Method for crystallizing outside desulfurization tower for flue gas desulfurization
By setting up an evaporation and crystallization unit outside the flue gas desulfurization unit, the original flue gas is divided into two channels for evaporation and crystallization outside the tower, which solves the equipment reliability and energy consumption problems in the existing processes, and realizes efficient and low-cost recycling of desulfurization by-products, which is suitable for large thermal power plants.
Patent Information
- Application Number
- CN202510799142.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-16
- Publication Date
- 2025-08-15
AI Technical Summary
The reliability, energy consumption and crystallization quality of the by-product recycling and preparation process equipment of existing flue gas desulfurization processes such as calcium, ammonia, and magnesium have made it difficult for these processes to be widely used in large thermal power plants.
A flue gas evaporation and crystallization unit is arranged outside the flue gas desulfurization unit, and the original flue gas is divided into two channels, one directly enters the desulfurization absorption tower, and the other first enters the evaporation and crystallization outside the tower. The high-temperature raw flue gas is mixed with the uncrystallized desulfurization absorber, and the desulfurization by-product crystallization is produced through adiabatic evaporation, and the mother liquid is recycled after solid-liquid separation.
It improves the operating safety, reliability and stability of the desulfurization process, reduces energy consumption and operating costs, adapts to the high requirements of large thermal power plants, and improves the adaptability and economicality of the crystallization process.
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Figure CN120479002A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of environmental protection, and relates to a flue gas desulfurization process technology that utilizes a portion of the waste heat of the original flue gas to achieve crystallization outside the desulfurization absorption tower, and is particularly suitable for flue gas desulfurization processes such as the sodium method and the ammonia method. Background Art
[0002] Currently, the most commonly used wet desulfurization processes for sulfur-containing flue gas desulfurization are calcium, ammonia, and sodium, with calcium being the dominant method. While sodium, magnesium, and ammonia desulfurization processes offer advantages over calcium desulfurization, such as higher efficiency, elimination of the three wastes, a favorable byproduct market, no need for new mining resources, and environmental friendliness, the reliability, energy consumption, and crystal quality of the byproduct recovery and preparation equipment in these desulfurization processes limit the overall availability and economic viability of the desulfurization equipment. This makes these desulfurization processes difficult to widely apply in applications with high reliability requirements, such as large-scale thermal power plants where flue gas desulfurization accounts for a large share of the market. Consequently, these desulfurization processes still only account for a small portion of the flue gas desulfurization market.
[0003] The crystallization method of desulfurization by-products is a key factor that affects the reliability, energy consumption and crystallization quality of the device. Currently, there are two main crystallization methods for by-products: in-tower crystallization and out-tower crystallization.
[0004] The existing in-tower crystallization process is to carry out direct contact and heat exchange between hot flue gas and ammonium sulfate slurry in a desulfurization absorption tower (including a double-tower structure), thereby achieving concentration of the absorption liquid and producing crystals of desulfurization by-products. This method can effectively save energy consumption, but the crystallization time is long, the crystal particles are small, and it is easy to cause blockage of the unit (especially in the desulfurization tower) and equipment abrasion. Complex anti-agglomeration flushing and anti-scouring wear structures are also required in the tower. The device is often shut down due to crystallization difficulties, agglomeration in the tower, damage to internal parts, etc., which seriously affects the safety, stability and long-term operation of the desulfurization unit. This is also a factor that seriously restricts the wider promotion of this type of desulfurization process, especially large coal-fired power plants rarely accept it.
[0005] The existing off-tower crystallization process involves installing a conventional single- or multi-effect evaporation crystallization unit outside the desulfurization tower. Uncrystallized desulfurization byproduct solution is drawn from the desulfurization tower, where high-temperature steam provides heat energy for evaporation, achieving concentrated crystallization. This process offers high crystallization efficiency and large crystal particles, but its high energy consumption, complex process, difficult operation and maintenance, and high operating costs have limited its adoption, limiting it to specialized projects. Most existing units are not operational.
[0006] Therefore, there is an urgent need for a more reliable and energy-saving flue gas desulfurization crystallization process to improve and upgrade this type of desulfurization process. Summary of the Invention
[0007] The purpose of the present invention is to provide a method for crystallization outside a desulfurization tower for flue gas desulfurization, wherein the raw flue gas entering the flue gas desulfurization is divided into two paths before entering the desulfurization absorption tower. One path goes directly to the desulfurization absorption tower of 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 desulfurization absorption tower of the flue gas desulfurization unit for desulfurization treatment. A portion of the high-temperature raw flue gas before entering the desulfurization absorption tower is extracted by a crystallization booster fan from the high-temperature raw flue gas before entering a flue gas evaporation crystallizer independently arranged outside the desulfurization absorption tower. In the flue gas evaporation crystallizer, this portion of the high-temperature raw flue gas is fully mixed and contacted with the uncrystallized desulfurization absorption liquid produced by the flue gas desulfurization unit, directly exchanged heat, and evaporated adiabatically. The high-temperature raw flue gas evaporates the water in the desulfurization absorption liquid and its own temperature is lowered. After the water in the desulfurization absorption liquid evaporates and concentrates to supersaturation, desulfurization by-product crystals are generated. The desulfurization absorption liquid slurry containing desulfurization byproduct crystals produced by the flue gas evaporation crystallizer is sent to the solid-liquid separation unit to separate the desulfurization byproduct solids. After solid-liquid separation, the mother liquor is returned to the evaporation crystallizer for recycling. The low-temperature raw flue gas discharged from the flue gas evaporation crystallizer is returned to the desulfurization unit for desulfurization and purification.
[0008] The technical solution of the present invention is: a method for crystallization outside a desulfurization tower for flue gas desulfurization, based on two units: a flue gas desulfurization unit and a flue gas evaporation and crystallization unit. The flue gas desulfurization unit includes a main flue gas duct subunit and a desulfurization absorption subunit; the flue gas evaporation and crystallization unit includes an evaporation and crystallization subunit and a solid-liquid separation subunit connected in sequence; the main flue gas duct subunit includes a pipeline connected to the desulfurization absorption tower as an inlet and outlet flue, and the pipeline is connected in series with a boiler induced draft fan and an air door: one pipeline of the main flue gas is connected to the desulfurization absorption tower, and the other pipeline is connected in parallel to the crystallization booster fan and the air duct and then to the evaporation and crystallization subunit; the evaporation and crystallization subunit is also provided with two pipelines connected to the desulfurization absorption tower, one is a pipeline for transporting the desulfurization by-product solution to the desulfurization absorption tower, and the other is a pipeline for returning the low-temperature sulfur-containing flue gas to the desulfurization absorption tower;
[0009] Desulfurization absorption subunit: includes desulfurization absorption tower, circulation pump, circulation tank, desulfurizer supply device, process water supply device, and oxidation air supply device;
[0010] The flue gas desulfurization unit desulfurizes and purifies the sulfur-containing high-temperature raw flue gas from the boiler and the sulfur-containing low-temperature raw flue gas from the evaporation and crystallization unit outside the tower, and then produces a high-concentration desulfurization by-product unsaturated solution, which is sent to the flue gas evaporation and crystallization unit for treatment;
[0011] The main flue duct subunit is used to provide the flue gas entering and exiting the flue gas desulfurization unit and the flue gas evaporation crystallization unit with power to overcome the resistance of the units and to distribute the flue gas flow between the two units. The damper is adjustable to distribute and regulate the flue gas flow between the flue gas desulfurization unit and the flue gas evaporation crystallization unit. The damper and fan of the secondary flue duct subunit should be adjustable within a range of 30%-100% of the design flow, so that all of the flow can be used primarily for the crystallization unit.
[0012] Desulfurization absorption subunit: used for desulfurization and purification of high-temperature raw flue gas from boilers and flue gas evaporation and crystallization units to produce high-concentration unsaturated solution of desulfurization by-products.
[0013] Flue gas evaporation and crystallization unit: It includes a secondary flue gas duct subunit, an evaporation and crystallization subunit, and a solid-liquid separation subunit. It is used to use a part of the high-temperature original flue gas to evaporate and concentrate the desulfurization by-product solution to produce desulfurization by-product crystalline solids; the desulfurization by-product crystalline solids are further processed or directly exported, and the low-temperature sulfur-containing flue gas discharged from the flue gas evaporation and crystallization unit is sent to the flue gas desulfurization unit for purification treatment.
[0014] A part of the waste heat of the original flue gas is used for crystallization outside the desulfurization absorption tower, and the desulfurization absorption and by-product crystallization output are completely separated. A flue gas evaporation crystallization unit is set up outside the flue gas desulfurization unit. The original flue gas that originally directly enters the flue gas desulfurization unit is divided into two routes. One route goes directly to the flue gas desulfurization unit, and the other route goes to the flue gas evaporation crystallization unit first. The desulfurization absorption liquid is evaporated and crystallized outside the tower to become low-temperature original flue gas and then enters the flue gas desulfurization unit for desulfurization treatment.
[0015] Furthermore, a crystallization booster blower extracts a portion of the high-temperature raw flue gas from the desulfurization unit before it enters the flue gas evaporation crystallizer, which is independently installed outside the desulfurization absorption tower. In the flue gas evaporation crystallizer, this portion of high-temperature raw flue gas is fully mixed and contacted with the uncrystallized desulfurization absorbent produced by the flue gas 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 desulfurization absorbent evaporates and concentrates to supersaturation, desulfurization by-product crystals are produced. The desulfurization absorbent slurry containing desulfurization by-product crystals produced by the flue gas evaporation crystallizer is sent to a solid-liquid separation unit to separate and produce the desulfurization by-product solids. After solid-liquid separation, the mother liquor is returned to the evaporation crystallizer for recycling. The low-temperature raw flue gas discharged from the flue gas evaporation crystallizer is returned to the desulfurization unit for desulfurization purification. Different settings can be used for different concentrations, such as ammonia, sodium, and magnesium methods.
[0016] Furthermore, the desulfurization absorption tower is equipped with multi-stage, multi-layer spray washing. The desulfurization absorption liquid in each washing stage forms a concentration gradient. The maximum concentration of the desulfurization absorption liquid is controlled below the saturation concentration of the desulfurization by-products. The entire desulfurization process is crystallization-free, maintaining efficient desulfurization while producing a high-concentration desulfurization by-product solution. The concentration of the produced high-concentration desulfurization by-product solution is 80%-99%, preferably 95%-97%, of the desulfurization by-product saturation concentration under operating conditions.
[0017] The desulfurization absorption tower is equipped with multi-stage, multi-layer spray washing. The desulfurization absorption liquid in each washing stage forms a concentration gradient. The maximum concentration of the desulfurization absorption liquid is controlled below the saturation concentration of the desulfurization by-product. The entire desulfurization process is crystallization-free, maintaining efficient desulfurization while producing a high-concentration desulfurization by-product solution. The concentration of the produced high-concentration desulfurization by-product solution is 80%-99% of the saturation concentration of the desulfurization by-product under operating conditions, preferably 95%-97%.
[0018] In the flue gas evaporation crystallization unit:
[0019] (1) Secondary flue gas duct subunit: It includes a booster fan and an evaporator inlet and outlet flue gas duct with an air damper, which is used to provide the flue gas entering and leaving the flue gas evaporation and crystallization unit with power to overcome the unit resistance and to distribute and adjust the flue gas flow between the flue gas desulfurization unit and the flue gas evaporation and crystallization unit.
[0020] (2) Evaporation crystallization subunit: Flue gas evaporation crystallizer, circulation pump, discharge pump and other equipment 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 subunit for treatment, and 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.
[0021] (3) Solid-liquid separation subunit: It includes thickening equipment, centrifugal separation or filtration equipment, feed liquid tank, mother liquor tank, pump, etc. It is used to separate the crystals from the slurry containing desulfurization by-product crystals produced by the flue gas evaporation crystallization unit to produce desulfurization by-product solid products, and the separated mother liquor is returned to the flue gas evaporation crystallization unit for recycling.
[0022] The flue gas flow rate entering the flue gas evaporation crystallization unit is determined according to the evaporation crystallization needs of the maximum by-product output, and the damper and fan adjustment range of the secondary flue sub-unit should be 30%-100% of the design flow rate.
[0023] The flue gas evaporation crystallizer is used to fully mix and contact the high-temperature raw flue gas with the uncrystallized desulfurization absorption liquid and solid-liquid separation mother liquor produced by the flue gas desulfurization unit, directly exchange heat, and evaporate adiabatically. The high-temperature raw flue gas evaporates the water in the desulfurization absorption liquid and lowers its own temperature. After the desulfurization absorption liquid evaporates and concentrates to supersaturation, desulfurization by-product crystals are generated. The gas-liquid contact in the flue gas evaporation crystallizer adopts large-particle spraying, bubbling, liquid column, orifice plate and other structures that are conducive to crystal growth and have self-cleaning capabilities. The temperature of the high-temperature raw flue gas entering the flue gas evaporation crystallizer is not less than 85°C (preferably 100°C-180°C) 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 evaporation crystallizer is not more than 75°C (preferably 60°C-70°C) and the relative humidity is not less than 50% (preferably 60%-80%).
[0024] When the flue gas desulfurization device has multiple flue gas desulfurization units, the flue gas evaporation crystallization unit can be set to be shared by multiple flue gas desulfurization units.
[0025] A flue gas desulfurization method for crystallization outside a desulfurization absorption tower is designed to solve the problems of complex unit structure, frequent failures, poor reliability, high construction costs, and high operating costs caused by the desulfurization circulating liquid being a solid-containing slurry in the existing desulfurization absorption tower, so as to meet the higher requirements of large thermal power plants for desulfurization units. The present application provides a process device that utilizes the waste heat of a portion of the original flue gas to perform crystallization outside a desulfurization absorption tower, and completely separates the desulfurization absorption and by-product crystallization output. A set of flue gas evaporation and crystallization units is set outside the flue gas desulfurization unit, and the flue gas originally directly entering the flue gas desulfurization unit is divided into two paths, one path directly going to the flue gas desulfurization unit, and the other path first going 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.
[0026] A crystallization booster blower extracts a portion of the high-temperature raw flue gas from the desulfurization unit before it enters the flue gas evaporation crystallizer, which is independently installed outside the desulfurization absorption tower. In the flue gas evaporation crystallizer, this portion of high-temperature raw flue gas is fully mixed and contacted with the uncrystallized desulfurization absorption liquid produced by the flue gas desulfurization unit, undergoing direct heat exchange and adiabatic evaporation. The high-temperature raw flue gas evaporates the water in the desulfurization absorption liquid and lowers its own temperature. After the water in the desulfurization absorption liquid evaporates and concentrates to supersaturation, desulfurization by-product crystals are generated. The desulfurization absorption liquid slurry containing desulfurization by-product crystals produced by the flue gas evaporation crystallizer is sent to the solid-liquid separation unit to separate the desulfurization by-product solids. After solid-liquid separation, the mother liquor is returned to the evaporation crystallizer for recycling. The low-temperature raw flue gas discharged from the flue gas evaporation crystallizer is returned to the desulfurization unit for desulfurization purification.
[0027] The beneficial effects of the present invention are as follows: This method utilizes a portion of the heat from the raw flue gas for crystallization outside the desulfurization tower, completely separating the desulfurization absorption from the crystallization of byproducts, and combining the advantages of both in-tower crystallization and out-tower steam evaporation crystallization. On the one hand, the circulating solution within the desulfurization absorption tower and the absorption circulation unit is a clear liquid free of crystalline solids, solving the problems of slurry wear, scaling, and clogging that plague the long-term operation of desulfurization units such as the ammonia process, and simplifying the desulfurization absorption process and structure. On the other hand, the desulfurization byproducts undergo flue gas evaporation and crystallization independently of the desulfurization absorption tower, significantly reducing the content of impurities such as chloride ions within the desulfurization absorption unit, avoiding severe corrosion within the desulfurization unit and impurity poisoning of the desulfurization liquid. It also prevents the crystallization process from affecting the desulfurization operation, and enhances the ability of the crystallization process and the entire device to adapt to impurity interference. This method significantly improves the operational safety, reliability, and stability of desulfurization processes such as the ammonia process. Furthermore, this method utilizes the raw flue gas as the heat source for the evaporation and crystallization of the desulfurization absorption liquid, eliminating the need for high-temperature steam. Compared with existing out-tower evaporation crystallization processes that use steam as a heat source, this method requires less investment, lowers operating costs, and is easier to operate. This method significantly improves the reliability and economic efficiency of flue gas desulfurization processes such as ammonia desulfurization, enabling these processes to meet the stringent desulfurization requirements of large thermal power plants and other applications, thus offering broad market application prospects. This method is particularly suitable for flue gas desulfurization processes such as sodium desulfurization, ammonia desulfurization, and magnesium desulfurization, as well as for retrofitting existing calcium desulfurization equipment with these processes. It offers significant economic, social, and environmental benefits.
[0028] The off-tower crystallization process of the present application combines the advantages of in-tower crystallization and off-tower steam evaporation crystallization, greatly improving the operational safety, reliability, stability, and operability of the desulfurization unit and reducing the construction cost of the desulfurization unit by more than 10%. In addition, this device utilizes part of the flue gas heat as a heat source for evaporation and crystallization of the desulfurization absorption liquid, without the need for external high-temperature steam. Compared with the existing conventional evaporation crystallization process using steam heating outside the tower, the energy cost is about 30% and the investment is more than 15% less. The flue gas evaporation crystallization unit independently provided by the present 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 achieving a more optimized operating cost. The present application greatly improves the reliability (availability is nearly 100%, and the main unit does not stop due to desulfurization) and economic efficiency of flue gas desulfurization processes such as the ammonia process, thereby enabling such desulfurization processes to meet the operating requirements of large thermal power plants, giving such processes a more profound vitality and a broad application market prospect. This device is particularly suitable for flue gas desulfurization processes such as the sodium method, ammonia method, and magnesium method, as well as for transforming existing calcium method desulfurization devices using such processes. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:
[0030] Figure 1 This is a unit diagram of a flue gas desulfurization method for crystallization outside a desulfurization tower;
[0031] Figure 2 This is a flow chart of an embodiment of a method for crystallization outside a desulfurization tower for flue gas desulfurization in this application.
[0032] Attachment Figure 1 Marking Description:
[0033] 1- Desulfurizer 2- Water 3- Oxidizing air 4- Desulfurization absorption subunit 5, 7, 8, 10- High-temperature raw flue gas 6- Boiler induced draft fan 9- Crystallization booster fan 11- Evaporation and crystallization subunit 12- Desulfurization by-product solution 13- Low-temperature raw flue gas 14- Slurry containing desulfurization by-product crystals 15- Solid-liquid separation subunit 16- Solid-liquid separation mother liquor 17- Solid desulfurization by-product 18- Clean flue gas 19- Flue gas evaporation and crystallization unit 20- Flue gas desulfurization unit;
[0034] Figure 2 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 of crystallizer 28-outlet flue gas damper of 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 DESCRIPTION
[0035] The following describes in detail embodiments of the present application. Examples of these embodiments are shown in the accompanying drawings, but unnecessary detailed descriptions may be omitted. This is to avoid unnecessary length in the following description 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 the present application and are not intended to limit the subject matter of the claims.
[0036] The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The terms "including" and "having" in the description and claims of this application and any variations thereof are open expressions, that is, they include the contents specified in this application but do not exclude other aspects.
[0037] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.
[0038] The present invention discloses a method for crystallization outside a desulfurization tower for flue gas desulfurization, which utilizes a portion of the original flue gas heat to perform crystallization outside the desulfurization tower, completely separates the desulfurization absorption from the by-product crystallization output, and arranges a flue gas evaporation crystallization unit outside the flue gas desulfurization unit to divide the flue gas originally entering the flue gas desulfurization unit directly into two paths, one path directly goes to the flue gas desulfurization unit, and the other path first goes to the flue gas evaporation crystallization unit to perform desulfurization absorption liquid evaporation crystallization outside the tower before entering the flue gas desulfurization unit for desulfurization treatment.
[0039] A crystallization booster blower extracts a portion of the high-temperature raw flue gas from the desulfurization unit before it enters the flue gas evaporation crystallizer, which is independently installed outside the desulfurization absorption tower. In the flue gas evaporation crystallizer, this portion of high-temperature raw flue gas is fully mixed and contacted with the uncrystallized desulfurization absorption liquid produced by the flue gas desulfurization unit, undergoing direct heat exchange and adiabatic evaporation. The high-temperature raw flue gas evaporates the water in the desulfurization absorption liquid and lowers its own temperature. After the water in the desulfurization absorption liquid evaporates and concentrates to supersaturation, desulfurization by-product crystals are generated. The desulfurization absorption liquid slurry containing desulfurization by-product crystals produced by the flue gas evaporation crystallizer is sent to the solid-liquid separation unit to separate the desulfurization by-product solids. After solid-liquid separation, the mother liquor is returned to the evaporation crystallizer for recycling. The low-temperature raw flue gas discharged from the flue gas evaporation crystallizer is returned to the desulfurization unit for desulfurization purification.
[0040] The mechanism of the present invention is shown in the attached Figure 1 , Figure 2 ;
[0041] The process of this application is further explained below with a specific embodiment:
[0042] Example 1:
[0043] The ammonia desulfurization device for the flue gas of a 400t / h boiler in a coal-fired power plant uses ammonia water as the desulfurizer and produces fertilizer-grade ammonium sulfate as a by-product. The original flue gas volume fed by the boiler induced draft fan is 500,000Nm 3 / h, flue gas temperature 110℃, SO2 content in original flue gas 2000mg / Nm 3 , dust content 10mg / Nm 3 , water content 6%. The flue gas desulfurization external crystallization process of the present invention is adopted, and the desulfurization units are all clear solutions for circulation.
[0044] Method and structure:
[0045] The unit diagram of the flue gas desulfurization method of crystallization outside the desulfurization tower is attached. Figure 1 The flow chart of the flue gas desulfurization crystallization method outside the desulfurization tower is attached. Figure 2 .
[0046] Main features: The ammonia desulfurization device for flue gas desulfurization and crystallization outside the desulfurization tower is equipped with two units: a flue gas desulfurization unit 20 and a flue gas evaporation crystallization unit 19:
[0047] (1) Flue gas desulfurization unit 20: It includes a main flue gas duct subunit and a desulfurization absorption subunit 4, and is used to desulfurize and purify the sulfur-containing high-temperature raw flue gas 5 from the boiler and the sulfur-containing low-temperature raw flue gas 13 from the flue gas evaporation and crystallization unit 19, and then produce a high-concentration unsaturated ammonium sulfate solution 12, which is sent to the flue gas evaporation and crystallization unit 19 for treatment;
[0048] (2) Flue gas evaporation and crystallization unit 19: It includes a secondary flue gas duct subunit, an evaporation and crystallization subunit 11, and a solid-liquid separation subunit 15. It is used to evaporate and concentrate the ammonium sulfate solution 12 with a portion of the high-temperature raw flue gas 8 to produce ammonium sulfate crystal solids 17. The ammonium sulfate crystal solids 17 are further processed or exported. 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.
[0049] The flue gas desulfurization unit 20 includes a main flue gas duct subunit and a desulfurization absorption subunit 4:
[0050] The flue gas desulfurization unit comprises:
[0051] (1) Main flue gas duct subunit: This includes the boiler induced draft fan 6, the desulfurization tower inlet and outlet flues with dampers, and other equipment. It is used to provide power for the flue gas entering and exiting the flue gas desulfurization unit 20 and the flue gas evaporation and crystallization unit 19 to overcome the unit resistance and to distribute and adjust the flue gas flow between the two units.
[0052] (2) Desulfurization absorption subunit 4: including desulfurization absorption tower ( Figure 2 Desulfurization absorption tower 21), circulation pump ( Figure 2 Circulation pump 36, circulation pump 37), circulation tank ( Figure 2 The intermediate circulation tank 38, desulfurizer supply device 1, process water supply device 2, oxidizing air supply device 3 and other equipment are used to desulfurize and purify the low-temperature raw flue gas 13 from the boiler high-temperature raw flue gas 5 and the flue gas evaporation and crystallization unit 19, and produce a high-concentration unsaturated ammonium sulfate solution 12.
[0053] Desulfurization absorption tower ( Figure 2 The middle desulfurization absorption tower 21 is equipped with multi-stage, multi-layer spray scrubbing. The desulfurization absorption liquid from each scrubbing stage forms a concentration gradient, with the maximum concentration of the desulfurization absorption liquid controlled below the saturation concentration of ammonium sulfate. This prevents crystallization throughout the desulfurization process, maintaining efficient desulfurization while producing a high-concentration ammonium sulfate solution. The resulting high-concentration ammonium sulfate solution 12 has a concentration of 80%-99%, preferably 95%-97%, of the saturation concentration of ammonium sulfate under operating conditions.
[0054] The flue gas evaporation and crystallization unit 19 includes a secondary flue gas duct subunit, an evaporation and crystallization subunit 11 , and a solid-liquid separation subunit 15 .
[0055] (1) Secondary flue gas duct sub-unit: It includes a booster fan 9 and an evaporator inlet and outlet flue gas duct with a damper, which is used to provide power for the flue gas entering and exiting the flue gas evaporation crystallization unit 19 to overcome the unit resistance and to distribute and adjust the flue gas flow between the desulfurization absorption unit 4 and the flue gas evaporation crystallization unit 19. The flue gas volume can be controlled by setting different concentrations for the ammonia method, sodium method, magnesium method, etc.; as long as the opening of the damper is controlled, the control basis is the temperature of the flue gas evaporation crystallizer or the crystallization condition, etc., and a reasonable heat is sufficient;
[0056] (2) Evaporation crystallization subunit 11: including flue gas evaporation crystallizer ( Figure 2 Middle crystallizer 30), circulation pump ( Figure 2 Circulation pump 14), discharge pump ( Figure 2 The equipment such as the solid-liquid separation pump 33 is used to evaporate and concentrate the high-concentration ammonium sulfate solution 12 from the flue gas desulfurization unit and the solid-liquid separation mother liquor 16 in the flue gas evaporation crystallizer to produce ammonium sulfate crystals. The slurry 14 containing ammonium sulfate crystals is sent to the solid-liquid separation subunit 15 for treatment. Figure 2 The low-temperature sulfur-containing flue gas discharged from the middle crystallizer 30) is treated in a flue gas desulfurization unit.
[0057] (3) Solid-liquid separation subunit 15: includes thickening equipment, centrifugal separation or filtration equipment, feed liquid tank, mother liquor tank, pump, etc. It is used to separate the crystals from 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 separated mother liquor 16 is returned to the flue gas evaporation crystallization unit 11 for recycling.
[0058] The flue gas flow rate into the flue gas evaporation crystallization unit 19 is 160000Nm 3 / h, the maximum by-product output is 2000kg / h, and the adjustment range of the secondary flue unit and the fan should be 30%-100% of the design flow rate.
[0059] Flue gas evaporation crystallizer ( Figure 2 The middle crystallizer 30 is used to fully mix and contact the high-temperature raw flue gas 10 with the uncrystallized desulfurization absorption liquid 12 and the solid-liquid separation mother liquor 16 produced by the flue gas desulfurization unit, directly exchange heat, and evaporate adiabatically. The high-temperature raw flue gas 10 evaporates the water in the desulfurization absorption liquid and then lowers its own temperature. After the water in the solution evaporates and concentrates to supersaturation, ammonium sulfate crystals are generated. Evaporation crystallizer ( Figure 2 The middle crystallizer (30) is equipped with a slurry tank and flue gas distribution pipes, 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°C 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°C and a relative humidity of 70%.
[0060] Within this range: the high-temperature raw flue gas entering the flue gas evaporation crystallizer has a temperature of no less than 85°C (preferably 100°C-180°C) and a water content of no more than 12% V / V (preferably no more than 8%); the low-temperature raw flue gas exiting the flue gas evaporation crystallizer has a temperature of no more than 75°C (preferably 60°C-70°C) and a relative humidity of no less than 50% (preferably 60%-80%). The higher the temperature, the easier it is to implement this solution, especially when the high-temperature raw flue gas temperature of a power plant boiler is higher.
[0061] The effect of this example:
[0062] The net sulfur dioxide content of flue gas emitted by flue gas desulfurization is less than 30mg / Nm 3 , dust content is less than 2mg / Nm 3 , droplet content is less than 20mg / Nm 3 The desulfurization process is all circulated with clear solution, and the desulfurization device can operate continuously and stably for more than 400 days (the average continuous operation time of the existing ammonia desulfurization device with in-tower crystallization process is generally less than 150 days). It eliminates the factors that seriously affect the stable operation of the desulfurization unit, such as scaling, blockage, internal parts damage, and circulation pump wear in the ammonia desulfurization process with in-tower crystallization. The availability of the device is greatly improved, and the purpose of not affecting the main production due to desulfurization is achieved, ensuring efficient operation synchronously with the main production device. The total investment cost is saved by about 10% compared with the existing in-tower crystallization process. The improved reliability saves 15% of the device operation and maintenance costs, and the operating cost is saved by 25% compared with the existing out-tower steam evaporation crystallization process. The average particle size of ammonium sulfate crystals is about 1.5mm, which is also greatly improved compared with the average particle size of about 0.15mm of in-tower crystallization, and the quality of ammonium sulfate has been significantly changed. The crystallization process of this method also improves the ability of the crystallization process to adapt to impurities. The existing in-tower evaporation crystallization often has difficulty in crystallization due to impurities such as desulfurization ammonia water impurities and flue gas dust. This method basically eliminates such phenomena.
[0063] The above embodiments do not limit the present invention in any way. They are used to explain the process principles and processes of this application. Any other improvements and applications made to the above embodiments in an equivalent manner are within the scope of protection of this application. These modifications, whether adjustments to the unit structure, process flow, or specific parameters, do not affect the actual effects of this application and should be included in the patent protection of this application.
Claims
1. A method for crystallization outside a desulfurization tower for flue gas desulfurization, characterized in that: Based on the following units, the flue gas desulfurization unit: includes a main flue gas duct subunit and a desulfurization absorption subunit; the flue gas evaporation and crystallization unit: includes a secondary flue gas duct subunit, an evaporation and crystallization subunit and a solid-liquid separation subunit connected in sequence; the main flue gas duct subunit includes a pipe connected to the desulfurization absorption tower as an inlet and outlet flue, and the pipe is connected in series with a boiler induced draft fan and an air damper: one pipe of the main flue gas is connected to the desulfurization absorption tower, and the other pipe is connected in parallel to the crystallization booster fan and the air duct and then to the evaporation and crystallization subunit; the evaporation and crystallization subunit is also provided with two pipes connected to the desulfurization absorption subunit, one is a pipe for transporting the desulfurization by-product solution produced by the desulfurization absorption subunit, and the other is a pipe for returning the low-temperature sulfur-containing flue gas to the desulfurization absorption subunit; the desulfurization absorption unit: includes a desulfurization absorption tower, a circulation pump, a circulation tank, a desulfurizer supply device, a process water supply device, and an oxidation air supply device; The flue gas desulfurization unit desulfurizes and purifies the sulfur-containing high-temperature raw flue gas from the boiler and the sulfur-containing low-temperature raw flue gas from the evaporation and crystallization unit outside the tower, and produces a high-concentration desulfurization by-product unsaturated solution, which is sent to the flue gas evaporation and crystallization unit for treatment; Flue gas evaporation and crystallization unit: It includes a secondary flue gas duct subunit, an evaporation and crystallization subunit, and a solid-liquid separation subunit, and is used to use a portion of the high-temperature raw flue gas to evaporate and concentrate the desulfurization by-product solution to produce desulfurization by-product crystalline solids; A part of the waste heat of the original flue gas is used for crystallization outside the desulfurization absorption tower, and the desulfurization absorption and by-product crystallization output are completely separated. A flue gas evaporation crystallization unit is set outside the flue gas desulfurization unit. The original flue gas that originally directly enters the flue gas desulfurization unit is divided into two routes. One route goes directly to the flue gas desulfurization unit, and the other route goes to the flue gas evaporation crystallization unit first. The desulfurization absorption liquid is evaporated and crystallized outside the tower to become low-temperature original flue gas and then enters the flue gas desulfurization unit for desulfurization treatment.
2. The method for crystallization outside the desulfurization tower for flue gas desulfurization according to claim 1, characterized in that: A portion of the high-temperature raw flue gas before entering the desulfurization unit is extracted by a crystallization booster fan and fed into a flue gas evaporation crystallizer independently arranged outside the desulfurization absorption tower. In the flue gas evaporation crystallizer, this portion of the high-temperature raw flue gas is fully mixed and contacted with the uncrystallized desulfurization absorption liquid produced by the flue gas desulfurization unit, directly exchanged heat, and evaporated adiabatically. The high-temperature raw flue gas evaporates the water in the desulfurization absorption liquid and lowers its own temperature. After the water in the desulfurization absorption liquid evaporates and concentrates to supersaturation, desulfurization by-product crystals are generated; the desulfurization absorption liquid slurry containing desulfurization by-product crystals produced by the flue gas evaporation crystallizer is sent to a solid-liquid separation unit for separation to produce solids of desulfurization by-products. After solid-liquid separation, the mother liquor is returned to the evaporation crystallizer for recycling; the low-temperature raw flue gas discharged from the flue gas evaporation crystallizer is returned to the desulfurization unit for desulfurization purification.
3. The method for crystallization outside the desulfurization tower for flue gas desulfurization according to claim 1, characterized in that: The desulfurization absorption tower is provided with multi-stage and multi-layer spray washing. The desulfurization absorption liquid of each washing stage forms a concentration gradient. The maximum concentration of the desulfurization absorption liquid is controlled below the saturation concentration of the desulfurization by-product. There is no crystallization in the entire desulfurization process, which not only maintains efficient desulfurization but also can produce a high-concentration desulfurization by-product solution; the concentration of the produced high-concentration desulfurization by-product solution is 80%-99% of the saturation concentration of the desulfurization by-product under operating conditions, preferably 95%-97%.
4. The method for crystallization outside the desulfurization tower for flue gas desulfurization according to claim 1, characterized in that: The flue gas flow rate entering the flue gas evaporation crystallization unit is determined according to the evaporation crystallization capacity of the maximum by-product design output, and the damper and fan adjustment range of the secondary flue sub-unit should be 30%-100% of the design flow rate.
5. The method for crystallization outside the desulfurization tower for flue gas desulfurization according to claim 1, characterized in that: The flue gas evaporation crystallizer is used to fully mix and contact the high-temperature raw flue gas with the uncrystallized desulfurization absorption liquid and solid-liquid separation mother liquor produced by the flue gas desulfurization unit, directly exchange heat, and evaporate adiabatically. After the high-temperature raw flue gas evaporates the water in the desulfurization absorption liquid, the water in the desulfurization absorption liquid evaporates and concentrates to supersaturation to produce desulfurization by-product crystals.
6. The method for crystallization outside the desulfurization tower for flue gas desulfurization according to claim 5, characterized in that: The gas-liquid contact in the flue gas evaporation crystallizer adopts a structure that is conducive to crystal growth and has self-cleaning ability, such as large-particle spraying, bubbling, liquid column, orifice plate; the temperature of the high-temperature raw flue gas entering the flue gas evaporation crystallizer is not less than 85°C (preferably 100°C-180°C), 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 evaporation crystallizer is not more than 75°C (preferably 60°C-70°C), and the relative humidity is not less than 50% (preferably 60%-80%).
7. The method for crystallization outside the desulfurization tower for flue gas desulfurization according to claim 1, characterized in that: When the flue gas desulfurization device has multiple flue gas desulfurization units, the flue gas evaporation crystallization unit can be set to be shared by multiple flue gas desulfurization units.