Flue gas desulfurization device adopting sodium-zinc dual-alkali method

Abstract

The utility model discloses a flue gas desulfurization device adopting a sodium-zinc dual-alkali method, relates to the field of separation by utilizing a physical or chemical method, and aims to enable flue gas containing SO2 to reach an ultra-low emission standard and obtain available SO2. Comprising a desulfurization tower, a reaction tank, a solid-liquid separator, a dryer and a decomposer, the desulfurization tower comprises a desulfurization section and a washing section on the upper portion of the desulfurization section, the desulfurization section is provided with a flue gas inlet, a rich liquid discharge outlet and a desulfurizer circulating inlet and outlet, the rich liquid discharge outlet is connected with the reaction tank, the reaction tank is provided with a feeding port and an overflow port, and the overflow port is connected with a barren liquor tank; an outlet of the barren liquor tank is connected with a desulfurizer circulating inlet, an underflow outlet of the reaction tank is connected with the solid-liquid separator, two outlets of the solid-liquid separator are respectively connected with the barren liquor tank and the dryer, the dryer corresponds to the decomposer, and a solid outlet of the decomposer corresponds to a feeding port of the reaction tank. The device disclosed by the utility model is used for removing SO2 in the flue gas.

Description

Technical Field

[0001] This utility model relates to the field of separation using physical or chemical methods, as well as the field of inorganic chemistry, specifically to a sodium-zinc dual-alkali flue gas desulfurization process and an apparatus for implementing the process. Background Technology

[0002] Currently, commonly used wet desulfurization technologies include: lime / limestone-gypsum method, sodium alkali method, zinc oxide method, ammonia method, ionic liquid (organic amine) method, and dual alkali method. With increasingly stringent environmental protection requirements in my country, many industries are required to meet ultra-low emission limits, i.e., SO2 ≤ 35 mg / Nm³ in emitted gases. 3 Most of the above-mentioned processes either fail to meet the emission standards for SO2 concentration, have high operating costs, or generate secondary pollution.

[0003] The lime / limestone-gypsum method for flue gas desulfurization (FGD) is a widely used technology. This method uses lime or limestone slurry to absorb SO2 in flue gas, reacting to produce calcium sulfate. After purification, the flue gas meets emission standards. However, this method requires limestone, electricity, and water. The main problems with this process are: continuous discharge of acidic wastewater containing chloride ions from the desulfurization system; the generation of desulfurization gypsum as a byproduct; and the production of 3 tons of difficult-to-utilize desulfurization gypsum for every ton of SO2 removed. Simultaneously, the removal of 1 mole of SO2 generates an equal mole of incremental CO2 emissions.

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

[0005] Ammonia desulfurization technology mainly uses ammonia water or liquid ammonia as an absorbent to absorb SO2 in flue gas. Absorbing 1 ton of SO2 requires approximately 0.5 tons of liquid ammonia. The main problems with ammonia desulfurization are: ammonia escape, the presence of large amounts of aerosols in the emitted flue gas, and the discharge of acidic wastewater containing chloride ions, causing secondary pollution.

[0006] Zinc oxide desulfurization is a commonly used method in lead and zinc enterprises, with the absorbent being self-produced zinc oxide dust or zinc oxide calcined sand. The main problems with zinc oxide desulfurization are: ZnSO3 has high viscosity, making it easy for it to deposit in equipment and pipelines, causing scaling and blockage, which is difficult to clean; the solution circulation volume is large, resulting in high power consumption; and the SO2 in the emitted flue gas is unstable.

[0007] Ionic liquid (organic amine) desulfurization technology is a regenerative desulfurization process that uses ionic liquids or organic amines as the main absorbents. It absorbs SO2 in flue gas at low temperatures and desorbs SO2 from the absorbent at high temperatures. The main problems are high investment and high energy consumption for regeneration steam.

[0008] Lime / limestone desulfurization processes all use slurry-like materials, making the desulfurization system prone to scaling and clogging. To address this, Japan and the United States developed the sodium-calcium double-alkali method. The sodium-calcium double-alkali method first uses an alkaline absorbent (such as NH4) + Na + and K + The process involves using a sodium-calcium double-alkali method for flue gas desulfurization. The absorbent is then regenerated using lime slurry or limestone powder. Because liquid-phase absorption is employed, and bisulfite is generally more soluble than sulfite, scaling problems commonly encountered in lime / limestone desulfurization are avoided. The sodium-calcium double-alkali method uses sodium compounds (sodium hydroxide, soda ash, or sodium sulfite) to absorb SO2. The absorbent is then reacted with lime and / or limestone to produce calcium sulfite and / or calcium sulfate precipitates. The regenerated sodium salt solution is returned to the desulfurization process. The gypsum produced as a byproduct of the sodium-calcium double-alkali method is called desulfurization gypsum, which is classified as solid waste.

[0009] This section introduces the desulfurization principle of the sodium-calcium dual-alkali method. During the absorption reaction, the main chemical reaction in the desulfurization process is: Na₂SO₃ + SO₂ + H₂O → 2NaHSO₃. The desulfurization liquid contains NaOH returned after regeneration and Na₂CO₃ added to the system. Sodium sulfite is generated during the desulfurization process, with the chemical reactions being: 2NaOH + SO₂ → Na₂SO₃ + H₂O and Na₂CO₃ + SO₂ → Na₂SO₃ + H₂O, respectively. During desulfurization, O₂ in the flue gas reacts with sodium sulfite to form sodium sulfate, with the reaction: Na₂SO₃ + O₂ → Na₂SO₄. The accumulation of sulfate will affect the desulfurization efficiency. When regeneration is performed using lime slurry, the chemical reaction is: 2NaHSO₃ + Ca(OH)₂ → Na₂SO₃ + CaSO₄. 3· 1 / 2H₂O↓ + 3 / 2H₂O and Na₂SO₃ + Ca(OH)₂ + 1 / 2H₂O → 2NaOH + CaSO₄ 3· 1 / 2H₂O↓, calcium sulfite is generally in the form of calcium sulfite hemihydrate. When regenerated using limestone powder, the chemical reaction is: 2NaHSO₃ + CaCO₃ → Na₂SO₃ + CaSO₄ 3· 1 / 2H₂O↓ + CO₂↑ + 1 / 2H₂O. Theoretically, the reaction is complete when neutralized with lime, but incomplete when neutralized with limestone.

[0010] The sodium-calcium double alkali desulfurization method has the following advantages: (1) Using sodium alkali as the absorbent, the system generally does not produce precipitates, and the desulfurization efficiency is high, which 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) 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 be adapted to absorption and regeneration cycle operation, and has the ability to keep all compounds in the solution, thereby avoiding scaling and clogging in the desulfurization system; (5) It can be used in solid absorbent systems, and since the cations are non-volatile, there is no problem of absorbent volatilization and the generation of ammonium mist during the desulfurization process, and it is much cheaper than potassium compounds.

[0011] The existing sodium-calcium dual-alkali process uses sodium salt as the desulfurizing agent, which can be regenerated with lime and / or limestone. The regenerated sodium salt solution is returned to the desulfurization system, generating calcium sulfite and / or calcium sulfate precipitates, known as desulfurized gypsum. The main problems with the sodium-calcium dual-alkali process are: the amount of desulfurized gypsum produced is too large, it contains a lot of impurities and water, and the decomposition temperature of calcium sulfite and / or calcium sulfate is high, generally being discarded as waste, generating a large amount of gypsum waste and causing secondary pollution.

[0012] As national environmental protection policies impose increasingly stringent restrictions on SO2 emissions from flue gas, efficient, economical, environmentally friendly, and stable removal of SO2 from flue gas without generating secondary pollution is crucial for enterprise development in order to meet the requirements of ecological environment and economic development.

[0013] Patent application CN 103736383 A discloses a soda ash flue gas desulfurization process and system. The process is based on the interconversion of sodium carbonate, sodium bisulfite, and sodium sulfite during absorption, utilizing the difference in solubility at a certain temperature to produce sodium sulfite crystals through saturated crystallization. However, the sodium sulfite produced by this process has limited industrial value and is mostly considered waste with no economic value. Utility Model Content

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

[0015] The technical solution adopted in this utility model is: sodium-zinc dual-alkali flue gas desulfurization process, which includes the following steps:

[0016] S1. Dust removal from flue gas containing SO2. For example, dust removal using a bag filter, with particulate matter in the flue gas after dust removal ≤5mg / Nm³. 3 .

[0017] S2. The flue gas after dust removal is further purified and cooled to obtain preliminarily purified flue gas. For example, the flue gas after dust removal is introduced into a scrubbing tower for purification and cooling through circulation scrubbing, using a primary or secondary scrubbing method, and cooled to 10℃~70℃.

[0018] S3. The pre-purified flue gas is introduced into the desulfurization tower. The flue gas and lean solution come into contact in the desulfurization tower to remove SO2 from the flue gas. The lean solution absorbs SO2 from the flue gas and becomes rich solution. The flue gas is then washed with water to recover sodium salts entrained in the flue gas. Finally, the flue gas is discharged after meeting the standards. The lean solution is a solution with more Na2SO3 and less NaHSO3, and the rich solution is a solution with less Na2SO3 and more NaHSO3.

[0019] To ensure that step S3 achieves ultra-low emission standards for SO2 concentration in flue gas, the desulfurization tower further comprises three consecutive sections connected from bottom to top: a rich liquid circulation section, a lean liquid circulation section, and a water washing section. The pre-purified flue gas first enters the rich liquid circulation section, where SO2 is removed from the flue gas by circulating rich liquid or a mixture of rich and lean liquid. Then it enters the lean liquid circulation section, where SO2 is removed from the flue gas by circulating lean liquid. Finally, it enters the water washing section for water washing.

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

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

[0022] S5. The substances in the reaction tank are subjected to solid-liquid separation to obtain a liquid lean liquid and a solid filter residue. Specifically, the equipment used for solid-liquid separation includes a chamber filter press, centrifuge, vacuum drum, or 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 between lean and rich liquids; the solid filter residue is heated and dehydrated to become anhydrous zinc sulfite, which is then decomposed by heating into zinc oxide solid and SO2 gas. The chemical reaction formula is: ZnSO3→ZnO+SO2↑. The zinc oxide solid 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, to convert the solid filter residue into anhydrous zinc sulfite, the specific heating and dehydration temperature is 50–200°C. The gas generated during heating and dehydration is introduced into the desulfurization tower along with the flue gas preliminarily purified in step S3. To promote the thermal decomposition of anhydrous zinc sulfite into solid zinc oxide and SO2 gas, the specific heating and decomposition temperature is 200–400°C.

[0025] To ensure that SO2 is fully removed from the flue gas in step S3, further steps are taken: in step S6, the pH value of the lean solution entering the desulfurization tower is controlled to be 4.5–7.0, and the Na2SO3 content and NaHSO3 content in the lean solution entering the desulfurization tower are controlled to be 5–30 wt% and 0–10 wt%; the Na2SO3 content and NaHSO3 content in the rich solution sent to the reaction tank in step S4 are 0–10 wt% and 5–40 wt%.

[0026] The SO2 gas obtained in step S6 is at a relatively high temperature and can be utilized as a resource after washing and cooling. Furthermore, the sodium-zinc dual-alkali flue gas desulfurization process also includes step S7, in which the gas obtained from the heating and decomposition of step S6 is washed to remove impurities, then cooled to finally obtain the SO2 gas product. For example, the gas obtained from the heating and decomposition of step S6 is washed in an SO2 gas scrubbing tower to remove solid particulate impurities, then cooled to 10–90°C and dehydrated to finally obtain the SO2 gas product.

[0027] This utility model also provides a sodium-zinc dual-alkali flue gas desulfurization device for implementing any of the above-mentioned sodium-zinc dual-alkali flue gas desulfurization processes. The purpose is also to enable flue gas containing SO2 to meet ultra-low emission standards, obtain SO2 gas that can be utilized by resources, and at the same time, not to produce waste such as desulfurization gypsum.

[0028] The sodium-zinc dual-alkali flue gas desulfurization unit includes a desulfurization tower, a reaction tank, a solid-liquid separator, a dryer, and a decomposer. The desulfurization tower comprises a desulfurization section and an upper water washing section. The top of the water washing section is equipped with a tower top chimney and circulating water inlets / outlets connected by pipelines with circulating water pumps. The desulfurization section has a flue gas inlet, a rich liquid discharge outlet, and a desulfurizing agent circulation inlet / outlet, connected by pipelines with desulfurizing agent circulation pumps. The rich liquid discharge outlet is connected to the reaction tank, which has a feed inlet and an overflow outlet. The outlet is connected to the lean liquid tank, and the outlet of the lean liquid tank is connected to the desulfurizing agent circulation inlet of the desulfurization tower. The bottom of the reaction tank is equipped with an underflow outlet, which 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 equipped 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, and the solid outlet of the dryer corresponds to the feed inlet of the decomposer. The decomposer is equipped 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] To ensure that the SO2 concentration in the flue gas discharged from the top chimney of the desulfurization tower meets the ultra-low emission standard, the desulfurization section of the desulfurization tower is further divided into upper and lower sections: a lower rich liquid circulation section and an upper lean liquid circulation section. The rich liquid circulation section is equipped with a rich liquid circulation inlet and outlet, which are connected by a pipeline and equipped with a desulfurizing agent circulation pump. The lean liquid circulation section is equipped with a lean liquid circulation inlet and outlet, which are connected by a pipeline and equipped with a desulfurizing agent circulation pump. The outlet of the lean liquid tank is connected to the lean liquid circulation inlet.

[0030] To facilitate the adjustment and control of the amount and pH value of the lean liquid entering the desulfurization tower through the lean liquid circulation inlet, a lean liquid circulation tank is further installed 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 installed between the outlet of the lean liquid tank and the lean liquid circulation tank.

[0031] To facilitate the adjustment of the washing process in the water washing section of the desulfurization tower, a circulating water tank is further connected in series on the pipes between the circulating water inlet and outlet of the water washing section of the desulfurization tower, and the circulating water tank is also equipped with a water replenishment port.

[0032] Solid-liquid separators are used to separate the solid and liquid components of the material flowing out of the underflow outlet of a reaction tank, resulting in a liquid lean liquor and a solid filter residue. Specifically, solid-liquid separators can be chamber filter presses, centrifuges, vacuum drums, or vacuum bag filters.

[0033] The dryer is used to heat and dehydrate the solid filter residue, which mainly contains ZnSO3·5 / 2H2O. After heating and dehydration, anhydrous zinc sulfite is obtained. The decomposer is used to heat and decompose the anhydrous zinc sulfite into solid zinc oxide and SO2 gas. To further remove impurities and cool the SO2 gas generated by the decomposer, the sodium-zinc dual-alkali flue gas desulfurization unit also includes an SO2 gas scrubbing tower. The gas outlet of the decomposer is connected to the inlet at the bottom of the SO2 gas scrubbing tower, and the top of the SO2 gas scrubbing tower has a gas outlet. The SO2 gas scrubbing tower has a washing water circulation inlet and outlet, which are connected by a pipeline, and a first washing water circulation pump and a washing water cooler are connected in series on the pipeline.

[0034] When the flue gas contains low levels of HCl, HF, and SO3, no washing is required before the flue gas enters the desulfurization tower. To further pretreat the flue gas entering the desulfurization tower using the sodium-zinc dual-alkali method, the desulfurization unit also includes a scrubbing tower. The scrubbing tower has a flue gas inlet and a flue gas outlet. The flue gas outlet is located at the top of the scrubbing tower and connected to the flue gas inlet of the desulfurization tower. The scrubbing tower also has at least one set of scrubbing water circulation inlets and outlets. These inlets and outlets are connected by pipes, and a second scrubbing water circulation pump is installed on the pipes. A scrubbing water storage section is located at the lower end of the scrubbing tower, and the scrubbing water storage section has a wastewater discharge outlet.

[0035] The following describes a structure for a scrubbing tower with two sets of scrubbing water circulation inlets and outlets. Specifically: a tower divider is located in the middle of the scrubbing tower, dividing it into a lower section and an upper section. The flue gas inlet is located in the lower section. Each section has a set of scrubbing water circulation inlets and outlets. A scrubbing water circulation tank is connected in series between the scrubbing water circulation inlets and outlets in the upper section. The scrubbing water circulation tank has a water supply inlet and is also connected to the lower section of the scrubbing tower via a pipe.

[0036] To cool the flue gas in the scrubbing tower and thus regulate the temperature of the flue gas entering the desulfurization tower, a heat exchanger is further installed between the scrubbing water circulation inlet at the top of the scrubbing tower and the flue gas exhaust outlet at the top of the scrubbing tower. For example, the heat exchanger is a plate heat exchanger or a tubular heat exchanger.

[0037] The beneficial effects of this invention are: this invention is used for desulfurization of flue gas containing SO2, and the SO2 content in the treated flue gas is ≤35mg / Nm³. 3 Particulate matter ≤5mg / Nm 3 Sulfuric acid mist ≤5mg / Nm 3This method can meet the ultra-low emission limits for flue gas. This invention recovers SO2 from flue gas to obtain SO2 gaseous products, which can be processed into sulfur-containing chemical products such as sulfuric acid, sulfur, and liquid SO2, thus making SO2 a resource in the flue gas. Compared to the existing sodium-calcium double-alkali desulfurization method, this invention uses ZnO instead of lime or limestone to form a solid filter residue (ZnSO3·5 / 2H2O) in the reaction tank. The solid filter residue is then dehydrated and decomposed by heating to obtain solid zinc oxide, which is then recycled. The entire process does not produce waste such as gypsum or wastewater; at the same time, it does not require the large quantities of purchased chemicals needed for other desulfurization processes, nor does it consume large amounts of steam, electricity, or other energy. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of one embodiment of the sodium-zinc dual-alkali flue gas desulfurization device of this utility model.

[0039] Attached reference numerals: 1. Scrubber tower; 1-1. Flue gas inlet; 1-2. Flue gas outlet; 1-3. First scrubbing water circulation pump; 1-4. Wastewater outlet; 1-5. Lower section of scrubbing tower; 1-6. Upper section of scrubbing tower; 1-7. Scrubbing water circulation tank; 1-8. Heat exchanger; 2. Desulfurization tower; 2-1. Water washing section; 2-2. Lean liquor circulation section; 2-3. Rich liquor circulation section; 2-4. Circulating water pump; 2-5. Circulating water tank; 2-6. Flue gas inlet; 2-7. Rich liquor outlet; 2-8. Desulfurizing agent circulation pump; 2-9. Lean liquor circulation tank; 3. Reaction tank; 3-1. Feed port; 3-2. Overflow port; 3-3. Underflow outlet; 4. Lean liquor tank; 4-1. Lean liquor pump; 5. Solid-liquid separator; 6. Dryer; 7. Decomposer; 8. SO2 gas scrubbing tower; 8-1. Second scrubbing water circulation pump; 8-2. Scrubbing water cooler. Detailed Implementation

[0040] The first subject of this utility model is a sodium-zinc dual-alkali flue gas desulfurization process, and the second subject is a sodium-zinc dual-alkali flue gas desulfurization device. Both subjects are used to remove SO2 from flue gas, enabling the emitted flue gas to meet ultra-low emission limits and reducing waste generated during the desulfurization process. Figure 1 As shown, the sodium-zinc dual-alkali flue gas desulfurization process of this utility model 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 from the flue gas. For example, flue gas containing SO2 is treated with a bag filter to control the particulate matter content in the flue gas after dust removal to ≤5mg / Nm³. 3 .

[0042] S2. The flue gas after dust removal is purified and cooled to obtain preliminarily purified flue gas.

[0043] Steps S1 and S2 are pretreatment processes for desulfurization, and the specific operations of these processes are determined based on the actual flue gas conditions. Generally, the flue gas after dust removal is fed into scrubbing tower 1 for impurity removal and cooling through circulating scrubbing. The scrubbing water is discharged from scrubbing tower 1 in a measured amount according to the pollutant concentration. For example, the temperature is lowered to 10℃~70℃. When the flue gas contains low levels of HCl, HF, and SO3, scrubbing is not necessary. The scrubbing tower can employ single-stage or two-stage scrubbing, but single-stage scrubbing is generally sufficient. For example, in... Figure 1 In the example shown, the scrubbing tower 1 is divided into a lower section 1-5 and an upper section 1-6. Each of the lower section 1-5 and the upper section 1-6 is equipped with a set of scrubbing water circulation inlets and outlets. The scrubbing water circulation inlets and outlets of the same set are connected by a pipe and a first scrubbing water circulation pump 1-3 is installed on the pipe. If the flue gas after dust removal is only scrubbed through the lower section 1-5 or the upper section 1-6, it is a first-level scrubbing. If the flue gas after dust removal is scrubbed through both the lower section 1-5 and the upper section 1-6, it is a second-level scrubbing.

[0044] S3. The pre-purified flue gas is introduced into desulfurization tower 2. The flue gas and lean liquid come into contact in desulfurization tower 2 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 sodium salts entrained in the flue gas. Finally, the washed flue gas meets the standards and is discharged.

[0045] The lean solution is a solution containing more Na2SO3 and less NaHSO3, while the rich solution is a solution containing less Na2SO3 and more NaHSO3. The process of desulfurizing flue gas is actually the process of desulfurizing agent absorbing SO2. The main chemical reaction formula of this process is: Na2SO3 + SO2 + H2O → 2NaHSO3. After the lean solution absorbs SO2 from the flue gas, it becomes the rich solution.

[0046] The flue gas entering desulfurization tower 2 inevitably contains O2. O2 reacts with Na2SO3 to form 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 solution in this step. The oxygen inhibitor is at least one of p-phenylenediamine and hydroquinone.

[0047] Both lean and rich liquors are desulfurizing agents, differing only in composition and desulfurization capacity. They can be interconverted and recycled. To ensure that the SO2 concentration in the exhaust gas meets ultra-low emission standards, desulfurization tower 2 comprises three consecutive sections connected from bottom to top: rich liquor circulation section 2-3, lean liquor circulation section 2-2, and water washing section 2-1. The pre-purified flue gas first enters the rich liquor circulation section 2-3, where rich liquor or a mixture of rich and lean liquor is used to circulate and remove SO2 from the flue gas. Then it enters the lean liquor circulation section 2-2, where lean liquor circulation completely removes SO2 from the flue gas. Finally, it enters the water washing section 2-1 for water washing.

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

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

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

[0051] Step S6 further dehydrates the solid filter residue by heating. The solid filter residue is mainly ZnSO3·5 / 2H2O, which becomes anhydrous zinc sulfite after dehydration. The dehydration temperature is generally controlled between 50 and 200°C. The gas generated during dehydration, along with the flue gas preliminarily purified in step S3, is introduced into desulfurization tower 2. Anhydrous zinc sulfite decomposes into solid zinc oxide and SO2 gas through heating. The chemical reaction is: ZnSO3 → ZnO + SO2↑. The decomposition temperature is generally controlled between 200 and 400°C. The solid zinc oxide obtained from the decomposition is sent to reaction tank 3 and used as ZnO in step S4, forming a ZnO cycle.

[0052] The SO2 gas obtained in step S6 is at a relatively high temperature and can be utilized as a resource after washing and cooling. The sodium-zinc dual-alkali flue gas desulfurization process also includes step S7, where the gas obtained from the heating and decomposition of step S6, mainly SO2 gas, is removed, cooled, and finally the SO2 gas product is obtained. For example, the gas obtained from the heating and decomposition of step S6 is washed in an SO2 gas scrubbing tower 8 to remove solid particulate impurities, then cooled to 10–90°C and dehydrated to finally obtain the SO2 gas product. The high concentration of the SO2 gas product can be sent to acid production systems, sulfur, liquid SO2, and other production facilities that produce sulfur-containing compounds.

[0053] The wastewater generated from washing in steps S2 and S7 is neutralized with alkaline substances, then evaporated, crystallized, and separated into solid and liquid components. The resulting condensate can be reused, and a small amount of waste salt is sent to a professional company for treatment, achieving zero wastewater discharge. The sodium-zinc dual-alkali flue gas desulfurization process uses zinc oxide and sodium salt recycling to recover SO2 from the flue gas, achieving the goal of recovering SO2 resources from the flue gas. Moreover, it does not produce desulfurization gypsum as in the sodium-calcium dual-alkali process, nor does it generate other solid waste. There is no wastewater discharge, and the emitted flue gas can meet ultra-low emission requirements.

[0054] Example 1.

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

[0056] Table 1. Environmental conditions for collecting flue gas in copper smelting.

[0057] Serial Number project data 1 flue gas volume <![CDATA[23.2×10 4 Nm 3 / h]]> 2 <![CDATA[SO2 concentration]]> <![CDATA[2500mg / Nm 3 Up to 11000 mg / Nm 3 ]]> 3 Particulate matter <![CDATA[≤200mg / Nm 3 ]]> 4 temperature 20~120℃, normal temperature 60℃ 5 acid mist <![CDATA[≤20mg / Nm 3 ]]> 6 Fluorine and chlorine content <![CDATA[≤2mg / Nm 3 <!-- 6 -->]]> 7 HCl <![CDATA[≤5mg / Nm 3 ]]> 8 Moisture content 2.90％

[0058] The flue gas collected in the copper smelting environment enters a membrane bag filter for dust removal. After passing through the membrane bag filter, the particulate matter content in the flue gas is ≤5mg / Nm³. 3The flue gas enters the scrubbing tower 1 via a booster fan, where it is sprayed to cool and remove impurities. Most particulate matter, HCl, HF, acid mist, and other impurities in the flue gas exiting scrubbing tower 1 have been removed, and the flue gas temperature drops to approximately 20°C. The flue gas is then sent to desulfurization tower 2. First, in the rich liquor circulation section 2-3, a mixture of lean and rich liquor is used as the desulfurizing agent to absorb SO2. Then, in the lean liquor circulation section 2-2, lean liquor is used to contact the flue gas. The temperature inside desulfurization tower 2 is controlled at approximately 21°C, and the pH value of the lean liquor entering desulfurization tower 2 is controlled at approximately 6.3. The Na2SO3 content in the lean liquor entering desulfurization tower 2 is approximately 21 wt%, and the NaHSO3 content is approximately 5 wt%. The rich liquor exiting desulfurization tower 2 contains approximately 5 wt% Na2SO3 and approximately 33 wt%. After SO2 removal, the flue gas is scrubbed in the water washing section 2-1 of desulfurization tower 2 using sprayed, circulating washing water to recover sodium salts entrained in the flue gas. The washing water is collected and recycled through circulating water tank 2-5. The scrubbed flue gas is discharged from the top chimney, with an SO2 content of approximately 18 mg / Nm³. 3 The particulate matter concentration is approximately 2 mg / Nm³. 3 The sulfuric acid mist concentration was approximately 2.7 mg / Nm³. 3 It meets the ultra-low emission limit requirements.

[0059] The lean liquor absorbs SO2 from the flue gas to become rich liquor. When the Na2SO3 content in the rich liquor is approximately 5 wt% and the NaHSO3 content is approximately 33 wt%, the rich liquor is discharged from desulfurization tower 2 and sent to reaction tank 3. ZnO produced in step S6 is then added to reaction tank 3. The clear liquid in reaction tank 3 flows by gravity to lean liquor tank 4, and the underflow from reaction tank 3 is sent to solid-liquid separator 5 via a pressurized pump. The filtrate produced by solid-liquid separator 5 flows by gravity to lean liquor tank 4, and the solid filter residue produced by solid-liquid separator 5 is sent to dryer 6. The filter residue mainly contains ZnSO3·5 / 2H2O. Dryer 6 heats and dehydrates the filter residue, for example, by controlling the dehydration temperature at approximately 135°C. The water vapor produced by dryer 6 is sent to desulfurization tower 2, and the anhydrous ZnSO3 produced by dryer 6 is sent to decomposer 7. Anhydrous ZnSO3 is decomposed into ZnO and SO2 in decomposer 7 by heating. For example, the heating temperature is controlled at approximately 365°C. The ZnO produced by heating is sent to reaction tank 3. The gas produced by heating is washed by SO2 gas scrubbing tower 8 to remove ZnO solid particles and other impurities. After cooling and dehydration, it becomes SO2 gas product. For example, the gas produced by heating is washed and cooled to approximately 60°C. The SO2 gas product can be sent to acid production systems, sulfur, liquid SO2, and other devices that produce sulfur-containing compounds.

[0060] The SO2 content in the flue gas after treatment using the above process is approximately 18 mg / Nm³. 3 The particulate matter concentration is approximately 2 mg / Nm³. 3 The sulfuric acid mist concentration is approximately 2.7 mg / Nm³.3 It meets the ultra-low emission limit requirements.

[0061] Example 2.

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

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

[0064] Serial Number project unit data 1 flue gas 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 Particulate matter <![CDATA[mg / Nm 3 ]]> ≤10

[0065] Boiler flue gas enters a membrane bag filter for dust removal. After passing through the membrane bag filter, the particulate matter content in the flue gas is ≤5mg / Nm³. 3 The flue gas enters the scrubbing tower 1 via a booster fan, where it is sprayed to cool and remove impurities. Most particulate matter, HCl, HF, acid mist, and other impurities are removed from the flue gas exiting the scrubbing tower 1, and the flue gas temperature drops to approximately 48°C. The flue gas is then sent to the desulfurization tower 2. First, in the rich liquor circulation section 2-3, a mixture of lean and rich liquor is used as the desulfurizing agent to absorb SO2. Then, in the lean liquor circulation section 2-2, lean liquor is used to contact the flue gas. The temperature inside the desulfurization tower 2 is controlled at approximately 50°C, and the pH value of the lean liquor entering the desulfurization tower 2 is controlled at approximately 6.7. The Na2SO3 content in the lean liquor entering the desulfurization tower 2 is approximately 23 wt%, and the NaHSO3 content is approximately 3 wt%. The rich liquor exiting the desulfurization tower 2 contains approximately 5.2 wt% Na2SO3 and approximately 35 wt% NaHSO3. After SO2 removal, the flue gas is scrubbed in the water washing section 2-1 of desulfurization tower 2 using sprayed, circulating washing water to recover sodium salts entrained in the flue gas. The washing water is collected and recycled through circulating water tank 2-5. The scrubbed flue gas is discharged from the top chimney, with an SO2 content of approximately 25 mg / Nm³. 3 The particulate matter concentration is approximately 2 mg / Nm³. 3 The sulfuric acid mist concentration is approximately 2 mg / Nm³. 3 It meets the ultra-low emission limit requirements.

[0066] The lean liquor absorbs SO2 from the flue gas to become rich liquor. When the Na2SO3 content in the rich liquor is approximately 5.2 wt% and the NaHSO3 content is approximately 35 wt%, the rich liquor is discharged from desulfurization tower 2 and sent to reaction tank 3. ZnO produced in step S6 is then added to reaction tank 3. The clear liquid in reaction tank 3 flows by gravity to lean liquor tank 4, and the underflow from reaction tank 3 is sent to solid-liquid separator 5 via a pressurized pump. The filtrate produced by solid-liquid separator 5 flows by gravity to lean liquor tank 4, and the solid filter residue produced by solid-liquid separator 5 is sent to dryer 6. The filter residue mainly contains ZnSO3·5 / 2H2O. Dryer 6 heats and dehydrates the filter residue, for example, by controlling the dehydration temperature at approximately 150°C. The water vapor produced by dryer 6 is sent to desulfurization tower 2, and the anhydrous ZnSO3 produced by dryer 6 is sent to decomposer 7. Anhydrous ZnSO3 is decomposed into ZnO and SO2 in decomposer 7 by heating. For example, the heating temperature is controlled at approximately 350°C. The ZnO produced by heating is sent to reaction tank 3. The gas produced by heating is washed by SO2 gas scrubbing tower 8 to remove ZnO solid particles and other impurities. After cooling and dehydration, it becomes SO2 gas product. For example, the gas produced by heating is washed and cooled to approximately 55°C. The SO2 gas product can be sent to acid production systems, sulfur, liquid SO2, and other devices that produce sulfur-containing compounds.

[0067] The SO2 content in the flue gas after treatment using the above process is approximately 25 mg / Nm³. 3 The particulate matter concentration is approximately 2 mg / Nm³. 3 The sulfuric acid mist concentration is approximately 2 mg / Nm³. 3 It meets the ultra-low emission limit requirements.

[0068] Example 3.

[0069] The sodium-zinc dual-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 for a certain sulfuric acid tail gas.

[0071] Serial Number project unit data 1 Exhaust gas volume <![CDATA[Nm 3 / h]]> 45000 2 temperature ℃ Approximately 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 desulfurization tower 2. First, in the rich liquid circulation section 2-3 of desulfurization tower 2, a mixture of lean and rich liquids is used as the desulfurizing agent to absorb SO2. Then, in the lean liquid circulation section 2-2, the lean liquid comes into contact with the sulfuric acid tail gas. The temperature inside desulfurization tower 2 is controlled at approximately 27℃, and the pH value of the lean liquid entering desulfurization tower 2 is controlled at approximately 6.5. The Na2SO3 content in the lean liquid entering desulfurization tower 2 is approximately 25wt%, and the NaHSO3 content is approximately 6wt%. The Na2SO3 content in the rich liquid exiting desulfurization tower 2 is approximately 8wt%, and the NaHSO3 content is approximately 31wt%. After SO2 removal, the sulfuric acid tail gas is washed in the water washing section 2-1 of desulfurization tower 2 using sprayed washing water to recover sodium salts entrained in the sulfuric acid tail gas. The washing water is collected and recycled through the circulating water tank 2-5. The washed sulfuric acid tail gas is discharged from the top chimney, with an SO2 content of approximately 30 mg / Nm³. 3 Particulate matter is approximately 1 mg / Nm³ 3 The sulfuric acid mist concentration is approximately 5 mg / Nm³. 3 It meets the ultra-low emission limit requirements.

[0073] The lean liquor absorbs SO2 from the flue gas to become rich liquor. When the Na2SO3 content in the rich liquor is approximately 8 wt% and the NaHSO3 content is approximately 31 wt%, the rich liquor is discharged from desulfurization tower 2 and sent to reaction tank 3. ZnO produced in step S6 is then added to reaction tank 3. The clear liquid in reaction tank 3 flows by gravity to lean liquor tank 4, and the underflow from reaction tank 3 is sent to solid-liquid separator 5 via a pressurized pump. The filtrate produced by solid-liquid separator 5 flows by gravity to lean liquor tank 4, and the solid filter residue produced by solid-liquid separator 5 is sent to dryer 6. The filter residue mainly contains ZnSO3·5 / 2H2O. Dryer 6 heats and dehydrates the filter residue, for example, by controlling the dehydration temperature at approximately 180°C. The water vapor produced by dryer 6 is sent to desulfurization tower 2, and the anhydrous ZnSO3 produced by dryer 6 is sent to decomposer 7. Anhydrous ZnSO3 is decomposed into ZnO and SO2 in decomposer 7 by heating. For example, the heating temperature is controlled at approximately 380°C. The ZnO produced by heating is sent to reaction tank 3. The gas produced by heating is washed by SO2 gas scrubbing tower 8 to remove ZnO solid particles and other impurities. After cooling and dehydration, it becomes SO2 gas product. For example, the gas produced by heating is washed and cooled to approximately 45°C. The SO2 gas product can be sent to acid production systems, sulfur, liquid SO2, and other devices that produce sulfur-containing compounds.

[0074] The SO2 content in the flue gas treated by the above process is approximately 30 mg / Nm³. 3 Particulate matter is approximately 1 mg / Nm³ 3 The sulfuric acid mist concentration is approximately 5 mg / Nm³. 3 It meets the ultra-low emission limit requirements.

[0075] The second subject of this utility model is a sodium-zinc dual-alkali flue gas desulfurization device, used to implement the sodium-zinc dual-alkali flue gas desulfurization process described in the first subject. See also Figure 1 The sodium-zinc dual-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 an upper water washing section 2-1. The top of the water washing section 2-1 is equipped with a tower top chimney. The water washing section 2-1 has a circulating water inlet and outlet connected by a pipeline, and a circulating water pump 2-4 is installed on the pipeline. The circulating water pump 2-4 pumps washing water, which is then sprayed onto the desulfurized flue gas for washing. To facilitate the adjustment of the washing process in the water washing section 2-1 of the desulfurization tower 2 and the replenishment of washing water, a circulating water tank 2-5 is 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. The circulating water tank 2-5 also has a water replenishment port.

[0077] The desulfurization section of desulfurization tower 2 is mainly used for desulfurizing flue gas. The desulfurization section is equipped with a flue gas inlet 2-6, a rich liquid discharge outlet 2-7, and a desulfurizing agent circulation inlet / outlet. Flue gas inlet 2-6 is the only inlet for flue gas to enter desulfurization tower 2 and is generally located at the bottom of the desulfurization section. The desulfurizing agent circulation inlet / outlet is connected by a pipeline, and a desulfurizing agent circulation pump 2-8 is installed on the pipeline. The desulfurizing agent circulation pump 2-8 sprays the desulfurizing agent into full contact with the flue gas within the desulfurization section.

[0078] To improve desulfurization efficiency and ensure that the SO2 concentration in the flue gas discharged from the top chimney of desulfurization tower 2 meets ultra-low emission standards, the desulfurization section of desulfurization tower 2 is divided into upper and lower sections: a lower rich-liquid circulation section 2-3 and an upper lean-liquid circulation section 2-2. The rich-liquid circulation section 2-3 has a rich-liquid circulation inlet and outlet connected by a pipeline, and a desulfurizing agent circulation pump 2-8 is installed on the pipeline. This desulfurizing agent circulation pump 2-8 is actually a rich-liquid circulation pump. The lean-liquid circulation section 2-2 also has a lean-liquid circulation inlet and outlet connected by a pipeline, and a desulfurizing agent circulation pump 2-8 is installed on the pipeline. This desulfurizing agent circulation pump 2-8 is actually a lean-liquid circulation pump. To facilitate the adjustment and control of the amount and pH value of the lean solution entering desulfurization tower 2 through the lean solution circulation inlet, a lean solution circulation tank 2-9 is connected in series on the pipeline between the lean solution circulation inlet and outlet of the lean solution circulation section 2-2 of desulfurization tower 2. The inlet of the desulfurizing agent circulation pump 2-8 of the lean solution circulation section 2-2 is connected to the lean solution circulation tank 2-9. The lean solution circulation tank 2-9 can store an appropriate amount of lean solution, facilitate the receipt of newly replenished lean solution, and allow for the adjustment of the composition and pH of the lean solution.

[0079] The rich liquid discharge port 2-7 of desulfurization tower 2 is the outlet for discharged desulfurizing agent that has been exhausted or is close to exhaustion. The exhausted or close to exhaustion desulfurizing agent is called rich liquid. The rich liquid discharge port 2-7 is connected to the reaction tank 3, and the rich liquid is discharged into the reaction tank 3. The rich liquid is discharged into the reaction tank 3 by gravity or pumping.

[0080] The reaction tank 3 is used to receive the rich solution and convert it into a lean solution. The reaction tank 3 is equipped with a feed port 3-1 for adding ZnO into the reaction tank 3. The reaction tank 3 is also equipped with an overflow port 3-2, which is connected to the lean solution tank 4. The lean solution in the reaction tank 3 can overflow into the lean solution tank 4, which serves as a temporary storage tank for the lean solution.

[0081] The bottom of the reaction tank 3 is equipped with an underflow outlet 3-3, which is used to discharge solids and some liquids that have settled at 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 installed 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 the lean liquid and enters the lean liquid tank 4, for example, by gravity flow. The outlet of the lean liquid tank 4 is connected to the desulfurizing agent circulation inlet of the desulfurization tower 2. When the desulfurization tower 2 is equipped 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 installed 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 underflow outlet 3-3 is connected to the solid-liquid separator 5. The solid-liquid separator 5 is used to separate the material flowing out of the underflow outlet 3-3 of the reaction tank 3 into solid and liquid components, yielding a liquid lean liquid and a solid filter cake. The solid-liquid separator 5 can be any existing type, such as a chamber filter press, centrifuge, vacuum drum, or vacuum bag filter. The solid outlet of the solid-liquid separator 5 corresponds to the feed inlet of the dryer 6; that is, the solid outlet of the solid-liquid separator 5 and the feed inlet of the dryer 6 are connected by a pipe, or they are not connected but the solid outlet of the solid-liquid separator 5 faces the feed inlet of the dryer 6. The filter cake 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 cake, whose main component is ZnSO3·5 / 2H2O. After heating and dehydration, anhydrous zinc sulfite is obtained, and some water vapor is generated simultaneously. Dryer 6 has a gas outlet and a solid outlet. The gas outlet of dryer 6 is connected to the flue gas inlet 2-6 of the desulfurization section of desulfurization tower 2. The water vapor generated by dryer 6 is sent to desulfurization tower 2. The solid outlet of dryer 6 corresponds to the feed inlet of decomposer 7. The solid outlet of dryer 6 and the feed inlet of decomposer 7 are connected by a pipeline, or they are not connected but the solid outlet of dryer 6 is directly opposite the feed inlet of decomposer 7. Decomposer 7 is used to heat and decompose anhydrous zinc sulfite into zinc oxide solid and SO2 gas. Decomposer 7 has a gas outlet and a solid outlet. The solid outlet of decomposer 7 corresponds to the feed port 3-1 of reaction tank 3. The solid outlet of decomposer 7 and the feed port 3-1 of reaction tank 3 are connected by a pipeline, or they are not connected but the solid outlet of decomposer 7 is directly opposite the feed port 3-1 of reaction tank 3. The solid generated by decomposer 7 is mainly zinc oxide, which is sent to reaction tank 3 to form a ZnO cycle. To remove impurities and cool the SO2 gas produced by decomposer 7, thus enabling resource utilization, the sodium-zinc dual-alkali flue gas desulfurization unit also includes an SO2 gas scrubbing tower 8. The gas outlet of decomposer 7 is connected to the inlet at the bottom of SO2 gas scrubbing tower 8, and a gas outlet is located at the top of SO2 gas scrubbing tower 8. The SO2 gas, after impurity removal and cooling, is discharged from the gas outlet at the top of SO2 gas scrubbing tower 8. SO2 gas scrubbing tower 8 is equipped with a scrubbing water circulation inlet and outlet, which are connected by a pipeline, and a second scrubbing water circulation pump 8-1 and a scrubbing water cooler 8-2 are connected in series on the pipeline.

[0083] Before entering desulfurization tower 2, the flue gas needs pretreatment. The method and equipment for pretreatment are determined by the conditions of the flue gas. For example, when the flue gas contains low levels of HCl, HF, and SO3, it does not require washing before entering desulfurization tower 2. To enable the sodium-zinc dual-alkali flue gas desulfurization unit to pretreat the flue gas entering desulfurization tower 2, the unit also includes a scrubbing tower 1, such as... Figure 1As shown. The scrubbing tower 1 has a flue gas inlet 1-1 and a flue gas outlet 1-2. The flue gas outlet 1-2 is located at the top of the scrubbing tower 1 and is connected to the flue gas inlet 2-6 of the desulfurization tower 2. The scrubbing tower 1 also has at least one set of scrubbing water circulation inlets and outlets. These inlets and outlets are connected by pipes, and a first scrubbing water circulation pump 1-3 is installed on the pipes. The first scrubbing water circulation pump 1-3 sprays scrubbing water onto the flue gas. A scrubbing water storage section is located at the lower end of the scrubbing tower 1. The scrubbing water storage section has a wastewater discharge outlet 1-4. The scrubbing water is discharged into the wastewater system in a measured amount according to the pollutant concentration.

[0084] The following describes a structure for a washing tower 1 with two sets of washing water circulation inlets and outlets. For example... Figure 1 As shown, the washing tower 1 has a split tray in the middle, which 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. The flue gas inlet 1-1 is located in the lower section 1-5. Each of the lower section 1-5 and the upper section 1-6 has a set of washing water circulation inlets and outlets. Each of the lower section 1-5 and the upper section 1-6 has a first washing water circulation pump 1-3. In order to replenish the washing water in time, a washing water circulation tank 1-7 is connected in series between the washing water circulation inlets and outlets of the upper section 1-6. The washing water circulation tank 1-7 has a water replenishment port. The inlet pipe of the first washing water circulation pump 1-3 is located in the washing water circulation tank 1-7, and the outlet pipe of the first 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 scrubbing tower 1 and thus regulate 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 scrubbing tower and the flue gas exhaust port 1-2 at the top of the scrubbing tower 1. For example, the heat exchanger 1-8 is a plate heat exchanger or a tubular heat exchanger.

Claims

1. A sodium-zinc dual-alkali flue gas desulfurization device, characterized in that: The system includes a desulfurization tower (2), a reaction tank (3), a solid-liquid separator (5), a dryer (6), and a decomposer (7). The desulfurization tower (2) includes a desulfurization section and a water washing section (2-1) above it. The top of the water washing section (2-1) is equipped with a tower top chimney. The water washing section (2-1) is equipped with a circulating water inlet and outlet, which are connected by a pipeline and equipped with a circulating water pump (2-4). The desulfurization section is equipped with a flue gas inlet (2-6), a rich liquid discharge outlet (2-7), and a desulfurizing agent circulation inlet and outlet, which are connected by a pipeline and equipped with a desulfurizing agent circulation pump (2-8). The rich liquid discharge outlet (2-7) is connected to the reaction tank (3). The reaction tank (3) is equipped with a feed inlet (3-1) and an overflow outlet (3-2). The overflow outlet (3-2) The reaction tank (3) is connected to the lean liquid tank (4), and the outlet of the lean liquid tank (4) is connected to the desulfurizing agent circulation inlet of the desulfurization tower (2). The bottom of the reaction tank (3) is provided with an underflow outlet (3-3), which is connected to the solid-liquid separator (5). The liquid outlet of the solid-liquid separator (5) is connected to the lean liquid tank (4), and the solid outlet of the solid-liquid separator (5) corresponds to the feed inlet of the dryer (6). 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), and the solid outlet of the dryer (6) corresponds to the feed inlet of the decomposer (7). The decomposer (7) is provided with a gas outlet and a solid outlet, and the solid outlet of the decomposer (7) corresponds to the feed port (3-1) of the reaction tank (3).

2. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 1, characterized in that: The desulfurization section of the desulfurization tower (2) is divided into two sections: 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 equipped with a rich liquid circulation inlet and outlet, which are connected by a pipeline and a desulfurizing agent circulation pump (2-8) is installed on the pipeline. The lean liquid circulation section (2-2) is equipped with a lean liquid circulation inlet and outlet, which are connected by a pipeline and a desulfurizing agent circulation pump (2-8) is installed on the pipeline. The outlet of the lean liquid tank (4) is connected to the lean liquid circulation inlet.

3. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 2, characterized in that: A lean liquid circulation tank (2-9) is connected in series on the pipe between the lean liquid circulation inlet and outlet of the lean liquid circulation section (2-2) of the desulfurization tower (2). 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 also provided between the outlet of the lean liquid tank (4) and the lean liquid circulation tank (2-9).

4. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 1, characterized in that: A circulating water tank (2-5) is connected in series on the pipe between the inlet and outlet of the water washing section (2-1) of the desulfurization tower (2), and the circulating water tank (2-5) is also equipped with a water replenishment port.

5. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 1, characterized in that: The solid-liquid separator (5) is a chamber filter press, centrifuge, vacuum drum or vacuum bag solid-liquid separation device.

6. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 1, characterized in that: It also includes an SO2 gas scrubbing tower (8), the gas outlet of the decomposer (7) is connected to the gas inlet at the bottom of the SO2 gas scrubbing tower (8), the top of the SO2 gas scrubbing tower (8) is provided with a gas outlet, the SO2 gas scrubbing tower (8) is provided with a washing water circulation inlet and outlet, the washing water circulation inlet and outlet are connected by a pipe and a second washing water circulation pump (8-1) and a washing water cooler (8-2) are connected in series on the pipe.

7. The sodium-zinc dual-alkali flue gas desulfurization device according to any one of claims 1 to 6, characterized in that: It also includes a scrubbing tower (1), which is provided with a flue gas inlet (1-1) and a flue gas outlet (1-2). The flue gas outlet (1-2) is located at the top of the scrubbing tower (1) and is connected to the flue gas inlet (2-6) of the desulfurization tower (2). The scrubbing tower (1) is also provided with at least one set of scrubbing water circulation inlets and outlets. The scrubbing water circulation inlets and outlets in the same set are connected by a pipeline and a first scrubbing water circulation pump (1-3) is provided on the pipeline. The lower end of the scrubbing tower (1) is provided with a scrubbing water storage section and a wastewater discharge outlet (1-4) is provided in the scrubbing water storage section.

8. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 7, characterized in that: The scrubbing tower (1) is provided with a tower-breaking plate in the middle, which divides the scrubbing tower (1) into a lower section (1-5) and an upper section (1-6). 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) of the scrubbing tower are each provided with a set of scrubbing water circulation inlet and outlet. The pipes between the scrubbing water circulation inlet and outlet of the upper section (1-6) of the scrubbing tower are also connected in series with a scrubbing water circulation tank (1-7). The scrubbing water circulation tank (1-7) is provided with a water supply port. The scrubbing water circulation tank (1-7) is also connected to the lower section (1-5) of the scrubbing tower through a pipe.

9. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 8, characterized in that: A heat exchanger (1-8) is provided between the washing water circulation inlet of the upper section (1-6) of the washing tower and the flue gas exhaust port (1-2) at the top of the washing tower (1).

10. The sodium-zinc dual-alkali flue gas desulfurization device as described in claim 9, characterized in that: The heat exchangers (1-8) are plate heat exchangers or tube heat exchangers.

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