Ethylene glycol purification system and ethylene glycol purification method

Abstract

The present application relates to the field of ethylene glycol purification, and in particular to an ethylene glycol purification system and an ethylene glycol purification method. The ethylene glycol purification system comprises a falling film evaporator, an MVR compression device, a one-effect flash tower, a two-effect flash tower, a three-effect flash tower, a four-effect flash tower, a five-effect flash tower, a two-effect reboiler, a three-effect reboiler, a four-effect reboiler, a five-effect reboiler, a one-effect condensate tank, a three-effect condensate tank, a four-effect condensate tank and a five-effect condensate tank. The ethylene glycol purification system has good purification effect, the one-effect uses a falling film evaporator+MVR compression device evaporation process, cancels the consumption of high-pressure steam, and uses new steam for two-effect evaporation, since the two-effect evaporation pressure is low, 1.1MPaA steam can be used; and since the one-effect evaporates a large amount of water in the raw material ethylene glycol with low energy consumption, the steam consumption of the subsequent multi-effect evaporation is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of ethylene glycol purification, and more specifically, to an ethylene glycol purification system and a method for ethylene glycol purification. Background Technology

[0002] Ethylene glycol is an important chemical raw material. The mainstream ethylene glycol production process currently involves the oxidation of ethylene to ethylene oxide, followed by the hydration of ethylene oxide to produce ethylene glycol. However, this process also involves side reactions, producing products such as diethylene glycol and triethylene glycol. Therefore, to minimize side reactions and maximize ethylene glycol yield, the molar ratio of water to ethylene oxide in the ethylene glycol reaction feed is typically around 25:1. Consequently, the concentration of ethylene glycol in the reaction product is only 10-15%. To produce high-purity ethylene glycol, the water in the reaction product needs to be evaporated to increase the ethylene glycol concentration to 80-90%, before proceeding to a subsequent distillation unit to produce 99+% ethylene glycol. Currently, multi-effect evaporation is used, typically four-effect or seven-effect evaporation processes.

[0003] The current multi-effect evaporation process requires high-grade steam for heating the first effect, usually 2MPaA steam produced by the ethylene glycol unit itself, with any shortfall supplemented by 3.5MPaA or 4.0MPaA steam from the pipeline network.

[0004] The quadruple-effect evaporation process utilizes all secondary steam, but due to the low pressure level of the secondary steam, a shortage of steam users can lead to an excess of low-pressure steam. While the quadruple-effect evaporation process can utilize all secondary steam, the limited number of effects results in a very large consumption of fresh steam. For example, in the EOEG unit of Refinery A, the feedstock ethylene glycol flow rate is 720 t / h, and the water flow rate through the quadruple-effect evaporation is 620 t / h, consuming 164 t / h of 2MPa steam.

[0005] The difference between a seven-effect condenser and a four-effect condenser is that the seven-effect condenser has three more effects with lower evaporation pressures, resulting in less secondary steam and avoiding excess low-pressure steam. However, the last effect in the seven-effect condenser is a vacuum effect, and the secondary steam from the vacuum effect needs to be condensed using circulating water, causing significant heat loss. For example, in the EOEG unit of Petrochemical Company B, the feedstock ethylene glycol has a flow rate of 465 t / h. The evaporation water volume through the seven-effect condenser is 395 t / h, consuming 59 t / h of 2MPa steam. The secondary steam supplied externally from the fifth and sixth effects totals 62 t / h, and the vacuum effect condenser consumes 3600 t / h of circulating water.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] One aspect of the present invention relates to an ethylene glycol purification system, comprising: a first-effect falling film evaporator, an MVR compressor, a first-effect flash evaporator, a second-effect flash evaporator, a third-effect flash evaporator, a fourth-effect flash evaporator, a fifth-effect flash evaporator, a second-effect reboiler, a third-effect reboiler, a fourth-effect reboiler, a fifth-effect reboiler, a first-effect condensate tank, a third-effect condensate tank, a fourth-effect condensate tank, and a fifth-effect condensate tank;

[0008] The inlet of the first-effect falling film evaporator is connected to the outlet of the first-effect flash evaporator; the MVR compression device is installed between the inlet of the first-effect falling film evaporator and the outlet of the first-effect flash evaporator; the inlet of the first-effect falling film evaporator is connected to the start-up steam pipeline; the outlet of the first-effect falling film evaporator is connected to the inlet of the first-effect flash evaporator; and the outlet of the first-effect flash evaporator is connected to the inlet of the first-effect falling film evaporator.

[0009] The liquid outlet of the first-effect flash evaporator is connected to the liquid inlet of the second-effect flash evaporator; the liquid outlet of the second-effect flash evaporator is connected to the liquid inlet of the second-effect reboiler; the gas outlet of the second-effect reboiler is connected to the gas inlet of the second-effect flash evaporator; the heat source inlet of the second-effect reboiler is connected to the second-effect steam pipeline.

[0010] The outlet of the double-effect flash evaporator is connected to the heat source inlet of the triple-effect reboiler; the outlet of the triple-effect reboiler is connected to the inlet of the triple-effect flash evaporator; the liquid outlet of the double-effect flash evaporator is connected to the liquid inlet of the triple-effect flash evaporator; the liquid outlet of the triple-effect flash evaporator is connected to the liquid inlet of the triple-effect reboiler; the liquid outlet of the triple-effect reboiler is connected to the inlet of the triple-effect condensate tank; and the outlet of the triple-effect condensate tank is connected to the heat source inlet of the triple-effect reboiler.

[0011] The outlet of the triple-effect flash distillation tower is connected to the heat source inlet of the quadruple-effect reboiler; the outlet of the quadruple-effect reboiler is connected to the inlet of the quadruple-effect flash distillation tower; the liquid outlet of the triple-effect flash distillation tower is connected to the liquid inlet of the quadruple-effect flash distillation tower; the liquid outlet of the quadruple-effect flash distillation tower is connected to the liquid inlet of the quadruple-effect reboiler; and the liquid outlet of the quadruple-effect reboiler is connected to the liquid inlet of the quadruple-effect condensate tank.

[0012] The outlet of the four-effect flash distillation tower is connected to the heat source inlet of the five-effect reboiler; the outlet of the five-effect reboiler is connected to the inlet of the five-effect flash distillation tower; the liquid outlet of the four-effect flash distillation tower is connected to the liquid inlet of the five-effect flash distillation tower; the liquid outlet of the five-effect flash distillation tower is connected to the liquid inlet of the five-effect condensate tank; the liquid outlet of the five-effect reboiler is connected to the liquid inlet of the five-effect condensate tank; and the outlet of the five-effect condensate tank is connected to the heat source inlet of the five-effect reboiler.

[0013] The first-effect flash evaporator, the second-effect flash evaporator, the third-effect flash evaporator, the fourth-effect flash evaporator, and the fifth-effect flash evaporator are connected to a deionized water pipeline above them; the first-effect falling film evaporator, the first-effect condensate tank, the third-effect condensate tank, the fourth-effect condensate tank, and the fifth-effect condensate tank are connected in sequence.

[0014] The ethylene glycol purification system described above employs a falling film evaporator + MVR compression device evaporation process in its first effect, serving as the heat source for the first-effect evaporation. This process evaporates 20%–40% of the water in the raw ethylene glycol in a single step, significantly reducing the amount of fresh steam required for the pipeline network. Furthermore, this invention eliminates the vacuum effect, allowing for the complete utilization of secondary steam without heat loss. It also avoids the heat loss associated with secondary steam in a vacuum effect and eliminates the need for the large amount of circulating water required by a vacuum effect condenser.

[0015] The single-effect falling film evaporator uses MVR compressor to pressurize the secondary steam for use as a falling film evaporator, which can achieve high-flow evaporation and the heat exchange temperature difference can be very small, around 3℃. The pressure ratio of the MVR compressor is also very small, resulting in low power consumption.

[0016] Preferably, a second-effect condensate tank is provided between the first-effect condensate tank and the third-effect condensate tank; the outlet of the second-effect reboiler is connected to the inlet of the second-effect condensate tank; the outlet of the second-effect condensate tank is connected to the second-effect steam pipe; and the outlet of the first-effect flash evaporator is connected to the second-effect steam pipe.

[0017] Preferably, the ethylene glycol purification system further includes: a six-effect flash distillation tower, a six-effect reboiler, and a six-effect condensate tank.

[0018] Preferably, the outlet of the five-effect flash distillation tower is connected to the heat source inlet of the six-effect reboiler; the outlet of the six-effect reboiler is connected to the inlet of the six-effect flash distillation tower; the outlet of the six-effect flash distillation tower is connected to the inlet of the six-effect reboiler; the outlet of the five-effect flash distillation tower is connected to the inlet of the six-effect flash distillation tower; the outlet of the six-effect reboiler is connected to the inlet of the six-effect condensate tank; and the outlet of the six-effect condensate tank is connected to the heat source inlet of the six-effect reboiler.

[0019] Preferably, the five-effect condensate tank and the six-effect condensate tank are connected together.

[0020] Preferably, a formaldehyde removal tower is installed above the four-effect condensate tank.

[0021] Preferably, a first pumping device is provided between the liquid outlet of the first-effect falling film evaporator and the liquid inlet of the first-effect flash evaporator.

[0022] The ethylene glycol purification system of the present invention, after a single-effect falling film evaporator, can employ a multi-effect evaporator with fewer or more effects, such as a single-effect MVR + two-effect or three-effect, four-effect, five-effect, seven-effect, etc.

[0023] Another aspect of the present invention relates to a method for purifying ethylene glycol, using the aforementioned ethylene glycol purification system, comprising the following steps:

[0024] Ethylene glycol dilute solution is subjected to falling film evaporation to obtain gas-liquid two-phase material and first-effect secondary steam condensate; the gas-liquid two-phase material is subjected to a first flash evaporation treatment to obtain a first-effect flash vapor phase and a first-effect flash liquid phase;

[0025] The first-effect flash vapor phase and the deionized water undergo a first countercurrent contact to obtain first-effect secondary steam; the first-effect secondary steam is pressurized to provide heat for the falling film evaporation of the dilute ethylene glycol solution; a portion of the first-effect flash liquid phase is mixed with the dilute ethylene glycol solution and then subjected to falling film evaporation; another portion of the first-effect flash liquid phase undergoes a second flash evaporation treatment to obtain a second-effect flash vapor phase and a second-effect flash liquid phase; the second-effect steam pipe provides a heat source for the second flash evaporation treatment;

[0026] The liquid phase of the second-effect flash evaporation undergoes a third flash evaporation treatment to obtain a vapor phase and a liquid phase of the third-effect flash evaporation; the vapor phase of the second-effect flash evaporation undergoes a second countercurrent contact with the deionized water to obtain secondary steam of the second-effect; the secondary steam of the second-effect provides a heat source for the third flash evaporation treatment; the condensate of the secondary steam of the first-effect enters the condensate tank of the third-effect through the condensate tank of the first-effect, mixes with the condensate of the secondary steam of the third-effect, and then enters the reboiler of the third-effect to undergo a reboiling reaction of the third-effect;

[0027] The triple-effect flash liquid phase undergoes a fourth flash evaporation process to obtain a quadruple-effect flash vapor phase and a quadruple-effect flash liquid phase; the triple-effect flash vapor phase undergoes a third countercurrent contact with deionized water to obtain triple-effect secondary steam; the triple-effect secondary steam provides a heat source for the fourth flash evaporation process;

[0028] The liquid phase of the fourth-effect flash evaporation undergoes a fifth flash evaporation process to obtain a fifth-effect flash vapor phase and a fifth-effect flash liquid phase; the fourth-effect flash vapor phase undergoes a fourth countercurrent contact with deionized water to obtain fourth-effect secondary steam; the fourth-effect secondary steam provides a heat source for the fifth flash evaporation process; the secondary steam condensate in the third-effect condensate tank enters the fifth-effect condensate tank through the fourth-effect condensate tank, mixes with the fifth-effect secondary steam condensate, and then enters the fifth-effect reboiler to undergo a fifth-effect reboiling reaction.

[0029] The method for purifying ethylene glycol is simple to operate, has good purification effect, low energy consumption, and low cost.

[0030] Preferably, the method for purifying ethylene glycol further includes:

[0031] The liquid phase of the five-effect flash evaporation undergoes a sixth flash evaporation process to obtain a six-effect flash vapor phase and a six-effect flash liquid phase; the five-effect flash vapor phase undergoes a fifth countercurrent contact with deionized water to obtain five-effect secondary steam; the five-effect secondary steam provides a heat source for the sixth flash evaporation process; the condensate from the secondary steam in the five-effect condensate tank enters the six-effect condensate tank, mixes with the condensate from the six-effect secondary steam, and then enters the six-effect reboiler for a six-effect reboiling reaction.

[0032] Preferably, the secondary steam condensate undergoes formaldehyde removal treatment after leaving the triple-effect condensate tank and before entering the quadruple-effect condensate tank.

[0033] Formaldehyde removal treatment can reduce the loss of stripping steam. Because the first effect maintains a high pressure and a large pressure difference with the second and third effects, the condensate from the second effect enters the condensate tank of the third effect, which can generate more flash steam that enters the third effect reboiler. This is beneficial for the utilization of the waste heat of the second effect condensate and reduces the amount of fresh steam used in the second effect reboiler.

[0034] Preferably, the starting pressure of the single-effect falling film evaporator is 1.9 to 2.1 MPaA (e.g., 1.9 MPaA, 1.94 MPaA, 1.98 MPaA, 2.02 MPaA, 2.06 MPaA or 2.1 MPaA).

[0035] Preferably, the pressure at the outlet of the single-effect flash evaporator is 1.2 to 1.9 MPa (e.g., 1.2 MPa, 1.3 MPa, 1.4 MPa, 1.6 MPa, 1.8 MPa or 1.9 MPa).

[0036] Preferably, the pressure of the double-effect flash evaporator is 0.7 to 0.8 MPa (e.g., 0.7 MPa, 0.72 MPa, 0.74 MPa, 0.76 MPa, 0.78 MPa or 0.8 MPa).

[0037] Preferably, the pressure of the triple-effect flash evaporator is 0.5 to 0.6 MPa (e.g., 0.5 MPa, 0.52 MPa, 0.54 MPa, 0.56 MPa, 0.58 MPa or 0.6 MPa).

[0038] Preferably, the pressure of the quadruple-effect flash evaporator is 0.4 to 0.5 MPa (e.g., 0.4 MPa, 0.42 MPa, 0.44 MPa, 0.46 MPa, 0.48 MPa or 0.5 MPa).

[0039] Preferably, the pressure of the five-effect flash evaporator is 0.3 to 0.4 MPa (e.g., 0.3 MPa, 0.32 MPa, 0.34 MPa, 0.36 MPa, 0.38 MPa or 0.4 MPa).

[0040] Preferably, the pressure of the six-effect flash evaporator is 0.2 to 0.3 MPa (e.g., 0.2 MPa, 0.22 MPa, 0.24 MPa, 0.26 MPa, 0.28 MPa or 0.3 MPa).

[0041] Preferably, the condensate tank has a condensate pressure of 1.5 to 1.6 MPa (e.g., 1.5 MPa, 1.52 MPa, 1.54 MPa, 1.56 MPa, 1.58 MPa, or 1.6 MPa).

[0042] Preferably, the double-effect reboiler is supplied with steam from an external pipeline network, and the steam pressure supplied by the external pipeline network is 0.9 to 1.1 MPa (e.g., 0.9 MPa, 0.94 MPa, 0.98 MPa, 1.04 MPa, 1.08 MPa or 1.1 MPa).

[0043] Preferably, the pressure of the triple-effect condensate tank is 0.7 to 0.8 MPa (e.g., 0.7 MPa, 0.72 MPa, 0.74 MPa, 0.76 MPa, 0.78 MPa or 0.8 MPa).

[0044] Preferably, the pressure of the quadruple-effect condensate tank is 0.5 to 0.6 MPa (e.g., 0.5 MPa, 0.52 MPa, 0.54 MPa, 0.56 MPa, 0.58 MPa or 0.6 MPa).

[0045] Preferably, the five-effect condensate tank has a pressure of 0.4 to 0.5 MPa (e.g., 0.4 MPa, 0.41 MPa, 0.43 MPa, 0.45 MPa, 0.47 MPa, 0.49 MPa, or 0.5 MPa).

[0046] Preferably, the pressure of the six-effect condensate tank is 0.3 to 0.4 MPa (e.g., 0.3 MPa, 0.31 MPa, 0.33 MPa, 0.35 MPa, 0.37 MPa, 0.39 MPa or 0.4 MPa).

[0047] The single-effect flash evaporator maintains a relatively high pressure of 1.25 MPaA. The top gas phase of the single-effect flash evaporator is compressed by an MVR device to increase the same pressure difference, resulting in a low pressure ratio and low power consumption.

[0048] The second-effect reboiler uses fresh steam from the pipeline network, but reduces its evaporation pressure to about 0.720 MPaA, maintaining a large pressure difference with the first-effect flash evaporator. This reduces the heating steam pressure level, requiring only 1.1 MPaA steam, compared to the traditional multi-effect evaporation process which can only use 2.0 MPaA steam. This lower pressure level is beneficial for the low-pressure steam balance of the entire plant.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] (1) The ethylene glycol purification system provided by the present invention has a good purification effect on ethylene glycol. The first effect adopts the evaporation process of falling film evaporator + MVR compression device, which eliminates the consumption of high-pressure steam and uses the new steam for the second effect evaporation. Since the second effect evaporation pressure is low, 1.1MPaA steam can be used. In addition, since the first effect evaporates a large amount of water in the raw material ethylene glycol with low energy consumption, the amount of steam used for subsequent multi-effect evaporation is greatly reduced. Moreover, the present invention has no vacuum effect, and the secondary steam can be fully utilized without heat loss. There is no heat loss of the secondary steam in the vacuum effect, and there is no need to consume a large amount of circulating water required by the vacuum effect condenser.

[0051] (2) The ethylene glycol purification method provided by the present invention is simple and easy to operate, has a good ethylene glycol purification effect, low purification energy consumption, and low cost. Attached Figure Description

[0052] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of the ethylene glycol purification system provided in Embodiment 1 of the present invention;

[0054] Figure 2 This is a schematic diagram of the ethylene glycol purification system provided in Embodiment 2 of the present invention;

[0055] Figure 3 This is a schematic diagram of the ethylene glycol purification system provided in Embodiment 3 of the present invention.

[0056] Figure label:

[0057] 1-First-effect falling film evaporator, 2-Start-up steam pipeline, 3-MVR compressor, 4-Deionized water pipeline, 5-First-effect flash evaporator, 6-Second-effect flash evaporator, 7-Third-effect flash evaporator, 8-Fourth-effect flash evaporator, 9-Fifth-effect flash evaporator, 10-Sixth-effect flash evaporator, 11-First pumping device, 12-Second-effect reboiler, 13-Third-effect reboiler, 14-Fourth-effect reboiler, 15-Fifth-effect reboiler, 16-Sixth-effect reboiler, 17-Second pumping device, 18-First-effect condensate tank, 19-Third-effect condensate tank, 20-Fourth-effect condensate tank, 21-Fifth-effect condensate tank, 22-Sixth-effect condensate tank, 23-Third pumping device, 24-Second-effect condensate tank, 25-Second-effect steam pipeline, 26-Formaldehyde removal tower. Detailed Implementation

[0058] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0059] Example 1

[0060] The ethylene glycol purification system provided in this embodiment, such as Figure 1 As shown, it includes: a single-effect falling film evaporator 1, an MVR compressor unit 3, a single-effect flash tower 5, a double-effect flash tower 6, a triple-effect flash tower 7, a quadruple-effect flash tower 8, a quintuple-effect flash tower 9, a double-effect reboiler 12, a triple-effect reboiler 13, a quadruple-effect reboiler 14, a quintuple-effect reboiler 15, a single-effect condensate tank 18, a triple-effect condensate tank 19, a quadruple-effect condensate tank 20, and a quintuple-effect condensate tank 21;

[0061] The inlet of the first-effect falling film evaporator 1 is connected to the outlet of the first-effect flash evaporator 5; the MVR compression device 3 is installed between the inlet of the first-effect falling film evaporator 1 and the outlet of the first-effect flash evaporator 5; the inlet of the first-effect falling film evaporator 1 is connected to the start-up steam pipeline 2; the outlet of the first-effect falling film evaporator 1 is connected to the inlet of the first-effect flash evaporator 5; and the outlet of the first-effect flash evaporator 5 is connected to the inlet of the first-effect falling film evaporator 1.

[0062] The liquid outlet of the first-effect flash evaporator 5 is connected to the liquid inlet of the second-effect flash evaporator 6; the liquid outlet of the second-effect flash evaporator 6 is connected to the liquid inlet of the second-effect reboiler 12; the gas outlet of the second-effect reboiler 12 is connected to the gas inlet of the second-effect flash evaporator 6; the heat source inlet of the second-effect reboiler 12 is connected to the second-effect steam pipeline 25.

[0063] The outlet of the double-effect flash distillation tower 6 is connected to the heat source inlet of the triple-effect reboiler 13; the outlet of the triple-effect reboiler 13 is connected to the inlet of the triple-effect flash distillation tower 7; the liquid outlet of the double-effect flash distillation tower 6 is connected to the liquid inlet of the triple-effect flash distillation tower 7; the liquid outlet of the triple-effect flash distillation tower 7 is connected to the liquid inlet of the triple-effect reboiler 13; the liquid outlet of the triple-effect reboiler 13 is connected to the water inlet of the triple-effect condensate tank 19; and the outlet of the triple-effect condensate tank 19 is connected to the heat source inlet of the triple-effect reboiler 13.

[0064] The outlet of the triple-effect flash distillation tower 7 is connected to the heat source inlet of the quadruple-effect reboiler 14; the outlet of the quadruple-effect reboiler 14 is connected to the inlet of the quadruple-effect flash distillation tower 8; the liquid outlet of the triple-effect flash distillation tower 7 is connected to the liquid inlet of the quadruple-effect flash distillation tower 8; the liquid outlet of the quadruple-effect flash distillation tower 8 is connected to the liquid inlet of the quadruple-effect reboiler 14; and the liquid outlet of the quadruple-effect reboiler 14 is connected to the liquid inlet of the quadruple-effect condensate tank 20.

[0065] The outlet of the four-effect flash distillation tower 8 is connected to the heat source inlet of the five-effect reboiler 15; the outlet of the five-effect reboiler 15 is connected to the inlet of the five-effect flash distillation tower 9; the liquid outlet of the four-effect flash distillation tower 8 is connected to the liquid inlet of the five-effect flash distillation tower 9; the liquid outlet of the five-effect flash distillation tower 9 is connected to the liquid inlet of the five-effect condensate tank 21; the liquid outlet of the five-effect reboiler 15 is connected to the liquid inlet of the five-effect condensate tank 21; and the outlet of the five-effect condensate tank 21 is connected to the heat source inlet of the five-effect reboiler 15.

[0066] The first-effect flash evaporator 5, the second-effect flash evaporator 6, the third-effect flash evaporator 7, the fourth-effect flash evaporator 8, and the fifth-effect flash evaporator 9 are connected to a deionized water pipeline 4; the first-effect falling film evaporator 1, the first-effect condensate tank 18, the third-effect condensate tank 19, the fourth-effect condensate tank 20, and the fifth-effect condensate tank 21 are connected in sequence; a formaldehyde removal tower 26 is installed above the fourth-effect condensate tank 20;

[0067] A first pumping device 11 is provided between the liquid outlet of the first-effect falling film evaporator 1 and the liquid inlet of the first-effect flash evaporator 5; the liquid outlet of the fifth-effect flash evaporator 9 is connected to a second pumping device 17; and the liquid outlet of the fifth-effect condensate tank 21 is connected to a third pumping device 23.

[0068] Example 2

[0069] The ethylene glycol purification system provided in this embodiment, such as Figure 2 As shown, the only difference from the ethylene glycol purification system provided in Example 1 is that a second-effect condensate tank 24 is provided between the first-effect condensate tank 18 and the third-effect condensate tank 19; the outlet of the second-effect reboiler 12 is connected to the inlet of the second-effect condensate tank 24; the outlet of the second-effect condensate tank 24 is connected to the second-effect steam pipe; and the outlet of the first-effect flash evaporator 5 is connected to the second-effect steam pipe.

[0070] Example 3

[0071] The ethylene glycol purification system provided in this embodiment, such as Figure 3 As shown, the only difference between the ethylene glycol purification system provided in Example 1 and the ethylene glycol purification system is that the ethylene glycol purification system further includes: a six-effect flash distillation tower 10, a six-effect reboiler 16 and a six-effect condensate tank 22;

[0072] The outlet of the five-effect flash distillation tower 9 is connected to the heat source inlet of the six-effect reboiler 16; the outlet of the six-effect reboiler 16 is connected to the inlet of the six-effect flash distillation tower 10; the outlet of the six-effect flash distillation tower 10 is connected to the inlet of the six-effect reboiler 16; the outlet of the five-effect flash distillation tower 9 is connected to the inlet of the six-effect flash distillation tower 10; the outlet of the six-effect reboiler 16 is connected to the inlet of the six-effect condensate tank 22; and the outlet of the six-effect condensate tank 22 is connected to the heat source inlet of the six-effect reboiler 16.

[0073] The five-effect condensate tank 21 and the six-effect condensate tank 22 are connected.

[0074] Example 4

[0075] The ethylene glycol purification method provided in this embodiment uses the ethylene glycol purification system provided in Example 3 and includes the following steps:

[0076] 1. A dilute ethylene glycol solution (ethylene glycol concentration approximately 13 vol%) enters the upper tube box of a single-effect falling film evaporator 1. The pressure of the single-effect flash evaporator is approximately 1.25 MPaA (absolute pressure, the same below). Under the influence of gravity, the dilute ethylene glycol solution flows downwards into the lower tube box along the evaporator tubes in a film-like manner. Heating steam is outside the tubes. The dilute ethylene glycol solution evaporates inside the tubes, and the single-effect falling film evaporator 1 evaporates 20%–40% of the water content from the raw ethylene glycol. The gas-liquid two-phase material in the lower tube box of the single-effect falling film evaporator 1 enters the single-effect flash evaporator 5 for gas-liquid separation. The gas phase in the single-effect flash evaporator 5 consists of water vapor and a small amount of ethylene glycol. It flows upwards and comes into countercurrent contact with the deionized water flowing downwards from the top of the flash evaporator, absorbing the ethylene glycol component in the gas phase and preventing ethylene glycol escape.

[0077] 2. The secondary steam from the top of the first-effect flash evaporator 5 enters the MVR compression unit 3, where the steam pressure is increased by about 0.2 MPa to about 1.45 MPaA. The pressurized secondary steam from the first-effect flash evaporator enters the shell side of the first-effect falling film evaporator 1. The pressure is higher than that inside the evaporator tubes, creating a temperature difference that provides heat for the evaporation of the dilute ethylene glycol solution inside the tubes. The condensate enters the condensate tank of the first-effect evaporator.

[0078] 3. After the liquid phase of the first-effect flash evaporator 5 comes out of the bottom of the tower, it is divided into two parts. One part is pressurized by the first pumping device 11 and returned to the upper tube box of the first-effect falling film evaporator 1 together with the raw material ethylene glycol dilute solution to continue evaporation. The other part enters the second-effect reboiler 12 by pressure.

[0079] 4. The pressure of the double-effect flash evaporator is about 0.720 MPaA. Fresh steam of 1.1 MPaA from the steam pipeline is used as the heat source. The heated material enters the double-effect flash evaporator 6 for gas-liquid separation. The gas phase is the secondary steam of the double-effect flash evaporator, which flows upward and countercurrently contacts the deionized water flowing downward from the top of the flash evaporator to absorb the ethylene glycol in the gas phase. Then it enters the shell side of the triple-effect reboiler 13 as a heat source. The liquid phase enters the tube side of the triple-effect reboiler 13 by its own pressure.

[0080] 5. The pressure of the triple-effect flash tower is about 0.584 MPa. The secondary steam from the top of the double-effect flash tower 6 is used as the heating source. The heated material enters the triple-effect flash tower 7 for gas-liquid separation. The gas phase is the secondary steam from the triple-effect flash tower, which flows upward and countercurrently contacts the deionized water flowing downward from the top of the flash tower to absorb the ethylene glycol in the gas phase. Then it enters the shell side of the quadruple-effect reboiler 14 as a heat source. The liquid phase enters the tube side of the quadruple-effect reboiler 14 by its own pressure.

[0081] 6. The pressure of the four-effect flash tower is about 0.455 MPa. The secondary steam from the top of the three-effect flash tower 7 is used as the heating source. The heated material enters the four-effect flash tower 8 for gas-liquid separation. The gas phase is the secondary steam from the four-effect flash tower, which flows upward and countercurrently contacts the deionized water flowing downward from the top of the flash tower to absorb the ethylene glycol in the gas phase. Then it enters the shell side of the five-effect reboiler 15 as a heat source. The liquid phase enters the tube side of the five-effect reboiler 15 by its own pressure.

[0082] 7. The pressure of the five-effect flash distillation tower is about 0.342 MPa. It uses the secondary steam from the top of the four-effect flash distillation tower 8 as the heating source. The heated material enters the five-effect flash distillation tower 9 for gas-liquid separation. The gas phase is the secondary steam from the five-effect flash distillation tower, which flows upward and countercurrently contacts the deionized water flowing downward from the top of the flash distillation tower to absorb the ethylene glycol in the gas phase. Then it is divided into two parts. One part enters the shell side of the five-effect reboiler 15 as a heat source, and the other part serves as the heat source for the reboiler of the CO2 desorption tower. The liquid phase enters the tube side of the five-effect reboiler 15 by its own pressure.

[0083] 8. The pressure of the six-effect flash tower is about 0.205 MPa. The secondary steam from the top of the five-effect flash tower 9 is used as the heating source. The heated material enters the six-effect flash tower 10 for gas-liquid separation. The gas phase is the secondary steam from the six-effect flash tower, which flows upward and countercurrently contacts the deionized water flowing downward from the top of the flash tower to absorb the ethylene glycol in the gas phase. Then it is divided into two parts. One part is used as the heating source for the ethylene glycol reaction feed, and the other part is used as the direct stripping steam for the ethylene oxide stripping tower. The liquid phase is the ethylene glycol solution concentrated to the target concentration, which is sent to the next processing unit by the second pumping device 17.

[0084] The condensate from each effect of the secondary steam is distilled using a staged flash evaporation process, the steps of which are as follows:

[0085] 1. The secondary steam condensate from the first effect enters the first effect condensate tank at a pressure of approximately 1.55 MPaA. The secondary steam condensate then enters the third effect condensate tank by its own pressure.

[0086] 2. The double-effect heating steam is 1.1MPaA fresh steam from the pipeline network, and the condensate from the fresh steam enters the condensate pipeline network of the unit;

[0087] 3. The condensate from the secondary steam of the third-effect reactor and the condensate from the secondary steam of the first-effect reactor enter the third-effect condensate tank together. The pressure is about 0.720 MPaA. The condensate undergoes flash evaporation in the tank, and the flash steam enters the third-effect reboiler 13 together with the secondary steam of the second-effect reactor. The condensate from the third-effect reactor enters the fourth-effect condensate tank 20 and the formaldehyde removal tower 26 by its own pressure.

[0088] 4. The condensate from the fourth-effect secondary steam tank and the condensate from the third-effect condensate tank enter the fourth-effect condensate tank and the formaldehyde removal tower 26 together, with a pressure of about 0.584 MPaA. The formaldehyde removal tower 26 is located above the fourth-effect condensate tank. The condensate first enters the formaldehyde removal tower 26, where the aldehyde components are removed by stripping. Then it flows by gravity to the fourth-effect condensate tank, where the formaldehyde removal steam is used as a heat source for heating other materials. The fourth-effect condensate enters the fifth-effect condensate tank 21 by its own pressure.

[0089] 5. The condensate from the fifth-effect secondary steam and the condensate from the fourth-effect condensate tank enter the fifth-effect condensate tank together, with a pressure of about 0.455 MPaA. The condensate undergoes flash evaporation in the tank, and the flash steam enters the fifth-effect reboiler 15 together with the fourth-effect secondary steam. The condensate from the fifth-effect enters the sixth-effect condensate tank 22 by its own pressure.

[0090] 6. The condensate from the secondary steam of the sixth effect and the condensate from the secondary steam of the fifth effect enter the sixth effect condensate tank together. The pressure is about 0.342 MPaA. The condensate undergoes flash evaporation in the tank, and the flash steam enters the sixth effect reboiler 16 together with the secondary steam of the fourth effect. The condensate from the sixth effect is pumped to the subsequent treatment unit.

[0091] Comparative Example 1

[0092] The EOEG unit (traditional seven-effect process) of a petrochemical company finally obtained ethylene glycol with a concentration of 77%.

[0093] A comparison was made between the EOEG unit (traditional seven-effect process) of a petrochemical company and the method of Example 4 of this invention. The concentration of the raw material ethylene glycol was the same, and the concentration of the concentrated ethylene glycol solution was also the same. Specific energy consumption details are shown in Table 1. Table 1 shows that the ethylene glycol purification method provided in Example 4 of this invention has an evaporation capacity of 138 t / h for the first effect, the MVR compressor 3 increases the secondary steam pressure from 1.25 MPaA to 1.45 MPaA, the MVR compressor 3 consumes 1520 kW of electricity, the second effect consumes 37 t / h of 1.1 MPaA fresh steam, and the total secondary steam supplied to the fifth and sixth effects is 80 t / h. Its operating energy consumption is far lower than the energy consumption of the company's EOEG unit before modification.

[0094] Table 1

[0095] 2.0MPaA new steam t / h -59 - 1.1 MPaA new steam t / h - -37 Five-effect external secondary steam supply t / h 15 21 Six-effect external secondary steam supply t / h 47 59 Circulating water t / h -3600 0 electricity kW 0 -1520 Energy consumption kgce / h -1580 3048

[0096] Note: "-" indicates consumption.

[0097] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. An ethylene glycol purification system, characterized in that, include: Single-effect falling film evaporator, MVR compressor unit, single-effect flash tower, double-effect flash tower, triple-effect flash tower, quadruple-effect flash tower, quintuple-effect flash tower, double-effect reboiler, triple-effect reboiler, quadruple-effect reboiler, quintuple-effect reboiler, single-effect condensate tank, triple-effect condensate tank, quadruple-effect condensate tank and quintuple-effect condensate tank; The inlet of the first-effect falling film evaporator is connected to the outlet of the first-effect flash evaporator; the MVR compression device is installed between the inlet of the first-effect falling film evaporator and the outlet of the first-effect flash evaporator; the inlet of the first-effect falling film evaporator is connected to the start-up steam pipeline; the outlet of the first-effect falling film evaporator is connected to the inlet of the first-effect flash evaporator; and the outlet of the first-effect flash evaporator is connected to the inlet of the first-effect falling film evaporator. The liquid outlet of the first-effect flash evaporator is connected to the liquid inlet of the second-effect flash evaporator; the liquid outlet of the second-effect flash evaporator is connected to the liquid inlet of the second-effect reboiler; the gas outlet of the second-effect reboiler is connected to the gas inlet of the second-effect flash evaporator; the heat source inlet of the second-effect reboiler is connected to the second-effect steam pipeline. The outlet of the double-effect flash evaporator is connected to the heat source inlet of the triple-effect reboiler; the outlet of the triple-effect reboiler is connected to the inlet of the triple-effect flash evaporator; the liquid outlet of the double-effect flash evaporator is connected to the liquid inlet of the triple-effect flash evaporator; the liquid outlet of the triple-effect flash evaporator is connected to the liquid inlet of the triple-effect reboiler; the liquid outlet of the triple-effect reboiler is connected to the inlet of the triple-effect condensate tank; and the outlet of the triple-effect condensate tank is connected to the heat source inlet of the triple-effect reboiler. The outlet of the triple-effect flash distillation tower is connected to the heat source inlet of the quadruple-effect reboiler; the outlet of the quadruple-effect reboiler is connected to the inlet of the quadruple-effect flash distillation tower; the liquid outlet of the triple-effect flash distillation tower is connected to the liquid inlet of the quadruple-effect flash distillation tower; the liquid outlet of the quadruple-effect flash distillation tower is connected to the liquid inlet of the quadruple-effect reboiler; and the liquid outlet of the quadruple-effect reboiler is connected to the liquid inlet of the quadruple-effect condensate tank. The outlet of the four-effect flash distillation tower is connected to the heat source inlet of the five-effect reboiler; the outlet of the five-effect reboiler is connected to the inlet of the five-effect flash distillation tower; the liquid outlet of the four-effect flash distillation tower is connected to the liquid inlet of the five-effect flash distillation tower; the liquid outlet of the five-effect flash distillation tower is connected to the liquid inlet of the five-effect condensate tank; the liquid outlet of the five-effect reboiler is connected to the liquid inlet of the five-effect condensate tank; and the outlet of the five-effect condensate tank is connected to the heat source inlet of the five-effect reboiler. The first-effect flash evaporator, the second-effect flash evaporator, the third-effect flash evaporator, the fourth-effect flash evaporator, and the fifth-effect flash evaporator are connected to a deionized water pipeline above them; the first-effect falling film evaporator, the first-effect condensate tank, the third-effect condensate tank, the fourth-effect condensate tank, and the fifth-effect condensate tank are connected in sequence. The starting pressure of the single-effect falling film evaporator is 1.9~2.1 MPaA; The pressure at the outlet of the single-effect flash evaporator is 1.2~1.9 MPa. The pressure of the double-effect flash evaporator is 0.7~0.8 MPa. The pressure of the triple-effect flash evaporator is 0.5~0.6 MPa. The pressure of the four-effect flash evaporator is 0.4~0.5 MPa. The pressure of the five-effect flash evaporator is 0.3~0.4 MPa. The pressure of the single-effect condensate tank is 1.5~1.6 MPa. The double-effect reboiler uses an external pipeline to supply steam, and the steam pressure supplied by the external pipeline is 0.9~1.1 MPa. The pressure of the triple-effect condensate tank is 0.7~0.8 MPa. The pressure of the four-effect condensate tank is 0.5~0.6 MPa. The pressure of the five-effect condensate tank is 0.4~0.5 MPa.

2. The ethylene glycol purification system according to claim 1, characterized in that, A second-effect condensate tank is provided between the first-effect condensate tank and the third-effect condensate tank; the outlet of the second-effect reboiler is connected to the inlet of the second-effect condensate tank; the outlet of the second-effect condensate tank is connected to the second-effect steam pipe; and the outlet of the first-effect flash evaporator is connected to the second-effect steam pipe.

3. The ethylene glycol purification system according to claim 2, characterized in that, The ethylene glycol purification system also includes: a six-effect flash distillation tower, a six-effect reboiler, and a six-effect condensate tank; The outlet of the five-effect flash distillation tower is connected to the heat source inlet of the six-effect reboiler; the outlet of the six-effect reboiler is connected to the inlet of the six-effect flash distillation tower; the outlet of the six-effect flash distillation tower is connected to the inlet of the six-effect reboiler; the outlet of the five-effect flash distillation tower is connected to the inlet of the six-effect flash distillation tower; the outlet of the six-effect reboiler is connected to the inlet of the six-effect condensate tank; and the outlet of the six-effect condensate tank is connected to the heat source inlet of the six-effect reboiler. The five-effect condensate tank and the six-effect condensate tank are connected.

4. The ethylene glycol purification system according to any one of claims 1 to 3, characterized in that, A formaldehyde removal tower is installed above the four-effect condensate tank.

5. The ethylene glycol purification system according to any one of claims 1 to 3, characterized in that, A first pumping device is installed between the liquid outlet of the first-effect falling film evaporator and the liquid inlet of the first-effect flash evaporator.

6. A method for purifying ethylene glycol, using the ethylene glycol purification system according to any one of claims 1 to 5, characterized in that, Includes the following steps: Ethylene glycol dilute solution is subjected to falling film evaporation to obtain gas-liquid two-phase material and first-effect secondary steam condensate; the gas-liquid two-phase material is subjected to a first flash evaporation treatment to obtain a first-effect flash vapor phase and a first-effect flash liquid phase; The first-effect flash vapor phase and the deionized water undergo a first countercurrent contact to obtain first-effect secondary steam; the first-effect secondary steam is pressurized to provide heat for the falling film evaporation of the dilute ethylene glycol solution; a portion of the first-effect flash liquid phase is mixed with the dilute ethylene glycol solution and then subjected to falling film evaporation; another portion of the first-effect flash liquid phase undergoes a second flash evaporation treatment to obtain a second-effect flash vapor phase and a second-effect flash liquid phase; the second-effect steam pipe provides a heat source for the second flash evaporation treatment; The liquid phase of the second-effect flash evaporation undergoes a third flash evaporation treatment to obtain a vapor phase and a liquid phase of the third-effect flash evaporation; the vapor phase of the second-effect flash evaporation undergoes a second countercurrent contact with the deionized water to obtain secondary steam of the second-effect; the secondary steam of the second-effect provides a heat source for the third flash evaporation treatment; the condensate of the secondary steam of the first-effect enters the condensate tank of the third-effect through the condensate tank of the first-effect, mixes with the condensate of the secondary steam of the third-effect, and then enters the reboiler of the third-effect to undergo a reboiling reaction of the third-effect; The triple-effect flash liquid phase undergoes a fourth flash evaporation process to obtain a quadruple-effect flash vapor phase and a quadruple-effect flash liquid phase; the triple-effect flash vapor phase undergoes a third countercurrent contact with deionized water to obtain triple-effect secondary steam; the triple-effect secondary steam provides a heat source for the fourth flash evaporation process; The liquid phase of the fourth-effect flash evaporation undergoes a fifth flash evaporation process to obtain a fifth-effect flash vapor phase and a fifth-effect flash liquid phase; the fourth-effect flash vapor phase undergoes a fourth countercurrent contact with deionized water to obtain fourth-effect secondary steam; the fourth-effect secondary steam provides a heat source for the fifth flash evaporation process; the secondary steam condensate in the third-effect condensate tank enters the fifth-effect condensate tank through the fourth-effect condensate tank, mixes with the fifth-effect secondary steam condensate, and then enters the fifth-effect reboiler to undergo a fifth-effect reboiling reaction.

7. The method for purifying ethylene glycol according to claim 6, characterized in that, The method for purifying ethylene glycol also includes: The liquid phase of the five-effect flash evaporation undergoes a sixth flash evaporation process to obtain a six-effect flash vapor phase and a six-effect flash liquid phase; the five-effect flash vapor phase undergoes a fifth countercurrent contact with deionized water to obtain five-effect secondary steam; the five-effect secondary steam provides a heat source for the sixth flash evaporation process; the condensate from the secondary steam in the five-effect condensate tank enters the six-effect condensate tank, mixes with the condensate from the six-effect secondary steam, and then enters the six-effect reboiler for a six-effect reboiling reaction.

8. The method for purifying ethylene glycol according to claim 6 or 7, characterized in that, After the secondary steam condensate leaves the triple-effect condensate tank, it undergoes formaldehyde removal treatment before entering the quadruple-effect condensate tank.

9. The method for purifying ethylene glycol according to claim 6 or 7, characterized in that, The starting pressure of the single-effect falling film evaporator is 1.9~2.1 MPaA; The pressure at the outlet of the single-effect flash evaporator is 1.2~1.9 MPa. The pressure of the double-effect flash evaporator is 0.7~0.8 MPa. The pressure of the triple-effect flash evaporator is 0.5~0.6 MPa. The pressure of the four-effect flash evaporator is 0.4~0.5 MPa. The pressure of the five-effect flash evaporator is 0.3~0.4 MPa. The pressure of the six-effect flash evaporator is 0.2~0.3 MPa.

10. The method for purifying ethylene glycol according to claim 6 or 7, characterized in that, The pressure of the single-effect condensate tank is 1.5~1.6 MPa. The double-effect reboiler uses an external pipeline to supply steam, and the steam pressure supplied by the external pipeline is 0.9~1.1 MPa. The pressure of the triple-effect condensate tank is 0.7~0.8 MPa. The pressure of the four-effect condensate tank is 0.5~0.6 MPa. The pressure of the five-effect condensate tank is 0.4~0.5 MPa. The pressure of the six-effect condensate tank is 0.3~0.4 MPa.

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