JP2912975B2 - Boiler combustion device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion device, and more particularly to a combustion device for a boiler suitable for reducing nitrogen oxides in exhaust gas.

[Conventional technology]

As a conventional small boiler having an evaporation amount of 10 t / h or less, a fire tube type or water tube type boiler is often used as shown in FIGS. 5 and 6, respectively.

The boiler body 1 includes a burner 2, a furnace 3, a heat transfer tube 4, an outer casing 5, a water chamber 6, a steam reservoir 7, or a lower header 8, an upper header 9, and the like. Boiler water supply 10
Is supplied to the water chamber 6 or the lower header 8 and is heated by the high-temperature gas of the furnace 3 to become hot water or steam. In the steam boiler, steam 11 is supplied from the steam reservoir 7 or the upper header 9.
On the other hand, in a hot water boiler, the hot water is taken out as hot water 12 from the water chamber 6 or the upper header 9.

On the other hand, the fuel 13 and the air 14 are supplied to the burner 2 by the pipes 15 and 16 and combust to generate high-temperature gas. A fan 17 is often provided for supplying the air 14, and a fuel pump 18 is provided for fuel oil. In addition, an air preheater 19 may be installed as waste heat recovery in order to improve thermal efficiency.

There is also a so-called catalytic combustion system that uses a catalyst for low NOx combustion.

[Problems to be solved by the invention]

The above prior art has a small and compact design, and its thermal efficiency is as high as 90% or more when an air preheater is provided.

However, because it is small, compact, and highly efficient,
The burner is burned under more severe conditions, and there is a problem that noise due to combustion noise is large and NOx is high.

On the other hand, the catalytic combustion method can perform low NOx combustion, but the combustion load is small and the combustion temperature is limited due to the performance of the catalyst (currently 1200 to 1000 ° C or less). Need to be taken. For this reason, the application to this kind of small boiler has a large problem in efficiency and installation area, and it is difficult to apply it, for example, the gas amount increases, non-gas loss is large and the efficiency is reduced.

An object of the present invention is to provide a boiler combustion device with low noise and low NOx.

[Means for solving the problem]

The purpose is to divide the fuel into two stages, catalytically burn the first stage using a catalyst, and use a two-stage burner that puts the second-stage combustion into the combustion gas generated there. This is achieved by providing the burner tile with a combustion gas self-circulation path.

That is, the present invention provides a first combustion section provided in a burner tile section facing a furnace in which primary fuel is burned in the presence of a catalyst, and a secondary fuel is introduced into combustion gas generated in the first combustion section. A boiler combustion device, comprising: a second combustion section that is burned and burned; and gas circulation means formed in the burner tile section and introducing combustion gas in the furnace into the first combustion section. Here, the gas circulating means includes a communication passage for communicating the furnace with the venturi throat forming the first combustion portion, and a primary combustion for the first combustion portion provided near an opening of the communication passage in the venturi throat. It is preferable to have a nozzle for air for use. Further, it is preferable that the injection speed of the secondary fuel is 100 m / sec or more. It is preferable that the venturi throat is provided with fuel oil vaporizing means.

Further, the present invention is a boiler combustion apparatus characterized in that a tubular catalyst is provided in a furnace, and a mixture of fuel and air is ejected and dispersed in the tubular catalyst by a dispersion pipe to perform catalytic combustion.

[Action]

In the above-described two-stage burner, fuel is burned with low noise and ultra-low NOx by the first-stage catalytic combustion to generate high-temperature combustion gas. In the second-stage combustion, low-NOx combustion can be stably performed by the high-temperature, low-O ₂ combustion gas generated by the first-stage combustion. Further, since the fuel is introduced into the high-temperature combustion gas, it is not necessary to increase the injection speed to the sonic speed despite the high load, and low noise can be achieved.

On the other hand, the self-circulation path provided in the burner tile is sufficient to raise the temperature of the high-temperature gas generated by the two-stage burner to the temperature required for catalytic combustion by the ejector effect of combustion air injection. By circulating, catalytic combustion can be stably burned, and further low O ₂ combustion can be achieved.
Can be further reduced.

〔Example〕

The present invention will be described more specifically with reference to examples. First
FIG. 1 is a diagram showing the overall configuration of a steam boiler according to the present invention. FIG. 2 is a diagram showing a combustion device according to the present invention.

The boiler body 1 includes a burner 2, a furnace 3, a heat transfer tube 4, an outer casing 5, a lower header 8, an upper header 9, an air preheater.
It consists of 19 mag. Boiler water supply 10 is lower header 8
And taken out from the upper header 9 as steam. On the other hand, the fuel 13 is supplied to the temporary fuel supply pipe 15 and the secondary fuel supply pipe.
The burners 2 are connected to a primary fuel seat 21 and a secondary fuel seat 22, respectively. The combustion air 14 is a primary air supply pipe 16,
It is branched into secondary air supply pipes 23 and connected to the primary air seat 24 and the secondary air seat 25 of the burner 2 via the air preheater 19, respectively.

The burner 2 has a triple pipe structure as shown in FIG. Outer pipe 26 is primary air pipe 24, inner pipe 27 is primary fuel pipe
21, an innermost pipe 28 is a mixed gas pipe of the secondary fuel 22 and the secondary air 25. A plurality of self-circulation paths 30 are provided in the burner tile 29 in the circumferential direction, and a venturi throat 31 is formed at an end of the outermost tube 26, and one end of the inner tube 27 is located on the downstream side from the tip of the inner tube 27. The next fuel is injected and mixed and sent to the catalyst layer 32. The mixed gas of the secondary fuel and the secondary air passes through the innermost pipe 28 and is injected at the output surface of the catalyst layer 32 from an injection nozzle tip 33 attached to the tip of the innermost pipe 28.

In addition, for starting, although not shown, a starting air preheater may be installed in the secondary air pipe 16 or an ignition device is installed,
The mixture of secondary fuel and secondary air may be ignited directly.
Although not shown, the burner main body 2 having a triple tube structure may be configured so that the distance from the venturi throat 31 can be variably adjusted by an adjustment bolt.

Next, the operation will be described. In catalytic combustion, it is necessary to preheat the fuel-air mixed gas to the ignition start temperature of the catalyst. In a conventional small boiler, the air preheating temperature when an air preheater is provided is at most about 150 ° C., and the temperature of 100 to 300 ° C. is still insufficient by the ignition start temperature of catalytic combustion. According to the present invention, a part of the combustion exhaust gas is self-circulated by the action of the venturi throat utilizing the air supply energy of the fuel air, so that the primary fuel and the primary air are heated to the ignition start temperature required for catalytic combustion. This has the effect of raising the temperature of the mixed gas and lowering the O ₂ concentration in the combustion air.

The residual O ₂ concentration in the high-temperature gas generated by catalytic combustion becomes about 8 to 13% due to exhaust gas circulation and catalytic combustion. In the low O ₂ state, it is usually difficult to burn the fuel, especially at 10 to 12% or less. However, when the secondary fuel is injected in a state where the high temperature gas surrounds the secondary fuel injection nozzle by catalytic combustion, the combustion reaction of the secondary fuel is stably performed in a low O ₂ state due to the effect of the high temperature gas. Stable secondary combustion becomes possible. However, if the secondary fuel injection speed is too slow (approximately
30 m / s), and the amount of surrounding low O ₂ gas involved decreases, resulting in O ₂ deficiency and unburned fuel. According to the test results of the present inventors, at least in order to prevent unburned
It has been found that an injection speed of 100 to 120 m / s or more is desirable, but it is not necessary to increase it to near the sound speed. Above the injection speed of about 100 m / s or more, the entrainment of the surrounding gas into the secondary fuel jet becomes large, and therefore, there is an effect of promoting the reduction of NOx by lowering the combustion flame temperature. Furthermore, the noise is small.

As a result of performing a combustion test with a two-stage burner having the above-mentioned venturi throat, it was possible to achieve an ultra-low NOx of 40 ppm even at an air / fuel ratio of 1.2.

The control of this burner adjusts the primary combustion or the primary air amount so that the primary combustion becomes a constant temperature, and the control of the burner load adjusts the secondary fuel secondary air amount. The protection circuit detects catalyst upstream and downstream temperature abnormalities and secondary combustion flame.

 FIG. 3 shows another embodiment according to the present invention.

This figure shows a burner for oil fuel such as kerosene, which is provided with a kerosene carburetor 34 in the venturi throat section 31, and eliminates the clogging of the primary fuel injection pipe, thereby enabling a stable supply of primary fuel. Of course, there is an effect, and
NOx can provide an efficient burner. The kerosene vaporizer may be a simple one such as inserting a wire mesh or the like into a pipe.

FIG. 4 shows another embodiment in which combustion is performed only by catalytic combustion. 32 is a cylindrical catalyst, 35 is a mixed gas pipe of fuel and air, 36 is a dispersion pipe, and 37 is a preheater. In this embodiment, the radiant heat from the catalyst can be effectively used, and an ultra-low NOx of 10 ppm or less can be achieved. This structure is particularly suitable for a hot water boiler.

〔The invention's effect〕

According to the present invention, it is possible to raise the temperature of the air / fuel mixture gas to the catalytic combustion ignition temperature by self-circulating the exhaust gas without separately installing a special preheating installation, and the catalytic combustion can be performed by the effect of the two-stage burner. + Low O ₂ gas phase, low flame temperature combustion is possible, and NOx generation is suppressed to about 70% or more of NOx generation compared to a normal burner (100 to 60 ppm).

Further, since the excess air ratio can be reduced to about the normal burner, a highly efficient boiler with a small exhaust gas loss can be applied.

In addition, a high combustion noise is not generated by the combined use of the catalytic combustion and the gas phase combustion, and the noise is low.

[Brief description of the drawings]

FIG. 1 is a block diagram of a boiler according to one embodiment of the present invention, and FIG.
FIG. 3 is an enlarged view of a burner according to the embodiment of the present invention, and FIG.
FIG. 4 is a block diagram showing another embodiment of the present invention, and FIGS. 5 and 6 are block diagrams of a conventional boiler. 2 ... burner, 3 ... furnace, 21 ... primary fuel seat, 22 ...
Secondary fuel seat, 23 ... Secondary air pipe, 24 ... Primary air seat, 25
… Secondary air seat, 29… Burner tile, 30… Exhaust gas circulation path, 31… Venturi throat, 32… Catalyst, 34…
… A fuel oil vaporizer.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masayuki Matsuda 6-9 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure factory of Babkotsuk Hitachi Ltd. (56) References JP-A-2-82019 (JP, A) 62-218727 (JP, A) JP-A-52-94530 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F23C 11/00 312 F23C 11/00 318 F23C 11/00 322 F23D 23/00

Claims (5)

(57) [Claims] 1. A first combustion section provided in a burner tile section facing a furnace in which primary fuel is burned in the presence of a catalyst, and a secondary fuel is introduced into combustion gas generated in the first combustion section. A combustion device for a boiler, comprising: a second combustion portion that is burned by combustion; and gas circulation means formed in the burner tile portion and introducing combustion gas in the furnace into the first combustion portion. 2. The gas circulation means according to claim 1, wherein the gas circulation means communicates with the furnace and the venturi throat forming the first combustion section, and a first passage provided near the opening of the communication passage in the venturi throat. A boiler combustion device comprising: a primary combustion air injection port for a combustion section. 3. The boiler combustion device according to claim 1, wherein the secondary fuel injection speed is 100 m / sec or more. 4. A combustion apparatus for a boiler according to claim 1, wherein a fuel oil vaporizing means is provided in the venturi throat portion. 5. A combustion apparatus for a boiler, wherein a tubular catalyst is provided in a furnace, and a mixture of fuel and air is jetted and dispersed in the tubular catalyst by a dispersion pipe to perform catalytic combustion.