A method for flue gas desulfurization by spraying in a thermal power plant

Abstract

The present application provides a kind of power plant flue spray desulfurization method, it is related to flue gas purification technical field, comprising the following steps: S1, flue gas temperature partition;S2, desulfurizer preparation;S3, first stage spray;S4, second stage spray;S5, third stage spray;S6, acoustic agglomeration;S7, demisting recovery.The present application provides a kind of power plant flue spray desulfurization method, divides temperature partition in the tail flue of power plant, and sets up three-stage gradient spray, combines surfactant mass transfer enhancement, acoustic agglomeration synergistic trapping technology, and the desulfurization efficiency can reach more than 98%, outlet concentration is stably lower than, meets ultra-low emission requirement.System calcium sulfur molar ratio is stably controlled at, relies on reasonable reagent residual amount to adapt to various variable working condition scenes, and operation is stable and reliable.The present application does not need independent absorption tower, and the area is small, flue gas resistance is low, equipment structure is simple, and operation and maintenance are convenient;Meanwhile, sulfur dust can be removed simultaneously, and slurry can be recycled, and supporting agent is green and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of flue gas purification technology, and in particular to a method for flue gas desulfurization by spraying in thermal power plants. Background Technology

[0002] Thermal power generation is the main source of electricity supply in my country. Coal-fired power plants emit large amounts of pollutants during the power generation process. The smoke, It is one of the main pollutants causing acid rain and air pollution; with increasingly stringent national standards for air pollutant emissions, especially the implementation of ultra-low emission policies, there are requirements for the emission of certain pollutants in the flue gas of coal-fired power plants. Emission concentration not higher than 35 (Standard condition, dry basis, 6%) This places higher demands on flue gas desulfurization technology.

[0003] Currently, limestone-gypsum wet desulfurization (WFGD) is the mainstream flue gas desulfurization technology in thermal power plants. This technology uses an independent absorption tower where flue gas comes into countercurrent contact with limestone slurry, achieving a desulfurization efficiency of 95%-99%. However, wet desulfurization systems have the following technical problems: First, the absorption tower is bulky; the diameter of a single 600MW unit's absorption tower is typically 12-16m, and the height is 30-40m, requiring a large footprint and high infrastructure investment. Second, the system resistance is high, typically 1000-1500Pa, increasing the power consumption of the induced draft fan. Third, the slurry circulation volume is large; the flow rate of a single circulation pump can reach several thousand cubic meters per hour, resulting in high operating energy consumption. Fourth, the system is complex, including multiple subsystems such as the absorption tower, slurry circulation system, oxidation system, and gypsum dewatering system, leading to a large maintenance workload.

[0004] To reduce the investment and operating costs of desulfurization systems, some researchers and engineers have proposed a scheme of direct spray desulfurization within the flue. This involves installing nozzles in the tail flue to directly spray desulfurization slurry into the flue, utilizing the flue space to complete the process. The absorption reaction is efficient, but existing flue gas spray desulfurization technology has the following problems: The residence time of flue gas in the flue is short, typically 10-15 m / s, with a limited effective reaction section length. The residence time of flue gas in the spray zone is only 1-3 seconds, far less than the 10-20 seconds in the absorption tower, resulting in insufficient desulfurization reaction and a desulfurization efficiency of only 60%-80%, making it difficult to meet ultra-low emission requirements. Furthermore, the droplet size control is unreasonable. Existing flue gas spray desulfurization technologies mostly use a single type of nozzle, producing relatively uniform droplets. Large droplets (>200 μm) have a small specific surface area. The mass transfer rate is low, and the reaction is not complete within a short residence time; although small-diameter droplets (<30μm) have a large specific surface area, they are easily entrained by flue gas and are discharged with the flue gas before fully reacting, resulting in waste of desulfurizing agent and increased outlet dust concentration; the desulfurization slurry... Mass transfer rate is limited. The process of mass transfer from the bulk gas phase to the interior of the desulfurization slurry film and the subsequent chemical reaction is controlled by the mass transfer resistance in the liquid phase. Conventional desulfurization slurries have high surface tension (typically 60-72 mN / m), which is unfavorable for... The dissolution and diffusion at the gas-liquid interface limit the overall desulfurization reaction rate. The temperature distribution in the flue is uneven, and the temperature of the flue gas gradually decreases during its flow in the flue, from 120-160℃ at the air preheater outlet to 80-120℃ at the dust collector inlet. The desulfurization reaction kinetics and droplet evaporation characteristics differ significantly in different temperature zones, but the existing technology does not adopt a differentiated spray strategy for temperature zones. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes a method for flue gas spray desulfurization in thermal power plants.

[0006] The present invention proposes a method for flue gas spray desulfurization in thermal power plants, comprising the following steps:

[0007] S1. Flue gas temperature zoning: The flue gas duct at the tail end of the thermal power plant is divided into three spray reaction zones along the flue gas flow direction: high temperature zone, medium temperature zone, and low temperature zone. The flue gas temperature in the high temperature zone is 120-160℃, the flue gas temperature in the medium temperature zone is 80-120℃, and the flue gas temperature in the low temperature zone is 50-80℃. The low temperature zone is equipped with acid dew point protection design and adopts anti-corrosion and heat-insulating structure to avoid acid dew corrosion.

[0008] S2. Desulfurizing agent preparation: Mix the desulfurizing agent stock solution with water to prepare a desulfurization slurry. The desulfurization slurry contains 3%-15% desulfurizing agent by mass, 0.01%-0.05% surfactant, and 0.1%-0.5% organic acid buffer. Adjust the pH value of the desulfurization slurry to 5.5-6.5. The effective calcium content of the slurry is precisely proportioned according to the calcium-sulfur ratio of 1.50-1.55 to ensure material balance and self-consistency.

[0009] S3, First-stage spraying: A first-stage spraying device is installed in the high-temperature zone, using pressure atomizing nozzles to atomize the desulfurization slurry into droplets with a median particle size of 150-250μm, at a liquid-to-gas ratio of 5-8. Under suitable conditions, the slurry is injected into the flue gas. The heat from the high-temperature flue gas accelerates the evaporation of moisture in the droplets, increasing the specific surface area of ​​the desulfurization slurry droplets. Simultaneously, the surfactant reduces the surface tension of the desulfurization slurry to 30-40 mN / m, promoting... Dissolution and absorption in liquid film.

[0010] S4. Second-stage spraying: A second-stage spraying device is installed in the medium-temperature zone, using a dual-fluid air-assisted atomizing nozzle to atomize the desulfurization slurry into droplets with a median particle size of 60-120μm, at a liquid-to-air ratio of 3-5. Under the conditions of injection into the flue, it achieves [the desired effect] in the medium temperature zone. The deep absorption reaction.

[0011] S5. Third-stage spraying: A third-stage spraying device is installed in the low-temperature zone. This device includes an ultrasonic atomizing unit, which atomizes the desulfurization slurry into fine droplets with a median particle size of 15-45 μm using ultrasonic atomization, with a liquid-to-gas ratio of 1-3. Under certain conditions, the solution is injected into the flue, utilizing the large specific surface area of ​​the fine droplets to target residual gases. For fine absorption, the total atomization volume of the ultrasonic atomizing device is perfectly matched with the flow rate of the three-stage spray slurry.

[0012] S6. Acoustic Agglomeration: An acoustic agglomeration device is installed in the flue section between the second-stage and third-stage spray devices. This device emits sound waves with a frequency of 1-5 kHz and a sound pressure level of 140-160 dB, causing unreacted submicron-sized desulfurization slurry droplets and fly ash particles in the flue gas to collide and agglomerate, forming agglomerates with a particle size of 5-20 μm. These agglomerates then enter the low-temperature zone and are captured by fine droplets or removed by subsequent dust removal equipment. Acoustic agglomeration significantly enhances flue gas dust collection, reducing outlet dust levels by 4-6%. This will synergistically improve desulfurization efficiency by 1-1.5 percentage points.

[0013] S7. Demisting and Recovery: A ridge-type demister is installed downstream of the third-stage spray device to intercept and recover unevaporated droplets carried in the flue gas. The recovered liquid is returned to the desulfurization slurry preparation system for recycling after pH testing.

[0014] Preferably, in step S1, the length ratio of the high temperature zone, the medium temperature zone, and the low temperature zone is (2-3):(1.5-2.5):(1-2), and a transition section with a length of 0.5-1.0m is provided between each zone.

[0015] Preferably, in step S2, the surfactant is an alkyl polysaccharide (APG), and the carbon chain length of the alkyl polysaccharide is [missing information]. The degree of polymerization is 1.2-1.8, and the HLB value is 12-16. Alkyl polysaccharide is a nonionic surfactant synthesized from natural fatty alcohols and glucose. It has good biodegradability and low toxicity, and can significantly reduce the surface tension of desulfurization slurry without affecting the chemical equilibrium of the desulfurization reaction. When the mass fraction of alkyl polysaccharide is 0.01%-0.05%, the surface tension of desulfurization slurry can be reduced from 65-72 mN / m to 30-40 mN / m, a reduction of 40%-55%. The reduction in surface tension allows the desulfurization slurry to form smaller droplets during atomization, while increasing the gas-liquid contact area and reducing the surface tension. The resistance to mass transfer from the gas phase to the liquid phase is reduced, thereby significantly increasing the desulfurization reaction rate.

[0016] Preferably, in step S2, the desulfurization main agent is a composite alkaline solution of calcium carbonate powder and sodium hydroxide, wherein the mass ratio of calcium carbonate powder to sodium hydroxide is (3-5):1, and the organic acid buffer is adipic acid and / or glutaric acid. Using the composite alkaline solution of calcium carbonate and sodium hydroxide as the desulfurization main agent, sodium hydroxide provides rapid alkaline buffering capacity, quickly reacting with the desulfurization reaction in the initial stage. The reaction produces sodium sulfite, maintaining a high driving force for the desulfurization reaction; calcium carbonate, as the main alkali source, provides continuous desulfurization capacity and reduces operating costs. The addition of organic acid buffers allows for release through dissociation when the pH of the desulfurization slurry decreases. Maintaining a relatively stable pH value in the slurry helps prevent fluctuations in desulfurization efficiency caused by drastic pH changes. At the same time, the presence of organic acids helps to inhibit the scaling tendency of desulfurization products.

[0017] Preferably, in steps S3-S5, the total liquid-to-gas ratio of the three spray stages is 9-16. The first-stage spray accounts for 45%-55% of the total liquid-to-gas ratio, the second-stage spray accounts for 25%-35%, and the third-stage spray accounts for 10%-20%. The first-stage spray bears the main desulfurization load, utilizing the longer residence time of large droplets in the high-temperature zone and the higher chemical reaction rate to complete most of the desulfurization. The first stage absorbs the sulfur dioxide; the second and third stages of spraying are responsible for deep desulfurization and fine desulfurization respectively, with the liquid-to-gas ratio decreasing step by step, thus achieving a reasonable distribution of desulfurization load and efficient utilization of desulfurizing agent.

[0018] Preferably, in step S5, the ultrasonic atomizing device operates at a frequency of 1.7-2.4 MHz, with a single ultrasonic atomizing device producing 50-200 L / h of atomization capacity. The generated fine droplets have a Sotter mean diameter (SMD) of 20-35 μm and a droplet size distribution uniformity index of 1.8-2.5. Ultrasonic atomization utilizes high-frequency vibration to generate capillary waves on the surface of the desulfurization slurry. When the vibration amplitude exceeds a critical value, the wave crest breaks to form fine droplets. This method produces droplets with uniform size, low energy consumption, and does not rely on a high-pressure pumping system, making it suitable for arrangement in the limited space within the flue.

[0019] Preferably, in step S6, the working gas source pressure of the acoustic agglomeration device is 0.3-0.6 MPa, the acoustic frequency is 2-4 kHz, the sound pressure level is 145-155 dB, and the acoustic duration is 0.5-2.0 s. Acoustic agglomeration technology utilizes the entrainment effect and radiation pressure generated by high-intensity sound waves in dust-laden and mist-laden flue gas to cause submicron-sized particles and droplets to move relative to each other and collide and agglomerate in the sound field, forming agglomerates with larger particle sizes. The formation of these agglomerates increases the effective collision cross-section of particles and droplets, which is beneficial for the capture and reuse of residual desulfurizing agent particles in the subsequent third-stage spraying phase. Furthermore, it increases the particle size, which is beneficial for subsequent dust removal equipment (such as electrostatic precipitators or bag filters), reducing the concentration of dust emitted from the outlet flue gas.

[0020] Preferably, steps S3-S5 further include the following control method: setting up a control point at the flue outlet. Online monitoring instruments and online dust concentration monitoring instruments collect data at the outlet in real time. Concentration C_out and outlet dust concentration D_out; when C_out is greater than 35 When adjusting, follow these priorities in sequence: First, increase the slurry flow rate of the third-stage spray, adjusting in steps of 3%-5% of the initial flow rate; if C_out is still greater than 35 after adjusting to the maximum flow rate of the third-stage spray... If C_out is less than 20, then increase the slurry flow rate of the second-stage spray; Furthermore, when the duration exceeds 30 minutes, the slurry flow rate of each spray level is reduced sequentially in the order of third, second, and first levels, with the single-level adjustment step not exceeding 2% of the initial flow rate; when D_out exceeds the set threshold, the flushing frequency of the ridge-type demister is increased. This control method employs a graded priority adjustment strategy to ensure... To minimize desulfurizing agent consumption and operating energy consumption while ensuring emissions meet standards.

[0021] Preferably, in step S3, the nozzles of the first-stage spray device are spiral solid cone pressure atomizing nozzles with a spray angle of 90°-120°. The nozzles are arranged in a staggered pattern on the flue cross-section, with a spacing of 0.4-0.8m between adjacent nozzles and a distance of not less than 0.3m between the nozzles and the flue wall. In step S4, the nozzles of the second-stage spray device are flat fan-shaped dual-fluid nozzles with a spray angle of 60°-90° and a compressed air pressure of 0.2-0.4MPa. The nozzles are arranged in a matrix on the flue cross-section, with a spacing of 0.3-0.6m between adjacent nozzles. In step S5, the ultrasonic atomizing device is installed at the central axis of the flue, with the outlet of the ultrasonic atomizing device facing the direction of flue gas flow. The ultrasonic atomizing device is equipped with a guide hood with an expansion angle of 15°-30°. The differentiated design of each stage of the spray device makes the distribution of droplets on the flue cross-section more uniform, effectively covering all areas of the flue cross-section and reducing flue gas short-circuiting and desulfurization blind spots.

[0022] The present invention proposes a flue gas spray desulfurization method for thermal power plants, which has the following beneficial effects: The present invention directly utilizes the existing tail flue gas duct of the thermal power plant as the reaction site, eliminating the need to build large independent absorption towers required for traditional wet desulfurization processes, thus significantly reducing the equipment footprint. Compared with traditional limestone-gypsum wet desulfurization systems, the footprint can be reduced. This effectively reduces civil engineering investment and site modification costs. At the same time, the entire spray desulfurization system has low flow resistance, with the total increase in flue gas system resistance being only [amount missing]. Far lower than traditional absorption towers The system reduces resistance loss and significantly lowers the energy consumption of the induced draft fan; it also eliminates the need for large auxiliary subsystems such as slurry circulation, oxidation, and gypsum dewatering, resulting in fewer pieces of equipment, a simpler pipeline layout, and less daily maintenance workload.

[0023] This invention incorporates an acoustic agglomeration device between two spray stages. Utilizing sound waves of specific frequencies and sound pressure levels, it causes submicron-sized droplets and fly ash particles in the flue gas to collide and agglomerate, forming large-diameter agglomerates. This enhances the capture effect of subsequent fine droplets on unreacted slurry particles, further improving desulfurization performance. Furthermore, by increasing the particle size, it reduces the capture difficulty for downstream dust removal equipment, significantly lowering the outlet dust concentration and achieving synergistic ultra-low emissions of sulfur dioxide and particulate matter.

[0024] Different types of nozzles and atomizing equipment are selected for each level of spraying device according to the zoned working conditions. Combined with differentiated installation layout, spray angle and structural design, the droplets are evenly distributed in the flue section, effectively eliminating flue gas short circuit and desulfurization blind zone, allowing flue gas to fully contact the desulfurization slurry, and ensuring uniform desulfurization effect of flue gas across the entire cross section.

[0025] A ridge-type demister is installed downstream of the desulfurization zone to efficiently intercept unevaporated droplets entrained in the flue gas. The recovered liquid is recycled back to the slurry preparation system after online pH monitoring, reducing slurry discharge and reagent loss. Furthermore, this invention uses biodegradable additives such as alkyl polysaccharides, adipic acid, and glutaric acid, which are non-toxic, produce no secondary pollution, and are environmentally friendly, meeting the environmental requirements for flue gas treatment. Attached Figure Description

[0026] Figure 1 This is a flowchart of a flue gas spray desulfurization method for thermal power plants proposed in this invention;

[0027] Figure 2 This is a schematic diagram of the arrangement of a three-stage spray device in the flue of a thermal power plant flue gas spray desulfurization method proposed in this invention.

[0028] In the diagram: 1. Flue; 2. High-temperature zone; 3. Medium-temperature zone; 4. Low-temperature zone; 5. First-stage spray device; 6. Second-stage spray device; 7. Third-stage spray device; 8. Ultrasonic atomizing device; 9. Acoustic agglomeration device; 10. Ridge-type demister; 11. Temperature sensor; 12. Online monitoring instrument. Detailed Implementation

[0029] Example 1

[0030] Reference Figure 1-2 This invention proposes a spray desulfurization method for flue gas in a thermal power plant. For a 300MW coal-fired power unit, the designed coal sulfur content is 1.0% (based on received basis), and the flue gas volume (standard state) under rated load is... The outlet flue gas temperature of the air preheater is 135℃, and the inlet temperature is... Concentration of 1800 (Standard condition, dry basis, 6%) ), requiring export Emission concentration ≤35 .

[0031] The specific operation of the spray desulfurization of flue gas duct 1 using the method of the present invention is as follows:

[0032] S1. Flue Gas Temperature Zoning: In the tail flue 1 (cross-sectional dimensions of flue 1 are 6m × 4m) between the air preheater outlet and the electrostatic precipitator inlet, three spray reaction zones are sequentially divided along the flue gas flow direction. The temperature distribution of each zone is measured as follows by installing thermocouple temperature sensors 11 on the wall of flue 1: High temperature zone 2 (2-8m from the air preheater outlet) flue gas temperature is 125-135℃, length is 6m; Medium temperature zone 3 (9-14m from the air preheater outlet) flue gas temperature is 95-115℃, length is 5m; Low temperature zone 4 (15-19m from the air preheater outlet) flue gas temperature is 60-80℃, length is 4m; A transition section of 0.8m is set between each zone. The wall of the low temperature zone is made of glass flake anti-corrosion and a 50mm thick hydrophobic insulation layer, and the wall temperature is maintained above 90℃, which is 15℃ higher than the acid dew point.

[0033] S2. Desulfurizing agent preparation: In the desulfurization slurry storage tank, mix calcium carbonate powder (purity ≥95%, particle size ≤44μm ≥90%) with 30% sodium hydroxide solution at a mass ratio of 4:1, and add 0.03% alkyl polysaccharide glycoside ( A desulfurization slurry with a degree of polymerization of 1.4 and an HLB value of 13.5 (calcium-sulfur ratio 1.53) and 0.3% adipic acid (mass fraction) was prepared by adding water to form a 3.5% desulfurization slurry (precisely proportioned according to a calcium-sulfur ratio of 1.53 to ensure material balance). Testing showed that the surface tension of this desulfurization slurry was 34 mN / m (25℃, Wilhelmy plate method), the pH value was 6.0, and the density was 1080 g / L. viscosity is (25℃).

[0034] In contrast, a conventional desulfurization slurry without alkyl polysaccharides (with the same other components and concentrations) was prepared, with a surface tension of 68 mN / m (25℃) and a pH of 6.0.

[0035] S3. First-stage spray: A first-stage spray device 5 is installed in high-temperature zone 2, consisting of 18 spiral solid cone pressure atomizing nozzles (6 rows × 3 columns, staggered arrangement), with a nozzle spacing of 0.6m × 0.5m. The outermost nozzle is 0.35m from the wall of flue 1. The nozzle working pressure is 0.4MPa, the spray angle is 100°, and the measured median atomized droplet diameter (Dv50) is 180μm. The first-stage spray slurry flow rate is 60... The corresponding liquid-to-gas ratio is 6.0. In high-temperature zone 2, the flue gas temperature is high, and the moisture in large-diameter droplets evaporates rapidly (the calculated evaporation rate is approximately...). During evaporation, the droplet size gradually decreases, and the specific surface area increases. Simultaneously, the presence of surfactants... The mass transfer coefficient in the liquid film is improved.

[0036] S4. Second-stage spray: A second-stage spray device 6 is installed in the intermediate temperature zone 3, consisting of 24 flat, fan-shaped dual-fluid nozzles (6 rows × 4 columns, matrix arrangement) with a nozzle spacing of 0.5m × 0.4m; the compressed air pressure is 0.3MPa, the spray angle is 75°, and the measured median atomized droplet diameter (Dv50) is 85μm. The second-stage spray slurry flow rate is 35... The compressed air consumption is 120. (Standard conditions), corresponding to a liquid-to-gas ratio of 3.5. In the intermediate temperature zone, the flue gas temperature is moderate, and medium-sized droplets exhibit good tracking ability and a large specific surface area, which is beneficial for... Deep absorption.

[0037] S5, Third-stage spray: A third-stage spray device 7 is installed in low-temperature zone 4, equipped with 125 ultrasonic atomizing devices, each with an atomization rate of 120 L / h and an operating frequency of 2.0 MHz; the ultrasonic atomizing device 8 is installed at the central axis of flue 1, with the mist outlet facing the direction of flue gas flow, and is externally equipped with a conical guide hood with an expansion angle of 20°. The measured SMD of the generated fine droplets is 28 μm, and the uniformity index is 2.1; the flow rate of the third-stage spray slurry is 15... The corresponding liquid-to-gas ratio is 1.5. In the low-temperature zone 4, the flue gas temperature is low, and the evaporation rate of the fine mist droplets is slow, allowing them to remain in a liquid state for a longer period and continuously absorb residual gases. .

[0038] S6. Acoustic Agglomeration: Two acoustic agglomeration devices are installed in section 1 of the flue gas 1.5m downstream of the second-stage spray device 6. The working gas source pressure is 0.4MPa, the acoustic frequency is 3kHz, the sound pressure level is 150dB, and the acoustic effect time is approximately 1.0s. Acoustic agglomeration causes submicron-sized unreacted droplets and fly ash particles generated by the first and second-stage sprays in the flue gas to collide and agglomerate. After agglomeration, the median particle size increases from 0.8-2.0μm before agglomeration to 8-15μm, reducing the outlet dust concentration by 4.5%. The desulfurization synergistic efficiency was improved by 1.2 percentage points, which improved the capture efficiency of residual desulfurizing agent particles by the subsequent third-stage spray micro-droplets, and also facilitated the collection of particulate matter by the electrostatic precipitator.

[0039] S7. Demisting and Recovery: A two-stage ridge-type demister 10 is installed 3m downstream of the third-stage spray device 7. The blade spacing of the first-stage demister is 30mm, and the blade spacing of the second-stage demister is 25mm. The designed demisting efficiency is ≥99% (for droplets with a particle size >20μm). The droplets intercepted by the ridge-type demisters flow into a collection tank. The pH value of the recovered liquid is detected by an online pH meter (actually measured to be 5.2-5.8), and then returned to the desulfurization slurry storage tank for recycling. The ridge-type demisters are automatically flushed every 4 hours, and the flushing water is returned to the slurry system.

[0040] The control process of the above method is as follows: install at the outlet of flue 1 Online monitoring instrument 12 (ultraviolet fluorescence method, measurement range 0-500) (accuracy ±2%) and online dust concentration monitor (light scattering method, range 0-50). (accuracy ±5%), real-time data transmission to the DCS control system; when the output Concentration C_out exceeds 35 At that time, the controller adjusts according to the following priority: first, the flow rate of the third-stage spray slurry is reduced from 15... Increase, with a step size of 0.5. (Approximately 3.3% of the initial flow), until C_out ≤ 35 Or the flow rate reaches the maximum value of 20 If C_out still exceeds the limit after adjusting the third-stage spray to the maximum flow rate, then reduce the slurry flow rate of the second-stage spray from 35... Increase, step size 1.5 (Approximately 4.3% of the initial flow), until C_out ≤ 35 Or the flow rate reaches the maximum value of 45 Only under extreme operating conditions (such as sudden changes in coal quality leading to changes in the inlet) Only when the concentration increases sharply should the flow rate of the first-stage spray slurry be adjusted; when C_out is below 20 Furthermore, when the duration exceeds 30 minutes, the flow rate of the spray slurry at each level should be reduced sequentially in the order of the third level, the second level, and the first level, with the single-level adjustment step not exceeding 2% of the initial flow rate, in order to avoid frequent adjustments that could cause system fluctuations.

[0041] Results of continuous operation test (average value over 72 hours):

[0042] Entrance Concentration: 1780-1850 (Standard condition, dry basis, 6%) );

[0043] exit Concentration: 22-31 (Standard condition, dry basis, 6%) );

[0044] Average desulfurization efficiency: 98.3%;

[0045] Calcium-sulfur molar ratio (Ca / S): 1.53;

[0046] Total liquid-to-gas ratio: 11.0 ;

[0047] Increase in system resistance: 280 Pa;

[0048] Exit dust concentration: 6.8 (Standard condition, dry basis, 6%) );

[0049] Alkyl polysaccharide consumption: approximately 0.06 kg / h;

[0050] Adipic acid consumption: approximately 0.6 kg / h.

[0051] Example 2

[0052] A 600MW coal-fired power unit is designed with coal containing 1.5% sulfur (on a received basis). The flue gas volume (standard condition) under rated load is: The outlet flue gas temperature of the air preheater is 142℃, and the inlet temperature is... The concentration is 2700 (Standard condition, dry basis, 6%) ), requiring export Emission concentration ≤35 .

[0053] The specific operation of the spray desulfurization of flue gas duct 1 using the method of the present invention is as follows:

[0054] S1. Flue Gas Temperature Zoning: In the tail flue duct 1 (cross-sectional dimensions of flue duct 1 are 8m × 5m), three spray reaction zones are sequentially divided along the flue gas flow direction. High-temperature zone 2 is 8m long with a flue gas temperature of 130-142℃; medium-temperature zone 3 is 6m long with a flue gas temperature of 100-120℃; and low-temperature zone 4 is 5m long with a flue gas temperature of 65-90℃. A 1.0m transition section is set between each zone. The low-temperature zone adopts a corrosion-resistant and heat-insulating structure, and the wall temperature is 15℃ higher than the acid dew point.

[0055] S2. Desulfurizing agent preparation: Mix calcium carbonate powder and 30% sodium hydroxide solution at a mass ratio of 3.5:1, and add 0.04% alkyl polysaccharide glycoside ( A mixture of equal masses of adipic acid and glutaric acid (with a degree of polymerization of 1.6 and an HLB value of 14.2) and 0.4% by mass of adipic acid and glutaric acid was prepared with water to form a desulfurization slurry with a mass fraction of 3.8% (accurately proportioned according to a calcium-to-sulfur ratio of 1.54). The surface tension of the desulfurization slurry was 32 mN / m (25℃), and the pH value was 6.2.

[0056] S3, First-stage spray: Install 32 spiral solid cone pressure atomizing nozzles (staggered arrangement) in high-temperature zone 2, with a nozzle spacing of 0.5m × 0.5m; nozzle working pressure is 0.5MPa, spray angle is 110°, and median atomized droplet size is 200μm; the first-stage spray slurry flow rate is 130... The corresponding liquid-to-gas ratio is 6.7. .

[0057] S4. Second-stage spray: 40 flat, fan-shaped dual-fluid nozzles (arranged in a matrix) are installed in the medium-temperature zone 3. The compressed air pressure is 0.35 MPa, the spray angle is 80°, and the median atomized droplet size is 95 μm. The slurry flow rate for the second-stage spray is 75... The corresponding liquid-to-gas ratio is 3.9. .

[0058] S5. Third-stage spraying: 200 ultrasonic atomizing devices are installed in low-temperature zone 4, each with an atomization rate of 150 L / h and an operating frequency of 1.8 MHz, producing micro-droplets with an SMD of 32 μm. The slurry flow rate of the third-stage spray is 30... The corresponding liquid-to-gas ratio is 1.6. .

[0059] S6. Acoustic Wave Agglomeration: Four acoustic wave agglomeration devices were installed, with an acoustic frequency of 2.5kHz and a sound pressure level of 152dB. Acoustic wave agglomeration reduced the outlet dust level by 5.2 dB. The desulfurization synergy efficiency increased by 1.3 percentage points.

[0060] S7. Demisting and recovery: A two-stage ridge-type demister is installed with a demisting efficiency of ≥99%.

[0061] Results of continuous operation test (average value over 72 hours):

[0062] Entrance Concentration: 2650-2780 ;

[0063] exit Concentration: 26-34 ;

[0064] Average desulfurization efficiency: 98.7%;

[0065] Calcium-sulfur molar ratio (Ca / S): 1.54 (material balance verification).

[0066] Total liquid-to-gas ratio: 12.2 ;

[0067] Increase in system resistance: 350 Pa;

[0068] Exit dust concentration: 7.5 .

[0069] Comparative Example 1

[0070] Under the same operating conditions as in Example 1, single-stage flue gas duct 1 spray desulfurization was performed using a conventional single-pressure atomizing nozzle (median particle size 200 μm). The desulfurization slurry did not contain alkyl polysaccharide surfactants, and the total liquid-to-gas ratio was 11.0. .

[0071] Test results (average over 72 hours):

[0072] exit Concentration: 125-210 ;

[0073] Average desulfurization efficiency: 89.5%;

[0074] Calcium-sulfur molar ratio (Ca / S): 1.58.

[0075] The results show that without the three-stage differentiated spraying strategy and surfactant-enhanced mass transfer technology of this invention, relying solely on single-stage conventional spraying results in a desulfurization efficiency of only 89.5%, which is far lower than the 98.3% of Example 1 of this invention, and cannot meet the ultra-low emission requirements.

[0076] Comparative Example 2

[0077] Under the same operating conditions as in Example 1, a three-stage spray was used without the addition of alkyl polysaccharide surfactant (surface tension 68 mN / m), and the total liquid-to-gas ratio was 11.0. .

[0078] Test results (average over 72 hours):

[0079] exit Concentration: 55-78 ;

[0080] Average desulfurization efficiency: 96.2%;

[0081] Calcium-sulfur molar ratio (Ca / S): 1.56.

[0082] The results showed that, although the three-stage spraying strategy itself could improve desulfurization efficiency without the addition of alkyl polysaccharide surfactants, the high surface tension of the desulfurization slurry... Mass transfer rate is limited, desulfurization efficiency is 96.2%, and the outlet... The concentration is still higher than 35 The ultra-low emission limit was exceeded, and the Ca / S ratio increased compared to Example 1, indicating a decrease in the utilization rate of the desulfurizing agent.

[0083] Comparative Example 3

[0084] The same operating conditions as in Example 1 were used, with three-stage spraying and surfactants, but without the acoustic agglomeration device 9.

[0085] Test results (average over 72 hours):

[0086] exit Concentration: 25-33 ;

[0087] Average desulfurization efficiency: 98.1%;

[0088] Exit dust concentration: 12.3 .

[0089] The results show that the acoustic agglomeration device 9 has a relatively small direct impact on desulfurization efficiency, but it significantly increases the concentration of flue gas at the outlet, reducing it by up to 4.5%. The results, far exceeding the system measurement error, indicate that the acoustic agglomeration technology primarily improves the subsequent dust removal effect through the agglomeration of submicron-sized particles and droplets, thus contributing to the achievement of… Ultra-low emissions in synergy with smoke and dust.

[0090] The results of the above embodiments and comparative examples are summarized in the table below:

[0091]

[0092] As shown in the table above, the desulfurization efficiencies of the methods of the present invention (Example 1 and Example 2) are 98.3% and 98.7%, respectively, and the outlet efficiency is... The concentrations were consistently below 35%. It meets ultra-low emission requirements; the Ca / S ratios are 1.53 and 1.54 respectively, indicating high desulfurization agent utilization; the outlet dust concentration is 6.8. and 7.5 Meets the ultra-low emission limit for particulate matter (10 The comparison results with the comparative examples fully demonstrate the synergistic effect of the three-stage differentiated spraying strategy, surfactant-enhanced mass transfer technology, and acoustic agglomeration-assisted technology of this invention.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for flue gas desulfurization by spraying in a thermal power plant, characterized in that, Includes the following steps: S1. Flue gas temperature zoning: The flue gas duct at the tail end of the thermal power plant is divided into three spray reaction zones along the flue gas flow direction: a high-temperature zone, a medium-temperature zone, and a low-temperature zone. The flue gas temperature in the high-temperature zone is 120-160℃, the flue gas temperature in the medium-temperature zone is 80-120℃, and the flue gas temperature in the low-temperature zone is 50-80℃. The flue gas duct wall in the low-temperature zone is made of glass flake anti-corrosion and hydrophobic insulation layer. The wall temperature is controlled to be more than 15℃ higher than the acid dew point to prevent acid dew corrosion. S2. Desulfurizing agent preparation: Mix the desulfurizing agent stock solution with water to prepare a desulfurizing slurry. The desulfurizing slurry contains 3%-15% desulfurizing agent, 0.01%-0.05% surfactant and 0.1%-0.5% organic acid buffer by mass fraction, and adjusts the pH value of the desulfurizing slurry to 5.5-6.

5. S3. First-stage spraying: A first-stage spraying device is installed in the high-temperature zone, using pressure atomizing nozzles to atomize the desulfurization slurry into droplets with a median particle size of 150-250 μm, at a liquid-to-gas ratio of 5-8. The solution is injected into the flue gas under specific conditions, utilizing the heat from the high-temperature flue gas to accelerate the evaporation of moisture in the droplets, increasing the specific surface area of ​​the desulfurization slurry droplets. Simultaneously, the surfactant reduces the surface tension of the desulfurization slurry to 30-40 mN / m, promoting... Dissolution and absorption in liquid films; S4. Second-stage spraying: A second-stage spraying device is installed in the intermediate temperature zone, using a dual-fluid air-assisted atomizing nozzle to atomize the desulfurization slurry into droplets with a median particle size of 60-120 μm, at a liquid-to-gas ratio of 3-5. Under the conditions of injection into the flue, it achieves [the desired effect] in the medium temperature zone. Deep absorption reaction; S5. Third-stage spraying: A third-stage spraying device is installed in the low-temperature zone. The third-stage spraying device includes an ultrasonic atomizing device, which atomizes the desulfurization slurry into fine droplets with a median particle size of 15-45 μm using ultrasonic atomization, with a liquid-to-gas ratio of 1-3. Under certain conditions, the solution is injected into the flue, utilizing the large specific surface area of ​​the fine droplets to target residual gases. For fine absorption, the number of ultrasonic atomizing devices is designed to match the atomization capacity of a single unit with the three-stage slurry flow rate, ensuring that the total atomization capacity matches the slurry flow rate. S6. Acoustic Agglomeration: An acoustic agglomeration device is installed in the flue section between the second-stage spray device and the third-stage spray device. This device emits sound waves with a frequency of 1-5 kHz and a sound pressure level of 140-160 dB, causing unreacted submicron-sized desulfurization slurry droplets and fly ash particles in the flue gas to collide and agglomerate, forming agglomerates with a particle size of 5-20 μm. These agglomerates then enter the low-temperature zone and are captured by the fine droplets or removed by subsequent dust removal equipment. Acoustic agglomeration can reduce the outlet dust concentration by 4.5%. The desulfurization synergistic efficiency improved by 1.2 percentage points; S7. Demisting and recovery: A ridge-type demister is installed downstream of the third-stage spray device to intercept and recover unevaporated droplets carried in the flue gas. The recovered liquid is returned to the desulfurization slurry preparation system for recycling after pH detection.

2. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In step S1, the length ratio of the high temperature zone, the medium temperature zone, and the low temperature zone is 2-3:1.5-2.5:1-2, and there is a transition section with a length of 0.5-1.0m between each zone.

3. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In step S2, the surfactant is an alkyl polysaccharide, and the carbon chain length of the alkyl polysaccharide is [missing information]. The degree of polymerization is 1.2-1.8, and the HLB value is 12-16.

4. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In step S2, the desulfurization agent is a composite alkaline solution of calcium carbonate powder and sodium hydroxide, wherein the mass ratio of calcium carbonate powder to sodium hydroxide is 3-5:1, and the organic acid buffer is adipic acid and / or glutaric acid.

5. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In step S1, the flue gas temperature in the high-temperature zone is 130-150℃, the flue gas temperature in the medium-temperature zone is 90-110℃, and the flue gas temperature in the low-temperature zone is 55-70℃.

6. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In steps S3-S5, the total liquid-to-gas ratio of the three spray stages is 9-16. The liquid-to-gas ratio of the first-stage spray accounts for 45%-55% of the total liquid-to-gas ratio, the liquid-to-gas ratio of the second-stage spray accounts for 25%-35% of the total liquid-to-gas ratio, and the liquid-to-gas ratio of the third-stage spray accounts for 10%-20% of the total liquid-to-gas ratio.

7. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In step S5, the ultrasonic atomizing device operates at a frequency of 1.7-2.4MHz, the atomization capacity of a single ultrasonic atomizing device is 50-200L / h, the generated fine droplets have a Soder mean diameter of 20-35μm, and the droplet size distribution uniformity index is 1.8-2.

5.

8. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In step S6, the acoustic agglomeration device is an acoustic agglomeration device with a working gas source pressure of 0.3-0.6MPa, an acoustic frequency of 2-4kHz, a sound pressure level of 145-155dB, and an acoustic action time of 0.5-2.0s.

9. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, Steps S3-S5 also include the following control methods: Set at the flue outlet Online monitoring instruments and online dust concentration monitoring instruments collect data at the outlet in real time. Concentration C_out and outlet dust concentration D_out; when C_out is greater than 35 When adjusting, follow the order of priority: First, increase the slurry flow rate of the third-stage spray, adjusting the step size to 3%-5% of the initial flow rate; If C_out is still greater than 35 after adjusting to the maximum flow rate of the third-level spray... This increases the slurry flow rate of the second-stage spray; When C_out is less than 20 Furthermore, if the duration exceeds 30 minutes, the slurry flow rate of each spray level should be reduced sequentially in the order of third level, second level, and first level, with the single-level adjustment step not exceeding 2% of the initial flow rate; When D_out exceeds the set threshold, increase the flushing frequency of the ridge demister.

10. The method for flue gas spray desulfurization in a thermal power plant according to claim 1, characterized in that, In step S3, the nozzles of the first-stage spray device are spiral solid cone pressure atomizing nozzles with a spray angle of 90°-120°. The nozzles are arranged in a staggered manner on the cross-section of the flue, with a spacing of 0.4-0.8m between adjacent nozzles and a distance of not less than 0.3m between the nozzles and the flue wall. In step S4, the nozzles of the second-stage spray device are flat fan-shaped dual-fluid nozzles with a spray angle of 60°-90° and a compressed air pressure of 0.2-0.4MPa. The nozzles are arranged in a matrix on the cross-section of the flue, and the distance between adjacent nozzles is 0.3-0.6m. In step S5, the ultrasonic atomizing device is installed at the central axis of the flue, with the outlet of the ultrasonic atomizing device facing the direction of flue gas flow. The ultrasonic atomizing device is equipped with a flow guide shroud, and the expansion angle of the flow guide shroud is 15°-30°.

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