Automatic dehydration method of ethylene tar under negative pressure

Abstract

The application provides a kind of ethylene tar negative pressure automatic dehydration method, belongs to the technical field of ethylene tar processing;In the application, the sequential control dehydration program is combined with the density detection alarm interlock program to realize the automatic dehydration of ethylene tar;The ethylene tar negative pressure automatic dehydration system described in the application cancels the tower kettle reboiler, adds the underground sewage tank for secondary oil-water separation, reduces the operating energy consumption while further recovering the waste oil, reduces the COD (chemical oxygen demand) content of the discharged sewage, reduces the treatment load of the sewage treatment plant, and has good practicability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ethylene tar processing, and particularly relates to a negative pressure automatic dehydration method for ethylene tar. BACKGROUND

[0002] Ethylene tar is a byproduct in the production of ethylene, accounting for about 10% to 20% of the ethylene output. It is mainly composed of carbon and hydrogen elements, with low sulfur and nitrogen content and basically no metal impurities. In addition, ethylene tar also contains water, and the water content is generally about 0.5%, which is affected by the operation of the quenching oil tower of the upstream ethylene cracking device. At present, except for 25% to 30% of ethylene tar used as fuel, the rest needs to be treated by distillation separation, that is, cracking naphthalene fraction and ethylene heavy tar are obtained by separation through a distillation column. Ethylene heavy tar is the raw material for downstream coating pitch or carbon black, and cracking naphthalene fraction needs to meet the requirements of SH / T 1794-2015 “Cracking Naphthalene Fraction” standard, so the water content needs to be controlled to be less than 1%. Since the density of cracking naphthalene fraction obtained by separating ethylene tar is usually 0.98 to 1.0 g / cm 3 , which is close to the density of water, it is difficult to separate free water by density difference, and it is easy to cause the water content of cracking naphthalene fraction to be greater than 1%, exceeding the water content index requirements in the standard, which has many adverse effects on the product quality of the subsequent system, equipment corrosion and winter antifreeze.

[0003] CN105038852A discloses a hydrogenation process for ethylene tar, in which it is recorded that the ethylene tar raw material is subjected to dehydration treatment in a pretreatment unit and mechanical impurities are removed, and the water content of the dehydrated ethylene tar raw material is less than 0.3wt% of the total amount of the raw material. However, this technology does not provide a specific dehydration process, and the dehydration rate is low, which does not meet the index requirements of precision dehydration.

[0004] CN110484289A discloses a tar negative pressure dehydration system and method, in which it is recorded that the tar is heated to 120 to 130℃ and then sent to a dehydration tower for dehydration, and the pressure of the dehydration tower is-30kPa to-50kPa, and the water content in the anhydrous tar is less than 0.8%. In this technology, the water content in the anhydrous tar is still constant, the dehydration rate is low, and the index requirements of precision dehydration are not met.

[0005] CN118240581A discloses a system and method for tar dehydration tower overhead oil and water cooling and separation, in which a dehydration tower overhead oil and water condensation cooling system in the traditional coking industry is used, which includes a condensation device, a cooling device, an oil and water separation device, a light oil intermediate tank, a separated water intermediate tank and the like. The dehydration tower overhead oil and water condensation cooling system integrates multiple devices in one tower body, which reduces the occupied area and cost, but still has problems such as difficulty in equipment inspection and maintenance, inability to accurately control the water content in the light oil and the oil content in the separated water.

[0006] Therefore, a device and a process method for ethylene tar dehydration and automatic dehydration are needed to be developed to reduce the adverse effects of water on the product quality of the subsequent system, equipment corrosion and winter antifreeze, improve the reliability of the water cutting system and reduce the labor intensity of the operator. SUMMARY

[0007] In view of the defects of low ethylene tar dehydration rate and inability to automatically dehydrate in the prior art, the present application provides a negative pressure automatic dehydration method for ethylene tar; the automatic dehydration of ethylene tar is realized by combining the sequential control dehydration program with the density detection alarm interlocking program in the present application; the tar negative pressure automatic dehydration system cancels the reflux and the column still reboiler, adds an underground sewage tank for secondary oil-water separation, reduces the operation energy consumption, further recovers the waste oil, reduces the COD (chemical oxygen demand) content of the discharged sewage, reduces the treatment load of the sewage treatment plant, and has good practicability.

[0008] In order to achieve the above technical purpose, the present application adopts the following technical means:

[0009] The present application first provides a tar negative pressure automatic dehydration system for ethylene, which comprises a heater, a dehydration tower, an oil-water separation tank, a sewage buffer tank and a secondary oil-water separation tank which are sequentially connected;

[0010] The dehydration tower column still is communicated with a column still pump, and the top of the dehydration tower is communicated with the oil-water separation tank through a water cooler and a pipeline;

[0011] A density detector, a shut-off valve one and an adjusting valve one are sequentially arranged between the oil-water separation tank and the sewage buffer tank, and the oil-water separation tank is further communicated with a light component extraction pump for collecting light components;

[0012] The secondary oil-water separation tank is communicated with a self-priming pump.

[0013] Preferably, the oil-water separation tank and the secondary oil-water separation tank are internally provided with a partition plate.

[0014] Preferably, the oil-water separation tank is communicated with a vacuum system, an adjusting valve four for controlling the flow of the heating medium is arranged on the heater, the adjusting valve four and the material outlet temperature of the heater form a control loop to automatically control the material outlet temperature of the heater.

[0015] Preferably, a pressure detector, a shut-off valve two and an adjusting valve two for connecting the vacuum system, an adjusting valve three and a shut-off valve three for nitrogen gas inlet are respectively arranged on the top of the sewage buffer tank.

[0016] A shut-off valve four for controlling the discharge of the sewage buffer tank is arranged on the pipeline communicated between the sewage buffer tank and the secondary oil-water separation tank.

[0017] The application also provides a method for automatically dehydrating ethylene tar under negative pressure, which is realized based on the above-mentioned system for automatically dehydrating ethylene tar under negative pressure and comprises the following steps:

[0018] (1) The ethylene tar is heated by a heater and then enters a dehydration tower, and anhydrous ethylene tar is obtained from a tower kettle, and a mixture of light components and sewage is obtained from gas phase at the top of the dehydration tower after the gas phase is cooled by a water cooler;

[0019] (2) The mixture of light components and sewage obtained in step (1) is sent to an oil-water separation tank to perform oil-water separation, and light components and sewage are obtained;

[0020] (3) The light components obtained in step (2) are sent out of the device by a light component extraction pump, and the sewage separated from the oil-water separation tank is sent to a sewage buffer tank;

[0021] (4) The sewage in the sewage buffer tank in step (3) is discharged to a secondary oil-water separation tank to perform secondary oil-water separation, the sewage in the water side is sent to a sewage treatment plant by a self-priming pump, and the sewage-containing dirty oil in the oil side is sent to an ethylene tar raw material tank after being recovered.

[0022] Preferably, in step (1), the heater controls the temperature of the ethylene tar entering the dehydration tower by adjusting the flow of the heating medium through a regulating valve four, and the temperature is controlled at 90-130°C, more preferably, the temperature is controlled at 100-110°C.

[0023] Preferably, in step (1), the dehydration tower has a pressure of-90 kPa to-80 kPa, a top temperature of 65-100°C, 6-8 theoretical plates, and no tower kettle reboiler.

[0024] The dehydration tower is a structured packing with a specific surface area of 200-300 m 2 / m 3 ;

[0025] The temperature of the mixture after being cooled by the water cooler is 30-40°C.

[0026] Preferably, in step (3), when the sewage separated from the oil-water separation tank enters the sewage buffer tank, a density detector is set with a low-density alarm value and a low-density low-alarm interlocking value.

[0027] When the density of the sewage decreases to 985.0-988.0 kg / m 3 , a low-density audible and visual alarm is triggered;

[0028] When the density of the sewage continues to decrease to 975.0-980.0 kg / m 3 , a low-density low-alarm is triggered and a water phase outlet shut-off valve is closed at the same time.

[0029] Preferably, the ethylene tar negative pressure automatic dehydration method comprises the following sequential control processes:

[0030] (A) Normal dehydration condition:

[0031] The oil-water separation tank outlet cut-off valve is in an open state, the regulating valve one controls the oil-water separation tank water bag boundary position to 50%, the sewage buffer tank top nitrogen cut-off valve three and the regulating valve three are in a closed state, the vacuum system regulating valve two and cut-off valve two are in an open state, and the sewage buffer tank bottom cut-off valve four is in a closed state.

[0032] (B) Sewage buffer tank drainage condition:

[0033] When the sewage buffer tank liquid level reaches 80%, the interlock cut-off valve one is closed, the regulating valve one is closed, the tank top vacuum system cut-off valve two and the regulating valve two are closed, the sewage buffer tank top nitrogen cut-off valve three is opened, the regulating valve three is opened, the sewage buffer tank pressure is controlled to 30 kPa, and the tank bottom cut-off valve four is opened.

[0034] (C) Resuming normal dehydration condition:

[0035] When the sewage buffer tank liquid level reaches 15%, the interlock cut-off valve four is closed, the nitrogen cut-off valve three and the regulating valve three are closed, the sewage buffer tank top vacuum system cut-off valve two is opened, the regulating valve two is opened, the cut-off valve one is opened, the regulating valve one is opened, and the oil-water separation tank water bag boundary position is adjusted to 50% through the regulating valve one.

[0036] Compared with the prior art, the beneficial effects of the present application are:

[0037] 1) The method and device of the present application realize automatic dehydration of ethylene tar through sequential control, improve the degree of automation, and reduce the labor intensity of the operator.

[0038] 2) The device of the present application increases the density detection and alarm interlocking system at the water phase outlet of the oil-water separation tank. 3 When the density decreases to 985.0-988.0 kg / m 3 , the low-density sound and light alarm is triggered to prompt the operator to check and confirm on site, and when the density continues to decrease to 975.0-980.0 kg / m 3 , the low-density low alarm is triggered and the water phase outlet cut-off valve is closed, ensuring the reliability of the water cutting system.

[0039] 3) This invention employs a two-stage oil-water separation process to further reduce the COD content of discharged wastewater and alleviate the treatment load on wastewater treatment plants. Furthermore, the water content in the anhydrous ethylene tar of this invention can be stably controlled to below 150 mg / kg, and the overall dehydration rate of the ethylene tar is greater than 97%, exceeding the traditional 90% dehydration rate, thus meeting the requirements for fine dehydration. Attached Figure Description

[0040] Figure 1 This is a flow chart of an automatic dehydration process for ethylene tar according to the present invention.

[0041] Attached reference numerals: 1-Heater, 2-Dehydration tower, 3-Water cooler, 4-Oil-water separator, 5-Density meter, 6-Shut-off valve one, 7-Regulating valve one, 8-Sewage buffer tank, 9-Shut-off valve two, 10-Regulating valve two, 11-Regulating valve three, 12-Shut-off valve three, 13-Shut-off valve four, 14-Secondary oil-water separator, 15-Self-priming pump, 16-Light component extraction pump, 17-Tower bottom pump, 18-Regulating valve four. Detailed Implementation

[0042] The following is in conjunction with the appendix Figure 1 The present invention will be further described in detail with reference to the embodiments.

[0043] Example 1:

[0044] This embodiment provides an automatic negative pressure dehydration system for ethylene tar, the structure of which is as follows: Figure 1 As shown, it specifically includes: a heater 1, a dehydration tower 2, an oil-water separator 4, a wastewater buffer tank 8, and a secondary oil-water separator 14 connected in sequence; the bottom of the dehydration tower 2 is connected to the bottom pump 17, and the top of the tower is connected to the oil-water separator 4 via a water cooler 3; a density detector 5, a shut-off valve 6, and a regulating valve 7 are sequentially installed between the oil-water separator 4 and the wastewater buffer tank 8; the oil-water separator 4 is also connected to a light component extraction pump 16 for collecting light components; the secondary oil-water separator 14 is connected to a self-priming pump 15.

[0045] In some embodiments, the oil-water separator 4 and the secondary oil-water separator 14 are equipped with baffles. The oil-water separator 4 is connected to a vacuum system, and the heater 1 is equipped with a regulating valve 4 18 to control the flow rate of the heating medium. The regulating valve 4 18 and the material outlet temperature of the heater 1 form a control loop to automatically control the material outlet temperature of the heater 1. The top of the sewage buffer tank 8 is equipped with a pressure detector, a shut-off valve 2 9 and a regulating valve 2 10 for connecting to the vacuum system, and a regulating valve 3 11 and a shut-off valve 3 12 for nitrogen gas inlet. The pipe connecting the sewage buffer tank 8 and the secondary oil-water separator 14 is equipped with a shut-off valve 4 13 to control the discharge from the bottom of the sewage buffer tank 8.

[0046] Example 2:

[0047] The present embodiment provides a dehydration method of the tar negative pressure automatic dehydration system described in embodiment 1, and specifically explains and describes it, which comprises:

[0048] (1) The ethylene tar is heated by the heater 1 and then enters the dehydration tower 2, and the waterless ethylene tar is obtained in the tower kettle, and the light component and the sewage mixture are obtained after the gas phase at the top is cooled by the water cooler 3. In the operation process, the ethylene tar feed heater 1 controls the flow of the heating medium through the regulating valve four 18, so as to control the temperature of the ethylene tar entering the dehydration tower 2 at 100-110℃.

[0049] The dehydration tower 2 is controlled at a pressure of-90 kPa to-80 kPa, and the top temperature is 65-100℃. The dehydration tower 2 has 6-8 theoretical plates, and the dehydration tower 2 has no tower kettle reboiler. The dehydration tower 2 is regular filler, and the specific surface area is 200-300m 2 / m 3 .

[0050] The temperature of the mixture after being cooled by the dehydration tower top water cooler 3 is 30-40℃.

[0051] (2) The light component and the sewage mixture obtained in step (1) are subjected to oil-water separation in the oil-water separation tank 4 with a partition plate to obtain the light component and the sewage.

[0052] (3) The light component obtained in step (2) is sent out of the device by the light component extraction pump 16, and the sewage separated from the water bag of the oil-water separation tank 4 is sent to the sewage buffer tank 8. The material pipeline from the oil-water separation tank 4 to the sewage buffer tank 8 contains the density detector 5, the shut-off valve one 6 and the regulating valve one 7 in sequence, wherein the density detector sets the low density alarm value and the low density low interlock value.

[0053] (4) The sewage in the sewage buffer tank in step (3) is discharged to the secondary oil-water separation tank 14 with a partition plate for secondary oil-water separation, the sewage in the water side is sent to the sewage treatment plant by the self-priming pump 15, and the sewage containing water in the oil side is sent to the ethylene tar raw material tank for recovery.

[0054] The top of the sewage buffer tank 8 is respectively provided with a pressure detector, a shut-off valve two 9 and a regulating valve two 10 for connecting the vacuum system, a regulating valve three 11 and a shut-off valve three 12 for nitrogen gas inlet, and a shut-off valve four 13 for controlling the discharge of the bottom of the sewage buffer tank 8 is arranged on the pipeline connecting the sewage buffer tank 8 and the secondary oil-water separation tank 14. In the actual operation process, the dehydration process is controlled in sequence as follows:

[0055] (A) Normal dehydration condition:

[0056] The oil-water separation tank 4 outlet cut-off valve 6 is in an open state, the regulating valve 7 is open, the sewage buffer tank 8 top nitrogen cut-off valve 3 11 and the regulating valve 3 12 are in a closed state, the sewage buffer tank 8 bottom cut-off valve 4 13 is in a closed state, and the sewage buffer tank 8 bottom cut-off valve 4 13 is in a closed state.

[0057] (B) Sewage buffer tank drainage working condition:

[0058] When the sewage buffer tank 8 liquid level reaches 80%, the interlock cut-off valve 6 is closed, the regulating valve 7 is closed, the sewage buffer tank top vacuum system cut-off valve 9 is closed, the regulating valve 2 10 is closed, the sewage buffer tank top nitrogen cut-off valve 3 12 is opened, the regulating valve 3 11 is opened, the sewage buffer tank pressure is controlled to 30 kPa, and the sewage buffer tank bottom cut-off valve 4 13 is opened.

[0059] (C) Resume normal dehydration working condition:

[0060] When the sewage buffer tank liquid level reaches 15%, the interlock cut-off valve 4 13 is closed, the nitrogen cut-off valve 3 12 is closed, the regulating valve 3 11 is closed, the sewage buffer tank top vacuum system cut-off valve 2 9 is opened, the regulating valve 2 10 is opened, the cut-off valve 6 is opened, the regulating valve 1 7 is opened, and the oil-water separation tank water package boundary position is adjusted to 50% through the regulating valve 1 7.

[0061] The whole process repeats the above-mentioned sequence control dehydration process to realize automatic dehydration in the whole process.

[0062] Example 3:

[0063] This embodiment further illustrates the dehydration method described in the present application by specific ethylene tar dehydration, which comprises the following steps:

[0064] (1) The ethylene tar flow is 20,000 kg / h, the water content is 0.5%, and after being heated by the heater 1, it enters the dehydration tower 2, and the water-free ethylene tar is obtained at the tower bottom. The light component and sewage mixture are obtained after the gas phase at the tower top is cooled by the water cooler 3. During the operation, the ethylene tar feed heater 1 controls the flow of the heating medium through the regulating valve 4 18, so as to control the temperature of the ethylene tar entering the dehydration tower 2 at 110°C.

[0065] The dehydration tower 2 pressure is controlled at -80 kPa, the tower top temperature is 85°C, the dehydration tower 2 has 6 theoretical plates, the dehydration tower 2 has no tower bottom reboiler, and the dehydration tower 2 is regular packing with a specific surface area of 250 m 2 / m 3 .

[0066] The temperature of the mixture after being cooled by the dehydration tower top water cooler 3 is 35°C.

[0067] (2) The mixture of light components and sewage obtained in step (1) is subjected to oil-water separation in the oil-water separation tank 4 with a partition plate to obtain light components and sewage;

[0068] (3) The light components obtained in step (2) are sent out of the device by a light component extraction pump 16, and the sewage separated from the water package of the oil-water separation tank is sent to the sewage buffer tank 8;

[0069] The material pipeline from the water package of the oil-water separation tank 4 to the sewage buffer tank 8 successively comprises a density detector 5, a shut-off valve one 6 and a regulating valve one 7, wherein the density detector is set to have a low density alarm value of 985 kg / m 3 , a low low interlock value of 975 kg / m 3 . When the low density alarm value of the density detector is triggered, the operator is reminded to check and confirm on site, and when the low low interlock value of the density detector is triggered, the interlock shut-off valve one 6 is closed.

[0070] (4) The sewage in the sewage buffer tank in step (3) is discharged to the secondary oil-water separation tank 14 with a partition plate for secondary oil-water separation, the sewage in the water side is sent to a sewage treatment plant by a self-priming pump 15, and the water-containing sewage oil in the oil side is sent to an ethylene tar raw material tank for recovery.

[0071] Sequential control dehydration process:

[0072] (A) Normal dehydration condition:

[0073] The shut-off valve one 6 at the outlet of the oil-water separation tank 4 is in an open state, the regulating valve one 7 is opened to control the water package boundary position of the oil-water separation tank 4 to 50%, the nitrogen shut-off valve three 11 and the regulating valve three 12 at the top of the sewage buffer tank 8 are in a closed state, the shut-off valve two 9 and the regulating valve two 10 of the vacuum system are in an open state, and the shut-off valve four 13 at the bottom of the sewage buffer tank 8 is in a closed state;

[0074] (B) Sewage buffer tank drainage condition:

[0075] When the liquid level of the sewage buffer tank 8 reaches 80%, the interlock shut-off valve one 6 is closed, the regulating valve one 7 is closed, the shut-off valve two 9 and the regulating valve two 10 of the vacuum system at the top of the tank are closed, the nitrogen shut-off valve three 12 and the regulating valve three 11 at the top of the sewage buffer tank are opened, the pressure of the sewage buffer tank is controlled to 30 kPa, and the shut-off valve four 13 at the bottom of the tank is opened;

[0076] (C) Resume normal dehydration condition:

[0077] When the sewage buffer tank liquid level reaches 15%, the interlock cut-off valve four 13 is closed, the nitrogen cut-off valve three 12 is closed, the regulating valve three 11 is closed, the sewage buffer tank top cut-off valve two 9 is opened, the regulating valve two 10 is opened, the cut-off valve one 6 is opened, and the regulating valve one 7 is opened, and the oil-water separation tank water package boundary level is adjusted to 50% through the regulating valve one 7.

[0078] The whole process repeats the above-mentioned sequence control dehydration process to realize automatic dehydration in the whole process.

[0079] Through the above process, the water content in the anhydrous ethylene tar is 136 mg / kg, and the dehydration rate of the ethylene tar reaches 97.2%.

[0080] Example 4:

[0081] The steps of the example are the same as those of example 3.

[0082] In step (1), the temperature of the ethylene tar entering the dehydration tower 2 is 100℃, the pressure of the dehydration tower 2 is controlled at-90 kPa, and the top temperature is 68℃.

[0083] Through the above process, the water content in the anhydrous ethylene tar is 70 mg / kg, and the dehydration rate of the ethylene tar reaches 98.6%.

[0084] In summary, the present application provides an ethylene tar negative pressure automatic dehydration system and method, which combines the sequence control dehydration program with the density detection alarm interlocking program to realize automatic dehydration of ethylene tar. The tar negative pressure automatic dehydration system described in the present application cancels the reflux and the column bottom reboiler, adds an underground sewage tank for secondary oil-water separation, reduces the operating energy consumption, further recovers waste oil, reduces the COD (chemical oxygen demand) content of the discharged sewage, reduces the treatment load of the sewage treatment plant, and has good practicability.

[0085] The above-mentioned embodiments are preferred embodiments of the present application, but the present application is not limited to the above-mentioned embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.

Claims

1. A method for automatic dehydration of ethylene tar under negative pressure, characterized by, The method is realized based on the ethylene tar negative pressure automatic dehydration system, and comprises the following steps: (1) ethylene tar is heated by a heater and then enters a dehydration tower, and anhydrous ethylene tar is obtained from the tower kettle, and a mixture of light components and sewage is obtained from the gas phase at the top of the tower after being cooled by a water cooler; the heater controls the temperature of the ethylene tar entering the dehydration tower by adjusting the flow of the heating medium, and the temperature is controlled at 90-130 DEG C; the dehydration tower is controlled at a pressure of-90 kPa to-80 kPa, the top temperature is 65-100 DEG C, and the dehydration tower has 6-8 theoretical plates; The dehydrating tower is regular packing, and the specific surface area is 200-300 m 2 / m 3 ; the temperature of the mixture after being cooled by the water cooler is 30-40 DEG C; (2) the mixture of light components and sewage obtained in step (1) is sent to an oil-water separation tank for oil-water separation, and light components and sewage are obtained; (3) the light components obtained in step (2) are sent out of the device by a light component extraction pump, and the sewage separated from the oil-water separation tank is sent to a sewage buffer tank; when the sewage separated from the oil-water separation tank enters the sewage buffer tank, a density detector sets a low density alarm value and a low density low alarm interlock value; When the sewage density drops to 985.0-988.0 kg / m 3 When the sewage density drops to 985.0-988.0 kg / m When the sewage density continues to decrease to 975.0-980.0 kg / m 3 When the sewage density continues to decrease to 975.0-980.0 kg / m (4) the sewage in the sewage buffer tank in step (3) is discharged to a secondary oil-water separation tank for secondary oil-water separation, the sewage in the water side is sent to a sewage treatment plant by a self-priming pump, and the sewage containing water in the oil side is sent to an ethylene tar raw material tank after being recovered; the ethylene tar negative pressure automatic dehydration system comprises a heater (1), a dehydration tower (2), an oil-water separation tank (4), a sewage buffer tank (8) and a secondary oil-water separation tank (14) which are sequentially communicated; the dehydration tower (2) is communicated with a tower kettle pump (17) at the tower kettle, and the top is communicated with the oil-water separation tank (4) by a water cooler (3) and a pipeline; the dehydration tower (2) is free of a tower kettle reboiler; a density detector (5), a shut-off valve I (6) and an adjusting valve I (7) are sequentially arranged between the oil-water separation tank (4) and the sewage buffer tank (8); the oil-water separation tank (4) is further communicated with a light component extraction pump (16) for conveying light components; a pressure detector, a shut-off valve II (9) and an adjusting valve II (10) for connecting a vacuum system, an adjusting valve III (11) and a shut-off valve III (12) for nitrogen gas inlet are respectively arranged on the top of the sewage buffer tank (8); a shut-off valve IV (13) for controlling the discharge of the bottom of the sewage buffer tank (8) is arranged on the pipeline communicating the sewage buffer tank (8) with the secondary oil-water separation tank (14); the secondary oil-water separation tank (14) is communicated with a self-priming pump (15).

2. The method of claim 1, wherein the negative pressure automatic dehydration of ethylene tar is characterized by, a partition is arranged in the oil-water separation tank (4) and the secondary oil-water separation tank (14).

3. The method of claim 1, wherein the negative pressure is applied to the ethylene tar at a temperature of 50 to 100°C. the oil-water separation tank (4) is communicated with a vacuum system, an adjusting valve IV (18) for controlling the flow of the heating medium is arranged on the heater (1), the adjusting valve IV (18) and the material outlet temperature of the heater (1) form a control loop, and the material outlet temperature of the heater (1) is automatically controlled.

4. The method of claim 1, wherein the pressure of the ethylene tar is reduced to a pressure of 0.1 to 0.5 Torr. the ethylene tar negative pressure automatic dehydration method comprises the following sequential control processes: (A) normal dehydration working condition: The oil-water separation tank outlet cut-off valve is in an open state, the regulating valve one controls the oil-water separation tank water package boundary position to 50%, the sewage buffer tank top nitrogen cut-off valve three and the regulating valve three are in a closed state, the vacuum system regulating valve two and the cut-off valve two are in an open state, and the sewage buffer tank bottom cut-off valve four is in a closed state; (B) Sewage buffer tank drainage working condition: When the sewage buffer tank liquid level reaches 80%, the interlock cut-off valve one is closed, the regulating valve one is closed, the tank top vacuum system cut-off valve two and the regulating valve two are closed, the sewage buffer tank top nitrogen cut-off valve three and the regulating valve three are opened, the sewage buffer tank pressure is controlled to 30 kPa, and the tank bottom cut-off valve four is opened; (C) Normal dewatering condition recovery: When the sewage buffer tank liquid level reaches 15%, the interlock cut-off valve four is closed, the nitrogen cut-off valve three and the regulating valve three are closed, the sewage buffer tank top vacuum system cut-off valve two and the regulating valve two are opened, the cut-off valve one and the regulating valve one are opened, and the oil-water separation tank water package boundary position is adjusted to 50% through the regulating valve one.

Images