INJECTION LANCE FOR INJECTING A LIQUID REDUCING REAGENT INTO A FLUE GAS FROM THE COMBUSTION OF FUEL IN A BOILER OR FURNACE TO REDUCE THE AMOUNT OF NITROGEN OXIDES IN THE FLUE GAS

Abstract

 The present application relates to 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, 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 and second cooling means to cool the surrounding pipe with air.

Description

Technical field

[0001] 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

[0002] The major air pollutants emanating from boilers and furnaces are nitrogen oxides (NO_x), including nitric oxide (NO), nitrogen dioxide (NO₂) and nitrous oxide (N₂O). The total NO and NO₂-concentration is typically referred to as NO_x (nitrogen oxides). Nitrogen oxides are mainly produced in the form of NO. Some NO₂ and N₂O 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.

[0003] 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.

[0004] 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.

[0005] Water-cooled injector lances penetrating the combustion area of a boiler or furnace are quite common. 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.

[0006] 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.

[0007] 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 and having an improved NO_x-reduction.

Summary

[0008] 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.

[0009] 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. 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. There is also no direct connection between the injectors and the surrounding pipe, due to different thermal expansion.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] The air used to cool the surrounding pipe more specifically has a pressure of between 0.01 bar and 0.5 bar.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 1100°C.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 (NO_x) present in flue gas provided from the combustion of fuel in a boiler or furnace.

Description of the figures

[0026] FIG. 1 shows a top view of an exemplary embodiment of an injection lance according to the application.

Detailed description

[0027] 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 1100°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).

[0028] 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.

[0029] Each of the injectors (3) can be fixed with the surrounding pipe (2) in the vicinity of each of their spraying nozzles (4).

[0030] 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.

[0031] 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).

[0032] 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.

[0033] 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).

[0034] 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).

[0035] 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).

[0036] 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).

Claims

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.

2. Injection lance according to claim 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.

3. Injection lance according to claim 2, wherein the atomizing air has an inlet temperature of between 10°C and 60°C.

4. Injection lance according to claim 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.

5. Injection lance according to any one of claims 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.

6. Injection lance according to claim 5, wherein the air used to cool the surrounding pipe has a pressure of between 0.01 bar and 0.5 bar.

7. Injection lance according to any one of claims 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.

8. Injection lance according to any one of claims 1 to 7, 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.

9. Injection lance according to any one of claims 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.

10. Injection lance according to any one of claims 1 to 9, wherein each of the injectors are connected with the surrounding pipe in the vicinity of their respective spraying nozzle.

11. Injection lance according to any one of claims 1 to 10, wherein the surrounding pipe is made out of a material that is resistant against a temperature of up to 1100°C.

12. A boiler or furnace comprising a combustion chamber having a roof and an injection lance according to any one of the claims 1 to 11 hanging essentially vertically from the roof of the combustion chamber of the boiler or furnace.

13. A boiler or furnace comprising a combustion chamber having a substantially vertical wall and an injection lance according to any one of the claims 1 to 11 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.

14. Boiler or furnace according to claim 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.

15. Boiler or furnace according to any one of claims 11 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.

Drawing