Self-purification treatment method for coal ash and furnace bottom slag generated by coal-fired power plant

Abstract

The invention discloses a self-purification treatment method for coal ash and furnace bottom slag generated by a coal-fired power plant. The method comprises the following steps: (1) mixing a mixture of the coal ash and the furnace bottom slag generated by the coal-fired power plant with alkaline waste minerals; (2) ball milling treatment: carrying out ball milling to form solid waste mixed liquid slurry; (3) conveying and stirring: conveying the solid waste mixed liquid slurry into a slurry stirring barrel for mixing and stirring, and conveying to a spray drying tower; (4) spray drying: fully spray-drying the solid waste mixed liquid slurry to obtain mixed powder; (5) flue gas dust removal and condensation cooling, wherein flue gas generated in the spray drying process is subjected to dust removal; introducing the dedusted flue gas into a condenser; (6) water and smoke self-purification: recovering liquid water obtained by the condenser and adding the liquid water into the solid waste mixture for ball milling; gas exhausted by the condenser is introduced into the slurry stirring barrel for self-purification, so that ultralow emission of waste gas is realized; and (7) carrying out high-temperature calcination on the mixed powder and the powder material to prepare a building material product.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental protection, and particularly relates to a self-purification treatment method of fly ash and bottom ash generated by a coal-fired power plant. BACKGROUND

[0002] In the process of coal-fired power plant burning coal for power generation, two types of solid waste, fly ash and bottom ash, are generated in addition to heat energy. Fly ash is extremely fine particulate matter (particle size is mostly 1-300 μm) taken out from the tail of the boiler by high-temperature flue gas, collected by electrostatic or bag-type dust collector, and accounts for about 70-80% of the total amount of ash, with SiO2 and Al2O3 as the main chemical composition, and with volcanic ash activity. Bottom ash is porous particles (particle size is mostly greater than 1 mm) formed by cooling of molten coal ash at the bottom of the furnace, which is similar to fly ash but has weaker activity. Fly ash, as the fine particulate residue after coal combustion, contains unburned carbon, oxides, silicates, aluminates, and trace amounts of heavy metal elements such as lead, cadmium, mercury, etc., and may also carry trace amounts of dioxins and other persistent organic pollutants. Bottom ash is mainly composed of inorganic minerals in coal, and also contains heavy metals and other harmful elements. These solid wastes have become a major challenge in environmental governance due to their high yield and complex composition characteristics.

[0003] Traditional fly ash and bottom ash treatment methods mainly include landfill, stacking, and partial resource utilization (such as for the preparation of building materials). However, the above methods have many problems, specifically:

[0004] (1) Landfill: Although it can temporarily solve the problem of waste storage, it will cause waste of land resources in the long run and there is a risk of leachate pollution of groundwater; in addition, the construction and maintenance cost of the landfill is high;

[0005] (2) Stacking: open-air stacking is easy to cause dust pollution, which not only affects air quality, but also may pose a threat to the health of surrounding residents; at the same time, stacking also occupies valuable land resources;

[0006] (3) Resource utilization such as preparation of building materials: due to the unstable quality of fly ash, specifically the large fluctuation in carbon content (fluctuation range 5-15%) and uneven particle fineness (particle size range 0.01-1 mm), the product quality is also unstable, such as the use in cement production will cause the difference in cement admixture strength to be 20-30%, which is difficult to meet the building material industry standard; and factors such as high transportation cost make the resource utilization of fly ash and bottom ash very limited; furthermore, the existing resource utilization technology will generate dust emission and wastewater treatment problems in the process of treating fly ash and bottom ash, thereby easily causing secondary pollution.

[0007] Therefore, developing an efficient, environmentally friendly and economically viable fly ash and slag treatment technology is of great significance for disposing of large amounts of solid waste, reducing environmental pollution and improving resource utilization. SUMMARY

[0008] The purpose of the present application is to provide a self-purification treatment method for fly ash and slag produced by coal-fired power plants, which effectively and comprehensively treats fly ash and slag produced by coal-fired power plants, and realizes resource utilization and reduces environmental pollution of waste gas, solid waste and waste liquid generated during treatment.

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions.

[0010] A self-purification treatment method for fly ash and slag produced by coal-fired power plants, comprising the following steps:

[0011] (1) Solid waste mixing: mixing fly ash and slag produced by coal-fired power plants with alkaline waste minerals to obtain a solid waste mixture by a feeder, and conveying the solid waste mixture to a wet ball mill;

[0012] (2) Ball milling treatment: adding water to the solid waste mixture obtained in step (1) and ball milling by a wet ball mill to form a solid waste mixed liquid slurry;

[0013] (3) Conveying and stirring: conveying the solid waste mixed liquid slurry to a mud stirring barrel for mixing and stirring to prevent solidification after supercooling, and conveying to a spray drying tower by a mud pump during stirring;

[0014] (4) Spray drying: fully spray drying the solid waste mixed liquid slurry in the spray drying tower by a high-temperature hot blast stove to obtain a mixed powder;

[0015] (5) Flue gas dust removal and condensation cooling: using a bag filter to remove dust from flue gas generated during the drying process in the spray drying tower; then, passing the dust-removed flue gas into a condenser, and the flue gas is instantaneously cooled in the condenser, wherein the water vapor is condensed into liquid water, and the volatile organic components are converted into powder materials; collecting the powder materials together with the mixed powder of step (4);

[0016] (6) Water smoke self-purification: recycling the liquid water obtained from the condenser and adding it to the solid waste mixture for secondary circulation; passing the gas discharged from the condenser to the mud stirring barrel for self-purification, and realizing ultra-low emission of waste gas after further reaction and absorption with the solid waste mixed liquid slurry;

[0017] (7) High-temperature calcination: high-temperature calcining the mixed powder of step (4) and the powder material of step (5) to produce building material products.

[0018] The fly ash and the bottom slag mixture is any mixture of fly ash and bottom slag, and the two are not limited in proportion.

[0019] The building material product can be sintered brick, ceramic tile, etc.

[0020] The high temperature generated by ball milling and the high temperature of the spray drying tower make the organic matter in the solid waste volatilize, and the heavy metals are solidified in the final product after high-temperature calcination, so as to achieve the purpose of removing the organic matter in the fly ash and the bottom slag and solidifying the heavy metals. At the same time, all the flue gas generated in the treatment process is subjected to condensation treatment, the separated harmful gas mainly acidic gas is sent to the mud stirring barrel to be reacted and absorbed by the alkaline substances in the liquid-solid waste mixed liquid slurry, realizing self-purification treatment of waste gas, without the need of additional use of high-cost adsorbent, achieving the effect of ultra-low emission of waste gas; the waste water generated by flue gas condensation provides the water source required for wet ball milling of the ball mill, and then realizes self-purification of waste water; the organic components not easy to volatilize in the flue gas are collected together with the mixed powder obtained by ball milling, and then can be subjected to high-temperature calcination to make sintered brick, ceramic tile, etc. to realize resource utilization, so as to achieve self-purification of solid waste. Therefore, compared with the prior art, the present application realizes self-purification treatment of waste gas, waste water and solid waste without secondary pollution risk.

[0021] Furthermore, the fly ash and the bottom slag mixture and the alkaline waste mineral are subjected to ball milling in the present application, so that the particle size is uniform, and thus the carbon content is basically consistent, ensuring the quality stability of the building material product.

[0022] Preferably, the alkaline waste mineral is contaminated soil and shale containing alkaline pollutants. The alkaline pollutants can react with the harmful gas in the flue gas to generate stable salts and solidify in the final product, realizing harmless treatment. The present application does not have specific limitation on the types of the alkaline pollutants, and the alkaline substances can achieve the purpose of the present application, such as the common alkaline pollutants in soil including carbonate and bicarbonate.

[0023] Preferably, in step (1), the addition amount of the fly ash and the bottom slag mixture is 40-60 parts by mass, the addition amount of the contaminated soil containing alkaline pollutants is 30-40 parts by mass, and the addition amount of the shale containing alkaline pollutants is 10-20 parts by mass.

[0024] Preferably, in step (2), the ball milling time is 6-8 h, so that the particle size of the solid waste mixed liquid slurry is 0.01-0.05 mm, which is beneficial to the production of building material products such as sintered brick and ceramic tile; and the ball milling time balances the energy consumption and production efficiency. The preferred ball-to-material ratio of the ball milling is 0.8-1.0.

[0025] Preferably, 20% of the mass of the solid waste mixture is added with water when the ball milling is first performed, and the liquid water obtained from the condenser is subsequently returned to the solid waste mixture without additional water.

[0026] Preferably, in step (4), the temperature of the spray drying tower is 700-800℃, and the humidity of the mixed powder is controlled at 6-8%.

[0027] Preferably, the temperature of the high-temperature calcination is ≥1200℃.

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] 1. Comprehensive treatment and recycling: The present application realizes the comprehensive treatment of fly ash and bottom slag generated by coal-fired power plants and other waste, forms a closed-loop recycling system, and achieves self-purification of solid waste.

[0030] 2. Self-purification mechanism: Through the recycling of condensate water and waste gas during the treatment process, the waste gas and wastewater during the treatment process are self-purified, reducing the dependence on external water sources and energy, and avoiding the use of high-cost waste gas adsorbents.

[0031] 3. Improve resource utilization: By optimizing the treatment process, the resource utilization rate of fly ash and bottom slag is improved, and silicates and aluminates in them can be directly used for building material products, reducing resource waste; and the present application uniformly controls the particle size and carbon content of the solid waste mixture through ball milling, ensuring that the quality of the building material products is stable and meets the building material industry standards.

[0032] 4. Reduce environmental impact: Based on the present application, self-purification treatment of waste gas, wastewater, and solid waste is realized, solving the problems of dust emission and wastewater treatment during the resource treatment of fly ash and bottom slag, reducing the negative impact of fly ash and bottom slag and the waste gas, solid waste, and wastewater generated during the treatment on the environment, and there is no secondary pollution; specifically, the organic components of the waste gas are recovered by calcination, and the wastewater is recycled, reducing resource waste by more than 90%, and the concentrations of particulate matter, nitrogen oxides, and SO2 in the emitted waste gas are all lower than the national standards. DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] Example 1:

[0035] The fly ash and slag mixture generated by the coal-fired power plant is mixed with the contaminated soil containing alkaline pollutants and shale at a mass ratio of 6:3:1 by a feeder, and then is transported to a wet ball mill to be ball milled at a ball-to-material ratio of 1.0 for 8 hours, to obtain a solid waste mixed liquid slurry; wherein 20% of the water of the solid waste mixture is added when the ball milling is first performed;

[0036] After the solid waste mixed liquid slurry is stirred by a mud stirring barrel, it is transported to a spray drying tower for drying, wherein the temperature in the tower is 800°C, to obtain a mixed powder;

[0037] The generated flue gas is further de-dusted by a bag filter, rapidly cooled by a condenser to remove part of the harmful gases that are soluble in water, and the water vapor in the flue gas changes into liquid water in the condensation process. This part of water is sent to the wet ball mill for co-disposal with the solid waste in the ball mill, and then is mixed into the mud stirring barrel for the next cycle of treatment. The harmful gases in the flue gas that are not soluble in water (mainly acidic gases) are discharged through the exhaust port of the mud stirring barrel, and are neutralized by reacting with the solid waste mixed liquid slurry to achieve self-purification. The non-volatile organic components in the flue gas are all converted into powder materials by the bag filter, which are transported together with the aforementioned mixed powder by a conveyor to a powder storage bin, and then are compacted by a dry powder press and calcined at 1200°C by a roller kiln to realize resource utilization and produce sintered bricks.

[0038] Through the above steps, the self-purification of waste gas, waste water and solid waste during the treatment of fly ash and slag is realized.

[0039] The concentrations of pollutants such as particulate matter, nitrogen oxides and acidic gases in the treated waste gas all meet the ultra-low emission standard, and the pollutant concentrations at the exhaust port meet the environmental protection requirements. The specific data are as follows: the concentration of organized particulate matter is reduced to 19.45 mg / m 3 , which is lower than the national ultra-low emission standard of 30 mg / m 3 ; the concentration of unorganized particulate matter is 0.13 mg / m 3 , which is lower than the national ultra-low emission standard of 1 mg / m 3 ; the concentration of nitrogen oxides is reduced to 188.46 mg / m 3 , which is lower than the national ultra-low emission standard of 240 mg / m 3 ; and the concentration of acidic gases (calculated as SO2) is reduced to 89.63 mg / m 3 , which is lower than the national ultra-low emission standard of 100 mg / m 3 .

[0040] The content of pollutants in the fly ash and slag mixture before and after treatment changed significantly, specifically: the polycyclic aromatic hydrocarbon naphthalene was 254.38 mg / kg before treatment and 0.18 mg / kg after treatment; the benzo[a]pyrene was 4.8 mg / kg before treatment and not detected after treatment; the benzo[a] anthracene was 24.6 mg / kg before treatment and not detected after treatment. The heavy metal arsenic was 68.48 mg / kg before treatment and the leaching concentration was 0.35 mg / L after treatment; the cadmium was 86.57 mg / kg before treatment and the leaching concentration was 0.57 mg / L after treatment.

[0041] Example 2:

[0042] The fly ash and slag mixture generated by the coal-fired power plant and the polluted soil containing alkaline pollutants and shale were mixed by a feeder in a mass ratio of 5:3:2 and then conveyed to a wet ball mill to be ball-milled for 8 hours at a ball-to-material ratio of 1.0 to obtain a solid waste mixed liquid slurry; wherein, 20% of water of the mass of the solid waste mixture was additionally added when the ball-milling was first performed;

[0043] The solid waste mixed liquid slurry was stirred by a mud slurry stirring barrel and then conveyed to a spray drying tower for drying, wherein the temperature in the tower was 800°C, to obtain a mixed powder;

[0044] The generated flue gas was further dedusted by a bag filter and then rapidly cooled by a condenser to take away part of the harmful gases that were soluble in water, and the water vapor in the flue gas would become liquid water in the condensation process. This part of water was sent to the wet ball mill for co-disposal with the solid waste in the ball mill and then mixed into the mud slurry stirring barrel to continue the next cycle of treatment. The harmful gases (mainly acidic gases) that were not soluble in water in the flue gas were led to the mud slurry stirring barrel to react with the solid waste mixed liquid slurry to achieve self-purification, and then discharged through the exhaust port of the mud slurry stirring barrel. The non-volatile organic components in the flue gas were all converted into powder materials by the condenser, which were conveyed together with the aforementioned mixed powder by a conveyor to a powder storage bin, compacted by a dry powder press, and then calcined at a high temperature of 1400°C by a roller kiln to realize resource utilization and produce sintered bricks;

[0045] Through the above steps, the self-purification of waste gas, waste water and solid waste in the process of treating fly ash and slag was realized.

[0046] The concentrations of pollutants such as particulate matter, nitrogen oxides and acidic gases in the treated flue gas all reached the ultra-low emission standard, and the pollutant concentrations at the emission port met the environmental protection requirements. The specific data are as follows: the concentration of organized particulate matter was reduced to 12.28 mg / m 3 , which was lower than the national ultra-low emission standard of 30 mg / m 3 ; the concentration of unorganized particulate matter was 0.15 mg / m 3 , which was lower than the national standard of 1 mg / m 3ultra-low emission standard; the concentration of nitrogen oxide emission is reduced to 196.44 mg / m 3 , lower than the national ultra-low emission standard of 240 mg / m 3 ; the concentration of acid gas (calculated as SO2) emission is reduced to 86.43 mg / m 3 , lower than the national ultra-low emission standard of 100 mg / m 3 .

[0047] The content of pollutants in the fly ash and slag mixture before and after treatment changes significantly, specifically: the content of naphthalene is 184.38 mg / kg before treatment and not detected after treatment; the content of benzo[a]pyrene is 4.2 mg / kg before treatment and not detected after treatment; the content of benzo[a]anthracene is 21.4 mg / kg before treatment and not detected after treatment. The content of arsenic is 68.48 mg / kg before treatment and the leaching concentration is 0.78 mg / L after treatment; the content of cadmium is 86.57 mg / kg before treatment and the leaching concentration is 0.49 mg / L after treatment.

[0048] Example 3

[0049] The fly ash and slag mixture generated by the coal-fired power plant and the contaminated soil containing alkaline pollutants and shale are mixed by a feeder in a mass ratio of 6:2:2 and then conveyed to a wet ball mill to be ball milled for 8 h at a ball-to-material ratio of 0.8 to obtain a solid waste mixed liquid slurry; wherein, 20% of water of the mass of the solid waste mixture is additionally added when the ball milling is first performed;

[0050] The solid waste mixed liquid slurry is stirred by a mud stirring barrel and then conveyed to a spray drying tower for drying, wherein the temperature in the tower is 800℃, to obtain a mixed powder;

[0051] The generated flue gas is further de-dusted by a bag filter and then rapidly cooled by a condenser to take away part of the harmful gases that are soluble in water, and the water vapor in the flue gas will become liquid water in the condensation process. This part of water is sent to the wet ball mill for co-disposal with the solid waste in the ball mill and then mixed into the mud stirring barrel to continue the next cycle of treatment. The harmful gases (mainly acid gases) that are not soluble in water in the flue gas are led to the mud stirring barrel to react with the solid waste mixed liquid slurry to achieve self-purification, and then discharged through the exhaust port of the mud stirring barrel. The non-volatile organic components in the flue gas are all converted into powder materials by the condenser, which are conveyed together with the aforementioned mixed powder by a conveyor to a powder storage bin, compacted by a dry powder press, and then calcined at a high temperature of 1200℃ by a roller kiln to realize resource utilization and produce sintered bricks;

[0052] The above steps realize the self-purification of waste gas, waste water and solid waste in the process of treating fly ash and slag.

[0053] The concentrations of pollutants such as particulate matter, nitrogen oxides, acid gases and the like in the treated flue gas all reach the ultra-low emission standard, and the pollutant concentrations at the emission port meet the environmental protection requirements, with the specific data as follows: the organized particulate matter concentration is reduced to 18.48 mg / m 3 , which is lower than the national ultra-low emission standard of 30 mg / m 3 ; the unorganized particulate matter concentration is 0.18 mg / m 3 , which is lower than the national ultra-low emission standard of 1 mg / m 3 ; the nitrogen oxide emission concentration is reduced to 168.26 mg / m 3 , which is lower than the national ultra-low emission standard of 240 mg / m 3 ; and the acid gas (calculated based on SO2) emission concentration is reduced to 72.93 mg / m 3 , which is lower than the national ultra-low emission standard of 100 mg / m 3 .

[0054] The pollutant contents in the mixture of fly ash and slag before and after treatment change significantly, wherein the naphthalene content is 196.32 mg / kg before treatment and 0.12 mg / kg after treatment; the benzo[a]pyrene content is 6.8 mg / kg before treatment and not detected after treatment; the benzo[a]anthracene content is 28.9 mg / kg before treatment and not detected after treatment; the arsenic content is 68.48 mg / kg before treatment and the leaching concentration is 0.55 mg / L after treatment; and the cadmium content is 86.57 mg / kg before treatment and the leaching concentration is 0.39 mg / L after treatment.

Claims

1. A self-purification treatment method for fly ash and bottom ash generated in a coal-fired power plant, characterized in that, Includes the following steps: (1) Solid waste mixing: The solid waste mixture obtained by mixing fly ash and bottom ash produced by coal-fired power plants with alkaline waste minerals through a feeder is then transported to a wet ball mill. (2) Ball milling treatment: Water is added to the solid waste mixture obtained in step (1), and ball milling is carried out using a wet ball mill to form a solid waste mixed liquid slurry; (3) Conveying and mixing: The solid waste mixed liquid slurry is conveyed to the mud mixing tank for mixing and stirring, and during the mixing process, it is conveyed to the spray drying tower by the mud pump; (4) Spray drying: The solid waste mixed liquid slurry is fully spray dried in a spray drying tower by a high-temperature hot air furnace to obtain a mixed powder; (5) Flue gas dust removal and condensation cooling: Use a bag filter to remove dust from the flue gas generated during the drying process in the spray drying tower; Then, the flue gas after dust removal is introduced into the condenser. The flue gas is cooled down instantly in the condenser, and the water vapor in it is condensed into liquid water. The organic components that are not easily volatilized are converted into powder materials. The powder materials are collected together with the mixed powder from step (4). (6) Water fume self-purification: The liquid water obtained from the condenser is recovered and added to the solid waste mixture for ball milling and secondary recycling; the gas discharged from the condenser is passed to the mud mixing tank for self-purification, and further reacted and absorbed with the solid waste mixed liquid slurry to achieve ultra-low emissions of waste gas. (7) High-temperature calcination: The mixed powder from step (4) and the powder material from step (5) are calcined together at high temperature to produce building material products.

2. The self-purification treatment method for fly ash and bottom ash generated in coal-fired power plants according to claim 1, characterized in that, The alkaline waste minerals are contaminated soil and shale containing alkaline pollutants.

3. The self-purification treatment method for fly ash and bottom ash generated in coal-fired power plants according to claim 2, characterized in that, In step (1), the amount of fly ash and bottom ash mixture added is 40 to 60 parts by mass, the amount of contaminated soil containing alkaline pollutants added is 30 to 40 parts by mass, and the amount of shale containing alkaline pollutants added is 10 to 20 parts by mass.

4. The self-purification treatment method for fly ash and bottom ash generated in coal-fired power plants according to claim 3, characterized in that, In step (2), the ball milling time is 6 to 8 hours and the ball-to-material ratio is 0.8 to 1.

0.

5. The self-purification treatment method for fly ash and bottom ash generated in coal-fired power plants according to claim 4, characterized in that, During the initial ball milling, 20% of the solid waste mixture by mass of water is added. Subsequently, the liquid water obtained from the condenser is returned to the solid waste mixture without adding any additional water.

6. The self-purification treatment method for fly ash and bottom ash generated in coal-fired power plants according to claim 5, characterized in that, In step (4), the temperature of the spray drying tower is 700-800°C, and the humidity of the mixed powder is controlled at 6-8%.

7. The self-purification treatment method for fly ash and bottom ash generated in coal-fired power plants according to claim 6, characterized in that, The high-temperature calcination temperature is ≥1200℃.