EXHAUST DUCT FOR A FOSSIL FUEL POWERED ENGINE COMPRISING A DILUTION SELECTIVE CATALYTIC REDUCTION SYSTEM

Abstract

An exhaust duct for a fossil fuel powered engine includes an exhaust gas passage, a cooling fluid passage, a mixing device for mixing cooling fluid with the hot exhaust gas and a selective catalytic reduction catalyst for removing nitrogen oxides arranged in the exhaust gas passage. The mixing device has a mixing chamber with a first wall and an opposed second wall, the first and second wall arranged upstream of the selective catalytic reduction catalyst in the exhaust gas passage and extending over the cross-sectional area of the exhaust gas passage, both walls perforated by through holes, wherein through holes of the first wall are connected with through holes of the second wall in pairs by pipes extending through the mixing chamber, the pipes perforated by at least one hole into the mixing chamber and the cooling fluid passage ending into the mixing chamber.

Claims

1. An exhaust duct for a fossil fuel powered engine comprising: an exhaust gas passage, a cooling fluid passage, a mixing device for mixing cooling fluid with hot exhaust gas, at least a selective catalytic reduction catalyst arranged in the exhaust gas passage for removing nitrogen oxides, and at least first means for supplying a reducing agent, wherein the mixing device comprises a mixing chamber with a first wall and an opposed second wall, the first and second wall arranged upstream of the selective catalytic reduction catalyst in the exhaust gas passage and extending over a cross-sectional area of the exhaust gas passage, both walls perforated by through holes, wherein through holes of the first wall are connected with through holes of the second wall in pairs by pipes extending through the mixing chamber, the pipes perforated by at least one hole into the mixing chamber and the cooling fluid passage ending into the mixing chamber.

2. The exhaust duct according to claim 1, wherein the first means for supplying a reducing agent are arranged in such a way, that reducing agent is supplied into the cooling fluid passage.

3. The exhaust duct according to claim 2, wherein the first means for supplying a reducing agent are arranged in such a way, that the reducing agent is injected at the fluid intake of a cooling fluid fan of the cooling fluid passage.

4. The exhaust duct according to claim 2, wherein the first means for supplying a reducing agent are adapted for supplying reducing agent comprising a urea component and/or an ammonia component.

5. The exhaust duct according to claim 2, wherein the first means for supplying a reducing agent comprise one or several injection nozzles adapted to spray the reducing agent as a liquid or vapour into the cooling fluid.

6. The exhaust duct according to claim 1, wherein the pipes of the mixing chamber comprise inside at least one turbulator for increasing the turbulence of the exhaust gas flowing through the pipes.

7. The exhaust duct according to claim 1, wherein the sum of a cross-sectional area of the through holes in the first and second wall are adapted to keep a pressure drop between an inlet of the exhaust gas passage and a downstream exit of the exhaust gas passage less or equal than 25 mbar.

8. The exhaust duct according to claim 1, wherein the openings of the through holes through the first and second wall are uniformly distributed on the surface of the first and second wall.

9. A power plant comprising: a gas turbine, and the exhaust duct of claim 1.

10. A mixing chamber for an exhaust duct of a fossil fuel powered engine for mixing cooling fluid with hot exhaust gas comprising: a first wall and an opposed second wall and at least one entrance for a cooling fluid passage of the exhaust duct, the first wall and second wall adapted to be arranged in an exhaust gas passage of the exhaust duct and to extend over a cross-sectional area of the exhaust gas passage, the first and second wall both perforated by through holes, wherein through holes of the first wall are connected with through holes of the second wall in pairs by pipes extending through the mixing chamber, the pipes perforated by at least one hole into the mixing chamber.

11. The exhaust duct according to claim 7, wherein the sum of the cross-sectional area of the through holes is 25% of the surface area of the first and second wall.

12. The power plant according to claim 9, wherein the gas turbine comprises a simple cycle gas turbine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] There are shown in

[0034] FIG. 1 a schematic representation of a gas turbine of the prior art, in a longitudinal section,

[0035] FIG. 2 a schematic representation of a power plant with a simple cycle gas turbine,

[0036] FIG. 3 a schematic representation of an exhaust duct for a gas turbine according to suggested art with a dilution-SCR system, in a longitudinal section,

[0037] FIG. 4 a schematic representation of a mixing chamber according to the invention, in a perspective view,

[0038] FIG. 5 a schematic representation of a pipe of the mixing chamber according to the invention, in a perspective view, and

[0039] FIG. 6 a schematic representation of an exhaust duct according to the invention, in a perspective view.

DETAILED DESCRIPTION OF INVENTION

[0040] FIG. 1 shows a sectional view of a gas turbine 1 according to the prior art, in a schematically simplified representation. In its interior, the gas turbine 1 has a rotor 3, which is mounted so as to be rotatable about a rotation axis 2, and which has a shaft 4, which is also referred to as a turbine rotor. Along the rotor 3, in succession, there is an intake housing 6, a compressor 8, a combustion system 9, having one or more combustion chambers 10, which each comprise a burner arrangement having burners 11, a fuel supply system (not represented) for the burners, and a combustion chamber housing 12, and a turbine 14 and an exhaust duct 15. The combustion chamber 10 may be, for example, an annular combustion chamber.

[0041] The combustion system 9 represented in FIG. 1 communicates with a, for example annular, hot-gas channel. There, a plurality of turbine stages connected in succession constituting the turbine 14. Each turbine stage is constituted by blade rings. As viewed in the direction of flow of a working medium, in the hot channel a row of guide blades 17 is succeeded by a row of rotor blades 18. The guide blades 17 in this case are fastened to an inner housing of a stator 19, whereas the rotor blades 18 of a row are attached, for example by means of a turbine disc, to the rotor 3. A generator (not represented), for example, is coupled to the rotor 3.

[0042] During operation of the gas turbine, air is sucked in through the intake housing 6 and compressed by the compressor 8. The compressor air L provided at the turbine-side end of the compressor 8 is guided along a burner plenum 7 to the combustion system 9 where, in the region of the burner arrangement, it is routed into the burners 11 and in the latter is mixed with fuel and/or enriched with fuel in the outlet region of the burner 11. Fuel supply systems in this case supply the burners with fuel. The mixture, or the compressor air and the fuel, is/are discharged from the burners 11 into the combustion chamber 10 and combusts/combust, forming a hot stream of working gas in a combustion zone within the combustion chamber housing 12 of the combustion chamber. From there, the stream of working gas flows along the hot-gas channel, past the guide blades 17 and the rotor blades 18. At the rotor blades 18, the stream of working gas expands in an impulse-transmitting manner, such that the rotor blades 18 drive the rotor 3, and the latter drives the generator (not represented) coupled thereto.

[0043] FIG. 2 shows a schematic representation of a power plant 22 according to prior art comprising a gas turbine 1, an exhaust duct 15 coupled to a turbine exit of the gas turbine 1 and a generator 23. The gas turbine 1 drives the rotor 3 during operation, and the rotor 3 drives the generator to generate electrical power. The hot flue gas leaving the exit port of the gas turbine 1 is flowing via the exhaust duct 15 into the atmosphere.

[0044] FIG. 3 shows schematically an exhaust duct 24 for a gas turbine 1 according to suggested art with a dilution selective catalytic reduction system (dilution-SCR system), in a longitudinal section. The gas turbine 1, which is a fossil fuel powered engine 26, is coupled with a turbine exit to an inlet of an exhaust duct 24. The exhaust duct 24 comprises an exhaust gas passage 27, wherein a cooling fluid passage 28 ends into the exhaust gas passage 27 via an entrance 30 for the cooling fluid passage 28. The entrance 30 acts as a mixing device 31. There is a cooling fluid fan 32 with a fluid intake 33 of the cooling fluid fan arranged at the opposite end of the cooling fluid passage 28. Downstream of the entrance 30 for the cooling fluid passage 28, there are first means 34 for supplying a reducing agent 36 arranged in the exhaust gas passage with injection nozzles 35 to spray reducing agent 36 into the exhaust gas passage 27. The first means 34 for supplying a reducing agent are fluidic connected to a storage tank 37, wherein the flow of the reducing agent 36 to the first means 34 is controlled by a distribution & flow control unit 38. Downstream of the first means 34 for supplying a reducing agent is a selective catalytic reduction catalyst 39 (also referred as SCR catalyzer) arranged followed downstream by a CO catalyzer 40, wherein the catalyzers extending over the cross-sectional area of the exhaust gas passage 27. The catalyzers with the first means 34, the distribution & flow control unit 38, the storage tank 37 and the cooling fluid passage 28 with fluid fan 32 forming together an exhaust gas purification apparatus 44 and a dilution selective catalytic reduction system 45 (dilution SCR-system).

[0045] During operation, the exhaust gas 41 produced by the gas turbine 1 is flowing into the exhaust gas passage 27 of the exhaust duct 24 and mixed with cooling fluid 42 from the cooling fluid passage 28 and sprayed with reducing agent 36 by injection nozzles 35 of the first means 34. Due to the reducing agent 36, some of the NO.sub.x components of the exhaust gas are reduced by the selective catalytic reduction catalyst 39 into H.sub.2O and N.sub.2. Some of the CO components of the fuel gas are eliminated by the CO catalyzer 40, wherein the purified fuel gas 43 leaves the exhaust duct at a downstream exit of the exhaust gas passage 27.

[0046] FIG. 4 shows schematically a mixing chamber 50 for an exhaust duct according to the invention. The mixing chamber 50 for mixing cooling fluid with hot exhaust gas comprising a first wall 51 and an opposed second wall 52 adapted to extend over the cross-sectional area of the exhaust gas passage, and at least one entrance 53 for a cooling fluid passage ending into the mixing chamber 50, the first wall 51 and the second wall 52 both perforated by through holes 54. As shown by FIG. 5 in more detail, the through holes 54 of the first wall 51 are connected with through holes 54 of the second wall 52 in pairs by pipes 55 extending through the mixing chamber 50, the pipes 55 perforated by at least one or two or more holes 56 into the mixing chamber 50. The sum of the cross-sectional areas 59 of the through holes 54 in the first wall 51 and second wall 52 are adapted to keep a pressure drop between an inlet (Pos. 66 of FIG. 6) of the exhaust gas passage and a downstream exit (Pos. 69 of FIG. 6) of the exhaust gas passage less or equal than 25 mbar. The openings 67 of the through holes 54 are uniformly distributed on the surface 68 of the first wall 51 and the second wall 52. The surface 68 having the same size as the cross-sectional area (Pos. 64 of FIG. 6) of the exhaust gas passage.

[0047] FIG. 5 shows schematically a pipe 55 of the mixing chamber 50 shown by FIG. 4 in more detail. The pipe 55 extending through the mixing chamber 50 and connecting through hole 54 of the first wall 51 with through hole 54 of the second wall 52. The pipe 55 is perforated by one or two or more holes 56 opens into the mixing chamber 50. The pipe 55 comprises inside turbulators 57 for increasing the turbulence of the exhaust gas flowing through the pipe, wherein cooling fluid 58 is sucked into the pipe 55 due to the static pressure produced by the flow in the pipe.

[0048] FIG. 6 shows schematically an exhaust duct 60 according to the invention with an exhaust gas passage 61, a cooling fluid passage 62, a mixing chamber 50 as shown by FIG. 4 constructed as a section 63 of the exhaust gas passage 61 comprising a first wall 51 and a opposed second wall 52 arranged upstream of a selective catalytic reduction catalyst 65 in the exhaust gas passage 61 and extending over the cross-sectional area 64 of the exhaust gas passage 61. Flue gas, entering the exhaust gas passage 61 at inlet 66 of the exhaust gas passage, is mixed in the pipes of the mixing chamber 50 with cooling fluid and reducing agent from the cooling fluid passage 62 and passing the catalyzer 65 on the way to a downstream exit 69 of the exhaust gas passage 61.