CN101732970A - Device and method for promoting fine particle matters to be removed in coal-burning wet flue gas desulfuration process - Google Patents

Abstract

Aiming at the characteristics of high water vapor content in flue gas in the coal-fired WFGD process equipped with a pre-washing tower, the invention provides a device and method for promoting the removal of fine particles by applying the principle of steam phase transition. A device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process. The device is composed of a pre-washing tower, a steam phase change chamber and a main desulfurization tower. Gas inlet and flue gas outlet, the flue gas inlet is connected to the flue gas outlet of the pre-scrubber tower, the flue gas outlet is connected to the flue gas inlet of the desulfurization main tower, and the flue gas inlet and the flue gas outlet of the steam phase change chamber are arranged successively There are steam nozzles, mist eliminators and rinse water nozzles.

Description

Device and method for promoting fine particle removal in coal-fired wet flue gas desulfurization process

1. Technical field

The invention belongs to a technology for promoting the removal of fine particles in coal-fired flue gas, in particular to a device for promoting the removal of fine particles by applying the principle of steam phase change in a coal-fired wet flue gas desulfurization process equipped with a pre-washing tower and methods.

2. Background technology

Inhalable particulate matter (PM ₁₀ ), especially fine particulate matter (PM _2.5 ) pollution with an aerodynamic diameter of less than 2.5 μm has become a prominent atmospheric environmental problem in China, and has increasingly attracted great attention from all over the world; the main reason is that the ratio of PM _2.5 fine particles to The large surface area is easy to enrich various heavy metals and chemical carcinogens, but it is difficult to effectively capture them by conventional dust removal technology, resulting in a large amount of fine particles being discharged into the atmosphere. For example, wet desulfurization towers (including demisters and desulfurization washing liquid) are difficult to capture PM _2.5 fine particles, but the removal efficiency of particles above 3-5μm can reach more than 70-80%; Wang Hui of Tsinghua University and others tested a 300MW The wet flue gas desulfurization (WFGD) system of a coal-fired power plant has a removal effect on fine particulate matter. It is found that the WFGD system has a removal efficiency of 74.5% for PM ₁₀ , but PM _2.5 increases instead ("Proceedings of the Chinese Society of Electrical Engineering" 2008 No. 28 roll). Coal combustion is the main primary source of fine particulate matter, and the basic situation of fine particulate matter as the primary pollutant of air pollution in my country will not change for a long period of time in the future. Therefore, controlling the pollution of coal-fired fine particles is a major demand for the national energy-saving and emission-reduction strategy. The main way of technology development is to make fine particles grow into larger particles through physical or chemical action, and then remove them, combine the existing coal-fired flue gas pollutant control equipment to optimize the process and use novel and reasonable technical principles to improve the efficiency of fine particles. The removal performance is an important technical development direction for the control of fine particles; among them, the combination of steam phase change pretreatment technology and the existing coal-fired boiler wet flue gas desulfurization technology is one of the most important ways to realize engineering applications. The mechanism of steam phase change to promote the growth of fine particles is: in the supersaturated water vapor environment, the water vapor takes fine particles as condensation nuclei to undergo a phase change, which increases the particle size and quality, and simultaneously produces the effects of diffusion swimming and thermophoresis. Promote the migration of fine particles, collide with each other, and further promote the coagulation and growth of fine particles. For this reason, the application of steam phase change pre-conditioning technology should first establish a supersaturated water vapor environment, but relying solely on adding steam to make the coal-fired flue gas with low original water vapor content and high flue temperature reach supersaturation is too energy-consuming. The combination of processes with higher water vapor content and lower smoke temperature has practical value.

At present, coal-fired wet flue gas desulfurization technology has become more and more mature and popular. In some WFGD processes, a pre-scrubbing tower is added in front of the desulfurization absorption tower (desulfurization main tower) to improve the SO ₂ absorption rate, dust removal and Improve the quality of gypsum, etc.; when the flue gas passes through the pre-washing tower, the high-temperature flue gas contacts with the medium-low temperature washing liquid, and a strong heat and mass transfer process occurs. The high-temperature flue gas vaporizes part of the washing liquid, and the relative humidity of the flue gas increases. It can approach or reach a saturated state, and the flue gas temperature drops from 100 to 150°C to about 50 to 65°C. However, neither the pre-scrubber nor the main desulfurization tower can reach the supersaturated water vapor environment required for steam phase transition. Therefore, adding a pre-scrubber can only increase the removal rate of _SO2 and coarse dust, and it is still difficult to capture fine particles. At the same time, in coal-fired power plants with WFGD systems installed, in addition to coal-fired fly ash, the fine particles discharged into the atmosphere include sulfuric acid mist and inorganic salt particles formed by desulfurization; the analysis by Meij in the Netherlands found that the fine particles discharged from the limestone/gypsum desulfurization system It basically belongs to PM _2.5 , and besides coal-fired fly ash, it also contains gypsum and unreacted limestone and other components (FuelProcessing Technology, 2004, 85(6-7): 641-656).

3. Contents of the invention

Purpose of the invention: The present invention aims at the characteristics of high water vapor content in the flue gas in the coal-fired WFGD process with a pre-scrubber, and provides a device and method for promoting the removal of fine particles by applying the principle of steam phase transition.

Technical solution: A device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process. The device is composed of a pre-washing tower, a steam phase change chamber and a main desulfurization tower. The pre-washing tower is provided with a waste liquid discharge port , flue gas inlet and flue gas outlet, between the flue gas inlet and the flue gas outlet, there are pre-washing liquid nozzles and pre-washing tower demisters; The flue gas outlet, the flue gas inlet and the flue gas outlet are provided with a desulfurization liquid nozzle and a desulfurization main tower demister in sequence; the steam phase change chamber is provided with a washing waste liquid outlet, a flue gas inlet and a flue gas outlet, The flue gas inlet is connected to the flue gas outlet of the pre-scrubbing tower, and the flue gas outlet is connected to the flue gas inlet of the main desulfurization tower. The steam nozzle, demister and washing machine are arranged in sequence between the flue gas inlet and flue gas outlet of the steam phase change chamber. The size of the water nozzle and steam phase change chamber is determined by the residence time of flue gas in the phase change chamber not less than 50-200ms required for water vapor to nucleate and condense on the surface of fine particles, and the lining is lined with corrosion-resistant low surface energy materials.

A device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process. The device is composed of a pre-washing tower, a steam phase change chamber and a main desulfurization tower. The washing tower is provided with a waste liquid discharge port, a flue gas inlet and a flue gas outlet, and a pre-washing liquid nozzle, a pre-washing tower demister and a steam phase change chamber are arranged in sequence between the flue gas inlet and the flue gas outlet. The variable chamber is provided with steam nozzles, mist eliminators and flushing water nozzles in sequence according to the flow direction of the flue gas; There are desulfurization liquid nozzles and demister demisters in the desulfurization main tower in sequence; the flue gas outlet of the pre-scrubber is connected with the flue gas inlet pipe of the desulfurization main tower.

A device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process, the pre-washing tower demister and the desulfurization main tower demister are baffle plate demisters, plate corrugated demisters or swirl plate demisters The demister in the steam phase change chamber is a plate corrugated demister or a wire mesh demister.

Corrosion-resistant low surface energy materials are polytetrafluoroethylene, tetrafluoroethylene vinyl ether copolymer or fluoroethylene vinyl ether copolymer coatings.

A method to promote the removal of fine particles in the coal-fired wet flue gas desulfurization process. The removal steps are: the coal-fired flue gas is washed and dedusted in the pre-washing tower, and then saturated or nearly saturated with water vapor, and then demisted by the pre-washing tower After removing the water mist, enter the steam phase change chamber, inject an appropriate amount of steam, the amount of steam added is determined by the increase of the supersaturation S of the flue gas from S≈1 to S=1.10～1.50, and the process required for the condensation and growth of fine particles is established. In a saturated water vapor environment, the condensed and grown fine particles are partially removed by the demister placed at the flue gas outlet of the steam phase change chamber; the flue gas enters the main desulfurization tower after removing part of the fine particles through the steam phase change chamber. The gas-liquid temperature difference at the inlet of the desulfurization main tower increases the supersaturation of the flue gas, causing the unremoved fine particles to undergo secondary condensation and grow up, and are removed by the desulfurization liquid and the demister of the desulfurization main tower.

A method for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process, the flue gas at the inlet of the desulfurization main tower is saturated or supersaturated flue gas, the temperature of the flue gas is 50-65°C, and the temperature of the imported desulfurization liquid is 30-45°C. The temperature of imported flue gas is 20-30℃ lower than that of imported flue gas.

A method for improving the removal of fine particles in the coal-fired flue gas desulfurization process, the PM2.5 fine particles include coal fly ash, sulfuric acid droplets or inorganic salt aerosol particles formed by desulfurization reactions.

Beneficial effects: Applying the principle of steam phase change to promote the removal of fine particles, first of all, a supersaturated water vapor environment should be established, but relying solely on adding steam to make the coal-fired flue gas with low original water vapor content and high smoke temperature (original water vapor content 5-8%, The energy consumption is too high when the flue gas temperature is 100-150°C) to reach supersaturation, and it is only of practical value when combined with a process with a high moisture content in the flue gas and a low flue temperature. In a coal-fired WFGD system with a pre-washing tower, after pre-washing, the flue gas can be saturated or nearly saturated with water vapor, and the temperature of the flue gas will drop to 50-65°C. Only a small amount of steam can be added to establish the condensation and growth of fine particles. Large required supersaturated water vapor environment. The present invention makes full use of the above-mentioned process characteristics, and adds a steam phase change chamber between the flue gas outlet of the pre-scrubbing tower and the flue gas inlet of the main desulfurization tower, or the space above the demister of the pre-scrubbing tower, and injects an appropriate amount of saturated steam at normal pressure to establish supersaturated water vapor. environment, make the fine particles condense and grow, and remove the condensed and grown dust droplets by the steam phase change chamber demister, and the fine particles that cannot be removed are increased by optimizing the gas-liquid temperature difference at the inlet of the desulfurization main tower. Large flue gas supersaturation causes secondary condensation and growth of fine particles in the desulfurization main tower, and is removed by the desulfurization liquid and the demister installed in the desulfurization main tower, thereby achieving efficient removal of fine particles. Compared with adding steam to the original coal-fired flue gas, the steam consumption can be significantly reduced. It can not only effectively remove coal-fired fly ash, but also remove sulfuric acid droplets and inorganic salt aerosol particles formed by desulfurization reactions. Using corrosion-resistant low surface energy materials as the wall surface or wall surface lining and coating of the steam phase change chamber can promote the condensation of water vapor on the surface of fine particles and inhibit its condensation on the wall surface of the steam phase change chamber, thereby enhancing the phase change effect. Solve corrosion problems caused by condensation of acidic pollutants. The process of the invention is simple, as long as the existing coal-fired wet flue gas desulfurization device is improved, a steam phase change chamber is added between the flue gas outlet of the pre-washing tower and the flue gas inlet of the main desulfurization tower or in the space above the demister of the pre-washing tower, Adding an appropriate amount of steam and properly optimizing the gas-liquid temperature difference at the inlet of the desulfurization main tower can make the existing coal-fired WFGD device have the effect of simultaneously promoting the coagulation and growth of fine particles and efficient removal, which can be widely used in pre-scrubbing towers Coal-fired power plant wet flue gas desulfurization unit.

4. Description of drawings

Fig. 1 is a process block diagram of the process of the present invention;

Fig. 2 is a schematic diagram of the device structure of Embodiment 1 of the present invention;

Fig. 3 is a schematic diagram of the device structure of Embodiment 2 of the present invention.

In the figure: 1-pre-scrubbing tower; 2-pre-scrubbing liquid nozzle; 3-pre-scrubbing tower demister; 4-steam phase change chamber; 5-steam nozzle; 6-steam phase change chamber demister; 7-washing Water nozzle; 8-desulfurization main tower; 9-desulfurization main tower demister; 10-desulfurization liquid nozzle; 11-circulation pump; A flue gas; B pre-washing liquid; C steam; D flushing waste liquid; E flushing water; F purification of flue gas; G desulfurization liquid; H waste liquid discharge;

5. Specific implementation

Below in conjunction with Fig. 1～3, the present invention is described in detail:

Example 1:

According to the present invention, a method for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process is shown in Figure 1 and Figure 2: the high-temperature coal-fired flue gas enters the pre-washing tower 1, and after contacting with the washing liquid, the flue gas temperature Decrease from 100-150°C to 50-65°C, be saturated or nearly saturated by water vapor, and remove coarse particles in the flue gas, then go through the pre-washing tower demister 3 to remove the water mist and then enter the steam phase change chamber 4, A proper amount of normal-pressure saturated steam is injected through the steam nozzle 5 to make the flue gas reach a supersaturated state, and the supersaturated water vapor takes the fine particles as condensation nuclei to undergo nucleation and condensation on the surface of the fine particles, and simultaneously produces diffusion swimming and thermophoresis, making the fine particles The particle size increases, the quality increases, and the condensed and grown dusty droplets are removed by the high-efficiency demister 6 placed at the flue gas outlet of the steam phase change chamber 4, and about 50-60% of fine particles are removed. The amount of steam added is determined by increasing the supersaturation S of the flue gas from S≈1 to S=1.10-1.50, so as to ensure that the particle size of the fine particles after coagulation and growth is above 3-5 μm, and at the same time suppress the homogeneous nucleation phenomenon, so that The heterogeneous nucleation process mainly takes place in the vapor phase change chamber 4 with fine particles as condensation nuclei. The demister flushing water nozzle 7 is installed in the steam phase change chamber, and the demister is flushed regularly to prevent the blockage of the demister from causing a significant increase in resistance, and the trapped fine particles are discharged with the flushing water waste. The supersaturated flue gas (S ≥ 1.0, temperature: 50-65°C) that removes part of the fine particles through the steam phase change chamber 4 enters the tower from the flue gas inlet at the lower part of the desulfurization main tower 8, and passes through the circulation pump 11 and the desulfurization liquid nozzle. 10 The sprayed medium and low temperature desulfurization liquid is in countercurrent contact, and the temperature of the imported desulfurization liquid is controlled at 30-45°C, which is 20-30°C lower than the temperature of the imported flue gas. The saturated flue gas is humidified and cooled during the countercurrent contact with the desulfurization liquid, and the supersaturation Further increase, so that the unremoved fine particles undergo secondary coagulation and growth, and the coagulated and grown dusty droplets are removed twice by the desulfurization liquid and the demister 9 installed in the main desulfurization tower. The concentration removal rate is 50-60%, and the total concentration removal rate is more than 80%. In addition to coal fly ash, the removed fine particles also include sulfuric acid droplets and inorganic salt particles formed by desulfurization. The purified flue gas is discharged from the flue gas outlet at the top of the desulfurization main tower.

As shown in Figure 2, a device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process of the present invention is mainly composed of a pre-washing tower 1, a steam phase change chamber 4, and a desulfurization main tower 8. The steam phase change chamber 4 is set between the flue gas outlet of the pre-washing tower 1 and the flue gas inlet of the desulfurization main tower 8, and the steam phase change chamber is provided with steam nozzles 5, demisters 6 and demister flushing in sequence according to the flow direction of the flue gas Water nozzle 7, the inner layer is lined with corrosion-resistant low surface energy materials, such as polytetrafluoroethylene, tetrafluoroethylene vinyl ether copolymer, fluoroethylene vinyl ether copolymer coating, etc.; steam phase change chamber 4 size (volume) It is determined that the residence time of flue gas in the phase change chamber is greater than the time required for the nucleation and condensation of water vapor on the surface of fine particles (about 50-200ms). Pre-washing tower 1, desulfurization main tower 8 and steam phase change chamber 4 flue gas outlets are all equipped with demisters, and pre-washing tower demister 3 and desulfurization main tower demister 9 use low-resistance demisters, such as baffles Demister, plate corrugated demister, swirl plate demister, steam phase change chamber demister 6 Select high-efficiency demisters, such as plate corrugated demisters and wire mesh demisters.

Example 2:

As shown in Figure 3, different from Example 1, a steam phase change chamber is not specially set between the flue gas outlet of the pre-scrubbing tower and the flue gas inlet of the desulfurization main tower, but the height of the pre-scrubbing tower 1 is appropriately increased to facilitate the pre-scrubbing The space above the demister 3 of the tower is used as a steam phase change chamber 4, and an appropriate amount of steam is injected. The high-efficiency demister 5 and the flushing water nozzle 7 of the demister are installed at the outlet of the flue gas at the top of the tower. The flue gas is pre-washed and removed. The particles enter the desulfurization main tower afterward, and the rest are the same as in Example 1.

Example 3:

A method for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process, the steps are: remove fine particles once: after the coal-fired flue gas is pre-washed and dust-removed, it is saturated or nearly saturated with water vapor, and water mist is removed After entering the steam phase change chamber, the residence time of the flue gas in the steam phase change chamber is ≥50-200 milliseconds, injecting saturated steam at normal pressure to establish the supersaturated water vapor environment required for the condensation and growth of fine particles, and the condensation and growth The fine particles are partially removed by the high-efficiency demister placed at the flue gas outlet of the steam phase change chamber, and the removal rate of the primary concentration is 50-60%; the secondary removal of fine particles: the supersaturated flue gas is removed by the steam phase change chamber After removing part of the fine particles, it enters the desulfurization main tower, and contacts with the medium and low temperature desulfurization liquid countercurrently, optimizes the gas-liquid temperature difference at the inlet of the desulfurization main tower, increases the supersaturation of the flue gas, and causes the unremoved fine particles to undergo secondary coagulation and grow up and be absorbed The desulfurization liquid and the mist eliminator installed in the desulfurization main tower are removed, the secondary concentration removal rate is 50-60%, and the total concentration removal rate is more than 80%.

A device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process, which consists of a pre-washing tower, a steam phase change chamber, and a main desulfurization tower. The steam phase change chamber is located between the flue gas outlet of the pre-scrubber and the flue gas inlet of the main desulfurization tower. There are steam nozzles, demisters and demister flushing water nozzles; the size of the steam phase change chamber is such that the residence time of the flue gas in the phase change chamber is greater than the time required for the nucleation and condensation of water vapor on the surface of fine particles (about 50~ 200ms) to determine that the lining has low surface energy materials that enhance the phase change effect and anti-corrosion dual effects, such as polytetrafluoroethylene, tetrafluoroethylene vinyl ether copolymer, fluoroethylene vinyl ether copolymer coating, etc. Install demisters at the flue gas outlets of the pre-scrubber, steam phase change chamber and main desulfurization tower, and use low-resistance demisters such as baffle demisters and plate corrugated demisters , Swirl plate demisters, steam phase change chamber demisters use high-efficiency demisters, such as plate corrugated demisters and wire mesh demisters.

Example 4:

The flue gas is produced by a fully automatic coal-fired boiler with a flue gas volume of 100Nm ³ /h. The pre-washing tower has a diameter of 150mm and a height of 2000mm. It has a built-in three-stage spray. The main desulfurization tower is a swirl plate with a diameter of 150mm and a height of 2500mm. Tower with 4 built-in swirl plates, the wet desulfurization technology is double alkali method, the steam phase change chamber is placed at the flue gas outlet of the pre-scrubber, and the pre-scrubber and steam phase change chamber flue gas outlets are respectively installed with plate wave plates Foggers, wire mesh demisters. The dust-containing flue gas produced by the coal-fired boiler enters the pre-washing tower. The flue gas temperature at the tower inlet is 143°C and the liquid-gas ratio is 10L/Nm ³ . 93%; then enter the steam phase change chamber, inject 0.070kg steam per Nm ³ flue gas, and the supersaturation degree of flue gas in the phase change chamber S≈1.35. The supersaturated flue gas (S≈1.16, temperature 60°C) that removes part of the fine particles through the steam phase change chamber enters the tower from the lower flue gas inlet of the desulfurization main tower. The temperature of the desulfurization liquid is 38°C, and the liquid-gas ratio is 3L/Nm ³ . According to the online test of the electric low-pressure impactor, the removal rate of the primary fine particle number concentration in the steam phase change chamber is 55%, the removal rate of the secondary fine particle number concentration in the desulfurization main tower is 58%, and the total removal rate of the fine particle number concentration reaches 81%.

Example 5:

The steam phase change chamber is placed in the space above the pre-washing tower mist eliminator, the pre-washing tower tower diameter is 150mm, the total tower height is 3000mm, the height of the pre-washing area and the steam phase changing area are respectively 2000mm and 1000mm, and the rest are basically the same as in Example 4; On-line test of electric low-voltage impactor, the total removal rate of fine particle number concentration is 80%.

Comparative example 1:

The test system of Example 4 is used, but no wire mesh demister is installed at the flue gas outlet of the steam phase change chamber, and no steam is injected. The flue gas temperature at the inlet of the desulfurization main tower is 57°C, and the relative humidity is 94%. The rest are basically the same as in Example 4; The total removal rate of the number concentration of fine particles is 26% through the online test of the electric scale low-voltage impactor.

Claims (7)

1. A device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process, characterized in that the device is composed of a pre-washing tower (1), a steam phase change chamber (4) and a desulfurization main tower (8), The pre-washing tower is provided with a waste liquid discharge port, a flue gas inlet and a flue gas outlet, and a pre-washing liquid nozzle (2) and a pre-washing tower demister (3) are sequentially arranged between the flue gas inlet and the flue gas outlet; The desulfurization main tower (8) is provided with a waste liquid discharge port, a flue gas inlet and a purified flue gas outlet, and a desulfurization liquid nozzle (10) and a desulfurization main tower demister ( 9); the steam phase change chamber (4) is provided with a flushing waste liquid outlet, a flue gas inlet and a flue gas outlet, the flue gas inlet is connected to the flue gas outlet of the pre-washing tower (1), and the flue gas outlet is connected to the desulfurization main The flue gas inlet of the tower is connected, and a steam nozzle (5), a demister (6) and a flushing water nozzle (7) are arranged in sequence between the flue gas inlet and the flue gas outlet of the steam phase change chamber (4), and the steam phase change The size of the chamber (4) is determined by the fact that the residence time of the flue gas in the phase change chamber is not less than 50-200ms required for the nucleation and condensation growth of water vapor on the surface of the fine particles, and is lined with corrosion-resistant low surface energy materials. 2. A device for promoting the removal of fine particles in a coal-fired wet flue gas desulfurization process, characterized in that the device is composed of a pre-washing tower (1), a steam phase change chamber (4) and a desulfurization main tower (8), The steam phase change chamber (4) is arranged in the pre-washing tower (1), and the pre-washing tower is provided with a waste liquid discharge port, a flue gas inlet and a flue gas outlet, and a preset Washing liquid nozzle (2), pre-scrubber demister (3) and steam phase change chamber (4), said steam phase change chamber (4) is provided with steam nozzle (5), defogger device (6) and flushing water nozzle (7); the desulfurization main tower (8) is provided with a waste liquid discharge port, a flue gas inlet and a purified flue gas outlet, and a desulfurization liquid is arranged between the flue gas inlet and the flue gas outlet The nozzle (10) and the demister (9) of the desulfurization main tower; the flue gas outlet of the pre-scrubber is connected with the flue gas inlet pipe of the desulfurization main tower; the size of the steam phase change chamber (4) is based on the The residence time is not less than the time required for water vapor to nucleate and condense on the surface of fine particles, 50-200ms, and the lining is lined with corrosion-resistant low-surface-energy materials. . 3. The device for promoting the removal of fine particles in the coal-fired wet flue gas desulfurization process according to claim 1 or 2, characterized in that the pre-washing tower demister (3), desulfurization main tower demister (10) It is a baffle plate demister, a plate corrugated demister or a swirl plate demister; the steam phase change chamber demister (6) is a plate corrugated demister or a wire mesh demister. 4. The device for promoting the removal of fine particles in the coal-fired wet flue gas desulfurization process according to claim 1 or 2, characterized in that the corrosion-resistant low surface energy material is polytetrafluoroethylene, tetrafluoroethylene vinyl ether Copolymer or fluoroethylene vinyl ether copolymer coatings. 5. The method for promoting the removal of fine particles in the coal-fired wet flue gas desulfurization process is characterized in that the removal step is: the coal-fired flue gas is saturated or nearly saturated by water vapor after being washed and dust-removed in the pre-washing tower, and then The demister in the pre-scrubber enters the steam phase change chamber after removing the mist, and injects an appropriate amount of steam. The amount of steam added is determined by the supersaturation S of the flue gas from S≈1 to S=1.10-1.50, and the fine particles are condensed and grown. Larger required supersaturated water vapor environment, the condensed and grown fine particles are partially removed by the demister placed at the outlet of the steam phase change chamber; the flue gas passes through the steam phase change chamber to remove part of the fine particles and then enters the desulfurization Main tower, by optimizing the gas-liquid temperature difference at the inlet of the desulfurization main tower, the supersaturation of the flue gas is increased, so that the unremoved fine particles undergo secondary condensation and grow up, and are removed by the desulfurization liquid and the demister of the desulfurization main tower. 6. The method for promoting the removal of fine particles in the coal-fired wet flue gas desulfurization process according to claim 5, characterized in that the flue gas at the inlet of the main desulfurization tower is saturated or supersaturated flue gas, and the flue gas temperature is 50 ~ 65°C, the temperature of the imported desulfurization liquid is 30-45°C, which is 20-30°C lower than the temperature of the imported flue gas. 7. The method for improving the removal of fine particles in the coal-fired wet flue gas desulfurization process according to claim 6, characterized in that the PM _2.5 fine particles include coal fly ash, sulfuric acid droplets or inorganic salts formed by desulfurization reactions Aerosol particles.

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