JPH02306004A - Combustion exhaust gas recirculation device - Google Patents

Abstract

PURPOSE:To lower the concentration of combustible matter in an exhaust gas recirculation system by burning by the catalytic action of a contact combustion catalyst the combustible matter that is contained in the combustion exhaust gas in a combustion gas recirculation system. CONSTITUTION:Fuel 13 is supplied to a burner 12 and when combustion air 14 is supplied to a wind box 4 through an air preheater 8, air ducts 15, 16, 17 from a forced draft fan 15, the mixture gas burns in the combustion section 10. And, most of the formed combustion exhaust gas 33 passes through a combustion exhaust gas duct 18, nitrogen removal device 7, and air preheater 8 from the outlet 11 of a furnace and is discharged from a chimney 9. And part of the combustion exhaust gas 33 is sent into the inside of a contact combustion catalyst reaction device 23 through a recirculation gas duct 19 from the outlet 11 of the furnace. When the combustible matter contained in the combustion exhaust gas 33 comes in contact with the contact combustion catalyst 24, it burns in a low concentration which is below the limit of its combustibility by the catalytic action in the contact combustion catalyst 24, and the exhaust gas which is made harmless is sent to the side of the combustion furnace 1 from a recirculation blower 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a combustion exhaust gas recirculation device, and in particular, a combustion method suitable for reducing the concentration of combustible components in an exhaust gas recirculation path provided in a combustion furnace. Regarding an exhaust gas recirculation device.

[Conventional technology]

Combustion furnaces such as boiler equipment are equipped with a combustion exhaust gas recirculation device that recirculates a portion of the combustion exhaust gas into the furnace in order to adjust the heat absorption rate of the furnace and reduce pollutants such as nitrogen oxides in the combustion exhaust gas. is provided. As a conventional device of this type, one shown in FIG. 7 is known.

In FIG. 7, a burner 2 is installed in the combustion section 10 of the combustion furnace 1.
, after-air port 3, and other combustion devices are provided, and these combustion devices are surrounded by a wind box 4. Burner 2
is supplied with fuel 13, and combustion air 14 for burning the fuel 13 is pressurized by a forced air blower 5, heated by an air preheater 8, and then sent to the wind box 4 via air ducts 15, 16, and 17. It is now being supplied. Most of the combustion exhaust gas 33 generated in the combustion section 10 is transferred to the furnace outlet 11.
．． Combustion exhaust gas duct 18. Denitration equipment7. The air is discharged from a chimney 9 via an air preheater 8. Further, a part of the combustion exhaust gas 33 is transferred from the furnace outlet 11 to the recirculation gas duct 19. It is designed to be sucked in by a recirculation blower 6. The combustion exhaust gas sent out from the recirculation blower 6 is then either directly injected into the combustion furnace 1 through the bottom recirculation gas duct 22 or is injected into the air duct 16.17 via the exhaust gas mixing duct 20.21, so that the air After being mixed with the air, it is supplied into the combustion furnace 1 via the air box 4, the burner 2 or the air box 4, and the after air port 3.

In such a boiler, the exhaust gas temperature near the furnace outlet 11 is approximately 250 to 400°C, and the temperature within the combustion section 10 reaches several thousand degrees Celsius. For this reason.

By injecting the combustion exhaust gas from the bottom of the furnace, it is possible to suppress the production of nitrogen oxides, and it is also possible to suppress heat absorption in the furnace combustion section 10.

However, in the conventional combustion furnace 1, the wind box 4 and the ducts 19, 20, 21 are heated due to residual fuel components or generation of flammable gas due to fuel leakage or abnormal combustion in the burner 2 in the wind box 4. Material may circulate or accumulate.

Particularly in partial load operation and in standstill conditions.

There is a possibility that the concentration of combustible substances may increase in the wind box 4 and the ducts 19, 20, 21 due to the difference in specific gravity. Therefore, in the conventional furnace 1, each duct 19, 20, 2
1. Install a combustible gas detector 12 in each wind box 4,
The combustible gas concentration is constantly monitored from the output of the detector 12, and when the detected concentration exceeds a reference value, an alarm is issued or a predetermined control action is performed.

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, no consideration is given to lowering the concentration of flammable substances in the recirculation system, and in order to monitor the increase in the concentration of flammable substances, it is necessary to use a flammable gas detector. The number of such devices must be increased to strengthen monitoring, which increases equipment costs and makes maintenance and inspection work troublesome.

An object of the present invention is to provide a combustion exhaust gas recirculation device that can remove combustible substances from combustion exhaust gas returned from a combustion furnace to a combustion furnace via a recirculation system.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a recirculation path that guides a part of the combustion exhaust gas discharged from the combustion furnace from the furnace outlet into the combustion furnace, and a recirculation path that supplies the combustion exhaust gas in the recirculation path to the combustion furnace side. This is a combustion exhaust gas recirculation device that includes a blower that performs combustion, and a catalytic combustion catalyst reactor that burns combustible substances in the combustion exhaust gas by contact with the combustion exhaust gas in the recirculation path.

[Effect]

When combustible substances in the flue gas supplied from the combustion furnace to the flue gas recirculation system come into contact with the catalytic combustion catalyst in the catalytic combustion catalytic reactor, the flammable substances at low concentrations below the flammable limit are This reduces the concentration of combustible substances.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, a combustion section 10 of a combustion furnace 1 includes a burner 2.
, after-air port 3 and other combustion devices are provided, and these combustion devices are surrounded by a wind box 4.

Fuel 13 is supplied to the burner 2, and combustion air 14 mixed with the fuel 13 is pressurized by a forced air blower 5, heated by an air preheater 8, and then passed through air ducts 15, 16, 17.
It is designed to be supplied to the wind box 4 via. A furnace outlet 11 of the combustion furnace 1 is connected to a chimney 9 via a combustion exhaust gas duct 18, a denitration device 7, and an air preheater 8.

The combustion exhaust gas recirculation system of the combustion furnace 1 is the recirculation gas duct 1.
9. It is composed of a catalytic combustion catalytic reactor 23, a recirculation blower 6, a bottom recirculation gas duct 22, and an exhaust gas mixing duct 20.21, and the bottom recirculation gas duct 22 is connected to the bottom of the combustion furnace 1.

Exhaust gas mixing ducts 20 and 21 are connected to air ducts 16 and 17, respectively, and flammable gas detectors 12 are installed in the ducts 19 and the wind box 4, respectively.

The recirculation gas duct 19, the bottom recirculation gas duct 22, and the exhaust gas mixing duct 20.21 are each configured as a recirculation furnace. Catalytic combustion catalytic reactor 2 inside
3 is installed.

The catalytic combustion catalytic reactor 23, as shown in FIG.
A catalytic combustion catalyst 24 is provided in a casing 34 connected to the recirculation gas duct 19 , and the catalytic combustion catalyst 24 is heated by a starter burner 25 . The catalytic combustion catalyst 24 is made by adding a catalyst carrier to a ceramic or metallic base material, and supports a catalyst component made of a noble metal or a metal oxide. The starting burner 25 is a gas-phase combustion type burner, and includes a fuel supply system 29 and an air supply system, and the air supply system is provided with a swirler 35. Note that a catalytic combustion type burner may be used as the starting burner 25, and the starting burner 25 may be omitted depending on the temperature of the recirculated exhaust gas.

In the above configuration, the fuel 13 is supplied to the burner 2,
Combustion air 14 is transferred from a forced air blower 15 to an air preheater 8;
When supplied to the wind box 4 via the air ducts 15 , 16 , 17 , the mixture of combustion air 14 and fuel 13 flows into the combustion section 1 .
Burns at 0. Most of the combustion exhaust gas 33 generated in the combustion section 10 flows from the furnace outlet 11 to the combustion exhaust gas duct 18.
, denitrification equipment7. It is discharged from the chimney 9 via the air preheater 8. Further, a portion of the combustion exhaust gas 33 is fed from the furnace outlet 11 through the recirculation gas duct 19 into the catalytic combustion catalytic reactor 23 . The temperature of the combustion exhaust gas 33 introduced into the recirculation gas duct 19 is usually about 250 to 400°C, and the combustion exhaust gas 33 contains combustible substances. When this combustible substance comes into contact with the catalytic combustion catalyst 24, it is combusted at a low concentration below the flammable limit due to the catalytic action of the catalytic combustion catalyst 24, and the detoxified exhaust gas is sent to the combustion furnace 1 side from the recirculation blower 6. be provided. That is, when a trace amount of combustible substances such as carbon monoxide and hydrocarbons contained in the exhaust gas 33 come into contact with the catalytic combustion catalyst 24, they are combusted at a low concentration below the flammable limit due to the catalytic action of the catalyst 24. This makes it possible to reduce the concentration of flammable substances in the recirculation system. Furthermore, since the reaction is a catalytic combustion reaction between the catalyst 24 and the combustible substance, combustion is possible even if the amount of the combustible substance is small. Furthermore, if a ceramic structure with a three-dimensional network structure having a filtration function is used as the base material of the catalytic combustion catalyst 24,
It is also possible to capture and burn carbon-containing fine particles that require a long time to burn.

The starting burner 25 is for raising the catalytic combustion catalyst 24 to a predetermined reaction temperature, and it is desirable to operate the starting burner 25 before operating the flue gas recirculation device. The operation of the starting burner 25 is controlled to either stop the starting burner 25 when the temperature is reached or to maintain a predetermined temperature.

Further, the starting burner 25 having the swirler 35 is connected to the fuel supply system 2.
Since the fuel from 9 and the air from the air supply system 28 are well mixed, and the flame is short, it is suitable for evenly heating the catalytic combustion catalyst 24.

Further, as shown in FIG. 3, it is also possible to install an electric heater 26 in the catalytic combustion catalytic reactor 23 instead of the starting burner 25. In this case, since the electric heat is mainly generated by radiation from the heater element of the electric heater 26, it is desirable to divide the catalytic combustion catalyst 34 into multiple stages and install the heater element of the electric heater 26 between each stage.) N
.

In addition, as shown in FIG. 4, a catalytic combustion catalytic reactor 2
It is also possible to install a heat exchanger 27 in the catalytic combustion catalyst 3 and supply a heat source from another system to the heat exchanger 27 to raise the catalytic combustion catalyst 24 to a predetermined temperature.

In addition, as shown in FIG. 5, a catalytic combustion catalytic reactor 2
3 in the recirculation gas duct 19, it is also possible to install it in the exhaust gas mixing duct 20.21. In this case, since it is only necessary to treat the amount of recirculated combustion exhaust gas excluding the bottom recirculated gas, it is possible to reduce the amount of catalyst in the catalytic combustion catalyst 24 as a whole.

In addition, as shown in FIG. 6, a catalytic combustion catalytic reactor 2
3 is provided with a bypass channel 30 that bypasses this reactor 23, and a bypass channel 30 is provided on the inlet side of the reactor 23 and the bypass channel 3.
If dampers 31 and 32 are installed at the reactor 23 and the amount of exhaust gas supplied to the reactor 23 is adjusted by the opening degree of the dampers 31 and 32, startup time can be shortened, pressure loss can be reduced, the life of the catalyst can be extended, and combustion exhaust gas can be reduced. It can contribute to improving the reliability of the recirculation system.

〔Effect of the invention〕

As explained above, according to the present invention, since the combustible substances contained in the combustion exhaust gas of the fuel exhaust gas recirculation system are combusted by the catalytic action of the catalytic combustion catalyst, the concentration of combustible substances in the exhaust gas recirculation system is It is possible to lower the
It can contribute to improving safety. Furthermore, it becomes possible to reduce the amount of dirt in the exhaust gas recirculation system, making it easier to maintain and inspect various equipment.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram of a catalytic combustion catalytic reactor, Fig. 3 is a block diagram of a catalytic combustion catalytic reactor using a heater, and Fig. 4 is a block diagram of a catalytic combustion catalytic reactor using a heater. A configuration diagram of a catalytic combustion catalytic reactor using an exchanger, FIG. 5 is a configuration diagram showing an example in which a catalytic combustion catalytic reactor is installed in an exhaust gas mixing duct,
FIG. 6 is a block diagram showing an embodiment in which a bypass flow path is provided in a catalytic combustion catalytic reactor, and FIG. 7 is a block diagram of a conventional example. ■... Combustion furnace, 2... Burner, 4...
・Wind box, 5... Forced blower, 6...
・Recirculation blower, 7... Denitrification device, 8...
Air preheater, 9...chimney. 10... Combustion part, 11... Furnace outlet. 12... Flammable gas detector, 15.16, 17... Air duct, 19... Recirculating gas duct, 20... Exhaust gas mixing duct, 22... Hearth recirculating gas duct. 23... Catalytic combustion catalytic reactor, 24... Catalytic combustion catalyst, 26... Electric heater, 27... Gas exchanger, 30... Bypass channel. Agent Tatsu Unuma Figure 1 ノ frill” 2:ノ／″－ノ3°? 2 Nu! /7/7: a-me 4: l, il! 7: Calendar 6f 8: I'y; f〃 12: Puffer fish 7. p'iJ et al. 19:l Eroto 4 Asowa 1 14:j;Bi8 Goo Fig. 5 Fig. 6

Claims (1)

[Claims] 1. A recirculation path that guides a portion of the combustion exhaust gas discharged from the combustion furnace from the furnace outlet into the combustion furnace, a blower that sends the combustion exhaust gas in the recirculation path to the combustion furnace side, and a combustion chamber in the recirculation path. A combustion exhaust gas recirculation device having a catalytic combustion catalyst reactor that burns combustible substances in the combustion exhaust gas by contact with the exhaust gas.