Sodium-zinc dual-alkali flue gas desulfurization process

Abstract

The invention discloses a flue gas desulfurization process adopting a sodium-zinc dual-alkali method, relates to the field of inorganic chemistry, and aims to enable flue gas containing SO2 to reach an ultra-low emission standard and obtain available SO2. According to the technical scheme, the flue gas desulfurization process adopting the sodium-zinc dual-alkali method comprises the following steps: firstly, carrying out dust removal, impurity removal and cooling on the flue gas containing SO2; then the flue gas is introduced into a desulfurization tower, the flue gas is in contact with barren liquor, and the barren liquor becomes rich liquor after absorbing SO2; and the flue gas is washed with water, and the washed flue gas is discharged after reaching the standard. After the rich solution is sent to a reaction tank, ZnO is added, most of NaHSO3 in the rich solution is converted into Na2SO3, and the rich solution is converted into barren solution; and performing solid-liquid separation on the clear liquid and the underflow in the reaction tank to obtain filtrate which is barren liquor, and returning the barren liquor to the desulfurization tower for cyclic utilization. And carrying out solid-liquid separation on the underflow of the reaction tank to obtain filter residues, carrying out heating dehydration, carrying out heating decomposition to obtain zinc oxide and SO2, and returning the zinc oxide to the reaction tank for recycling. The method is used for removing SO2 in the flue gas.

Description

Technical Field

[0001] The invention relates to the field of separation by physical or chemical methods, and also to the field of inorganic chemistry, and specifically to a sodium-zinc double alkali flue gas desulfurization process, and a device for implementing the process. Background Art

[0002] The commonly used wet desulfurization technologies include: lime / limestone-gypsum method, sodium alkali method, zinc oxide method, ammonia method, ionic liquid (organic amine) method, double alkali method, etc. With the increasing requirements for environmental protection in my country, many industries require ultra-low emission limits, that is, SO2 in the emission gas ≤ 35mg / Nm 3 Most of the above processes cannot meet the requirements of emission standards for SO2 concentration or have high operating costs or produce secondary pollution.

[0003] The lime / limestone-gypsum flue gas desulfurization process is a widely used flue gas desulfurization technology. The lime / limestone-gypsum desulfurization technology uses lime or limestone slurry to absorb SO2 in the flue gas, react to form calcium sulfate, and the flue gas can meet the emission standards after purification. The lime / limestone-gypsum method consumes limestone, electricity and water. The main problems of this process are: the desulfurization system continuously discharges acidic wastewater containing chloride ions, producing desulfurization gypsum by-products. For every ton of SO2 removed, 3 tons of desulfurization gypsum that is difficult to comprehensively utilize will be produced; at the same time, every 1 mole of SO2 removed will produce an equal mole of CO2 incremental emissions.

[0004] The sodium-alkali desulfurization method uses sodium carbonate or sodium hydroxide as an absorbent to absorb SO2 in the flue gas to obtain Na2SO3. The sodium-alkali method requires the consumption of sodium carbonate or sodium hydroxide, as well as electricity and water. It has a high desulfurization efficiency. The main problems of the sodium-alkali desulfurization method are: the absorbent cost is high and the obtained Na2SO3 product is difficult to sell.

[0005] Ammonia desulfurization technology mainly uses ammonia water and liquid ammonia as absorbents to absorb SO2 in flue gas. Ammonia desulfurization consumes about 0.5 tons of liquid ammonia to absorb 1 ton of SO2. The main problems of ammonia desulfurization are: ammonia escape, a large amount of aerosol in the flue gas, and acidic wastewater containing chloride ions, causing secondary pollution.

[0006] The zinc oxide method is a commonly used desulfurization method for lead and zinc enterprises. The absorbent is self-produced zinc oxide dust or zinc oxide roasted sand. The main problems of zinc oxide desulfurization are: ZnSO3 is relatively viscous, and ZnSO3 in the circulating fluid is easy to deposit in equipment and pipelines, causing pipeline scaling and blockage, and scaling cleaning is difficult; the solution circulation volume is large, the power consumption is high; SO2 in the exhaust gas is unstable.

[0007] Ionic liquid (organic amine) desulfurization technology uses a regenerative desulfurization process with ionic liquid or organic amine as the main absorbent, absorbing SO2 in the flue gas at low temperature and desorbing SO2 from the absorbent at high temperature. The main problems are large investment and high regeneration steam energy consumption.

[0008] The lime / limestone desulfurization process uses slurry materials, and the desulfurization system is prone to scaling and clogging. In response to this, Japan and the United States created the sodium-calcium double-alkali method. The sodium-calcium double-alkali method first uses an alkaline absorption liquid (such as NH4 + 、Na + and K + The flue gas desulfurization is carried out by using sodium compounds (sodium hydroxide, soda ash or sodium sulfite) and then regenerating the absorption liquid with lime milk or limestone powder. Since liquid phase absorption is used, and bisulfite is usually more soluble than sulfite, the scaling problem often encountered in lime / limestone desulfurization can be avoided. The sodium-calcium double alkali method uses sodium compounds (sodium hydroxide, soda ash or sodium sulfite) to absorb SO2, and the absorption liquid is then reacted with lime and / or limestone to generate calcium sulfite and / or calcium sulfate precipitation, and the regenerated sodium salt solution is returned to the desulfurization. The byproduct gypsum produced by the sodium-calcium double alkali method is called desulfurization gypsum, which is a solid waste.

[0009] Let me introduce the desulfurization principle of the sodium-calcium double alkali method. During the absorption reaction, the main chemical reaction formula of the desulfurization process is: Na2SO3+SO2+H2O→2NaHSO3. The desulfurization liquid contains NaOH returned after regeneration and Na2CO3 supplemented by the system. Sodium sulfite is generated during the desulfurization process. The chemical reaction formulas are: 2NaOH+SO2→Na2SO3+H2O and Na2CO3+SO2→Na2SO3+H2O. During the desulfurization process, O2 in the flue gas reacts with sodium sulfite to generate sodium sulfate. The reaction formula is: Na2SO3+O2→Na2SO4. The accumulation of sulfate will affect the desulfurization efficiency. When regenerating with lime slurry, the chemical reaction formula is: 2NaHSO3+Ca(OH)2→Na2SO3+CaSO 3· 1 / 2H2O↓+3 / 2H2O and Na2SO3+Ca(OH)2+1 / 2H2O→2NaOH+CaSO 3· 1 / 2H2O↓, the general form of calcium sulfite is hemihydrate calcium sulfite. When regenerated with limestone powder, the chemical reaction formula is: 2NaHSO3+CaCO3→Na2SO3+CaSO 3· 1 / 2H2O↓+CO2↑+1 / 2H2O. Theoretically, the neutralization reaction is complete with lime, but incomplete with limestone.

[0010] The sodium-calcium dual alkali desulfurization method has the following advantages: (1) With sodium alkali as the absorbent, the system generally does not produce precipitates, has high desulfurization efficiency, and can achieve ultra-low emission levels; (2) The regeneration of the absorbent and the precipitation of desulfurization gypsum occur outside the desulfurization tower, avoiding tower blockage and wear, improving operational reliability, and reducing operating costs; (3) The sodium-based absorbent absorbs SO2 quickly, so a smaller liquid-to-gas ratio can be used to achieve a higher desulfurization rate; (4) The chemical mechanism of sodium sulfite-sodium bisulfite can adapt to the absorption and regeneration cycle operation, and has the ability to keep all compounds in solution, thereby avoiding scaling and clogging in the desulfurization system; (5) It can be used in solid absorbent systems, and because the cation is non-volatile, there is no problem of absorbent volatilization and generation of ammonium mist during the desulfurization process, and it is much cheaper than potassium compounds.

[0011] The existing sodium-calcium double alkali method uses sodium salt as a desulfurizing agent, which can be regenerated with lime and / or limestone. The regenerated sodium salt solution is returned to the desulfurization system to generate calcium sulfite and / or calcium sulfate precipitation, which is called desulfurized gypsum. The main problems of the sodium-calcium double alkali process are: the amount of desulfurized gypsum produced is too large, containing a large amount of impurities and water, and the decomposition temperature of calcium sulfite and / or calcium sulfate is relatively high, which is generally discarded in the form of waste, generating a large amount of gypsum waste and forming secondary pollution.

[0012] As national environmental protection policies have become increasingly stringent on SO2 emissions from flue gas, in order to meet the requirements of ecological environment and economic development, it is very important for enterprise development to remove SO2 from flue gas efficiently, economically, environmentally friendly and stably without causing secondary pollution.

[0013] The patent application publication number CN 103736383 A discloses a soda ash flue gas desulfurization process and a flue gas desulfurization system. The soda ash flue gas desulfurization process is based on the mutual conversion of sodium carbonate, sodium bisulfite and sodium sulfite during the absorption process, and produces sodium sulfite crystals by saturated crystallization using the different solubility at a certain temperature. The sodium sulfite produced by this process has limited industrial utilization value and is mostly waste with no economic value. Summary of the invention

[0014] The present invention first provides a sodium-zinc dual alkali flue gas desulfurization process, the purpose of which is to make the flue gas containing SO2 meet ultra-low emission standards, obtain SO2 gas that can be recycled, and at the same time do not produce waste such as desulfurization gypsum.

[0015] The technical solution adopted by the present invention is: a sodium zinc double alkali flue gas desulfurization process, comprising the following steps:

[0016] S1. Remove dust from flue gas containing SO2. For example, remove dust through bag filter, and the particulate matter in the flue gas after dust removal is ≤5mg / Nm 3 .

[0017] S2. Remove impurities and cool down the flue gas after dust removal to obtain preliminarily purified flue gas. For example, the flue gas after dust removal is passed into a washing tower to remove impurities and cool down through a circulating washing method, using a primary washing method or a secondary washing method, and cool down to 10°C to 70°C.

[0018] S3. The flue gas after preliminary purification is passed into the desulfurization tower, where the flue gas contacts the lean liquid to remove SO2 from the flue gas. The lean liquid absorbs SO2 from the flue gas and becomes rich liquid. The flue gas is then washed with water to recover the sodium salt entrained in the flue gas. Finally, the flue gas after water washing is discharged after meeting the standards. The lean liquid is a solution containing more Na2SO3 and less NaHSO3, and the rich liquid is a solution containing less Na2SO3 and more NaHSO3.

[0019] In order to ensure that step S3 can achieve the SO2 concentration in the flue gas to meet the ultra-low emission standards, further: the desulfurization tower includes three consecutive sections connected from bottom to top, namely a rich liquid circulation section, a lean liquid circulation section and a water washing section; the flue gas after preliminary purification first enters the rich liquid circulation section, and the SO2 in the flue gas is removed by circulating rich liquid or a mixture of rich liquid and lean liquid, and then enters the lean liquid circulation section, and the SO2 in the flue gas is removed by circulating lean liquid, and finally enters the water washing section for water washing.

[0020] The flue gas entering the desulfurization tower contains O2, which reacts with Na2SO3 to generate Na2SO4, and the chemical reaction formula is: Na2SO3+O2→Na2SO4. In order to inhibit the oxidation of Na2SO3, further: step S3 further adds an oxygen inhibitor to the lean liquid, and the oxygen inhibitor is at least one of p-phenylenediamine and hydroquinone.

[0021] S4. The rich liquid produced in the desulfurization tower in step S3 is sent to the reaction tank, and ZnO is added to the reaction tank. NaHSO3 in the rich liquid reacts chemically with ZnO, and the chemical reaction formula is: 2NaHSO3+ZnO+3 / 2H2O→Na2SO3+ZnSO3·5 / 2H2O.

[0022] S5. Perform solid-liquid separation on the substances in the reaction tank to obtain liquid barren liquid and solid filter residue. Specifically: the equipment used for solid-liquid separation is a chamber filter press, a centrifuge, a vacuum drum or a vacuum bag solid-liquid separation device.

[0023] S6. The lean liquid obtained in step S5 is sent to the desulfurization tower and used as the lean liquid in step S3, forming a cycle of lean liquid and rich liquid; the solid filter residue is heated and dehydrated to become anhydrous zinc sulfite, and then decomposed into solid zinc oxide and SO2 gas by heating. The chemical reaction formula is: ZnSO3→ZnO+SO2↑; the solid zinc oxide obtained by heating and decomposition is sent to the reaction tank and used as ZnO in step S4, forming a cycle of ZnO.

[0024] In step S6, in order to convert the solid filter residue into anhydrous zinc sulfite, specifically: the temperature of heating and dehydration is 50-200°C, and the gas generated by heating and dehydration is introduced into the desulfurization tower together with the flue gas preliminarily purified in step S3. In order to promote the thermal decomposition of anhydrous zinc sulfite into zinc oxide solid and SO2 gas, specifically: the temperature of thermal decomposition is 200-400°C.

[0025] In order to fully remove SO2 from the flue gas in step S3, further: in step S6, the pH value of the lean liquid entering the desulfurization tower is controlled to be 4.5-7.0, the Na2SO3 content in the lean liquid entering the desulfurization tower is controlled to be 5-30wt%, and the NaHSO3 content is controlled to be 0-10wt%; the Na2SO3 content in the rich liquid sent to the reaction tank in step S4 is 0-10wt%, and the NaHSO3 content is 5-40wt%.

[0026] The SO2 gas obtained in step S6 has a high temperature and can be recycled after washing and cooling. Furthermore, the sodium zinc double alkali flue gas desulfurization process also includes step S7, in which the gas obtained by heating and decomposing in step S6 is washed to remove impurities, and then cooled to finally obtain a SO2 gas product. For example, the gas obtained by heating and decomposing in step S6 is washed in a SO2 gas washing tower to remove solid particulate impurities, and then cooled to 10-90°C and dehydrated to finally obtain a SO2 gas product.

[0027] The present invention also provides a sodium-zinc double alkali flue gas desulfurization device for implementing any of the above-mentioned sodium-zinc double alkali flue gas desulfurization processes, with the same purpose of making the flue gas containing SO2 meet ultra-low emission standards, obtaining SO2 gas that can be utilized as a resource, and at the same time not generating waste such as desulfurization gypsum.

[0028] The sodium zinc double alkali flue gas desulfurization device comprises a desulfurization tower, a reaction tank, a solid-liquid separator, a dryer and a decomposer. The desulfurization tower comprises a desulfurization section and a water washing section on its upper part. The top of the water washing section is provided with a tower top chimney. The water washing section is provided with a circulating water inlet and outlet. The circulating water inlet and outlet are connected by a pipeline and a circulating water pump is provided on the pipeline. The desulfurization section is provided with a flue gas inlet, a rich liquid discharge port and a desulfurizer circulation inlet and outlet. The desulfurizer circulation inlet and outlet are connected by a pipeline and a desulfurizer circulation pump is provided on the pipeline. The rich liquid discharge port is connected to the reaction tank. The reaction tank is provided with a feeding port and an overflow port. The flow port is connected to the lean liquid tank, the outlet of the lean liquid tank is connected to the desulfurizer circulation inlet of the desulfurization tower, the bottom of the reaction tank is provided with an underflow outlet, the underflow outlet is connected to the solid-liquid separator, the liquid outlet of the solid-liquid separator is connected to the lean liquid tank, and the solid outlet of the solid-liquid separator corresponds to the feed inlet of the dryer; the dryer is provided with a gas outlet and a solid outlet, the gas outlet of the dryer is connected to the flue gas inlet of the desulfurization section of the desulfurization tower, the solid outlet of the dryer corresponds to the feed inlet of the decomposer, the decomposer is provided with a gas outlet and a solid outlet, and the solid outlet of the decomposer corresponds to the feed inlet of the reaction tank.

[0029] In order to ensure that the SO2 concentration in the flue gas discharged through the chimney on the top of the desulfurization tower reaches the ultra-low emission standard, further: the desulfurization section of the desulfurization tower is divided into two sections, namely the lower rich liquid circulation section and the upper lean liquid circulation section. The rich liquid circulation section is provided with a rich liquid circulation inlet and outlet, which are connected by a pipeline and a desulfurizer circulation pump is provided on the pipeline; the lean liquid circulation section is provided with a lean liquid circulation inlet and outlet, which are connected by a pipeline and a desulfurizer circulation pump is provided on the pipeline, and the outlet of the lean liquid tank is connected to the lean liquid circulation inlet.

[0030] In order to facilitate the adjustment and control of the amount, pH value, etc. of the lean liquid entering the desulfurization tower through the lean liquid circulation inlet, further: a lean liquid circulation tank is connected in series on the pipeline between the lean liquid circulation inlet and outlet of the lean liquid circulation section of the desulfurization tower, the outlet of the lean liquid tank is connected to the lean liquid circulation tank, and a lean liquid pump is provided between the outlet of the lean liquid tank and the lean liquid circulation tank.

[0031] In order to facilitate the regulation of the washing process of the water washing section of the desulfurization tower, further: a circulating water tank is connected in series on the pipeline between the circulating water inlet and outlet of the water washing section of the desulfurization tower, and the circulating water tank is also provided with a water replenishment port.

[0032] The solid-liquid separator is used to separate the solid and liquid of the material flowing out of the bottom flow outlet of the reaction tank, and obtains liquid lean liquid and solid filter residue after solid-liquid separation. Specifically: the solid-liquid separator is a chamber filter press, a centrifuge, a vacuum drum or a vacuum bag solid-liquid separation device.

[0033] The dryer is used to heat and dehydrate the solid filter residue, which mainly contains ZnSO3·5 / 2H2O. After the filter residue is heated and dehydrated, anhydrous zinc sulfite is obtained. The decomposer is used to heat and decompose anhydrous zinc sulfite into zinc oxide solid and SO2 gas. In order to remove impurities and cool the SO2 gas generated by the decomposer, further: the sodium zinc double alkali flue gas desulfurization device also includes a SO2 gas washing tower, the gas outlet of the decomposer is connected to the air inlet at the bottom of the SO2 gas washing tower, the top of the SO2 gas washing tower is provided with a gas outlet, the SO2 gas washing tower is provided with a washing water circulation inlet and outlet, the washing water circulation inlet and outlet are connected by a pipeline, and a washing water circulation pump and a washing water cooler are provided in series on the pipeline.

[0034] When the flue gas contains low levels of HCl, HF, and SO3, the flue gas does not need to be washed before entering the desulfurization tower. In order for the sodium-zinc double alkali flue gas desulfurization device to pre-treat the flue gas entering the desulfurization tower, further: the sodium-zinc double alkali flue gas desulfurization device also includes a washing tower, the washing tower is provided with a flue gas inlet and a flue gas exhaust port, the flue gas exhaust port is located at the top of the washing tower and is connected to the flue gas inlet of the desulfurization tower, the washing tower is also provided with at least one group of washing water circulation inlets and outlets, the washing water circulation inlets and outlets in the same group are connected by pipelines and a washing water circulation pump is provided on the pipeline, and a washing water storage part is provided at the lower end of the washing tower, and the washing water storage part is provided with a wastewater discharge port.

[0035] The following provides a structure in which a washing tower is provided with two groups of washing water circulation inlets and outlets. Specifically: a tower plate is provided in the middle of the washing tower, and the tower plate divides the washing tower into a lower section and an upper section of the washing tower. The flue gas inlet is located in the lower section of the washing tower. The lower section and the upper section of the washing tower are each provided with a group of washing water circulation inlets and outlets. A washing water circulation tank is also provided in series with the pipe between the washing water circulation inlets and outlets of the upper section of the washing tower. The washing water circulation tank is provided with a water replenishment port, and the washing water circulation tank is also connected to the lower section of the washing tower through a pipe.

[0036] In order to cool the flue gas in the scrubber and thus adjust the temperature of the flue gas entering the desulfurization tower, a heat exchanger is provided between the scrubbing water circulation inlet at the upper section of the scrubber and the flue gas exhaust port at the top of the scrubber. For example, the heat exchanger is a plate heat exchanger or a tube heat exchanger.

[0037] The beneficial effects of the present invention are as follows: the present invention is used to desulfurize flue gas containing SO2, and the SO2 in the treated flue gas is ≤35mg / Nm 3 , particulate matter ≤5mg / Nm 3 , sulfuric acid mist ≤5mg / Nm 3, which can meet the requirements of ultra-low emission limits for flue gas. The present invention recovers SO2 in flue gas to obtain SO2 gas products, which can be processed into sulfuric acid, sulfur, liquid SO2 and other sulfur-containing chemical products, so as to make SO2 in flue gas a resource. Compared with the existing sodium-calcium double alkali desulfurization, the present invention uses ZnO to replace lime or limestone to form a solid filter residue (ZnSO3·5 / 2H2O) in the reaction tank. The solid filter residue is heated, dehydrated and decomposed to obtain solid zinc oxide and recycled. The whole process does not produce waste such as gypsum or wastewater; at the same time, it does not require a large amount of purchased chemicals required by other desulfurization processes, nor does it consume a large amount of steam, electricity and other energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of an embodiment of the sodium-zinc dual alkali flue gas desulfurization process of the present invention.

[0039] Figure numerals: washing tower 1, flue gas inlet 1-1, flue gas exhaust port 1-2, washing water circulation pump 1-3, wastewater discharge port 1-4, washing tower lower section 1-5, washing tower upper section 1-6, washing water circulation tank 1-7, heat exchanger 1-8, desulfurization tower 2, water washing section 2-1, lean liquid circulation section 2-2, rich liquid circulation section 2-3, circulating water pump 2-4, circulating water tank 2-5, flue gas inlet 2-6, rich liquid discharge port 2-7, desulfurizer circulation pump 2-8, lean liquid circulation tank 2-9, reaction tank 3, feeding port 3-1, overflow port 3-2, bottom flow outlet 3-3, lean liquid tank 4, lean liquid pump 4-1, solid-liquid separator 5, dryer 6, decomposer 7, SO2 gas washing tower 8, washing water circulation pump 8-1, washing water cooler 8-2. DETAILED DESCRIPTION

[0040] The first subject of the present invention is a sodium zinc double alkali flue gas desulfurization process, and the second subject is a sodium zinc double alkali flue gas desulfurization device. Both subjects are used to remove SO2 from flue gas, so that the flue gas emissions meet the ultra-low emission limit requirements and reduce the waste generated during the desulfurization process. Figure 1 As shown, the sodium-zinc dual alkali flue gas desulfurization process of the present invention includes the following steps.

[0041] S1. Dust removal is performed on flue gas containing SO2. The purpose of dust removal is to remove particulate matter in the flue gas. For example, the flue gas containing SO2 is dedusted by a bag filter, and the particulate matter in the flue gas after dust removal is controlled to be ≤5mg / Nm 3 .

[0042] S2. Remove impurities and cool the flue gas after dust removal to obtain preliminarily purified flue gas.

[0043] Step S1 and step S2 are the pre-treatment procedures for desulfurization. The specific operation of the pre-treatment procedure is determined according to the actual situation of the flue gas. Generally, the flue gas after dust removal is passed into the washing tower 1 to remove impurities and cool down by circulating washing, and the washing water is quantitatively discharged from the washing tower 1 according to the concentration of pollutants. For example, the temperature is reduced to 10°C to 70°C. When the flue gas contains low levels of HCl, HF, and SO3, the flue gas does not need to be washed. The washing tower adopts one-stage washing or two-stage washing, and generally one-stage washing is sufficient. For example, in Figure 1 In the example shown, the washing tower 1 is divided into a washing tower lower section 1-5 and a washing tower upper section 1-6. The washing tower lower section 1-5 and the washing tower upper section 1-6 are each provided with a group of washing water circulation inlets and outlets. The washing water circulation inlets and outlets of the same group are connected by pipes and a washing water circulation pump 1-3 is provided on the pipe. If the flue gas after dust removal is washed only through the washing tower lower section 1-5 or the washing tower upper section 1-6, it is primary washing. If the flue gas after dust removal is washed through the washing tower lower section 1-5 and the washing tower upper section 1-6, it is secondary washing.

[0044] S3. The flue gas after preliminary purification is passed into the desulfurization tower 2, where the flue gas contacts with the lean liquid to remove SO2 in the flue gas. The lean liquid absorbs the SO2 in the flue gas and becomes a rich liquid. The flue gas is then washed with water to recover the sodium salt entrained in the flue gas. Finally, the washed flue gas is discharged after meeting the standards.

[0045] Among them, the lean solution is a solution containing more Na2SO3 and less NaHSO3, and the rich solution is a solution containing less Na2SO3 and more NaHSO3. The process of flue gas desulfurization is actually the process of desulfurization agent absorbing SO2. The main chemical reaction formula of this process is: Na2SO3+SO2+H2O→2NaHSO3. The lean solution absorbs SO2 in the flue gas and becomes rich liquid.

[0046] The flue gas entering the desulfurization tower 2 inevitably contains O2, which reacts with Na2SO3 to generate Na2SO4, and the chemical reaction formula is: Na2SO3+O2→Na2SO4. In order to inhibit the oxidation of Na2SO3, an oxygen inhibitor is added to the lean liquid in this step, and the oxygen inhibitor is at least one of p-phenylenediamine and hydroquinone.

[0047] Lean liquid and rich liquid are both desulfurizers, but they have different compositions and desulfurization capabilities, and can be converted and circulated mutually. In order to ensure that the SO2 concentration in the exhaust flue gas reaches the ultra-low emission standard, the desulfurization tower 2 includes three continuous sections connected from bottom to top, namely the rich liquid circulation section 2-3, the lean liquid circulation section 2-2 and the water washing section 2-1. The flue gas after preliminary purification first enters the rich liquid circulation section 2-3, and the SO2 in the flue gas is removed by circulating the rich liquid or a mixture of rich liquid and lean liquid, and then enters the lean liquid circulation section 2-2, and the SO2 in the flue gas is completely removed by circulating the lean liquid, and finally enters the water washing section 2-1 for water washing.

[0048] S4. The rich liquid produced by the desulfurization tower 2 in step S3 is sent to the reaction tank 3, and ZnO is added to the reaction tank 3, and the rich liquid is converted into a lean liquid in the reaction tank 3. NaHSO3 in the rich liquid reacts chemically with ZnO, and the chemical reaction formula is: 2NaHSO3+ZnO+3 / 2H2O→Na2SO3+ZnSO3·5 / 2H2O. ZnO is added to the reaction tank 3, and most of the NaHSO3 in the rich liquid is converted into Na2SO3, that is, the rich liquid is converted into a lean liquid, and the clear liquid and the bottom flow of the reaction tank 3 are filtered and separated to obtain the filtrate, that is, the lean liquid.

[0049] S5. Perform solid-liquid separation on the substances in the reaction tank 3 to obtain liquid barren liquid and solid filter residue. Specifically, the equipment used for solid-liquid separation is a chamber filter press, a centrifuge, a vacuum drum or a vacuum bag solid-liquid separation device.

[0050] S6. The lean liquid obtained in step S5 is sent to the desulfurization tower 2 and used as the lean liquid in step S3, forming a cycle of lean liquid and rich liquid. In order to fully remove SO2 from the flue gas, step S6 controls the pH value of the lean liquid to 4.5-7.0, and then uses it as the lean liquid in step S3, and controls the Na2SO3 content in the lean liquid entering the desulfurization tower 2 to be 5-30wt%, and the NaHSO3 content to be 0-10wt%; the Na2SO3 content in the rich liquid sent to the reaction tank 3 in step S4 is 0-10wt%, and the NaHSO3 content is 5-40wt%.

[0051] Step S6 also heats and dehydrates the solid filter residue, which is mainly ZnSO3·5 / 2H2O. After heating and dehydration, it becomes anhydrous zinc sulfite. The temperature of heating and dehydration is generally controlled at 50-200°C. The gas generated by heating and dehydration is introduced into the desulfurization tower 2 together with the flue gas preliminarily purified in step S3. Anhydrous zinc sulfite is decomposed into zinc oxide solid and SO2 gas by heating. The chemical reaction formula is: ZnSO3→ZnO+SO2↑. The temperature of heating and decomposition is generally controlled at 200-400°C. The zinc oxide solid obtained by heating and decomposition is sent to the reaction tank 3 and used as ZnO in step S4 to form a ZnO cycle.

[0052] The SO2 gas obtained in step S6 has a high temperature and can be recycled after washing and cooling. The sodium zinc double alkali flue gas desulfurization process also includes step S7, in which the gas obtained by heating and decomposing step S6 is mainly SO2 gas, and then it is removed from the gas and cooled to finally obtain a SO2 gas product. For example, the gas obtained by heating and decomposing step S6 is washed in the SO2 gas washing tower 8 to remove solid particulate impurities, and then cooled to 10-90°C and dehydrated to finally obtain a SO2 gas product. The SO2 gas product has a high concentration and can be sent to acid production systems, sulfur, liquid SO2 and other production equipment for producing S-containing compounds.

[0053] The wastewater generated by washing in step S2 and step S7 is neutralized with alkaline substances and then evaporated, crystallized, and separated into solid and liquid to obtain condensed water that can be reused. A small amount of waste salt is sent to a professional company for treatment, so that no wastewater can be discharged. The sodium-zinc double alkali flue gas desulfurization process uses zinc oxide and sodium salt to circulate and recover SO2 in the flue gas, thereby achieving the purpose of recovering SO2 resources in the flue gas. It does not produce desulfurized gypsum in the sodium-calcium double alkali process, nor does it produce other solid wastes. There is no wastewater discharge, and the exhaust smoke can meet the ultra-low emission requirements.

[0054] Example 1.

[0055] The sodium-zinc double alkali flue gas desulfurization process is used for flue gas desulfurization in the copper smelting environment. The flue gas conditions are shown in Table 1.

[0056] Table 1 Conditions for collecting flue gas in copper smelting environment.

[0057] Serial number project data 1 Smoke volume <![CDATA[23.2×10 4 Nm 3 / h]]> 2 <![CDATA[SO2 concentration]]> <![CDATA[2500mg / Nm 3 , up to 11000mg / Nm 3 ]]> 3 Particles <![CDATA[≤200mg / Nm 3 ]]> 4 temperature 20~120℃, normal 60℃ 5 Acid mist <![CDATA[≤20mg / Nm 3 ]]> 6 Fluorine and chlorine content <![CDATA[≤2mg / Nm 3 ]]> 7 HCl <![CDATA[≤5mg / Nm 3 <!-- 6 -->]]> 8 Water content 2.90％

[0058] The smoke from the copper smelting environment enters the coated bag dust collector for dust removal. After the smoke passes through the coated bag dust collector, the particulate matter in the smoke is ≤5mg / Nm 3 , the flue gas enters the scrubber 1 through the booster fan, and is sprayed to cool down and remove impurities. Most of the impurities such as particulate matter, HCl, HF, acid mist, etc. in the flue gas coming out of the scrubber 1 have been removed, and the flue gas temperature drops to about 20°C. The flue gas is sent to the desulfurization tower 2, and the mixed liquid of lean liquid and rich liquid is first used as a desulfurizer to absorb SO2 in the rich liquid circulation section 2-3, and then the lean liquid is used to contact the flue gas in the lean liquid circulation section 2-2, and the temperature in the desulfurization tower 2 is controlled at about 21°C, and the pH value of the lean liquid entering the desulfurization tower 2 is controlled at about 6.3. The Na2SO3 content in the lean liquid entering the desulfurization tower 2 is about 21wt%, and the NaHSO3 content is about 5wt%; the Na2SO3 content in the rich liquid discharged from the desulfurization tower 2 is about 5wt%, and the NaHSO3 content is about 33wt%. The flue gas after SO2 removal is washed by spraying washing water in the washing section 2-1 of the desulfurization tower 2 to recover the sodium salt carried in the flue gas. The washing water is collected and recycled through the circulating water tank 2-5. The flue gas after water washing is discharged from the top chimney. The SO2 in the discharged flue gas is about 18mg / Nm 3 , the particle size is about 2mg / Nm 3 , sulfuric acid mist is about 2.7mg / Nm 3 , meeting the ultra-low emission limit requirements.

[0059] The lean liquid absorbs SO2 in the flue gas to become a rich liquid. When the Na2SO3 content in the rich liquid is about 5wt% and the NaHSO3 content is about 33wt%, the rich liquid is discharged from the desulfurization tower 2 and sent to the reaction tank 3, and then the ZnO produced in step S6 is added to the reaction tank 3. The clear liquid in the reaction tank 3 flows by gravity to the lean liquid tank 4, and the bottom flow of the reaction tank 3 is sent to the solid-liquid separator 5 through a pressure pump. The filtrate produced by the solid-liquid separator 5 flows by gravity to the lean liquid tank 4, and the solid filter residue produced by the solid-liquid separator 5 is sent to the dryer 6. The filter residue mainly contains ZnSO3·5 / 2H2O. The dryer 6 heats and dehydrates the filter residue. For example, the heating and dehydration temperature is controlled at about 135°C. The water vapor produced by the dryer 6 is sent to the desulfurization tower 2, and the anhydrous ZnSO3 produced by the dryer 6 is sent to the decomposer 7. Anhydrous ZnSO3 is decomposed into ZnO and SO2 by heating in the decomposer 7. For example, the temperature of the decomposition is controlled at about 365°C. The ZnO produced by the decomposition is sent to the reaction tank 3. The gas produced by the decomposition is washed by the SO2 gas washing tower 8 to remove impurities such as ZnO solid particles, and then cooled and dehydrated to become the SO2 gas product. For example, the gas produced by the decomposition is washed and cooled to about 60°C. The SO2 gas product can be sent to the acid production system, sulfur, liquid SO2 and other devices for producing S-containing compounds.

[0060] The SO2 content of the flue gas after treatment according to the above process is about 18mg / Nm 3 , the particle size is about 2mg / Nm 3 , sulfuric acid mist is about 2.7mg / Nm 3 , meeting the ultra-low emission limit requirements.

[0061] Example 2.

[0062] The sodium zinc double alkali flue gas desulfurization process is used for flue gas desulfurization of coal-fired power plant boilers. The flue gas conditions are shown in Table 2.

[0063] Table 2 Conditions of boiler flue gas in a coal-fired power plant.

[0064] Serial number project unit data 1 Smoke volume <![CDATA[Nm 3 / h]]> 155000 2 Flue gas temperature ℃ 140～160 3 <![CDATA[CO2]]> ％ 10.21 4 <![CDATA[H2O]]> ％ 6.10 5 <![CDATA[N2]]> ％ 75.69 6 <![CDATA[O2]]> ％ 8.00 7 <![CDATA[SO3]]> <![CDATA[mg / Nm 3 ]]> ＜50 8 <![CDATA[SO2]]> <![CDATA[mg / Nm 3 ]]> 21000 9 HCl <![CDATA[mg / Nm 3 ]]> 80 10 HF <![CDATA[mg / Nm 3 ]]> 410 11 Particles <![CDATA[mg / Nm 3 ]]> ≤10

[0065] The boiler flue gas enters the coated bag dust collector for dust removal. After the flue gas passes through the coated bag dust collector, the particulate matter in the flue gas is ≤5mg / Nm 3. The flue gas enters the scrubber 1 through the booster fan, and is sprayed to cool down and remove impurities. Most of the impurities such as particulate matter, HCl, HF, acid mist, etc. in the flue gas coming out of the scrubber 1 have been removed, and the flue gas temperature has dropped to about 48°C. The flue gas is sent to the desulfurization tower 2, and the mixed liquid of lean liquid and rich liquid is first used as a desulfurizer in the rich liquid circulation section 2-3 to absorb SO2, and then the lean liquid is used to contact the flue gas in the lean liquid circulation section 2-2, and the temperature in the desulfurization tower 2 is controlled at about 50°C, and the pH value of the lean liquid entering the desulfurization tower 2 is controlled at about 6.7. The Na2SO3 content in the lean liquid entering the desulfurization tower 2 is about 23wt%, and the NaHSO3 content is about 3wt%; the Na2SO3 content in the rich liquid discharged from the desulfurization tower 2 is about 5.2wt%, and the NaHSO3 content is about 35wt%. The flue gas after SO2 removal is washed by spraying washing water in the washing section 2-1 of the desulfurization tower 2 to recover the sodium salt carried in the flue gas. The washing water is collected and recycled through the circulating water tank 2-5. The flue gas after water washing is discharged from the top chimney. The SO2 in the discharged flue gas is about 25mg / Nm 3 , the particle size is about 2mg / Nm 3 , sulfuric acid mist is about 2mg / Nm 3 , meeting the ultra-low emission limit requirements.

[0066] The lean liquid absorbs SO2 in the flue gas to become a rich liquid. When the Na2SO3 content in the rich liquid is about 5.2wt% and the NaHSO3 content is about 35wt%, the rich liquid is discharged from the desulfurization tower 2 and sent to the reaction tank 3, and then the ZnO produced in step S6 is added to the reaction tank 3. The clear liquid in the reaction tank 3 flows by gravity to the lean liquid tank 4, and the bottom flow of the reaction tank 3 is sent to the solid-liquid separator 5 through a pressure pump. The filtrate produced by the solid-liquid separator 5 flows by gravity to the lean liquid tank 4, and the solid filter residue produced by the solid-liquid separator 5 is sent to the dryer 6. The filter residue mainly contains ZnSO3·5 / 2H2O. The dryer 6 heats and dehydrates the filter residue. For example, the heating and dehydration temperature is controlled at about 150°C. The water vapor produced by the dryer 6 is sent to the desulfurization tower 2, and the anhydrous ZnSO3 produced by the dryer 6 is sent to the decomposer 7. Anhydrous ZnSO3 is decomposed into ZnO and SO2 by heating in the decomposer 7. For example, the temperature of the decomposition is controlled at about 350°C. The ZnO produced by the decomposition is sent to the reaction tank 3. The gas produced by the decomposition is washed by the SO2 gas washing tower 8 to remove impurities such as ZnO solid particles, and then cooled and dehydrated to become the SO2 gas product. For example, the gas produced by the decomposition is washed and cooled to about 55°C. The SO2 gas product can be sent to the acid production system, sulfur, liquid SO2 and other devices for producing S-containing compounds.

[0067] The SO2 content in the flue gas after treatment according to the above process is about 25mg / Nm 3 , the particle size is about 2mg / Nm 3 , sulfuric acid mist is about 2mg / Nm3 , meeting the ultra-low emission limit requirements.

[0068] Example 3.

[0069] The sodium zinc double alkali flue gas desulfurization process is used for sulfuric acid tail gas desulfurization, and the flue gas conditions are shown in Table 3.

[0070] Table 3 Conditions of a sulfuric acid tail gas.

[0071] Serial number project unit data 1 Exhaust volume <![CDATA[Nm 3 / h]]> 45000 2 temperature ℃ Approx. 80 3 <![CDATA[N2]]> ％ 94.65 4 <![CDATA[O2]]> ％ 4.91 5 <![CDATA[SO2]]> ％ 0.44 6 <![CDATA[SO3]]> <![CDATA[mg / Nm 3 ]]> ＜50

[0072] The sulfuric acid tail gas is directly sent to the desulfurization tower 2. First, a mixture of lean liquid and rich liquid is used as a desulfurizer to absorb SO2 in the rich liquid circulation section 2-3 of the desulfurization tower 2. Then, the lean liquid is used to contact the sulfuric acid tail gas in the lean liquid circulation section 2-2. The temperature in the desulfurization tower 2 is controlled at about 27°C. The pH value of the lean liquid entering the desulfurization tower 2 is controlled to be about 6.5. The Na2SO3 content in the lean liquid entering the desulfurization tower 2 is about 25wt%, and the NaHSO3 content is about 6wt%; the Na2SO3 content in the rich liquid discharged from the desulfurization tower 2 is about 8wt%, and the NaHSO3 content is about 31wt%. After removing SO2, the sulfuric acid tail gas is circulated and washed with sprayed washing water in the washing section 2-1 of the desulfurization tower 2 to recover the sodium salt entrained in the sulfuric acid tail gas. The washing water is collected and recycled through the circulating water tank 2-5. The sulfuric acid tail gas after washing is discharged from the top chimney, and the SO2 in the discharged flue gas is about 30mg / Nm 3 , the particle size is about 1mg / Nm 3 , sulfuric acid mist is about 5mg / Nm 3 , meeting the ultra-low emission limit requirements.

[0073] The lean liquid absorbs SO2 in the flue gas to become a rich liquid. When the Na2SO3 content in the rich liquid is about 8wt% and the NaHSO3 content is about 31wt%, the rich liquid is discharged from the desulfurization tower 2 and sent to the reaction tank 3, and then the ZnO produced in step S6 is added to the reaction tank 3. The clear liquid in the reaction tank 3 flows by gravity to the lean liquid tank 4, and the bottom flow of the reaction tank 3 is sent to the solid-liquid separator 5 through a pressure pump. The filtrate produced by the solid-liquid separator 5 flows by gravity to the lean liquid tank 4, and the solid filter residue produced by the solid-liquid separator 5 is sent to the dryer 6. The filter residue mainly contains ZnSO3·5 / 2H2O. The dryer 6 heats and dehydrates the filter residue. For example, the heating and dehydration temperature is controlled at about 180°C. The water vapor produced by the dryer 6 is sent to the desulfurization tower 2, and the anhydrous ZnSO3 produced by the dryer 6 is sent to the decomposer 7. Anhydrous ZnSO3 is decomposed into ZnO and SO2 by heating in the decomposer 7. For example, the temperature of the decomposition is controlled at about 380°C. The ZnO produced by the decomposition is sent to the reaction tank 3. The gas produced by the decomposition is washed by the SO2 gas washing tower 8 to remove impurities such as ZnO solid particles, and then cooled and dehydrated to become the SO2 gas product. For example, the gas produced by the decomposition is washed and cooled to about 45°C. The SO2 gas product can be sent to the acid production system, sulfur, liquid SO2 and other devices for producing S-containing compounds.

[0074] The SO2 content in the flue gas after treatment according to the above process is about 30mg / Nm 3 , the particle size is about 1mg / Nm 3 , sulfuric acid mist is about 5mg / Nm 3 , meeting the ultra-low emission limit requirements.

[0075] The second subject of the present invention is a sodium-zinc dual alkali flue gas desulfurization device, which is used to implement the sodium-zinc dual alkali flue gas desulfurization process described in the first subject. Figure 1 The sodium-zinc double alkali flue gas desulfurization device includes a desulfurization tower 2, a reaction tank 3, a solid-liquid separator 5, a dryer 6 and a decomposer 7.

[0076] The desulfurization tower 2 includes a desulfurization section and a water washing section 2-1 on its upper part. The top of the water washing section 2-1 is provided with a tower top chimney. The water washing section 2-1 is provided with a circulating water inlet and outlet. The circulating water inlet and outlet are connected by a pipeline and a circulating water pump 2-4 is provided on the pipeline. The circulating water pump 2-4 is used to pump washing water so that the washing water washes the flue gas after desulfurization by spraying. In order to facilitate the adjustment of the washing process of the water washing section 2-1 of the desulfurization tower 2 and the replenishment of washing water, a circulating water tank 2-5 is also connected in series on the pipeline between the circulating water inlet and outlet of the water washing section 2-1 of the desulfurization tower 2, and the circulating water tank 2-5 is also provided with a water replenishment port.

[0077] The desulfurization section of the desulfurization tower 2 is mainly used for desulfurization of flue gas. The desulfurization section is provided with a flue gas inlet 2-6, a rich liquid discharge port 2-7 and a desulfurizer circulation inlet and outlet. The flue gas inlet 2-6 is the only inlet for flue gas to enter the desulfurization tower 2 and is generally arranged at the bottom of the desulfurization section. The desulfurizer circulation inlet and outlet are connected by a pipeline and a desulfurizer circulation pump 2-8 is arranged on the pipeline. The desulfurizer circulation pump 2-8 fully contacts the desulfurizer with the flue gas in the desulfurization section by spraying.

[0078] In order to improve the desulfurization efficiency and ensure that the SO2 concentration in the flue gas discharged through the chimney on the top of the desulfurization tower 2 reaches the ultra-low emission standard, the desulfurization section of the desulfurization tower 2 is divided into two sections, namely the lower rich liquid circulation section 2-3 and the upper lean liquid circulation section 2-2. The rich liquid circulation section 2-3 is provided with a rich liquid circulation inlet and outlet, which are connected by a pipeline and a desulfurizer circulation pump 2-8 is provided on the pipeline. The desulfurizer circulation pump 2-8 is actually a rich liquid circulation pump. The lean liquid circulation section 2-2 is provided with a lean liquid circulation inlet and outlet, which are connected by a pipeline and a desulfurizer circulation pump 2-8 is provided on the pipeline. The desulfurizer circulation pump 2-8 is actually a lean liquid circulation pump. In order to facilitate the regulation and control of the amount, pH value, etc. of the lean liquid entering the desulfurization tower 2 through the lean liquid circulation inlet, a lean liquid circulation tank 2-9 is also connected in series on the pipeline between the lean liquid circulation inlet and outlet of the lean liquid circulation section 2-2 of the desulfurization tower 2, and the inlet of the desulfurizer circulation pump 2-8 of the lean liquid circulation section 2-2 is connected to the lean liquid circulation tank 2-9. The lean liquid circulation tank 2-9 can store an appropriate amount of lean liquid, and is also convenient for receiving newly added lean liquid, as well as adjusting the composition and pH of the lean liquid.

[0079] The rich liquid discharge port 2-7 of the desulfurization tower 2 is the outlet for the desulfurization agent that has failed or is close to failure to be discharged from the desulfurization tower 2. The desulfurization agent that has failed or is close to failure is rich liquid. The rich liquid discharge port 2-7 is connected to the reaction tank 3, and the rich liquid is discharged to the reaction tank 3. The rich liquid is discharged to the reaction tank 3 by gravity or pumping.

[0080] The reaction tank 3 is used to receive the rich liquid and convert the rich liquid into the lean liquid. The reaction tank 3 is provided with a feed port 3-1, and the feed port 3-1 is used to add ZnO into the reaction tank 3. The reaction tank 3 is also provided with an overflow port 3-2, and the overflow port 3-2 is connected to the lean liquid tank 4. The lean liquid in the reaction tank 3 can overflow into the lean liquid tank 4, and the lean liquid tank 4 plays the role of temporarily storing the lean liquid.

[0081] The bottom of the reaction tank 3 is provided with an underflow outlet 3-3, which is used to discharge the solid and part of the liquid that sink to the bottom of the reaction tank 3. The underflow outlet 3-3 is connected to the solid-liquid separator 5, and a pressure pump is preferably provided between the underflow outlet 3-3 and the solid-liquid separator 5. The liquid outlet of the solid-liquid separator 5 is connected to the lean liquid tank 4. The liquid separated by the solid-liquid separator 5 is lean liquid and enters the lean liquid tank 4, for example, by gravity. The outlet of the lean liquid tank 4 is connected to the desulfurization agent circulation inlet of the desulfurization tower 2. When the desulfurization tower 2 is provided with a lean liquid circulation tank 2-9, the outlet of the lean liquid tank 4 is connected to the lean liquid circulation tank 2-9. A lean liquid pump 4-1 is generally provided between the outlet of the lean liquid tank 4 and the lean liquid circulation tank 2-9. The lean liquid pump 4-1 is used to pump the lean liquid in the lean liquid tank 4 into the lean liquid circulation tank 2-9.

[0082] The bottom flow outlet 3-3 is connected to the solid-liquid separator 5. The solid-liquid separator 5 is used to separate the solid and liquid of the material flowing out of the bottom flow outlet 3-3 of the reaction tank 3, and obtain a liquid lean liquid and a solid filter residue after solid-liquid separation. The solid-liquid separator 5 is an existing one, such as a chamber filter press, a centrifuge, a vacuum drum or a vacuum bag solid-liquid separation device. The solid outlet of the solid-liquid separator 5 corresponds to the feed port of the dryer 6, that is, the solid outlet of the solid-liquid separator 5 is connected to the feed port of the dryer 6 through a pipeline, or the two are not connected but the solid outlet of the solid-liquid separator 5 is facing the feed port of the dryer 6. The filter residue can be automatically or manually transferred from the solid-liquid separator 5 to the dryer 6. The dryer 6 is used to heat and dehydrate the solid filter residue. The component of the filter residue is mainly ZnSO3·5 / 2H2O. After the filter residue is heated and dehydrated, anhydrous zinc sulfite is obtained, and some water vapor is generated at the same time. The dryer 6 is provided with a gas outlet and a solid outlet. The gas outlet of the dryer 6 is connected to the flue gas inlet 2-6 of the desulfurization section of the desulfurization tower 2. The water vapor generated by the dryer 6 is sent to the desulfurization tower 2. The solid outlet of the dryer 6 corresponds to the feed port of the decomposer 7. The solid outlet of the dryer 6 is connected to the feed port of the decomposer 7 through a pipeline, or the two are not connected but the solid outlet of the dryer 6 is directly opposite to the feed port of the decomposer 7. The decomposer 7 is used to heat and decompose anhydrous zinc sulfite into zinc oxide solid and SO2 gas. The decomposer 7 is provided with a gas outlet and a solid outlet. The solid outlet of the decomposer 7 corresponds to the feed port 3-1 of the reaction tank 3. The solid outlet of the decomposer 7 is connected to the feed port 3-1 of the reaction tank 3 through a pipeline, or the two are not connected but the solid outlet of the decomposer 7 is directly opposite to the feed port 3-1 of the reaction tank 3. The solid generated by the decomposer 7 is mainly zinc oxide, and the zinc oxide is sent to the reaction tank 3 to form a ZnO cycle. In order to remove impurities and cool down the SO2 gas generated by the decomposer 7 and realize resource utilization. The sodium zinc double alkali flue gas desulfurization device also includes a SO2 gas washing tower 8. The gas outlet of the decomposer 7 is connected to the air inlet at the bottom of the SO2 gas washing tower 8. The top of the SO2 gas washing tower 8 is provided with a gas outlet. The SO2 gas after impurities removal and cooling is discharged from the gas outlet at the top of the SO2 gas washing tower 8. The SO2 gas washing tower 8 is provided with a washing water circulation inlet and outlet, which are connected by a pipeline and a washing water circulation pump 8-1 and a washing water cooler 8-2 are provided in series on the pipeline.

[0083] The flue gas needs to be pretreated before entering the desulfurization tower 2. The pretreatment method and device are determined by the flue gas conditions. For example, when the flue gas contains low levels of HCl, HF, and SO3, the flue gas does not need to be washed before entering the desulfurization tower 2. In order for the sodium zinc double alkali flue gas desulfurization device to pre-treat the flue gas entering the desulfurization tower 2, the sodium zinc double alkali flue gas desulfurization device also includes a washing tower 1, such as Figure 1As shown. The scrubber 1 is provided with a flue gas inlet 1-1 and a flue gas exhaust port 1-2. The flue gas exhaust port 1-2 is located at the top of the scrubber 1 and is connected to the flue gas inlet 2-6 of the desulfurization tower 2. The scrubber 1 is also provided with at least one group of washing water circulation inlets and outlets. The washing water circulation inlets and outlets in the same group are connected by pipes and a washing water circulation pump 1-3 is provided on the pipes. The washing water circulation pump 1-3 allows the washing water to wash the flue gas by spraying. The lower end of the scrubber 1 is provided with a washing water storage part, and the washing water storage part is provided with a wastewater outlet 1-4. The washing water is quantitatively discharged into the wastewater system according to the concentration of pollutants.

[0084] The following provides a structure in which a washing tower 1 is provided with two groups of washing water circulation inlets and outlets. Figure 1 As shown, a tower cut-off plate is provided in the middle of the washing tower 1, and the tower cut-off plate divides the washing tower 1 into a lower section 1-5 and an upper section 1-6. The lower section 1-5 and the upper section 1-6 are connected, and the flue gas inlet 1-1 is located in the lower section 1-5. The lower section 1-5 and the upper section 1-6 are each provided with a group of washing water circulation inlets and outlets, and the lower section 1-5 and the upper section 1-6 are each provided with a washing water circulation pump 1-3. In order to replenish washing water in time, a washing water circulation tank 1-7 is also arranged in series in the pipeline between the washing water circulation inlets and outlets of the upper section 1-6 of the washing tower, and the washing water circulation tank 1-7 is provided with a water replenishment port, wherein: the water inlet pipe of the washing water circulation pump 1-3 is located in the washing water circulation tank 1-7, and the water outlet pipe of the washing water circulation pump 1-3 is connected to the washing water circulation inlet. The washing water circulation tank 1-7 is also connected to the lower section 1-5 of the washing tower through a pipeline, so that the washing water circulation tank 1-7 can replenish washing water to the lower section 1-5 of the washing tower.

[0085] In order to cool the flue gas in the scrubber 1 and thus adjust the temperature of the flue gas entering the desulfurization tower 2, a heat exchanger 1-8 is provided between the scrubbing water circulation inlet of the upper section 1-6 of the scrubber and the flue gas exhaust port 1-2 at the top of the scrubber 1. For example, the heat exchanger 1-8 is a plate heat exchanger or a tube heat exchanger.

Claims

1. The sodium-zinc double alkali flue gas desulfurization process is characterized by: The steps include: S1. Dust removal for flue gas containing SO2; S2. removing impurities and cooling the flue gas after dust removal to obtain preliminarily purified flue gas; S3. The flue gas after preliminary purification is passed into a desulfurization tower (2), where the flue gas contacts with a lean liquid to remove SO2 from the flue gas, and the lean liquid absorbs SO2 from the flue gas to become a rich liquid; the flue gas is then washed with water to recover the sodium salt entrained in the flue gas; finally, the flue gas after washing is discharged after meeting the standards; wherein the lean liquid is a solution containing more Na2SO3 and less NaHSO3, and the rich liquid is a solution containing less Na2SO3 and more NaHSO3; S4. The rich liquid produced by the desulfurization tower (2) in step S3 is sent to the reaction tank (3), ZnO is added to the reaction tank (3), and NaHSO3 in the rich liquid reacts with ZnO, and the chemical reaction formula is: 2NaHSO3+ZnO+3 / 2H2O→Na2SO3+ZnSO3·5 / 2H2O; S5. The substance in the reaction tank (3) is subjected to solid-liquid separation to obtain a liquid lean liquid and a solid residue; S6. The lean liquid obtained in step S5 is sent to the desulfurization tower (2) and used as the lean liquid in step S3, forming a cycle of lean liquid and rich liquid; the solid filter residue is heated and dehydrated to become anhydrous zinc sulfite, and then decomposed into solid zinc oxide and SO2 gas by heating. The chemical reaction formula is: ZnSO3→ZnO+SO2↑; the solid zinc oxide obtained by heating and decomposition is sent to the reaction tank (3) and used as ZnO in step S4, forming a cycle of ZnO.

2. The sodium-zinc double alkali flue gas desulfurization process according to claim 1, characterized in that: Step S1: Dust is removed by bag filter, and the particulate matter in the flue gas after dust removal is ≤5mg / Nm 3 .

3. The sodium-zinc double alkali flue gas desulfurization process according to claim 1, characterized in that: In step S2, the dust-removed flue gas is passed into a washing tower (1) to remove impurities and cool down through a circulating washing method, using a primary washing method or a secondary washing method, and the temperature is reduced to 10° C. to 70° C.

4. The sodium-zinc double alkali flue gas desulfurization process according to claim 1, characterized in that: The desulfurization tower (2) includes three sections connected in sequence from bottom to top, namely a rich liquid circulation section (2-3), a lean liquid circulation section (2-2) and a water washing section (2-1); the flue gas after preliminary purification first enters the rich liquid circulation section (2-3), where the SO2 in the flue gas is removed by circulating the rich liquid or a mixture of the rich liquid and the lean liquid, then enters the lean liquid circulation section (2-2), where the SO2 in the flue gas is removed by circulating the lean liquid, and finally enters the water washing section (2-1) for water washing.

5. The sodium-zinc double alkali flue gas desulfurization process according to claim 1, characterized in that: In step S3, an antioxidant is added to the lean solution, and the antioxidant is at least one of p-phenylenediamine and hydroquinone.

6. The sodium-zinc double alkali flue gas desulfurization process according to claim 1, characterized in that: In step S5, the equipment used for solid-liquid separation is a chamber filter press, a centrifuge, a vacuum drum or a vacuum bag solid-liquid separation device.

7. The sodium-zinc double alkali flue gas desulfurization process according to claim 1, characterized in that: In step S6, the temperature of heating and dehydration is 50-200°C, and the gas generated by heating and dehydration is introduced into the desulfurization tower (2) together with the flue gas preliminarily purified in step S3; the temperature of heating and decomposition is 200-400°C.

8. The sodium-zinc dual alkali flue gas desulfurization process according to any one of claims 1 to 7, characterized in that: In step S6, the pH value of the lean liquid entering the desulfurization tower (2) is controlled to be 4.5-7.0, and the Na2SO3 content in the lean liquid entering the desulfurization tower (2) is controlled to be 5-30wt%, and the NaHSO3 content is controlled to be 0-10w%; in step S4, the Na2SO3 content in the rich liquid sent to the reaction tank (3) is controlled to be 0-10wt%, and the NaHSO3 content is controlled to be 5-40wt%.

9. The sodium-zinc double alkali flue gas desulfurization process according to any one of claims 1 to 7, characterized in that: The step S7 is also included, in which the gas obtained by heating and decomposing in the step S6 is washed to remove impurities, and then cooled to finally obtain a SO2 gas product.

10. The sodium-zinc dual alkali flue gas desulfurization process according to claim 9, characterized in that: The gas obtained by the thermal decomposition in step S6 is washed in a SO2 gas washing tower (8) to remove solid particulate impurities, then cooled to 10-90°C and dehydrated to finally obtain a SO2 gas product.

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