A method and device for enhancing WFGD system to remove CPM collaboratively

Abstract

The present application provides a method and device for enhancing the synergistic removal of CPM in a WFGD system. The method comprises a desulfurization tower, a cold water spray layer, a desulfurization slurry spray layer, a hot alkaline solution spray layer, and a demister. The method is as follows: first, the hot alkaline solution spray layer sprays high-temperature fine alkaline droplets, which can regulate the flue gas cooling and humidification rate to a certain extent and precipitate Ca(OH)2, CaCO3, or CaSO4 particles, inducing CPM to transform into a particle state through heterogeneous condensation with the precipitated fine particles as condensation nuclei, hindering the transformation of CPM into submicron droplets through homogeneous condensation. The competitive evaporation of the high-temperature fine droplets will increase the water vapor partial pressure around the slurry droplets, reduce the evaporation rate of the slurry droplets, and block the re-release of CPM during the evaporation of the slurry droplets. While reacting with SO2, the alkaline droplets can also induce the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of the alkaline droplets. The present application can effectively enhance the removal of CPM by the wet flue gas desulfurization system, improve the desulfurization efficiency, and is suitable for coal-fired boilers equipped with a wet flue gas desulfurization system.

Description

Technical Field

[0001] The present invention relates to the field of deep treatment of flue gas after wet flue gas desulfurization, and in particular to a method and device for enhancing the coordinated removal of CPM in a WFGD system. Background Art

[0002] CPM refers to substances that are gaseous in the flue gas environment but immediately transform into solid or liquid particles through condensation or reactions after cooling and dilution after leaving the flue gas and entering the atmosphere. Once in the atmosphere, CPM rapidly condenses into a large number of submicron particles, becoming precursors to secondary aerosols in the ambient air and considered one of the main causes of haze.

[0003] Currently, ultra-low emission dust removal retrofits for domestic coal-fired power plants often utilize low-temperature electrostatic precipitators (ESPs), desulfurization-coordinated high-efficiency ESPs, and wet ESPs. These technologies, while achieving efficient FPM removal, also contribute to the synergistic removal of CPM. Given the urgent need to improve the removal efficiency of fine particulate matter (CPM) using conventional pollutant control facilities, the use of various physical or chemical processes to enlarge fine particles and then remove them is an important technical approach to enhancing the removal of fine particulate matter using conventional pollutant control facilities, such as wet flue gas desulfurization. Among these technologies, water vapor phase change technology, based on the condensation properties of supersaturated water vapor on particle surfaces, is particularly well-suited for integration with processes such as wet flue gas desulfurization, where the water vapor content is high.

[0004] Wet flue gas desulfurization (WFGD) systems are typically deployed between dry and wet ESPs. Leveraging their complex internal physical and chemical processes, they can not only further capture CPM that has penetrated the dry ESP, but also alter the chemical composition and phase distribution of CPM in the flue gas, thereby affecting the capture efficiency of subsequent desulfurization and mist removal systems and wet ESPs. Therefore, fully leveraging the WFGD system's synergistic conversion / removal of CPM is one of the key approaches to controlling its emissions.

[0005] This patent discloses a method and device for enhancing the synergistic removal of CPM in a WFGD system. First, a hot alkaline solution spray layer sprays high-temperature fine alkaline droplets, which can regulate the flue gas cooling and humidification rate to a certain extent and precipitate Ca(OH)2, CaCO3, or CaSO4 particles. This induces CPM to transform into a particle state through heterogeneous condensation using the precipitated fine particles as condensation nuclei, hindering the transformation of CPM into submicron droplets through homogeneous condensation. The competitive evaporation of the high-temperature fine droplets increases the water vapor partial pressure around the slurry droplets, reduces the evaporation rate of the slurry droplets, and hinders the re-release of CPM during the evaporation process of the slurry droplets. While reacting with SO2, the alkaline droplets can also induce the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of the alkaline droplets, reducing the possibility of their subsequent participation in chemical reactions to re-form CPM. It can also effectively capture FPM in the flue gas, reduce the FPM concentration in the flue gas, and reduce the possible double decomposition reaction of CPM after heterogeneous condensation on the FPM surface, thereby reducing the re-release of CPM. Secondly, injecting low-temperature, fine droplets into the cold water spray layer can deeply cool and humidify the flue gas, thereby creating a supersaturated water vapor field in the desulfurization and scrubbing zone, inhibiting the evaporation of desulfurization slurry droplets and preventing the re-release of CPM in the slurry. The supersaturated water vapor field created strengthens the condensation and growth of water vapor using CPM particles as condensation nuclei, which are then intercepted and removed by the subsequent desulfurization and mist removal system. Therefore, we propose a method and device for enhancing the synergistic removal of CPM in the WFGD system. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and device for synergistically removing CPM by wet desulfurization in response to the urgent need to improve the CPM removal efficiency of wet desulfurization systems, thereby enhancing the removal of CPM by wet desulfurization systems.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] Enhance the WFGD system to synergistically remove CPM to improve the above problems.

[0009] The specific application is as follows:

[0010] A method for enhancing the collaborative removal of CPM from a WFGD system, characterized by:

[0011] First, the hot alkali liquid spray layer sprays out high-temperature fine alkali droplets. While reacting with SO2, the alkali droplets induce the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of the alkaline droplets. The high-temperature alkali droplets also effectively capture FPM in the flue gas. Secondly, low-temperature fine droplets are sprayed into the cold water spray layer to deeply cool and humidify the flue gas, which is used to establish a supersaturated water vapor field in the desulfurization washing area and inhibit the evaporation of desulfurization slurry droplets.

[0012] As the preferred technical solution of this application, the high-temperature fine alkaline droplets are Ca(OH)2 or CaCO3 supernatant, and the temperature of the high-temperature fine alkaline droplets is higher than the desulfurization slurry temperature, which is generally between 38 and 42 degrees.

[0013] As a preferred technical solution of this application, the high-temperature, fine alkaline droplets can regulate the flue gas cooling and humidification rate to a certain extent and precipitate Ca(OH)2, CaCO3, or CaSO4 particles. This induces CPM to transform into a particle state through heterogeneous condensation using the precipitated fine particles as condensation nuclei, hindering the CPM's transformation into submicron droplets through homogeneous condensation. The competitive evaporation of the high-temperature, fine droplets increases the water vapor partial pressure around the slurry droplets, reduces their evaporation rate, and hinders the re-release of CPM during the evaporation process.

[0014] As a preferred technical solution of this application, the uniformly sprayed high-temperature fine alkaline droplets react with SO2 while also inducing the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of the alkaline droplets, reducing the possibility of subsequent chemical reactions to re-form CPM.

[0015] As the preferred technical solution of this application, the sprayed high-temperature fine alkaline droplets can also effectively capture FPM in the flue gas to reduce the FPM concentration in the flue gas, reduce the double decomposition reaction that may occur after CPM condenses on the FPM surface through heterogeneous phase, and thereby reduce the re-release of CPM.

[0016] As the preferred technical solution of this application, the low-temperature droplets can deeply cool and humidify the flue gas, thereby establishing a supersaturated water vapor field in the desulfurization washing area, inhibiting the evaporation of desulfurization slurry droplets, and preventing the re-release of CPM in the slurry; the supersaturated water vapor field formed is used to strengthen the condensation and growth of water vapor with particulate CPM as condensation nuclei, and then being intercepted and removed by the subsequent desulfurization and demisting system.

[0017] As the preferred technical solution of this application, the uniform spraying of an appropriate amount of high-temperature fine alkali droplets and the uniform spraying of an appropriate amount of low-temperature fine droplets can be satisfied by a metering pump to deliver the liquid volume. The low-temperature fine droplets are water, and the temperature is lower than the desulfurization slurry temperature.

[0018] A device for implementing a method for enhancing the coordinated removal of CPM in a WFGD system includes a desulfurization tower and a metering pump. The device is characterized in that a cold water spray layer and a hot alkali solution spray layer are provided in the middle of the desulfurization tower, and a demister is provided on the top of the tower.

[0019] As the preferred technical solution of the present application, the desulfurization tower includes a spray tower, a swirl plate tower, a packed tower, or a turbulent ball tower. The cold water spray layer in the middle of the desulfurization tower adopts a solid cone nozzle, and the demister is a baffle demister.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In the scheme of this application:

[0022] 1. Evenly spraying an appropriate amount of high-temperature, fine alkali droplets into the hot alkali solution spray layer can regulate the flue gas cooling and humidification rate to a certain extent and precipitate Ca(OH)2, CaCO3, or CaSO4 particles, inducing CPM to transform into a particle state through heterogeneous condensation using the precipitated fine particles as condensation nuclei, hindering the transformation of CPM into submicron droplets through homogeneous condensation. The competitive evaporation of the high-temperature, fine droplets increases the water vapor partial pressure around the slurry droplets, reduces the evaporation rate of the slurry droplets, and hinders the re-release of CPM during the evaporation process.

[0023] 2. The evenly sprayed fine alkaline droplets react with SO2 and can also induce the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of alkaline droplets, reducing the possibility of their subsequent participation in chemical reactions to re-form CPM.

[0024] 3. High-temperature fine alkaline droplets can also effectively capture FPM in the flue gas, reduce the concentration of FPM in the flue gas, reduce the double decomposition reaction that may occur after CPM condenses on the FPM surface through heterogeneous phase, and thus reduce the re-release of CPM.

[0025] 4. The low-temperature fine droplets sprayed into the cold water spray layer can deeply cool and humidify the flue gas, thereby establishing a supersaturated water vapor field in the desulfurization washing area, inhibiting the evaporation of desulfurization slurry droplets and preventing the re-release of CPM in the slurry;

[0026] 5. The supersaturated water vapor field is used to strengthen the condensation and growth of water vapor with particle-state CPM as condensation nuclei, and then it is intercepted and removed by the subsequent desulfurization and demisting system; BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the device structure of the enhanced WFGD system collaborative CPM removal method provided in this application;

[0028] Indicated in the figure:

[0029] 1. Water storage tank; 2. Liquid storage tank; 3. Metering pump; 4. Demister; 5. Desulfurization slurry spray layer; 6. Cold water spray layer; 7. Hot alkali solution spray layer; 8. Liquid feed pump; 9. Desulfurization tower; 10. Solid cone nozzle DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0031] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents some embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features and technical solutions in the embodiments can be combined with each other in the absence of conflict.

[0032] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0033] This embodiment proposes a method for enhancing the synergistic removal of CPM by the WFGD system. First, an appropriate amount of high-temperature fine alkali droplets are evenly sprayed into the hot alkali liquid spray layer 7 of the desulfurization tower 9. The contact between high-temperature flue gas and high-temperature fine alkaline droplets can, to a certain extent, regulate the flue gas cooling and humidification rate and precipitate Ca(OH)2, CaCO3 or CaSO4 particles, inducing CPM to transform into a particle state through heterogeneous condensation with the precipitated fine particles as condensation nuclei, hindering the transformation of CPM into submicron droplets through homogeneous condensation; the competitive evaporation of high-temperature fine droplets will increase the water vapor partial pressure around the slurry droplets, reduce the evaporation rate of the slurry droplets, and block the re-release of CPM during the evaporation process of the slurry droplets; while reacting with SO2, the fine alkaline droplets can also induce the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of the alkaline droplets, reducing the possibility of their subsequent participation in chemical reactions to re-form CPM; the injected high-temperature fine alkaline droplets can also effectively capture FPM in the flue gas, reduce the FPM concentration in the flue gas, reduce the possible decomposition reaction of CPM after heterogeneous condensation on the FPM surface, and thereby reduce the re-release of CPM.

[0034] Secondly, a suitable amount of low-temperature, fine droplets is sprayed into the cold water spray layer 6 in the middle of the desulfurization tower 9. This deeply cools and humidifies the flue gas, thereby creating a supersaturated water vapor field in the desulfurization scrubbing zone, inhibiting the evaporation of the desulfurization slurry droplets and preventing the re-release of CPM in the slurry. This supersaturated water vapor field strengthens the condensation and growth of water vapor using CPM particles as condensation nuclei, which are then intercepted and removed by the subsequent desulfurization and demisting system. The high-temperature, fine alkaline droplets are Ca(OH)2 or CaCO3 supernatant, with a temperature higher than the desulfurization slurry temperature; the low-temperature, fine droplets are water, with a temperature lower than the desulfurization slurry temperature.

[0035] Flue gas from coal-fired power plant boilers or industrial boilers enters desulfurization tower 9. First, a suitable amount of high-temperature, fine alkaline droplets are sprayed into the tower's hot alkaline solution spray layer 7. These droplets are composed of supernatant Ca(OH)2 or CaCO3, with a temperature higher than that of the desulfurization slurry. The average droplet size is 30-100 μm and is sourced from a liquid storage tank 2. These high-temperature droplets regulate the flue gas cooling and humidification rate to a certain extent and precipitate Ca(OH)2, CaCO3, or CaSO4 particles. This induces the conversion of CPM to a particle state through heterogeneous condensation using the precipitated fine particles as condensation nuclei, hindering the conversion of CPM to submicron droplets through homogeneous condensation. Secondly, a suitable amount of low-temperature, fine droplets are sprayed into the tower's cold water spray layer 6. These droplets are composed of water at a temperature of 20-30°C and have an average droplet size of 30-100 μm. They are sourced from a water storage tank 1. Low-temperature droplet evaporation is used to deeply cool and humidify the flue gas, thereby creating a supersaturated water vapor field in the desulfurization scrubbing zone, inhibiting the evaporation of desulfurization slurry droplets and preventing the re-release of CPM in the slurry. The supersaturated water vapor field is used to strengthen the condensation and growth of water vapor using particulate CPM as condensation nuclei, and then being intercepted and removed by the subsequent baffle demister 4. The wet flue gas desulfurization process is the limestone-gypsum method.

[0036] like Figure 1 The device for enhancing the WFGD system's synergistic CPM removal method comprises a water tank 1, a liquid tank 2, a metering pump 3, a cold water spray layer 6, a hot alkali solution spray layer 7, a desulfurization tower 9, and a demister 4. The cold water spray layer 6 is located in the middle of the desulfurization tower 9, the hot alkali solution spray layer 7 is located below the desulfurization slurry spray layer 5, and the demister 4 is located at the top of the tower. The cold water spray layer 6 uses a solid cone nozzle 10. The desulfurization tower 9 includes a spray tower, a swirl plate tower, a packed tower, or a turbulent ball tower. The demister 4 is a baffle demister. High-temperature fine alkali droplets and low-temperature fine droplets are stored in the liquid tank 2 and the water tank 1, respectively, and are sprayed in by the metering pump 3. The desulfurization tower 9 is provided with a water tank 1 for cold water and a liquid tank 2 for hot alkali solution, and is connected to a cold water spray layer 6 and a hot alkali solution spray layer 7 via a metering pump 3. The cold water spray layer 6 is 1-2 meters away from the high-efficiency mist eliminator 4. The desulfurization tower 9 can be a spray tower, a cyclone plate tower, a packed tower, a turbulent ball tower, or other tower types. The average particle size of the spray droplets in the cold water spray layer 6 is 30-100 μm; the cold water temperature is 20-30°C, which is more than 10°C lower than the desulfurized clean flue gas temperature, and the liquid-gas ratio is controlled at 1L / Nm 3 about.

[0037] The flue gas is generated by a fully automatic coal-fired boiler with a flue gas volume of 500Nm 3 / h, the system consists of a desulfurization tower 9, a metering pump 3, a slurry spray layer 5, a cold water spray layer 6, a hot alkali solution spray layer 7, and a demister 4. Limestone / gypsum method is used for flue gas desulfurization. The wet desulfurization tower 9 adopts a spray tower with a tower diameter of 25mm and a tower height of 5200mm, and a demister 4 is installed on the top of the spray tower. The flue gas enters the desulfurization tower 9 and comes into contact with the high-temperature fine alkaline droplets sprayed from the hot alkali solution spray layer 7, which regulates the flue gas cooling and humidification rate to a certain extent. Then it comes into contact with the low-temperature fine droplets sprayed from the cold water spray layer 6 of the desulfurization tower 9. The cold water spray layer 6 adopts a solid cone nozzle 10, the cold water temperature is 17°C, and the liquid-gas ratio is 0.9L / Nm 3 The temperature of the desulfurized flue gas can be reduced to 6°C as measured by the Vaisala-HMT37 temperature and humidity transmitter. The CPM at the outlet of desulfurization tower 9 was tested by Method 202 and was 3mg / m 3 .

[0038] In response to the urgent need to improve the removal efficiency of CPM in wet flue gas desulfurization systems, the present invention provides a technology and device for enhancing the synergistic removal of CPM by WFGD. Through the method of graded spraying, CPM can be transformed and removed in the WFGD process mainly towards the path of heterogeneous condensation, nucleation condensation and growth, and slurry droplet collision and capture, and at the same time, with the help of a supersaturated water vapor field, the re-release of CPM in the slurry evaporation process is suppressed, thereby achieving a reduction in CPM emission concentration. The hot alkaline solution spray layer 7 is uniformly sprayed with an appropriate amount of high-temperature fine alkaline droplets, and the cold water spray layer 6 is uniformly sprayed with an appropriate amount of low-temperature fine droplets to deeply cool and humidify the flue gas, thereby establishing a supersaturated water vapor field in the desulfurization washing area, suppressing the evaporation of desulfurization slurry droplets, and preventing the re-release of CPM in the slurry; on the other hand, the supersaturated water vapor field formed is utilized to strengthen the condensation and growth of water vapor with particulate CPM as condensation nuclei, which is then intercepted and removed by the subsequent desulfurization and demisting system.

[0039] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Although this specification has described the present invention in detail with reference to the above embodiments, the present invention is not limited to the above specific implementation methods. Therefore, any modification or equivalent replacement of the present invention; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the invention are included in the scope of the claims of the present invention.

Claims

1. A method for enhancing the synergistic removal of CPM from a WFGD system, characterized by: First, the hot alkali liquid spray layer sprays high-temperature fine alkali droplets with a particle size of 30-100μm. While reacting with SO2, the alkali droplets induce the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of the alkaline droplets. The high-temperature alkali droplets also effectively capture FPM in the flue gas. Secondly, the cold water spray layer sprays low-temperature fine droplets with a particle size of 30-100μm to deeply cool and humidify the flue gas, thereby establishing a supersaturated water vapor field in the desulfurization washing area and suppressing the evaporation of desulfurization slurry droplets. The device for implementing this method includes: a cold water spray layer and a desulfurization slurry spray layer arranged alternately in the middle of the desulfurization tower, and both ends of the middle spray zone are desulfurization slurry spray layers. The high-temperature fine alkali droplets are Ca(OH)2 or CaCO3 supernatant, and the temperature of the high-temperature fine alkali droplets is higher than the temperature of the desulfurization slurry, and the injection position is between the flue gas inlet and the lowest desulfurization slurry spray layer; the low-temperature fine droplets are water, and the temperature is lower than the desulfurization slurry temperature; The high-temperature fine alkaline droplets can regulate the flue gas cooling and humidification rate to a certain extent and precipitate Ca(OH)2, CaCO3 or CaSO4 particles, inducing CPM to transform into a particle state through heterogeneous condensation with the precipitated fine particles as condensation nuclei, and hindering the transformation of CPM into submicron droplets through homogeneous condensation.

2. The method for enhancing the WFGD system to collaboratively remove CPM according to claim 1, characterized in that: The high-temperature fine alkaline droplets react with SO2 and simultaneously induce the dissolution / absorption of acidic and hydrophilic components in CPM on the surface of the alkaline droplets, thereby reducing the possibility of their subsequent participation in chemical reactions to re-form CPM.

3. The method for enhancing the WFGD system to collaboratively remove CPM according to claim 2, characterized in that: The high-temperature fine alkaline droplets can effectively capture FPM in the flue gas to reduce the FPM concentration in the flue gas, reduce the double decomposition reaction of CPM after it condenses on the FPM surface through heterogeneous phase, and thus reduce the re-release of CPM.

4. The method for enhancing the WFGD system to collaboratively remove CPM according to claim 1, characterized in that: The low-temperature fine droplets can deeply cool and humidify the flue gas, thereby establishing a supersaturated water vapor field in the desulfurization and washing area. The supersaturated water vapor field is used to inhibit the evaporation of desulfurization slurry droplets and prevent the re-release of CPM in the slurry.

5. The method for enhancing the WFGD system to collaboratively remove CPM according to claim 4, characterized in that: The supersaturated water vapor field can enhance the condensation and growth of water vapor with particle-state CPM as condensation nuclei, and is removed by the subsequent demisting system.

6. The method for enhancing the WFGD system to collaboratively remove CPM according to claim 3, characterized in that: The high-temperature fine alkali mist droplets and the low-temperature fine mist droplets are delivered by a metering pump (3) to meet their liquid delivery volume.

7. A device for implementing the enhanced WFGD system collaborative CPM removal method according to any one of claims 1 to 6, comprising a desulfurization tower (9) and a metering pump (3), characterized in that: The desulfurization tower (9) has a cold water spray layer (6) and a desulfurization slurry spray layer (5) arranged alternately in the middle, and both ends of the middle spray zone are desulfurization slurry spray layers, a hot alkali solution spray layer (7) is provided at the lower part, and a demister (4) is provided at the top of the tower.

8. The device for enhancing the WFGD system collaborative CPM removal method according to claim 7, characterized in that: The desulfurization tower (9) includes a spray tower, a swirl plate tower, a packed tower, or a turbulent ball tower. The cold water spray layer (6) in the middle of the desulfurization tower (9) adopts a solid cone nozzle (10), and the demister is a baffle demister (4).

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