JPH04169708A - Low-nox burner - Google Patents

Abstract

PURPOSE:To contrive suppression of NOx formation, by supplying combustion air in two stages, using first-stage combustion air for combustion in a reducing atmosphere, and supplying second-stage combustion air at positions arranged alternately with positions for a self-recirculating gas on a circle so that string form oxidizing combustion regions and non-string form reducing combustion regions are formed alternately with each other. CONSTITUTION:Combustion air is fed from a blower l into a wind box 2. A portion of the combustion air passes through a regulatable damper 3, and is put into a swirl flow by a stabilizer 5 provided at the tip of a nozzle chamber 4, to be ejected into a furnace 6. An oil is pressurized by an oil pump 7, and is fed through an oil pipe 8 to be sprayed from a nozzle 9 as fine particles, which are mixed with the swirling combustion-air flow, whereby combustion is started. Second-stage combustion air is fed through a gap between an outer casing 10 and an inner tube 11, and is divided at a front wall 12 of an inducing nozzle 17 into a plurality of portions. The portions are ejected through chambers 13 toward air ports 14, and are mixed with a reducing atmosphere to perform blue-flame combustion, forming string form a plurality of oxidizing combustion regions in the furnace 6. A portion of the resultant combustion gas performs self-circulation while releasing heat, and enters a circulating gas inlet port 16, to be blown again into the furnace 6 through a gas outlet port 20.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a low NO
This relates to an X burner.

(Prior Art) As the NOx suppression combustion technology in burners, a) an exhaust gas recirculation method, b) a two-stage combustion method, and C) a split flame catalytic combustion method are known.

The exhaust gas recirculation system (a) is a system in which the exhaust gas is recirculated through a recirculation passage in which the flue a is branched, as shown in FIG. This method has the following advantages and disadvantages.

1) It is said that this is the most effective and reliable NOx suppression technology when the recirculation gas temperature is as low as around 300°C.

On the other hand, in the combustion gas self-circulation system shown by symbol C in Fig. 8, the temperature of the circulating gas is as high as 1000 to 1300°C, so the NOx suppression effect is small and the oxygen partial pressure decreases, resulting in no combustion. It becomes stable. Although the combustion gas self-recirculation method is simple, it is not expected to be very effective with current technology.

2) Exhaust gas recirculation method uses fresh combustion air (○, = 21%)
In order to mix around 20 parts of exhaust gas (02 = 3 to 8%) to 100 parts of air (02 = 1s to 19%), it is necessary to increase the combustion chamber volume (10 to 16%).

3) Exhaust gas recirculation method requires large equipment cost and installation area;
Heat equipment with a capacity of 0 x 10'Kcal/h or less is relatively expensive.

Next, (b) two-stage combustion method (see Figures 9 and 10)
has the following problems:

1) The first stage oxidizing flame combustion and the second stage reducing flame combustion as shown in Fig. 10 can be carried out with a gas or oil burner of 100 X 10'Kcal/h or less, but 100XI○4Kcal/
An oil burner with a capacity of less than h is impractical because the combustion port requires a large space due to its structure.

2) The first-stage reducing flame combustion and the second-stage oxidizing flame combustion as shown in FIG. 9 can be performed with a gas burner, but oil burners tend to generate soot.

Also, if heat dissipation during the first stage reduction flame combustion is not sufficient,
The N
Does not suppress OX.

3) The two-stage combustion method allows the burner flame port to be freely designed and is relatively easy to install on large burners with sufficient mounting surface space.
Small burners have restrictions on the dimensions of their combustion ports, which poses problems if the installation space is small.

4) When installing multiple oil nozzles, it is possible to install them on the same plane, but it is unreasonable to install them in front and behind the combustion direction axis, which may cause trouble.

Furthermore, (c) split flame method (concentration combustion method) (11th
Figures 13) are a combination of near-rich flame and oil-stain flame as shown in Figure 11. 1) Large oil burners and gas burners use multiple nozzles to split flames relatively freely. It can be made, but
For gun type burners, when the burner mouth has a diameter of 165II11 or more and is less than 10' OX 10' Kcal/h, multiple nozzles are installed in the design and the combustion amount is individually varied to create a split flame (concentration combustion) (No. 13). There are some difficulties in creating the figure.

2) It is possible to create split flames by devising a supply method on the air side rather than on the fuel side, and it is more economical than creating split flames on the fuel side. The smooth, I-split flame bundles the flames into a single ray and efficiently dissipates heat, suppressing the flame temperature and reducing NO
X can be suppressed.

(Problems to be Solved by the Invention) The low NOX burner according to the present invention combines a split flame method and a self-recirculation method, and provides a new method for supplying combustion air and recirculation gas to form a split flame with an oil nozzle. However, the part where the flame temperature exceeds 1300"C is a part of the combustion region with a striped oxidizing flame, so it is necessary to suppress the generation of NOx to a small extent, and the combustion region with a striped reducing flame that reduces NO. comes close to the NO generating part and diffuses, resulting in NOX generated
An object of the present invention is to provide a low NOX burner that can minimize the generation of NOX due to its ability to reduce NOX.

(Means for solving the problem) Combustion air is supplied in two stages, the first stage is combusted in a reducing atmosphere, and the second stage air is supplied alternately with self-recirculating gas on the circumference. The striped oxidation combustion region and the non-striated reduction combustion region are arranged alternately to form split flames in the centrifugally expanding annular reduction combustion airflow, and combustion occurs in the striped oxidation flame combustion region. Once completed, the remaining air diffuses into the strip-reducing flame combustion region, causing slow combustion under conditions of low oxygen partial pressure. The striped oxidation combustion airflow and the striped reduction combustion airflow that are alternately configured are regarded as one bundle of airflow.

This combustion air flux gradually loses its inertia and decelerates to complete combustion, but a portion of it self-circulates from the outer periphery of the flame to the circulating gas inlet of the burner. In addition, a part of the flow is made to flow into the negative pressure section generated at the center of the flame as a circulating flow.

(Example) An explanation will be given based on the drawings. In Fig. 1, combustion air enters a wind box 2 from a blower 1, and a part of it passes through an adjustable damper 3 and a stabilizer 5 installed at the tip of a nozzle chamber 4.
As a result, it becomes a gentle swirling flow and is ejected into the furnace 6. The oil is pressurized by the oil pump 7, passes through the oil pipe 8, is sprayed into fine particles from the nozzle 9, mixes with the swirling combustion air stream, and starts combustion. The amount of first-stage combustion air supplied via the damper 3 is 15 to 40% of the total amount of combustion air to form a reducing atmosphere (oxygen-deficient combustion).

The combustion air in the second stage passes through the gap between the outer cylinder 10 and the inner cylinder 11, and is divided into a plurality of parts at the front wall 12 of the in-juice nozzle 17, and is ejected from the chamber 13 toward the air port 14, where it mixes with the reducing atmosphere. A plurality of strip-shaped oxidation flame combustion areas are formed in the furnace 6, and combustion occurs with blue flame.

A part of this combustion gas self-circulates while dissipating heat, enters the circulating gas inlet 16 and returns to the furnace 6 from the circulating gas outlet 2°.
It squirts inside. Reference numeral 17 is an in-juice nozzle for applying negative pressure to the circulating gas suction port 16 to facilitate circulation of combustion gas. The ignition transformer 18 sends high-voltage electricity to the tip of the ignition electrode 19 to ignite the air mixture with an electric spark.

A plurality of circulating gas outlets 20 are provided on the circumference (second
), they are arranged in a ring shape alternately adjacent to the air ports 14. Therefore, the combustion air flow (02=21%) and the circulating gas flow (
02 = 2%) is blown out alternately in strips, surrounding the first stage reducing atmosphere (see Figure 5 A), but what is involved in combustion is mixing with the combustion air flow that advances straight. In the region where it mixes with the circulating gas flow, the oil particles are exposed to high temperatures in an oxygen-deficient state, further promoting gasification but not leading to combustion. In other words, multiple flames are formed as shown in Figure 6. Since the flame is divided into stripes, heat radiation from the flame is carried out easily and rapidly, and the generation of NOx can be suppressed.

(Function) Conventional split flame type low NOX burners are equipped with multiple oil nozzles to split the flame, but because the flame is directional, the flame becomes rod-shaped and mixes poorly with the combustion air. Excess air was required to be 30% or more. Furthermore, if combustion is performed at a low air ratio (excess air of 20% or less), soot will be generated, so there are restrictions on the low oxygen combustion of the split flame type low NOx burner.

The low NOX burner of the present invention is a burner that combines a split flame method and a self-recirculation method, and has a mechanism for evaporating oil particles in the initial stage of combustion.It first forms a reducing flame with one oil nozzle and generates atomized particles. This burner is a split flame type burner that alternately arranges and supplies combustion air and recirculated gas to a reducing atmosphere flow that has been evaporated into oil and gas to form a strip-shaped oxidation combustion region and a reduction combustion region.

In the split flame method, fuel-rich and air-rich zones are created to reduce NOx, which is called concentrated combustion.5 However, in the burner of the present invention, in the initial stage of the combustion process, the dense reducing atmosphere in which oil particles are evaporated is centrifuged. This method generates soot at a low air ratio (excess air 15%) by supplying combustion air and recirculating gas alternately to form striped areas of oxidative combustion and reductive combustion on the combustion flame surface. was completely zero, and we were able to achieve a NOX reduction rate of 60%. By the way, 30,000Kca
In a practical test using an l/h hot water boiler, the NOx value was 88ppm with a NOx-free burner.
Using a burner, NOX value 32ppm O2 = O% conversion,
Achieved an astonishing NOX reduction rate of 64% (by the way, the Tokyo Metropolitan Government's low NOX equipment certification standard value ha80 PpH+02)
= 0% conversion).

In addition, in the burner of the present invention, 15 to 40% of the total amount of combustion air is swirled into the nozzle chamber 4 via the stabilizer 5 as the first stage combustion air, mixed with fine oil particles sprayed from the oil nozzle 9, and ignited. Then, a reducing atmosphere is formed, and the inertia of the swirling air from the stabilizer 5 causes the air to diffuse in the centrifugal direction.

During this time, the heat produced by combustion is used for evaporation and vaporization of oil particles, so the flame temperature does not exceed 1200°C.

Further, a plurality of second-stage combustion air ports 14 and recirculation gas blow-off ports 20 are arranged adjacently and alternately.

The combustion air ejected from the air port 14 mixes with the first-stage reducing atmosphere gas flow and diffuses to form a strip-shaped oxidation flame, which is rapidly combusted. The first-stage reducing atmosphere gas stream mixed with the recirculating gas blown out from the recirculating gas outlet 20 is either vaporized by the heat retained in the recirculating gas and the heat from the striped oxidizing flame and becomes a high-temperature gas stream, or becomes an oxygen-deficient gas stream. It follows the linear oxidation flame in a state where combustion cannot continue due to the atmosphere, but when the combustion of the linear oxidation flame reaches its premature stage, it spreads with the remaining air and starts the third stage of slow combustion (sixth stage).
(see figure) and combustion is completed.

(Effects) The combustion method according to the present invention supplies combustion air in two stages, the first stage burns in a reducing atmosphere, the second stage air is divided and supplied alternately with self-recirculating gas, and centrifugal The oxidizing combustion region and the reducing combustion region are arranged alternately in a strip shape in a reducing atmosphere flow that spreads across the area to form divided flames. When combustion in the striped oxidation combustion region reaches its final stage, the remaining air diffuses into the reduction combustion region and completes slow combustion. The flow flows back from the outer periphery of the flame to the circulation suction port of the burner, and the - part becomes a circulating flow that flows into the negative pressure section generated at the center of the flame, contributing to suppression of NOx generated at the center of the flame.

With this combustion method, the flame temperature exceeds 1300° C. only in a part of the strip-shaped oxidation combustion region, and the generation of NOX can be suppressed to a small level. In addition, the strip-shaped reduction combustion region that reduces N○ flows in parallel with the strip-shaped oxidation combustion region that generates No, and has the function of reducing NOX generated by its diffusion, so the generation of NOX can be further minimized. be able to.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a low NOx burner implementing the method of the present invention. FIG. 2 is a sectional view taken along the line nn in FIG. 1. Figure 3 is a view in the direction of the ■ arrow in Figure 1. FIG. 4 is a sectional view taken along the arrow ■ in FIG. FIG. 5 is a diagram showing combustion conditions according to the method of the present invention. FIG. 6 is a left side view of FIG. 1. FIGS. 7 and 8 are explanatory diagrams of a known combustion gas self-circulation system. FIG. 9 and FIG. 10 are explanatory diagrams of a known two-stage combustion system. 11 to 13 are explanatory diagrams of a known split flame method. In the figure: 1 Blower 2 Wind box 3 Damper 4 Nozzle chamber 5 Stabilizer 6 Furnace 7 Oil pump 8 Oil pipe 9 Nozzle 10 Outer cylinder 11 Inner cylinder 12 Front wall 13 Chamber
14 Air port 16 Circulating gas inlet 1 Fin Juice nozzle 18 Ignition transformer 19 Ignition electrode 20 Gas outlet or above

Claims (1)

[Claims] Combustion air is supplied in two stages, the first stage burns in a reducing atmosphere, and the second stage air and self-recirculating gas are alternately arranged and supplied on the circumference in one stage, which diffuses centrifugally. A strip-shaped oxidizing combustion region and a strip-shaped reducing non-combustion region are alternately formed surrounding the annular reducing atmosphere to form a divided flame, and when the combustion in the strip-shaped oxidizing combustion region is not yet completed, The remaining air diffuses into the reduction combustion area and completes the third stage of slow combustion, and before that stage, the annular flame gradually loses its inertia and decelerates, and at the same time, a portion of the flame reaches the burner circulation inlet from the outer periphery of the flame. A low NO_X burner with a circulating flow that flows back to the flame and partially flows into the negative pressure area generated in the center of the flame.