Denitration agent for flue gas treatment and preparation method thereof

Abstract

The invention belongs to the technical field of flue gas denitration agents, and discloses a denitration agent for flue gas treatment and a preparation method thereof. The denitration agent comprises 50-80 parts of a composite amino precursor and 5-20 parts of a catalyst. The composite amino precursor comprises urea and coated ammonium carbamate, and the catalyst is modified aluminum oxide. Urea and ammonium carbamate are used as ammonia preparation precursors, ammonium carbamate is used as an intermediate product of urea hydrolysis, after addition, the concentration of the intermediate product of urea hydrolysis is increased, the reaction can be promoted to be carried out in the ammonia gas generation direction, the ammonia gas yield is improved, and the problem of low ammonia gas yield of single urea is effectively solved. Moreover, the ammonium carbamate is subjected to coating treatment, so that the storage stability of the ammonium carbamate is enhanced, and the polyurethane coating can be dissolved in water during hydrolysis, thereby releasing the ammonium carbamate.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas denitration agents, and in particular to a denitration agent for flue gas treatment and a preparation method thereof. Background Art

[0002] With the increasingly strict restrictions on the emission of nitrogen oxides (NOx) from industrial flue gas, the research and development of efficient denitration processes have attracted more and more attention. The core of the denitration process lies in providing the reducing agent ammonia efficiently and stably. Currently, liquid ammonia, urea solution, and urea hydrolysis or pyrolysis to produce ammonia are the three major ammonia production methods. Among them, the urea hydrolysis or pyrolysis technology is widely used in industries such as thermal power and steel due to its high safety (no need to store liquid ammonia) and easily available raw materials.

[0003] In the traditional urea hydrolysis denitration process, the urea solution is hydrolyzed under certain temperature and pressure conditions, first generating the intermediate product ammonium carbamate (NH2CO2NH4), and then further decomposing into NH3 and CO2 (reaction formula: NH2CONH2 + H2O → NH2CO2NH4 → 2NH3 + CO2). However, in actual industrial applications, there are still some problems with urea hydrolysis to produce ammonia, and the expected effect cannot be achieved. For example, the conversion rate of urea hydrolysis is generally low (below 40%), resulting in insufficient ammonia production per unit mass of urea. It is necessary to add an excessive amount of urea to improve the denitration efficiency. However, the excessive addition of raw materials increases the cost and the burden of waste liquid treatment. To address the above problems, existing solutions improve the hydrolysis efficiency by increasing the hydrolysis temperature or introducing the catalyst phosphate. However, high-temperature hydrolysis will increase the risk of equipment corrosion and consume more energy. The phosphate catalyst dissolves in water, bringing pressure to the subsequent waste liquid treatment.

[0004] Therefore, how to provide a denitration agent with a high ammonia yield is an urgent problem to be solved currently. Summary of the Invention

[0005] The purpose of the present invention is to provide a denitration agent for flue gas treatment and a preparation method thereof, so as to solve the above problems existing in the use of urea as an ammonia production raw material.

[0006] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a denitration agent for flue gas treatment, which comprises the following raw materials in parts by mass: 50 - 80 parts of a composite amino precursor, 5 - 20 parts of a catalyst, and 1 - 5 parts of a corrosion inhibitor;

[0008] The composite amino precursor includes urea and coated ammonium carbamate; the corrosion inhibitor is benzotriazole.

[0009] Preferably, in the above denitration agent for flue gas treatment, the mass ratio of urea to coated ammonium carbamate is 1 - 3:1 - 2.

[0010] Preferably, in the above denitrating agent for flue gas treatment, the film layer of the coated ammonium carbamate is polyurethane; the core of the coated ammonium carbamate is a mixture of ammonium carbamate and an anti-hydrolysis agent; the mass ratio of polyurethane, ammonium carbamate, and anti-hydrolysis agent is 0.1 - 0.5:1 - 10:0.01 - 0.1.

[0011] Preferably, in the above denitrating agent for flue gas treatment, the preparation method of the coated ammonium carbamate is as follows: mix ammonium carbamate and an anti-hydrolysis agent and then perform dry granulation to obtain composite particles; place the composite particles in a coating machine and spray polyurethane emulsion for coating; after coating, perform drying at room temperature to obtain the coated ammonium carbamate.

[0012] Preferably, in the above denitrating agent for flue gas treatment, the rotation speed of the coating is 50 - 200 rpm; the coating time is 0.5 - 2 h; the coating temperature is 25°C.

[0013] Preferably, in the above denitrating agent for flue gas treatment, the catalyst is modified alumina; the particle size of the catalyst is 500 - 800 μm.

[0014] Preferably, in the above denitrating agent for flue gas treatment, the preparation method of the modified alumina is as follows: treat alumina by oxygen plasma, and then mix it with a silane coupling agent and water for modification to obtain the modified alumina.

[0015] The present invention also provides a preparation method of a denitrating agent for flue gas treatment, including the following steps:

[0016] Mix a composite amino precursor, a catalyst, and an inhibitor to obtain a denitrating agent for flue gas treatment.

[0017] The present invention also provides an application of a denitrating agent for flue gas treatment in flue gas denitrification. The method of flue gas denitrification is as follows: hydrolyze the denitrating agent for flue gas treatment in a hydrolysis reactor to obtain ammonia; use the ammonia for flue gas denitrification.

[0018] Preferably, in the above application, the hydrolysis temperature is 110 - 140°C; the hydrolysis pressure is 0.4 - 0.6 MPa.

[0019] Through the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention uses urea and ammonium carbamate as ammonia production precursors. On the one hand, it enriches the types of ammonia sources. On the other hand, as an intermediate product of urea hydrolysis, the addition of ammonium carbamate increases the concentration of intermediate products in urea hydrolysis, which can promote the reaction to proceed in the direction of ammonia production, improve the ammonia yield, and effectively solve the problem of low ammonia yield of single urea. Moreover, the addition of ammonium carbamate reduces the heat input required to maintain the reaction balance during hydrolysis, lowers the hydrolysis temperature, enables ammonia production by hydrolysis at a lower temperature, and reduces the corrosion of the hydrolysis reactor while reducing energy consumption. In addition, the present invention also performs a coating treatment on ammonium carbamate, enhancing the storage stability of ammonium carbamate while the polyurethane coating can be dissolved in water during hydrolysis to release ammonium carbamate.

[0021] (2) The denitration agent of the present invention also adds modified alumina as a hydrolysis catalyst. Oxygen plasma activation and silane coupling agent modification can increase the hydrophilicity of alumina, improve the dispersion of the catalyst in water, and the catalyst can be dispersed in water during hydrolysis to effectively promote the hydrolysis of amino precursors. Moreover, after hydrolysis is completed, the catalyst can be effectively recovered by separation, reducing the burden of waste liquid treatment caused by soluble catalysts dissolving in water.

[0022] (3) The denitration agent of the present invention also adds a corrosion inhibitor, which can form a protective film on the metal surface and slow down the corrosion of the denitration agent on the reactor during hydrolysis.

[0023] (4) The denitration agent of the present invention can produce ammonia by hydrolysis, with mild reaction conditions, a simple ammonia production method, and no corrosion to equipment when using this denitration agent to treat flue gas, which can extend the service life of the equipment. Detailed Embodiments

[0024] The present invention provides a denitration agent for flue gas treatment, comprising the following raw materials in parts by mass: 50 - 80 parts of a composite amino precursor, 5 - 20 parts of a catalyst, and 1 - 5 parts of a corrosion inhibitor.

[0025] In the present invention, the mass fraction of the composite amino precursor is preferably 52 - 78 parts, more preferably 60 - 70 parts, and even more preferably 68 parts.

[0026] In the present invention, the mass fraction of the catalyst is preferably 8 - 17 parts, more preferably 10 - 15 parts, and even more preferably 12 parts.

[0027] In the present invention, the mass fraction of the corrosion inhibitor is preferably 1.5 - 4 parts, more preferably 2 - 3.5 parts, and even more preferably 2.5 parts.

[0028] In the present invention, the corrosion inhibitor is preferably benzotriazole.

[0029] In the present invention, the composite amino precursor preferably includes urea and coated ammonium carbamate.

[0030] In the present invention, the mass ratio of the urea to the coated ammonium carbamate is preferably 1-3:1-2, more preferably 1-2:1, and still more preferably 1:1.

[0031] In the present invention, the film layer of the coated ammonium carbamate is preferably polyurethane; the core of the coated ammonium carbamate is preferably a mixture of ammonium carbamate and a hydrolysis inhibitor; the mass ratio of the polyurethane, ammonium carbamate, and hydrolysis inhibitor is preferably 0.1-0.5:1-10:0.01-0.1, more preferably 0.2-0.5:2-8:0.01-0.07, and still more preferably 0.4:5:0.05.

[0032] In the present invention, the hydrolysis inhibitor is preferably the polycarbodiimide hydrolysis inhibitor Stabaxol P from Rhein Chemie.

[0033] In the present invention, the preparation method of the coated ammonium carbamate is as follows: ammonium carbamate and a hydrolysis inhibitor are mixed and then dry granulated to obtain composite particles; the composite particles are placed in a coating machine, and a polyurethane emulsion is sprayed for coating; after the coating is completed, it is dried at room temperature to obtain the coated ammonium carbamate.

[0034] In the present invention, the polyurethane emulsion is preferably an aqueous polyurethane emulsion, PU667 purchased from Nanjing Chuhai New Material Technology Co., Ltd.

[0035] In the present invention, the dry granulation method is preferably: mixing ammonium carbamate and a hydrolysis inhibitor, tabletting, and pulverizing; the particle size of the composite particles is preferably 300-600 μm, more preferably 300-500 μm, and still more preferably 400 μm.

[0036] In the present invention, the rotation speed of the coating is preferably 50-200 rpm, more preferably 60-150 rpm, and still more preferably 80 rpm; the coating time is preferably 0.5-2 h, more preferably 0.5-1.5 h, and still more preferably 1 h; the coating temperature is preferably 25 °C.

[0037] In the present invention, the catalyst is preferably modified alumina; the particle size of the catalyst is preferably 500-800 μm, more preferably 600-750 μm, and still more preferably 700 μm.

[0038] In the present invention, the preparation method of the modified alumina is: alumina is treated by oxygen plasma, and then mixed with a silane coupling agent and water for modification to obtain the modified alumina.

[0039] In the present invention, the conditions for the oxygen plasma treatment are as follows: the power is preferably 80 - 200 W, more preferably 90 - 160 W, and still more preferably 100 W; the time is preferably 20 - 120 s, more preferably 30 - 100 s, and still more preferably 50 s; the treatment atmosphere is preferably oxygen; the temperature is preferably 20 - 160 °C, more preferably 50 - 120 °C, and still more preferably 60 °C.

[0040] In the present invention, the silane coupling agent is preferably KH550 and / or KH560, more preferably KH550 or KH560, and still more preferably KH550.

[0041] In the present invention, the dosage ratio of alumina, silane coupling agent, and water is preferably 80 - 100 g: 1 - 5 mL: 30 - 50 mL, more preferably 82 - 90 g: 2 - 4 mL: 40 - 50 mL, and still more preferably 85 g: 3 mL: 50 mL.

[0042] In the present invention, the modification temperature is preferably 60 - 90 °C, more preferably 70 - 85 °C, and still more preferably 80 °C; the modification time is preferably 1 - 3 h, more preferably 1 - 2 h, and still more preferably 2 h.

[0043] The present invention also provides a preparation method for a denitration agent for flue gas treatment, comprising the following steps:

[0044] Mix the composite amino precursor, catalyst, and corrosion inhibitor to obtain a denitration agent for flue gas treatment.

[0045] The present invention also provides an application of a denitration agent for flue gas treatment in flue gas denitration. The method for flue gas denitration is as follows: hydrolyze the denitration agent for flue gas treatment in a hydrolysis reactor to obtain ammonia; use the ammonia for flue gas denitration.

[0046] In the present invention, the hydrolysis temperature is preferably 110 - 140 °C, more preferably 115 - 135 °C, and still more preferably 125 °C; the hydrolysis pressure is preferably 0.4 - 0.6 MPa, more preferably 0.4 - 0.5 MPa, and still more preferably 0.5 MPa.

[0047] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0048] Example 1

[0049] This embodiment provides a denitration agent for flue gas treatment, which comprises the following raw materials in parts by mass: 68 parts of a composite amino precursor, 12 parts of a catalyst, and 2.5 parts of benzotriazole. The composite amino precursor is a mixture of urea and coated ammonium carbamate with a mass ratio of 1:1.

[0050] The preparation method of the above-mentioned denitration agent for flue gas treatment includes the following steps:

[0051] Mix ammonium carbamate with an anti-hydrolysis agent, tablet, and crush to a particle size of 400 μm to obtain composite particles; place the composite particles in a coating machine, spray polyurethane emulsion at 80 rpm and coat at 25°C for 1 h, and the mass ratio of polyurethane, ammonium carbamate, and anti-hydrolysis agent is 0.4:5:0.05; after coating, carry out drying at room temperature to obtain polyurethane-coated ammonium carbamate;

[0052] Perform oxygen plasma treatment on alumina under the conditions of: power of 100 W, time of 50 s, treatment atmosphere of oxygen, and temperature of 60°C to obtain activated alumina; then mix the activated alumina with KH550 and water in a dosage ratio of 85 g:3 mL:50 mL and modify at 80°C for 2 h to obtain modified alumina with a particle size of 700 μm;

[0053] Mix urea, polyurethane-coated ammonium carbamate, modified alumina, and benzotriazole evenly to obtain a denitration agent for flue gas treatment.

[0054] Example 2

[0055] This embodiment provides a denitration agent for flue gas treatment, which comprises the following raw materials in parts by mass: 52 parts of a composite amino precursor, 8 parts of a catalyst, and 1 part of benzotriazole. The composite amino precursor is a mixture of urea and coated ammonium carbamate with a mass ratio of 2:1.

[0056] The preparation method of the above-mentioned denitration agent for flue gas treatment includes the following steps:

[0057] Mix ammonium carbamate with an anti-hydrolysis agent, tablet, and crush to a particle size of 300 μm to obtain composite particles; place the composite particles in a coating machine, spray polyurethane emulsion at 100 rpm and coat at 25°C for 0.5 h, and the mass ratio of polyurethane, ammonium carbamate, and anti-hydrolysis agent is 0.2:5:0.01; after coating, carry out drying at room temperature to obtain polyurethane-coated ammonium carbamate;

[0058] The alumina is subjected to oxygen plasma treatment under the following conditions: power is 150 W, time is 40 s, treatment atmosphere is oxygen, and temperature is 80 °C to obtain activated alumina; then the activated alumina, KH550, and water are mixed at a dosage ratio of 100 g: 1 mL: 50 mL and modified at 60 °C for 3 h to obtain modified alumina with a particle size of 700 μm;

[0059] Urea, polyurethane-coated ammonium carbamate, modified alumina, and benzotriazole are mixed evenly to obtain a denitration agent for flue gas treatment.

[0060] Example 3

[0061] This example provides a denitration agent for flue gas treatment, which contains the following raw materials in parts by mass: 60 parts of a composite amino precursor, 15 parts of a catalyst, and 2 parts of benzotriazole. Among them, the composite amino precursor is a mixture of urea and coated ammonium carbamate with a mass ratio of 1:2.

[0062] The preparation method of the above-mentioned denitration agent for flue gas treatment includes the following steps:

[0063] Ammonium carbamate and an anti-hydrolysis agent are mixed, tableted, and crushed to a particle size of 400 μm to obtain composite particles; the composite particles are placed in a coating machine, and at a rotation speed of 150 rpm, a polyurethane emulsion is sprayed for coating at 25 °C for 1.5 h, and the mass ratio of polyurethane, ammonium carbamate, and anti-hydrolysis agent is 0.1:7:0.03; after the coating is completed, it is dried at room temperature to obtain polyurethane-coated ammonium carbamate;

[0064] The alumina is subjected to oxygen plasma treatment under the following conditions: power is 100 W, time is 80 s, treatment atmosphere is oxygen, and temperature is 120 °C to obtain activated alumina; then the activated alumina, KH560, and water are mixed at a dosage ratio of 80 g: 3 mL: 50 mL and modified at 80 °C for 1 h to obtain modified alumina with a particle size of 700 μm;

[0065] Urea, polyurethane-coated ammonium carbamate, modified alumina, and benzotriazole are mixed evenly to obtain a denitration agent for flue gas treatment.

[0066] Example 4

[0067] This example provides a denitration agent for flue gas treatment, which contains the following raw materials in parts by mass: 80 parts of a composite amino precursor, 5 parts of a catalyst, and 4 parts of benzotriazole. Among them, the composite amino precursor is a mixture of urea and coated ammonium carbamate with a mass ratio of 3:2.

[0068] The preparation method of the above-mentioned denitration agent for flue gas treatment includes the following steps:

[0069] Mix ammonium carbamate with a hydrolysis inhibitor, tablet, and crush to a particle size of 400 μm to obtain composite particles; place the composite particles in a coating machine, spray polyurethane emulsion at a rotation speed of 160 rpm, and coat at 25 °C for 2 h. The mass ratio of polyurethane, ammonium carbamate, and hydrolysis inhibitor is 0.5:1:0.07; after coating, dry at room temperature to obtain polyurethane-coated ammonium carbamate;

[0070] Perform oxygen plasma treatment on alumina under the conditions of: power of 100 W, time of 60 s, treatment atmosphere of oxygen, and temperature of 120 °C to obtain activated alumina; then mix the activated alumina with KH550 and water in a dosage ratio of 90 g:5 mL:40 mL, and modify at 90 °C for 1 h to obtain modified alumina with a particle size of 700 μm;

[0071] Mix urea, polyurethane-coated ammonium carbamate, modified alumina, and benzotriazole evenly to obtain a denitration agent for flue gas treatment.

[0072] Comparative Example 1

[0073] This comparative example provides a denitration agent. Specifically refer to Example 1, the difference is that the coated ammonium carbamate is replaced with urea.

[0074] Comparative Example 2

[0075] This comparative example provides a denitration agent. Specifically refer to Example 1, the difference is that the catalyst is not subjected to modification treatment.

[0076] Prepare the denitration agents of Examples 1-4 and Comparative Examples 1-2 into solutions with a solid content of 50% by adding water, hydrolyze in a hydrolysis reactor at 125 °C and a pressure of 0.5 MPa for 30 min, and the results of the ammonia mass concentration are shown in Table 1. Then dilute the generated ammonia to 5% and spray it into the furnace for flue gas denitration. The reaction temperature is 900 °C, and the NO x concentration in the flue gas is 400 mg / m 3 , test the NO x concentration in the outlet flue gas, and calculate the denitration rate. The results are shown in Table 1.

[0077] Table 1 Results of ammonia mass concentration and denitration rate

[0078] Denitration agent Ammonia mass concentration % Denitration rate % Example 1 43 91 Example 2 39 87 Example 3 38 88 Example 4 42 90 Comparative example 1 29 73 Comparative example 2 34 85

[0079] As can be seen from Table 1, the ammonia mass concentration generated by the hydrolysis of the denitration agent of the present invention can reach more than 40%, the hydrolysis efficiency is high, the ammonia production is large, and the denitration rate for flue gas treatment can reach more than 90%, showing good denitration effect. By comparison, it can be known that the addition of ammonium carbamate and the modification of the catalyst in the present invention can improve the ammonia production to a certain extent, which is beneficial to flue gas denitration.

[0080] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A denitrification agent for flue gas treatment, characterized in that: The invention comprises the following raw materials in parts by weight: 50 to 80 parts of a composite amino precursor, 5 to 20 parts of a catalyst, and 1 to 5 parts of a corrosion inhibitor; The composite amino precursor includes urea and coated ammonium carbamate; and the corrosion inhibitor is benzotriazole.

2. The denitrification agent for flue gas treatment according to claim 1, characterized in that: The mass ratio of the urea to the coated ammonium carbamate is 1-3:1-2.

3. The denitrification agent for flue gas treatment according to claim 2, characterized in that: The film layer of the coated ammonium carbamate is polyurethane; the core of the coated ammonium carbamate is a mixture of ammonium carbamate and an anti-hydrolysis agent; the mass ratio of the polyurethane, ammonium carbamate and anti-hydrolysis agent is 0.1-0.5:1-10:0.01-0.

1.

4. The denitrification agent for flue gas treatment according to claim 3, characterized in that: The preparation method of the coated ammonium carbamate comprises: mixing ammonium carbamate and an anti-hydrolysis agent and then performing dry granulation to obtain composite particles; placing the composite particles in a coating machine and spraying polyurethane emulsion for coating; and drying at room temperature after coating to obtain the coated ammonium carbamate.

5. The denitrification agent for flue gas treatment according to claim 4, characterized in that: The coating rotation speed is 50-200 rpm; the coating time is 0.5-2h; and the coating temperature is 25°C.

6. A denitrification agent for flue gas treatment according to claim 2 or 3, characterized in that: The catalyst is modified alumina; the particle size of the catalyst is 500-800 μm.

7. The denitrification agent for flue gas treatment according to claim 6, characterized in that: The preparation method of the modified aluminum oxide is as follows: aluminum oxide is treated by oxygen plasma, and then mixed with a silane coupling agent and water for modification to obtain the modified aluminum oxide.

8. The method for preparing a denitrification agent for flue gas treatment according to any one of claims 1 to 7, characterized in that: The following steps are involved: The composite amino precursor, the catalyst and the corrosion inhibitor are mixed to obtain a denitrification agent for flue gas treatment.

9. Use of a denitrification agent for flue gas treatment according to any one of claims 1 to 7 in flue gas denitrification, characterized in that: The flue gas denitrification method comprises: hydrolyzing a denitrification agent used for flue gas treatment in a hydrolysis reactor to obtain ammonia; and using the ammonia for flue gas denitrification.

10. The use according to claim 9, characterized in that: The temperature of the hydrolysis is 110-140° C.; the pressure of the hydrolysis is 0.4-0.6 MPa.