Ultralow-density high-strength ceramsite proppant and preparation method thereof

Abstract

The invention relates to the technical field of ceramsite proppants, in particular to an ultralow-density high-strength ceramsite proppant and a preparation method thereof. The ceramsite proppant is prepared from the following raw materials in mass ratio: 20-75 parts of coal ash, 20-40 parts of spontaneous combustion coal gangue and 5-10 parts of composite mineralizer. The matching range of the fly ash and the spontaneous combustion coal gangue is wide, industrial solid waste resources can be flexibly utilized, the production cost is reduced, and environmental protection is promoted. Through a composite mineralizing agent and a particle size matching process, the influence of impurities and large pores in the raw materials is effectively reduced, a uniform small pore structure is formed, and the strength is greatly improved while the ultra-low volume density is kept to be smaller than 1.40 g / cm. The compressive strength of the prepared 40 / 70-mesh ceramsite proppant reaches 52MPa, the crushing rate is less than 10%, the crushing rate is far beyond the 35MPa standard which can be produced in the industry, the strength stability is excellent, the fluctuation is less than 10%, and the harsh demand of oil and gas exploitation on the ultra-low-density high-strength proppant is met.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramsite proppants, and more specifically, to an ultra-low density and high-strength ceramsite proppant and a preparation method thereof. Background Art

[0002] In recent years, with the progress of oil and gas field exploitation technologies, the demand for ultra-low density and high-strength ceramsite proppants has been increasing day by day. Traditional ceramsite proppants are mostly prepared from high-aluminum raw materials (such as bauxite). Although they can meet the strength requirements, the cost is relatively high, and the raw material resources are limited. To reduce the cost of oil and gas exploitation, the industry urgently needs to develop a technology for preparing high-performance ceramsite proppants using low-aluminum solid waste materials.

[0003] In the Shanxi region, there are rich industrial solid wastes such as self-combusted coal gangue and power plant fly ash. Their aluminum content is relatively low, and the impurity content is relatively high, especially there are many unburned carbon residues, resulting in a loose and porous structure of the materials. These problems seriously restrict their application in the production of ceramsite proppants. The low aluminum content affects the sintering activity. Traditional high-aluminum raw materials (such as bauxite) usually have an aluminum content of ≥40%, while the aluminum content of self-combusted coal gangue and fly ash is relatively low, making it difficult to form sufficient high-strength crystal phases such as mullite. Impurities and unburned carbon residues affect the performance. Unburned carbon residues are prone to generating pores at high temperatures, resulting in a loose structure of the ceramsite and reducing the compressive strength. At the same time, impurities (such as Fe2O3, CaO, etc.) may affect the sintering stability and increase the performance fluctuations of the products. The utilization rate of solid waste is low, and the environmental pollution is serious. A large amount of fly ash and self-combusted coal gangue stored not only occupy land but also may cause problems such as dust and leachate pollution. There is an urgent need for an efficient resource utilization approach.

[0004] Currently, the ultra-low density ceramsite proppants in the industry generally have problems of insufficient strength or high cost. Therefore, developing a high-performance ceramsite proppant based on low-aluminum solid waste raw materials, optimizing the mineralizer and process, is of great significance for reducing the cost of oil and gas exploitation and promoting the resource utilization of solid waste. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. For this reason, an object of one aspect of the present invention is to provide an ultra-low density and high-strength ceramsite proppant. The mass ratio of the raw materials of the ceramsite proppant is fly ash, self-combusted coal gangue and a composite mineralizer, and the mass ratio is 20-75:20-75:5-10.

[0006] Preferably, the composite mineralizer is calcined talc, dolomite, bentonite and purple wood section soil, and the mass ratio is 2:1:2:2.

[0007] Preferably, the bentonite is Guangxi white clay.

[0008] Preferably, the fly ash has an Al2O3 content of 32.4, an SiO2 content of 48.4, an Fe2O3 content of 4.24, a TiO2 content of 1.26, and a CaO content of 1.16; the self - combusted coal gangue has an Al2O3 content of 28.14, an SiO2 content of 60.16, an Fe2O3 content of 2.55, a TiO2 content of 0.36, and a CaO content of 1.58; the calcined talc has an Al2O3 content of 0.49, an SiO2 content of 64.45, an Fe2O3 content of 0.31, a TiO2 content of 0.04, a CaO content of 3.81, and an MgO content of 31.98; the dolomite has a CaO content of 30.68 and an MgO content of 20.77; the Guangxi white clay has an Al2O3 content of 30.30, an SiO2 content of 48.59, an Fe2O3 content of 1.73, a TiO2 content of 1.66, and a CaO content of 0.72; the purple wood - joint clay has an Al2O3 content of 366.41, an SiO2 content of 38.59, an Fe2O3 content of 1.06, a TiO2 content of 1.2, and a CaO content of 0.49.

[0009] Dolomite introduces CaO and MgO; calcined talc introduces MgO. The purpose of introducing MgO by calcined talc is to prevent the calcium in dolomite from being too high, which will affect the strength of the final product. Dolomite is also called dolomite rock, with the chemical formula CaMg(CO3)2, which is a carbonate of calcium and magnesium carbonate. Dolomite will decompose at high temperature, producing carbon dioxide, calcium oxide and magnesium oxide; while calcined talc mainly provides magnesium oxide. In the matrix, due to the presence of calcium and magnesium oxides, it is easy to form a liquid phase, which improves the densification degree of the matrix and plays a strengthening role. Purple wood - joint clay and Guangxi white clay mainly provide plasticity to ensure a certain strength during the ball - forming process of semi - finished products.

[0010] Another object of the present invention is to provide a preparation method of an ultra - low - density and high - strength ceramsite proppant. The specific steps of the preparation method are as follows: S1. Prepare fly ash, self - combusted coal gangue and a composite mineralizer respectively according to the ratio; S2. Wet ball - milling: After mixing the self - combusted coal gangue in S1 with water, wet - mill it in a ball mill; Dry grinding: Put the fly ash and the composite mineralizer in S1 into a Raymond mill for grinding respectively, and conduct powder - selection treatment; S3. Drying and powder - making: Spray the wet - milled self - combusted coal gangue slurry into a specific space by spray - drying, and use the convective hot air in the space to dry the atomized slurry into powder; S4. Batching and mixing: After mixing the processed fly ash, self - combusted gangue and composite mineralizer, put them into a mixer to make them evenly mixed; this step is a key step. Purpose: Gradate powders with different particle sizes within a specific proportion range, use fine - particle - size powder particles to fill the gaps of large - particle - size powders, and subdivide the larger air - tight pores of the final ceramsite into multiple small pores to enhance the mechanical properties of the particles.

[0011] S5. Pelletizing: Conducted on a sugar - coating machine. First, prepare seed pellets, and then while adding powder materials and spraying water in the sugar - coating machine, roll to obtain smooth - shaped ceramsite blanks. S6. Screening: Use a hoist to lift the semi - finished embryo bodies (referred to as rough materials in the industry) made by the sugar - coating machine into a drum sieve. The drum sieve is divided into an upper sieve and a lower sieve. Each layer of sieve uses a sieve mesh of a specific model to screen out the over - coarse and over - fine semi - finished products in the rough materials to obtain semi - finished products with appropriate particle sizes. S7. Drying: Send the obtained semi - finished products into a rotary dryer and use convective hot air to dry the moisture of the semi - finished products. S8. Firing: Continuously add the dried semi - finished products into a rotary kiln in a certain quantity. The rotary kiln is heated by natural gas. Through the mutual cooperation of process parameters such as the fan and rotation speed, the semi - finished products entering the rotary kiln continue to be fired, and complex physical and chemical changes occur inside to obtain pre - finished products. S9. Polishing: Rub and squeeze the fired pre - finished products against each other in a device with a grinding disc to grind off the protrusions adhering to the surface of the products, making the surface of the particles smoother. S10. Dust removal: Since the polished finished products are mixed with ground fine powder or very small particles, continuously sprinkle the materials into a container, and use the interaction of blowing and exhaust to suck away the dust suspended in the air, and finally obtain the finished products.

[0012] Preferably, in S2, wet - grind for 20 - 30 hours to make the particle size of the mixture reach 5 - 18 μm, and 90% of the particle size < 12 μm.

[0013] Preferably, in S2, the particle size ground by a Raymond mill reaches 30 - 60 μm, and 88% of the particle size < 45 μm is sufficient.

[0014] Preferably, in S6, the aperture of the upper sieve is 40 mesh (425 μm), and the aperture of the lower sieve is 50 mesh (300 μm).

[0015] Preferably, in S7, use convective hot air to dry the moisture of the semi - finished products from 10% to 1%.

[0016] Preferably, in S8, the firing temperature is 1150 - 1260 °C, and the heat - preservation time is 90 min.

[0017] The beneficial effects of the present invention are as follows: The raw materials of the present invention have wide adaptability: the mixing ratio range of fly ash and self - combusted gangue is broad, which can flexibly utilize industrial solid waste resources, reduce production costs and promote environmental protection.

[0018] Significant structural optimization: Through the compound mineralizer and particle size matching process, the influence of impurities and large pores in the raw materials is effectively reduced, forming a uniform small - pore structure, which greatly improves the strength while maintaining an ultra - low density bulk density < 1.40 g / cm³.

[0019] Performance breakthroughs industry standards: The prepared 40 / 70 - mesh ceramsite proppant has a compressive strength of 52 MPa and a crushing rate < 10%, far exceeding the industry standard of 35 MPa, and has excellent strength stability with a < 10% fluctuation, meeting the stringent requirements of oil and gas exploitation for ultra - low - density and high - strength proppants.

[0020] Efficient resource utilization: By activating the reaction activity of minerals such as kaolinite and corundum in fly ash and gangue, high - value utilization of solid waste is realized, with both economic and environmental benefits.

[0021] The additional aspects and advantages of the present invention will become apparent in the following description or be understood through the practice of the present invention. Detailed implementation manners

[0022] In order to more clearly understand the above - mentioned objects, features and advantages of the present invention, the present invention will be further described in detail below with specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0023] Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from this description. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0024] Embodiment 1 S1. Prepare 65 parts of fly ash, 28 parts of self - combusted gangue, 2 parts of calcined talc, 1 part of dolomite, 2 parts of Guangxi white clay and 2 parts of purple wood - knot clay respectively according to the proportion; S2. Wet ball - milling: After mixing the self - combusted gangue in S1 with water, wet - mill it in a ball mill for 20 - 30 hours to make the particle size of the mixture reach 5 - 18 um, with 90% of the particle size < 12 um; Dry grinding: Put the fly ash, calcined talc, dolomite, Guangxi white clay and purple wood - knot clay in S1 into a Raymond mill respectively for grinding until the particle size reaches 30 - 60 um, with 88% of the particle size < 45 um, and then carry out powder selection treatment; S3. Drying and powder - making: Spray the wet - milled self - combusted gangue slurry into a specific space by spray drying, and use the hot - air convection in the space to dry the atomized slurry into powder. S4, batching and mixing: the treated fly ash, spontaneous combustion coal gangue and composite mineralizer are mixed and put into a mixer to mix them evenly; S5, balling: in a sugar coating machine, first prepare a ball seed, then add powder and spray water in the sugar coating machine, and roll to obtain a smooth ceramsite body; S6. Screening: The semi-finished product embryos made by the sugar coating machine are lifted into the drum screen by a hoist. The drum screen is divided into an upper screen and a lower screen. Each layer of the screen uses a specific type of screen to screen out the semi-finished products that are too coarse and too fine in the raw material. The aperture of the upper screen is 40 mesh, and the aperture of the lower screen is 50 mesh, so as to obtain the semi-finished products with appropriate particle size; S7, drying: the semi-finished product is sent to a rotary dryer, and the moisture content of the semi-finished product is dried from 10% to 1% by hot air convection; S8, firing: the semi-finished products after drying are continuously added into the rotary kiln in a certain amount, and the rotary kiln is heated by natural gas, the fan speed is 7m / s-10m / s, and the kiln speed is 280s / r-320s / r. The semi-finished products entering the rotary kiln are continued to be fired at a temperature of 1150-1170°C for 90 minutes. Due to the addition of spontaneous combustion coal gangue in S1, the ringing phenomenon in the kiln can be effectively alleviated. Through the matching process of wet grinding and dry grinding in step S2, powders of different particle sizes are proportioned, and the larger particle size particles provide skeleton support, and the wet grinding ultra-high fineness particles provide filling, so that the crystal phase of the final sintered product is more stable, and the internal closed gap distribution is more uniform and compact. Under the premise of ensuring that the ultra-low density (stacking density ≤1.40g / cm³) is met, the compressive strength of the ceramsite is effectively improved, which can reach 52MPa, and a pre-finished product is obtained; S9, polishing: the fired pre-finished products are rubbed and squeezed against each other in a device with a grinding disc to grind off the protrusions adhering to the surface of the finished product so that the surface of the particles becomes smoother; S10. Powder removal: Because the finished product after polishing is mixed with fine powder or very small particles ground off, the material is continuously sprinkled into the container, and the dust suspended in the air is extracted by the interaction of blowing and exhausting, and finally the finished product is obtained.

[0025] Embodiment 2 S1. Prepare 55 parts of fly ash, 38 parts of spontaneous combustion coal gangue, 2 parts of burnt talc, 1 part of dolomite, 2 parts of Guangxi white mud and 2 parts of Zimujie soil respectively in proportion; S2, wet ball milling: mix the spontaneous combustion gangue in S1 with water, and then wet grind it in a ball mill for 20-30 hours to make the particle size of the mixture reach 5-18um, of which 90% of the particle size is less than 12um; dry grinding: put the fly ash, burned talc, dolomite, Guangxi white mud and purple wood soil in S1 into Raymond mill respectively to grind the particle size to 30-60um, of which 88% of the particle size is less than 45um, and then undergo powder selection treatment; S3, Drying and Powdering: Spray the wet-ground spontaneous combustion coal gangue slurry into a specific space by spray drying, and use the hot air convection in the space to dry the atomized slurry into powder; S4, batching and mixing: the treated fly ash, spontaneous combustion coal gangue and composite mineralizer are mixed and put into a mixer to mix them evenly; S5, balling: in a sugar coating machine, first prepare a ball seed, then add powder and spray water in the sugar coating machine, and roll to obtain a smooth ceramsite body; S6. Screening: The semi-finished product embryos made by the sugar coating machine are lifted into the drum screen by a hoist. The drum screen is divided into an upper screen and a lower screen. Each layer of the screen uses a specific type of screen to screen out the semi-finished products that are too coarse and too fine in the raw material. The aperture of the upper screen is 40 mesh, and the aperture of the lower screen is 50 mesh, so as to obtain the semi-finished products with appropriate particle size; S7, drying: the semi-finished product is sent to a rotary dryer, and the moisture content of the semi-finished product is dried from 10% to 1% by hot air convection; S8, firing: the semi-finished products after drying are continuously added into the rotary kiln in a certain amount, and the rotary kiln is heated by natural gas, the fan speed is 7m / s-10m / s, and the kiln speed is 280s / r-320s / r. The semi-finished products entering the rotary kiln are continued to be fired at a temperature of 1160-1220°C for 90 minutes. Due to the addition of spontaneous combustion coal gangue in S1, the ringing phenomenon in the kiln can be effectively alleviated. Through the combination process of wet grinding and dry grinding in step S2, powders of different particle sizes are proportioned, and the larger particle size particles provide skeleton support, and the wet grinding ultra-high fineness particles provide filling, so that the crystal phase of the final sintered product is more stable, and the internal closed gap distribution is more uniform and compact. Under the premise of ensuring that the ultra-low density (stacking density ≤1.40g / cm³) is met, the compressive strength of the ceramsite is effectively improved, which can reach 52MPa, and a pre-finished product is obtained; S9, polishing: the fired pre-finished products are rubbed and squeezed against each other in a device with a grinding disc to grind off the protrusions adhering to the surface of the finished product so that the surface of the particles becomes smoother; S10. Powder removal: Because the finished product after polishing is mixed with fine powder or very small particles ground off, the material is continuously sprinkled into the container, and the dust suspended in the air is extracted by the interaction of blowing and exhausting, and finally the finished product is obtained.

[0026] Embodiment 3 S1. Prepare 20 parts of fly ash, 73 parts of spontaneous combustion coal gangue, 2 parts of burnt talc, 1 part of dolomite, 2 parts of Guangxi white mud and 2 parts of purple wood soil respectively in proportion; S2, wet ball milling: mix the spontaneous combustion gangue in S1 with water, and then wet grind it in a ball mill for 20-30 hours to make the particle size of the mixture reach 5-18um, of which 90% of the particle size is less than 12um; dry grinding: put the fly ash, burned talc, dolomite, Guangxi white mud and purple wood soil in S1 into Raymond mill respectively to grind the particle size to 30-60um, of which 88% of the particle size is less than 45um, and then undergo powder selection treatment; S3, Drying and Powdering: Spray the wet-ground spontaneous combustion coal gangue slurry into a specific space by spray drying, and use the hot air convection in the space to dry the atomized slurry into powder; S4, batching and mixing: the treated fly ash, spontaneous combustion coal gangue and composite mineralizer are mixed and put into a mixer to mix them evenly; S5, balling: in a sugar coating machine, first prepare a ball seed, then add powder and spray water in the sugar coating machine, and roll to obtain a smooth ceramsite body; S6. Screening: The semi-finished product embryos made by the sugar coating machine are lifted into the drum screen by a hoist. The drum screen is divided into an upper screen and a lower screen. Each layer of the screen uses a specific type of screen to screen out the semi-finished products that are too coarse and too fine in the raw material. The aperture of the upper screen is 40 mesh, and the aperture of the lower screen is 50 mesh, so as to obtain the semi-finished products with appropriate particle size; S7, drying: the semi-finished product is sent to a rotary dryer, and the moisture content of the semi-finished product is dried from 10% to 1% by hot air convection; S8, firing: the semi-finished products after drying are continuously added into the rotary kiln in a certain amount, and the rotary kiln is heated by natural gas, the fan speed is 7m / s-10m / s, and the kiln speed is 280s / r-320s / r, so that the semi-finished products entering the rotary kiln are kept at a temperature of 1230-1260°C and the time is 90min for further firing. Due to the large amount of spontaneous combustion coal gangue added in S1, the ringing phenomenon in the kiln can be effectively avoided. Through the matching process of wet grinding and dry grinding in step S2, powders of different particle sizes are proportioned, and the larger particle size particles provide skeleton support, and the wet grinding ultra-high fineness particles provide filling, so that the crystal phase of the final sintered product is more stable, and the internal closed gap distribution is more uniform and compact. Under the premise of ensuring that the ultra-low density (stacking density ≤1.40g / cm³) is met, the compressive strength of the ceramsite is effectively improved, which can reach 52MPa, and a pre-finished product is obtained; S9, polishing: the fired pre-finished products are rubbed and squeezed against each other in a device with a grinding disc to grind off the protrusions adhering to the surface of the finished product so that the surface of the particles becomes smoother; S10. Powder removal: Because the finished product after polishing is mixed with fine powder or very small particles ground off, the material is continuously sprinkled into the container, and the dust suspended in the air is extracted by the interaction of blowing and exhausting, and finally the finished product is obtained.

[0027] The products of the embodiments were tested and compared with the industry standards, and the results are shown in Table 1 below.

[0028] Table 1. Comparison Table of Embodiment Performance Results The pressure of the product made with an ultra-low density specification of 40 / 70 and a bulk density < 1.40 g / cm³ is much higher than 35 MPa, which can be mass-produced in the current industry, by < 10%, and can reach 52 MPa with a breakage rate < 10%.

[0029] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can also have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ultra-low density and high-strength ceramic proppant, characterized in that: The raw materials of the ceramsite proppant are fly ash, self-igniting coal gangue and composite mineralizer in a mass ratio of 20-75:20-75:5-10.

2. The ultra-low density and high-strength ceramic proppant according to claim 1, wherein: The composite mineralizer is burnt talc, dolomite, bentonite and purple wood earth, and the mass ratio is 2:1:2:

2.

3. The ultra-low density and high-strength ceramsite proppant according to claim 2, wherein: The bentonite is Guangxi white mud.

4. An ultra-low density and high-strength ceramsite proppant according to claim 3, characterized in that: The fly ash has an Al2O3 content of 32.4, a SiO2 content of 48.4, a Fe2O3 content of 4.24, a TiO2 content of 1.26, and a CaO content of 1.16; the spontaneous combustion coal gangue has an Al2O3 content of 28.14, a SiO2 content of 60.16, a Fe2O3 content of 2.55, a TiO2 content of 0.36, and a CaO content of 1.58; the burned talc has an Al2O3 content of 0.49, a SiO2 content of 64.45, a Fe2O3 content of 0.31, and a TiO2 content of 0.0 4. The CaO content is 3.81, and the MgO content is 31.98; the CaO content of dolomite is 30.68, and the MgO content is 20.77; the Al2O3 content of Guangxi white mud is 30.30, the SiO2 content is 48.59, the Fe2O3 content is 1.73, the TiO2 content is 1.66, and the CaO content is 0.72; the Al2O3 content of purple wood soil is 366.41, the SiO2 content is 38.59, the Fe2O3 content is 1.06, the TiO2 content is 1.2, and the CaO content is 0.

49.

5. The preparation method of an ultra-low density and high-strength ceramic proppant according to claim 4, wherein: The specific steps of the preparation method are as follows: S1. Prepare fly ash, spontaneous combustion coal gangue and composite mineralizer in proportion; S2, wet ball milling: mix the spontaneous combustion coal gangue in S1 with water and place it in a ball mill for wet grinding; dry grinding: put the fly ash and composite mineralizer in S1 into Raymond mill for grinding, and then select the powder; S3, Drying and Powdering: Spray the wet-ground spontaneous combustion coal gangue slurry into a specific space by spray drying, and use the hot air convection in the space to dry the atomized slurry into powder; S4, batching and mixing: the treated fly ash, spontaneous combustion coal gangue and composite mineralizer are mixed and put into a mixer to mix them evenly; S5, balling: in a sugar coating machine, first prepare a ball seed, then add powder and spray water in the sugar coating machine, and roll to obtain a smooth ceramsite body; S6. Screening: The semi-finished product embryos made by the sugar coating machine are lifted into the drum screen by a hoist. The drum screen is divided into an upper screen and a lower screen. Each layer of the screen uses a specific type of screen to screen out the semi-finished products that are too coarse and too fine in the raw material to obtain the semi-finished products with appropriate particle size; S7, drying: sending the semi-finished product into a rotary dryer, and using hot air convection to dry the semi-finished product; S8, sintering: the semi-finished products after drying are continuously added into the rotary kiln according to a certain amount, and the rotary kiln is heated by natural gas, so that the semi-finished products entering the rotary kiln continue to be sintered to obtain pre-finished products; S9, polishing: the fired pre-finished products are rubbed and squeezed against each other in a device with a grinding disc to grind off the protrusions adhering to the surface of the finished product so that the surface of the particles becomes smoother; S10, Powder removal: Since the polished finished products are mixed with ground fine powder or very small particles, the material is continuously scattered into the container, and the dust suspended in the air is removed by the interaction of air blowing and exhaust, and finally the finished product is obtained.

6. The preparation method of an ultra-low density and high-strength ceramsite proppant according to claim 5, characterized in that: In S2, wet grinding is carried out for 20 - 30 hours to make the particle size of the mixture reach 5 - 18 um, and 90% of the particle size < 12 um.

7. The preparation method of an ultra-low density and high-strength ceramsite proppant according to claim 5, wherein: In S2, the particle size ground by the Raymond mill reaches 30 - 60 um, and 88% of the particle size < 45 um is sufficient.

8. The preparation method of an ultra-low density and high-strength ceramsite proppant according to claim 5, characterized in that: In S6, the upper sieve aperture is 40 mesh, and the lower sieve aperture is 50 mesh.

9. The preparation method of an ultra-low density and high-strength ceramsite proppant according to claim 5, characterized in that: In S7, the moisture content of the semi-finished product is dried from 10% to 1% by hot air convection.

10. The preparation method of an ultra-low density and high-strength ceramsite proppant according to claim 5, characterized in that: In S8, the firing temperature is 1150 - 1260 °C, and the heat preservation time is 90 min.

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