Silica fume enhanced unfired sulfur-fixing ash ceramsite and preparation method thereof

Abstract

The invention discloses silica fume reinforced unfired solid sulfur ash ceramsite and a preparation method thereof. The silica fume enhanced unfired fluidized bed combustion ash ceramsite is prepared from the following raw materials in percentage by mass: 55 to 65 percent of fluidized bed combustion ash, 2 to 8 percent of lime, 2 to 5 percent of desulfurized gypsum, 5 to 10 percent of silica fume, 16 to 25 percent of cement clinker and 8 to 12 percent of water. The preparation method of the silica fume enhanced unfired solid sulfur ash ceramsite comprises the following steps: pretreating the raw materials, metering the raw materials, mixing and homogenizing, granulating and balling with a balling disc, standing, curing with steam and screening. The cylinder compressive strength of the prepared silica fume reinforced unfired solid sulfur ash ceramsite can reach 11.7-16.1 MPa, and the 1h water absorption rate is 3%-8%. According to the silica fume enhanced unfired solid sulfur ash ceramsite, the silica fume and the cement clinker are used for synergistically improving the early strength, the problem that the ceramsite is broken due to insufficient cylinder compressive strength caused by unstable activity of the solid sulfur ash is solved, meanwhile, the reaction process is accelerated by adopting a steam curing method, and the production period is shortened. The ceramsite can realize large-scale resource utilization of the fluidized bed combustion ash, the production period is short, and the prepared ceramsite has the characteristics of light weight, high strength and low water absorption and has good economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of building material preparation. It relates to a silica fume-reinforced non-fired desulfurized ash slag ceramsite and its preparation method. Background Art

[0002] Desulfurized ash slag is a by-product of circulating fluidized bed coal combustion technology. In recent years, circulating fluidized bed coal combustion technology has been widely applied and emphasized in thermal power plants around the world, which has also led to a large amount of desulfurized ash slag emissions. The global annual production exceeds 280 million tons, and about 120 million tons in China. The accumulation of desulfurized ash slag not only occupies a large amount of land, but also causes pollution of air, soil and groundwater, resulting in serious environmental pollution. Therefore, the resource utilization of desulfurized ash slag has high economic, environmental and social benefits.

[0003] Ceramsite preparation technology is a widely used method for disposing of solid waste. The produced ceramsite can be used as concrete aggregate, greening material, industrial adsorption material, etc., and has a wide range of application scenarios. Desulfurized ash slag contains a certain amount of active SiO2 and Al2O3, and has certain pozzolanic activity and potential cementitiousness. Using desulfurized ash slag as the siliceous material for preparing ceramsite and supplementing calcareous materials by adding cement and lime has sufficient theoretical basis. However, since desulfurized ash slag is different from common fly ash, the content of its active SiO2 and Al2O3 fluctuates greatly, resulting in unstable pozzolanic activity of desulfurized ash slag and low activity of many batches of desulfurized ash slag. Active SiO2 is the key reaction phase for forming calcium silicate hydrate in steam curing, and calcium silicate hydrate is the source of the strength of cement-based materials. When preparing ceramsite by steam curing, it is difficult to ensure that the ceramsite obtains sufficient strength when using a large proportion of desulfurized ash slag, which may lead to the breakage of ceramsite and insufficient cylinder compressive strength; at the same time, the content of f-CaO in desulfurized ash slag is relatively high, which is likely to have an adverse effect on the volume stability of ceramsite, especially it is extremely easy to cause expansion and cracking under the process technical conditions of using high temperature to accelerate the reaction.

[0004] Based on the above properties, there is an urgent need for a new method to solve the problems that the content of SiO2 and Al2O3 in desulfurized ash slag as the main raw material is unstable and the activity of many batches of desulfurized ash slag is low, which may lead to easy breakage of ceramsite. At the same time, it is also necessary to solve the volume stability problem of desulfurized ash slag under high temperature conditions to shorten the production cycle, reduce the production cost of ceramsite, and also solve the problem of resource utilization of desulfurized ash slag. Summary of the Invention

[0005] The purpose of the present invention is to provide a silica fume-reinforced non-fired desulfurized ash slag ceramsite and a preparation method thereof. By adding silica fume with small particle size and high active SiO2 content as supplementary siliceous material, the strength of the ceramsite is improved, and the problems of cracking and insufficient cylinder compressive strength caused by insufficient active SiO2 and poor volume stability of desulfurized ash slag are solved. At the same time, the production cycle is shortened through the steam curing process. The technology of preparing high-strength non-fired ceramsite with desulfurized ash slag as the main siliceous material in a short production cycle is realized.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A silica fume-reinforced non-fired desulfurized ash slag ceramsite and a preparation method thereof, characterized in that the raw material mass percentage composition of the silica fume-reinforced non-fired desulfurized ash slag ceramsite is: 55% - 65% desulfurized ash slag, 2% - 8% lime, 2% - 5% desulfurized gypsum, 5% - 10% silica fume, 16% - 25% cement clinker, 8% - 12% water.

[0007] According to the above scheme, the specific surface area of the silica fume is greater than 2.2×10 4 / m 2 ·kg -1 , the average particle size is less than 0.15μm, and the SiO2 content is greater than 94%.

[0008] According to the above scheme, the chemical composition of the desulfurized ash slag is: CaO 5.0% - 10%, SiO2 45 - 60%, Fe2O3 3% - 6%, Al2O3 21.0% - 25%, MgO 1.4% - 1.7%, SO3 0.5% - 2.7%, f-CaO < 5.5%, and the loss on ignition is 0.7% - 3.0%.

[0009] According to the above scheme, the desulfurized gypsum is used as an additive to control the setting time, and the CaSO4 content > 85%.

[0010] According to the above scheme, the cement clinker is a general cement clinker, and the 28-day compressive strength is not less than 52.5MPa.

[0011] According to the above scheme, the CaO content in the lime > 95.0%.

[0012] The preparation method of a silica fume-reinforced non-fired desulfurized ash slag ceramsite according to the present invention is characterized by including the following steps:

[0013] A. Pretreatment of raw materials

[0014] The desulfurized ash slag, lime, desulfurized gypsum and cement clinker are ground by a ball mill, and the grinding diameter is controlled ≤ 150μm.

[0015] B. Homogenization of raw material mixture

[0016] Weigh and mix the pre-treated silica fume, sulfur-fixing ash residue, lime, desulfurized gypsum, and cement clinker according to the ratio to obtain a mixed powder.

[0017] C. Pelletizing

[0018] Feed the mixed powder into a disk pelletizer (YZ-500) and continuously roll it while gradually spraying water metered according to the ratio. The mixed powder forms micro-nuclei under the cohesion of the sprayed water. During the rolling process, the particle size gradually increases. After reaching the required particle size, it is sieved to obtain green balls, which are then sent to the curing system. The green balls that do not meet the particle size requirements are crushed and reused.

[0019] D. Curing of green balls

[0020] It is divided into two stages: static curing and steam curing.

[0021] Static curing stage: The green balls are statically cured in a static curing chamber (temperature 25°C ± 2°C, relative humidity above 95%) for 24 hours. After having a certain strength, they are transferred to a steam curing box.

[0022] Steam curing stage: During steam curing, the heating and cooling rates should not be greater than 20°C - 30°C / h. First, place the statically cured green balls in the steam curing box at room temperature, and gradually increase the temperature to 60°C. Under the condition of relative humidity above 95%, steam cure for 3 - 6 hours. Then gradually increase the temperature to 100°C, relative humidity above 95%, and continue to cure for 12 - 18 hours. Finally, take them out after cooling to room temperature to obtain silica fume-reinforced non-fired sulfur-fixing ash residue ceramsite.

[0023] E. Screening and optimization

[0024] Further screen and classify the cured finished ceramsite, and remove a small amount of damaged ceramsite to obtain finished products of silica fume-reinforced non-fired sulfur-fixing ash residue ceramsite with different particle sizes.

[0025] The principle of the present invention is:

[0026] The fixed sulfur ash residue contains a large amount of active SiO2 and Al2O3, and has certain pozzolanic activity and potential cementitious properties. It can be used as the main siliceous material for preparing ceramsite, while cement clinker and lime, as the main calcareous materials, can provide Ca(OH)2 required for the secondary hydration reaction. The contents of active SiO2 and Al2O3 in the fixed sulfur ash residue fluctuate greatly, resulting in unstable pozzolanic activity of the fixed sulfur ash residue and relatively low activity in many batches. At the same time, the f-CaO contained in the fixed sulfur ash residue is likely to cause volume stability problems. In the present invention, silica fume with an active SiO2 content exceeding 94% is used as a supplementary siliceous material to enhance the cylinder compressive strength of ceramsite. Silica fume has good pozzolanic activity and an extremely small particle size. Under steam curing conditions, it can rapidly react with the cement hydration product Ca(OH)2 to increase the content of calcium silicate hydrate and improve the microscopic pore structure, thereby increasing the cylinder compressive strength of the non-fired fixed sulfur ash residue ceramsite, and solving the breakage problem caused by the large fluctuation of the active SiO2 content in the fixed sulfur ash residue and unstable pozzolanic activity. On the basis of improving this problem, an optimized steam curing process is adopted to accelerate the reaction process, shortening the production cycle on the premise of avoiding the volume stability problem caused by f-CaO.

[0027] A silica fume-reinforced non-fired fixed sulfur ash residue ceramsite and its preparation method provided by the present invention have the following advantages compared with the existing ceramsite products and their preparation methods:

[0028] (1) The silica fume-reinforced non-fired fixed sulfur ash residue ceramsite prepared by the present invention has a particle size of 1 - 16 mm, a bulk density of 1000 - 1150 kg / m 3 3, an apparent density of 1450 - 1720 kg / m3, a cylinder compressive strength of 11.7 - 16.1 MPa, a 1-hour water absorption rate of 3% - 8%, and a softening coefficient ≥ 0.93. All performance parameters are superior to the existing non-fired fixed sulfur ash residue ceramsite and meet the requirements of the national standard specification GB / T17431.1 - 2010 "Lightweight Aggregates and Their Test Methods Part 1: Lightweight Aggregates".

[0029] (3) The present invention uses a steam curing process to prepare non-fired fixed sulfur ash residue ceramsite. Compared with the traditional sintering method and natural curing method, the process has lower energy consumption and a shorter cycle (within 72 h), and has good economic benefits and practical potential. Specific Embodiments

[0030] In order to better understand the technical solution of the present invention, the technical solution provided by the present invention will be described in detail below in combination with embodiments.

[0031] In the following embodiments, the chemical composition of the fixed sulfur ash residue is: CaO 9.6%, SiO2 52.4%, Fe2O3 5.8%, Al2O3 22.0%, MgO 1.7%, SO3 2.7%, loss on ignition 3.0%, f-CaO 5.5%.

[0032] The chemical composition of the lime is as follows: CaO 96.0%, SiO2 0.2%, Fe2O3 0.5%, Al2O3 0.5%, MgO 1.5%, loss on ignition 1.1%.

[0033] The CaSO4 content of the desulfurized gypsum is 85%.

[0034] The specific surface area of the silica fume is 2.2×10 4 / m 2 ·kg -1 , average particle size 0.15 μm, SiO2 content 94%.

[0035] The chemical composition of the cement clinker is as follows: CaO 62.1%, SiO2 18.5%, Fe2O3 4.1%, Al2O3 4.6%, MgO 3.5%, loss on ignition 1.2%.

[0036] Example 1

[0037] The mass percentages of the raw materials for a silica fume-reinforced non-fired sulfur-fixed ash slag ceramsite are shown in Table 1 as follows:

[0038] Table 1 Raw material ratio of Example 1

[0039]

[0040] The preparation process includes the following steps:

[0041] A. Weigh the raw materials according to the ratio in Table 1, and feed the metered sulfur-fixed ash slag, lime, desulfurized gypsum and cement clinker into a ball mill for grinding, controlling the grinding diameter ≤ 150 μm.

[0042] B. Mix the silica fume with the ground sulfur-fixed ash slag, lime, desulfurized gypsum and cement clinker according to the ratio to obtain a mixed powder.

[0043] C. Feed the mixed powder into a disk granulator (YZ-500) and continuously roll it while gradually spraying the metered water according to the ratio. The mixed powder forms micro ball nuclei under the cohesion of the sprayed water, and the particle size gradually increases during the rolling process to obtain green balls.

[0044] D. Place the green balls in a static curing room (temperature 25 ± 2 °C, relative humidity above 95%) for 24 hours. After having a certain strength, transfer them to a steam curing box. First, put the cured green balls into the steam curing box at room temperature, gradually increase the temperature to 60 °C within 2 h, relative humidity above 95%, and steam cure for 4 h. Then gradually increase the temperature to 100 °C within 2 h, relative humidity above 95%, and continue to cure for 16 h. Finally, slowly cool to room temperature at a rate not higher than 20 °C / h and then take out.

[0045] E. Sieving the ceramsite with a 10-20 mm square-hole sieve to obtain 10-20 mm ceramsite enhanced with silica fume and free of firing and sulfur-fixing ash residue.

[0046] According to the national standard: GB / T 17431.2-2010 "Lightweight Aggregates and Their Test Methods Part 2: Test Methods for Lightweight Aggregates", various properties of the ceramsite enhanced with silica fume and free of firing and sulfur-fixing ash residue prepared in Example 1 were tested, and the results are shown in Table 2.

[0047] Table 2 Performance Indexes of the Ceramsite Prepared in Example 1

[0048]

[0049] Example 2

[0050] The mass percentages of the raw materials of a ceramsite enhanced with silica fume and free of firing and sulfur-fixing ash residue are shown in Table 3:

[0051] Table 3 Raw Material Ratio of Example 2

[0052]

[0053] The preparation process includes the following steps:

[0054] A. Weigh the raw materials according to the ratio in Table 1, and feed the measured sulfur-fixing ash residue, lime, desulfurized gypsum and cement clinker into a ball mill for grinding, controlling the grinding diameter ≤ 150 μm.

[0055] B. Mix the silica fume and the ground sulfur-fixing ash residue, lime, desulfurized gypsum and cement clinker evenly according to the ratio to obtain a mixed powder.

[0056] C. Feed the mixed powder into a disk granulator (YZ-500) and continuously roll it while gradually spraying the measured water according to the ratio. The mixed powder forms micro-nuclei under the cohesion of the sprayed water, and the particle size gradually increases during the rolling process to obtain green balls.

[0057] D. Place the green balls in a static curing room (temperature 25 ± 2 °C, relative humidity above 95%) for 24 hours. After having a certain strength, transfer them to a steam curing box. First, put the cured green balls into the steam curing box at room temperature, and gradually increase the temperature to 60 °C within 3 hours, with a relative humidity above 95%, and steam cure for 6 hours. Then gradually increase the temperature to 100 °C within 3 hours, with a relative humidity above 95%, and continue to cure for 18 hours. Finally, slowly cool to room temperature at a rate not higher than 20 °C / h and then take out.

[0058] E. Sieving the ceramsite with a 10-15 mm square-hole sieve to obtain 10-15 mm ceramsite enhanced with silica fume and free of firing and sulfur-fixing ash residue.

[0059] According to the national standard: GB / T 17431.2-2010 "Lightweight Aggregates and Their Test Methods - Part 2: Test Methods for Lightweight Aggregates", various properties of the ceramsite prepared in Example 2 were tested, and the results are shown in Table 4.

[0060] Table 4 Performance Indexes of the Ceramsite Prepared in Example 2

[0061]

[0062] Example 3

[0063] The mass percentages of raw materials of a silica fume-reinforced non-fired desulfurized ash slag ceramsite are shown in Table 5:

[0064] Table 5 Raw Material Mix Ratio of Example 3

[0065]

[0066] The preparation process includes the following steps:

[0067] A. Weigh the raw materials according to the mix ratio in Table 1, and feed the metered desulfurized ash slag, lime, desulfurized gypsum, and cement clinker into a ball mill for grinding, controlling the grinding diameter ≤ 150 μm.

[0068] B. Mix the silica fume and the ground desulfurized ash slag, lime, desulfurized gypsum, and cement clinker evenly according to the mix ratio to obtain a mixed powder.

[0069] C. Feed the mixed powder into a disk granulator (YZ-500) and continuously roll it while gradually spraying the metered water according to the mix ratio. The mixed powder forms micro ball nuclei under the cohesion of the sprayed water, and the particle size gradually increases during the rolling process to obtain green balls.

[0070] D. Place the green balls in a static curing chamber (temperature 25 ± 2 °C, relative humidity above 95%) for 24 hours. After having a certain strength, transfer them to a steam curing chamber. First, put the cured green balls into the steam curing chamber at room temperature, and gradually increase the temperature to 60 °C within 2 hours, with a relative humidity above 95%, and steam cure for 5 hours. Then, gradually increase the temperature to 100 °C within 2 hours, with a relative humidity above 95%, and continue to cure for 15 hours. Finally, slowly cool to room temperature at a rate not higher than 20 °C / h and then take out.

[0071] E. Screen the ceramsite using a 10 - 15 mm square-hole sieve to obtain 10 - 15 mm silica fume-reinforced non-fired desulfurized ash slag ceramsite.

[0072] According to the national standard: GB / T 17431.2-2010 "Lightweight Aggregates and Their Test Methods - Part 2: Test Methods for Lightweight Aggregates", various properties of the ceramsite prepared in Example 3 were tested, and the results are shown in Table 6.

[0073] Performance Indexes of the Ceramsite Prepared in Example 3 in Table 6

[0074]

[0075] The above examples show that the process of preparing the non-fired sulfur-fixed ash ceramsite by using the steam curing process with sulfur-fixed ash slag as the main raw material and adding silica fume to increase the strength is feasible. The prepared silica fume-reinforced non-fired sulfur-fixed ash ceramsite meets the requirements of GB / T 17431.1-2010 "Lightweight Aggregates and Their Test Methods - Part 1: Lightweight Aggregates".

[0076] The ratios and process parameters (time, temperature, etc.) involved in the present invention are not limited to the above examples and can all achieve the present invention within the value range.

Claims

1. A non-fired solid sulfur-fixing ash ceramsite reinforced with silica fume, characterized in that, The content of each component is as follows: 55% - 65% sulfur-fixed ash residue, 2% - 8% lime, 2% - 5% desulfurized gypsum, 5% - 10% silica fume, 16% - 25% cement clinker, and 8% - 12% water.

2. The unburned sulfur-fixed ash ceramsite reinforced with silica fume according to claim 1, characterized in that The specific surface area of the silica fume is greater than 2.2×10 4 / m 2 ·kg -1 , the average particle size is less than 0.15 μm, and the SiO2 content is greater than 94%.

3. A kind of fly ash-based sulfur-fixing slag ceramsite reinforced with silica fume according to claim 1, characterized in that, The chemical composition of the sulfur-fixed ash residue is: CaO 5.0% - 10%, SiO₂ 45 - 60%, Fe₂O₃ 3% - 6%, Al₂O₃ 21.0% - 25%, MgO 1.4% - 1.7%, SO₃ 0.5% - 2.7%, f-CaO < 5.5%, and loss on ignition 0.7% - 3.0%.

4. A kind of silica fume reinforced non-fired solid sulfur ash ceramsite according to claim 1, characterized in that The desulfurized gypsum is used as an additive to control the setting time, and the CaSO₄ content > 85%.

5. A kind of silica fume enhanced non-fired solid sulfur ash ceramsite according to claim 1, characterized in that, The cement clinker is a general-purpose cement clinker, and its 28-day compressive strength is not less than 52.5 MPa.

6. A kind of silica fume enhanced non-fired solid sulfur ash slag ceramsite according to claim 1, characterized in that, The CaO content in the lime > 95.0%.

7. The preparation method of the silica fume reinforced non-fired desulfurized ash ceramsite according to any one of claims 1 to 6, characterized in that It includes the following steps: A. Pretreatment of raw materials Use a ball mill to grind the sulfur-fixed ash residue, lime, desulfurized gypsum, and cement clinker, and control the grinding diameter ≤ 150 μm; B. Mixing and homogenization of raw materials Weigh and mix the pretreated silica fume, sulfur-fixed ash residue, lime, desulfurized gypsum, and cement clinker according to the ratio to obtain a mixed powder; C. Pelletizing Feed the mixed powder into a disk pelletizer (YZ-500) to continuously roll and gradually spray the water metered according to the ratio. The mixed powder forms micro-nuclei under the cohesion of the sprayed water. During the rolling process, the particle size gradually increases. After reaching the required particle size, it is sieved to obtain green pellets, which are then sent to the curing system. The green pellets that do not meet the particle size requirements are crushed and reused; D. Curing of green pellets It is divided into two stages: static curing and steam curing; Static curing stage: The green pellets are cured statically in a curing chamber (temperature 25°C ± 2°C, relative humidity above 95%) for 24 hours. After having a certain strength, they are transferred to a steam curing box. Steam curing stage: During steam curing, the heating and cooling rates should not be greater than 20°C - 30°C / h. First, place the statically cured green pellets in the steam curing box at room temperature, and gradually increase the temperature to 60°C. Under the condition of relative humidity above 95%, steam cure for 3 - 6 h. Then gradually increase the temperature to 100°C, relative humidity above 95%, and continue to cure for 12 - 18 h. Finally, take them out after cooling to room temperature to obtain silica fume-reinforced non-fired sulfur-fixed ash residue ceramsite; E. Screening and optimization Further screen and classify the cured finished ceramsite, and remove a small amount of damaged ceramsite to obtain finished products of silica fume-reinforced non-fired sulfur-fixed ash residue ceramsite with different particle sizes.

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