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Complex technology of processing fly ash of thermal power station
    Integrated processing technology of dry fly ash

On the possible disposal of ash ash, is collected in cyclones and electrostatic precipitators with burning coals, wrote a huge amount of material. The problem noticed half a century ago. During this time, the city, especially the mega-cities in Siberia, have been inundated with waste, the main part of which are ash. However, significant results were achieved.

One of the main reasons for this - heterogeneity and instability of the produced ash that does not provide a reliable beneficial effect at its disposal in the construction industry - the main potential customers. Processing a huge amount of ash produced around megacities with known technology - the classifiers and mills, given the low consumer price and the strong discrepancy in the dates of production and consumption, is guaranteed to be unprofitable production.

Fly ash - a scarce commodity

Incomplete consumption of manufactured ash gives the energy sector alone problem, because in this case, you have two ash disposal system. Removal of ash and dump the contents were used approximately 30% of the cost of energy and heat CHP. However, given the market value of the lost ground near the mega-cities, reduce the cost of land and property at a considerable distance from the stations and ash dumps, direct damage to human health and nature, in particular the pollution of air with dust and soluble salts and alkaline water and underground water, the proportion actually should be much higher.

Fly ash in developed countries is a commodity, with the deficit, as heat and electricity. High-quality fly ash, conforming to the standards and suitable for use in concrete as an additive, linking excess of lime and reduces water demand, costs, for example, in the U.S. on a par with Portland cement ~ $ 60/t.

The idea of exports to the U.S. recycled coal ash may be reasonable. Poor-quality fly ash, such as low-temperature "clean" fluidized bed boilers, which burn low-quality coal with high sulfur content (Zeran station in Warsaw), is proposed for the negative value of about -5 $ / ton, provided that the consumer takes it all. A similar situation in Australia. Thus, the processing of fly ash can be profitable only if, thanks to technology, a number of higher-quality products that consumers will find the full or nearly full in a limited area near the site of production. In standard use of ash ash as an additive to concrete or building ceramics problem can not be solved fundamentally due to the limited capacity of the local market. Moreover, addition of fly ash in concrete unstable composition is possible without loss of quality only in very limited quantities, making meaningless the whole idea.

Prospects processing

From a chemical point of view not to use ash ash - is absurd. We can distinguish at least 3 types of advanced processing evils:

1) fly ash from the burning of brown coal (Booze), such as the Kansk-Achinsk coal basin, with a high content of oxide and calcium sulfate, ie, close in composition to Portland cement and high chemical potential - stored energy;

2) acid ash from the burning coals (Coos), consisting mainly of glass, including microspheres;

3) ash with high content of rare earth elements.

It should be noted that in nature there are no two identical coal, so there is no similar evils. It should always go for the local processing technologies ash entrainment in a particular region, because the main consumers should be located near the source of ash. Any technology will be the most remarkable only in that case, if the local market will be able to "swallow" all or almost all the mass of processed ash.

For complex processing of ash carryover proposed to use the possibility of a new class of technology - the so-called electromassclassifier (EMC). This technique is based on the recently discovered a new phenomenon - the formation in rotating turbulent flows of dense gas of charged aerosols (gas-dust plasma) and their division in the internal electric fields.

The phenomenon tribo charging particles friction or shock is known to mankind since time immemorial, but so far science is unable to predict even the sign of the charge.

Benefits of EHR

Despite limiting the complexity of the phenomenon, Technology EMC looks very simple and has advantages for all parameters on conventional air separator or jet mill, disintegrator.

One major advantage - a full environmental friendliness, because the processes are carried out in a closed volume, ie, EMC does not require any additional devices such as compressors or dust collection systems - cyclones or filters, even when working with nanopowders. Fine fraction of aerosol loaded with a single sign, the aerosol is removed from the Coulomb force through the center, against the force of viscosity Stokes and centrifugal force. The particles are discharged on the walls of the cell capture or via charged ions in the atmosphere, and the charge is returned to the chamber aerosol generation.

Thus, in the technique of EMC, the process of separation of powders on an unlimited number of fractions with the circulation of the charge. In the separation of inhomogeneous systems, including fly ash, a separation not only particle size but also on other physical characteristics.

Another important advantage of EMC - the opportunity to realize simultaneously a number of different operations in one pass (eg, separation from mechanical activation or grinding), both in continuous and a discrete version. The huge mass of ash with high content of fine particles is not possible to separate the known technique, because it is inefficient dust collection of fine particles having the highest value and simultaneously representing the greatest danger to humans and the environment.

Select from the ashes of ash fine fraction in the EHR enables efficient continuous separation of a large fraction of other parameters such as particle size, the magnetic susceptibility, density, particle shape, electrical properties. The range of performance techniques EMC is unique: from the portion of 1 gram to 10 tons / hour of continuous operation with a rotor diameter of not more than 1,5 m. The range of dispersion of the separated material is also wide: from hundreds of microns up to ~ 0.03 m - EMC also far exceeds all known types of techniques, approaching the wet separation using centrifuges.

Processing technologies ash

Features EMC providing a flexible "smart technology" recycling of ash with a focus on market potential of its individual components. A detailed examination of the various evils of ablation, including the TEC-3 and HPS-5 Novosibirsk, allowed the development of optimal schemes of their processing and manufacturing technology to offer construction materials to recycling of the bulk product from the ashes.

Booze, obtained in particular at the CHP-3, consists mainly of glass spherical particles with the variation of calcium and iron. These particles possess astringent properties and reaction with water, slower than Portland cement, but form a cement stone. But along with them there are particles of unburned carbon in the form of coke, the contents of which can reach up to 7%, grains of calcium oxide CaO (5 30%) and calcium sulfate CaSO4 (5 15%), covered with glass, inactive minerals - quartz and magnetite. Cox has a uniquely negative effect on the strength of stone, such macropores.

But the most negative role played by grain CaO, especially large ones. These grains react with water with a significant increase in volume and markedly slower than the main mass of ash, including for the encapsulation of glass.

Effect of large CaO particles can be compared with a time bomb. The strength of the stone on the basis of the ash is usually low and averages about 10 MPa (100 kg/cm2), but due to the unstable composition varies from 0 to 30 MPa. Consumer value is the lower boundary, ie, zero. For the selection of a suitable composition of ash is required express analysis, which requires an expensive spectrometer. The selection for the utilization of only a part of ash does not represent any interest either.

Mechanical treatment of fly ash on EMC in the mode of mechanical activation of the surface of the particles with simultaneous separation of approximately 50% of the fine fraction less than 60 microns solve these problems.

Optimum shelf life of activated fine fraction of ash with an additional increase in the strength of stone at ~ 5 MPa is 1 5 days, after which the cracks are closed with a fall in activity below the original.

This feature requires the processing of ash binder ash mainly by consumers themselves. The strength of rock under optimal conditions of activation and storage is no longer falls below 10 MPa and with small additions of cement, about 10%, and calcium chloride CaCl2 about 1% (so-called. Winter supplement, activating the reaction with small grains of sand) ash binder becomes full, but cheap material for the preparation sanforized concrete M100-M300.

Make determined by the strength of concrete after 28 days of exposure, but the concrete with ash binder is gaining strength and further increasing it to 2 3 times (in the usual concrete - only 30%). A large fraction can be easily recycled: the separation of particle size or triboelectric separator provides a large fraction of coke, which can be returned back to the boiler on a magnetic separator separates fraction of spherical particles of magnetite that can be used, for example, as a special pigment. Balance after mixing with water for 1 2 weeks is a plaster or mortar.

Concrete from the fly ash

The figure shows the strength of stone with various ratios of cement and ash binder. Can be divided into 3 areas: concrete is not a high mark on the basis of ash binder with small additions of cement, normal concrete with small addition of 10 20% ash binder, and the concrete maximum strength with the addition of ash binder 25 50%. If you use the ash binder as an additive, then the entire market in the metropolis will be able to consume only a small share of the ash.

Manufacture of concrete with high fly ash binder to 50%, despite the attraction is a high risk zone. This is due to the fact that the proportion of calcium sulfate CaSO4 in the ash varies between 5 and its high content may lead to the formation of ettringita for reaction with alumina cement component with a large increase after the formation of solid rock. In this regard, education ettringita plague called for concrete.

Relatively easy to find the application nizkomarochnomu concrete. In this case, the maximum amount of ash binder, for example, from the ashes of CHP-3 will be 60 thousand tons per year, from which you can make 200 thousand cubic meters. m of concrete. It will be sufficient for the construction of 3000 low-rise individual houses, or to cover 200 km of local roads width of 8 m. The ash can be stored in dry conditions indefinitely, so the mismatch in the timing of production and consumption does not affect the quality of the processing of ash at the site.

Treatment of acid Coos, representing mostly glass spherical particles, including hollow microspheres, and the remnants of unburned carbon in the form of coke to 5% is also easily implemented using EMC technology. Y microspheres, constituting about 5% of ash, there are many special applications, up to the medicine.

The main consumers of Coos, in addition to manufacturers of concrete, are brick factories. Unfortunately, the clay in Russia are generally thin and the ashes of additives are not necessary. The potential capacity of the regional market for products from Coos still several times lower than the volume of ash produced. Option export to developed countries of products from the ashes should count.

In Britain, low-grade waste lay in road foundations. Up to 10 20% generated Koos can be disposed of with advantage as flokkulyanta in production gruntoblokov with organized construction of a semi-ekoposelkah individual low-rise housing. The holistic concept of affordable luxury housing on the basis of local resources and wastes described in the "low-rise New Russia" and is available on the Internet. In general, Koos market should be formed within a few years if the investment.

What is recycling?

Unfortunately, as the construction of roads and construction of individual land tenure through a totally dependent on the officials. These areas are traditionally the least transparent, that promotes corruption. Innovations in these areas really are not possible without the political will of the authorities.

Loss-use of coal is particularly beneficial to the state from a strategic point of view, since at no additional cost to double production of binders and besides the expense of coal greatly reduce the consumption of gas within the country, which will increase its sales abroad. Production of alternative binders based on fly ash will ensure competition in the concrete is not a high mark.
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