Method for enhancing carbon dioxide sequestration using fluorinated flushing water in cementitious filling materials

Abstract

This invention discloses a method for enhancing the storage of carbon dioxide using fluoride-containing flushing water to strengthen cementitious backfill materials. The method involves constructing waterproof and airtight walls at the locations of the connecting roadway, the transport roadway of the adjacent working face, the return airway of the adjacent working face, the transport roadway of the cemented backfill working face, and the return airway of the cemented backfill working face. Hardened cemented backfill material is filled into the goaf area of ​​the working face. After filling, an injection port and a drainage port are respectively provided at the top and bottom of the hardened cemented backfill material. The limiting water pressure and warning water pressure of the water storage area in the goaf area of ​​the working face are determined. Mine water is injected into the hardened cemented backfill material for hydration. Power plant tail gas is mixed with fluoride-containing flushing water to obtain an acidic fluoride-containing mixed solution, which is then injected into the hydrated hardened cemented backfill material. This invention can simultaneously achieve the resource utilization of hardened cemented backfill material in the goaf area, effective defluorination of flushing wastewater from pithead coal-fired power plants, and economical, safe, and efficient storage of carbon dioxide from pithead coal-fired power plants.

Description

Technical Field

[0001] This invention relates to a method for sealing carbon dioxide, specifically a method for sealing carbon dioxide using fluorinated ash water-reinforced cementitious filling materials. Background Technology

[0002] The massive emission of carbon dioxide is the most significant cause of global warming, and coal-fired power generation is the primary mode of carbon dioxide emission. Currently, most coal-fired power plants release carbon dioxide directly into the atmosphere without treatment. Only a small number of power plants capture, separate, and purify the emitted carbon dioxide (to a purity greater than 90%), then transport it via pipeline to suitable geological reservoirs for underground storage, such as abandoned oil fields, deep saline aquifers, and unminable coal seams. Carbon dioxide takes hundreds to thousands of years to be fixed as carbonate minerals in geological reservoirs, during which time there is a risk of leakage, and its safety remains controversial. Coal combustion in power plants also generates large amounts of wastewater, among which ash flushing wastewater is one of the main types of wastewater, accounting for nearly half of the total wastewater. The pollutants in ash flushing wastewater are mainly suspended solids, pH, and fluoride. After clarification, the wastewater is alkaline, with fluoride ion concentrations reaching tens of milligrams per liter, exceeding the discharge standard of 3 milligrams per kilogram for fluoride content in agricultural irrigation wastewater. Direct discharge of ash flushing wastewater not only leads to excessive levels of suspended solids and fluoride in the receiving water body, but also causes soil salinization in the vicinity, damaging the normal ecological environment.

[0003] Backfilling mining involves filling mined-out areas underground or on the surface with materials such as gangue, sand, and gravel to control rock movement and surface subsidence. Based on the backfill materials used and the transportation method, backfilling mining methods are divided into: dry backfilling mining, hydraulic backfilling mining, and cemented backfilling mining. Cemented backfilling mining in coal mines uses cement and its substitutes, or other cementing materials, mixed with fly ash and other materials to prepare a cementing backfill material for filling the mined-out areas. On the one hand, the hardened cementing material increases the strength of the backfill; on the other hand, after backfilling, the alkaline substances containing calcium and magnesium ions in the hardened cementing material can react with carbon dioxide to form stable carbonate minerals. Since the alkaline substances in hardened cementitious filling materials are mainly hydroxides (Ca(OH)2, Mg(OH)2), hydrated silicates and aluminosilicates, among which hydrated silicates and aluminosilicates have weak hydration capacity, the high-density liquid or supercritical carbon dioxide injection method has poor carbon dioxide mineralization and sequestration capacity, which seriously affects the rate and potential of carbon dioxide mineralization and sequestration of cementitious materials. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for sequestering carbon dioxide using fluoride-containing flushing wastewater to enhance the cemented backfill material. This method can simultaneously achieve the resource utilization of hardened cemented backfill material in goaf areas, the effective defluorination of flushing wastewater from coal-fired power plants at mine mouths, and the economical, safe, and efficient sequestration of carbon dioxide from coal-fired power plants at mine mouths.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for sealing carbon dioxide using fluorinated flushing water to enhance the cementitious filling material, comprising the following steps:

[0006] S1: Construct waterproof and airtight walls at the locations of the cemented backfill working face connecting roadway, adjacent working face transport roadway, adjacent working face return airway, cemented backfill working face transport roadway, and cemented backfill working face return airway.

[0007] S2: Fill the goaf area of ​​the working face with hardened cemented backfill material. After filling, an injection port and a drainage port are respectively provided at the top and bottom of the hardened cemented backfill material.

[0008] S3: Determine the limiting water pressure P in the water storage area of ​​the goaf area of ​​the working face. x Warning water pressure P j ;

[0009] S4: Inject mine water into the hardened cementitious filling material for hydration;

[0010] S5: Mix the power plant exhaust gas with the clarified fluoride-containing flushing water to obtain an acidic fluoride-containing mixed solution. Then, inject the acidic fluoride-containing mixed solution into the hydrated hardened cementitious backfill material. This accelerates the dissolution and release of calcium and magnesium ions from alkaline substances, while simultaneously increasing the porosity of the hardened cementitious backfill material, mineralizing carbon dioxide, and achieving rapid carbon dioxide sequestration and purification of the fluoride-containing flushing water.

[0011] Furthermore, in step S1, the waterproof sealing wall consists of a brick wall, a cohesive soil layer, and a concrete wall, arranged sequentially from one side of the working face goaf area to the other. The permeability coefficient of the cohesive soil layer should be less than 1×10⁻⁶. -5 cm / s.

[0012] Furthermore, in step S1, the compressive strength of the waterproof and airtight wall is not less than P:

[0013]

[0014] In the formula: L is the narrowest waterproof coal pillar width, taken as the width of the coal pillar in the section, in meters; K is the safety factor; M is the coal seam thickness or mining height, in meters; K p Tensile strength of coal, MPa;

[0015] Furthermore, in step S3, the water storage area is a closed space formed by the coal seam floor, the waterproof and airtight wall of the connecting roadway, the waterproof and airtight wall of the mining roadway, the boundary waterproof coal pillars around the waterproof and airtight walls, the section waterproof coal pillars, the main roadway waterproof coal pillars, and the overlying strata outside the water-conducting fracture zone.

[0016] Furthermore, in step S2, the hardened cementitious filling material contains one or more alkaline substances rich in calcium, magnesium, and iron, and the alkaline substances include one or more of oxides, hydroxides, hydrated silicates, and aluminosilicate minerals.

[0017] Furthermore, in step S4, the injection volume of mine water is controlled at the warning water pressure P. j 50% to 80%.

[0018] Furthermore, in step S5, the carbon dioxide concentration in the power plant exhaust gas should be greater than 20%; the clarified fluoride-containing flushing water should be alkaline.

[0019] Furthermore, in step S5, the acidic fluorine-containing mixed solution is injected using pulsed pressure and the injection cycle is once every 2 to 3 years.

[0020] Compared with existing technologies, this invention uses hardened cemented backfill material from goaf filling as a carbon dioxide reservoir, allowing for local use of carbon dioxide and solving the problem of long-distance transportation of carbon dioxide tail gas from coal-fired power plants at the mine mouth. It also achieves resource utilization of the hardened cemented backfill material. Using fluoride-containing flushing wastewater from power plants as the solvent for carbon dioxide and mine water as the hydration solution for the hardened cemented backfill material, it solves the problem of treating flushing wastewater from power plants, achieving the recycling of both fluoride-containing flushing wastewater and mine water, saving water resources, and preventing the discharge of fluoride-containing flushing wastewater from power plants from damaging the ecological environment. Furthermore, the alkaline substances in the carbon dioxide and hardened cemented backfill material are mineralized into carbonic acid. Salt minerals enable the safe sequestration of carbon dioxide, improve the strength of cemented backfill, and achieve better control of rock strata movement and surface subsidence. Compared with high-density liquid or supercritical carbon dioxide injection methods, this invention injects carbon dioxide in the form of an aqueous solution, eliminating the need for separation and high purification of power plant tail gas rich in sulfur dioxide and hydrogen fluoride. Furthermore, sulfate and fluoride ions in the acidic mixed solution can significantly increase the dissolution rate of minerals such as aluminosilicates in the cemented backfill material, thereby saving carbon dioxide purification costs, reducing the risk of carbon dioxide leakage, accelerating the mineralization and sequestration rate of carbon dioxide, and achieving effective defluorination of flushing water. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0022] Figure 2 This is a schematic plan view of the goaf structure of the working face of the present invention;

[0023] Figure 3 for Figure 2 Schematic diagram of AA section in the middle;

[0024] In the diagram: 1-Goaf of the working face, 2-Drainage outlet, 3-Purified water, 4-First transport device, 5-Underground production water, 6-Surface production water, 7-Pithead coal-fired power plant, 8-Clarified fluoride-containing ash flushing water, 9-Power plant tail gas, 10-Mixed solution, 11-Second transport device, 12-Mine water, 13-Injection port, 14-Hardened cemented backfill material, 15-Boundary waterproof coal pillar, 16-Return airway of adjacent working face, 17-Transport roadway of cemented backfill working face, 18-Connecting roadway, 19-Section waterproof coal pillar, 20-Waterproof sealing wall of connecting roadway, 21-Waterproof sealing wall of mining roadway, 22-Waterproof coal pillar of main roadway, 23-Main roadway, 24-Return airway of cemented backfill working face, 25-Transport roadway of adjacent working face, 26-Coal seam floor, 27-Overlying strata, 28-Water-conducting fracture zone. Detailed Implementation

[0025] The invention will now be further described with reference to the accompanying drawings.

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a technical solution, such as Figures 1 to 3 As shown, it includes the following steps:

[0028] S1: Construct waterproof and airtight walls at the following locations: cemented backfill working face connecting roadway 18, adjacent working face transport roadway 25, adjacent working face return airway 16, cemented backfill working face transport roadway 17, and cemented backfill working face return airway 24; the one at cemented backfill working face connecting roadway 18 is the connecting roadway waterproof and airtight wall 20, and the other locations are the mining roadway waterproof and airtight walls 21.

[0029] The compressive strength of the waterproof sealed wall shall not be less than the compressive strength P of the waterproof coal pillar.

[0030] Where: L is the narrowest waterproof coal pillar width, taken as the width of the section coal pillar, 15m; K is the safety factor, generally taken as 2-5, in this embodiment it is taken as 2; M is the coal seam thickness or mining height, taken as 3m; K pThe tensile strength of coal is taken as 0.5 MPa. Substituting the data into the above formula, we get p = 1.5 MPa. Under the condition of meeting the compressive strength requirements of the waterproof sealing wall, the design and construction of the waterproof sealing wall can be further carried out. The waterproof sealing wall consists of a brick wall, a cohesive soil layer, and a concrete wall, arranged sequentially from one side of the working face goaf 1 towards the other. The permeability coefficient of the cohesive soil layer should be less than 1 × 10⁻⁶. -5 cm / s.

[0031] S2: Fill the goaf 1 of the working face with hardened cemented backfill material 14. After filling, an injection port 13 and a drainage port 2 are respectively provided at the top and bottom of the hardened cemented backfill material 14. The injection port 13 is connected to the second transport device 11. The hardened cemented backfill material 14 contains one or more alkaline substances rich in calcium, magnesium, and iron. The alkaline substances include one or more of oxides, hydroxides, hydrated silicates, and aluminosilicate minerals. The oxides include one or more of CaO, MgO, and Fe2O3. The hydroxides include Ca(OH)2 and / or Mg(OH)2.

[0032] In this embodiment, the hardened cementitious filling material 14 is mainly composed of coal gangue + fly ash + silicate cement + water. The chemical composition of coal gangue is shown in Table 1, the chemical composition of fly ash is shown in Table 2, and the chemical composition of silicate cement is shown in Table 3.

[0033] Element Loss <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO content / % 13.86 46.3 17.09 7.12 9.33 1.78

[0034] Table 1 Chemical composition of coal gangue

[0035] Element Loss <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO content / % 6.43 48.41 28.18 5.2 3.95 1.62

[0036] Table 2 Chemical Composition of Fly Ash

[0037] Element Loss <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO content / % 6.43 48.41 28.18 5.2 3.95 1.62

[0038] Table 3 Chemical composition of silicate cement

[0039] S3: Determine the limiting water pressure P in the water storage area of ​​goaf 1 in the working face. x Warning water pressure P j The water storage area is a closed space formed by the overlying strata 27 outside the coal seam floor 26, the waterproof sealing wall 20 of the connecting roadway, the waterproof sealing wall 21 of the mining roadway, the waterproof coal pillars around the waterproof sealing walls (i.e., the boundary waterproof coal pillars 15), the section waterproof coal pillars 19, the main roadway waterproof coal pillar 22, and the water-conducting fracture zone 28. The main roadway waterproof coal pillar 22 is located beside the main roadway 23. The water pressure is limited to P. x Since the bearing capacity of the waterproof and airtight wall is equal to the bearing capacity P = 1.5 MPa calculated in step S1, it can be seen that the limiting water pressure P x =1.5MPa; Warning water pressure Pj According to the limiting water pressure P x 80% of it is determined to be 1.2 MPa.

[0040] S4: Inject mine water 12 into the hardened cementitious backfill material 14 for hydration; as shown in Tables 1-3, the hardened cementitious backfill material 14 contains alkaline substances rich in calcium, magnesium, and iron, including oxides (CaO, MgO, and Fe2O3), hydroxides (Ca(OH)2, Mg(OH)2), hydrated calcium silicate, and aluminosilicate minerals, which can react with carbon dioxide to form carbonate minerals. Under acidic conditions, alkaline substances can dissolve and release Ca. 2+ Mg 2+ Alkaline metal ions react with carbon dioxide to form carbonate minerals. For example, the main minerals in silicate cement include tricalcium silicate (3CaO·SiO2), dicalcium silicate (2CaO·SiO2), tricalcium aluminate (3CaO·Al2O3), and tetracalcium aluminoferrite (4CaO·Al2O3·Fe2O3). After hydration, silicate cement produces CaO·SiO2·YH2O, Ca(OH)2, 3CaO·Al2O3·6H2O, and CaO·Fe2O3·H2O. The hydration products can further react with aqueous carbon dioxide solution to produce the following reactions:

[0041]

[0042]

[0043]

[0044]

[0045]

[0046] Ca 2+ (aq)+CO3 2- (aq)→CaCO3(s)

[0047] H + (aq)+(OH) - (aq)→H₂O(aq)

[0048] In practical applications, the injection volume of mine water 12 is controlled at the warning water pressure P. j 50-80% of the solution is at 0.6-0.96 MPa; the pH of the hydrated solution is 7-8; under conditions of quantitative carbon dioxide mineralization, when the pH is greater than 8, clay and other minerals will be produced in the solution, consuming Ca. 2+ Mg 2+ Alkaline metal ions, etc., thereby reducing the ability of hardened cementitious filling material 14 to mineralize carbon dioxide.

[0049] S5: The power plant tail gas 9 from the pithead is mixed with the clarified fluoride-containing flushing water 8 to obtain an acidic fluoride-containing mixed solution 10. This acidic fluoride-containing mixed solution 10 is then injected into the hydrated, hardened cemented backfill material 14. The pH of the mixed solution 10 is 3.2-5. The carbon dioxide concentration in the power plant tail gas 9 should be greater than 20%. When the concentration is greater than 20%, the energy consumption for capturing carbon dioxide in the aqueous solution is lower throughout the entire cycle compared to ammonia-assisted capture technology. The clarified fluoride-containing flushing water 8 is alkaline, which allows for the dissolution of more carbon dioxide. Furthermore, the fluoride ions in the acidic solution will significantly increase the dissolution rate of aluminosilicate minerals in fly ash, coal gangue, and other materials, releasing more Ca2+. 2+ Mg 2+ The presence of alkaline metal ions reduces the fluoride content in wastewater. The dissolution rate of aluminosilicate minerals varies with temperature, solution composition, and saturation state, as described by the following formula:

[0050]

[0051] In the formula: r represents the normalized steady-state dissolution rate of the geometric surface area of ​​the aluminosilicate mineral. Indicates H in the solution + The activity, Indicates Al in solution 3+ The activity of A A E is a constant. A σ represents the activation energy, R represents the gas constant, and T represents the absolute temperature. According to Daux's research, when normalized to a single Si atom, σ equals 1, and ΔG... r This refers to the Gibbs free energy of the reaction used to dissolve the surface layer of hydrated aluminosilicate minerals. Fluoride and sulfate ions in a mixed solution can reduce the Al concentration in the solution through the following reaction. 3+ With Al in the solution 3+ As the concentration of calcium ions decreases, the dissolution rate of aluminosilicate minerals increases exponentially, releasing more calcium. 2+ Mg 2+ Alkaline metal ions are used to increase the rate of carbon dioxide mineralization and storage, while simultaneously achieving effective fluoride reduction.

[0052] Al 3+ +F - →AlF 2-

[0053] AlF 2- +F - →AlF2 -

[0054] Al 3+ +SO4 2- →Al(SO4) + .

[0055] The injection method for mixed solution 10 is pulsed pressure injection, and the injection volume is controlled at the warning water pressure P. j The pulsed pressure injection method can reduce the blockage of hardened cementitious filling material 14 by mineralized carbonate minerals. In practical applications, the injection cycle of the mixed solution 10 is once every 2-3 years. After mineralization, the purified water 3, after passing the test (i.e., the fluoride content in the purified water 3 is less than 3 mg / kg), is transported out through the first transport device 4 and can be used as underground production water 5, surface production water 6, and water for the mine-mouth coal-fired power plant 7. This realizes the recycling of power plant flushing wastewater and mine water, saves water resources, and avoids the damage to the ecological environment caused by the discharge of power plant flushing wastewater and mine water. According to experimental research, using carbon dioxide solution injection, more than 95% of the injected carbon dioxide is mineralized into carbonate minerals in about two years. Compared with high-density liquid or supercritical carbon dioxide injection methods, this greatly shortens the mineralization time.

[0056] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any minor modifications, equivalent substitutions, and improvements made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for sealing carbon dioxide using fluorinated flushing water to enhance the cementitious filling material, characterized in that, Includes the following steps: S1: Construct waterproof sealing walls at the following locations: cemented backfill working face connecting roadway (18), adjacent working face transport roadway (25), adjacent working face return airway (16), cemented backfill working face transport roadway (17), and cemented backfill working face return airway (24). S2: Fill the goaf area (1) of the working face with hardened cemented filling material (14). After filling, an injection port (13) and a drainage port (2) are respectively provided at the top and bottom of the hardened cemented filling material (14). S3: Determine the limiting water pressure P of the goaf area (1) water storage area of ​​the working face. x Warning water pressure P j ; S4: Inject mine water (12) into the hardened cemented filling material (14) for hydration; S5: Mix the power plant tail gas (9) with the clarified fluorine-containing flushing water (8) to obtain an acidic fluorine-containing mixed solution (10), and then inject the acidic fluorine-containing mixed solution (10) into the hydrated hardened cementitious filling material (14).

2. The method for sealing carbon dioxide using fluorinated flushing water to enhance the cementitious filling material according to claim 1, characterized in that: In step S1, the waterproof sealing wall consists of a brick wall, a cohesive soil layer, and a concrete wall, arranged sequentially from one side of the working face goaf (1) to the other side. The permeability coefficient of the cohesive soil layer should be less than 1×10⁻⁶. -5 cm / s.

3. The method for sealing carbon dioxide using fluoride-containing flushing water to enhance the cementitious filling material, as described in claim 1, is characterized in that: In step S1, the compressive strength of the waterproof and airtight wall shall not be less than P: In the formula: L is the narrowest waterproof coal pillar width, taken as the width of the coal pillar in the section, in meters; K is the safety factor; M is the coal seam thickness or mining height, in meters; K p denoted as the tensile strength of coal, in MPa.

4. The method for sealing carbon dioxide using fluoride-containing flushing water to enhance the cementitious filling material, as described in claim 1, is characterized in that: In step S3, the water storage area is a closed space formed by the overlying strata (27) outside the coal seam floor (26), the waterproof sealing wall of the connecting roadway (20), the waterproof sealing wall of the mining roadway (21), the boundary waterproof coal pillar (15) around the waterproof sealing wall, the section waterproof coal pillar (19), the main roadway waterproof coal pillar (22), and the water-conducting fracture zone (28).

5. The method for sealing carbon dioxide using fluorinated flushing water to enhance the cementitious filling material according to claim 1, characterized in that: The hardened cementitious filling material (14) in step S2 contains one or more alkaline substances rich in calcium, magnesium, and iron. The alkaline substances include one or more of oxides, hydroxides, hydrated silicates, and aluminosilicate minerals.

6. The method for sealing carbon dioxide using fluorinated flushing water to enhance the cementitious filling material according to claim 1, characterized in that: In step S4, the injection volume of mine water (12) is controlled at the warning water pressure P. j 50% to 80%.

7. The method for sealing carbon dioxide using fluorinated flushing water to enhance the cementitious filling material according to claim 1, characterized in that: In step S5, the carbon dioxide concentration in the power plant tail gas (9) should be greater than 20%; the clarified fluoride-containing flushing water (8) should be alkaline.

8. The method for sealing carbon dioxide using fluorinated flushing water to enhance the cementitious filling material according to claim 1, characterized in that: In step S5, the acidic fluorine-containing mixed solution (10) is injected using a pulsed pressure injection method, and the injection cycle is once every 2 to 3 years.

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