Our country is a large coal-producing country, using coal as the basic fuel for electricity production. In recent years, my country's energy industry has developed steadily, with an annual growth rate of power generation capacity of 7.3%. The rapid development of the power industry has brought about a sharp increase in fly ash emissions. The total amount of fly ash emitted by coal-fired thermal power plants has increased year by year. Increased, fly ash emissions reached 125 million tons in 1995, about 150 million tons in 2000, and will reach 200 million tons in 2010, causing huge pressure on my country's national economic construction and ecological environment. On the other hand, our country is a country with limited resource reserves per capita. The comprehensive utilization of fly ash, turning waste into treasure and harm into benefit, has become an important technical and economic policy in our country's economic construction and is a solution to our country's economic construction. Electric power production is an important means of solving the contradiction between environmental pollution and resource shortage. It is also one of the tasks faced by electric power production. After development, fly ash has been widely used in construction, building materials, water conservancy and other departments.
In the 1970s, the global energy crisis, environmental pollution and depletion of mineral resources strongly inspired the research and development of fly ash utilization. Many international fly ash conferences were held, and research work It is becoming more and more in-depth and its application has also made great progress. Fly ash has become an eye-catching emerging building material raw material and chemical product raw material in the international market that is rich in resources, low in price, and brings benefits and eliminates harm, and is favored by people. At present, most of the research work on fly ash has shifted from theoretical research to applied research, especially the research and development and utilization of important resources. The products produced using fly ash are constantly increasing, and the technology is constantly being updated. Compared with the past, the comprehensive utilization of fly ash at home and abroad has undergone major changes, mainly as follows: the guiding ideology of fly ash management has changed from a simple environmental perspective in the past to comprehensive management and resource utilization; the comprehensive utilization of fly ash The methods of utilization have evolved from the past applications in roadbed, fill, concrete admixtures, soil modification, etc. to the current applications in cement raw materials, cement admixtures, large water conservancy project projects, pumped concrete, and large-volume concrete products. , advanced fillers and other advanced utilization methods.
Advantages of using fly ash
Adding fly ash into concrete saves a lot of cement and fine aggregate; reduces water consumption; improves the consistency of the concrete mixture workability; enhance the pumpability of concrete; reduce the creep of concrete; reduce the heat of hydration and thermal expansion; improve the impermeability of concrete; and increase the surface finish of concrete.
Use of fly ash
National Standard Level 1: The new modern concrete technology that uses the composite technology of high-quality fly ash and high-efficiency water-reducing agent to produce high-grade concrete is developing rapidly across the country.
National Standard Level 2: High-quality fly ash is especially suitable for preparing pumped concrete, large-volume concrete, impermeable structural concrete, sulfate-resistant concrete and soft water erosion-resistant concrete as well as underground and underwater engineering concrete, pressure Slurry concrete and roller compacted concrete.
National Standard Level 3: Fly ash concrete has the advantages of good workability, strong pumpability, improved finishing, improved impact resistance, and enhanced frost resistance.
Fly ash is a volcanic ash-like mixed material formed after high-temperature combustion of pulverized coal. It is a coal-burning power plant that grinds coal into pulverized coal below 100 microns, sprays preheated air into the furnace to burn in a suspended state, and produces high-temperature flue gas mixed with a large amount of incombustibles, which is collected by a dust collection device. fly ash. The chemical composition of fly ash is similar to that of clay, and its main components are silica, aluminum oxide, iron oxide, calcium oxide and unburned carbon. At present, fly ash is mainly used to produce fly ash cement, fly ash bricks, fly ash silicate blocks, fly ash aerated concrete and other building materials. It can also be used as agricultural fertilizer and soil conditioner. Recycling industrial raw materials and making environmental materials.
Application of fly ash in the cement industry and concrete engineering: Fly ash replaces clay raw materials to produce cement. It is a hydraulic cementitious material made by grinding Portland cement clinker and fly ash with an appropriate amount of gypsum. It is used in the cement industry The unburned carbon in fly ash can be used as ingredients; fly ash can be used as cement mixture; fly ash can produce low-temperature synthetic cement. The production principle is to steam curing the batch materials to generate hydrates, and then undergo dehydration and low-temperature solid phase reaction. Form cement minerals; fly ash makes clinker-free cement, including lime fly ash cement and pure fly ash cement. Lime fly ash cement is made by mixing dry fly ash with 10%-30% quicklime or slaked lime and A hydraulic cementitious material made by mixing and grinding a small amount of gypsum, or grinding them separately and then mixing them uniformly; fly ash is used as an admixture for mortar or concrete, and fly ash is added to concrete to replace part of the cement or fine aggregate. , can not only reduce costs, but also improve the workability of concrete, improve water impermeability, gas resistance, sulfate resistance and chemical corrosion resistance, reduce the heat of hydration, improve the high temperature resistance of concrete, and reduce particle separation and water precipitation. phenomenon, reduce the shrinkage and cracking of concrete and inhibit the corrosion of steel bars in concrete by stray current. Application of fly ash in building products: Steamed fly ash bricks use power plant fly ash and quicklime or other alkaline activators as the main raw materials. An appropriate amount of gypsum can also be added, and a certain amount of cinder or water can be added. A wall material formed from aggregates such as quenched slag, processed, stirred, digested, rolled, pressed, and cured with normal or high-pressure steam; sintered fly ash bricks are made from fly ash, clay and other industrial Waste materials are used as raw materials, which are processed, stirred, formed, dried and fired into bricks; foamed fly ash insulation bricks are produced by autoclaving, using fly ash as the main raw material, adding a certain amount of lime and foaming agent, and after batching, A new type of insulating brick made by stirring, injection molding and autoclaving; fly ash silicate block, using fly ash, lime, gypsum as cementing materials, cinder, blast furnace slag, etc. as aggregates, mixed with water , wall materials made by vibration molding and steam curing; fly ash aerated concrete is made of fly ash as raw material, adding appropriate amounts of quicklime, cement, gypsum and aluminum powder, adding water to stir to form a slurry, and pouring into the mold to steam curing. A porous lightweight building material; fly ash ceramsite is an artificial lightweight bone made from fly ash as the main raw material, mixed with a small amount of binder and solid fuel, mixed, pelletized, and fired at high temperature. Material; fly ash lightweight heat-resistant insulation bricks are made of fly ash, burnt stone, soft soil and wood chips. They have high thermal insulation efficiency, high refractoriness, low thermal conductivity, and can reduce the thickness of the furnace wall. , shorten the firing time, reduce fuel consumption, improve thermal efficiency and reduce costs. Fly ash is used as agricultural fertilizer and soil conditioner: fly ash has good physical and chemical properties and can be widely used to transform heavy clay, raw soil, acidic soil and saline-alkali soil to make up for its shortcomings of acidity, thinness and stickiness. It contains a large amount of citrus-soluble silicon, calcium, magnesium, phosphorus and other nutrients necessary for crops, so it can be used as agricultural fertilizer. Recycling industrial raw materials: Recovering coal resources, using flotation method to add flotation reagents to the slurry water containing coal fly ash, and then using air flotation technology to make the coal particles adhere to the air bubbles and float up to separate from the ash; recovery of metallic material pulverized coal The ash contains Fe2O3, Al2O3, and a large amount of rare metals; the hollow microspheres are sorted. The hollow microspheres have small mass, high strength, high temperature resistance and good insulation. They can be used as ideal fillers for plastics and for lightweight refractory materials and High-efficiency thermal insulation materials, used in the petrochemical industry, military industry, and tank brakes. As environmentally friendly materials: Fly ash can be used to make environmentally friendly materials such as molecular sieves, flocculants and adsorbent materials; fly ash can also be used to treat fluorine-containing wastewater, electroplating wastewater, heavy metal-containing wastewater and oily wastewater. The Al2O3 contained in fly ash , CaO and other active components, which can produce complexes with fluorine or colloidal ions that have a flocculating effect on fluorine. It also contains zeolite, mullite, carbon particles and silica gel, etc., and has inorganic ion exchange characteristics and adsorption and decolorization effects.