furnace

Abstract

The furnace 1 comprises at least one first burner 11 that supplies a first fuel F1 containing nitrogen to the combustion space S, at least one port 21, 31 that supplies at least an oxidant to the combustion space S, and a recirculation conduit R that recirculates exhaust gas Ex from the combustion space S to the combustion space S, wherein more than half of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the at least one port 21, 31.

Description

[Technical Field]

[0001] This application claims the benefit of priority from Japanese Patent Application No. 2024-139528, filed on August 21, 2024, the contents of which are incorporated herein by reference. [Background technology]

[0002] The furnace may use a nitrogen-containing fuel, such as ammonia. For example, U.S. Patent No. 6,299,949 discloses a boiler that uses ammonia and a fossil fuel. In some embodiments, the boiler includes a first burner configured to burn the fossil fuel and a second burner for supplying the ammonia fuel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-178823 Summary of the Invention [Problem to be solved by the invention]

[0004] Combustion of nitrogen-containing fuels produces NOx, which can be a problem when using nitrogen-containing fuels in such furnaces.

[0005] The present disclosure aims to provide a furnace that can reduce NOx when nitrogen-containing fuels are used. [Means for solving the problem]

[0006] A furnace according to one aspect of the present disclosure includes: a first fuel in fluid communication with a tank storing liquid ammonia, the first fuel being gaseous ammonia vaporized from the liquid ammonia in the tank, or liquid ammonia in the tank;to the combustion space, at least one second burner to supply a second fuel that is more combustible than ammonia and an oxidizer to the combustion space, at least one air port to supply the oxidizer to the combustion space, and a recirculation conduit to recirculate exhaust gas from the combustion space to the combustion space, the recirculation conduit supplying half or more of the exhaust gas flowing through the recirculation conduit to the at least one second burner and the at least one air port.

[0008] The recirculation conduit may not supply the exhaust gas flowing through the recirculation conduit to the at least one first burner.

[0009] The recirculation conduit is Kuto The at least one air port may be connected to at least one second burner and at least one air port, but not to at least one first burner.

[0010] The recirculation conduit shall be connected to at least one primary burner, at least one Kuto The fuel cell may be connected to at least one second burner and at least one air port.

[0012] At least a portion of the at least one air port may be located downstream of the at least one first burner.

[0013] The exhaust gas flowing through the recirculation conduit may contain solid particles.

[0014] The furnace may be a gas-fired furnace and the solid particles may be added to the exhaust gas flowing through the recirculation conduit. [Effects of the Invention]

[0015] According to the present disclosure, NOx can be reduced when a fuel containing nitrogen is used. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view of a boiler equipped with a furnace according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a burner. [Figure 3] FIG. 3 is a schematic diagram showing an airport. [Figure 4] FIG. 4 is a schematic cross-sectional view of a boiler including a furnace according to the second embodiment. [Figure 5] FIG. 5 is a schematic cross-sectional view of a boiler including a furnace according to a third embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view of a boiler including a furnace according to a fourth embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view of a boiler including a furnace according to a fifth embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view of a boiler including a furnace according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Specific dimensions, materials, numerical values, etc. shown in the embodiments are merely examples for ease of understanding and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present disclosure are not shown.

[0018] FIG. 1 is a schematic cross-sectional view of a boiler 100 including a furnace 1 according to a first embodiment. In this embodiment, the furnace 1 is applied to the boiler 100. In other embodiments, the furnace 1 may be applied to other equipment. For example, the boiler 100 includes the furnace 1 and a flue 2. The furnace 1 also includes a first burner group 10, a second burner group 20, an air port group 30, and a control device 90. The boiler 100 and the furnace 1 may further include other components.

[0019] The furnace 1 extends vertically. In this embodiment, the furnace 1 has a rectangular shape when viewed from above. In this embodiment, the furnace 1 includes four side walls, including a front wall 1F, a rear wall 1R, a right wall, and a left wall. Each of the side walls extends vertically and horizontally. The front wall 1F and the rear wall 1R are shown in FIG. 1. The furnace 1 defines a combustion space S. In this disclosure, the combustion space refers to a space in which fuel is combusted. An outlet is provided at the bottom of the furnace 1. For example, a hopper (not shown) may be provided at the outlet.

[0020] The furnace 1 combusts a first fuel F1 containing nitrogen and a second fuel F2 that is more flammable than the first fuel F1. For example, the furnace 1 may combust only the first fuel F1 or only the second fuel F2, as needed. A flame is generated by the combustion. For example, the boiler 100 includes a superheater (not shown) installed on the upper part of the furnace 1. The superheater exchanges heat between the exhaust gas generated in the furnace 1 and water, thereby generating steam. For example, the boiler 100 may further include components (not shown), such as a reheater, an economizer, or an air preheater.

[0021] The furnace 1 is connected to a flue 2. The flue 2 guides the exhaust gas Ex from the boiler 100 to a chimney (not shown).

[0022] The first burner group 10 includes at least one first burner 11. In this embodiment, the first burner group 10 includes multiple first burners 11. In other embodiments, the first burner group 10 may include only a single first burner 11. The first burner 11 is provided on the side walls of the furnace 1, in this embodiment, on the front wall 1F and the rear wall 1R. For example, the first burner group 10 includes multiple first burners 11 arranged in a single vertical row. In other embodiments, the multiple first burners 11 may be arranged in multiple vertical rows. On each of the front wall 1F and the rear wall 1R, the multiple first burners 11 are arranged spaced apart from each other in the left-right direction.

[0023] The second burner group 20 includes at least one second burner (at least one port) 21. In this embodiment, the second burner group 20 includes a plurality of second burners 21. In other embodiments, the second burner group 20 may include only a single second burner 21. The second burner 21 is provided on the side walls of the furnace 1, in this embodiment, on the front wall 1F and the rear wall 1R. For example, the second burner group 20 includes a plurality of second burners 21 arranged in a single vertical row. In other embodiments, the plurality of second burners 21 may be arranged in multiple vertical rows. On each of the front wall 1F and the rear wall 1R, the plurality of second burners 21 are arranged spaced apart from each other along the left-right direction.

[0024] In this embodiment, the first burner group 10 is arranged upstream of the second burner group 20, i.e., the multiple first burners 11 are arranged below the multiple second burners 21. The arrangement of the first burners 11 and the second burners 21 is not limited to this. For example, the first burner group 10 may be arranged downstream of the second burner group 20, i.e., the multiple first burners 11 may be arranged above the multiple second burners 21. Also, for example, the first burners 11 and the second burners 21 may be arranged alternately with each other in at least one of the vertical and horizontal directions.

[0025] The first burners 11 inject a first fuel F1 into the combustion space S. In this embodiment, the first fuel F1 includes ammonia. For example, each first burner 11 is fluidly connected to a tank (first fuel supply source) 3 via a first fuel conduit L1. For example, the tank 3 stores liquid ammonia. For example, a vaporizer (not shown) may be provided in the first fuel conduit L1, and gaseous ammonia may be supplied to each first burner 11. Alternatively, liquid ammonia may be supplied to each first burner 11. In another embodiment, an ammonia producer may be used as the ammonia supply source.

[0026] The second burners 21 inject a second fuel F2 into the combustion space S. In this embodiment, the second fuel F2 is a fuel that is more flammable than ammonia. For example, the second fuel F2 may be a gas fuel such as natural gas or hydrogen. Alternatively, for example, the second fuel F2 may be a solid fuel such as pulverized coal. Alternatively, the second fuel F2 may be a mixed fuel of a gas fuel and a solid fuel. For example, each second burner 21 is fluidly connected to the second fuel source 4 by a second fuel conduit L2. For example, if the second fuel F2 is a gas fuel, the second fuel source 4 may be a tank. Alternatively, for example, if the second fuel F2 is pulverized coal, the second fuel source 4 may be a pulverizer.

[0027] Each of the first burner 11 and the second burner 21 injects an oxidizer into the combustion space S. For example, the oxidizer may be air A or a mixture of air A and exhaust gas Ex. For example, each of the first burner 11 and the second burner 21 is in fluid communication with an air conduit L3 via a wind box (not shown). The air conduit L3 supplies air A to the first burner 11 and the second burner 21. For example, the air conduit L3 may be in fluid communication with a compressor (not shown) that supplies ambient air around the furnace 1 to the first burner 11.

[0028] It should be noted that in FIG. 1, the first fuel conduit L1, the second fuel conduit L2 and the air conduit L3 are shown only for the burners 11, 21 on the rear wall 1R, but they are also connected to the burners 11, 21 on the front wall 1F.

[0029] The airport group 30 includes at least one airport (at least one port) 31. In this embodiment, the airport group 30 includes multiple airports 31. In other embodiments, the airport group 30 may include only a single airport 31. The airport 31 is provided on each of the side walls of the furnace 1, in this embodiment, the front wall 1F and the rear wall 1R. In this embodiment, the multiple airports 31 are arranged in a single row in the vertical direction. In other embodiments, the multiple airports 31 may be arranged in multiple rows in the vertical direction. In each of the front wall 1F and the rear wall 1R, the multiple airports 31 are arranged spaced apart from each other in the left-right direction.

[0030] The airport group 30 is disposed downstream of the first burner group 10 and the second burner group 20. That is, the airport group 30 is disposed above the first burner group 10 and the second burner group 20. The airport group 30 is disposed spaced apart from the second burner group 20 in the vertical direction. For example, the distance between the airport group 30 and the second burner group 20 in the vertical direction may be longer than the distance between the first burner group 10 and the second burner group 20 in the vertical direction.

[0031] The airports 31 inject an oxidizer into the combustion space S. For example, the oxidizer may be air A or a mixture of air A and exhaust gas Ex. For example, each airport 31 is in fluid communication with an air conduit L4 via an air box (not shown). The air conduit L4 supplies air A to the airports 31. For example, the air conduit L4 may be in fluid communication with a compressor (not shown) that supplies ambient air around the furnace 1 to the airports 31.

[0032] It should be noted that although the air conduit L4 is shown in FIG. 1 only for the air ports 31 on the rear wall 1R, the air conduit L4 is in fluid communication with all of the air ports 31.

[0033] The furnace 1 of this embodiment includes a recirculation conduit R. The recirculation conduit R is configured to recirculate the flue gas Ex from the combustion space S back to the combustion space S. For example, the recirculation conduit R extends from the outlet of the boiler 50. In other embodiments, for example, the recirculation conduit R may branch off from the flue 2. For example, the recirculation conduit R may extend from a position upstream of a denitration device (not shown) or from a position downstream of the denitration device. Furthermore, for example, the recirculation conduit R may extend from another position on the boiler 50. For example, the recirculation conduit R may be provided with a fan (not shown) that adjusts the flow rate of the flue gas Ex drawn from the boiler 50 into the recirculation conduit R. For example, the fan may be communicatively connected to the control device 90 via a wire or wirelessly and controlled by the control device 90. For example, the control device 90 may adjust the flow rate of the flue gas Ex flowing through the recirculation conduit R by controlling the output of the fan.

[0034] In this embodiment, the recirculation conduit R is configured to selectively supply the exhaust gas Ex to the first burner 11, the second burner 21, and the air port 31. Specifically, in this embodiment, the recirculation conduit R includes a first recirculation conduit R1 and a second recirculation conduit R2. The first recirculation conduit R1 is connected to each of the burners 11 and 21. The second recirculation conduit R2 is connected to each of the air ports 31.

[0035] It should be noted that in FIG. 1, the first recirculation conduit R1 and the second recirculation conduit R2 are shown only for the burners 11, 21 and the air port 31, respectively, on the rear wall 1R, but they are also connected to the burners 11, 21 and the air port 31, respectively, on the front wall 1F.

[0036] 2 is a schematic diagram showing burners 11 and 21. For example, the first burner 11 and the second burner 21 may differ from each other in that the first burner 11 injects a first fuel F1 and the second burner 21 injects a second fuel F2. That is, the first burner 11 and the second burner 21 may differ from each other in that the first burner 11 is in fluid communication with the tank 3 and the second burner 21 is in fluid communication with the second fuel supply source 4. In other respects, the first burner 11 and the second burner 21 may be identical to each other. Therefore, in FIG. 2, the first burner 11 and the second burner 21 are described as having similar configurations.

[0037] For example, each burner 11 , 21 may include a body 12 and an oxidant passage 13 .

[0038] For example, the main body 12 includes an injection hole 12a for injecting the first fuel F1 or the second fuel F2 into the combustion space S. The main body 12 is in fluid communication with the first fuel conduit L1 or the second fuel conduit L2. For example, a valve V1 may be provided in the fuel conduits L1 and L2. The valve V1 functions as a fuel adjuster that adjusts the flow rates of the fuels F1 and F2 flowing through the fuel conduits L1 and L2. The valve V1 is connected to a control device 90 via wire or wireless communication and is controlled by the control device 90. For example, the control device 90 may adjust the flow rates of the fuels F1 and F2 injected from each burner 11 and 21 by controlling the opening degree of the valve V1.

[0039] The oxidant flow path 13 supplies the oxidant to the combustion space S. The oxidant flow path 13 is in fluid communication with the combustion space S. For example, the oxidant flow path 13 supplies the oxidant to the combustion space S from the radially outer side of the injection hole 12a. For example, the oxidant flow path 13 is disposed radially outer than the injection hole 12a. For example, the oxidant flow path 13 is continuous in the circumferential direction and has a generally truncated conical shape in this embodiment.

[0040] The oxidant flow path 13 is fluidly connected to the air conduit L3. For example, the air conduit L3 may be provided with a valve V2. The valve V2 functions as a first air adjuster that adjusts the flow rate of air A flowing through the air conduit L3. Note that the first air adjuster is not limited to the valve V2 and may be, for example, a damper. The valve V2 is communicatively connected to the control device 90 via wire or wirelessly and is controlled by the control device 90. For example, the control device 90 adjusts the flow rate of air A supplied from the burners 11, 21 to the combustion space S by controlling the opening degree of the valve V2.

[0041] The oxidant flow path 13 is fluidly connected to the first recirculation conduit R1. A damper D1 is provided in the first recirculation conduit R1. The damper D1 functions as a first exhaust gas adjuster that adjusts the flow rate of the exhaust gas Ex flowing through the first recirculation conduit R1. Note that the first exhaust gas adjuster is not limited to the damper D1 and may be, for example, a valve. The damper D1 is connected to the control device 90 via wire or wireless communication and is controlled by the control device 90. For example, the control device 90 adjusts the flow rate of the exhaust gas Ex supplied from the burners 11, 21 to the combustion space S by controlling the opening degree of the damper D1.

[0042] 3 is a schematic diagram showing an airport port 31. For example, the airport port 31 may include a body 32.

[0043] For example, the main body 32 includes an injection hole 32a for injecting an oxidizer into the combustion space S. The main body 32 is fluidly connected to the air conduit L4. For example, a valve V3 may be provided in the air conduit L4. The valve V3 functions as a second air adjuster that adjusts the flow rate of air A flowing through the air conduit L3. Note that the second air adjuster is not limited to the valve V3 and may be, for example, a damper. The valve V3 is connected to the control device 90 via wire or wireless communication and is controlled by the control device 90. For example, the control device 90 adjusts the flow rate of air A supplied from the air port 31 to the combustion space S by controlling the opening degree of the valve V3.

[0044] The main body 32 is fluidly connected to the second recirculation conduit R2. For example, the second recirculation conduit R2 may be provided with a damper D2. The damper D2 functions as a second exhaust gas adjuster that adjusts the flow rate of the exhaust gas Ex flowing through the second recirculation conduit R2. Note that the second exhaust gas adjuster is not limited to the damper D2 and may be, for example, a valve. The damper D2 is communicatively connected to the control device 90 via wire or wirelessly and is controlled by the control device 90. For example, the control device 90 adjusts the flow rate of the exhaust gas Ex supplied from the air port 31 to the combustion space S by controlling the opening degree of the damper D2.

[0045] For example, the above-described furnace 1 may be realized by modifying an existing furnace that uses fossil fuel. For example, piping for supplying ammonia may be added to some or all of the multiple burners that burn fossil fuel. In this case, some of the multiple burners may be used as second burners 21, and some or all of the remaining burners may be used as first burners 11.

[0046] Furthermore, for example, an existing furnace may be equipped with an air port for two-stage combustion (which may also be referred to as an "over-air port"). Therefore, for example, when the furnace 1 according to this embodiment is realized by modifying an existing furnace, the existing over-air port may be used as the airport port 31.

[0047] Returning to FIG. 1 , the control device 90 controls the furnace 1. The control device 90 may also control at least some of the other components of the boiler 100. For example, the control device 90 may control the entire boiler 100. The control device 90 includes components such as a processor 90a, a memory device 90b, and a connector 90c, which are connected to each other via a bus. For example, the processor 90a includes a CPU (Central Processing Unit). For example, the memory device 90b includes a hard disk, a ROM for storing programs, and a RAM as a work area. The control device 90 is connected to each component of the furnace 1 via the connector 90c so as to be able to communicate with them via wired or wireless communication. For example, the control device 90 may further include other components, such as a display device such as a liquid crystal display or a touch panel, and an input device such as a keyboard, buttons, or a touch panel. For example, the operation of the control device 90 may be realized by the processor 90a executing a program stored in the memory device 90b.

[0048] Next, the operation of the furnace 1 will be described.

[0049] The first burner 11 injects a first fuel F1 and an oxidizer into the combustion space S. The second burner 21 injects a second fuel F2 and an oxidizer into the combustion space S. The first fuel F1 and the second fuel F2 are combusted in the combustion space S (first-stage combustion).

[0050] In the first-stage combustion, the control device 90 adjusts the flow rates of the first fuel F1 and air A supplied from the first burner 11 so that the first burner 11 burns the first fuel F1 in a fuel-rich combustion. For example, in the first-stage combustion, the control device 90 adjusts the flow rates of the first fuel F1 and air A supplied from the first burner 11 so that the first burner 11 burns the first fuel F1 at an air ratio of less than 1.0.

[0051] The airport 31 injects an oxidizer into the combustion space S. Combustion gas from the first burner 11 and the second burner 21 flows to a region in front of the airport 31. Unburned fuel contained in the combustion gas is completely combusted by air from the airport 31 (second-stage combustion).

[0052] For example, the control device 90 adjusts the flow rates of the second fuel F2 and air A supplied from the second burner 21, and the flow rate of air A supplied from the air port 31 so that the air ratio of the entire furnace 1 exceeds 1.

[0053] Generally, the exhaust gas Ex recirculated to the combustion space S can reduce the flame temperature and oxygen concentration, and therefore reduce NOx (especially thermal NOx). However, some fuels containing nitrogen, such as ammonia, may have low combustibility. If the exhaust gas Ex is supplied as part of the oxidizer to such fuel, combustion may become unstable. In this embodiment, the first fuel F1 contains nitrogen. Therefore, the exhaust gas Ex may destabilize the combustion of the first fuel F1. This may lead to misfires, reduced combustion efficiency, and an increase in NOx due to an increase in unburned ammonia.

[0054] In this embodiment, in order to reduce NOx and stabilize the combustion in the first burner 11, more than half of the exhaust gas Ex flowing through the recirculation pipe R is supplied to the second burner 21 and the air port 31.

[0055] For example, the control device 90 may control the dampers D1 and D2 so that no exhaust gas Ex is supplied to the first burner 11, and all of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the second burner 21 and the air port 31.

[0056] With this configuration, exhaust gas Ex is not supplied to the first burner 11, so combustion in the first burner 11 can be stabilized. This also makes it possible to suppress an increase in NOx due to an increase in unburned ammonia. Furthermore, with this configuration, exhaust gas Ex is supplied to the second burner 21 and the airport 31, so the oxygen concentration and combustion temperature of the combustion in the second burner 21 and the second-stage combustion in the airport 31 are reduced. Therefore, the generation of NOx is suppressed.

[0057] For example, the amount of exhaust gas Ex distributed to each of the second burner 21 and the airport 31 may be determined by experiment or analysis so that the amount of NOx does not exceed a predetermined upper limit value.

[0058] In another embodiment, the control device 90 may control the dampers D1 and D2 to supply to the first burner 11 an amount of exhaust gas Ex that is less than the amount of exhaust gas Ex supplied to the second burner 21 and the airport 31. For example, the amount of exhaust gas Ex distributed to the first burner 11 may be determined by experiment or analysis to an extent that combustion in the first burner 11 does not become unstable.

[0059] Even with this configuration, combustion in the first burner 11 does not become unstable, making it possible to suppress an increase in NOx due to an increase in unburned ammonia. Furthermore, with this configuration, most of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the second burner 21 and the airport 31, reducing the oxygen concentration and combustion temperature of the combustion in the second burner 21 and the second-stage combustion in the airport 31. This therefore suppresses the generation of NOx.

[0060] In addition, in this embodiment, the furnace 1 is configured so that the exhaust gas Ex flowing through the recirculation conduit R contains solid particles.

[0061] For example, the solid particles may be ash.

[0062] For example, when the second fuel F2 contains pulverized coal, ash is produced in the combustion in the second burner 21. Therefore, the exhaust gas Ex flowing through the recirculation conduit R contains solid particles.

[0063] For example, if the second fuel F2 is a gas fuel such as hydrogen or natural gas, no ash is produced in the combustion in the furnace 1. In this case, for example, the recirculation conduit R may include an inlet 5 for adding solid particles to the exhaust gas Ex. In this case, for example, the solid particles may be ash produced in another combustor.

[0064] For example, when the first fuel F1 contains ammonia, the solid particles promote the decomposition of the ammonia attached to the solid particles into hydrogen. Therefore, the NOx (fuel NOx) generated from the ammonia can be reduced. In addition, the hydrogen stabilizes the combustion in the combustion space S.

[0065] In addition, the solid particles improve the heat transfer from the combustion gas to the inner wall of the furnace 1. Therefore, the inner wall of the furnace 1 can recover more heat from the combustion gas, thereby improving the efficiency of the furnace 1.

[0066] The furnace 1 as described above includes at least one first burner 11 that supplies a nitrogen-containing first fuel F1 to the combustion space S, at least one second burner 21 and an air port 31 that supply at least an oxidizer to the combustion space S, and a recirculation conduit R that recirculates exhaust gas Ex from the combustion space S to the combustion space S. The recirculation conduit R is configured to supply at least half of the exhaust gas Ex flowing through the recirculation conduit R to the second burner 21 and the air port 31. This configuration prevents the combustion of the first burner 11 from becoming unstable, thereby suppressing an increase in NOx due to an increase in unburned first fuel F1. Furthermore, this configuration supplies exhaust gas Ex to the second burner 21 and the air port 31, thereby reducing the oxygen concentration and combustion temperature of the combustion in the second burner 21 and the second-stage combustion in the air port 31. This reduces NOx emissions.

[0067] In the furnace 1, the first fuel F1 contains ammonia. Ammonia is known as a fuel with low combustibility. With this configuration, it is possible to reduce NOx while suppressing instability of ammonia combustion in the first burner 11.

[0068] Furthermore, in the furnace 1, the recirculation conduit R does not need to supply the exhaust gas Ex flowing through the recirculation conduit R to the first burner 11. In this case, the instability of combustion in the first burner 11 can be further suppressed.

[0069] In the furnace 1, the recirculation conduit R is connected to at least one first burner 11, and also to at least one second burner 21 and the air port 31. With this configuration, the exhaust gas Ex can be supplied to the first burner 11 to the extent that the combustion in the first burner 11 does not become unstable.

[0070] Furthermore, in the furnace 1, the at least one port for supplying an oxidizer to the combustion space S includes at least one second burner 21 for supplying a second fuel F2 that is more flammable than the first fuel F1 and an oxidizer to the combustion space S, and at least one air port 31 for supplying the oxidizer to the combustion space S. With this configuration, the second fuel F2 that is more flammable than the first fuel F1 is used, thereby stabilizing combustion in the combustion space S. Furthermore, with this configuration, the amount of exhaust gas distributed to each of the second burner 21 and the air port 31 can be adjusted depending on, for example, the amount of NOx generated.

[0071] Furthermore, in the furnace 1, at least a portion of at least one airport port 31, in this embodiment, all of the airport ports 31, are located downstream of the first burner 11. With this configuration, a reduction region is formed in the combustion space S, making it possible to decompose NOx temporarily generated in the first burner 11 and the second burner 21. Note that in other embodiments, it is not necessary for all of the airport ports 31 to be located downstream of the first burner 11; for example, at least one of the multiple airport ports 31 may be located downstream of the first burner 11.

[0072] In addition, in the furnace 1, the exhaust gas flowing through the recirculation conduit R contains solid particles. Alternatively, the furnace 1 may be a gas-fuel-fired furnace, and solid particles may be added to the exhaust gas Ex flowing through the recirculation conduit R. When the first fuel F1 contains ammonia, the solid particles promote the decomposition of the ammonia attached to the solid particles into hydrogen. This reduces the NOx (fuel NOx) generated from the ammonia. The hydrogen also stabilizes combustion in the combustion space S. The solid particles also improve the heat transfer from the combustion gas to the inner wall of the furnace 1. This allows the inner wall of the furnace 1 to recover more heat from the combustion gas. This improves the efficiency of the furnace 1.

[0073] Next, other embodiments will be described.

[0074] 4 is a schematic cross-sectional view of a boiler 100 including a furnace 1A according to a second embodiment. The furnace 1A differs from the furnace 1 according to the first embodiment in that the recirculation conduit R is not connected to the first burner 11. In other respects, the furnace 1A may be the same as the furnace 1.

[0075] In this embodiment, all of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the second burner 21 and the air port 31, and the exhaust gas Ex is not supplied to the first burner 11.

[0076] The furnace 1A described above can achieve the same effects as the furnace 1 according to the first embodiment. Furthermore, in the furnace 1A, the recirculation conduit R is connected to at least one second burner 21 and the air port 31, but is not connected to at least one first burner 11. Therefore, the structure of the recirculation conduit R can be simplified.

[0077] 5 is a schematic cross-sectional view of a boiler 100 including a furnace 1B according to a third embodiment. The furnace 1B differs from the furnace 1A according to the second embodiment in that the first burner group 10 is disposed downstream of the second burner group 20. That is, in this embodiment, the plurality of first burners 11 are disposed above the plurality of second burners 21. In other respects, the furnace 1B may be the same as the furnace 1A.

[0078] The furnace 1B as described above can achieve the same effects as the furnace 1 according to the first embodiment.

[0079] 6 is a schematic cross-sectional view of a boiler 100 including a furnace 1C according to a fourth embodiment. The furnace 1C differs from the furnace 1A according to the second embodiment in that the recirculation conduit R is connected only to the air port 31. In other respects, the furnace 1C may be the same as the furnace 1A.

[0080] In this embodiment, all of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the airport port 31, and the exhaust gas Ex is not supplied to the first burner 11 or the second burner 21.

[0081] The furnace 1C as described above can achieve the same effects as the furnace 1 according to the first embodiment.

[0082] 7 is a schematic cross-sectional view of a boiler 100 including a furnace 1D according to a sixth embodiment. The furnace 1D differs from the furnace 1A according to the second embodiment in that the furnace 1D does not include an air port 31. In other respects, the furnace 1D may be the same as the furnace 1A.

[0083] In this embodiment, all of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the second burner 21, and the exhaust gas Ex is not supplied to the first burner 11.

[0084] In this embodiment, the first burner 11 injects a first fuel F1 and an oxidizer into the combustion space S. The first fuel F1 is combusted in the combustion space S.

[0085] As in the first embodiment, the control device 90 adjusts the flow rates of the first fuel F1 and air A supplied from the first burner 11 so that the first burner 11 burns the first fuel F1 in a fuel-rich combustion. For example, the control device 90 adjusts the flow rates of the first fuel F1 and air A supplied from the first burner 11 so that the first burner 11 burns the first fuel F1 at an air ratio of less than 1.0.

[0086] The second burner 21 injects the second fuel F2 and the oxidizer into the combustion space S. The combustion gas from the first burner 11 flows to a region in front of the second burner 21. Unburned ammonia contained in the combustion gas is completely burned by the flame from the second burner 21.

[0087] For example, the control device 90 adjusts the flow rates of the second fuel F2 and air A supplied from the second burner 21 so that the air ratio of the furnace 1D as a whole exceeds 1.

[0088] Even with this configuration, exhaust gas Ex is not supplied to the first burner 11, so combustion in the first burner 11 can be stabilized and an increase in NOx due to an increase in unburned ammonia can be suppressed. Furthermore, with this configuration, all of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the second burner 21, so the oxygen concentration and combustion temperature of combustion in the second burner 21 are reduced. Therefore, the generation of NOx is suppressed.

[0089] The furnace 1D as described above can achieve the same effects as the furnace 1 according to the first embodiment.

[0090] 8 is a schematic cross-sectional view of a boiler 100 including a furnace 1E according to a sixth embodiment. The furnace 1E differs from the furnace 1C according to the fourth embodiment in that the furnace 1E does not include a second burner 21. In other respects, the furnace 1E may be the same as the furnace 1C.

[0091] In this embodiment, first burners 11 are arranged instead of the second burners 21. In this embodiment, the first burner group 10 includes a plurality of first burners 11 arranged in two vertical stages. The number of stages is not limited to two, and may be one stage, or may be three or more stages. In this embodiment, the furnace 1E does not include the second fuel supply source 4 and the second fuel conduit L2.

[0092] In this embodiment, the first burner 11 injects a first fuel F1 and an oxidizer into the combustion space S. The first fuel F1 is combusted in the combustion space S (first stage combustion).

[0093] As in the first embodiment, in the first-stage combustion, the control device 90 adjusts the flow rates of the first fuel F1 and air A supplied from the first burner 11 so that the first burner 11 burns the first fuel F1 in a fuel-rich combustion. For example, in the first-stage combustion, the control device 90 adjusts the flow rates of the first fuel F1 and air A supplied from the first burner 11 so that the first burner 11 burns the first fuel F1 at an air ratio of less than 1.0.

[0094] The airport 31 injects an oxidizer into the combustion space S. The combustion gas from the first burner 11 flows into a region in front of the airport 31. Unburned ammonia contained in the combustion gas is completely fueled by the air from the airport 31 (second-stage combustion).

[0095] For example, the control device 90 adjusts the flow rate of the air A supplied from the air port 31 so that the air ratio of the entire furnace 1E exceeds 1.

[0096] Even with this configuration, exhaust gas Ex is not supplied to the first burner 11, so combustion in the first burner 11 can be stabilized and an increase in NOx due to an increase in unburned ammonia can be suppressed. Furthermore, with this configuration, all of the exhaust gas Ex flowing through the recirculation conduit R is supplied to the airport 31, so the oxygen concentration and combustion temperature of combustion in the airport 31 are reduced. Therefore, the generation of NOx is suppressed.

[0097] The furnace 1E as described above can achieve the same effects as the furnace 1 according to the first embodiment.

[0098] Although the embodiments have been described above with reference to the accompanying drawings, the present disclosure is not limited to the above-described embodiments. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that such modifications also fall within the technical scope of the present disclosure.

[0099] For example, in the above embodiment, the furnace is applied to the boiler 100. In other embodiments, the furnace may be applied to other facilities, such as an industrial furnace or a cracking furnace.

[0100] For example, in the above embodiment, ammonia is used as the nitrogen-containing first fuel. For example, blast furnace gas (BFG), converter gas (LDG), and coke oven gas (COG) each contain nitrogen, so NOx generation can be a problem even when these fuels are used. Therefore, in other embodiments, BFG, LDG, or COG may be used as the first fuel. In still other embodiments, the first fuel may include at least one of ammonia, BFG, LDG, and COG.

[0101] For example, in some embodiments, the furnace includes a first burner 11 to which a first fuel F1 and air A are supplied, and a second burner 21 to which a second fuel F2, air A, and exhaust gas Ex are supplied. That is, in the above embodiments, the first burner 11 and the second burner 21 have mutually different functions. In other embodiments, the furnace may include multiple burners having the same function to which the first fuel F1, the second fuel F2, air A, and exhaust gas Ex are selectively supplied, and some of the multiple burners may be used as the first burners 11, and some or all of the remaining burners may be used as the second burners 21.

[0102] The disclosure can promote the use of ammonia, which leads to reduced CO2 emissions, and thereby contribute, for example, to Sustainable Development Goals (SDGs) Goal 7 "Ensure access to affordable, reliable, sustainable and modern energy" and Goal 13 "Take urgent action to combat climate change and its impacts." [Explanation of symbols]

[0103] 1 furnace 1A furnace 1B Furnace 1C Furnace 1D Furnace 1E Furnace 11 First burner 21 Secondary burner (at least one port) 31 Airports (at least one port) A. Air (oxidizer) Ex Exhaust gas (oxidizer) F1 1st fuel F2 2nd fuel R recirculation conduit S Combustion space

Claims

1. At least one first burner fluidly connected to a tank for storing liquid ammonia and supplying, as a first fuel, gaseous ammonia vaporized from the liquid ammonia from the tank or the liquid ammonia from the tank to a combustion space; at least one second burner for supplying a second fuel and an oxidizer more combustible than ammonia to the combustion space; at least one air port for supplying oxidant to the combustion space; a recirculation conduit for recirculating exhaust gas from the combustion space to the combustion space, the recirculation conduit supplying at least half of the exhaust gas flowing through the recirculation conduit to the at least one second burner and the at least one air port; Furnace.

2. the recirculation conduit does not supply the exhaust gas flowing through the recirculation conduit to the at least one first burner; 10. The furnace of claim 1.

3. the recirculation conduit is connected to the at least one second burner and the at least one air port, but is not connected to the at least one first burner; 10. The furnace of claim 1.

4. the recirculation conduit is connected to the at least one first burner, the at least one second burner, and the at least one air port; 10. The furnace of claim 1.

5. 10. The furnace of claim 1, wherein at least a portion of said at least one air port is located downstream of said at least one first burner.

6. The exhaust gas flowing through the recirculation conduit contains solid particles.

10. The furnace of claim 1.

7. The furnace is a gas-fuel-fired furnace, the solid particles are added to the exhaust gas flowing through the recirculation conduit; 7. The furnace of claim 6.

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