Chlorinated fatty acid methyl ester tail gas treatment system and method

Abstract

The invention discloses a chlorinated fatty acid methyl ester tail gas treatment system and method.The system comprises a security kettle, a first-stage falling film absorber, a reaction absorption kettle, a second-stage falling film absorber, a third-stage falling film absorber and an alkaline washing tower which are sequentially arranged upstream and downstream; the tail gas enters the security kettle for reaction to remove chlorine in the tail gas, then enters the first-stage falling film absorber for hydrogen chloride absorption and then enters the reaction absorption kettle for reaction to remove chlorine in the tail gas again, and the tail gas after reaction in the reaction absorption kettle enters the second-stage falling film absorber and the third-stage falling film absorber for hydrogen chloride absorption; and the tail gas absorbed by the three-stage falling film absorber enters an alkaline washing tower to be absorbed and then is discharged at high altitude. According to the system, chlorine in tail gas can be completely treated, the tail gas finally entering the alkaline washing tower only contains a trace amount of hydrogen chloride, alkaline washing wastewater is only a small amount of wastewater containing sodium chloride, and sodium hypochlorite-containing wastewater which is difficult to treat is not generated; hydrogen chloride in the tail gas is absorbed through the three-stage falling film, and the treated tail gas meets the emission requirement.

Description

A system and method for treating the exhaust gas of chlorinated fatty acid methyl esters Technical Field

[0001] This invention relates to the field of chlorinated fatty acid methyl ester tail gas treatment technology, and in particular to a chlorinated fatty acid methyl ester tail gas treatment system and method. Background Technology

[0002] Chlorinated fatty acid methyl esters are yellow, transparent, oily liquids. They are inexpensive, highly effective flame retardants, have good plasticizing properties and compatibility with PVC, and suitable viscosity. Containing chlorine, they can replace chlorinated paraffin, improving the flame retardancy and electrical insulation of products. They are widely used in cable materials, flooring materials, water pipes, films, the automotive industry, and the construction industry. Chlorinated fatty acid methyl esters are produced by reacting unsaturated fatty acid methyl esters with excess chlorine gas in the presence of a catalyst. The chlorination reaction produces a large amount of hydrogen chloride. Furthermore, because chlorine is in excess during the reaction, the hydrogen chloride produced and the unreacted chlorine gas together form exhaust gases. Direct release into the atmosphere would cause environmental impact.

[0003] Currently, the common treatment method for chlorinated fatty acid methyl ester tail gas is to first pass the tail gas through a multi-stage absorption tower to convert hydrogen chloride into hydrochloric acid, and then through an alkaline scrubbing tower for absorption before venting. Specifically, the tail gas is first passed through a water scrubbing tower, using water as the absorbent, where the hydrogen chloride in the tail gas is absorbed by the water to become hydrochloric acid. However, this requires multiple stages of water scrubbing to completely absorb the hydrogen chloride in the tail gas, making the process complex, time-consuming, and only recovering a low concentration of hydrochloric acid (25%–28%), resulting in poor economic efficiency. The tail gas after water scrubbing is then passed through an alkaline scrubbing tower, using sodium hydroxide solution as the absorbent, to convert chlorine in the tail gas into sodium hypochlorite. The tail gas after multi-stage absorption meets emission standards, but this process consumes a large amount of alkali solution, resulting in high costs, and the recovered product, sodium hypochlorite, has low economic value. Furthermore, since the composition of fatty acid methyl esters varies from batch to batch, the above-mentioned method of tail gas treatment will result in frequent changes in the concentration of hydrogen chloride in the tail gas, and the quality and concentration of hydrochloric acid and sodium hypochlorite will be unstable, making them unsuitable for recycling and reuse. The recovered products cannot be processed. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention provide a system and method for treating the exhaust gas of chlorinated fatty acid methyl esters.

[0006] In a first aspect, the present invention proposes a tail gas treatment system for chlorinated fatty acid methyl esters, comprising:

[0007] A safety reactor is used to react the exhaust gas with fatty acid methyl esters to remove chlorine. A primary falling film absorber is located downstream of the safety reactor, and the exhaust gas from the safety reactor reaction enters the primary falling film absorber for hydrogen chloride absorption. A reaction absorption reactor is located downstream of the primary falling film absorber, and the exhaust gas from the primary falling film absorber enters the reaction absorption reactor to react with fatty acid methyl esters again to remove chlorine. A secondary falling film absorber is located downstream of the reaction absorption reactor, and the exhaust gas from the reaction absorption reactor enters the secondary falling film absorber for hydrogen chloride absorption. A tertiary falling film absorber is located downstream of the secondary falling film absorber, and the exhaust gas from the secondary falling film absorber enters the tertiary falling film absorber for hydrogen chloride absorption. An alkaline scrubbing tower is located downstream of the tertiary falling film absorber, and the exhaust gas from the tertiary falling film absorber enters the alkaline scrubbing tower for absorption before being discharged at high altitude.

[0008] Furthermore, it also includes a reactant buffer tank, on which a reactant delivery pump is installed on the bottom outlet pipeline of the reactant buffer tank. After the liquid reactant from the safety vessel and the reaction absorption vessel enters the reactant buffer tank, it is sent to the production unit by the reactant delivery pump.

[0009] Furthermore, a safety circulation pump and a safety cooler are installed on the bottom outlet pipeline of the safety vessel. The liquid reactants are pumped by the safety circulation pump to the safety cooler for cooling and then flow back to the safety vessel.

[0010] Furthermore, the bottom of the safety vessel is connected to a safety separation tank via a pipeline. After the liquid phase reactants undergo gas-liquid separation in the safety separation tank, the top gas phase flows back to the safety vessel, and the bottom liquid phase enters the reactant buffer tank. A safety gas-liquid separator is installed on the gas phase outlet pipeline at the top of the safety vessel.

[0011] Furthermore, an absorption circulation pump and an absorption venturi are installed on the bottom outlet pipeline of the reaction absorption vessel, and the liquid phase reactants and the tail gas from the first-stage falling film absorber enter the reaction absorption vessel together under the action of the absorption venturi.

[0012] Furthermore, the bottom of the reaction absorption vessel is connected to an absorption separation tank via a pipe. After the liquid phase reactants undergo gas-liquid separation in the absorption separation tank, the top gas phase flows back to the reaction absorption vessel, and part of the bottom liquid phase overflows into the safety vessel, while the other part enters the reactant buffer tank.

[0013] Furthermore, an online chlorine detector is installed on the gas phase outlet pipeline at the top of the reaction absorption vessel to control the chlorine concentration in the gas phase at the top of the reaction absorption vessel to be within 5 mg / m³. 3 the following.

[0014] Furthermore, the bottom outlet of the first-stage falling film absorber is connected to a concentrated acid tank. During the reaction, the concentration of hydrochloric acid in the concentrated acid tank is controlled at 31.3%~31.8%, and the hydrochloric acid in the concentrated acid tank is sent outside the boundary as finished hydrochloric acid. The bottom outlet of the second-stage falling film absorber is connected to a medium acid tank, and the hydrochloric acid in the medium acid tank enters the first-stage falling film absorber as an absorbent. The bottom outlet of the third-stage falling film absorber is connected to a dilute acid tank, and the hydrochloric acid in the dilute acid tank enters the second-stage falling film absorber as an absorbent.

[0015] Furthermore, it also includes a dilute acid tank, in which dilute acid is used as an absorbent and enters the three-stage falling film absorber, the concentration of which is 18%~22%.

[0016] Secondly, this invention proposes a method for treating the tail gas of chlorinated fatty acid methyl esters, utilizing the system proposed in the first aspect, comprising the following steps: the reaction tail gas enters a safety vessel and reacts with fatty acid methyl esters from a reaction absorption vessel to remove chlorine from the tail gas; the reacted tail gas enters a primary falling film absorber for hydrogen chloride absorption; the tail gas after absorption by the primary falling film absorber enters a reaction absorption vessel and reacts with fatty acid methyl esters to further remove chlorine, ensuring that the chlorine content is below 5 mg / m³. 3 The tail gas after the reaction in the reaction absorption vessel enters the secondary falling film absorber and the tertiary falling film absorber in sequence for hydrogen chloride absorption, and then enters the alkaline washing tower for alkaline washing before being discharged at high altitude.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: by setting up a safety vessel and a reaction absorption vessel, the present invention can completely treat the chlorine gas in the tail gas, and the tail gas that finally enters the alkaline washing tower contains only trace amounts of hydrogen chloride. The alkaline washing wastewater is only a small amount of wastewater containing sodium chloride, and no difficult-to-treat wastewater containing sodium hypochlorite is generated.

[0018] The present invention relates to the treatment of chlorinated fatty acid methyl ester tail gas, which employs a safety reactor and a reaction absorption reactor to recover chlorine from the reaction tail gas, and uses a three-stage falling film reactor to absorb hydrogen chloride from the tail gas. The hydrogen chloride content in the treated tail gas components is below 2 mg / m³. 3 Below, the chlorine content is 5 mg / m³ 3 the following.

[0019] This invention uses a method of countercurrent absorption of approximately 20% hydrochloric acid to increase the concentration of hydrochloric acid, and the concentration of by-product hydrochloric acid can reach 31.3%~31.8%, which meets the concentration requirements of industrial hydrochloric acid. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic diagram of the chlorinated fatty acid methyl ester tail gas treatment system of the present invention.

[0021] Explanation of reference numerals in the attached diagram: 1. Safety vessel; 2. Safety circulating pump; 3. Safety cooler; 4. Safety separation tank; 5. Safety gas-liquid separator; 6. Reaction absorption vessel; 7. Absorption circulating pump; 8. Absorption separation tank; 9. Absorption venturi; 10. Reactant buffer tank; 11. Reactant transfer pump; 12. First-stage falling film absorber; 13. Second-stage falling film absorber; 14. Third-stage falling film absorber; 15. Concentrated acid tank; 16. Concentrated acid transfer pump; 17. Medium acid tank; 18. Medium acid circulating pump; 19. Sub-dilute acid tank; 20. Sub-dilute acid circulating pump; 21. Dilute acid tank; 22. Dilute acid circulating pump; 23. Alkali washing induced draft fan; 24. Alkali washing tower; 25. Alkali washing circulating pump. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] Traditional methods for absorbing the tail gas from chlorinated fatty acid methyl esters have the following problems: Fatty acid methyl esters are recycled raw materials. Due to differences in the composition of fatty acid methyl esters from different production batches, excessive chlorine in the reaction mixture, and incomplete reactions, the tail gas contains chlorine. Traditional treatment methods directly introduce the reaction tail gas containing hydrogen chloride and chlorine into the tail gas treatment system, resulting in significant waste of raw material chlorine, increased production costs, and reduced production efficiency. The presence of chlorine in the tail gas during absorption leads to free chlorine in the byproduct hydrochloric acid, giving it a yellowish color and poor quality. Furthermore, the traditional method of directly introducing the tail gas into the system raises the temperature during absorption, which is detrimental to hydrogen chloride absorption and increases the difficulty of tail gas treatment. Excessive temperature can damage absorption equipment and create safety hazards; traditional tail gas treatment methods often result in incomplete hydrogen chloride absorption, leaving a large amount of hydrogen chloride in the alkaline scrubbing tower, consuming large amounts of liquid alkali, and making the absorbed sodium hypochlorite wastewater difficult to treat. Furthermore, the tail gas can easily escape from the device, polluting the environment upon release into the air; the hydrochloric acid concentration is low, and due to variations in the composition of different batches of raw fatty acid methyl esters, the hydrogen chloride content in the tail gas also varies, leading to large fluctuations in the concentration of the byproduct hydrochloric acid. Only a low concentration of 25%~28% hydrochloric acid can be recovered, which does not meet industrial hydrochloric acid standards, resulting in poor economic efficiency; traditional chlorinated fatty acid methyl ester tail gas treatment produces tail gas with hydrogen chloride >8mg / m³. 3 Chlorine gas >10mg / m³ 3 The exhaust gas contains high levels of hydrogen chloride and chlorine, posing a significant environmental burden on the factory.

[0024] To address the shortcomings of existing technologies, this invention provides a system and method for treating the tail gas of chlorinated fatty acid methyl esters. This system removes hydrogen chloride and chlorine from the tail gas produced by chlorinated fatty acid methyl esters, ensuring that the final tail gas meets emission standards. Furthermore, the absorbed hydrochloric acid concentration can reach 31.3% to 31.8%, which meets and exceeds the concentration requirements for industrial hydrochloric acid.

[0025] The following description, in conjunction with the accompanying drawings, describes the exhaust gas treatment system and method for chlorinated fatty acid methyl esters proposed in this invention.

[0026] As shown in Figure 1, the tail gas treatment system for chlorinated fatty acid methyl esters of the present invention includes a safety vessel 1, a primary falling film absorber 12, a reaction absorption vessel 6, a secondary falling film absorber 13, a tertiary falling film absorber 14, an alkaline washing tower 24, and a reactant buffer tank 10.

[0027] Inside the safety vessel 1, the reaction tail gas reacts with fatty acid methyl ester to produce chlorinated fatty acid methyl ester, thereby removing chlorine from the tail gas. A safety circulation pump 2 and a safety cooler 3 are sequentially installed on the bottom outlet pipeline of the safety vessel 1. The outlet end of the safety cooler 3 is connected to the safety vessel 1. During the reaction, the liquid reactants are pumped by the safety circulation pump 2 to the safety cooler 3 for cooling and then returned to the safety vessel 1.

[0028] In this invention, a safety circulation pump 2 and a safety cooler 3 are installed on the bottom outlet pipeline of the safety vessel 1 to remove the heat generated during the reaction process, ensuring efficient chlorine reaction, while avoiding damage due to excessive temperature and eliminating safety hazards.

[0029] The bottom of the safety vessel 1 is connected to the safety separation tank 4 via a pipeline. The inlet of the safety separation tank 4 is connected to the bottom outlet of the safety vessel 1, the top outlet of the safety separation tank 4 is connected to the top inlet of the safety vessel 1, and the bottom outlet of the safety separation tank 4 is connected to the top inlet of the reactant buffer tank 10. After the liquid reactants undergo gas-liquid separation in the safety separation tank 4, the top gas phase flows back to the safety vessel 1, while the bottom liquid phase enters the reactant buffer tank 10. A reactant transfer pump 11 is installed on the bottom outlet pipeline of the reactant buffer tank 10. The bottom liquid phase is sent to the production unit for recycling via the reactant transfer pump 11, which improves the utilization rate of chlorine, avoids waste of raw material chlorine, reduces production costs, and improves production efficiency.

[0030] A safety gas-liquid separator 5 is installed on the top gas phase outlet pipeline of the safety vessel 1. The top inlet of the safety gas-liquid separator 5 is connected to the top outlet of the safety vessel 1, and the top outlet of the safety gas-liquid separator 5 is connected to the top inlet of the first-stage falling film absorber 12. The bottom outlet of the safety gas-liquid separator 5 is connected to the top inlet of the safety vessel 1. During the safety reaction in the safety vessel 1, the top gas phase generated is separated into liquid and liquid phases by the safety gas-liquid separator 5. The liquid phase reactants are separated and recovered to the safety vessel 1, while the gas phase is sent to the first-stage falling film absorber 12 for absorption.

[0031] This invention removes chlorine from the tail gas before it enters the absorption system by setting up a safety vessel 1 before the tail gas absorption system. Fresh fatty acid methyl ester reacts with chlorine in the tail gas, thus eliminating the influence of chlorine on the absorption process. The hydrochloric acid obtained by absorption has no free chlorine and is of good quality.

[0032] In some embodiments, the safety vessel 1 is made of enamel, with an operating temperature controlled at 60~65℃ and an operating pressure of -0.02MPaG. A jacket is installed around the safety vessel 1, and circulating water is used for cooling. The exhaust gas inlet of the safety vessel 1 is equipped with four inner tubes, each with small holes to ensure uniform dispersion of the exhaust gas within the safety vessel 1. The safety cooler 3 is made of graphite, cooling the temperature from 90~100℃ to 60~65℃, with circulating water carrying away the heat. The safety gas-liquid separator 5 is made of fiberglass, with an operating temperature controlled at 60~65℃ and an operating pressure of -0.02MPaG.

[0033] The safety vessel 1 of this invention adopts a dual-effect synchronous cooling system of jacketed circulating water and external circulating cooler to strictly control the temperature of the safety vessel 1 between 60 and 65°C, ensuring that the chlorine gas can be completely reacted, while avoiding damage due to excessive temperature and eliminating safety hazards.

[0034] The primary falling film absorber 12 is located downstream of the safety vessel 1. The tail gas from the top outlet of the safety gas-liquid separator 5 enters the primary falling film absorber 12 via the top of the absorber. Hydrochloric acid from the neutral acid tank 17 enters the primary falling film absorber 12 from the top under the action of the neutral acid circulation pump 18 to absorb hydrogen chloride in the tail gas. After absorption, the tail gas enters the reaction absorption vessel 6 from the bottom of the absorber 12 via the absorption venturi 9. After the neutral acid absorbs the tail gas, it flows from the bottom of the absorber 12 into the concentrated acid tank 15. The concentrated acid in the tank 15 is sent to the outside of the boundary as the finished concentrated acid via the concentrated acid transfer pump 16.

[0035] In this invention, a primary absorption reaction is carried out in the primary falling film absorber 12. The tail gas from the safety vessel 1 contains hydrogen chloride and trace amounts of chlorine. The tail gas enters from the top of the primary falling film absorber 12 and undergoes falling film absorption with the circulating absorption acid solution in the primary falling film absorber 12. The concentration of hydrochloric acid in the primary falling film absorber 12 is controlled at 31.3%~31.8%. The concentrated hydrochloric acid at the bottom of the primary falling film absorber 12 flows into the concentrated acid tank 15 and is sent to the outside of the boundary as the finished concentrated acid via the concentrated acid transfer pump 16.

[0036] An absorption circulation pump 7 and an absorption venturi 9 are sequentially installed on the bottom outlet pipeline of the reaction absorption vessel 6. The outlet end of the absorption venturi 9 is connected to the inlet end of the reaction absorption vessel 6. The lower gas phase outlet end of the first-stage falling film absorber 12 is connected to the inlet end of the absorption venturi 9. The liquid phase reactants and the tail gas from the first-stage falling film absorber 12 enter the reaction absorption vessel 6 together under the action of the absorption venturi 9. Fresh fatty acid methyl esters from outside the boundary enter the reaction absorption vessel 6. Inside the reaction absorption vessel 6, the tail gas from the first-stage falling film absorber 12 reacts with the fatty acid methyl esters, thereby removing residual chlorine in the tail gas and ensuring that the chlorine is completely reacted.

[0037] The bottom of the reaction absorption vessel 6 is connected to the absorption separation tank 8 via a pipe. The inlet end of the absorption separation tank 8 is connected to the bottom outlet end of the reaction absorption vessel 6, the top gas phase outlet end of the absorption separation tank 8 is connected to the top inlet end of the reaction absorption vessel 6, the bottom liquid phase outlet end of the absorption separation tank 8 is connected to the top inlet end of the reactant buffer tank 10, and the upper liquid phase outlet end of the absorption separation tank 8 is connected to the upper inlet end of the safety vessel 1. The liquid level in the absorption separation tank 8 is controlled to be higher than that in the safety vessel 1, ensuring that the liquid reactants in the absorption separation tank 8 can overflow into the safety vessel 1. After the liquid reactants in the reaction absorption vessel 6 undergo gas-liquid separation in the absorption separation tank 8, the top gas phase flows back to the reaction absorption vessel 6, and part of the bottom liquid phase overflows into the safety vessel 1 to react with the tail gas entering the safety vessel 1. The other part enters the reactant buffer tank 10 and is then sent to the production unit by the reactant transfer pump 11.

[0038] In some embodiments, an online chlorine detector is installed on the gas phase outlet pipeline at the top of the reaction absorption vessel 6 to control the chlorine concentration in the gas phase at the top of the reaction absorption vessel 6 to be within 5 mg / m³. 3 The following applies: When the concentration of chlorine exceeds the range, the circulation rate of the safety circulation pump 2 in the safety vessel 1 is increased, and the heat transfer rate of the safety cooler 3 is increased.

[0039] The reaction absorption process takes place in the reaction absorption vessel 6. Fresh fatty acid methyl esters from outside the boundary enter the reaction absorption vessel 6. The reaction absorption vessel 6 is equipped with an absorption circulation pump 7 and an absorption venturi 9. The tail gas from the first-stage falling film absorber 12 is mixed with the fatty acid methyl esters and then sent into the reaction absorption vessel 6. The residual chlorine in the tail gas reacts further with the fatty acid methyl esters in the reaction absorption vessel 6 to ensure that the chlorine is completely reacted. The reaction mixture is discharged from the bottom of the reaction absorption vessel 6 and separated into liquid and gas phases by the absorption separation tank 8. The liquid phase reactant enters the reactant buffer tank 10, and the gas phase returns to the reaction absorption vessel 6. The liquid level in the absorption separation tank 8 is controlled to be higher than that in the safety vessel 1 to ensure that the liquid phase reactant in the absorption separation tank 8 can overflow into the safety vessel 1.

[0040] In some embodiments, the reaction absorption vessel 6 is made of enamel material, and the operating temperature is controlled at 50°C and the operating pressure is -0.02 MPaG; the reaction absorption vessel 6 is equipped with a jacket, and circulating water is used to remove the heat during the reaction absorption process; the absorption venturi 9 is made of fiberglass material, and the operating temperature is controlled at 50°C and the operating pressure is -0.095 MPaG.

[0041] This invention utilizes a reaction absorption vessel 6 located after a primary falling film absorber 12 to further react fresh fatty acid methyl esters with residual chlorine in the tail gas. After the chlorinated fatty acid methyl ester tail gas passes through the primary falling film absorber 12, most of the hydrogen chloride in the tail gas has been absorbed by the falling film, resulting in an increase in the relative chlorine content in the tail gas after primary falling film absorption. Due to the significant reduction in the total tail gas volume, the gas velocity within the reaction absorption vessel 6 is noticeably lower. The increased relative chlorine content significantly improves reaction efficiency, and the reduced gas velocity prolongs the reaction time between the tail gas and the fatty acid methyl ester. Because fresh fatty acid methyl esters contain numerous unsaturated double bonds, chlorine can rapidly undergo an addition reaction with the fatty acid methyl ester upon introduction, ensuring complete reaction of the residual chlorine in the tail gas and preventing its impact on subsequent production equipment.

[0042] The upper gas phase outlet of the reaction absorption vessel 6 is connected to the upper inlet of the secondary falling film absorber 13. The tail gas after the reaction in the reaction absorption vessel 6 enters the secondary falling film absorber 13 through the upper inlet. Hydrochloric acid from the hypodilute acid tank 19 enters the secondary falling film absorber 13 from the top under the action of the hypodilute acid circulation pump 20 to absorb hydrogen chloride in the tail gas. After absorption, the tail gas flows out from the bottom of the secondary falling film absorber 13 and enters the tertiary falling film absorber 14. The bottom outlet of the secondary falling film absorber 13 is connected to the neutral acid tank 17. After the hypodilute acid absorbs the tail gas, it flows from the bottom of the secondary falling film absorber 13 into the neutral acid tank 17. The hydrochloric acid in the neutral acid tank 17 enters the primary falling film absorber 12 as the absorbent.

[0043] In this invention, a secondary absorption reaction is carried out in a secondary falling film absorber 13. The tail gas from the reaction absorption vessel 6 contains hydrogen chloride and enters from the top of the secondary falling film absorber 13. In the secondary falling film absorber 13, it undergoes falling film absorption with the circulating absorption acid solution. The concentration of hydrochloric acid in the secondary falling film absorber 13 is controlled at 22%~25%. The absorption acid solution at the bottom of the secondary falling film absorber 13 flows into the intermediate acid tank 17 and is then pumped to the primary falling film absorber 12 by the intermediate acid circulation pump 18 as the absorption liquid. The tail gas after absorption is sent to the tertiary falling film absorber 14 for further absorption.

[0044] The lower gas phase outlet of the secondary falling film absorber 13 is connected to the upper inlet of the tertiary falling film absorber 14. The tail gas absorbed by the secondary falling film absorber 13 enters the tertiary falling film absorber 14. Dilute acid from the dilute acid tank 21, acting as the absorbent, enters the tertiary falling film absorber 14 under the action of the dilute acid circulation pump 22 to absorb hydrogen chloride from the tail gas. The tail gas absorbed by the tertiary falling film absorber 14 then enters the alkaline scrubbing tower 24 under the action of the induced draft fan. The bottom of the tertiary falling film absorber 14 is connected to a hypodilute acid tank 19, and hydrochloric acid from the hypodilute acid tank 19 enters the secondary falling film absorber 13 as the absorbent. In some embodiments, the concentration of dilute acid in the dilute acid tank 21 is 18%~22%.

[0045] In this invention, a three-stage absorption reaction is carried out in a three-stage falling film absorber 14. The tail gas from the two-stage falling film absorber 13 contains hydrogen chloride and enters from the top of the three-stage falling film absorber 14. In the three-stage falling film absorber 14, it undergoes falling film absorption with the circulating absorption acid solution. The concentration of hydrochloric acid in the three-stage falling film absorber 14 is controlled at 20%~22%. The absorption acid solution at the bottom of the three-stage falling film absorber 14 flows into the dilute acid tank 19 and is then pumped to the two-stage falling film absorber 13 by the dilute acid circulation pump 20 as the absorption liquid. The tail gas after absorption by the three-stage falling film absorber 14 is sent to the alkaline scrubbing tower 24 for absorption.

[0046] In some embodiments, the primary falling film absorber 12, the secondary falling film absorber 13, and the tertiary falling film absorber 14 of the present invention are all vertical circular block type, made of graphite material, with the operating temperature controlled at 50°C and the operating pressure at -0.02MPaG, and the heat in the falling film absorption process is carried away by circulating water.

[0047] The alkaline washing process takes place in alkaline washing tower 24. Tail gas containing trace amounts of hydrogen chloride from the three-stage falling film absorber 14 is drawn to alkaline washing tower 24 by alkaline washing induced draft fan 23, absorbed by the sodium hydroxide solution, and then discharged at high altitude from alkaline washing tower 24. Waste alkaline solution at the bottom of alkaline washing tower 24 is circulated back to alkaline washing tower 24 for spray absorption via alkaline washing circulation pump 25. The absorbed sodium chloride-containing alkaline wastewater is sent to an off-site treatment area. The operating temperature of alkaline washing tower 24 is controlled at 35~37.1℃, and the operating pressure is atmospheric pressure. The alkaline solution concentration inside alkaline washing tower 24 is approximately 8%~11%, prepared by mixing 32% alkaline solution and condensate in a specific ratio. The air pressure of alkaline washing induced draft fan 23 is approximately 10 kPa. The main body of alkaline washing tower 24 is made of steel lined with PTFE, with two sections of 50x50x5 PTFE Raschig ring packing with a height of 6100 mm inside, supported and fixed by hump packing. A trough-type liquid distributor is installed at the top of the tower, and a demister is installed at the top of the tower.

[0048] The hydrogen chloride content in the tail gas after treatment in alkaline scrubbing tower 24 is 2 mg / m³. 3 Below, the chlorine concentration is 5 mg / m³ 3 The following meet the emission standards.

[0049] The method for treating the tail gas of chlorinated fatty acid methyl esters of the present invention utilizes the system of the present invention and includes the following steps: (1) the reaction tail gas enters a safety vessel and reacts with fatty acid methyl esters from a reaction absorption vessel to remove chlorine from the tail gas; (2) the reacted tail gas enters a first-stage falling film absorber for hydrogen chloride absorption; (3) the tail gas after absorption by the first-stage falling film absorber enters a reaction absorption vessel and reacts with fatty acid methyl esters to remove chlorine again, ensuring that the chlorine content is 5 mg / m³. 3 The following; (4) The tail gas after the reaction in the reaction absorption vessel enters the secondary falling film absorber and the tertiary falling film absorber in sequence for hydrogen chloride absorption, and then enters the alkaline washing tower for alkaline washing and is discharged at high altitude.

[0050] In step (1), a safety reaction occurs. The tail gas from the production unit enters from the top of the safety vessel 1, and the tail gas pipe is inserted below the liquid level in the safety vessel 1. The chlorine in the tail gas reacts with the fatty acid methyl esters filling the safety vessel 1 to generate chlorinated fatty acid methyl esters. The safety vessel 1 is equipped with a safety circulation pump 2 and a safety cooler 3 to remove the heat generated during the reaction. The reaction mixture is discharged from the bottom of the safety vessel 1. After gas-liquid separation by the safety separator 4, the liquid phase reactant flows into the reactant buffer tank 10, and after being pressurized by the reactant transfer pump 11, it is sent back to the production unit to continue the reaction. The gas phase discharged from the safety vessel 1 is separated from the liquid phase reactant by the safety gas-liquid separator 5 and recovered to the safety vessel 1. The tail gas is sent to the primary falling film absorber 12 for absorption.

[0051] Step (2) is a primary absorption reaction. The tail gas from the safety vessel 1 contains hydrogen chloride and trace amounts of chlorine. The tail gas enters from the top of the primary falling film absorber 12 and undergoes falling film absorption with the circulating absorption acid in the primary falling film absorber 12. The concentrated hydrochloric acid at the bottom of the primary falling film absorber 12 flows into the concentrated acid tank 15 and is sent to the outside of the boundary as the finished concentrated acid via the concentrated acid transfer pump 16.

[0052] Step (3) is the reaction absorption process. Fresh fatty acid methyl ester from outside the boundary enters the reaction absorption vessel 6. The reaction absorption vessel 6 is equipped with an absorption circulation pump 7 and an absorption venturi 9. The tail gas from the first-stage falling film absorber 12 is mixed with the fatty acid methyl ester and then sent into the reaction absorption vessel 6. The residual chlorine in the tail gas reacts further with the fatty acid methyl ester in the reaction absorption vessel 6 to ensure that the chlorine is completely reacted. The reaction mixture is discharged from the bottom of the reaction absorption vessel 6. After gas-liquid separation by the absorption separation tank 8, the liquid phase reactant enters the reactant buffer tank 10, and the gas phase returns to the reaction absorption vessel 6.

[0053] Step (4) consists of a two-stage absorption reaction process, a three-stage absorption reaction process, and an alkaline washing process. The tail gas from the reaction absorption vessel 6 contains hydrogen chloride and enters from the top of the two-stage falling film absorber 13. In the two-stage falling film absorber 13, it undergoes falling film absorption with the circulating absorption acid. The absorption acid at the bottom of the two-stage falling film absorber 13 flows into the intermediate acid tank 17 and is then pumped to the first-stage falling film absorber 12 by the intermediate acid circulation pump 18 as the absorbent. The tail gas after absorption is sent to the three-stage falling film absorber 14 for further absorption. The tail gas from the two-stage falling film absorber 13 contains hydrogen chloride and enters from the top of the three-stage falling film absorber 14. In the three-stage falling film absorber 14, it undergoes falling film absorption with the circulating absorption acid. The absorption acid at the bottom of the three-stage falling film absorber 14 flows into the sub-dilute acid tank 19 and is then pumped to the two-stage falling film absorber 13 by the sub-dilute acid circulation pump 20 as the absorbent. The tail gas after absorption by the three-stage falling film absorber 14 is sent to the alkaline washing tower 24 for absorption. The tail gas containing trace amounts of hydrogen chloride from the three-stage falling film absorber 14 is drawn to the alkaline washing tower 24 by the alkaline washing induced draft fan 23. After being absorbed by the sodium hydroxide solution, it is discharged from the alkaline washing tower 24 at high altitude. The waste alkaline liquid at the bottom of the alkaline washing tower 24 is circulated to the alkaline washing tower 24 for spray absorption by the alkaline washing circulation pump 25. The absorbed alkaline wastewater containing sodium chloride is sent to the outside of the boundary for treatment.

[0054] Example 1 (1) The tail gas of chlorinated fatty acid methyl ester (containing hydrogen chloride and chlorine) is divided into four branches at a flow rate of 3.12 t / h and enters from the top of the safety vessel 1 and is inserted below the liquid surface. Small holes are set on the inner tubes to ensure complete contact between gas and liquid reaction. The fatty acid methyl ester comes from the absorption separation tank 8. The operating temperature of the safety vessel 1 is controlled at 60~65℃ and the operating pressure is -0.02MPaG. The fatty acid methyl ester reacts with chlorine in the safety vessel 1 to generate chlorinated fatty acid methyl ester. The liquid phase reactant is discharged from the bottom of the safety vessel 1. After hydrogen chloride is separated by the safety separation tank 4, it is sent to the production unit for recycling at a flow rate of 11.53 t / h. The gas phase at the top of the safety vessel 1 is separated into gas and liquid by the safety gas-liquid separator 5. The liquid phase reactant containing fatty acid methyl ester and chlorinated fatty acid methyl ester is returned to the safety vessel 1. The tail gas (containing hydrogen chloride and trace amounts of chlorine) is sent to the first-stage falling film absorber 12 for hydrogen chloride absorption. The jacket of the safety vessel 1 is cooled by circulating water.

[0055] (2) The tail gas from the safety vessel 1, containing hydrogen chloride and trace amounts of chlorine, is fed into the upper part of the first-stage falling film absorber 12 at a flow rate of 3.11 t / h. The circulating hydrochloric acid from the second-stage falling film absorber 13 enters the first-stage falling film absorber 12 at a flow rate of 60 t / h. Hydrogen chloride is absorbed in the first-stage falling film absorber 12, and the concentration of hydrochloric acid in the first-stage falling film absorber 12 is controlled at 31.8%. The hydrochloric acid absorbed by the first-stage falling film absorber 12 is sent to the outside of the boundary as finished hydrochloric acid at a flow rate of 21.10 t / h. The tail gas after absorption is sent from the lower part of the first-stage falling film absorber 12 to the reaction absorption vessel 6 for further removal of residual chlorine. The operating temperature of the first-stage falling film absorber 12 is controlled at 50℃, and the operating pressure is -0.02 MPaG.

[0056] (3) Fresh fatty acid methyl esters from outside the boundary enter the reaction absorption vessel 6 at a flow rate of 11.52 t / h. Tail gas from the first-stage falling film absorber 12 at a flow rate of 0.71 t / h is drawn into the reaction absorption vessel 6 through the absorption venturi 9. The fresh fatty acid methyl esters and the residual chlorine in the tail gas react in the reaction absorption vessel 6 to generate chlorinated fatty acid methyl esters, ensuring that the chlorine in the tail gas is completely consumed by the reaction. After the liquid phase reactant is separated from hydrogen chloride by the absorption separation tank 8, 9.72 t / h overflows to the safety vessel 1 as the raw material reaction liquid for the safety vessel 1. The liquid level in the absorption separation tank 8 is controlled to be higher than that in the safety vessel 1, ensuring that the liquid phase reactant in the absorption separation tank 8 overflows to the safety vessel 1. 1.81 t / h is sent to the production unit for recycling. The hydrogen chloride-containing tail gas after reaction absorption is sent to the second-stage falling film absorber 13 for further absorption. The operating temperature of the reaction absorption vessel 6 is controlled at 50℃, and the operating pressure is -0.02 MPaG.

[0057] (4) The tail gas containing hydrogen chloride from the reaction absorption vessel 6 enters the upper part of the secondary falling film absorber 13 at a flow rate of 0.70 t / h. The circulating hydrochloric acid from the tertiary falling film absorber 14 enters the secondary falling film absorber 13 at a flow rate of 60 t / h. Hydrogen chloride is absorbed in the secondary falling film absorber 13, and the hydrochloric acid concentration in the secondary falling film absorber 13 is controlled at 23%. The hydrochloric acid absorbed by the secondary falling film absorber 13 is used as the absorbent in the primary falling film absorber 12 at a flow rate of 18.69 t / h. The tail gas after absorption is sent to the tertiary falling film absorber 14 for further absorption. The operating temperature of the secondary falling film absorber 13 is controlled at 50℃, and the operating pressure is -0.02 MPaG.

[0058] (5) Hydrogen chloride tail gas from the secondary falling film absorber 13 enters the upper part of the tertiary falling film absorber 14 at a flow rate of 0.23 t / h. 20% dilute hydrochloric acid from the dilute acid tank 21 enters the tertiary falling film absorber 14 at a flow rate of 17.49 t / h. Hydrogen chloride is absorbed in the tertiary falling film absorber 14, and the hydrochloric acid concentration in the tertiary falling film absorber 14 is controlled at 21%. The hydrochloric acid absorbed by the tertiary falling film absorber 14 is used as the absorbent in the secondary falling film absorber 13 at a flow rate of 18.22 t / h. The tail gas after absorption is sent to the alkaline washing system from the lower part of the tertiary falling film absorber 14. The operating temperature of the tertiary falling film absorber 14 is controlled at 50℃, and the operating pressure is -0.02 MPaG.

[0059] (6) The tail gas containing trace amounts of hydrogen chloride from the three-stage falling film absorber 14 is drawn to the alkaline scrubbing tower 24, and the alkaline spray rate of the alkaline scrubbing tower 24 is controlled at 5 t / h. The operating temperature of the alkaline scrubbing tower 24 is controlled at 35~37.1℃, the operating pressure is atmospheric pressure, and the concentration of alkaline solution in the alkaline scrubbing tower 24 is controlled at about 10%. The treated tail gas is discharged at high altitude, and its composition is tested to be: hydrogen chloride 2 mg / m³. 3 Chlorine 5mg / m 3Alkali washing tower 24 generates 0.03 t / h of sodium chloride-containing wastewater, which is then discharged outside the boundary area.

[0060] The following examines the concentration of by-product hydrochloric acid produced by the first-stage falling film absorber 12 when different concentrations of dilute hydrochloric acid are used as the absorbent in the three-stage falling film absorber 14.

[0061] The tail gas treatment operation of Example 1 was repeated, except that the concentration of hydrochloric acid in the absorbent of the three-stage falling film absorber 14 was different. During the tail gas treatment process, the byproduct hydrochloric acid produced by the first-stage falling film absorber 12 was sampled and analyzed. The results are shown in Table 1 below: Table 1:

[0062] The results show that using different concentrations of dilute hydrochloric acid as the absorbent in the three-stage falling film absorber 14 has a significant impact on the concentration of by-product hydrochloric acid. When water is used as the absorbent in the three-stage falling film absorber 14, the concentration of by-product hydrochloric acid is very low; when dilute hydrochloric acid is used as the absorbent, the concentration of by-product hydrochloric acid is significantly increased. After the concentration of dilute hydrochloric acid reaches 20%, further increasing the concentration of hydrochloric acid no longer significantly increases the concentration of by-product hydrochloric acid. It is evident that a dilute hydrochloric acid concentration between 16% and 25% can meet the concentration requirements of by-product hydrochloric acid, with 18% to 22% being optimal.

[0063] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0064] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0065] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A tail gas treatment system for chlorinated fatty acid methyl esters, characterized in that, include: A safety reactor is used to react the exhaust gas with fatty acid methyl esters to remove chlorine. A safety circulation pump and a safety cooler are installed on the bottom outlet pipeline of the safety reactor. The liquid reactants are pumped by the safety circulation pump to the safety cooler for cooling and then returned to the safety reactor. A primary falling film absorber is located downstream of the safety reactor, and the exhaust gas from the safety reactor reaction enters the primary falling film absorber for hydrogen chloride absorption. A reaction absorption reactor is located downstream of the primary falling film absorber, and the exhaust gas after absorption by the primary falling film absorber enters the reaction absorption reactor to react with fatty acid methyl esters again to remove chlorine. An online chlorine detector is installed on the gas phase outlet pipeline at the top of the reaction absorption reactor to control the chlorine concentration in the gas phase at the top of the reaction absorption reactor to 5 mg / m³. 3 The following describes a secondary falling film absorber located downstream of the reaction absorption vessel. The tail gas from the reaction in the reaction absorption vessel enters the secondary falling film absorber for hydrogen chloride absorption. The bottom outlet of the primary falling film absorber is connected to a concentrated acid tank. During the reaction, the hydrochloric acid concentration in the concentrated acid tank is controlled at 31.3%~31.8%. The hydrochloric acid in the concentrated acid tank is sent outside the boundary as the finished product. The bottom outlet of the secondary falling film absorber is connected to a neutral acid tank. The hydrochloric acid in the neutral acid tank enters the primary falling film absorber as the absorbent. The bottom outlet of the tertiary falling film absorber is connected to... A secondary dilute acid tank is used as an absorbent in the secondary falling film absorber. A tertiary falling film absorber is installed below the secondary falling film absorber. The exhaust gas after absorption by the secondary falling film absorber enters the tertiary falling film absorber for hydrogen chloride absorption. An alkaline scrubbing tower is installed downstream of the tertiary falling film absorber. The exhaust gas after absorption by the tertiary falling film absorber enters the alkaline scrubbing tower for absorption and is then discharged at high altitude. A dilute acid tank, containing dilute acid at a concentration of 18% to 22%, is used as an absorbent in the tertiary falling film absorber.

2. The system as described in claim 1, characterized in that, It also includes a reactant buffer tank, and a reactant transfer pump is installed on the bottom outlet pipeline of the reactant buffer tank. After the liquid reactant from the safety vessel and the reaction absorption vessel enters the reactant buffer tank, it is sent to the production device by the reactant transfer pump.

3. The system as described in claim 1, characterized in that, The bottom of the safety vessel is connected to the safety separation tank via a pipeline. After the liquid phase reactants undergo gas-liquid separation in the safety separation tank, the top gas phase flows back to the safety vessel, and the bottom liquid phase enters the reactant buffer tank. A safety gas-liquid separator is installed on the gas phase outlet pipeline at the top of the safety vessel.

4. The system as described in claim 1, characterized in that, An absorption circulation pump and an absorption venturi are installed on the bottom outlet pipeline of the reaction absorption vessel. The liquid phase reactants and the tail gas from the first-stage falling film absorber enter the reaction absorption vessel together under the action of the absorption venturi.

5. The system as described in claim 1, characterized in that, The bottom of the reaction absorption vessel is connected to the absorption separation tank via a pipe. After the liquid phase reactants undergo gas-liquid separation in the absorption separation tank, the top gas phase flows back to the reaction absorption vessel, and part of the bottom liquid phase overflows into the safety vessel, while the other part enters the reactant buffer tank.

6. A method for treating the tail gas of chlorinated fatty acid methyl esters, characterized in that, The system according to any one of claims 1 to 5 comprises the following steps: the reaction tail gas enters a safety vessel and reacts with fatty acid methyl ester from the reaction absorption vessel to remove chlorine from the tail gas; the reacted tail gas enters a first-stage falling film absorber for hydrogen chloride absorption; the tail gas after absorption by the first-stage falling film absorber enters the reaction absorption vessel and reacts with fatty acid methyl ester to remove chlorine again, ensuring that the chlorine content is below 5 mg / m³. 3 The tail gas after the reaction in the reaction absorption vessel enters the secondary falling film absorber and the tertiary falling film absorber in sequence for hydrogen chloride absorption, and then enters the alkaline washing tower for alkaline washing before being discharged at high altitude.

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