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Use of ash and slag waste from thermal power plants. Use of ash and slag waste from thermal power plants in construction Wood ash as a raw material for production

Everyone knows that one of the most universal and ancient fertilizers is wood ash. It not only fertilizes and alkalizes the soil, but creates favorable conditions for the life of soil microorganisms, especially nitrogen-fixing bacteria. It also increases the vitality of plants. It has a more favorable effect on the harvest and its quality than industrial ones. potash fertilizers, since it contains almost no chlorine.

The Technoservice company was able to organize the production of deep recycling of bark and wood waste, and, as a result, received an environmentally friendly complex fertilizer with prolonged action - granulated wood ash (GWA).

Main advantages of DZG:

An attractive feature of this product is its new granular format. The size of the granules ranges from 2 to 4 mm, convenient for packaging and transportation, it is easy to transport by any type of transport in containers or bags, and it is convenient to apply to the soil by any type of equipment. The granular format contributes to more favorable working conditions for staff.
Handling and applying pulverized ash is a very complex process. To reduce dust levels when applying agricultural fertilizers, it is more effective to use granulated ash. Granulation facilitates the process of adding ash, and also slows down the process of dissolving ash in the soil. Slow solubility is an advantage because cropland is not subject to the shock associated with changes in acidity and nutrient conditions.
Adding granulated wood ash is the most effective way to combat soil acidification. In addition, the soil structure is restored - it becomes loose.
Granulated wood ash contains everything, except nitrogen, that is essential for plants. DZG practically does not contain chlorine, so it is good to use for plants that react negatively to this chemical element.
Granulated wood ash is stored and stored indefinitely in standard dry warehouses for storing mineral fertilizers with natural humidity and air ventilation.

Investment in land

Ash fertilizers from Technoservice are the best investment in your land. Granulated wood ash is an effective, environmentally friendly and income-generating element for a responsible farmer.

By introducing DZG, you guarantee an increase in the value of your land and its preservation for future generations. This way, you can benefit from your soil as a long-term investment. Thanks to a successful choice of object, even unprofitable land will turn into a part of the farm property completely covered with crops. Natural proportions nutrients, long duration of exposure, slow solubility and uniform distribution make DZG Tekhnoservice LLC an excellent solution both for agriculture and from an environmental point of view!

DZG - to increase productivity!

During field research, in accordance with developed in Leningrad region program carried out in 2008-2011. on acidic soddy-podzolic soil, taken out of agricultural use about 5 years earlier, the following conclusions were drawn:

Wood ash from boiler houses is suitable for increasing fertility and eliminating high acidity of soddy-podzolic soils.
A total increase in crop yield of 25-64% over 3 years of crop rotation was obtained due to just one measure: liming of slightly acidic soddy-podzolic soil with wood ash from boiler houses.
With complex soil cultivation together with mineral and organic fertilizers, significantly higher yields can be achieved.
It is recommended to use wood ash from boiler houses as a chemical ameliorant when carrying out periodic and maintenance liming of acidic soddy-podzolic soils.

According to the All-Russian Scientific Research Institute of Agrochemistry D.N. Pryanishnikov, DZG can be used as a mineral fertilizer with ameliorant properties for the main application to agricultural crops and ornamental plantings on acidic and slightly acidic soils in open and protected ground.

Approximate norms and timing of application in agricultural production:

all crops - main or pre-sowing application at the rate of 1.0-2.0 t/ha;
all crops - the main application (as an ameliorant to reduce soil acidity) at the rate of 7.0-15.0 t/ha with a frequency of 1 time in 5 years.

Approximate doses, timing and methods of applying agrochemicals on private farms:

vegetable, flower and ornamental, fruit and berry crops - applied during soil cultivation in autumn or spring or during sowing (planting) at the rate of 100-200 g/m2;
vegetable, flower and ornamental, fruit and berry crops - applied during soil cultivation in autumn or spring (as an ameliorant to reduce soil acidity) at the rate of 0.7-1.5 kg/m2 with a frequency of 1 time in 5 years.

G. Khabarovsk

During the activities of electric power industry enterprises, a lot of ash waste. The annual supply of ash to ash dumps in the Primorsky Territory is from 2.5 to 3.0 million tons per year, in the Khabarovsk Territory - up to 1.0 million tons (Fig. 1). Within the city of Khabarovsk alone, more than 16 million tons of ash are stored in ash dumps.

Ash and slag waste (ASW) can be used in the production of various concretes and mortars. Ceramics, thermal and waterproofing materials, road construction, where they can be used instead of sand and cement. Dry fly ash from electric precipitators at CHPP-3 is more widely used. But the use of such waste for economic purposes is still limited, including due to its toxicity. They accumulate a significant amount hazardous elements. The dumps are constantly dusty, the mobile forms of the elements are actively washed away by precipitation, polluting the air, water and soil. The use of such waste is one of the most current problems. This is possible by removing or extracting harmful and valuable components from the ash and using the remaining ash mass in the construction industry and fertilizer production.

Brief characteristics of ash and slag waste

At the examined thermal power plants, coal combustion occurs at a temperature of 1100-1600 C. When the organic part of coal is burned, volatile compounds are formed in the form of smoke and steam, and the non-combustible mineral part of the fuel is released in the form of solid focal residues, forming a dusty mass (ash), as well as lumps slags The amount of solid residues for hard and brown coals ranges from 15 to 40%. Coal is crushed before combustion and, for better combustion, a small (0.1-2%) amount of fuel oil is often added to it.
When pulverized fuel is burned, small and light ash particles are carried away by the flue gases, and they are called fly ash. The size of fly ash particles ranges from 3-5 to 100-150 microns. The amount of larger particles usually does not exceed 10-15%. Fly ash is collected by ash collectors. At CHPP-1 in Khabarovsk and Birobidzhan CHPP, ash collection is wet using scrubbers with Venturi pipes; at CHPP-3 and CHPP-2 in Vladivostok, ash collection is dry using electric precipitators.
Heavier ash particles settle on the underflow and fuse into lump slags, which are aggregated and fused ash particles ranging in size from 0.15 to 30 mm. The slag is crushed and removed with water. Fly ash and crushed slag are first removed separately, then mixed to form an ash and slag mixture.
In addition to ash and slag, the composition of the ash and slag mixture constantly contains particles of unburned fuel (underburning), the amount of which is 10-25%. The amount of fly ash, depending on the type of boiler, type of fuel and its combustion mode, can be 70-85% of the mass of the mixture, slag 10-20%. The ash and slag pulp is removed to the ash dump through pipelines.
During hydraulic transport and at the ash and slag dump, ash and slag interact with water and carbon dioxide in the air. Processes similar to diagenesis and lithification occur in them. They quickly erode and, when dried at a wind speed of 3 m/sec, begin to generate dust. The color of ZShO is dark gray, layered in cross-section, due to the alternation of different-grained puffs, as well as the deposition of white foam consisting of aluminosilicate hollow microspheres.
Average chemical composition The ASH of the surveyed CHPPs is given in Table 1 below.

Table 1

Limits of the average content of the main components of ASH

Component			Component
Component			Component
SiO2	51- 60	54,5		3,0 – 7,3
TiO2	0,5 – 0,9	0,75	Na2O	0,2 – 0,6	0,34
Al2O3	16-22	19,4	K2O	0,7 – 2,2	1,56
Fe2O3	5 -8		SO 3	0,09 – 0,2	0,14
	0,1 – 0,3	0,14	P2O5	0,1-0,4	0,24

Ashes from thermal power plants using hard coal, compared to ashes from thermal power plants using brown coal, are characterized by an increased content of SO3 and ppm, and a lower content of oxides of silicon, titanium, iron, magnesium, and sodium. Slags – high content of oxides of silicon, iron, magnesium, sodium and low content of oxides of sulfur, phosphorus, p.p.p. In general, the ashes are highly siliceous, with a fairly high content of aluminates.
The content of impurity elements in ASW according to spectral semi-quantitative analysis of ordinary and group samples is shown in Table 2. According to the reference book, gold and platinum are of industrial value, with Yb and Li approaching this in maximum values. The content of harmful and toxic elements does not exceed permissible values, although the maximum contents of Mn, Ni, V, Cr are close to the toxicity “threshold”.

table 2

Element	CHPP-1		CHPP-3			CHPP-1			CHPP-3
	Avg.	Max.	Avg.			Avg.	Max.		Avg.
Ni	40-80			60-80	Ba	1000	2000-3000		800-1000
Co		60- 1 00			Be
Ti	3000	6000	3000	6000	Y	10-80
V	60-100				Yb
Cr		300- 2000	40-80	100-600	La
Mo					Sr		600-800				300-1000
W					Ce
Nb					Sc
Zr	100-300	400-600		600-800	Li
Cu	30-80			80-100	B
Pb	10-30	60-100	30-60		K	8000		10000-30000		6000-8000		10000
Zn		80-200		1 00
Sn		3-40			Au	0,07	0,5-25,0		0,07		0,5-6,0
Ga	10-20				Pt mg/t	10-50	300-500

The composition of ASH includes crystalline, glassy and organic components.

Crystalline matter is represented by both primary minerals of the mineral substance of the fuel and new formations obtained during the combustion process and during hydration and weathering in the ash dump. In total, up to 150 minerals are found in the crystalline component of the ashes. The predominant minerals are meta- and orthosilicates, as well as aluminates, ferrites, aluminoferrites, spinels, dendritic clay minerals, oxides: quartz, tridymite, cristobalite, corundum, -alumina, oxides of calcium, magnesium and others. Often noted, but not large quantities, ore minerals - cassiterite, wolframite, stanine and others; sulfides - pyrite, pyrrhotite, arsenopyrite and others; sulfates, chlorides, very rarely fluorides. As a result of hydrochemical processes and weathering, secondary minerals appear in ash dumps - calcite, portlandite, iron hydroxides, zeolites and others. Of great interest are native elements and intermetallic compounds, among which are found: lead, silver, gold, platinum, aluminum, copper, mercury, iron, nickel iron, chromium ferrides, cuprous gold, various alloys of copper, nickel, chromium with silicon and others.

Finding droplet-liquid mercury, despite high temperature coal combustion is a fairly common occurrence, especially in the heavy fraction of enrichment products. This probably explains mercury contamination of soils when using ASW as a fertilizer without special purification.

The glassy substance, a product of incomplete transformations during combustion, makes up a significant part of the ash. It is represented by differently colored, predominantly black glass with a metallic sheen, various spherical glassy, mother-of-pearl microspheres (balls) and their aggregates. They make up the bulk of the slag component of the ashes. In composition they are oxides of aluminum, potassium, sodium and, to a lesser extent, calcium. These also include some products of heat treatment of clay minerals. Often microspheres are hollow inside and form foamy formations on the surface of ash dumps and settling ponds.

Organic matter is represented by unburned fuel particles (under-burn). Converted in the firebox organic matter very different from the original and is in the form of coke and semi-coke with very low hygroscopicity and volatile release. The amount of underburning in the studied ashes was 10-15%.

Valuable and useful components of AShO

Among the components of aluminosilicate, those of practical interest in the ash are iron-containing magnetic concentrate, secondary coal, aluminosilicate hollow microspheres and an inert mass of aluminosilicate composition, a heavy fraction containing an admixture of noble metals, rare and trace elements.

As a result of many years of research, positive results have been obtained for the extraction of valuable components from ash and slag waste (ASW) and their complete recycling (Fig. 2).

By creating a sequential technological chain of various instruments and equipment, secondary coal, iron-containing magnetic concentrate, heavy mineral fraction and inert mass can be obtained from ASW.

Secondary carbon. During a technological study using the flotation method, a coal concentrate was isolated, which we called secondary coal. It consists of particles of unburnt coal and products of its thermal processing - coke and semi-coke, and is characterized by increased calorific value(>5600 kcal) and ash content (up to 50-65%). After adding fuel oil, recycled coal can be burned at a thermal power plant, or by making briquettes from it, it can be sold to the population as fuel. It is extracted from the AShO by floatation. Yield up to 10-15% by weight of processed ASW. Coal particle sizes are 0-2 mm, less often up to 10 mm.

Iron-containing magnetic concentrate obtained from ash and slag waste consists of 70-95% spherical magnetic aggregates and scale. The remaining minerals (pyrrhotite, limonite, hematite, pyroxenes, chlorite, epidote) are present in quantities from single grains to 1-5% of the weight of the concentrate. In addition, rare grains of platinum group metals, as well as alloys of iron-chromium-nickel composition, are sporadically observed in the concentrate.

Externally, it is a fine-grained powdery mass of black and dark gray color with a predominant particle size of 0.1-0.5 mm. Particles larger than 1 mm are no more than 10-15%.

The iron content in the concentrate ranges from 50 to 58%. Composition of magnetic concentrate from ash and slag waste from the ash dump of CHPP-1: Fe - 53.34%, Mn - 0.96%, Ti - 0.32%, S - 0.23%, P - 0.16%. According to spectral analysis, the concentrate contains Mn up to 1%, Ni the first tenths of a percent, Co up to 0.01-0.1%, Ti -0.3-0.4%, V - 0.005-0.01% , Cr – 0.005-0.1 (rarely up to 1%), W – from the next. up to 0.1%. The composition is good iron ore with ligating additives.

The yield of the magnetic fraction according to magnetic separation data in laboratory conditions ranges from 0.3 to 2-4% of the ash mass. According to literature data, when processing ash and slag waste by magnetic separation under industrial conditions, the yield of magnetic concentrate reaches 10-20% of the ash mass, with the extraction of 80-88% Fe2O3 and the iron content of 40-46%.

Magnetic concentrate from ash and slag waste can be used for the production of ferrosilicon, cast iron and steel. It can also serve as a feedstock for powder metallurgy.

Aluminosilicate hollow microspheres are a dispersed material composed of hollow microspheres ranging in size from 10 to 500 microns (Fig. 3). Bulk density of the material is 350-500 kg/m3, specific density is 500-600 kg/m3. The main components of the phase-mineral composition of microspheres are aluminosilicate glass phase, mullite, and quartz. Hematite, feldspar, magnetite, hydromica, and calcium oxide are present as impurities. The predominant components of their chemical composition are silicon, aluminum, and iron (Table 3). Microimpurities of various components are possible in quantities below the threshold of toxicity or industrial significance. The content of natural radionuclides does not exceed permissible limits. The maximum specific effective activity is 350-450 Vk/kg and corresponds to second class building materials (up to 740 Vk/kg).

SiO2

52-58

Na2O

0,1-0,3

TiO2

0,6-1,0

K2O

Al2O3

SO 3

no more than 0.3

Fe2O3

3,5-4,5

P2O5

0,2-0,3

Humidity

No more than 10

Buoyancy

Not less than 90

Content of Ni, Co, V, Cr, Cu, Zn no more than 0.05% of each element
Due to their regular spherical shape and low density, microspheres have the properties of an excellent filler in a wide variety of products. Promising directions The industrial uses of aluminosilicate micropheres are the production of spheroplastics, road marking thermoplastics, grouting and drilling fluids, heat-insulating radio-transparent and lightweight building ceramics, heat-insulating non-firing materials and heat-resistant concrete.
Abroad, microspheres are widely used in various industries. In our country, the use of hollow microspheres is extremely limited and they are disposed of together with ash in ash dumps. For thermal power plants, microspheres are “harmful material” that clogs recycling water supply pipes. Because of this, in 3-4 years it is necessary to completely replace the pipes or carry out complex and expensive cleaning work.
The inert mass of aluminosilicate composition, constituting 60-70% of the mass of the alumina, is obtained after removing (extracting) from the ash all the above concentrates and useful components and the heavy fraction. In composition it is close to general composition ash, but will contain an order of magnitude less glands, as well as harmful and toxic ones. Its composition is mainly aluminosilicate. Unlike ash, it will have a finer, uniform granulometric composition (due to before grinding when extracting the heavy fraction). Due to its environmental and physical-chemical properties it can be widely used in production building materials, construction and as a fertilizer - a substitute for lime flour (meliorant).
Coals burned at thermal power plants, being natural sorbents, contain impurities of many valuable elements (Table 2), including rare earths and precious metals. When burned, their content in the ash increases 5-6 times and can be of industrial interest.
The heavy fraction extracted by gravity using advanced enrichment plants contains heavy metals, including precious metals. By finishing, precious metals and, as they accumulate, other valuable components (Cu, rare, etc.) are extracted from the heavy fraction. The gold yield from individual studied ash dumps is 200-600 mg per ton of ashes. The gold is thin and cannot be recovered by conventional methods. The technology used to extract it is know-how.
Many people are involved in recycling waste. More than 300 technologies for their processing and use are known, but they are mostly devoted to the use of ash in construction and the production of building materials, without affecting the extraction of both toxic and harmful components, as well as useful and valuable ones.
We have developed and tested in laboratory and semi-industrial conditions circuit diagram processing of ASW and its complete disposal (Fig.).
When processing 100 thousand tons of ASW you can get:
- secondary coal – 10-12 thousand tons;
- iron ore concentrate – 1.5-2 thousand tons;
- gold – 20-60 kg;
- building material (inert mass) – 60-80 thousand tons.
In Vladivostok and Novosibirsk, similar types of ASW processing technologies have been developed, possible costs have been calculated and the necessary equipment has been provided.
The extraction of useful components and complete utilization of ash and slag waste through the use of their beneficial properties and the production of building materials will free up occupied space and reduce the negative impact on the environment. Profit is a desirable but not decisive factor. The costs of processing technogenic raw materials to obtain products and simultaneous neutralization of waste may be higher than the cost of the product, but the loss in this case should not exceed the costs of reducing negative impact waste to the environment. And for energy enterprises, recycling of ash and slag waste means reducing technological costs for main production.

Literature

1. Bakulin Yu.I., Cherepanov A.A. Gold and platinum in ash and slag waste from thermal power plants in Khabarovsk // Ores and Metals, 2002, No. 3, p. 60-67.
2. Borisenko L.F., Delitsyn L.M., Vlasov A.S. Prospects for the use of ash from coal thermal power plants./ZAO Geoinformmark, M.: 2001, 68 p.
3. Kizilshtein L.Ya., Dubov I.V., Shpitsgauz A.P., Parada S.G. Components of ashes and slags of thermal power plants. M.: Energoatomizdat, 1995, 176 p.
4. Components of ashes and slags of thermal power plants. M.: Energoatomizdat, 1995, 249 p.
5. Composition and properties of ash and slag from thermal power plants. Reference manual, ed. Melentyeva V.A., L.: Energoatomizdat, 1985, 185 p.
6. Tselykovsky Yu.K. Some problems of using ash and slag waste from thermal power plants in Russia. Energetic. 1998, No. 7, pp. 29-34.
7. Tselykovsky Yu.K. Experience of industrial use of ash and slag waste from thermal power plants // New in Russian energy. Energoizdat, 2000, No. 2, pp. 22-31.
8. Valuable and toxic elements in commercial coals of Russia: Directory. M.: Nedra, 1996, 238 p.
9. Cherepanov A.A. Ash and slag materials // Main problems of studying and mining of mineral raw materials of the Far Eastern economic region. DVER mineral resource complex at the turn of the century. Section 2.4.5. Khabarovsk: Publishing house DVIM-Sa, 1999, p.128-120.
10. Cherepanov A.A. Noble metals in ash and slag waste from Far Eastern thermal power plants // Pacific Geology, 2008. Vol. 27, No. 2, pp. 16-28.

List of drawings
to the article by A.A. Cherepanov
Use of ash and slag waste from thermal power plants in construction

Fig.1. Filling the ash dump of CHPP-1, Khabarovsk
Fig.2. Schematic diagram complex processing ash and slag waste from thermal power plants.
Fig.3. Aluminosilicate hollow microspheres ZShO.

During the combustion of fuel, waste is generated, which is called fly ash. Special devices are installed near the fireboxes to capture these particles. They are a dispersive material having components less than 0.3 mm in size.

What is fly ash?

Fly ash is a finely dispersed material with small particle sizes. It is formed when burned solid fuel in conditions elevated temperatures(+800 degrees). It contains up to 6% of unburned substance and iron.

Fly ash is formed when mineral impurities contained in fuel are burned. Its content is different for different substances. For example, in firewood the fly ash content is only 0.5-2%, in fuel peat 2-30%, and in brown and hard coal 1-45%.

Receipt

Fly ash is formed during fuel combustion. The properties of the substance obtained in boilers differ from those created in the laboratory. These differences affect the physicochemical characteristics and composition. In particular, when burned in a furnace, melting occurs minerals fuel, which leads to the appearance of components of an unburned composite. This process, called mechanical underburning, is associated with an increase in temperature in the firebox to 800 degrees and above.

To capture fly ash, special devices are required, which can be of two types: mechanical and electrical. When operating the GZU, it is spent a large number of water (10-50 m 3 of water per 1 ton of ash and slag). This is a significant drawback. To get out of this situation, a reverse system is used: water, after being cleaned of ash particles, is re-entered into the main mechanism.

Main characteristics

Workability. The smaller the particles, the greater the impact of fly ash. The addition of ash increases the homogeneity of the concrete mixture and its density, improves placement, and also reduces the consumption of mixing water with the same workability.
Reducing the heat of hydration, which is especially important in the hot season. The ash content in the solution is proportional to the decrease in the heat of hydration.
Capillary absorption. When adding 10% fly ash to cement, capillary absorption of water increases by 10-20%. This, in turn, reduces frost resistance. To eliminate this drawback, it is necessary to slightly increase air entrainment through special additives.
Resistance in aggressive water. Cements that consist of 20% ash are more resistant to immersion in aggressive water.

Pros and cons of using fly ash

Adding fly ash to the mixture entails a number of advantages:

Clinker consumption is reduced.
Grinding improves.
Strength increases.
Workability improves, making formwork easier to remove.
Shrinkage is reduced.
Reduces heat generation during hydration.
The time until cracks appear increases.
Improves resistance to water (both clean and aggressive).
The mass of the solution decreases.
Fire resistance increases.

Along with the advantages, there are also some disadvantages:

The addition of ash with a high content of underburned changes the color of the cement solution.
Reduces initial strength at low temperatures.
Reduces frost resistance.
The number of mixture components that need to be controlled increases.

Types of fly ash

There are several classifications by which fly ash can be divided.

Depending on the type of fuel that is burned, ash can be:

Anthracite.
Carboniferous.
Lignite.

According to their composition, ash is:

Acidic (with calcium oxide content up to 10%).
Basic (content above 10%).

Depending on the quality and further use, 4 types of ash are distinguished - from I to IV. Moreover, the latter type of ash is used for concrete structures that are used in difficult conditions.

Fly ash processing

For industrial purposes, unprocessed fly ash is most often used (without grinding, sifting, etc.).

When fuel burns, ash is formed. Light and small particles are carried away from the furnace due to the movement of flue gases and are captured by special filters in ash collectors. These particles are fly ash. The remaining part is called dry selection ash.

The ratio between these fractions depends on the type of fuel and design features the firebox itself:

with solid removal, 10-20% of ash remains in the slag;
with liquid slag removal - 20-40%;
in cyclone-type furnaces - up to 90%.

During processing, particles of slag, soot and ash may enter the air.

Dry fly ash is always sorted into fractions under the influence of electric fields that are created in the filters. Therefore, it is most suitable for use.

To reduce the loss of substance during calcination (up to 5%), fly ash must be homogenized and sorted into fractions. Ash, which is formed after the combustion of low-reaction coals, contains up to 25% of the combustible mixture. Therefore, it is further enriched and used as an energy fuel.

Where is fly ash used?

Ashes are widely used in various spheres of life. This could be construction, agriculture, industry, sanitation

Fly ash is used in the production of certain types of concrete. Application depends on its type. Granulated ash is used in road construction for the foundation of parking lots, solid waste storage areas, bicycle paths, and embankments.

Dry fly ash is used to strengthen soils as an independent binder and quickly hardening substance. It can also be used for the construction of dams, dams and other

For production, ash is used as a cement substitute (up to 25%). As a filler (fine and coarse), ash is included in the process in the production of slag concrete and blocks used in the construction of walls.

Widely used in the production of foam concrete. Adding ash to the foam concrete mixture increases its aggregative stability.

Ashes in agriculture used as potash fertilizers. They contain potassium in the form of potash, which is easily soluble in water and available to plants. In addition, ash is rich in other useful substances: phosphorus, magnesium, sulfur, calcium, manganese, boron, micro- and macroelements. The presence of calcium carbonate makes it possible to use ash to reduce soil acidity. Ash can be applied to various crops in the garden after plowing, fertilize the trunk circles of trees and shrubs with it, and also add meadows and pastures. It is not recommended to use ash simultaneously with other organic or mineral fertilizers (especially phosphorus).

The ash is used for sanitation in conditions where there is no water. It increases the pH level and kills microorganisms. It is used in latrines, as well as in places where wastewater sludges.

From all of the above, we can conclude that a substance such as fly ash is widely used. The price for it varies from 500 rubles. per ton (for large wholesale) up to 850 rubles. It should be noted that when using self-pickup from distant regions, the cost may vary significantly.

GOST standards

Documents have been developed and are in force that control the production and processing of fly ash:

GOST 25818-91 “Fly ash for concrete”.
GOST 25592-91 “TPP ash and slag mixtures for concrete.”

To control the quality of produced ash and mixtures using it, other additional standards are used. At the same time, sampling and all types of measurements are also carried out in accordance with the requirements of GOSTs.

Energy companies Krasnoyarsk Territory and the Republic of Khakassia, part of the Siberian Generating Company group, sold and brought into economic circulation in 2013 662,023 thousands of tons of ash and slag waste (ASW).

Over the year, the Krasnoyarsk branch of SGK increased the volume of involvement of ammonia waste into economic turnover by 4% - from 637.848 thousand tons in 2012 to 662.023 thousand tons in 2013.

The growth of economic turnover of ash and slag waste (a by-product of coal combustion at thermal power plants) allows reduce the load on the environment in the cities where the company operates. It is worth noting that the main volume of ash and slag waste (625.5 thousand tons) last year was used for the sale of large environmental project for the reclamation of ash dump No. 2 of the Nazarovo State District Power Plant. Reclamation of a waste ash dump with an area of 160 hectares, located in the area of the Chulym River, will make it possible to return these lands to economic use. For example, after a few there may appear green spaces.

In addition, the Krasnoyarsk branch of SGK continues to sell ash and slag waste to enterprises in the construction industry. The company first started selling dry ash and slag in 2007. At that time, only 7 thousand tons of waste were sold. In 2013, sales volumes amounted to 36.525 thousand tons of ash and slag waste. Thus, the average annual sales volumes of ash and slag waste have increased over the 6 years of operation in this market more than five times. T This increase in demand indicates that builders highly value this type of raw material. At the same time, ash and slag waste is purchased not only by enterprises from the Krasnoyarsk Territory, but also from other regions of Russia.

Thanks to the active work of SGK in this direction, last year the volume of ash waste sold and involved in economic turnover (662,023 thousand tons) turned out to be 34% higher than the amount of ash and slag waste generated by the energy enterprises of the branch (495 thousand tons).

In 2014, the Krasnoyarsk branch of SGK will continue to work on involving ash and slag waste into economic circulation, thereby reducing its accumulation and reducing the load on the environment. Work on the reclamation of ash dump No. 2 of the Nazarovskaya State District Power Plant will continue. In addition, the company is considering opportunities and market expansion marketing of dry ash and slag and for the needs of not only the construction industry, but also other industries.

Use of ash and slag waste from thermal power plants in construction

During the activities of electric power enterprises, a lot of ash and slag waste is generated. The annual supply of ash to ash dumps in the Primorsky Territory is from 2.5 to 3.0 million tons per year, in the Khabarovsk Territory - up to 1.0 million tons (Fig. 1). Within the city of Khabarovsk alone, more than 16 million tons of ash are stored in ash dumps.

Ash and slag waste (ASW) can be used in the production of various concretes, mortars, ceramics, thermal and waterproofing materials, and road construction, where they can be used instead of sand and cement.
Dry fly ash from electric precipitators at CHPP-3 is more widely used. But the use of such waste for economic purposes is still limited, including due to its toxicity. They accumulate a significant amount of hazardous elements.
The dumps are constantly dusty, the mobile forms of the elements are actively washed away by precipitation, polluting the air, water and soil.
The use of such waste is one of the most pressing problems. This is possible by removing or extracting harmful and valuable components from the ash and using the remaining ash mass in the construction industry and fertilizer production.

Brief characteristics of ash and slag waste

At the examined thermal power plants, coal combustion occurs at a temperature of 1100-1600o C.
When the organic part of coal is burned, volatile compounds are formed in the form of smoke and steam, and the non-combustible mineral part of the fuel is released in the form of solid focal residues, forming a dusty mass (ash), as well as lump slag.
The amount of solid residues for hard and brown coals ranges from 15 to 40%.

Coal is crushed before combustion and, for better combustion, fuel oil is often added in a small amount of 0.1-2% to it.
When pulverized fuel is burned, small and light ash particles are carried away by the flue gases, and they are called fly ash. The size of fly ash particles ranges from 3-5 to 100-150 microns. The amount of larger particles usually does not exceed 10-15%.

Fly ash is collected by ash collectors.
At CHPP-1 in Khabarovsk and Birobidzhan CHPP, ash collection is wet using scrubbers with Venturi pipes; at CHPP-3 and CHPP-2 in Vladivostok, it is dry using electric precipitators.
Heavier ash particles settle on the underflow and fuse into lump slags, which are aggregated and fused ash particles ranging in size from 0.15 to 30 mm.
The slag is crushed and removed with water. Fly ash and crushed slag are first removed separately, then mixed to form an ash and slag mixture.

In addition to ash and slag, the composition of the ash and slag mixture constantly contains particles of unburned fuel (underburning), the amount of which is 10-25%. The amount of fly ash, depending on the type of boiler, type of fuel and its combustion mode, can be 70-85% of the mass of the mixture, slag 10-20%.
The ash and slag pulp is removed to the ash dump through pipelines.
During hydraulic transport and at the ash and slag dump, ash and slag interact with water and carbon dioxide in the air.
Processes similar to diagenesis and lithification occur in them. They quickly erode and, when dried at a wind speed of 3 m/sec, begin to generate dust.
The color of ZShO is dark gray, layered in cross-section, due to the alternation of different-grained puffs, as well as the deposition of white foam consisting of aluminosilicate hollow microspheres.
The average chemical composition of the ashes of the surveyed thermal power plants is given in Table 1 below.

Table 1. Limits of the average content of the main components of ashes

The content of Ni, Co, V, Cr, Cu, Zn is not more than 0.05% of each element.
Due to their regular spherical shape and low density, microspheres have the properties of an excellent filler in a wide variety of products. Promising areas for the industrial use of aluminosilicate microspheres are the production of spheroplastics, road marking thermoplastics, grouting and drilling fluids, heat-insulating radio-transparent and lightweight building ceramics, heat-insulating non-firing materials and heat-resistant concrete.

Abroad, microspheres are widely used in various industries. In our country, the use of hollow microspheres is extremely limited and they are disposed of together with ash in ash dumps.
For thermal power plants, microspheres are “harmful material” that clogs recycling water supply pipes. Because of this, it is necessary to completely replace pipes in 3-4 years or carry out complex and expensive cleaning work.

The inert mass of aluminosilicate composition, constituting 60-70% of the mass of the alumina, is obtained after removing (extracting) from the ash all the above concentrates and useful components and the heavy fraction. In composition it is close to the general composition of ash, but it will contain an order of magnitude less iron, as well as harmful and toxic ones.
Its composition is mainly aluminosilicate. Unlike ash, it will have a finer, uniform granulometric composition due to before grinding when extracting the heavy fraction.
Due to its environmental and physico-chemical properties, it can be widely used in the production of building materials, construction and as a fertilizer - a substitute for lime flour (meliorant).

Coals burned at thermal power plants, being natural sorbents, contain impurities of many valuable elements (Table 2), including rare earths and precious metals. When burned, their content in the ash increases 5-6 times and can be of industrial interest.
The heavy fraction extracted by gravity using advanced enrichment plants contains heavy metals, including precious metals. By finishing, precious metals and, as they accumulate, other valuable components (Cu, rare, etc.) are extracted from the heavy fraction.
The gold yield from individual studied ash dumps is 200-600 mg per ton of ashes.
The gold is thin and cannot be recovered by conventional methods. The technology used to extract it is know-how.

Many people are involved in recycling waste. More than 300 technologies for their processing and use are known, but they are mostly devoted to the use of ash in construction and the production of building materials, without affecting the extraction of both toxic and harmful components, as well as useful and valuable ones.

We have developed and tested in laboratory and semi-industrial conditions a basic scheme for processing ASW and its complete disposal.
When processing 100 thousand tons of ASW you can get:
- secondary coal – 10-12 thousand tons;
- iron ore concentrate – 1.5-2 thousand tons;
- gold – 20-60 kg;
- building material (inert mass) – 60-80 thousand tons.

In Vladivostok and Novosibirsk, similar technologies for processing ASW have been developed, possible costs have been calculated and the necessary equipment has been provided.
The extraction of useful components and complete utilization of ash and slag waste through the use of their beneficial properties and the production of building materials will free up occupied space and reduce the negative impact on the environment. Profit is a desirable but not decisive factor.
The costs of processing technogenic raw materials to produce products and simultaneous neutralization of waste may be higher than the cost of the product, but the loss in this case should not exceed the costs of reducing the negative impact of waste on the environment. And for energy enterprises, recycling of ash and slag waste means reducing technological costs for main production.

Literature

V.V. Salomatov, Doctor of Technical Sciences Institute of Thermophysics SB RAS, Novosibirsk

Ash and slag waste from thermal power plants using Kuznetsk coal and ways of their large-scale recycling

Scope of processing solid waste coal thermal power plants today are extremely low, which causes the accumulation of huge quantities of ash and slag in ash dumps, requiring the withdrawal of significant areas from circulation.

Meanwhile, the ash and slag of Kuznetsk coal (KU) contains valuable components, such as Al, Fe, and rare metals, which are raw materials for other industries. However, with traditional methods of burning these coals, it is not possible to use coal ash and slag on a large scale, since due to the formation of mullite they are highly abrasive and chemically inert to many reagents. Attempts to use ash and slag of such a mineralogical composition in the production of building materials lead to intense wear and tear technological equipment and a decrease in productivity due to a slowdown in the physical and chemical processes of interaction between ash components and reagents.

It is possible to avoid mullitation of Kuznetsk coal ash by changing the temperature conditions of their combustion. Thus, the use of a fluidized bed for burning coal at 800...900 oC allows one to obtain less abrasive ash, and its main mineralogical phases will be metakaolinite, ?Al2O3; quartz, glass phase.

Utilization of ash and slag waste from thermal power plants during low-temperature combustion of HRSG

The amount of ash and slag waste from the most typical thermal power plant with an electrical power of 1295/1540 MW and a thermal power of 3500 Gcal/h is about 1.6...1.7 million tons per year.

Chemical composition of Kuznetsk coal ash:

SiO2 = 59%; Al2O3 = 22%; Fe2O3 = 8%; CaO = 2.5%; MgO = 0.8%; K2O = 1.4%; Na2O = 1.0%; TiO2 = 0.8%; CaSO4 = 3.5%; C = 1.0%.

The use of Kuznetsk coal ash is most effective in the production of aluminum sulfate and alumina using Kazakh technologies Polytechnic Institute. Based on the material composition of HRSG ash and its quantity, the recycling scheme is presented in Figure 1.

In Russia, only 6 special types of alumina are produced, while in Germany alone there are about 80. Their range of applications is very wide - from the defense industry to the production of catalysts for the chemical, tire, light and other industries. The needs for alumina in our country are not covered by our own resources, as a result of which part of the bauxite (raw materials for the production of alumina) is imported from Jamaica, Guinea, Yugoslavia, Hungary and other countries.

The use of Kuznetsk coal ash will somewhat improve the situation with the deficiency of aluminum sulfate, which is a means for treating waste and drinking water, and is also used in large quantities in the pulp and paper, woodworking, light, chemical and other sectors of industry. Aluminum sulfate deficiency only in the region Western Siberia is 77...78 thousand tons.

In addition, the dispersed composition of alumina obtained after sulfuric acid processing makes it possible to obtain various types of special alumina, the need for which will be satisfied to a certain extent when they are produced in an amount of 240 thousand tons.

Waste from the production of aluminum sulfate and alumina is a raw material component for the production of liquid glass, white cement, binders for backfilling mined-out mining areas, container and window glass.

The need for these materials is increasing, and the demand for them currently significantly exceeds their production volumes. Approximate technical and economic indicators of these productions are presented in Table 1.

Table 1. Main technical and economic indicators for processing Kuznetsk coal ash

Name productions	Power, thousand tons	Price USD/t	Self, USD/t	Cap. attachments, million dollars	Ek Effect, million dollars	Term we pay back years
Production of special types alumina	240	33	16	20	4	5
Sulphate production aluminum	50	12	7	1	0,25	4
Production ferroalloys	100	27	16	5	1	5
Liquid production glass	500	11	8	6	2	3
White production cement	1000	5	4	3	0.65	4,6
Production of binders materials	600	3	2	3	0,6	5
Glass production	300	18	15	5	1	5
TOTAL				42	9	4,7

In addition, it is advisable to produce rare and trace metals from HRH ash, primarily gallium, germanium, vanadium and scandium.

Due to the fact that the thermal power plant, according to its schedule, operates with variable load throughout the year, the ash output is uneven. Ash processing plants must operate rhythmically. Storing dry ash presents certain difficulties. In this regard, it is proposed that winter time Part of the ash is sent for granulation using pelletizers produced by Uralmash. After pelletizing and drying, the granules are fired in the boiler furnace, and then sent by pneumatic transport for temporary storage in a dry warehouse. Ash granules can later be used as a raw material base for the construction industry or used in road construction.

Storing granules in an open dry warehouse does not require special protective measures and does not create a dust hazard. The capacity of such an ash dump is approximately 350...450 thousand tons, the area is about 300-300 m2. Therefore, it may be located in close proximity to the CHP site.

The best utilization indicators will be for ash and slag waste obtained after combustion of HRSG in boiler units with a circulating fluidized bed (CFB), which Russia does not yet produce. Boilers with CFB not only provide a sharp reduction in emissions of nitrogen and sulfur oxides, but also produce ash and slag waste, which can be successfully used in industry to produce alumina and building materials. This makes it possible to reduce the cost of the power plant by sharply reducing the areas required for ash storage and reduce pollution environment. The reduction of dust at thermal power plants with CFB boilers occurs, firstly, due to a reduction in the area of the ash dump, and secondly, due to the fact that the ash obtained from burning Kuznetsk coal in the CFB contains gypsum and has astringent properties. With some wetting of such ash, it will harden, which will eliminate dusting even if the ash dump dries out.

Since the ash is transported to industrial enterprises pneumatic transport, water consumption is also slightly reduced. In addition, there are no wastewater from an ash dump, which at thermal power plants with traditional pulverized coal boilers contain salts of heavy metals and other harmful substances.

Production of aluminum sulfate and alumina

The technology for producing aluminum sulfate and alumina based on low-temperature combustion ash is presented in Figure 2.

The optimal conditions for implementing this technology are the following:

burning coal ( temperature regime 800...900 oC);
grinding (grinding fineness – 0.4 mm (not less than 90%));
sulfuric acid opening (temperature 95...105 oC, duration 1.5...2 hours, sulfuric acid concentration 16...20%);
separation of liquid and solid phases (filter fabric article L-136, vacuum 400...450 mm Hg, nutsch filter 0.37...0.42 m3/m2? h);
two-stage sludge washing;
hydrolytic decomposition (temperature 230 °C, time 2 hours);
thermal decomposition (temperature 760...800 oC).

The resulting product aluminum sulfate (50 thousand tons per year), after granulation and packaging in plastic bags, is sent to consumers. The completed technical and economic assessment shows the feasibility of producing aluminum sulfate based on low-temperature combustion ash.

Aluminum sulfate, obtained from ash, is a good coagulant for industrial wastewater treatment.

Sishtof after sulfuric acid treatment, due to the low content of iron oxides (less than 0.5...0.7%), is a substitute for sand in the production of white cement, and the presence of 4...6% gypsum in it will allow intensifying the processes of cement production.

Production of ferroalloys and building materials

The production of ferroalloys based on the mineral part of coal has been thoroughly developed. Industrial technologies for producing ferrosilicoaluminum and ferrosilicon from ash and slag wastes, which are similar in composition to Kuznetsk coal ashes and their magnetic component, which can be isolated by magnetic separation methods, have been tested. The resulting alloys were tested on an industrial scale for metallurgical plants countries for steel deoxidation and gave positive results.

Obtaining building materials based on syshtof does not require changing the existing technologies of these industries. Sishtof is used as a raw material component and replaces quartz, as well as other silicon-containing products used in the production of building materials. In addition, silicon oxide, the content of which in systof is 75...85%, is presented mainly in the form of amorphous silica with high chemical activity, which makes it possible to predict an improvement in the performance and quality of cement and binders. The minimum amount of ferrous and other coloring compounds in sishtof makes it possible to obtain white cement based on it, the demand for which is very great.

Technologies for producing cement, binders, and liquid glass have also been developed in industry.

Conclusion

Ash and slag waste produced by burning Kuznetsk coal in power steam generators using the circulating fluidized bed technology, new for Russia, is in demand for large-scale recycling. It is economically efficient to produce from them, using technologies already mastered in industry, very scarce ferroalloys, aluminum sulfate, special types of alumina, liquid glass, white cement, and binding materials.

Bibliography V.V. Salomatov Environmental technologies at thermal and nuclear power plants: monograph / V.V. Salomatov. – Novosibirsk: NSTU publishing house, – 2006. – 853 p.

74rif.ru/zolo-kuznezk.html, energyland.info/117948

As often happens, it was not us who came up with the idea of using ash to produce building materials, but the practical West - ash and slag materials have long been widely used there in construction and housing and communal services. The main value of the new method of producing building materials from ash is environmental protection.

Rejoice, environmentalists and Greenpeace: the risk of environmental disasters associated with the risk of erosion of ash dumps and ash pollution of the environment is being minimized. There are colossal cost savings - after all, a lot of money is spent on maintaining ash storage facilities. The remaining advantages of ash recycling lie in the economic benefits of using this recyclable material.

Brick made from ash is suitable for building both a residential building and production premises, and a fence. It can even be used as cladding. The recipe for making such a brick is extremely simple: 5% water, 10% lime, the rest is ash (salt and pepper to taste).

The current price of such bricks, produced, for example, at the Omsk plant (SibEK LLC - Siberian Effective Brick) is 5–6 rubles, which makes this “product” very competitive.

Brick tests prove its high quality and wide application possibilities. Strength, water absorption, and frost resistance are not inferior to sand-lime brick. The thermal conductivity index is close to that of wood. And the appearance is practically pleasing perfect form- the size tolerances of such bricks are no more than 0.5 millimeters, and this, if you think about it, is again saving - this time on the amount of grout mortar. In addition, ash brick is lighter, more convenient to lay, and allows it to be perfectly level. For improvement appearance bricks, you can add dyes to its composition.

Life pushes you to search for new ideas and solutions. The use of ash as a raw material for bricks and other building materials is truly a successful and very timely find. The number of “killed birds with one stone” in this case is much more than the notorious two. And once again the saying is confirmed that everything valuable is under our feet.

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