A method for improving the carbonization performance of low-carbon clinker by using ettringite

Abstract

The invention discloses a method for improving the carbonization performance of low-carbon clinker by utilizing ettringite. The method comprises the following steps: mixing low-carbon clinker, ettringite and water, and pressing and molding the mixture; drying the molded sample, and then carbonizing the mixture for 12-24 hours under the conditions of a CO2 concentration of 15-20%, a temperature of 50-70°C, a humidity of 50-80%, and an air pressure of 0.1-0.3MPa to obtain a carbonized clinker; and adding ettringite to the low-carbon clinker so that the ettringite is gradually carbonized under the CO2 condition and releases water to retain water, thereby providing partial carbonization strength and extending the effective carbonization time of the low-carbon clinker, thereby effectively improving the carbonization strength and carbon fixation rate of the low-carbon clinker, and the low-carbon clinker can be used in a carbonization environment with high temperature and low CO2 concentration in the tail gas of a cement industrial kiln.

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 ettringite. 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] Whether it is possible to provide a method that can prolong the effective carbonization time of low-carbon clinker, thereby effectively improving the carbonization intensity and carbon fixation rate of low-carbon clinker, has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to provide a method for improving the carbonization performance of low-carbon clinker by utilizing ettringite. By adding ettringite to the low-carbon clinker, the ettringite is gradually carbonized under CO2 conditions and releases water to retain water, thereby providing partial carbonization strength and extending the effective carbonization time of the low-carbon clinker, thereby effectively improving the carbonization strength and carbon fixation rate of the low-carbon clinker, and can be used in a carbonization environment with high temperature and low CO2 concentration in the exhaust gas of a cement industrial kiln.

[0007] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0008] A method for improving the carbonization performance of low-carbon clinker by using ettringite comprises the following steps:

[0009] (1) mixing low carbon clinker, ettringite and water and pressing into a shape;

[0010] (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.

[0011] 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.

[0012] According to the above scheme, the main mineral of the ettringite in step (1) is 3CaO·Al2O3·3CaSO4·32H2O, and its content is not less than 90wt%.

[0013] According to the above scheme, the amount of ettringite in step (1) is 5-25wt% of the low carbon clinker, and the amount of water is 15-20wt% of the total amount of low carbon clinker and ettringite.

[0014] According to the above scheme, in step (2), the sample is dried under natural conditions.

[0015] According to the above scheme, the moisture content of the molded sample after drying in step (2) is 4-10wt%.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (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. It will cause water loss too quickly and reduce the effective carbonization time. The water content that does not affect gas diffusion and is suitable for carbonization reaction is 4-10%. By adding ettringite to low carbon clinker, ettringite can be gradually carbonized under the conditions of CO2 (reactant) and H2O (medium). The reaction equation is: 3CaO·Al2O3·3CaSO4·32H2O+3CO2→3CaSO4·2H2O+3Ca CO3+Al2O3·xH2O+(26-x)H2O. As the carbonization progresses, water is released, which makes the water content suitable for carbonization last longer during the carbonization process. In addition, ettringite dissolves OH during the carbonization process. - , increase the alkalinity of the reaction system, thereby further improving the carbonization efficiency of the system.

[0018] (2) Inorganic calcium sulfonate is cheaper than organic water retainers, has no thickening side effect, and 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.

[0019] (3) CaSO4·2H2O, CaCO3, and Al2O3·xH2O formed after the carbonization of calcium sulfoxide can be used as strength components to fill the pores of the material to improve the strength, without the thickening side effect of organic water-retaining agents. Among them, aluminum glue (Al2O3·xH2O) has strong bonding properties and can further improve the integrity and strength of the carbonized material. DETAILED DESCRIPTION

[0020] 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.

[0021] The specific implementation method discloses a method for improving the carbonization performance of low-carbon clinker by using ettringite, comprising the following steps:

[0022] (1) mixing low carbon clinker, ettringite and water and pressing into a shape;

[0023] (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.

[0024] Specifically, the mineral composition of low-carbon clinker is one or a mixture of CS, C3S2, C2S, and C3S.

[0025] Specifically, the main mineral of ettringite is 3CaO·Al2O3·3CaSO4·32H2O, and the content is not less than 90wt%.

[0026] Specifically, the amount of ettringite used is 5-25wt% of the low-carbon clinker, and the amount of water used is 15-20wt% of the total amount of the low-carbon clinker and ettringite.

[0027] Specifically, the molded sample is dried under natural conditions, and the moisture content after drying is 4-10wt%.

[0028] In the following specific examples, low carbon clinker and ettringite were obtained for jade mineral composition analysis. The mineral compositions of the low carbon clinker used in the embodiments of the present invention are shown in Table 1, respectively, and ground to R45μm≤20%:

[0029] Table 1 Mineral composition

[0030] 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

[0031] Calcium aluminate is synthesized from 3CaO·Al2O3 and CaSO4:

[0032] Calcium carbonate and aluminum oxide are mixed in a molar ratio of 3:1, and calcined at 1400°C for 1 hour to obtain 3CaO·Al2O3; 3CaO·Al2O3 and dihydrate gypsum are mixed and stirred in a solution in a molar ratio of 1:3, stirred at room temperature, and vacuum dried and stored after stirring for 24 hours; the content of the obtained calcium sulfonate 3CaO·Al2O3·3CaSO4·32H2O is ≥99wt%, and the powder is ground to a fineness of R45μm≤20%.

[0033] Example 1

[0034] 1. Ratio

[0035] 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). The calculated moisture content of this ratio is 17.6 / (100+10+17.6)=13.79%.

[0036] 2. Sample preparation

[0037] 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.

[0038] 3. Pre-drying and carbonization

[0039] 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.

[0040] Example 2

[0041] 1. Ratio

[0042] Weigh 100 parts of low-carbon clinker 2, 20 parts of ettringite, and 19.2 parts of water (16% of the total amount of low-carbon clinker and ettringite). The calculated moisture content of this ratio is 19.2 / (100+20+19.2)=13.79%.

[0043] 2. Sample preparation

[0044] 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.

[0045] 3. Pre-drying and carbonization

[0046] 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.

[0047] Example 3

[0048] 1. Ratio

[0049] Weigh 100 parts of low-carbon clinker 3, 15 parts of ettringite, and 18.4 parts of water (16% of the total amount of low-carbon clinker and ettringite). The calculated moisture content of this ratio is 18.4 / (100+15+18.4)=13.79%.

[0050] 2. Sample preparation

[0051] 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.

[0052] 3. Pre-drying and carbonization

[0053] 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.

[0054] Comparative Example 1

[0055] Compared with Example 1, in step 1, no calcium aluminate 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.

[0056] Comparative Example 2

[0057] Compared with Example 2, in step 1, no calcium aluminate 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.

[0058] Comparative Example 3

[0059] Compared with Example 3, in step 1, no calcium aluminate 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.

[0060] The carbonization conditions and strength after carbonization of the low carbon clinker in each embodiment and comparative example are shown in Table 2.

[0061] Table 2 Carbonization conditions and strength of low carbon clinker after carbonization

[0062]

[0063]

[0064] It can be seen from Table 2 that by adding ettringite, the carbonization strength and carbon fixation rate of low-carbon clinker are significantly improved.

[0065] 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 by using ettringite, characterized in that The following steps are involved: (1) mixing low carbon clinker, ettringite and water, and pressing them into a shape; the mineral composition of the low carbon clinker is one or a mixture of CS, C3S2, C2S and C3S; the amount of ettringite is 5-25wt% of the low carbon clinker, and the amount of water is 15-20wt% of the total amount of the low carbon clinker and ettringite; (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.

2. The method for improving the carbonization performance of low-carbon clinker by using ettringite as claimed in claim 1, characterized in that The main mineral of the ettringite in step (1) is 3CaO·Al2O3·3CaSO4·32H2O, and its content is not less than 90wt%.

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

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

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