Combustion system

Abstract

A combustion system 100 comprises: at least one first burner 11 that supplies an ammonia-containing fuel F and an oxidant to a combustion space S; at least one air port 31 which is disposed downstream of the at least one first burner 11 in the combustion space S and which supplies an oxidant to the combustion space S; and a recirculation conduit R that supplies an exhaust gas Ex from the combustion space S to the at least one first burner 11 and the at least one air port 31.

Description

Combustion System

[0001] This application claims the benefit of priority from Japanese Patent Application No. 2024-071137, filed on April 25, 2024, the contents of which are incorporated herein by reference.

[0002] In some combustion systems, ammonia is used as a fuel. For example, Patent Document 1 discloses a boiler that uses ammonia and a fossil fuel. The boiler includes a burner configured to combust the fossil fuel and a port for supplying the ammonia fuel.

[0003] Japanese Patent Application Laid-Open No. 2019-178823

[0004] Ammonia is CO ２ However, when ammonia is burned, NOx is generated. Therefore, when ammonia is used in the above-mentioned combustion systems, NOx can be a problem.

[0005] The present disclosure aims to provide a combustion system that can reduce NOx when ammonia is used as fuel.

[0006] A combustion system according to one aspect of the present disclosure includes at least one first burner that supplies a fuel containing ammonia and an oxidizer to a combustion space, at least one air port that is positioned downstream of the at least one first burner in the combustion space and supplies the oxidizer to the combustion space, and a recirculation conduit that supplies exhaust gas from the combustion space to at least one of the at least one first burner and the at least one air port.

[0007] The combustion system may include a first sensor that measures the NOx concentration in the exhaust gas from the combustion space, an exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the recirculation conduit, and a control device that is communicatively connected to the first sensor and the exhaust gas adjuster, and that controls the exhaust gas adjuster to adjust the flow rate of the exhaust gas flowing through the recirculation conduit based on the NOx concentration from the first sensor.

[0008] The recirculation conduit may include a first recirculation conduit that supplies exhaust gas to at least one first burner and a second recirculation conduit that supplies the exhaust gas to at least one air port, and the exhaust gas adjuster may include a first exhaust gas adjuster that adjusts the flow rate of exhaust gas flowing through the first recirculation conduit and a second exhaust gas adjuster that adjusts the flow rate of exhaust gas flowing through the second recirculation conduit, and the control device may control at least one of the first exhaust gas adjuster and the second exhaust gas adjuster based on the NOx concentration from the first sensor to adjust the ratio between the flow rate of exhaust gas flowing through the first recirculation conduit and the flow rate of exhaust gas flowing through the second recirculation conduit.

[0009] The combustion system may include a second sensor that measures an ammonia concentration in the exhaust gas from the combustion space, an exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the recirculation conduit, and a control device that is communicatively connected to the second sensor and the exhaust gas adjuster, and that controls the exhaust gas adjuster to adjust the flow rate of the exhaust gas flowing through the recirculation conduit based on the ammonia concentration from the second sensor.

[0010] The recirculation conduit may include a first recirculation conduit that supplies exhaust gas to at least one first burner and a second recirculation conduit that supplies exhaust gas to at least one air port, the exhaust gas adjuster may include a first exhaust gas adjuster that adjusts the flow rate of exhaust gas flowing through the first recirculation conduit and a second exhaust gas adjuster that adjusts the flow rate of exhaust gas flowing through the second recirculation conduit, and the control device may control at least one of the first exhaust gas adjuster and the second exhaust gas adjuster based on the ammonia concentration from the second sensor to adjust the ratio between the flow rate of exhaust gas flowing through the first recirculation conduit and the flow rate of the exhaust gas flowing through the second recirculation conduit.

[0011] The at least one first burner may include multiple stages of first burners arranged along the vertical direction, and the flow rate of exhaust gas supplied to a lower stage of the first burner among the multiple stages of first burners may be lower than the flow rate of exhaust gas supplied to an upper stage of the first burner among the multiple stages of first burners.

[0012] The combustion system may include a heat exchanger that heats exhaust gas from the combustion space, and the recirculation conduit may supply the exhaust gas heated by the heat exchanger to at least one of the at least one first burner and the at least one air port.

[0013] The combustion system may comprise at least one second burner for injecting a second fuel into the combustion space, the second fuel being more combustible than ammonia.

[0014] The at least one first burner may inject ammonia and a third fuel that is more combustible than ammonia into the combustion space.

[0015] According to the present disclosure, NOx can be reduced when ammonia is used as a fuel.

[0016] Fig. 1 is a schematic diagram of a combustion system according to a first embodiment. Fig. 2 is a schematic diagram of a burner. Fig. 3 is a schematic diagram of an air port. Fig. 4 is a graph showing the relationship between exhaust gas recirculation rate and NOx, with respect to the effect of exhaust gas recirculation on NOx. Fig. 5 is a schematic diagram of a combustion system according to a second embodiment. Fig. 6 is a schematic diagram of a combustion system according to a third embodiment.

[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] 1 is a schematic diagram of a combustion system 100 according to a first embodiment. In this embodiment, the combustion system 100 is applied to a boiler 50. In other embodiments, the combustion system 100 may be applied to other equipment. For example, the combustion system 100 includes the boiler 50 and a control device 90. The combustion system 100 may further include other components.

[0019] The boiler 50 includes a furnace 1 .

[0020] The furnace 1 extends in the vertical direction. 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 in the vertical and horizontal directions. The front wall 1F and the rear wall 1R are shown in FIG. 1 . The right wall and the left wall are not shown. 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 may be provided at the outlet.

[0021] The furnace 1 burns a fuel F containing ammonia. For example, in this embodiment, the furnace 1 may use only ammonia as the fuel F. In this case, the furnace 1 may use a small amount of fossil fuel for ignition. For example, in other embodiments, the furnace 1 may use a mixture of ammonia and other fuels as the fuel F. The furnace 1 may also use a fuel that does not contain ammonia, if necessary.

[0022] Combustion of the fuel F generates exhaust gas Ex in the combustion space S. For example, the boiler 50 includes a superheater (not shown) installed on the upper part of the furnace 1. The superheater exchanges heat between the exhaust gas Ex and water, thereby generating steam. Furthermore, for example, the boiler 50 may further include a component (not shown) such as a coal economizer.

[0023] The boiler 50 is connected to a flue 2. The flue 2 guides the exhaust gas Ex from the boiler 50 to a chimney (not shown).

[0024] The furnace 1 includes a burner group 10 and an air port group 30 .

[0025] The burner group 10 includes at least one burner (first burner) 11. In this embodiment, the burner group 10 includes multiple burners 11. In other embodiments, the burner group 10 may include only a single burner 11. The 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 burner group 10 includes multiple burners 11 arranged in multiple stages along the vertical direction, in this embodiment, three stages. In other embodiments, the multiple burners 11 may be arranged in a single stage. In each stage, the multiple burners 11 are arranged along the horizontal direction.

[0026] The burners 11 inject fuel F containing ammonia into the combustion space S. The fuel F is combusted in the combustion space S. For example, the fuel F may be gaseous ammonia or liquid ammonia. For example, each burner 11 is fluidly connected to a tank (ammonia supply source) 3 via a fuel conduit L1. For example, the tank 3 stores liquid ammonia. For example, a vaporizer (not shown) may be provided in the fuel conduit L1, and gaseous ammonia may be supplied to each burner 11. Alternatively, liquid ammonia may be supplied to each burner 11. In another embodiment, an ammonia manufacturing machine may be used as the ammonia supply source.

[0027] The burners 11 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 burner 11 is connected to an air conduit L2. The air conduit L2 supplies air to the burners 11. For example, the air conduit L2 may be in fluid communication with a compressor (not shown) that supplies ambient air around the furnace 1 to the burners 11.

[0028] Although the fuel conduit L1 and the air conduit L2 are shown in FIG. 1 only for the burner 11 on the rear wall 1R, the fuel conduit L1 and the air conduit L2 are also connected to the burner 11 on the front wall 1F.

[0029] The airport group 30 includes at least one airport 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 the side walls of the furnace 1, in this embodiment, on the front wall 1F and the rear wall 1R. In this embodiment, the multiple airports 31 are arranged in a single tier. In other embodiments, the multiple airports 31 may be arranged in multiple tiers along the vertical direction. The multiple airports 31 are arranged along the horizontal direction.

[0030] The airport group 30 is disposed downstream of the burner group 10 in the combustion space S. Specifically, the airport group 30 is disposed above the burner group 10. The airport group 30 is disposed spaced apart from the burner group 10 in the vertical direction. For example, the distance between the airport group 30 and the burner group 10 in the vertical direction may be longer than the distance between adjacent burners 11 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 connected to an air conduit L3. The air conduit L3 supplies air to the airports 31. 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 airports 31.

[0032] Although the air duct L3 is shown in FIG. 1 only connected to the air port 31 on the rear wall 1R, the air duct L3 is also connected to the air port 31 on the front wall 1F.

[0033] The furnace 1 of this embodiment includes a recirculation conduit R. The recirculation conduit R is configured to supply exhaust gas Ex from the combustion space S to at least one of the burner 11 and the air port 31. In this embodiment, 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 in the boiler 50.

[0034] A fan (exhaust gas adjuster) 4 is provided in the recirculation conduit R. The fan 4 adjusts the flow rate of the exhaust gas Ex drawn from the boiler 50 into the recirculation conduit R. The fan 4 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 adjusts the flow rate of the exhaust gas Ex flowing through the recirculation conduit R by controlling the output of the fan 4.

[0035] In this embodiment, the recirculation conduit R is configured to be able to supply the exhaust gas Ex to both the burners 11 and the air ports 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 burner 11. The second recirculation conduit R2 is connected to each air port 31.

[0036] It should be noted that although the first recirculation conduit R1 and the second recirculation conduit R2 are shown in FIG. 1 only for the burner 11 and the air port 31 on the rear wall 1R, the first recirculation conduit R1 and the second recirculation conduit R2 are also connected to the burner 11 and the air port 31 on the front wall 1F, respectively.

[0037] 2 is a schematic diagram showing the burners 11. For example, each burner 11 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 fuel F into the combustion space S. The above-mentioned fuel conduit L1 is connected to the main body 12. A valve V1 is provided in the fuel conduit L1. The valve V1 functions as a fuel adjuster that adjusts the flow rate of the fuel F flowing through the fuel conduit L1. The valve V1 is connected to the control device 90 so as to be able to communicate with it via wire or wirelessly, and is controlled by the control device 90. For example, the control device 90 may adjust the flow rate of the fuel F injected from each burner 11 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 air conduit L2 is connected to the oxidizer flow path 13. A valve V2 is provided in the air conduit L2. The valve V2 functions as a first air adjuster that adjusts the flow rate of air A flowing through the air conduit L2. Note that the first air adjuster is not limited to the valve V2 and may be, for example, a damper. The valve V2 is connected to the control device 90 so as to be able to communicate with it 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 burner 11 to the combustion space S by controlling the opening degree of the valve V2.

[0041] The oxidant flow path 13 is 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 so as to be able to communicate with it 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 burner 11 to the combustion space S by controlling the opening degree of the damper D1.

[0042] For example, the control device 90 may adjust parameters such as the air ratio in the burner 11, the ratio between air A and exhaust gas Ex in the oxidizer of the burner 11, and the concentration of oxygen in the oxidizer of the burner 11, by controlling the fan 4, the valve V1, the valve V2, and the damper D1. When the burner 11 injects a mixed gas of air A and exhaust gas Ex into the combustion space S, the "air ratio in the burner 11" may be interpreted as the ratio of the amount of oxygen in the mixed gas actually supplied from the oxidizer flow path 13 to the theoretical amount of oxygen required to combust the fuel F injected from the burner 11. For example, when the burner 11 supplies a mixed gas of air A and exhaust gas Ex as the oxidizer to the combustion space S, the concentration of oxygen in the air A is reduced by the exhaust gas Ex.

[0043] 3 is a schematic diagram showing an airport port 31. For example, the airport port 31 may include a body 32.

[0044] For example, the main body 32 includes an injection hole 32a for injecting an oxidizer into the combustion space S. The air conduit L3 is connected to the main body 32. A valve V3 is provided in the air conduit L3. 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 wired 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.

[0045] 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, if the furnace 1 according to this embodiment is realized by modifying an existing furnace, the existing over-air port may be used as the air port 31.

[0046] In this embodiment, the second recirculation conduit R2 is connected to the main body 32. A damper D2 is provided in the second recirculation conduit R2. 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 connected to the control device 90 via wired 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 air port 31 to the combustion space S by controlling the opening degree of the damper D2.

[0047] For example, the control device 90 may adjust parameters such as the ratio between air A and exhaust gas Ex in the oxidizer of the airport 31 and the concentration of oxygen in the oxidizer of the airport 31 by controlling the fan 4, the valve V3 and the damper D2.

[0048] 1 , a first sensor Se1 is provided in the recirculation conduit R. The location of the first sensor Se1 is not limited thereto. The first sensor Se1 measures the NOx concentration in the exhaust gas Ex from the combustion space S, in this embodiment, the NOx concentration in the exhaust gas Ex flowing through the recirculation conduit R. The first sensor Se1 is connected to the control device 90 via wire or wireless communication and transmits measurement data to the control device 90.

[0049] A second sensor Se2 is provided in the recirculation conduit R. The location of the second sensor Se2 is not limited to this. The second sensor Se2 measures the concentration of ammonia in the exhaust gas Ex from the combustion space S, in this embodiment, the concentration of ammonia in the exhaust gas Ex flowing through the recirculation conduit R. For example, the exhaust gas Ex contains unburned ammonia. The second sensor Se2 is connected to the control device 90 via wire or wireless communication and transmits measurement data to the control device 90.

[0050] For example, a heat exchanger 5 may be provided in the recirculation conduit R. The heat exchanger 5 heats the exhaust gas Ex flowing through the recirculation conduit R. For example, the heat source of the heat exchanger 5 may be a heat medium such as extracted air from a boiler 50. The heat source of the heat exchanger 5 is not limited to this. For example, a valve V4 may be provided in the pipe through which the heat medium flows. The valve V4 is connected to the control device 90 so as to be able to communicate with the control device 90 via a wire or wirelessly, and is controlled by the control device 90. For example, the control device 90 may adjust the flow rate of the heat medium passing through the heat exchanger 5 and adjust the temperature of the exhaust gas Ex by controlling the opening degree of the valve V4.

[0051] The control device 90 controls the combustion system 100. For example, the control device 90 may be implemented by one or more computers. The control device 90 includes components such as a processor 90a, a storage device 90b, and a connector 90c, which are connected to one another via a bus. For example, the processor 90a includes a central processing unit (CPU). For example, the storage device 90b includes a hard disk, a read-only memory (ROM) for storing programs, and a random access memory (RAM) as a work area. The control device 90 is connected to each component of the furnace 1 via the connector 90c for 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 implemented by the processor 90a executing a program stored in the storage device 90b.

[0052] Next, the operation of the furnace 1 will be described.

[0053] The burner 11 injects fuel F and an oxidizer into the combustion space S. The fuel F is combusted in the combustion space S (first stage combustion).

[0054] The airport 31 injects an oxidizer into the combustion space S. The combustion gas from the 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).

[0055] In this embodiment, in the first-stage combustion, the oxidizer injected from the burner 11 contains exhaust gas Ex in addition to air A. Therefore, the oxygen concentration in the oxidizer is reduced compared to when the oxidizer contains only air A. As a result, the combustion temperature is reduced in the first-stage combustion. The reduction in combustion temperature leads to a reduction in thermal NOx in the first-stage combustion. Therefore, NOx can be reduced.

[0056] Furthermore, in this embodiment, the oxidizer injected from the air port 31 in the second-stage combustion contains exhaust gas Ex in addition to air A. Therefore, the oxygen concentration in the oxidizer is reduced compared to when the oxidizer contains only air A. This reduces the combustion temperature in the second-stage combustion. The reduction in combustion temperature leads to a reduction in thermal NOx in the second-stage combustion. Therefore, NOx can be reduced.

[0057] The control device 90 adjusts the flow rate of the exhaust gas Ex flowing through the recirculation pipe R based on at least one of the concentration of NOx from the first sensor Se1 and the concentration of unburned ammonia from the second sensor Se2.

[0058] For example, if the concentration of NOx is higher than a predetermined upper limit, the control device 90 may control the output of the fan 4 to increase the flow rate of the exhaust gas Ex flowing through the recirculation conduit R. This increases the amount of exhaust gas Ex supplied to the burner 11 and the airport 31. That is, the concentration of oxygen in the oxidizer supplied from the burner 11 and the airport 31 is reduced. This reduces the combustion temperature, making it possible to reduce NOx.

[0059] Furthermore, for example, when the concentration of unburned ammonia is higher than a predetermined upper limit, the control device 90 may control the output of the fan 4 to reduce the flow rate of the exhaust gas Ex flowing through the recirculation conduit R. This reduces the amount of exhaust gas Ex supplied to the burner 11 and the airport 31. That is, the concentration of oxygen in the oxidizer supplied from the burner 11 and the airport 31 increases. This promotes combustion and reduces the amount of unburned ammonia.

[0060] In addition, the control device 90 may adjust the ratio between the flow rate of the exhaust gas Ex flowing through the first recirculation conduit R1 and the flow rate of the exhaust gas Ex flowing through the second recirculation conduit R2 based on at least one of the NOx concentration from the first sensor Se1 and the unburned ammonia concentration from the second sensor Se2.

[0061] For example, if the NOx concentration is higher than a predetermined upper limit, the control device 90 may control at least one of the dampers D1 and D2 to increase the proportion of the flow rate of the exhaust gas Ex flowing through the first recirculation conduit R1. This reduces the oxygen concentration in the oxidizer supplied from the burner 11. For example, a large amount of thermal NOx may be generated in the first-stage combustion. Therefore, in this case, the combustion temperature in the first-stage combustion is reduced, allowing the NOx to be reduced.

[0062] Furthermore, for example, when the concentration of unburned ammonia is higher than a predetermined upper limit, the control device 90 may control at least one of the dampers D1 and D2 to reduce the proportion of the flow rate of the exhaust gas Ex flowing through the first recirculation conduit R1. This increases the concentration of oxygen in the oxidizer supplied from the burner 11. For example, a large amount of unburned ammonia may be generated in the first-stage combustion. Therefore, in this case, combustion in the first-stage combustion is promoted, and the amount of unburned ammonia can be reduced.

[0063] The control device 90 may adjust the flow rate of the exhaust gas Ex depending on the position of the burner 11. For example, the control device 90 may control the multiple dampers D1 so that the flow rate of the exhaust gas Ex supplied to the lower burners 11 is lower than the flow rate of the exhaust gas Ex supplied to the upper burners 11, i.e., so that the oxygen concentration in the lower burners 11 is higher than the oxygen concentration in the upper burners 11. When the oxygen concentration in the lower burners 11 is high, the NOx concentration is reduced. This is because the residence time from the lower burners 11 to the airport 31 is longer, and as a result, the generated NOx is more easily reduced compared to the upper burners 11. For example, as described above, in the present embodiment, the burner group 10 includes multiple burners 11 arranged in three stages. Therefore, for example, the control device 90 may control the multiple dampers D1 so that the flow rate of the exhaust gas Ex supplied to the lower-stage burner 11 is lower than the flow rate of the exhaust gas Ex supplied to the middle-stage burner 11, and so that the flow rate of the exhaust gas Ex supplied to the middle-stage burner 11 is lower than the flow rate of the exhaust gas Ex supplied to the upper-stage burner 11.

[0064] Furthermore, in this embodiment, the exhaust gas Ex supplied to the burner 11 and the airport 31 is heated in the heat exchanger 5. Generally, ammonia is difficult to combust. Therefore, when the exhaust gas Ex is added to the oxidizer, the concentration of oxygen in the oxidizer decreases, and there is a possibility that the ammonia will not burn sufficiently. However, as described above, in this embodiment, the exhaust gas Ex is heated in the heat exchanger 5. Therefore, the ammonia supplied to the burner 11 is heated by the oxidizer. When the ammonia is heated, the combustibility of the ammonia is improved. Therefore, the combustibility of the ammonia in the burner 11 is improved.

[0065] Figure 4 is a graph showing the relationship between the exhaust gas recirculation rate and NOx, with regard to the effect of exhaust gas recirculation on NOx. Exhaust gas recirculation reduces the oxygen concentration in the combustion air supplied from the burner and OAP (Over Air Port), lowering the flame temperature. This makes it possible to suppress the generation of NOx (thermal NOx) generated from nitrogen in the air.

[0066] In particular, the proportion of thermal NOx in NOx generation is large for fuels with low N content. Therefore, as shown in Figure 4, for fuels with low N content, the NOx reduction effect becomes greater when the exhaust gas recirculation rate is increased, i.e., when the oxygen concentration in the combustion air is reduced. For this reason, it is generally known that exhaust gas recirculation is effective in reducing NOx in gas fuels and heavy oil fuels. In the present invention, ammonia in a gaseous state is injected from the burner, but by reducing the oxygen concentration, it is possible to reduce thermal NOx generated during ammonia combustion.

[0067] From the above viewpoint, when the burner 11 is an ammonia-fired burner, for example, the control device 90 may store predetermined lower and upper limit values ​​of the oxygen concentration corresponding to the predetermined lower and upper limit values ​​of the air ratio. The control device 90 may control the valve V1, the valve V2, and the damper D1 of the burner 11 to adjust the flow rate of the fuel (ammonia) F, the flow rate of the air A, and the flow rate of the exhaust gas Ex so that the oxygen concentration is maintained within a range between the lower and upper limit values ​​of the oxygen concentration.

[0068] As described above, the combustion system 100 according to this embodiment includes the burner 11 that supplies the ammonia-containing fuel F and the oxidizer to the combustion space S, the air port 31 that is disposed downstream of the burner 11 in the combustion space S and supplies the oxidizer to the combustion space S, and the recirculation conduit R that supplies the exhaust gas Ex from the combustion space S to at least one of the burner 11 and the air port 31. With this configuration, the oxygen concentration in the oxidizer can be reduced in at least one of the first-stage combustion and the second-stage combustion. This allows the combustion temperature to be lowered, thereby reducing NOx emissions.

[0069] The combustion system 100 also includes a first sensor Se1 that measures the NOx concentration in the exhaust gas Ex from the combustion space S, an exhaust gas adjuster (fan 4, damper D1, and damper D2) that adjusts the flow rate of the exhaust gas Ex flowing through the recirculation conduit R, and a control device 90 that is communicatively connected to the first sensor Se1 and the exhaust gas adjuster. The control device 90 controls the exhaust gas adjuster based on the NOx concentration from the first sensor Se1 to adjust the flow rate of the exhaust gas Ex flowing through the recirculation conduit R. With this configuration, the flow rate of the exhaust gas Ex can be adjusted so that the NOx concentration falls within a desired range.

[0070] Furthermore, in the combustion system 100, the recirculation conduit R includes a first recirculation conduit R1 that supplies the exhaust gas Ex to the burner 11 and a second recirculation conduit R2 that supplies the exhaust gas Ex to the air port 31, the exhaust gas adjuster includes a damper D1 that adjusts the flow rate of the exhaust gas Ex flowing through the first recirculation conduit R1 and a damper D2 that adjusts the flow rate of the exhaust gas Ex flowing through the second recirculation conduit R2, and the control device 90 controls at least one of the dampers D1 and D2 based on the NOx concentration from the first sensor Se1 to adjust the ratio between the flow rate of the exhaust gas Ex flowing through the first recirculation conduit R1 and the flow rate of the exhaust gas Ex flowing through the second recirculation conduit R2. With this configuration, when exhaust gas Ex is supplied to both the burner 11 and the airport 31, the ratio of the flow rate of the exhaust gas Ex supplied to the burner 11 and the flow rate of the exhaust gas Ex supplied to the airport 31 can be adjusted so that the NOx concentration falls within the intended range.

[0071] The combustion system 100 also includes a second sensor Se2 that measures the ammonia concentration in the exhaust gas Ex from the combustion space S, and the control device 90 is communicatively connected to the second sensor Se2. Based on the ammonia concentration from the second sensor Se2, the control device 90 controls the exhaust gas adjuster to adjust the flow rate of the exhaust gas Ex flowing through the recirculation conduit R. With this configuration, it is possible to reduce ammonia (e.g., unburned ammonia) in the exhaust gas Ex.

[0072] Furthermore, in the combustion system 100, the control device 90 controls at least one of the dampers D1 and D2 based on the ammonia concentration from the second sensor Se2 to adjust the ratio between the flow rate of the exhaust gas Ex flowing through the first recirculation conduit R1 and the flow rate of the exhaust gas Ex flowing through the second recirculation conduit R2. With this configuration, when the exhaust gas Ex is supplied to both the burner 11 and the airport 31, it is possible to adjust the ratio between the flow rate of the exhaust gas Ex supplied to the burner 11 and the flow rate of the exhaust gas Ex supplied to the airport 31 so as to reduce the ammonia concentration in the exhaust gas Ex.

[0073] Furthermore, in the combustion system 100, at least one burner 11 includes multiple stages of burners 11 arranged along the vertical direction, and the flow rate of the exhaust gas Ex supplied to the upper stage burners 11 is higher than the flow rate of the exhaust gas Ex supplied to the lower stage burners 11. With this configuration, the oxygen concentration in the lower stage burners 11 is higher than the oxygen concentration in the upper stage burners 11. As described above, when the oxygen concentration in the lower stage burners 11 is high, the NOx concentration is reduced. Therefore, with the above configuration, the NOx concentration can be reduced.

[0074] The combustion system 100 also includes a heat exchanger 5 that heats the exhaust gas Ex from the combustion space S, and the recirculation conduit R supplies the exhaust gas Ex heated by the heat exchanger 5 to at least one of the burner 11 and the air port 31. With this configuration, the ammonia is heated by the oxidizer containing the heated exhaust gas Ex. When the ammonia is heated, the combustibility of the ammonia is improved. Therefore, the combustibility of the ammonia in the burner 11 is improved.

[0075] Next, other embodiments will be described.

[0076] 5 is a schematic diagram of a combustion system 100A according to a second embodiment. The combustion system 100A differs from the combustion system 100 according to the first embodiment in that some of the burners 11 are used as second burners 21 that inject a second fuel F2, which is more flammable than ammonia, into the combustion space S. For example, in the combustion system 100A, the burner 11 used as the second burner 21 is fluidly connected to a tank (second fuel supply source) 6 that stores the second fuel F2, instead of the tank 3 that stores ammonia. In other embodiments, for example, the burner 11 used as the second burner 21 may be fluidly connected to both the tank 3 and the tank 6, and may selectively switch between the fuel F and the second fuel F2. The combustion system 100A may otherwise be the same as the combustion system 100.

[0077] In this embodiment, the upper burners 11 are used as the second burners 21. In other embodiments, burners 11 at other positions may be used as the second burners 21.

[0078] For example, the second burner 21 is connected to the tank 6 by a second fuel conduit L4. The second fuel supply source is not limited to the tank 6.

[0079] 2 , a valve V5 is provided in the second fuel conduit L4. The valve V5 functions as a second fuel adjuster that adjusts the flow rate of the second fuel F2 flowing through the second fuel conduit L4. The valve V5 is communicably connected to the control device 90 via wire or wirelessly, and is controlled by the control device 90. For example, the control device 90 may adjust the flow rate of the second fuel F2 injected from each second burner 21 by controlling the opening degree of the valve V5.

[0080] For example, in the present embodiment, the second fuel F2 may be a fuel including a fossil fuel such as natural gas. The second fuel F2 is not limited thereto. For example, in other embodiments, the second fuel F2 may be a fuel including hydrogen.

[0081] The second burner 21 injects a second fuel F2 containing a fossil fuel into the combustion space S. For example, the combustion speed of a fossil fuel such as natural gas is faster than the combustion speed of ammonia. Therefore, the combustibility in the combustion space S is improved.

[0082] The combustion system 100A as described above has the same effects as the combustion system 100 according to the first embodiment. In particular, the combustion system 100A includes at least one second burner 21 that injects a second fuel F2, which is more flammable than ammonia, into the combustion space S. Therefore, combustibility in the combustion space S is improved.

[0083] Next, still another embodiment will be described.

[0084] 6 is a schematic diagram of a combustion system 100B according to the third embodiment. The combustion system 100B differs from the combustion system 100 according to the first embodiment in that the burner 11 injects a fuel F containing ammonia and a third fuel F3 that is more flammable than ammonia into the combustion space S. The other configurations of the combustion system 100B may be the same as those of the combustion system 100.

[0085] For example, in the present embodiment, the third fuel F3 may be a fuel containing hydrogen. The third fuel F3 is not limited thereto. For example, in other embodiments, the third fuel F3 may be a fuel containing a fossil fuel.

[0086] For example, in this embodiment, the combustion system 100B includes a cracking device (third fuel supply source) 7. Each burner 11 is in fluid communication with the cracking device 7 and receives a third fuel F3 from the cracking device 7. For example, in this embodiment, a third fuel conduit L5 is connected in parallel to the fuel conduit L1 at a position upstream of the point where the fuel conduit L1 branches toward the multiple burners 11. The cracking device 7 is provided in the third fuel conduit L5. The connection of the cracking device 7 to the burners 11 is not limited to this.

[0087] The cracker 7 receives a portion of the ammonia flowing through the fuel conduit L1 via a third fuel conduit L5. The cracker 7 decomposes the ammonia into hydrogen and nitrogen. The cracker 7 includes a catalyst that decomposes the ammonia into hydrogen and nitrogen. Such a catalyst includes, for example, at least one of Ru, Rh, Pt, and Pd. The cracker 7 returns a third fuel F3 containing hydrogen and nitrogen to the fuel conduit L1 via the third fuel conduit L5. In another embodiment, a tank that stores hydrogen may be used as the third fuel supply source.

[0088] A valve V6 is provided in the third fuel conduit L5. The valve V6 functions as a third fuel adjuster that adjusts the flow rate of ammonia flowing from the fuel conduit L1 to the cracking device 7, i.e., the flow rate of the third fuel F3 supplied from the cracking device 7 to the burner 11. The valve V6 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 ammonia flowing from the fuel conduit L1 to the cracking device 7, i.e., the flow rate of the third fuel F3 supplied from the cracking device 7 to the burner 11, by controlling the opening degree of the valve V6.

[0089] Each burner 11 injects a fuel F containing ammonia and a third fuel F3 containing hydrogen into the combustion space S. The combustion speed of hydrogen is faster than the combustion speed of ammonia, so the combustibility in each burner 11 is improved.

[0090] The combustion system 100B as described above has the same effects as the combustion system 100 according to the first embodiment. In particular, in the combustion system 100B, the burner 11 injects ammonia and a third fuel F3 that is more flammable than ammonia into the combustion space S. Therefore, the combustibility in the burner 11 is improved.

[0091] 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.

[0092] For example, in the above embodiment, the recirculation conduit R includes both the first recirculation conduit R1 and the second recirculation conduit R2. That is, in the above embodiment, the recirculation conduit R is configured to be able to supply the exhaust gas Ex to both the burner 11 and the airport 31. In other embodiments, the recirculation conduit R may include only one of the first recirculation conduit R1 and the second recirculation conduit R2. That is, in other embodiments, the recirculation conduit R may be configured to supply the exhaust gas Ex to only one of the burner 11 and the airport 31.

[0093] The present disclosure provides ２ It can promote the use of ammonia, which leads to reduced emissions, thereby contributing, for example, to Sustainable Development Goal (SDG) 7 "Ensure access to affordable, reliable, sustainable and modern energy" and SDG 13 "Take urgent action to combat climate change and its impacts".

[0094] 4 Fan (exhaust gas adjuster) 5 Heat exchanger 11 Burner (first burner) 21 Second burner 31 Airport 90 Control device 100 Combustion system 100A Combustion system 100B Combustion system D1 Damper (exhaust gas adjuster, first exhaust gas adjuster) D2 Damper (exhaust gas adjuster, second exhaust gas adjuster) Ex Exhaust gas F Fuel (ammonia) F2 Second fuel F3 Third fuel R Recirculation conduit R1 First recirculation conduit R2 Second recirculation conduit S Combustion space Se1 First sensor Se2 Second sensor

Claims

1. A combustion system comprising: at least one first burner that supplies a fuel including ammonia and an oxidizer to a combustion space; at least one air port that is disposed in the combustion space downstream of the at least one first burner and that supplies an oxidizer to the combustion space; and a recirculation conduit that supplies exhaust gas from the combustion space to at least one of the at least one first burner and the at least one air port.

2. The combustion system of claim 1, comprising: a first sensor that measures the NOx concentration in the exhaust gas from the combustion space; an exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the recirculation conduit; and a control device that is communicatively connected to the first sensor and the exhaust gas adjuster, and that controls the exhaust gas adjuster based on the NOx concentration from the first sensor to adjust the flow rate of the exhaust gas flowing through the recirculation conduit.

3. The combustion system according to claim 2, wherein the recirculation conduit includes: a first recirculation conduit that supplies the exhaust gas to the at least one first burner; and a second recirculation conduit that supplies the exhaust gas to the at least one air port; the exhaust gas adjuster includes: a first exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the first recirculation conduit; and a second exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the second recirculation conduit; and the control device controls at least one of the first exhaust gas adjuster and the second exhaust gas adjuster based on the NOx concentration from the first sensor to adjust the ratio between the flow rate of the exhaust gas flowing through the first recirculation conduit and the flow rate of the exhaust gas flowing through the second recirculation conduit.

4. The combustion system according to claim 1, comprising: a second sensor that measures an ammonia concentration in the exhaust gas from the combustion space; an exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the recirculation conduit; and a control device that is communicatively connected to the second sensor and the exhaust gas adjuster, and that controls the exhaust gas adjuster based on the ammonia concentration from the second sensor to adjust the flow rate of the exhaust gas flowing through the recirculation conduit.

5. The combustion system according to claim 4, wherein the recirculation conduit includes: a first recirculation conduit that supplies the exhaust gas to the at least one first burner; and a second recirculation conduit that supplies the exhaust gas to the at least one air port; the exhaust gas adjuster includes: a first exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the first recirculation conduit; and a second exhaust gas adjuster that adjusts the flow rate of the exhaust gas flowing through the second recirculation conduit; and the control device controls at least one of the first exhaust gas adjuster and the second exhaust gas adjuster based on the ammonia concentration from the second sensor to adjust the ratio between the flow rate of the exhaust gas flowing through the first recirculation conduit and the flow rate of the exhaust gas flowing through the second recirculation conduit.

6. The combustion system according to claim 1, wherein the at least one first burner includes first burners in multiple stages arranged along a vertical direction, and the flow rate of the exhaust gas supplied to a first burner in a lower stage among the first burners in the multiple stages is lower than the flow rate of the exhaust gas supplied to a first burner in an upper stage among the first burners in the multiple stages.

7. The combustion system according to claim 1, wherein the combustion system comprises a heat exchanger that heats exhaust gas from the combustion space, and the recirculation conduit supplies the exhaust gas heated by the heat exchanger to at least one of the at least one first burner and the at least one air port.

8. The combustion system according to claim 1, comprising at least one second burner for injecting a second fuel into the combustion space, the second fuel being more combustible than ammonia.

9. The combustion system of claim 1, wherein the at least one first burner injects ammonia and a third fuel that is more combustible than ammonia into the combustion space.

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