RS58920B1 - Lance system, boiler- containing lance system and method for reducing nox - Google Patents

Description

The present invention relates to an injection system, a boiler system containing an injection system and a process for reducing NOX.

Technical field

Combustion of carbonaceous materials and fossil fuels, for example in waste incineration plants or steam plants, produces nitrogen oxides (NOX). In accordance with legal requirements, measures must be taken to control the combustion process or clean the flue gases or combustion gases so that little NOX is formed, or the NOX of the combustion gases is reduced to reduce emissions to the atmosphere.

The formation of NOX is the subject of complex reaction mechanisms, where the main sources of NOX are the oxidation of nitrogen from combustion air (thermal NOX) and the oxidation of nitrogen for fuel (NOX fuel).

Thermal NOX essentially occurs at temperatures higher than about 1200°C to 1500°C, because only at these temperatures does the molecular oxygen present in the air significantly transform into atomic oxygen (thermal oxidation) and combine with nitrogen from the air. The rate of formation of thermal NOX depends exponentially on the temperature and is proportional to the oxygen concentration.

The primary nitrogen compounds found in the fuel first break down into secondary nitrogen compounds (simple amines and cyanides), which are converted into NOX or N2 during combustion. In case of lack of oxygen, the formation of N2 is preferred, that is, the formation of NOX is suppressed, or even vice versa. The formation of NOX fuel is only slightly dependent on temperature and continues even at low temperatures.

In the state of the art, NOX reduction is carried out by primary measures such as placing air on the burner and furnace height. Air distribution along the height of the furnace is done in such a way that the area of the burner belt is usually substoichiometric. Thus, the burners receive only part of the amount of air required for complete combustion. The remaining air required for combustion (combustion air) is then usually added a considerable distance above the burner belt. This procedure is called the OFA procedure (air above combustion). The addition takes place by means of so-called air nozzles above the combustion. The two basic types of overhead air nozzles are wall nozzles and overhead air sprinklers.

Depending on the combustion system and the geometry of the furnace, the wall nozzles are placed on one wall, two walls or even on all four walls. It is also common in the prior art to accept the combustion air over several levels at different heights of the furnace. The aim is to achieve the best possible mixing between the rising flue gas and the combustion air added via the air nozzles above the combustion. Due to the substoichiometric operation of the burner belt area, the flue gas still contains unburned constituents, such as carbon monoxide, but also coke particles, etc., which need to be converted by adding air.

Nozzle design in terms of injection angle and current pulse (= mass flow [air] x velocity) requires precise knowledge of furnace flow to achieve optimal results.

Another basic device for injecting the necessary air for combustion is the so-called. Sprinklers. They protrude into the furnace or boiler and feed air into the flue gas through a multitude of small nozzles along the nozzle. By placing a plurality of injectors and a plurality of nozzle systems per injection system, an even distribution of combustion air across the cross-sectional area is achieved.

These nozzles are also often mounted in an area within the first heating surfaces that are connected downstream of the furnace. This offers the practical advantage that the nozzles are then no longer self-supporting elements, but can be placed on the peripheral surfaces of the heater. Static design is greatly simplified.

When arranging the injectors, as with the air nozzles above the combustion, it should be noted how the flue gas flow is formed and in what temperature range the injection is performed. Carbon monoxide conversion requires a combination of residence time and temperature.

In order to increase the efficiency of the air above the combustion, wall nozzles can often be combined on several levels and, for example, are realized as sprinklers as the last stage in relation to the flow of flue gases.

The application of the described air injectors above combustion is described, for example, in Pinkert et al. presented in 2011 in the framework of furnace air distribution (Pinkert et al. "Modernisierung der 360 MWel-Blöcke mit Braunkohlefeuerung im Kraftwerk Bełchatów", Kraftwerktechnisches Kolloquium Dresden, 2011).

Application of SNCR as a secondary measure for the reduction of nitrogen oxides

The invention relates to a process for reducing unwanted substances by injecting a reagent into the flue gas of a steam generator, where the reagent is injected by means of a syringe into the furnace of the steam generator. Further, the invention relates to injectors or a system for injecting reagents into a steam generator furnace to reduce unwanted substances in the flue gas. In addition, the invention also relates to a steam generator furnace having such a device.

Methods and devices of the mentioned type are already known. The reactants are, for example, ammonia and/or urea, which can reduce the proportion of nitrogen oxides in the flue gas. The corresponding processes are called selective non-catalytic reduction (SNCR). In selective non-catalytic reduction (SNCR) of nitrogen oxides, reducing agents in aqueous solution (typically ammonia water, urea) or gases (ammonia) are injected into hot incinerator flue gases. The reaction of the reducing agent with nitric oxide and oxygen produces molecular nitrogen, water and carbon dioxide. For example, for ammonia or urea as a reducing agent, the following simplified reaction occurs:

4 NH3+ 4 NO O2 → 4 N2+ 6 H2O

NH2CONH2+ 2 NO 1⁄2 O2→ 2 N2+ CO2+ 2 H2O

The optimal temperature range for the described reactions depends on the composition of the flue gases and is between 900 and 1100°C.

One of the main problems with SNCR technology is mixing the reducing agent into the flue gas in the correct temperature range. Basically, SNCR technology is successfully used in small and medium-sized boilers, and especially in waste incineration plants. In addition to small cross-sections, it is often an advantage that after combustion, before entering the first convective heating surfaces, the flue gas passes through one or two so-called empty passages. In this case, the flue gas already transfers energy on the walls of these empty passages and already reaches low temperatures before entering the convective heating surfaces, for example, to prevent corrosion problems in the heating surfaces (e.g. in biomass, waste wood and waste incineration boilers). In contrast, this often means that the temperature range relevant to SNCR technology is achieved within empty passages. Together with the relatively small dimensions, SNCR technology can be used efficiently and optimally here.

In contrast, the application of SNCR technology in large power plants presents a number of additional problems, as follows.

Cross-sectional dimensions of the combustion chamber

On the one hand, the large dimensions make it difficult to mix the reducing agent across the cross section. Combustion air mixing, with large volumes compared to SNCR, and thus high impulse currents that aid mixing over large sections, presents problems and is the subject of intensive optimization.

Temperature profile in a dust-burning furnace of a large power plant:

In the design of combustion chambers (dust combustion) for burning different solid fuels, the leading parameter is the end temperature of the furnace (= FACE = Temperature of the gas at the outlet of the furnace). This temperature indicates the temperature of the flue gases exiting the combustion chamber and entering the convective heating surfaces and usually depends on the softening behavior of the ash used. The goal is to maintain FACE below the ash softening point to minimize failures on convective heating surfaces. These temperatures depend on the fuel used, but are typically in the range 1050 to 1150°C for lignite, typically in the range 1000 to 1300°C for hard coal, and in the range 1000 to 1100°C for large boilers converted to use wood biomass. For the application of SNCR technology, this means that the optimum temperature range is often not within the range of free space of the furnace, but is only achieved within the slope of the heating surface. This is where injection is problematic. On the one hand, the heating pipes must not be affected by the cold reducing agent that is injected, but on the other hand, a large mixing pulse is required because of the distances, and thus the residence time between the slopes of the heating surface is at a low level. In addition, due to the slope of the heating surface, the temperature of the flue gas decreases rapidly, where the residence time in the flue gas is limited for optimal reaction sequences.

The temperature profile in the combustion chamber is additionally influenced by a large number of combustion types and boiler geometries.

Furnace and boiler geometry

In large power plants, various variants of dust combustion are used, such as front combustion, counter-combustion, and all-wall combustion, angular combustion, tangential combustion, which is carried out with vortex or jet burners. In addition, there are boiler geometries such as towers or two-pass boilers, where a large number of heating surface arrangements are known. In addition to the reduction of flue gas temperature along the flow direction, the temperature distribution transverse to the main flow direction should also be taken into account, because they can occur especially prominently, for example, in two-pass boilers due to flow direction.

DE 44 34 943 C2 describes the injection of a reducing agent using two-substance nozzles with simultaneous measurement of the boiler temperature profile and injection level, where the optimum temperature range is determined. By changing the position and angle of the nozzles, they can be adjusted to the optimal temperature range.

DE 102008004 008 A1 discloses direct spraying of an aqueous reducing agent into the flue gas.

EP 0530255 B1 (DE000069120812T2) describes the injection of a NOX-reducing mixture of liquid and gas into the flue gas within the optimum temperature range for the reaction, and the mixture is injected into the liquid droplets which evaporate before hitting the surface. In addition to injection into the furnace, the document also describes the use of an injection procedure using a nozzle placed between the slopes of the heating surfaces, which are equipped with a plurality of nozzles in order to achieve equal distribution across the cross-section into the flue gas.

The disadvantage is that the injection of droplets inside the heating surfaces involves the risk of the still not completely vaporized droplets reaching the heating pipes. In this case, due to local temperature gradients and the erosive effect, depending on the speed of the droplets, long-term damage can be expected. Even if designed correctly, these nozzles are exposed to flue gases at temperatures ranging from 900°C to 1050°C, the flue gases also contain solid erosive substances (dust, coke) and corrosive substances (sulphur, containing substances, ash components). The nozzles, which disperse the liquid into finely divided droplets using a propellant, are therefore subject to aging. As a result, it cannot be excluded that during operation the nozzles no longer produce the optimal droplet sizes as when new, but, for example, larger droplets that can cause the problems described on the surfaces of the heating pipes.

DE 19781 750 T1 (VO 97/41947 A1) describes an injector for injecting non-aqueous NH3i air into a furnace. The sprinkler consists of three pipes, which are placed one inside the other, where ammonia is introduced into the inner pipe and enters the gap between the inner and middle pipe at the inner end, where it also meets and mixes with air, which enters the gap between the middle and outer pipe. The ammonia/air mixture flows through a number of openings from the inner space of the middle tube through radial channels that bridge the gap between the middle and outer tubes, on the flue gas boiler.

DE 102010 050 334 A1 discloses spraying a liquid reducing agent into the flue gas, where the droplets evaporate before any contact with the wall. The described device provides a vertical nozzle that is introduced through the ceiling of the boiler, which provides sprayed liquid at its end in a horizontal direction or at an angle to the horizontal from -10 to 60°.

Document DE 102004026 697 A1 describes a procedure for injecting a reducing agent together with the upper air. For this purpose, a part of the air above the combustion is introduced by means of the first OVA nozzles in the flow direction, and another part of the air above the combustion is introduced with the second nozzle, in which at the same time there is an injection nozzle for introducing the nitrogen oxide reduction agent.

DE 102012110 962 A1 describes the injection of a reducing agent via wall-mounted multi-substance nozzles. In this case, for example, the air needed to process the air above the combustion can be used as a so-called enveloping medium, in order to initially protect the reducing agent from the flue gas, and to simultaneously achieve a greater depth of penetration for preferably large dimensions of the furnace.

EP 2 962 743 A1 discloses the introduction of a reducing agent with control valves, a sensor for measuring NOX concentrations across a boiler cross-section and a controller that controls the amount of reducing agent introduced. In addition, the use of reducing agent injection injectors is described, where one or more reducing agent injectors are introduced, and these injectors also provide, for example, air above combustion. It is specifically proposed here to introduce a number of injectors with different penetration depths into the nozzles, which can then inject different amounts of reducing agent into the nozzles based on the measurement data present. Since more than one injector is supplied with a plurality of reducing agent injectors, the cross-section of the boiler can be practically divided into segments, each of which can be supplied with individual amounts of reducing agent. The described technology of adding the reducing agent via OFA injectors enables the distribution of the reducing agent across the cross section. In addition, the amount of reducing agent in certain quadrants can be controlled individually. This is achieved by the fact that the injectors of the reducing agent extend at different depths in the OVA injector. Injected there, the reducing agent leaves the injector through the nearest outlet of the injector into the flue gas. Spraying at the nozzle exits involves the danger of droplets coming out of the nozzle.

US 5,342,592 discloses an injection nozzle of complicated construction comprising an outer tubular jacket with a cooling circuit. This outer tubular sheath has a number of openings along the sheath. This tubular casing also has an internal channel into which the injection nozzle is inserted. This in turn consists of an inner tube and an outer tube, where the gap is formed. The reducing agent passes through the inner space of the inner tube and pushes the gas through the opening. The reducing agent passes from the inner space of the inner tube and through channels that separate from the inner tube that bridges the gap, directly into the flue gas stream. Coming from the gap, the pressure gas meets the reducing agent at the nozzles, i.e. at the outlet of the branching channel of the inner pipe, and enters the flow of flue gases.

US 2004/0201142 A1 discloses an injector for injecting a mixture of steam and ammonia gas having two built-in pipes, where a number of openings are placed along the outer pipe, which are connected by channels towards the inner space of the inner pipe. The feed tube, which enters the outer tube at the end of the outer tube, has openings and supplies the reducing agent/steam mixture to the space between the inner tube and the outer tube. The mixture flows along the gap to the opposite closed end of the nozzle or outer tube. At the closed end of the outer tube, the mixture enters the open end of the inner tube and, via channels branching from the inner tube (which bridges the gap and is not connected to them), directly into the flue gas flow.

US 5,281,403 describes an injection system having an inner tube and an outer tube forming an opening through which a reducing agent is passed. At the inner end of the injection system, the reducing agent is fed into a channel located in the inner cavity of the inner tube, where the channel is equipped with multiple nozzles. A carrier gas is introduced into the inner cavity. Conductor nozzles located within the inner cavity inject the reagent into the flue gas through a corresponding outlet in the injection system, where the reagent is mixed simultaneously with the carrier gas directed into the inner cavity, and exits the injection system also through said outlet.

Prior art injection systems for injectable reactants involve complicated construction, so they are prone to failure, maintenance intensive and also expensive. Moreover, using prior art injection systems it is not possible to avoid liquid drops reaching the heating surfaces or heating surface pipes. This causes corrosion damage to the heating surfaces.

Subject matter of the invention

The technical object of the invention is to provide a simply constructed and cost-effective injection system for mixing nitrogen oxides with a reducing agent in the combustion gas as evenly distributed as possible. In addition, the aim was to provide an injector with which the reducing agent can be injected near or between the slopes of the heating surface. In addition, the goal when using a reducing agent dissolved in water is that the heating surface pipes are not affected by the liquid medium containing the reducing agent in order to reduce or avoid corrosion damage to the heating surfaces.

The technical problem is solved by an injection system for introducing a reducing agent into a boiler for selective non-catalytic reduction of nitrogen oxides in combustion gases, which has an inner part designed to be placed inside the boiler, and an outer part designed to be disposed outside the boiler, where the injection system comprises an inner tube and an outer tube, where the inner tube is placed inside the outer tube at least along the inner part of the injection system, where an intermediate space is formed between the outer wall of the inner tube and the inner wall external pipes,

where according to the invention

along the inner tube, a larger number of first outlet openings are placed in the peripheral wall of the inner tube and

along the outer tube, a number of other exit openings are placed in the peripheral wall of the outer tube,

the first outlet openings of the inner tube are open to the interstitial space,

the inner space of the inner tube is in flow connection with the intermediate space via the first outlet openings of the inner tube and the intermediate space is in flow connection with the outside via the second outlet openings of the outer tube.

With the injection system according to the invention, the nitrogen oxide reducing agent can be mixed with the combustion gas as evenly as possible. Furthermore, the design and functioning of the injection system allows the reducing agent to be injected near or between the slopes of the heating surface, in purely gaseous form, without the risk of liquid droplets. When using a reducing agent dissolved in water, according to the invention, it is ensured that the tubes of the heating surface are not affected by the liquid medium containing the reducing agent. According to the invention, this is achieved by a tube-in-tube combination, where the outer diameter of the inner tube is smaller than the inner diameter of the outer tube. Preferably, the ratio of the inner diameter of the outer tube to the outer diameter of the inner tube is from 1:0.1 to 1:0.9, preferably from 1:0.3 to 1:0.6.

According to the invention, only one (number 1) inner tube is mounted inside the outer tube. Preferably, the inner tube extends substantially along the entire length of the outer tube in the inner portion. The end of the inner tube (the inner end) is located on the inner part of the injection system, which is conveniently closed, may be in contact with the end of the outer tube, which is also located in the inner part, but will generally have a certain distance. In the inner part, the inner tube extends inside the outer tube 50% to 100%, preferably 60% to 100%, preferably 70% to 100%, more preferably 95% to 100%, particularly preferably 98% to 100%, and most preferably 99% to 100% of the distance located in the inner part of the outer tube.

As already explained, along the inner tube there are a number of first outlet openings in the peripheral wall of the inner tube placed and along the outer tube there are a number of second outlet openings in the peripheral wall of the outer tube.

The number and positioning of other outlets (external pipe outlets) depends on the arrangement or division of heating surfaces or heating pipes on the boiler. Other outlets are positioned so that they do not direct flow directly onto the heating surfaces or heating surface pipes. In addition, the number and arrangement of other outlets depends on the structure of the flue gas flow and at which point in the cross-section of the furnace the amounts of reducing agent or oxidizing agent (combustion air) are required. Therefore, the number, arrangement and size of other exit openings may vary. A plurality of other exit openings in the peripheral wall of the outer tube preferably means here at least 4, 6, 8, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100.

In a preferred embodiment of the injection system according to the invention, a plurality of pairs of other outlet openings are provided in the outer pipe, in each case two other outlet openings facing each other, where in particular in each case a pair of other outlet openings is positioned so that the outlet openings are aligned with the free space between the tubes of the heating surface. In one embodiment, a pair of other exit ports may be aligned in each free space between the heating surface tubes. This embodiment is shown in Figure 3. In an alternative embodiment, only every other free space between the heating surface tubes can be equipped with two other exit openings. This embodiment is shown in Figure 4. Since several injection systems are provided in the boiler, the injection into the heating surfaces can be performed in a way where they repel each other (see Figure 4). In a particularly preferred embodiment, however, a pair of opposing second outlet openings is provided in each free space between the heating surface tubes. Depending on the requirements of the denitrification task, the flow field in question and the temperature field, it is also possible to provide additional embodiments, such as, for example, a feed into every third free space between the heating surface tubes, etc. Depending on the type of boiler or on the distribution of heating surfaces, other outlet openings or pairs of other outlet openings can be placed at equal intervals or at unequal intervals along the longitudinal axis of the injection system.

With regard to the inner tube, a greater number of first outlet openings in the peripheral wall of the inner tube preferably means at least 4, 6, 8, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. The first outlet openings in the peripheral wall of the inner tube are

a) placed significantly evenly along the inner tube, or

b) in relation to the direction towards the inner end of the inner tube

i) distributed with a decreasing number or with a decreasing total cross-sectional area of exit openings per unit length, or

ii) distributed with an increasing number or with an increasing total cross-sectional area of exit openings per unit length.

The first exit openings preferably follow the arrangement scheme of the other exit openings. Preferably, every other outlet and/or every pair of other outlets is connected to one or two first outlets. The first outlet openings are preferably placed in relation to the direction of flow in the intermediate space (between the inner and outer pipes) upstream of the other outlet openings. In the following embodiment, a large number, preferably at least 20, 40, 60, 80, 100, 200, 400 first outlet openings are placed in the inner tube. Therefore, the inner tube can be designated as perforated with the first outlet openings. It is understood that even in the embodiment of the perforated inner tube according to the invention, areas of the inner tube are excluded from the perforation, which are adjacent to other exit openings in the outer tube.

As mentioned above, it is preferable to have a chamber in front of the boiler for mixing the reducing agent and the oxidizing agent (preferably air). From there, the mixture enters the inner space of the inner tube. Further, the invention utilizes the gaseous medium (air above combustion) required in the combustion process. At the same time, when using a reducing agent dissolved in water, it is ensured that the evaporation is in the construction of the nozzle, so that the pipes of the heating surface are not threatened by possible droplet impact.

The construction of the injection system according to the invention with two built-in tubes, an inner tube and an outer tube, represents a simple construction procedure. This results in lower production and maintenance costs. With this design, in particular, damage to the injection system by distortion due to temperature fluctuations can be avoided. This is because the two built-in pipes

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preferably not tightly connected.

In a preferred embodiment of the injection system, the diameter of the outer tube decreases towards the inner end. This measure serves to maintain the mass flow rate in the interstitial space and to reduce the weight of the injection system. Rejuvenation of the outer tube can be done continuously or in stages. In a further embodiment, the diameter of the inner tube may also decrease in the direction of the inner end.

According to the present invention, in the case of adding a reducing agent with liquid components, complete evaporation is achieved by first letting the reducing agent mixed with a hot oxidizing agent (preferably air) into the inner tube, and then letting it into the space between the inner tube and the outer tube through the first outlet ports, where it mixes again with the hot oxidizing agent (preferably air) and then leaves the injection systems through the second outlet port in outer tube. In accordance with the present invention, the interphase (residual) evaporation within the interspace between the inner tube and the outer tube is achieved by having the first outlet ports of the inner tube open into the interspace. This means that the second outlet openings of the outer tube are placed offset in relation to the first outlet openings of the inner tube. The "offset" arrangement of the first to the second outlet according to the present invention also has a functional meaning. A structurally offset arrangement, for example of radial openings as the first and second exit openings, will usually functionally fulfill the requirement that the mixture containing the reducing agent from the inner tube first passes into the intermediate space, so that it mixes with the second gaseous oxidizing medium and is completely vaporized. The functional aspect of the "displaced" arrangement also means that, for example, the first outlet opening with an inclined tubular connection (whose axis is not normal to the longitudinal axis of the inner tube) is directed towards the inner wall of the outer tube, and is not directed towards the second outlet opening, also if the position of this second outlet opening in relation to the first outlet opening is radial and/or displaced or arranged in the longitudinal direction. In the latter case, the desired mixing of the reducing agent in the intermediate space with the oxidizing agent which is additionally added depending on the distance to the second outlet opening and their dimensions cannot be given, because the liquid coming out of the first outlet opening would be at least partially injected directly through the second outlet opening, as is the case in the prior art. This is undesirable according to the invention, because the mixture from the inner space of the inner tube was first completely inside the interstitial space before exiting the outer tube.

Therefore, according to the present invention, the first exit openings, especially those in the form of nozzles, pipes or pipe sockets, are not directed in the direction or to another opening present in the immediate vicinity. This means that the axes of the first outlet openings of the inner tube are directed towards the inner wall of the outer tube. This means that, according to the invention, the axes of each first outlet opening intersect the inner wall of the outer tube at the closed part of the wall of the outer tube. With this measure, it is achieved that the first outlet openings of the inner tube open into the intermediate space.

As explained above, the first outlet openings of the inner tube and the second outlet openings of the outer tube are positioned so that the mixture exiting the first outlet openings cannot directly pass through the second outlet openings to the outside. The first exit openings of the inner tube and the second exit openings of the outer tube are, therefore, offset from each other. One of ordinary skill in the art understands that "offset" here means not just an arbitrary axis, which is, for example, normal to the longitudinal axis of the inner tube, as would be the case with the simplest form of exit openings - a radially extended opening - which does not extend simultaneously through the first and second exit openings. "Offset" also means that, for example, in the case of slanted outlets, the axis of the first outlet does not extend over the second outlet, but intersects the inner wall of the outer tube.

In a particularly preferred embodiment, the cross-sectional distance of the axis of each first outlet opening (inner tube outlet) to the circumference of the nearest second outlet (outer tube outlet) is at least 1.5 times, more preferably at least 2.0 times the radius of the corresponding first outlet.

Due to the arrangement of the inner tube with the outer tube, at least along the inner part of the injection system, an intermediate space is defined between the inner tube and the outer tube, which extends over the entire circumference of the inner tube. In addition, it is preferable that the space between the outer wall of the inner tube and the inner wall of the outer tube extends over the entire length of the inner tube. The inner end of the inner tube is usually preferably closed, or provided with one or more first openings. Again, these first exit ports opened into the interstitial space.

In a preferred embodiment, the injection system is constructed to

a) deliver the mixture containing the reducing agent and the oxidizing agent through the inner space of the inner tube and lead it from there into the space between the inner tube and the outer tube through the first openings; and

b) separately deliver further oxidizing agent to the intermediate space between the inner pipe and the outer pipe;

c) mixes a mixture containing a reducing agent and an oxidizing agent from a) and a further oxidizing agent from b) in the intermediate space; and

d) allow the mixture from c) to exit the outer tube from the interstitial space through other openings.

The measure according to b), according to which the additional oxidizing agent is introduced separately into the intermediate space between the inner tube and the outer tube, means that the further oxidizing agent is not fed through the inner tube, but through its own supply of the outer tube.

Further, it is preferable that this delivery of further oxidizing agent to the interspace is placed on the outer part of the injection system, which is designed to deliver to the interspace between the inner tube and the outer tube a gaseous oxidizing agent, preferably air. Thus, the outer tube has an inner end and an outer end, where the outer end is in flow communication with the delivery for introducing the gaseous oxidizing agent into the interstitial space.

In a further preferred embodiment, the mixing chamber is arranged on the outer part of the injection system, which is in flow connection with the inner space of the inner tube and is designed to deliver to this inner space a liquid containing a reducing agent, where the mixing chamber contains an inlet for a reducing agent and an inlet for a gaseous oxidizing agent, preferably air. More preferably, the mixing chamber and/or the delivery of the reducing agent to the mixing chamber comprises the delivery of a propellant gas.

The introduction of the gaseous oxidizing agent into the mixing chamber is preferably performed so that the gaseous oxidizing agent flows tangentially into the mixing chamber. This measure serves to improve the mixing of the reducing agent and the gaseous oxidizing agent. In addition, means, especially baffles or vortex bodies, may be placed in the mixing chamber to improve the mixing of the liquid containing the reducing agent with the gaseous oxidizing agent.

The supply of the reducing agent can be performed as a nozzle for one substance, if only the reducing agent is introduced into the mixing chamber, or as a nozzle with two substances, if the reducing agent is introduced together with the pressure gas (preferably compressed air) into the mixing chamber.

The first outlet openings of the inner tube can be designed differently. The first outlet openings are preferably selected from the group consisting of rods, nozzles, tubes and tube sockets.

The corresponding axis of the first outlet opening of the inner tube is preferably oriented as follows:

i) radial;

ii) inclined radially in the direction of liquid flow (and passes through the longitudinal axis of the inner tube);

iii) tangentially at right angles to the longitudinal axis of the inner tube (and lies in the plane of the cross-section passing through the outlet);

iv) inclined tangentially to the direction of liquid flow in the interstitial space.

The construction of the first outlet openings can be different and in particular serves to determine the direction of the mixture containing the reducing agent coming out of the inner tube. Therefore, the preferred construction of the first outlet openings of the inner tube is the tangential direction in relation to the inner tube, so that the inlet flow into the surrounding outer tube, i.e. into the space between the inner and outer tubes, additional twist and improved mixing with the oxidizing agent (preferably combustion air) introduced separately

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into the interspace. The first outlet openings can be oriented tangentially and in the direction of the liquid flow inside the outer tube. Individual first exit openings may have individual and different opening dimensions. Therefore, it is possible, for example, to distribute the output mass flow in different amounts along the length of the inner tube into the surrounding outer tube. The first outlet openings can only be designed as openings in the inner tube, which can then be present in a larger number. Since the first outlet openings are the inner tube, the radial openings can be arranged in the shell or wall of the inner tube.

During operation, the mass flow contains a reducing agent that passes through the inner space of the inner tube and does not combine with the gaseous oxidizing agent that is additionally and separately supplied to the intermediate space between the inner tube and the outer tube, before exiting the inner tube through the first exit opening into the intermediate space. In this case, the inner space of the inner tube is in flow communication with the intermediate space only through the first outlet openings provided in the liner or wall of the inner tube and, if present, through the first outlet opening at the inner end of the inner tube.

Other outlet openings of the outer tube may also be differently designed. The other exit openings are preferably selected from the group consisting of openings, nozzles, pipes and pipe sockets.

In a preferred embodiment, the corresponding axis of the second outlet opening of the outer tube is directed radially at right angles to the longitudinal axis of the outer tube. If the injection system is placed horizontally in the boiler, then the corresponding axis of the second outlet will also be oriented horizontally or preferably inclined downwards relative to the horizontal, i.e. it is oriented at an angle opposite to the combustion gas flow. If the injection system is placed vertically in the boiler, then the corresponding axis of the second opening can be oriented horizontally.

Since the injection system is placed vertically especially in two-pass boilers, and in these boilers, the direction of flow of the combustion gas stream at the position of the injection system is usually not oriented upwards, but horizontally or horizontally with respect to the horizontal at an angle of 0 to 80°, it makes sense to orient the axis of the second outlet opening in the injection systems obliquely in opposition to the main flow of combustion gas. If the injection system is arranged vertically inside the boiler, then the corresponding axis of the second outlet is inclined against the direction of the combustion gas flow.

In both embodiments, it is preferred to arrange the inclination of the axis of the second exit port opposite to the combustion gas flow. This measure serves to extend the residence time of the reducing agent in the correct temperature range of the combustion gas stream.

The measure "opposite to the combustion gas flow direction" here means an angle from 0 to less than 90° with respect to the combustion gas flow direction (opposite to this flow direction).

A further preferred embodiment of the injection system is constructed so that the distance between the inner tube and the outer tube is maintained by spacers, and these spacers are preferably selected from the group consisting of needles, rods, strips, baffles. In order to avoid distortion and accompanying damage, the inner tube and the outer tube are preferably not fixed together, but the spacers are fixed either on the outer side of the inner tube, and preferably not on the inner side of the outer tube, or the spacers are fixed on the inner side of the outer tube, and preferably not on the outer side of the inner tube.

In a further preferred embodiment, baffles are placed in the interspace so that the flow within the interspace is set in rotation (twisting) around the inner tube. The flow of the mixture around the inner tube causes more turbulence and improved mixing.

The invention further provides a boiler having at least one fuel supply, at least one oxidizing agent supply, one or more levels of heating surfaces and at least one injection system according to the invention as described above; where the internal part of the injection system is inside the boiler, and the external part of the injection system is outside the boiler.

In a boiler, fuel and combustion air are combined for combustion. The resulting flue gas or combustion gas flows through the furnace and then over the downstream heating surfaces arranged in the flue gas flow. The furnace is operated with air distribution, so the combustion air added to the burner is not sufficient for complete fuel conversion, but is sub-stoichiometric. Above the burner, air is added above the combustion, for example, under the convective heating surfaces using wall nozzles for further combustion. In the area of the heating surfaces, below, between them or above them, one or more injection systems according to the invention are arranged, which supply the reducing agent of nitrogen oxide. Depending on the type of boiler, injection systems can be arranged horizontally or vertically in the boiler. The reducing agent is mixed with a part of the air above the combustion required for the combustion process and is introduced into the inner space of the inner tube and passes through the first exit hole in the inner tube into the space between the inner tube and the outer tube. The other part of the combustion air is also supplied via the injection system to the combustion gas directly or by leaking into the outer tube, i.e. into the space between the inner tube and the outer tube. In the intermediate space, the remaining liquid is evaporated. Finally, the gas mixture containing the reducing agent passes through other exit openings in the outer tube into the flue gas stream.

Conveniently and preferably, the mixing chamber, the supply of the reducing agent to the mixing chamber, the supply of the gaseous oxidizing agent to the mixing chamber are located outside the boiler. Preferably, a propellant gas supply is further arranged to distribute the reducing agent from the mixing chamber.

In the next preferred embodiment, the boiler means are arranged in the mixing chamber, separately

1

baffles or twisted bodies to improve mixing of the liquid containing the reducing agent, while further gaseous oxidizing agent is supplied. These additional means, located in the mixing chamber, such as baffles or vortex bodies, increase turbulence and result in improved and faster mixing.

Furthermore, it is preferable that the inlet for the introduction of the gaseous oxidizing agent into the intermediate space between the inner tube and the outer tube is placed outside the boiler.

The arrangement of the injection system according to the invention in the boiler depends on the prevailing temperatures of the combustion gas, at which nitrogen oxide is to be reduced. The optimum temperature for NOX conversion by selective non-catalytic process is in the range of 900°C to 1100°C. This temperature usually occurs at the level of the heating surfaces. Therefore, injection systems usually have to be arranged in the area of the heating surfaces. The injection system is attached to the boiler wall (which defines the outer part and the inner part of the injection system) and extends into the interior of the boiler either supported or in contact with the heating surface. In a preferred embodiment of the boiler, the internal part of the at least one injection system is arranged according to any of measures a) to e):

a) the inner part of the injection system supports springs inside the boiler;

b) the internal part of the injection system rests on the heating surfaces;

c) the internal part of the injection system is mounted below the heating surfaces and is suspended by supports attached to the support pipes of the heating surfaces or is suspended by supports attached to the heating surfaces;

d) the internal part of the injection system is supported or attached to the supports attached to the support pipes of the heating surfaces or is attached to the supports attached to the heating surfaces;

e) the internal part of the injection system is placed in the gap between two levels of heating surfaces.

The orientation of the injection system in the boiler can be horizontal or vertical. In the so-called tower boiler, the heating surfaces are arranged horizontally in the boiler, so that the injection system according to the invention can be placed on the heating surfaces and thereby spread horizontally on the heating surfaces or is otherwise attached to the heating surfaces as mentioned above. For other types of boilers, e.g. in so-called two-pass boilers, the heating surfaces can be suspended and introduced from above. In this case, the pipes of the heating surfaces extend vertically, so that the injection systems according to the invention cannot be placed on the heating pipes. In this type of boiler, suitable supports can be provided so that the injection systems can be mounted on the existing ones

1

support pipes in a horizontal position. Alternatively, the injection systems in this type of boiler can also be installed vertically hanging from the ceiling of the system.

In preferred embodiments of the boiler according to the invention, one or more injection systems according to the invention can be installed. More preferably, the plurality of injection systems are distributed evenly across the internal cross-section of the boiler so that the reducing agent can reach the entire combustion gas flow surface. By placing more injectors and a larger number of other exit openings along the injection system, an even distribution of the reducing agent and the oxidizing agent is achieved. The injection systems can also be placed one above the other in one or more horizontal planes, especially in the case of a horizontal orientation of the injection system. Between several horizontal levels of the injection system, heating surfaces or one or more slopes of heating surfaces or parts thereof may or may not be arranged.

In a particularly preferred embodiment of the boiler, multiple injection systems are placed parallel to one another, preferably at right angles to the panels of adjacent heating surfaces. In this case, the other outlet openings of the parallel outer pipes are arranged opposite each other (Figure 3) or are arranged in a mixed arrangement (Figure 4).

In the arrangement of the injection system in the area of the heating surfaces, the arrangement and orientation of the second outlet opening in the outer pipe of the injection system depends on the construction or division of the adjacent, nearest heating surface. The arrangement of the second outlet opening is such that it does not flow directly into the pipe of the heating surface. In accordance with the present invention, in the boiler, the injection system or injection systems are arranged to mix a mixture containing a reducing agent and an oxidizing agent into the combustion gases passing through the passages of the heating surfaces. In this case, the injection system is located on the heating surface. Alternatively or additionally, the mixture is mixed below the heating surface, so that the reducing agent can flow upwards through the passages of the heating surfaces, together with the combustion gas and can be mixed with the combustion gas. In this case, the injection systems are placed under the heating surfaces.

As already explained above, boiler injection systems can be installed horizontally or vertically. In the horizontal arrangement of the injection system, the corresponding axis of the second outlet is also placed horizontally or is preferably inclined downwards with respect to the horizontal, i.e. according to the direction of flow of the combustion gas stream. Even with a vertical orientation of the injection system in the boiler, the orientation of the axis of the second outlet depends on the direction of flow of the combustion gas stream. Preferably, the axes of the second outlet opening are inclined with respect to the flow direction of the combustion gas stream.

In both embodiments, the slope of the axis of the second outlet is inclined relative to the combustion gas flow.

1

This measure serves to extend the residence time of the reducing agent in the correct temperature range of the combustion gas stream.

The subject invention also provides a process for reducing the concentration of nitrogen oxides in the combustion gas, and the process is carried out in a boiler according to the invention described above, which includes the steps:

a) generation of combustion gas in the combustion zone of the boiler, where the combustion gas contains nitrogen oxides;

b) introducing a gaseous oxidizing agent, preferably by air, into the combustion zone of the boiler above and downstream of the combustion zone;

c) injecting a selective reducing agent together with a gaseous oxidizing agent into the combustion gas stream in the boiler downstream of the supply of the gaseous oxidizing agent according to b);

d) reaction with a reducing agent of nitrogen oxides to form N2,

where according to the invention the reducing agent is introduced into the boiler via one or more injection systems, where the reducing agent is mixed with a gaseous oxidizing agent, preferably with air, and previously with a pressure gas, and is introduced into the inner tube of the corresponding injection system, then the mixture of reducing agent/oxidizing agent from the inner tube is introduced into the interspace between the inner tube and the outer tube via the first opening, it is mixed in the interspace with separately supplied additional with a gaseous oxidizing agent, preferably air, and passes through another opening into the boiler, where it exits through other openings in completely gaseous form.

The procedure as well as the preferred procedures and features have already been explained above.

As a nitrogen oxide reducing agent, a nitrogen-containing compound selected from the group consisting of urea, ammonia, cyanuric acid, hydrazine, ethanolamine, biuret, triuret, amelide, ammonium salts of organic and inorganic acids (for example, ammonium acetate, ammonium sulfate, ammonium bisulfite, ammonium bisulfite, ammonium formate, ammonium carbonate, ammonium bicarbonate, ammonium nitrate, ammonium oxalate), preferably urea or ammonia. The reducing agent is preferably dissolved in an aqueous solution (eg as an aqueous solution of ammonia or urea dissolved in water) or introduced into the mixing chamber in gaseous (ammonia) form.

In a preferred method, the gaseous oxidizing agent is introduced tangentially into the mixing chamber. In one embodiment of the process, the reducing agent is introduced into the mixing chamber by means of single-substance nozzles, or by means of dual-substance nozzles together with a pressure gas (preferably compressed air). In a further preferred method, the reducing agent and the oxidizing agent are further fluidized in the mixing chamber by means arranged in the mixing chamber, in particular

1

baffles or vortex bodies, in order to improve the mixing of the liquid containing the reducing agent with the gaseous oxidizing agent.

In a further preferred method, the oxidizing agent (preferably air) introduced into the mixing chamber and the additional oxidizing agent (preferably air) separately introduced into the intermediate space, independently of each other, have a temperature of 200°C to 400°C.

In addition, it is preferable that a gaseous oxidizing agent or a mixture containing a reducing agent and an oxidizing agent in the space between the inner tube and the outer tube is placed in rotation (vortex) around the inner tube. This is primarily done by reinforcing the appropriate internal interspace. The flow of the mixture around the inner tube causes more turbulence and improved mixing.

Especially preferably, the gaseous oxidizing agent, preferably the air that is led into the injection systems (into the inner space of the inner tube and, separately, into the intermediate space between the inner and outer tubes) is part of the oxidizing agent that is needed or consumed in the combustion process in the boiler.

In a preferred embodiment of the process, the reducing agent as it exits the outer pipe of the injection system encounters combustion gas having a temperature in the range of 900°C to 1100°C, preferably 950°C to 1050°C.

The invention will be described in more detail with reference to the drawings.

Figure 1 shows a schematic longitudinal section through a furnace or boiler.

Figure 2 is a view of the injection system shown in Figure 1.

Figures 3 and 4 show different arrangements of several boiler injection systems.

Figure 1 shows a schematic longitudinal section through the furnace or boiler 1. In the boiler, the supply of fuel 2 and air for combustion 3, which are connected for combustion, are shown schematically. The generated combustion gas 4 flows through the furnace and the downstream heating surfaces 10, 11, 12, which are arranged in the combustion gas stream. The furnace starts with air distribution. This means that the combustion air 3 added to the burner is not sufficient for the complete conversion of the fuel 2. For further combustion, the combustion air 5 is added, for example, under the convective heating surfaces 10, 11, 12 by means of wall nozzles. In the embodiment illustrated in the figure, the reducing agent of nitrogen oxide is mixed with the pressure gas 8 for fine distribution with a part of the required air above the combustion 7 inside the mixing chamber 15 via one or more horizontally extended injection systems 9 and leads into the inner space 23 of the inner pipe 16. Another part of the oxidizing agent 6 (combustion air) is also supplied via the injection system 9 to the combustion gas by passing into the outer part 21 in the outer tube 17 and finally in the intermediate space 22 between the inner tube 16 and the outer tube 17. In the illustrated embodiment, the injection system 9 rests on the heating surface 10. The embodiment of the system for

1

the injector 9, shown in Figure 1, has an outer tube 17 whose diameter decreases towards the inner end.

Figure 2 shows the outline of the injection system 9 shown in Figure 1. Inside the boiler 1 are given heating surfaces 10 on which or in the vicinity of which the injection system 9 is located. The injection system has an inner pipe 16 and an outer pipe 17. According to the invention, only one inner pipe 16 is contained in the outer pipe 17. 21 of the injection system), the reducing agent 13 is distributed by the propellant 14. If it is a reducing agent dissolved in a liquid, it is dispersed in this way. At the same time, part of the liquid 7 required in the process is introduced into the mixing chamber 15, which in a suitable embodiment is the combustion air 7. The supply of combustion air can, for example, also take place tangentially to the mixing chamber 15 in order to improve the mixing. The mixed liquid consisting of pressure gas 14, reducing agent 13 and combustion air 7 leaves the mixing chamber 15 and enters the inner pipe 16. In the inner part 20 of the injection system 9, located in the boiler 1, the mixture gradually leaves the inner pipe 16 in the direction of flow through the openings 18 and enters the intermediate space 22 between the inner pipe 16 and the outer pipe 17. The openings 18 in the inner tube 16 are sized so that along the length of the inner tube 16 there is an even distribution in the intermediate space 22 between the inner tube 16 and the outer tube 17.

A part of the liquid 6 required in the process is also supplied to the external pipe 17 in which the mixture exiting the internal pipe 16 is introduced, and thus they are mixed within the intermediate space 22, before they exit together from the external pipe 17 through the openings 19, provided for this purpose, in the surrounding stream of combustion gas 4. The openings 19 of the external pipe 17 are dimensioned so that over the length of the external pipe 17 there is an outflow into the surrounding combustion gas 4 as uniform as possible.

The openings 18 of the inner tube 16 may also be oriented tangentially to the exterior of the inner tube 16 in order to achieve better mixing in the interspace 22 between the outer and inner tubes. Likewise, the openings 18 may also represent a plurality of openings which, due to their plurality, achieve good mixing with the medium 6 entering the outer tube 17.

In accordance with the present invention, complete vaporization is achieved by first passing a reducing agent mixed with a hot oxidizing agent (preferably air) into the inner tube 16, which is then transferred through the first outlet openings 18 into the intermediate space 22 between the inner tube 16 and the outer tube 17, where in the intermediate space 22 it is again mixed with the hot oxidizing agent (preferably air), and then exits the system for injection 9 through the second outlet opening 19 in the outer pipe 17.

In order to achieve (residual) evaporation of the reducing agent in the intermediate space 22, in accordance with

2

according to the invention, the first outlet openings 18 of the inner tube 16 open into the intermediate space 22. This means that the second outlet openings 19 of the outer tube 17 are placed offset in relation to the first outlet openings 18 of the inner tube 16. In Figure 2, the first outlet openings 18 are schematically shown in the form of tubes or nozzles, the axes of which are normal to the longitudinal axis of the inner tube 16 and the injection system 9. The axis of each first outlet opening 18 is directed to the inner wall of the outer tube 17. This prevents the liquid coming out of the first outlet opening 18 from being directly dispersed through the second outlet opening 19, but instead, the reducing agent is first mixed in the intermediate space 22 with the additionally supplied oxidizing agent 6 and can completely evaporate inside the intermediate space 22 before exiting the outer tube 17.

As mentioned, the axis of each first exit opening 18 intersects the inner wall of the outer tube 17 at the closed part of the wall of the outer tube 17. The distance of the intersection of the axis of a given or arbitrary first exit opening 18 of the inner tube 16 to the edge of the nearest second exit opening 19 of the outer tube 17 is at least 1.5 times the radius of the corresponding first exit opening 18.

Figure 3 shows a preferred arrangement of a plurality of injection systems 9 on or near the heating surface tubes 10. In the illustrated embodiment, the outlet openings 19 of the outer tube 17 are arranged opposite each other, where the outlet openings 19 stop in the space between the individual heating surface tubes.

Fig. 4 shows another preferred arrangement of a plurality of injection systems 9 on or near the heating surface pipe 10. In the embodiment shown, the outlet openings 19 of the outer pipe 17 are arranged offset (mixed with each other) opposite to each other.

List of reference numbers

1: boiler/combustion chamber/furnace

2: fuel

3: combustion air

4: combustion gas

5: oxidizing agent/combustion air

6: oxidizing agent/combustion air inside the outer tube (the space between the inner tube and the outer tube)

7: oxidizing agent/combustion air inside the inner tube

8: reducing agent and propellant gas

9: injection system

10: heating surface

11: heating surface

12: heating surface

: reducing agent

: thrust gas

: outer mixing chamber : inner tube

: outer tube

: outlet openings of the inner tube) : outlet openings of the outer tube

: inner part

: outer part

: interspace

: the inner space of the inner tube

Claims (16)

Patent claims 1. An injection system (9) for introducing reducing agents into the boiler (1) for the selective non-catalytic reduction of nitrogen oxides in the combustion gases, with an inner part (20) designed to be inside the boiler (1) and an outer part (21) designed to be outside the boiler (1), where the injection system (9) comprises an inner tube (16) and an outer tube (17), where the inner tube (16) is arranged inside the outer tube (17) at least along the inner part (20) of the injection system (9), where the intermediate space (22) is formed between the outer wall of the inner tube (16) and the inner wall of the outer tube (17), where along the inner tube (16) a plurality of first outlet openings (18) are arranged in the peripheral wall of the inner tube (16), and along the outer tube (17) a plurality of other outlet openings (19) are located in the peripheral wall of the outer tube (17), where the first outlet openings (18) of the inner tube (16) open into the intermediate space (22), the inner space (23) of the inner tube (16) is in flow connection with the intermediate space (22) via the first outlet opening (18) of the inner tube (16) and the intermediate space (22) is in flow connection with the outside via the second outlet opening (19) of the outer tube (17), characterized in that the axes of each first outlet opening (18) intersect the inner wall of the outer tube (17) in the closed part of the wall of the outer tube (17). 2. The injection system (9) according to claim 1, characterized in that the injection system (9) is designed to a) bring the mixture containing the reducing agent and the oxidizing agent through the inner space (23) of the inner tube (16) and from there to the intermediate space (22) between the inner tube (16) and the outer tube (17) through the first openings (18); and b) brings a separate further oxidizing agent into the intermediate space (22) between the inner tube (16) and the outer tube (17); c) mixes the mixture containing the reducing agent and the oxidizing agent from a) and the further oxidizing agent from b) in the intermediate space (22); and d) allow the mixture from c) to leave the outer pipe of the intermediate space (22) through other openings (19). 3. Injection system (9) according to patent claim 1 or 2, characterized in that a mixing chamber (15) is placed in the outer part (21) of the injection system, which is in 2 flow connection with the inner space (23) of the inner tube (16) and is designed as a supply of liquid containing a reducing agent to the said inner space (23), where the said mixing chamber (15) contains a supply of a reducing agent (13) and a supply for a gaseous oxidizing agent (7). 4. The injection system (9) according to patent claim 3, characterized in that means are arranged in the mixing chamber (15), in particular baffles or vortex bodies, in order to improve the mixing of the liquid containing the reducing agent with the gaseous oxidizing agent supplied via the inlet (7). 5. The injection system (9) according to any one of claims 1 to 4, characterized in that the corresponding axis of the first outlet opening (18) of the inner tube (16) is oriented as follows: i) radially; or ii) inclined radially in the direction of liquid flow; or iii) tangentially at right angles to the longitudinal axis of the inner tube (16); or iv) inclined tangentially in the direction of liquid flow in the intermediate space (22). 6. Injection system (9) according to any one of claims 1 to 5, characterized in that the distance between the inner tube (16) and the outer tube (17) is maintained by spacers, preferably selected from the group consisting of needles, rods, nets, partitions; where the spacers are fixed either on the outside of the inner tube (16) and preferably not fixed to the inside of the outer tube (17) or the spacers are fixed on the inside of the outer tube (17) and preferably not fixed to the outside of the inner tube (16). 7. An injection system (9) according to any one of claims 1 to 6, characterized in that the baffles are arranged in the intermediate space (22) so that the fluid flow within the intermediate space (22) is set in rotation around the inner tube (16). 8. The injection system (9) according to any one of claims 1 to 7, characterized in that the distance and point of intersection of the axes of each first outlet opening (18) to the edge of the nearest second outlet opening (19) is at least 1.5 times greater than the radius of the corresponding first outlet opening (18). 9. A boiler (1) comprising at least one fuel feed (2), at least one oxidizing agent feed (3, 5), one or more heating surface levels (10, 11, 12) and at least one injection system (9) according to any one of claims 1 to 8; where the inner part (20) of the injection system is placed inside the boiler (1) and the outer part (21) of the injection system (9) is placed outside the boiler (1). 10. Boiler (1) according to patent claim 9, depending on claims 3 to 8, characterized in that the mixing chamber (15), the reducing agent (13) entering the mixing chamber (15) and the gaseous oxidizing agent (7) entering the mixing chamber (15) are located outside the boiler (1). 11. Boiler (1) according to patent claim 9 or 10, depending on claims 3 to 8, characterized in that means are placed in the mixing chamber (15), in particular partitions or a vortex body, in order to improve the mixing of the liquid containing the reducing agent with the gaseous oxidizing agent supplied via the inlet (7). 12. Boiler (1) according to any one of patent claims 9 to 11, characterized in that the supply (6) of the gaseous oxidizing agent in the intermediate space (22) between the inner tube (16) and the outer tube (17) is placed outside the boiler (1). 13. Boiler (1) according to any of claims 9 to 12, characterized in that the internal part (20) of at least one injection system (9) is arranged according to any of measures a) to e): a) the inner part (20) of the injection system (9) is pushed into the interior of the boiler (1); b) the inner part (20) of the injection system (9) rests on the heating surfaces (10, 11, 12); c) the inner part (20) of the injection system (9) is placed under the heating surfaces (10, 11, 12) and is suspended from the supports attached to the support pipes of the heating surfaces (10, 11, 12) or is suspended from the supports attached to the heating surfaces (10, 11, 12); d) the inner part (20) of the injection system (9) is supported or fixed to the supports attached to the supporting pipes of the heating surfaces (10, 11, 12) or is fixed to the supports attached to the heating surfaces; e) the inner part (20) of the injection system (9) is placed in the gap between the two levels of heating surfaces (10, 11, 12). 14. A process for reducing the concentration of nitrogen oxides in the combustion gas (4), where the process is carried out in a boiler (1) according to any of claims 9 to 13, and contains the following steps: a) generation of combustion gas (4) in the combustion zone of the boiler (1), where combustion gas (4) includes nitrogen oxides; b) introducing the gaseous oxidizing agent (5), preferably by air, into the combustion zone of the boiler (1) above and downstream of the combustion zone; c) injecting the selective reducing agent (13) together with the gaseous oxidizing agent (7, 6) into the combustion gas stream (4) inside the boiler (1) downstream of the supply of the gaseous oxidizing agent (5) according to b); d) reaction of the reducing agent with nitric oxide to form N2, 2 characterized in that the reducing agent (13) is introduced into the boiler (1) via one or more injection systems (9), where the reducing agent is mixed with the gaseous oxidizing agent (7) and fed into the inner tube (16) of the corresponding injection system (9), then the reducing agent/oxidizing agent mixture from the inner tube (16) is introduced into the intermediate space (22) between the inner tube (16) and the outer tube (17) via of the first opening (18), is mixed in the intermediate space (22) with a specially supplied additional oxidizing agent, preferably air, and is drawn through other openings (19) to the boiler (1), where it exits through the other openings (19) in completely gaseous form. 15. The method according to patent claim 14, characterized in that the oxidizing agent that is fed into the mixing chamber (15), and the further oxidizing agent that is separately introduced into the intermediate space (22), independently of each other have a temperature of 200°C to 400°C. 16. The method according to patent claim 14 or 15, characterized in that the reducing agent, when leaving the outer tube (17) of the injection system (9), encounters combustion gas having a temperature in the range of 900°C to 1100°C, preferably 950°C to 1050°C. 2