Ethylene glycol continuous recovery system for polyester device

Abstract

The utility model discloses an ethylene glycol continuous recovery system for a polyester device, which is characterized in that a crude ethylene glycol discharged material is connected with a lower inlet of a first rectifying tower through a tube pass of a feeding preheater, and a top outlet of the first rectifying tower is connected with tube pass inlets of an ORC generator set and a tower top condenser; a tube pass outlet of the tower top condenser is connected with a No.1 tower top receiving tank; an outlet of the No.1 tower top receiving tank is connected with a top reflux inlet of the No.1 rectifying tower, a reflux inlet of the No.1 tower top receiving tank and a sewage treatment station through a process water delivery pump; a bottom outlet of the first rectifying tower is connected with a distillation still, a gas phase outlet of the distillation still is connected with a second rectifying tower, a top outlet of the second rectifying tower is connected with an inlet of a second tower top receiving tank through a shell pass of a feeding preheater, and an outlet of the second tower top receiving tank is connected with a slurry preparation unit and an inlet of a tower top circulating pump. An outlet of the tower top circulating pump is connected with a reflux inlet of the second rectifying tower. According to the system, high-purity ethylene glycol can be obtained, the product quality is stable, and the energy consumption is low.

Description

Technical Field

[0001] The utility model relates to a polyester production device, in particular to an ethylene glycol continuous recovery system for a polyester device, belonging to the technical field of polyester production devices. Background Art

[0002] Polyethylene terephthalate (PET) is a biodegradable material with a domestic production capacity of nearly 80 million tons. With huge production capacity and fierce competition, more and more manufacturers are beginning to try new developments and try to add different diols for modified and differentiated production.

[0003] Modified differentiated production, the addition of multiple diols, the gas phase components removed by polycondensation are complex, not only containing ethylene glycol, but also other diols, oligomers, water, etc. After the polycondensation gas phase is condensed, it cannot be directly recycled for pulping like conventional polyester. Generally, an ethylene glycol recovery system is configured to remove other diols, water and oligomers.

[0004] The Chinese utility model patent with announcement number CN 205269091U provides a semi-continuous ethylene glycol refining system, including an EG refining kettle and an EG refining tower located above the EG refining kettle, the upper wall of the EG refining kettle is connected with a crude EG inlet, a reboiler is installed on the top wall of the EG refining kettle, the bottom outlet of the EG refining kettle is connected with the inlet of a kettle bottom circulation pump, the outlet of the kettle bottom circulation pump is connected with the tube side inlet of the reboiler, the tube side outlet of the reboiler is communicated with the inner cavity of the EG refining kettle, the top wall of the EG refining kettle is also communicated with the bottom of the EG refining tower through an evaporation pipe, a refining tower EG outlet is provided in the middle of the EG refining tower, the refining tower EG outlet is connected with the inlet of a qualified EG receiving tank, and a refining tower water vapor outlet is provided at the top of the EG refining tower. The EG recovered by this system has high precision, few impurities, stable product quality, and reduces the intensity of manual operation, saving labor costs. Except for slag discharge, it basically does not require people to go to the site for operation. It has a high degree of automation, low slag discharge frequency, and reduces EG consumption. However, there are still the following shortcomings:

[0005] 1. The condensate of the polycondensation gas phase is semi-continuously recovered, but the recovery volume is small, which restricts the production capacity of the device, and the product differences are large, resulting in a lot of waste;

[0006] 2. Low processing capacity and low operational flexibility;

[0007] 3. Single tower processing, no buffer equipment, any slight fluctuation in parameters will affect product quality;

[0008] 4. On the one hand, the top steam and side steam are cooled by cooling water, and the energy is not fully utilized; on the other hand, the system has a large heat demand, the heat is not fully utilized, and the supporting cooling water volume is large;

[0009] 5. At atmospheric pressure and high temperature, there are many side reactions in ethylene glycol and the consumption is high.

[0010] 6. The finished product is withdrawn from the middle side. The requirements for the side withdrawal position are very high. It requires operators to monitor the system throughout the process. Personnel are prone to fatigue and have high requirements for the operating ability of operators. Summary of the Utility Model

[0011] The purpose of the present utility model is to overcome the problems existing in the prior art and provide a continuous ethylene glycol recovery system for polyester plants, which can effectively separate multi-components removed from the polycondensation reaction, obtain ethylene glycol with a purity of 99.5%, have few side reactions, stable product quality and low energy consumption.

[0012] To solve the above technical problems, a continuous ethylene glycol recovery system for a polyester plant of the present utility model includes a crude ethylene glycol storage tank. The outlet of the crude ethylene glycol storage tank is connected to the tube-side inlet of a feed preheater through a crude ethylene glycol transfer pump. The tube-side outlet of the feed preheater is connected to the lower inlet of a first distillation column. The top outlet of the first distillation column is connected to the tube-side inlet of an ORC generator set and a top condenser. The tube-side outlet of the top condenser is connected to the top inlet of a first top receiving tank. The bottom outlet of the first top receiving tank is connected to the inlet of a process water transfer pump. The outlet of the process water transfer pump is respectively connected to the top reflux port of the first distillation column, the reflux port of the first top receiving tank and a sewage treatment station;

[0013] The bottom outlet of the first distillation column is connected to the top inlet of a distillation kettle. The top gas-phase outlet of the distillation kettle is connected to the bottom of a second distillation column. The top outlet of the second distillation column is connected to the shell-side inlet of the feed preheater. The shell-side exhaust port of the feed preheater is connected to a vacuum pump group. The shell-side outlet of the feed preheater is connected to the top inlet of a second top receiving tank. The bottom outlet of the second top receiving tank is connected to a pulp preparation unit and the inlet of a top circulation pump. The outlet of the top circulation pump is connected to the top reflux port of the second distillation column.

[0014] Further, the outlet of the process water transfer pump is also connected to the top reflux port of the first top receiving tank.

[0015] Further, the outlet of the top circulation pump is also connected to the top reflux port of the second top receiving tank.

[0016] Further, a falling film reboiler is installed at the top of the distillation kettle. The bottom outlet of the distillation kettle is connected to the inlet of a material circulation pump. The outlet of the material circulation pump is connected to the top material inlet of the falling film reboiler and a natural gas heat transfer oil furnace.

[0017] Further, the outlet of the material circulation pump is connected to the natural gas heat-conducting oil furnace through an external discharge regulating valve, and the opening degree of the external discharge regulating valve is controlled by the bottom liquid level of the distillation kettle.

[0018] Further, the bottom outlet of the second tower top receiving tank is connected to the pulp preparation unit through a discharge regulating valve, and the opening degree of the discharge regulating valve is controlled by the liquid level of the second tower top receiving tank.

[0019] Further, a heat medium coil is provided in the lower liquid phase space of the first rectification tower, a heating jacket is provided on the lower outer wall of the distillation kettle, the heat medium outlets of the heat medium coil of the rectification tower and the heating jacket are both connected to the inlet pipeline of the heat medium circulation pump, and the outlet pipeline of the heat medium circulation pump is connected to the heat medium inlets of the heat medium coil of the rectification tower and the heating jacket.

[0020] Further, the outlet pipeline of the heat medium circulation pump is also connected to the shell-side heat medium inlet of the falling film reboiler, and the shell-side heat medium outlet of the falling film reboiler is connected to the inlet pipeline of the heat medium circulation pump.

[0021] Further, the inlet pipeline of the heat medium circulation pump is also connected to the primary heat medium supply oil pipe through a heat medium regulating valve, and the opening degree of the heat medium regulating valve is controlled by the bottom temperature of the distillation kettle.

[0022] Compared with the prior art, the utility model has achieved the following beneficial effects: 1. Two towers are used for continuous recovery. The first rectification tower separates water and light components, and the second rectification tower analyzes to obtain high-purity ethylene glycol. It has a large supporting production capacity, good scale effect, and strong product competitiveness;

[0023] 2. Continuous recovery is realized, the parameters are stable, the product quality is stable, and the product purity is high;

[0024] 3. Ethylene glycol is rectified under reduced pressure to avoid side reactions of ethylene glycol and reduce the consumption of ethylene glycol;

[0025] 4. The water vapor at the top of one tower is used for ORC power generation. On the one hand, the use of cooling water is reduced, and on the other hand, the external power consumption of the device is reduced, and the production cost is lowered;

[0026] 5. The ethylene glycol steam of the second tower is recycled to heat the medium at the bottom of the first tower, and the energy is fully utilized, saving energy and reducing consumption;

[0027] 6. The system has a high operation flexibility, can meet the operation at 20% - 120% load, has a high degree of automation, and is easy to operate and understand. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following further describes the present utility model in detail with reference to the drawings and specific embodiments. The drawings are only for reference and illustration, and are not used to limit the present utility model.

[0029] Figure 1 This is a flow chart of the continuous ethylene glycol recovery system for the polyester device of the present utility model;

[0030] In the figure: 1. First distillation column; 2. ORC generator set; 3. Sewage treatment station; 4. Distillation kettle; 5. Natural gas heat transfer oil furnace; 6. Second distillation column; 7. Pulp preparation unit; 8. Vacuum pump group;

[0031] T0. Crude ethylene glycol storage tank; T1. First top receiving tank; T2. Second top receiving tank;

[0032] B1. Crude ethylene glycol transfer pump; B2. Process water transfer pump; B3. Material circulation pump; B4. Heat medium circulation pump; B5. Top circulation pump;

[0033] H1. Feed preheater; H2. Falling film reboiler; C1. Top condenser;

[0034] G1. Primary heat medium supply oil pipe; G2. Primary heat medium return oil pipe. Specific embodiments

[0035] In the following description of the present utility model, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present utility model and simplifying the description, rather than indicating that the device must have a specific orientation.

[0036] In order to make the technical means, creative features, achieved purposes and effects realized by the present utility model easy to understand, the present utility model will be further described below with reference to specific drawings.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present utility model belongs. The terms used in the description of the present utility model herein are only for the purpose of describing specific embodiments and are not intended to limit the present utility model.

[0038] Such as Figure 1As shown in the figure, the continuous ethylene glycol recovery system for polyester plants of the present utility model includes a crude ethylene glycol storage tank T0, a feed preheater H1, a first distillation column, an ORC power generation unit 2, a distillation kettle 4, and a second distillation column 6. The outlet of the crude ethylene glycol storage tank T0 is connected to the inlet of the crude ethylene glycol transfer pump B1. The outlet of the crude ethylene glycol transfer pump B1 is connected to the inlet of the cold side of the tube side of the feed preheater H1. The outlet of the cold side of the tube side of the feed preheater H1 is connected to the lower inlet of the first distillation column 1. The top outlet of the first distillation column 1 is connected to the ORC power generation unit 2. The top outlet of the first distillation column 1 is also connected to the inlet of the tube side of the top condenser C1. The outlet of the tube side of the top condenser C1 is connected to the top inlet of the first top receiving tank T1. The bottom outlet of the first top receiving tank T1 is connected to the inlet of the process water transfer pump B2. The outlet of the process water transfer pump B2 is respectively connected to the top reflux port of the first distillation column 1, the top reflux port of the first top receiving tank T1, and the sewage treatment station 3.

[0039] A distillation column heat medium coil is provided in the lower liquid phase space of the first distillation column 1 for heating. The bottom outlet of the first distillation column 1 is connected to the top inlet of the distillation kettle 4.

[0040] A falling film reboiler H2 is installed at the top of the distillation kettle 4. The bottom outlet of the distillation kettle 4 is connected to the inlet of the material circulation pump B3. One of the outlets of the material circulation pump B3 is connected to the top material inlet of the falling film reboiler H2. The second outlet of the material circulation pump B3 is connected to the natural gas heat-conducting oil furnace 5 through an external discharge regulating valve. The opening of the external discharge regulating valve is controlled by the bottom liquid level of the distillation kettle 4.

[0041] A heating jacket is provided on the lower outer wall of the distillation kettle 4. The upper heat medium outlet of the heating jacket is connected to the inlet pipeline of the heat medium circulation pump B4. The outlet pipeline of the heat medium circulation pump B4 is connected to the lower heat medium inlet of the heating jacket.

[0042] The outlet pipeline of the heat medium circulation pump B4 is also connected to the shell side heat medium inlet of the falling film reboiler H2. The shell side heat medium outlet of the falling film reboiler H2 is connected to the inlet pipeline of the heat medium circulation pump B4.

[0043] The outlet pipeline of the heat medium circulation pump B4 is also connected to the inlet of the distillation column heat medium coil. The outlet of the distillation column heat medium coil is connected to the inlet pipeline of the heat medium circulation pump B4.

[0044] The inlet pipeline of the heat medium circulation pump B4 is also connected to the primary heat medium supply pipe G1 and the primary heat medium return pipe G2. The primary heat medium supply pipe G1 injects a certain amount of primary heat medium into the secondary heat medium circulation system through a heat medium regulating valve to adjust the temperature of the secondary heat medium.

[0045] The top gas-phase outlet of the distillation kettle 4 is connected to the bottom of the second rectification column 6. The top outlet of the second rectification column 6 is connected to the shell-side hot-side inlet of the feed preheater H1. The shell-side hot-side outlet of the feed preheater H1 is connected to the top inlet of the second top receiving tank T2. The shell-side exhaust port of the feed preheater H1 is connected to the vacuum pump group 8.

[0046] The bottom outlet of the second top receiving tank T2 is connected to the inlet of the top circulation pump B5. One of the outlets of the top circulation pump B5 is connected to the top reflux port of the second rectification column 6, and the second outlet of the top circulation pump B5 is connected to the top reflux port of the second top receiving tank T2. The bottom outlet of the second top receiving tank T2 is also connected to the sizing unit 7 through a discharge regulating valve, and the opening of the discharge regulating valve is controlled by the liquid level of the second top receiving tank T2.

[0047] The working process of the continuous ethylene glycol recovery system for this polyester plant is as follows:

[0048] The crude ethylene glycol containing water, ethylene glycol, and high-boiling substances from the esterification and polycondensation of the plant is stored in the crude ethylene glycol storage tank T0, and then is transported by the crude ethylene glycol transfer pump B1 into the cold side of the feed preheater H1. After heat exchange with the refined ethylene glycol steam purified from the hot side, it enters the lower part of the first rectification column 1. The bottom of the column is heated by a secondary heat medium through a coil to 160 °C, the top temperature is controlled at 66 °C, and the top pressure is 30 KPa(A).

[0049] The water vapor coming out from the top goes to the ORC power generation unit 2 for power generation, and the power is supplied for the use of the plant. The excess steam is condensed by the top condenser C1 and enters the first top receiving tank T1, and is sent out by the process water transfer pump B2. Part of it is refluxed to the top of the first rectification column 1 to ensure the top temperature, and the excess part is sent to the sewage treatment station 3.

[0050] The ethylene glycol and high-boiling substances at the bottom of the first rectification column enter the distillation kettle 4. The bottom temperature of the column is controlled by the flow rate of the primary heat medium and is stabilized at 200 °C. Further rectification separation is carried out by the second rectification column 6, and the purity of ethylene glycol is ensured by controlling the top temperature. The vacuum pump group 8 is started, the steam flows from bottom to top, and the liquid flows from top to bottom for mass transfer and heat transfer. Ethylene glycol with a purity ≥ 99.5% is obtained at the top. The top temperature is controlled at 160 °C, and the pressure is 30 KPa(A). The top steam is condensed after heat exchange with the crude ethylene glycol on the hot side of the feed preheater H1 and enters the second top receiving tank T2. After being pressurized by the top circulation pump B5, part of it is refluxed to the second rectification column 6 to control the top temperature, part of it is refluxed to the second top receiving tank T2, and the excess part is sent to the sizing through a cascade control regulating valve for the liquid level.

[0051] The high-boiling substances at the bottom of the column are pressurized by the material circulation pump B3 and sent to the natural gas heat-conducting oil furnace 5 for combustion as fuel.

[0052] In addition, to prevent high-boiling substances from accumulating on the coil pipes and carbonizing, which may affect heat transfer, the heating of the recovery kettle is changed to a falling-film reboiler H2. The material is lifted to the top of the falling-film reboiler H2 by the material circulation pump B3 for forced circulation, and a falling film is formed on the inner wall of each falling-film tube and flows downward to exchange heat with the secondary heat medium of the recovery kettle in the shell side.

[0053] The above is only the preferred and feasible embodiment of the present invention, which shows and describes the basic principles, main features and advantages of the present invention. The patent protection scope of the present invention is not limited thereby. Those skilled in the art should understand that the present invention is not limited by the above embodiments. Except for the above embodiments, without departing from the spirit and scope of the present invention, the present invention may have other implementation manners. The present invention will also have various changes and improvements. Any technical solutions formed by equivalent substitution or equivalent transformation shall fall within the protection scope required by the present invention. The protection scope required by the present invention is defined by the appended claims and their equivalents. The technical features not described in the present invention can be achieved by or adopted the prior art, and will not be elaborated herein.

Claims

1. A continuous ethylene glycol recovery system for a polyester plant, comprising a crude ethylene glycol storage tank, characterized in that: The outlet of the crude ethylene glycol storage tank is connected to the inlet of the tube side of the feed preheater through a crude ethylene glycol transfer pump. The outlet of the tube side of the feed preheater is connected to the lower inlet of the first distillation column. The top outlet of the first distillation column is connected to the inlet of the tube side of the ORC power generation unit and the top condenser. The outlet of the tube side of the top condenser is connected to the top inlet of the first top receiving tank. The bottom outlet of the first top receiving tank is connected to the inlet of the process water transfer pump. The outlet of the process water transfer pump is respectively connected to the top reflux port of the first distillation column, the reflux port of the first top receiving tank and the sewage treatment station. The bottom outlet of the first distillation column is connected to the top inlet of the distillation kettle. The top gas phase outlet of the distillation kettle is connected to the bottom of the second distillation column. The top outlet of the second distillation column is connected to the inlet of the shell side of the feed preheater. The shell side exhaust port of the feed preheater is connected to the vacuum pump group. The outlet of the shell side of the feed preheater is connected to the top inlet of the second top receiving tank. The bottom outlet of the second top receiving tank is connected to the inlet of the sizing unit and the top circulating pump. The outlet of the top circulating pump is connected to the top reflux port of the second distillation column.

2. The continuous ethylene glycol recovery system for a polyester plant according to claim 1, wherein, The outlet of the process water transfer pump is also connected to the top reflux port of the first top receiving tank.

3. The continuous ethylene glycol recovery system for a polyester plant according to claim 1, wherein, The outlet of the top circulating pump is also connected to the top reflux port of the second top receiving tank.

4. The continuous ethylene glycol recovery system for a polyester plant according to claim 1, wherein, A falling film reboiler is installed at the top of the distillation kettle. The bottom outlet of the distillation kettle is connected to the inlet of the material circulating pump. The outlet of the material circulating pump is connected to the top material inlet of the falling film reboiler and the natural gas heat-conducting oil furnace.

5. The continuous ethylene glycol recovery system for a polyester plant according to claim 4, wherein The outlet of the material circulating pump is connected to the natural gas heat-conducting oil furnace through an external discharge regulating valve. The opening of the external discharge regulating valve is controlled by the bottom liquid level of the distillation kettle.

6. The continuous ethylene glycol recovery system for a polyester plant according to claim 1, wherein, The bottom outlet of the second top receiving tank is connected to the sizing unit through a discharge regulating valve. The opening of the discharge regulating valve is controlled by the liquid level of the second top receiving tank.

7. The continuous ethylene glycol recovery system for a polyester plant according to claim 1, characterized in that, A distillation column heat medium coil is provided in the lower liquid phase space of the first distillation column. A heating jacket is provided on the lower outer wall of the distillation kettle. The heat medium outlets of the distillation column heat medium coil and the heating jacket are both connected to the inlet pipeline of the heat medium circulating pump. The outlet pipeline of the heat medium circulating pump is connected to the heat medium inlets of the distillation column heat medium coil and the heating jacket.

8. The continuous ethylene glycol recovery system for a polyester plant according to claim 7, characterized in that, The outlet pipeline of the heat medium circulating pump is also connected to the shell side heat medium inlet of the falling film reboiler. The shell side heat medium outlet of the falling film reboiler is connected to the inlet pipeline of the heat medium circulating pump.

9. The continuous ethylene glycol recovery system for a polyester plant according to claim 8, wherein, The inlet pipeline of the heat medium circulating pump is also connected to the primary heat medium supply oil pipe through a heat medium regulating valve. The opening of the heat medium regulating valve is controlled by the bottom temperature of the distillation kettle.

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