Dust collection system and dust collection method

Abstract

To suitably collect fine particles included in an exhaust gas.SOLUTION: A dust collection system 10 comprises: a circulation path where an exhaust gas discharged from a boiler circulates; a nozzle 20 of a droplet supply part which supplies droplets CL lower in temperature than the exhaust gas to the exhaust gas circulating in the circulation path; and an electrostatic flocculation part which is arranged in the circulation path downstream from the supply position of the droplets CL, and forms an electric field in the flow passage of the exhaust gas and then electrostatically charges the fine particles M included in the exhaust gas and the droplets CL to cause the fine particles M and droplets CL to collide against each other.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[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, 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 to remove dust by enlarging the dust in the exhaust gas using condensed moisture in the gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 2-104821 Summary of the Invention [Problem to be solved by the invention]

[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 fine particles having a small particle size 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 properly captured.

[0005] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a dust collection system and a dust collection method that are capable of suitably collecting fine particles contained in exhaust gas. [Means for solving the problem]

[0006] In order to solve the above problems, the dust collection system and dust collection method of the present disclosure employ the following measures. A 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 lower temperature than the exhaust gas to the exhaust gas flowing through the flow path.

[0007] A dust collection method according to one embodiment of the present disclosure includes a step 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 a step of collecting fine particles contained in the exhaust gas. Effect of the Invention

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

[0009] [Figure 1] 1 is a schematic configuration diagram showing a boiler system according to a first embodiment of the present disclosure. [Diagram 2] 1 is a schematic configuration diagram showing a dust collection system according to a first embodiment of the present disclosure. [Diagram 3] FIG. 1 is a schematic side view showing a dust collection system according to a first embodiment of the present disclosure. [Figure 4] 1 is a perspective view showing a schematic configuration of a dust collection system according to a first embodiment of the present disclosure. [Diagram 5] 1 is a cross-sectional view showing a schematic configuration of a dust collection system according to a first embodiment of the present disclosure. [Figure 6] FIG. 2 is an explanatory diagram illustrating the process of the dust collection system according to the first embodiment of the present disclosure. [Figure 7] 4A to 4C are explanatory diagrams illustrating the effects of the dust collection system according to the first embodiment of the present disclosure. [Figure 8] 4 is a graph showing a relationship between a gas temperature decrease range and dust collection efficiency in the dust collection system according to the first embodiment of the present disclosure. [Figure 9] 4 is a graph showing the relationship between the gas temperature decrease range and the diameter of fine particles (SO3 mist) in the dust collection system according to the first embodiment of the present disclosure. [Figure 10] FIG. 4 is a schematic configuration diagram showing a boiler system according to a second embodiment of the present disclosure. [Figure 11] FIG. 4 is a schematic side view showing a dust collection system according to a second embodiment of the present disclosure. [Figure 12] 10 is a graph showing a relationship between a position in an exhaust gas flow direction and a saturated water vapor amount of the exhaust gas in a dust collection system according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 a system for treating exhaust gas combusted by a combustion device, but the present disclosure is not limited thereto. The dust collection system can be used to collect 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 a system for collecting fine particles, such as dust, at a work site such as a demolition work. Furthermore, the fine particles are not limited to solids, and may be liquid such as droplets or tar.

[0011] As shown in Fig. 1, the dust collection system 10 according to the present 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 burning 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] As shown in Figures 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 equipment 7 flows, a droplet supply unit 12 that supplies droplets having a lower temperature than 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 to collide with the droplets, and a wet electrostatic dust collector 14 that collects the droplets with fine particles attached. 3 and 4, a demister 15 may be provided instead of the wet electrostatic precipitator 14. Alternatively, without providing either the wet electrostatic precipitator 14 or the demister 15, 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.

[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 injects 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 a wet electrostatic precipitator 14 that has been cooled in a cooling tower is guided to 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 supplying unit 12 supplies droplets to the exhaust gas so that the temperature of the exhaust gas is reduced to within a range of 5°C or more and 30°C or less. In addition, the droplet supply unit 12 has a ratio of the flow rate of the droplets to the flow rate of the exhaust gas flowing through the flow path 11 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 per minute. 3 More than 10m 3 The droplets are supplied so that the ratio is as follows: The droplet flow rate (L / min) and the exhaust gas flow rate (m 3 / min) and its 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 droplets at a speed of 20 meters per second or more. The spray angle θ of the droplets from the nozzle 20 of the droplet supply unit 12 is set to be 5 degrees or more and 120 degrees or less.

[0019] The electrostatic agglomeration section 13 is disposed downstream of the nozzle 20 of the droplet supply section 12 of the flow path 11. The electrostatic agglomeration section 13 forms an electric field in an area through which the fine particles and the droplets pass, and charges the fine particles and the droplets. The charged fine particles and the 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 taken into the droplets. As shown in Figs. 4 and 5, the electrostatic agglomeration section 13 has a discharge electrode 30 and an earth electrode 31. A predetermined voltage is applied to the discharge electrode 30. The earth electrode 31 is a plate-shaped electrode disposed facing the discharge electrode 30. The earth electrode 31 is disposed so that the direction along the flow direction A1 is the surface. This makes it possible to suppress the earth electrode 31 from becoming a resistance to the flow of the exhaust gas. The earth electrode 31 is grounded.

[0020] Electrostatic agglomeration unit 13 forms an electric field between discharge electrode 30 and earth electrode 31 by applying a predetermined voltage to discharge electrode 30. That is, an electric field for agglomeration 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 may apply a predetermined voltage to earth electrode 31 without grounding it.

[0021] In this embodiment, the electrostatic agglomeration unit 13 is disposed downstream of the nozzle 20, but this is not limited thereto. A part of the electrostatic agglomeration unit 13 may be disposed upstream of the nozzle 20. In other words, the nozzle 20 may be disposed inside the electrostatic agglomeration unit 13. Moreover, the discharge electrode 30 and the earth electrode 31 may be shaped like a pipe instead of a plate.

[0022] As shown in FIG. 2, the wet electrostatic precipitator 14 is disposed downstream of the electrostatic agglomeration section 13 of the flow path 11. The wet electrostatic precipitator 14 forms an electric field in an area through which fine particles and liquid droplets pass, and collects 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, and collects them by causing them to adhere to the ground electrode.

[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 are attached.

[0024] Next, a dust collection method of the dust collection system 10 will be described. 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 temperature reducing tower 7a by supplying liquid 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 nozzle 20 is arranged.

[0026] When 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. When the water film W covers the fine particles M, the particle size of the fine particles M becomes coarse to 1 μm or more (when the fine particles are in a liquid state such as SO3 mist, the saturated water vapor condenses into the SO3 mist, the liquid film mixes with the SO3 mist, and the particles become uniform and coarse). That is, as shown in FIG. 6(a), when the droplets CL are supplied from the nozzle 20, the particle distribution changes from a fine particle distribution 82 to a particle distribution 83. That is, although the number of particles of the fine particles M does not change, the particle diameter of each particle becomes larger.

[0027] When the fine particles M become coarse, the fine particles M 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 collides with the liquid droplets, and the coarsened SO3 mist mixes with the liquid droplets, becoming uniform and coarsened.) In addition, 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 liquid droplet distribution 84 corresponding to the liquid droplets CL, as shown in FIG. 6(b). In other words, the exhaust gas E is in a state in which the liquid droplets CL and the coarsened fine particles M are mixed together.

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

[0029] In addition, when a wet electrostatic precipitator 14 is provided downstream of the electrostatic agglomeration section 13 as shown in FIG. 2, the electric field formed by the wet electrostatic precipitator 14 causes the droplets CL that have ingested the 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 collects the particulate matter M contained in the exhaust gas.

[0031] According to this embodiment, the following advantageous effects are obtained. 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 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 the condensed water is attached become coarser compared to the fine particles before the attachment by the amount of condensed water that is covered. 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 particulate matter together with the liquid droplets, and therefore the particulate matter contained in the exhaust gas can be suitably collected.

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

[0033] In this embodiment, an electrostatic agglomeration section 13 is provided which charges the fine particles and droplets contained in the exhaust gas and causes the fine particles to collide with the droplets. This makes it easier for the coarsened fine particles to collide with the droplets. 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.

[0034] Generally, when the particle size of the fine particles is 1 μm or more, the fine particles are likely to collide with liquid 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 is lowered 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 tend to coarsen to 1 μm or more. In this embodiment, the droplet supply unit 12 supplies droplets so that the temperature of the exhaust gas is reduced in the range of 5°C or more and 30°C or less. This reduces the temperature of the exhaust gas in the range of 5°C or more and 30°C or less. This makes it possible to suitably condense the saturated water vapor contained in the exhaust gas and cause 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 extent of the decrease in temperature of exhaust gas, the change in diameter of fine particles (mist), and the collection efficiency of fine particles will be described with reference to FIGS. Figure 7 shows the 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 large enough to easily collide with liquid droplets. Also, when the exhaust gas temperature is reduced by 5°C or more, about 40% of the fine particles can be collected by gravitational settling. In particular, as shown in Fig. 8, it was found that when the exhaust gas temperature is decreased by 10°C or more, the fine particles become 1.0 μm or larger and can be sufficiently coarsened. Also, as shown in Fig. 9, it was found that when the exhaust gas temperature is decreased by 10°C or more, the fine particles can be sufficiently collected (about 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. or more and 30° C. or less. 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 makes it possible to lower the temperature of the exhaust gas in the range of 5°C or more and 30°C or less. This makes it possible to suitably condense the saturated water vapor contained in the exhaust gas and attach the condensed water 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] Moreover, in this embodiment, the droplet supply unit 12 supplies droplets having a particle size of 30 μm or more and 200 μm or less. This makes it easier for the fine particles not covered with condensed water to collide with the condensed water. In this way, the fine particles not covered with condensed water can be made to collide preferentially with the condensed water rather than with the droplets. This makes it possible to favorably attach the condensed water to the fine particles. Therefore, the fine particles contained in the exhaust gas can be favorably coarsened, and the fine particles can be favorably collected.

[0040] When the water vapor in saturated steam condenses, fine particles and liquid droplets exist in the exhaust gas. Since the particle diameter of the fine particles in the exhaust gas is small, the number density np (pieces / m3) in the exhaust gas is large. On the other hand, the number density nd of the liquid droplets is set to be larger than that of the fine droplets, so the number density nd is smaller than that 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. In other words, 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), then 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 approximately 1 / 3 of λ2, the water vapor collides with the fine particles three times more than with the droplets, so that the fine particles can be preferentially coarsened.

[0044] Assuming that the fine particle concentration (number density) and size (0.5 μm) in the exhaust gas downstream of a typical boiler are the same, the droplet gas-liquid ratio is 0.1 to 5, and the droplet diameter is 30 μm to 200 μm, achieving the relationship λ1 < λ2.

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

[0046] In this embodiment, the fine particles and the liquid droplets can easily collide with each other, so that the fine particles can easily 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 weight of the droplets. 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 providing an electrical collection device (e.g., a wet electric dust collector) which has a complex structure. Therefore, the structure can be simplified compared to the case where an electrical collection device is provided.

[0047] [Second embodiment] Next, a second embodiment of the present disclosure will be described with reference to FIGS. 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 denoted by the same reference numerals and detailed descriptions thereof will be omitted.

[0048] As shown in FIGS. 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 path 11. Specifically, the high-temperature droplet supply unit 120 injects liquid into the flow path 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 cooling 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 heating 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 section 133 is provided between the dry electrostatic precipitator 6 and the desulfurization device 7 .

[0051] According to this embodiment, the following advantageous effects are obtained. In this embodiment, the high-temperature droplet supply unit 120 is provided upstream of the droplet supply unit 12 and supplies droplets having a higher temperature than the exhaust gas to the flow path 11. The high-temperature droplet supply unit 120 supplies high-temperature droplets to the flow path 11, so that the temperature of the exhaust gas flowing through the flow path 11 increases and the amount of moisture increases. This can increase 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, so that the amount of water condensed can be increased. Therefore, the water vapor can be preferably attached to the fine particles as condensed water. Therefore, the fine particles contained in the exhaust gas can be preferably coarsened, so that the fine particles can be preferably 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 amount of saturated water vapor in the exhaust gas will be described with reference to Fig. 12. As shown in Figs. 11 and 12, the amount of saturated water vapor increases at a position (P1) where high-temperature droplets HL are sprayed from the high-temperature droplet supply unit 120. The amount of saturated water vapor 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 amount of saturated water vapor.

[0053] In addition, in this embodiment, the wastewater from the wet electrostatic precipitator 14 is utilized in the droplet supply unit 12 and the high-temperature droplet supply unit 120, so that the efficiency of the entire dust collection system 10 can be improved compared to a structure that does not utilize wastewater. In addition, in this embodiment, the heat of the exhaust gas is used to heat the wastewater, which can improve 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 are possible without departing from the spirit and scope of the present disclosure.

[0055] The dust collection system and the 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 lower temperature than 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 the condensed water is attached become coarser by the amount of condensed water that is covered compared to the fine particles before the attachment. The coarsening of the fine particles (more precisely, the fine particles covered by condensed water) can facilitate collision between the fine particles and the droplets. The fine particles that collide with the droplets adhere to the droplets. As a result, it is possible to facilitate collection of the fine particles together with the droplets. Therefore, the fine particles contained in the exhaust gas can be suitably collected.

[0057] In addition, in the above configuration, the exhaust gas is cooled by simply supplying low-temperature droplets. This eliminates the need to provide a separate large-scale device (such as a heat exchanger) for cooling the exhaust gas. Therefore, the structure can be simplified compared to the case where a separate device for improving the collection efficiency is provided.

[0058] In addition, the dust collection system according to a second aspect of the present disclosure, in the above-mentioned first aspect, further comprises an electrostatic agglomeration section (13) 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.

[0059] The above-mentioned configuration includes an electrostatic agglomeration section that charges the fine particles and droplets contained in the exhaust gas and causes the fine particles and droplets to collide with each other. This makes it easier for the coarsened fine particles to collide with the droplets. 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.

[0060] In addition, 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 section 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.

[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. In general, in the concentration of fine particles in exhaust gas downstream of a combustion device, when the temperature of the exhaust gas is lowered 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 lowering 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 is reduced in a range of 5°C or more and 30°C or less. This reduces the temperature of the exhaust gas in a range of 5°C or more and 30°C or less. This makes it possible to suitably condense the saturated water vapor contained in the exhaust gas and cause 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 and 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 per minute. 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 of the droplets to the flow rate of the exhaust gas (flow rate / min) is 1:0.1 to 10. This makes it possible to lower the temperature of the exhaust gas in the range of 5°C or more and 30°C or less. This makes it possible to suitably condense the saturated water vapor contained in the exhaust gas and attach the condensed water 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] Further, in the dust collection system according to a fifth aspect of the present disclosure, in the above-mentioned fourth aspect, the droplet supply section 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 having 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 caused to collide preferentially with the condensed water rather than with the droplets. This makes it possible to favorably attach the condensed water to the fine particles. Therefore, the fine particles contained in the exhaust gas can be favorably coarsened, and the fine particles can be favorably 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 a spray angle of the droplets from the droplet supply unit is 5 degrees or more and 120 degrees or less.

[0068] In the above configuration, the droplets can be sprayed at high speed over a wide area. Therefore, turbulent mixing of the fine particles and water vapor can be promoted. Therefore, the condensed water can 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.

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

[0070] In the above configuration, a high-temperature droplet supplying section is provided upstream of the droplet supplying section and supplies droplets having a higher temperature than the exhaust gas to the flow path. The high-temperature droplet supplying section 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 makes it possible to increase the amount of water vapor in the exhaust gas. Therefore, downstream of the high-temperature droplet supplying section, the droplet supplying section supplies low-temperature droplets to the flow path, thereby increasing the amount of water to be condensed. This makes it possible to suitably attach the water vapor to the fine particles as condensed water. Therefore, the fine particles contained in the exhaust gas can be suitably coarsened, making it possible to suitably collect the fine particles.

[0071] Furthermore, the dust collection system according to an eighth aspect of the present disclosure is the same as the seventh aspect, except that it further includes a wet electrostatic precipitator (14) provided downstream of the electrostatic coagulation 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-described configuration, the wastewater from the wet electrostatic precipitator is utilized in the droplet supply section and the high-temperature droplet supply section, so that the efficiency of the entire dust collection system can be improved compared to a structure that does not utilize wastewater. In addition, in the above-described configuration, the heat of the exhaust gas is used to heat the wastewater, which can improve the efficiency of the entire dust collection system compared to a structure that does not use the heat of the exhaust gas.

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

[0074] In the above configuration, the fine particles and the liquid droplets can easily collide with each other, so that the fine particles can easily 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 weight of the droplets. 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 providing an electrical collection device with a complex structure. Therefore, the structure can be simplified compared to the case where an electrical collection device is provided. An example of an electrical collection device is an electric dust collector that uses a discharge electrode and an earth electrode to form an electric field in an area where fine particles and liquid droplets pass, and collects the fine particles and liquid droplets at the earth electrode.

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

[0076] 1: Boiler system 2: Boiler 3: Push-in fan 4: Denitration equipment 5: Air preheater 6: Dry electrostatic precipitator 7: Desulfurization equipment 8: Chimney 10: Dust collection system 11: Distribution Channels 12:Droplet supply section 13: Electrostatic agglomeration section 14: Wet electrostatic precipitator 15: Demistar 20: Nozzle 30: Discharge electrode 31: Earth pole 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 piping 133:Heat exchange section 134:Heating drainage piping 135: Pump

Claims

1. a flow path through which exhaust gas containing saturated water vapor discharged from the combustion device flows; 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.

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

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

4. The droplet supply unit is configured such that a ratio of a flow rate of the droplets to be supplied and a 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. The 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 droplet supply unit sprays the droplets at a speed of 20 meters per second or more, 2. The dust collection system according to claim 1, wherein a spray angle of the droplets from the droplet supply unit is set to be equal to or greater than 5 degrees and equal to or less than 120 degrees.

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

8. A wet electrostatic precipitator provided downstream of the electrostatic agglomeration section of the flow path; A cooling unit that cools the wastewater from the wet electrostatic precipitator; a cooling drainage pipe that guides the drainage water cooled in the cooling unit to the droplet supply unit; a heat exchange unit that heats the wastewater by exchanging heat between the wastewater from the wet electrostatic precipitator and the exhaust gas discharged from the combustion device; A heated drainage pipe that guides the drainage heated in the heat exchange unit to the high-temperature droplet supply unit, The droplet supply unit supplies the introduced wastewater to the distribution path as the droplets, The dust collection system according to claim 7 , wherein the high-temperature droplet supply unit supplies the introduced wastewater as the droplets to the circulation path.

9. The dust collection system according to claim 2 , wherein a collector that electrically collects the fine particles is not provided downstream of the electrostatic agglomeration section in the flow path.

10. A step 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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