Reactor for reducing nitrogen oxides

Abstract

A reactor for reducing the concentration of NOx in a stream, comprising: an inlet for the stream; an outlet for a stream containing a reduced NOx concentration; one or more catalyst beds comprising a ceramic or metal foam having a NOx reduction catalyst; one or more flow paths from the inlet to the outlet, the flow paths passing through at least one catalyst bed, where the catalyst bed is closed at the top and bottom such that the flow paths passing through the catalyst bed pass through the sides of the catalyst bed in a lateral flow form.

Description

[0001] This application is a divisional application of the invention patent application filed on December 20, 2016, with Chinese application number 201680075116.9 and entitled "A reactor for reducing nitrogen oxides".

[0002] Refer to relevant applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 270853, filed on December 22, 2015. Technical Field

[0003] This invention relates to a method for comprising one or more NO atoms on ceramic or metal foam. x A reactor for reducing catalysts and a method for reducing NO in gas streams x Methods for determining concentration. Background Technology

[0004] Nitrogen oxides are common byproducts and / or desirable intermediates in many industrial processes, including the manufacture of chemicals such as nitric acid or combustion processes in air. Nitrogen oxides of the formula NO and NO2 are often referred to together as NO. x NO x NO is a large-scale pollutant, and efforts have been made to reduce NO in exhaust gases from processes that generate it. x Great efforts were made to remove NO from the airflow. x The method is commonly referred to in this field as NO removal. x The method, and the catalyst used in it is called NO removal. x catalyst.

[0005] Prior art describes processes in which dust in a gas stream containing NOx to be treated is captured on a catalyst and then removed from the catalyst by washing or other means. For example, U.S. Patent 4044102 describes a reactor that effectively reduces nitrogen oxides and dust from a flue gas stream. The catalyst is conveyed in a moving bed, allowing it to contact the gas and carry away the dust. The catalyst then exits through an outlet, where it is regenerated and the dust is removed. The patent teaches a preferred method for removing NO... x Dust was previously removed from the gas to prevent it from accumulating on the surface of the catalyst bed and in the gaps between catalyst particles.

[0006] As another example, U.S. Patent 5,413,699 describes a reactor containing dust and NO. x The gas passes through the catalyst bed at a sufficient velocity to fluidize the catalyst bed. Particles deposited on the catalyst are removed or washed away by fluidization to prevent NO removal. x Catalyst scaling. The patent teaches 10-50 mg / Nm³.3 The dust load is too high to make commercially available NO removal products effective. x The catalyst has a long service life.

[0007] In addition, numerous patents and published applications relate to the use of ceramic foam to treat diesel engine exhaust gases. For example, U.S. Patent 5,536,477 describes a ceramic foam filter with the ability to substantially capture all soot present in the exhaust gas stream.

[0008] Fixed-bed catalyst systems can remove NOx from industrial production streams at relatively low temperatures due to their excellent activity; however, they also tend to trap most of the particles in the gas stream and therefore experience a rapid increase in pressure drop. On the other hand, honeycomb catalyst systems allow particulate matter to pass through easily, but they have much lower activity and therefore require much higher operating temperatures. Preferably, a catalyst and a method are provided that allow efficient removal of NOx from particulate-containing gas streams at low temperatures, while allowing most dust to pass through the catalyst bed without being trapped on the catalyst.

[0009] The reactor can also be configured in this way to prevent dust from accumulating on the fixed-bed NOx reduction catalyst. Summary of the Invention

[0010] This invention provides a method for reducing NO in logistics. x The reactor, containing a concentration of NO, includes: an inlet for the stream; and a reactor containing reduced NO. x The outlet of the stream with a concentration of NO; ​​one or more catalyst beds comprising NO x A ceramic or metal foam of a reduction catalyst; one or more flow paths from inlet to outlet, the flow paths passing through at least one catalyst bed, wherein the catalyst bed is closed at the top and bottom, such that the flow paths through the catalyst bed pass through the sides of the catalyst bed in a transverse flow manner.

[0011] The present invention also provides a method for reducing NO in dust-containing airflow. x Methods for determining concentration include: making the product containing NO x A first gas flow enters a reactor comprising one or more catalyst beds; the first gas flow is brought into contact with a ceramic or metal foam catalyst bed having interconnected pores that provide a lateral flow path through the catalyst bed, wherein the catalyst bed comprises NO. x Reduction catalyst to produce NO with reduced x A second gas stream of a concentration of [missing information]; and delivering the second gas stream out of the contact area, wherein the first gas stream has a concentration of at least 5 mg / Nm³. 3 The dust concentration, and the second airflow includes at least 50% of the dust in the first airflow. Attached Figure Description

[0012] Figure 1 Showing the results of Example 1 Figure 2 Showing the results of Example 2 Figure 3 An embodiment of a lateral flow reactor (LFR) is depicted. Detailed Implementation

[0013] The ceramic or metal foam catalyst bed of the present invention allows particles in the gas stream to pass through while treating the gas to reduce NO. x The catalyst can be used to treat exhaust gases from industrial complexes. Ceramic foams for emission control of automotive engines, already described, have a high pore count per inch to capture soot and particulate matter. The foam of the present invention has a lower pore count per inch. The term "dust" as used herein includes any small particles that may remain on the catalyst bed as the airflow passes through.

[0014] The foam of this invention allows most dust to pass through without clogging the system, while simultaneously treating exhaust gas to remove NO. x The catalyst bed of the present invention is particularly suitable for treating exhaust gases from industrial production processes and stationary turbines.

[0015] Furthermore, when the catalyst is arranged in a transverse flow configuration within a catalyst module, a lower pressure drop can be achieved, a key factor in treating flue gas streams. A catalyst module is a container housing one or more catalyst beds, typically arranged in parallel. The catalyst beds can be very thin, and they can be stacked side-by-side in a transverse flow reactor (LFR). The thin nature of the catalyst beds allows for a lower pressure drop, which is advantageous in flue gas treatment applications. Additionally, the thin layers of ceramic or metal foam allow dust to pass through more easily without being trapped within the foam. Thicker foams have a higher likelihood of clogging by dust and particles. The use of multiple very thin foam layers results in a higher flow area and a lower ratio of dust concentration to the foam's surface area. This reduces the likelihood of catalyst bed clogging and lowers the overall pressure drop of the foam, as pressure drop is inversely proportional to the flow area of ​​the filter, according to Darcy's law.

[0016] Due to the tortuous channels within the foam structure, gas molecules mix upon entering the channels, and diffusion to the active catalytic sites on the foam surface is enhanced. On the other hand, typical honeycomb catalysts or other bulk materials with straight flow paths exhibit limited diffusion to the active catalytic sites. This is further amplified if the linear velocity of the gas flow is low, for example, less than 20 m / s, resulting in laminar flow.

[0017] In the reactor, gas enters through a plurality of inlet channels that are closed at one end. The gas must then pass laterally through a fixed catalyst bed to reach the outlet channel.

[0018] Each catalyst bed has a lateral thickness of less than 15 cm, preferably less than 10 cm (i.e., traversing the bed along the gas flow direction). A single catalyst bed preferably has a lateral thickness of 2.5 to 15 cm, more preferably 4 to 10 cm.

[0019] In the reactor, the gas flow passes through one or more catalyst beds from the inlet and reaches the reactor outlet. In one embodiment, the gas flow passes through only one catalyst bed as it travels from the inlet to the outlet.

[0020] exist Figure 3 An embodiment of a transverse flow reactor (LFR) is shown. An LFR can be a vessel of any shape containing one or more catalyst beds. For example, the gas stream can pass through one catalyst bed and then through another catalyst bed located downstream of the first catalyst bed. Figure 3 In this reactor, reactor 1 has a flue gas inlet 2 and a treated gas outlet 3. The flue gas enters from inlet 2 through inlet zone 4 and into inlet zone 7. The flue gas passes through one of the fixed catalyst beds 6 and enters outlet zone 8. The fixed catalyst beds are closed at both ends. The sidewalls of the fixed catalyst beds are permeable. The treated gas then flows to outlet 3. A closing plate 9 separates the catalyst beds and outlet zone 8 from inlet zone 4 to prevent flow around the catalyst beds. An additional closing plate 15 is located between the catalyst beds and the reactor wall. The gas flows laterally across the catalyst beds.

[0021] Ceramic foam can include materials that provide sufficient strength and are NO x The reduction catalyst can be any ceramic material that provides a suitable support. The ceramic foam preferably includes cordierite, titanium dioxide, alumina, or mixtures thereof.

[0022] Metal foam can also include materials that provide sufficient strength and are also NO. x Any metallic material is suitable as a support for the reduction catalyst. Metal foams preferably include nickel, iron, aluminum, chromium, or alloys thereof.

[0023] In one embodiment, ceramic foam can be prepared by filling the pores of a foaming polymer (e.g., polyurethane) with an aqueous slurry of ceramic (e.g., Al₂O₃, ZrO₂). The slurry may contain water particles with a diameter of 0.1 to 10 μm and contain appropriate amounts of wetting agents, dispersing stabilizers, and viscosity modifiers. The wet foam is dried in air and calcined at a temperature exceeding 1000°C. The polymer evaporates or burns, and the ceramic particles sinter. In another embodiment, the viscosity of the slurry can be increased by adding a thickener. This method is further described in J. T. Richardson, "Properties of Ceramic Foam Catalyst Supports: Pressure Drop," Applied Catalysis A: General, 204 (2000), 19-32, which is incorporated herein by reference.

[0024] In one embodiment, the metal foam can be produced by a powder metallurgy process that converts nickel or iron foam into a high-temperature stable alloy. In this process, the nickel or iron foam is continuously expanded, first coated with a binder solution using a spraying technique, and then coated with a high-alloy powder. The foam is then cut into sheets of the desired size. This method is further described in G. Walther et al., “A New PM Process for Manufacturing of Alloyed Foams for High Temperature Applications,” PM 2010 World Congress - Foams and Porous Materials, which is incorporated herein by reference.

[0025] The foam has at least 60%, preferably at least 70%, and more preferably at least 80% void space. Void space is defined as the volume of the open structure divided by the total volume of the structure (openings and ceramic or metal) and then multiplied by 100.

[0026] The ceramic and metal foams have an interconnected internal tortuous pore structure. This can also be described as having a mesh structure. This structure causes the airflow through the foam to be turbulent, which, compared to laminar flow within honeycomb channels, improves contact with the catalyst.

[0027] The tortuosity of the ceramic or metal foam is preferably greater than 1.0, more preferably greater than 1.5, and most preferably greater than 2.0. Tortuosity can be calculated as the ratio of the length of the flow path of the gas through the ceramic or metal foam to the length of the shortest straight path from the inlet to the outlet of the ceramic or metal foam. The straight channel path has a tortuosity of 1.0.

[0028] Ceramic or metal foams have approximately 5 to 50 pores per inch, preferably approximately 10 to 30 pores per inch. The number of pores per inch affects the foam's ability to allow dust to pass through the catalyst bed.

[0029] In one embodiment, the metal foam has a concentration of 0.4 to 0.75 g / cm³. 3 The density range provides a range of lightweight foams that can be used to process these gases.

[0030] Any NO x Reduction catalysts are suitable for the methods of this invention, such as those described in U.S. Patent 6,419,889. An exemplary catalyst from U.S. Patent 6,419,889 comprises a titanium dioxide support and one or more metal compounds selected from the group consisting of vanadium, molybdenum, and tungsten. In one embodiment, NO... x The reduction catalyst is vanadium on a titanium dioxide catalyst. In another embodiment, NO x The reduction catalyst is vanadium and tungsten on a titanium dioxide catalyst.

[0031] Other suitable catalysts include oxides of metals such as aluminum, copper, iron, cobalt, tin, chromium, nickel, manganese, titanium, silver, platinum, rhodium, palladium, or mixtures thereof. Metal oxides can be supported on any conventional support or other material, such as alumina, silicon-alumina, magnesium-alumina, titanium dioxide, alumina, calcium oxide-alumina, chromium oxide-alumina, or silicon dioxide-chromium oxide-alumina.

[0032] In addition, zeolite catalysts containing copper or iron can be used for NO. x Reduction. A preferred example is iron-exchanged zeolite β. Zeolite catalysts may include other metals such as platinum, ruthenium, palladium, osmium, rhodium, or mixtures thereof.

[0033] The catalyst may have a nitrogen adsorption capacity of approximately 70 m. 2 / g to approximately 150 m 2 The surface area is between / g. The catalyst can have a bimodal pore distribution, in which more than 90% of the pore volume exists in pores with a diameter of up to about 100 nm, where the pore volume is considered to exist in pores with diameters between about 1 nm and about 104 nm.

[0034] Catalysts can be prepared by impregnating or depositing a support with a metal compound after drying and calcining the support, or after extrusion, followed by drying and subsequent calcination of the support. Impregnation can be performed by contacting the support with an aqueous solution of the metal compound. In one embodiment, a metal oxalate solution can be used for impregnation. Catalysts can also be prepared by co-milling the support with the metal compound to form a solid mixture. Catalysts formed according to these methods can be ground or milled to a specific particle size distribution in a slurry before being coated onto a ceramic or metal foam.

[0035] Another method of incorporating catalysts into foams is to deposit them by impregnating the pore volume of a support and then depositing the impregnated support onto the foam. Further methods involve preparing a wash-coated slurry of a metal (e.g., titanium and vanadium) and then depositing it onto the foam.

[0036] NO x The reduction catalyst may also include a binder material that helps to bind the catalyst to a support and / or to a ceramic or metal foam.

[0037] Used to reduce NO in particulate-containing airflow x Methods for determining concentration include making the NO content... x The first airflow enters the contact zone. This airflow may originate from multiple sources, including power plants, pyrolysis furnaces, incinerators, metallurgical plants, fertilizer plants, and chemical plants. The airflow contains a large amount of dust.

[0038] The airflow includes at least 5 mg / Nm 3 The method of this invention can handle dust with a concentration of at least 10 mg / Nm³. 3 Airflow containing dust. The method is capable of handling airflows with a dust concentration of at least 20 mg / Nm³. 3 Dust, preferably at least 30 mg / Nm 3 Dust, and more preferably at least 70 mg / Nm³. 3 Airflow of dust.

[0039] The gas stream contacts a ceramic or metal foam catalyst bed, wherein the catalyst bed includes NO. x The catalyst is reduced to generate a second gas stream. The catalyst bed has one or more flow paths through it, which enable the gas stream to interact with NO. x Contact with the reduction catalyst.

[0040] NO in airflow x The reduction can be carried out at a pressure ranging from 0 kPa to 1200 kPa and at a temperature ranging from 100°C to 400°C. The temperature is preferably between 100°C and 350°C, more preferably between 100°C and 250°C, and most preferably between 140°C and 220°C.

[0041] Many catalysts require higher temperatures to achieve NO. x High conversion of NO. A catalyst with high activity and selectivity at the above temperatures is preferred, allowing for the use of lower temperatures. Under contact conditions, NO... x Reduction catalysts can remove at least most of NO through chemical transformation. x The second gas stream contains up to 40% NO present in the feed gas stream. x The second airflow contains up to 25% of the NO present in the first airflow. x Preferably, up to 5% of NO is present in the first airflow. x Furthermore, more preferably, at most 1% of the NO present in the first airflow x .

[0042] The second gas flow contains at least 50% of the dust present in the first gas flow fed into the catalyst bed. The second gas flow preferably includes at least 60% of the dust present in the first gas flow, and more preferably at least 80% of the dust present in the first gas flow.

[0043] Example Example 1 In this example, a fixed catalyst bed (A) of NOx removal catalyst agglomerates and a fixed catalyst bed (B) of ceramic foam NOx removal catalyst were tested to determine the effect of passing an airflow with a high dust load through the catalyst bed. The catalyst agglomerates were 3.2 mm trilobal agglomerates. The ceramic foam NOx removal catalyst had 18 pores per inch. The tests were conducted in a dust filtration laboratory and included passing an airflow with a dust concentration of 70 mg / Nm³. 3 Air containing dust particles was passed through the catalyst bed. The average particle size of the dust was 1 micrometer. Two types of catalyst beds were compared using the same particle size and concentration. The pressure drop of the catalyst bed was measured at ambient temperature and pressure. The results of the tests were shown in... Figure 1 In the figure, back pressure is plotted as a function of the time, in minutes, for a dust-laden airflow through the catalyst bed.

[0044] As shown in the figure, the ceramic foam catalyst initially has a lower back pressure than the catalyst agglomerates. Furthermore, when dust passes through the catalyst bed, the back pressure of the ceramic foam increases only slightly, while the back pressure of the agglomerate catalyst rapidly increases to the maximum system design pressure. At this point, the catalyst agglomerates must be cleaned before they can be used further.

[0045] In addition to measuring back pressure, the amount of dust passing through the ceramic foam catalyst bed was also measured. Initially, when the test began, 60% of the dust entering the ceramic foam passed through the catalyst bed. After a given time, the amount of dust passing through the foam ceramic catalyst bed was determined to be 64%. This example demonstrates that ceramic foam catalyst beds can operate under high dust conditions, while catalyst agglomerates cannot operate effectively under high dust conditions.

[0046] Example 2 In this example, three catalysts were tested to determine their activity for NOx conversion. The first test (C) used a ceramic foam catalyst with 30 pores per inch. The second test (D) used a ceramic foam catalyst with 18 pores per inch. The third test (E) used 3.2 mm trefoil catalyst pellets. The tests were conducted in a fixed-bed reactor, with identical catalyst loading volumes for all three tests. The space velocity for all three tests was maintained at a constant 22,000 hr⁻¹, and the tests were performed at ambient pressure. The inlet gas composition was 300 ppm NH₃, 200 ppm NO, 10% H₂O, 7.5% O₂, with the remainder being nitrogen. The NO concentration before and after the catalyst bed was monitored using a Fourier transform infrared spectroscopy (FTIR) instrument. The results of this example are shown in... Figure 2 As can be seen from the figure, the ceramic foam exhibits activity comparable to that of the catalyst agglomerates, and even higher activity at higher temperatures.

[0047] These examples demonstrate that ceramic foam catalysts can be used to effectively reduce NOx levels in airflows, and that ceramic foam catalyst beds can be used under high dust conditions.

[0048] Various preferred features and embodiments of the present invention will now be described with reference to the following numbered paragraphs: 1. A method for reducing NO in logistics x Concentration reactors, including: a. The entry point for the aforementioned logistics; b. Contains reduced NO x Export of concentrated logistics; c. One or more catalyst beds, comprising NO x Ceramic or metal foam of reduction catalyst; d. One or more flow paths from the inlet to the outlet through at least one catalyst bed. The catalyst bed is closed at the top and bottom, such that the flow path through the catalyst bed flows laterally across the sides of the catalyst bed.

[0049] 2. The reactor according to paragraph 1, wherein the catalyst bed has a lateral thickness of less than 15 cm.

[0050] 3. The reactor according to paragraph 1, wherein the catalyst bed has a lateral thickness of 2.5 to 15 cm.

[0051] 4. The reactor according to any one of paragraphs 1 to 3, wherein one or more flow paths each pass through only one catalyst bed between the inlet and the outlet.

[0052] 5. The reactor according to any one of paragraphs 1 to 4, wherein the NO x The reduction catalyst includes vanadium, molybdenum, tungsten, or mixtures thereof.

[0053] 6. A method for reducing NO in dust-laden airflow x Methods for determining concentration include: a. To make it contain NO x The first gas stream enters the reactor containing one or more catalyst beds; b. Contact the first gas flow with a ceramic or metal foam catalyst bed having interconnected pores, the interconnected pores providing a lateral flow path through the catalyst bed, wherein the catalyst bed comprises NO. x Reduction catalyst to produce NO with reduced x The concentration of the second gas flow; and c. Allow the second airflow to exit the contact area. The first airflow has a concentration of at least 5 mg / Nm 3 The dust concentration, and the second airflow contains at least 50% of the dust in the first airflow.

[0054] 7. The method according to paragraph 6, wherein the first gas flow has a concentration of at least 10 mg / Nm³. 3 Dust concentration.

[0055] 8. The method according to paragraph 6, wherein the first gas flow has a concentration of at least 20 mg / Nm³. 3 Dust concentration.

[0056] 9. The method according to paragraph 6, wherein the first gas flow has a concentration of at least 30 mg / Nm³. 3 Dust concentration.

[0057] 10. The method according to paragraph 6, wherein the first gas flow has a concentration of at least 70 mg / Nm³. 3 Dust concentration.

[0058] 11. The method according to any one of paragraphs 6 to 10, wherein the second airflow comprises at least 60% of the dust content in the first airflow.

[0059] 12. The method according to any one of paragraphs 6 to 11, wherein the second airflow comprises at least 80% of the dust content in the first airflow.

[0060] 13. The method according to any one of paragraphs 6 to 12, wherein the second gas flow contains up to 40% of the NO present in the first gas flow. x .

[0061] 14. The method according to any one of paragraphs 6 to 13, wherein the second gas flow contains up to 25% of the NO present in the first gas flow. x .

[0062] 15. The method according to any one of paragraphs 6 to 14, wherein the second gas flow contains up to 5% of the NO present in the first gas flow. x .

[0063] 16. The method according to any one of paragraphs 6 to 15, wherein the second gas flow contains at most 1% of the NO present in the first gas flow. x .

[0064] 17. The method according to any one of paragraphs 6 to 16, wherein the contact is performed at a temperature in the range of 100 to 250°C.

[0065] 18. The method according to any one of paragraphs 6 to 16, wherein the contact is performed at a temperature in the range of 140 to 220°C.

[0066] 19. The method according to any one of paragraphs 6 to 18, wherein the ceramic or metal foam catalyst bed has 5 to 50 pores per inch.

[0067] 20. The method according to any one of paragraphs 6 to 18, wherein the ceramic or metal foam catalyst bed has 10 to 30 pores per inch.

Claims

1. A method for reducing NO in exhaust gases x The catalyst includes: Ceramic or metal foam carrier; and One or more NOs deposited on the ceramic or metal foam carrier x Reduction catalyst, wherein one or more NO x The reduction catalyst comprises a support material and one or more metal compounds deposited on the support material, wherein the NO x The reducing catalyst has a bimodal pore distribution, wherein more than 90% of the pore volume exists in pores having a diameter of up to 100 nanometers (nm), and wherein the pore volume exists in pores having a diameter between about 1 nm and about 104 nm.

2. The catalyst according to claim 1, wherein one or more NO... x The surface area of ​​the reduction catalyst was measured by nitrogen adsorption at 70 m² / g (m²). 2 / g) to 150 m 2 Between / g.

3. The catalyst according to claim 1, wherein the ceramic or metal foam has at least 60% void space.

4. The catalyst of claim 1, wherein the ceramic or metal foam has about 5 to about 50 pores per inch.

5. The catalyst according to claim 1, wherein the ceramic or metal foam has a content of about 0.4 to about 0.75 g / cm³. 3 The density of ).

6. The catalyst according to claim 1, wherein the one or more metal compounds comprise vanadium, molybdenum, tungsten, or mixtures thereof.

7. The catalyst according to claim 1, wherein the support material is titanium dioxide, alumina, silicon-alumina, magnesium oxide-alumina, calcium oxide-alumina, chromium oxide-alumina, or silicon dioxide-chromium oxide-alumina.

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