A method for treating an acid tail gas

Abstract

The application discloses an acid tail gas treatment method, comprising the following steps: inputting the acid tail gas into an absorption regeneration tower, using a proportioning solution to absorb and treat the acid tail gas; performing solid-liquid separation on the proportioning solution so as to continue using; and performing regeneration treatment on the absorbed acid tail gas. Through the addition of a chelating agent, the iron ion catalyst can be kept in an ionic state in the proportioning solution, and the catalytic effect is enhanced. Through the addition of a surfactant, the probability that sulfur particles are wrapped by hydrocarbons is reduced, and the sulfur recovery efficiency is improved. The catalyst used in the method can be regenerated and recycled, and no waste water, waste gas and waste residue are discharged, so that the treatment method is more environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of waste gas treatment technology, and particularly relates to a method for treating acidic exhaust gas. Background Technology

[0002] Acidic exhaust gases containing hydrogen sulfide require treatment before being released into the air. Treatment can convert hydrogen sulfide into sulfur for recovery, but the catalyst used in this process needs to be continuously fed into the treatment equipment. Therefore, a method for treating acidic exhaust gases that can produce sulfur and regenerate and recycle the catalyst is needed. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for treating acidic exhaust gas.

[0004] The present invention is achieved through the following technical solutions.

[0005] The present invention provides a method for treating acidic exhaust gas, comprising the following steps: S1: The acidic tail gas is fed into the absorption and regeneration tower, and the acidic tail gas is sequentially absorbed, defoamed, and washed using a proportioned solution; S2: Perform solid-liquid separation on the prepared solution to obtain solid sulfur; S3: The proportioned solution after solid-liquid separation is fed into the absorption and regeneration tower for reuse in the absorption of acidic tail gas; The prepared solution, in parts by mass, includes one or more of the following: 70-100 parts water, 25-40 parts catalyst, 10-30 parts chelating agent, 1-5 parts bactericide, 10-20 parts surfactant, 5-10 parts defoamer, and 5-20 parts alkaline solution.

[0006] Preferably, during the absorption process in the absorption and regeneration tower, the pressure of the acidic tail gas is controlled at 0.0005-0.002 MPaG, the air flow rate is 480-570 Nm3 / h, and the specific gravity of the solution is <1.3; The defoaming and washing processes are performed using existing demisters and washers.

[0007] Preferably, the iron ion concentration in the absorption and regeneration tower is controlled at 300-600 ppmw / w, the thiosulfate content is controlled at 20-100 g / kg, and the sulfur content in the solution is controlled at 0.4-1.5%wt.

[0008] Preferably, the pH value of the prepared solution is 7.8-9.5, and the ORP value is -80 to -280mv.

[0009] Preferably, the temperature of the prepared solution is 30-50°C.

[0010] Preferably, the temperature of the prepared solution is 2-3°C higher than the temperature of the acidic exhaust gas.

[0011] Preferably, the catalyst is an iron ion catalyst containing 50,000-55,000 ppm of free iron ions.

[0012] Preferably, the alkaline solution is a 40-50% sodium hydroxide solution.

[0013] Preferably, the catalyst, chelating agent, surfactant, and alkaline solution need to be continuously added to the regeneration tower during the treatment process.

[0014] Preferably, the addition rates of the catalyst, chelating agent, surfactant, and alkaline solution are: catalyst 0.2-0.4 L / h, chelating agent 1.5-2 L / h, surfactant 0.1-0.2 L / h, and alkaline solution 3-6 L / h.

[0015] The beneficial effects of this invention are as follows: This invention enhances the catalytic effect of iron ion catalyst by adding a chelating agent to maintain its ionic state in the solution. The addition of a surfactant reduces the probability of sulfur particles being encapsulated by hydrocarbons, thus improving sulfur recovery efficiency. The catalyst used in this method is regenerable and recyclable, producing no wastewater, waste gas, or waste residue, making the treatment method relatively environmentally friendly. Detailed Implementation

[0016] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0017] Example 1: A method for treating acidic exhaust gas includes the following steps: S1: The acidic tail gas is fed into the absorption and regeneration tower, and the acidic tail gas is sequentially absorbed, defoamed, and washed using a proportioned solution; S2: Solid sulfur is obtained by solid-liquid separation of the prepared solution using a frame filter press; S3: The proportioned solution after solid-liquid separation is fed into the absorption and regeneration tower for reuse in the absorption of acidic tail gas; The prepared solution, in parts by mass, includes 90 parts water, 30 parts catalyst, 22 parts chelating agent, 3 parts bactericide, 14 parts surfactant, 8 parts defoamer, and 13 parts alkaline solution. During the treatment process, parameters such as pH, ORP, and iron ions in the prepared solution can be monitored, and the addition ratio of each component can be adjusted based on the monitoring results.

[0018] During the absorption and regeneration process in the absorption tower, the pressure of the acidic tail gas is controlled at 0.0001 MPaG, and the air flow rate is 430 Nm³. 3 / h, solution specific gravity <1.3; The defoaming and washing processes are performed using existing demisters and washers.

[0019] The iron ion concentration in the absorption and regeneration tower is controlled at 300 ppmw / w, the thiosulfate content is controlled at 20 g / kg, and the sulfur content in the solution is controlled at 0.4%wt.

[0020] The pH value of the prepared solution is 7.8, and the ORP value is -80mv.

[0021] The temperature of the prepared solution is 30°C.

[0022] The temperature of the prepared solution is 2°C higher than that of the acidic exhaust gas to prevent the coagulation of hydrocarbons and excess moisture.

[0023] The catalyst is an iron ion catalyst containing 50,000-55,000 ppm of free iron ions.

[0024] The alkaline solution is a 40% sodium hydroxide solution.

[0025] The catalyst, chelating agent, surfactant, and alkaline solution need to be continuously added to the regeneration tower during the treatment process. The addition rates are: catalyst 0.2 L / h, chelating agent 1.5 L / h, surfactant 0.1 L / h, and alkaline solution 3 L / h.

[0026] Example 2: A method for treating acidic exhaust gas includes the following steps: S1: The acidic tail gas is fed into the absorption and regeneration tower, and the acidic tail gas is sequentially absorbed, defoamed, and washed using a proportioned solution; S2: Solid sulfur is obtained by solid-liquid separation of the prepared solution using a frame filter press; S3: The proportioned solution after solid-liquid separation is fed into the absorption and regeneration tower for reuse in the absorption of acidic tail gas; The prepared solution, in parts by mass, includes 100 parts water, 40 parts catalyst, 30 parts chelating agent, 5 parts bactericide, 20 parts surfactant, 10 parts defoamer, and 20 parts alkaline solution. During the treatment process, parameters such as pH, ORP, and iron ions in the prepared solution can be monitored, and the addition ratio of each component can be adjusted based on the monitoring results.

[0027] During the absorption and regeneration process in the absorption tower, the pressure of the acidic tail gas is controlled at 0.002 MPaG, and the air flow rate is 570 Nm³. 3 / h, solution specific gravity <1.3; The defoaming and washing processes are performed using existing demisters and washers.

[0028] The iron ion concentration in the absorption and regeneration tower is controlled at 600 ppmw / w, the thiosulfate content is controlled at 100 g / kg, and the sulfur content in the solution is controlled at 1.5%wt.

[0029] The pH value of the prepared solution is 9.5, and the ORP value is -280mv.

[0030] The temperature of the prepared solution is 50°C.

[0031] The temperature of the prepared solution is 3°C higher than that of the acidic exhaust gas to prevent the coagulation of hydrocarbons and excess moisture.

[0032] The catalyst is an iron ion catalyst containing 50,000-55,000 ppm of free iron ions.

[0033] The alkaline solution is a 50% sodium hydroxide solution.

[0034] The catalyst, chelating agent, surfactant, and alkaline solution need to be continuously added to the regeneration tower during the treatment process. The addition rates are: catalyst 0.4 L / h, chelating agent 2 L / h, surfactant 0.2 L / h, and alkaline solution 6 L / h.

[0035] Example 3: A method for treating acidic exhaust gas includes the following steps: S1: The acidic tail gas is fed into the absorption and regeneration tower, and the acidic tail gas is sequentially absorbed, defoamed, and washed using a proportioned solution; S2: Solid sulfur is obtained by solid-liquid separation of the prepared solution using a frame filter press; S3: The proportioned solution after solid-liquid separation is fed into the absorption and regeneration tower for reuse in the absorption of acidic tail gas; The prepared solution, in parts by mass, includes 70 parts water, 25 parts catalyst, 10 parts chelating agent, 1 part bactericide, 10 parts surfactant, 5 parts defoamer, and 5 parts alkaline solution. During the treatment process, parameters such as pH, ORP, and iron ions in the prepared solution can be monitored, and the addition ratio of each component can be adjusted based on the monitoring results.

[0036] During the absorption and regeneration process in the absorption tower, the pressure of the acidic tail gas is controlled at 0.0005 MPaG, and the air flow rate is 480 Nm³. 3 / h, solution specific gravity <1.3; The defoaming and washing processes are performed using existing demisters and washers.

[0037] The iron ion concentration in the absorption and regeneration tower is controlled at 500 ppmw / w, the thiosulfate content is controlled at 60 g / kg, and the sulfur content in the solution is controlled at 1%wt.

[0038] The pH value of the prepared solution is 8, and the ORP value is -150mv.

[0039] The temperature of the prepared solution is 40°C.

[0040] The temperature of the prepared solution is 3°C higher than that of the acidic exhaust gas to prevent the coagulation of hydrocarbons and excess moisture.

[0041] The catalyst is an iron ion catalyst containing 50,000-55,000 ppm of free iron ions.

[0042] The alkaline solution is a 45% sodium hydroxide solution.

[0043] The catalyst, chelating agent, surfactant, and alkaline solution need to be continuously added to the regeneration tower during the treatment process.

[0044] The addition rates of the catalyst, chelating agent, surfactant, and alkaline solution are as follows: catalyst 0.248 L / h, chelating agent 1.748 L / h, surfactant 0.138 L / h, and alkaline solution 4.8 L / h.

[0045] The processes in Examples 1-3 can produce sulfur with a moisture content of <35% and a purity of >99.5%, and the formulation solutions can be regenerated and recycled.

[0046] Comparative Example 1: An acidic exhaust gas treatment method, based on Example 1, differs only in that the solution is expressed in parts by mass, comprising 40 parts water, 10 parts catalyst, 8 parts chelating agent, 5 parts bactericide, 5 parts surfactant, 2 parts defoamer, and 1 part alkaline solution.

[0047] Comparative Example 2: An acidic exhaust gas treatment method, based on Example 1, differs only in that the solution is expressed in parts by mass, comprising 150 parts water, 60 parts catalyst, 50 parts chelating agent, 40 parts bactericide, 40 parts surfactant, 30 parts defoamer, and 35 parts alkaline solution.

[0048] In Examples 1-3 and Comparative Examples 1 and 2, the main components of the acidic exhaust gas were air and hydrogen sulfide, and the total flow rate of the acidic gas was 12000 Nm³. 3 / h, average H2S concentration 1000ppm, sulfur content 460kg / d.

[0049] The results of the gas emission after the acidic exhaust gas was treated in Examples 1-3 and Comparative Examples 1 and 2 are shown in the table below.

[0050] As can be seen from the table above, the acidic gas treated using the method of this embodiment can greatly reduce the sulfur content and effectively reduce the pollution of the acidic gas to the environment.

[0051] The methods in Examples 1-3 are based on a DN2400*19250 absorption and regeneration tower prepared using existing technology. Acidic tail gas directly enters the empty section of the primary high-efficiency absorption and regeneration tower, while high-concentration gas enters the liquid phase section. The gas is then fed into the regeneration tower below the prepared solution. After one bubbling absorption, it mixes with the low-concentration gas from the empty section and enters the secondary absorption and regeneration tower for further reaction. The mixed gas then contacts the catalyst solution countercurrently. Hydrogen sulfide in the gas first dissolves in the liquid phase and then reacts with the iron ions in the liquid phase catalyst to generate elemental sulfur, reducing ferric ions to ferrous ions. Simultaneously, the oxygen in the acidic gas oxidizes some of the ferrous ions in the catalyst solution to ferric ions. To prevent insufficient oxygen content in the acidic gas from affecting catalyst activity, a total flow rate of 520 Nm³ from the blower is required in both absorption and regeneration towers according to the ORP test parameters. 3 / h of air is uniformly introduced into the catalyst solution through the bottom distributor to oxidize ferrous ions.

[0052] An air purging ring with nozzles is installed at the bottom of the absorption and regeneration tower cone. Compressed air is used periodically to purge the bottom of the cone to prevent sulfur adhesion. The sulfur generated in the absorption and regeneration tower settles at the bottom as a sulfur slurry with a solid content of 5-15 wt%. The sulfur slurry containing a high concentration of sulfur particles is pumped to a plate and frame filter press. After filtration, the sulfur product is obtained, and the filtrate is recovered in a filtrate tank and returned to the absorption and regeneration tower.

[0053] The method of the present invention provides a low-temperature, low-cost method for removing hydrogen sulfide: H₂S + 1 / 2O₂ → H₂O + S° (1) This reaction occurs in an aqueous solution and is carried out using an iron ion catalyst. The reaction can be divided into two parts: absorption and regeneration, as shown below: Absorption portion H₂S(g) + H₂O ↔ H₂S(l) + H₂O (2) H2S(l)↔H + +HS - (3) HS-+2Fe 3+ →2Fe 2+ +H + +S (4) The overall equation for the absorption part (consolidation of equations 2, 3, and 4) H2S(g) + 2Fe 3+ →2H + +S+2Fe 2+(5) Regeneration section 1 / 2O2(g)+H2O↔1 / 2O2(l)+H2O (6) 1 / 2O2(l) + H2O + 2Fe 2+ →2OH-+2Fe 3+ (7) Overall equation for the regeneration part (superposition of equations 6 and 7) 1 / 2O2 (gas) + H2O + 2Fe 2+ →2OH-+2Fe 3+ (8) The superposition of equations 5 and 8 yields the improved Claus reaction equation, as shown in (1).

[0054] The elemental sulfur produced in the reaction exists in particulate form in the solution and must be removed using liquid-solid separation techniques (such as sedimentation and filtration).

[0055] In aqueous solutions, iron ions undergo the following side reaction to form a precipitate: Fe 3+ +3OH - →Fe(OH)3(s) (9) Fe 2+ +S 2- →FeS(s) (10) To prevent the aforementioned side reactions from occurring, this invention employs a composite chelating agent. The chelating agent can form stable chemical bonds with ferric and ferrous ions, thereby keeping the ferric ions stable over a wide pH range.

[0056] Equation 1 shows that the reaction does not involve H+. + Ions and OH - The net product of ions is formed, so the pH of the solution will not change. However, the side reaction will release H₂. + The presence of ions lowers the pH of the solution, ultimately reducing the total amount of H2S absorbed. One side reaction is the formation of thiosulfate, but a certain amount of thiosulfate ions (S2O3) are also absorbed. 2- It is beneficial to the BLUER-PRO process, as it can inhibit the degradation of chelating agents.

[0057] 2HS - +2O2→S2O3 2- +H2O (11) When this reaction is combined with the ionization reaction (Equation 3), it can be seen that with the increase of thiosulfate (S2O3) 2- This will produce excess H. + ion.

[0058] In addition, the carbon dioxide in the acid gas is easily soluble in water, forming bicarbonate (HCO3). - ) and carbonates (CO3) 2- This causes the pH of the solution to decrease, and the reaction is as follows: CO2(g) + H2O(l) ↔ H2CO3(l) (12) H2CO3(l)↔H + +HCO3 - (13) HCO3 - ↔CO3 2- +H + (14) To stabilize the pH of the solution, an alkaline substance such as sodium hydroxide needs to be added. Its reaction with carbon dioxide is as follows: CO2(g) + H2O(l) ↔ H2CO3(l) (15) H2CO3(l)+2NaOH↔Na2CO3+2H2O (16) Na₂CO₃ + H₂CO₃ ↔ 2NaHCO₃ (17) In the formation of bicarbonate (HCO3) - ) and carbonates (CO3) 2- After buffering, carbon dioxide absorption is significantly reduced. Generally, a weakly alkaline solution with a pH of 8.0-9.5 is suitable for most reactions; however, in some cases, a higher pH can improve reaction efficiency. A higher pH promotes the formation of thiosulfate ions, reduces oxygen absorption, and ultimately hinders the condensation of elemental sulfur; conversely, a too-low pH will inhibit the absorption of H₂S gas. It is important to emphasize that the system's pH value needs to be monitored.

[0059] Since sulfur exists in particulate form in the aqueous solution, solid-liquid separation must be performed using a precipitation-like method. Because sulfur is approximately twice as dense as water, the precipitation rate is relatively fast. Exceptions include the following two special cases: 1. In the initial operation phase of the process according to this invention, when the catalyst solution is first added to the system, it easily forms fine sulfur particles, which are difficult to separate. When the sulfur concentration in the solution reaches 4-6 g / L (0.4-0.6 wt%), the sulfur particles are approximately 15 micrometers in size, which is within the operable range. These sulfur particles will act as "mother particles," thereby promoting the formation of larger particles of 100-150 micrometers.

[0060] 2. Tiny bubbles or hydrocarbons can adhere to the surface of sulfur particles, causing them to float on the solution surface instead of settling. Normally, these floating particles are wetted by the solution, but unwetted sulfur particles also exist, and their aggregation can cause blockage. Therefore, XR-SR6 surfactant should be continuously added to the solution to facilitate the wetting and settling of sulfur particles.

[0061] As shown in Equation 1, water is generated simultaneously with sulfur production. However, the water evaporated by the heat of sulfur formation, the water carried away by acid gas and air, and the excess water generated by the sulfur production all require water replenishment to maintain the normal liquid levels in the absorption tower and oxidation tower.

[0062] The temperature of the prepared solution should be higher than that of the acidic exhaust gas to prevent the condensation of hydrocarbons and excess moisture. Typically, a temperature difference of 2-3°C is sufficient. An external solution heat exchanger can be used to control the temperature of the prepared solution.

[0063] Redox properties are one of the reference indicators for the reactivity of a mixed solution. This parameter is related to the rate of oxidation reaction in the mixed solution, and the concentration of ferric ions (Fe2+). 3+ ) and ferrous ions (Fe 2+ The ratio is relevant. Generally, a redox value between -80mV and -280mV in the solution indicates moderate catalyst activity in the system. Excessively high redox value (greater than -75mV) may lead to excessive sulfate formation, while excessively low redox value (< -300mV to -350mV) may cause precipitation of iron ion catalyst.

[0064] Specific gravity (SG) of the solution is an indirect parameter for measuring the dissolved salt content. Commonly used dissolved salts include NaHCO3 and Na2CO3 (alkaline), Na2S2O3 and Na2SO4. Because the amount of H2S gas and oxygen absorbed by the aqueous solution decreases as the dissolved salt concentration increases, the concentration of dissolved salts is very important. Normally, the specific gravity of the solution should be less than 1.3. If it is too high, a portion of the solution needs to be drained and fresh catalyst and water added.

[0065] The materials used in the formulation solution of this invention were purchased from Yantai Xinrui Environmental Protection Technology Co., Ltd., specifically: XR-SR1 iron ion catalyst: The iron ion catalyst is a complex with a chemical framework. XR-SR1 contains 50,000-55,000 ppm of free iron ions. Since the solution will be lost during the washing of the sulfur cake, the catalyst XR-SR1 needs to be added. The proportion added can be adjusted according to the concentration of iron ions.

[0066] XR-SR2 chelating agent: The role of chelating agents is to maintain the ionic state of the iron ion catalyst in the solution. During the treatment process, a small amount of type A chelating agent will be destroyed and degraded by oxidation, and some chelating agent will be lost due to sulfur cake. Therefore, XR-SR2 needs to be continuously added as a replenishment. The iron ion chelating agent XR-SR2 is a special mixture of type A and type B chelating agents.

[0067] As mentioned above, the loss of type A chelating agents is related to the concentration of thiosulfate in the formulation solution because thiosulfate can stabilize the chelating agent. If the sulfur cake is not washed sufficiently, the concentration of thiosulfate in the formulation solution will decrease.

[0068] XR-SR3 bactericide: Excessive biological activity (bacteria) can reduce the catalytic reaction efficiency. Adding a small amount of bactericide to the solution can reduce biological activity. XR-SR3 inhibits bacterial growth during the treatment process and needs to be added to the absorption regeneration tower periodically as needed.

[0069] XR-SR6 surfactant: Sulfur particles sometimes adhere to microbubbles, and sometimes are encapsulated by hydrocarbons. Adding surfactants to the solution ensures the sulfur in the solution is wetted, reducing its impact. If the solution contains other organic matter or oil, the amount of surfactant needs to be increased accordingly.

[0070] Silicone-based defoamers: Foam generated during the treatment process. Excessive addition of XR-SR6 and XR-SR3, and the presence of organic matter in the acid gas, can all cause foam generation. Add no more than 0.5 liters of pure defoamer (or 1 liter of a solution of 50% defoamer and 50% water) at a time.

[0071] Sodium hydroxide solution: Sodium hydroxide is added to control the pH value of the circulating solution.

Claims

1. A method for treating acidic exhaust gas, characterized in that, Includes the following steps: S1: The acidic tail gas is fed into the absorption and regeneration tower, and the acidic tail gas is sequentially absorbed, defoamed, and washed using a proportioned solution; S2: Perform solid-liquid separation on the prepared solution to obtain solid sulfur; S3: The proportioned solution after solid-liquid separation is fed into the absorption and regeneration tower for reuse in the absorption of acidic tail gas; The prepared solution, in parts by mass, includes one or more of the following: 70-100 parts water, 25-40 parts catalyst, 10-30 parts chelating agent, 1-5 parts bactericide, 10-20 parts surfactant, 5-10 parts defoamer, and 5-20 parts alkaline solution.

2. The method for treating acidic exhaust gas as described in claim 1, characterized in that: During the absorption and regeneration process in the absorption tower, the pressure of the acidic tail gas is controlled at 0.0005-0.002 MPaG, and the air flow rate is 480-570 Nm³. 3 / h, solution specific gravity <1.3; The defoaming and washing processes are performed using existing demisters and washers.

3. The method for treating acidic exhaust gas as described in claim 1, characterized in that: The iron ion concentration in the absorption and regeneration tower is controlled at 300-600 ppmw / w, the thiosulfate content is controlled at 20-100 g / kg, and the sulfur content in the solution is controlled at 0.4-1.5%wt.

4. The method for treating acidic exhaust gas as described in claim 1, characterized in that: The pH value of the prepared solution is 7.8-9.5, and the ORP value is -80 to -280mv.

5. The method for treating acidic exhaust gas as described in claim 1, characterized in that: The temperature of the prepared solution is 30-50℃.

6. The method for treating acidic exhaust gas as described in claim 1, characterized in that: The temperature of the prepared solution is 2-3°C higher than the temperature of the acidic exhaust gas.

7. The method for treating acidic exhaust gas as described in claim 1, characterized in that: The catalyst is an iron ion catalyst containing 50,000-55,000 ppm of free iron ions.

8. The method for treating acidic exhaust gas as described in claim 1, characterized in that: The alkaline solution is a 40-50% sodium hydroxide solution.

9. The method for treating acidic exhaust gas as described in claim 1, characterized in that: The catalyst, chelating agent, surfactant, and alkaline solution need to be continuously added to the regeneration tower during the treatment process.

10. The method for treating acidic exhaust gas as described in claim 9, characterized in that: The addition rates of the catalyst, chelating agent, surfactant, and alkaline solution are as follows: catalyst 0.2-0.4 L / h, chelating agent 1.5-2 L / h, surfactant 0.1-0.2 L / h, and alkaline solution 3-6 L / h.

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