JP7498654B2 - Burner, its control method, and combustion furnace - Google Patents

Description

The present invention relates to a burner that burns a mixture of solid fuel and nitrogen-containing gas fuel, and a combustion furnace equipped with said burner.

In the current trend of reducing carbon dioxide (CO ₂ ), the use of CO ₂ -free fuels that do not generate carbon dioxide is required. One such fuel is ammonia (NH ₃ ). Although ammonia is known as a flame-retardant substance, it is a hydrogen carrier substance having three hydrogen atoms like methane, and is relatively easy to handle because it liquefies even at room temperature when pressurized, and has been attracting attention as a CO ₂ -free fuel. On the other hand, ammonia contains a large amount of nitrogen, so it is prone to generating NOx. Therefore, Patent Document 1 proposes a burner capable of co-firing ammonia gas with a solid fuel that suppresses the increase in NOx.

The burner in Patent Document 1 includes a fuel supply nozzle that sprays a mixture of solid fuel such as pulverized coal and a carrier gas for the solid fuel, an air nozzle that is disposed outside the fuel supply nozzle and separates and sprays combustion air radially outward from the mixture, and an ammonia supply nozzle that sprays ammonia gas from downstream of the outlet of the fuel supply nozzle. The ammonia supply nozzle supplies ammonia gas toward a reduction region immediately downstream of the outlet of the fuel supply nozzle, where oxygen has been consumed by the combustion of the fuel and the oxygen concentration has become low.

JP 2019-174051 A

As disclosed in Patent Document 1, ammonia gas that is not premixed with air is supplied to an oxygen-lean recirculation zone (reduction zone), where the reduction reaction to nitrogen (N ₂ ) proceeds preferentially, accelerating the denitrification reaction in the furnace. As a result, the concentration of nitrogen oxides contained in the combustion exhaust gas can be suppressed.

However, because ammonia gas has a relatively slow combustion rate, if an excessive amount of ammonia gas is supplied directly to the recirculation zone, the amount of gas fuel that circulates without being completely burned in the recirculation zone will increase, which may result in a localized drop in the gas temperature in the recirculation zone.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a burner for burning a mixture of solid fuel and gas fuel, and a combustion furnace equipped with the same, that avoids a local temperature drop in the recirculation zone formed near the burner outlet.

The burner according to one aspect of the present invention comprises:
a fuel supply nozzle having a cylindrical shape extending in a burner axial direction, having a fuel outlet formed by a flame stabilizing plate provided at a downstream end, and into which solid fuel and carrier air are introduced;
at least one flow passage disposed on an outer circumferential side of the fuel supply nozzle and configured to supply combustion air separately from the air-fuel mixture ejected from the fuel supply nozzle;
the gas fuel supply pipe is inserted into the fuel supply nozzle, has a gas fuel supply port located upstream of the fuel outlet, and supplies gas fuel containing nitrogen into the fuel supply nozzle.

With the burner of the above configuration, the gas fuel is premixed with the carrier air in the fuel supply nozzle before being ejected from the fuel nozzle. Therefore, in the recirculation area formed downstream of the fuel nozzle, an increase in the amount of gas fuel that cannot be completely burned due to an increase in the combustion speed of the gas fuel can be suppressed. As a result, a local temperature drop in the recirculation area can be avoided.

Moreover, a burner according to another aspect of the present invention includes:
a fuel supply nozzle having a cylindrical shape extending in a burner axial direction, having a fuel outlet formed by a flame stabilizing plate provided at a downstream end, and into which solid fuel and carrier air are introduced;
at least one flow passage disposed on an outer circumferential side of the fuel supply nozzle and configured to supply combustion air separately from the air-fuel mixture ejected from the fuel supply nozzle;
a gas fuel supply pipe that is inserted into the fuel supply nozzle, has a gas fuel supply port provided at a downstream end, and supplies a gas fuel containing a nitrogen component from the gas fuel supply port to a mixed gas consisting of the solid fuel and the carrier air;
the gas fuel supply pipe is supported so as to be displaceable in the burner axial direction so that the gas fuel supply port is displaceable in the burner axial direction relative to the fuel nozzle.

With the burner of the above configuration, it is possible to adjust the amount of setback from the fuel outlet of the gas fuel supply port into the fuel supply nozzle. Therefore, when the amount of gas fuel supply increases, by increasing the amount of setback of the gas fuel supply port, the increase in the flow rate of the fuel gas in the recirculation area formed immediately downstream of the fuel outlet is suppressed, and the recirculation area can be maintained. This makes it possible to avoid a local temperature drop in the recirculation area.

Further, a method for controlling a burner according to one aspect of the present invention includes the steps of:
a fuel supply nozzle having a cylindrical shape extending in a burner axial direction, having a fuel outlet formed by a flame stabilizing plate provided at a downstream end, and into which solid fuel and carrier air are introduced;
at least one flow passage disposed on an outer circumferential side of the fuel supply nozzle and configured to supply combustion air separately from the air-fuel mixture ejected from the fuel supply nozzle;
a gas fuel supply pipe that is inserted into the fuel supply nozzle, has a gas fuel supply port provided at a downstream end, and supplies a gas fuel containing a nitrogen component from the gas fuel supply port to a mixed gas consisting of the solid fuel and the carrier air;
and an actuator for displacing the gas fuel supply pipe in the burner axial direction,
Detecting a position of the gas fuel supply port relative to the fuel nozzle along the burner axis direction;
Detecting the amount of gas fuel supplied from the gas fuel supply pipe;
When the gas fuel supply amount is within a predetermined range, the actuator is operated so that the position of the gas fuel supply port moves away from the fuel nozzle upstream as the gas fuel supply amount increases.

According to the burner control method configured as above, when the amount of gas fuel supply increases, the amount of retreat of the gas fuel supply port increases, suppressing an increase in the flow rate of the fuel gas in the recirculation area formed immediately downstream of the fuel nozzle, and the recirculation area can be maintained. This makes it possible to avoid a local temperature drop in the recirculation area. Therefore, it is possible to suppress an increase in the amount of unburned gas fuel in the recirculation area.

Also, a combustion furnace according to another aspect of the present invention includes a high-temperature reduction zone having a reducing atmosphere and including at least one burner;
and a low-temperature oxidation zone into which the combustion gas generated in the high-temperature reduction zone flows and which has a lower temperature than the high-temperature reduction zone and an oxidizing atmosphere.

With the burner and combustion furnace of the above configuration, solid fuel and nitrogen-rich gas fuel are mixed and burned in the high-temperature reduction zone, and NOx generated from the nitrogen contained in the solid fuel and gas fuel is denitrified in the furnace, making it possible to suppress NOx emissions. Furthermore, a water-gasification reaction occurs in which water generated from the hydrogen contained in the solid fuel and/or gas fuel is converted into active gas, improving combustion efficiency.

According to the present invention, in a burner that burns solid fuel and gas fuel together and in a combustion furnace equipped with the burner, it is possible to avoid a local temperature drop in the recirculation area formed near the burner outlet.

FIG. 1 is a schematic cross-sectional view of a boiler equipped with a burner according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a burner according to a first embodiment of the present invention. FIG. 3 is a diagram for explaining a method of calculating the gas fuel supply position with the fuel nozzle as a reference. FIG. 4 is a graph showing a first example of a change in the gas fuel supply position relative to a change in the gas fuel supply amount. FIG. 5 is a graph showing a second example of a change in the gas fuel supply position relative to a change in the gas fuel supply amount. FIG. 6 is a schematic cross-sectional view of a burner according to a second embodiment of the present invention. FIG. 7 is a block diagram showing the flow of control by the control device. FIG. 8 is a schematic cross-sectional view of a burner according to a third embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of a burner according to a fourth embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the schematic configuration of a boiler 10 equipped with a burner according to one embodiment of the present invention will be described.

[General configuration of boiler 10]
Fig. 1 is a diagram showing a schematic configuration of a boiler 10 equipped with a burner 5 (5A to 5D) according to an embodiment of the present invention. The boiler 10 shown in Fig. 1 includes a combustion furnace 2 that burns fuel, and a boiler body 40 and a superheater 42 that generate steam using the combustion heat. The boiler 10 is a thermal boiler that uses powdered or granular fossil fuel (solid fuel) as its main fuel.

A vertical combustion chamber 20 is formed inside the combustion furnace 2. In the combustion furnace 2 according to this embodiment, a high-temperature reduction zone 21 is formed in the lower part of the combustion chamber 20, a low-temperature oxidation zone 22 is formed in the upper part of the combustion chamber 20, and a constriction section 23 is formed between the high-temperature reduction zone 21 and the low-temperature oxidation zone 22. However, the combustion furnace 2 may be configured such that the high-temperature reduction zone 21 is formed in the upper part of the combustion chamber 20, and the low-temperature oxidation zone 22 is formed in the lower part of the combustion chamber 20.

The portion of the inner wall of the combustion furnace 2 that forms the high-temperature reduction zone 21 is covered with a refractory material 25. The refractory material 25 can withstand high temperatures of approximately 2000°C. The lower furnace wall of the combustion furnace 2 is provided with multiple burners 5 that blow fuel and air for the first stage combustion into the high-temperature reduction zone 21. A mixture of fuel and air is blown from each burner 5 into the combustion chamber 20, generating a flame.

The burners 5 are provided on each of a pair of opposing furnace walls. Each furnace wall is provided with at least one burner stage in the vertical direction, and each burner stage is formed by a plurality of burners 5 arranged in the horizontal direction. The burners 5 thus arranged opposite each other are staggered so that the burner axes of the burners 5 do not intersect.

The outlet of the high-temperature reduction zone 21 (i.e., the upper part of the high-temperature reduction zone 21) is connected to the inlet of the low-temperature oxidation zone 22 (i.e., the lower part of the low-temperature oxidation zone 22) via the constriction section 23. The smallest horizontal cross-sectional area of the constriction section 23 is approximately 20 to 50% of the horizontal cross-sectional area of the high-temperature reduction zone 21.

Multiple air nozzles 26 are provided on the upper furnace wall of the combustion furnace 2. Air for second-stage combustion is blown from each air nozzle 26 into the low-temperature oxidation zone 22. In this embodiment, multiple air nozzle stages are provided in the vertical direction, and each air nozzle stage is formed by multiple air nozzles 26 lined up in the horizontal direction.

The area between the constriction section 23 and the multiple air nozzles 26 in the low-temperature oxidation zone 22 above and below forms the cooling section 24. The furnace wall of the cooling section 24 is a water-cooled wall in which the water pipes (not shown) of the boiler body 40 are laid out.

The outlet of the low-temperature oxidation zone 22 (i.e., the upper part of the low-temperature oxidation zone 22) is connected to the inlet of the flue 28. The superheater tube 43 of the superheater 42 is provided in the upstream part of the flue 28. In addition, a water pipe (not shown) of the boiler body 40 may be laid on the wall of the flue 28 downstream of the superheater tube 43. The flue 28 is provided with an exhaust gas denitration device 41 downstream of the superheater tube 43. The exhaust gas denitration device 41 is composed of, for example, a container containing a solid catalyst that comes into contact with the exhaust gas and a device that injects an appropriate amount of chemicals upstream of the catalyst. In the flue 28, a first NOx sensor 32 is provided upstream of the exhaust gas denitration device 41, and a second NOx sensor 33 is provided downstream of the exhaust gas denitration device 41. The flue 28 is connected to the outlet of the flue 28 with an exhaust gas treatment system 30. The exhaust gas treatment system 30 is equipped with a fuel economizer 31 that uses the residual heat of the combustion exhaust gas to preheat the air sent to the burner 5.

In the boiler 10 configured as described above, the air ratio between the fuel supplied to the high-temperature reduction zone 21 and the air for the first stage combustion is maintained at less than 1 (for example, about 0.7). Furthermore, the high-temperature reduction zone 21, which is covered with refractory material 25, is less susceptible to temperature drops inside the furnace than other parts of the furnace. As a result, the high-temperature reduction zone 21 is in a high-temperature reducing atmosphere (an atmosphere with an air shortage in which the amount of air is less than the theoretical amount of air) with an average temperature of about 1500°C, and fuel gasification is promoted in the high-temperature reduction zone 21.

In the high-temperature reduction zone 21, the fuel is gasified to generate combustion gas. The generated combustion gas flows into the low-temperature oxidation zone 22 through the constriction 23. The air ratio of the low-temperature oxidation zone 22 is maintained at 1 or more (for example, about 1.1) by the air for second-stage combustion supplied to the low-temperature oxidation zone 22 from the air nozzle 26. This creates an oxidizing atmosphere in the low-temperature oxidation zone 22, which promotes the combustion of the combustion gas in the low-temperature oxidation zone 22.

In the low-temperature oxidation zone 22, the combustion of the unburned fuel in the combustion gas is completed (i.e., complete combustion occurs). The combustion exhaust gas from the low-temperature oxidation zone 22 flows out to the exhaust gas treatment system 30 through the flue 28. The heat of the combustion exhaust gas is recovered by the water pipes installed in the flue 28 and the furnace wall, and steam is generated in the boiler body 40. In addition, the heat of the combustion exhaust gas is recovered by the superheater tube 43 installed in the flue 28, and superheated steam is generated in the superheater 42. The generated superheated steam is used, for example, in a steam turbine (not shown) of a power generation facility.

When fuel is burned, the nitrogen contained in the fuel is oxidized to generate fuel NOx, and nitrogen in the air is oxidized at high temperature to generate thermal NOx. In a reducing atmosphere, the higher the combustion temperature, the lower the amount of NOx generated, and in an oxidizing atmosphere, the lower the combustion temperature, the lower the amount of NOx generated. In the boiler 10 according to this embodiment, the generation of fuel NOx is suppressed by burning the fuel in the high-temperature reducing atmosphere of the high-temperature reduction zone 21, and the generation of thermal NOx is suppressed by completely burning the unburned fuel in the combustion gas in the low-temperature oxidation atmosphere of the low-temperature oxidation zone 22. In the boiler 10 according to this embodiment, the amount of NOx generated is effectively reduced by adopting the above-mentioned two-stage combustion method. Furthermore, in the high-temperature reduction zone 21, water (H ₂ O) is generated by the combustion of the fuel, and a water-gasification reaction occurs in which this water is converted into active gases such as hydrogen (H ₂ ) and carbon monoxide (CO), thereby improving the combustion efficiency.

[Burner 5]
The burner 5 provided in the boiler 10 having the above configuration is a multi-fuel burner that uses a solid fuel as a main fuel and a nitrogen-containing gas fuel as an auxiliary fuel. The solid fuel is a powdered or granular fossil fuel such as pulverized coal. In the boiler 10 having the above configuration, it is desirable for the gas fuel to contain a large amount of hydrogen in order to improve the combustion efficiency by the action of the water-gasification reaction. An example of such a gas fuel is ammonia gas.

The flame generated by the burner 5 has a recirculation region under reducing conditions. Combustion is performed under the reducing conditions of this recirculation region, thereby suppressing the generation of NOx. The steady flame of the burner 5 is formed based on a balance between the combustion speed and the flow speed of the mixture. However, if there is an excess of gas fuel flowing into the recirculation region or if the gas fuel has a slow combustion speed, the amount of gas fuel that does not burn in the recirculation region increases, and the temperature of the recirculation region drops locally. This also leads to a weakening of the water-gasification reaction. This phenomenon is more pronounced the more excess gas fuel flows into the recirculation region and the slower the combustion speed of the gas fuel. Therefore, the burner 5 according to this embodiment has a structure that can optimize the gas fuel supply method according to the amount of gas fuel supplied and the type of gas fuel. Below, the first to fourth embodiments of the burner 5 are described.

First Embodiment
Fig. 2 is a schematic cross-sectional view of a burner 5A according to a first embodiment of the present invention. The burner 5A shown in Fig. 2 is equipped with a fuel supply nozzle 71. The fuel supply nozzle 71 has a cylindrical shape with a predetermined burner axis 70 as its axis. The extension direction of this burner axis 70 is referred to as the "burner axis direction X". Powdered solid fuel and carrier air for carrying the solid fuel are introduced into the fuel supply nozzle 71. The carrier air becomes primary air (primary combustion air).

A first flame stabilizing plate 77 is provided at the downstream end of the fuel supply nozzle 71, and is continuous in the circumferential direction. The first flame stabilizing plate 77 expands in diameter like a trumpet as it progresses toward the downstream end of the fuel supply nozzle 71. A fuel outlet 71a is formed by the first flame stabilizing plate 77. A swirl adjustment vane 711 is provided inside the downstream end of the fuel supply nozzle 71, upstream of the first flame stabilizing plate 77. A dispersion vane 713 is provided inside the fuel supply nozzle 71, upstream of the swirl adjustment vane 711.

A heavy oil burner 79, through which the burner axis 70 passes, is inserted into the axial center of the fuel supply nozzle 71. The downstream end of the heavy oil burner 79 is located near the downstream end of the fuel supply nozzle 71. Therefore, the flow passage cross section at the downstream end of the fuel supply nozzle 71 is annular (donut-shaped) with the burner axis 70 at its center.

At least one gas fuel supply pipe 91 is inserted into the fuel supply nozzle 71. The downstream end of the gas fuel supply pipe 91 is a gas fuel supply port 91a facing the burner axial direction X. High-pressure gas fuel is introduced into the gas fuel supply pipe 91, and the high-pressure gas fuel is supplied into the fuel supply nozzle 71 from the gas fuel supply port 91a.

The gas fuel supply port 91a is located upstream of the gas flow from the fuel ejection port 71a. That is, the gas fuel supply port 91a is located at a position retreated from the fuel ejection port 71a along the burner axial direction X into the fuel supply nozzle 71. The position of the gas fuel supply port 91a in the burner axial direction X relative to the fuel ejection port 71a is referred to as the "gas fuel supply position x _g ". The burner 5A has a support device 81 that supports the gas fuel supply pipe 91 so as to be displaceable in the burner axial direction X. In one example, the support device 81 is composed of a jig that holds the gas fuel supply pipe 91, a slider attached to the jig, and a rail on which the slider runs. In another example, the support device 81 is composed of a jig that holds the gas fuel supply pipe 91, a pinion attached to the jig, and a rack with which the pinion meshes. However, the mode of the support device 81 is not limited to the above.

Since the gas fuel supply position _xg is set back from the fuel outlet 71a as described above, the gas fuel supplied from the gas fuel supply port 91a is mixed with the solid fuel and the carrier air inside the fuel supply nozzle 71. A mixture 51 consisting of the solid fuel, the gas fuel, and the carrier gas is ejected from the fuel outlet 71a.

An inner throat 72 is provided on the outer periphery of the fuel supply nozzle 71. Secondary air (secondary combustion air) is supplied from a wind box (not shown) to a flow path 72f formed between the inner throat 72 and the fuel supply nozzle 71. The secondary air outlet 72a, which is the downstream end of the inner throat 72, is located on the outer periphery of the fuel outlet 71a of the fuel supply nozzle 71, and secondary air 52 is ejected from the secondary air outlet 72a on the outer periphery of the mixture 51 ejected from the fuel supply nozzle 71.

An outer throat 73 is provided on the outer periphery of the inner throat 72. Tertiary air (air for tertiary combustion) is supplied from a wind box (not shown) to a flow path 73f formed between the outer throat 73 and the inner throat 72. The outlet 73a of the outer throat 73 is located on the outer periphery side of the fuel outlet 71a of the fuel supply nozzle 71, and the tertiary air 53 is ejected from the outlet 73a of the outer throat 73 on the outer periphery side of the secondary air 52 ejected from the inner throat 72.

The inner throat 72 has a second flame plate 72b at the opening edge at the downstream end, which expands in a trumpet shape as it moves downstream. Furthermore, the outer throat 73 has an outer guide 73b at the opening edge at the downstream end, which expands in a trumpet shape as it moves downstream. The first flame plate 77 and the second flame plate 72b guide the secondary air 52 ejected from the secondary air outlet 72a so as to move radially outward from the mixture 51 ejected from the fuel supply nozzle 71. The second flame plate 72b and the outer guide 73b guide the tertiary air 53 ejected from the outer throat 73 so as to move radially outward from the secondary air 52 ejected from the inner throat 72. In this way, the secondary air 52 and the tertiary air 53 are ejected so as to expand radially from the burner axis 70.

In the burner 5A having the above configuration, the mixture 51 is ejected as a swirling flow from the fuel outlet 71a of the fuel supply nozzle 71 by the action of the dispersion vane 713 and the swirl adjustment vane 711. The swirling flow of the mixture 51 and the action of the first flame holding plate 77 form a recirculation area 50 immediately downstream of the fuel outlet 71a. In this recirculation area 50, a circulating flow is generated that returns the ejection flow of the mixture 51 from the fuel outlet 71a toward the fuel outlet 71a, and high-temperature combustion gas is constantly exchanged with unburned circulating gas. As a result, the volatile components of the solid fuel in the mixture 51 are quickly burned, and an outer peripheral ignition flame 55 is generated immediately downstream of the fuel outlet 71a of the fuel supply nozzle 71 and radially outside the recirculation area 50. In this way, the initial generation of NOx is suppressed by early ignition with relatively little mixing with oxygen. Furthermore, the combustion air and the mixture 51 are mixed in stages, in the order of secondary air 52 and tertiary air 53, to generate denitration combustion and suppress the generation of NOx.

The recirculation region 50 is under high-temperature reducing conditions where oxygen is consumed by the combustion of fuel and the oxygen concentration is low. Therefore, in the recirculation region 50, nitrogen oxides (NO) generated from the nitrogen content in the solid fuel are reduced to nitrogen (N ₂ ). Ammonia has the property of combining with oxygen contained in nitrogen oxides. Therefore, when the gas fuel is ammonia gas (NH ₃ ), if ammonia gas is supplied to the recirculation region 50 under reducing conditions, the reduction reaction to nitrogen and water (H ₂ O) proceeds preferentially. In this way, in the mixed combustion of solid fuel and ammonia gas, the generation of nitrogen oxides is suppressed, and water that undergoes a hydrogen gas shift reaction is generated.

[Method of calculating gas fuel supply position _xg ]
FIG. 3 is a diagram for explaining a method of calculating the gas fuel supply position x _g based on the fuel nozzle 71 a. As shown in FIG. 3, the position of the fuel nozzle 71 a in the burner axial direction X is x = 0. The position of the fuel nozzle 71 a in the burner axial direction X is the position of the downstream end of the flame stabilizing plate 77 in the burner axial direction X. The value of x increases as the fuel nozzle 71 retreats into the fuel supply nozzle 71. In other words, the position retreated into the fuel supply nozzle 71 is a positive value, and the position advanced outside the fuel supply nozzle 71 is a negative value. The position of the gas fuel supply port 91 a in the burner axial direction X (i.e., the gas fuel supply position x _g ) is x = x _g . It is assumed that the position of the center 50 c of the recirculation region 50 relative to the fuel nozzle 71 a is constant, and the distance in the burner axial direction X between the gas fuel supply port 91 a and the center 50 c of the recirculation region 50 is L. The amount of gas fuel supplied from the gas fuel supply port 91 a is assumed to be Q, the pipe radius of the gas fuel supply pipe 91 is assumed to be r 0 , and the pipe cross-sectional area of the gas fuel supply pipe 91 is assumed to be A.

Since the gas fuel jet flows against the backflow region of the recirculation region 50, if the gas fuel jet velocity is too high, the recirculation region 50 may be damaged. Since the function of the recirculation region 50 is directly linked to the combustion state, it can be considered that there is an optimal value for the flow velocity V of the gas fuel at the center 50c of the recirculation region 50. By maintaining the flow velocity V of the gas fuel at the center 50c of the recirculation region 50 at an optimal value, a stable recirculation region 50 is maintained. The flow velocity V of the gas fuel at the center 50c of the recirculation region 50 can be expressed by the following equation (1).

In equation (1), the variables are the gas fuel supply amount Q and the distance L in the burner axial direction X between the gas fuel supply port 91a and the center 50c of the recirculation area 50. In order to maintain the flow velocity V of the gas fuel at the center 50c of the recirculation area 50 at a predetermined value, for example, if the gas fuel supply amount Q is doubled, the distance L also doubles. In other words, by adjusting the distance L in response to changes in the gas fuel supply amount Q, the flow velocity V of the gas fuel at the center 50c of the recirculation area 50 can be kept constant.

The optimal gas fuel flow velocity V at the center 50c of the recirculation region 50 is a value specific to the burner 5A depending on the types of gas fuel and solid fuel, etc., and may be set based on the results of simulations, experiments, etc. A distance L at which the gas fuel flow velocity V at the center 50c of the recirculation region 50 is constant is obtained based on the gas fuel supply amount Q, and a position _xg of the gas fuel supply port 91a in the burner axial direction X is obtained based on this distance L.

The adjustment of the gas fuel supply position _xg may be performed only when the gas fuel supply amount Q is within a predetermined range. That is, as shown in Fig. 4, the gas fuel supply position _xg may be set as a predetermined reference position _x0 until the gas fuel supply amount Q exceeds a predetermined threshold value _QA , and after the gas fuel supply amount Q exceeds the predetermined threshold value _QA , the gas fuel supply position _xg may be changed so that the distance from the fuel ejection port 71a increases with an increase in the gas fuel supply amount Q.

In addition, in adjusting the gas fuel supply position _xg , if the gas fuel supply amount Q based on the detected gas fuel supply amount is significantly lower than a predetermined minimum supply amount _Q0 , the gas fuel supply position _xg may take a negative value as shown in Fig. 5. In this case, the gas fuel supply port 91a is in a state of advancing beyond the fuel ejection port 71a. However, since melting damage of the gas fuel supply pipe 91 is expected, a lower limit is set for the gas fuel supply position _xg . The minimum supply amount _Q0 is the minimum supply amount of gas fuel necessary to maintain combustion, and is set in advance.

Second Embodiment
Next, a second embodiment will be described. Fig. 6 is a schematic cross-sectional view of a burner 5B according to a second embodiment of the present invention. In the description of this embodiment, the same or similar members as those of the burner 5A according to the first embodiment described above are denoted by the same reference numerals in the drawings, and the description thereof will be omitted.

6, the burner 5B according to the second embodiment is provided with, in addition to the support device 81 in the burner 5A according to the first embodiment, a position adjustment device 8B that automatically adjusts the gas fuel supply position _xg in accordance with the detection value of the gas fuel supply amount Q. Therefore, the position adjustment device 8B will be described in detail below, and the rest of the description will be omitted.

The position adjustment device 8B consists of an actuator 85, a position detector 86, a flow rate detector 87, and a control device 88.

The actuator 85 displaces the gas fuel supply pipe 91 in the burner axial direction X. For example, at least one of a pneumatic cylinder, an electric cylinder, an electric motor and a rack and pinion, etc. may be used as the actuator 85. Note that the actuator 85 is not limited to one that displaces the entire gas fuel supply pipe 91, and may be one that displaces only a downstream portion of the gas fuel supply pipe 91. Operation of the actuator 85 displaces the position of the gas fuel supply port 91a in the burner axial direction X, i.e., the gas fuel supply position _xg .

The position detector 86 directly or indirectly detects the gas fuel supply position _xg based on the fuel outlet 71a. The position detector 86 is a sensor that detects an operating amount such as a piston stroke of the actuator 85 or a rotational position of the motor, and the gas fuel supply position _xg may be indirectly detected based on the detected value. The position detector 86 may also be a contact or non-contact displacement sensor that directly detects the displacement amount of the gas fuel supply pipe 91.

The flow rate detector 87 directly or indirectly detects the amount Q of gas fuel supplied from the gas fuel supply pipe 91 to the mixture of solid fuel and conveying air. The flow rate detector 87 may be a flow rate sensor provided in the gas fuel supply pipe 91 or in a gas fuel supply system to the gas fuel supply pipe 91, and detects the flow rate of gas fuel introduced into the gas fuel supply pipe 91. Alternatively, the flow rate detector 87 may be a sensor that detects the opening of a valve provided in the gas fuel supply system or the output of a compression pump, and the amount Q of gas fuel supplied may be indirectly detected based on the detection value.

The control device 88 controls the flow rate at the center 50c of the recirculation region 50 to be constant by operating the actuator 85 to adjust the gas fuel supply position _xg detected by the position detector 86 based on the gas fuel supply amount Q detected by the flow rate detector 87.

7 is a block diagram showing the flow of control by the control device 88. The control device 88 acquires the gas fuel supply amount Q detected by the flow rate detector 87. Next, the target position calculator of the control device 88 calculates the distance L between the gas fuel supply port 91a and the center 50c of the recirculation area 50 based on the acquired gas fuel supply amount Q, and calculates the target position _xp of the gas fuel supply position _xg based on the distance L. Then, the control device 88 operates the actuator 85 so that the gas fuel supply position _xg detected by the position detector 86 becomes equal to the target position _xp . In detail, the control device 88 calculates the deviation between the target position _xp and the gas fuel supply position _xg detected by the position detector 86, calculates the control amount based on this deviation, calculates the operation amount of the actuator 85 based on the control amount, and outputs the operation amount to the actuator 85.

In this manner, in the burner 5B according to the present embodiment, the gas fuel supply position _xg is automatically adjusted by the operation of the position adjustment device 8B so that the flow velocity of the gas fuel at the center 50c of the recirculation region 50 is maintained at a predetermined value. Therefore, even if short-term or long-term fluctuations occur in the gas fuel supply amount Q, an appropriate temperature of the recirculation region 50 is maintained, and combustion can be performed under reducing conditions in the recirculation region 50 while suppressing the generation of NOx.

Third Embodiment
Next, a third embodiment will be described. Fig. 8 is a schematic cross-sectional view of a burner 5C according to a third embodiment of the present invention. In the description of this embodiment, the same or similar members as those in the first and second embodiments are denoted by the same reference numerals in the drawings, and the description thereof will be omitted.

When the amount of fuel that does not burn completely in the recirculation zone 50 increases due to a change in the flow rate of the gas fuel, a local temperature drop occurs in the recirculation zone 50. Therefore, as shown in Fig. 8, the burner 5C according to the third embodiment is provided with a position adjustment device 8C that automatically adjusts the gas fuel supply position _xg according to a change in the flame intensity in the recirculation zone 50, in addition to the support device 81 in the burner 5A according to the first embodiment described above. Therefore, the position adjustment device 8C will be described in detail below, and the rest of the description will be omitted.

The position adjustment device 8C includes an actuator 85, a position detector 86, a flame intensity detection device 90, and a control device 89. A detailed description of the actuator 85 and the position detector 86 will be omitted, and the description of the second embodiment will be cited.

The flame intensity detection device 90 has a flame sensor that detects light (e.g., infrared or ultraviolet light) emitted from the flame, and a calculator that measures the flame intensity (light emission intensity) based on the detection value of the flame sensor (both not shown). For example, an optical flame sensor that detects the color and wavelength of the flame is used as the flame sensor. In this case, the flame intensity of the flame can be calculated based on the color and wavelength of the flame. The flame intensity detection device 90 can be one with a known configuration used in conventional burners.

The control device 89 controls the flame intensity in the recirculation region 50 to be constant by operating the actuator 85 to adjust the gas fuel supply position _xg based on the flame intensity detected by the flame intensity detection device 90. More specifically, the control device 89 determines a target position _xp of the gas fuel supply position _xg so that the flame intensity detected by the flame intensity detection device 90 becomes a predetermined reference intensity. For example, when the detected flame intensity becomes lower than the reference intensity, the control device 89 calculates a value of the target position _xp so that the target position _xp is farther away from the fuel ejection port 71a than the currently detected gas fuel supply position _xg . Here, the control device 89 may store in advance a relationship between the detected flame intensity and the target position _xp and use this to determine the target position _xp . Then, the control device 89 operates the actuator 85 so that the gas fuel supply position _xg detected by the position detector 86 becomes equal to the target position _xp .

In this way, in the burner 5C according to this embodiment, the position of the gas fuel supply port 91a is automatically adjusted by the operation of the position adjustment device 8C so that the appropriate flame intensity in the recirculation area 50 is maintained. Therefore, even if there are short-term or long-term fluctuations in the amount of gas fuel supply, the appropriate temperature in the recirculation area 50 is maintained, and combustion can be generated that suppresses the generation of NOx under reducing conditions in the recirculation area 50.

Fourth Embodiment
Next, a fourth embodiment will be described. Fig. 9 is a schematic cross-sectional view of a burner 5D according to a fourth embodiment of the present invention. In the description of this embodiment, the same or similar members as those in the first embodiment described above are denoted by the same reference numerals in the drawings, and the description thereof will be omitted.

When the amount of fuel that does not burn completely in the recirculation area 50 increases due to a change in the flow rate of the gas fuel, the high-temperature reducing combustion weakens, and the amount of NOx contained in the combustion exhaust gas increases. Therefore, as shown in Fig. 9, the burner 5D according to the fourth embodiment is provided with a position adjustment device 8D that automatically adjusts the gas fuel supply position _xg in accordance with the NOx value of the exhaust gas from the boiler 10, in addition to the support device 81 in the burner 5A according to the first embodiment described above. Therefore, the position adjustment device 8D will be described in detail below, and the rest of the description will be omitted.

The position adjustment device 8D includes an actuator 85, a position detector 86, a NOx sensor (the second NOx sensor 33 or the first NOx sensor 32), and a control device 92. A detailed description of the actuator 85 and the position detector 86 will be omitted, and the description of the second embodiment will be cited.

As shown in FIG. 1, the second NOx sensor 33 is provided at the outlet of the boiler 10 and detects the NOx value of the exhaust gas from the boiler 10. However, the NOx sensor may be the first NOx sensor 32 provided upstream of the flue gas denitrification device 41 in the flue 28 of the boiler 10.

The control device 92 controls the amount of NOx contained in the exhaust gas (NOx value) to a range of a predetermined reference NOx value by operating the actuator 85 to adjust the position x _g of the gas fuel supply port 91a detected by the position detector 86 based on the NOx value detected by the second NOx sensor 33 (or the first NOx sensor 32). More specifically, the control device 89 determines the target position x p of the gas fuel supply port 91a so that the NOx value detected by the second NOx sensor 33 (or the first NOx sensor 32) falls within the range of a predetermined reference NOx value. For example, when the detected NOx value is larger than the reference NOx value, the control device 92 determines the target position x _p so that the value of the target position x _{p is} larger than the detected gas fuel supply position x _g . Here, the control device 92 may store in advance the relationship between the detected NOx value and the target position x _p and use this to determine the target position x _p . Then, the control device 92 operates the actuator 85 so that the gas fuel supply position x _g detected by the position detector 86 becomes the target position x _p .

In this way, in the burner 5D according to this embodiment, the position of the gas fuel supply port 91a is automatically adjusted by the operation of the position adjustment device 8D so that the NOx value falls within the range of the reference NOx value, i.e., so that proper combustion in the recirculation area 50 is maintained. Therefore, even if short-term or long-term fluctuations occur in the amount of gas fuel supply, the NOx value of the exhaust gas from the boiler 10 is suppressed.

[Summary]
As described above, the combustion furnace 2 according to this embodiment includes the high-temperature reduction zone 21 of a reducing atmosphere in which at least one burner 5, 5A to 5D is provided, and the low-temperature oxidation zone 22 of an oxidizing atmosphere at a lower temperature than the high-temperature reduction zone 21, into which the combustion gas generated in the high-temperature reduction zone 21 flows.

The burner 5A according to the first embodiment is cylindrical and extends in the burner axial direction X. It has a fuel outlet 71a formed by a flame stabilizing plate 77 at the downstream end, and includes a fuel supply nozzle 71 into which solid fuel and carrier air are introduced, at least one flow path 72f, 73f that is disposed on the outer periphery of the fuel supply nozzle 71 and supplies the combustion air 52, 53 separately from the air-fuel mixture 51 ejected from the fuel supply nozzle 71, and a gas fuel supply pipe 91 that is inserted into the fuel supply nozzle 71 and has a gas fuel supply port 91a located upstream of the fuel outlet 71a, and supplies gas fuel containing nitrogen into the fuel supply nozzle 71.

According to the burner 5A having the above configuration, the gas fuel is premixed with the carrier air in the fuel supply nozzle 71 and then ejected from the fuel ejection port 71a. For example, when the gas fuel is a fuel with a slow burning speed such as ammonia, or when a large amount of gas fuel is supplied at one time, the gas fuel supply position _xg is retracted further into the fuel supply nozzle 71 than the fuel ejection port 71a, thereby ensuring the mixing time between the gas fuel and the carrier air (primary air). As a result, the gas fuel is partially premixed, the equivalence ratio (theoretical air-fuel ratio/actual air-fuel ratio) approaches 1, and the combustion speed of the gas fuel can be raised. Therefore, in the recirculation region 50 formed downstream of the fuel ejection port 71a, the combustion speed of the gas fuel increases, and the increase in the unburned gas fuel can be suppressed. As a result, the local temperature drop in the recirculation region 50 can be avoided.

From another perspective, the burner 5A according to the first embodiment is provided with a fuel supply nozzle 71 having a cylindrical shape extending in the burner axial direction X and a fuel outlet 71a formed by a flame stabilizing plate 77 provided at the downstream end, into which solid fuel and transport air are introduced, at least one flow path 72f, 73f arranged on the outer periphery of the fuel supply nozzle 71 for supplying combustion air 52, 53 separately from the mixture gas 51 ejected from the fuel supply nozzle 71, a gas fuel supply pipe 91 inserted into the fuel supply nozzle 71 and having a gas fuel supply port 91a provided at the downstream end, which supplies gas fuel containing nitrogen from the gas fuel supply port 91a to the mixture gas consisting of the solid fuel and the transport air, and a nozzle support device 81 for supporting the gas fuel supply pipe 91 so as to be displaceable in the burner axial direction X so that the gas fuel supply port 91a is displaceable in the burner axial direction X relative to the fuel outlet 71a. The burner 5A having the above configuration may further include an actuator 85 that displaces the gas fuel supply pipe 91 in the burner axial direction X.

According to the burner 5A having the above configuration, it is possible to adjust the retreat amount of the gas fuel supply port 91a from the fuel ejection port 71a into the fuel supply nozzle 71 (i.e., the gas fuel supply position x _g ). Therefore, when the gas fuel supply amount increases, the retreat amount of the gas fuel supply port 91a can be increased to suppress an increase in the flow rate of the gas fuel at the center 50c of the recirculation area 50, and the recirculation area 50 can be maintained. In addition, since the gas fuel supply port 91a is retreated from the fuel ejection port 71a, the degree of premixing of the gas fuel and the carrier air in the fuel supply nozzle 71 can be increased. Therefore, in the recirculation area 50 formed downstream of the fuel ejection port 71a, the combustion speed of the gas fuel increases, and the increase in the gas fuel that cannot be burned can be suppressed. As a result, a local temperature drop in the recirculation area 50 can be avoided.

Furthermore, the burner 5B according to the second embodiment is equipped with, in addition to the components of the burner 5A according to the first embodiment, a position detector 86 which detects a position _xg of the gas fuel supply port 91a relative to the fuel nozzle 71a along the burner axial direction X, a flow rate detector 87 which detects the amount of gas fuel supply from the gas fuel supply pipe 91, and a control device 88 which operates the actuator 85 based on the detected amount of gas fuel supply so that the position of the gas fuel supply port 91a moves away upstream from the fuel nozzle 71a as the amount of gas fuel supply increases when the amount of gas fuel supply is within a predetermined range.

A control method for a burner 5B according to a second embodiment is a control method for a burner 5B comprising: a fuel supply nozzle 71 having a cylindrical shape extending in a burner axial direction X and a fuel outlet 71a formed by a flame stabilizing plate 77 provided at a downstream end, into which a solid fuel and a carrier air are introduced; at least one flow path 72f, 73f arranged on the outer periphery of the fuel supply nozzle 71 and supplying combustion air separately from a gas-fuel mixture 51 ejected from the fuel supply nozzle 71; a gas fuel supply pipe 91 inserted into the fuel supply nozzle 71, having a gas fuel supply port 91a provided at a downstream end, and supplying a gas fuel containing a nitrogen component from the gas fuel supply port 91a to a gas mixture consisting of the solid fuel and the carrier air; and an actuator 85 for displacing the gas fuel supply pipe 91 in the burner axial direction X,
Detecting the position of the gas fuel supply port 91a relative to the fuel nozzle 71a along the burner axial direction X;
Detecting the amount of gas fuel supplied from the gas fuel supply pipe 91;
When the gas fuel supply amount is within a predetermined range, the actuator 85 is operated so that the position of the gas fuel supply port 91a moves upstream away from the fuel ejection port 71a as the gas fuel supply amount increases.

The burner 5B and its control method configured as described above provide the following effects in addition to the effects of the burner 5A according to the first embodiment. That is, when the amount of gas fuel supply increases, the position of the gas fuel supply port 91a is automatically adjusted so that the increase in the flow rate of the gas fuel in the recirculation area 50 is suppressed.

In the above-described burner 5B, the control device 88 may determine a target position xp of the gas fuel supply port _91a so that the flow velocity of the gas fuel at the center 50c in the burner axial direction X of the recirculation area 50 formed downstream of the fuel nozzle 71a is constant, and may operate the actuator 85 so that the position _xg of the gas fuel supply port 91a becomes the target position _xp .

Similarly, in the above-described control method for the burner 5B, a target position xp of the gas fuel supply port 91a may be obtained so that the flow velocity of the gas fuel at the center 50c in the burner axial direction X of the recirculation region 50 formed downstream of the fuel nozzle 71a is constant, and the actuator 85 may be operated so that the position _xg of the gas fuel supply port 91a becomes the target _{position xp .}

This allows the flow rate of the gas fuel at the center 50c of the recirculation area 50 in the burner axial direction X to be constant, and a stable recirculation area 50 is maintained.

Moreover, the burner 5C according to the third embodiment is equipped with, in addition to the burner 5A according to the first embodiment, a flame intensity detection device 90 for detecting the flame intensity in the recirculation region 50 formed downstream of the fuel outlet 71a, a position detector 86 for detecting the position _xg of the gas fuel supply port 91a relative to the fuel outlet 71a along the burner axial direction X, and a control device 89 for controlling the flame intensity in the recirculation region 50 to a predetermined value by operating the actuator 85 based on the detected flame intensity to adjust the position _xg of the gas fuel supply port 91a.

Similarly, the control method for the burner 5C according to the third embodiment detects the flame intensity in the recirculation zone 50 formed downstream of the fuel injection port 71a, and operates the actuator 85 to adjust the position _xg of the gas fuel supply port 91a based on the detected flame intensity so that the flame intensity in the recirculation zone 50 becomes a predetermined reference temperature.

According to the burner 5C and the control method thereof having the above-described configuration, when a localized low temperature spot occurs in the recirculation zone 50 due to a fluctuation in the amount of gas fuel supply or the like, the position _xg of the gas fuel supply port 91a is automatically adjusted so that the flame intensity in the recirculation zone 50 is appropriately maintained.

Moreover, the burner 5D according to the fourth embodiment is equipped with, in addition to the burner 5A according to the first embodiment, a NOx sensor 33 for detecting the NOx value of the combustion exhaust gas, a position detector 86 for detecting a position _xg of the gas fuel supply port 91a relative to the fuel nozzle 71a along the burner axial direction X, and a control device 92 for controlling the NOx value so that it falls within a predetermined reference NOx value range by operating an actuator 85 based on the NOx value to adjust the position _xg of the gas fuel supply port 91a.

Similarly, the control method for the burner 5D according to the fourth embodiment detects the NOx value of the combustion exhaust gas, and operates the actuator 85 to adjust the position _xg of the gas fuel supply port 91a based on the NOx value so that the NOx value falls within a predetermined reference NOx value range.

The burner 5D and its control method configured as described above can avoid local temperature drops in the recirculation area 50 caused by fluctuations in the amount of gas fuel supplied, and can suppress increases in the NOx value of the exhaust gas.

The combustion furnace 2 equipped with the burners 5A-5D of the above configuration burns solid fuel and nitrogen-rich gas fuel in the high-temperature reduction zone 21, denitrifying NOx generated from the nitrogen contained in the solid fuel and gas fuel in the furnace, thereby suppressing NOx emissions. Furthermore, a water-gasification reaction occurs in which water generated from the hydrogen contained in the solid fuel and/or gas fuel is converted into active gas, improving combustion efficiency. Here, when the gas fuel is ammonia gas, ammonia has poor combustibility, so simply burning the two fuels together reduces combustion efficiency, but the application of the present invention makes it possible to suppress the reduction in combustion efficiency.

The above describes a preferred embodiment of the present invention, but the present invention also includes modifications of the specific structure and/or details of the function of the above embodiment without departing from the spirit of the present invention. The above configuration can be modified, for example, as follows:

For example, in the above embodiment, the combustion furnace 2 of the boiler 10 is configured to perform two-stage combustion by forming a high-temperature reduction zone 21 and a low-temperature oxidation zone 22, but the combustion furnace to which the burner 5 (burners 5A to 5D) is applied is not limited to the above configuration. The burner 5 (burners 5A to 5D) according to the above embodiment can be widely used as a mixed combustion burner for solid fuel and gas fuel that achieves low NOx.

In addition, in the position adjustment devices 8B to 8D of the above embodiment, the gas fuel supply port 91a is displaced by inserting and removing the gas fuel supply pipe 91 into the fuel supply nozzle 71, but the position adjustment devices 8B to 8D are not limited to this. For example, the gas fuel supply pipe 91 may be configured to be telescopically extendable and retractable from an outer tube inserted into the fuel supply nozzle 71 and an inner tube inserted into the outer tube, and the gas fuel supply port 91a may be displaced by moving the inner tube back and forth relative to the outer tube.

2: Combustion furnace 5, 5A to 5D: Burners 8B to 8D: Position adjustment device 10: Boiler 20: Combustion chamber 21: High-temperature reduction zone 22: Low-temperature oxidation zone 32, 33: NOx sensor 50: Recirculation area 50c: Center 51: Air-fuel mixture 52, 53: Combustion air 70: Burner axis 71: Fuel supply nozzle 71a: Fuel nozzle 72f, 73f: Flow path (for combustion air) 77: Flame holder 81: Nozzle support device 85: Actuator 86: Position detector 87: Flow rate detector 88, 89, 92: Control device 90: Flame intensity detection device 91: Gas fuel supply pipe 91a: Gas fuel supply port

Claims (14)

a fuel supply nozzle having a cylindrical shape extending in a burner axial direction, having a fuel outlet formed by a flame stabilizing plate provided at a downstream end, and into which solid fuel and carrier air are introduced;
at least one flow passage disposed on an outer circumferential side of the fuel supply nozzle and configured to supply combustion air separately from the air-fuel mixture ejected from the fuel supply nozzle;
a gas fuel supply pipe that is inserted into the fuel supply nozzle, has a gas fuel supply port located upstream of the fuel outlet, and supplies a gas fuel containing a nitrogen component into the fuel supply nozzle.
Burner. The gas fuel is ammonia gas.
2. A burner according to claim 1. a fuel supply nozzle having a cylindrical shape extending in a burner axial direction, having a fuel outlet formed by a flame stabilizing plate provided at a downstream end, and into which solid fuel and carrier air are introduced;
at least one flow passage disposed on an outer circumferential side of the fuel supply nozzle and configured to supply combustion air separately from the air-fuel mixture ejected from the fuel supply nozzle;
a gas fuel supply pipe that is inserted into the fuel supply nozzle, has a gas fuel supply port provided at a downstream end, and supplies a gas fuel containing a nitrogen component from the gas fuel supply port to a mixed gas consisting of the solid fuel and the carrier air;
a nozzle support device that supports the gas fuel supply pipe displaceably in the burner axial direction so that the gas fuel supply port is displaceable in the burner axial direction with respect to the fuel ejection port.
Burner. an actuator for displacing the gas fuel supply pipe in the burner axial direction;
4. A burner according to claim 3. a position detector for detecting a position of the gas fuel supply port relative to the fuel nozzle along the burner axis direction;
a flow rate detector for detecting a gas fuel supply amount, which is a flow rate of the gas fuel supplied from the gas fuel supply port;
a control device that operates the actuator so that a position of the gas fuel supply port moves away from the fuel outlet upstream as the gas fuel supply amount increases when the gas fuel supply amount is within a predetermined range.
5. A burner according to claim 4. The control device includes:
determining a target position of the gas fuel supply port so that a flow velocity of the gas fuel at a center in the burner axial direction of a recirculation region formed downstream of the fuel injection port becomes constant, and operating the actuator so that the position of the gas fuel supply port becomes the target position;
6. A burner according to claim 5. a flame intensity detection device for detecting a flame intensity in a recirculation region formed downstream of the fuel injection port;
a position detector for detecting a position of the gas fuel supply port relative to the fuel nozzle along the burner axis direction;
and a control device that operates the actuator to adjust a position of the gas fuel supply port based on the detected flame intensity, thereby controlling the flame intensity in the recirculation zone to a predetermined value.
5. A burner according to claim 4. A NOx sensor for detecting a NOx value in the combustion exhaust gas;
a position detector for detecting a position of the gas fuel supply port relative to the fuel nozzle along the burner axis direction;
and a control device that controls the NOx value to be within a range of a predetermined reference NOx value by operating the actuator to adjust the position of the gas fuel supply port based on the NOx value.
5. A burner according to claim 4. The gas fuel is ammonia gas.
A burner according to any one of claims 3 to 8. A high-temperature reduction zone in a reducing atmosphere provided with a burner according to any one of claims 1 to 9;
A low-temperature oxidation zone, into which the combustion gas generated in the high-temperature reduction zone flows and which has a lower temperature than the high-temperature reduction zone and an oxidizing atmosphere,
Combustion furnace. a fuel supply nozzle having a cylindrical shape extending in a burner axial direction, having a fuel outlet formed by a flame stabilizing plate provided at a downstream end, and into which solid fuel and carrier air are introduced;
at least one flow passage disposed on an outer circumferential side of the fuel supply nozzle and configured to supply combustion air separately from the air-fuel mixture ejected from the fuel supply nozzle;
a gas fuel supply pipe that is inserted into the fuel supply nozzle, has a gas fuel supply port provided at a downstream end, and supplies a gas fuel containing a nitrogen component from the gas fuel supply port to a mixed gas consisting of the solid fuel and the carrier air;
and an actuator for displacing the gas fuel supply pipe in the burner axial direction,
Detecting a position of the gas fuel supply port relative to the fuel nozzle along the burner axis direction;
Detecting a gas fuel supply amount, which is a flow rate of the gas fuel supplied from the gas fuel supply port;
operating the actuator such that, when the gas fuel supply amount is within a predetermined range, a position of the gas fuel supply port moves away from the fuel ejection port upstream as the gas fuel supply amount increases;
How to control the burner. determining a target position of the gas fuel supply port so that a flow velocity of the gas fuel at a center in the burner axial direction of a recirculation region formed downstream of the fuel injection port becomes constant, and operating the actuator so that the position of the gas fuel supply port becomes the target position;
A method for controlling a burner according to claim 11. Detecting a flame intensity in a recirculation zone formed downstream of the fuel injection port;
Operate the actuator to adjust a position of the gas fuel supply port based on the detected flame intensity so that the flame intensity in the recirculation zone becomes a predetermined reference temperature.
A method for controlling a burner according to claim 11. Detects NOx levels in combustion exhaust gas,
operating the actuator to adjust a position of the gas fuel supply port based on the NOx value so that the NOx value falls within a range of a predetermined reference NOx value;
A method for controlling a burner according to claim 11.

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