Method for desulfurization of caustic soda process tail gas

Abstract

The present application belongs to the technical field of zinc hydrometallurgy, and relates to a method for desulfurization of tail gas by caustic soda method. In the method, caustic soda and water are fully mixed and stirred in a lye preparation tank to prepare caustic soda slurry with a concentration of 10% to 15%, the caustic soda slurry is sent into an intermediate tank by a delivery pump, and part of the caustic soda slurry is sent into a desulfurization tower from the intermediate tank as absorbent. The method has the advantages that the caustic soda method tail gas desulfurization process technology is mature and reliable, the system is simple, the liquid / gas ratio is small, no scaling and plugging occur, the equipment cost is low, the land occupation is small, the desulfurization efficiency is high, the method is more suitable for tail gas desulfurization with large concentration fluctuation, and has certain popularization value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of zinc hydrometallurgy, in particular to a method for desulfurization of caustic soda tail gas. BACKGROUND

[0002] Zinc hydrometallurgy mainly includes roasting, leaching (see leaching), leach liquor purification and electrodeposition processes. After roasting of zinc concentrate, neutral leaching is carried out with electrolytic waste liquid to dissolve most of the zinc oxide, and the obtained slurry is separated into supernatant and underflow slurry. After purification of the supernatant, metal zinc is produced by electrodeposition and cast into ingots. The underflow slurry is subjected to acid leaching to dissolve the residual zinc oxide, and the acid leaching liquid is returned to the neutral leaching; the acid leaching slag containing about 20% zinc needs to be further treated, and the traditional method uses a rotary kiln to volatilize and recover zinc, lead and part of the dispersed metals. In the process of zinc hydrometallurgy, flue gas containing SO2 is generated, which needs to be desulfurized.

[0003] In the prior art, patent number CN115006970A discloses a desulfurization regeneration tail gas treatment method and system. In this scheme, HPF desulfurization tail gas is introduced into a dry quenching furnace and combusted, then enters a desulfurization device with dry quenching furnace circulating gas for treatment, and finally reaches the standard for emission, achieving the purpose of purifying desulfurization regeneration tail gas, reducing combustible components in the dry quenching furnace, improving the efficiency of the dry quenching coke waste heat boiler, and ensuring the stable operation of the dry quenching coke system. However, the desulfurization process of this scheme is relatively complex, and there are problems of large occupied area and high equipment cost, which is not suitable for tail gas desulfurization with large concentration fluctuations.

[0004] Whether the tail gas can be discharged up to standard is not only related to the environmental protection image of the enterprise, but also related to the survival and development of the enterprise. Therefore, it is urgent to explore new tail gas desulfurization technical solutions.

[0005] At present, no effective solution has been proposed for the problems in the related art. SUMMARY

[0006] (I) Technical problems solved

[0007] In view of the deficiencies of the prior art, the present application provides a method for desulfurization of caustic soda tail gas, thereby solving the problems in the background art.

[0008] (II) Technical solutions

[0009] To achieve the advantages of low equipment cost, small occupied area, high desulfurization efficiency and adaptability to tail gas desulfurization with large concentration fluctuations, the specific technical solutions adopted by the present application are as follows:

[0010] A method for desulfurization of caustic soda tail gas, characterized in that it comprises the following steps:

[0011] 1. The caustic soda and water are mixed and stirred in the lye preparation tank to prepare a caustic soda slurry with a concentration of 10% to 15%, the caustic soda slurry is sent to the intermediate tank by the delivery pump, and part of the caustic soda slurry is sent to the desulfurization tower as the absorption liquid from the intermediate tank.

[0012] 2. When the acid-making tail gas enters the desulfurization system, the flue gas is introduced into the desulfurization tower, and the sulfur dioxide in the flue gas is absorbed by the countercurrent contact with the caustic soda circulating liquid. When the circulating liquid continuously absorbs sulfur dioxide, the acidity of the circulating liquid will continuously increase with the absorption of sulfur dioxide.

[0013] 3. The circulating liquid is introduced into the acidification tank after fully reacting with the flue gas from the outlet of the absorption tower in the desulfurization tower. The sulfite generated in the process of absorbing sulfur dioxide by the tail gas desulfurization circulating liquid reacts with the added sulfuric acid (or acidic waste liquid) in the tank, and the generated sulfur dioxide is returned to the drying tower for conversion and absorption recycling. The sodium sulfate in the circulating liquid is sent to the leaching process by the slurry delivery pump, and the sodium sulfate in the leaching process is used as the iron removal agent instead of ammonium carbonate. The sodium sulfate solution is sent to the leaching and precipitation tank, and it is determined whether there is sulfur dioxide gas. If no sulfur dioxide gas is precipitated, it indicates that the conversion of Na2SO3 to Na2SO4 is good and the resolution is complete.

[0014] 4. An electric precipitator is arranged at the upper part of the alkali washing tower. After the electric precipitator removes the particles, water droplets and acid mist entrained in the flue gas, the flue gas from the electric precipitator is discharged through the tail gas chimney for detection and emission after reaching the standard.

[0015] The preferred scheme is:

[0016] The concentration of the caustic soda slurry must be controlled between 10% and 15%. If it is too low, it will affect the desulfurization efficiency, and if it is too high, it will easily cause pipeline blockage.

[0017] The pH value of the circulating liquid is 6.0 to 8.0, which ensures that the circulating liquid has stable ability to remove sulfur dioxide gas.

[0018] The concentration of sulfur dioxide in the flue gas after desulfurization is ≤400 mg / Nm3, which meets the emission standard.

[0019] The temperature of the flue gas discharge is 25±5℃, which meets the emission standard.

[0020] The process technology method for removing SO2 in flue gas by caustic soda method is mainly used in harsh environmental requirements and is completed in two steps: the first step is the dissolution and absorption of SO2 gas, and the second step is the recovery or treatment of desulfurization product Na2SO3. This method uses NaOH or Na2CO3 as the absorbent to absorb the flue gas containing SO2. The flue gas containing SO2 is fully contacted with the NaOH solution in the absorption tower. In this process, SO2 and SO3 gas are dissolved and absorbed to generate Na2SO3 and Na2SO4.

[0021] 2NaOH + SO2 = Na2SO3 + H2O

[0022] 2NaOH + SO3 = Na2SO4 + H2O

[0023] At the same time, due to the presence of oxygen in the flue gas, the following side reaction will occur: 2Na2SO3 + O2 = 2Na2SO4

[0024] Na2SO3 that is not completely oxidized is decomposed by adding sulfuric acid or a solution containing sulfuric acid (such as electrolytic waste liquid) to produce Na2SO4 solution for use in other systems, and the reaction formula is:

[0025] Na2SO3 + H2SO4 = Na2SO4 + SO2 + H2O

[0026] (III) beneficial effects

[0027] Compared with the prior art, the present application provides a method for desulfurization of tail gas by caustic soda method, which has the following beneficial effects:

[0028] The present application adopts the caustic soda method tail gas desulfurization process technology, which has the advantages of mature and reliable process, simple system, small liquid / gas ratio, no scaling and plugging, low equipment cost, small land occupation, high desulfurization efficiency, and is more suitable for tail gas desulfurization with large concentration fluctuation, and has certain popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0030] Figure 1 is the process flow diagram of the present application. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments.

[0032] Embodiment one, a caustic soda method tail gas desulfurization, comprising the following steps:

[0033] Step one: caustic soda and water are fully mixed and stirred in the lye preparation tank to prepare caustic soda slurry with a concentration of 14%, and the caustic soda slurry is sent to the intermediate tank by a delivery pump, and part of the caustic soda slurry is sent to the desulfurization tower as absorption liquid from the intermediate tank.

[0034] Step two, when the acid tail gas enters the desulfurization system, the flue gas is introduced into the desulfurization tower, and the sulfur dioxide in the flue gas is absorbed by countercurrent contact with the caustic soda circulating liquid. When the circulating absorption liquid continuously absorbs sulfur dioxide, the acidity of the circulating liquid will continuously increase with the absorption of sulfur dioxide. In order to ensure that the circulating liquid has stable ability to remove sulfur dioxide gas, the pH value of the circulating liquid is controlled at 7.0.

[0035] Step three, after the circulating liquid in the desulfurization tower fully reacts with the flue gas from the outlet of the absorption tower, it is introduced into the acidification tank. The sulfite generated in the process of tail gas desulfurization circulating liquid absorbing sulfur dioxide reacts with the added sulfuric acid (or acidic waste liquid) in the tank, and the generated sulfur dioxide returns to the flue gas inlet of the drying tower for conversion and absorption recycling. The sodium sulfate in the circulating liquid is pumped into the leaching process by slurry delivery pump, and the sodium sulfate liquid is sent to the leaching and alum precipitation tank. There is no sulfur dioxide gas precipitation.

[0036] Step four, an electric precipitator is arranged at the upper part of the alkali washing tower. After the electric precipitator removes the particles, water droplets and acid mist entrained in the flue gas, the flue gas from the electric precipitator is discharged through the tail gas chimney after detection. The concentration of sulfur dioxide in the desulfurized flue gas is 245 mg / Nm3, and the flue gas discharge temperature is 24℃.

[0037] Example two, a caustic soda method tail gas desulfurization, comprising the following steps:

[0038] Step one: caustic soda and water are fully mixed and stirred in the lye preparation tank to prepare a caustic soda slurry with a concentration of 12%. The caustic soda slurry is sent to the intermediate tank by the delivery pump, and part of the caustic soda slurry is sent to the desulfurization tower as the absorption liquid.

[0039] Step two, when the acid tail gas enters the desulfurization system, the flue gas is introduced into the desulfurization tower, and the sulfur dioxide in the flue gas is absorbed by countercurrent contact with the caustic soda circulating liquid. When the circulating absorption liquid continuously absorbs sulfur dioxide, the acidity of the circulating liquid will continuously increase with the absorption of sulfur dioxide. In order to ensure that the circulating liquid has stable ability to remove sulfur dioxide gas, the pH value of the circulating liquid is controlled at 7.0.

[0040] Step three, after the circulating liquid in the desulfurization tower fully reacts with the flue gas from the outlet of the absorption tower, it is introduced into the acidification tank. The sulfite generated in the process of tail gas desulfurization circulating liquid absorbing sulfur dioxide reacts with the added sulfuric acid (or acidic waste liquid) in the tank, and the generated sulfur dioxide returns to the flue gas inlet of the drying tower for conversion and absorption recycling. The sodium sulfate in the circulating liquid is pumped into the leaching process by slurry delivery pump, and the sodium sulfate liquid is sent to the leaching and alum precipitation tank. There is no sulfur dioxide gas precipitation.

[0041] Step four, the upper part of the alkali washing tower is provided with an electric precipitator, after the electric precipitator removes the particles, water droplets and acid mist entrained in the flue gas, the flue gas of the electric precipitator is discharged through the tail gas chimney after reaching the standard, the concentration of sulfur dioxide in the flue gas after desulfurization is 286 mg / Nm3, and the flue gas emptying temperature is 28℃.

[0042] Working principle: caustic soda and water are fully mixed and stirred in the lye preparation tank to prepare a caustic soda solution with a concentration of 10%-15%, the caustic soda solution is delivered to the intermediate tank, part of the caustic soda solution is sent to the desorption tower from the intermediate tank, the caustic soda solution circulating liquid is fully reacted with the flue gas from the outlet of the absorption tower in the desulfurization tower, then introduced into the acidification tank, reacted with the added sulfuric acid (or acid waste liquid) in the tank, the generated sulfur dioxide is returned to the flue gas inlet pipe of the drying tower, and then the conversion and absorption are recycled, the sodium sulfate in the caustic soda solution circulating liquid is sent to the leaching process by a delivery pump, and the sodium sulfate in the leaching process alum tank is used as a deironing agent to replace ammonium carbonate for deironing.

[0043] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for desulfurization of caustic soda process off-gas, characterized in that It comprises the following steps: 1.1, the caustic soda and water are fully mixed and stirred in a lye preparation tank to prepare a caustic soda slurry with a concentration of 10%-15%, the caustic soda slurry is sent into an intermediate tank by a delivery pump, and part of the caustic soda slurry is sent into a desulfurization tower from the intermediate tank as an absorption liquid; 1.2, when the acid gas tail gas enters the desulfurization system, the flue gas is introduced into the desulfurization tower, and the sulfur dioxide in the flue gas is absorbed by the caustic soda circulating liquid through countercurrent contact, when the sulfur dioxide is continuously absorbed by the circulating absorption liquid, the acidity of the circulating liquid will continuously increase with the absorption of sulfur dioxide; 1.3, the circulating liquid is introduced into an acidification tank after fully reacting with the flue gas from the outlet of the absorption tower in the desulfurization tower, the sulfite generated in the process of absorbing sulfur dioxide by the tail gas desulfurization circulating liquid reacts with the added sulfuric acid or acidic waste liquid in the tank, the generated sulfur dioxide is returned to the drying tower for conversion and absorption and recycling, the sodium sulfate in the circulating liquid is sent into the leaching process by a slurry delivery pump, the sodium sulfate is used as a ferric removal agent to replace ammonium carbonate in the ferric removal tank of the leaching process, the sodium sulfate solution is sent to the leaching and alum precipitation tank, and it is judged whether there is sulfur dioxide gas, if there is no sulfur dioxide gas, it indicates that the conversion of Na2SO3 to Na2SO4 is good and the resolution is complete; 1.4, an electric precipitator is arranged at the upper part of the alkali washing tower, after the electric precipitator removes the particles, water droplets and acid mist entrained in the flue gas, the flue gas of the electric precipitator is discharged through the tail gas chimney after reaching the standard and being detected; The pH value of the circulating liquid is 6.0-8.0; The concentration of sulfur dioxide in the desulfurized flue gas is ≤400 mg / Nm 3 ; The flue gas emptying temperature is 25±5℃.

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