A method for improving the carbonization performance of low-carbon clinker using hydroxyl AFm

Abstract

The invention discloses a method for improving the carbonization performance of low-carbon clinker by using hydroxyl AFm. The method comprises the following steps: mixing low-carbon clinker, hydroxyl AFm and water, and pressing and molding the mixture; drying the molded sample, and carbonizing the mixture for 12-24 hours under the conditions of CO2 concentration of 15-20%, temperature of 50-70°C, humidity of 50-80%, and air pressure of 0.1-0.3MPa to obtain carbonized clinker; adding hydroxyl AFm to the low-carbon clinker gradually releases OH under CO2 conditions. ‑ It can retain water and increase the alkalinity of the system to promote carbonization. After carbonization, no CaSO4·(0.5‑2)H2O with low strength and poor durability will appear. It can be used in the carbonization environment of high temperature and low CO2 concentration in the exhaust gas of cement industrial kiln, and can effectively improve the carbonization strength and carbon fixation rate of low-carbon clinker.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and in particular relates to a method for improving the carbonization performance of low-carbon clinker by utilizing hydroxyl-type AFm. Background Art

[0002] The cement industry is one of the world's largest sources of carbon dioxide emissions, accounting for 5%-8% of global emissions, of which 60% comes from the calcination of limestone. It is in urgent need of a low-carbon transformation. Low-carbon cement clinker has been a hot research topic in recent years. Its main mineral composition is low-calcium minerals C3S2, CS, β-C2S, and γ-C2S. Compared with silicate cement clinker mainly composed of C3S minerals, it requires less limestone in the ingredients, has a low calcination temperature, and can absorb a large amount of CO2 gas. It not only reduces carbon emissions from the cement industry in many ways, but can also be used to prepare building materials with excellent physical properties.

[0003] In the research of low-carbon clinker, a CO2 concentration of 50-100% is often used for carbonization, which has a good effect. However, the actual ultimate goal is to use industrial exhaust gas for carbonization to reduce carbon emissions. Usually, the CO2 concentration in industrial exhaust gas is less than 30%, which is the main reason for the low carbonization strength of the material and the difficulty in application.

[0004] The CO2 concentration in the exhaust gas of cement industrial kilns is generally 15-20%, the carbonization rate is slow, and the requirements for other carbonization conditions will become harsh. Among them, the effect of moisture on carbonization will become more significant, and it is an important factor in whether carbonization can be carried out quickly and continuously. Too much moisture will hinder the diffusion of CO2, and too little moisture will significantly reduce the carbonization rate. The moisture inside the material will gradually dissipate during the carbonization process, which is particularly obvious in the high temperature environment of 50-70℃ in the kiln exhaust gas, which will cause the moisture to be lost too quickly and reduce the effective carbonization time. Therefore, to obtain a higher degree of carbonization, material density, carbonization strength and carbon fixation rate, it is necessary to maintain a moisture content suitable for carbonization longer during the carbonization process.

[0005] Calcium aluminate can be gradually carbonized under the conditions of CO2 (reactant) and H2O (medium). The reaction equation is: 3CaO·Al2O3·3CaSO4·32H2O+3CO2→3CaSO4·2H2O+3CaCO3+Al2O3·xH2O+(26-x)H2O. As the carbonization proceeds, water is released, and the moisture content suitable for carbonization is maintained longer during the carbonization process. However, the product contains CaSO4·2H2O, which will reduce the strength and durability of the material after carbonization to a certain extent.

[0006] Whether it is possible to provide a method that can both prolong the effective carbonization time of low-carbon clinker and promote carbonization without negatively affecting the performance after carbonization has become a technical problem that needs to be solved urgently. Summary of the invention

[0007] The present invention aims to provide a method for improving the carbonization performance of low-carbon clinker by using hydroxyl AFm, by adding hydroxyl AFm to low-carbon clinker, so that hydroxyl AFm gradually releases OH under CO2 conditions. - It can retain water and increase the alkalinity of the system to promote carbonization. After carbonization, no CaSO4·(0.5-2)H2O with low strength and poor durability will appear. It can be used in the carbonization environment of high temperature and low CO2 concentration in the exhaust gas of cement industrial kiln, and can effectively improve the carbonization strength and carbon fixation rate of low-carbon clinker.

[0008] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0009] A method for improving the carbonization performance of low-carbon clinker by using hydroxyl AFm comprises the following steps:

[0010] (1) Mix low carbon clinker, hydroxyl type AFm and water and press into shape;

[0011] (2) After the molded sample is dried, it is carbonized for 12-24 hours under the conditions of CO2 concentration of 15-20%, temperature of 50-70°C, humidity of 50-80%, and air pressure of 0.1-0.3 MPa to obtain carbonized clinker.

[0012] According to the above scheme, the mineral composition of the low carbon clinker in step (1) is one or a mixture of CS, C3S2, C2S, and C3S.

[0013] According to the above scheme, the main mineral of the hydroxyl-type AFm in step (1) is 3CaO·Al2O3·Ca(OH)2·12H2O, and its content is not less than 90wt%.

[0014] According to the above scheme, the amount of hydroxyl AFm in step (1) is 5-30wt% of the low-carbon clinker, and the amount of water is 15-20wt% of the total amount of low-carbon clinker and hydroxyl AFm.

[0015] According to the above scheme, in step (2), the sample is dried under natural conditions.

[0016] According to the above scheme, the moisture content of the molded sample after drying in step (2) is 4-10wt%.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) Low carbon clinker will gradually lose water during the carbonization process, which is particularly obvious in the high temperature environment of 50-70℃ of cement kiln exhaust gas, which will cause water to lose too quickly and reduce the effective carbonization time. The moisture content that does not affect gas diffusion and is suitable for carbonization reaction is 4-10%. By adding hydroxyl AFm to low carbon clinker, hydroxyl AFm can be gradually carbonized under the conditions of CO2 (reactant) and H2O (medium). The reaction equation is: 3CaO·Al2O3·Ca(OH)2·12H2O+4CO2→4CaCO3+Al2O3·xH2O+(13-x)H2O. As the carbonization proceeds, water is released, so that the moisture content suitable for carbonization can be maintained longer during the carbonization process.

[0019] (2) Compared with ettringite, hydroxyl-type AFm can dissolve more OH during carbonization. - , which can significantly increase the alkalinity of the reaction system, thereby further improving the carbonization efficiency of the system. The same amount of hydroxyl-type AFm can form more CaCO3 and Al2O3·xH2O as strength components after carbonization to fill the pores of the material to improve the strength. There will be no CaSO4·(0.5-2)H2O with low strength and poor durability, and there is no thickening side effect of organic water-retaining agents. Among them, aluminum glue (Al2O3·xH2O) has strong bonding properties, which can further improve the integrity and strength of the carbonized material.

[0020] (3) Compared with organic water retainers, hydroxyl-type AFm is cheaper and has no thickening side effect. It can be used at a temperature of 50-70°C in the tail gas of cement industrial kilns. Low-concentration CO2 carbonization requires better gas diffusion, and high temperature is conducive to gas diffusion. Although organic water retainers such as cellulose ethers can also play a role in water retention, they will gradually become ineffective when the temperature is higher than 30°C, and will thicken and reduce the ion mobility in the water, resulting in a decrease in the carbonization reaction rate. DETAILED DESCRIPTION

[0021] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0022] The specific embodiment provides a method for improving the carbonization performance of low-carbon clinker by using hydroxyl AFm, comprising the following steps:

[0023] (1) Mix low carbon clinker, hydroxyl type AFm and water and press into shape;

[0024] (2) After the molded sample is dried, it is carbonized for 12-24 hours under the conditions of CO2 concentration of 15-20%, temperature of 50-70°C, humidity of 50-80%, and air pressure of 0.1-0.3 MPa to obtain carbonized clinker.

[0025] Specifically, the mineral composition of low carbon clinker is one or a mixture of CS, C3S2, C2S, and C3S.

[0026] Specifically, the main mineral of hydroxyl-type AFm is 3CaO·Al2O3·Ca(OH)2·12H2O, and its content is not less than 90wt%.

[0027] Specifically, the amount of hydroxyl AFm used is 5-30wt% of the low-carbon clinker, and the amount of water used is 15-20wt% of the total amount of the low-carbon clinker and hydroxyl AFm.

[0028] Specifically, the molded sample is dried under natural conditions; the moisture content after drying is 4-10wt%

[0029] Low carbon clinker and hydroxyl type AFm were obtained for jade mineral composition analysis. The mineral compositions of the low carbon clinker used in the embodiment of the present invention are shown in Table 1, and ground to R45μm≤20%:

[0030] Table 1 Mineral composition

[0031] name <![CDATA[β-C2S]]> <![CDATA[C3S2]]> CS <![CDATA[C2AS]]> <![CDATA[SiO2]]> Low carbon clinker 1 20.5 64.3 6.1 8.7 0.4 Low carbon clinker 2 65.2 25.1 0 9.5 0.2 Low carbon clinker 3 3.2 65.4 22.4 8.3 0.7

[0032] Hydroxyl AFm is synthesized using 3CaO·Al2O3, CaO, and H2O:

[0033] Firing 3CaO·Al2O3: Calcium carbonate and aluminum oxide are mixed in a molar ratio of 3:1, and calcined at 1400°C for 1h to obtain 3CaO·Al2O3; 3CaO·Al2O3 and analytical pure CaO are mixed and stirred in a solution in a molar ratio of 1:1, the stirring temperature is set to 5°C, and after stirring for 3 days, vacuum drying and storage are carried out; the content of 3CaO·Al2O3·Ca(OH)2·12H2O in the obtained hydroxyl-type AFm is ≥99%, and the powder is ground to a fineness of R45μm≤20%.

[0034] Example 1

[0035] 1. Ratio

[0036] Weigh 100 parts of low-carbon clinker 1, 10 parts of hydroxyl AFm, and 17.6 parts of water (16% of the total amount of low-carbon clinker and hydroxyl AFm). The calculated moisture content of this ratio is 17.6 / (100+10+17.6)=13.79%.

[0037] 2. Sample preparation

[0038] The prepared raw materials were put into a mixer, mixed rapidly for 1 min, and then pressed into a cylindrical sample with a diameter of 2 cm and a height of 2 cm at a molding pressure of 10 MPa.

[0039] 3. Pre-drying and carbonization

[0040] The sample was dried under natural conditions to a moisture content of 9%, and finally carbonized for 24 hours under the conditions of a carbon dioxide concentration of 18%, a temperature of 60°C, a humidity of 60%, and an air pressure of 0.2 MPa, after which the compressive strength and carbon fixation rate were measured.

[0041] Example 2

[0042] 1. Ratio

[0043] Weigh 100 parts of low-carbon clinker 2, 20 parts of hydroxyl AFm, and 19.2 parts of water (16% of the total amount of low-carbon clinker and hydroxyl AFm). The calculated moisture content of this ratio is 19.2 / (100+20+19.2)=13.79%.

[0044] 2. Sample preparation

[0045] The prepared raw materials were put into a mixer, mixed rapidly for 1 min, and then pressed into a cylindrical sample with a diameter of 2 cm and a height of 2 cm at a molding pressure of 10 MPa.

[0046] 3. Pre-drying and carbonization

[0047] The sample was dried under natural conditions to a moisture content of 6%, and finally carbonized for 24 hours under the conditions of a carbon dioxide concentration of 18%, a temperature of 70°C, a humidity of 70%, and an air pressure of 0.15 MPa, after which the compressive strength and carbon fixation rate were measured.

[0048] Example 3

[0049] 1. Ratio

[0050] Weigh 100 parts of low-carbon clinker 3, 15 parts of hydroxyl AFm, and 18.4 parts of water (16% of the total amount of low-carbon clinker and hydroxyl AFm). The calculated moisture content of this ratio is 18.4 / (100+15+18.4)=13.79%.

[0051] 2. Sample preparation

[0052] The prepared raw materials were put into a mixer, mixed rapidly for 1 min, and then pressed into a cylindrical sample with a diameter of 2 cm and a height of 2 cm at a molding pressure of 10 MPa.

[0053] 3. Pre-drying and carbonization

[0054] The sample was dried under natural conditions to a moisture content of 7%, and finally carbonized for 24 hours under the conditions of a carbon dioxide concentration of 20%, a temperature of 65°C, a humidity of 65%, and an air pressure of 0.2 MPa, after which the compressive strength and carbon fixation rate were measured.

[0055] Comparative Example 1

[0056] Compared with Example 1, in step 1, no hydroxyl AFm is added, 100 parts of low-carbon clinker 1 and 16 parts of water (16% of the low-carbon clinker) are weighed, and the remaining steps are the same.

[0057] Comparative Example 2

[0058] Compared with Example 2, in step 1, no hydroxyl AFm is added, 100 parts of low-carbon clinker 2 and 16 parts of water (16% of the low-carbon clinker) are weighed, and the remaining steps are the same.

[0059] Comparative Example 3

[0060] Compared with Example 3, in step 1, no hydroxyl AFm is added, 100 parts of low-carbon clinker 3 and 16 parts of water (16% of the low-carbon clinker) are weighed, and the remaining steps are the same.

[0061] Comparative Example 4

[0062] Compared with the use of ettringite to replace hydroxyl-type AFm in step 1 of Example 1, ettringite is synthesized by 3CaO·Al2O3, CaSO4·2H2O, and H2O, and the content of 3CaO·Al2O3·3CaSO4·32H2O is ≥99%, and the fineness R45μm is ≤20%. Weigh 100 parts of low-carbon clinker 1, 10 parts of ettringite, and 17.6 parts of water (16% of the total amount of low-carbon clinker and ettringite), and the remaining steps are the same.

[0063] The carbonization conditions and strength after carbonization of the low carbon clinker in each embodiment and comparative example are shown in Table 2.

[0064] Table 2 Carbonization conditions and strength of low carbon clinker after carbonization

[0065]

[0066] It can be seen from Table 2 that the carbonization strength and carbon fixation rate of the low-carbon clinker are significantly improved by adding hydroxyl AFm, and the effect of adding hydroxyl AFm in Example 1 is better than that of adding ettringite in Comparative Example 4.

[0067] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A method for improving the carbonization performance of low-carbon clinker using hydroxyl AFm, characterized in that The following steps are involved: (1) Mix low carbon clinker, hydroxyl AFm and water and press them into shape; the mineral composition of the low carbon clinker is one or a mixture of CS, C3S2, C2S and C3S; the main mineral of the hydroxyl AFm is 3CaO·Al2O3·Ca(OH)2·12H2O, and the content is not less than 90wt%; the amount of hydroxyl AFm is 5-30wt% of the low carbon clinker, and the amount of water is 15-20wt% of the total amount of low carbon clinker and hydroxyl AFm; (2) After the molded sample is dried, carbonization is performed for 12-24 hours under the conditions of CO2 concentration of 15-20%, temperature of 50-70°C, humidity of 50-80%, and air pressure of 0.1-0.3 MPa to obtain carbonized clinker.

2. The method for improving the carbonization performance of low-carbon clinker by using hydroxyl type AFm as claimed in claim 1, characterized in that In step (2), the sample is dried under natural conditions.

3. The method for improving the carbonization performance of low-carbon clinker by using hydroxyl type AFm as claimed in claim 1, characterized in that The moisture content of the sample after drying in step (2) is 4-10wt%.

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