CN110743344B - Method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite - Google Patents

Method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite Download PDF

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CN110743344B
CN110743344B CN201910957258.3A CN201910957258A CN110743344B CN 110743344 B CN110743344 B CN 110743344B CN 201910957258 A CN201910957258 A CN 201910957258A CN 110743344 B CN110743344 B CN 110743344B
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flue gas
sulfur dioxide
sodium metabisulfite
sodium
absorption
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CN110743344A (en
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姚树明
李剑胜
陶政修
易瑶筝
周雪姣
曾超
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Zhuzhou Xiangsante Environmental Protection Co ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/77—Liquid phase processes
    • B01D53/78—Liquid phase processes with gas-liquid contact
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/48—Sulfur compounds
    • B01D53/50—Sulfur oxides
    • B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
    • B01D53/502—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound characterised by a specific solution or suspension
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
    • C01D5/14—Preparation of sulfites
    • C01D5/145—Pyrosulfites or metabisulfites
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    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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    • Y02P20/10—Process efficiency

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Abstract

The invention provides a method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite, which contains SO2After the flue gas is washed and purified, Na-containing gas is generated by reaction after absorption of absorption liquid2SO3‑NaHSO3The mixed absorption liquid enters a neutralization tower to react with a sodium carbonate solution to generate saturated sodium sulfite liquid, the saturated sodium sulfite liquid and the sulfur dioxide-containing acid-making waste flue gas are absorbed and reacted to generate supersaturated sodium bisulfite solution, the supersaturated sodium bisulfite solution is contacted with sulfur dioxide to generate sodium metabisulfite solid, and the solid is dried by air flow after centrifugation to form an anhydrous sodium metabisulfite product. The invention has the advantages of short process flow, high desulfurization efficiency, low energy consumption, low operation cost, stable product quality and no secondary pollution, and is suitable for removing and recycling sulfur dioxide in flue gas of various industrial kilns and coal-fired boilers in the industries of metallurgy, steel, thermal power and the like.

Description

Method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite
Technical Field
The invention relates to the technical field of chemical industry, in particular to a method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite.
Background
Sulfur dioxide (SO)2) Is one of the main pollutants in the atmosphere, has great influence on human health, mainly damages respiratory organs and causes acute and chronic harm. The most serious acute poisoning events of atmospheric pollution in the world are related to sulfur dioxide pollution. At present, the emission of sulfur dioxide in China is the first place in the world, mainly comes from the combustion of fossil fuels, the roasting of sulfur-containing ores, smelting, chemical production and other thermal processes, and the emission of a large amount of sulfur dioxide causesThe air pollution not only seriously affects the health of people, but also hinders the development of economy, so the pollution of the environment caused by the emission of sulfur dioxide is a great problem to be solved urgently in order to realize the sustainable development of economy and environment.
In order to control the pollution of the atmosphere caused by the emission of sulfur dioxide, people have been conducting related research as early as 19 th century, but the research and application of large-scale desulfurization technology are started from 60 th century, and more than 200 kinds of SO are developed through years of research2And (4) control technology. These techniques can be divided into: the desulfurization method before combustion, the desulfurization method during combustion and the desulfurization method after combustion, namely the flue gas desulfurization method is the only desulfurization method for large-scale commercial application in the world at present and is the most main technical means for controlling sulfur dioxide pollution.
The flue gas desulfurization technology mainly utilizes various alkaline absorbents or adsorbents to capture sulfur dioxide in flue gas and convert the sulfur dioxide into a sulfur compound or elemental sulfur which is stable and easy to mechanically separate, so that the aim of desulfurization is fulfilled. The main flue gas desulfurization technologies for the current industrialization are as follows:
ordinary wet limestone-gypsum method. The method uses the slurry of lime or limestone to absorb SO in the flue gas2The process technology is mature, and the desulfurization efficiency is stable and can reach more than 90%. The method has the disadvantages that the quality of the gypsum is difficult to ensure, secondary pollution is easy to cause, and the operation cost is higher.
Spray drying. The method is a flue gas desulfurization method adopting lime milk as an absorbent, belongs to semi-dry desulfurization, has the desulfurization efficiency of 80-90 percent, and has lower one-time investment than a wet limestone-gypsum method. The method has the disadvantages of high requirements on equipment, easy blockage of spray heads and high operating cost.
An absorption regeneration method. The magnesium oxide method, the double alkali method and the W-L method are mainly used. The desulfurization efficiency can reach about 95 percent, and the technology is mature. The method has the disadvantages of large occupied area and high operation cost.
Sodium alkali method. The method generally adopts NaOH as a desulfurizer, has high desulfurization efficiency, can achieve single-stage efficiency of more than 90 percent, and has mature technology. The method has the disadvantages of long system flow, large investment, consumption of a large amount of steam for recovering the desulfurization byproducts and high operation cost.
At present, there are two main methods for producing sodium metabisulfite products:
the first method is to use sulfur as raw material, send compressed air into a combustion furnace to burn at 800 ℃ with 600 plus materials, generate 10-15% sulfur dioxide flue gas, remove sublimed sulfur and other impurities through cooling and dust removal and filtration, introduce the flue gas into a reactor at 50 ℃ to perform countercurrent contact reaction with a reaction kettle connected in series with three stages of sodium carbonate, and prepare a sodium metabisulfite product through centrifugation, drying and packaging. The main reaction equation:
S+02 =SO2 (1)
2SO2+Na2CO3+H20=2NaHSO3+CO2 (2)
2NaHSO3+Na2CO3=2Na2SO3+H20+CO2 (3)
Na2SO3+SO2+H20=2NaHSO3 (4)
2NaHSO3 = Na2S205+H20 (5)
and the second method comprises the steps of burning pyrite as a raw material to prepare SO2 gas, carrying out countercurrent contact reaction on the SO2 gas and a suspension prepared from sodium carbonate in a three-stage reaction kettle connected in series, and carrying out centrifugation, drying and packaging to obtain a sodium metabisulfite product. The main reaction equation is as follows:
gas making: 4FeS2+l102=8SO2+2Fe203 (1)
3FeS2+802=SO2+Fe304 (2)
Preparing alkali: na (Na)2C03+2NaHSO3=Na2SO3+H20+C02 (3)
Synthesizing: na (Na)2SO3+H20+SO2=+2NaHSO3 (4)
Na2C03+H2 O+2SO2=2NaHSO3+C02 (5)
2NaHSO3=Na2S205+H20 (6)
The main production yield of sodium metabisulfite in China is concentrated on coastal areas, such as: 10 ten thousand tons (basic self-use) are produced in each year by Guangzhou Chinese patent chemical industry Co., Ltd, 3 ten thousand tons are produced in each year by Guangzhou Union chemical industry Co., Ltd, 4 ten thousand tons are produced by Tianjin Jingming chemical industry Co., Ltd, 8 ten thousand tons are produced in a Hippocampus chemical plant, 10 ten thousand tons are produced in each year by Shandong Weifang Kailong chemical industry Co., Ltd, 3 ten thousand tons are produced in each year by three Jiang chemical industries Co., Ltd in Tang mountain, and 15 thousand tons are produced in several factories (for example, Yueyang Sanxiang, Changshouyue, etc.) in Hunan lake north, and the total national yield of sodium metabisulfite products for domestic or international market sale is about 80 ten thousand tons.
Along with the rapid development of economy in China and the continuous development of national industrialization, the cognition and the requirement of people on environmental protection and food safety are improved. The perfection of the relevant laws and regulations of the state and the enhancement of the management. Further promoting the application of sodium metabisulfite in the development of the following industries: (1) additives which are widely applied in the food industry and have certain harm to human bodies such as; sodium formaldehyde, etc. are strictly prohibited by the national regulations. (2) The industrial electroplating and sewage treatment industries are also accelerated to develop nationwide. (3) Increases in mining and oil production such as; gold ore, cobalt ore, etc.
The demand of the medicine industry, the rubber industry, the printing and dyeing industry, the chemical industry and the like is increased year by year, and at present, only millions of tons of sodium pyroxide products meeting the requirements of customers can be provided domestically. According to the statistics of the China chemical engineering society, the market consumption is over millions of tons. The sodium pyrosulfite product has large market demand in China, the current market price is 1700 + 2500 yuan per ton, especially the development of the bamboo product industry in the northern Fujian is fast in recent years, the sodium pyrosulfite product serving as the bamboo product preservative has larger market capacity in the northern Fujian and has competitiveness in the market sale radius, and the sodium pyrosulfite product serving as the fruit thinning preservative has very large market capacity in the aspect of food preservation along with the gradual increase of the fruit thinning preservation amount.
The application field and the usage amount of sodium metabisulfite are further expanding and increasing, and market survey shows that the usage amount of sodium metabisulfite in China is rapidly increasing at a speed of 10% every year, and at the moment, the application field and the usage amount of sodium metabisulfite are the good development period of the sodium metabisulfite industry.
Disclosure of Invention
The invention provides a method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite, and aims to provide a method for efficiently preparing sodium metabisulfite, which has the advantages of low operation cost, high desulfurization efficiency and environmental friendliness.
The invention provides a method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite, which comprises the following steps:
s1, flue gas purification and cooling: will contain SO2The flue gas is introduced into water, and the temperature of the flue gas is reduced;
S2. SO2absorption: the purified and cooled SO2The flue gas is introduced into an absorption device, and is in reverse contact with absorption liquid in the absorption device to carry out absorption reaction, and sulfur dioxide in the flue gas reacts with the absorption liquid to generate Na-containing2SO3-NaHSO3The flue gas is absorbed to obtain the clean flue gas which reaches the standard and is discharged;
s3, soda ash neutralization: the Na-containing compound obtained in step S22SO3-NaHSO3The mixed solution and sodium carbonate solution are subjected to neutralization reaction in a neutralization tower to generate saturated sodium sulfite solution, carbon dioxide gas is released, and a part of the neutralized solution is returned to the step S2 to absorb SO2The other part of the smoke enters step S4 for processing;
s4 preparation of sodium metabisulfite: and (2) introducing the acid making waste flue gas containing high-concentration sulfur dioxide into an absorption device, carrying out absorption reaction with the solution containing saturated sodium sulfite generated in the step S3 to generate supersaturated sodium bisulfite solution, contacting the supersaturated sodium bisulfite solution with sulfur dioxide again to generate sodium metabisulfite solid, and drying the centrifuged solid through air flow to form an anhydrous sodium metabisulfite product.
As a further improvement of the present invention, the SO-containing step in step S12In flue gas of2The content of (B) is 0.1-2.0%.
As a further improvement of the invention, the temperature of the flue gas is reduced to 60-70 ℃ in step S1.
As a further improvement of the invention, in the step S2, the absorption liquid contains 30-40% of sodium carbonate, 15-20% of sodium sulfite and 5-10% of sodium bisulfite by mass ratio, and the pH value is 6.5-7.
As a further improvement of the invention, the mass fraction of the sodium carbonate solution in step S3 is 30-40 wt%.
As a further improvement of the invention, in the step S3, the neutralization is carried out to control the pH value of the reaction end point to be 6.8-7 and the neutralization reaction temperature to be 40-80 ℃.
As a further improvement of the invention, the concentration of the sulfur dioxide in the acid making waste flue gas containing high-concentration sulfur dioxide in the step S4 is 5-10%.
As a further improvement of the invention, the pH value of the solution containing saturated sodium sulfite in the step S4 is 3-4.
As a further improvement of the invention, the absorption device is a rotary shear flow scrubber or a spray scrubber.
As a further improvement of the invention, the absorption device is a combination of a rotary cut flow scrubber and a spray scrubber.
The invention has the following beneficial effects:
1. the operation cost is low. The method adopts sodium carbonate as a main liquid desulfurization absorbent, and has lower operation cost compared with the traditional sodium-alkali method which adopts sodium hydroxide as the desulfurization absorbent; the invention realizes the continuity of the preparation of the byproduct sodium metabisulfite by continuously contacting with the flue gas of the acid-making sulfur dioxide through the continuous neutralization forced crystallization process, has smaller system volume and less investment, and has lower production and operation cost compared with the traditional method for preparing the desulfurization byproduct sodium metabisulfite by burning sulfur and pyrite.
2. The desulfurization efficiency is high. According to the invention, in the flue gas absorption stage, rotary-cut flow washing or spray washing absorption or a combined absorption mode of the rotary-cut flow washing or the spray washing absorption can be adopted according to the concentration of sulfur dioxide in the flue gas, the application range of the absorbed sulfur dioxide concentration is wide, and the desulfurization efficiency can reach more than 99%;
3. is environment-friendly. The invention adopts the technology of combining flue gas absorption, absorption liquid neutralization crystallization, low-concentration sulfur dioxide and sulfur dioxide in acid making flue gas, and a drying system adopts full-closed circulation operation, and a desulfurization product is industrial-grade anhydrous sodium metabisulfite, so that secondary pollution is not generated.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a connection diagram of the production apparatus of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
the embodiment is a first specific embodiment of the method for preparing the sodium metabisulfite product from the low-concentration sulfur dioxide in the flue gas, which is disclosed by the invention:
the process of preparing sodium pyrosulfite product includes the following steps:
(1) and purifying the flue gas: the temperature is 280 ℃ and SO2The content is 0.1% (i.e. 2860 mg/Nm)3) 50000Nm smoke of zinc smelting rotary kiln3H, sending the flue gas into a water washing tower for water washing to remove dust and SO in the flue gas3The dust content of the flue gas after water washing is 30mg/Nm3The temperature of the flue gas is reduced to 60 ℃;
（2）、SO2absorption: SO after purification and temperature reduction20.1% smoke 50000Nm3H, entering a two-stage series rotary-cut flow washer, and mixing with Na in the two-stage series rotary-cut flow washer2CO330wt%-Na2SO315wt%-NaHSO310wt% of absorption liquid (pH value is 6.5) is in reverse contact to generate absorption reaction, and the flue gas is absorbed to form clean flue gas containing SO2160mg/m3To be discharged after reaching the standard, SO2The absorption was 94.41%; the sulfur dioxide in the flue gas reacts with the absorption liquid to generate Na2SO330wt%-NaHSO335wt% of mixed solution is 0.5 t/h;
(3) and soda ash neutralization: na (Na)2SO330wt%-NaHSO335wt% of mixed solution 12t, added to 20m3While gradually adding 6t of sodium carbonate solution with solute content of 30%, carrying out neutralization reaction in the neutralization tower at 40 deg.C to obtain solution with pH of 6.8, reacting to obtain saturated sodium sulfite solution of 17.25t and carbon dioxide gas of 0.75t, and returning 5.25t of the neutralized sodium sulfite solution to the step (2) for absorbing SO2The smoke and the other part of 12.00t enter the step (4) for treatment;
(4) and preparing a product: the generated saturated sodium sulfite solution with the pH value of 3 is fed into a three-stage absorption tower for absorbing SO2Generating supersaturated sodium bisulfite solution 19.2t by using sulfur dioxide flue gas with 10 percent of acid making and high concentration; contacting the supersaturated sodium bisulfite solution with sulfur dioxide, reacting at 50 deg.C to generate Na2S2O5The solid sodium metabisulfite with the content of 96.5 percent is 8.95t, the yield is 99.39 percent, and the sodium metabisulfite product is obtained after metering and packaging.
Example 2:
the embodiment is a second specific example of the method for preparing the sodium metabisulfite product from the low-concentration sulfur dioxide in the flue gas, which is disclosed by the invention:
the process of preparing sodium pyrosulfite product includes the following steps:
(1) and purifying the flue gas: the temperature is 250 ℃ and SO2The content is 1.0% (i.e. 28600 mg/Nm)3) 60000Nm smoke of zinc smelting rotary kiln3H, sending the flue gas into a water washing tower for water washing to remove dust and SO in the flue gas3The dust content of the flue gas after water washing is 28mg/Nm3The temperature of the flue gas is reduced to 65 ℃;
(2) SO2 absorption: SO after purification and temperature reduction2Smoke with content of 1.0% 60000Nm3The solution enters a two-stage serial spraying scrubber, and Na is contained in the two-stage serial spraying scrubber2CO335wt%-Na2SO318wt%-NaHSO3The 7wt% absorption liquid (pH value is 6.8) is in reverse contact to generate absorption reaction, and the flue gas is absorbed to form clean flue gas containing SO2175mg/m3To be discharged after reaching the standard, SO2The absorption rate was 99.39%; the sulfur dioxide in the flue gas reacts with the absorption liquid to generate Na2SO328wt%-NaHSO332wt% of mixed solution is 7.2 t/h;
(3) and soda ash neutralization: na (Na)2SO328wt%-NaHSO332wt% of the mixed solution 14.4t, added to 25m3While gradually adding 7t of sodium carbonate solution with solute content of 35%, carrying out neutralization reaction in the neutralization tower at 60 deg.C to obtain solution with pH of 6.9, reacting to obtain saturated sodium sulfite solution 20.5t, discharging carbon dioxide gas 0.9t, and returning 6.5t of the neutralized sodium sulfite solution to the step (2) for absorbing SO2The smoke and the other part of 14.00t enter the step (4) for treatment;
(4) and preparing a product: the generated saturated sodium sulfite solution (pH value is 3.5) with 14.00t is sent into a three-stage absorption tower to absorb SO2Generating supersaturated sodium bisulfite solution 21t by using high-concentration sulfur dioxide flue gas with the acid making content of 5%; contacting the supersaturated sodium bisulfite solution with sulfur dioxide, reacting at 60 deg.C to generate Na2S2O5The solid sodium metabisulfite with the content of 96.8 percent is 10.29t, the yield is 99.35 percent, and the sodium metabisulfite product is obtained after metering and packaging.
Example 3:
the embodiment is a third specific embodiment of the method for preparing the sodium metabisulfite product from the low-concentration sulfur dioxide in the flue gas, which is disclosed by the invention:
the process of preparing sodium pyrosulfite product includes the following steps:
(1) and purifying the flue gas: the temperature is 250 ℃ and SO2The content is 2.0% (i.e. 57200 mg/Nm)3) 50000Nm smoke of zinc smelting rotary kiln3H, sending the flue gas into a water washing tower for water washing to remove dust and SO in the flue gas3The dust content of the flue gas after water washing is 29mg/Nm3The temperature of the flue gas is reduced to 70 ℃;
(2) SO2 absorption: SO after purification and temperature reduction22.0% smoke 50000Nm3H, entering a secondary scrubber in which a rotary-cut flow scrubber and a spray scrubber are connected in series, and reacting with Na-containing water in the secondary scrubber connected in series2CO340wt%-Na2SO320wt%-NaHSO35wt% of absorption liquid (pH value is 7.0) is in reverse contact to generate absorption reaction, and the flue gas is absorbed to form clean flue gas containing SO2192mg/m3To be discharged after reaching the standard, SO2The absorption rate was 99.66%; the sulfur dioxide in the flue gas reacts with the absorption liquid to generate Na2SO332wt%-NaHSO340wt% of mixed solution is 10 t/h;
(3) and soda ash neutralization: na (Na)2SO332wt%-NaHSO340wt% of the mixed solution 10t, added to 20m3While gradually adding 5t of sodium carbonate solution with solute content of 40%, carrying out neutralization reaction in the neutralization tower at 80 deg.C to obtain solution with pH of 7.0, reacting to obtain saturated sodium sulfite solution with pH of 14.2t, discharging carbon dioxide gas with pH of 0.8t, and returning 5.5t of the neutralized sodium sulfite solution to the step (2) for absorbing SO2The smoke and the other part of 8.7t enter the step (4) for treatment;
(4) and preparing a product: the generated saturated sodium sulfite solution (pH value is 4.0) with 8.7t is sent into a three-stage absorption tower to absorb SO2High-concentration acid making product with 12 percent of contentOxidizing sulfur flue gas to generate supersaturated sodium bisulfite solution of 14.1 t; contacting the supersaturated sodium bisulfite solution with sulfur dioxide, reacting at 60 deg.C to generate Na2S2O57.56t of sodium metabisulfite solid with the content of 97.2 percent, the yield is 99.42 percent, and sodium metabisulfite products are obtained after metering and packaging.
Test example 1
The method and the traditional process are used for producing 1t of industrial Na2S2O3And (3) comparison:
TABLE 1
Figure DEST_PATH_IMAGE001
As can be seen from the above table, the sodium metabisulfite prepared by the method of the present invention produces 1t of industrial Na each time2S2O3The cost is 224 yuan, which is obviously lower than that of the traditional process production method (730 yuan).
Test example 2
Comparing the method of the invention with other methods:
the utility of the by-product desulfurization method is shown in Table 2 below:
TABLE 2
Figure DEST_PATH_IMAGE002
The overall comparison with other desulfurization processes is shown in table 3 below:
TABLE 3
Figure DEST_PATH_IMAGE003
Compared with the prior art:
the invention has low operation cost. The method adopts sodium carbonate as a main liquid desulfurization absorbent, and has lower operation cost compared with the traditional sodium-alkali method which adopts sodium hydroxide as the desulfurization absorbent; the invention realizes the continuity of the preparation of the byproduct sodium metabisulfite by continuously contacting with the flue gas of the acid-making sulfur dioxide through the continuous neutralization forced crystallization process, has smaller system volume and less investment, and has lower production and operation cost compared with the traditional method for preparing the desulfurization byproduct sodium metabisulfite by burning sulfur and pyrite.
The invention has high desulfurization efficiency. According to the invention, in the flue gas absorption stage, rotary-cut flow washing or spray washing absorption or a combined absorption mode of the rotary-cut flow washing or the spray washing absorption can be adopted according to the concentration of sulfur dioxide in the flue gas, the application range of the absorbed sulfur dioxide concentration is wide, and the desulfurization efficiency can reach more than 99%;
the invention is environment-friendly. The invention adopts the technology of combining flue gas absorption, absorption liquid neutralization crystallization, low-concentration sulfur dioxide and sulfur dioxide in acid making flue gas, and a drying system adopts full-closed circulation operation, and a desulfurization product is industrial-grade anhydrous sodium metabisulfite, so that secondary pollution is not generated.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (7)

1. A method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite is characterized by comprising the following steps:
s1, flue gas purification and cooling: will contain SO2The flue gas is introduced into water, and the temperature of the flue gas is reduced;
S2. SO2absorption: the purified and cooled SO2The flue gas is introduced into an absorption device, and is in reverse contact with absorption liquid in the absorption device to carry out absorption reaction, and sulfur dioxide in the flue gas reacts with the absorption liquid to generate Na-containing2SO3-NaHSO3The flue gas is absorbed to obtain the clean flue gas which reaches the standard and is discharged; the absorption liquid contains 30-40% of sodium carbonate, 15-20% of sodium sulfite and 5-10% of sodium bisulfite by mass ratio, and the pH value is 6.5-7;
s3, soda ash neutralization: the Na-containing compound obtained in step S22SO3-NaHSO3The mixed solution and sodium carbonate solution are subjected to neutralization reaction in a neutralization tower to generate saturated sodium sulfite solution, and the saturated sodium sulfite solution is placedCarbon dioxide gas is discharged, and a part of the neutralized solution is returned to the step S2 for absorbing SO2The other part of the smoke enters step S4 for processing; the mass fraction of the sodium carbonate solution is 30-40 wt%;
s4 preparation of sodium metabisulfite: introducing the acid making waste flue gas containing high-concentration sulfur dioxide into an absorption device, carrying out absorption reaction on the acid making waste flue gas and the solution containing saturated sodium sulfite generated in the step S3 to generate supersaturated sodium bisulfite solution, contacting the supersaturated sodium bisulfite solution with sulfur dioxide to generate sodium metabisulfite solid, and drying the solid after centrifugation by airflow to form an anhydrous sodium metabisulfite product;
the absorption device is a rotary shear flow washer or a spray washing tower.
2. The method for removing low-concentration sulfur dioxide from flue gas and preparing sodium metabisulfite according to claim 1, wherein the SO-containing step S12In flue gas of2The content of (B) is 0.1-2.0%.
3. The method for removing low-concentration sulfur dioxide and preparing sodium metabisulfite in flue gas as claimed in claim 1, wherein the temperature of the flue gas is reduced to 60-70 ℃ in step S1.
4. The method for removing low-concentration sulfur dioxide from flue gas and preparing sodium metabisulfite according to claim 1, wherein the neutralization is performed in step S3 to control the reaction end point pH value to be 6.8-7 and the neutralization reaction temperature to be 40-80 ℃.
5. The method for removing low-concentration sulfur dioxide in flue gas and preparing sodium metabisulfite as recited in claim 1, wherein the concentration of sulfur dioxide in the acid-making waste flue gas containing high-concentration sulfur dioxide in step S4 is 5-10%.
6. The method for removing low-concentration sulfur dioxide from flue gas and preparing sodium metabisulfite according to claim 1, wherein the pH of the solution containing saturated sodium sulfite in step S4 is 3-4.
7. The method for removing low-concentration sulfur dioxide from flue gas and preparing sodium metabisulfite according to claim 1, wherein the absorption device is a combination of a cyclone scrubber and a spray scrubber.
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