[1 ] The present application relates to an injection lance for delivering a liquid reducing reagent into a flue gas of a boiler or furnace, thereby reducing the amount of nitrogen oxides (NO _x ) present in said flue gas. Background

[2] The major air pollutants emanating from boilers and furnaces are nitrogen oxides (ΝΟχ), including nitric oxide (NO), nitrogen dioxide (N0 ₂ ) and nitrous oxide (N ₂ 0). The total NO and N0 ₂ -concentration is typically referred to as NO _x (nitrogen oxides). Nitrogen oxides are mainly produced in the form of NO. Some N0 ₂ and N ₂ 0 are also formed, but with lower concentrations. These air pollutants are the subject of growing concern because these compounds are toxic and are the precursors to acid rain deposition as well as photochemical smog. Furthermore, nitrous oxide contributes to the greenhouse effect.

[3] It is known that the introduction of liquid reducing reagents directly into the flue gas in the combustion chamber can remove a significant proportion of NO _x . The liquid reducing reagent is typically an aqueous solution of urea or ammonia.

[4] For boilers and furnaces, it is challenging to guarantee a good distribution of the liquid reducing reagent or to inject the liquid reducing reagent in the area with the right temperature. In a power boiler, for instance, the area with the right temperature is often close to the superheaters. A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam.

[5] Water-cooled injector lances penetrating the combustion area of a boiler or furnace are quite common. One such injection lance is described in WO 2013/055285. The main problem with this technology is that the wall temperature of the injector lance must be kept at temperatures over 150°C to avoid corrosion by the acid components in the flue gas. As cooling water, condensate from the boiler or furnace cycle can be used, which is at a temperature below 100°C. To control the temperature of the cooling water at approximately 150°C, a heat exchanger for the condensate and the cooling water, a pumping module for the cooling water as well for the condensate and a temperature control equipment are necessary. This system is thus costly and requires maintenance.

[6] In WO 88/05762, a process and apparatus for reducing the concentration of pollutants in an effluent from the combustion of a fuel is described. The process and apparatus enable injection of an effluent treatment fluid at independently variable droplet sizes and distance of injection to a wide variety of distribution patterns within a flue gas passage. An atomization conduit, positioned coaxially around a treatment fluid conduit, extends into the effluent and supplies an atomization fluid. The supply conduit is axially slidable with respect to the atomization conduit and supplying a treatment fluid through the supply conduit. The relative axial position of the supply conduit and the atomization conduit is adjusted and the rate of flow of the atomization fluid is selected to inject droplets of a size effective to a desired distance within the passage. In an alternate embodiment, the probe is provided with a cooling conduit disposed outside of and around a portion of the atomization conduit. An appropriate cooling fluid, such as air, water or steam, may be circulated or flowed through the cooling conduit to maintain the cooling of both the atomization and supply conduits in the high temperature environment of a boiler.

[7] The purpose of the application is to provide an injector lance arranged for reducing the amount of NO _x present in a flue gas of a burner or a furnace that can be installed in the combustion chamber in the right temperature window, having an improved NO _x -reduction, and requiring little maintenance.

Summary

[8] A first aspect of the present application provides in an injection lance for injecting a liquid reducing reagent into a flue gas from the combustion of fuel in a combustion chamber of a power boiler or furnace to reduce the amount of nitrogen oxides in the flue gas, wherein the injection lance comprises

at least two oblong separate injectors having a different length and each having a single spraying nozzle at the end thereof for spraying the liquid reducing agent;

first cooling means to cool the injectors with air; an surrounding pipe coaxial with and disposed around the injectors and provided with at least one opening per injector spaced along its length and located in the vicinity of the respective spraying nozzles to allow the spraying nozzles to spray the liquid reducing agent through the openings into the flue gas;

second cooling means to cool the surrounding pipe with air.

[9] Additionally or alternatively, the injection lance as described herein can be described as an injection lance for injecting a liquid reducing reagent into a flue gas comprising at least two separate oblong injectors having a different length, each injector comprising an internal pipe, an external pipe, and a spraying nozzle; a surrounding pipe disposed around the at least two injectors and comprising at least one opening per injector for allowing passage of sprayed reducing agent into the flue gas. Typically, the spraying nozzle is disposed at the injector's end. Typically, the injectors are oblong structures.

[10] The injection lance according to the application has the advantage that it improves the NOx-reduction by reducing the baseline and providing a better distribution due to the turbulence created by the injected air. It also requires little maintenance. This injection lance is furthermore more cost efficient compared to the ones known in the state of the art. Also, the openings in the vicinity of the spraying nozzles enhance the mixing of the liquid reducing reagent with the flue gas. The surrounding pipe furthermore helps significantly in the reduction of the temperature of the liquid reducing reagent. Generally, there is also no direct connection between the injectors and the surrounding pipe, due to different thermal expansion.

[1 1 ] Generally speaking, the first cooling means can be considered to consist of the annular space between the internal pipe and the external pipe of the injectors. The second cooling means can generally be considered to consist of the space between the surrounding pipe and the external pipe of the injectors. Accordingly, the first and second cooling means are arranged to cool the injectors, respectively the surrounding pipe regardless of whether or not the spraying nozzles are spraying liquid reducing agent in a flue gas.

[12] Typically, the opening in the injection lance is aligned with the spraying nozzle, i.e. it typically has approximately the same longitudinal position as the spraying nozzle. Accordingly, sprayed reducing agent can be efficiently entered into a flue gas. [13] In an embodiment, the end of the injection lance is open. This allows enhanced cooling of the entirety of the injection lance. Alternatively, the end of the injection lance comprises a flow-influencing feature, e.g. a plate for changing the direction of cooling air flow, e.g. by 90°.

[14] In some embodiments, the injection lance comprises between 2 and 10 injectors, for example between 4 and 8 injectors. This strikes a good balance between the possibility of uniformly providing reducing agent in a flue stream, and the complexity of the injection lance.

[15] In an embodiment, the injection lance comprises several sets of two or more injectors, the injectors of any one set having the same length, and the injectors of different sets having a different length. In one embodiment, the injection lance comprises three sets of two injectors, wherein a first set of injectors has a length between 8300 and 8600 mm, wherein a second set of injectors has a length between 8700 and 9990 mm, and wherein a third set of injectors has a length between 10800 mm and 1 1200 mm.

[16] In an embodiment, the injection lance has a length between 8 and 13 m, for example a length between 10 and 1 1 m.

[17] In an embodiment, the external diameter of the internal pipe of the injectors is between 5.0 and 20.0 mm, for example between 8.0 and 12.0 mm. In an embodiment, the thickness of the internal pipe of the injector is between 0.50 mm and 2.0 mm, for example between 0.80 mm and 1 .2 mm.

[18] In an embodiment the external diameter of the external pipe of the injectors is between 15.0 and 25.0 mm, preferably between 20.0 and 25.0 mm. In an embodiment, the thickness of the external pipe of the injectors is between 2.0 and 3.0 mm, for example between 2.4 mm and 2.8 mm.

[19] In an embodiment, the injectors are slideably connected to the surrounding pipe. Preferably, the injection lance is provided with a flange for slideably connecting the injectors to the surrounding pipe. The slideable connection allows movement in the axial direction of the injection lance, and prevents unacceptably high stresses from occurring in response to thermal expansion.

[20] In an embodiment, the surrounding pipe has an external diameter of 1 10 mm to 170 mm, for example a diameter of 130 mm to 150 mm. In an embodiment, the surrounding pipe has a thickness of 2.0 -10.0 mm, for example a thickness of 4.0 to 6.0 mm.

[21 ] In an embodiment, the injection lance comprises a connection for receiving air to cool the surrounding pipe, and each injector comprises a connection for receiving atomization air and a connection for receiving a liquid reducing agent wherein, for each injector, the connection for receiving a liquid reducing agent is operably connected to a cylindrical space inside the internal pipe of the injector; the connection for receiving atomization air is operably connected to an annular space between the internal pipe and the external pipe; and, the connection for receiving air to cool the surrounding pipe is operably connected to the space between the surrounding pipe and the injector.

[22] In an embodiment, the connection for receiving the air to cool the surrounding pipe is a cylindrical tube which is oriented at an angle of 30° to 60°, for example an angle of 40° to 50°, with respect to the axis of the surrounding piping.

[23] In an embodiment, each injector comprises one and no more than one spraying nozzle, the spraying nozzle preferably being located at the injectors' end.

[24] In an embodiment, each spraying nozzle is associated with an opening in the surrounding pipe, the axial distance between associated spraying nozzles and openings being less than 20 to 60 mm.

[25] In an embodiment, each injector is connected to the surrounding pipe at a distance between 20 and 60 mm, preferably between 30 and 50 mm, from their spraying nozzle and from the corresponding opening in the surrounding pipe. In this embodiment, the injectors are preferably slideably connected to the surrounding pipe. In particular, the injection lance preferably comprises flange for slideably connecting the injectors to the surrounding pipe. The slideable connection allows movement in the axial direction of the injection lance, and prevents unacceptably high stresses from occurring in response to thermal expansion: the surrounding piping (2) is typically subjected to more thermal dilation than the injectors (3) because the temperature of the injectors is generally cooler than that of the surrounding piping (2). By providing the above-mentioned slideable connection, this difference in thermal dilation can be accommodated efficiently.

[26] In an embodiment, the injection lance further comprises an injector support structure comprising an injector support rod and one or more multi-armed structures, the multi-armed structures comprising two or more support beams and two or more injector holders, the number of support beams being equal to the number of injector holders, and the number of injector holders preferably being equal to the number of injectors, the support beams being radially disposed around the injector support rod, and each support beam connecting an injector holder to the injector support rod. Typically, the injection lance comprises 2 to 10, for example 4-8 injectors. The injector support rod typically has a diameter of 5.0 mm to 20 mm, for example a diameter of 10 to 15 mm.

[27] In some embodiments, the distance between adjacent multi-armed structures is between 500 mm and 4000 mm, preferably between 1000 and 2000 mm, more preferably between 1400 and 1600 mm.

[28] Typically, the injectors are concentrically arranged around the injector support rod.

[29] In an embodiment, the injection lance is made from an iron-chromium-nickel alloy.

[30] According to an embodiment of an injection lance according to the application, the first cooling means are arranged to cool the injectors with atomizing air that is used for atomizing the liquid reducing agent that is then sprayed by the respective spraying nozzles into the flue gas in the combustion chamber.

[31 ] In a possible embodiment of an injection lance according to the application, the atomizing air has a temperature of between 10°C and 60°C.

[32] The atomizing air more specifically has a pressure of between 0.5 bar and 4 bar, and most specifically between 1 bar and 3 bar.

[33] In an embodiment of an injection lance according to the application, the second cooling means are arranged to cool the surrounding pipe with air having a temperature of between 10°C and 250°C.

[34] In an embodiment, the air used to cool the surrounding pipe more has a pressure of between 0.01 bar and 0.5 bar.

[35] In an embodiment of an injection lance according to the application, each of the spraying nozzles has a droplet size and/or a spraying direction that are adjustable by changing the atomizing air pressure, the ratio of the atomizing air to the sprayed liquid reducing agent and/or the type of spraying nozzle. An adjustable droplet size allows manipulation of the penetration distance of the droplet, i.e. the bigger the droplet, the longer the time until it is vaporized.

[36] In an embodiment of an injection lance according to the application, the injection lance comprises a flow control unit for continuously controlling the flow of the liquid reducing reagent towards each of the spraying nozzles.

[37] In an embodiment of an injection lance according to the application, the first and second cooling means are arranged to cool the injectors, respectively the surrounding pipe in case the spraying nozzles are not spraying liquid reducing agent into the flue gas.

[38] In an embodiment of an injection lance according to the application, each of the injectors is connected with the surrounding pipe in the vicinity of their respective spraying nozzles. In the case the injectors would expand, possibly in a different way, then each of the injectors are able of move within the surrounding pipe, but their spraying nozzle situated at the end of the injectors will remain in the correct position where the respective openings in the surround pipe are provided.

[39] In an injection lance according to the application, the surrounding pipe is made out of a material that is resistant against a temperature of up to 1 100°C. One suitable material class is iron-chromium-nickel alloys. In particular a material having the following composition is suitable: a carbon content less than 0.40 %, a silicon content between 1 .0% and 3.0 %, a manganese content less than 4.0%, a phosphorous content of less than 0.90%, a sulphur content of less than 0.06%, a chromium content between 20.0% and 30.0%, and a nickel content between 15.0% and 25.0%, the remainder being made up out of iron, and all percentages being expressed as weight percentages. Preferably, a material having the following composition is used: a carbon content less than 0.20%, a silicon content between 1 .5 and 2.5%, a manganese content lower than 2.0%, a phosphorous content lower than 0.045%, a sulphur content lower than 0.03%, a chromium content between 24.0 and 26.0%, and a nickel content between 19.0 and 22.0%, the remainder being made up out of iron, and all percentages being expressed as weight percentages.

[40] In some embodiments, the injection lance comprises a flow control unit for continuously controlling the flow of the liquid reducing reagent towards each of the spraying nozzles. Accordingly, the amount of liquid reducing agent added to the flue gas stream can be effectively adapted according to actual process conditions. [41 ] According to a second aspect of the application, a boiler or furnace is provided having a combustion chamber comprising a roof and an injection lance according to the application as described above which is hanging essentially vertically from the roof of the combustion chamber.

[42] Additionally or alternatively, the boiler or surface can be described as follows: a boiler or furnace comprising a combustion chamber having a roof and an injection lance, the injection lance hanging essentially vertically from the roof of the combustion chamber of the boiler or furnace.

[43] According to a third aspect of the application, a boiler or furnace is provided with a combustion chamber comprising a substantially vertical wall and an injection lance according to the application as described above which is arranged in an essentially horizontal position attached to the substantially vertical wall, wherein between the injectors and the surrounding pipe, a supporting beam is arranged to maintain the injectors centrally disposed within the surrounding pipe.

[44] Additionally or alternatively, the boiler or furnace comprises a combustion chamber having a substantially vertical wall and an injection lance arranged in an essentially horizontal position attached to the substantially vertical wall, wherein the injector support structure is arranged to maintain the injectors centrally disposed within the surrounding pipe.

[45] In some embodiments, the connections are disposed outside of the boiler or furnace.

[46] In some embodiments, the injector lance has a certain penetration depth in the combustion chamber of the boiler or furnace, and the boiler or furnace is arranged with an adaptation mechanism to change the penetration depth of the injector lance. Typically, the adaptation mechanism is an automatic adaptation mechanism.

[47] In an embodiment of a boiler or furnace according to the application, the boiler or furnace is provided with one or more connections external to the combustion chamber for receiving the atomizing and ambient air and the liquid reducing reagent.

[48] In an embodiment of a boiler or furnace according to the application, the injector lance has a certain penetration depth in the combustion chamber of the boiler or furnace, and the boiler or furnace is arranged with an adaptation mechanism to change the penetration depth of the injector lance. For low load for example, the lance is completely inserted into the combustion chamber, while for higher load, the injection needs to be done further up in the combustion chamber and therefore the injection lance is partially lifted.

[49] In a further aspect, the present application relates to a method for reducing the amount of nitrogen oxides (NO _x ) present in flue gas provided from the combustion of fuel in a boiler or furnace, said method comprises the step of adding to said flue gas a liquid reducing reagent such as an aqueous urea or ammonia solution using an injection lance as described herein.

[50] Additionally or alternatively, the method for reducing nitrogen oxide emissions as described herein comprises the steps:

- providing an injection lance as described herein;

- providing cooling air to a space between the surrounding pipe and the injectors, preferably at a flow rate of 0.50 to 4.0x10 ³ m ³ /h and at a pressure of 0.01 to 0.5 bar, more preferably at a flow rate of 1 .0 to 2.0 m ³ /h and at a pressure of 40-50 mbar.

- providing atomization air to an annular space between the injectors' internal pipe and external pipe, preferably at a flow rate of 2.5-30.0 Nm ³ /h and at a pressure of 0.50 to 4.0 bar, more preferably at a flow rate of 5.0-15.0 Nm ³ /h and at a pressure of 1.0 to 3.0 bar;

- providing a liquid reducing agent to the internal pipe of the one or more injectors; and,

- spraying the liquid reducing agent in a flue gas.

[51 ] The flow rate of cooling rate is given at inlet conditions, i.e. at ambient conditions. The pressure of the cooling air is given with respect to the pressure of the flue gas. The pressure of the atomizing air is given with respect to atmospheric pressure.

[52] The temperature of the flue gas is mostly between 800°C and 1250°C, and typically between 850°C and 1050°C.

[53] The total quantity of reducing agent which is injected into the flue gas typically depends on the NOx concentration in the flue gas, the flue gas flow, and the chemical efficiency by which the reducing agent reduces the NOx contaminants. Accordingly, the flow rate of the reducing agent can vary significantly, for example in the range of 0 to 500 l/h per nozzle, and typically in the range of 5 to 200 l/h per nozzle. It is noted that generally, the total reducing agent flow is distributed over the different nozzles. In an embodiment, the reducing agent is diluted with water in order to maintain the total liquid flow in each nozzle in the range of 20-300 l/h, or 40-200 l/h - the specific range may depend on the specific type of nozzle which is used.

[54] In an embodiment, the temperature of the atomizing air at the connection for receiving atomization air is between 10°C and 60°C.

[55] In an embodiment, the cooling air provided to the a space between the surrounding pipe and the injectors has an inlet temperature between 10°C and 250°C. Typically, ambient air is used as cooling air.

[56] In an embodiment, the temperature of the atomizing air at the connection for receiving atomization air is between 10°C and 60°C.

[57] In an embodiment, the method further comprises the step of adjusting the droplet size and/or spraying direction by changing the atomizing air pressure, the ratio of the atomizing air to the sprayed liquid reducing agent and/or the type of spraying nozzle.

[58] In a further aspect, the present application relates to the use of injection lance as described herein for injecting a liquid reducing reagent such as an aqueous urea or ammonia solution to in combustion chamber thereby reducing the amount of nitrogen oxides (ΝΟχ) present in flue gas provided from the combustion of fuel in a boiler or furnace.

[59] The present invention is further elucidated by way of the following specific embodiments:

[60] Specific embodiment 1. An injection lance for injecting a liquid reducing reagent into a flue gas from the combustion of fuel in a combustion chamber of a boiler or furnace to reduce the amount of nitrogen oxides in the flue gas, wherein the injection lance comprises

at least two oblong separate injectors having a different length and each having a single spraying nozzle at the end thereof for spraying the liquid reducing agent in the flue gas in the combustion chamber;

first cooling means to cool the injectors with air;

- an surrounding pipe coaxial with and disposed around the injectors and provided with at least one opening per injector spaced along its length and located in the vicinity of the respective spraying nozzles to allow the spraying nozzles to spray the liquid reducing agent through the openings into the flue gas;

second cooling means to cool the surrounding pipe with air.

[61 ] Specific embodiment 2. Injection lance according to specific embodiment 1 , wherein the first cooling means are arranged to cool the injectors with atomizing air that is used for atomizing the liquid reducing agent that is then sprayed by the respective spraying nozzles into the flue gas in the combustion chamber.

[62] Specific embodiment 3. Injection lance according to specific embodiment 2, wherein the atomizing air has an inlet temperature of between 10°C and 60°C.

[63] Specific embodiment 4. Injection lance according to specific embodiment 2 or 3, wherein the atomizing air has a pressure of between 0.5 bar and 4 bar, more specifically between 1 bar and 3 bar.

[64] Specific embodiment 5. Injection lance according to any one of specific embodiments 1 to 4, wherein the second cooling means are arranged to cool the surrounding pipe using air having a temperature of between 10°C and 250°C.

[65] Specific embodiment 6. Injection lance according to specific embodiment 5, wherein the air used to cool the surrounding pipe has a pressure of between 0.01 bar and 0.5 bar.

[66] Specific embodiment 7. Injection lance according to any one of specific embodiments 2 to 6, wherein each of the spraying nozzles has a droplet size and/or a spraying direction that are adjustable by changing the atomizing air pressure, the ratio of the atomizing air to the sprayed liquid reducing agent and/or the type of spraying nozzle.

[67] Specific embodiment 8. Injection lance according to any one of specific embodiments 1 to 8, wherein the injection lance comprises a flow control unit for continuously controlling the flow of the liquid reducing reagent towards each of the spraying nozzles.

[68] Specific embodiment 9. Injection lance according to any one of specific embodiments 1 to 8, wherein the first and second cooling means are arranged to cool the injectors, respectively the surrounding pipe in case the spraying nozzles are not spraying liquid reducing agent into the flue gas. [69] Specific embodiment 10. Injection lance according to any one of specific embodiments 1 to 9, wherein each of the injectors are connected with the surrounding pipe in the vicinity of their respective spraying nozzle.

[70] Specific embodiment 1 1. Injection lance according to any one of specific embodiments 1 to 1 1 , wherein the surrounding pipe is made out of a material that is resistant against a temperature of up to 1 100°C.

[71 ] Specific embodiment 12. A boiler or furnace comprising a combustion chamber having a roof and an injection lance according to any one of specific embodiments 1 to 12 hanging essentially vertically from the roof of the combustion chamber of the boiler or furnace.

[72] Specific embodiment 13. A boiler or furnace comprising a combustion chamber having a substantially vertical wall and an injection lance according to any one of specific embodiments 1 to 1 1 arranged in an essentially horizontal position attached to the substantially vertical wall, wherein between the one or more injectors and the surrounding pipe, a supporting beam is arranged to maintain the injectors centrally disposed within the surrounding pipe.

[73] Specific embodiment 14. Boiler or furnace according to specific embodiment 12 or 13, wherein the boiler or furnace is provided with one or more connections external to the combustion chamber for receiving the atomizing and ambient air and the liquid reducing reagent.

[74] Specific embodiment 15. Boiler or furnace according to any one of specific embodiments 1 1 to 14, wherein the injector lance has a certain penetration depth in the combustion chamber of the boiler or furnace, and the boiler or furnace is arranged with an adaptation mechanism to change the penetration depth of the injector lance.

Description of the figures

[75] FIG. 1 shows a top view of an exemplary embodiment of an injection lance according to the application.

[76] Fig. 2 shows a lateral view of an injection lance.

[77] Fig. 3 shows a cross section of an injection lance.

[78] Fig. 4 shows a cross section of an injection lance.

[79] Fig. 5 shows a cross section of an injection lance.

[80] Fig. 6 shows a lateral section of an injection lance. [81 ] Fig. 7 shows a lateral section of an injection lance.

[82] Fig. 8 shows injectors in an injector assembly.

[83] Fig. 9 shows an injector support structure.

Throughout the figures, the following numbering is adhered to: 1 - injection lance; 2 - surrounding piping; 3 - injector; 4 - spraying nozzle; 5 - wall; 6 - connection for receiving atomization air; 7 - connection for receiving air to cool the surrounding pipe; 8 - connection for receiving liquid reducing agent; 9 - blind flange; 10 - opening; 1 1 - end of the injection lance; 12 - internal pipe of injector; 13 - external pipe of injector; 14 - multi-armed structure; 15 - reducer; 16 - pin; 17 - protrusion; 19 -flange; 20 - injector support ring; 22 - injector support rod; 23 - injector holder; 24 - injector holder; 25 - dovetail end; 26 - support beam; 28 - fitting; 29 - distributive seat; 30 - end of injector; 31 - fitting.

Detailed description

[84] An injection lance (1 ) according to the application, of which an exemplary embodiment is shown in FIG. 1 , is arranged for injecting a liquid reducing reagent, more specific an aqueous urea or ammonia solution, into a flue gas produced by the combustion of fuel in a combustion chamber of boiler, for instance a power boiler, or a furnace in order to reduce the amount of NO _x in the flue gas. The injection lance (1 ) comprises a surrounding pipe (2) made out of high temperature resistant steel, more in particular resistant against temperatures up to 1 100°C. This surrounding pipe (2) is coaxial with and disposed around at least two oblong separate injectors (3) that at the end thereof each have a single spraying nozzle (4) (see FIG. 1 ) for spraying the liquid reducing reagent through one opening (10) per injector (3) in the surrounding pipe (2) provided in the vicinity of the respective spraying nozzle (4) such that the sprayed liquid reducing agent can enter into the combustion chamber of the boiler or furnace to reduce the amount of NO _x in the flue gas. The injectors (3) inject the liquid reducing agent in particular under an angle of between 0° and 30°. Each of the spraying nozzles (4) can have a droplet size and/or a spraying direction that are adjustable by changing the pressure of the atomizing air, the ratio of the atomizing air to the sprayed liquid reducing agent and/or the type of spraying nozzle. The spraying direction can be made adjustable more specifically by changing the type of spraying nozzle and the position thereof within the injection lance (1 ). [85] The injection lance (1 ) can comprise a flow control unit for continuously controlling the flow of the liquid reducing reagent towards each of the spraying nozzles (4). The exemplary embodiment as shown in FIG. 1 is provided with three oblong injectors (3) extending into the surrounding pipe (2) and each having a different length.

[86] Each of the injectors (3) can be fixed with the surrounding pipe (2) in the vicinity of each of their spraying nozzles (4).

[87] The injection lance (1 ) furthermore comprises first cooling means to cool the injectors with air. The air that is used to cool the injectors (3) is more specifically the atomizing air that is used to atomize the liquid reducing agent or in other words to reduce the liquid reducing agent to a fine spray in each of the injectors (3). The atomizing air more specifically has an inlet temperature of between 10°C and 60°C and has a pressure of between 0.5 and 4 bar, and more in particular a pressure of between 1 and 3 bar. It is remarked that further in the injection lance (1 ), the temperature can be higher.

[88] The injection lance (1 ) furthermore comprises second cooling means that are arranged to cool the surrounding pipe (2) with air having a temperature of between 10°C and 250°C. The air to cool the surrounding pipe (2) more specifically has a pressure of between 0.01 and 0.5 bar. This air can be obtained from any air source having the right temperature and pressure. This air can for instance be produced by an air blower which injects air at the beginning of the surrounding pipe (2). It can however also be cold combustion air. Furthermore, it can also be air that is coming from ammonia stripping of the ash produced in the combustion chamber. During transport of fly ash together with the flue gas, ammonia is adsorbed on the fly ash. Since the fly ash is however sold, the amount of ammonia that is allowable is limited. In case the ammonia content in the fly ash is too high, there exists a technique in which fly ash is put into a hot air stream through which ammonia content is desorbed from the fly ash again. This ammonia loaded hot air stream can also be sued as the cooling air for the surrounding pipe (2).

[89] The first cooling means, respectively the second cooling means can be provided to cool the injectors (3) with atomizing air, respectively the surrounding pipe (2) with air, even when the injectors (3) are not spraying liquid reducing agent into the flue gas. [90] As can be seen in FIG. 1 , outside the wall (5) of the combustion chamber, connections can be provided for

receiving the atomizing air (connections 6),

the air to cool the surrounding pipe (2) (connections 7); and

- the liquid reducing agent (connections 8).

[91 ] The injection lance (1 ) according to the application as described above can be installed in an essentially horizontal as well as in an essentially vertical way in the combustion chamber. When the injection lance (1 ) is positioned in an essentially vertical way, the injection lance (1 ) more specifically hangs from the roof of the combustion chamber of the boiler or the furnace. When the injection lance (1 ) is positioned in an essentially horizontal way, the injection lance (1 ) more specifically is provided with a supporting beam (not shown on the figures) between the injectors (3) and the surrounding pipe (2) to keep the injectors centrally disposed within the surrounding pipe (2).

[92] The injection lance (1 ) optionally can be provided movable within the combustion chamber, for instance by providing a hoist fixed at the roof of the combustion chamber or a retractable support for a horizontally positioned injection lance (1 ).

[93] In one embodiment, the injection lance (1 ) has a certain penetration depth in the combustion chamber of the boiler or the furnace which can be adapted by means of an adaptation mechanism, for instance a compression seal fitting (gland) (not shown on the FIGs) that is located where the injectors (3) penetrate the blind flange (9) (see FIG. 1 ) and that secures the injectors (3) to the blind flange (9).

[94] Typically, the injectors (3) are slideably secured to the blind flange (9), i.e. the injectors are allowed to slide through the blind flange (9) during normal operation. This allows efficiently compensating for thermal dilation of the injection lance: the surrounding piping (2) is typically subjected to more thermal dilation than the injectors (3) because the temperature of the injectors is generally cooler than that of the surrounding piping (2). By providing the above-mentioned slidable connection, this difference in thermal dilation is effectively taken into account.

[95] When the injection lance is used in a combustion chamber, the combustion chamber may comprise a support pipe connected to a flange, which in turn is connected to the wall of the injection chamber. The injection lance can be inserted in the support pipe, such that it penetrates the combustion chamber wall.

[96] One or more exemplary embodiments of the present injection lance (1 ) are further described by reference to Figs. 2 to 9.

[97] Fig. 2 shows a lateral view of an injection lance (1 ). The length of the injection lance, i.e. the distance between the wall (5) and its end (1 1 ) is 10500 mm. The end (1 1 ) of the injection lance may be open, or it may comprise a plate for changing the direction of cooling air flow, e.g. by 90°. The injection lance comprises a surrounding piping (2) having an external diameter of 140 mm and having a thickness of 5 mm. The connection (7) for receiving the air to cool the surrounding pipe is a cylindrical tube which is oriented at an angle of 45° with respect to the axis. The injection lance comprises a total of six injectors (3).

[98] Figs 3 to 7 show various cross sections through the injection lance (1 ). Fig. 8 shows a lateral view of the injectors (3). Fig. 9 shows an injector support structure (31 ).

[99] Figs. 3-5 show cross sections of the injection lance. In particular, Fig. 3 shows cross section C-C, Fig. 4 shows cross section D-D, and Fig. 5 shows cross section E- E, the locations of which are indicated in Fig. 2. It shows location of the injectors (3) inside the injection lance. In particular, the injection lance comprises six injectors (3) which are each held by an injection holder (23). In turn, the injection holders (23) are held in place by a multi-armed structure (14) which is connected to an injector support rod (22). The injectors are tubular objects having an internal pipe (12) and an external pipe (13). The external diameter of the external pipe (13) of the injectors (3) is 21 mm and its thickness is 3 mm. The external diameter of the internal pipe (12) of the injectors (3) is 10 mm, and its thickness is 1 mm. A pin (16) provides a secure connection between the multi-armed structure (14) and the surrounding piping (2). The protrusions (17) support the injectors (3).

[100] Figs. 6 and 7 respectively show lateral sections J-J and H-H, the positions of which are indicated in Fig. 3. Two injectors (3) are shown, each having an internal pipe (12) for carrying a liquid reductant, and an external pipe (13) for carrying atomization air.

[101 ] Fig. 8 shows the injectors (3) in an injector assembly. The injectors are connected to a flange (19), which allows connecting them to a surrounding pipe. The injectors are further connected to injector holders (23) for connecting them to multi- armed structures, which keep the injectors in place with respect to each other. Each injector (3) comprises a connection for receiving atomizing air and a connection for receiving a liquid reducing agent. The injection lance (1 ) comprises three sets of two injectors (3). These three sets have different lengths. In particular, a first set of injectors has a length of 8500 mm, a second set of injectors has a length of 8900 mm, and a third set of injectors has a length of 1 1000 mm. The use of sets of injectors (3) having different lengths allows injecting reducing agents in a furnace or super heater at various locations, which results in improved reagent homogeneity in the furnace or boiler. During normal operation, the 6 concentrically arranged injectors, each comprising a connection for receiving atomizing air and a connection for receiving a liquid reducing agent. The injectors are concentrically arranged around an injector support rod (22). During normal operation, both the injectors and the injector support rods are arranged to be movable along the longitudinal axis of the injection lance. In particular, they are slideably connected to a flange (19). This reduces the occurrence of thermal stresses which may occur during normal operation at high temperature.

[102] Fig. 9 shows an injector support structure (31 ). It comprises an injector support rod (22) and several multi-armed structures for fixing the relative position of the injectors. The multi-armed structure comprises 6 support beams (26) and 6 injector holders (23). The support beams (26) connect the injector holders (23) to the injector support rod (22). The injector support rod has a diameter of 10 mm.

[103] The injectors (3) are slideably disposed within the reducers (15). Accordingly, a single injector can be taken out for maintenance without extracting the complete lance. The protrusions (17) help to keep the injectors (3) in place.

[104] The injectors (3) can pass through the injector holders (23) of the multi-armed structure (14) which are located along the length of the injection lance, but not through the injector holders (24) of the injector support ring (20) near the end of the injection lance: the injector holders (24) of the injector support ring (20) have a smaller diameter than the injector holders (23) of the multi-armed structure (14).

[105] The injectors each comprise a connection for receiving atomization air (6) and a connection for receiving a liquid reducing agent (8). At the injector's end (30), a spraying nozzle (4) is disposed. The injector comprises an internal pipe (12) and an external pipe (13). The internal pipe (12) is in fluid connection with a connection (8) for receiving liquid reducing agent. The external pipe (13) is connected to a connection (6) for receiving atomization air.

[106] In an exemplary mode of operation, cooling air is provided to the space between the external duct and the injectors at a flow rate between 1 .0-2.0x10 ³ m ³ /h at a pressure of 50 mbar. The flow-rate by which the cooling air is provided can be varied by means of a fan. Atomization air is provided to the injector, and particularly to the space between the injectors' internal pipe and external pipe. The atomization air is provided at a pressure of 2 bar, at a flow rate of 5.0-15.0 Nm ³ /h for each nozzle separately, in which the symbol "Nm ³ " denotes cubic meter under standard conditions. Liquid reducing agent flows through the injectors' internal pipe.