Gas turbine tail gas denitration catalyst

Abstract

The invention discloses a gas turbine tail gas denitration catalyst. The catalyst comprises the following components in parts by weight: 5-20 parts of copper oxide, 5-15 parts of cerium dioxide, 2-8 parts of ferric oxide and 45-60 parts of modified fly ash, the specific surface area BET of the modified fly ash is larger than or equal to 64m < 2 > / g, the total pore volume is larger than or equal to 0.8 cm < 3 > / g, the denitration efficiency of the catalyst reaches 80% or above within the temperature interval of 300-450 DEG C, and the denitration requirement of gas turbine tail gas is met; meanwhile, the environmental problem caused by discharge of the fly ash is solved, resource utilization of the fly ash is achieved, and the manufacturing cost of the gas turbine tail gas denitration catalyst is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of pollutant treatment, and particularly relates to a denitration catalyst for gas turbine exhaust gas. Background Art

[0002] Environmental pollution problems such as ozone and acid rain caused by nitrogen oxides (NO x ) are becoming increasingly prominent. How to effectively eliminate NO x has become an important topic in the current environmental protection field.

[0003] The ammonia selective catalytic reduction method (NH3-SCR) is the most efficient and widely used denitration technology for removing NO from flue gas. The core of this technology is the research of catalysts. Currently, commercial NH3-SCR catalysts are mainly V2O5-TiO2 or V2O5-WO3(MoO3)-TiO2. The precursor of the active component V2O5 in such catalysts is generally highly toxic, harmful to the human body and the environment, and the cost is relatively high. Therefore, it is necessary to develop a low-cost commercial NH3-SCR high-efficiency catalyst to meet the needs of enterprises.

[0004] The emissions of fly ash, a derivative of coal, are also increasing year by year. Currently, most fly ash is used in the construction industry with relatively low added value such as making cement and concrete, and most of it is still stacked in place or landfilled, which not only occupies a large amount of precious land resources but also easily causes secondary pollution.

[0005] Fly ash is the main solid waste discharged from boilers using coal as the main fuel. Its main component is SiO2, followed by a small amount of Fe2O3, Al2O3, CaO, etc. According to different coal types burned, the component composition ratio of fly ash will vary. The overall solution of fly ash in water is weakly alkaline. In terms of application, according to the material and phase characteristics of fly ash itself, fly ash is widely used as an adhesive in the construction industry, as an adhesive for cement and concrete. At the same time, due to the fluffy nature and large porosity of fly ash materials, the materials have strong adsorption and a relatively high specific surface area, and are also used as catalysts and adsorbents in research.

[0006] Essentially, fly ash is composed of small spheres such as low-iron or high-iron glass beads and porous glass beads. Therefore, the material itself has a relatively large specific surface area. So in research, fly ash can be used as a catalyst support to obtain a relatively large specific surface area. At the same time, there are strong weak acid sites on the surface of the catalyst after preparation means. This characteristic helps to improve the activity of the loaded metal components in the SCR reaction.

[0007] The Chinese patent publication number CN117339601A discloses a fly ash-based supported denitration catalyst and its preparation method. The invention puts fly ash, NaOH solution and surfactant into a wet ball mill at the same time, and after wet ball milling, the obtained slurry is filtered and dried for 3-5 hours with hot air at 70-90°C to obtain an alkali-modified fly ash carrier; the alkali-modified fly ash carrier is added to the pre-prepared Mn-Ce precursor solution for ultrasonic impregnation for 1-2 hours, and then filtered and dried for 3-5 hours with hot air at 70-90°C, and then filtered and dried for 3-5 hours with hot air at 110-130°C to obtain a fly ash-based supported denitration catalyst. The catalyst can effectively remove nitrogen oxides in flue gas, and has the characteristics of low cost and simple preparation method, which largely meets the requirements of industrial flue gas denitration. The fly ash is turned into treasure, but the method only performs simple processing on the fly ash and directly loads the active metal. The flue gas purification method of the present invention has no effect on NO under normal flue gas conditions. x The removal rate is as high as over 90% at 225°C, but the catalytic effect cannot be effectively exerted at higher temperatures.

[0008] Chinese patent CN202311362626.2 discloses an iron-chromium modified fly ash denitration catalyst and its preparation method and application. First, the iron salt and the chromium salt are dissolved in deionized water respectively, and then mixed and ultrasonicated to obtain a uniform and transparent solution; then the fly ash carrier is added to the solution and stirred thoroughly, and then left to age overnight; finally, the static product is dried, calcined and ground to obtain the iron-chromium modified fly ash denitration catalyst Fe-Cr / FA. The iron-chromium modified fly ash denitration catalyst, the fly ash carrier can adsorb nitrogen oxides on the surface and near the surface of the catalyst, so that it is in full contact with the catalyst and improves the catalytic efficiency; and it can make the active metal oxides evenly distributed on the surface of the carrier, so that the catalyst surface has more active sites, and the removal efficiency of nitrogen oxides can reach more than 80% in the temperature range above 500°C, and reach 100% at 600°C, but the denitration effect at 300-450°C is only about 50%, which cannot meet the gas turbine exhaust denitration work.

[0009] Considering that the exhaust temperature of gas turbines is mostly between 300-450°C, the existing denitrification catalysts with fly ash as the carrier can only achieve a good denitrification effect at high or low processing temperatures, and the effect of directly using them for denitrification in gas turbines is not good. Summary of the invention

[0010] The object of the present invention is to provide a denitration catalyst for gas turbine exhaust gas. The catalyst has a denitration efficiency of more than 80% in the temperature range of 300-450 °C, meeting the denitration requirements of gas turbine exhaust gas; at the same time, it solves the environmental problems caused by fly ash emissions, realizes the resource utilization of fly ash, and effectively reduces the manufacturing cost of the denitration catalyst for gas turbine exhaust gas.

[0011] To achieve the above object, the technical solution of the present invention is as follows:

[0012] A denitration catalyst for gas turbine exhaust gas, the catalyst comprising the following components in parts by weight: 5-20 parts of copper oxide, 5-15 parts of cerium dioxide, 2-8 parts of iron oxide, and 45-60 parts of modified fly ash;

[0013] The specific surface area BET of the modified fly ash is ≥ 64 m 2 / g, and the total pore volume is ≥ 0.8 cm 3 / g.

[0014] Preferably, the copper oxide is 10-20 parts.

[0015] Furthermore, the specific modification steps of the modified fly ash are as follows:

[0016] 1) Add 10%-15% of the total weight of fly ash of lime and 3%-5% of the total weight of fly ash of cement to the fly ash, mix evenly to form a block, and then activate it under steam at 700-900 °C for 10 h-24 h, and then dry it under high pressure of 70-90 atm for 12 h-20 h, and obtain block fly ash after natural cooling;

[0017] 2) Crush the block fly ash into particles with a particle size of 0.35-0.65 mm, then pickle it with concentrated nitric acid at a temperature of 60-80 °C for 8 h-12 h, wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 300-500 °C for 24 h-48 h to obtain a modified fly ash carrier.

[0018] After a series of modification treatments of fly ash with lime and cement in the present invention, the specific surface area and structural strength of fly ash itself are greatly improved. The specific surface area BET of the modified fly ash is ≥ 64 m 2 / g, and the total pore volume is ≥ 0.8 cm 3 / g, which can better exert the ability of the catalyst active component in a high-temperature environment such as 300-450 °C. In addition, the modified fly ash has a greatly improved specific surface area and can better act as a carrier for the NH3-SCR catalyst, improving the conversion efficiency of NO to NO2.

[0019] The present invention selects cerium dioxide and copper oxide as the main active components. Cerium dioxide and copper oxide have unique redox capabilities and acid-base properties, which can enhance the conversion of NO to NO2 in gas-phase reactions, thereby contributing to the improvement of NO x removal efficiency.

[0020] The present invention selects iron oxide as an additive. The Fe-based catalyst has a low activity for the conversion of SO2 to SO3, so it has good sulfur poisoning resistance.

[0021] The present invention uses lime and cement to modify fly ash. The silicate component of cement has strong thermal stability. Lime reacts with nitric acid to produce calcium nitrate that is easily soluble in water, leaving a large number of pores, increasing the porosity and specific surface area. During the modification process, it is activated with steam at 700 - 900 °C for 10 h - 24 h, which improves the pore structure and specific surface area while enhancing the thermal stability of the catalyst support. In addition, the steam can effectively clean the impurities on the surface of the support, which helps to load the active components of the catalyst subsequently.

[0022] After the support is steam-activated, the pores are filled with water and dried at a high pressure of 70 - 90 atm for 12 h - 20 h to keep the support with high structural strength. If it is directly dried at normal pressure, the rapid evaporation of water will cause the pore structure of the support to be damaged.

[0023] Subsequent activation, drying and other means greatly improve the thermal stability and pore structure of the modified fly ash, enabling it to maintain good catalytic activity at 300 - 450 °C. When the temperature is too high, the pore structure of fly ash will be damaged by heat, the specific surface area will decrease significantly, and the active sites will decrease, resulting in a decrease in activity.

[0024] Advantages of the present invention

[0025] The catalyst of the present invention uses CuO-CeO2-Fe2O3 as the active components and the modified fly ash modified by lime and cement as the support. Due to the modified fly ash having a high specific surface area and structural strength, the BET specific surface area of the modified fly ash is ≥64 m 2 / g, and the total pore volume is ≥0.8 cm 3 / g, which can better exert the ability of the active components of the catalyst in high-temperature environments such as 300 - 450 °C. This catalyst is tested for denitrification under simulated flue gas conditions in a fixed bed. The results show that when the space velocity is 30000 h -1 , the volume concentration of NO is 1000 ppm, and the volume concentration of SO2 is 200 ppm, the denitrification efficiency reaches over 80% in the temperature range of 300 - 450 °C.

[0026] The catalyst of the present invention does not use the toxic active component V2O5, which reduces environmental pollution and achieves the purpose of reducing costs and improving the safety of use. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a graph showing the denitrification efficiency of the catalysts of the examples and comparative examples of the present invention at different temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be further described below in conjunction with examples and drawings.

[0029] Example 1

[0030] Preparation of modified fly ash:

[0031] 1) Add 15% lime and 3% cement to the fly ash in proportion, mix evenly to form blocks, then activate them under steam at 900 °C for 24 h, and then dry them under high pressure of 90 atm for 12 h. After natural cooling, block fly ash is obtained;

[0032] 2) Crush the block fly ash into particles with a particle size of 0.35 - 0.65 mm, then pickle it with 70% concentrated nitric acid at 70 °C for 11 h, wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 300 °C for 40 h to obtain a modified fly ash carrier.

[0033] Configure the catalyst according to the components in Table 1 and measure the denitrification performance of the catalyst.

[0034] Example 2

[0035] Preparation of modified fly ash:

[0036] 1) Add 12% lime and 4% cement based on the total weight of the fly ash to the fly ash, mix evenly to form blocks, then activate them under steam at 850 °C for 18 h, and then dry them under high pressure of 85 atm for 15 h. After natural cooling, block fly ash is obtained;

[0037] 2) Crush the block fly ash into particles with a particle size of 0.35 - 0.65 mm, then pickle it with 69% concentrated nitric acid at 80 °C for 12 h, wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 350 °C for 48 h to obtain a modified fly ash carrier.

[0038] Configure the catalyst according to the components in Table 1 and measure the denitrification performance of the catalyst.

[0039] Example 3

[0040] Preparation of modified fly ash:

[0041] 1) Add 13% lime and 5% cement to fly ash in proportion, mix evenly to form blocks, then activate them under steam at 700 °C for 15 h, and then dry them under high pressure of 80 atm for 20 h. After natural cooling, blocky fly ash is obtained;

[0042] 2) Crush the blocky fly ash into particles with a particle size of 0.35 - 0.65 mm, then pickle it with 65% concentrated nitric acid at a temperature of 65 °C for 10 h, wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 500 °C for 30 h to obtain a modified fly ash carrier.

[0043] Prepare the catalyst according to the components in Table 1 and measure the denitrification performance of the catalyst.

[0044] Example 4

[0045] Preparation of modified fly ash:

[0046] 1) Add 10% lime and 4% cement to fly ash in proportion, mix evenly to form blocks, then activate them under steam at 800 °C for 10 h, and then dry them under high pressure of 70 atm for 18 h. After natural cooling, blocky fly ash is obtained;

[0047] 2) Crush the blocky fly ash into particles with a particle size of 0.35 - 0.65 mm, then pickle it with 67% concentrated nitric acid at a temperature of 60 °C for 8 h, wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 400 °C for 24 h to obtain a modified fly ash carrier.

[0048] Prepare the catalyst according to the components in Table 1 and measure the denitrification performance of the catalyst.

[0049] Comparative Example 1

[0050] Take an appropriate amount of fly ash, the solid waste from a thermal power plant, and crush it into fly ash particle carriers of a certain particle size. After screening, the particle size distribution is 0.35 - 0.65 mm. Pickle the fly ash particles with 70% concentrated nitric acid at 80 °C for 12 h, then wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 300 °C for 48 h to obtain a modified fly ash carrier.

[0051] Prepare the catalyst according to the components in Table 1 and measure the denitrification performance of the catalyst.

[0052] Comparative Example 2

[0053] Take an appropriate amount of fly ash, the solid waste from a thermal power plant, and crush it into fly ash particle carriers of a certain particle size. After screening, the particle size distribution is 0.35 - 0.65 mm. Pickle the fly ash particles with 70% concentrated nitric acid at 80 °C for 12 h, then wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 300 °C for 48 h to obtain a modified fly ash carrier.

[0054] The catalyst was prepared according to the components in Table 1, and the denitrification performance of the catalyst was measured.

[0055] Simulation of flue gas denitrification experiment: When the space velocity was 30,000 h -1 , the NO volume concentration was 1000 ppm, NH3 / NO = 1.0, and the oxygen concentration was 3%, 200 ppm SO2 was introduced, and the reaction was controlled by a heating electric furnace to rise from 200 °C to 500 °C, with a temperature interval of 50 °C. When the catalyst reached the stable catalytic stage, the denitrification effects of the catalysts of the examples and comparative examples on NO in the flue gas were recorded. x The results are as follows Figure 1 .

[0056] Figure 1 This is the denitrification efficiency curve graph of the catalysts of the examples and comparative examples of the present invention at different temperatures. It can be seen from the graph that the catalyst prepared with modified fly ash as the carrier in the present invention has the best denitrification effect at 300 - 400 °C, and the denitrification efficiency is above 80%.

[0057] In Comparative Example 1 and Comparative Example 2, only acid modification was used for fly ash, and the BET specific surface area and total pore volume of the obtained modified fly ash were much smaller than those of the modified fly ash of the present invention. The catalysts in Comparative Example 1 and Comparative Example 2 had the highest denitrification efficiency at 300 °C, and the denitrification efficiency decreased rapidly with the increase of temperature. They were not suitable for denitrification under the conditions of fixed - bed simulated flue gas at 300 - 450 °C.

[0058] Table 1

[0059]

Claims

1. A denitration catalyst for gas turbine exhaust gas, characterized in that, The catalyst comprises the following components in parts by weight: 5-20 parts of copper oxide, 5-15 parts of cerium dioxide, 2-8 parts of iron oxide, and 45-60 parts of modified fly ash; The specific surface area BET of the modified fly ash is ≥ 64 m 2 / g, and the total pore volume is ≥ 0.8 cm 3 / g.

2. The gas turbine tail gas denitration catalyst according to claim 1, wherein The copper oxide is 10-20 parts.

3. The gas turbine tail gas denitration catalyst according to claim 1, wherein, The specific modification steps of the modified fly ash are as follows: 1) Add 10%-15% of the total weight of lime and 3%-5% of the total weight of cement to the fly ash, mix evenly to form a block, then activate it with steam at 700-900 °C for 10h-24h, and then dry it under a high pressure of 70-90 atm for 12h-20h, and obtain block fly ash after natural cooling; 2) Crush the block fly ash into particles with a particle size of 0.35-0.65 mm, then pickle it with concentrated nitric acid at a temperature of 60-80 °C for 8h-12h, wash it with distilled water until neutral, and then dry it in a vacuum drying oven at 300-500 °C for 24h-48h to obtain a modified fly ash carrier.

4. The gas turbine tail gas denitration catalyst according to claim 3, characterized in that, The mass fraction of the concentrated nitric acid is 65%-70%.

5. The gas turbine tail gas denitration catalyst according to claim 3, characterized in that, In step 2), the ratio of concentrated nitric acid to fly ash during pickling is 5-10 ml: 1 g.

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