Method for purifying yellow phosphorus tail gas

Abstract

The invention provides a yellow phosphorus tail gas purification method. The yellow phosphorus tail gas purification method comprises the following steps: tail gas pressurization, water washing cooling dust removal and demisting, multi-stage countercurrent acid washing desulfurization, dephosphorization and demisting, alkali washing and demisting and the like. The yellow phosphorus tail gas is dephosphorized, desulfurized and purified by adopting multi-stage sulfuric acid countercurrent washing, most saturated steam brought by the yellow phosphorus tail gas is removed in advance by utilizing the water absorption of low-concentration sulfuric acid in the first two sections of acid washing, meanwhile, alkaline H3P is absorbed in the low-concentration sulfuric acid, and most H3P is oxidized and removed by introducing oxygen through circulating sulfuric acid, so that the consumption of 98% of sulfuric acid is greatly reduced, and the energy consumption is reduced. High-concentration sulfuric acid is subjected to acid pickling in the later two stages, sulfur and phosphorus impurities are removed through oxidation by means of the oxidizability of the high-concentration sulfuric acid, oxygen is introduced into washing circulating sulfuric acid to oxidize H3P and H2S dissolved in the sulfuric acid, and consumption of 98% of sulfuric acid is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of yellow phosphorus tail gas purification, and in particular to a method for purifying yellow phosphorus tail gas. Background Art

[0002] Yellow phosphorus tail gas contains waste gases such as carbon monoxide, sulfur dioxide, carbon dioxide, hydrogen fluoride, silicon tetrafluoride, phosphine, and hydrogen sulfide. Carbon monoxide is a colorless, odorless, flammable, toxic gas that will have a serious impact on air quality. The unorganized emission of yellow phosphorus tail gas will lead to an increase in the concentration of harmful gases in the surrounding air. The phosphine in the tail gas is very harmful to plants and humans, and may cause health problems such as respiratory diseases and nervous system damage. Long-term exposure to an environment containing yellow phosphorus tail gas may also increase the risk of serious diseases such as cancer. Most of the yellow phosphorus tail gas is directly discharged. It is ignited with an open flame when it enters the atmosphere from the chimney and is discharged into the atmosphere after burning, causing huge energy waste and ecological damage. The emission of yellow phosphorus tail gas will damage the surrounding ecosystem and affect plant growth and ecological balance.

[0003] Patent CN101530722B proposes a method for purifying yellow phosphorus tail gas, which specifically includes washing the yellow phosphorus tail gas with water and then sending it into a wet tube electrostatic precipitator to remove dust and coal tar, so as to obtain a purified coal gas with a dust and coal tar content of less than 10 mg / Nm3. The dust and coal tar content of the gas obtained after purifying the yellow phosphorus tail gas by the method of the present invention is less than 10 mg / Nm3; the dust content is about 5 mg / Nm3, which is conducive to subsequent dephosphorization, desulfurization and temperature and pressure swing adsorption deep purification treatment. The method of the present invention can be widely used in the purification of industrial yellow phosphorus tail gas, and the coal gas collected after purification can be used for power generation or subsequent purification as a carbon-chemical raw material, such as industrial production of formic acid and other fields.

[0004] Patent CN103768907B proposes a method for deep purification of yellow phosphorus tail gas by oxidation alkali washing, which includes: first washing the yellow phosphorus tail gas produced by the yellow phosphorus industry to remove dust; then alkali washing the tail gas after washing with NaOH solution; the tail gas after alkali washing is then oxidized and alkali washed with sodium hypochlorite solution to obtain purified yellow phosphorus tail gas; the washing waste liquid after oxidation alkali washing reacts with CaO, the precipitate is filtered out, and the obtained filtrate enters the sodium hypochlorite generator to generate sodium hypochlorite solution, which is returned to the oxidation alkali washing step for reuse. This method allows sodium hypochlorite to be recycled, which can not only greatly reduce the amount of sodium hypochlorite used, but also reduce equipment corrosion. After washing by this method, the phosphorus and phosphine content of the discharged tail gas is ≤100mg / m3, and the water content should be ≤20g / m3. It meets the requirement that the sulfur and phosphorus impurity content as fuel must be less than 100mg / m3.

[0005] In summary, although the above two purification methods can purify phosphorus-containing tail gas to a certain extent, their purification methods are single. For example, the first purification method adopts a single water washing treatment method, which has the following shortcomings in purifying phosphorus-containing tail gas:

[0006] First, the purification effect is limited: water washing can only remove some water-soluble phosphorus compounds, and the removal effect of insoluble or insoluble phosphorus substances is poor, which may cause the phosphorus content in the tail gas to remain high and fail to meet the emission standards;

[0007] Second, secondary pollution occurs. During the washing process, the treatment of phosphorus-containing wastewater becomes a new problem. If not properly treated, the discharge of phosphorus-containing wastewater may cause water pollution.

[0008] Third, phosphorus compounds are not effectively recycled and utilized, but are directly washed away by water, resulting in a waste of resources.

[0009] Fourth, the effect on exhaust gas with complex components is poor. If the exhaust gas contains other impurities, such as dust, organic matter, etc., water washing may not be able to effectively remove these impurities at the same time, affecting the overall purification effect. For example, the second purification method uses water washing and alkaline washing. Water washing and alkaline washing have the following obvious deficiencies when treating phosphorus-containing exhaust gas: First, the removal efficiency is limited. Water washing mainly relies on dissolution and absorption, but for some insoluble phosphorus-containing compounds, the removal effect may not be good. Although alkaline washing can react with acidic phosphorus-containing substances, it may not be able to effectively remove some chemically stable phosphorus-containing compounds. Second, the lack of a pickling step may result in certain specific types of phosphorus-containing compounds being unable to be fully treated, and a certain amount of phosphorus-containing substances still remain in the treated exhaust gas. Summary of the invention

[0010] The purpose of the present invention is to provide a method for purifying yellow phosphorus tail gas, which solves the problem of insufficient purification of yellow phosphorus tail gas.

[0011] To achieve the above purpose, the present invention provides the following technical solution: a method for purifying yellow phosphorus tail gas, comprising the following steps:

[0012] A method for purifying yellow phosphorus tail gas comprises the following steps:

[0013] Step 1, tail gas pressurization: Use a fan to pressurize the yellow phosphorus tail gas to the required range, and send it to the various levels of purification processes at the back end in turn. The purified yellow phosphorus tail gas is finally sent to the use end of the process for utilization;

[0014] Step 2: Water washing, cooling, dust removal and mist removal: The pressurized yellow phosphorus tail gas first enters the water washing device, and uses cold spray water from the yellow phosphorus production system to cool and reduce the saturated water vapor content in the yellow phosphorus tail gas, while further deeply purifying dust, fluorine, and P 4And other impurities, and finally go to the next process after being defogged by the gas-liquid separator;

[0015] Step 3, multi-stage countercurrent pickling, desulfurization, dephosphorization and demisting: the yellow phosphorus tail gas after water washing, cooling, dust removal and demisting enters the multi-stage countercurrent pickling device, which includes primary pickling, secondary pickling, tertiary pickling, quaternary pickling, etc. (matching the number of stages according to the purification requirements), and 98% sulfuric acid is added at the last stage, and it countercurrents to the first stage step by step. Each level of pickling has an independent washing acid circulation cooling system and oxygen supplement oxidation system. The first-stage pickling liquid is discharged and separated into dilute sulfuric acid and sulfur according to the index. The dilute sulfuric acid is used for comprehensive utilization of the phosphate ore flotation device and the sulfur removal sulfuric acid device. The yellow phosphorus tail gas after desulfurization and dephosphorization is finally demisted and sent to the next process;

[0016] Among them, the main reaction equations occurring in multi-stage pickling are as follows:

[0017] P 4 +5HSO → 5SO 2 ↑+4H 3 PO 4 +4H 2 O;

[0018] 3PH 3 +4H 2 SO 4 →3H 3 PO 4 +4S↓+4H 2 O;

[0019] 3H 2 S+H 2 SO 4 →4S↓+4H 2 O;

[0020] 3AsH 3 +4H 2 SO 4 →3H 3 AsO 4 +4S↓+4H 2 O;

[0021] 3CS 2 +2H 2 SO 4 →3CO 2 ↑+8S↓+2H 2 O;

[0022] 3COS+H 2 SO 4 →3CO 2 ↑+4S↓+H 2 O;

[0023] Step 4, alkaline washing and demisting: send the yellow phosphorus tail gas containing a small amount of SO2 and sulfuric acid mist after acid washing to the alkaline washing device, use alkaline circulating washing liquid for washing and neutralization, add lime milk to maintain the pH of the circulating washing liquid within the required range, and convert calcium sulfite into calcium sulfate through air oxidation of the circulating washing liquid. The circulating liquid is discharged according to the process requirements for solid-liquid separation, the liquid is returned to the circulation system for utilization, and the solid calcium sulfate is discharged and sent to the cement plant for comprehensive utilization;

[0024] The main reaction equation is as follows:

[0025] Ca(OH) 2 +H 2 SO 4 →CaSO 4 ↓+2H 2 O;

[0026] Ca(OH) 2 +SO 2 →CaSO 3 ↓+H 2 O;

[0027] 2CaSO 3 +O 2 →2CaSO 4 ↓.

[0028] Preferably, in the tail gas pressurization of step 1, the yellow phosphorus tail gas is pressurized to the required pressure under the action of a pressurized fan, so as to overcome the resistance of the purification devices at various levels at the rear end and ensure that the pressure at the end of the purified yellow phosphorus tail gas meets the requirements. At the same time, increasing the pressure is beneficial to reducing the saturated water vapor amount of the yellow phosphorus tail gas and reducing the amount of 98% sulfuric acid used at the rear end;

[0029] Preferably, in step 2, cooling circulating water is introduced into the water washing device, which comes from the cold spray cooling water system of the yellow phosphorus production device, and wastewater discharged from the water washing device is discharged to the wastewater treatment system of the yellow phosphorus production device for treatment and then recycled.

[0030] Preferably, in step 3, each level of circulating washing sulfuric acid is cooled by circulating cooling water in a cooler to control the temperature of sulfuric acid at 40-60°C, each level of circulating washing acid has an oxygen oxidation system, and the cooler is a graphite heat exchanger or a silicon carbide heat exchanger.

[0031] Preferably, in step 3, the final pickling device is supplemented with more than 98% sulfuric acid, and the circulating sulfuric acid is countercurrently discharged to the previous pickling device until the sulfuric acid concentration of the first pickling device reaches 35-40% (containing 6-8% phosphoric acid) and is discharged to obtain dilute sulfuric acid and sulfur through solid-liquid separation, which are respectively sent to the phosphate ore concentrator and the sulfuric acid device for comprehensive utilization.

[0032] Preferably, in step 4, the pH is controlled at 5-6 by adding lime milk during the alkali washing process, so as to prevent the CO in the yellow phosphorus tail gas from being 2 Being absorbed causes increased alkali consumption.

[0033] Preferably, in step 4, gas-liquid separation and demisting are performed after alkali washing to reduce the adverse effects caused by the washing liquid and particulate matter entering the yellow phosphorus tail gas use end.

[0034] Preferably, the blower used in the method is a centrifugal blower, a Roots blower or a vacuum pump.

[0035] Preferably, the cooling device, pickling device and alkali washing device used in the method may be an empty tower, a packed tower or a super gravity tower.

[0036] Compared with the prior art, the present invention can at least achieve the following beneficial effects:

[0037] 1. Use cold water spray to cool down the yellow phosphorus tail gas, reduce the saturated water vapor content in the yellow phosphorus tail gas, and further remove dust, fluorine and elemental phosphorus. Finally, remove mist to reduce the entrainment of water foam particles in the yellow phosphorus tail gas;

[0038] 2. Use multi-stage pickling towers to pickle the yellow phosphorus tail gas. Low-concentration sulfuric acid is used in the first two stages of the pickling towers to mainly utilize its water absorption to remove a large amount of saturated water vapor brought by the front stage of the yellow phosphorus tail gas in advance, greatly reducing the consumption of sulfuric acid. 3 P can also be absorbed in low-concentration sulfuric acid, which greatly reduces the consumption of high-concentration oxidized sulfuric acid and also reduces the consumption of sulfuric acid. High-concentration sulfuric acid is used in the last two pickling towers to utilize its oxidizing property to remove sulfur and phosphorus impurities. Each level of pickling has an independent washing acid circulation cooling system and oxygen supplement oxidation system. H dissolved in sulfuric acid 3 P and H 2 S can be purified by oxygen oxidation absorption, further reducing the consumption of sulfuric acid;

[0039] 3. In the pickling process, sulfuric acid is added at the last stage, and the sulfuric acid flows back to the first stage step by step, so that the sulfuric acid can be reused and its consumption can be reduced. Finally, the by-products such as waste acid and sulfur obtained in the first stage washing can also be recycled as resources. In addition, by-products such as gypsum can also be generated in the alkali washing process. The economic benefits can be improved by recycling the by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the patent flow chart of the present invention;

[0041] Figure 2 This is a schematic diagram of the air entrainment process of the patented furnace of the present invention;

[0042] Figure 3This is a schematic diagram of the tail gas purification water washing process of the present invention;

[0043] Figure 4 This is a schematic diagram of the first-stage pickling process of tail gas purification in the present invention;

[0044] Figure 5 This is a schematic diagram of the secondary pickling process for tail gas purification according to the present invention;

[0045] Figure 6 This is a schematic diagram of the three-stage pickling process for tail gas purification of the present invention;

[0046] Figure 7 This is a schematic diagram of the four-stage pickling process for tail gas purification according to the present invention;

[0047] Figure 8 This is a schematic diagram of the tail gas purification alkali washing process of the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the patent of the present invention to clearly and completely describe the technical solutions in the embodiments of the patent of the present invention. Obviously, the described embodiments are only part of the embodiments of the patent of the present invention, not all of them. Based on the embodiments in the patent of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the patent of the present invention.

[0049] See also Figures 1 to 8 The present invention provides a technical solution: a method for purifying yellow phosphorus tail gas, comprising the following steps:

[0050] Step 1, tail gas pressurization: Use a fan to pressurize the yellow phosphorus tail gas to the required range, and send it to the various levels of purification processes at the back end in turn. The purified yellow phosphorus tail gas is finally sent to the use end of the process for utilization;

[0051] Step 2: Water washing, cooling, dust removal and mist removal: The pressurized yellow phosphorus tail gas first enters the water washing device, and uses cold spray water from the yellow phosphorus production system to cool and reduce the saturated water vapor content in the yellow phosphorus tail gas, while further deeply purifying dust, fluorine, and P 4 The above cooling water comes from the cold spray water treatment system of the yellow phosphorus device, and is recycled and returned to the cold spray water treatment system of the yellow phosphorus device for comprehensive utilization after regeneration.

[0052] Step 3, multi-stage countercurrent pickling, desulfurization, dephosphorization and demisting: the yellow phosphorus tail gas after water washing, cooling, dust removal and demisting enters the multi-stage countercurrent pickling device, which includes primary pickling, secondary pickling, tertiary pickling, quaternary pickling, etc. (matching the number of stages according to the purification requirements), and 98% sulfuric acid is added at the last stage, and it countercurrents to the first stage step by step, so as to achieve the purpose of multi-stage countercurrent pickling. Each level of pickling has an independent washing acid circulation cooling system and an oxygen supply oxidation system. The primary pickling liquid is discharged and separated into dilute sulfuric acid and sulfur according to the index. The dilute sulfuric acid is used for the phosphate ore flotation device and the sulfur removal sulfuric acid device for comprehensive utilization. The yellow phosphorus tail gas after desulfurization and dephosphorization is finally demisted and sent to the next process; during washing, only fresh sulfuric acid needs to be added to the fourth-stage pickling tower, and no additional sulfuric acid needs to be added to the other three-stage pickling towers. Instead, it is washed with sulfuric acid in the next-stage pickling tower and then countercurrently flows to the previous stage to reduce the amount of sulfuric acid. Oxygen is introduced into the washed sulfuric acid and the washed sulfuric acid is cooled. The purpose of introducing oxygen is to dissolve H in the sulfuric acid. 3 P and H 2 S can be purified by oxygen oxidation absorption, which further reduces the consumption of sulfuric acid. The sulfuric acid concentrations of the first-stage pickling tower, the second-stage pickling tower, the third-stage pickling tower and the fourth-stage pickling tower increase in sequence. Furthermore, the first-stage and second-stage pickling towers use sulfuric acid of lower concentration to remove a large amount of saturated water vapor brought by the front section of the yellow phosphorus tail gas in advance by utilizing its water absorption, which greatly reduces the consumption of sulfuric acid. 3 P can also be absorbed in low-concentration sulfuric acid, which greatly reduces the consumption of high-concentration oxidized sulfuric acid and also reduces the consumption of sulfuric acid, and collects the waste acid discharged from the primary pickling tower;

[0053] Among them, the main reaction equations occurring in multi-stage pickling are as follows:

[0054] P 4 +5HSO → 5SO 2 ↑+4H 3 PO 4 +4H 2 O;

[0055] This is white phosphorus (P 4 ) reacts with sulfuric acid, in which white phosphorus is oxidized and sulfuric acid is reduced. Sulfur dioxide gas, phosphoric acid and water are produced. This reaction reflects the reducing property of white phosphorus and the oxidizing property of sulfuric acid;

[0056] 3PH 3 +4H 2 SO 4 →3H 3 PO 4 +4S↓+4H 2 O;

[0057] Phosphine (PH 3) reacts with sulfuric acid to generate phosphoric acid, sulfur and water. The phosphorus in phosphine is oxidized, and part of the sulfur in sulfuric acid is reduced to sulfur.

[0058] 3H 2 S+H 2 SO 4 →4S↓+4H 2 O;

[0059] Hydrogen sulfide (H 2 S) reacts with sulfuric acid to produce elemental sulfur and water;

[0060] The sulfur element in hydrogen sulfide is oxidized, and part of the sulfur element in sulfuric acid is reduced to elemental sulfur;

[0061] 3AsH 3 +4H 2 SO 4 →3H 3 AsO 4 +4S↓+4H 2 O;

[0062] Arsine (AsH 3 ) reacts with sulfuric acid to produce arsenic acid (H 3 AsO 4 ), sulfur and water, the arsenic in arsine is oxidized, and part of the sulfur in sulfuric acid is reduced to sulfur;

[0063] 3CS 2 +2H 2 SO 4 →3CO 2 ↑+8S↓+2H 2 O;

[0064] Carbon disulfide (CS 2 ) reacts with sulfuric acid to generate carbon dioxide gas, sulfur and water. The carbon and sulfur elements in carbon disulfide undergo oxidation reactions, and part of the sulfur element in sulfuric acid is reduced to sulfur.

[0065] 3COS+H 2 SO 4 →3CO 2 ↑+4S↓+H 2 O;

[0066] Carbon oxysulfide (COS) reacts with sulfuric acid to generate carbon dioxide gas, sulfur and water. The carbon and sulfur elements in the carbon oxysulfide are oxidized, and part of the sulfur element in the sulfuric acid is reduced to sulfur.

[0067] Step 4, alkaline demisting: send the yellow phosphorus tail gas containing a small amount of SO2 and sulfuric acid mist after acid washing into the alkaline device, use alkaline circulating washing liquid for washing and neutralization, add lime milk to maintain the pH of the circulating washing liquid within the required range, and convert calcium sulfite into calcium sulfate through air oxidation of the circulating washing liquid. The circulating liquid is discharged according to the process requirements for solid-liquid separation, the liquid is returned to the circulation system for utilization, and the solid calcium sulfate is discharged and sent to the cement plant for comprehensive utilization;

[0068] The main reaction equation is as follows:

[0069] Ca(OH) 2 +H 2 SO 4 →CaSO 4 ↓+2H 2 O;

[0070] This is an acid-base neutralization reaction. Calcium hydroxide (Ca(OH) 2 ) is a base, sulfuric acid (H 2 SO 4 ) is a strong acid. They react to form calcium sulfate (CaSO 4 ) precipitation and water (H 2 O);

[0071] Ca(OH) 2 +SO 2 →CaSO 3 ↓+H 2 O;

[0072] In this reaction, sulfur dioxide (SO 2 ) is an acidic oxide, and calcium hydroxide is a base. They react to form calcium sulfite (CaSO 2 ) sediment and water;

[0073] 2CaSO 3 +O 2 →2CaSO 4 ↓.

[0074] Calcium sulfite (CaSO 3 ) is oxygen (O 2 ) is oxidized to form calcium sulfate (CaSO 4 )precipitation.

[0075] The blower used in the method is a centrifugal blower, a Roots blower or a vacuum pump. Under the action of the pressure blower, the yellow phosphorus tail gas is pressurized to the required pressure to overcome the resistance of the purification devices at all levels at the rear end, and to ensure that the pressure at the end of the purified yellow phosphorus tail gas meets the requirements. At the same time, increasing the pressure is beneficial to reduce the saturated water vapor amount of the yellow phosphorus tail gas and reduce the amount of 98% sulfuric acid used at the rear end. After the multi-stage pickling process and the first-stage alkali washing process, the sulfur and phosphorus impurities in the tail gas can be effectively oxidized and absorbed, the purity of the tail gas can be improved, and the phosphorus content can be reduced. The water washing, pickling and alkali washing methods are used to improve the purification effect of the phosphorus-containing tail gas. The by-products produced by the pickling process and the alkali washing process can also be recycled and reused as resources, reducing the cost of the entire purification process.

[0076] In this embodiment, in step 2, after the exhaust gas enters the treatment area, the liquid sprayed from the nozzle is fully in contact with the exhaust gas. In this process, the fine water droplets in the liquid will capture the particulate matter and pollutants in the exhaust gas. The contact mode between the liquid and the exhaust gas can be countercurrent, cocurrent or crosscurrent, depending on the design of the dust collector and the characteristics of the exhaust gas;

[0077] During the entire spray dust removal process, it is necessary to monitor the exhaust gas treatment effect in real time, including parameters such as particle concentration, gas temperature, humidity, etc. According to the monitoring results, adjust the equipment's operating parameters, such as the spray angle of the nozzle, the flow rate of the water pump, etc. At the same time, regularly maintain the equipment, replace worn parts, and clean the nozzles and pipe blockages to ensure the long-term stable operation of the equipment;

[0078] The tail gas and liquid mixture after spraying treatment enters the gas-liquid separation device. Common gas-liquid separation methods include cyclone separation, gravity sedimentation, filtration, etc. The separated gas is discharged from the dust collector, and the liquid is returned to the water source for recycling;

[0079] In this embodiment, in step 3, multi-stage pickling can more thoroughly remove various impurities in the tail gas, including phosphorus compounds, oxides and other harmful components. Through the effect of multiple pickling, the purification effect is improved, the harm of harmful substances to the environment and human body is reduced, the purity of the tail gas is improved, and the content of corrosive substances in the tail gas is reduced, the corrosion damage to the processing equipment and pipelines is reduced, the service life of the equipment is extended, the maintenance and replacement costs are reduced, and it is helpful to better separate valuable components such as phosphorus in the tail gas, creating favorable conditions for subsequent resource recovery and reuse;

[0080] In this step, understand the key parameters such as the composition, concentration and flow rate of phosphorus-containing tail gas, prepare the required pickling reagents, such as hydrochloric acid, sulfuric acid, etc., and ensure that their quality and purity meet the requirements, and equip the operators with complete personal protective equipment, including protective glasses, masks, gloves, protective clothing, etc.;

[0081] Check the tightness of the pickling equipment to ensure that there is no leakage during the pickling process, and adjust the temperature, pressure, flow and other control parameters of the equipment to meet the requirements of the pickling process;

[0082] After pickling, clean the equipment in time to remove residual reactants and products. Pay attention to safety during the cleaning process to prevent chemical residues from corroding the equipment.

[0083] In this embodiment, in step 4, first, a suitable alkali solution needs to be prepared. For this purpose, lime milk is applied as the alkali solution. The concentration and formula of the alkali solution need to be formulated according to the specific exhaust gas composition and treatment requirements;

[0084] The preparation process must strictly follow the relevant chemical safety and operating specifications, let the phosphorus-containing tail gas enter the alkali washing device, ensure that the flow rate and pressure of the tail gas entering are within the tolerance range of the equipment, and the tail gas fully contacts and reacts with the alkali solution in the alkali washing device;

[0085] In this process, the alkali solution will react chemically with the phosphorus-containing compounds in the tail gas, converting them into harmless or easy-to-handle substances. In order to enhance the reaction effect, the reaction efficiency can be improved by stirring, increasing the contact area, etc. The tail gas after the reaction and the treated liquid are separated, and appropriate separation equipment is used. The separated tail gas is subsequently tested and treated to ensure that it meets the emission standards;

[0086] Regularly maintain and inspect the alkaline cleaning device and related equipment, including clearing blockages, replacing worn parts, and testing equipment operating parameters.

[0087] In the step 2, cooling circulating water is introduced into the water washing device in the step 2, which comes from the cold spray cooling water system of the yellow phosphorus production device, and the wastewater discharged from the water washing device is discharged to the wastewater treatment system of the yellow phosphorus production device for treatment and then recycled.

[0088] In this embodiment,

[0089] In step 3, the circulating washing sulfuric acid of each level is cooled by cooling circulating water in the cooler to control the temperature of sulfuric acid at 40-60°C. In the present invention, since heat is released during the entire absorption process in the multi-stage pickling process, a circulating acid graphite cooler is set at each washing stage to control the temperature of the circulating acid at about 40-60°C, thereby reducing the occurrence of related side reactions and ensuring the absorption efficiency. The circulating washing acid at each level has an oxygen oxidation system. The purpose of introducing oxygen is to dissolve H 3 P and H 2 S can be purified by oxygen oxidation absorption, further reducing the consumption of sulfuric acid.

[0090] For step 3, a more specific implementation method is that the fourth-stage pickling tower is supplemented with fresh 98% sulfuric acid, the third-stage pickling tower uses 93% sulfuric acid from the fourth-stage pickling tower, the second-stage pickling tower uses 85% sulfuric acid from the third-stage pickling tower, and the first-stage pickling tower uses 60% sulfuric acid from the second-stage pickling tower. The lower concentration of sulfuric acid used in the first and second pickling towers is used to remove a large amount of saturated water vapor brought by the front section of the yellow phosphorus tail gas in advance by utilizing its water absorption, thereby greatly reducing the consumption of sulfuric acid. 3 P can also be absorbed in low-concentration sulfuric acid, which greatly reduces the consumption of high-concentration oxidized sulfuric acid and sulfuric acid. Finally, the waste acid is discharged from the primary pickling tower, and the sulfur produced in the reaction process is enriched in the primary absorption liquid. The sulfur is taken out through the filter press and sent to the sulfur acid production unit. The waste acid obtained after the primary pickling contains 35% sulfuric acid and 6.35% phosphoric acid, which is transported to the dilute acid storage tank through a pipeline for comprehensive utilization of phosphate ore flotation, turning waste into treasure and reducing costs.

[0091] In step 4, the pH is controlled at 5-6 by adding lime milk during the alkali solution process, and air is introduced for oxidation to ensure that sulfite is converted into orthosulfate. On the premise of ensuring the neutralization effect of SO2 and sulfuric acid mist, the CO in the yellow phosphorus tail gas is prevented from 2 The absorption causes the alkali consumption to increase, and the pH is the optimal range for calcium sulfite oxidation. The tail gas delivered by the primary alkali washing tower in step 4 is transported to the gas-liquid separator in the primary alkali washing through a pipeline, and after gas-liquid separation in the gas-liquid separator in the primary alkali washing, it is transported to the user end for comprehensive energy utilization. After alkali washing, gas-liquid separation and demisting are performed to reduce the bad effects caused by the washing liquid and particulate matter entering the user end of the yellow phosphorus tail gas.

[0092] The "one embodiment", "another embodiment", "embodiment", "preferred embodiment" and the like mentioned in this specification refer to the specific features, structures or characteristics described in conjunction with the embodiment included in at least one embodiment generally described in this application. The same expression appearing in multiple places in the specification does not necessarily refer to the same embodiment. Further, when a specific feature, structure or characteristic is described in conjunction with any embodiment, it is claimed that the realization of such feature, structure or characteristic in conjunction with other embodiments also falls within the scope of the present invention.

[0093] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for purifying yellow phosphorus tail gas, characterized in that: The following steps are involved: Step 1, tail gas pressurization: Use a fan to pressurize the yellow phosphorus tail gas to the required range, and send it to the various levels of purification processes at the back end in turn. The purified yellow phosphorus tail gas is finally sent to the use end of the process for utilization; Step 2, water washing, cooling, dust removal and demisting: the pressurized yellow phosphorus tail gas first enters the water washing device, and is cooled by cold spray water from the yellow phosphorus production system to reduce the saturated water vapor content in the yellow phosphorus tail gas, while further deeply purifying dust, fluorine, P4 and other impurities, and finally goes to the next process after demisting in the gas-liquid separator; Step 3, multi-stage countercurrent pickling, desulfurization, dephosphorization and demisting: the yellow phosphorus tail gas after water washing, cooling, dust removal and demisting enters the multi-stage countercurrent pickling device, which includes primary pickling, secondary pickling, tertiary pickling, quaternary pickling, etc., and 98% sulfuric acid is added at the last stage, and it countercurrents to the first stage step by step. Each level of pickling has an independent washing acid circulation cooling system and oxygen supplement oxidation system. The primary pickling liquid is discharged and separated into dilute sulfuric acid and sulfur according to the index. The dilute sulfuric acid is used for comprehensive utilization of the phosphate ore flotation device and the sulfur removal sulfuric acid device. The yellow phosphorus tail gas after desulfurization and dephosphorization is finally demisted and sent to the next process; Among them, the main reaction equations occurring in multi-stage pickling are as follows: P4+5H2SO→5SO2↑+4H3PO4+4H2O; 3PH3+4H2SO4→3H3PO4+4S↓+4H2O; 3H2S+H2SO4→4S↓+4H2O; 3AsH3+4H2SO4→3H3AsO4+4S↓+4H2O; 3CS2+2H2SO4→3CO2↑+8S↓+2H2O; 3COS+H2SO4→3CO2↑+4S↓+H2O; Step 4, alkaline washing and demisting: send the yellow phosphorus tail gas containing a small amount of SO2 and sulfuric acid mist after acid washing to the alkaline washing device, use alkaline circulating washing liquid for washing and neutralization, add lime milk to maintain the pH of the circulating washing liquid within the required range, and convert calcium sulfite into calcium sulfate through air oxidation of the circulating washing liquid. The circulating liquid is discharged according to the process requirements for solid-liquid separation, the liquid is returned to the circulation system for utilization, and the solid calcium sulfate is discharged and sent to the cement plant for comprehensive utilization; The main reaction equation is as follows: Ca(OH)2+H2SO4→CaSO4↓+2H2O; Ca(OH)2+SO2→CaSO3↓+H2O; 2CaSO3+O2→2CaSO4↓.

2. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: In the tail gas pressurization of step 1, the yellow phosphorus tail gas is pressurized to the required pressure under the action of the pressure-boosting fan, so as to overcome the resistance of the purification devices at various levels at the rear end and ensure that the pressure at the end of use of the purified yellow phosphorus tail gas meets the requirements. At the same time, increasing the pressure is beneficial to reducing the saturated water vapor content of the yellow phosphorus tail gas and reducing the amount of 98% sulfuric acid used at the rear end.

3. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: In the step 2, cooling circulating water is introduced into the washing device, which comes from the cold spray cooling water system of the yellow phosphorus production device, and the wastewater discharged from the washing device is discharged to the wastewater treatment system of the yellow phosphorus production device for treatment and then recycled.

4. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: In step 3, each level of circulating washing sulfuric acid is cooled by circulating cooling water in a cooler to control the temperature of sulfuric acid at 40-60° C. Each level of circulating washing acid has an oxygen oxidation system, and the cooler is a graphite heat exchanger or a silicon carbide heat exchanger.

5. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: In step 3, the final pickling device is supplemented with more than 98% sulfuric acid, and the circulating sulfuric acid is countercurrent to the previous pickling device in sequence until the sulfuric acid concentration of the first pickling device reaches 35-40% (containing 6-8% phosphoric acid) and is discharged. Dilute sulfuric acid and sulfur are obtained through solid-liquid separation and sent to the phosphate ore concentrator and sulfuric acid device for comprehensive utilization.

6. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: In the step 4, during the alkali washing process, the pH is controlled at 5-6 by adding lime milk, and under the premise of ensuring the neutralization effect of SO2 and sulfuric acid mist, the CO2 in the yellow phosphorus tail gas is prevented from being absorbed and causing an increase in alkali consumption.

7. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: In the step 4, gas-liquid separation and demisting are performed after alkali washing to reduce the adverse effects caused by the washing liquid and particulate matter entering the yellow phosphorus tail gas use end.

8. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: The blower used in this method is a centrifugal blower, a Roots blower or a vacuum pump.

9. A method for purifying yellow phosphorus tail gas according to claim 1, characterized in that: The cooling device, acid washing device and alkali washing device used in the method can be an empty tower, a packed tower or a super gravity tower.

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