Brick production on coal refining waste

Contents

Paper

Introduction

1. Production nomenclature

2. Raw materials

3. Estimated Production Program

4. Basis of production method

5. Description of physical and chemical processes of material production

6.Process Description

7. Main Process Equipment

Conclusion

List of used literature

Graphic Material List

Sheet 1 - Product Manufacturing Flow Chart

Sheet 2 - Production Flow Sheet

Project Description

The purpose of the course work in the discipline "Technology of construction ceramics" is to consolidate theoretical knowledge, develop the ability to compile and design technological and structural documentation, and master the methods of technological calculation of processes.

In this course work, the technology of producing ceramic bricks on coal-rich wastes according to the semi-dry method of mass preparation is considered. The main processes and regularities that take place in the process of product production are also considered.

Introduction

Ceramic brick is the first artificial stone material created by man. Its history is several millennia. Thanks to the talent of architects, the skill of bricklayers, the high strength and frost resistance of bricks, the quality of masonry solutions through the centuries, brick buildings have reached our time in almost all countries of the world.

Modern knowledge about the structure and properties of raw materials, their behavior at different technological ranges, a high level of development of technology and equipment allows you to produce ceramic products with a predetermined set of properties. Architects - our contemporaries got almost unlimited opportunities to implement their projects using ceramic bricks. [1]

Currently, a wide range of products is used as wall products: ceramic and silicate bricks and stone, full ceramic concrete and three-layer wall panels, full and hollow stones and blocks of heavy and light concrete on porous aggregates, blocks and stones from arbolite and peat of the Geocar type, stones and blocks from cellular concrete, etc. The most common type of wall products are small-piece ceramic and silicate bricks and stones, of which about 40% of the houses of the existing housing stock were built in Russia, and in housing construction. [2]

In 2015, Tatarstan commissioned 2.4 million square meters of housing, which is 100 percent of the annual plan. Over the past five years, 2.4 million square meters of housing has been introduced in Tatarstan, and by this indicator the republic is steadily among the ten leaders among the regions of the Russian Federation. [3]

The need for building materials is increasing accordingly. The capacity available in the republic for the production of small-piece wall materials currently amounts to only 964.0 million units. bricks per year, including for the production of ceramic bricks - 479.7.

In the whole republic, the deficit for the production of small-piece wall materials of production capacities (excluding production facilities under construction) by 2015 is 649 million units. bricks per year (of which about 120 million pieces of face and 529 million pieces of wall), and by 2030, respectively, 1,377 million pieces of face. bricks per year (of which approximately 240 million pieces of face and 1,137 million pieces of wall).

This indicates the high investment attractiveness of brick production development in the Republic of Tatarstan. [4]

Raw materials

The main raw materials for the production of ceramic bricks and stone are refractory clay, chamotte, and an organic additive - coal dust that burns out during firing.

Refractory clays belong to sedimentary rocks. The most important clay minerals are kaolinite Al2O3 ٠ 2SiO2 ٠ 2H2O, montmorillonite A12O3 ٠ 4SiO2 ٠ nH2O, etc. Refractory clays have refractoriness from 1350 to 1580 ° C. They are characterized by a high content of Al2O3 alumina (2042%), high binding ability and plasticity. They were formed from granites, gneisses, porphyres and other rocks consisting of quartz, feldspar, etc. They contain a small amount of impurities of quartz, feldspar, mica, calcium and magnesium carbonates. [11]

In the production of wall ceramics, clay raw materials are rarely used in pure form, more often it is used together with various additional materials. [6]

Chamotte is a ceramic material obtained by firing clay at a temperature equal to the firing temperature of articles from the same clay. It is a more process-efficient detergent, improving simultaneously the drying and burning, forming properties of the clay.

Powder obtained by grinding burnt brick wastes is used as shamot in factories. [12]

During the firing process, the coal burns, forming pores in the finished product, which contributes to the improvement of the thermal insulation structure of the brick. Coal mining waste can be used for the same purpose. [10] The use of coal refining waste reduces fuel consumption for brick production. [6]

Coal dust is a dry fine powder with particle sizes from the smallest dust with a size of 0.1 μm to larger (300... 500 μm). Fineness of grinding is characterized by residues on standard sieves with a size of 50 cells; 90; 200; 500 and 1000 μm. The bulk density of fresh ash dust is within 500... 700 kg/m3, and uplotnѐnnoy 800... 900 kg/m3.

Justification of production method

Properties of raw materials, type of products, volume of production, methods of preparation of raw materials determine the general principles of technological schemes of products production. Methods of processing raw materials and mass preparation - plastic, semi-dry or slip - most fully determine differences in technological schemes of products production .

Process scheme of products production by semi-dry method of raw materials processing and mass preparation is used in production of common and efficient bricks, hollow stones at semi-dry pressing of products, when clay raw materials are used with reduced ductility and humidity.

Semi-dry pressing of products has a number of advantages over plastic molding: a long and complex drying process of raw materials is eliminated, the production cycle duration is reduced by almost 2 times, the products have the correct shape and more accurate dimensions, they give a significantly lower shrinkage during firing . [6]

This method is promising from the standpoint of complex mechanization. The use of the semi-dry method in the production of bricks makes it possible to set raw material on roasting cars and exclude its reloading from drying cars to roasting cars from the technology. This determines the possibility of using reliable machines - raw brick gardens on furnace cars. [7]

Description of physical and chemical processes of material production

The most important physicochemical properties of products (strength, density, frost resistance) are acquired as a result of firing. During firing, heat and mass exchange processes occur simultaneously, significantly complicated by phase and chemical transformations. Depending on the properties of the clay raw materials, these processes proceed without disturbing the integrity of the products or leading to their deformation - fracture and warping, especially in calcination-sensitive clays .

A feature of the firing of unglazed coarse ceramic products is that clay raw materials pass partially from a solid state to a melt as a heterogeneous system, in a certain temperature range under the oxidizing atmosphere of the furnace. The resulting glass phase, even in minor amounts, binds the unalloyed minerals in the structure of the ceramic tile when cooled.

The temperature mode of firing bricks and effective ceramic stones is conditionally divided into four periods: drying (200 ° C), heating (about 700-800 ° C), actual firing (cocoa 900-1050 ° C), cooling (cooling to 40-50 ° C).

Additional drying is carried out for complete removal of closing water and hygroscopic water, as well as for uniform heating of semi-finished product weight up to 100-200 ° С. The most intensive removal of water occurs at 80-120 ° C, which is associated with the possibility of cracking raw materials. The temperature during the drying period rises slowly, with sufficient traction preventing the condensation of fumes on the crude and its steaming.

Heating to 800 ° C, i.e. before the beginning of elastic deformations, is initially carried out by flue gases and then by burning fuel. In the initial stage of this period (300 ° C), burnout of organic impurities begins, ending with a slow increase in temperature to 450 ° C, at a fast - about 700-800 ° C. The coke residue burns out by the end of the second period (700-800 ° C). The rate of burnout of substances is inversely proportional to the square of the thickness of the product and largely depends on the excess air in the furnace gases.

In the middle of the period at 500-650 ° C, constitutional water is intensively released, minerals containing iron, for example siderite FeCO3, dissociate with the release of CO2. In the reducing medium created by burning the fuel inside the tile of articles when introducing fuel into the mass or with water irrigation, part of the iron (III) oxide is reduced to iron (II) oxide to form low-melting eutectbques (iron glasses), especially when the temperature rises to 850-900 ° C, which contribute to the compaction of the tile. At 550 ° C and the presence of a reducing medium, the dissociation of sulfides and sulfates begins with the release of SO2, and at 700-800 ° C, the dissociation of CaCO3 and MgCO3 carbonates ends at 950-1000 ° C with the release of CO2, and an increase in porosity of the products. Starting at 700 C and above, the alkalis in the clay react with the other clay components to form a melt, the amount of which also increases with increasing temperature. During the formation of the shingle, the liquid phase (melt) continuously changes. The amount of melt produced at the same temperature depends on the chemical composition of the clay materials and additives, the reactivity and dispersion of the mass components, the quality of the furnace medium and the heating time. With a small content of the liquid phase, sufficient mechanical strength of the articles is not provided, with excessive deformation of the articles during firing is possible. In this period of burning of articles (700-800 ° C), the crystal lattice of clay-forming minerals is slightly destroyed, therefore, physical and mechanical parameters such as shrinkage, strength, plastic deformation, modulus of elasticity vary slightly. The porosity of the articles increases by the end of the period.

The brewer is characterized by achieving the maximum permissible firing temperature of the articles, ripening the tile and aging usually at 900-1050 ° C. The temperature is increased carefully, since elastic deformations occur at 800-900 ° C, which is associated with the destruction of the crystalline lattice of clay minerals and significant structural changes in the tile. The weighing period is characterized by a change in fire shrinkage beginning at 750,850 ° C, depending on the properties of the raw material, and ending by the time the final firing temperature is reached. The viscosity of the mass of articles and porosity at 900-950 ° C are sharply reduced, especially in raw materials rich in carbonates. The dissociation of carbonates by the time atom almost completely ends. Oxides of alkali and alkaline-earth metals, making clay easy to melt, contribute to its rapid softening by increasing the amount of melt and thereby drastically reduce the porosity of the mass of products. Iron-containing minerals, along with alkalis, are the most easily fusible components, especially FeO, since this oxide melts at a temperature of 150-200 ° C lower than Fe2O3. Since in clays iron is most often found in the form of Fe2O3, its transition to FeO is possible only in the reducing medium obtained by burning fuel pressed into the articles, or by introducing water into the furnace at the final stage of burning. Therefore, firing of articles in a reducing medium at 900-1000 ° C is equivalent to firing in a conventional (oxidizing) medium at 1050-1100 ° C, without deformation of the articles. To equalize the temperature in the furnace and more complete physical and chemical processes at the end of the weigher, 3-5 hours are held.

Short-term maintenance also contributes to the intensive flow of silica transformations, the formation of mullite, although the completion of these processes is transferred to a region of higher temperatures than the firing temperatures of the articles. Therefore, the increase in the strength of the product tile, starting at 800-850 ° C and continuing until the end of firing (900-1050 ° C), is explained not so much by the influence of the newly formed compounds as by the action of the melt, which, due to the energy of surface tension, brings together and binds larger particles of mass - dehydrated particles of clay matter and quartz grains.

In semi-dry pressing, the aggregate grains are, as it were, pressed into the clay particles and in firing, the particles bind only at contact points.

Cooling begins with a small "quench" zone and is characterized by a slow decrease in temperature (about 30 ° C per hour) to 550-500 ° C without heat removal to avoid internal stresses and cracking of the products. Cracks can most likely appear in the range of 600-400 ° C as a result of polymorphic transformations of quartz (at 573 ° C) and the transition of the melt from a viscous to a solid state.

Further cooling to a final temperature of 40-60 ° C occurs quickly, and the permissible temperature difference increases to 120-125 ° C/h. The amount of air required to completely cool the products is an average of 6500-7500 kg per 1000 pieces of conditional brick. At the same time, in the area of ​ ​ the brewer, the excess air coefficient will be about 3.5-4.5 and the suction fan must remove about 22,000-30,000 kg of gas per 1000 pieces of fired conventional brick from the furnace.

Decontaminating (shamot) and burning (coal) additives increase the porosity of the semi-finished product, reduce the sensitivity to firing and create conditions for its rapid heating at high-speed firing. [6]

Process Description

A kind of semi-dry pressing method is a resource-saving method of pressing using carbon-rich wastes.

The process line ensures sequential execution of the following operations: clay extraction, its drying, grinding, preparation of additives, mixing and additional wetting of the mass. The powder is pressed into the mold of the hydraulic press, and the raw material is stacked on the oven car to pass the firing. Burnt products are unloaded, packaged and sent to the finished products warehouse. [9]

Extraction of raw materials is carried out in open pits 1 by means of multicoat excavators 2. Clay is sent from the pit to the raw material storage by 4 dump trucks 3.

Processing of clay raw materials in order to destroy the natural structure is carried out using natural and mechanical treatment.

Semi-dry method of mass preparation consists in coarse grinding of initial raw material, its drying, fine grinding, screening of large inclusions, its mixing with additives and humidification. [7 ]

A scraper conveyor 5 is used to feed clay into production from the clay storage tanks.

Dosing of clay components and their uniform supply for subsequent treatment are carried out by box feeder 6. The box feeders not only dose but also partially loosen the raw materials.

Then, for preliminary grinding, the clays are supplied to special machines - quarrying rollers 7, grinding and removing solid inclusions from the clay. The stone-separating rollers 7 have a screw thread on the surface of the rollers, on which tight inclusions measuring from 35 to 180 mm are "screwed" from the rollers to the side and removed by means of a discharge tray.

After preliminary grinding, clay raw material is fed to drying drum 9 by means of tape feeder 8. The drums are set at an angle of 35 ° to the horizon. The flue gases are diluted in the mixing chamber with cold air to 650800 ° C before being fed into the drying drum. The exhaust gas temperature is 110140 ° C and the velocity is 1.52 m/s. A sharp decrease in the temperature of the coolant at the beginning of the drum is associated with heating of cold clay and losses to the environment. Specific heat consumption - 4145 kJ/kg of evaporated moisture. Clay temperature after drying - not more than 6080 ° С.

The dried clay in the drying drum enters the belt feeder 10 and is fed for grinding to the grinding runners 11. Batch dry milling mixing runners are designed for grinding and mixing semi-dry clays, chamotte and other materials. Material loaded into runners is moved under rollers by fixed scrapers. After achieving sufficient grinding and mixing by means of a separate drive, the material is lowered into the discharge scraper and, under the action of centrifugal forces, moving along the scraper, is discharged from the bowl into the leak. The crushed clay passes through the vibrator 12 and is fed by the belt feeder 13 to the elevator 14 which feeds the material into the clay feed bin 15. From here the raw material is dosed on the weighing dispenser 16 and fed to the rod mixer 32.

Additive preparation technology consists of the following operations:

Shamot is prepared from combat products. The fighting of the articles by means of the frontal loader 23 from the fighting warehouse of the brick 22 is supplied to the box feeder 24, which feeds the fighting for preliminary crushing on the cheek crushers 25. The pre-ground material is then fed by the belt conveyor 26 to a finer mill into the ball mill 27. The resulting powder passes through the vibrating screen 29 and is fed by the belt feeder 13 to the elevator 28 which feeds the material into the chamotte hopper 30. From where the chamotte is dosed on the weighing dispenser 31 and fed to the rod mixer 32.

Coal dust does not require special preparation. It is brought in the tanker trucks 17 and is loaded into the service hopper 19 by the air lift 18. From the supply hopper 19, the fine powder material is fed by the screw feeder 20 to the weighing dispenser 21. From here, the discarded material is fed into the rod mixer 32.

In the rod mixer 32, the charge components are mixed (homogenized). The mixer is a rotary drum in which the treated material is triturated and further mixed under the action of rod loading. At the same time, the mass is added to the design humidity of 78%.

The finished press powder from the mixer 32 is fed by the tape feeder 33 to the stock 34. The ready-to-press molding mass is weighed on the weighing dispenser 35 by the screw feeder 36 to the press 37.

The beginning of the pressing of the ceramic powder is accompanied by its compaction due to the displacement of the particles relative to each other and their approach. Air is removed from the system.

The next stage of compaction is characterized by plastic irreversible deformation of particles. This increases the contact surface between the particles. At the same time, the compaction of each elementary particle is accompanied by the squeezing of moisture from its depth layers onto the contact surface of the particle. Both of these factors cause the adhesion between the particles to increase.

In the third stage of compaction, elastic deformation of particles occurs. Such deformations are most likely for thin elongated particles in the form of needles and plates, which can bend according to the scheme of a clamped cantilever or beam resting on two supports.

The last stage of compaction is accompanied by brittle destruction of particles, in which the compaction receives a small compaction and the greatest adhesion due to strong further development of the contact surface. [7]

The pressed raw brick is laid with the help of a machine gun 38 on a furnace car 39 forming stacks. A furnace car with stacks of raw brick 41 is conveyed to a tunnel furnace 43 by means of an electric transmission trolley 42 and a pusher 40. Straight tunnel furnaces are continuous furnaces in which the semi-finished product is fired on wagons moving along the furnace. The tunnel furnace has three permanent zones: preparation (heating), burning (weighing) and cooling (cooling). [6 ]

The articles are fired at a temperature of 10001050 ° C. The temperature mode of brick firing is conditionally divided into four periods: drying (up to 200 ° C), heating (700800 ° C), actual firing (weighing - 9001050 ° C, cooling (cooling to 4050 ° C).

The baked articles 44 are stacked on a wooden pallet 47 by a crane relay 45 and conveyed by a roller conveyor 48 to a packaging device 49 for mechanically stacking the bags onto pallets and automatically packing them into a heat shrink film. The finished products are delivered to the finished product warehouse 51 by the forklift 50.

Conclusion

Annually, about 15 million tons of waste are sent from coal-processing plants of our country to dumps. The ash part of these wastes is in most cases clay with an Al2O3 content of up to 16%, and the combustion temperature of the wastes reaches 8400 kJ per 1 kg. Using them as a burnout additive is economically and technologically advantageous because it provides a more uniform distribution of the combustible mass in the calcined articles.

The main feature of the technology of brick production on coal enrichment wastes according to the semi-dry method of pressing is the reduction of heat and resource costs. Metal consumption is also reduced due to elimination of long-term process of brick drying.

Ceramic brick and stone are used for masonry and facing of bearing, self-supporting and non-bearing walls and other elements of buildings and structures.

The advantages of ceramic bricks include the following:

- high strength;

- good heat capacity;

- high level of sound insulation;

-aesthetics;

-ecologic.

The fire resistance of ceramic bricks is very high. Under the influence of fire, such a wall can be up to 10 hours, which increases the possibility of its use.

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