the cyclone separator is provided with an air inlet that is connected to the top outlet of the condensation condenser, its bottom drain outlet is connected to the condensate collection tank, and its top exhaust outlet is connected to the inlet of the cold trap. The cold trap is a vertical shell-and-tube heat exchanger, and its shell side is connected to a freezing medium pipeline or a heating medium pipeline. The vertical sprayer has an air inlet at the top that is connected to the top outlet of the cold trap. Inside it is a spray inner cylinder and an EG nozzle for spraying ethylene glycol inside and outside the spray inner cylinder. Its bottom outlet is connected to a condensate receiving tank. The overflow outlet of the condensate receiving tank is connected to the EG nozzle of the vertical sprayer through a condensate pump, a plate heat exchanger and an EG spray pipe, forming an ethylene glycol spray circulation loop. The inlet of the vacuum pump unit is connected to the exhaust port on the side wall of the vertical sprayer.

[0010] Furthermore, the cyclone separator has a central inner cylinder coaxial with it at the center of its inner cavity, and the lower end of the central inner cylinder extends into the cone hopper at the bottom of the cyclone separator; a condenser coil is provided in the annular space between the outer wall of the central inner cylinder and the inner wall of the cyclone separator.

[0011] Furthermore, the cold trap is configured as two units, one for use and one for backup, and each cold trap is equipped with a pressure transmitter for detecting pressure difference on its inlet and outlet pipes.

[0012] Furthermore, the vertical sprayer comprises, from top to bottom, a small-diameter section, a conical expansion section, a large-diameter section, and a conical contraction section connected in sequence; the inner spray cylinder is located within the large-diameter section, and its upper flared end is connected to the lower inner wall of the conical expansion section; the EG nozzle includes an upper nozzle located on the conical wall of the conical expansion section and facing the inner cavity of the inner spray cylinder, and a lower nozzle located on the side wall of the large-diameter section and facing the annular space between the outer wall of the inner spray cylinder and the inner wall of the large-diameter section.

[0013] Furthermore, the bottom wall of the condensate receiving tank is provided with an upwardly extending baffle, which divides the condensate receiving tank into a receiving side and an overflow side; the bottom outlet of the vertical sprayer is connected to the receiving side, and the overflow side outlet is connected to the inlet of the condensate pump through an EG circulation pipe.

[0014] Furthermore, both the condensate pump and the plate heat exchanger are provided in two sets and are connected in parallel; the cold side inlet of each plate heat exchanger is connected to a cooling water supply pipe, and the cold side outlet is connected to a cooling water return pipe.

[0015] Furthermore, the vacuum pump assembly includes a multi-stage Roots vacuum pump and a single-stage claw vacuum pump connected in series.

[0016] Furthermore, the top vent of the condensate collection tank is connected to the top space of the cyclone separator via a pipe.

[0017] Furthermore, the bottom outlet of the condensate collection tank and the bottom outlet of the cold trap are both connected to the main condensate recovery pipe.

[0018] Furthermore, the outer wall of the cylinder and cone of the cyclone separator is provided with a separator jacket.

[0019] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. This invention achieves efficient staged collection and recovery of NPG vapor, solving the system blockage problem. Targeting the tendency of neopentyl glycol (NPG) to sublimate under vacuum, this invention designs a four-stage treatment system consisting of a polycondensation condenser, a cyclone separator, a cold trap, and a vertical sprayer.

[0020] In the low vacuum stage (>5kPa), the high-temperature process steam is first liquefied in large quantities in the polycondensation condenser, and the uncondensed aerosols and tiny droplets enter the cyclone separator. The cyclone separator, through its unique combination of a central inner cylinder and condensing coil, generates centrifugal force while enhancing cooling, achieving efficient separation of aerosols. The two-stage series connection can capture over 95% of NPG, effectively preventing premature crystallization and blockage of NPG in pipelines and equipment. During the high vacuum phase (≤5kPa), the system automatically switches to cold trap capture mode. NPG vapor condenses directly into a solid within the cold trap tube and is captured. The one-in-one-out design and steam defrosting function ensure continuous and stable operation of the device. Each batch can specifically capture approximately 30kg of NPG, greatly reducing the load on the downstream system.

[0021] 2. The core vacuum equipment is protected, ensuring long-term stable system operation. After the first three stages of collection, residual trace amounts of NPG powder and organic gases enter the vertical sprayer. The "washing-baffle-rewashing" path formed by the spray inner cylinder and the two-stage EG nozzles ensures full contact between the ethylene glycol spray liquid and the gas, dissolving residual NPG and capturing solid particles. The baffle design in the condensate receiving tank further separates undissolved solids. This design effectively prevents solid particles and viscous substances from entering the mechanical vacuum pump unit, avoiding pump wear, jamming, and vacuum level reduction, thus guaranteeing the lifespan of the core vacuum equipment and the reliability of the system.

[0022] 3. Significantly reduces waste liquid production and lowers raw material and energy costs. This invention, through precise graded collection, directly recovers most of the NPG in pure or mixed form to the upstream process for recycling via the condensate recovery pipe. Only a very small portion (≤5kg / batch) of NPG enters the ethylene glycol spray circulation system, which only needs to be replenished with approximately 95kg of fresh ethylene glycol to maintain the working fluid performance. Compared to traditional jet pump systems where hundreds of kilograms of ethylene glycol mixture need to be processed due to the large amount of NPG dissolved, waste liquid generation is reduced by approximately 80%, significantly lowering the energy consumption and cost of subsequent separation and treatment.

[0023] 4. Excellent overall vacuum performance, broadening the range of raw material selection. This invention ultimately employs a vacuum pump unit consisting of a three-stage Roots pump connected in series with a single-stage claw pump. With the effective protection of a vertical sprayer, it can stably establish and maintain the high vacuum environment required for the reaction (absolute pressure up to 60 Pa). This allows the production unit to reliably use the cost-effective neopentyl glycol (NPG) to replace the expensive 1,4-cyclohexanediethanol (CHDM), reducing raw material costs by approximately 60%-70% and eliminating dependence on imported CHDM. This provides a reliable technical solution for the low-cost production of PCTG products and the self-sufficiency of raw materials. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The drawings are provided for reference and illustration only and are not intended to limit this utility model. Wherein: Figure 1 This is a flowchart of the vacuum system of the PCTG intermittent production device of this utility model; Figure reference numerals: 1. Polycondensation condenser; 2. Cyclone separator; 2a. Central inner cylinder; 2b. Condensate coil; 3. Cold trap; 4. Vertical sprinkler; 4a. Sprayer inner cylinder; 4b. EG nozzle; 5. Condensate collection tank; 6. Condensate receiving tank; 7. Condensate pump; 8. Plate heat exchanger; 9. Vacuum pump unit; G1. Process steam exhaust pipe; G2. Condensate total recovery pipe; G3. EG circulation pipe; G4. EG spray pipe; G5. Cooling water supply pipe; G6. Cooling water return pipe; G7. Process tail gas exhaust pipe. Detailed Implementation

[0025] To make the technical means, creative features, achieved objectives and effects of this utility model easier to understand, the present utility model will be further described below with reference to specific illustrations. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. The following description, in conjunction with the appendix… Figure 1 The present invention will be further described in detail with reference to specific embodiments.

[0027] like Figure 1 As shown, the vacuum system of the PCTG intermittent production unit of this utility model includes a polycondensation condenser 1, a cyclone separator 2, a cold trap 3, a vertical sprayer 4, a condensate collection tank 5, a condensate receiving tank 6, a condensate pump 7, a plate heat exchanger 8, and a vacuum pump group 9. The process steam generated by the PCTG intermittent production unit is discharged through the process steam discharge pipe G1. The outlet of the process steam discharge pipe G1 is connected to the inlet of the lower end wall side wall of the polycondensation condenser 1. The polycondensation condenser 1 is a vertical shell and tube heat exchanger. The bottom outlet of the lower end wall of the polycondensation condenser 1 is connected to the inlet of the condensate collection tank 5 through a drain valve. The shell side of the polycondensation condenser 1 is connected to a low-temperature heat medium. The top outlet of the upper end wall of the polycondensation condenser 1 is connected to the air inlet of the upper side wall of the cyclone separator 2.

[0028] The cyclone separator 2 has a central inner cylinder 2a coaxial with its inner cavity. A conical hopper is located at the lower end of the cyclone separator 2. The upper end of the central inner cylinder 2a is welded to the inner wall of the upper head, and the lower end of the central inner cylinder 2a extends into the conical hopper. A condenser coil 2b is installed in the annular space between the inner wall of the cyclone separator 2 cylinder and the outer wall of the central inner cylinder 2a. A separator jacket is provided on the outer walls of the cyclone separator 2 cylinder and the conical hopper. The bottom outlet of the conical hopper of the cyclone separator 2 is connected to the inlet of the condensate collection tank 5 via a drain valve.

[0029] The top center exhaust port of the cyclone separator 2 is connected to the inlet of the lower head side wall of the cold trap 3 through the cold trap inlet valve. The cold trap 3 is a vertical shell-and-tube heat exchanger. The shell side is connected to chilled water pipes for freezing NPG and also to steam pipes for melting NPG.

[0030] The top outlet of the upper end cap of the cold trap 3 is connected to the upper air inlet of the vertical sprayer 4. The vertical sprayer 4 includes, from top to bottom, a small-diameter section, a conical expanding section, a large-diameter section, and a conical contracting section connected in sequence. The inner cavity of the large-diameter section is provided with a spray inner cylinder 4a. The upper end of the spray inner cylinder 4a is connected to the lower inner wall of the conical expanding section. The conical wall of the conical expanding section and the middle side wall of the large-diameter section are respectively provided with EG nozzles 4b. The upper EG nozzle 4b sprays EG into the inner cavity of the spray inner cylinder 4a, and the lower EG nozzle 4b sprays EG into the annular space between the spray inner cylinder 4a and the large-diameter section.

[0031] The bottom outlet of the vertical sprayer 4 is connected to the top inlet of the condensate receiving tank 6. The bottom wall of the condensate receiving tank 6 is provided with an upwardly extending baffle, which divides the condensate receiving tank 6 into a receiving side and an overflow side. The top inlet of the condensate receiving tank 6 is located above the receiving side. The baffle leaves undissolved NPG powder particles in the EG circulating liquid at the bottom of the condensate receiving tank 6. Clean EG overflows from the top of the baffle into the overflow side. The overflow side outlet of the condensate receiving tank 6 is connected to the inlet of the condensate pump 7. The outlet of the condensate pump 7 is connected to the hot side inlet of the plate heat exchanger 8. The hot side outlet of the plate heat exchanger 8 is connected to the EG spray pipe G4. The outlet of the EG spray pipe G4 is connected to each EG nozzle 4b of the vertical sprayer 4. The condensate pump 7 and the plate heat exchanger 8 are both configured in two sets in parallel. The cold side inlet of each plate heat exchanger 8 is connected to the cooling water supply pipe G5, and the cold side outlet of each plate heat exchanger 8 is connected to the cooling water return pipe G6.

[0032] The exhaust port on the middle side wall of the vertical sprayer 4 is connected to the inlet of the vacuum pump group 9. The vacuum pump group 9 includes a three-stage Roots vacuum pump and a single-stage claw vacuum pump connected in series. The outlet of the vacuum pump group 9 is connected to the exhaust gas system through the process exhaust gas discharge pipe G7.

[0033] The top exhaust port of the condensate collection tank 5 is connected to the top air inlet of the cyclone separator 2, which facilitates the discharge of non-condensable gas in the condensate collection tank 5.

[0034] The bottom outlet of the cyclone separator 2 is connected to the inlet of the condensate collection tank 5 through a drain valve. The bottom outlet of the condensate collection tank 5 is connected to the condensate total recovery pipe G2 through a drain valve. The bottom outlet of the lower end cap of the cold trap 3 is connected to the condensate total recovery pipe G2 through a drain valve.

[0035] At the end of the PCTG batch production unit, excess neopentyl glycol (NPG) and ethylene glycol (EG) are distilled off from the reactor and enter the vacuum system. When the reaction is in a low vacuum stage, process steam at 220°C from the reactor (containing a large amount of NPG, a small amount of ethylene glycol, and trace amounts of water, acetaldehyde, and nitrogen) enters the tube side of the polycondensation condenser 1, where it exchanges heat with the low-temperature heat medium in the shell side, cooling to 150°C, below the boiling points of NPG and EG. A large amount of process steam liquefies, forming an NPG mixture containing EG, which enters the condensate collection tank 5.

[0036] The process steam discharged from the vapor phase outlet of the tube side of the condensation condenser 1 enters the cyclone separator 2 for centrifugal separation. Inside the cyclone separator 2, it comes into contact with the condensation coil 2b and continues to cool down to 135°C. NPG and EG in the process steam continue to liquefy. The gas-liquid mixture generates centrifugal force under the structural action of the central inner cylinder 2a, capturing the mixture and allowing it to flow into the condensate collection tank 5 by gravity. The NPG collected in this step accounts for about 95% of the total vaporization.

[0037] When the reaction enters the high vacuum stage, with a vacuum degree of ≤5KPa, neopentyl glycol will directly sublimate. At this time, the outlet valves of the polycondensation condenser 1 and the cyclone separator 2 are cut off, and the condensate collection tank 5 is isolated from the vacuum system.

[0038] NPG vapor from the exhaust pipe of cyclone separator 2 enters the tube side of cold trap 3, where it indirectly exchanges heat with the cooling medium, cooling down to 30°C and sublimating into a solid that adheres to the inner wall of the condenser tubes. The cold trap is configured with one operating unit and one standby unit; the shell side is used alternately with chilled water and heating steam. NPG crystallization adheres to the inner wall and blocks the equipment. Pressure transmitters (PTs) are installed before and after the cold trap. When the pressure difference between the PTs exceeds 1 kPa, cold trap blockage is confirmed. At this point, the standby unit is switched, cold trap 3 is disconnected from the system, and atmospheric pressure is restored. Then, the shell side of cold trap 3 is switched to steam heating to 140°C, at which point the NPG melts into a liquid and enters the condensate collection tank 5. Approximately 30 kg of NPG per batch is captured in cold trap 3.

[0039] The NPG containing impurities discharged from the bottom of the condensate collection tank 5 and the molten NPG discharged from the bottom of the cold trap 3 are both discharged through the condensate total recovery pipe G2 and returned to the upstream for recycling.

[0040] After being captured by the cold trap 3, the residual organic gas and a small amount of NPG powder enter the vertical sprayer 4. First, they enter the small-diameter section of the sprayer, and after being sprayed by the EG nozzle 4b above, they enter the inner spray cylinder 4a. After flowing out from the lower end of the inner spray cylinder 4a, they bend upwards and enter the annular space between the inner spray cylinder 4a and the large-diameter section of the sprayer, where they are again sprayed by the EG nozzle 4b below. After NPG powder comes into contact with ethylene glycol sprayed from the two-stage EG nozzles, it dissolves in the ethylene glycol. The sprayed ethylene glycol falls to the bottom of the vertical sprayer 4 and is discharged into the condensate receiving tank 6 for collection. Solid particles remain at the bottom of the receiving side of the condensate receiving tank 6. EG overflows from the top of the baffle to the overflow side, and after being discharged from the overflow side outlet, it enters the condensate pump 7 through the EG circulation pipe G3. After being pressurized by the condensate pump 7, it is sent to the hot side of the plate heat exchanger 8 to exchange heat with the cooling water on the cold side. The cooled ethylene glycol returns to the two-stage EG nozzles 4b of the vertical sprayer 4 through the EG spray pipe G4 for circulation spraying. ≤5kg of NPG from each batch will enter the sprayed ethylene glycol, and 95kg of ethylene glycol needs to be added to the spraying system to replace the working fluid.

[0041] The gas treated by the vertical sprayer 4 mainly consists of non-condensable gases such as air and nitrogen, as well as a small amount of acetaldehyde and ethylene glycol vapors. These are extracted by the vacuum pump group 9 and sent to the exhaust gas system for further treatment through the process exhaust gas discharge pipe.

[0042] The above description is merely a preferred embodiment of the present utility model, showing and describing the basic principles, main features, and advantages of the present utility model. It is not intended to limit the scope of patent protection of the present utility model. Those skilled in the art should understand that the present utility model is not limited to the above embodiments. In addition to the above embodiments, the present utility model may have other implementations without departing from the spirit and scope of the present utility model. Various changes and improvements to the present utility model are also possible. All technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of protection claimed by the present utility model. The scope of protection claimed by the present utility model is defined by the appended claims and their equivalents. Technical features not described in the present utility model can be implemented by or using existing technology, and will not be elaborated here.

Claims

1. A vacuum system for a PCTG intermittent production unit, characterized in that: It includes a condensation condenser (1), a cyclone separator (2), a cold trap (3), a vertical sprayer (4), and a vacuum pump group (9) connected in sequence along the process steam flow direction. The inlet of the condensation condenser (1) is used to connect to the process steam discharge pipe (G1), and its bottom drain port is connected to the condensate collection tank (5). The upper side wall of the cyclone separator (2) is provided with an air inlet that is connected to the top outlet of the condenser condenser (1), its bottom drain outlet is connected to the condensate collection tank (5), and its top exhaust outlet is connected to the inlet of the cold trap (3). The cold trap (3) is a vertical shell-and-tube heat exchanger, and its shell side is connected to the freezing medium pipeline or the heating medium pipeline. The vertical sprayer (4) has an air inlet at the top that is connected to the top outlet of the cold trap (3). Inside it is a spray inner cylinder (4a) and an EG nozzle (4b) for spraying ethylene glycol inside and outside the spray inner cylinder (4a). Its bottom outlet is connected to a condensate receiving tank (6). The overflow outlet of the condensate receiving tank (6) is connected to the EG nozzle (4b) of the vertical sprayer (4) through the condensate pump (7), plate heat exchanger (8) and EG spray pipe (G4) to form an ethylene glycol spray circulation loop. The inlet of the vacuum pump unit (9) is connected to the exhaust port on the side wall of the vertical sprayer (4).

2. The vacuum system of the PCTG intermittent production unit according to claim 1, characterized in that: The cyclone separator (2) has a central inner cylinder (2a) coaxial with it at the center of its inner cavity, and the lower end of the central inner cylinder (2a) extends into the cone at the bottom of the cyclone separator (2); a condenser coil (2b) is provided in the annular space between the outer wall of the central inner cylinder (2a) and the inner wall of the cyclone separator (2).

3. The vacuum system of the PCTG intermittent production unit according to claim 1, characterized in that: The cold trap (3) is configured as two units, one for use and one for backup, and each cold trap (3) is equipped with a pressure transmitter for detecting pressure difference on the inlet and outlet pipes.

4. The vacuum system of the PCTG intermittent production unit according to claim 1, characterized in that: The vertical sprayer (4) includes, from top to bottom, a small diameter section, a conical expansion section, a large diameter section, and a conical contraction section connected in sequence; the inner spray cylinder (4a) is located inside the large diameter section of the sprayer, and its upper end of the bell mouth is connected to the lower inner wall of the conical expansion section; the EG nozzle (4b) includes an upper nozzle located on the conical wall of the conical expansion section and facing the inner cavity of the inner spray cylinder (4a), and a lower nozzle located on the side wall of the large diameter section of the sprayer and facing the annular space between the outer wall of the inner spray cylinder (4a) and the inner wall of the large diameter section of the sprayer.

5. The vacuum system of the PCTG intermittent production unit according to claim 1, characterized in that: The bottom wall of the condensate receiving tank (6) is provided with an upwardly extending baffle, which divides the condensate receiving tank (6) into a receiving side and an overflow side; the bottom outlet of the vertical sprayer (4) is connected to the receiving side, and the overflow side outlet is connected to the inlet of the condensate pump (7) through the EG circulation pipe (G3).

6. The vacuum system of the PCTG intermittent production unit according to claim 1, characterized in that: The condensate pump (7) and the plate heat exchanger (8) are each provided in two sets and are connected in parallel; the cold side inlet of each plate heat exchanger (8) is connected to the cooling water supply pipe (G5) and the cold side outlet is connected to the cooling water return pipe (G6).

7. The vacuum system of the PCTG intermittent production unit according to claim 1, characterized in that: The vacuum pump assembly (9) includes a multi-stage Roots vacuum pump and a single-stage claw vacuum pump connected in series.

8. The vacuum system of the PCTG intermittent production unit according to claim 7, characterized in that: The top exhaust port of the condensate collection tank (5) is connected to the top space of the cyclone separator (2) via a pipe.

9. The vacuum system of the PCTG intermittent production unit according to claim 1, characterized in that: The bottom outlet of the condensate collection tank (5) and the bottom outlet of the cold trap (3) are both connected to the condensate main recovery pipe (G2).

10. The vacuum system of the PCTG intermittent production unit according to any one of claims 1 to 9, characterized in that: The cyclone separator (2) has a separator jacket on the outer wall of its cylinder and cone.

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