Dust collection system and dust collection method

Abstract

The purpose of the present invention is to optimally trap and collect fine particles included in exhaust gas. A dust collection system (10) comprises: a circulation path through which exhaust gas disc

Description

Dust collection system and dust collection method

[0001] The present disclosure relates to a dust collection system and a dust collection method.

[0002] In power plants that burn fossil fuels and waste treatment plants that burn waste, dust collection systems that capture fine particles contained in exhaust gas are installed as exhaust gas treatment devices (for example, see Patent Document 1). Patent Document 1 describes an apparatus that supercools a portion of the exhaust gas in a supercooler and rapidly mixes it with uncooled exhaust gas, thereby causing the condensed moisture in the gas to enlarge the dust in the exhaust gas and remove it.

[0003] Japanese Utility Model Application Laid-Open Publication No. 2-104821

[0004] When a dust collection system is adopted that injects liquid droplets into exhaust gas to capture fine particles contained in the exhaust gas with the liquid droplets, there is a possibility that small fine particles contained in the exhaust gas will not adhere to the liquid droplets properly even if the liquid droplets are injected into the exhaust gas. If the fine particles do not adhere to the liquid droplets properly, there is a possibility that the fine particles contained in the exhaust gas will not be captured properly.

[0005] The present disclosure has been made in consideration of the above circumstances, and aims to provide a dust collection system and a dust collection method that can suitably collect fine particles contained in exhaust gas.

[0006] In order to solve the above problems, the dust collection system and dust collection method of the present disclosure employ the following means: The dust collection system according to one aspect of the present disclosure includes a flow path through which exhaust gas containing saturated water vapor discharged from a combustion device flows, and a droplet supply unit that supplies droplets having a temperature lower than that of the exhaust gas to the exhaust gas flowing through the flow path.

[0007] A dust collection method according to one aspect of the present disclosure includes a step of supplying droplets having a lower temperature than exhaust gas containing saturated water vapor that is discharged from a combustion device and flows through a flow path, and a step of collecting fine particles contained in the exhaust gas.

[0008] According to the present disclosure, fine particles contained in exhaust gas can be suitably collected.

[0009] FIG. 1 is a schematic configuration diagram showing a boiler system according to a first embodiment of the present disclosure. FIG. 2 is a schematic configuration diagram showing a dust collection system according to the first embodiment of the present disclosure. FIG. 3 is a schematic side view showing a dust collection system according to the first embodiment of the present disclosure. FIG. 4 is a perspective view showing a schematic configuration of a dust collection system according to the first embodiment of the present disclosure. FIG. 5 is a cross-sectional view showing a schematic configuration of a dust collection system according to the first embodiment of the present disclosure. FIG. 6 is an explanatory diagram illustrating the processing of the dust collection system according to the first embodiment of the present disclosure. FIG. 7 is an explanatory diagram illustrating the effect of the dust collection system according to the first embodiment of the present disclosure. FIG. 8 is a graph showing the relationship between the gas temperature decrease width and dust collection efficiency in the dust collection system according to the first embodiment of the present disclosure. FIG. 9 is a graph showing the relationship between the gas temperature decrease width and the diameter of fine particles (SO3 mist) in the dust collection system according to the first embodiment of the present disclosure. FIG. 10 is a schematic configuration diagram showing a boiler system according to a second embodiment of the present disclosure. FIG. 11 is a schematic side view showing a dust collection system according to the second embodiment of the present disclosure. FIG. 12 is a graph showing the relationship between the position in the exhaust gas flow direction and the saturated water vapor amount of the exhaust gas in the dust collection system according to the second embodiment of the present disclosure.

[0010] First Embodiment A first embodiment of a dust collection system and a dust collection method according to the present disclosure will be described below with reference to the drawings. In this embodiment, the dust collection system will be described as treating exhaust gas burned by a combustion device, but the present disclosure is not limited thereto. The dust collection system can be used to capture various fine particles contained in gas. For example, the dust collection system can be used as a system for collecting fine particles contained in the air in a manufacturing plant, or as a system for collecting fine particles, such as dust, at a work site such as demolition work. Furthermore, the fine particles are not limited to solids, and may be liquids such as droplets or tar.

[0011] As shown in FIG. 1 , a dust collection system 10 according to this embodiment is provided in a boiler system 1. The boiler system 1 includes a boiler 2, a forced draft fan 3 that supplies air to the boiler 2, a denitration device 4 that denitrifies exhaust gas discharged from the boiler 2, an air preheater 5 that exchanges heat between the exhaust gas discharged from the denitration device 4 and the air supplied to the boiler 2, a dry electrostatic precipitator 6 to which the exhaust gas discharged from the air preheater 5 is guided, a desulfurization device 7 to which the exhaust gas discharged from the dry electrostatic precipitator 6 is guided, a dust collection system 10 that supplies liquid droplets to the exhaust gas discharged from the desulfurization device 7, and a chimney 8 to which the exhaust gas discharged from the dust collection system 10 is guided. The boiler 2 generates steam by combusting fuel. The boiler 2 discharges exhaust gas generated during combustion. The desulfurization device 7 has a temperature reducing tower 7a that reduces the temperature of the exhaust gas by supplying cooling water to the exhaust gas.

[0012] Next, a detailed description will be given of the dust collection system 10. The dust collection system 10 collects fine particles contained in exhaust gas. In the following description, the fine particles are also referred to as "mist."

[0013] 2 and 3 , the dust collection system 10 includes a flow path 11 through which exhaust gas discharged from components such as the boiler 2 and the temperature reducing tower 7a of the desulfurization device 7 flows, a droplet supply unit 12 that supplies droplets having a temperature lower than that of the exhaust gas to the exhaust gas flowing through the flow path 11, an electrostatic agglomeration unit 13 that charges fine particles and droplets contained in the exhaust gas and causes the fine particles and droplets to collide with each other, and a wet electrostatic precipitator 14 that collects the droplets with fine particles attached. As shown in FIGS. 3 and 4 , a demister 15 may be provided instead of the wet electrostatic precipitator 14. Alternatively, fine particles may be removed from the exhaust gas by gravity settling due to the weight of the droplets to which the fine particles are attached, without providing either the wet electrostatic precipitator 14 or the demister 15.

[0014] The flow path 11 is a pipe through which the exhaust gas generated in the boiler 2 flows in a flow direction A1. In the flow path 11, a droplet supply unit 12, an electrostatic agglomeration unit 13, and a wet electrostatic precipitator 14 are arranged in this order from the upstream side in the flow direction A1.

[0015] The droplet supply unit 12 supplies droplets CL to the exhaust gas flowing through the flow path 11. Specifically, the droplet supply unit 12 sprays liquid into the flow path 11 to form a large number of droplets CL. The droplet supply unit 12 includes a plurality of nozzles 20. The nozzles 20 spray the liquid to form droplets having a particle size within a predetermined range. As shown in FIG. 1 , wastewater from the wet electrostatic precipitator 14 is cooled in a cooling tower and is introduced into the nozzles 20.

[0016] The temperature of the droplets supplied by the droplet supply unit 12 is lower than the temperature of the exhaust gas flowing through the flow path 11. In other words, the temperature of the droplets supplied by the droplet supply unit 12 is lower than the temperature of the exhaust gas to which the droplets are supplied.

[0017] The droplet supply unit 12 supplies droplets to the exhaust gas so that the temperature of the exhaust gas falls within a range of 5° C. to 30° C. The droplet supply unit 12 also supplies droplets to the exhaust gas so that the ratio of the flow rate of the droplets to the flow rate of the exhaust gas flowing through the flow path 11 is such that when the flow rate of the droplets is 1 liter per minute, the flow rate of the exhaust gas is 0.1 m / min. ３ More than 10m ３ The droplets are supplied so that the ratio is as follows: That is, the flow rate of the droplets (L / min) and the flow rate of the exhaust gas (m ３ / min) and the ratio (L / m ３ ) is said to be between 0.1 and 10.

[0018] The droplet supply unit 12 supplies droplets having a particle size of 30 μm or more and 200 μm or less. The droplet supply unit 12 sprays the droplets at a speed of 20 m / s or more. The spray angle θ of the droplets from the nozzle 20 of the droplet supply unit 12 is 5 degrees or more and 120 degrees or less.

[0019] The electrostatic agglomeration unit 13 is disposed downstream of the nozzle 20 of the droplet supply unit 12 in the flow path 11. The electrostatic agglomeration unit 13 forms an electric field in the area through which the fine particles and droplets pass, charging the fine particles and droplets. The charged fine particles and droplets move in the electric field by diffusion and electrophoresis, and collide (agglomerate) with each other. When the fine particles collide with the droplets, they are absorbed into the droplets. As shown in FIGS. 4 and 5 , the electrostatic agglomeration unit 13 has a discharge electrode 30 and a ground electrode 31. A predetermined voltage is applied to the discharge electrode 30. The ground electrode 31 is a plate-shaped electrode disposed facing the discharge electrode 30. The ground electrode 31 is disposed with its surface facing the flow direction A1. This prevents the ground electrode 31 from acting as a resistance to the flow of exhaust gas. The ground electrode 31 is grounded.

[0020] Electrostatic agglomeration unit 13 applies a predetermined voltage to discharge electrode 30 to form an electric field between discharge electrode 30 and earth electrode 31. That is, an agglomeration electric field is formed between discharge electrode 30 and earth electrode 31. Note that electrostatic agglomeration unit 13 only needs to be able to form an electric field between discharge electrode 30 and earth electrode 31, and a predetermined voltage may be applied to earth electrode 31 without grounding it.

[0021] In this embodiment, electrostatic agglomeration unit 13 is arranged downstream of nozzle 20, but this is not limiting. A part of electrostatic agglomeration unit 13 may be arranged upstream of nozzle 20. In other words, nozzle 20 may be arranged inside electrostatic agglomeration unit 13. Furthermore, discharge electrode 30 and earth electrode 31 may be pipe-shaped instead of plate-shaped.

[0022] As shown in FIG. 2 , the wet electrostatic precipitator 14 is disposed downstream of the electrostatic agglomeration section 13 in the flow path 11. The wet electrostatic precipitator 14 forms an electric field in a region through which fine particles and liquid droplets pass, thereby collecting the fine particles and liquid droplets. The wet electrostatic precipitator 14 has a discharge electrode (not shown) and a ground electrode (not shown). The wet electrostatic precipitator 14 applies a predetermined voltage to the discharge electrode, thereby forming an electric field between the discharge electrode and the ground electrode. By forming an electric field, the wet electrostatic precipitator 14 moves the fine particles and liquid droplets contained in the exhaust gas toward the ground electrode, where they adhere to the ground electrode and are collected.

[0023] 3 and 4, a demister 15 may be provided in place of the wet electrostatic precipitator 14. The demister 15 collects droplets to which fine particles have adhered.

[0024] Next, we will explain the dust collection method of the dust collection system 10. The dust collection system 10 according to this embodiment applies an electrostatic field to fine particles in the exhaust gas containing saturated water vapor discharged from the cooling tower 7 a by supplying droplets having a lower temperature than the exhaust gas.

[0025] 3, exhaust gas E containing fine particles M is supplied to the dust collection system 10. The exhaust gas that has flowed into the dust collection system 10 moves along a flow direction A1, and droplets are supplied in a region where the nozzles 20 are arranged.

[0026] As the droplets CL are supplied from the nozzle 20, the temperature of the exhaust gas E containing saturated water vapor drops, and the saturated water vapor condenses into fine particles M. As a result, a water film W is formed that covers the fine particles M. As the water film W covers the fine particles M, the particle size of the fine particles M becomes coarser to 1 μm or more (note that, in the case where the fine particles are in a liquid state such as SO3 mist, saturated water vapor condenses on the SO3 mist, and the liquid film mixes with the SO3 mist, becoming uniform and coarsening). That is, as shown in FIG. 6( a), as the droplets CL are supplied from the nozzle 20, the particle distribution changes from fine particle distribution 82 to particle distribution 83. That is, although the number of fine particles M remains the same, the particle diameter of each particle increases.

[0027] When the fine particles M become coarser, they collide with the liquid droplets CL, and the fine particles M adhere to the liquid droplets CL. (Note that when the fine particles are in a liquid state such as SO3 mist, the coarsened SO3 mist and the liquid droplets collide, and the coarsened SO3 mist mixes with the liquid droplets, becoming uniform and coarsening.) Furthermore, the liquid droplets CL that have taken in the fine particles M are charged in the downstream electrostatic agglomeration section 13, promoting collisions between the fine particles M and the liquid droplets CL. At this time, the distribution of particles contained in the exhaust gas E includes a particle distribution 83 corresponding to the fine particles M and a droplet distribution 84 corresponding to the liquid droplets CL, as shown in Figure 6(b). In other words, the exhaust gas E contains a mixture of liquid droplets CL and coarsened fine particles M.

[0028] The droplets CL that have taken in the fine particles M are guided to the demister 15 and simply collected, as shown by arrow A2. Alternatively, the droplets CL that have taken in the fine particles M settle due to gravity and are separated from the exhaust gas E, as shown by arrow A3. In the dust collection system 10, the particle size distribution of the exhaust gas that has passed through the electrostatic agglomeration unit 13 becomes a fine particle distribution 82a and a droplet distribution 84, as shown in Fig. 6(c). Here, the fine particle distribution 82a is smaller than the fine particle distribution 82 because the fine particles are integrated with the droplets.

[0029] As shown in FIG. 2, when a wet electrostatic precipitator 14 is provided downstream of the electrostatic agglomeration section 13, the electric field formed by the wet electrostatic precipitator 14 causes droplets CL that have taken in fine particles M to be collected by the earth electrode 31 (see FIG. 4) of the wet electrostatic precipitator 14.

[0030] In this manner, the dust collection system 10 according to this embodiment captures the particulate matter M contained in the exhaust gas.

[0031] According to this embodiment, the following advantageous effects are achieved. In this embodiment, the droplet supply unit 12 supplies droplets having a lower temperature than the exhaust gas to the flow path 11. As a result, the exhaust gas is cooled by the droplets supplied from the droplet supply unit 12. When the exhaust gas is cooled, saturated water vapor contained in the exhaust gas condenses on the surfaces of the fine particles. At this time, the saturated water vapor condenses on the surfaces of the fine particles like a film that covers the entire fine particles. As a result, the fine particles after condensed water adhesion become coarser than the fine particles before adhesion by the amount of condensed water that covers them. The coarsening of the fine particles (more precisely, the fine particles covered by condensed water) makes it easier for the fine particles and the droplets to collide. The fine particles that collide with the droplets adhere to the droplets. This makes it easier to collect the fine particles together with the droplets. Therefore, the fine particles contained in the exhaust gas can be suitably collected.

[0032] In addition, in this embodiment, the exhaust gas is cooled simply by supplying low-temperature droplets. This eliminates the need for a separate large-scale device (such as a heat exchanger) to cool the exhaust gas. Therefore, the structure can be simplified compared to when a separate device for improving collection efficiency is provided.

[0033] In this embodiment, an electrostatic agglomeration unit 13 is provided which charges the particulate matter and droplets contained in the exhaust gas and causes the particulate matter and droplets to collide with each other. This makes it easier for the coarse particulate matter and droplets to collide with each other. The particulate matter that collides with the droplets adheres to the droplets. This makes it easier to collect the particulate matter together with the droplets. Therefore, the particulate matter contained in the exhaust gas can be collected in an appropriate manner.

[0034] Generally, when the particle diameter of the fine particles is 1 μm or more, the fine particles are more likely to collide with the droplets. Generally, in the concentration of fine particles in the exhaust gas downstream of a combustion device such as a boiler 2, when the temperature of the exhaust gas drops within a temperature range of 5°C or more and 30°C or less, the fine particles become 1 μm or more due to condensed water. Therefore, by lowering the temperature of the exhaust gas within this temperature range, fine particles of 1 μm or less are easily coarsened to 1 μm or more. In this embodiment, the droplet supply unit 12 supplies droplets so that the temperature of the exhaust gas drops within a range of 5°C or more and 30°C or less. As a result, the temperature of the exhaust gas drops within a range of 5°C or more and 30°C or less. This allows the saturated water vapor contained in the exhaust gas to be suitably condensed, and the condensed water to adhere to the fine particles. Therefore, the fine particles contained in the exhaust gas can be suitably coarsened, and the fine particles can be suitably collected.

[0035] The relationship between the temperature drop of the exhaust gas, the change in the diameter of the fine particles (mist), and the fine particle collection efficiency will be explained using Figures 7 to 9. Figure 7 shows a test apparatus. In the test apparatus, droplets at 20°C were sprayed into exhaust gas containing fine particles at 60°C. The average diameter of the droplets was 55 μm, and the average diameter of the fine particles was 0.47 μm.

[0036] As shown in Figures 8 and 9, when the exhaust gas temperature is reduced by 5°C or more, the diameter of the fine particles becomes coarse to a size that makes them more susceptible to collision with liquid droplets. Furthermore, when the exhaust gas temperature is reduced by 5°C or more, approximately 40% of the fine particles can be collected by gravitational settling. In particular, as shown in Figure 8, when the exhaust gas temperature is reduced by 10°C or more, the fine particles become 1.0 μm or larger, allowing for sufficient coarsening. Furthermore, as shown in Figure 9, when the exhaust gas temperature is reduced by 10°C or more, the fine particles can be sufficiently collected (approximately 90%) by gravitational settling.

[0037] 8 and 9, it can be seen that the droplet supply unit 12 can suitably collect fine particles by supplying droplets so that the temperature of the exhaust gas drops within a range of 5° C. to 30° C. In particular, it can be seen that it is more suitable to set the temperature drop range to 10° C. or more.

[0038] In this embodiment, the flow rate of the droplets (L / min) and the flow rate of the exhaust gas (m ３ The droplet supply unit 12 supplies droplets so that the ratio of the flow rate (rpm) to the flow rate (rpm) is 1:0.1 to 10. This allows the temperature of the exhaust gas to be lowered in the range of 5°C or higher and 30°C or lower. This allows the saturated water vapor contained in the exhaust gas to be suitably condensed, and the condensed water to adhere to the fine particles. Therefore, the fine particles contained in the exhaust gas can be suitably coarsened, and the fine particles can be suitably collected.

[0039] Furthermore, in this embodiment, the droplet supply unit 12 supplies droplets with a particle size of 30 μm or more and 200 μm or less. This makes it easier for fine particles not covered with condensed water to collide with the condensed water. In this way, fine particles not covered with condensed water can be made to collide preferentially with the condensed water rather than with the droplets. This allows the condensed water to adhere to the fine particles in an optimal manner. Therefore, the fine particles contained in the exhaust gas can be effectively coarsened, and the fine particles can be effectively collected.

[0040] When the water vapor in saturated steam condenses, fine particles and liquid droplets exist in the exhaust gas. Because the particle diameter of the fine particles in the exhaust gas is small, the number density np (numbers / m3) in the exhaust gas is large. On the other hand, because the liquid droplets are set larger than the fine droplets, the number density nd is smaller than the number density of the fine particles.

[0041] The probability of saturated water vapor colliding with fine particles and liquid droplets is determined by the magnitude of the mean free path λ. That is, if the number density of fine particles is N1 (particles / m3), the diameter is D1 (m), and the number density of liquid droplets is N2 (particles / m3), and the diameter is D2 (m), the respective mean free paths λ are expressed by the following equations (1) and (2). In the following equations, λ1 is the mean free path of water vapor and fine particles, and λ2 is the mean free path of water vapor and liquid droplets.

[0042] λ1=1 / (N1×πD1 ２ )...(1) λ2=1 / (N2×πD2 ２ ) ... (2)

[0043] If the droplet size is adjusted so that λ1 is about 1 / 3 of λ2, the water vapor will collide with the fine particles three times more than with the droplets, and the fine particles can be preferentially coarsened.

[0044] When the concentration (number density) and size (0.5 μm) of fine particles in exhaust gas downstream of a typical boiler are taken as the droplet gas-liquid ratio is 0.1 to 5, and the droplet diameter is 30 μm to 200 μm, the relationship λ1 < λ2 can be achieved.

[0045] In addition, in this embodiment, droplets are sprayed over a wide area at high speed. This promotes turbulent mixing of the fine particles and water vapor. This allows condensed water to adhere to the fine particles. This allows the fine particles contained in the exhaust gas to be coarsened and the fine particles to be collected.

[0046] In this embodiment, the fine particles and the liquid droplets can be made to collide more easily, which makes it easier for the fine particles to adhere to the liquid droplets. The fine particles attached to the liquid droplets are easily separated from the exhaust gas by gravity settling due to the droplets' own weight. Furthermore, the fine particles attached to the liquid droplets can be easily collected by a simple repair device such as a demister. Therefore, the fine particles can be separated and collected from the exhaust gas without installing an electrical collector (e.g., a wet electrostatic precipitator) with a complex structure. Therefore, the structure can be simplified compared to when an electrical collector is installed.

[0047] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to Figures 10 to 12. The dust collection system 100 of this embodiment differs from the first embodiment in that it includes a high-temperature droplet supply unit 120. It also differs from the first embodiment in that it includes a structure for reusing wastewater from the wet electrostatic precipitator 14. Since the other structures are similar to those of the first embodiment, the same components are designated by the same reference numerals and detailed descriptions thereof will be omitted.

[0048] As shown in Figures 10 and 11, the dust collection system 100 includes a high-temperature droplet supply unit 120. The high-temperature droplet supply unit 120 is provided upstream of the droplet supply unit 12 in the exhaust gas flow, and supplies droplets HL having a higher temperature than the exhaust gas to the flow channel 11. Specifically, the high-temperature droplet supply unit 120 injects liquid into the flow channel 11 to form a large number of droplets HL. The high-temperature droplet supply unit 120 includes a plurality of nozzles 121. The nozzles 121 spray the liquid to form droplets having a particle size within a predetermined range. The nozzles 121 are provided downstream of the desulfurization device 7.

[0049] The dust collection system 100 also includes a cooling tower (cooling section) 131 that cools the wastewater from the wet electrostatic precipitator 14, a cooled wastewater pipe 132 that guides the wastewater cooled in the cooling tower 131 to the droplet supply section 12, a heat exchange section 133 that heats the wastewater by exchanging heat between the wastewater from the wet electrostatic precipitator 14 and the exhaust gas discharged from the boiler 2, a heated wastewater pipe 134 that guides the wastewater heated in the heat exchange section 133 to the high-temperature droplet supply section 120, and a pump 135 that circulates the wastewater from the wet electrostatic precipitator 14.

[0050] The droplet supply unit 12 supplies the introduced wastewater as droplets CL to the flow path 11. The high-temperature droplet supply unit 120 supplies the introduced wastewater as droplets HL to the flow path 11. The heat exchange unit 133 is provided between the dry electrostatic precipitator 6 and the desulfurization device 7.

[0051] This embodiment provides the following advantageous effects. The present embodiment includes a high-temperature droplet supply unit 120 that is provided upstream of the droplet supply unit 12 and supplies droplets with a temperature higher than that of the exhaust gas to the flow path 11. The high-temperature droplet supply unit 120 supplies high-temperature droplets to the flow path 11, thereby increasing the temperature of the exhaust gas flowing through the flow path 11 and increasing the amount of moisture. This increases the amount of water vapor in the exhaust gas. Therefore, downstream of the high-temperature droplet supply unit 120, the droplet supply unit 12 supplies low-temperature droplets to the flow path 11, thereby increasing the amount of water condensed. This allows the water vapor to be effectively attached to the fine particles as condensed water. Therefore, the fine particles contained in the exhaust gas can be effectively coarsened, allowing the fine particles to be effectively collected. This is particularly effective when the temperature of the exhaust gas is lower than a predetermined temperature.

[0052] The relationship between the position in the exhaust gas flow direction and the saturated water vapor amount of the exhaust gas will be described with reference to Fig. 12. As shown in Figs. 11 and 12, the saturated water vapor amount increases at a position (P1) where high-temperature droplets HL are sprayed from the high-temperature droplet supply unit 120. The saturated water vapor amount continues to increase between positions P1 and P2. At a position (P2) where low-temperature droplets CL are sprayed from the droplet supply unit 12, the saturated water vapor condenses, thereby reducing the saturated water vapor amount.

[0053] Furthermore, in this embodiment, the wastewater from the wet electrostatic precipitator 14 is used in the droplet supply unit 12 and the high-temperature droplet supply unit 120, which improves the efficiency of the entire dust collection system 10 compared to a structure that does not use wastewater. Also, in this embodiment, the heat of the exhaust gas is used to heat the wastewater. This improves the efficiency of the entire dust collection system 10 compared to a structure that does not use the heat of the exhaust gas.

[0054] The present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure.

[0055] The dust collection system and dust collection method described in the above-described embodiments can be understood, for example, as follows: A dust collection system according to a first aspect of the present disclosure includes a flow path (11) through which exhaust gas containing saturated water vapor discharged from a combustion device (2) flows, and a droplet supply unit (12) that supplies droplets having a temperature lower than that of the exhaust gas to the exhaust gas flowing through the flow path.

[0056] In the above configuration, the droplet supply unit supplies droplets having a lower temperature than the exhaust gas to the flow path. As a result, the exhaust gas is cooled by the droplets supplied from the droplet supply unit. When the exhaust gas is cooled, saturated water vapor contained in the exhaust gas condenses on the surface of the fine particles. At this time, the saturated water vapor condenses on the surface of the fine particles like a film that covers the entire fine particles. As a result, the fine particles after condensed water adhesion become coarser than the fine particles before adhesion by the amount of condensed water covering them. The coarsening of the fine particles (more precisely, the fine particles covered by condensed water) makes it easier for the fine particles and the droplets to collide. The fine particles that collide with the droplets adhere to the droplets. This makes it easier to collect the fine particles together with the droplets. Therefore, the fine particles contained in the exhaust gas can be suitably collected.

[0057] Furthermore, in the above configuration, the exhaust gas is cooled simply by supplying low-temperature droplets. This eliminates the need for a separate large-scale device (such as a heat exchanger) to cool the exhaust gas. This simplifies the structure compared to when a separate device is provided to improve collection efficiency.

[0058] In addition, the dust collection system according to a second aspect of the present disclosure is the first aspect described above, and further includes an electrostatic agglomeration section (13) that is arranged in the flow path downstream of the droplet supply position, forms an electric field in the exhaust gas flow path, charges the fine particles and the droplets contained in the exhaust gas, and causes the fine particles and the droplets to collide with each other.

[0059] The above configuration includes an electrostatic agglomeration unit that charges the particulate matter and droplets contained in the exhaust gas and causes the particulate matter and droplets to collide with each other. This makes it easier for the coarse particulate matter and droplets to collide with each other. The particulate matter that collides with the droplets adheres to the droplets. This makes it easier to collect the particulate matter together with the droplets. Therefore, the particulate matter contained in the exhaust gas can be collected in an appropriate manner.

[0060] Furthermore, in the dust collection system according to a third aspect of the present disclosure, in the first or second aspect described above, the droplet supply unit supplies the droplets so that the temperature of the exhaust gas is reduced within a range of 5°C or more and 30°C or less.

[0061] Generally, when the particle size of the fine particles is 1 μm or more, the fine particles are more likely to collide with liquid droplets. Generally, in the concentration of fine particles in the exhaust gas downstream of the combustion device, when the temperature of the exhaust gas decreases within the temperature range of 5°C or more and 30°C or less, the amount of condensed water adhering to the fine particles increases. Therefore, by decreasing the temperature of the exhaust gas within this temperature range, fine particles of 1 μm or less tend to coarsen to 1 μm or more.

[0062] In the above configuration, the droplet supply unit supplies droplets so that the temperature of the exhaust gas decreases within a range of 5°C or more and 30°C or less. As a result, the temperature of the exhaust gas decreases within a range of 5°C or more and 30°C or less. This allows the saturated water vapor contained in the exhaust gas to be suitably condensed, and the condensed water to adhere to the fine particles. Therefore, the fine particles contained in the exhaust gas can be suitably coarsened, and the fine particles can be suitably collected.

[0063] Further, in the dust collection system according to a fourth aspect of the present disclosure, in any one of the first to third aspects, the droplet supply unit is configured such that a ratio of a flow rate of the droplets to be supplied to a flow rate of the exhaust gas flowing through the flow path is such that when the flow rate of the droplets is 1 liter per minute, the flow rate of the exhaust gas is 0.1 m / min. ３ More than 10m ３ The droplets are supplied in the following ratio:

[0064] In the above configuration, the flow rate of the droplets (L / min) and the flow rate of the exhaust gas (m ３The droplet supply unit supplies droplets so that the ratio of the flow rate (rpm) to the flow rate (rpm) is 1:0.1 to 10. This allows the temperature of the exhaust gas to be lowered in the range of 5°C or higher and 30°C or lower. This allows the saturated water vapor contained in the exhaust gas to be suitably condensed, and the condensed water to adhere to the fine particles. Therefore, the fine particles contained in the exhaust gas can be suitably coarsened, and the fine particles can be suitably collected.

[0065] Furthermore, in the dust collection system according to a fifth aspect of the present disclosure, in the fourth aspect, the droplet supply unit supplies the droplets having a particle size of 30 μm or more and 200 μm or less.

[0066] In the above configuration, the droplet supply unit supplies droplets with a particle size of 30 μm or more and 200 μm or less. This makes it easier for fine particles not covered with condensed water to collide with the condensed water. In this way, fine particles not covered with condensed water can be made to collide preferentially with the condensed water rather than with the droplets. This allows the condensed water to be preferably attached to the fine particles. Therefore, the fine particles contained in the exhaust gas can be preferably coarsened, and the fine particles can be preferably collected.

[0067] Furthermore, in a dust collection system according to a sixth aspect of the present disclosure, in any one of the first to fifth aspects, the droplet supply unit sprays the droplets at a speed of 20 meters per second or more, and the spray angle of the droplets from the droplet supply unit is 5 degrees or more and 120 degrees or less.

[0068] With the above configuration, droplets can be sprayed over a wide area at high speed. This promotes turbulent mixing of the fine particles and water vapor. This allows condensed water to adhere to the fine particles. This allows the fine particles contained in the exhaust gas to be coarsened and the fine particles to be collected.

[0069] Furthermore, the dust collection system according to a seventh aspect of the present disclosure is any of the first to sixth aspects, and further includes a high-temperature droplet supply unit (120) that is provided upstream of the droplet supply unit and supplies droplets having a temperature higher than that of the exhaust gas to the flow path.

[0070] The above configuration includes a high-temperature droplet supply unit that is provided upstream of the droplet supply unit and supplies droplets having a higher temperature than the exhaust gas to the flow path. The high-temperature droplet supply unit supplies high-temperature droplets to the flow path, thereby increasing the temperature of the exhaust gas flowing through the flow path and increasing the amount of moisture. This increases the amount of water vapor in the exhaust gas. Therefore, downstream of the high-temperature droplet supply unit, the droplet supply unit supplies low-temperature droplets to the flow path, thereby increasing the amount of water condensed. This allows the water vapor to be effectively attached to the fine particles as condensed water. Therefore, the fine particles contained in the exhaust gas can be effectively coarsened, allowing the fine particles to be effectively collected.

[0071] Furthermore, the dust collection system according to an eighth aspect of the present disclosure is the seventh aspect, and further comprises: a wet electrostatic precipitator (14) provided downstream of the electrostatic agglomeration section in the flow path; a cooling section (131) that cools wastewater from the wet electrostatic precipitator; a cooled wastewater pipe (132) that guides the wastewater cooled in the cooling section to the droplet supply section; a heat exchange section (133) that heats the wastewater by exchanging heat between the wastewater from the wet electrostatic precipitator and the exhaust gas discharged from the combustion device; and a heated wastewater pipe (134) that guides the wastewater heated in the heat exchange section to the high-temperature droplet supply section, wherein the droplet supply section supplies the introduced wastewater to the flow path as droplets, and the high-temperature droplet supply section supplies the introduced wastewater to the flow path as droplets.

[0072] In the above configuration, the wastewater from the wet electrostatic precipitator is used in the droplet supply unit and the high-temperature droplet supply unit, thereby improving the efficiency of the entire dust collection system compared to a configuration that does not use wastewater. Also, in the above configuration, the heat of the exhaust gas is used to heat the wastewater. This improves the efficiency of the entire dust collection system compared to a configuration that does not use the heat of the exhaust gas.

[0073] Furthermore, the dust collection system according to a ninth aspect of the present disclosure is any of the first to seventh aspects, in which a collection device for electrically collecting the fine particles is not provided downstream of the electrostatic agglomeration section of the flow path.

[0074] The above configuration facilitates collision between fine particles and liquid droplets, thereby facilitating the adhesion of fine particles to the liquid droplets. Fine particles attached to the liquid droplets are easily separated from the exhaust gas by gravity settling due to the droplets' own weight. Furthermore, fine particles attached to the liquid droplets are easily collected by a simple repair device such as a demister. Therefore, fine particles can be separated and collected from the exhaust gas without the need for an electrical collection device with a complex structure. Therefore, the structure can be simplified compared to when an electrical collection device is provided. An example of an electrical collection device is an electric dust collector that forms an electric field using a discharge electrode and a ground electrode in the area where the fine particles and liquid droplets pass, and collects the fine particles and liquid droplets with the ground electrode.

[0075] In addition, the dust collection method according to the first aspect of the present disclosure includes a step of supplying droplets having a lower temperature than exhaust gas containing saturated water vapor that is discharged from a combustion device (2) and flows through a circulation path, and a step of collecting fine particles contained in the exhaust gas.

[0076] 1: Boiler system 2: Boiler 3: Forced draft fan 4: Denitrification device 5: Air preheater 6: Dry electrostatic precipitator 7: Desulfurization device 8: Chimney 10: Dust collection system 11: Flow path 12: Droplet supply section 13: Electrostatic agglomeration section 14: Wet electrostatic precipitator 15: Demister 20: Nozzle 30: Discharge electrode 31: Earth electrode 82: Fine particle distribution 82a: Fine particle distribution 83: Particle distribution 84: Droplet distribution 100: Dust collection system 120: High-temperature droplet supply section 121: Nozzle 131: Cooling tower 132: Cooling drainage pipe 133: Heat exchange section 134: Heated drainage pipe 135: Pump

Claims

1. A dust collection system comprising: a flow path through which exhaust gas containing saturated water vapor discharged from a combustion device flows; and a droplet supply unit that supplies droplets having a lower temperature than the exhaust gas to the exhaust gas flowing through the flow path.

2. The dust collection system of claim 1, further comprising an electrostatic agglomeration section that is disposed in the flow path downstream of the supply position of the droplets, forms an electric field in the flow path of the exhaust gas, charges the fine particles and the droplets contained in the exhaust gas, and causes the fine particles and the droplets to collide with each other.

3. A dust collection system according to claim 1, wherein the droplet supply unit supplies the droplets so that the temperature of the exhaust gas is reduced in the range of 5°C or more and 30°C or less.

4. The droplet supply unit is configured such that the ratio of the flow rate of the droplets to be supplied to the flow rate of the exhaust gas flowing through the flow path is 0.1 m / min when the flow rate of the droplets is 1 liter / min. ３ More than 10m ３ 2. The dust collection system of claim 1, wherein the droplets are provided in a ratio such that:

5. A dust collection system according to claim 4, wherein the droplet supply unit supplies the droplets having a particle size of 30 μm or more and 200 μm or less.

6. The dust collection system according to claim 1, wherein the droplet supply unit sprays the droplets at a speed of 20 meters per second or more, and a spray angle of the droplets from the droplet supply unit is 5 degrees or more and 120 degrees or less.

7. The dust collection system according to claim 1, further comprising a high-temperature droplet supply section provided upstream of said droplet supply section and supplying droplets having a temperature higher than that of said exhaust gas to said flow path.

8. A dust collection system as described in claim 7, comprising: a wet electrostatic precipitator provided downstream of an electrostatic coagulation section in the flow path; a cooling section for cooling wastewater from the wet electrostatic precipitator; a cooled wastewater piping for guiding the wastewater cooled by the cooling section to the droplet supply section; a heat exchange section for heating the wastewater by exchanging heat between the wastewater from the wet electrostatic precipitator and the exhaust gas discharged from the combustion device; and a heated wastewater piping for guiding the wastewater heated by the heat exchange section to the high-temperature droplet supply section, wherein the droplet supply section supplies the introduced wastewater to the flow path as droplets, and the high-temperature droplet supply section supplies the introduced wastewater to the flow path as droplets.

9. A dust collection system according to claim 2, wherein a collection device for electrically collecting the fine particles is not provided downstream of the electrostatic agglomeration section in the flow path.

10. A dust collection method comprising the steps of: supplying liquid droplets having a lower temperature than exhaust gas containing saturated water vapor discharged from a combustion device and flowing through a flow path; and collecting fine particles contained in the exhaust gas.

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