JP4652609B2 - Coal combustion ash melting method and melt processing system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a volume reduction process of coal combustion ash discharged in large quantities from a power plant.
[0002]
[Prior art]
Coal has abundant reserves and is more economical than other fossil fuels. Thermal power plants that use large amounts of coal are expected to be expanded or newly constructed in the future. Coal contains about 10 to 20% ash, and the amount of coal combustion ash emissions is expected to increase with the expansion and construction of thermal power plants. Therefore, a method for treating coal combustion ash discharged from a power plant has become a major issue.
[0003]
Coal-burning ash discharged from thermal power plants can be broadly divided into three categories: bottom ash discharged from the clinker hopper in the furnace, cinder ash recovered from the economizer, and fly ash recovered from the dust collector. The Coal-burning ash is used effectively as raw materials such as cement, but more than half of the coal-burning ash is used as landfill for nearby beaches as waste. In the case of landfill disposal, the elution water of coal combustion ash is highly alkaline, which may cause environmental conservation problems. For this reason, coal-burning ash is designated as managed industrial waste. In addition, it is difficult to secure a land for disposal of coal combustion ash, and it is desired to use the ash effectively other than landfill.
[0004]
In order to use coal-burning ash as a raw material for cement, it is necessary to reduce the unburned content in the ash as much as possible. The coal combustion ash recovered at the pulverized coal furnace plant usually contains 3 to 5% unburned content. Coal ash with a lot of unburned content is not worth using as raw materials such as cement.
[0005]
JP-A-10-1339 discloses a technique related to a coal-fired boiler that uses coal-burning ash as a raw material for cement admixture or concrete aggregate. This consists of a furnace and an ash melting furnace, in which the bottom ash from the furnace is melted into slag. In addition, high-quality fly ash is a system that can be used as it is.
[0006]
On the other hand, there is a technique described in Japanese Patent Application Laid-Open No. 10-81398 as a technique for converting coal combustion ash into slag in a gasification furnace and reducing the volume. This is to use pulverized coal used in the furnace as the fuel for the gasifier.
[0007]
Japanese Patent Application Laid-Open Nos. 2000-283429 and 2000-283433 disclose a technique in which carbide generated from waste is used as thermal fuel.
[0008]
Japanese Patent Application Laid-Open No. 9-243044 discloses a technique for melting coal combustion ash using carbide as an auxiliary fuel.
[0009]
Furthermore, Japanese Patent Application Laid-Open No. 2-122109 discloses a technique for melting municipal waste incineration ash using a carbonized material as an auxiliary fuel.
[0010]
[Problems to be solved by the invention]
Among the above-described conventional techniques, the techniques disclosed in Japanese Patent Application Laid-Open Nos. 2000-283429 and 2000-283433 merely use the carbide generated from the waste as a fuel for a boiler and the like. It is not recognized that it is used for melting and volume reduction processing of coal combustion ash discharged in large quantities.
[0011]
Japanese Patent Laid-Open No. 9-243044 discloses a technique for melting coal combustion ash using carbide as a supplementary fuel. However, it is recognized that coal combustion ash is melted using carbide generated from waste as fuel. It has not been.
[0012]
Furthermore, the technique described in Japanese Patent Laid-Open No. 2-122109 is to melt municipal waste incineration ash using carbonized material as a supplementary fuel, and uses carbide generated from waste itself including municipal waste as fuel. The point of melting coal combustion ash is not recognized.
[0013]
By the way, in order to melt coal combustion ash as disclosed in JP-A-10-1339 and JP-A-10-81398, the inside of the melting furnace must have a melting point of ash or higher, that is, about 1200 to 2500 ° C or higher. . However, when the melting furnace is operated in such a high temperature state, there are problems such that the amount of heat input (fuel amount) increases and the furnace body is exposed to severe thermal conditions and damage is accelerated.
[0014]
Therefore, in order to lower the melting point of coal combustion ash, a technique for mixing and melting the coal combustion ash with an additive is disclosed in Japanese Patent Laid-Open No. 9-210338. According to this method, since the temperature in the ash melting furnace can be lowered, the above-mentioned problems can be avoided. However, it becomes necessary to purchase additives and fuel for melting coal-burning ash, which increases the cost of ash treatment.
[0015]
An object of the present invention is to realize a volume reduction process by melting coal combustion ash discharged in large quantities from a power plant at low cost.
[0016]
[Means for Solving the Problems]
The problem is that when the coal combustion ash in the exhaust gas discharged from the pulverized coal furnace is melted in the ash melting furnace to generate molten slag, the carbide generated from the waste is used as the fuel (or the carbide generated from the waste). Is achieved by melting coal ash with coal and coal as fuel.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited to the examples.
Example 1
An embodiment of the present invention is shown in FIG.
[0018]
Coal 1 is transported from the coal yard to a coal pulverizer 9 by a coal handling facility and crushed. The pulverized coal is supplied by a coal feeder to a coal conveyance pipe 10 in which coal conveyance air flows. Coal is supplied to a burner 7 provided in the furnace 6 and burns in the furnace 6.
[0019]
The air blower 18 supplies combustion air to the burner 7. Combustion air from the air blower 18 is heated by the air residual heater 14, passes through the air pipe 19, and travels toward the burner 7. The combustion air is heated to about 300 ° C., contributes to the combustion of the coal without cooling the furnace 6 and stably burns the coal.
[0020]
The coal combustion gas heats the wall surface of the furnace 6, and the denitration device 13 while heating a superheater, a reheater installed in the downstream side of the furnace 6, a economizer such as an air after-heater (both not shown). Head for. NOx in the exhaust gas is removed by the denitration device 13 so as to be below the regulation value. Downstream of the denitration device 13, there is an air residual heater 14 that warms the combustion air using the residual heat of the exhaust gas. Further, the exhaust gas is dedusted from fly ash in the exhaust gas by a dust collector 15 located downstream of the air residual heater 14 and enters a desulfurizer 16. The exhaust gas is removed from the sulfur oxide by the desulfurization device 16 to become clean exhaust gas, and is discharged from the chimney 17.
[0021]
The fly ash 3 collected at the front stage of the dust collector 15 and the bottom ash 2 collected by the furnace 6 are supplied to the ash melting furnace 28. The fly ash 4 collected at the front stage of the dust collector 15 has a small particle size and a small amount of unburned matter, and can be used as a cement material. For this reason, no treatment is performed in the ash melting furnace 28.
[0022]
As the fuel of the ash melting furnace 28, it is preferable to use a material obtained by carbonizing waste and removing foreign matters in the carbide, or a product obtained by carbonizing the waste and removing foreign matters in the carbide and mixing with coal.
[0023]
The reason for using the former is that the waste generated at the power plant can be used as fuel, and the fuel cost can be reduced. Also, the melting temperature of coal combustion ash is as high as about 1200 ° C. to 2500 ° C., and the melting point of coal combustion ash can be lowered by mixing a carbide having a low melting point. Thereby, even if the temperature in the furnace of the ash melting furnace 28 is about 1200-1800 degreeC, ash can be fuse | melted. Furthermore, the energy required to heat the ash melting furnace 28 is reduced as compared with the case where only coal is used as fuel. On the other hand, the reason for using the latter is that coal has an effect of keeping the combustion state constant by adding coal, since the calorific value is more stable than that of carbide.
[0024]
Thus, volume reduction processing by melting of coal combustion ash discharged in large quantities from the power plant can be realized at low cost by using carbide generated from waste as fuel.
[0025]
In addition, when coal and coal generated from waste are mixed and coal combustion ash is melted using this mixture as fuel, the carbide mixed with coal lowers the melting point of coal combustion ash, thus reducing the energy required for melting. .
[0026]
As described above, the carbide may be generated by using the waste in the power plant, but it is also possible to collect and use garbage such as ordinary households or industrial waste. Since the waste is used as the fuel for the ash melting 28, the fuel cost of the ash melting process can be reduced. Moreover, since the carbide | carbonized_material discharged | emitted from the carbonization apparatus is mixed with a metal etc., it isolate | separates from a carbide | carbonized_material with a selector.
[0027]
In FIG. 1, carbides generated from waste and coal 1 are pulverized by a pulverizer 20 and supplied to a burner of an ash melting furnace 28. The particle size is adjusted as necessary. In FIG. 1, carbide and coal 1 are charged into the hopper 22 and pulverizer 20. However, as shown in FIG. 2, coal 1 is charged into the hopper 22 and pulverizer 20, and the carbide is pulverized exclusively for carbide. It may be pulverized in advance by the vessel 29 and supplied directly to the fuel supply pipe 23.
[0028]
The combustion air in the ash melting furnace 28 is warmed as necessary, and is supplied to the air nozzle through the air conveyance pipe 21.
[0029]
When coal combustion ash is introduced into a high-temperature gas atmosphere, the coal combustion ash is melted and recovered as slag. The slag is discharged from the ash melting furnace 28 and then cooled by a cooling device. The cooled slag 5 has a wide range of uses as a roadbed material. Also, when landfilling, the volume of coal combustion ash can be greatly reduced, leading to space saving at the final disposal site.
[0030]
However, since the exhaust gas of the ash melting furnace 28 contains harmful substances such as NOx and SOx, it is returned to the outlet of the furnace 6 and discharged through the denitration device 13 and the desulfurization device 16. FIG. 1 shows an example in which the combustion exhaust gas from the ash melting furnace 28 is introduced between the furnace 6 and the denitration apparatus 13. Here, it must be considered that the combustion exhaust gas discharged from the ash melting furnace 28 contains dioxins due to the presence of chlorine contained in the carbide. On the other hand, if exhaust gas is input to the upstream side of the denitration device 13, dioxins in the combustion exhaust gas are oxidized and decomposed in the denitration device 13 (Chemical Engineering 64 (3) 128-130 (2000)). It must be considered that the fly ash in the exhaust gas also contains dioxin, but this is recovered by the dust collector 15 installed downstream. This ensures that dioxins emitted from the power plant are below the environmental regulations. Further, since the exhaust gas is introduced downstream of the furnace 6, there is no need to change the structure of the furnace 6 itself.
[0031]
According to the present embodiment, dioxins generated in the ash melting furnace 28 can be recovered by the denitration device 13 and the dust collector 15.
(Example 2)
An example in which the combustion exhaust gas from the ash melting furnace 28 is introduced into the furnace bottom of the furnace 6 will be described with reference to FIG. In the conventional pulverized coal furnace, the temperature in the vicinity of the lowermost burner installed in the furnace 6 is lower than that of the other downstream burners, so the ignitability of coal is poor. In particular, when the load is low, the temperature in the furnace is lowered, and ignition is more difficult. On the other hand, the temperature of the combustion exhaust gas from the ash melting furnace 28 is as high as about 1000 to 2000 ° C. at the outlet of the ash melting furnace. When this gas is introduced into the furnace 6 at a high temperature, the temperature at the bottom of the furnace rises, and the ignition performance of coal is improved. Conventionally, the temperature of the gas charged into the furnace bottom is about 300 to 400 ° C., so the temperature of the combustion exhaust gas only needs to be higher.
[0032]
According to the present embodiment, the dioxins generated in the ash melting furnace 28 can be decomposed again by high-temperature combustion in the furnace 6.
(Example 3)
An example provided with a desalting apparatus for removing chlorine contained in carbide will be described with reference to FIG. In the figure, the combustion exhaust gas from the ash melting furnace 28 is input between the furnace 6 and the denitration apparatus 13, but may be input to the bottom of the furnace 6 as in the second embodiment.
[0033]
Since the waste contains chlorine, dioxins and hydrogen chloride are generated when the carbide generated in the carbonizer is burned. However, if chlorine is removed from the carbide in advance using a desalting apparatus, the amount of dioxins and hydrogen chloride generated by combustion in the ash melting furnace 28 is reduced. If the amount of hydrogen chloride generated is small, the problem of chlorine corrosion that occurs in cooling pipes downstream of the ash melting furnace is eliminated.
Example 4
An example of using carbide generated outside the power plant will be described with reference to FIG.
[0034]
In the figure, the combustion exhaust gas from the ash melting furnace 28 is input between the furnace 6 and the denitration apparatus 13, but may be input to the bottom of the furnace 6 as in the second embodiment. In the figure, the desalted carbide is supplied. However, if the dioxin generated by the presence of chloride can be sufficiently decomposed during the combustion of the waste, the desalting apparatus is not necessarily required.
[0035]
If you purchase carbide produced by local governments and use it as fuel, you can save space because you don't have to own a carbonization device in the power plant. Equipment such as waste carbonization equipment is not required and equipment costs can be reduced. In addition, there is an advantage that the carbide can be supplied stably compared to the case where the carbide is provided only within the power plant.
(Example 5)
An example in which a waste heat recovery boiler 30 that recovers waste heat from the ash melting furnace 28 and a power generation device 25 that drives the steam turbine 24 with the waste heat recovery boiler 30 to generate power is installed in the ash melting furnace 28 will be described with reference to FIG. .
[0036]
Since the combustion exhaust gas from the ash melting furnace 28 is as high as about 1000 to 2000 ° C., a waste heat recovery boiler 30 is attached downstream of the ash melting furnace 28 and the steam turbine 24 is driven to generate power. The electricity generated in the waste heat recovery boiler 30 can be used as power for the ash melting furnace system. After the heat recovery, the combustion exhaust gas is further exchanged with the combustion air of the ash melting furnace 28, and the fly ash in the combustion gas is recovered by the dust collector 26 and then released from the chimney 27 to the atmosphere.
[0037]
According to the present embodiment, the ash can be melted without changing the existing boiler system. Further, the electricity generated in the waste heat recovery boiler 30 can be used as power for the ash melting furnace system.
[0038]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the volume reduction process by melting of coal combustion ash discharged | emitted in large quantities from a power plant can be implement | achieved at low cost by using the carbide | carbonized_material produced | generated from the waste as a fuel.
[Brief description of the drawings]
FIG. 1 is a system diagram of a pulverized coal furnace showing an embodiment of the present invention.
FIG. 2 is a view showing an example in which a transportation pipe to a carbide ash melting furnace is changed.
FIG. 3 is a system diagram of a pulverized coal furnace showing an example in which combustion exhaust gas from an ash melting furnace is charged into the furnace bottom of the furnace.
FIG. 4 is a system diagram of a pulverized coal furnace showing an example provided with a desalting apparatus.
FIG. 5 is a system diagram of a pulverized coal furnace showing an example in which carbide generated outside a power plant is used.
FIG. 6 is a system diagram of a pulverized coal furnace showing an example in which a waste heat recovery boiler that recovers waste heat of an ash melting furnace and a power generation device that generates power by driving a steam turbine with the waste heat recovery boiler are installed in the ash melting furnace It is.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Coal, 2 ... Bottom ash, 3 ... Fly ash collect | recovered in the front | former stage of the dust collector 15, 4 ... Fly ash collect | recovered in the back | latter stage of the dust collector 15, 5 ... Decooled slag, 6 ... Furnace, 7 ... Burner, 8 ... Hopper, 9 ... Crusher, 10 ... Coal conveying pipe, 11 ... GR port, 12 ... Cyclone, 13 ... Denitration device, 14 ... Air heat exchanger, 15 ... Dust collector, 16 ... Desulfurization device, 17 DESCRIPTION OF SYMBOLS ... Chimney, 18 ... Blower, 19 ... Air conveyance pipe, 20 ... Crusher, 21 ... Air conveyance pipe, 22 ... Hopper, 23 ... Carbide supply piping, 24 ... Turbine, 25 ... Generator, 26 ... Dust collector, 27 ... chimney, 28 ... ash melting furnace, 29 ... pulverizer, 30 ... waste heat recovery boiler.

Claims (11)

In the method for melting coal combustion ash, in which coal combustion ash in the exhaust gas discharged from the pulverized coal furnace is melted in an ash melting furnace to produce molten slag,
A method for melting coal combustion ash, comprising melting coal combustion ash using carbide generated from waste as fuel. In the method for melting coal combustion ash, in which coal combustion ash in the exhaust gas discharged from the pulverized coal furnace is melted in an ash melting furnace to produce molten slag,
A method for melting coal combustion ash, comprising mixing carbon generated from waste and coal and melting coal combustion ash using the mixture as fuel. 3. The method for melting coal combustion ash according to claim 1, wherein a carbide generated from waste outside the power plant is used as a fuel for melting the coal combustion ash. A dust collector that collects coal combustion ash in the exhaust gas discharged from the pulverized coal furnace, a transport system that supplies the coal combustion ash collected by the dust collector to the ash melting furnace, and a power supply that is supplied from the transport system In a coal combustion ash melting treatment system having an ash melting furnace that melts coal combustion ash to produce molten slag,
A coal combustion ash melting treatment system comprising a carbonization device for carbonizing waste, and having a step of melting coal combustion ash using the carbide generated from the waste as a fuel. A dust collector that collects coal combustion ash in the exhaust gas discharged from the pulverized coal furnace, a transport system that supplies the coal combustion ash collected by the dust collector to the ash melting furnace, and a power supply that is supplied from the transport system In a coal combustion ash melting treatment system having an ash melting furnace that melts coal combustion ash to produce molten slag,
A coal combustion ash melting treatment system comprising: a carbonization device for carbonizing waste, and mixing carbonized coal generated from the waste with coal, and melting the coal combustion ash using the mixture as a fuel. 6. The coal combustion ash melting treatment system according to claim 4 or 5, further comprising a pipe for introducing the combustion exhaust gas generated from the ash melting furnace between the pulverized coal furnace and the denitration device. The coal combustion ash melting treatment system according to any one of claims 4 to 6, further comprising a pipe for introducing the combustion exhaust gas generated from the ash melting furnace to the bottom of the pulverized coal fired furnace. 8. The coal combustion ash melting treatment system according to any one of claims 4 to 7, further comprising a desalting apparatus that removes chlorine contained in the carbide. The coal combustion ash melting treatment system according to any one of claims 4 to 8, wherein a carbide generated from waste outside the power plant is used as a fuel for melting the coal combustion ash. The waste heat recovery boiler that recovers waste heat of the ash melting furnace, a power generation device that drives a steam turbine with the waste heat recovery boiler to generate electric power, according to any one of claims 4, 5, 8, and 9, Coal combustion ash melting characterized by comprising a dust collector that collects fly ash in the exhaust gas of an ash melting furnace, and a chimney that releases the exhaust gas after the fly ash is collected by the dust collector into the atmosphere Processing system. A pulverized coal-fired power plant comprising the melt treatment system according to any one of claims 4 to 10.

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