CN104941379A - Method and device for promoting simultaneous removal of mercury and fine particulate matters during wet flue gas desulfurization - Google Patents

Abstract

The present invention aims at the disadvantages of low flue gas temperature and high humidity after wet desulfurization, and cannot effectively remove PM _2.5 and mercury, and provides a method that uses the principle of water vapor phase transition to remove SO ₂ while promoting the coordinated removal of mercury and fine particles Methods and devices. The coal-fired flue gas enters the water-vapor phase change chamber after wet desulfurization, and the flue gas is supersaturated by injecting saturated steam at normal pressure. On the one hand, the supersaturated water vapor drags gaseous mercury to enrich on the surface of particles through thermophoresis and diffusion swimming; On the one hand, nucleation condensation occurs on the surface of the fine particles enriched in particulate mercury as condensation nuclei, which increases the particle size and quality of the fine particles, and the condensed and grown dust-laden mercury droplets are finally removed by the high-efficiency demister . The present invention only improves the existing coal-fired wet desulfurization device, adding a water-vapor phase change chamber behind the desulfurization tower, and adding steam can make the wet-process desulfurization device have the effect of synergistically removing fine particles and mercury, and can be widely used in coal-fired Wet flue gas desulfurization in power plants has huge economic and social benefits.

Description

Method and device for promoting coordinated removal of mercury and fine particles in wet flue gas desulfurization

technical field

The invention relates to a technology for promoting the coordinated removal of mercury and fine particles in coal-fired flue gas, in particular to a method and device for promoting the coordinated removal of mercury and fine particles by applying the principle of water vapor phase transition in wet flue gas desulfurization.

Background technique

PM _2.5 pollution, which has an aerodynamic diameter less than or equal to 2.5 microns, has become a prominent atmospheric environmental problem in China. Countries attach great importance to it; the main reason is that PM _2.5 has a large specific surface area, which is easy to accumulate various heavy metal pollutants (such as As, Se, Hg, Cr, Pb, Cd, etc.), and becomes the carrier and reaction of heavy metal pollutants. According to reports, about 75% to 90% of heavy metals are distributed in fine particles, and the smaller the particles, the higher the heavy metal content. Among them, because mercury and its compounds are extremely toxic even at very low concentrations, and are volatile and non-degradable, they can accumulate for a long time after entering the human body through respiration in the form of aerosols, dust or steam. It causes physical growth retardation, causes various cancers and heart diseases, and poses great harm to the ecological environment and human health. Coal-fired power plants are the main pollution sources that cause the increase of PM _2.5 and mercury in the atmospheric environment in China. Controlling the emission of PM _2.5 and mercury pollution from coal-fired power plants is a key issue that needs to be solved urgently.

In view of the fact that traditional pollutant control facilities (such as dust removal and wet desulfurization) have the effect of removing particulate matter, the capture effect is not good only because the particle size of PM _2.5 is too small or there are certain defects in the pollution control facilities themselves. Therefore, the current technical development directions for effective control of PM _2.5 include the following aspects: (1) Process optimization combined with traditional pollutant control facilities to improve its removal effect on PM _2.5 , such as electric bag composite dust removal, new electric dust removal, etc. (2) After the particle size of PM _2.5 is increased through different technical means, traditional pollutant control facilities are used to remove it, such as the use of external field effects such as electricity, sound, chemistry, and water vapor phase change to increase the particle size of PM _2.5 . Among them, the water vapor phase change technology uses supersaturated water vapor to condense in different phases on the surface of PM _2.5 to increase its mass and particle size, so that it can be effectively captured by conventional dust removal equipment, especially suitable for the moisture content in flue gas such as wet desulfurization. Higher process combined.

At present, coal-fired wet flue gas desulfurization (WFGD) technology has become more and more mature and popular, and large and medium-sized coal-fired power plants generally install WFGD systems after dust collectors. During the flue gas desulfurization process, the high-temperature flue gas is in contact with the medium-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 at the outlet of the desulfurization tower increases greatly and approaches or reaches a saturated state. Adding a small amount of water vapor can achieve the supersaturated conditions required for the phase transition of water vapor, and realize the condensation, growth and removal of PM _2.5 . However, the application of water vapor phase change technology in the existing wet flue gas desulfurization process only considers the removal of _SO2 and fine particles, and does not involve the coordinated removal of mercury in flue gas.

Contents of the invention

The present invention aims at the shortcomings of the existing wet flue gas desulfurization (WFGD) method that cannot effectively remove PM _2.5 , mercury, and high water vapor content in the desulfurized clean flue gas. With the method of synergistic removal of fine particles, the water vapor phase change technology is used to promote the condensation and growth of fine particles and the condensation of gaseous mercury and particulate mercury on the surface of fine particles to achieve the effect of synergistic and efficient removal of fine particles and mercury. Another object of the present invention is to provide a device for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization.

The concrete technical scheme that the present invention adopts is as follows:

The method of promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization, the specific process is as follows: the coal-fired flue gas enters the water vapor phase change chamber after wet desulfurization, and the flue gas is decomposed by injecting atmospheric saturated steam into the water vapor phase change chamber. When the supersaturated state is reached, the supersaturated water vapor takes fine particles as condensation nuclei to condense on its surface, and the condensed and grown dust-laden droplets are captured by the demister; at the same time, the supersaturated water vapor enriches mercury in the fine particles On the surface, supersaturated water vapor nucleates and condenses on the surface of mercury-containing fine particles, and the condensed and grown-up dust-laden droplets are finally removed by the demister, thereby realizing the synergistic removal of fine particles and mercury in coal-fired flue gas.

The flue gas temperature after the wet desulfurization is 45-65° C., and the relative humidity is ≥90%.

The degree of supersaturation of the water vapor phase change chamber is 1.10˜1.25.

The fine particulate matter is PM _2.5 with an aerodynamic diameter of less than or equal to 2.5 μm, including fly ash in raw coal-fired flue gas, sulfuric acid droplets and inorganic salt aerosol particles formed in the wet desulfurization process.

The wet desulfurization process is one of limestone-gypsum method, ammonia method, double alkali method, sodium alkali method and seawater method.

A device for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization, comprising a wet desulfurization tower, a water vapor phase change chamber, a steam system, a demister, a flushing water system, and a flushing waste liquid outlet; the wet method The flue gas outlet of the desulfurization tower is connected to the flue gas inlet of the water vapor phase change chamber, and the water vapor phase change chamber is independently arranged outside the wet desulfurization tower or inside the wet desulfurization tower; the steam system, demister and flushing The water system is located in the water vapor phase change chamber, the steam system injects saturated steam at normal pressure into the water vapor phase change chamber, the demister is installed at the flue gas outlet of the water vapor phase change chamber, and the flushing water system is used to flush the demister; The flush waste liquid outlet is located at the bottom of the water vapor phase change chamber.

The water-vapor phase change chamber is a cylindrical or square structure, and its lining is made of corrosion-resistant low surface energy material.

The demister is a wire mesh demister or a plate corrugated demister.

The steam system is a steam nozzle; the flushing water system is a flushing water nozzle.

The size of the water vapor phase change chamber is determined by the fact that the residence time of flue gas in the water vapor phase change chamber is not less than the time required for supersaturated water vapor to nucleate and condense on the surface of fine particles; the time required for the condensation to grow is 50-200ms .

The present invention uses the principle of water vapor phase transition to promote the removal of fine particles and mercury. Firstly, a supersaturated water vapor environment should be established, but simply relying on adding steam makes the original water vapor content low (5-8%) and the smoke temperature high (100-150°C). The energy consumption of coal-fired flue gas reaching supersaturation is too high, and this technology can only be of practical value when combined with a process with high water vapor content and low flue temperature. In the process of wet flue gas desulfurization, the high-temperature flue gas is in contact 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 at the outlet of the desulfurization tower increases greatly and approaches or When the saturation state is reached, and the temperature of the flue gas drops to 45-65°C, only a small amount of water vapor is added to achieve the supersaturation conditions required for the phase transition of water vapor, and PM _2.5 can be condensed and grown to be removed efficiently.

The present invention makes full use of the above-mentioned process characteristics, and installs a water vapor phase change chamber after the wet flue gas desulfurization, and injects saturated steam at normal pressure to make the high-humidity flue gas reach a supersaturated state. On the one hand, the supersaturated water vapor is dragged by thermophoresis and diffusion Gaseous mercury is enriched on the surface of fine particles; on the other hand, nucleation and condensation occurs on the surface of fine particles enriched in particulate mercury as condensation nuclei, which increases the particle size and quality of fine particles, and the condensed and grown-up content The mercury content of dust droplets is greatly increased, which is removed by the high-efficiency demister placed at the outlet of the water vapor phase change chamber, thereby achieving synergistic and efficient removal of fine particles and mercury.

In addition, the process of the present invention is simple, and it only needs to improve the existing coal-fired wet flue gas desulfurization device, add a water vapor phase change chamber behind the desulfurization tower, and add a small amount of steam to make the existing coal-fired flue gas wet desulfurization device have The synergistic effect of removing fine particles and mercury can be widely used in wet flue gas desulfurization devices of coal-fired power plants, which is expected to produce huge economic and social benefits, and has broad application prospects.

Description of drawings

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

Fig. 2 is process block diagram of process of the present invention;

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

Among them, 1-wet desulfurization tower; 2-desulfurization liquid nozzle; 3-desulphurization tower demister; 4-water vapor phase change chamber; 5-steam nozzle; 6-water vapor phase change chamber demister; 7-washing water nozzle ; A- original coal-burning flue gas; B- desulfurization waste liquid; C- desulfurization liquid;

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

A device for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization (as shown in Figure 1), comprising a wet desulfurization tower 1, a main body of a water vapor phase change chamber, a steam nozzle 5, and a demister 6 for a water vapor phase change chamber And the flushing water nozzle 7, the steam nozzle 5, the water vapor phase change chamber demister 6 and the flushing water nozzle 7 are arranged in the water vapor phase change chamber main body.

Among them, the wet desulfurization tower 1 is equipped with the original coal-fired flue gas inlet, the high-humidity flue gas outlet, the desulfurization liquid inlet, the desulfurization waste liquid outlet, the desulfurization liquid nozzle 2, and the desulfurization tower demister 3, and the desulfurization tower demister 3 is located at At the high-humidity flue gas outlet at the top of the wet desulfurization tower 1 , the high-humidity flue gas outlet of the wet desulfurization tower 1 is connected to the flue gas inlet of the water vapor phase change chamber 4 .

In addition, the water vapor phase change chamber 4 is provided with a flue gas inlet, a flue gas outlet, a steam nozzle 5, a water vapor phase change chamber demister 6, a flushing water nozzle 7 and a flushing waste liquid outlet; through the steam nozzle 5, the water vapor phase change chamber 4 Atmospheric pressure saturated steam is injected; the demister 6 of the water vapor phase change chamber is a wire mesh eliminator or a plate corrugated demister, which is arranged at the flue gas outlet of the water vapor phase change chamber; the flushing water at the outlet of the water vapor phase change chamber 4 The nozzle 7 regularly flushes the mist eliminator 6 of the water vapor phase change chamber to prevent the clogging of the mist eliminator 6 of the water vapor phase change chamber, resulting in a significant increase in resistance; the flushing waste liquid outlet is located at the bottom of the water vapor phase change chamber 4; the water vapor phase change chamber 4 is a cylinder Or square structure, the inner lining is made of corrosion-resistant low surface energy materials with double effects of enhancing phase change effect and anti-corrosion, such as polytetrafluoroethylene, tetrafluoroethylene vinyl ether copolymer, fluoroethylene vinyl ether copolymer, etc.; water vapor The size of the phase change chamber 4 is determined by the fact that the residence time of the flue gas in the water vapor phase change chamber 4 is not less than the time (50-200 ms) required for the nucleation and condensation of water vapor on the surface of fine particles; the outlet of the flushing waste liquid is located in the water vapor phase The bottom of the variable chamber 4 is used to flush out the waste liquid.

As shown in Figure 2, the specific process of the method for promoting the synergistic removal of mercury and fine particulate matter in the wet flue gas desulfurization of the present invention is as follows: first, the original coal-fired flue gas A with lower moisture content and higher temperature (temperature T : 100～150℃, water content H ₂ O: 5～8%) enters the wet flue gas desulfurization system, in the wet desulfurization tower 1, there is a strong heat and mass exchange with the desulfurization liquid C, so that the outlet of the wet desulfurization tower 1 The relative humidity of the net flue gas has greatly increased and is close to saturation (the flue gas temperature drops to 45-65°C, the relative humidity is ≥90%, and the supersaturation S is about 1), and the volatile mercury is mainly in two forms: gaseous and particulate exist. The wet flue gas desulfurization process is any one of limestone-gypsum method, ammonia method, double-alkali method, sodium-alkali method, and seawater method.

After the desulfurized high-humidity flue gas enters the water vapor phase change chamber 4, the supersaturation S of the high humidity flue gas in the water vapor phase change chamber 4 reaches 1.10-1.25 by injecting atmospheric pressure saturated steam D into the water vapor phase change chamber 4 . Among them, supersaturated water vapor uses fine particles as condensation nuclei to undergo nucleation and condensation on its surface, making its particle size and mass increase, and the condensed and grown dust-laden droplets are captured by the demister 6 in the water vapor phase change chamber set. At the same time, the gaseous mercury that can be dragged by thermophoresis and diffusion during the phase transition of water vapor is enriched on the surface of fine particles. The particle size and mass of fine particles increase, and the mercury content of dusty liquid droplets after condensation and growth increases greatly, which is removed by the demister 6 in the water vapor phase change chamber, so as to realize the coordinated removal of fine particles and mercury in coal-fired flue gas remove. Then the water vapor phase change chamber demister 6 is flushed regularly by the flushing water nozzle 7 at the outlet of the water vapor phase change chamber 4, to prevent the water vapor phase change chamber demister 6 from clogging and causing resistance to significantly increase, so that the trapped mercury contains Fine particles can be discharged with the flushing water waste liquid E. The fine particulate matter removed refers to PM _2.5 with an aerodynamic diameter less than or equal to 2.5 μm, including fly ash in the original coal-fired flue gas, sulfuric acid droplets and inorganic salt aerosol particles formed in the wet flue gas desulfurization process.

Example 1:

The original flue gas flow rate produced by the fully automatic coal-fired boiler is 150Nm ³ /h, the number concentration of fine particles is 5.02×10 ⁷ /cm ³ , and the total mercury concentration is 1.50μg/m ³ ; after limestone-gypsum wet desulfurization , the flue gas temperature at the outlet of the wet desulfurization tower 1 drops from 120°C to 55°C, and the relative humidity is 97%; it enters the water vapor phase change chamber 4, and a wire mesh demister is installed at the exit of the phase change chamber, and the steam passes through the phase change chamber Nozzle 5 injects 0.06kg/m ³ (flue gas) saturated steam at atmospheric pressure. It has been measured that after the water vapor phase change is applied in the wet desulfurization process, the number concentration of fine particles in the flue gas passing through the outlet of the wire mesh demister can be reduced from 4.02×10 ⁷ /cm ³ to 1.65×10 ⁷ /cm ³ , adding Steam can increase the removal efficiency of fine particle number concentration from 20% to 67%; after adding steam, the total mercury concentration in the flue gas passing through the outlet of the wire mesh demister can be reduced from 1.23μg/m ³ to 0.82μg/m ³ , Mercury removal efficiency can be increased from 18% to 45%.

Example 2:

As shown in Figure 3, different from Example 1, the water-vapor phase change chamber 4 is not installed separately behind the wet desulfurization tower 1, but the height of the wet desulfurization tower 1 is appropriately increased, and the wet desulfurization tower demister 3 The space above is used as the water vapor phase change chamber 4, and injects an appropriate amount of normal pressure saturated water vapor, and the outlet of the water vapor phase change chamber 4 at the top of the tower is provided with a high-efficiency wire mesh eliminator, and all the other are the same as embodiment 1.

Claims (10)

1. The method for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization is characterized in that the specific process is as follows: the coal-fired flue gas enters the water vapor phase change chamber after wet desulfurization, and injects normal The saturated steam makes the flue gas reach a supersaturated state, and the supersaturated water vapor takes fine particles as condensation nuclei to condense on its surface, and the condensed and grown dusty droplets are captured by the demister; at the same time, the supersaturated water vapor Mercury is enriched on the surface of fine particles, supersaturated water vapor nucleates and condenses on the surface of mercury-containing fine particles, and the condensed and grown-up dust-laden droplets are finally removed by the demister, so that fine particles in coal-fired flue gas and Co-removal of mercury. 2. The method for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization according to claim 1, characterized in that the temperature of the flue gas after the wet desulfurization is 45-65°C and the relative humidity is ≥90 %. 3. The method for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization according to claim 1 or 2, characterized in that the degree of supersaturation of the water vapor phase change chamber is 1.10-1.25. 4. The method for promoting the coordinated removal of mercury and fine particulate matter in wet flue gas desulfurization according to claim 1 or 2, characterized in that the fine particulate matter is PM _2.5 with an aerodynamic diameter less than or equal to 2.5 μm, Including fly ash, sulfuric acid mist droplets and inorganic salt aerosol particles formed in the wet desulfurization process in the original coal-fired flue gas. 5. The method for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization according to claim 1 or 2, characterized in that the wet desulfurization process is limestone-gypsum method, ammonia method, double alkali One of the method, the sodium-alkali method, and the seawater method. 6. A device for realizing the method for promoting the coordinated removal of mercury and fine particles in wet flue gas desulfurization as claimed in claim 1, characterized in that the device comprises a wet desulfurization tower, a water vapor phase change chamber, a steam System, demister, flushing water system and flushing waste liquid outlet; the flue gas outlet of the wet desulfurization tower is connected with the flue gas inlet of the water vapor phase change chamber, and the water vapor phase change chamber is independently set outside the wet desulfurization tower Or be located inside the wet desulfurization tower; the steam system, demister and flushing water system are located in the water vapor phase change chamber, the steam system injects saturated steam at normal pressure into the water vapor phase change chamber, and the demister is located in the water vapor phase change chamber At the flue gas outlet, the flushing water system is used to flush the demister; the flushing waste liquid outlet is located at the bottom of the water vapor phase change chamber. 7. The device according to claim 6, wherein the water-vapor phase change chamber is a cylindrical or square structure, and its inner lining is a corrosion-resistant low surface energy material. 8. The device according to claim 6 or 7, characterized in that the demister is a wire mesh demister or a corrugated plate demister. 9. The device according to claim 6 or 7, wherein the steam system is a steam nozzle; the flushing water system is a flushing water nozzle. 10. The device according to claim 6 or 7, characterized in that, the size of the water vapor phase change chamber is such that the residence time of flue gas in the water vapor phase change chamber is not less than that of supersaturated water vapor nucleation and condensation on the surface of fine particles The required time is determined; the time required for coagulation growth is 50-200ms.