Fly ash treatment device and method for treating fly ash

Abstract

To perform carbonation processing of fly ash for inhibiting elution of heavy metals contained in the fly ash efficiently.SOLUTION: A fly ash processing device 100 includes: a dust collector 3 which removes dust from exhaust gas exhausted from a waste incinerator; a heat exchanger 7 which heats water supplied from the outside with the exhaust gas from which the dust has been removed by the dust collector 3 to generate steam; and a fly ash carbonation device 8 which places a humidified exhaust gas, which is generated by supplying the steam generated by the heat exchanger 7 to exhaust gas branched from the exhaust gas from which the dust has been removed by the dust collector 3, in contact with fly ash discharged from the dust collector 3 to carbonate the fly ash.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fly ash treatment device and a fly ash treatment method. [Background technology]

[0002] The exhaust gas discharged from a waste incinerator that incinerates waste contains a large amount of soot (fly ash), which is removed by dust removal equipment such as a bag filter. The fly ash discharged after dust removal contains heavy metals such as lead and cadmium, and it is stipulated that heavy metals must be immobilized and stabilized to prevent elution of heavy metals so that the amount of elution of heavy metals is below the prescribed regulated value when the waste is disposed of in a landfill.

[0003] A typical stabilization treatment for heavy metals is, for example, mixing a chemical with fly ash to fix and stabilize the heavy metals. However, the treatment method of mixing a chemical with fly ash has a problem that the treatment cost is high because the chemical used is expensive. As a treatment method other than the method of mixing a chemical with fly ash, there is a method (carbonation treatment) of lowering the hydrogen ion exponent (pH) of the alkaline fly ash by carbonating the alkaline components in the fly ash, as disclosed in Patent Documents 1 and 2, for example. Patent Document 1 discloses a carbonation device that adds water to fly ash to make it wet ash with a moisture content of 20%, and carbon dioxide gas such as combustion gas or combustion exhaust gas is brought into contact with the wet ash to carbonate the fly ash. In this carbonation device, the pH of the fly ash is lowered by carbonation, and the elution of heavy metals is suppressed. Patent Document 2 discloses a waste incineration facility in which fly ash to which water is supplied in a spray form is agitated, and carbon dioxide concentrated gas generated from exhaust gas from which moisture has been removed is brought into contact with the fly ash to which water has been supplied. This waste incineration facility fixes carbon dioxide in the fly ash, lowering the pH of the fly ash and suppressing the elution of heavy metals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-033748 A [Patent Document 2] JP 2018-047395 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the carbonation device disclosed in Patent Document 1, water is supplied to the alkaline fly ash prior to the carbonation treatment, which causes the alkaline fly ash particles to bond together with the water, resulting in poor contact between the alkaline fly ash particles and carbon dioxide gas. When the contact between the alkaline fly ash particles and carbon dioxide gas is poor, the carbonation reaction cannot be rapidly promoted, and the carbonation treatment takes a long time. In the waste incineration facility disclosed in Patent Document 2, water is supplied to the alkaline fly ash prior to the carbonation treatment, which causes the alkaline fly ash particles to bond together with the water, resulting in poor contact between the alkaline fly ash particles and carbon dioxide gas, resulting in poor carbonation reaction, and therefore limited improvement in the efficiency of the carbonation treatment.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide a technique capable of efficiently carrying out a carbonation treatment of fly ash in order to suppress the elution of heavy metals contained in the fly ash. [Means for solving the problem]

[0007] A fly ash treatment device according to one aspect of the present invention includes a dust removal device that removes dust from an exhaust gas discharged from a waste incinerator, a heat exchanger that generates water vapor by heating water supplied from outside with the exhaust gas after dust removal by the dust removal device, and a fly ash carbonation device that brings fly ash discharged from the dust removal device into contact with humidified exhaust gas generated by supplying the water vapor to exhaust gas branched from the exhaust gas after dust removal by the dust removal device, thereby carbonates the fly ash.

[0008] In the fly ash treatment device according to the present invention, the flue gas to which the water vapor is supplied may be configured to be branched off from the flue gas supplied from the dust remover to the heat exchanger.

[0009] In the fly ash treating apparatus according to the present invention, the flue gas to which the water vapor is supplied may be branched off from the flue gas discharged from the heat exchanger.

[0010] In the fly ash treatment apparatus according to the present invention, the humidified flue gas that has come into contact with the fly ash may be mixed with flue gas discharged from the waste incinerator.

[0011] In addition, a fly ash treatment method according to one aspect of the present invention includes removing dust from exhaust gas discharged from a waste incinerator using a dust remover, heating water supplied from an external source to a heat exchanger using the exhaust gas after dust removal by the dust remover to generate steam, supplying the steam to exhaust gas branched off from the exhaust gas after dust removal by the dust remover to generate humidified exhaust gas, and bringing the humidified exhaust gas into contact with fly ash discharged from the dust remover to carbonate the fly ash. Effect of the Invention

[0012] According to the present invention, it is possible to efficiently carry out carbonation treatment of fly ash in order to suppress the elution of heavy metals contained in the fly ash. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a fly ash treatment device according to an embodiment and a waste incineration system including the fly ash treatment device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below.

[0015] 1 is a block diagram showing a schematic configuration of a fly ash treatment device 100 according to an embodiment of the present invention and a waste incineration system 1000 including the fly ash treatment device 100. The fly ash treatment device 100 is provided between a waste incinerator 1 and a chimney 2.

[0016] The waste incinerator 1 is an incinerator that incinerates waste. Exhaust gas generated in the waste incinerator 1 flows to the boiler 1A. The boiler 1A generates steam by heating water preheated in an economizer 1B (described later) with the exhaust gas flowing from the waste incinerator 1. The steam generated in the boiler 1A flows to the steam turbine 21.

[0017] The steam turbine 21 is connected to a generator (not shown) and rotates with the steam sent from the boiler 1A to cause the generator to generate electricity. The steam supplied to the steam turbine 21 is discharged to the condenser 22. The condenser 22 cools and condenses the steam discharged from the steam turbine 21, returning it to water. The condensate tank 23 stores the water returned from the steam by the condenser 22. The deaerator 24 removes oxygen contained in the water stored in the condensate tank 23. The water from which oxygen has been removed by the deaerator 24 is supplied to the economizer 1B. The economizer 1B heats the water supplied from the deaerator 24 with exhaust gas circulating from the boiler 1A. The water heated by the economizer 1B flows to the boiler 1A.

[0018] The exhaust gas that has passed through the economizer 1B passes through an upstream flue A connected to the economizer 1B. An alkaline agent supplying device 4 is connected to the upstream flue A. The alkaline agent supplying device 4 supplies an alkaline agent to the exhaust gas in the upstream flue A. The alkaline agent supplied by the alkaline agent supplying device 4 is, for example, slaked lime. The exhaust gas passing through the upstream flue A passes through the fly ash treatment device 100 together with the alkaline agent supplied from the alkaline agent supplying device 4.

[0019] The fly ash treatment device 100 is a device that performs a dust removal process on the exhaust gas supplied from the upstream flue A, a carbonation process to lower the pH of the fly ash, and a stabilization process to reduce the amount of heavy metals leaching from the carbonated fly ash to below a predetermined regulatory value (standard value).

[0020] The carbonation process carried out in the fly ash processing device 100 involves contacting the exhaust gas discharged from the waste incinerator 1 with the fly ash, and carbon dioxide in the exhaust gas reacts with alkaline components such as Ca(OH)2 and CaO contained in the fly ash to carbonize it. This carbonation lowers the pH of the fly ash to suppress the elution of heavy metals, and also causes the carbon dioxide in the exhaust gas to react with the lead in the fly ash to produce lead carbonate, which makes it difficult to elute.

[0021] Among the heavy metals contained in fly ash, the regulation value (standard value) for the amount of lead eluted, which is particularly high, is 0.3 mg / L when the fly ash is disposed of in a landfill. In addition, when fly ash is effectively used as a resource, an environmental standard for soil is required, which is 0.01 mg / L. Therefore, when the fly ash is disposed of in a landfill or used as a resource, it must be treated to make the fly ash less than the above regulation value. Lead is an amphoteric metal, and in a pH range below 12, its solubility drops significantly and it becomes difficult to dissolve. Therefore, by performing a carbonation process by reacting the fly ash with carbon dioxide gas (carbon dioxide) to make the pH of the fly ash below 12, the amount of lead eluted can be reduced drastically. In addition, the reaction of heavy metals such as lead to be carbonated and become difficult to dissolve also progresses, suppressing the elution of heavy metals.

[0022] In addition, the stabilization treatment performed in the fly ash treatment device 100 involves mixing a stabilizer with the carbonation-treated fly ash to fix and stabilize the heavy metals contained in the fly ash, thereby reducing the amount of heavy metals eluted to a prescribed regulated value (standard value) or less. In the present invention, by performing a treatment to lower the pH of the fly ash to suppress the elution of heavy metals and a treatment to generate lead carbonate to make it difficult to elute, the amount of stabilizer used for the fixation and stabilization treatment of heavy metals can be reduced, thereby reducing the fly ash treatment cost.

[0023] The fly ash treatment device 100 includes a dust remover 3, a downstream flue B1, a flue C1, a flue C2, a blower 6A, a heat exchanger 7, a duct D, a fly ash carbonation device 8, and a fly ash treatment facility 9.

[0024] The dust remover 3 is composed of, for example, a bag filter, and the flue gas that has flowed through the upstream flue A and has been supplied with an alkaline agent enters the dust remover 3. The dust remover 3 removes dust from the flue gas by collecting fly ash in the flue gas that has entered. This flue gas contains moisture (water vapor). The dust remover 3 is connected to a fly ash carbonation device 8 and a downstream flue B1. The flue gas from which dust has been removed by the dust remover 3 flows into the downstream flue B1. The fly ash collected by the dust remover 3 is supplied to the fly ash carbonation device 8.

[0025] The downstream flue B1 is connected to a flue C1 and a heat exchanger 7. The exhaust gas that travels from the dust collector 3 to the downstream flue B1 branches into the flue C1 and the heat exchanger 7. The flue C1 may be connected to a downstream flue B2 located on the chimney 2 side of the heat exchanger 7, instead of being connected to the downstream flue B1.

[0026] A blower 6A is connected to the flue C1. The blower 6A extracts a part of the exhaust gas from the downstream flue B1 and supplies the extracted exhaust gas to the flue C2 connected to the fly ash carbonation device 8. The exhaust gas extracted by the blower 6A has a temperature of 200°C or less (for example, 160 to 180°C) when it is extracted from the downstream flue B1. Here, the reason why the temperature of the exhaust gas is set to 200°C or less is because a guideline has been established that the exhaust gas temperature at the inlet of the dust removal device 3 composed of a bag filter should be approximately 200°C or less in order to deal with dioxins contained in the exhaust gas from the waste incinerator 1.

[0027] The heat exchanger 7 is a device that generates water vapor by heating water supplied from the outside with exhaust gas supplied from the downstream flue B1. The exhaust gas that has passed through the heat exchanger 7 flows through the downstream flue B2 connected to the heat exchanger 7, and is released into the atmosphere from the chimney 2 via the blower 6B and the downstream flue B3. The water vapor generated in the heat exchanger 7 flows through a duct D connected to the flue C2, passes through the blower 6A, and is blown into the exhaust gas flowing through the flue C2. The duct D may be connected to the flue C1 instead of the flue C2.

[0028] The exhaust gas supplied to the fly ash carbonation device 8 by the blower 6A is cooled and humidified by the steam blown from the heat exchanger 7 through the duct D. In this way, the dust-removed exhaust gas, which originally contains moisture (water vapor), is further blown with water vapor to humidify the exhaust gas, and a humidified exhaust gas is generated, which promotes the carbonation reaction of the fly ash in the fly ash carbonation device 8, which will be described later.

[0029] The fly ash carbonation device 8 is a device that receives the fly ash discharged from the dust collector 3 and the humidified flue gas humidified by the steam generated in the heat exchanger 7 and carbonates the fly ash. The fly ash carbonation device 8 is connected to a return pipe 11 that is connected to the upstream flue A. In this embodiment, the humidified flue gas supplied to the fly ash carbonation device 8 is used for a carbonation reaction of the fly ash by contacting with the fly ash supplied from the dust collector 3.

[0030] The fly ash carbonation device 8 preferably has a fluidized bed forming means (not shown) for forming a fluidized bed of fly ash by supplying humidified exhaust gas in a vessel receiving the fly ash, and a stirring means (not shown) for stirring the fluidized bed. The stirring means stirs the fluidized bed with a stirring blade provided in the vessel, so that the gas-solid contact between the fly ash and the humidified exhaust gas is well maintained and the carbonation reaction of the fly ash is promoted. The fly ash carbonation device 8 is not limited to the above-mentioned form and can be variously modified. For example, the fly ash carbonation device 8 can be a kiln in which the vessel receives the fly ash and the humidified exhaust gas and rotates around its axis. The fly ash carbonation device 8 may form a moving bed that receives the fly ash and the humidified exhaust gas, or may form a fixed bed by operating in a batch mode.

[0031] The humidified flue gas after being used in the carbonation reaction of the fly ash in the fly ash carbonation device 8 flows through the return pipe 11 and returns to the upstream flue A. The humidified flue gas returned to the upstream flue A is supplied with an alkaline agent from the alkaline agent supply device 4 together with the flue gas discharged from the waste incinerator 1, and is sent again to the dust remover 3. The fly ash that has been carbonated in the fly ash carbonation device 8 is sent to the fly ash treatment facility 9.

[0032] The fly ash treatment equipment 9 is supplied with a stabilizer from the outside, and mixes (kneads) the stabilizer with the fly ash supplied from the fly ash carbonation equipment 8 to fix and stabilize (stabilize) the heavy metals contained in the fly ash, thereby reducing the amount of eluted heavy metals to below the standard value.

[0033] Next, the operation and effect of the fly ash treatment device 100 will be described. In this embodiment, the flue gas discharged from the waste incinerator 1 is neutralized by receiving an alkaline agent from the alkaline agent supply device 4 in the upstream flue A, and then sent to the dust remover 3 at a temperature of 200°C or less (for example, 160 to 180°C) for dust removal. At this time, the dust remover 3 captures the alkaline agent together with the fly ash in the flue gas. The flue gas from which dust has been removed in the dust remover 3 passes through the downstream flue B1, the heat exchanger 7, the downstream flue B2, the blower 6B, and the downstream flue B3, and is appropriately subjected to a detoxification treatment before being released into the atmosphere from the chimney 2.

[0034] In addition, a part of the flue gas in the downstream flue B1 is diverted from the downstream flue B1 to the flue C1 by the blower 6A. The flue gas diverted to the flue C1 is cooled and humidified by the steam blown from the heat exchanger 7 through the duct D to become humidified flue gas, which then flows through the flue C2 and is sent to the fly ash carbonation device 8. The humidified flue gas is maintained at 100°C or higher. Therefore, the steam blown into the flue gas does not condense.

[0035] The water vapor generated in the heat exchanger 7 only needs to have a temperature and pressure at which it does not condense, and does not need to be high-temperature and high-pressure like the water vapor supplied to the steam turbine 21, so there is no need to degas the water supplied to the heat exchanger 7. In the heat exchanger 7, the exhaust gas that heats the water is located downstream of the dust remover 3 in the direction of travel of the exhaust gas, so that the dust that causes corrosion of the heat exchanger 7 is almost completely removed by the dust remover 3, and most of the acidic gas components are removed, so that the influence of corrosion due to the dust and acidic gas components can be reduced. In addition, the heat exchanger 7 is smaller than the boiler 1A, so it can be installed in the flue, and can be easily attached to a waste treatment system that does not have a heat exchanger 7. Furthermore, if the steam flowing from the boiler 1A to the steam turbine 21 is branched off and supplied to the flue C2, the efficiency of power generation drops because the amount of steam used for power generation is reduced, but in this embodiment, the steam for humidifying the exhaust gas is generated in a system separate from the steam used for power generation, so that carbonation treatment can be performed while stably supplying electricity without reducing the efficiency of power generation by the steam turbine 21. Furthermore, when generating steam for humidifying the exhaust gas, the heat of the exhaust gas is utilized in the heat exchanger 7, so that steam can be generated efficiently.

[0036] In the fly ash carbonation device 8, the fly ash collected and discharged in the dust collector 3 comes into contact with the humidified flue gas generated by the steam from the heat exchanger 7, whereby the fly ash is carbonated. Specifically, the alkaline components CaO and Ca(OH)2 in the fly ash react with the carbon dioxide gas (carbon dioxide) in the humidified flue gas to become carbonated, and become CaCO3, which lowers the pH of the fly ash. Here, since the temperature of the humidified flue gas supplied to the fly ash carbonation device 8 is 100 to 200 °C, the moisture in the humidified flue gas is in a water vapor state during the carbonation reaction, and adheres to the surface of the fly ash particles without condensing, and exists as adhering water. In this way, the amount of adhering water on the fly ash surface increases as the reaction field for the carbonation reaction is formed larger, and the carbon dioxide in the humidified flue gas and the fly ash proceed to carbonation reaction through the adhering water on the surface of the fly ash particles.

[0037] As a result, the carbonation reaction of the fly ash and the lead in the fly ash proceeds efficiently, and the carbonation treatment of the fly ash is promoted. In addition, this carbonation reaction causes the lead in the fly ash to become a sparingly soluble region, suppressing the elution of lead. In addition, the lead in the fly ash reacts with the carbon dioxide in the humidified flue gas to become carbonated, and the form of lead changes from soluble PbCl2 or PbO to sparingly soluble PbCO3, suppressing the elution of lead. In this way, the fly ash treatment device 100 performs a process to lower the pH of the fly ash to suppress the elution of heavy metals and a process to generate lead carbonate to make the lead less elutable, thereby reducing the amount of stabilizer used for the fixation and stabilization treatment of heavy metals, thereby reducing the fly ash treatment cost.

[0038] In this embodiment, the moisture in the humidified exhaust gas does not condense into a large amount of water droplets and coexist with the fly ash, so the fly ash does not bond with each other through moisture to form clumps, which reduces the reactivity of the carbonation reaction and thus does not take a long time for the carbonation reaction. Also, in this embodiment, drain water is not generated due to condensation of moisture in the exhaust gas, so there is no need to provide a device for treating the drain water.

[0039] The upper limit temperature of the humidified flue gas supplied to the fly ash carbonator 8 is set to 200°C because the closer the temperature of the humidified flue gas is to 200°C, the longer the time for the carbonation reaction will be, even if the moisture content is increased. On the other hand, the lower limit temperature of the humidified flue gas supplied to the fly ash carbonator 8 is set to 100°C because if the temperature of the humidified flue gas is set to less than 100°C, the water vapor in the humidified flue gas will condense into water droplets, and the coexistence of these water droplets with the fly ash will cause the fly ash to become lumpy, which will reduce the carbonation reaction. In addition, if the prevention of acid dew-point corrosion of the equipment is also taken into consideration, it is preferable to set the lower limit temperature of the humidified flue gas to 140°C.

[0040] The humidified flue gas after being used for carbonating the fly ash in the fly ash carbonation device 8 is sent by the return pipe 11 to the upstream side of the position where the alkaline agent is supplied by the alkaline agent supply device 4, and is returned to the upstream flue A. Here, the humidified flue gas may be sent downstream of the position where the alkaline agent is supplied by the alkaline agent supply device 4 and upstream of the dust remover 3, and returned to the upstream flue A. The amount of this flue gas returned to the upstream flue A is significantly smaller than the amount of flue gas discharged from the waste incinerator 1, and the impact on the equipment subsequent to the dust remover 3 is at a negligible level.

[0041] The fly ash carbonated in the fly ash carbonation device 8 is mixed with a stabilizer in the fly ash treatment facility 9. As a result, the heavy metals in the fly ash are fixed and stabilized (stabilization treatment), and the amount of eluted heavy metals is reduced to below the standard value. The stabilized fly ash is discharged from the fly ash treatment facility 9 and then disposed of in a landfill. In this embodiment, the amount of stabilizer used in the fly ash treatment facility 9 can be significantly reduced. [Explanation of symbols]

[0042] 1 Waste incinerator 1A Boiler 1B Economizer 2. Chimney 3 Dust removal equipment 4. Alkaline agent supply device 6A, 6B blower 7 Heat exchanger 8 Fly ash carbonation equipment 9 Fly ash processing equipment 11 Return pipe 21 Steam turbine 22 Condenser 23 Condensate Tank 24 Deaerator 100 Fly ash processing equipment 1000 Waste Incineration System A Upstream flue B1, B2, B3 downstream flue C1, C2 flue D Duct

Claims

1. A dust removal device that removes dust from exhaust gas discharged from a waste incinerator; a heat exchanger for heating water supplied from the outside with the exhaust gas after dust removal by the dust removal device to generate water vapor; a fly ash carbonation device that brings fly ash discharged from the dust collector into contact with a humidified flue gas generated by supplying the water vapor to a flue gas branched from the flue gas removed by the dust collector, thereby carbonating the fly ash; Equipped with The flue gas to which the water vapor is supplied is flue gas branched off from the flue gas supplied from the dust remover to the heat exchanger.

2. A dust removal device for removing dust from exhaust gas discharged from a waste incinerator; a heat exchanger for heating water supplied from the outside with the exhaust gas after dust removal by the dust removal device to generate water vapor; a fly ash carbonation device that brings fly ash discharged from the dust collector into contact with a humidified flue gas generated by supplying the water vapor to a flue gas branched from the flue gas removed by the dust collector, thereby carbonating the fly ash; Equipped with The humidified flue gas that has come into contact with the fly ash is mixed with flue gas discharged from the waste incinerator.

3. The exhaust gas to which the water vapor is supplied is exhaust gas branched off from the exhaust gas discharged from the heat exchanger. The fly ash treatment device according to claim 2 .

4. The exhaust gas discharged from the waste incinerator is removed by a dust removal device, a heat exchanger heats water supplied from the outside with the exhaust gas after dust removal by the dust removal device to generate steam; supplying the water vapor to an exhaust gas branched from the exhaust gas from which dust has been removed by the dust remover to generate a humidified exhaust gas; contacting the humidified exhaust gas with fly ash discharged from the dust collector to carbonate the fly ash; The exhaust gas to which the water vapor is supplied is exhaust gas branched off from the exhaust gas supplied from the dust collector to the heat exchanger. Fly ash processing method.

5. Dust is removed from exhaust gas discharged from a waste incinerator using a dust removal device, a heat exchanger heats water supplied from the outside with the exhaust gas after dust removal by the dust removal device to generate steam; supplying the water vapor to an exhaust gas branched from the exhaust gas from which dust has been removed by the dust remover to generate a humidified exhaust gas; contacting the humidified exhaust gas with fly ash discharged from the dust collector to carbonate the fly ash; The humidified exhaust gas that has been in contact with the fly ash is mixed with the exhaust gas discharged from the waste incinerator. Fly ash processing method.

6. The exhaust gas to which the water vapor is supplied is exhaust gas branched off from the exhaust gas discharged from the heat exchanger. The method for treating fly ash according to claim 5.

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