RU2200137C2 - Method of production of hydraulic binder - Google Patents

Abstract

FIELD: manufacture of building materials; production of hydraulic binders. SUBSTANCE: proposed method includes preparation of raw material mixture containing silica oxide SiO₂, calcium oxide CaO, magnesium oxide MgO, aluminum oxide Al₂O₃, ferrous iron FeO and ferric iron Fe₂O₃ followed by heat treatment and grinding of product thus obtained; content of said oxides in raw material mixture is no less than 70%; heat treatment of raw material mixture thus prepared is performed in presence of reductant by heating to temperature of 1300-500 C, after which melt is heated to 1800 C and iron-containing product is separated; then, melt is cooled to 1500 C and grinding of product is performed after granulation of melt; oxides contained in granulate have the following ration: (CaO+MgO)/SiO₂-0.5-1.7 and Al₂O₃/SiO₂-0.3-0.6. Water in the amount of 30 to 35% of weight of solid product may be added to ground product. Granulation of melt may be performed by cooling it with natural gas; gas formed after granulation of melt may be used as reductant. Wastes of coal concentration process or low-grade coal may be used as reductant. Ground product may be additionally mixed with finely-dispersed filler at ratio of 1?0.1-2). Ash-and-slag wastes of thermal power plants may be used as finely-dispersed filler. Flyash of coat thermal power plants and red mud of silica production process may be also used as finelydispersed filler. Water in the amount of 30 to 35% of weight of mixture may be added to mixture. Solutions of NaOH and/or KOH and/or Na₂CO₃ and/or Na₂SO₃ and/or K₂SO₃, and/or CaSO₃ may be added to mixture. Amount of said solutions is no less than 2-10 mass/% in terms of dry substance. EFFECT: reduced power requirements; improved quality of product; enhanced ecological safety. 14 cl, 1 dwg

Description

 The invention relates to the field of building materials and the environment and can be used to obtain a hydraulic binder.

Closest to the claimed solution is a method of obtaining a hydraulic binder from a raw material mixture comprising SiO ₂ , CaO, MgO, FeO and Fe ₂ O ₃ .

To obtain cement in this way, a raw mixture is prepared, the main components of which are limestone and clay in a ratio of 3: 1. These components are thoroughly mixed in the wet state, iron-containing additives - pyrite cinders are added to them, then the resulting raw material mixture is fired in rotary kilns at a temperature not exceeding 1450 ^o C. As a result of firing, solid particles with a diameter of 5-10 mm are obtained - cement clinker. The resulting clinker is subjected to grinding, gypsum in the amount of 5% is added to it, then the finished Portland cement is sent to the finished goods warehouse (GB 1596264, publ. 26.08.1981).

 This method has several disadvantages.

 Portland cement obtained in this way poorly resists the action of aggressive waters, when hardening it emits a significant amount of heat, which prevents its use in the construction of large monolithic structures, its strength is limited by an activity index of 60 MPa. These shortcomings characterize it as not high enough.

 In addition, the production of cement in this way is very costly from the point of view of the consumption of fuel and energy resources due to its high content of calcium oxide (75-80%), the formation of which consumes a significant proportion of the total amount of energy spent in the production of Portland cement.

 Portland cement production makes a significant contribution to environmental pollution, primarily dust emissions. In addition, for the extraction of clay and limestone - the main components of the raw material mixture for the production of Portland cement, quarries are used that grow as they are produced and capture more and more agricultural land, the price of which is constantly growing.

 The objective of this invention is to develop a method for producing a hydraulic binder, not inferior in main indicators to Portland cement, by changing the composition of the raw material mixture and intensifying the process of its heat treatment, improving the technological process, as a result, the consumption of fuel and energy resources is reduced, the energy consumption of the finished product is generally reduced, environmental pollution, its quality increases.

The problem is solved in such a way that in the method of producing a hydraulic binder, including the preparation of a raw material mixture, its heat treatment and grinding of the obtained product, according to the invention, the raw material mixture is obtained based on the following ratio of oxides in it:
% SiO ₂ +% CaO +% MgO +% Al ₂ O ₃ +% Fe ₂ O ₃ +% FeO = not less than 70%
after which the resulting mixture is heated in the presence of a reducing agent to a temperature of 1300-1500 ^o C, then the resulting melt is heated to a temperature of 1800 ^o C and the iron-containing product is separated, the melt is cooled to a temperature of 1500 ^o C, and grinding is carried out after granulation of the obtained product, while in the composition granules provide the following ratio of oxides: (CaO + MgO) / SiO ₂ - 0.5-1.7; Al ₂ O ₃ / SiO ₂ 0.3-0.6.

 In addition, the author believes that it is advisable to granulate the melt by any known methods, for example, water, however, the most effective way to granulate the melt is to use natural gas for this purpose. This makes it possible to use a significant part of the thermal energy of the melt for the conversion (conversion) of natural gas into a reducing gas, and not to lose it, as is the case with granulation with water.

 The resulting reducing gas is used to reduce iron oxides contained in the raw material mixture and to obtain an iron-containing product - ferrosilicon - a valuable raw material for the metallurgical industry.

 Coal wastes and low-grade coal can be used as a reducing agent.

 The product-granulate obtained as a result of melt granulation is subjected to grinding, then finely dispersed filler is added to it, ashes and slag waste or coal-fired thermal power plants ash, red mud - waste from alumina production, in the ratio of ground product / filler, as 1: (0 , 1-2).

Water is added to the resulting mixture in an amount of 30-35% by weight of the mixture, or solutions of NaOH, and / or KOH, and / or Na ₂ CO ₃ , and / or Na ₂ SO ₃ , and / or K ₂ SO ₃ , and / or CaSO ₃ , and the ratio of these substances to the grinding product is 2-10 wt.%.

 The author has proved that the combination of all the features of the invention allows to achieve the result specified in the task.

In accordance with the claimed method, the heat treatment of the raw material mixture is carried out at temperatures reaching 1300-1500 ^o C. In the process of increasing the temperature, the calcareous component decomposes into calcium oxide CaO and carbon dioxide CO ₂ . Then, as a result of the interaction of the particles of the mineral mixture with carbon, the process of reducing iron from the oxides that are in the mineral mixture begins.

When the temperature reaches about 1450 ^° C., the melting of the raw material mixture begins. The necessity of melting the raw mix is caused by the fact that in the liquid phase the processes of homogenization of the mixture by chemical composition occur several times faster than in the solid phase, and accordingly, the formation of new mineral compounds is accelerated. This ensures a higher intensity of the process of processing the feedstock into a new product.

When the temperature rises to 1800 ^o With the melt becomes more mobile. By lowering the viscosity of the melt, the process of separating the iron-containing product from the mineral mass is intensified. The presence of metal particles in the mass of the melt does not make it possible to granulate it. Thus, increasing the temperature to 1800 ^o With provides the final product of higher quality. The iron-containing product obtained at this temperature is ferrosilicon - a mixture of iron with oxides of other metals, for example nickel, chromium. It is a valuable raw material for the metallurgical industry, and its implementation positively affects the economic indicators of the proposed method.

When lowering the temperature of the melt to 1500 ^o C there is a partial regeneration of its thermal energy, which is used in the process, for example for pre-heating the raw material mixture. This saves fuel and energy resources, which positively affects the economic efficiency of the proposed method.

 Granulation of the melt allows you to save the glassy structure of the resulting product and its latent hydraulic activity, which is lost during the gradual cooling of the melt and its crystallization.

The granulate obtained is subjected to grinding to particle sizes having a corresponding specific surface area of at least 3000 cm ² / g. Finely dispersed filler is added to the grinding product, which is mainly used ashes and slag waste and ash from coal-fired thermal power plants, red mud - waste from alumina production. The amount of filler added is directly proportional to the quality (activity) of the obtained grinding product and is determined by the ratio of grinding product / filler = 1: (0.1-2). When the filler content is less than 0.1 of the weight of the grinding product, the activity of the obtained hydraulic binder becomes unreasonably high, which increases its cost (due to reduced yield) and narrows the scope of a possible, economically effective application. When the filler content is in an amount greater than twice the weight of the grinding product, an astringent of reduced activity is obtained, which also has a narrower scope. Thus, the given limits for the content of finely divided filler are optimal.

Ordinary water in the amount of 30-35% of the weight of the solid mixture, or the active component, represented by solutions of substances NaOH, and / or KOH, and / or Na ₂ CO ₃ , and / or Na, is added to the grinding product of the granulate or its mixture with a finely divided filler. ₂ SO ₃ and / or K ₂ SO _s, and / or SaSO _3, wherein the ratio of said substances to the product of grinding is 2-10 wt.%.

 The claimed method is as follows (see drawing).

From the bins 1, 2, 3, using the appropriate feeders 4, 5, 6 and the conveyor 7, the components of the raw material mixture containing oxides SiO ₂ , CaO, MgO, Al ₂ O ₃ , Fe ₂ O ₃ , FeO are fed to the mixer 8 in the required proportions . As such components, chalk and limestone mining waste, ash and slag waste, or ash from coal-fired thermal power plants, low-grade coal, coal preparation waste, and red mud, waste from alumina production, are mainly used in certain combinations.

 Other types of waste or industrial products that contain the above oxides in the indicated ratio can also be used.

 If the number of components of the raw mix is more than three, the number of bins and dispensers increases accordingly.

 When using low-grade coal or coal waste, the organic part of the fuel is partially used as a reducing agent.

In mixer 8, the components are thoroughly mixed. From the mixer, the mixture is continuously supplied to the heat treatment unit 9. This installation has any known design that allows the melting of mineral raw materials. In the installation 9, the mixture is gradually heated to a temperature of 1500 ^o C. At a temperature of 1300 ^o C the decomposition of the calcareous component ends to produce calcium oxide CaO and carbon dioxide CO ₂ . When the temperature reaches 1500 ^o C, the mixture begins to melt and enters the bath 10. The bottom of the bath has a slight slope in the direction from the beginning of the bath to its end. The slope is designed so that molten metal flows down the bottom of the bath 10 to its lowest point and accumulates there. In the front of the bath 10, the melt is blown by high-temperature combustion products of fossil fuels. The process of burning fuel is carried out with a lack of oxygen, so these combustion products have a reduction potential. Due to this, when the melt is purged, the final reduction of iron oxides that are contained in the mineral component occurs. In addition, the melt is mixed and homogenized, which is important for the final product.

In the middle part of the bath 10, the melt is heated to a temperature of 1800 ^o C, by one of the known methods, for example by electric heating using electrodes 11. In this case, the viscosity of the melt decreases sharply, those particles of the reduced metal are in it, freely fall to the bottom of the bath 10. In the back bath temperature of the melt decreases to 1500 ^o C due to the supply of cold air to its surface. In this case, partial regeneration of the thermal energy of the melt occurs. When the surface of the melt reaches a certain level, it flows out through a drain 12 into the melt granulation unit 13 with cold water. The molten metal that accumulates at the bottom of the bath 10 is periodically removed through a drain 12 in special containers not shown in the drawing.

 One of the features of the proposed method is that the granulation of the obtained melt can be carried out by any known means, for example, water, however, the use of natural gas for this is most economically feasible, since it makes it possible to utilize part of the thermal energy of the melt, which is lost during granulation with water. In this case, on the one hand, there is a sharp cooling of the melt particles, and on the other hand, the conversion (conversion) of natural gas into reducing gas.

 In the case of using natural gas for granulation of the melt, the granulation process is organized as follows.

 In the upper part of the bath containing the melt, a fluidized bed is formed by blowing it with high-temperature products of combustion of the fuel-oxygen mixture. The diameter of the melt droplets carried out from the mass of the melt during its purging is selected based on the need to ensure its cooling rate close to the cooling rate during water granulation. To ensure these conditions, flue gases at the exit from the purge zone must have a design speed equal to the speed of the melt droplets of a certain diameter.

 Cold natural gas is fed into the stream of dispersed melt and flue gases entering the upper zone of the bath to cool and granulate the melt. Such granulation will allow cooling not only due to contact with cold natural gas, but also due to heat removal as a result of the endothermic effect of the reaction of interaction of natural gas with high-temperature combustion products leaving the purge zone together with the dispersed melt.

As a result of this interaction, together with the granulate, a hot reducing gas is obtained that is close in chemical composition to the reducing gases of high-temperature oxygen conversion, which are used as a substitute for coke in the blast furnace process. The obtained granulate is sent to warehouse 16, where it is stored until it is used at the production site, or until loading into wagons and dispatch to other regions of Ukraine. The clinker used locally is fed to the grinding unit 15, where it is milled to a grain fineness corresponding to a specific surface area of at least 3000 cm ² / g. The result is a clean hydraulic binder, part of which is sent to the storage hopper 17, where it is stored until it is used.

 Another part of the obtained clean hydraulic binder is sent to the mixer 19, where finely dispersed filler, mainly ash and slag waste, fly ash, dump ash of coal-fired thermal power plants, red mud is the waste of alumina production in the amount required for it from the hopper 18a using a batcher 18a obtaining a mixed hydraulic binder with calculated indicators of mechanical and physico-chemical properties. The resulting mixture is thoroughly mixed and get a mixed hydraulic binder. To the obtained mixed hydraulic binder, ordinary water in the amount of 30-35% of the weight of the mixed binder, or the active component in an amount of from 2 to 10%, is added from the hopper 20 using the dispenser 20a.

The active components in accordance with the invention are solutions of substances NaOH, KOH, Na ₂ CO ₃ , Na ₂ SO ₃ , K ₂ SO ₃ , CaSO ₃ .

 Ready-to-use mixed hydraulic binder is loaded into concrete trucks 21 and delivered to the place of use.

 The invention is illustrated by the following examples of specific performance.

Example 1
Preparing a raw mix of the following composition:
Limestone - 600 kg.

Ash and slag waste of coal thermal
power plants - 400 kg.

The sum of% SiO ₂ +% CaO +% MgO +% Al ₂ O ₃ +% Fe ₂ O ₃ +% FeO was 71.5%.

The components of the mixture from storage bins 1, 2 (see drawing) through the appropriate dispensers 3, 4 by means of a conveyor 7 are fed into the mixer 8, where the mixture is homogenized. The resulting mixture is continuously loaded into the heat treatment unit 9. Here, the mixture is gradually heated to a temperature of 1300 ^o C. Heating is carried out by high-temperature combustion products of solid pulverized, liquid or gaseous fuel supplied to the installation using the appropriate burners. The molten slag enters the bath 10. The bath has a slight bias in one direction for the possibility of movement of the melt. In the front of the bath 10, the temperature is maintained at 1500 ^o C by blowing it with high-temperature combustion products of fossil fuels. The purge provides mixing of the melt and its further homogenization, and, consequently, a high degree of uniformity in the chemical composition of the granulate subsequently obtained. In the middle part of the bath 10, the temperature is brought up to 1800 ^{° C. by} any known method, for example by electric heating using electrodes 11. In this part of the bath, the slag and the reduced metal (ferrosilicon) are completely separated, which accumulates at the bottom of the bath. After the temperature of the slag is reduced to 1500 ^o C, the slag through the drain 12 in the rear of the bath 10 is continuously supplied to the granulation unit with cold water 13. The molten reduced metal is periodically removed through the drain 14 in the tank, not shown in the drawing. From 1000 kg of the raw material mixture, 36 kg of iron-containing product are obtained in the form of ferrosilicon and 660 kg of molten slag. After granulation with water, the resulting clinker is fed for grinding to the grinding unit 15. In accordance with one of the features of the proposed method, the obtained clinker can be used in other regions to obtain a hydraulic binder according to the proposed method, or as an active mineral additive in the production of Portland cement at existing cement plants . In this case, the granular clinker enters the warehouse in a storage tank 16, from where it is then loaded onto wagons.

As a result of wet grinding of clinker to particle sizes, which are characterized by a specific free surface area of at least 3000 cm ² / g, a pure hydraulic binder is obtained in the amount of 660 kg of the following composition,%: SiO ₂ - 41.5; CaO - 27.6; Al ₂ O ₃ - 25.4; MgO - 0.5; the rest is 5.0.

In this case, (CaO + MgO) / SiO ₂ = 0.7, and Al ₂ О ₃ / SiO ₂ = 0.6.

From the grinding plant 15, the milled clinker is continuously fed into the hopper 17, equipped with a dispenser 17a. In the hopper 18 with the dispenser 18a are ash and slag waste. Both components in quantity, kg:
Pure hydraulic binder - 660
Ash and slag waste - 460
served in the mixer 19, where they receive a mixed hydraulic binder in an amount of 1120 kg 340 kg of caustic soda solution containing 21 kg of NaOH are supplied to the obtained mixed hydraulic binder from the tank 20 by means of a dispenser 20a. The result is a mixed hydraulic binder, which is characterized by the following strength indicators: at the age of 3 days - 180 kg / cm ² ; at the age of 7 days - 290 kg / cm ² ; at the age of 28 days - 403 kg / cm ² ,
which corresponds to Portland cement brand M400.

 From the mixer, the finished mixed hydraulic binder is fed to the place of use, for example, using concrete trucks 21.

Example 2
Preparing a raw mix, which includes, kg:
Coal preparation waste with an ash content of 80% - 820
Quicklime - 180
The sum of% SiO ₂ +% CaO +% MgO +% Al ₂ O ₃ +% Fe ₂ O ₃ +% FeO was 81.6%.

As a result of firing and subsequent melting, 40 kg of reduced iron and 780 kg of slag of the following composition are obtained,%: SiO ₂ — 46.3; CaO 23.1; Al ₂ O ₃ - 19.3; the rest is 11.3.

In this case, (CaO + MgO) / SiO ₂ = 0.5, and Al ₂ О ₃ / SiО ₂ = 0.4.

After grinding, 250 kg of a solution containing 35 kg of NaOH are added to the specified amount of pure hydraulic binder. The result is a hydraulic binder, which is characterized by the following strength indicators: at the age of 3 days - 90 kg / cm ² ; at the age of 7 days - 170 kg / cm ² ; at the age of 28 days - 304 kg / cm ² ,
which corresponds to Portland cement brand M300.

Example 3
Preparing a raw mix of the following composition, kg:
Sand - 300
Limestone - 200
Red mud - 500
The sum of% SiO ₂ +% CaO +% MgO +% Al ₂ O ₃ +% Fe ₂ O ₃ +% FeO was 84.1%.

From 100 kg of the raw material mixture, 210 kg of iron-containing product are obtained in the form of ferrosilicon and 650 kg of molten slag of the following composition,%; SiO ₂ 24.6; CaO - 33.1; Al ₂ O ₃ - 14.2; MgO - 7.5; the rest is 20.6.

In this case, (CaO + MgO) / SiО ₂ = 1.7, and Al ₂ О ₃ / SiО ₂ = 0.6.

After granulation of the slag and its grinding, 1300 kg of red mud are added to it. The mixture is stirred, then 680 liters of pure water are added to it. The result is a mixed hydraulic binder, which is characterized by the following strength indicators: at the age of 3 days - 75 kg / cm ² ; at the age of 7 days - 180 kg / cm ² ; at the age of 28 days - 310 kg / cm ² ,
which corresponds to Portland cement brand M300.

 From the mixer, the finished mixed hydraulic binder is fed to the place of use, for example using concrete trucks 21.

Example 4
A raw mix of the following composition was prepared, kg:
Red mud - 550
Sand - 250
Quicklime - 250
The sum of% SiO ₂ +% CaO +% MgO +% Al ₂ O ₃ +% Fe ₂ O ₃ +% FeO was 93.0%.

From 1050 kg of the raw material mixture, as a result of heat treatment in accordance with the invention, 225 kg of iron-containing product and 717 kg of molten slag of the following composition were obtained,%: SiO ₂ - 31.4; CaO - 46.0; Al ₂ O ₃ - 9.8; the rest is 12.8.

Moreover, (CaO + MgO) / SiO ₂ = 1.5, and Al ₂ O ₃ / SiO ₂ = 0.3.

After grinding the granulated slag, 215 kg of a solution containing 35 kg of KOH was added to it. The result was a clean hydraulic binder, which is characterized by the following strength indicators: at the age of 3 days - 192 kg / cm ² ; at the age of 7 days - 310 kg / cm ² ; at the age of 28 days - 423 kg / cm ² ,
which corresponds to Portland cement brand M400.

 Thus, the inventive method allows to reduce the energy intensity of the finished product, improve the quality of the obtained binder and significantly reduce environmental pollution.

Claims (11)

1. A method of obtaining a hydraulic binder, including the preparation of a raw material mixture containing oxides of silica SiO ₂ , calcium CaO, magnesium MgO, aluminum Al ₂ O ₃ and ferrous and ferric iron FeO and Fe ₂ O ₃ , its heat treatment and grinding of the obtained product, characterized in that the total content of these oxides in the raw material mixture is at least 70%, and the heat treatment of the prepared raw material mixture is carried out in the presence of a reducing agent by heating to 1300-1500 ^o С, then the obtained melt is heated to 1800 ^o С and iron-containing is separated the product, the melt is cooled to 1500 ^o C, and the grinding of the obtained product is carried out after granulation of the melt, while the composition of the granulate provides the following ratio of oxides: (CaO + MgO) / SiO ₂ - 0.5-1.7; Al ₂ O ₃ / SiO ₂ 0.3-0.6.  2. The method according to p. 1, characterized in that to the obtained grinding product add water in an amount of 30-35% by weight of the solid product.  3. The method according to p. 1, characterized in that the granulation of the melt is carried out by cooling it with natural gas.  4. The method according to p. 1, characterized in that as the reducing agent use the gas formed after granulation of the melt.  5. The method according to p. 1, characterized in that as a reducing agent use waste coal or low-grade coal.  6. The method according to p. 1, or 3, or 4, or 5, characterized in that the grinding product is additionally mixed with an acceptable finely divided filler at a ratio of 1: (0.1-2).  7. The method according to p. 6, characterized in that as a finely divided filler, ash and slag waste from coal-fired thermal power plants is used.  8. The method according to p. 6, characterized in that as the finely dispersed filler use fly ash of coal-fired thermal power plants.  9. The method according to p. 6, characterized in that as a finely divided filler using red mud is a waste of alumina production.  10. The method according to any one of paragraphs. 6-9, characterized in that to the resulting mixture of grinding product and filler add water in an amount of 30-35% by weight of the mixture. 11. The method according to any one of paragraphs. 6-9, characterized in that to the resulting mixture of the grinding product and the filler are additionally added solutions of NaOH, and / or KOH, and / or Na ₂ CO ₃ and / or Na ₂ SO ₃ and / or K ₂ SO ₃ , and / or CaSO ₃ , and the amount of these solutions from the grinding product is 2-10 wt. % in terms of dry matter.