JP2013108668A - Non-catalytic denitrification method for stoker type incinerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-catalytic denitrification method for a stoker type incinerator capable of suppressing lost heat and improving a NOx removal rate.SOLUTION: In a stoker type incinerator 2 equipped with a main combustion chamber 10a for the drying, combustion and post-combustion of wastes while moving them on stages of a plurality of stokers 11, 12, 13 sequentially and a secondary combustion chamber 10b for the secondary combustion of unburned gas contained in the combustion exhaust gas generated in the main combustion chamber 10a, a combustion exhaust gas is extracted from a post-combustion zone 22 in which post-combustion in the main combustion chamber 10a is executed, an ammonia containing combustion exhaust gas containing an ammonia gas is generated by blowing urea aqueous into the extracted combustion exhaust gas and then the generated ammonia containing combustion exhaust gas is blown into a NOx reduction zone 23 arranged downstream of the combustion exhaust gas flow of a secondary combustion zone 14.

Description

  The present invention relates to a non-catalytic denitration method for a stoker-type incinerator that incinerates general waste and industrial waste.

  In general, a stoker-type incinerator is configured to dry, burn, and post-combust waste that is supplied into a combustion chamber while sequentially moving the plurality of stoker stages on the combustion chamber (for example, Patent Documents). 1).

Japanese Patent Laid-Open No. 11-230517

  In this type of stoker-type incinerator, as a technology for suppressing the generation of nitrogen oxides (NOx), a catalyst that reacts with a reducing agent using a catalyst in addition to improvements in combustion methods such as a two-stage combustion method and exhaust gas circulation method There are a denitration method and a non-catalytic denitration method in which a reducing agent is blown into the furnace.

The catalyst denitration method is achieved, for example, by incorporating an exhaust gas heating device and a catalyst denitration device downstream of a dust collector provided in the middle of a combustion exhaust gas treatment flow. Here, the exhaust gas heating device heats about 150 ° C. exhaust gas from the dust collector to about 210 ° C. As a heat source, in the case of a waste incineration treatment facility with a boiler, superheated steam from the boiler ( 400 ° C. or 300 ° C.) is used. Further, the catalytic denitration device is a device that causes ammonia (NH ₃ ) and NOx to react on the catalyst and decomposes NOx into N ₂ and H ₂ O. However, since the decomposition rate greatly depends on the reaction temperature, It is necessary to keep the exhaust gas temperature at least 200 ° C. or higher.

  The non-catalytic denitration method is achieved, for example, by attaching a urea water blowing device to an incinerator. Here, the urea water blowing device blows urea water into a predetermined temperature region in the incinerator through a spray nozzle, and by blowing urea water into the furnace in a mist state with this urea water blowing device, NOx can be reduced and denitrated.

  However, the above catalyst denitration method requires an exhaust gas heating device that heats the exhaust gas introduced into the catalyst denitration device in addition to the catalyst denitration device, and thus has a problem that the equipment cost increases. Further, there is a problem that the energy of the heat source used in the exhaust gas heating device becomes lost energy, which causes a decrease in power generation efficiency, for example.

On the other hand, the conventional non-catalytic denitration method has the following problems.
(1) Since it is necessary to dilute with about 10 times the water in order to improve the mixing in the furnace while keeping the spray state of urea water blown into the incinerator constant, the recoverable heat amount is the latent heat of evaporation of the diluted water Decrease by minutes.
(2) Even if urea water is diluted with 10 times the amount of water, the amount is small, and mixing with combustion exhaust gas is not sufficient, and the NOx removal rate stops at 30 to 40% with an equivalent ratio of 1.2.

  The present invention has been made in view of the above-described problems, and provides a non-catalytic denitration method for a stoker-type incinerator that can suppress heat loss and improve the NOx removal rate. It is the purpose.

In order to achieve the above object, a non-catalytic denitration method for a stoker-type incinerator according to the present invention includes:
A main combustion chamber for drying, burning, and post-combusting while sequentially moving waste on a plurality of stoker stages; and a secondary combustion chamber for secondary combustion of unburned gas contained in the combustion exhaust gas generated in the main combustion chamber; In a stoker-type incinerator equipped with
Combustion exhaust gas is extracted from a post-combustion zone where post-combustion is performed in the main combustion chamber, urea water is blown into the extracted combustion exhaust gas to generate ammonia-containing combustion exhaust gas containing ammonia gas, and the ammonia-containing combustion exhaust gas is It blows in the downstream of the combustion exhaust gas flow of the secondary combustion zone in which secondary combustion is performed.

  In the present invention, it is preferable that dust removal is performed on the combustion exhaust gas extracted from the post-combustion zone (second invention).

According to the present invention, an ammonia-containing combustion exhaust gas produced by blowing urea water into a combustion exhaust gas from a post-combustion zone having a high oxygen concentration and an unburned gas such as CO or an acidic gas concentration such as HCl or SOx is low. Since it is blown into the downstream side of the combustion exhaust gas flow in the secondary combustion zone, it is sufficiently mixed with the in-furnace combustion exhaust gas, a high NOx removal effect can be obtained, and the NOx removal rate can be improved.
Ammonia generated as a result of urea water being blown into the combustion exhaust gas at a relatively high temperature (500 ° C. or higher) from the post-combustion zone without being diluted with water and vaporizing the urea water with the thermal energy of the combustion exhaust gas Since the ammonia-containing combustion exhaust gas containing gas is blown into the downstream side of the combustion exhaust gas flow in the secondary combustion zone, heat loss can be suppressed.

Schematic system configuration diagram of a waste incineration facility equipped with a stoker-type incinerator according to an embodiment of the present invention

  Next, a specific embodiment of a non-catalytic denitration method for a stoker type incinerator according to the present invention will be described with reference to the drawings.

<Description of schematic configuration of waste incineration facility>
In the waste incineration treatment facility 1 shown in FIG. 1, the waste is burned in the incinerator 2. The exhaust gas generated by the combustion of the waste in the incinerator 2 is used for heat exchange in the boiler 3 and is also used for heating the feed water to the boiler 3 in the economizer 4, and then the temperature reducing tower 5. After being cooled down to a predetermined temperature, it is sent to a dust collector 6 using a bag filter. The exhaust gas from which dust has been removed by the dust collector 6 is discharged out of the system by the induction fan 7 via the chimney 8.

<Description of incinerator>
The incinerator 2 is a stoker-type incinerator and includes a combustion chamber 10 for burning waste. The combustion chamber 10 includes a main combustion chamber 10a and a secondary combustion chamber 10b.
In the main combustion chamber 10a, drying is performed while sequentially moving waste on a plurality of stokers arranged in the lower part, that is, on the drying stoker 11, the combustion stoker 12, and the post-combustion stoker 13 arranged in order from the upper stage to the lower stage. Combustion and post-combustion are performed.
In the secondary combustion chamber 10b, a secondary combustion zone 14 is provided in which unburned gas contained in the combustion exhaust gas generated in the main combustion chamber 10a is subjected to secondary combustion by the secondary combustion air blown into the chamber. .

  In addition to the conventionally known primary combustion air blowing device 15 and secondary combustion air blowing device 16, an exhaust gas recirculation device 17 is attached to the incinerator 2.

<Description of exhaust gas recirculation device>
The exhaust gas recirculation device 17 includes a combustion exhaust gas extraction pipe 18, a dust collector 19, a recirculation gas blower 20, and a blowing nozzle 21.
The flue gas extraction line 18 is a line for extracting flue gas from the post-combustion zone 22 where post-combustion is performed on the post-combustion stoker 13, and the post-combustion stoker in the furnace wall constituting the main combustion chamber 10a. 13 is connected to the furnace wall located above 13.
The dust collector 19 uses a ceramic filter having excellent heat resistance and chemical resistance, and is effective for dust contained in the combustion exhaust gas at a relatively high temperature (500 ° C. or higher) extracted by the combustion exhaust gas extraction pipe 18. It has the function to remove automatically.
The recirculation gas blower 20 is a blower excellent in heat resistance such as made of ceramics, and has a function of sending the combustion exhaust gas from which dust is removed by the dust collector 19 toward the blow nozzle 21 as a recirculation gas.
The blowing nozzle 21 is disposed in the upper part of the incinerator 2 so as to face the NOx reduction zone 23 provided on the downstream side of the combustion exhaust gas flow in the secondary combustion zone 14. Note that the arrangement and the number of the nozzles 21 are determined so that the inside of the incinerator 2 is uniformly stirred.
The recirculation gas blower 20 and the blowing nozzle 21 are connected by a recirculation gas flow line 24. By the operation of the recirculation gas blower 20, the recirculation gas from the dust collector 19 (withdrawn from the post-combustion zone 22 and subjected to dust removal treatment). The subsequent combustion exhaust gas) can be blown out from the blowing nozzle 21 toward the NOx reduction zone 23 through the recirculation gas flow pipe 24.

<Description of urea water mixing device>
A urea water mixing device 25 is attached to the exhaust gas recirculation device 17.
The urea water mixing device 25 is configured to mix the urea water stored in the urea water storage tank 26 into the reflux gas flow line 24 through the urea water flow line 28 by the operation of the feed pump 27. Yes.
In this urea water mixing device 25, the adjustment of the amount of urea water mixed into the reflux gas flow pipe 24 is achieved by rotational control of the electric motor 29 that drives the feed pump 27. A motor controller 30 is attached to the electric motor 29, and the rotation of the electric motor 29 is controlled according to a control signal from the motor controller 30.
The motor controller 30 feeds back a measurement signal from a NOx concentration meter 31 that measures the NOx concentration of the combustion exhaust gas immediately before being discharged from the chimney 8 so that the NOx concentration in the combustion exhaust gas becomes a regulation value or less. A control signal is transmitted to the electric motor 29.

<Description of effects>
In the present embodiment, the combustion exhaust gas in the post-combustion zone 22 having a high oxygen concentration and a low concentration of unburned gas such as CO and acidic gas such as HCl and SOx is extracted via the combustion exhaust gas extraction pipe 18. The flue gas extracted from the post-combustion zone 22 is subjected to dust removal processing by a dust collector 19 using a ceramic filter, and then sent to the blowing nozzle 21 by the recirculating gas blower 20 via the recirculating gas circulation pipe 24. It is done.
The urea water stored in the urea water storage tank 26 is mixed into the reflux gas circulation pipe 24 through the urea water circulation pipe 28 by the operation of the feed pump 27.
The combustion exhaust gas flowing through the reflux gas circulation pipe 24 is a high-temperature exhaust gas of 500 ° C. or higher, and the urea water blown into the reflux gas circulation pipe 24 can be easily evaporated.
The urea water blown into the reflux gas flow line 24 is evaporated and decomposed to become ammonia gas, and the ammonia-containing combustion exhaust gas containing this ammonia gas is blown into the NOx reduction zone 23 through the blow nozzle 21.

According to the present embodiment, ammonia-containing combustion generated by blowing urea water into the combustion exhaust gas from the post-combustion zone 22 having a high oxygen concentration and a low concentration of unburned gas such as CO and acidic gas such as HCl and SOx. Since the exhaust gas is blown into the NOx reduction zone 23, the exhaust gas is sufficiently mixed with the in-furnace combustion exhaust gas, a high NOx removal effect can be obtained, and the NOx removal rate can be improved.
Further, urea water is blown into the combustion exhaust gas of 500 ° C. or higher from the post-combustion zone 22 without being diluted with water, and further contains ammonia gas generated as a result of evaporation of the urea water by the thermal energy of the combustion exhaust gas. Since the ammonia-containing combustion exhaust gas is blown into the NOx reduction zone 23, the heat loss can be suppressed, and the remaining unburned gas can be completely burned with a significant contribution to the combustion promoting effect.

In addition, the NOx removal rate can be achieved at a much higher NOx removal rate (about 70 to 80%) than the conventional non-catalytic denitration method in which the equivalent ratio is about 30 to 40%, and the catalyst Since there is no need to use a denitration method or a catalyst denitration method alone, no catalyst denitration device is required, and no exhaust gas heating device is required to maintain the activity of the catalyst. It leads to improvement.
Further, the urea water is evaporated into the incinerator 2 after evaporating with the combustion exhaust gas, and in the conventional structure in which the urea water is directly blown into the furnace, the spraying of the urea water spray nozzle becomes defective due to clogging. In such a case, the urea water hits the boiler water pipe and may damage the boiler water pipe, but it is possible to prevent the occurrence of such a problem.

  As mentioned above, although the non-catalytic denitration method of the stoker type incinerator of this invention was demonstrated based on one embodiment, this invention is not limited to the structure described in the said embodiment, The range which does not deviate from the meaning The configuration can be changed as appropriate.

  The non-catalytic denitration method for a stoker-type incinerator according to the present invention has the characteristics that it can suppress heat loss and improve the NOx removal rate. It can use suitably for the use of the waste gas treatment of the stoker type incinerator to incinerate.

DESCRIPTION OF SYMBOLS 1 Waste incineration processing facility 2 Incinerator 10a Main combustion chamber 10b Secondary combustion chamber 14 Secondary combustion zone 18 Flue gas extraction pipe line 19 Dust collector 20 Reflux gas blower 21 Blowing nozzle 22 Post combustion zone 23 NOx reduction zone 24 Reflux Gas distribution line 26 Urea water storage tank 27 Feed pump 28 Urea water distribution line

Claims (2)

A main combustion chamber for drying, burning, and post-combusting while sequentially moving waste on a plurality of stoker stages; and a secondary combustion chamber for secondary combustion of unburned gas contained in the combustion exhaust gas generated in the main combustion chamber; In a stoker-type incinerator equipped with
Combustion exhaust gas is extracted from a post-combustion zone where post-combustion is performed in the main combustion chamber, urea water is blown into the extracted combustion exhaust gas to generate ammonia-containing combustion exhaust gas containing ammonia gas, and the ammonia-containing combustion exhaust gas is A non-catalytic denitration method for a stoker-type incinerator, characterized in that it is blown downstream of a combustion exhaust gas flow in a secondary combustion zone in which secondary combustion is performed.   The non-catalytic denitration method for a stoker type incinerator according to claim 1, wherein a dust removal treatment is performed on the combustion exhaust gas withdrawn from the post-combustion zone.

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