Combustion system of a boiler with fuel flow distribution means in the burner and method of combustion

Abstract

A combustion system and method, particularly for use in power generation boilers, are provided. The combustion system 1 includes a burner (3, 3', 3") for supplying a mixture (8) of fuel and primary air or gas to a combustion chamber (6) via at least one fuel nozzle (4); a conduit (11, 47) in fluid communication with at least one fuel nozzle (4) for guiding the mixture (8) of fuel and primary air or gas to the at least one fuel nozzle (4); and a deflector device (21) positioned within the conduit (11, 47) upstream of the at least one fuel nozzle (4) to deflect the incoming mixture of fuel and primary air or gas. The flow (8) is deflected. The deflector device (21) includes an injection device (22) arranged to inject auxiliary gas (23) into the duct (11, 47) to deflect the incoming fuel and primary air or gas mixture (8) in a direction from the center of the duct (11, 47) to the outer region, thereby increasing the concentration of the fuel and primary air or gas mixture (8) in the outer region (17) of the fuel nozzle (4) and decreasing the concentration of the fuel and primary air or gas mixture (8) in the central section (16) of the fuel nozzle (4).

Description

[0001] The present invention relates to a combustion system, and more specifically, to a combustion system for a boiler used for power generation having a fuel flow distribution device in the burner, and a method of combustion using such a combustion system.

[0002] Boilers typically have a combustion system with a heating furnace capable of burning solid fuels such as bituminous coal, lignite, and biomass. Such combustion systems usually include a mill arranged to pulverize the solid fuel (e.g., coal) and ducts for supplying the pulverized fuel to one or more burners. The pulverized coal and air (gas) are supplied to the boiler's combustion chamber and ignited to produce hot flue gas, which can be used to generate steam for power generation or other applications (e.g., industrial).

[0003] Instead of pulverized fuel, other fuel types, such as gaseous fuels (e.g., natural gas), can also be used for combustion in boilers. For example, fuel gas mixtures derived from refinery gases are also desirable. Refinery gases are gaseous byproducts of oil refineries, generated during crude oil processing. Refinery gases may have a low calorific value and can be mixed with natural gas and / or gaseous liquefied petroleum gas (LPG) and fed into heating furnaces.

[0004] Typically generated during the combustion of fossil fuel pollutants, including nitrogen oxides (NOx), particulate matter (PM), and carbon monoxide (CO), these pollutants can pose health hazards to humans and animals, have adverse environmental impacts, and exacerbate global warming if released into the atmosphere. Global emission standards (including those in the US and EU) regulate acceptable emission limits for NOx, CO, and other pollutants. However, further reductions in actual emission levels are needed.

[0005] NOx emissions can be reduced by lowering the flame temperature, but this may also reduce the radiant heat transferred from the flame, thus decreasing boiler efficiency. Some NOx control technologies used in boilers have lowered NOx levels by changing the air / fuel mixing pattern to reduce flame temperature. Lower flame temperatures and reduced mixing intensity can lead to higher CO levels. High flame temperatures, tight air / fuel mixing, and near-complete fuel combustion are crucial for low CO emissions. High CO emission levels are primarily caused by incomplete combustion due to poor burner design or inadequate combustion conditions (e.g., an unsuitable air-fuel ratio).

[0006] Other problems may arise due to operating conditions. For example, in burners that burn pulverized coal, the pulverizer typically operates with a fairly constant air / gas volumetric flow across the entire load range. At low loads, the air-fuel ratio therefore decreases, and the pulverized coal-air / gas mixture becomes lean and difficult to ignite. Furthermore, it may be difficult to stabilize the flame sufficiently, leading to flameout or backlash. Poor fuel quality and / or inadequate distribution patterns supplied to the boiler's combustion chamber can exacerbate this situation.

[0007] The goal is for the combustion system used in boilers to flexibly utilize different types and qualities of fuel, including pulverized fuels such as coal, petroleum coke, bituminous coal, lignite, and biomass, as well as a wide range of mixed gas fuels, such as refinery and other exhaust gases, while ensuring safe ignition and combustion of fuels, sufficient flame stability, and high efficiency performance under full and partial loads, and reducing NOx and CO emissions throughout the entire operating range.

[0008] Pulverized fuel (PF) burners (e.g., pulverized coal (PC) burners) are typically designed with and operate deflectors, impellers, injectors, or other structural features in ducts extending into the burner to alter the distribution of pulverized fuel across the cross-section of the burner nozzle outlet. By distributing the pulverized fuel throughout the nozzle outlet in a desired manner, different fuel concentrations and air-fuel ratios can be achieved in different regions of the nozzle outlet, thereby influencing the combustion process, including flame stability, fuel burnout, and emission levels.

[0009] US 4,669,398 A discloses a pulverized fuel combustion apparatus comprising a first pulverized fuel injection chamber, a second pulverized fuel injection chamber, and a make-up air chamber. The first pulverized fuel injection chamber is configured such that the total amount of primary and secondary air to be consumed is less than the stoichiometric amount of air required to burn the pulverized fuel. The second pulverized fuel injection chamber is configured such that the total amount of primary and secondary air is substantially equal to the stoichiometric amount of air required for the pulverized fuel. The make-up air chamber is used to inject make-up air into the furnace. These three chambers are arranged close to each other and control NOx generation during the combustion of the pulverized fuel.

[0010] EP 3 026 338 A1 discloses a combustion system for a boiler and a method for burning solid fuels. The combustion system includes a burner that supplies a mixed stream of fuel and primary air to the boiler's combustion chamber via a fuel nozzle. The mixed stream of fuel and primary air is supplied to the burner through a duct of a pulverizer that grinds the fuel to a desired fineness. A fuel concentrator, including a deflector and a distributor, is arranged in the duct to concentrate the mixed stream of fuel and primary air at the center of the fuel nozzle. The concentrated fuel-rich jet at the nozzle outlet center is described as improving the vaporization of the mixed stream of fuel and primary air, improving the burner's NOx emission performance, and enhancing ignition and flame stability.

[0011] US 6,120,281 A discloses a combustion method utilizing tangential combustion, in which a mixture of coal and primary air is discharged from a burner located at a corner of a furnace toward an imaginary circle positioned at the center of the furnace. Two streams of air are discharged from air nozzles also located at a corner of the furnace; one stream flows toward the center of the furnace, supporting combustion with the fuel, while the other stream is directed along the inner surface of the furnace boundary wall to maintain an oxidizing atmospheric environment and minimize corrosion and slagging.

[0012] The object of this invention is to eliminate or at least reduce the deficiencies of existing combustion systems and methods for boiler design as described above. Specifically, the object of this invention is to provide a combustion system and a combustion method suitable for boilers that can flexibly use different types and qualities of fuel while providing safe fuel ignition and combustion, sufficient flame stability, and high efficiency, reducing NOx and CO emissions over a wide operating range. Preferably, this is achieved using a simple and low-wear combustion system design.

[0013] According to a first aspect, the present invention provides a combustion system, particularly for a boiler, comprising at least one burner for supplying a mixture of fuel and gas to a combustion chamber via at least one fuel nozzle; a conduit in fluid communication with the at least one fuel nozzle for guiding the mixture of fuel and gas to the at least one fuel nozzle; and a deflector device positioned within the conduit upstream of the at least one fuel nozzle to deflect the incoming mixture of fuel and gas. The deflector device includes an injection device arranged to inject auxiliary gas into the conduit to deflect the incoming mixture of fuel and gas along a direction from the center of the conduit to an outer region.

[0014] This invention employs a "fluid deflector" that uses a fluid in the form of an auxiliary gas ejected from an injection device to deflect the incoming fuel and gas mixture from the center of the duct to its outer region, near one or more duct walls, instead of using solid deflectors, impellers, or injectors as used in conventional systems. The ejected auxiliary gas impacts the incoming fuel and gas mixture and diffuses it to create distinct fuel-rich and fuel-lean zones at the burner or fuel nozzle outlet, providing a typical device for low-NOx burners.

[0015] According to the present invention, and compared to various devices used in conventional designs that concentrate a fuel-rich jet at the center of the fuel nozzle outlet, this injection device is positioned relative to the fuel nozzle and configured to deflect the incoming fuel-air mixture to increase the concentration of the fuel-air mixture in the outer region of the fuel nozzle and decrease the concentration of the fuel-air mixture in the middle or central section of the fuel nozzle. This promotes improved homogenization of the fuel flow entering and burning in the combustion chamber.

[0016] It should be noted that the gas mentioned herein can be any air, gas (hot or cold), or mixture of air and gas that can be used for combustion with fuel in the combustion chamber and for the combustion of the fuel-air mixture. The gas may also be referred to interchangeably herein as primary air or primary air and gas. The gas may also include a certain amount of recirculated fuel gas produced by combustion in the combustion chamber. Similarly, the auxiliary gas mentioned herein can be any air, gas, or mixture of air and gas suitable for performing its functions as described herein. The auxiliary gas may be obtained from primary air or gas or from the secondary air supply of the burner, and may be at least partially generated by combustion and recirculated to the injection device. It may also be fresh air obtained externally and pushed to the injection device by means of a fan or blower, for example, especially when the boiler does not have sufficient primary and / or secondary air to provide the auxiliary gas, or when the calorific value or grinding grade of the coal or gaseous fuel is low and additional air is advantageous. The terms “air” and “gas” are used herein only to distinguish gaseous fluid flows for ease of description and understanding.

[0017] The combustion system of this invention can use any desired fuel. In preferred applications, it can use pulverized fuel (PF), such as pulverized coal, petroleum coke, bituminous coal, lignite, biomass, etc. For example, the fuel can also be a fuel-gas mixture obtained from refinery gases or other exhaust gases.

[0018] In a burner that burns PF fuel, the pulverized fuel can be supplied by a pulverizer or mill connected to a conduit. The pulverizer can operate with a fairly constant air / gas volume flow across the entire load range. The deflector device of the present invention then increases the PF fuel concentration in the outer region of the burner outlet, thus supporting flame stability and ignition, especially in low-load burner operation scenarios.

[0019] In a preferred embodiment of the invention, the injection device may include an auxiliary gas nozzle configured to receive auxiliary gas and inject it at least at an angle opposite to the flow direction of the fuel and gas mixture. That is, the injected auxiliary gas has at least a counter-current component opposite to the flow direction of the fuel and gas mixture. Therefore, the fuel and gas mixture can be effectively deflected and distributed to the sides of the conduit as needed. The auxiliary gas nozzle may also be tilted to induce swirling motion in the incoming fuel flow.

[0020] In a particularly preferred embodiment, the auxiliary gas nozzle may be a counter-current nozzle having a nozzle outlet oriented opposite to the flow direction of the fuel and gas mixture, such that the jet of injected auxiliary gas impacts the incoming fuel and gas mixture in the opposite direction. Uniform deflection and distribution of the fuel and gas mixture can be achieved in all external sections of the fuel nozzle outlet.

[0021] It may be advantageous to install the auxiliary gas nozzle (especially a counter-current nozzle) in the horizontal section of the duct that is directly connected to the fuel nozzle, particularly in the section downstream of the last duct bend where there are no bends. Furthermore, the auxiliary gas nozzle can be positioned on the horizontal centerline of the duct section, i.e., on the central axis of the burner. This allows for a high degree of control over the fuel distribution pattern generated at the nozzle outlet.

[0022] By employing any configuration of the auxiliary gas nozzle (especially a counter-current nozzle), injecting auxiliary gas through the nozzle, at least partially in a direction opposite to the main fuel flow, enriches the outer layer of the fuel flow. This increases the fuel concentration in the outer section of the burner outlet, reduces the fuel concentration in the middle section of the burner outlet, and ensures a uniform fuel flow across the cross-section. All of this contributes to improved ignition performance, a larger effective ignition zone within the low-load operating range, and a burner with low NOx and CO emissions. Low NOx emission levels are achieved in the reducing atmospheric environment within the internal flame, effectively reducing NOx through the reduction of volatiles and coke, and reducing the high-oxygen-level area in the outer flame of the ignition zone due to the increased fuel concentration in this area. The auxiliary gas nozzle requires virtually no maintenance, as it does not include any wear-prone components affected by the fuel and gas mixture, such as solid deflectors, impellers, etc. This significantly reduces corrosion and wear on the burner hardware.

[0023] For lignite burners using core air, a portion of the core air can be redirected and reused, and this portion of core air can be injected into the duct in a counter-current manner. Only minor modifications are required to existing low-NOx lignite burners.

[0024] The combustion system of any of the above embodiments may also include means arranged to change the outlet velocity of the auxiliary gas injected from the injection device, particularly the auxiliary gas nozzle outlet. For example, the control equipment of the combustion system may adjust a flow regulating valve in the feed line connected to the auxiliary gas nozzle. Furthermore, or alternatively, the injection device (particularly the auxiliary gas nozzle) may include a throttling device configured to change the flow cross-section of the auxiliary gas nozzle to adjust the velocity of the injected auxiliary gas. In other words, the injection device or injection nozzle may have a variable orifice to allow for changes in the cross-sectional dimensions and thus affect the velocity of the injected auxiliary gas. In some embodiments, an additional blower or fan with adjustable or controllable speed may be provided to change the outlet velocity of the auxiliary gas.

[0025] Advantageously, altering the velocity of the injected auxiliary gas achieves the same effect as changing the position and size of fluid or solid deflectors, impellers, or injectors in conventional systems. The velocity of the injected countercurrent auxiliary gas determines the size and location of the obstruction to the incoming fuel and gas mixture. This facilitates easy control of the efficiency of deflecting the coal particles or mixed gas fuel flow from the center to the outside of the fuel-gas flow. Therefore, the combustion system can be easily adapted to different types and qualities of fuel, including pulverized fuels with varying degrees of grinding and / or dryness, where flexible adjustment of the auxiliary gas flow rate also allows for easy response to different burner operating conditions.

[0026] In another configuration of any embodiment of the combustion system described above, the injection device (especially the auxiliary gas nozzle) can be arranged to be adjustable according to its orientation in space, such that the injection angle or discharge angle can be changed or adjusted as needed relative to at least two of the three orthogonal axes X, Y, and Z. In such a configuration, even during burner operation (online), the velocity and swirl quantity of the injected auxiliary gas can be adjusted as needed, depending on the fuel type and operating mode, such as partial load operation. An additional blower or fan can be used if necessary.

[0027] Any embodiment including the aforementioned auxiliary gas nozzle (especially a counterflow nozzle) may further include a shielding device disposed in a conduit upstream of and near the feed line that supplies auxiliary gas to the auxiliary gas nozzle to protect the feed line from corrosion and abrasion by the incoming mixture of fuel and gas. For example, the shielding device may be in the form of a semi-cylindrical housing or plate and made of a wear-resistant material.

[0028] In some advantageous embodiments, the combustion system may further include a flow guide disposed in front of, for example upstream of, the auxiliary gas nozzle outlet and having a concave surface facing the auxiliary gas nozzle outlet to diffuse the injected auxiliary gas onto the sides of the duct. Preferably, the flow guide may be disc-shaped or bowl-shaped to uniformly distribute the injected auxiliary gas outward toward the duct wall surrounding the duct. This can enhance the deflection effect of the countercurrent nozzle.

[0029] The combustion systems described so far can have burners and conduits of any shape or size. For example, the cross-section of the conduit can be circular or rectangular. In some specific types of combustion systems, the burner can be a circular burner comprising a tubular primary conduit for supplying a mixture of fuel and gas to the combustion chamber, the downstream end of the primary conduit defining a fuel nozzle, and at least one tubular secondary conduit arranged concentrically with and around the primary conduit for supplying secondary air (or gas) to the combustion zone of the combustion chamber. The burner may optionally also have a tubular tertiary conduit arranged concentrically with and around the secondary conduit for supplying tertiary air (or gas) to the combustion zone of the combustion chamber. Deflector devices may include swirl tubes arranged to provide auxiliary gas and inject the auxiliary gas into the conduit in one direction to deflect the incoming mixture of fuel and gas toward an external region of the primary conduit and to induce a swirling motion of the mixture of fuel and gas around the longitudinal axis of the primary conduit.

[0030] The swirling tube allows the incoming fuel and gas mixture to be deflected from the center of the duct outwards into the duct, while simultaneously creating a swirling flow of fuel and gas to improve mixing and form a preferred fuel distribution, wherein a fuel-rich zone is formed in the outer region of the fuel nozzle outlet and a fuel-lean zone is formed in the center of the fuel nozzle outlet, in order to achieve a large fireball with a stable flame in the combustion zone, improve fuel burnout, and reduce NOx and CO emission levels.

[0031] In some embodiments, the circular burner may further include a core tube disposed at the center of the circular burner within a primary conduit for supplying supplemental core air to the combustion chamber. The swirl tube may be an auxiliary tube configured to surround the core tube and abut against it at its downstream end. The auxiliary tube may have an elongated, inclined slot extending at an angle relative to the longitudinal direction of the auxiliary tube and a plane perpendicular to the longitudinal direction through the wall of the auxiliary tube. The elongated slot is positioned close to the sealed downstream end, at a distance from the burner outlet.

[0032] In other embodiments, the swirl tube may be a closed tube disposed within the primary conduit at the center of a circular burner and having a closed downstream end. The closed tube may have an elongated, inclined slot that extends at an angle relative to the longitudinal direction of the closed tube and a plane perpendicular to the longitudinal direction through the wall of the closed tube, wherein the elongated slot is positioned close to the closed downstream end, at a certain distance from the burner outlet.

[0033] In any of the foregoing embodiments, auxiliary gas can be supplied to the auxiliary tube and the closed tube respectively, and the auxiliary gas flow can be made through the auxiliary tube and the closed tube, exiting through a swirl or cutout into the primary conduit. Because the swirls are arranged at an angle, they create a twist or vortex in the discharged auxiliary gas, and this swirling gas will deflect fuel particles or the gas-fuel mixture flow to the outer region of the gas and fuel conduit. The swirling tube can be non-metallic and does not include any impeller or other devices protruding into the primary conduit, thereby reducing pressure loss and wear.

[0034] According to another aspect, a combustion method is provided. The method includes supplying a mixture of fuel and gas to a combustion chamber via a duct through at least one fuel nozzle and at least one burner, and using an injection device to deflect the incoming mixture of fuel and gas in the duct, the injection device injecting auxiliary gas into the duct to deflect the incoming mixture of fuel and gas along a direction from the center to the outer region of the duct, thereby increasing the concentration of the mixture of fuel and gas in the outer region of the fuel nozzle and decreasing the concentration of the mixture of fuel and gas in the middle or central section of the fuel nozzle.

[0035] The combustion method of the present invention can be performed using a combustion system according to any of the foregoing embodiments, and the same beneficial effects can be achieved. To avoid repetition, reference is generally made to the above description of embodiments of the combustion systems of the present invention and their advantages, which are equally applicable to the method of the present invention.

[0036] In some embodiments of the method, an auxiliary gas nozzle (preferably a countercurrent nozzle) may be used to deflect the incoming fuel and gas mixture in the conduit. The countercurrent nozzle receives the auxiliary gas and injects it in a countercurrent direction opposite to the flow direction of the fuel and gas mixture or at least at an angle opposite to the flow direction of the fuel and gas mixture.

[0037] In other embodiments of the method, a vortex tube can be used to deflect the incoming fuel and gas mixture in the conduit. The vortex tube is disposed in the conduit and arranged to provide auxiliary gas and inject the auxiliary gas into the conduit in one direction through an inclined channel, so as to deflect the incoming fuel and gas mixture toward the outer region of the primary conduit and induce a swirling motion of the fuel and gas mixture around the longitudinal axis of the primary conduit.

[0038] Further details of advantageous embodiments of the invention are available from the dependent claims, drawings, and associated detailed description. The invention is described in more detail below with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention that are not limited in any way, wherein the same reference numerals are used to name the same elements throughout the drawings. In the drawings:

[0039] Figure 1 This is a simplified perspective view of a combustion system including a counterflow nozzle according to an exemplary embodiment of the present invention;

[0040] Figure 2 yes Figure 1 Side view of the combustion system shown;

[0041] Figure 3 This is a front view of the outlet of a burner having two fuel nozzles and secondary air nozzles above and below the fuel nozzles according to an exemplary embodiment of the present invention;

[0042] Figure 4 yes Figures 1 to 3 A top view of the combustion system shown;

[0043] Figure 5 yes Figures 1 to 4 The schematic side view of one of the fuel nozzles of the combustion system shown in the figure illustrates the flow of the mixed fuel and gas in the combustion chamber and the resulting flame to illustrate the operation of the combustion system according to an embodiment of the invention;

[0044] Figure 6 This is a top view of a combustion system including modifications to the deflector device of the combustion system according to another exemplary embodiment of the present invention;

[0045] Figure 7 yes Figure 6 The enlarged schematic cross-sectional view of the combustion system shown in the figure illustrates the flow of the mixed fuel and gas;

[0046] Figure 8 This is a side view of a combustion system including a circular burner and a swirl tube according to another exemplary embodiment of the present invention;

[0047] Figure 9 yes Figure 8 A perspective view of the swirl tube used in a circular burner, shown in a simplified enlarged schematic diagram;

[0048] Figure 10 This is a side view of another circular burner including a combustion system and a swirl tube, according to another exemplary embodiment of the present invention;

[0049] Figure 11 yes Figure 10 A partial side view of the combination of core air tube and swirl tube used in a circular burner, shown in a simplified enlarged schematic diagram;

[0050] Figure 12 This is a top view of a boiler with a tangential arrangement of burners according to an exemplary embodiment of the present invention; and

[0051] Figure 13 This is a front view of a boiler with a burner front combustion arrangement according to an exemplary embodiment of the present invention, indicating the direction of fuel swirl.

[0052] Figure 1 An example of a boiler 2 for power generation according to an exemplary embodiment of the present invention is shown. Figure 1 Not shown in the text but Figure 5 A side view of the combustion system 1 used together (shown in the figure). Figure 2 , Figure 3 and Figure 4 It shows Figure 1 Side view, front view and top view of combustion system 1, and Figure 5 A partial schematic diagram of a combustion system 1 arranged at a boiler 2 is shown to illustrate its operation. In the exemplary embodiment shown, the combustion system 1 includes a burner 3, which includes at least one, in the present case, two fuel nozzles 4 at its free end for supplying fuel to the combustion chamber 6 of the boiler 2 through at least one fuel nozzle 4. Figure 2 and Figure 5 (Shown in the diagram) A mixed flow of fuel and gas is supplied. The burner 3 is connected to a fuel source (not shown) via a conduit system 7. In a preferred application, the burner 3 may be connected to a pulverizer or mill (not shown) arranged to grind solid fuels (such as coal, coke, lignite, biomass, etc.) to the desired fineness and supply the pulverized fuel and gas mixture 8 to the burner 3 via the conduit system 7 and further to the fuel nozzle 4. The combustion system 1 is particularly suitable for use as a combustion system 1 for burning lignite.

[0053] Although Figures 1 to 4 The combustion system 1 shown is illustrated and described as comprising a pulverized fuel burner 3 to supply a mixed stream 8 of pulverized fuel and gas to and through a fuel nozzle 4 into a combustion chamber 6 for combustion. However, the combustion system 1 can use any desired fuel, and in particular, fuel-gas mixtures obtained from, for example, refinery gases or other combustible exhaust gases. Any description of pulverized fuels (PF) (such as pulverized coal) should also apply to other types of fuels, especially fuel-gas mixtures from refinery gases.

[0054] In addition, although Figures 1 to 4 The combustion system shown includes one burner 3 and two fuel nozzles, but the combustion system may include any number of burners 3 and / or fuel nozzles 4, one, two, three or more.

[0055] See again Figures 1 to 4 In this example, the duct system 7 includes a first duct section 9 and a second duct section 11. In operation and as shown in the figures, the first duct section is the vertical duct section 9 and a common duct for the downstream portion of the burner 3. In operation and as shown in the figures, the second duct section is fluidly connected to the first vertical duct section 9 via a corresponding bend 12 and also fluidly connected to the horizontal duct section of the fuel nozzle 4. The combustion system 1 may also have a separate first vertical duct section 9 for each individual burner 3. For example, the cross-section of each of the duct section 9 and the duct section 11 may be rectangular.

[0056] Referring particularly to 3, a front view of the outlet 13 of a burner 3, comprising two fuel nozzles 4 and a secondary air nozzle 14, is shown in simplified view. Each fuel nozzle 4 is subdivided into a central nozzle section 16 located in the middle or center of each fuel nozzle 4 and circumferential nozzle sections 17 arranged around the central nozzle section 16. In the exemplary embodiment shown, four circumferential nozzle sections 17 are located at each corner of the central nozzle section 16 and around each corner.

[0057] Secondary air nozzles 14 are arranged above and below each fuel nozzle 4, for example, to inject secondary air 15 into the combustion chamber 6 of the boiler 2 to achieve stable combustion of the fuel and gas mixture 8 in the combustion chamber 6. The axis C of the secondary nozzle 14 (see...) Figure 5 The fuel nozzle 4 is parallel to the axis B of the fuel nozzle 4. The fuel nozzle 4 may have a circumferential fuel nozzle passage 18 in fluid communication with the circumferential nozzle section 17 of the nozzle outlet 13, and a core air tube 19 in fluid communication with the central nozzle section 16 of the nozzle outlet 13.

[0058] Refer again Figure 1 , Figure 2 and Figure 4 As can be seen, the combustion system 1 of the exemplary embodiment includes a deflector device 21 positioned within each second horizontal conduit section 11 (hereinafter simply referred to as conduit 11) of the conduit system 7 downstream of the corresponding bend 12 and upstream of the corresponding fuel nozzle 4 to deflect the incoming fuel and gas mixture 8 before supplying it to the fuel nozzle 4. The deflector device 21 includes an injection device 22 arranged to inject auxiliary gas 23 into the conduit 11 to deflect the incoming fuel and gas mixture 8 along a direction from the center of the conduit 11 to an outer region.

[0059] exist Figures 1 to 5 In the exemplary embodiment shown, the injection device 22 includes an auxiliary gas nozzle 24 configured to receive auxiliary gas 23 and inject it at least at an angle to the flow direction 26 of the incoming fuel and gas mixture 8. Specifically, the auxiliary gas nozzle 24 may be a counter-current nozzle having a nozzle outlet 27 directed upstream (i.e., opposite to the flow direction 26 of the fuel and gas), such that the jet of injected auxiliary gas 23 impacts the incoming fuel and gas mixture 8 in the opposite direction. Therefore, the incoming fuel and gas mixture 8 can be uniformly deflected and distributed outwards to the sides or walls 28 of the duct 11, thereby increasing the concentration of the fuel and gas mixture 8 in the outer region or circumferential nozzle section 17 of the fuel nozzle 4 and decreasing the concentration of the fuel and gas mixture 8 in the middle region or central section 16 of the fuel nozzle 4. This provides the desired fuel flow distribution for improved ignition and combustion in the combustion chamber 6.

[0060] For example, as in Figure 1 and Figure 4As can be seen, a feed line 29 is provided in fluid communication with the counterflow nozzle 24 to supply auxiliary gas 23 to the counterflow nozzle 24. In the example shown, the feed line 29 extends through the sidewall of the burner 3, but it can be supplied through any conduit wall 28 of the conduit 11. The auxiliary gas 23 supplied through the feed line 29 can be any available air, gas, or air and gas mixture suitable for performing the deflection function of the present invention. Specifically, the auxiliary gas 23 can be obtained from the gas or secondary air supply of the burner 3. It may also include at least a portion of recirculated gas (not shown), which is generated in the combustion chamber 6 and can be guided back and mixed with additional air or gas and supplied to the feed line 29. When there is insufficient primary and / or secondary air available in the boiler 2, fresh air can be obtained from the outside and supplied to the feed line 29 via a blower or fan. Using or adding fresh air can enhance fuel combustion, especially when the pulverized fuel has a low grinding grade or the calorific value of the pulverized fuel or fuel-gas mixture is low.

[0061] Continue to refer to Figure 1 and Figure 4 The shielding device 31 may be arranged in the conduit 11, for example, upstream of the portion of the feed line 29 extending within the conduit 11, to protect the feed line 29 from the incoming mixture of fuel and gas 8 and prevent corrosion and abrasion. For example, the shielding device 31 may be in the form of a semi-cylindrical housing or plate, positioned close to the feed line 29 and potentially partially surrounding its sides. The shielding device 31 is made of abrasion-resistant material, such as steel, alloy, or abrasion-resistant plastic. The shielded feed line 29 may be made of any material, including plastic. The shielding device 31 may be omitted if not required.

[0062] So far, we will now refer to another source. Figure 5 The operation of the combustion system 1 will be described in more detail. Figure 5 It shows Figures 1 to 4The combustion system 1 is shown in sections, for example, only a portion of the burner 3 and a portion of the conduit system 7 including the vertical conduit section 9 and the horizontal conduit section 11, for clarity, including the fuel nozzle 4 at the free end of the burner 3 and two secondary nozzles 14 positioned above and below the fuel nozzle 4. The vertical axis A indicates the outer boundary or wall of the combustion chamber 6 of the boiler 2, where the outlet 13 of the fuel nozzle 4 is located. A fuel and gas mixture 8 is supplied through the conduit system 7. For example, the fuel can be pulverized fuel, especially pulverized coal, or a fuel-gas mixture containing refinery gases or exhaust gases. The fuel and gas mixture 8 is supplied through the vertical conduit section 9 and is diverted in the bend 12 from a vertically upward flow direction to a horizontal flow direction 26 toward the fuel nozzle 4. When the fuel and gas mixture 8 reaches the vicinity of the deflector device 21, it is deflected by the deflector device 21 to the side or wall 28 of the conduit 11.

[0063] More specifically, the auxiliary gas 23 is discharged from the nozzle outlet 27 of the countercurrent nozzle 24 in a countercurrent direction generally opposite to the flow direction 26 of the fuel and gas mixture 8 at the center of the duct 11. When the injected auxiliary gas 23 impacts the incoming fuel and gas mixture 8, it effectively deflects the mixture 8 outwards, i.e., upwards, downwards, and to the side of the duct 11, causing the mixture 8 to flow around the deflector device 21. This can be achieved solely by fluid (i.e., the auxiliary gas 23) and requires no solid deflector, injector, or impeller within the duct 11.

[0064] The velocity of the discharged auxiliary gas 23 can be selected based on the position of the counterflow nozzle 24 in the duct 11, the feed capacity relative to the outlet 13 of the fuel nozzle 4, the feed line 29 and the counterflow nozzle 24, the type and quality of the fuel used, and the operating conditions. This concentrates the rich fuel jet 32 ​​in the outer region of the duct 11 and reaches the outer region of the fuel nozzle 4 or the circumferential nozzle section 17, while the concentration of the fuel and gas mixture flowing around the counterflow nozzle 24 and reaching the central nozzle section 16 of the fuel nozzle 4 (i.e., the lean fuel jet 33) is reduced. This provides favorable fuel distribution at the fuel nozzle outlet 13 at the inlet of the combustion chamber 6, which greatly improves the ignition, combustion and burnout of the fuel in the combustion chamber 6, and provides a large, extended and stable flame 34 in the combustion chamber 6.

[0065] As in Figure 5As can be seen, the low-pressure zone 36, which serves as the ignition stabilization zone, is generally formed downstream of the central nozzle section 16 of the fuel nozzle 4, which is located between the upper and lower split fuel gas streams. These upper and lower split fuel gas streams generally enter the combustion chamber 6 from the circumferential nozzle section 17. Gas and fuel particles are drawn into the low-pressure zone 36 from the lower portion of the upper fuel gas stream 37, which includes a fuel-rich jet 32, and the upper portion of the lower fuel gas stream 38, which also includes a fuel-rich jet 32, and are ignited. This stabilizes the ignition because a portion of the thermal combustion products formed during ignition are recirculated within the low-pressure ignition stabilization zone 36, such as… Figure 5 As indicated by the circular arrow 39, this provides the necessary ignition energy to ignite the fuel particles, which are then drawn from the upper fuel gas stream 37 and the lower fuel gas stream 38 into region 36. This further facilitates stable ignition because the fuel-gas ratio increases within the ignition stability zone 36, which in turn reduces the amount of energy required to initiate ignition.

[0066] Therefore, combustion system 1 provides a burner 3 with improved ignition performance, a larger effective ignition zone, and low NOx and CO emissions within the low-load operating range. Low NOx emission levels are achieved through a reducing atmospheric environment within the internal flame (i.e., low-pressure zone 36), thereby effectively reducing NOx by reducing volatile matter, coke, or other fuel particles in this zone. This is achieved by reducing the ignition zone (i.e., low-pressure zone 36). Figure 5 The high oxygen level zones in the outer flame of zones 37 and 38 further reduce NOx emissions. The large ignition zone with widely distributed fuel particles facilitates complete combustion of fuel in flame 34, thereby further reducing CO emissions. Burner 3 has low maintenance costs because it does not include any vulnerable components within duct 11, such as solid deflectors, which would otherwise be affected by the mixing of fuel and gas. This significantly reduces corrosion and wear on the burner 3's hardware.

[0067] Combustion system 1 can be modified in various aspects. For example, and as... Figure 5 As can be seen, the secondary air nozzle 14 can be fixed in a tilted manner or preferably arranged to tilt at an angle relative to the axis B of the fuel nozzle 4, so as to allow adjustment of the angle at which the secondary air 15 is injected into the combustion chamber 6. The tilting of the secondary air allows for further control of the flame 34 and combustion.

[0068] Figure 4Additional optional modifications are shown. It can be seen that the combustion system 1 may include means arranged to change the exit velocity of the auxiliary gas 23 injected from the injection device 22, particularly the nozzle outlet 27 of the countercurrent nozzle 24. In one exemplary embodiment, a flow regulating valve 40 may be arranged in fluid communication with the feed line 29 and may be controlled by a control device (not shown) of the combustion system 1 to adjust the flow rate and velocity of the auxiliary gas 23 fed through the feed line 29 to the countercurrent nozzle 24.

[0069] As an alternative, a blower or fan 41 may be provided to draw gas from a gas supply or to draw fresh air from the outside, and to provide it as auxiliary gas 23 to the feed line 29. The speed of the blower or fan 41 may be adjustable, and in a preferred embodiment, the speed may be controlled during operation to allow the outlet speed of the auxiliary gas 23 to be changed by adjusting or controlling the speed of the blower or fan 41.

[0070] In another embodiment that may be used as an alternative, or in addition, the combustion system 1 may include a throttling device 42 configured to change the flow cross-section of the auxiliary gas nozzle 24 to adjust the velocity of the injected auxiliary gas 23. The auxiliary gas nozzle 24 may have a variable orifice that can be controlled during operation by a control device (not shown), for example, to change the size of its cross-section and thus change the velocity of the injected auxiliary gas 23.

[0071] In all these embodiments, changing the velocity of the injected auxiliary gas 23 achieves the same effect as changing the position and size of the deflector device 21 or any solid deflector, impeller, or injector in a conventional system. The velocity of the injected countercurrent auxiliary gas 23 determines the size and position of the obstruction presented to the incoming fuel and gas mixture 8. This facilitates easy control of the efficiency of deflecting fuel particles or the fuel mixture from the center to the outside of the fuel gas flow 8. Therefore, the combustion system 1 can be easily adapted to different types and qualities of fuel, including pulverized fuels with different grind sizes and / or dryness levels. For example, for fuels with a larger proportion of larger fuel particle sizes and / or higher dryness levels, the velocity of the injected auxiliary gas 23 can be increased to provide greater momentum for effectively deflecting and distributing the fuel outward. The velocity of the injected auxiliary gas 23 can be decreased by adjusting the fuel mixture for fuels with high grind sizes and a larger proportion of small fuel particle sizes, as well as fuels that are not pulverized and require lower momentum for deflection.

[0072] The velocity of the injected auxiliary gas 23 can also be adjusted according to the burner operating conditions. When the pulverizer or mill supplies the burner 3 with pulverized fuel with a low gas-fuel ratio, the full-load operating speed can be increased, and when the gas-fuel ratio supplied by the pulverizer is increased, the partial-load operating speed can be reduced. This further enables flexible adjustment of the auxiliary gas 23 flow rate and optimizes ignition, combustion, and pollutant emission levels to cope with different burner operating conditions.

[0073] As an additional modification, in any embodiment of the combustion system 1 described above, the injection device 22 (in particular the auxiliary gas nozzle 24) can be arranged to be adjustable according to its orientation in space. Specifically, the injected auxiliary gas nozzle 24 can be arranged to be adjustable so that it can be adjusted relative to the target location as needed. Figure 4 At least two of the three orthogonal axes X, Y, and Z shown can be used to modify or adjust the nozzle outlet 27 and the injection or discharge angle. Specifically, adjusting the nozzle outlet 27 in the YZ plane perpendicular to the axis B of the fuel nozzle 4 can facilitate the deflection of the incoming fuel and gas mixture 8 to the desired direction. Due to the bend 12, the incoming fuel and gas mixture 8 can be concentrated in the upper region of the duct 11, and then a portion of the mixture 8 can be deflected downward toward the bottom portion of the duct wall 28. It can also be expected that the fuel and gas mixture 8 can be deflected laterally toward the duct 11 depending on some boiler conditions. Furthermore, the upwardly inclined nozzle outlet 27, which is also inclined toward the side of the duct 11, can induce a swirling motion in the fuel and gas mixture 8. The swirling mixture 8 exiting the fuel nozzle outlet 27 can also improve fuel distribution, ignition, and combustion in the combustion chamber 6.

[0074] Another optional embodiment of combustion system 1 is in Figure 6 and Figure 7 As shown in the figure, Figure 7 It shows Figure 6 The enlarged cutout section of the burner 3 is shown in the diagram. In this exemplary embodiment, the combustion system 1 may also include a flow guide 43 disposed in front, for example, upstream of the nozzle outlet 27 of the auxiliary gas nozzle 24. The flow guide 43 may be disc-shaped or bowl-shaped and includes a concave surface 44 facing the auxiliary gas nozzle outlet 27.

[0075] from Figure 7 As can be seen from the detailed view, the concave surface 24 of the flow guiding device 43 functions during operation to diffuse the injected auxiliary gas 23 outward toward the conduit wall 28 of the conduit 11, such as... Figure 7As indicated by arrow 46. Then, the diffused auxiliary gas 46 impinges on the fuel and gas mixture 8 flowing around the deflector device 21, and further deflects the mixture 8 already deflected by the guide device 43 to enhance the overall distribution effect of the mixture 8. The guide device 43 may preferably be made of a wear-resistant material.

[0076] refer to Figure 8 and Figure 9 This illustrates another embodiment of the combustion system 1 according to the invention. The combustion system 1 is particularly suitable for use as a coal combustion system 1, but other solid or gaseous fuels can also be used, as described above. In this exemplary embodiment, the combustion system 1 includes a circular burner 3' that includes a tubular primary conduit 47 for supplying a mixed flow 8 of fuel and primary air to the combustion chamber 6. Although the term "primary air" is generally used with... Figure 8 and 9 The types of coal combustion systems shown herein are used in combination, but primary air may include any air, gas (hot or cold gas), or air and gas mixture, which may be mixed with fuel and combustion. The terms “primary air” and “gas” as used otherwise herein are interchangeable. The downstream end 48 of the primary conduit 47 defines the fuel nozzle 4. The burner 3' additionally includes a tubular secondary conduit 49 arranged concentrically around the primary conduit 47 for supplying secondary air 51 to the combustion chamber 6. In the example shown, the burner 3' additionally includes a tubular tertiary conduit 52 arranged concentrically around the secondary conduit 49 for supplying tertiary air 53 to the combustion chamber 6. The primary conduit 47, secondary conduit 49, and tertiary conduit 52 are all arranged concentrically with each other. The tertiary conduit 52 may be omitted if not required, but preferably, it is provided to increase flame expansion and improve the performance of the burner 3' depending on the ignition and combustion of the fuel.

[0077] As in Figure 8 and Figure 9 As can be seen, the deflector device 21 in the burner 3' includes a swirling tube 54, which is arranged to provide auxiliary gas 23 and along... Figure 8 Arrow 56 indicates that the auxiliary gas 23 is injected into the duct 11 so as to deflect the incoming fuel and primary air mixture 8 toward the outer region of the primary duct 47 and cause the fuel and primary air mixture 8 to swirl around the longitudinal axis B of the primary duct 47 and the fuel nozzle 4.

[0078] The swirl tube 54 is a closed tube 57 disposed within the primary conduit 47 at the center of the circular burner 3' and having a closed downstream end 58. The closed end 58 is positioned at a distance from the nozzle outlet 27 of the burner 3'. The closed tube 57 includes elongated inclined slots 59, which are circumferentially distributed around the closed tube 57 and extend from the inside to the outside of the tube 57 through the wall 61 of the closed tube 57. The slots 59 are inclined such that they are arranged at an angle relative to the longitudinal direction along the axis B of the closed tube 57 and also relative to a plane perpendicular to the longitudinal direction. The slots 59 are positioned close to the closed downstream end 58.

[0079] During operation, auxiliary gas 23 is supplied through closed tube 57 and flows toward its closed end 58. Auxiliary gas 23 can be supplied from any suitable air and / or gas source, such as from a primary air supply, secondary air supply, or tertiary air supply, or from an external air / gas source. Auxiliary gas 23 exits from the interior of closed tube 57 through through channel 59 and is thereby deflected, such that it has both radial and axial motion components, as well as a swirling component around primary conduit 47, after passing through channel 59. This swirling air 56 then impinges on the incoming fuel and air flow 8, causing the mixed flow 8 to deflect toward the outer region of primary conduit 47 (i.e., toward conduit wall 28), and also inducing swirling motion in the mixed flow 8. Thus, the fuel and primary air mixed flow 8 receives rotational pulses and causes the mixed flow to move away from closed tube 57 and closer to the outer wall 28 of primary conduit 47. This causes a swirling fuel-air mixture 8 to enter the combustion chamber 6, which has a higher fuel concentration in the outer region 17 and a higher fuel concentration in the central section 16 of the nozzle outlet 27 of the burner 3'. Therefore, utilizing... Figures 1 to 7 The auxiliary gas nozzle 24 in the implementation scheme achieves substantially the same effects, including improving ignition and combustion performance, expanding the combustion zone, stabilizing the flame, improving fuel burnout, and reducing NOx and CO emission levels. For the avoidance of repetition, see reference to [other sources]. Figures 1 to 7 The description of the effects and advantages of the implementation scheme is also applicable to [the specific implementation scheme]. Figure 8 and Figure 9 Combustion system 1.

[0080] refer to Figure 10 and Figure 11 This illustrates another embodiment of the combustion system 1 with a circular burner 3' according to the present invention. This embodiment generally corresponds to Figure 8 and Figure 9 The embodiments shown are such that the same reference numerals indicate the same components used in both embodiments, and Figure 8 and Figure 9 The description of the implementation plan is also applicable accordingly. Figure 10 and Figure 11 The implementation plan is as follows, unless otherwise stated below.

[0081] exist Figure 10 and Figure 11 In an exemplary embodiment, the circular burner 3” further includes a primary conduit 47, a secondary conduit 49, and an optional tertiary conduit 52 arranged concentrically with each other. Additionally, the boiler 3’ includes a core air pipe 62 disposed within the primary conduit 47 at the center of the circular burner 3” for supplying supplemental core air 63 to the combustion chamber 6. In the example shown, the swirl tube 54 is an auxiliary tube 64 arranged around the core air pipe 62 and sealing against the core air pipe at its downstream end 66. The pipe 64 includes an elongated inclined slot 59 circumferentially distributed around the pipe 64 near the sealed downstream end 66 and extending at an angle to the longitudinal direction corresponding to axis B and a plane perpendicular to the longitudinal direction of the auxiliary tube 64 through the wall 61 of the auxiliary tube 64. The elongated slot 59 and… Figure 8 and Figure 9 The burner 3' shown in the embodiment has the same or substantially similar through-slot 59 as the one shown in the figure, and provides the same effect. Figure 11 Enlarged cut sections of the auxiliary tube 64 and the core air tube 62 are shown, along with an elongated inclined through-slot 59.

[0082] During operation, auxiliary gas 23 is supplied from a suitable source through an annular space 67 defined between the auxiliary tube 64 and the core air tube 62. The auxiliary gas 23 flows through the annular space 67 to the sealed downstream end 66 and exits through a through-slot 59 into the primary duct 47, where it is deflected in both the radial and axial directions and also receives twisting or swirling around the auxiliary tube 64. The swirling auxiliary gas 56 causes the fuel-air flow 8 to deflect towards the outer region of the primary duct 47 and also induces swirling motion in the mixed flow 8 as it impinges on the incoming fuel and primary air or gas mixture 8 flowing through the primary duct 47. Therefore, the fuel and primary air or gas mixture 8 receives a rotating pulse and causes it to move away from the closed tube 57 and closer to the outer wall 28 of the primary duct 47. This induces the swirling fuel-air / gas mixture 8 to enter the combustion chamber 6, where the fuel concentration is higher in the outer region 17 and also higher in the central section 16 of the nozzle outlet 27 of the burner 3'. As a result, the distribution of fuel air / gas flow into combustion chamber 6 has been improved, which lays the foundation for safe fuel ignition and combustion, sufficient flame stability, and high efficiency in full-load and partial-load operation, while reducing NOx and CO emissions throughout the operating range.

[0083] Figure 12A top view of a boiler 2 with a tangential arrangement of burners 3 (or 3' or 3") according to an exemplary application of the invention is shown. A mixed flow 8 of fuel and air is injected from the burners 3 (3', 3") located on the boiler wall 68 surrounding the combustion chamber 6 in a tangential direction relative to an imaginary circle 69, so as to form a vertical vortex at the center of the combustion chamber 6. Such an arrangement can be advantageously used, for example, in boilers burning lignite, and the burners 3, 3', and 3" of the invention are particularly suitable for this application. The burners 3 (3', 3") can also be arranged in the corners of the combustion chamber 6. The advantages achieved by the burners 3, 3', and 3" result in corresponding advantages and improve the overall performance and efficiency of boilers burning lignite.

[0084] Figure 13 A front view of a boiler 2 with a front combustion arrangement of burners according to an exemplary embodiment of the present invention is shown. Any of the burners described above, 3, 3', and 3" can be advantageously used for... Figure 13 Boiler 2 is shown in the image. Figure 13 The direction of the fuel swirl of the fuel and primary air mixture 8 is also indicated, as the mixture exits the fuel nozzle 4 of the burner 3 (3', 3") and enters the combustion chamber 6 along the circular arrow 71. In the example shown, the deflector device 21 (e.g., auxiliary gas nozzle 24 or swirl tube 54) may be arranged to induce the swirl motion indicated by arrow 71 to improve cross-mixing of fuel and air entering the combustion zone of the combustion chamber 6. Specifically, adjacent burners 3 (3', 3") may be selectively arranged to induce swirls along the same direction 71a or opposite directions 71b, which not only enhances cross-mixing of air and fuel but also avoids the creation of hot spots in specific areas of the combustion chamber 6.

[0085] The burner 3 (3', 3") can be arranged to achieve a swirling pattern that provides any desired fuel-air flow to the combustion chamber 6 to improve performance according to operating conditions. Advantageously, this can be achieved by using only auxiliary gas 23 injected from auxiliary gas nozzle 24 or swirling tube 54, without requiring any complex hardware structure to generate swirling flow in the fuel-air flow within the burner. Furthermore, the velocity of the injected auxiliary gas 23 can be varied to adequately respond to changes in fuel type or altered operating conditions.

[0086] A combustion system and method, particularly for use in power generation boilers, are provided. The combustion system 1 includes a burner 3, burner 3', and burner 3'', the burner being used to supply a mixture 8 of fuel and primary air or gas to a combustion chamber 6 via at least one fuel nozzle 4; conduits 11 and 47, the conduits being in fluid communication with at least one fuel nozzle 4 for guiding the mixture 8 of fuel and primary air or gas to at least one fuel nozzle 4; and a deflector device 21, the deflector device being positioned within the conduits 11 and 47 upstream of at least one fuel nozzle 4 to deflect the incoming mixture 8 of fuel and primary air or gas. The deflector device 21 includes an injection device 22, the injection device being arranged to inject auxiliary gas 23 into the conduits 11 and 47 to deflect the incoming mixture 8 of fuel and primary air or gas along a direction from the center of the conduits 11 and 47 to the outer region, thereby increasing the concentration of the mixture 8 of fuel and primary air or gas in the outer region 17 of the fuel nozzle 4 and decreasing the concentration of the mixture 8 of fuel and primary air or gas in the central section 16 of the fuel nozzle 4.

Claims

1. A combustion system, comprising: at least one burner (3, 3', 3") for supplying a mixed flow (8) of fuel and gas to a combustion chamber (6) through at least one fuel nozzle (4); a conduit (11, 47) in fluid communication with the at least one fuel nozzle (4) for conducting the mixed flow of fuel and gas to the at least one fuel nozzle (4); and a deflector device (21) positioned within the conduit (11, 47) upstream of the at least one fuel nozzle (4) to deflect the incoming mixed flow (8) of fuel and gas; wherein the deflector device (21) comprises a jetting arrangement (22) arranged to jet an auxiliary gas (23) into the conduit (11, 47) to deflect the incoming mixed flow (8) of fuel and gas in a direction from a center of the conduit (11, 47) to an outer region, characterized in that the jetting arrangement (22) comprises an auxiliary gas nozzle (24) configured to receive the auxiliary gas (23) and inject the auxiliary gas (23) in a direction opposite to or at least at an oblique angle to a flow direction (26) of the mixed flow (8) of fuel and gas, wherein the auxiliary gas nozzle (24) is a counterflow nozzle having a nozzle outlet (27) oriented opposite to the flow direction (26) of the mixed flow (8) of fuel and gas. The combustion system is for a boiler.

2. The combustion system of claim 1, wherein The jetting arrangement (22) is positioned relative to the fuel nozzle (4) and configured to deflect the incoming mixed flow (8) of fuel and gas to increase a concentration of the mixed flow (8) of fuel and gas in an outer region (17) of the fuel nozzle (4) and to decrease a concentration of the mixed flow (8) of fuel and gas in a center section (16) of the fuel nozzle (4).

3. The combustion system of claim 1, wherein, The fuel is a pulverized fuel, or a fuel gas mixture obtained from refinery gas.

4. The combustion system of claim 1, wherein The fuel is a pulverized coal.

5. The combustion system of claim 4, wherein The auxiliary gas nozzle (24) is mounted in a horizontal conduit portion (11) of the conduit (7) directly connected to the fuel nozzle (4), on a centerline of the conduit portion (11).

6. The combustion system of claim 1, wherein 7. The combustion system according to any one of claims 1 to 6, further comprising a device (40, 41, 42) arranged to change an exit velocity of the auxiliary gas (23) jetted from the nozzle outlet (27) of the auxiliary gas nozzle (24). The auxiliary gas nozzle (24) comprises a throttling device (42) configured to alter a flow cross section of the auxiliary gas nozzle (24) to adjust a velocity of the jetted auxiliary gas (23).

8. The combustion system of claim 7, wherein, The at least one auxiliary gas nozzle (24) is adjustable in its orientation in space to alter a jet angle of the auxiliary gas (23).

9. The combustion system of any one of claims 1 to 6, wherein, ​ 10. The combustion system according to any one of claims 1 to 6, further comprising a shielding device (31) arranged in the duct (11) upstream of a feed line (29) to the auxiliary gas nozzle (24) supplying the auxiliary gas (23) to the auxiliary gas nozzle (24) for protecting the feed line (29) from the incoming fuel and gas mixture flow (8).

11. The combustion system according to any one of claims 1 to 6, further comprising a flow guiding device (43) arranged in front of the nozzle outlet (27) of the auxiliary gas nozzle (24) and having a concave surface (44) facing the direction of the auxiliary gas nozzle outlet (27) for diffusing the injected auxiliary gas (23) to the side of the duct (11).

12. A method of combustion, the method of combustion comprising: supplying a fuel and gas mixture flow (8) by at least one burner (3, 3’, 3”) through at least one fuel nozzle (4) through a duct (11, 47) to a combustion chamber (6); and deflecting the incoming fuel and gas mixture flow (8) in the duct (11, 47) using injection means (22) injecting an auxiliary gas (23) into the duct (22, 47) to deflect the incoming fuel and gas mixture flow in a direction from the center to the outer region of the duct (11, 47) in order to increase the concentration of the fuel and gas mixture flow (8) in an outer region (17) of the fuel nozzle (4) and to decrease the concentration of the fuel and gas mixture flow (8) in a central section (16) of the fuel nozzle (4), characterized in that deflecting the incoming fuel and gas mixture flow (8) in the duct (11) is performed using an auxiliary gas nozzle (24) receiving the auxiliary gas (23) and injecting the auxiliary gas (23) in a counter flow direction opposite to the flow direction (26) of the fuel and gas mixture flow (8) in the duct (11) or at least at an inclined angle to the flow direction (26) of the fuel and gas mixture flow (8) in the duct (11).

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