A power producing apparatus comprising a system for reducing nitrogen oxides in the flue gas and a method for reducing nitrogen oxides in the flue gas of a power producing apparatus

Abstract

A power producing apparatus comprising a system for reducing nitrogen oxides in the flue gas stream of the power producing apparatus using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas and a re- lated method are disclosed, the flue gas comprising nitrogen oxides, oxygen and even- tually water. In particular, the method comprises the steps of cooling and condensing at least a part of the flue gas stream into a condensate comprising at least part of the nitrogen oxides of the flue gas stream, separating the condensate from the remaining flue gas stream, and collecting the condensate. The system comprises a duct along which one or more heat exchanging areas are arranged, to cool the gas stream and condensate at least a part of the gas stream into a condensate stream comprising at least part of the nitrogen oxides of the gas stream, and wherein the system also comprises condensate collectors configured to collect a respective condensate stream and direct it to a respective condensate withdrawal line.

Description

A power producing apparatus comprising a system for reducing nitrogen oxides in the flue gas and a method for reducing nitrogen oxides in the flue gas of a power producing apparatusDescriptionTECHNICAL FIELD

[0001] The present disclosure concerns a power producing apparatus comprising a system for reducing the amount of a nitrogen oxides in the flue gas, the power producing apparatus using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas and a related method. Embodiments disclosed herein specifically concern power producing apparatuses comprising systems and methods for reducing nitrogen oxides in the flue gas by means of refrigeration of the flue gas, including cooling and condensation of the nitrogen oxides and subsequent collection of the condensate.BACKGROUND ART

[0002] It is known that nitrogen oxides (NOx) are a group of gases that include nitric oxide (NO) nitrogen dioxide (NO2) and nitrous oxide (N2O). Nitrogen oxides are produced by human activities such as combustion of fossil fuels, transportation, and agriculture. Nitrous oxide (N2O) is one of the nitrogen oxides that contributes to global warming. It is over 300 times more effective at trapping heat in the atmosphere than carbon dioxide. In detail, the global warming potential (GWP) of nitrous oxide is 310 which means it has a warming effect 310 times greater than carbon dioxide over a 100- year time horizon.

[0003] It is also known that gas turbines are commonly used to generate power at power stations by combusting fuel therein. In particular, the basic operation of a gas turbine is a Brayton cycle with air as the working fluid: atmospheric air flows through a compressor that brings it to a higher pressure; energy is then added by injecting fuel into the air in a combustion chamber and igniting it so that a combustion generates a high-temperature flow; this high-temperature pressurized gas enters a turbine, producing a shaft work output in the process, used to drive the compressor; the unused energy comes out in the flue gases that can be repurposed for external work, such as directlyproducing thrust in a turbojet engine, or rotating a second, independent turbine (known as a power turbine) that can be connected to a fan, propeller, or electrical generator. The purpose of the gas turbine determines the design so that the most desirable split of energy between the thrust and the shaft work is achieved. The fourth step of the Brayton cycle (cooling of the working fluid) is omitted, as gas turbines are open systems that do not reuse the same air.

[0004] Commonly used fuels include natural gas, propane, diesel, biogas and biodiesel. One of the main problems associated with combusting fuels such as these in gas turbines is the resultant production of carbon dioxide (CO2) gas. Increased CO2 levels in the atmosphere are detrimental to the environment and are a known cause of global warming. As such, there is a need to provide fuels for use in gas turbines which do not generate CO2 upon combustion, or from which CO2 must be removed prior to combustion.

[0005] Carbon-free fuels include ammonia and hydrogen. However, both ammonia and hydrogen have problems associated with their use as fuel in a gas turbine. The main problem associated with the use of ammonia as fuel in gas turbines is that during the combustion process ammonia is oxidized to nitrogen oxides. Additionally, due to the low heat content and low reactivity of ammonia with oxygen, the ammonia combustion within the gas turbine presents stability issues (blow-out) over the entire range of the gas turbine operating conditions. On the other hand, even if the combustion of hydrogen still produces NOXpolluting agents, stability issues (blow-out) disappear. Nevertheless, a number of problems is associated with the use of hydrogen as fuel, including storage problems and the fact that hydrogen is an extremely flammable gas.

[0006] There are several systems available to reduce nitrogen oxides (NOx) in a gas stream. One of the most common methods is Selective Catalytic Reduction (SCR). This process involves converting nitrogen oxides, with the aid of a catalyst into diatomic nitrogen (N2) and water (H2O). A reductant, typically anhydrous ammonia (NH3), aqueous ammonia (NH4OH), or a urea (CO(NH2)2) solution, is added to a stream of flue or exhaust gas and is reacted onto a catalyst. As the reaction drives toward completion, nitrogen (N2), and carbon dioxide (CO2), in the case of urea use, are produced.

[0007] Another method is Selective Non-Catalytic Reduction (SNCR). This process involves injecting either ammonia or urea at a location where the flue gas is between 760 and 1090 °C to react with the nitrogen oxides.

[0008] Both SCR and SNCR have been shown to be effective in reducing NOx emissions from various sources such as power plants, industrial boilers, and municipal solid waste, but they have high CAPEX and OPEX. Under certain conditions, specific cost ($ / MWh) of SCR and SNCR can even reach significant cost of gas turbine itself.

[0009] Accordingly, an improved power producing apparatus comprising a system and method for reducing nitrogen oxides in the flue gas of the power producing apparatus, the power producing apparatus, in particular a gas turbine, using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, to address the issues of cost of the systems of the current art would be beneficial and would be welcomed in the technology.SUMMARY

[0010] In one aspect, the subject matter disclosed herein is directed to a refrigeration based solution to separate nitrogen oxides from a flue gas of a power producing apparatus, in particular a gas turbine, using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, the flue gas comprising nitrogen oxides, oxygen and eventually water.

[0011] In another aspect, the subject matter disclosed herein concerns a method to condensate and separate nitrogen oxides from a flue gas stream of a power producing apparatus using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, the flue gas comprising nitrogen oxides, oxygen and eventually water, the system comprising the following steps:- cooling and condensing at least a part of the flue gas stream into a condensate comprising at least part of the nitrogen oxides of the flue gas stream, through contact with a cooling surface,- separating the condensate from the remaining flue gas stream, and- collecting the condensate.

[0012] In still another aspect, the subject matter disclosed herein concerns a methodto condensate and separate nitrogen oxides from a flue gas stream of a power producing apparatus, in particular a gas turbine, using a fuel comprising one or more of ammonia through contact with a cooling surface, wherein a step of cooling and condensing at least a part of the flue gas stream comprises the following sub-steps: cooling down the flue gas stream to a temperature below the condensation temperature of at least some NOx and above water solidification temperature, preferably to a temperature ranging from 5 to 20°C, to obtain a first condensate and an intermediate residual flue gas stream, the first condensate including at least part of the NOx and water of the flue gas stream; separating the first condensate from the intermediate residual flue gas stream and collecting the first condensate; cooling down the intermediate residual flue gas stream to a temperature below the condensation temperature of at least N2O and NO, preferably below the condensation temperature of at least NO2, N2O4 and N2O5, in particular a temperature ranging from -160 to -190°C, to obtain a second condensate and a final residual flue gas stream, the second condensate including at least part of the N2O and NO of the flue gas stream; and separating the second condensate from the final residual flue gas stream and collecting the second condensate.

[0013] In another aspect, the subject matter disclosed herein concerns a power producing apparatus, in particular a gas turbine, comprising a system to condensate and separate nitrogen oxides from the flue gas stream of the power producing apparatus, the power producing apparatus, more in particular a gas turbine, using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, the system comprising a duct for the flue gas stream, wherein one or more heat exchanging areas are arranged inside the duct, the heat exchanging areas being configured to cool and condensate at least a part of the flue gas stream into a condensate stream comprising at least part of the nitrogen oxides of the flue gas stream, each heat exchanging area comprising a respective heat exchanging surface, configured to exchange heat with said flue gas stream and to form a condensation surface, and wherein the system also comprises a condensate collector of each heat exchanging area, thecondensate collector being configured to collect the condensate stream from the respective heat exchanging area, the condensate collector being connected to a respective condensate withdrawal line.

[0014] In still another aspect, the system comprises two heat exchanging areas, a first heat exchanging area upstream and a second heat exchanging area downstream, the first heat exchanging area comprising a respective heat exchanging surface and being connected to a respective condensate collector and a respective condensate withdrawal line and the second heat exchanging area comprising a respective second heat exchanging surface and being connected to a respective condensate collector and a respective condensate withdrawal line, wherein the temperature of the heat exchanging surface of the first heat exchanging area is below the condensation temperature of at least some NOx and above water solidification temperature, namely ranging from 5 to 20°C, and the temperature of the heat exchanging surface of the second heat exchanging area is below the condensation temperature of at least N2O and NO and preferably below the condensation temperature of at least NO2, N2O4 and N2O5, namely ranging from -160 to -190°C.

[0015] In one aspect, each heat exchanging area comprises a cooling side on an opposite side of a wall with respect to the heat exchanging surface, the cooling side being contacted by a cooling fluid, such as chilled water, liquid natural gas or liquid nitrogen.

[0016] In still another aspect, the system also comprises one or more additional heat exchanging areas, arranged upstream the heat exchanging areas configured to cool and condensate at least a part of the flue gas stream, the additional heat exchanging areas comprising a cooling side on an opposite side of a wall with respect to a heat exchanging surface, the cooling side being contacted by one heat exchanging fluid, the heat exchanging fluid on the cooling side of each additional heat exchanging area being the same or being different from the heat exchanging fluid of the other additional heat exchanging areas by exchanging heat between the flue gas stream and one of more fluids, which are chosen amongst a fuel of the gas turbine, a working fluid of an auxiliary thermodynamic systems, a working fluid of a heat recovery steam generator of a steam turbine.

[0017] In still another aspect, the cooling fluids on the cooling side of one or moreheat exchanging areas and / or the heat exchanging fluid on the cooling side of one or more additional heat exchanging area, is flown in a closed circuit, the closed circuit comprising additional heat exchangers configured to lower the temperature of the cooling fluid and / or the heat exchanging fluid.

[0018] In particular, the proposed solution is highly efficient to separate nitrogen oxides from a flue gas stream comprising more than 50ppm of nitrogen oxides compounds.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig.1 illustrates a schematic of a power producing apparatus comprising a system for reducing nitrogen oxides in a flue gas stream of the power producing apparatus, the power producing apparatus using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, according to a first embodiment; andFig.2 illustrates a schematic of a power producing apparatus comprising a system for reducing nitrogen oxides in a flue gas stream of the power producing apparatus, the power producing apparatus using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, according to a second embodiment.DETAILED DESCRIPTION OF EMBODIMENTS

[0020] According to one aspect, the present subject matter is directed to power producing apparatuses comprising systems and methods for reducing nitrogen oxides in a flue gas stream of the power producing apparatus, the power producing apparatus, in particular a gas turbine, using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, by means of refrigeration of the flue gas stream, thus causing condensation of the nitrogen oxides, together with other components of the flue gas stream having a condensation temperature equal to or lower that the nitrogen oxides condensation temperature, and subsequent collection of thecondensate. Specifically, in the embodiments disclosed herein a refrigeration system is provided, which includes a duct with an inlet and an outlet for a flue gas stream and comprising one or more heat exchanging areas between the inlet and the outlet of the duct, to cool the flue gas stream and subsequently condensate at least a part of the flue gas stream into a condensate stream comprising at least part of the nitrogen oxides of the flue gas stream, the system also comprising means to collect and withdraw the condensate. In particular, the system can comprise two heat exchanging areas, in particular a first heat exchanging area and a second heat exchanging area, downstream the first heat exchanging area, the temperature of the first heat exchanging area being such to allow the condensation of at least some NOXand at the same time to avoid water solidification, in order to condensate and withdraw the NOXcondensate together with liquid water and the temperature of the second heat exchanging area being such to condensate of at least N2O and NO, and preferably of at least NO2, N2O4 and N2O5.

[0021] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0022] When introducing elements of various embodiments the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0023] Referring now to the drawings, Fig.1 shows a schematic of a system 10 of a power producing apparatus according to a first embodiment. The system 10 can becomprised of a duct 11, comprising a flue gas stream inlet 12 and a flue gas stream outlet 13, and two heat exchanging areas, namely an upstream heat exchanging area14 and a downstream heat exchanging area 15. Each heat exchanging area 14, 15 comprises a heat exchanging surface 140, 150, configured to exchange heat with said flue gas stream and to form a condensation surface. In particular, the heat exchanging surfaces 140, 150 are inclined extended surfaces arranged to form a descending path towards respective condensate collectors 16, 17, which are in turn connected to respective condensate withdrawal lines 18, 19.

[0024] In particular, the heat exchanging areas are configured to cool and condensate at least a part of the flue gas stream into a condensate stream comprising at least part of the nitrogen oxides of the flue gas stream, the temperature of the heat exchanging surface 140 of the upstream heat exchanging area 14 is below the condensation temperature of at least some NOxand above water solidification temperature, and the temperature of the heat exchanging surface 150 of the downstream heat exchanging area15 is below the condensation temperature of at least N2O and NO and can be below the condensation temperature of at least NO2, N2O4 and N2O5. For example, the temperature of the heat exchanging surface 140 of the upstream heat exchanging area 14 can be comprised between 5 and 20°C, while the temperature of the heat exchanging surface 150 of the downstream heat exchanging area 15 can be comprised between - 160 and -190°C.

[0025] In particular, each heat exchanging area 14, 15 comprises a cooling side on an opposite side of a wall with respect to the heat exchanging surface 140, 150, the cooling side being contacted by a cooling fluid, the cooling fluid of the upstream heat exchanging area 14 being chilled water of a first cooling circuit 141; while the cooling fluid of the downstream heat exchanging area 15 is a low temperature cooling fluid of a second cooling circuit 151, which is chosen amongst liquid natural gas or liquid nitrogen, and preferably is liquid nitrogen.

[0026] Advantageously, the duct 11 is thermally insulated from the surrounding environment and can be made of aluminum cladded material. The heat exchanging surfaces 140, 150, the condensate collectors 16, 17 and the condensate withdrawal lines 18, 19 can also be cladded or entirely made of aluminum and / or aluminum oxide.

[0027] Still with reference to Fig. 1, the duct 11 is conveniently arranged in an ascending configuration, the flue gas stream inlet 12 being arranged in a lower position and the flue gas stream outlet 13 being arranged in an upper position. In particular, the duct 11 is straight and is arranged vertically.

[0028] With continuing reference to Fig.1, Fig.2 illustrates a system 10 of a second embodiment of a power producing apparatus. The same reference numbers as used in Fig.1 designate the same parts, components or elements, which are not described again. In the embodiment of Fi . 2 the system 10 comprises one or more additional heat exchanging areas 20, arranged upstream the heat exchanging areas 14, 15 configured to cool and condensate at least a part of the flue gas stream to condensate a stream comprising at least part of the NOXof the flue gas stream, the additional heat exchanging areas 20 comprising heat exchanging surfaces 200 configured to pre-cool the flue gas stream. In particular, each additional heat exchanging area 20 comprises a cooling side contacted by one heat exchanging fluid, the heat exchanging fluid on the cooling side of each additional heat exchanging area 20 being the same or being different from the heat exchanging fluid of the other additional heat exchanging areas 20. In the exemplary embodiment shown with reference to Fig.2, the flue gas stream is a flue gas of a gas turbine using a fuel comprising ammonia and the heat exchanging fluid on the cooling side of at least one of the additional heat exchanging areas 20 is a fuel of the gas turbine. The heat exchanging fluid on the cooling side of at least one of the additional heat exchanging areas can also be a working fluid of an auxiliary thermodynamic system or a heat recovery steam generator of a steam turbine.

[0029] Still with reference to Fig.2, the additional heat exchanging areas 20 are arranged in an additional duct portion 21, arranged horizontally, while the duct 11 is arranged vertically. The heat exchanging fluid on the cooling side of the additional heat exchanging areas 20 is flown in a closed circuit 90, the closed circuit comprising additional heat exchangers 91, 92, 93 configured to lower the temperature of the heat exchanging fluid.Example 1

[0030] The method and the system to separate nitrogen oxides from a flue gas streamas previously described with reference to Fig.2 were verified by theoretical calculations on the flue gas of gas turbines operating on fuels like ammonia or mixtures of hydrogen and ammonia together with air with an exhaust gas at a temperature ranging between 480 to 600 °C with NOx levels of 200 to 500 ppm comprising: NO, N2O, NO2, N2O5 and N2O4.

[0031] The physical properties of the NOx are detailed herein below.

[0032] NOSharp, sweet-smelling, colourless gasMelting point: -163.6°CBoiling point: -151.8°C- Relative Density: 1.04 (air = 1)

[0033] N2OBoiling point: -88 °C

[0034] NO2- Reddish-brown gas with irritating odourMelting point: -9.3 °C Boiling point: 21.15 °C Vapour Density: 1.58

[0035] N2O4Boiling point: 21 °C

[0036] N2O5Boiling point: 47 °CChemical properties

[0037] NO only burns when heated with hydrogen, and forms nitric acid (a strong acid) when dissolved in water. NO2 is sparingly soluble in water to form nitrous acid (a weak acid).

[0038] In order to calculate how to remove NOx the flue gas was considered to condensate according to two alternative scenarios. According to a first scenario, the phasechange from vapour to liquid was considered for each component of the flue gas stream, without interaction between the components of the flue gas stream, while according to a second scenario, the phase change from gas to liquid was considered for each component of the flue gas stream, with interaction between the components of the flue gas stream, forming new products.

[0039] The results obtained through the theoretical study of the system of the present disclosure were compared with those of two systems of the prior art, namely a SCR NOx control system and a water injection system, and are summarized in the following table:

[0040] While the invention has been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

Claims

A power producing apparatus comprising a system for reducing nitrogen oxides in the flue gas and a method for reducing nitrogen oxides in the flue gas of a power producing apparatusCLAIMS1. A method to separate nitrogen oxides from a flue gas stream of a power producing apparatus using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, the flue gas stream comprising nitrogen oxides, oxygen and eventually water, the method comprising the following steps:- cooling and condensing at least a part of the flue gas stream into a condensate comprising at least part of the nitrogen oxides of the flue gas stream, through contact with a cooling surface,- separating the condensate from the remaining flue gas stream, and- collecting the condensate.

2. The method of claim 1, wherein said step of cooling and condensing comprises the following sub-steps:- cooling down the flue gas stream to a temperature below the condensation temperature of at least some NOXand above water solidification temperature, to obtain a first condensate and an intermediate residual flue gas stream, the first condensate including at least part of the NOXand water of the flue gas stream;- separating the first condensate from the intermediate residual flue gas stream and collecting the first condensate;- cooling down the intermediate residual flue gas stream to a temperature below the condensation temperature of at least N2O and NO, to obtain a second condensate and a final residual flue gas stream, the second condensate including at least part of the N2O and NO of the flue gas stream; and- separating the second condensate from the final residual flue gas stream and collecting the second condensate.

3. The method of claim 2, wherein said step of cooling the intermediate residual flue gas stream comprises cooling down the intermediate residual flue gas stream to a temperature below the condensation temperature of at least NO2, N2O4 and4. The method of one or more of claims 2-3, wherein said step of cooling the flue gas stream to a temperature below the condensation temperature of at least some NOXand above water solidification temperature comprises cooling down the flue gas stream to a temperature ranging from 5 to 20°C.

5. The method of one or more of claims 2-4, wherein said step of cooling the intermediate residual flue gas stream below the condensation temperature of at least N2O and NO and preferably below the condensation temperature of at least NO2, N2O4 and N2O5 comprises cooling down the intermediate residual flue gas stream to a temperature ranging from -160 to -190°C.

6. The method of one or more of the preceding claims, wherein said step of cooling and condensing at least a part of the flue gas stream is operated under atmospheric pressure.

7. A power producing apparatus, in particular a gas turbine, comprising a system (10) to condensate and separate nitrogen oxides from the flue gas, the power producing apparatus using a fuel comprising one or more of ammonia, hydrogen and natural gas together with air or an oxidizing gas, the flue gas stream comprising nitrogen oxides, oxygen and eventually water, the system comprising a duct (11), the duct (11) comprising a gas stream inlet (12) connected to a flue gas outlet of the power producing apparatus and a gas stream outlet (13) downstream, wherein one or more heat exchanging areas (14, 15) are arranged inside the duct (11), the heat exchanging areas (14, 15) being configured to cool and condensate at least a part of the flue gas stream into a condensate stream comprising at least part of the nitrogen oxides of the flue gas stream, each heat exchanging area (14, 15) comprising a respective heat exchanging surface (140, 150), configured to exchange heat with said flue gas stream and to form a condensation surface, and wherein the system (10) also comprises a condensate collector (16, 17) of each heat exchanging area (14, 15), the condensate collector (16, 17) being configured to collect the condensate stream from the respective heat exchanging area (14, 15), the condensate collector (16, 17) being connected to a respective condensate withdrawal line (18, 19).

8. The power producing apparatus of claim 7, wherein said heat exchanging areas (14, 15) are arranged in at least two subsequent portions of the duct (10), proceeding downstream from the flue gas stream inlet (12) towards the flue gas stream outlet (13).

9. The power producing apparatus of claim 8, wherein said heat exchanging surfaces (140, 150) are inclined extended surfaces arranged to form a descending path towards said condensate collectors (16, 17).

10. The power producing apparatus of claim 7, wherein the temperature of said heat exchanging areas (14, 15) decreases from the heat exchanging areas (14) upstream to the heat exchanging areas (15) downstream.

11. The power producing apparatus of one or more of claims 7-10, wherein said heat exchanging areas (14, 15) are arranged in two subsequent portions of the duct (10), respectively a first heat exchanging area (14) and a second heat exchanging area (15), downstream the first heat exchanging area, the first heat exchanging area (14) comprising a respective heat exchanging surface (140) and being connected to a respective condensate collector (16) and a respective condensate withdrawal line (18) and the second heat exchanging area (15) comprising a respective heat exchanging surface (150) and being connected to a respective condensate collector (17) and a respective condensate withdrawal line (19), wherein the temperature of the heat exchanging surface (140) of the first heat exchanging area (14) is below the condensation temperature of at least some NOxand above water solidification temperature, and the temperature of the heat exchanging surface (150) of the second heat exchanging area (15) is below the condensation temperature of at least N2O and NO.

12. The power producing apparatus of claim 11, wherein the temperature of the heat exchanging surface (150) of the second heat exchanging area (15) is below the condensation temperature of at least NO2, N2O4 and N2O5.

13. The power producing apparatus of claim 12, wherein the temperature of the heat exchanging surface (140) of the first heat exchanging area (14) ranges from 5 to 20°C.

14. The power producing apparatus of one or more of claims 11-13,wherein the temperature of the heat exchanging surface (150) of the second heat exchanging area (15) ranges from -160 to -190°C.

15. The power producing apparatus of one or more of claims 9-14, wherein each heat exchanging area (14, 15) comprises a cooling side on an opposite side of a wall with respect to the heat exchanging surface (140, 150), the cooling side being contacted by a cooling fluid.

16. The power producing apparatus of claim 15, wherein the cooling fluid of the first heat exchanging area (14) is chilled water.

17. The power producing apparatus of one or more of claims 11-16, wherein the cooling fluid of the second heat exchanging area (15) is a low temperature cooling fluid.

18. The power producing apparatus of claim 17, wherein the low temperature cooling fluid is chosen amongst liquid natural gas or liquid nitrogen, preferably liquid nitrogen.

19. The power producing apparatus of one or more of claims 7-18, wherein the duct (11) is thermally insulated from the surrounding environment.

20. The power producing apparatus of one or more of claims 7-19, wherein the duct (11) is made of aluminum cladded material.

21. The power producing apparatus of one or more of claims 9-20, wherein the heat exchanging surfaces (140, 150) are cladded or entirely made of aluminum and / or aluminum oxide.

22. The power producing apparatus of one or more of claims 7-21, wherein the condensate collectors (16, 17) are cladded or entirely made of aluminum and / or aluminum oxide.

23. The power producing apparatus of one or more of claims 7-22, wherein the condensate withdrawal lines (18, 19) are cladded or entirely made of aluminum and / or aluminum oxide.

24. The power producing apparatus of one or more of claims 7-23,wherein the duct (11) is arranged in an ascending configuration, the gas stream inlet (12) being arranged in a lower position and the gas stream outlet (13) being arranged in an upper position.

25. The power producing apparatus of claim 24, wherein the duct (11) is straight with cross-section of circular or rectangular shape.

26. The power producing apparatus of claim 24 or 25, wherein the duct (11) is arranged vertically.

27. The power producing apparatus of one or more of claims 7-26, also comprising one or more additional heat exchanging areas (20), arranged upstream the heat exchanging areas (14, 15) configured to cool and condensate at least a part of the gas stream to condensate a stream comprising at least part of the NOXof the gas stream.

28. The power producing apparatus of claim 27, wherein the additional heat exchanging areas (20) comprise a heat exchanging surface configured to pre-cool the gas stream.

29. The power producing apparatus of claim 28, wherein each additional heat exchanging area (20) comprises a cooling side on an opposite side of a wall with respect to the heat exchanging surface, the cooling side being contacted by one heat exchanging fluid, the heat exchanging fluid on the cooling side of each additional heat exchanging area (20) being the same or being different from the heat exchanging fluid of the other additional heat exchanging areas (20).

30. The power producing apparatus of claim 29, wherein the gas stream is a flue gas of a gas turbine and the heat exchanging fluid on the cooling side of at least one additional heat exchanging area (20) is a fuel of the gas turbine.

31. The power producing apparatus of claim 29 or 30, wherein the heat exchanging fluid on the cooling side of at least one additional heat exchanging area (20) is a working fluid of an auxiliary thermodynamic systems.

32. The power producing apparatus of claim 31, wherein the heat exchanging fluid on the cooling side of at least one additional heat exchanging area (20) is a working fluid of a heat recovery steam generator of a steam turbine.

33. The power producing apparatus of one or more of claims 27-32, wherein the one or more additional heat exchanging areas (20) are arranged in an additional duct portion (21).

34. The power producing apparatus of claim 33, wherein the additional duct portion (21) is arranged horizontally, with cross-section of circular or rectangular shape.

35. The power producing apparatus of claim 34, wherein the additional duct portion (21) is arranged horizontally and the duct (11) is arranged vertically.

36. The power producing apparatus of one or more of claims 15-18, 29, 31, 32, wherein the cooling fluid on the cooling side of one or more heat exchanging areas (14, 15) and / or the heat exchanging fluid on the cooling side of one or more additional heat exchanging area (20), is flown in a closed circuit, the closed circuit comprising additional heat exchangers configured to lower the temperature of the cooling fluid and / or the heat exchanging fluid.

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