A method for curing cement bricks with exhaust steam

Abstract

This invention discloses a method for curing cement bricks with exhaust steam, comprising the following steps: 1) passing exhaust steam through a gas-liquid filter; 2) compressing the exhaust steam after passing through the gas-liquid filter and spraying it into a high-temperature carbon-containing gas to obtain a mixed gas; 3) compressing the mixed gas to obtain high-temperature carbon-containing steam; 4) using the high-temperature carbon-containing steam to cure the cement brick blanks. This invention, by adjusting the curing atmosphere of cement bricks, can achieve high-value-added resource utilization of exhaust steam and industrial waste gases or waste heat such as carbon dioxide tail gas, and can effectively improve the mechanical properties, shrinkage resistance, and water resistance of the resulting cement brick products; moreover, the curing method involved is relatively simple, easy to operate, and environmentally friendly, making it suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and specifically relates to a method for curing cement bricks with exhaust steam. Background Technology

[0002] Currently, the most common curing methods for cement bricks are natural curing and autoclaving. Natural curing consumes less energy but requires a longer curing time and a larger storage area. Autoclaving, on the other hand, has a shorter curing time and produces cement bricks with higher strength, but it consumes a large amount of high-temperature, high-pressure steam, resulting in higher energy consumption. Therefore, reducing energy consumption during the curing process while ensuring high turnover efficiency of cement bricks has become an important direction for the industry's development.

[0003] During the clinker calcination process in cement plants, a large amount of high-temperature waste gas (350–450°C) is generated from the kiln tail. Currently, this waste gas is mainly used for power generation to reduce energy consumption. However, even after the high-temperature waste gas from the kiln tail is heated by the boiler, the discharged gas still reaches a temperature of 90–150°C, resulting in low thermal efficiency. Furthermore, the high-temperature, high-pressure steam generated in the boiler becomes exhaust steam after being used for power generation, resulting in a significant decrease in temperature and pressure. However, this low-temperature, low-pressure steam still possesses a high enthalpy (the enthalpy of 45°C steam is 2636 kJ / kg in the literature). Currently, there are two main methods for treating exhaust steam: direct discharge or condensation and recycling. However, neither method fully utilizes the latent heat of the exhaust steam. Summary of the Invention

[0004] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a method for curing cement bricks using waste heat from cement plant power generation. By adjusting the curing atmosphere of the cement bricks, high-value-added resource utilization of waste steam and industrial waste gases or waste heat containing carbon dioxide can be achieved, and the mechanical properties, shrinkage resistance, and water resistance of the resulting cement brick products can be effectively improved. Furthermore, the curing method involved is relatively simple and easy to operate, making it suitable for widespread application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for curing cement bricks with exhaust steam includes the following steps:

[0007] 1) Exhaust steam passes through a gas-liquid filter to remove large condensate droplets;

[0008] 2) Compress the exhaust gas after passing through the gas-liquid filter and inject it into the high-temperature carbon-containing gas to obtain a mixed gas;

[0009] 3) The mixed gas is compressed to 0.3–0.8 MPa to obtain high-temperature carbon-containing steam;

[0010] 4) High-temperature carbon-containing steam is used to cure cement brick blanks.

[0011] In the above scheme, the temperature of the exhaust steam is 40-80℃ and the pressure is 0.05-0.1MPa.

[0012] In the above scheme, the pore size of the gas-liquid filter screen is 500-1000 mesh.

[0013] In the above scheme, the pressure of the compressed exhaust steam is 0.12 to 0.15 MPa.

[0014] In the above scheme, the temperature of the high-temperature carbon-containing gas is 300-400℃, the pressure is 0.05-0.1MPa, and the carbon dioxide concentration is 15-30%.

[0015] Furthermore, the high-temperature carbon-containing gas can be selected from high-temperature carbon-containing waste gas, specifically cement kiln tail gas, metal smelting plant waste gas, or thermal power plant waste gas, etc.

[0016] In the above scheme, the velocity at which the compressed exhaust gas is injected into the high-temperature carbon-containing gas is 15-30 m / s.

[0017] In the above scheme, the mass ratio of high-temperature carbon-containing gas to compressed exhaust gas in the mixed gas is 1:1.2 to 1.8.

[0018] In the above scheme, the high-temperature carbon-containing steam has a temperature of 150-180℃, a pressure of 0.3-0.8MPa, a carbon dioxide concentration of 8-12 vol%, and a relative humidity of 75-90%.

[0019] In the above scheme, the steps of curing brick blanks with high temperature carbon-containing steam include: first, evacuating the vacuum to a degree of -0.04 to -0.08 MPa; then, introducing high temperature carbon-containing steam to adjust the temperature inside the autoclave to the target temperature of 150 to 180°C and the target pressure of 0.3 to 0.8 MPa; performing constant temperature treatment; and then cooling the temperature to 80 to 100°C before opening the autoclave to end the curing process.

[0020] In the above scheme, the constant temperature treatment time is 4 to 6 hours.

[0021] Furthermore, during the process of introducing high-temperature carbon-containing steam, the heating rate inside the reactor is controlled (by controlling the flow rate of high-temperature carbon-containing steam and auxiliary heating, etc.) to be 1.0 to 1.5 °C / min.

[0022] Furthermore, the cooling rate of the cooling step is 2–3 °C / min.

[0023] In the above scheme, the raw materials used for the cement brick blank and their weight proportions include: 10-15 parts of ordinary Portland cement, 20-50 parts of aggregate, 30-80 parts of stone powder, and 8-12 parts of water; after the raw materials are measured, mixed, and sieved, they are pressed into brick blanks.

[0024] In the above scheme, the ordinary silicate cement is P·O42.5 grade or higher.

[0025] In the above scheme, the aggregate includes, but is not limited to, waste concrete, mining aggregate waste, slag, etc., with a particle size of 1-15mm and a soundness index of 10-30%.

[0026] In the above scheme, the stone powder has a particle size of 0.01 to 1 mm and a quartz content of less than 20 wt%.

[0027] In the above scheme, the stirring time is 2 to 5 minutes and the stirring rate is 60 to 120 r / min.

[0028] In the above scheme, the sieving process uses a screen with a mesh size of 15-20mm, and the undersize material is pressed into shape.

[0029] In the above scheme, the compression molding pressure is 5-15 MPa.

[0030] The cement bricks prepared according to the above scheme have high strength (strength grade up to MU20) and low shrinkage (drying shrinkage 0.02% to 0.03%).

[0031] The performance optimization mechanism for cement brick curing described in this invention includes:

[0032] 1) After filtration, the exhaust steam removes larger condensate droplets. It is then mixed with the high-temperature cement kiln exhaust gas using a high-speed injection method. Smaller condensate droplets are further dispersed and rapidly exchange heat to form high-temperature steam, improving the efficiency of high-temperature carbon-containing steam preparation and effectively controlling its relative humidity. During curing, the initial temperature of the brick blanks is low. Using saturated steam for curing easily leads to the formation of a large amount of condensate on the brick blank surface, inhibiting the diffusion of carbon dioxide into the brick blank. However, when using high-temperature carbon-containing steam for curing, the steam is not saturated, significantly reducing condensate on the brick blank surface and ensuring simultaneous carbonization and hydration. Furthermore, a carbonization product layer forms on the brick blank surface in the early stages of curing, suppressing cracking caused by uneven heating and temperature stress during curing.

[0033] 2) During the curing process of the brick blank, the cement inside the brick blank reacts rapidly under high temperature conditions to generate reaction products such as hydrated calcium silicate and calcium hydroxide. Among them, hydrated calcium silicate can provide high cementitious strength, while calcium hydroxide has little contribution to strength and has strong water absorption. Since the alkalinity and solubility of calcium hydroxide are higher than those of hydrated calcium silicate, under the high temperature, high pressure, and high humidity carbon-containing steam curing conditions provided by this invention, the hydrated product calcium hydroxide preferentially reacts with carbon dioxide in the high temperature carbon-containing steam to generate calcite, effectively retaining the high-performance hydrated calcium silicate (significantly avoiding hydrated calcium silicate from participating in the carbonization reaction to form silica gel, etc.); and the resulting calcite has high strength, low shrinkage, and good water resistance, further increasing the strength, shrinkage performance, and water resistance of the brick blank.

[0034] 3) High temperature environment can significantly increase the diffusion rate of carbon dioxide, and the moisture content of the brick blank gradually decreases during the curing process, providing a rapid diffusion channel for carbon dioxide; it promotes the carbonization reaction to proceed more evenly inside and outside the brick blank, avoiding the performance degradation caused by uneven carbonization inside and outside the brick blank.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] 1) The exhaust steam has a high enthalpy, and there is basically no loss in the process of mixing with the kiln tail exhaust gas to prepare high-temperature carbon-containing steam. The thermal efficiency is much higher than that of using kiln tail exhaust gas to prepare steam. After treatment, the exhaust steam is mixed with the kiln tail exhaust gas by high-speed injection, which improves the heat exchange rate between the two gases and can effectively control the relative humidity of the mixed gas, effectively ensuring the carbon dioxide diffusion rate and coordinating the carbonization and hydration rates.

[0037] 2) This invention uses high-temperature, high-pressure, and high-humidity carbon-containing steam to cure cement brick blanks, allowing carbonization and hydration reactions to occur simultaneously with high reaction efficiency. Furthermore, by utilizing the characteristics of rapid carbon dioxide diffusion but low solubility under the above curing conditions, the carbonization reaction is promoted, primarily carbonizing the cement hydration product calcium hydroxide to improve performance, while effectively avoiding the decomposition of hydrated calcium silicate by carbonization, which leads to performance degradation. The resulting cement brick products possess both good mechanical properties and water resistance.

[0038] 3) The preparation method involved in this invention is relatively simple and can realize the high-value-added resource utilization of various industrial waste gases, with significant economic and environmental benefits, and is suitable for promotion and application. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to embodiments, so as to facilitate a clearer understanding of the present invention, but these embodiments do not constitute a limitation on the present invention.

[0040] In the following examples and comparative examples, the cement used to prepare the cement brick blanks was P·O42.5 ordinary Portland cement, and the aggregate used was mine aggregate waste with a particle size of 1-5 mm and a soundness index of 12%. The stone powder had a particle size of 0.01-0.5 mm, a limestone content of 78 wt%, a clay mineral content of 13 wt%, and a quartz content of 8 wt%.

[0041] The method for preparing the cement brick blank includes the following steps: 12 parts (by weight, the same below) of ordinary silicate cement, 35 parts of aggregate, 53 parts of stone powder and 10 parts of water are stirred at a speed of 90 r / min for 5 min and then passed through a 15 mm sieve and pressed into brick blanks under a pressure of 12 MPa.

[0042] In the following embodiments, the cement kiln tail gas is taken from Huaxin Cement Wuxue Plant, with a temperature of 375°C, a pressure of 0.1 MPa, and a carbon dioxide concentration of 22%. The waste heat power generation exhaust steam from the cement plant is taken from Huaxin Cement Wuxue Plant, with a temperature of 52°C and a pressure of 0.08 MPa.

[0043] Example 1

[0044] A method for curing cement bricks with exhaust steam includes the following preparation steps:

[0045] 1) Pass the exhaust steam through an 800-mesh gas-liquid filter to remove larger condensate droplets;

[0046] 2) Compress the exhaust gas after passing through the gas-liquid filter to 0.15 MPa, and inject it into the cement kiln tail gas at a speed of 25 m / s through a gas injector to obtain a mixed gas, wherein the mass ratio of cement kiln tail gas to compressed exhaust gas is 1:1.2.

[0047] 3) The mixed gas is compressed to 0.8 MPa to obtain high-temperature carbon-containing steam; its temperature is 180℃, the carbon dioxide concentration is 9 vol%, and the relative humidity is 78%.

[0048] 4) When curing brick blanks with high-temperature carbon-containing steam, first perform vacuuming to a vacuum degree of -0.06MPa; then introduce high-temperature carbon-containing steam and control the temperature inside the autoclave to rise to 160℃ at a rate of 1.2℃ / min, with a pressure of 0.6MPa; enter the constant temperature stage and control the constant temperature time to 6h; after the constant temperature is completed, lower the temperature to 90℃ at a rate of 2.5℃ / min and then open the autoclave to end the curing process.

[0049] Example 2

[0050] A method for curing cement bricks with exhaust steam is similar to that in Example 1, except that the temperature during the constant temperature stage is 180°C and the pressure is 0.8 MPa.

[0051] Example 3

[0052] A method for curing cement bricks with exhaust steam is similar to that in Example 1, except that the mass ratio of cement kiln tail gas to exhaust gas is 1:1.5, the mixed gas is compressed to 0.8 MPa to obtain high-temperature carbon-containing steam; the temperature is 165°C, the carbon dioxide concentration is 8 vol%, and the relative humidity is 86%.

[0053] Comparative Example 1

[0054] A method for curing cement bricks is similar to that in Example 1, except that saturated steam (temperature 195℃, pressure 1.3MPa) is used to cure the brick blanks, and the brick blanks are cured at a constant temperature of 180℃ and pressure of 1.1MPa for 6 hours.

[0055] Comparative Example 2

[0056] A method for curing cement bricks is similar to that in Example 1, except that the mass ratio of cement kiln tail gas to exhaust gas is 1:2, the mixed gas is compressed to 0.8 MPa, and high-temperature carbon-containing steam with a temperature of 152°C, a carbon dioxide concentration of 6 vol%, and a relative humidity of 92% is obtained; the brick blanks are cured at a constant temperature of 152°C for 6 hours.

[0057] Comparative Example 3

[0058] A method for curing cement bricks is similar to that in Example 1, except that the mass ratio of cement kiln tail gas to exhaust gas is 1:0.6, the mixed gas is compressed to 0.8 MPa, and high-temperature carbon-containing steam with a temperature of 212°C, a carbon dioxide concentration of 14 vol%, and a relative humidity of 59% is obtained.

[0059] Comparative Example 4

[0060] A method for curing cement bricks is similar to that in Example 1, except that the exhaust gas used is not filtered through a gas-liquid filter and is directly used to prepare a mixed gas. The mixed gas is compressed to 0.8 MPa to obtain high-temperature carbon-containing steam. The temperature is 171°C, the carbon dioxide concentration is 7 vol%, and the relative humidity is 93%.

[0061] Comparative Example 5

[0062] A method for curing cement bricks is similar to that of Comparative Example 1, except that after steam curing, the bricks are then carbonized for 3 hours (carbon dioxide concentration 20%, temperature 195℃, pressure 0.3MPa, relative humidity 90%).

[0063] The cement bricks obtained in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests according to standard GB / T 2542-2012, and the results are shown in Table 1.

[0064] Table 1. Test Results of Cement Brick Performance

[0065]

[0066] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for curing cement bricks with exhaust steam, characterized in that, Includes the following steps: 1) Exhaust steam passing through a gas-liquid filter screen; 2) Compress the exhaust gas after passing through the gas-liquid filter and inject it into the high-temperature carbon-containing gas to obtain a mixed gas; 3) The mixed gas is compressed to obtain high-temperature carbon-containing steam; 4) High-temperature carbon-containing steam is used to cure cement brick blanks; The high-temperature carbon-containing steam has a temperature of 150~180℃, a pressure of 0.3~0.8MPa, a carbon dioxide concentration of 8~12vol%, and a relative humidity of 75~90%. The steps for high-temperature carbon-containing steam curing of brick blanks include: first, vacuuming is performed with a vacuum degree of -0.04 to -0.08 MPa; then, high-temperature carbon-containing steam is introduced, and the temperature inside the autoclave is adjusted to reach the target temperature of 150 to 180℃ and the target pressure of 0.3 to 0.8 MPa; constant temperature treatment is performed, and then the temperature is lowered to 80 to 100℃ before the autoclave is opened to end the curing process.

2. The method according to claim 1, characterized in that, The temperature of the exhaust steam is 40~80℃ and the pressure is 0.05~0.1MPa.

3. The method according to claim 1, characterized in that, The pore size of the gas-liquid filter screen is 500~1000 mesh.

4. The method according to claim 1, characterized in that, The pressure of the compressed exhaust steam is 0.12~0.15 MPa.

5. The method according to claim 1, characterized in that, The high-temperature carbon-containing gas has a temperature of 300~400℃, a pressure of 0.05~0.1MPa, and a carbon dioxide concentration of 15~30%.

6. The method according to claim 1, characterized in that, The mass ratio of high-temperature carbonaceous gas to compressed exhaust gas in the mixed gas is 1:1.2~1.

8.

7. The method according to claim 1, characterized in that, The raw materials used in the cement brick blank and their weight proportions include: 10-15 parts of ordinary Portland cement, 20-50 parts of aggregate, 30-80 parts of stone powder, and 8-12 parts of water.

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