Marine boiler with injectors for sncr agent

Abstract

A marine boiler (100) is disclosed comprising a burner (110) configured to burn an amino fuel to generate a flame and a furnace (120) configured to be heated by the flame. The furnace comprises a burner inlet (112) allowing the burner to release the flame into an inlet region (10) of the furnace, an exhaust outlet (114) allowing combustion gases to be exhausted from an outlet region (20) of the furnace and an injector outlet (116) for introducing a selective non-catalytic reduction (SNCR) agent into the outlet region to reduce the level of nitrogen oxides in the combustion gases. The injector outlet is arranged to introduce the SNCR agent in an outer peripheral portion of the interior of the furnace. A method for reducing the level of nitrogen oxides in the combustion gases of a marine boiler is also disclosed.

Description

Technical Field

[0001] This invention relates to marine boilers, and more particularly to techniques for reducing nitrogen oxide (NOx) emissions from such boilers. Background Technology

[0002] Marine boilers routinely use carbon-based fuels to generate the heat necessary for steam production. While efficient in generating the required heat, the use of these carbon-based fuels is under increasing scrutiny due to their contribution to carbon dioxide emissions and global warming.

[0003] To mitigate environmental impacts, a shift towards ammonia fuels has been proposed. Ammonia is a promising alternative because it contains no carbon, which helps eliminate carbon dioxide emissions during combustion. However, this shift presents new environmental challenges in terms of increased levels of nitrogen oxides (NOx) in exhaust gases. NOx emissions cause air pollution, which is harmful to the environment and poses a threat to human health.

[0004] Therefore, there is a need for an improved technology to effectively reduce NOx emissions from marine boilers operating on ammonia fuels. Summary of the Invention

[0005] The objective of this disclosure is to provide a technique that addresses at least some of the concerns mentioned above.

[0006] According to a first aspect of the invention, a marine boiler is provided. The marine boiler includes: a burner configured to burn an amino fuel to generate a flame; and a stove configured to be heated by the flame to transfer heat to a heat medium in thermal contact with the stove. The stove includes: a burner inlet that allows the burner to release a flame into an inlet region of the stove; and an exhaust outlet that allows combustion gases to exit from an outlet region of the stove. Furthermore, an injector outlet is provided for introducing a selective non-catalytic reduction (SNCR) agent into the outlet region to reduce the level of nitrogen oxides in the combustion gases. The injector outlet is arranged to introduce the SNCR agent into an outer peripheral portion inside the stove.

[0007] According to a second aspect, a method for reducing the level of nitrogen oxides in combustion gases of a marine boiler is provided. The method includes burning an ammonia fuel to generate a flame, and directing the flame into a furnace of the boiler, wherein the furnace includes an inlet zone and an outlet zone, the flame being released into the inlet zone, and the outlet zone including an outlet for discharging combustion gases from the furnace. Furthermore, the method includes injecting a selective non-catalytic reduction (SNCR) agent into the outlet zone from an outer peripheral portion inside the furnace to reduce the level of nitrogen oxides in the combustion gases.

[0008] Conventionally, selective catalytic reduction (SCR) is used to reduce NOx emissions. In SCR, an SCR agent (such as ammonia or urea) is injected into the exhaust gas before it passes through the catalyst bed, promoting a chemical reaction that converts NOx into nitrogen and water vapor. SCR units are typically installed downstream of the boiler exhaust outlet and require additional infrastructure, such as SCR agent storage and handling systems, and space for the catalyst. Space requirements can be challenging, especially in marine applications where available space is often limited. To address the increased NOx levels generated when boilers operate on ammonia fuels, the inventors propose using an SNCR process to reduce NOx levels in the combustion gas before it reaches the SCR unit. By pre-treating the combustion gas to reduce NOx levels, the SCR unit can be omitted, or a less powerful or smaller SCR unit can be sufficient to handle the remaining NOx.

[0009] SNCR processes are typically effective only within a specific temperature range, which is relatively high compared to the temperature range in which the catalytically assisted SCR unit operates. The inventors recognized that boilers can be operated in such a way that it is possible to utilize the temperature gradient inside the furnace to achieve the appropriate temperature conditions for a highly efficient SNCR process. When burning ammonia fuels, a flame with a temperature of approximately 1500-1800°C can be obtained in the furnace inlet zone. Due to thermal radiation from the flame to the furnace interior through the heat transfer medium, the temperature of the combustion gases is observed to decrease relatively rapidly as the combustion gases move toward the exhaust outlet, resulting in a temperature of approximately 1100°C or lower in the furnace outlet zone. By injecting an SNCR agent in this zone, a relatively efficient SNCR process can be achieved to reduce the NOx content in the combustion gases as they travel toward the exhaust outlet and any downstream exhaust pipe systems.

[0010] Furthermore, injecting the SNCR agent into the furnace makes it possible to utilize any swirl or recirculation zone within the furnace to achieve improved mixing with the combustion gases, and it is possible to retain the mixture in the outlet zone for a sufficiently long period of time to allow the SNCR process to occur before the combustion gases exit through the exhaust outlet. Therefore, the injection of the selective non-catalytic reduction (SNCR) agent occurs downstream of the combustion zone.

[0011] SNCR processes are typically exothermic, in which heat is released into the combustion gases within the furnace. This can be advantageous over techniques where heat is released downstream of the furnace, as the furnace can operate with higher thermal efficiency and thus releases more heat before the combustion gases reach the downstream exhaust system.

[0012] By introducing the SNCR agent into the outer periphery of the furnace interior, the injector structure (whose outlet can form part of it) is less exposed to heat and therefore lasts longer before it needs replacement. Furthermore, the placement of the injector outlet allows the SNCR agent to be introduced in a way that promotes mixing, as an upward-moving recirculation zone that can exist on the furnace interior wall prevents the SNCR agent from being drawn into the flame and consumed by it.

[0013] In some examples, the SNCR agent includes ammonia, which is preferably anhydrous ammonia (i.e., pure ammonia not dissolved in water), ammonia with negligible water content, or ammonia dissolved in water (such as, for example, urea). The absence of water reduces the reaction time of the SNCR process because otherwise time would be spent waiting for water to evaporate before the reaction can occur. Generally, reducing the reaction time is desirable because it increases the likelihood that the combustion gases will remain in the appropriate temperature range long enough for the SNCR process to take place. Excessively long reaction times risk leading to inefficient or incomplete SNCR processes.

[0014] Therefore, it is advantageous to use SNCR agents that are injected in the gas phase, as there is no need to spend time on the phase transition from the liquid phase to the gas phase. In the same way, it is desirable to use SNCR agents with the lowest possible water content, such as anhydrous ammonia discussed above.

[0015] In some examples, the SNCR agent can be the same as the ammonia fuel. In other words, the ammonia fuel can be used both as a fuel for the burner and as an SNCR agent. This allows for infrastructure simplification, as separate storage and processing systems for both fuel and SNCR agent are not required. Alternatively, the fact that the SNCR agent is readily available as a fuel can be used.

[0016] In the example, the injector outlet is arranged to introduce SNCR agent into the recirculation zone of the stove. The recirculation zone, also known as the swirling zone, can be understood as a zone in the stove where the combustion gas flow does not move directly from the inlet zone to the outlet. Alternatively, the combustion gases can be recirculated back towards the flame to another part of the stove. In other words, the combustion gas flow can be swirled in the recirculation zone, thereby allowing for improved mixing of the SNCR agent with the combustion gases. Advantageously, the injector outlet can be arranged to introduce SNCR agent into the portion of the recirculation zone where the combustion gas flow moves away from the flame, thereby preventing the SNCR agent from being drawn into the flame and consumed by it. The location and nature of the recirculation zone can be determined by the geometry of the stove, the relative position and configuration of the burner inlet and outlet, and the orientation of the flame and the fuel flow supplied to the flame. Several examples shown will be discussed in the detailed description.

[0017] The injector outlet can be arranged to introduce the SNCR agent in a direction substantially normal to the inner wall of the furnace. Therefore, the SNCR agent can be injected radially with reference to the circumference of the furnace. In other examples, the injector outlet can be arranged to introduce the SNCR agent in a direction substantially tangential to the inner wall (or in other words, circumferentially along the furnace wall). The direction in which the SNCR agent is injected into the furnace can vary depending on the furnace configuration and the temperature distribution / gradient within the furnace. Due to heat transfer to the water, the temperature within the furnace tends to be lower closer to the furnace wall. If the temperature at the center of the furnace is too high for the SNCR reaction, it is advantageous to inject the SNCR agent circumferentially along the wall (where the temperature may be lower). If the temperature at the furnace wall is too low for the SNCR reaction, it is advantageous to inject the SNCR agent radially toward the center of the furnace (where the temperature may be higher). In yet another example, the injector outlet can be substantially flush with the inner wall, so that the injector structure is less exposed to the heat generated by the flame and the passing combustion gas flow.

[0018] The burner can be configured to direct the flame in a direction away from the exhaust outlet. In the case of a vertical boiler where the outlet zone is arranged above the inlet zone and the exhaust outlet is arranged at the top of the furnace, this means that the flame can be directed downwards towards the bottom of the furnace. By directing the flame towards the bottom of the furnace, better utilization of the furnace (e.g., more efficient combustion) can be achieved.

[0019] The boiler may include a discharge pipe system fluidly connected to a discharge outlet to direct combustion gases away from the furnace. At least a portion of the discharge pipe system, disposed downstream of the discharge outlet, may be referred to as the convective section of the boiler, and includes heat transfer devices for transferring heat from the combustion gases to a heat medium (such as water) and for cooling the combustion gases before they are discharged from the boiler. The discharge pipe system may include boiler tubes or tube bundles, which are at least partially wrapped with or otherwise in thermal contact with the heat medium.

[0020] In some examples, the exhaust system includes an SCR cleaning arrangement or SCR unit for further reducing the NOx level in the combustion gases after they are exhausted from the stove. The SCR unit can therefore be located downstream of the stove and configured to treat at least some of the NOx remaining after the SNCR process. It will be understood that the NOx level reaching the SCR cleaning arrangement can be relatively low due to the upstream SNCR process, and a relatively small and compact SCR cleaning arrangement can be used. This is particularly advantageous in marine applications where space is typically limited.

[0021] Additional emission reduction components can be provided to further clean the combustion gases. In the example, an oxidation catalyst can be positioned downstream of the SCR cleaning arrangement to remove residual ammonia from the combustion gases.

[0022] In some examples, a gas analyzer or sensor arrangement may be provided to generate sensor signals indicating the characteristics of the combustion gases, such as the level of residual nitrogen oxides in the combustion gases after the SNCR process and (if applicable) after the SCR process. The sensor arrangement may be positioned in the exhaust pipe system at a location that allows the sensor arrangement to measure the NOx level in the combustion gases leaving the outlet zone of the furnace. The sensor signals can be used as control signals or feedback for controlling boiler operation. For example, the sensor signals can be used to control the injection of SNCR into the outlet zone or to control the operation of the burner. If the sensor signals and therefore the NOx level indicate that the SNCR process is not working as efficiently as expected, the burner may be operated to adjust the temperature in the outlet zone and / or cause the injector to adjust the amount of SNCR agent supplied to the outlet zone. The controller may be configured to control the SNCR process such that at least 50% (such as 90% or even 95%) of the NOx content is removed.

[0023] In some examples, a temperature sensor may be provided, configured to measure the temperature in the outlet zone. The temperature can be used by a controller to control boiler operation to maintain the temperature in the outlet zone within a range suitable for SNCR processes, which may be between 700 and 1100°C. The temperature in the outlet zone can be adjusted, for example, by causing the burner to adjust the flame temperature or intensity or by changing the heat transfer efficiency with the heat medium. The latter can be achieved, for example, by increasing the heat medium flow (which allows more heat to be removed by the heat medium) or by decreasing the temperature of the heat medium supplied to the boiler.

[0024] Ammonia fuels can be liquid or gaseous fuels, which include ammonia. The amount of ammonia included in the ammonia fuel may depend on the type of boiler in which the gaseous ammonia fuel will be burned. Ammonia can be stored as liquefied ammonia, which occupies less space than gaseous ammonia and thus requires less storage space. Ammonia can then be converted to a gaseous phase and mixed with oxygen or air before ignition in the burner.

[0025] SNCR agents are broadly understood as chemical substances capable of chemically reducing NOx to nitrogen and water vapor. SNCR agents can be injected into the furnace in either the gas or liquid phase. Typically, SNCR agents include ammonia, which can be provided in anhydrous form or mixed with water.

[0026] The boiler according to this disclosure is preferably configured to be arranged on a marine vessel (such as a ship). The terms "marine boiler" and "boiler" are therefore used interchangeably throughout this disclosure. However, it should be noted that the boiler is not limited to use on ships. It is also possible to use the boiler in other marine applications (such as platforms) or land-based applications.

[0027] The medium to be heated, also known as the heat medium, can be any suitable medium, such as water. The medium may undergo a partial or complete phase change or a partial or complete phase change during its passage through the boiler, such as from a liquid phase to a gaseous phase. For example, the boiler may include: a medium inlet arranged to receive a medium that is at least partially in the liquid phase (e.g., in the form of liquid water); and a medium outlet arranged to discharge a medium that is at least partially in the gaseous phase (e.g., in the form of steam).

[0028] Heat can be transferred to the heat medium via the walls of the furnace and / or by means of a heat exchanger system. Examples of such heat exchanger systems include one or more pipes or conduits through which the heat medium is separated from the combustion gases. In one example, the heat medium is transferred through pipes that are subsequently exposed to the heat of the combustion gases. In another example, the combustion gases are transferred through pipes that are subsequently exposed to the heat medium.

[0029] Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only with reference to the accompanying drawings. Attached Figure Description

[0030] Various aspects and examples of this disclosure will be readily understood from the embodiments discussed in the following detailed description and accompanying drawings, in which: Figure 1 The diagram shows a vertical cross-section of a boiler, including stoves and burners, based on some examples.

[0031] Figure 2a The horizontal cross-section of an oven is shown based on some examples.

[0032] Figure 2b A perspective view of an injector structure for injecting SNCR agent into a furnace, based on some examples, is shown.

[0033] Figure 3 These are schematic diagrams based on some examples of boiler and exhaust pipe systems.

[0034] Figure 4 This is a flowchart outlining methods for reducing NOx levels emitted from boilers, based on some examples. Detailed Implementation

[0035] Figure 1This is a schematic cross-section of a boiler 100 based on some examples. The boiler 100 includes a burner 110 and a furnace 120, wherein the furnace 120 is configured to be heated by a flame F generated by the burner 110 and directed into the interior of the furnace 120 via a burner inlet 112. The heat generated by the flame F can be transferred to a heat medium, such as liquid water 130, which is in thermal contact with the furnace 120. In this example, the water 130 at least partially surrounds the furnace 120. Depending on the application and specific configuration of the boiler 100, the boiler 100 can be operated to generate hot water or steam 132.

[0036] The heating flame F is guided into the interior of the furnace 120 via the burner inlet 112, while the combustion gases produced by the combustion process that generates the flame F can exit the furnace 120 via the exhaust outlet 114. In this example, the combustion gases can be conveyed from the exhaust outlet 114 by passing them through an exhaust pipe bundle 152 (which carries water 130) for further heat transfer / cooling of the combustion gases; these combustion gases may also be referred to as flue gas or exhaust gas. The pipe bundle 152 may form part of the exhaust pipe system 150, which will be referred to as... Figure 3 Let's discuss this in more detail.

[0037] The interior of the furnace 120 can be divided into an inlet zone 10 and an outlet zone 20, into which the flame F, or at least a portion thereof, can be released, and where combustion gases can be discharged from the furnace 120 via an exhaust outlet 114 from the outlet zone 20. Therefore, the outlet zone 20 can be arranged close to the exhaust outlet 114, which is located at the top of the furnace 120 in the vertically oriented boiler 100 shown in this example, while the inlet zone 10 can be arranged below the outlet zone 20, closer to the burner inlet 112 and the bottom of the furnace 120. During operation, a temperature gradient caused by the combustion gases can be observed in the furnace 120, which release their heat to the surrounding water 130 and thus gradually cool as they move toward the exhaust outlet 114. As a result, the temperature in the outlet zone 20 of the furnace may be lower than the temperature in the inlet zone 10.

[0038] Burner 110 is configured to burn ammonia fuel to generate flame F. The fuel can be supplied in the form of liquid or gaseous ammonia (which can be mixed with an oxidizer such as air or oxygen to enable combustion). While ammonia is a potentially carbon-free fuel that can help eliminate carbon dioxide emissions during combustion, it can lead to an increase in nitrogen oxide (NOx) levels in the exhaust gases. Therefore, a selective non-catalytic reduction (SNCR) process can be employed, which involves injecting an SNCR agent into the outlet zone 20 to reduce NOx levels in the flue gas.

[0039] The SNCR process involves a chemical redox reaction in which nitrogen oxides, ammonia provided by the SNCR agent, and oxygen are converted into molecular nitrogen and water, as described by the following illustrative and simplified equation: 4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O .

[0040] The reaction typically requires sufficient reaction time within a certain temperature range to be effective. Therefore, both temperature and time windows must be considered when designing and operating the boiler 100. An additional layer of complexity is mixing, as NOx needs to encounter sufficient ammonia within both the temperature and time windows for the SNCR process to occur.

[0041] exist Figure 1 In the ammonia-fueled boiler 100 shown, the flame F typically has a temperature of approximately 1500-1800°C, which is too high to guarantee an efficient SNCR process. Due to thermal radiation that causes heat transfer to the interior of the furnace 120 surrounding the water 130, the temperature of the combustion gas or flue gas can drop relatively rapidly to approximately 700-1100°C in the outlet zone 20. By injecting the SNCR agent in this zone 20, the temperature gradient inside the furnace 120 can be used to achieve a relatively efficient SNCR process, thereby reducing the NOx content in the combustion gas as it travels toward the exhaust outlet 114.

[0042] The SNCR agent can be injected into the outlet region 20 via one or more injector outlets 116, each of which forms an opening allowing the SNCR agent to pass into the stove 120. The injector outlets 116 may form part of an injector structure 140 including a tube or conduit arranged to deliver the SNCR agent to the stove 120, wherein the injector outlets 116 may form a nozzle and / or a portion of the outlet region 20 for releasing the SNCR agent in a certain direction. In this example, the nozzle 116 is arranged to introduce the SNCR agent into the outer peripheral portion of the interior of the stove 120. The following is in conjunction with... Figure 2a and Figure 2b A specific and more detailed example of injector outlet 116 is discussed.

[0043] The position and orientation of nozzle 116 can be determined not only by the temperature of the combustion gases but also by the flow pattern of the combustion gases as they move within the furnace 120. Advantageously, the SNCR agent can be injected into the outlet zone 20, where the combustion gases are recirculated or swirled before exiting through the exhaust outlet 114. This recirculated or swirling flow promotes mixing of the SNCR agent with the combustion gases and increases the time during which the combustion gases are exposed to the SNCR agent in the outlet zone 20.

[0044] The furnace 120 typically includes multiple recirculation zones in which the combustion gas flow rotates or recirculates toward the flame F. The size and shape of the recirculation zones may depend on the design of the burner 110 and the furnace 120, as well as the operating conditions of the boiler 100. In this example, where the flame F is slightly downward and the exhaust outlet 114 is arranged at the top of the furnace 120, several recirculation zones can be formed in the upper portion of the furnace 120, which may have suitable temperatures for SNCR reactions to occur. However, it is proposed to inject the SNCR agent in the portion of the recirculation zone exhibiting an upward flow near the wall, because a downward flow would risk drawing the SNCR agent into the flame (where it would burn instead of participating in the SNCR reaction). Therefore, by arranging the injection point in the portion of the furnace wall where the flow tends to move away from the flame, the mixing between the SNCR agent and the combustion gas can be enhanced, and a more efficient SNCR process can be obtained.

[0045] In this example, where the flame F is directed downwards and the outlet 114 is arranged at the top of the stove 120, such an upward flow of combustion gases is observed in the outlet region 20 at the wall above the burner inlet 112 and at the wall on the lateral side of the flame F, while a downward flow is observed along the wall opposite to the burner inlet 112. Therefore, in this example, one or more injector outlets 116 may be arranged in the outlet region 20 along any portion of the stove wall except for the portion opposite to the burner inlet 112. Advantageously, the injector outlets 116 are arranged to introduce the SNCR agent in the circumferential direction of the wall to promote the diffusion and mixing of the SNCR agent within the stove 120.

[0046] However, it will be understood that the above is merely an example of an exemplary configuration, and other boiler designs may exhibit other flow patterns that affect the location of the injection points in the outlet zone 20.

[0047] In this example, liquid or gaseous ammonia can be used both as fuel for burner 110 and as an SNCR agent (and, if applicable, for any downstream SCR cleaning arrangement). Using ammonia instead of, for example, urea or another ammonia / water solution can advantageously reduce reaction time, as water might otherwise need to evaporate before the SNCR reaction can occur. By eliminating or at least reducing the amount of water injected into outlet zone 20, the necessary duration of the SNCR reaction can be reduced.

[0048] Figure 2a It is a cross-section taken through the outlet area 20 of the furnace 120 of the boiler 100, which can be connected with... Figure 1 The boiler 100 shown is similarly configured. The cross-section shows the arrangement of the injector outlets 116, which in this example are four, arranged to introduce SNCR agent into the outer peripheral portion of the interior of the furnace 120. Each of the injector outlets 116 can form a nozzle 116 of the injector structure 140', 140'', as... Figure 2b As shown in the perspective view, nozzles 116 are arranged on a conduit 142 extending through the outer wall of the furnace 120. Each injector configuration 140 may include one or more nozzles 116 oriented to inject SNCR agent in a certain direction within the outlet zone 20. Figure 2a In this process, each injector structure 140', 140'' includes first and second nozzles 116 oriented in a circumferential direction along the furnace wall (wherein... Figure 2a The SNCR agent is injected onto the burner (indicated by the arrow). The injector structure 140' closest to the burner 110 and the burner inlet can be arranged to guide the SNCR agent away from the burner 110, while the injector structure 140'' closest to the wall portion opposite to the burner 110 can be arranged to guide the SNCR agent away from that wall portion (i.e., towards the other two injector structures 140'). As a result, the SNCR agent can be introduced into the region of the inlet region 20, where there is an upward flow of combustion gases to allow the SNCR agent to mix with the combustion gases.

[0049] As mentioned above, the injector outlet 116 may be provided in the form of a nozzle 116 extending through the wall of the stove 120 into the wall of the stove 120. The injector structure 140 may include a conduit or pipe 142 for delivering the SNCR agent from the outside of the stove 120 into the interior of the stove 120. One or more nozzles 116 may be arranged on a portion of the pipe 142 disposed on the inner side of the stove wall to allow the SNCR agent to be injected into the stove 120. Advantageously, the injector structure 140 may be arranged relatively close to the stove wall because the temperature may be lower closer to the wall than closer to the center of the stove 120. In other words, the injector structure 140 may protrude into the stove by a relatively short distance to reduce the risk of heat-induced damage to the injector structure 140. In some examples, the relatively short protrusion may be understood as a few millimeters or centimeters. In some examples, the injector outlet 116 may even be flush with the inner wall of the stove 120. In some examples, a heat transfer medium 130 (i.e., water or steam) can be used to cool the injector and thus reduce the risk of heat-induced damage.

[0050] It will be understood that the walls of the stove 120 (which may also be referred to as the circumferential walls) can have any suitable shape, and this is not necessarily limited to... Figure 2a The circular cross-section is indicated in the diagram. Circumferential walls may have elliptical, polygonal, rectangular, or other shaped cross-sections. Walls may also be of various designs, such as solid or hollow walls, and / or have uniform or non-uniform thickness.

[0051] Figure 3 This is a schematic illustration of an example boiler 100, which can be compared with the above-mentioned reference. Figure 1 The boiler 100 discussed is similarly configured. Figure 3 A discharge pipe system 150 is further shown, which is fluidly connected to a discharge outlet 114 to direct combustion gases away from the stove 120 and ultimately into the atmosphere. The discharge pipe system 150 may include one or more gas treatment components for further cleaning the combustion gases.

[0052] In this example, a selective catalytic reduction (SCR) clean arrangement 154 or an SCR unit is provided to further reduce NOx emissions from combustion gases. The SCR clean arrangement 154 is configured to add an SCR agent, such as anhydrous ammonia, ammonia water, or a urea solution, to the exhaust gas stream. The SCR agent can therefore be similar to an SNCR agent. The mixture reacts on a catalyst bed, which typically comprises various porous ceramic materials, such as titanium dioxide, supporting active catalytic components of base metals such as vanadium, molybdenum, and tungsten. The reaction typically has an optimal temperature range between 360°C and 450°C, but can be operated at lower temperatures (such as down to about 280°C) with longer residence times. Therefore, to achieve a suitable temperature for the exhaust gas, the exhaust gas can pass through a tube bundle 152, which is filled with water (e.g., Figure 1 (As shown in the diagram). When the reaction is driven toward completion, molecular nitrogen and water are produced (in the case of using ammonia) or carbon dioxide (in the case of using urea).

[0053] The exhaust system 150 may also include an oxidation catalyst 156 for removing residual ammonia from the exhaust gas. The oxidation catalyst 156 may, for example, comprise a platinum group metal, including one or more of platinum, palladium, rhodium, ruthenium, iridium, and osmium. Advantageously, platinum group metals exhibit relatively high activity for the oxidation of ammonia and relatively low activity for the oxidation of nitrogen oxides. Other possible catalysts include copper oxide, manganese oxide, and iron oxide.

[0054] A gas analyzer 158 may be added downstream of the SCR cleaning arrangement 154 to obtain information about the characteristics of the exhaust gas, including, for example, NOx, oxygen, or hydrogen levels. The gas analyzer 158 may be configured to provide real-time information about the characteristics of the exhaust gas. This information about the exhaust gas characteristics may be provided as a sensor signal, which may be used as an input to a controller (not shown) arranged to control boiler operation. In an example, the controller may use the information about the NOx level provided by the gas analyzer 158 to control the injection of SNCR agent into the furnace 120 and / or the injection of SCR agent into the SCR cleaning arrangement 154. This information about the characteristics can therefore be used as feedback in a loop controlling the operation of the boiler 100 and the cleaning of its exhaust gas. For example, the controller may be configured to increase the amount of SNCR agent injected into the outlet zone 20 of the furnace 120 in response to the NOx level in the combustion gases exceeding a predetermined threshold. In an example, the SNCR agent may be injected at a flow rate corresponding to a reduction in NOx concentration of at least 50% (such as 90% or even 95%). In another example, the controller can be configured to generate an alarm signal if it determines that the NOx level exceeds a threshold.

[0055] It will be understood that, in some examples, the controller may be configured to control the injection of SNCR agent based on predetermined values ​​(e.g., determined by a lookup table or predetermined function depending on one or more operating parameters of boiler 100).

[0056] Figure 4 This is a flowchart illustrating a method 200 for reducing NOx levels emitted from boiler 100, which can be connected to... Figure 1 , Figure 2a -b and Figure 3 Any of the boilers in the boiler 100 shown are similarly configured.

[0057] In this example, ammonia fuel can be combusted 210 to generate flame F. The ammonia fuel can be supplied to burner 110, for example, in liquid form, whereby the fuel can be atomized, mixed with air, and ignited to form flame F. Flame F can be directed 220 through burner inlet 110 into furnace 120 and further into inlet zone 10. As the combustion gases move through the interior of furnace 120 toward exhaust outlet 114, heat from flame F and the combustion gases can be transferred to the heat transfer medium 130 of boiler 100. Exhaust outlet 114 is arranged in or near the outlet zone 20 of the furnace, where the temperature of the combustion gases reaches a level suitable for a highly efficient SNCR reaction to occur. This temperature is typically between 700 and 1100°C (e.g., 760 and 1090°C). According to this method, an SNCR agent 230 is injected 230 into outlet zone 20 from the outer periphery of the interior of furnace 120 to reduce the NOx level in the combustion gases. In some examples, the temperature in outlet zone 20 can be maintained or controlled 240 within a range that allows the SNCR process to occur. This can be achieved, for example, by controlling the operation of burner 110 (and thus the heat delivered by the flame) and / or cooling of the combustion gases (e.g., by changing the flow and / or temperature of the heat medium heated by the combustion gases). In another example, a sensor signal 250 indicating the level of NOx in the combustion gases downstream of outlet zone 114 can be received 250.

[0058] As mentioned above, the operation of boiler 100 can be controlled by a controller or control unit, which can be integrated into boiler 100 or located in a separate location physically separate from boiler 100. (The last sentence appears to be incomplete and possibly refers to a different context.) Figure 3 As discussed, the controller is communicatively connected to the gas analyzer 158. The controller can be arranged to control the operation of one or more of the burner 110 (and thus flame generation), the injector structure 140 (and thus the flow rate / amount of SNCR agent added to the furnace), and the SCR cleaning arrangement 154 (and thus the amount of SCR agent injected into the SCR cleaning process).

[0059] The control unit may generally include one or more processors and one or more non-transitory computer-readable media storing first computer-executable instructions that, when executed by the one or more processors, cause the boiler 100 to perform actions. Figure 4 The diagram illustrates at least a portion of the actions described above. Generally, the control unit may include circuitry configured to implement (using one or more non-transitory computer-readable media) the functions described herein. By way of example, suitable processors for executing the instruction program include both general-purpose microprocessors and special-purpose microprocessors, as well as a single processor or one or more processors or cores of any type of computer. The processor may be supplemented or incorporated into an ASIC (Application-Specific Integrated Circuit). Those skilled in the art will understand that the exemplary embodiments described above can be implemented in any suitable software, hardware, or firmware configuration or combination thereof. Exemplary hardware platforms for implementing the exemplary embodiments may include, for example, Intel x86-based platforms with compatible operating systems, such as Windows OS; Mac platforms and MAC OS; and mobile devices with operating systems such as iOS, Android, etc. In another example, exemplary embodiments of the methods described above may be embodied as programs containing lines of code stored on a non-transitory computer-readable storage medium that can be executed on a processor or microprocessor at compile time.

[0060] Furthermore, modifications to the disclosed embodiments can be understood and implemented by those skilled in the art from a study of the figures, disclosure, and appended claims in practicing the claimed invention. In addition, preferred embodiments and examples of the invention are disclosed in the figures and description, and although specific terminology is used, it is used only in a general and descriptive sense and not for limiting purposes. The scope of the invention is set forth in the following claims, wherein the word 'comprising' does not exclude other elements or steps, and the indefinite article 'a' or 'an' does not exclude a plurality.

Claims

1. A marine boiler (100), comprising: A burner (110) configured to burn amino fuel to generate a flame; as well as A stove (120) configured to be heated by the flame to transfer heat to a heat medium (130) in thermal contact with the stove; The stove includes: A burner inlet (112) allows the burner to release the flame into the inlet area (10) of the stove. An exhaust outlet (114) allows combustion gases to escape from the outlet area (20) of the stove, and Injector outlet (116), the injector outlet (116) is used to introduce a selective non-catalytic reduction (SNCR) agent into the outlet zone to reduce the level of nitrogen oxides in the combustion gas; The injector outlet is arranged to introduce SNCR agent into the outer peripheral portion inside the furnace.

2. The marine boiler according to claim 1, wherein, The SNCR agent is the same as the amino fuel.

3. The marine boiler according to claim 1 or 2, wherein, The injector outlet is configured to spray the SNCR agent in the gas phase.

4. The marine boiler according to any one of the preceding claims, wherein, The injector outlet is arranged to introduce the SNCR agent into the recirculation zone of the furnace.

5. The marine boiler according to claim 4, wherein, The injector outlet is arranged to introduce the SNCR agent into a portion of the recirculation zone in which the combustion gas flow moves away from the flame.

6. The marine boiler according to any one of the preceding claims, wherein, The injector outlet is arranged to introduce the SNCR agent in a direction substantially normal to the inner wall of the furnace.

7. The marine boiler according to any one of claims 1-5, wherein, The injector outlet is arranged to introduce the SNCR agent in a direction substantially tangential to the inner wall of the furnace.

8. The marine boiler according to any one of the preceding claims further comprises a discharge pipe system (150), said discharge pipe system (150) being fluidly connected to the discharge outlet to guide the combustion gases away from the furnace, wherein, The exhaust pipe system includes a selective catalytic reduction (SCR) cleaning arrangement (154) for further reducing the level of nitrogen oxides in the combustion gases.

9. The marine boiler according to claim 8, wherein, The discharge pipe system also includes an oxidation catalyst (156) downstream of the SCR cleaning arrangement for removing residual ammonia from the combustion gases.

10. The marine boiler according to claim 8 or 9, wherein, The discharge pipe system includes a sensor arrangement (158) operable to generate a sensor signal indicating the level of nitrogen oxides in the combustion gas.

11. A method (200) for reducing the level of nitrogen oxides in combustion gases of a marine boiler, comprising: Flame is generated by burning (210) amino fuel; The flame is directed (220) into the furnace of the boiler, the furnace including an inlet area and an outlet area, the flame being released into the inlet area, and the outlet area including an outlet for discharging combustion gases from the furnace; as well as Selective non-catalytic reduction (SNCR) agent (230) is injected (into) the outlet zone from the outer periphery of the interior of the furnace to reduce the level of nitrogen oxides in the combustion gases.

12. The method of claim 11, further comprising controlling the combustion of the ammonia fuel to maintain (240) the temperature in the outlet zone within a temperature range of 700-1100°C, thereby allowing the SNCR process to occur.

13. The method of claim 11 or 12, further comprising injecting an SNCR agent into a portion of the recirculation zone of the stove, wherein, The portion includes a stream of combustion gases that moves away from the flame.

14. The method according to any one of claims 11-13, further comprising receiving (250) a sensor signal indicating the level of nitrogen oxides in the combustion gas downstream of the outlet zone, wherein, The injection of SNCR agent into the outlet area is performed based on the sensor signals.

15. The method according to any one of claims 11-14, comprising injecting the amino fuel as an SNCR agent.

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