JP3040846B2 - Gas fuel combustion method and combustion apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for burning gaseous fuel, and particularly to nitrogen oxides (hereinafter, referred to as "combustion") emitted during combustion even in a compact combustion space.
The present invention relates to a highly efficient gaseous fuel combustion method and apparatus capable of reducing the concentration of unburned components such as NOx and carbon monoxide (CO).

[0002]

2. Description of the Related Art A large number of cogeneration systems and district cooling / heating facilities are being planned along with urban redevelopment plans. Along with these facilities, boilers installed in urban and suburban areas are increasing. In an overpopulated urban area, environmental regulations are becoming stricter, and in particular, emission control of NOx, which causes photochemical smog, is stricter, and technological development for reducing the amount generated by combustion is being actively conducted.

[0003] On the other hand, liquefied natural gas (LN) is used as a boiler fuel having a low content of polluting components generated during combustion.
There are gaseous fuels such as G). When these fuels are used, the fuel does not contain nitrogen oxides, so that countermeasures can be taken relatively easily. However, in recent years, rising land prices have made boilers installed in urban areas as small as possible in terms of installation area and equipment, and further demands for energy conservation, high reliability, etc., assuming low pollution. As a result, the situation cannot be solved simply by fuel conversion.

FIG. 10 shows the combustion test results of a premixed gas burner, where the abscissa is the air-fuel ratio and the ordinate is the nitrogen oxide (NOx) concentration obtained by converting the oxygen (O ₂ ) concentration in the exhaust gas to 0%. It is a summary. When the premixed gas burner is burned alone while changing the air-fuel ratio, a in FIG.
The data indicated by b, c, e, and f are obtained, and the NOx generation characteristic is indicated by an upwardly convex curve that has a maximum value near the air-fuel ratio of 1.

[0005] N generated in these gas-fired boilers
Ox is mainly thermal NOx generated by oxidizing nitrogen in combustion air under a high temperature atmosphere in a furnace. Thermal NOx generation is highly temperature dependent and increases with increasing flame temperature. The flame temperature depends on the mixture ratio (air-fuel ratio) of fuel and combustion air. In premixed combustion, the combustion temperature becomes the highest when the fuel is burned with the amount of air that can completely burn the fuel (theoretical air amount). It becomes lower even when the fuel becomes excessive or the fuel becomes excessive. Therefore, the above-described NOx generation result is obtained.

[0006] By reducing the flame temperature, NOx
As a method for reducing the generation amount of lean, lean combustion, two-stage combustion, exhaust gas recirculation, and lean-burn combustion methods have been developed and are employed in many combustion devices. The lean burn method is a method of burning by increasing the air-fuel ratio of a premix combustion burner. In this method, as shown by the point f in the above figure, the amount of heat discharged to the outside by the flue gas increases because the amount of excess air is increased to reduce the combustion temperature, and the thermal efficiency of the boiler decreases. In addition, since the capacity of the blower for combustion air is increased, power and equipment costs are increased, which is not preferable.

The two-stage combustion method is a method mainly used for a diffusion combustion burner, and is an effective means because it has an excellent effect of reducing NOx and does not require an excessive amount of excess air. It is easy to be released, and to prevent this,
It is necessary to secure a gas residence time in the furnace by increasing the size of the combustion device. The exhaust gas recirculation method is an effective means because it has an excellent NOx reduction effect and can also suppress unburned components such as CO. However, the necessity of a gas recirculation blower and flow path increases the equipment cost, Are not used for small devices.

[0008] The gray-scale combustion is a method of combusting a combination of an air-deficient diffusion flame and an air-excess premixed flame (Japanese Patent Publication No. 52-2).
No. 8251) and a method of injecting and burning exhaust gas between nozzles of the diffusion flame and the premixed flame (Japanese Patent Laid-Open No. 53-9).
No. 7638), there are various proposals. However, the principle of the concentration combustion using a basic premix burner is as follows. For example, when two burners are burned in a furnace under the conditions of a and b in the above-mentioned figure, The average air-fuel ratio at the furnace outlet is indicated by a one-dot chain line in the figure.
05. The NOx value at the furnace outlet at that time is indicated by a point d, which is higher than the average value d 'of a and b, but lower than the point c indicating the NOx value at the time of combustion by one burner having the same air-fuel ratio. Similarly, when combustion is performed under the conditions e and f in the figure, the outlet NOx value is point g, which is higher than the average value g ', but lower than the NOx values at points c and d.

[0009] In these methods, the burners (a, e) which are in the condition of excess fuel are burner (b, b) which are in the condition of excess air.
Since combustion is performed using the excess oxygen content of f), a reaction occurs in a high-temperature combustion field, and thus the value becomes higher than expected as in d and g. Conversely, if the furnace is large and the flame is cooled, it will endlessly approach d 'and g'. Therefore, the furnace is small and the volumetric heat load of the combustion chamber (kcal / m ³
When h) is high, the time required for mixing the combustion gas of each burner is not sufficient, so that the flame of the excess fuel burner is prolonged and unburned components such as CO are easily discharged directly from the furnace. Further, the inventors of the present invention have found that if the burner with excess fuel and the burner with excess air are too close to each other, the flames of the burners interfere with each other from the beginning of combustion and mix with each other to significantly reduce the NOx reduction effect of the rich and lean combustion. Confirmed by experiment.

[0010]

As described above, the conventional combustion method developed for the purpose of reducing the flame temperature reduces the thermal NOx by suppressing local high temperature by performing slow combustion. Therefore, since the furnace volume is increased, the size of the combustion device is increased, and the economy is reduced. This is a fatal drawback in large cities due to strict NOx regulations and high land prices. Further, even in the case of using a premixed flame of a short flame to make up for this, if the combustion is performed under a condition where the excess air amount is high to lower the combustion temperature, the amount of heat carried away by the exhaust gas increases and the boiler efficiency decreases, which is not preferable. .

On the other hand, when the furnace is small, if the burner with excess fuel and the burner with excess air are too close to each other, the flames of both burners interfere with each other from the initial stage of combustion and mix with each other. The air-fuel ratio of one burner is 1.
The present inventors have confirmed through experiments that the combustion becomes almost zero, and that the NOx reduction effect of the concentration combustion is significantly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a combustion method capable of reducing NOx even in a small-sized combustion apparatus without increasing the size of the combustion apparatus. Accordingly, it is an object of the present invention to provide a highly efficient gaseous fuel combustion method and a combustion apparatus that burn while reducing the generation of pollutant components.

[0013]

According to a first aspect of the present invention, there is provided a method of burning gaseous fuel by providing two or more premixed gas burners on a furnace wall in a gas flow direction in a furnace. At least two or more premixed gas burner stages are provided from the upstream side to the downstream side, and an air inlet stage is provided between the gas burner stages to reduce the air-fuel ratio of the burner in the burner stage downstream of the burner to 1. The air burner of the remaining burner stages has an air-fuel ratio of less than 1.0, and the amount of air supplied from the air inlet between the burner stages is 30 times the supply air amount of the entire combustion apparatus. % Or less.

According to a second aspect, in the first aspect,
The ratio of the total amount of air supplied by the air inlet and an adjacent gas burner upstream of the air inlet to the theoretical amount of combustion air to the amount of gas supplied to the gas burner is 1
The present invention relates to a method for burning gaseous fuel, characterized in that the fuel is burned excessively by making it smaller. A third invention provides a method of burning gaseous fuel by providing two or more premixed gas burners on the furnace wall, wherein at least two or more premixed gas burners are provided along the gas flow direction in the furnace, and the gas burners are provided between the burners. An air inlet is provided on the wall of the furnace, and air is not supplied from the air inlet during low-load combustion, and the air-fuel ratio of each premixed gas burner is uniform, and combustion is performed with slightly excess air. When the load rises when the gas temperature reaches 1400 ° C., air is not supplied from the air inlet and the gas burner upstream of the air inlet has an air-fuel ratio of 1
Excessive fuel combustion, the gas burner on the downstream side is excessive air combustion with an air-fuel ratio of 1 or more.
At the time of high load combustion exceeding 00 ° C., the excess fuel ratio of the upstream gas burner and the excess air ratio of the downstream gas burner are increased, and air is supplied from the air inlet to prevent the interference of the upstream gas burner combustion. The present invention relates to a method of burning gaseous fuel, characterized in that it is prevented.

According to a fourth aspect of the present invention, in a gaseous fuel combustion apparatus having two or more premixed gas burners on a furnace wall, at least two or more stages are provided on the furnace wall along the gas flow direction in the furnace from upstream to downstream. A premixed gas burner stage, and an air inlet stage between the burner stages; a pitch L along the gas flow direction between the gas burner stage and the air inlet stage; and an opening width of the gas burner and the air inlet in the L direction. Ratio L / D with D
And a gas burner upstream of the air inlet is an excess fuel burner, and a gas burner downstream of the air inlet is an excess air burner.

According to a fifth aspect, in the fourth aspect,
The gas burners and air inlets of the premixed gas burner stage and the air inlet stage are provided in multiple rows, and the ratio R / of the pitch R between the burners or air inlets along the row direction and the burner or air inlet opening width W in the R direction. The present invention relates to a gaseous fuel combustion device wherein W is 1 or more.

[0017]

[Function] In order to improve the boiler efficiency, burn the fuel with an air amount close to the theoretical air amount to reduce the amount of heat discharged to the outside of the boiler system, and at the same time, reduce the heat dissipation by making the combustion chamber smaller. is important. Further, it is necessary to reduce the volume of the flame in the furnace in order to reduce unburned components such as CO as much as possible. For this reason, the burner premixes the fuel gas and the air inside the burner, and provides a flame stabilizer at the burner outlet so that the air-fuel mixture collides so as not to be parallel to the main flow direction of the fuel-air mixture. Preferably, a circulating flow of hot combustion gas is formed downstream of the flame stabilizer. In such a burner, when the air-fuel mixture burns, a part of the combustion gas is mixed from inside and outside of the jet by the jet of the air-fuel mixture colliding with the flame stabilizer at a high speed and supplied into the furnace. The generation of thermal NOx is remarkably suppressed by the high-speed combustion by the premixed gas and the effect of recirculating the combustion exhaust gas together with stable ignition.

Incidentally, as a result of the study of the present inventors, as the combustion heat load (kcal / m ³ h) in the combustion chamber of the boiler is increased, the fuel supply amount in the same furnace increases, and the volume of the flame increases. Since NOx generated increases as the size increases, it has been found that it is necessary to use two or more burners and reduce NOx generated in the burner section. In addition, when the combustion heat load is increased, the temperature of the entire combustion chamber becomes higher. In particular, when the gas temperature at the furnace outlet exceeds 1400 ° C., the burner on the furnace outlet side is more emptied than in the case of uniform combustion conditions between the burners. It is better to use a lean-burn combustion system with a fuel ratio of 1 or more and other burners with an air-fuel ratio of 1 or less.
It has been found that, since the value is reduced and the gas temperature in the combustion chamber is high, unburned components such as CO are easily burned and do not increase. Further, when the gas temperature at the furnace outlet exceeds 1500 ° C., the concentration combustion ratio of the burners is increased, and air is sent between the two burners to cut off the mutual interference of the respective flames of the concentration combustion. It was found that low NOx can be achieved. These facts are different from the low NOx reduction by slow combustion. The present invention performs lean / burn combustion under premixed high-speed combustion to reduce thermal NOx. Furthermore, by setting the furnace to a high heat load, the average gas temperature in the furnace can be raised, and the incineration of unburned components such as CO is achieved, achieving high heat load, low NOx, and highly efficient combustion of low unburned portions. Things. In addition, as the load decreases, the air supply between the burners is stopped, and the ratio of rich and low combustion is reduced.Furthermore, when the normal combustion heat load is reached, the burners are burned at the same air-fuel ratio. By reducing the number of combustion units, low-NOx and high-efficiency combustion can be performed at all loads. Further, since a plurality of burners are used, the load reduction width is wider than that of a single burner, and the operability is improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a schematic structure of a burner for a low NOx boiler according to an embodiment of the present invention as viewed from the furnace side. In this embodiment, the burner is composed of nine square premix burners 10. I have.

FIG. 2A is a front view (as viewed from the inside of the furnace) of the premix burner. FIG. 2B is a cross-sectional view taken along line AA in FIG. A fuel nozzle 4 having a large number of ejection ports and also serving as a mixer is installed upstream of the ejection port 2 of the burner. The gaseous fuel 7 ejected from the nozzle and the air flow 8 supplied from the air supply duct 5 are provided. Are rapidly mixed by a venturi mixer-like structure in which the flow speed is narrowed and the speed is increased, and diffusion of fuel to the upstream side of the air flow is prevented. In addition, a flame arrester 3 (a plurality of wire meshes having a mesh size of about 40) is provided at the burner outlet and at the opening of the tip of the burner, and a plate-like holding member having a width smaller than the opening width of the burner is provided. The firearm 1 is installed and can burn safely. The flame stabilizer 1 is installed at right angles to the main flow direction of the mixture jet, and the length of each side of the flame stabilizer is smaller than the length of the corresponding side of the burner so that it can be slightly inserted and removed. The shape of the flame can be adjusted. As other combustion devices, not shown here, an ignition device,
A flame detection device, a fuel flow control device, a fuel cutoff device in case of misfire, an air flow control device, various measuring meters, a recorder, and the like are provided.

FIG. 3A is a perspective view of a boiler provided with the burner shown in FIG. This boiler is a two-drum type natural circulation type water tube boiler.
7, stored in the downcomer 18 and the steam drum 16, the heat absorption in the furnace raises the water temperature in the water wall tube 17, causing a density difference with the water in the downcomer 18. Circulating through the downcomer 18 to the water drum 15. When the circulating water becomes saturated, steam is generated by the amount of heat absorbed in the furnace and separated into steam and water in the steam drum, and the steam is extracted through a superheater or the like as necessary.

FIG. 3B is a layout view of the burners as viewed from the inside of the furnace. As shown in the figure, each of the burner stages A, B, and C comprising one row, two rows, and three rows. Are arranged from the upstream side of the furnace to the downstream side. Each burner is installed such that the outlet of the premixed gas shown as burner outlet 2 in FIG. 2 (b) coincides with the surface of the combustion furnace wall. The premixed gas ejected from the burner collides with the flame stabilizer and spreads in the furnace in a V-shape in the left-right direction. Based on basic research results, the burner interval is set to L so that the jet does not directly interfere. / D = 4.
The distance between the side wall adjacent to the wall surface to which the burner was attached and the burner was also set to 5D. Here, L is the burner interval, and D is the width of the burner outlet.

FIG. 4 is a horizontal sectional view of a furnace of a boiler to which the present invention is applied. As is clear from the figure, the gas outlet of the boiler furnace 30 is located in the furnace outlet screen tube section of the opposing wall 20 of the burner. For this reason, the gas flow in the furnace flows from right to left when viewed from the furnace front wall 31 to which the burner is attached, so that the burner stages A, B, and C from the upstream side.
As shown in FIG. 3 (b), burner rows 1, 2, and 3 were arranged from the bottom of the furnace to the top.

These burners are configured so that the optimum arrangement can be examined by changing D so that the combustion amount per unit becomes 1/3 to 1/6 of the rated heat load of the boiler. The steam generation amount of the boiler of this embodiment is 10 t / h, and the steam pressure is 20 kg / h.
cm ² g, boiler furnace volumetric heat load is 150 × 10 ⁴ kca
l / m ³ h, which is more than three times that of a boiler of this class, which is less than 50 × 10 ⁴ kcal / m ³ h, so that the installation area of the boiler itself is also small. It is less than 1/2.

Next, specific embodiments of the present invention will be described. Example 1 In FIG. 5, an arrangement in which L / D = 3 and R / W = 2 using burners with 1 and 3 rows in the A stage and 1 and 3 examples in the C stage (L, D,
For R and W, see FIG. 3B).
05 (oxygen concentration in exhaust gas is 1%) constant, the air flow rate of each burner is uniform, and the supply of fuel and air to unused burners is set to zero. The generation characteristics of NOx and CO are summarized and shown. The fuel used was city gas (LNG). As is apparent from the figure, the target CO concentration (100 ppm) cannot be achieved without increasing the air-fuel ratio at a load of 90% or more, but the target CO concentration is achieved without any problem at a load of 90% or less.

Embodiment 2 FIG. 6 shows that, under the same burner and the same arrangement as FIG. 5, the oxygen concentration in the exhaust gas is 1%, and the air flow rate of each burner is uniform.
At 100% and 80% load, the lean burn, that is, the gas flow in the furnace increases the fuel flow rate of the upstream burners (A1, A3), decreases the fuel flow rate of the downstream burners (C1, C3), and reduces the air-fuel ratio. It shows the generation characteristics of NOx and CO when burning by applying a bias. As is apparent from the figure, at a load of 100%, the application range is remarkably narrowed due to generation of CO. However, at a load of about 80%, the NOx value is lower than that of the case where the air-fuel ratio shown in FIG. Are satisfied.

Embodiment 3 FIG. 7 shows a combustion burner (A1, A3, C1, C2) in which 10% of the total air flow rate is supplied from the same burner as in FIGS. C3) is a test similar to that of Example 2 under the condition that the remaining air is uniformly distributed and the oxygen concentration in the exhaust gas is 1%, that is, a load of 10%.
At 0% and 80%, the in-furnace gas flow increased the fuel flow in the upstream burners (A1, A3), reduced the fuel flow in the downstream burners (C1, C3), and biased the air-fuel ratio. It shows the generation characteristics of NOx and CO in the case. At 100% load, both NOx and CO were reduced, and the operation range for achieving the target value was significantly widened. Moreover, even when the load is low, NOx and CO hardly change. As described above, it is effective to add combustion air from the middle of the lean-burn combustion burner so as to perform combustion so as to cut off flame interference between the burners.

That is, the fuel which has not been completely burned by the premixed burner at the uppermost stream of the furnace in which the excess fuel is present is burned by incorporating air for preventing interference and recirculated gas by its own jet, and further burned by the excess air burner. Burn with excess oxygen generated. Therefore, it is particularly effective when the total amount of the air amount to the excess fuel burner and the amount of air for blocking interference is smaller than the theoretical combustion air amount for the amount of fuel supplied to the excess fuel burner. In addition, the amount of air for blocking the interference can be increased when the oxygen concentration in the final exhaust gas is increased, and can be increased to about 30%. Since the mixture itself is inhibited, if the amount is more than that, CO is likely to be generated.

Embodiment 4 FIG. 8 shows that the L / L of the same burner as in FIG.
Test results obtained by changing D are arranged for NOx and CO generation characteristics. The figure shows the case without the air-fuel ratio bias and the case with 20%.

If the L / D of the burner is 2 or less, the NOx value increases due to interference between the burners. Also, when L / D is increased, CO tends to increase. This tendency is that the lean-burn combustion, that is, the gas flow in the furnace, increases the fuel flow rate of the upstream burners (A1, A3), decreases the fuel flow rate of the downstream burners (C1, C3), and applies a bias to the air-fuel ratio to burn. It is noticeable when

FIG. 9A shows an example of applying a burner system having the effect of the present invention to a boiler. This figure shows burner 1
0 and the air supply port 12 are provided on opposing walls before and after the boiler. The burner for adjusting the excess fuel is a lower stage upstream of the gas flow of the boiler furnace, and the burner for adjusting the excess air is an upper burner downstream of the gas flow. FIG. 9B shows an embodiment in which the same effect is applied to a large-capacity boiler. This figure shows the water cooling wall with the burner viewed from inside the boiler furnace.
Three burners 10 and two air supply ports 12 are provided, the uppermost burner is adjusted to excess air, the other two burners are excessively fueled, and an air inlet between the burners and an air inlet are provided. The ratio of the total amount of air supplied by the gas burner on the more upstream side (lower side) to the stoichiometric amount of air supplied to the gas burner is smaller than 1, and combustion with an excessive amount of fuel leads to higher efficiency. Combustion becomes possible. In the case of such a large-sized boiler, a method of mixing combustion exhaust gas into burner combustion air is generally used.However, in the present invention, mixing exhaust gas into combustion air can be applied without any problem in principle. In particular, supplying exhaust gas mixed air to the air supply port 12 is preferable for preventing interference between burners. As shown in the figure, the number and relative positional relationship between the burner and the air supply port are not particularly limited, but in the burner system, the distance between the burner stages in the gas flow direction is L, the opening distance of the burner on L. Is D, L / D is 2 or more, and the distance R between the burner rows and the opening distance W of the burner on R are R / D.
W is greater than one.

Although not shown, in the burner system of the present invention, the gas flow in the furnace is swirled, and this combustion method can also be applied to the so-called tangential firing combustion method, and the effect is improved. further,
In the burner system of the present invention, for example, the data (FIGS. 5 to 7) in the above-described embodiment is obtained based on boiler load change information such as a fuel amount, an air amount, a steam flow rate, a furnace outlet gas temperature, and a fuel supply gas pressure. As is evident, by controlling the burn / burn ratio of the burner and the amount of air between the burners, a smooth load change is possible, which is useful for improving the combustion efficiency.

[0033]

According to the present invention, a furnace outlet temperature of 1500 is provided.
Even in a boiler with a high furnace heat load of over ℃, high efficiency combustion with low pollution is possible. Therefore, the required device volume and installation area can be reduced to 1/2 to 1/3. Also, by changing the combustion method according to the boiler load, stable operation in a load range of 100 to 10% becomes possible.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of an installation state of a burner of a gas combustion apparatus according to the present invention.

FIGS. 2 (a) and (b) FIGS. 2 (a) and (b)
1A is a structural view of a burner of a gas combustion apparatus according to an embodiment of the present invention, FIG. 1A is a front view, and FIG.

3 (a) and (b) FIG. 3 (a) is a perspective view of a boiler to which the present invention is applied, and FIG. 3 (b) is a layout view of a burner as viewed from the inside of a furnace.

FIG. 4 is a horizontal sectional view of the boiler of FIG. 3 (a).

FIG.

FIG.

FIG. 7 and

FIGS. 5, 6, 7 and 8 show data of a combustion test example to which the present invention is applied.

9 (a) and (b) FIG. 9 (a) is a view showing an example of application to a boiler provided with burners on front and rear walls.
(B) is an Example figure of this invention seen from the inside of the burner mounting water wall.

FIG. 10 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flame stabilizer, 2 ... Burner outlet, 3 ... Flame arrestor, 4 ... Fuel nozzle, 5 ... Air supply duct, 6 ... Support, 7 ... Fuel gas jet, 8 ... Air flow, 10 ... Burner, 1
2: air supply port, 15: water drum, 16: steam drum,
17 ... water wall pipe, 18 ... downcomer pipe, 20 ... opposing wall of burner,
21: furnace exit screen tube, 25: convection heat transfer tube, 26
... wind box, 30 ... furnace, 31 ... furnace front wall, 32 ... gas flow.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenshi Kobayashi 6-9 Takaracho, Kure City, Hiroshima Prefecture Inside the Kure Plant, Katsu Plant (72) Inventor Yoshiyuki Takasugi 6-9 Takaracho Kure City, Hiroshima Prefecture Babcock Day (72) Inventor Tatsuzo Enomoto 6-9 Takara-cho, Kure-shi, Hiroshima Babcock-Hitachi Kure Factory (56) References JP-A-53-97638 (JP, A) JP-A-61 −29606 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F23C 11/00 329

Claims (5)

(57) [Claims] 1. A method of burning gaseous fuel by providing two or more premixed gas burners on a furnace wall, wherein at least two or more premixed gas burner stages are provided from upstream to downstream along a gas flow direction in the furnace. In addition to the above, an air inlet stage is provided between the gas burner stages, and the air-fuel ratio of the burner in the burner stage downstream of the burner is set to an excessive air combustion larger than 1.0, and the burners in the remaining burner stages are adjusted to the air-fuel ratio. 1.0
A smaller fuel excess combustion, and the supply air amount from the air inlet between the burner stages is 30% of the supply air amount of the entire combustion device.
A method for burning gaseous fuel, characterized by the following. 2. The ratio of the total amount of air supplied by the air inlet and an adjacent gas burner upstream of the air inlet to a ratio of a theoretical combustion air amount to a supply gas amount in the gas burner according to claim 1. A method for burning gaseous fuel, characterized in that the fuel is burned excessively by making it smaller than 1. 3. A method of burning gaseous fuel by providing two or more premixed gas burners on a furnace wall surface, wherein at least two or more premixed gas burners are provided along a gas flow direction in the furnace, and the gas burners are provided between the premixed gas burners. An air inlet is provided on the furnace wall, and air is not supplied from the air inlet during low-load combustion, and the air-fuel ratio of each premixed gas burner is uniform, and combustion is performed in a slightly excessive air state. When the temperature rises to 1400 ° C., when the load rises, air is not supplied from the air inlet and the gas burner upstream of the air inlet is overburned with an air-fuel ratio of less than 1, and the gas burner downstream is air-fuel ratio of 1. In the case of high-load combustion in which the furnace outlet gas temperature exceeds 1500 ° C., the excess air ratio of the upstream gas burner and the excess air combustion of the downstream gas burner A method of burning gaseous fuel, characterized by increasing the excess ratio and supplying air from an air inlet to prevent interference with upstream and downstream gas burner combustion. 4. A gaseous fuel combustion system having two or more premixed gas burners provided on a furnace wall, wherein at least two premixed gas burners are provided on the furnace wall along the gas flow direction from the upstream to the downstream in the furnace.
A plurality of premixed gas burner stages, and an air inlet stage between the burner stages, a pitch L along the gas flow direction between the gas burner stage and the air inlet stage, and an L direction of the gas burner and the air inlet. A gas burner upstream of the air inlet is an excess fuel burner, and a gas burner downstream of the air inlet is an excess air burner. Combustion equipment. 5. The burner according to claim 4, wherein the gas burners and the air inlets of the premixed gas burner stage and the air inlet stage are provided in multiple rows, and the burners in the row direction or the pitch R between the air inlets and the burner in the R direction are provided. A gaseous fuel combustion device, wherein a ratio R / W of an air inlet opening width W is set to 1 or more.