Efficient and energy-saving method for purifying vinyl chloride by calcium carbide process

Abstract

The invention provides an efficient and energy-saving method for purifying vinyl chloride through a calcium carbide method, belongs to the technical field of vinyl chloride purification, and solves the problems that the vinyl chloride purification effect is poor, and resources cannot be efficiently utilized. Devices used in the method comprise a cooler, a falling film absorber, a water washing tower and an alkaline washing tower, and the water washing tower is provided with a bubble cap section and a filler layer; the water washing tower is connected with a diluted hydrochloric acid tank and a diluted hydrochloric acid cooler, the diluted hydrochloric acid cooler is connected to the bubble cap section and a filler layer, and the filler layer is arranged in the middle of the alkaline washing tower; the cooled crude vinyl chloride enters a falling film absorber for pre-absorption of hydrogen chloride; carrying out acid gas reaction absorption on the absorbed vinyl chloride and diluted hydrochloric acid; and the absorbed vinyl chloride is in contact reaction with alkali liquor for further absorption. According to the method, the chloroethylene product which is high in purity and meets the production requirement is obtained, in the process, the operation load of a subsequent water washing tower and an alkaline washing tower is reduced, the consumption of primary water and alkaline liquor is reduced, recycling of resources is achieved, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of vinyl chloride purification, and in particular relates to a highly efficient and energy-saving method for purifying vinyl chloride by a calcium carbide process. Background Art

[0002] In the current production process of vinyl chloride by calcium carbide method, acetylene and hydrogen chloride are mainly used in a scientific ratio. Under the catalytic action of mercuric chloride catalyst, crude vinyl chloride monomer is produced by reaction in the converter. After purification, compression and distillation system, the crude vinyl chloride monomer is sent to the polymerization kettle for production with a purity of 99.9%. Before the purification of vinyl chloride, the system usually sets up a first-stage and a second-stage converter for vinyl chloride synthesis reaction. The first-stage converter requires the conversion index of acetylene ≤30% and hydrogen chloride ≤40%, and the second-stage conversion requires the index of acetylene ≤3% and hydrogen chloride ≤5%. The main purpose of setting up vinyl chloride purification is to remove the unreacted hydrogen chloride and other acidic substances in the conversion process. The acetylene and other substances contained in vinyl chloride can be removed by the subsequent pressurized distillation device to ensure that the purity of the final vinyl chloride monomer meets the requirements of the subsequent polymerization reaction.

[0003] The core of the purification principle of vinyl chloride by the calcium carbide method is to remove impurity gases in vinyl chloride through chemical reactions. In the process of producing vinyl chloride by the calcium carbide method, calcium carbide reacts with water to form acetylene, and acetylene reacts with hydrogen chloride to form vinyl chloride. Since industrial calcium carbide contains a large amount of impurities, impurity gases such as hydrogen sulfide and phosphine will be generated during the hydrolysis reaction. Therefore, the purification process of vinyl chloride by the calcium carbide method generally has prominent problems such as high energy consumption, great difficulty, waste of resources that cannot be reused, high equipment requirements, and high risk of environmental pollution. Summary of the invention

[0004] The purpose of the present invention is to provide a highly efficient and energy-saving method for purifying vinyl chloride by the calcium carbide process, so as to solve the problems of poor purification effect of vinyl chloride and inefficient utilization of resources.

[0005] The technical scheme of the present invention is: an efficient and energy-saving method for purifying vinyl chloride by calcium carbide method, the device structure used is as follows, including a cooler, a falling film absorber, a water washing tower and an alkali washing tower connected in sequence, the falling film absorber is connected to the bottom of the water washing tower, the upper part of the water washing tower is respectively provided with a bubble section and a packing layer from top to bottom, the bottom of the water washing tower is sequentially connected with a dilute hydrochloric acid tank and a dilute hydrochloric acid cooler, the dilute hydrochloric acid cooler is respectively connected to the bubble section and the packing layer of the water washing tower, and the middle part of the alkali washing tower is provided with a packing layer; The method comprises the following steps: Step 1: Cooling water is introduced into the cooler for indirect heat exchange cooling to reduce the temperature of the crude vinyl chloride entering the cooler, and the cooled crude vinyl chloride enters the falling film absorber for pre-absorption of hydrogen chloride; Step 2: After being absorbed by the falling film absorber, the vinyl chloride enters from the bottom of the water scrubber, and the dilute hydrochloric acid in the dilute hydrochloric acid tank is cooled by the hydrochloric acid cooler and then enters the bubble section and the packing section at the top of the water scrubber respectively, and the vinyl chloride reacts with the dilute hydrochloric acid to absorb the acid gas; Step 3: After being absorbed by the water washing tower, the vinyl chloride flows out from the top of the tower and is sent to the packing layer set in the middle of the alkali washing tower. The vinyl chloride contacts and reacts with the alkali solution for further absorption, and finally the purified vinyl chloride is passed out from the top of the alkali washing tower.

[0006] As a further improvement of the present invention, the cooler and the bottom of the falling film absorber are respectively connected to concentrated hydrochloric acid tanks.

[0007] As a further improvement of the present invention, an alkali solution circulation tank is connected between the top and the bottom of the alkali washing tower, and an alkali adding pipeline is arranged on the alkali solution circulation tank.

[0008] As a further improvement of the present invention, the concentrated hydrochloric acid tank outlet is connected to a concentrated hydrochloric acid pipeline, the dilute hydrochloric acid tank inlet is connected to a dilute hydrochloric acid pipeline, and an external hydrochloric acid desorption system is connected between the dilute hydrochloric acid pipeline and the concentrated hydrochloric acid pipeline.

[0009] As a further improvement of the present invention, the cooler, the falling film absorber and the dilute hydrochloric acid cooler are respectively provided with a heat exchange inlet pipe and a heat exchange outlet pipe.

[0010] As a further improvement of the present invention, the outlet of the dilute hydrochloric acid cooler is connected to the falling film absorber.

[0011] As a further improvement of the present invention, a primary water replenishment pipeline is provided on the top of the water washing tower.

[0012] As a further improvement of the present invention, baffles are respectively provided in the concentrated hydrochloric acid tank and the dilute hydrochloric acid tank.

[0013] The beneficial effects of the present invention are as follows: In view of the prominent problems of high energy consumption, great difficulty, waste of resources and inability to reuse, high equipment requirements and high environmental pollution risks in the purification process of vinyl chloride by the calcium carbide method, the present invention adopts the principle of combined utilization of a cooler, a falling film absorber, a water washing tower and an alkali washing tower, and according to the principle that the solubility of hydrogen chloride in water decreases with increasing temperature, the falling film absorber is fully utilized for pre-absorption, and then the vinyl chloride entering through the bottom of the water washing tower is reversely contacted with the dilute hydrochloric acid entering through the top of the tower to absorb the acidic gas in the packing layer and the bubble section, and finally a packing layer is arranged in the middle of the alkali washing tower for the vinyl chloride to contact and react with the alkali solution for further absorption, and finally a vinyl chloride product with high purity that meets the production demand is obtained, and in this process, the operating load of the subsequent water washing tower and the alkali washing tower is reduced, the primary water and alkali solution consumption is reduced, the recycling and reuse of resources is realized, and the production cost is reduced.

[0014] The main purpose of setting up a water washing tower is to remove acidic substances. During the reaction of acetylene and hydrogen chloride to produce vinyl chloride, there may be a small amount of incompletely reacted hydrogen chloride and other acidic impurities remaining. Water washing can neutralize and remove these acidic substances, reduce the impact on subsequent processes, and lower the temperature. The vinyl chloride gas generated by the reaction has a high temperature, and the water washing process also plays a cooling role, which helps to control the operating conditions of subsequent processes; at the same time, water washing can remove some impurities that are easily soluble in water, preparing for subsequent more sophisticated purification steps.

[0015] The purpose of setting up an alkaline washing tower is to further remove acidic impurities. Although water washing can remove most acidic substances, some acidic impurities such as trace amounts of hydrogen chloride may still exist. Alkaline washing uses alkaline solutions (usually sodium hydroxide solutions) to more effectively neutralize and remove these acidic residues and improve the purity of vinyl chloride; remove impurities such as sulfides. Harmful gases such as hydrogen sulfide may be produced during the production process. Alkaline washing can effectively remove such harmful impurities and reduce the risk of equipment corrosion and environmental pollution; protect subsequent equipment. Alkaline washing can prevent acidic impurities from entering sensitive equipment such as distillation towers, reduce equipment corrosion, and extend service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the device used in the present invention.

[0017] In the figure: 1-cooler; 2-falling film absorber; 3-water washing tower; 4-alkali washing tower; 5-concentrated hydrochloric acid tank; 6-diluted hydrochloric acid tank; 7-alkali solution circulation tank; 8-diluted hydrochloric acid cooler; 9-heat exchange inlet pipe; 10-heat exchange outlet pipe; 11-valve; 12-vinyl chloride pipeline; 13-acid pipeline; 14-alkali pipeline; 15-primary water replenishment pipeline; 16-concentrated hydrochloric acid pipeline; 17-diluted hydrochloric acid pipeline; 18-concentrated acid pump; 19-diluted hydrochloric acid pump; 20-alkali solution circulation pump; 21-baffle; 22-alkali adding pipeline. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0019] like Figure 1 As shown, a highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide method, the device structure used is as follows, including a cooler 1, a falling film absorber 2, a water scrubber 3 and an alkali scrubber 4 connected in sequence, the falling film absorber 2 is connected to the bottom of the water scrubber 3, the upper part of the water scrubber 3 is respectively provided with a bubble section and a packing layer from top to bottom, the bottom of the water scrubber 3 is sequentially connected with a dilute hydrochloric acid tank 6 and a dilute hydrochloric acid cooler 8, the dilute hydrochloric acid cooler 8 is respectively connected to the bubble section and the packing layer of the water scrubber 3, and a packing layer is provided in the middle of the alkali scrubber 4; The method comprises the following steps: Step 1: Cooling water is introduced into the cooler 1 for indirect heat exchange cooling to reduce the temperature of the crude vinyl chloride entering the cooler 1, and the cooled crude vinyl chloride enters the falling film absorber 2 for pre-absorption of hydrogen chloride; Step 2: The vinyl chloride absorbed by the falling film absorber 2 enters from the bottom of the water scrubber 3, and the dilute hydrochloric acid in the dilute hydrochloric acid tank 6 is cooled by the hydrochloric acid cooler 8 and then enters the bubble section and the packing section at the top of the water scrubber 3 respectively, and the vinyl chloride reacts with the dilute hydrochloric acid to absorb the acid gas; Step 3: The vinyl chloride absorbed by the water washing tower 3 flows out from the top of the tower and is sent to the packing layer arranged in the middle of the alkali washing tower 4. The vinyl chloride contacts and reacts with the alkali solution for further absorption, and finally the purified vinyl chloride is passed out from the top of the alkali washing tower 4.

[0020] The cooler 1 and the falling film absorber 2 are respectively connected to a concentrated hydrochloric acid tank 5 at the bottom; an alkali liquid circulation tank 7 is connected between the top and the bottom of the alkali washing tower 4, and an alkali adding pipeline 22 is provided on the alkali liquid circulation tank 7; the outlet of the concentrated hydrochloric acid tank 5 is connected to a concentrated hydrochloric acid pipeline 16, and the inlet of the dilute hydrochloric acid tank 6 is connected to a dilute hydrochloric acid pipeline 17, and an external hydrochloric acid desorption system is connected between the dilute hydrochloric acid pipeline 17 and the concentrated hydrochloric acid pipeline 16; the cooler 1, the falling film absorber 2 and the dilute hydrochloric acid cooler 8 are respectively provided with a heat exchange inlet pipe 9 and a heat exchange outlet pipe 10; the outlet of the dilute hydrochloric acid cooler 8 is connected to the falling film absorber 2; a primary water replenishment pipeline 15 is provided on the top of the water washing tower 3; baffles 21 are respectively provided in the concentrated hydrochloric acid tank 5 and the dilute hydrochloric acid tank 6.

[0021] Embodiment 1, Cooler 1 is set at the front end of the system. Cooler 1 is designed as a graphite shell-and-tube heat exchanger. A vinyl chloride pipeline 12 is set at the top of cooler 1. The shell side of cooler 1 is provided with a heat exchange inlet pipe 9 and a heat exchange outlet pipe 10 to form a heat exchange pipeline. 5°C water is passed into the heat exchange pipeline for heat exchange. A U-shaped acid seal pipeline is set at the bottom of cooler 1. Its design purpose is to cool down the vinyl chloride before entering the purification device based on the principle that the solubility of hydrogen chloride in water decreases with the increase of temperature, so as to ensure that the hydrogen chloride and acid gas contained in the vinyl chloride are fully absorbed during the purification process. During the operation of the device, it is required to adjust the 5°C cooling water valve of the shell side of cooler 1 to control the circulation volume to ensure that the material temperature at the outlet of cooler 1 is ≤15°C, which is convenient for subsequent production.

[0022] The crude vinyl chloride from the conversion system is sent to the tube side of cooler 1 through the vinyl chloride pipeline 12, and is indirectly cooled by heat exchange with the 5°C cooling water in the shell side heat exchange pipeline of cooler 1 to reduce the temperature of the crude vinyl chloride from the conversion, so as to facilitate the subsequent adsorption of the falling film absorber 2. An acid pipeline 13 is set at the bottom of cooler 1 to discharge the condensed acid in the tube side of cooler 1 to the concentrated hydrochloric acid tank 5 for collection and utilization. A vinyl chloride pipeline 12 is set at the gas phase outlet of cooler 1 to send the cooled vinyl chloride to the falling film absorber 2. An acid pipeline 13 is set at the bottom of the falling film absorber 2 to flow the absorbed concentrated hydrochloric acid through the pipeline to the concentrated hydrochloric acid tank 5 by gravity for secondary utilization.

[0023] After being cooled by the cooler 1, the vinyl chloride enters the falling film absorber 2 for pre-absorption of hydrogen chloride. The advantages of the falling film absorber 2 are its high absorption efficiency, good thermal management ability and operational flexibility. It is suitable for handling the absorption of high-concentration and highly corrosive gases. The design adopts a vertically installed tube structure. Each tube is equivalent to a small wet wall tower. A jacket is arranged on the outside to form a heat exchange pipeline by arranging a heat exchange inlet pipe 9 and a heat exchange outlet pipe 10. 5°C water is passed into the heat exchange pipeline for cooling circulation. The absorption temperature is lowered by indirect heat exchange to remove the heat released during the absorption process. A distributor or film distributor is arranged on the top of the tube to evenly distribute the absorption liquid (usually water) to the inner wall of the tube to form a continuous liquid film. The gas inlet is located at the upper part of the falling film absorber 2. The co-current operation mode is adopted to carry out the contact absorption of hydrogen chloride and dilute hydrochloric acid. The principle of designing jacket cooling is also based on the principle that the solubility of hydrogen chloride in water decreases with the increase of temperature. It is required to control the gas phase outlet temperature of the falling film absorber 2 to be ≤10°C during operation.

[0024] A vinyl chloride pipeline 12 is arranged at the gas phase outlet of the falling film absorber 2 to deliver the vinyl chloride absorbed by the falling film absorber 2 to the inlet of the water washing tower 3; a dilute hydrochloric acid tank 6 is arranged at the bottom of the water washing tower 3, and a dilute hydrochloric acid pump 19 is arranged at the bottom; an acid pipeline 13 is arranged at the outlet of the dilute hydrochloric acid pump 19, and after being cooled by the dilute hydrochloric acid cooler 8, the dilute hydrochloric acid is controlled by two valves 11 to deliver the dilute hydrochloric acid to the bubble section and the packing section of the water washing tower 3 respectively; a three-way connecting pipeline is arranged on the pipeline, and part of the dilute hydrochloric acid is controlled by the valve 11 to be delivered to the falling film absorber 2 as an absorption liquid through the pipeline, and the dilute hydrochloric acid absorbed in the tower continues to flow to the dilute hydrochloric acid tank 6 for repeated use; a primary water replenishment pipeline 15 is arranged at the top of the water washing tower 3 for water replenishment, and a valve 11 for water replenishment control is arranged on the primary water replenishment pipeline 15.

[0025] The water washing tower 3 is a combined absorption tower. The tower body of the water washing tower 3 is required to be made of glass fiber reinforced plastic. The heavy metal frame in the tower needs to be designed with anti-corrosion protection. Other structures in the tower are made of corrosion-resistant materials. The water washing tower 3 is set up in two stages of work design. The upper part of the tower is provided with a bubble cap section for absorbing hydrogen chloride, and the lower part of the tower is provided with a corrugated plate packing layer for absorbing hydrogen chloride. Vinyl chloride enters from the bottom of the water washing tower 3 and flows out from the top of the water washing tower 3. A primary water replenishment pipeline 15 is set at the top of the water washing tower 3 for replenishment. A dilute hydrochloric acid tank 6 is set at the bottom of the water washing tower 3. Before the system is operated, primary water is passed into the water washing tower 3 from the top of the water washing tower 3 and then flows into the dilute hydrochloric acid tank 6. The dilute hydrochloric acid cooler 8 is a graphite shell and tube heat exchanger. The shell side is provided with a heat exchange pipeline to cool the circulating dilute hydrochloric acid to ensure the absorption effect in the water washing tower 3. The purpose of setting the dilute hydrochloric acid cooler 8 is to reduce the temperature of the dilute hydrochloric acid, using the principle that the solubility of hydrogen chloride in water decreases with increasing temperature. The main function of setting the primary water replenishment pipeline 15 at the top of the water scrubber 3 is to use lower temperature water to reduce the gas temperature, prevent corrosion of the cold exchange equipment, and ensure mass transfer efficiency through water flow distribution. It ensures the effective operation of the primary water replenishment pipeline at the top of the water scrubber 3 and improves the efficiency and safety of the equipment. Before designing the water scrubber 3, it is necessary to calculate the system flux, set pressure monitoring and temperature monitoring at the top and bottom of the tower respectively, and during operation, the tower pressure difference is required to be ≤3Kpa, and the temperature difference between the inlet temperature and the outlet temperature is ≤5℃.

[0026] The vinyl chloride entering through the bottom of the water washing tower 3 is reversely contacted with the dilute hydrochloric acid entering through the top of the tower to absorb the acidic gas in the packing layer and the bubble section. Then, a vinyl chloride pipeline 12 is arranged at the top of the water washing tower 3, and the vinyl chloride absorbed by the water washing tower 3 flows out from the top of the tower and is sent to the alkali washing tower 4 for further absorption. The alkali washing tower 4 is designed based on the absorption principle of the packing tower, and its main function is to remove other acidic gases contained in the vinyl chloride that has not been completely absorbed by the water washing tower 3 for further absorption. At the same time, sodium hydroxide alkali solution is used to adjust the pH value of the vinyl chloride, so that the pH value of the vinyl chloride after water alkali washing is controlled between 7 and 9 to ensure the quality of the polymerized product.

[0027] A foaming device is arranged at the top of the alkali washing tower 4, and the overall flux design of the tower body needs to meet the process production requirements. A tower kettle and a feed port are arranged at the bottom of the alkali washing tower 4, a packing layer is arranged in the middle of the alkali washing tower 4 for vinyl chloride to contact and react with alkali solution, an alkali solution spray and a liquid distributor are arranged on the top of the packing layer to achieve uniform distribution of the alkali solution, and a collector is arranged on the top of the alkali washing tower 4 to separate the alkali solution foam carried by the gas phase vinyl chloride during the flow process to prevent the alkali solution from entering the subsequent process.

[0028] An alkali liquid circulation tank 7 is arranged at the bottom of the alkali washing tower 4, an alkali liquid circulation pump 20 is arranged at the outlet of the alkali liquid circulation tank 7, and an alkali pipeline 14 is arranged at the outlet of the alkali liquid circulation pump 20 to transport the alkali liquid to the top of the alkali washing tower 4. Through the action of spraying and liquid distributor, the alkali liquid passes through the liquid distributor and filler at the top of the alkali washing tower 4 to conduct reverse contact reaction with the vinyl chloride entering the bottom of the tower. The reacted vinyl chloride is sent to the subsequent process through the vinyl chloride pipeline 12 at the top of the alkali washing tower 4. The alkali liquid in the alkali washing tower 4 flows to the alkali liquid circulation tank 7 through the alkali pipeline 14 at the bottom of the alkali washing tower 4 by gravity and repeats the cycle. An alkali adding pipeline 22 is arranged at the top of the alkali liquid circulation tank 7, and a valve 11 is arranged on the alkali adding pipeline 22 for control, so as to facilitate the external addition of alkali liquid. The alkali concentration of the alkali liquid in the alkali liquid circulation tank 7 is required to be 10%-15%. If the alkali concentration index is exceeded or deviated, the alkali liquid should be replaced in time. The temperature index of the vinyl chloride at the outlet of the alkali washing tower 4 is required to be ≤30℃.

[0029] The hydrochloric acid produced by the cooler 1 and the falling film absorber 2 has a high concentration. A baffle 21 is set in the concentrated hydrochloric acid tank 5 and the dilute hydrochloric acid tank 6. The main function of the baffle 21 in the hydrochloric acid tank is to prevent the hydrochloric acid from volatilizing and to keep warm, so as to achieve full mixing of the concentrated washing hydrochloric acid in the circulation tank. A concentrated acid pump 18 is set at the bottom of the concentrated hydrochloric acid tank 5, and a concentrated hydrochloric acid pipeline 16 is set at the outlet to transport the concentrated hydrochloric acid to the externally connected hydrochloric acid desorption system. The desorbed dilute hydrochloric acid is returned to the dilute hydrochloric acid tank 6 through the dilute hydrochloric acid pipeline 17 for reuse.

[0030] During the operation of the device, the concentrated hydrochloric acid pipeline 16, the dilute hydrochloric acid pipeline 17, and the primary water replenishment pipeline 15 require dynamic flow balance. The dilute hydrochloric acid in the dilute hydrochloric acid tank 6 is replenished by the primary water added from the top of the water washing tower 3. During the operation of the device, it is necessary to add primary water to adjust and control the liquid level balance in the concentrated hydrochloric acid tank 5 and the dilute hydrochloric acid tank 6 to be stable.

[0031] The accuracy requirements of all regulating valves in the device must meet the requirements of AN3I / FCI70-2, and the adjustment accuracy must be ±1%; the device is used to recover flammable and explosive media, and the design and installation must comply with chemical fire and explosion protection requirements, and nitrogen must be used for replacement before operation.

[0032] Before the device is put into operation, all valves 11 related to the system are opened, and nitrogen is connected to conduct pressure test and leak test on the whole system. The pressure test is qualified at 1.02pa; nitrogen is used to replace the whole system, and multi-point sampling is performed, and the oxygen content is required to be ≤0.2%; the heat exchange pipes on the cooler 1, the falling film absorber 2 and the dilute hydrochloric acid cooler 8 are opened; the valve 11 is opened to use the primary water replenishment pipe 15 to add the primary water to the dilute hydrochloric acid tank 6 through the water washing tower 3, and the liquid level of the dilute hydrochloric acid tank 6 is 70%-80%, and the valve 11 is closed; the valve 11 on the alkali adding pipe 22 at the top of the alkali circulation tank 7 is opened to replenish the alkali circulation tank 7 with alkali, and the alkali concentration is required to be 10%-15%. The valve is closed when the liquid level reaches 70%-80%. 11; start the dilute hydrochloric acid pump 19 to establish a circulation with the water washing tower 3, start the alkali liquid circulation pump 20 to establish a circulation with the alkali washing tower 4; open all valves 11 on the vinyl chloride pipeline 12 between the cooler 1 and the alkali washing tower 4, open the valve 11 on the three-way acid pipeline 13 to add absorption liquid to the falling film absorber 2; when the liquid level of the concentrated hydrochloric acid tank 5 reaches 70%-80%, start the concentrated acid pump 18 to transport the concentrated hydrochloric acid to the hydrochloric acid desorption system through the concentrated hydrochloric acid pipeline 16, and after the desorption, the dilute hydrochloric acid is returned to the dilute hydrochloric acid tank 6 through the dilute hydrochloric acid pipeline 17 for repeated absorption and utilization; if the liquid level of the dilute hydrochloric acid tank 6 drops during the operation of the system, it is necessary to promptly open the valve 11 on the primary water replenishment pipeline 15 to ensure the stability of the liquid level of the acid circulation system.

Claims

1. A highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide process, characterized in that: The device used has the following structure, comprising a cooler (1), a falling film absorber (2), a water washing tower (3) and an alkali washing tower (4) connected in sequence, the falling film absorber (2) being connected to the bottom of the water washing tower (3), the upper part of the water washing tower (3) being provided with a bubble cap section and a packing layer from top to bottom, the bottom of the water washing tower (3) being connected in sequence with a dilute hydrochloric acid tank (6) and a dilute hydrochloric acid cooler (8), the dilute hydrochloric acid cooler (8) being connected to the bubble cap section and the packing layer of the water washing tower (3), respectively, and the middle part of the alkali washing tower (4) being provided with a packing layer; The method comprises the following steps: Step 1: Cooling water is introduced into the cooler (1) for indirect heat exchange cooling to reduce the temperature of the crude vinyl chloride entering the cooler (1), and the cooled crude vinyl chloride enters the falling film absorber (2) for pre-absorption of hydrogen chloride; Step 2: After being absorbed by the falling film absorber (2), the vinyl chloride enters the bottom of the water scrubber (3), and the dilute hydrochloric acid in the dilute hydrochloric acid tank (6) is cooled by the hydrochloric acid cooler (8) and then enters the bubble section and the packing section at the top of the water scrubber (3) respectively, and the vinyl chloride reacts with the dilute hydrochloric acid to absorb the acid gas; Step 3: After being absorbed by the water washing tower (3), the vinyl chloride flows out from the top of the tower and is sent to the packing layer arranged in the middle of the alkali washing tower (4). The vinyl chloride contacts and reacts with the alkali solution for further absorption, and finally the purified vinyl chloride is discharged from the top of the alkali washing tower (4).

2. The method for purifying vinyl chloride by the calcium carbide process with high efficiency and energy saving according to claim 1, characterized in that: The cooler (1) and the falling film absorber (2) are respectively connected to a concentrated hydrochloric acid tank (5) at the bottom.

3. A highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide method according to claim 1 or 2, characterized in that: An alkali liquid circulation tank (7) is connected between the top and the bottom of the alkali washing tower (4), and an alkali adding pipeline (22) is provided on the alkali liquid circulation tank (7).

4. A highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide method according to claim 3, characterized in that: The outlet of the concentrated hydrochloric acid tank (5) is connected to a concentrated hydrochloric acid pipeline (16), the inlet of the dilute hydrochloric acid tank (6) is connected to a dilute hydrochloric acid pipeline (17), and an external hydrochloric acid desorption system is connected between the dilute hydrochloric acid pipeline (17) and the concentrated hydrochloric acid pipeline (16).

5. A highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide method according to claim 4, characterized in that: The cooler (1), the falling film absorber (2) and the dilute hydrochloric acid cooler (8) are respectively provided with a heat exchange inlet pipe (9) and a heat exchange outlet pipe (10).

6. A highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide method according to claim 5, characterized in that: The outlet of the dilute hydrochloric acid cooler (8) is connected to the falling film absorber (2).

7. A highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide method according to claim 6, characterized in that: A primary water replenishment pipeline (15) is provided at the top of the water washing tower (3).

8. A highly efficient and energy-saving method for purifying vinyl chloride by calcium carbide method according to claim 7, characterized in that: Baffles (21) are respectively provided in the concentrated hydrochloric acid tank (5) and the dilute hydrochloric acid tank (6).

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