JP5279062B2 - Combustion exhaust gas treatment method and combustion exhaust gas treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating combustion exhaust gas causing little problems like sticking of molten ash when removing dust or corrosion due to acidic gas, increasing power generation amount by increase of heat recovery amount or a boiler, and reducing consumption amount of water. <P>SOLUTION: The apparatus includes the boiler 18 recovering heat from combustion exhaust gas, a neutralizing means 45 adding an Na-based chemical in the range of 300-350&deg;C after heat recovery, a dust collector 17 removing dust from the exhaust gas after adding the chemical, an ammonia supply part 57 supplying ammonia to the exhaust gas after removing dust, a catalytic denitrification column 58 decomposing NOx by a catalyst, a heat recovering unit 59 recovering heat from the exhaust gas after denitrification, and dioxin removal means 21, 22 removing dioxins from the exhaust gas after heat recovery. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a combustion exhaust gas treatment method and a combustion exhaust gas treatment apparatus for treating combustion exhaust gas discharged from a combustion furnace, a waste incinerator or the like.

  Conventionally, as an apparatus for treating flue gas, Patent Document 1 discloses that after flue gas is heat recovered by an air preheater, acid gas neutralization is performed by blowing slaked lime in a spray tower, and dust is removed by a ceramic filter. After that, a flue gas treatment apparatus has been proposed in which NOx is decomposed in a catalytic denitration tower by blowing ammonia and exhausted from a chimney through a white smoke prevention device.

  However, in this device, the neutralizing agent is sprayed in the spray tower in the atmosphere of 480 ° C. after the air preheater (semi-dry type), so the heat quantity accompanying the vaporization of water is taken away from the exhaust gas, and the energy efficiency is increased. There is a problem of lowering. Moreover, in this apparatus, since slaked lime is used for the neutralization reaction of acid gas, it is necessary to make the spray tower installation position into a high temperature range.

  Further, in Patent Document 2, after removing combustion exhaust gas with a high-temperature filter, heat recovery is performed with a steam superheater and a boiler, NOx decomposition is performed with a catalytic denitration tower, heat recovery is performed with an economizer, and an exhaust gas treatment device is installed. Combustion exhaust gas treatment devices that pass through the chimney and have been proposed have been proposed.

  However, in this apparatus, since a high-temperature filter is provided immediately after the combustion chamber (in the region of 750 to 800 ° C.), there is a concern about corrosion such as caging by acid gas, and the actual gas amount increases due to high temperature. There was also a problem such as adhesion due to molten ash.

  In Patent Document 3, after recovering heat from combustion exhaust gas with a boiler, the temperature is reduced in a temperature reducing tower sprayed with water to prevent dioxin resynthesis, and after neutralization, heated to a temperature suitable for catalytic denitration reaction. Then, an exhaust gas treatment apparatus that performs treatment catalyst denitration treatment and the like has been disclosed.

  However, this apparatus is disadvantageous in terms of loss of heat of vaporization due to water spray and the amount of water used, and there is a problem that it is necessary to perform heating before the treatment catalyst denitration treatment, resulting in reduced energy efficiency. .

JP-A-7-96134 JP-A-9-313886 JP 2002-257328 A

  Therefore, the object of the present invention is that problems such as adhesion due to molten ash and corrosion due to acidic gas are less likely to occur during dust removal, and it is possible to increase the amount of heat recovery and increase the amount of power generated by the boiler. It is an object to provide a combustion exhaust gas treatment method and a combustion exhaust gas treatment apparatus that can reduce the combustion temperature.

The above object can be achieved by the present invention as described below.
That is, the combustion exhaust gas treatment method of the present invention includes a step of recovering heat from combustion exhaust gas with a boiler, a step of neutralizing acidic gas by adding a Na-based chemical in a temperature range of 300 to 350 ° C. after heat recovery, and A step of removing dust from the exhaust gas after addition of the chemical, a step of supplying ammonia to the exhaust gas after dust removal and decomposing NOx in the catalytic denitration tower, a step of recovering heat from the exhaust gas after denitration, And a step of removing dioxins and heavy metals from the exhaust gas after heat recovery.

  According to the combustion exhaust gas treatment method of the present invention, an Na-based chemical is added in a temperature range of 300 to 350 ° C. to neutralize the acidic gas and remove dust. Therefore, the exhaust gas has a temperature of about 300 ° C. However, the acid gas and concentration are reduced to a level that does not require consideration of corrosion. In addition, it is not necessary to perform heating prior to the subsequent denitration treatment, and heat can be absorbed until the exhaust gas becomes a low temperature, so that the amount of evaporation by the boiler can be increased. Moreover, since dioxins are removed after heat recovery, it is not necessary to provide a temperature reducing tower or the like, and the amount of water used can be reduced. Furthermore, since dust removal is performed at 350 ° C. or lower, problems such as adhesion due to molten ash and corrosion due to acidic gas hardly occur. As a result, problems such as adhesion due to molten ash and corrosion due to acidic gas are unlikely to occur during dust removal, and the amount of heat recovered by the boiler and the subsequent heat recovery device can be increased, heating the exhaust gas before the denitration device. Therefore, it is possible to provide a combustion exhaust gas treatment method capable of reducing the amount of water used without using any steam for the purpose of use.

  In the above, it is preferable to remove the dioxins and heavy metals by blowing activated carbon into exhaust gas and filtering it with a bag filter. According to this configuration, dioxins can be efficiently removed by adsorbing dioxins with activated carbon and capturing them with a bag filter.

The dust removal is preferably performed with a bag filter made of ceramic filter cloth. According to this configuration, since the ceramic filter cloth is used as the constituent material of the bag filter, sufficient heat resistance can be obtained.
On the other hand, the combustion exhaust gas treatment apparatus of the present invention comprises a boiler that recovers heat from combustion exhaust gas, a neutralization treatment means that adds Na-based chemicals in a temperature range of 300 to 350 ° C. after the heat recovery, and exhaust gas after the chemicals are added. A dust collector for removing dust, an ammonia supply unit for supplying ammonia to the exhaust gas after dust removal, a catalyst denitration tower for decomposing NOx with a catalyst, a heat recovery unit for recovering heat from the exhaust gas after denitration, And dioxins removing means for removing dioxins from the exhaust gas after recovery.

  According to the combustion exhaust gas treatment apparatus of the present invention, since the neutral gas is neutralized by adding a Na-based chemical in the temperature range of 300 to 350 ° C. by the neutralization treatment means, it is necessary to perform heating prior to the subsequent denitration treatment. Therefore, the amount used for heating the exhaust gas of the steam generated in the boiler can be eliminated, and the amount of power generation can be increased by feeding to the steam turbine. In addition, since dioxins are removed after heat recovery and dust removal by means of dioxins removal, there is no need to provide a temperature reducing tower to prevent dioxin resynthesis, reducing the amount of water used and increasing the amount of heat recovered be able to. Furthermore, since dust removal is performed at 350 ° C. or less with a dust collector, problems such as adhesion due to molten ash and corrosion due to acidic gas are unlikely to occur. As a result, problems such as adhesion due to molten ash and corrosion due to acidic gas are less likely to occur during dust removal, increasing the amount of heat recovered by the boiler and heat recovery device, and reducing the amount of water used. A combustion exhaust gas treatment apparatus can be provided.

  Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a process flow chart showing an example of the flue gas treatment method of the present invention, and FIG. 2 is a schematic configuration diagram showing an example of the flue gas treatment apparatus of the present invention.

  In the present embodiment, as shown in FIG. 2, the combustion exhaust gas treatment of the present invention is applied to a pyrolysis gasification melting plant which is a treatment plant for general waste such as household waste and industrial waste such as car shredder dust and electrical appliances. An example in the case of applying the device will be shown. The processing plant may be a stoker-type incinerator. This pyrolysis gasification and melting plant comprises a pretreatment facility 1, a pyrolysis facility 2, a pyrolysis residue sorting facility 3, a high temperature combustion melting facility 4, a boiler power generation facility 5, and an exhaust gas treatment facility 6.

  First, a process and an apparatus for generating combustion exhaust gas that is an object of exhaust gas treatment of the present invention will be described.

  In the pretreatment facility 1, the waste stored in the waste pit 7 is crushed by a crusher, and the crushed waste is sent to the thermal decomposition facility 2 by a transport device or the like. In the pyrolysis facility 2, the waste from the waste pit 7 is conveyed and supplied to the pyrolysis drum 12, and heated gas is supplied from the hot stove 102 to the pyrolysis drum 12.

  While the waste is indirectly heated with this heated gas, the waste is pyrolyzed into a pyrolysis gas and a pyrolysis residue of about 450 ° C in an oxygen-free or low-oxygen atmosphere, and the pyrolysis gas is burned at a high temperature described later. It sends to the melting furnace 13 and sends the pyrolysis residue to the pyrolysis residue sorting equipment 3.

  In the pyrolysis residue sorting equipment 3, the pyrolysis residue from the pyrolysis drum 12 is sent to the screen 55 side through the cooling vibration conveyor 14 and the like, and iron, aluminum, glass sorted through the magnetic separator or the aluminum sorter 53 is used. Collect etc. The pyrolysis residue after the selection of iron, aluminum, etc. is pulverized by a pulverizer 56 (the pulverized product is hereinafter referred to as “carbon residue”). The carbon residue is sent to the carbon residue silo 61, and the carbon residue in the carbon residue silo 61 is blown into the high temperature combustion melting furnace 13 from the furnace top side.

  In the high-temperature combustion melting equipment 4, pyrolysis gas, carbon residue, and dust collection dust are blown into the high-temperature combustion melting furnace 13 from the top of the furnace, and these are swirled. Incineration ash and dust collection dust are melted and discharged continuously from the bottom of the furnace. The discharged slag is accommodated in the slag container 50 and reused as a road pavement material. The combustion exhaust gas generated by the combustion is used for the exhaust gas treatment of the present invention.

  The combustion exhaust gas treatment method of the present invention includes a step of recovering heat from combustion exhaust gas with a boiler 18 as shown in FIG. This step can be performed using a boiler power generation facility 5 as shown in FIG. That is, the combustion exhaust gas treatment apparatus of the present invention includes a boiler 18 that recovers heat from the combustion exhaust gas.

  In the boiler power generation facility 5, the exhaust gas is cooled in the boiler radiation zone and is made uniform in the evaporator tube group, and then sent to the superheated steam tube group. Steam is recovered by the boiler 18 and recovered as electricity by the turbine / generator.

  In this heat recovery, the temperature of the exhaust gas from the boiler 18 is set to 300 to 350 ° C.

  As shown in FIG. 1, the combustion exhaust gas treatment method of the present invention includes a step of neutralizing acidic gas by adding a Na-based chemical in a temperature range of 300 to 350 ° C. after heat recovery. This step can be performed using an exhaust gas treatment facility 6 as shown in FIG. That is, the flue gas treatment apparatus of the present invention includes neutralization treatment means 45 for adding Na-based chemicals in a temperature range of 300 to 350 ° C. after heat recovery.

  According to this structure, unlike the slaked lime used by the prior art, the sodium-type chemical | medical agent as a neutralization chemical | medical agent has high neutralization efficiency even if it is 300 degreeC or more, Therefore, Exhaust gas (for example, 300- It is possible to efficiently remove acidic gases such as HCl and SOx in the exhaust gas. For this reason, the influence of poisoning on the denitration catalyst of the denitration facility in the subsequent process can be reduced, and it is not necessary to reheat the exhaust gas fed to the denitration facility.

  Examples of the sodium-based drug used include sodium carbonate, caustic soda, and a composite agent thereof in addition to sodium hydrogen carbonate (bicarbonate).

In this invention, it is preferable to grind | pulverize, adjusting a particle size so that the average particle diameter may be set to 10-50 micrometers just before introduction | transduction of the said sodium type chemical | medical agent. When the average particle diameter of the sodium-based drug is within this range, the reactivity is high, and it is advantageous that the removal efficiency of acidic components in the exhaust gas can be further increased. If the average particle size of the sodium-based drug is less than 10 μm, the reactivity can be improved, but if a bag filter or the like is used as the dust collecting means in the subsequent process, clogging may occur. When the average particle size of the aqueous solution exceeds 50 μm, the removal efficiency of the acidic component decreases. The average particle size of the sodium-based drug is more preferably 10 to 30 μm, further preferably 10 to 20 μm.

  Sodium bicarbonate as a neutralizing agent is preferably supplied as a solid. For example, in order to supply a predetermined amount from a medicine storage tank, it is provided in the middle of a pipe via a single quantitative feeder of a medicine supply means. Preferably, the air is blown into a duct, which is an exhaust gas path upstream of the dust collector 17, together with air by a suction fan or a blower (not shown). It is more preferable that a pulverizing means for finely pulverizing sodium hydrogen carbonate is arranged next to such a quantitative feeder. Further, the pulverizing means may be provided with an adjusting means for adjusting the particle size of the medicine to be supplied.

As shown in FIG. 1, the combustion exhaust gas treatment method of the present invention includes a step of removing dust from the exhaust gas after addition of the chemical. This step can be performed using the exhaust gas treatment facility 6 and the dust collector 17 as shown in FIG. That is, the combustion exhaust gas treatment apparatus of the present invention includes the dust collector 17 that removes dust from the exhaust gas after the addition of the chemical.

In the present invention, the dust removal is preferably performed with a ceramic filter cloth bag filter, and the dust collector 17 is preferably provided with a ceramic filter cloth bag filter. When such a bag filter is used, reaction products and dust can be removed while causing a reaction between the acid gas and the Na-based chemical. As a result, the outlet gas of the bag filter can have an acid gas of several ppm and a dust concentration of 0.01 mg / Nm ³ or less.

  The solid (powder / granule) containing the neutralizing agent removed / separated by the dust collector 17 is preferably subjected to a heavy metal elution prevention treatment together with a reaction product from the subsequent bag filter using a chemical agent or the like.

  As shown in FIG. 1, the combustion exhaust gas treatment method of the present invention includes a step of supplying ammonia to exhaust gas after dust removal and decomposing NOx in a catalyst denitration tower 58. Therefore, as shown in FIG. 2, the combustion exhaust gas treatment apparatus of the present invention includes an ammonia supply unit 57 that supplies ammonia to the exhaust gas after dust removal, and a catalyst denitration tower 58 that decomposes NOx with a catalyst. Yes.

  The NOx decomposition in the catalytic denitration tower 58 by blowing in ammonia has a higher decomposition rate at higher temperatures, and 1.7% in the temperature range of 300 to 400 ° C. compared to the efficiency in the temperature range of 210 ° C., which is the conventional method. The NOx concentration in the exhaust gas can be further reduced, and the ammonia consumption can be reduced.

Ammonia can be supplied using an ammonia cylinder, an ammonia evaporator, a transport facility (pneumatic transport), or the like. The temperature of the exhaust gas in the ammonia supply portion is preferably in the temperature range of 300 to 350 ° C.
As shown in FIG. 1, the combustion exhaust gas treatment method of the present invention includes a step of recovering heat from exhaust gas after denitration with a heat recovery device. For this reason, the combustion exhaust gas treatment apparatus of the present invention includes a heat recovery device 59 for recovering heat from the exhaust gas after denitration, as shown in FIG.

  In the present invention, it is preferable to employ an economizer (a economizer) of the boiler 18 as the heat recovery unit 59.

  Since the heat recovery device 59 installed in the cleaned exhaust gas has a minute amount of dust and acid gas of a few ppm, adoption of finned tubes and narrowing of the tube pitch makes the heat recovery device 59 compact. . In addition, since there is no concern about corrosion due to acid gas, the temperature of the water supply to the heat recovery device can be set to about 60 ° C., so that the exhaust gas temperature is about 160 ° C. Also, dioxin resynthesis in the temperature range of 300 ° C. to 200 ° C. is unlikely to occur because there is no metal component such as hydrogen chloride, which is a cause of resynthesis, copper, which is a catalyst component in dust, and unburned carbon.

  The combustion exhaust gas treatment method of the present invention includes a step of removing residual dioxins and heavy metals from the exhaust gas after heat recovery, as shown in FIG. For this reason, as shown in FIG. 2, the combustion exhaust gas treatment apparatus of the present invention includes dioxins removing means for removing dioxins and heavy metals from the exhaust gas after heat recovery. The temperature of the exhaust gas after heat recovery is preferably set to 130 to 160 ° C.

  In the present invention, it is preferable to remove dioxins by blowing activated carbon into exhaust gas and filtering it with a bag filter. In the present embodiment, an example in which the dioxins removing unit includes an activated carbon supply unit 21 and a dust collector 22 is shown. Since the exhaust gas after heat recovery contains dioxins and heavy metals generated during combustion, it is preferable to remove the dioxins and heavy metals with activated carbon blowing and a bag filter.

  As shown in FIG. 2, the combustion exhaust gas treatment apparatus of the present embodiment includes a suction fan 23 on the downstream side of the dust collector 22, and the exhaust gas is supplied to the chimney 25. Furthermore, by providing the white smoke prevention device 24, it is possible to prevent the exhaust gas from becoming white smoke. The white smoke prevention device used in winter does not have a water spray quenching tower as in the prior art, so the moisture contained in the combustion gas is about 20%, so it can be downsized and the consumption of steam as a heating source is reduced. To do.

  The white smoke prevention device 24 can be composed of, for example, an air blower 24a and a heater 24b.

  According to the combustion exhaust gas treatment method and the combustion exhaust gas treatment apparatus of the present invention as described above, the following effects can be obtained.

1) Increase in heat recovery amount When the conventional boiler / economizer outlet temperature is 230 ° C. and the boiler / economizer outlet temperature is 160 ° C. in the present invention, the heat recovery rate is increased by 7.5%.

2) Increase in power generation The amount of power generation is increased by 14% due to the increase in the heat recovery amount and the elimination of the conventional exhaust gas heater for the catalyst denitration tower.

3) Decrease in water consumption 150kg / ton of treated waste is not required when the outlet temperature of the conventional boiler / economizer is 220 ° C and the outlet temperature of the quenching tower is 160 ° C.

[Another embodiment]
(1) In the above-described embodiment, the example in which dioxins are removed by blowing activated carbon into exhaust gas and filtering with a bag filter is shown. However, since the decomposition of dioxins in the catalytic denitration tower occurs, the emission regulation value Depending on the type, activated carbon blowing and bag filters can be eliminated.

  (2) In the above-described embodiment, an example is shown in which a bag filter is used as a dust collector for exhaust gas after neutralization. However, any dust collection method may be used as long as dust collection is possible at 300 ° C. or higher. For example, a fixed bed filter or the like can be used.

  (3) In the above-described embodiment, an example in which the combustion exhaust gas treatment apparatus of the present invention is applied to a pyrolysis gasification and melting plant has been shown. However, the combustion exhaust gas treatment apparatus of the present invention is an exhaust gas from a stoker incinerator. It can also be applied to processing.

Process flow chart showing an example of the combustion exhaust gas treatment method of the present invention Schematic configuration diagram showing an example of a combustion exhaust gas treatment apparatus of the present invention

Explanation of symbols

17 Dust collector 18 Boiler 21 Activated carbon supply means (Dioxin removal means)
22 Dust collector (dioxin removal means)
45 Neutralization treatment means 57 Ammonia supply section 58 Catalyst denitration tower

Claims (8)

Heat recovery from the combustion exhaust gas with a boiler so that the combustion exhaust gas reaches a temperature of 300 to 350 ° C., and neutralization treatment of acid gas by adding a Na-based chemical in the temperature range of 300 to 350 ° C. after the heat recovery A step of removing dust from the exhaust gas after addition of the chemical in a temperature range of 300 to 350 ° C., and supplying ammonia to the exhaust gas after dust removal in a temperature range of 300 to 350 ° C. to decompose NOx in a catalyst denitration tower A combustion exhaust gas treatment method comprising: a step, a step of recovering heat from exhaust gas after denitration, and a step of removing dioxins and heavy metals from the exhaust gas after heat recovery in a temperature range of 130 to 160 ° C. The combustion exhaust gas treatment method according to claim 1, wherein the Na-based chemical is a solid sodium-based chemical having an average particle diameter of 10 to 50 μm. The combustion exhaust gas treatment method according to claim 1 or 2, wherein the dioxins and heavy metals are removed by blowing activated carbon into the exhaust gas and filtering with a bag filter. The combustion exhaust gas treatment method according to any one of claims 1 to 3, wherein the dust removal is performed by a bag filter made of ceramic filter cloth. A boiler that recovers heat from the combustion exhaust gas so that the combustion exhaust gas has a temperature of 300 to 350 ° C., a neutralization treatment means that adds a Na-based chemical in a temperature range of 300 to 350 ° C. after the heat recovery, and 300 to 350 ° C. A dust collector that removes dust from the exhaust gas after addition of the chemical in the temperature range, an ammonia supply unit that supplies ammonia to the exhaust gas after dust removal , and a catalyst that decomposes NOx with a catalyst in the temperature range of 300 to 350 ° C. A combustion exhaust gas treatment apparatus including a denitration tower, a heat recovery unit that recovers heat from exhaust gas after denitration, and dioxins removal means that removes dioxins from exhaust gas after heat recovery in a temperature range of 130 to 160 ° C. The combustion exhaust gas treatment apparatus according to claim 5, wherein the Na-based chemical is a solid sodium-based chemical having an average particle size of 10 to 50 μm. The combustion exhaust gas treatment apparatus according to claim 5 or 6, wherein the dioxins and heavy metals are removed by blowing activated carbon into the exhaust gas and filtering it with a bag filter. The combustion exhaust gas treatment apparatus according to any one of claims 5 to 7, wherein the dust removal is performed by a bag filter made of ceramic filter cloth .

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