Flue gas cleaning system for reducing nitrogen oxides and oxidising carbon monoxide from the flue gas of a power plant

Abstract

The invention relates to a flue gas cleaning system (1) and to a method for operating a flue gas cleaning system (1) for selectively catalytically reducing nitrogen oxides (NOx) and oxidising carbon monoxide (CO) from the flue gas (2) of a power plant (3). According to the invention, the flue gas cleaning system (1) comprises a catalyst (4) which contains a highly active layer (5) based on vanadium and is designed for operating temperatures of up to 720°C.

Description

[0001] Description

[0002] Flue gas cleaning system for the reduction of nitrogen oxides and oxidation of carbon monoxide from the flue gas of a power plant

[0003] The present invention relates to a flue gas cleaning plant and a method for reducing nitrogen oxides (NOx) and oxidizing carbon monoxide (00) from the flue gas of a power plant.

[0004] In many countries, legislation requires comprehensive treatment of flue gases from power plants, particularly a significant reduction of toxic NOx gases such as nitrogen monoxide (NO) and nitrogen dioxide (NO2). Nitrogen oxides are produced during the combustion of fossil fuels and are responsible for air pollution and the formation of smog. Therefore, in flue gas cleaning systems, the flue gas from the power plant is first cleaned by a deduster to remove particles. The dedusted flue gas is then enriched with ammonia and passed through the SCR catalyst to reduce the nitrogen oxide content.

[0005] Flue gas purification systems use DeNOx catalysts, which reduce nitrogen oxides through selective catalytic reduction, thus removing the harmful NOx from the flue gas. The SCR process is based on a chemical reaction in which nitrogen oxides are converted into nitrogen and water. Ammonia (NH3) is used as the reducing agent.

[0006] Conventional DeNOx catalysts are designed for a maximum operating temperature of approximately 420°C. Exceeding this maximum operating temperature will result in the catalyst being destroyed. To prevent this, conventional DeNOx catalysts are operated at temperatures below 420°C. Since the flue gas still has temperatures of around 650°C when it enters the flue gas cleaning system, cooling is necessary. This is achieved by quenching the flue gas with fresh air. This cools the flue gas to approximately 400°C. The additional intake of fresh air reduces the efficiency and operating flexibility of the power plant.

[0007] The object of the invention is to provide a flue gas cleaning system for the reduction of nitrogen oxides and oxidation of carbon monoxide from the flue gas of a power plant, which does not suffer any loss of efficiency due to quenching and nevertheless has a high degree of operational flexibility.

[0008] The object of the invention directed to a device is achieved by a flue gas cleaning system for the selective catalytic reduction of nitrogen oxides and oxidation of carbon monoxide from the flue gas of a power plant, with a catalyst which contains a highly active layer based on vanadium and is designed for operating temperatures up to 720 ° C.

[0009] The highly active vanadium-based layer acts as a catalyst to promote the chemical reaction between the nitrogen oxides and the ammonia. Upon contact with the catalyst, the nitrogen oxides are selectively converted into nitrogen and water, without affecting the catalyst.

[0010] At the same time, the oxidation of carbon monoxide also takes place in the flue gas cleaning system. Carbon monoxide is a toxic gas that is also produced during the combustion of fossil fuels. The SCR catalyst with its vanadium coating also has an oxidizing effect, which causes carbon monoxide to be converted into carbon dioxide. The use of a flue gas cleaning system with a vanadium-based SCR catalyst makes it possible to significantly reduce the emissions of nitrogen oxides and carbon monoxide. The system thus contributes to improving air quality and reducing the environmental impact of power plants.

[0011] The highly active layer consists of a support material with a highly active vanadium-based coating, or of a support material homogenized with vanadium as the catalytically active material. A homogeneously extruded honeycomb structure can be used as the support material for the catalyst. Vanadium is an inexpensive and readily available material for the selective catalytic reduction of nitrogen oxides.

[0012] The essential advantage of the invention is that the flue gas cleaning system is designed for operating temperatures up to 720 °C, and the catalyst can be operated directly downstream of a gas turbine without cooling the flue gas. The catalyst's design for operating temperatures up to 720 °C allows for flexible operation, even allowing higher temperatures to occur briefly. The invention allows a flue gas cleaning system to be designed and built much more simply than the prior art.

[0013] In an advantageous further development of the invention, ammonia water (NH4OH) can be fed as a reducing agent to the catalyst for the selective catalytic reduction of nitrogen oxides (NOx). This simplifies the process configuration, since with this approach, no ammonia water needs to be evaporated before it is fed into the feed network. The system is thus easier to control and maintain, as exhaust fans are no longer required.

[0014] The flue gas cleaning system is advantageously designed for use in combined cycle power plants to increase efficiency and operating flexibility. The catalyst is installed directly downstream of the gas turbine.

[0015] The object directed to a process is achieved by a process for the selective catalytic reduction of nitrogen oxides (NOx) and oxidation of carbon monoxide (CO) from the flue gas of a power plant, with a catalyst which contains a highly active layer based on vanadium, wherein the catalyst is operated at temperatures up to 720 ° C.

[0016] The advantages described for the device claims apply equally to the method claims.

[0017] In an advantageous further development of the process, ammonia water (NH40H) is fed to the catalyst as a reducing agent for the selective catalytic reduction of nitrogen oxides (NOx).

[0018] The process is advantageously used in gas and steam power plants to increase efficiency and operating flexibility.

[0019] The invention is described in more detail below with reference to the figures. In these figures:

[0020] Figure 1 A schematic representation of a flue gas cleaning system according to the state of the art.

[0021] Figure 2 An embodiment of the flue gas cleaning system according to the invention.

[0022] Figure 1 shows a schematic representation of a power plant 3 with a flue gas cleaning system 1 for cleaning a flue gas 2. The flue gas cleaning system 1 is arranged in the flue gas duct 8 downstream of a gas turbine 10 and is a component of a waste heat steam generator 9. The waste heat steam generator 9 comprises a catalyst 7 for the selective catalytic reduction (SCR) of nitrogen oxides, which is arranged in the flue gas duct 8 between two evaporator surfaces of the heat exchanger 11.

[0023] The catalyst 7 is a conventional SCR catalyst according to the state of the art. It is designed for an operating temperature of up to 420 °C and uses ammonia (NH3) as the reducing agent, and is arranged between the evaporator heating surfaces of the heat exchanger 11. In order to avoid thermal destruction of the catalyst 7, operating temperatures below 420 °C must be ensured. Since the flue gas still has temperatures of around 650 °C when it enters the heat recovery steam generator 9, the exhaust gas 2 must be cooled. This is done by quenching the flue gas with fresh air. The flue gas is cooled to approx. 400 °C. The additional intake of fresh air reduces the efficiency and operating flexibility of the power plant.

[0024] Figure 2 shows an embodiment of the flue gas cleaning system according to the invention.

[0025] The flue gas cleaning system 1 comprises a high-temperature DeNOx catalyst 4 for the selective catalytic reduction of nitrogen oxides (NOx) and oxidation of carbon monoxide (CO) from the flue gas 2. To achieve high-temperature resistance, the catalyst 4 contains a highly active layer 5 based on vanadium, which makes it temperature-resistant for operating temperatures between 420 °C and 720 °C.

[0026] The highly active layer 5 based on vanadium acts as a catalyst to promote the chemical reaction between the nitrogen oxides and the ammonia. Through contact with the catalyst 4, the nitrogen oxides are selectively converted into nitrogen and water. The catalyst 4 requires no cooling of the flue gas 2 and can be operated directly downstream of a gas turbine. In an advantageous further development of the invention, ammonia water (NH4OH) can be fed to the catalyst as a reducing agent for the selective catalytic reduction of nitrogen oxides (NOx). The reducing agent 6 is used without cooling or evaporator. This simplifies the process configuration because with this approach no ammonia water needs to be evaporated before it is fed into the feed network. The system is therefore easier to control and maintain because exhaust fans are no longer required.

[0027] In a situation of increasing penetration of renewable energy sources into power grids and the transition to hydrogen-based energy storage systems, the combustion of gas in existing gas turbine power plants will inevitably lead to an increase in NOx emissions. In this case, retrofitting such power plants with the catalyst according to the invention will be a simple and cost-effective solution.

Claims

Patent claims 1. Flue gas cleaning system (1) for the selective catalytic reduction of nitrogen oxides (NOx) and oxidation of carbon monoxide (CO) from the flue gas (2) of a power plant (3), with a catalyst (4) which contains a highly active layer (5) based on vanadium, wherein the catalyst (4) is arranged downstream of a gas turbine and is designed for operating temperatures between 420°C and 720°C, wherein ammonia water (NH4OH) can be fed to the catalyst (4) as a reducing agent (6) for the selective catalytic reduction of nitrogen oxides (NOx).

2. Flue gas cleaning system (1) according to claim 1, which is designed for use in gas and steam power plants in order to increase efficiency and operating flexibility.

3. Process for the selective catalytic reduction of nitrogen oxides (NOx) and oxidation of carbon monoxide (CO) from the flue gas (2) of a power plant (3), with a catalyst (4) which contains a highly active layer (5) based on vanadium, wherein the catalyst (4) is operated after a gas turbine and at operating temperatures between 420°C and 720°C, and wherein ammonia water (NH4OH) is supplied to the catalyst (4) as a reducing agent (6) for the selective catalytic reduction of nitrogen oxides (NOx).

4. A process for removing nitrogen oxide (NOx) according to claim 3, which is operated in combined cycle power plants to increase efficiency and operating flexibility.

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