A flue gas desulfurization device with crystallization outside a desulfurization absorption tower

Abstract

A flue gas desulfurization device of desulfurization absorption tower external crystallization, comprising the following units, a flue gas desulfurization unit: comprising a main flue gas duct subunit, a desulfurization absorption subunit; a flue gas evaporation crystallization unit: comprising a secondary flue gas duct subunit, an evaporation crystallization subunit and a solid-liquid separation subunit connected in sequence; the desulfurization absorption subunit comprises a desulfurization absorption tower, a circulating pump, a circulating tank, a desulfurizer supply device, a process water supply device and an oxidizing air supply device; the main flue gas duct subunit comprises a pipeline connected to the desulfurization absorption tower as an inlet and outlet flue; a boiler induced draft fan and a damper are connected in series on the pipeline; one pipeline of the main flue gas is connected to the desulfurization absorption tower, and another pipeline is connected in parallel to a crystallization booster fan and a flue which is connected to the evaporation crystallization subunit; the evaporation crystallization subunit is additionally provided with two pipelines connected to the desulfurization absorption tower, one of which is used to introduce a desulfurization byproduct solution from the desulfurization absorption tower, and the other of which is used to return low-temperature flue gas to the desulfurization absorption tower.

Description

Technical fields:

[0001] This utility model belongs to the field of environmental protection and relates to a flue gas desulfurization process device that utilizes a portion of the waste heat of the original flue gas to achieve crystallization outside the desulfurization absorption tower. It is particularly suitable for flue gas desulfurization using sodium method, ammonia method, etc. Background Technology

[0002] Currently, the most commonly used flue gas desulfurization methods are wet desulfurization processes such as calcium, ammonia, and sodium methods, with the calcium method being the dominant one. Although sodium, magnesium, and ammonia methods have advantages over calcium methods, such as higher efficiency, no waste, good by-product market, no need for new mining resources, and greater environmental friendliness, the reliability, energy consumption, and crystal quality of by-product recovery and preparation processes limit the overall availability and economic efficiency of desulfurization units. This makes it difficult for these desulfurization processes to be widely used in large-scale thermal power plants and other applications where high reliability is required, and these types of desulfurization processes still only account for a small portion of the flue gas desulfurization market.

[0003] The crystallization method of desulfurization byproducts is a key factor restricting the reliability, energy consumption, and crystal quality of the equipment. Currently, there are two main methods for crystallizing byproducts: in-tower crystallization and out-of-tower crystallization. The application of desulfurization absorption in industries such as thermal power and metallurgy has resulted in a significant number of published technical patents, and the processes of the main units have become relatively mature.

[0004] The existing in-tower crystallization process involves direct contact and heat exchange between hot flue gas and ammonium sulfate slurry within the desulfurization absorption tower (including dual-tower structures). This concentrates the absorbent liquid and produces crystallized desulfurization byproducts. While this process effectively saves energy, the crystallization time is long, the crystal particles are small, and it easily causes blockages and equipment erosion in the unit (especially inside the desulfurization absorption tower). The tower also requires complex structures to prevent caking and scouring. The unit often shuts down due to difficulties in crystallization, caking within the tower, and damage to internal components, seriously affecting the safety, stability, and long-term operation of the desulfurization unit. This is a major factor restricting the wider adoption of this type of desulfurization process, especially since large coal-fired power plants rarely accept it.

[0005] Existing external crystallization processes involve setting up conventional single-effect or multi-effect evaporation crystallization units outside the desulfurization absorption tower. Uncrystallized desulfurization byproduct solutions are drawn from the absorption tower and heated by high-temperature steam to evaporate the solution, achieving concentration and crystallization. For example, Chinese Patent 2018220791521 discloses an evaporation crystallization device for ammonia-based desulfurization units. While this process boasts high crystallization efficiency and large crystal particles, its high energy consumption, complex process, difficult operation and maintenance, and high operating costs limit its adoption. It is rarely used, only in a few projects with specific requirements, and most existing systems are not yet operational.

[0006] Therefore, there is an urgent need for a more reliable and energy-efficient flue gas desulfurization crystallization process device to improve the performance of such desulfurization process devices. Summary of the Invention

[0007] The purpose of this invention is to provide a flue gas desulfurization device with external crystallization outside the desulfurization absorption tower. The raw flue gas entering the desulfurization unit is divided into two paths before entering the absorption tower. One path goes directly to the absorption tower of the desulfurization unit, while the other path first goes to the flue gas evaporation and crystallization unit to evaporate and crystallize the desulfurization absorbent outside the tower before entering the absorption tower for desulfurization treatment. A portion of the high-temperature raw flue gas is drawn from the pre-desulfurization absorption tower using a crystallization booster fan and fed into a separately installed flue gas evaporation and crystallization unit outside the absorption tower. In the evaporation and crystallization unit, this portion of high-temperature raw flue gas is fully mixed and contacted with the uncrystallized desulfurization absorbent produced by the desulfurization unit, undergoing direct heat exchange and adiabatic evaporation. The high-temperature raw flue gas evaporates the water in the desulfurization absorbent, lowering its own temperature. After the water in the desulfurization absorbent evaporates and concentrates to supersaturation, crystallization of desulfurization byproducts is produced. The desulfurization absorbent slurry containing desulfurization byproduct crystals produced by the flue gas evaporator crystallizer is sent to the solid-liquid separation unit to separate the solid desulfurization byproducts. After solid-liquid separation, the mother liquor is returned to the evaporator crystallizer for recycling. The low-temperature raw flue gas discharged from the flue gas evaporator crystallizer is sent back to the desulfurization unit for desulfurization purification.

[0008] The technical solution of this utility model is: a flue gas desulfurization device with external crystallization of a desulfurization absorption tower, comprising a flue gas desulfurization unit: this unit includes a main flue gas duct subunit, a desulfurization absorption subunit, and a flue gas evaporation crystallization unit: including an evaporation crystallization subunit and a solid-liquid separation subunit connected in sequence; the desulfurization absorption subunit includes a desulfurization absorption tower, a circulating pump, a circulating tank, a desulfurizing agent supply device, a process water supply device, and an oxidation air supply device; the main flue gas duct subunit includes a pipe connected to the desulfurization absorption tower as an inlet and outlet flue, with a boiler induced draft fan and a damper connected in series on the pipe; one main flue gas pipe is connected to the desulfurization absorption tower, and another pipe is connected in parallel to a crystallization booster fan and a duct, which is then connected to the evaporation crystallization subunit; the evaporation crystallization subunit is further provided with two pipes connected to the desulfurization absorption tower, one of which introduces the desulfurization by-product solution from the desulfurization absorption tower, and the other is for returning low-temperature flue gas to the desulfurization absorption tower.

[0009] The desulfurization absorption tower is equipped with multi-stage and multi-layer spray washing.

[0010] The flue gas evaporation crystallization unit includes a secondary flue gas duct sub-unit. This sub-unit comprises a booster fan and dampers connected in series in the inlet and outlet flues of the evaporation crystallization sub-unit. These components provide the power to overcome the unit's resistance and regulate the flow rate of the flue gas entering and exiting the evaporation crystallization unit, as well as distributing the flow between the flue gas desulfurization unit and the evaporation crystallization unit. The dampers are adjustable, allowing for the distribution and regulation of the flue gas flow between the two units. The adjustment range of the dampers and fans in the secondary flue gas duct sub-unit should preferably be 30%-100% of the design flow rate (i.e., all of it can be initially used in the crystallizer).

[0011] This utility model relates to a flue gas desulfurization device with external crystallization of desulfurization absorption towers. It addresses the problems of complex unit structures, frequent failures, poor reliability, and high construction and operating costs associated with existing desulfurization absorption tower processes that crystallize desulfurization byproducts within the tower due to the solid-containing circulating liquid. This device aims to meet the higher requirements of large-scale thermal power plants for desulfurization units. The application provides a process device that utilizes a portion of the waste heat from the original flue gas for external crystallization of the desulfurization absorption tower, completely separating desulfurization absorption from byproduct crystallization. A flue gas evaporation and crystallization unit is installed outside the flue gas desulfurization unit. The flue gas that originally directly enters the desulfurization unit is divided into two paths: one path goes directly to the desulfurization unit, and the other path first goes to the evaporation and crystallization unit to evaporate and crystallize the desulfurization absorption liquid outside the tower before entering the desulfurization unit for desulfurization treatment.

[0012] A portion of the high-temperature raw flue gas is drawn from the flue gas before it enters the desulfurization unit using a crystallization booster fan and fed into a separately installed flue gas evaporator crystallizer outside the desulfurization absorption tower. In the evaporator crystallizer, this portion of high-temperature raw flue gas is thoroughly mixed and contacted with the uncrystallized desulfurization absorbent produced by the desulfurization unit, undergoing direct heat exchange and adiabatic evaporation. The high-temperature raw flue gas evaporates the water in the desulfurization absorbent, lowering its own temperature. After the water in the desulfurization absorbent evaporates and concentrates to supersaturation, desulfurization byproduct crystals are produced. The desulfurization absorbent slurry containing the desulfurization byproduct crystals produced by the evaporator crystallizer is sent to a solid-liquid separation unit to separate the solid desulfurization byproducts. The mother liquor after solid-liquid separation is returned to the evaporator crystallizer for recycling. The low-temperature raw flue gas discharged from the evaporator crystallizer is sent back to the desulfurization unit for desulfurization purification.

[0013] Beneficial Effects: This application presents a process that utilizes a portion of the heat from the raw flue gas for external crystallization in the desulfurization absorption tower, completely separating desulfurization absorption from by-product crystallization. It combines the advantages of in-tower crystallization and external steam evaporation crystallization. On one hand, the circulating solution inside the desulfurization absorption tower and in the absorption circulation unit is a clear liquid without crystalline solids, solving the problems of slurry wear, scaling, and blockage that plague long-term operation of ammonia-based desulfurization units, and simplifying the desulfurization absorption process and structure. On the other hand, the desulfurization by-products undergo flue gas evaporation crystallization independently outside the desulfurization absorption tower, significantly reducing the content of impurities such as chloride ions in the desulfurization absorption unit. This avoids severe corrosion within the desulfurization unit and impurity poisoning of the desulfurization liquid, and also prevents the crystallization process from affecting desulfurization operation, improving the crystallization process and the overall device's ability to adapt to impurity interference. This application greatly improves the operational safety, reliability, and stability of ammonia-based and other desulfurization processes. Furthermore, this device utilizes the raw flue gas as the heat source for the evaporation crystallization of the desulfurization absorption liquid, eliminating the need for high-temperature steam. Compared to existing external evaporation crystallization processes using steam as a heat source, it offers lower investment, lower operating costs, and easier operation. This application significantly improves the reliability and economy of flue gas desulfurization processes such as ammonia-based methods, enabling these processes to meet the high operational requirements of large thermal power plants and other similar facilities, thus possessing broad market application prospects. This device is particularly suitable for flue gas desulfurization processes such as sodium-based, ammonia-based, and magnesium-based methods, as well as for retrofitting existing calcium-based desulfurization units using these processes. It offers significant economic, social, and environmental benefits.

[0014] The external crystallization device of this application combines the advantages of internal crystallization and external steam evaporation crystallization, significantly improving the operational safety, reliability, stability, and operability of the desulfurization unit, while reducing its construction costs. Furthermore, this device utilizes a portion of the flue gas heat as a heat source for the evaporation crystallization of the desulfurization absorbent, eliminating the need for external high-temperature steam. This is more energy-efficient and requires less investment compared to existing conventional evaporation crystallization processes that use external steam heating. The independent flue gas evaporation crystallization unit set up in this application does not affect the normal operation of the flue gas desulfurization unit. The operating time and output of the flue gas evaporation crystallization unit can be flexibly adjusted according to production conditions, thereby optimizing operating costs. This application significantly improves the reliability and economy of flue gas desulfurization processes such as ammonia-based methods, enabling these processes to meet the operational requirements of large-scale thermal power plants, giving them greater longevity and a broad market prospect. This device is particularly suitable for flue gas desulfurization processes such as sodium-based, ammonia-based, and magnesium-based methods, as well as for retrofitting existing calcium-based desulfurization units using these processes. Attached Figure Description

[0015] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0016] Figure 1This is a unit structure diagram of a flue gas desulfurization device with external crystallization in a desulfurization absorption tower according to this application;

[0017] Figure 2 This is a flowchart illustrating an embodiment of a flue gas desulfurization device for external crystallization in a desulfurization absorption tower, as described in this application.

[0018] Appendix Figure 1 Marker explanation:

[0019] 1-Desulfurizing agent 2-Water 3-Oxidizing air 4-Desulfurization absorption unit 5, 7, 8, 10-High temperature raw flue gas 6-Boiler induced draft fan 9-Crystallization booster fan 11-Evaporation crystallization unit 12-Desulfurization by-product solution 13-Low temperature raw flue gas 14-Slurry containing desulfurization by-product crystals 15-Solid-liquid separation unit 16-Solid-liquid separation mother liquor 17-Solid desulfurization by-product 18-Clean flue gas 19-Flue gas evaporation crystallization unit 20-Flue gas desulfurization unit;

[0020] Figure 2 In the middle: 21-Desulfurization absorption tower 22-Slurry pool 23-Desulfurization tower inlet 24-Desulfurization tower clean flue gas outlet 25-Raw flue gas 26-Raw flue gas duct 27-Inlet flue gas damper for crystallizer 28-Outlet flue gas damper for crystallizer 29-Crystallization flue gas booster fan 30-Crystallizer 31-Solid-liquid separation unit 32-Solid-liquid separation mother liquor return pump 33-Solid-liquid separation unit feed pump 34-Crystallization circulation pump 35-Crystallizer feed pump 36-Desulfurization cooling and washing circulation pump 37-Desulfurization circulation pump 38-Desulfurization circulation tank 39-Desulfurization absorption tower inlet damper. Detailed Implementation

[0021] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0022] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having" and any variations thereof in the specification and claims of this application are open-ended expressions, that is, they include the content specified in this application but do not exclude other aspects.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions, and all technical features and optional technical features of this application can be combined to form new technical solutions.

[0024] The present invention describes a flue gas desulfurization device with external crystallization of a desulfurization absorption tower. It utilizes a portion of the original flue gas heat for external crystallization of the desulfurization absorption tower, completely separating the desulfurization absorption from the by-product crystallization output. A flue gas evaporation and crystallization unit is set up outside the flue gas desulfurization unit. The flue gas that originally directly enters the flue gas desulfurization unit is divided into two paths: one path goes directly to the flue gas desulfurization unit, and the other path first goes to the flue gas evaporation and crystallization unit to evaporate and crystallize the desulfurization absorption liquid outside the tower before entering the flue gas desulfurization unit for desulfurization treatment.

[0025] A portion of the high-temperature raw flue gas is drawn from the flue gas before it enters the desulfurization unit using a crystallization booster fan and fed into a separately installed flue gas evaporator crystallizer outside the desulfurization absorption tower. In the evaporator crystallizer, this portion of high-temperature raw flue gas is thoroughly mixed and contacted with the uncrystallized desulfurization absorbent produced by the desulfurization unit, undergoing direct heat exchange and adiabatic evaporation. The high-temperature raw flue gas evaporates the water in the desulfurization absorbent, lowering its own temperature. After the water in the desulfurization absorbent evaporates and concentrates to supersaturation, desulfurization byproduct crystals are produced. The desulfurization absorbent slurry containing the desulfurization byproduct crystals produced by the evaporator crystallizer is sent to a solid-liquid separation unit to separate the solid desulfurization byproducts. The mother liquor after solid-liquid separation is returned to the evaporator crystallizer for recycling. The low-temperature raw flue gas discharged from the evaporator crystallizer is sent back to the desulfurization unit for desulfurization purification.

[0026] This utility model comprises two units: a flue gas desulfurization unit and a flue gas evaporation and crystallization unit.

[0027] (1) Flue gas desulfurization unit: includes main flue gas duct sub-unit and desulfurization absorption sub-unit, used to desulfurize and purify the sulfur-containing high-temperature raw flue gas from the boiler and the sulfur-containing low-temperature raw flue gas from the external evaporation and crystallization unit to meet emission standards, and generate high-concentration desulfurization by-product unsaturated solution, which is sent to the flue gas evaporation and crystallization unit for treatment.

[0028] (2) Flue gas evaporation and crystallization unit: includes a secondary flue gas duct sub-unit, an evaporation and crystallization sub-unit, and a solid-liquid separation sub-unit. It is used to evaporate and concentrate a portion of the high-temperature raw flue gas to produce desulfurization by-product solution to produce desulfurization by-product crystal solid. The desulfurization by-product crystal solid is then processed further or sold directly. The low-temperature sulfur-containing flue gas discharged from the flue gas evaporation and crystallization unit is then purified by the flue gas desulfurization unit.

[0029] The flue gas desulfurization unit includes a main flue gas duct subunit and a desulfurization absorption subunit.

[0030] (1) Main flue gas duct unit: includes equipment such as boiler induced draft fan, inlet and outlet flue gas ducts of desulfurization absorption tower with dampers. It is used to provide power for the flue gas entering and leaving the flue gas desulfurization unit and flue gas evaporation and crystallization unit to overcome the unit resistance and to distribute and regulate the flue gas flow between the two units.

[0031] (2) Desulfurization absorption unit: includes equipment such as desulfurization absorption tower, circulating pump, circulating tank, desulfurizing agent supply device, process water supply device, and oxidation air supply device. It is used to desulfurize and purify low-temperature raw flue gas from high-temperature boiler flue gas and flue gas evaporation and crystallization unit, and to produce a high-concentration unsaturated solution of desulfurization by-product.

[0032] The desulfurization absorption tower is equipped with multi-stage, multi-layer spray washing. The desulfurization absorbent from each stage forms a concentration gradient, and the highest concentration of the absorbent is controlled below the saturation concentration of the desulfurization byproducts. The entire desulfurization process is crystallization-free, maintaining high-efficiency desulfurization while producing a high-concentration desulfurization byproduct solution. The concentration of the produced high-concentration desulfurization byproduct solution is 80%-99% of the saturation concentration of desulfurization byproducts under operating conditions, preferably 95%-97%.

[0033] The flue gas evaporation and crystallization unit includes a secondary flue gas duct sub-unit, an evaporation and crystallization sub-unit, and a solid-liquid separation sub-unit.

[0034] (1) Secondary flue gas duct sub-unit: includes a booster fan and evaporator inlet and outlet flue gas ducts with dampers, used to provide power for the flue gas entering and leaving the flue gas evaporation and crystallization unit to overcome the unit resistance and to distribute and regulate the flue gas flow between the flue gas desulfurization unit and the flue gas evaporation and crystallization unit.

[0035] (2) Evaporation and crystallization sub-unit: equipment such as flue gas evaporation crystallizer, circulating pump, and discharge pump are used to evaporate and concentrate the high-concentration desulfurization by-product solution and solid-liquid separation mother liquor from the flue gas desulfurization unit in the flue gas evaporation crystallizer to produce desulfurization by-product crystals. The slurry containing desulfurization by-product crystals is sent to the solid-liquid separation sub-unit for treatment. The low-temperature sulfur-containing flue gas discharged from the flue gas evaporation crystallizer is sent to the flue gas desulfurization unit for purification treatment.

[0036] (3) Solid-liquid separation unit: includes thickening equipment, centrifugal separation or filtration equipment, feed tank, mother liquor tank, pump, etc. It is used to separate the crystals in the slurry containing desulfurization by-product crystals generated by the flue gas evaporation and crystallization unit to produce solid desulfurization by-product products, and the separated mother liquor is sent back to the flue gas evaporation and crystallization unit for recycling.

[0037] The flue gas flow rate of the flue gas evaporation and crystallization unit is determined according to the evaporation and crystallization requirements of the maximum by-product yield. The damper and fan adjustment range of the secondary flue unit should be 30%-100% of the design flow rate.

[0038] The flue gas evaporator crystallizer is used to thoroughly mix and contact the high-temperature raw flue gas with the uncrystallized desulfurization absorbent and solid-liquid separation mother liquor produced by the flue gas desulfurization unit. Direct heat exchange and adiabatic evaporation occur, and the high-temperature raw flue gas evaporates the water in the desulfurization absorbent, lowering its own temperature. After the water in the desulfurization absorbent evaporates and concentrates to supersaturation, desulfurization byproducts crystallize. The gas-liquid contact within the flue gas evaporator crystallizer employs structural forms that promote crystal growth and provide self-cleaning capabilities, such as large-particle spraying, bubbling, liquid columns, and perforated plates.

[0039] The temperature of the high-temperature raw flue gas entering the flue gas evaporator crystallizer is not less than 85℃ (preferably 100℃-180℃), and the water content is not more than 12% V / V (preferably not more than 8%); the temperature of the low-temperature raw flue gas exiting the flue gas evaporator crystallizer is not more than 75℃ (preferably 60℃-70℃), and the relative humidity is not less than 50% (preferably 60%-80%).

[0040] When there are multiple flue gas desulfurization units in a flue gas desulfurization system, the flue gas evaporation and crystallization unit can be set up to be shared by multiple flue gas desulfurization units.

[0041] The flue gas flow rate of the flue gas evaporation and crystallization unit is determined according to the evaporation and crystallization capacity of the maximum by-product design output. The damper and fan adjustment range of the secondary flue unit should be 30%-100% of the design flow rate.

[0042] The mechanism of this utility model is shown in the appendix. Figure 1 , Figure 2 ;

[0043] The process method of this application will be further explained below with reference to a specific embodiment:

[0044] Example 1:

[0045] A coal-fired power plant's 400t / h boiler flue gas ammonia desulfurization unit uses ammonia water as the desulfurizing agent, with fertilizer-grade ammonium sulfate as a byproduct. The boiler induced draft fan draws 500,000 Nm³ of raw flue gas for desulfurization. 3 / h, flue gas temperature 110℃, SO2 content in raw flue gas 2000mg / Nm³ 3 Dust content 10mg / Nm 3 The water content is 6%. This utility model employs an external crystallization process for flue gas desulfurization absorption towers, where all desulfurization units use a circulating solution.

[0046] Structure and Methods:

[0047] A unit diagram of the external crystallization method for flue gas desulfurization absorption tower is attached. Figure 1 The flowchart of the method for external crystallization in flue gas desulfurization absorption tower is attached. Figure 2 .

[0048] Main features: This ammonia-based desulfurization unit, which uses external crystallization outside the desulfurization absorption tower for flue gas desulfurization, is equipped with two units: a flue gas desulfurization unit 20 and a flue gas evaporation and crystallization unit 19.

[0049] (1) Flue gas desulfurization unit 20: includes main flue gas duct sub-unit and desulfurization absorption sub-unit 4, used to desulfurize and purify sulfur-containing high-temperature raw flue gas 5 from boiler and sulfur-containing low-temperature raw flue gas 13 from flue gas evaporation and crystallization unit 19 to meet emission standards, and generate high-concentration ammonium sulfate unsaturated solution 12, which is sent to flue gas evaporation and crystallization unit 19 for treatment;

[0050] (2) Flue gas evaporation and crystallization unit 19: includes a secondary flue gas duct sub-unit, an evaporation and crystallization sub-unit 11, and a solid-liquid separation sub-unit 15. It is used to evaporate and concentrate ammonium sulfate solution 12 with a portion of high-temperature raw flue gas 8 to produce ammonium sulfate crystal solid 17. The ammonium sulfate crystal solid 17 is sent for further processing or sold externally. The low-temperature sulfur-containing flue gas 13 discharged from the flue gas evaporation and crystallization unit 19 is sent to the flue gas desulfurization unit 20 for treatment.

[0051] Flue gas desulfurization unit 20 includes a main flue gas duct sub-unit and a desulfurization absorption sub-unit 4.

[0052] (1) Main flue gas duct unit: includes boiler induced draft fan 6, desulfurization absorption tower inlet and outlet flue gas ducts with dampers, etc. It is used to provide power for the flue gas entering and leaving the flue gas desulfurization unit 20 and flue gas evaporation and crystallization unit 19 to overcome the unit resistance and to distribute and regulate the flue gas flow between the two units.

[0053] (2) Desulfurization absorption unit 4: includes desulfurization absorption tower ( Figure 2 Desulfurization absorption tower 21), circulating pump ( Figure 2 Circulation pump 36, circulation pump 37), circulation tank ( Figure 2 Equipment including a central circulation tank 38), a desulfurizing agent supply device 1, a process water supply device 2, and an oxidation air supply device 3. These are used for desulfurization and purification of the boiler's high-temperature raw flue gas 5 and the low-temperature raw flue gas 13 from the flue gas evaporation and crystallization unit 19, producing a high-concentration unsaturated ammonium sulfate solution 12.

[0054] Desulfurization absorption tower ( Figure 2 The desulfurization absorption tower 21) is equipped with multi-stage, multi-layer spray washing. The desulfurization absorbent from each stage forms a concentration gradient, and the highest concentration of the desulfurization absorbent is controlled below the saturation concentration of ammonium sulfate. The entire desulfurization process is free of crystallization, maintaining high-efficiency desulfurization while producing a high-concentration ammonium sulfate solution. The concentration of the produced high-concentration ammonium sulfate solution 12 is 80%-99% of the saturation concentration of ammonium sulfate under operating conditions, preferably 95%-97%.

[0055] The flue gas evaporation and crystallization unit 19 includes a secondary flue gas duct sub-unit, an evaporation and crystallization sub-unit 11, and a solid-liquid separation sub-unit 15.

[0056] (1) Secondary flue gas duct sub-unit: includes booster fan 9 and evaporator inlet and outlet flue gas duct with damper, used to provide power for the flue gas entering and leaving flue gas evaporation crystallization unit 19 to overcome the unit resistance and to distribute and regulate the flue gas flow between the desulfurization absorption unit 4 and the flue gas evaporation crystallization unit 19.

[0057] (2) Evaporation and Crystallization Unit 11: Includes a flue gas evaporation crystallizer ( Figure 2 Medium crystallizer 30), circulating pump ( Figure 2 Circulating pump 34), Discharge pump ( Figure 2 Equipment such as the solid-liquid separation condenser pump 33 is used to evaporate and concentrate the high-concentration ammonium sulfate solution 12 and solid-liquid separation mother liquor 16 from the flue gas desulfurization unit in the flue gas evaporator crystallizer to produce ammonium sulfate crystals. The slurry 14 containing ammonium sulfate crystals is sent to the solid-liquid separation sub-unit 15 for processing, and the slurry is discharged from the flue gas evaporator crystallizer. Figure 2 The low-temperature sulfur-containing flue gas discharged from the intermediate crystallizer 30 is treated by the flue gas desulfurization unit.

[0058] (3) Solid-liquid separation unit 15: includes thickening equipment, centrifugal separation or filtration equipment, feed tank, mother liquor tank, pump, etc. It is used to separate the crystals in the slurry 14 containing ammonium sulfate crystals produced by the flue gas evaporation crystallization unit 19 to produce ammonium sulfate solid product 17, and the separation mother liquor 16 is sent back to the flue gas evaporation crystallization unit 11 for recycling.

[0059] The flue gas flow rate of the flue gas evaporation and crystallization unit 19 is 160,000 Nm³. 3 / h, maximum by-product output 2000kg / h, the damper and fan adjustment range of the secondary flue unit should be 30%-100% of the design flow rate.

[0060] Flue gas evaporation crystallizer ( Figure 2 The intermediate crystallizer 30 is used to fully mix and contact the high-temperature raw flue gas 10 with the uncrystallized desulfurization absorbent 12 and solid-liquid separation mother liquor 16 produced by the flue gas desulfurization unit, through direct heat exchange and adiabatic evaporation. The high-temperature raw flue gas 10 evaporates the water in the desulfurization absorbent, lowering its own temperature. After the solution is supersaturated due to water evaporation and concentration, ammonium sulfate crystals are produced. ​ The intermediate crystallizer (30) is equipped with a slurry pool and a flue gas distribution pipe, and gas-liquid contact is achieved through bubbling. The high-temperature raw flue gas entering the flue gas evaporation crystallizer has a temperature of 110℃ and a water content of 6% V / V; the low-temperature raw flue gas exiting the flue gas evaporation crystallizer has a temperature of 65℃ and a relative humidity of 70%.

[0061] The effect of this embodiment:

[0062] The sulfur dioxide content in the flue gas after desulfurization is less than 30 mg / Nm³. 3Dust content less than 2mg / Nm 3 The droplet content is less than 20 mg / Nm 3 The desulfurization process involves circulating a clear solution, allowing the desulfurization unit to operate continuously and stably for over 400 days (compared to an average continuous operating time of less than 150 days for existing in-tower crystallization ammonia desulfurization units). The raw flue gas entering the flue gas evaporation crystallization unit can be adjusted based on the amount of byproducts, while the amount of flue gas processed by the flue gas desulfurization absorption tower remains constant. This ensures stable operation of the desulfurization unit and eliminates factors that severely affect its stable operation, such as scaling, blockage, internal component damage, and circulating pump wear, present in in-tower crystallization ammonia desulfurization processes. This significantly improves the unit's availability and ensures that desulfurization does not disrupt main production, guaranteeing synchronized and efficient operation with the main production unit. The total investment cost is reduced by approximately 10% compared to existing in-tower crystallization processes, and the improved reliability reduces operating and maintenance costs by 15%. Operating costs are also reduced by 25% compared to existing external steam evaporation crystallization processes. The average particle size of the ammonium sulfate crystals is approximately 1.5 mm, significantly higher than the average particle size of approximately 0.15 mm in in-tower crystallization, resulting in a marked improvement in ammonium sulfate quality. The crystallization process described in this application also improves the crystallization process's ability to adapt to impurities. Existing evaporation crystallization in towers often encounters difficulties in crystallization due to impurities such as desulfurized ammonia water and flue gas dust. This application basically eliminates such phenomena.

[0063] The above embodiments are not intended to limit this utility model in any way, but are used to explain the process principle and flow of this application. Any other improvements and applications made to the above embodiments by equivalent transformation are within the protection scope of this utility model. These modifications, whether adjustments to unit structure, process flow, or specific parameters, do not affect the actual effect of this application and should be included within the patent protection scope of this application.

Claims

1. A flue gas desulfurization device for external crystallization of a desulfurization absorption tower, characterized in that... It includes the following units: Flue gas desulfurization unit: includes main flue gas duct sub-unit and desulfurization absorption sub-unit; The flue gas evaporation and crystallization unit comprises a secondary flue gas duct sub-unit, an evaporation and crystallization sub-unit, and a solid-liquid separation sub-unit connected in sequence. The desulfurization absorption unit includes a desulfurization absorption tower, a circulating pump, a circulating tank, a desulfurizing agent supply device, a process water supply device, and an oxidation air supply device. The main flue gas duct unit includes a pipe connected to the desulfurization absorption tower as an inlet and outlet flue. A boiler induced draft fan and a damper are connected in series on the pipe. One pipe of the main flue gas is connected to the desulfurization absorption tower, and the other pipe in parallel is connected to a crystallization booster fan and a duct, which is then connected to the evaporation and crystallization unit. The evaporation and crystallization unit is also equipped with two pipes connected to the desulfurization absorption tower. One pipe introduces the desulfurization by-product solution from the desulfurization absorption tower, and the other pipe returns the low-temperature flue gas to the desulfurization absorption tower.

2. The flue gas desulfurization device for external crystallization of the desulfurization absorption tower according to claim 1, characterized in that, The desulfurization absorption tower is equipped with multi-stage and multi-layer spray washing.

3. The flue gas desulfurization device for external crystallization of the desulfurization absorption tower according to claim 1, characterized in that, The flue gas evaporation and crystallization unit includes a secondary flue gas duct subunit: the secondary flue gas duct subunit includes a booster fan and a damper connected in series in the inlet and outlet flues of the evaporation and crystallization subunit, which are used to provide the flue gas entering and leaving the flue gas evaporation and crystallization unit with the power to overcome the unit resistance and to distribute and regulate the flue gas flow between the flue gas desulfurization unit and the flue gas evaporation and crystallization unit.

4. The flue gas desulfurization device for external crystallization of the desulfurization absorption tower according to claim 1, characterized in that, Evaporation and crystallization unit: Includes flue gas evaporation crystallizer, circulation pump and discharge pump, used to evaporate and concentrate the high-concentration desulfurization by-product solution and solid-liquid separation mother liquor from the flue gas desulfurization unit in the flue gas evaporation crystallizer to produce desulfurization by-product crystals. The slurry containing desulfurization by-product crystals is sent to the solid-liquid separation unit for processing, and the low-temperature sulfur-containing flue gas discharged from the flue gas evaporation crystallizer is sent to the flue gas desulfurization unit for processing.

5. The flue gas desulfurization device for external crystallization of the desulfurization absorption tower according to claim 1, characterized in that, Solid-liquid separation unit: includes thickening equipment, centrifugal separation or filtration equipment, feed tank, mother liquor tank and pump; This is used to separate the solid desulfurization byproducts from the slurry produced by the flue gas evaporation crystallization unit, and the mother liquor is sent back to the flue gas evaporation crystallization unit for recycling.

6. The flue gas desulfurization device for external crystallization of the desulfurization absorption tower according to claim 1, characterized in that, The flue gas flow rate of the flue gas evaporation and crystallization unit is determined based on the evaporation and crystallization capacity of the maximum designed by-product output. The damper and fan adjustment range of the secondary flue unit is 30%-100% of the design flow rate.

7. The flue gas desulfurization device for external crystallization of the desulfurization absorption tower according to claim 4, characterized in that, The flue gas evaporator crystallizer is used to fully mix and contact the high-temperature raw flue gas with the uncrystallized desulfurization absorbent and solid-liquid separation mother liquor produced by the flue gas desulfurization unit, directly exchange heat, and perform adiabatic evaporation. The high-temperature raw flue gas evaporates the water in the desulfurization absorbent and then lowers its own temperature. After the water in the desulfurization absorbent evaporates and is concentrated to supersaturation, desulfurization by-product crystallization is produced. The gas-liquid contact in the flue gas evaporator crystallizer adopts a structure with large-particle-diameter spraying, bubbling, liquid column and orifice plate to facilitate crystal growth and has self-cleaning ability.

8. The flue gas desulfurization device for external crystallization of the desulfurization absorption tower according to claim 1, characterized in that, When there are multiple flue gas desulfurization units in a flue gas desulfurization system, the flue gas evaporation and crystallization unit is set up to be shared by multiple flue gas desulfurization units.

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