RU2847031C2 - Method and apparatus for producing carbonised building materials - Google Patents

Abstract

FIELD: metallurgy; chemistry.

SUBSTANCE: invention relates to equipment for production of carbonate hardening articles from industrial wastes of metallurgy and carbon dioxide. Invention relates to production of carbonized construction materials. Process employs recycled water which forms a condensate in carbonisation chambers when saturating articles with carbon dioxide. Present method enables to repeatedly and fully involve in process of moulding water, which additionally contains small amount of dissolved CO₂, beneficial effect on carbonisation process.

EFFECT: recycling carbon dioxide (CO₂), optimization of the process of producing carbonised building materials and composition of the equipment of the process line, absence of reaction water effluent.

10 cl, 10 dwg, 5 tbl

Description

The invention relates to equipment for producing carbonated products from man-made metallurgical waste and carbon dioxide. It addresses the fundamental problem of reducing the economy's carbon footprint, particularly in the oil and gas refining, metallurgy, and construction industries. It is based on the development of scientific and technological foundations for the absorption and binding of anthropogenic CO2 by various metallurgical slags and sludges as a result of their processing into raw materials for building materials and products. The production line for carbonized building materials can be used in the production of concrete products, bricks, and paving slabs, as well as in the construction of buildings and structures requiring materials with increased strength and durability.

For the purposes of this application, the following definitions apply:

The carbonization process is a process that results in the saturation of any product with carbon dioxide;

Secondary products of metallurgy are metallurgical slags, a by-product of metal production after cleaning from the remains of valuable components, sent to the waste heap.

Construction materials are materials used in construction for the construction, repair and reconstruction of buildings, such as hollow bricks, paving slabs, concrete blocks and others.

TOM - man-made metallurgical waste (slag, sludge, etc.).

The carbonization process for building materials addresses the fundamental problem of reducing the economy's carbon footprint, particularly in the oil and gas refining, metallurgy, and construction industries. It is based on the development of scientific and technological foundations for the absorption and binding of anthropogenic CO2 by various metallurgical slags and sludges as a result of their processing into raw materials for building materials and products. Furthermore, this technology for producing building materials, given specific regional, logistical, economic, and technical conditions, may be more easily implemented than traditional production technologies for similar building materials.

The prior art contains numerous known solutions in terms of equipment, process lines and installations or production complexes intended for the production of building materials such as ceramic bricks, clinker bricks, paving slabs, etc. For example, a complex for the production of ceramic bricks [RU 2051032, published: 27.12.1995] or building bricks, a method and a set of equipment for their production [RU 2275343, published: 27.04.2006] or a process line for the production of ceramic bricks [RU 2726000, published: 08.07.2020] or a stationary molding complex for the production of concrete products [RU 2694671, published: 16.07.2019].

At the same time, solutions for the production of carbonized building materials are also known.

In particular, prior art discloses solutions that utilize by-products or secondary products from metallurgical production (in particular slags and sludges) as raw materials. In the Arcelormittal solution according to the invention [WO 2019064052, published 04.04.2019], molten steelmaking slag containing at least 2% by weight of free lime is solidified to produce solidified slag particles having a diameter of less than 1 mm. During solidification, the molten steelmaking slag is brought into contact with at least one first carbonization gas. The solidified slag particles are cooled to a temperature of 300°C or lower at a rate of 1 to 100°C/min, wherein during cooling, the solidified slag particles are brought into contact with at least one second carbonization gas. A device for continuously producing solidified steelmaking slag comprises a closed chamber containing a solidification device, a device for injecting a first carbonization gas, a device for injecting a second carbonization gas, a lower porous wall, and a device for injecting a third carbonization gas through the lower porous wall. This ensures the production of solidified slag with a low free lime content while maintaining a short processing time.

Also known from the prior art are a number of solutions related to equipment for carbonate hardening and forced carbonization of building materials.

A device for producing bricks is known [CN112318681, published 05.02.2021]. The invention discloses a method of operating a device for producing a brick body carbonized with carbon dioxide, and relates to the field of producing bricks for construction. The invention specially develops two processes of pre-carbonization and secondary carbonization, so that demolding and rapid strengthening are smoothly completed after the temporary stabilization of the shape and strength of the brick body. All systems in the device operate in accordance with a sequence of process operations, so that loading, molding, compaction and transportation of the brick mold are carried out simultaneously, the addition of brick material and uniform mixing are performed during the pre-carbonization process, productivity is increased due to the two-stage process and the transportation system; The upper conveyor belt and the lower conveyor belt rotate by means of a rotating shaft, the brick bodies are removed from the molds through spring stoppers in the brick molds, and the demoulding of the brick bodies and the effective cyclic use of empty brick molds are achieved through electromagnetic adsorption, release and transportation of the conveyor belts.

A technical solution is known in the field of carbonization and graphitization equipment [CN219433778 (U), published 07/28/2023]. The integrated carbonization and graphitization furnace comprises a furnace body and an internal container chamber, which is located in the center of the furnace body interior. The furnace body and the outer door are connected so as to rotate relative to the inner part. A cylindrical exhaust opening is formed in the upper part of the furnace body; inlet and outlet openings for cooling water are located on the outer side door of the furnace; an air inlet opening and an air outlet opening are formed on the left and right sides of the furnace body, respectively.

The closest analogue is the "Method for producing composite carbonized products" [RU 2549258 published: 20.04.2015]. The invention relates to the construction industry and can be used for the production of wall products. The method for producing composite carbonized products includes molding the products from a molding mass obtained on the basis of slaked calcium or dolomite lime and a filler in the form of waste from the extraction and processing of limestones with a fraction of up to 5 mm, molding is carried out under a pressure of 50-150 kgf/cm2, carbonization of the products with carbon dioxide at a flow rate of 0.2 l/cm2 min for 3-6 hours. The method ensures the production of an artificial material with a strength of 9-20 MPa at an average density of 1350-1700 kg/m3, the softening coefficient of which is 0.77-0.88.

The features of the invention, which coincide with the features of the closest analogue, are the presence in the method of producing composite carbonized products of molding the products by pressing from a molding mass, carbonization with carbon dioxide.

The main drawback of the prototype describing the method for producing composite products is the use of slaked calcium or dolomite lime in the process. The use of yet another additional component increases the cost and complicates the production process, while not changing their fundamental properties. Furthermore, the additional component inevitably impacts in-plant logistics and storage, as well as the composition of the process equipment. Involving an additional component in the process inevitably entails the use of bulky equipment, such as additional crushers, dryers, molds, etc. Furthermore, there is a lack of understanding of how the use of slaked calcium or dolomite lime in the molding process affects the carbonation process. Calcium and magnesium oxides, silicon oxide, and other substances found in industrial metallurgical waste, which are the main components of the proposed technical solution, are the substances that bind and react with carbon dioxide to create a highly durable carbonized material. In addition, the prototype inevitably faces the problem of recycling reaction water, which forms as condensate during the carbonation process.

PROBLEMS AND TECHNICAL RESULTS

The technical result of the invention is the utilization of carbon dioxide (CO2). It also optimizes the manufacturing process of carbonized building materials and the composition of the process line equipment. Another technical result is the elimination of reaction water waste.

In one cycle (16 hours of operation), the production line will produce over 36,000 bricks and utilize up to 13 tons of CO2. Building products produced using this technology will contain up to 15% CO2.

Another distinctive feature of this method for producing carbonate-hardened products is the use of recycled water, which forms as condensate in carbonation chambers during the saturation of the products with carbon dioxide. This method allows for the full and repeated use of water in the molding process, which additionally contains small amounts of dissolved CO2, which has a beneficial effect on carbonation. Reusing recycled water reduces water consumption and the cost of constructing on-site treatment facilities. An additional advantage is the incorporation of dissolved CO2 into the product structure already at the molding and raw material mixing stage. The use of recycled water stimulates carbonation reactions within the product mass, which consequently increases product strength. This achieves not only high surface strength, primarily due to the gas-phase carbonization process in the chamber, but also liquid-phase carbonization of the raw materials during the mixing stage of the initial components.

Thus, the technical result is ensured by the method of producing carbonized building materials, including the preparation of raw materials, which are mineral raw materials and man-made metallurgical waste, by drying, grinding and sorting, wherein man-made metallurgical waste and mineral filler are used as raw materials, mixing and homogenization, adding water, molding, pressing, stacking, forced carbonization in a carbonation chamber at atmospheric pressure, room temperature and a CO2 concentration of at least 80% by volume. for 4 - 6 hours, wherein condensate from the carbonation chamber is returned to the molding stage and is involved as impregnation in a ratio of fresh water to recirculated water of 5:1, and the process of carbonate hardening in the chamber occurs without forced circulation of the gas mixture in the chamber.

And a plant for the production of carbonized building materials, including a raw material preparation unit, a molding unit, a carbonate curing unit, including at least one sealed carbonation chamber with process lines for the supply and removal of carbon dioxide, a carbon dioxide preparation unit, a product packaging section, while from the carbonate curing unit the reaction water recirculation line goes to the molding unit.

DESCRIPTION OF DRAWINGS AND DRAWINGS

The method and installation for producing carbonized building materials are illustrated by several images. Specifically, Figure 1 shows the general process flow diagram of the installation, where:

1. Slag drying drum;

2. Crushing and sorting complex;

3. Slag/sludge mill;

4. Slag/screenings storage bin;

5. Silo for ground sludge/slag;

6. Doser/Bunker scales;

7. Raw material mixer - preparation of molding mixture (mixing);

8. Molding press - preparation of products;

9. Carbonation hardening section - consists of 8 carbonation chambers;

10. Packaging unit - transfer of finished carbonate hardening products from reusable pallets to disposable pallets;

11. Finished goods warehouse.

12. Water capacity;

Interstage processes:

13. Bucket loader;

14. Belt conveyor – delivery of raw materials and other components;

15. Screw conveyor – movement of mixtures through the stages of preparation;

16. Manipulator - placing formed products on pallets;

17. Forklift;

Figure 2 shows a diagram of the material flows for the production of carbonate-hardened bricks.

Figure 3 shows photographs of manufactured samples of carbonate-hardened building products, where: a - a pilot batch of paving slabs based on steel-smelting slag after molding, b - a pilot batch of paving slabs based on electric steel-smelting slag after molding, c - a pilot batch of bricks based on nepheline sludge after molding; d - general view of the tested products.

Figure 4 shows photographs illustrating the general course of testing for silicate decomposition, in particular: a - view of the test products, b - general view of the products before the steaming cycle, c - general view of the test products after the 3rd steaming cycle, g - general view of the test products after the 3rd steaming cycle, d - brick after the 3rd steaming cycle, e - tile after the 3rd steaming cycle, g - example of a brick compression test after the 3rd steaming cycle, h - example of a tile compression test after the 3rd steaming cycle.

Figures 5-7 show X-ray diffraction patterns of material samples. Figures 8-10 show thermograms of material samples.

Figures 5 - 10 provide data based on steelmaking slag, electric steelmaking slag and nepheline sludge.

DETAILED DESCRIPTION OF THE GROUP OF INVENTIONS

Raw material base:

- nepheline sludge;

- steelmaking slag;

- electric steelmaking slag.

- waste from stone mining and rock processing (mineral raw materials);

- carbon dioxide captured from exhaust gas streams (concentration ≈80 vol.%).

Composition of the technological line:

- raw materials storage area;

- a raw material preparation unit in which slags are prepared (drying, grinding, classification), mineral raw materials (classification);

- carbon dioxide preparation unit;

- molding block;

- carbonization hardening block;

- product packaging section;

- finished goods warehouse.

The raw materials storage area is a warehouse facility that includes covered storage areas for sludge/slag and mineral raw materials.

The raw material preparation unit is a platform where the following equipment, which is part of the installation, is located:

- drum dryer for drying sludge/slag and mineral raw materials;

- crushing, grinding and sorting complex for processing sludge/slag and mineral raw materials;

- belt and screw conveyors for feeding prepared raw materials for processing and storage;

- pneumatic transport for transporting ground raw materials to the silo;

- silo for storing ground raw materials;

- consumption bins for storing mineral filler.

The carbon dioxide preparation unit is a standard piece of equipment for cleaning, settling and providing the required temperature and pressure of the gas, which is then fed into the carbonation chambers.

The molding unit includes:

- high-speed mixer-activator with a dosing complex;

- hydraulic presses for semi-dry pressing;

- robots for stacking molded products on pallets;

- water container;

- belt and screw conveyors for transporting raw materials and molding sand.

The carbonization curing unit is a complex of carbonization chambers and a manipulator complex for loading and unloading pallets with products and transporting products after carbonization to the packaging area.

The product packaging section is located in a covered workshop and is equipped with a machine for transferring products from pallets to pallets and a machine for packaging products in polyethylene film.

The finished goods warehouse is a covered area. Forklifts are used for storing and loading finished goods.

DESCRIPTION IN STATICS

The installation includes the following main elements:

- raw materials storage area;

- a raw material preparation unit in which slags are prepared (drying, grinding, classification), mineral raw materials (classification);

- carbon dioxide preparation unit;

- molding block;

- carbonization hardening block;

- product packaging unit.

The basic technological scheme for the production of carbonate hardening products is shown in Figure 1.

Brief description of the installation operation.

The drum dryer (1) is used to dry sludge/slag and mineral raw materials delivered from the raw material storage warehouse by a bucket loader (13). The dryer is followed by a crushing, grinding, and screening complex, which processes and crushes sludge/slag and mineral raw materials to a specific particle size (if necessary). It includes equipment such as a crusher (2), a slag/sludge mill (3), a slag/screenings storage bin (4), and a ground sludge/slag silo (5). All equipment is connected by belt (14) and screw (15) conveyors for feeding the prepared raw materials for processing and storage. Next come hopper scales or a batcher (6). The mixer (7) is located after the scales. The carbon dioxide preparation unit was not developed separately; this equipment is not unique. For industrial applications, it is assumed that standard solutions in the field of CO2 capture will be used, such as amine purification of flue gases with subsequent storage of CO2 in a gas holder and then direct supply of gas to the carbonation chamber. Next, there is a molding block, which contains a high-speed mixer-activator (7) with dispensers (6); one or more hydraulic presses (8) for semi-dry pressing; robots for placing molded products on pallets; a water tank (12); belt and screw conveyors for transporting raw materials and molding sand. In which the formation of products (bricks, paving slabs, etc.) takes place, as well as the necessary piping and shut-off and control valves. A manipulator (16) is used to move the formed products. The carbonation hardening block consists of eight free-standing carbonation chambers (9). Gas from the CO2 preparation and storage area is supplied to the carbonation chamber. The water generated during carbonation is also discharged directly from the carbonation chambers (9) into a water tank (12), which is then recycled into the mixer (7). Finished carbonated products from the carbonation chambers (9) are transferred from reusable pallets to disposable pallets using stacking machines in the packaging unit (10). The pallets with the products are transported to the finished product warehouse (11) using forklifts (17).

In order to ensure an optimal and continuous production process, the installation can optionally include several carbonization chambers, depending on the performance of the other equipment in the installation and the logistics organization.

The carbonation chamber is designed with top or bottom CO2 supply and a false floor and false ceiling, which optimizes the distribution of the temperature field, CO2 concentration and minimizes the movement of the gas flow inside the chamber.

According to the first embodiment of the invention, the carbonization chamber includes a housing, a door that ensures the tightness of the internal volume of the chamber, process pipelines for the supply and removal of CO2 as a working medium in the chamber, a space for placing carbonized products subject to carbonate hardening, in which a false floor is provided for supplying CO2 to the lower part of the chamber and a gas supply chamber under the false floor, and a false ceiling is also provided, and a vacuum space in the intake area, which is located in a niche above the level of the false ceiling at the top of the rear wall of the chamber, made inclined from the rear wall to the door.

According to a second embodiment, the carbonization chamber of the invention includes a housing, a door that ensures the tightness of the internal volume of the chamber, pipelines for supplying and removing the working gas - CO2, and a false ceiling, wherein the pipeline for supplying the working gas is located at the top, above the false ceiling, above which a gas accumulation space is organized, and the false ceiling is a porous structure that ensures the filling of the chamber with the working gas under the action of gravity.

Drainage lines are routed from the carbonization chamber(s), collecting condensed CO2-saturated moisture. The drainage lines are routed to the molding press.

DESCRIPTION IN DYNAMICS

Raw materials arrive at the plant by truck, are stored in covered warehouses, and are then transported to the production unit.

The installation works as follows.

Preparation of raw materials consists of drying, grinding, sorting (classifying) and storing the prepared raw materials.

Man-made raw materials (slag, sludge) are fed from the warehouse to a drum dryer (1) for drying, after which they are crushed in an automated crushing and sorting complex (2) and sent for grinding to a centrifugal impact mill (3) to produce a fine-grained product with the required specific surface area. After grinding, they are sent to a sludge/slag storage silo (5).

The mineral is fed to the dryer (1), then crushed (if necessary) and then fed to the storage bin (4).

Ground industrial raw materials from the silo (5) and mineral raw materials from the feed bin (4) are loaded using a dosing device (6), a DU-300 type dosing device, into a high-speed mixer-activator (7) (homogenizer) and mixed. After homogenization of the mixture of industrial raw materials and mineral filler, the required amount of water is added from a water tank (12) to the mixer and mixed to evenly distribute the water throughout the mixture. If necessary, additional components, such as pigments, are added to the mixer. This prepares the molding sand.

The molding sand is prepared using water, including recycled water, generated during the carbonation process of the slag minerals. CO2-saturated water, recirculated from the carbonization chamber(s) for molding, is mixed with fresh water in a 1:5 ratio.

The molding mixture is fed from the mixer (7) via a belt conveyor (14) into the feed hopper of a hydraulic press (8), such as the industrially known A-350 molding press. The press presses the required assortment of molded parts at a specific pressing pressure of 20–30 MPa. The molded parts are then placed on reusable pallets by a stacking robot. After each layer of molded parts is filled, a worker manually lays a 5 mm thick polymer mesh on the surface of each layer, except the top one, to ensure gas access to all surfaces of the molded parts.

Next, the pallets with the products are fed to the carbonization hardening section using a manipulator complex (16).

Hardening of the products occurs in carbonization chambers (9), which are separate, hermetically sealed, periodic chambers. Loading and unloading of products into the carbonization chamber can be accomplished, in particular, using a manipulator complex (16). Each chamber can accommodate eight pallets of products.

The manipulator complex represents mechanical devices that ensure the transportation of pallets with products to the chamber, loading of pallets with products into the chamber, removal of pallets with products from the chamber and placing of products on pallets, transportation of pallets with products to the place of decoration and/or packaging of products (10).

After loading the products into the carbonization chamber(s) (9), the door is hermetically sealed and a gas mixture with a CO2 concentration of approximately 80 vol.% is introduced. From the moment the gas is introduced into the chamber, the process of forced carbonization of the products begins.

After the required time for carbonization of the products has elapsed, the gas supply to the carbonization chamber (9) is shut off, air is blown through it for 10 minutes, after which it is opened, the finished products are unloaded using a manipulator complex and transported to the place where they are transferred to pallets and packaged.

Transfer of bricks from pallets to pallets is performed by a stacker manipulator. Before transfer, the bricks on the pallet are shifted so that they fit snugly against each other. A stack of bricks is transferred from the pallets to the transport pallet using a stacker manipulator. Two stacks of bricks, formed on two pallets, are placed on a single transport pallet. Pallets with bricks can be moved, for example, along a roller conveyor to the packaging station for shrink wrapping using an automatic pallet wrapper.

The packed pallet with products is removed from the roller conveyor of the packaging post by a forklift (17) and “tied” with strapping tape manually using a manual strapping machine.

The packaged products, in particular, can be moved by a forklift (17) to the finished product warehouse (11) and stored in stacks.

Reaction water.

During carbonization, reaction water and heat are released at a rate of 353.7 kJ/mol. To maintain the temperature in the carbonization chamber at 20 to 30°C, it must be cooled. During this process, the released reaction water will condense. Water contained in the prepared furnace gases will also condense. According to the process flow diagram, the condensed water is removed from the carbonization chamber, collected in a container, for example, using pumps, and then used to prepare the molding sand.

The initial data for calculating the amount of released reaction water and water entering the carbonation chamber with furnace gases are:

- moisture content of the molding mixture - 8% by weight;

- mass of gas mixture - 405.82 kg;

- the average moisture content in gases after installation of the KCA LCH-35/11-1000 is 4.9% by weight.

Calculation of the water released during the reaction (water evaporating as a result of heating the material).

According to the chemical reaction equation (2.1), two water molecules are required to carbonate one molecule of γ-Ca2SiO4. 1426 kg * 0.445 = 634.57 kg of γ-Ca2SiO4 were carbonated. This means the following amount of chemically bound water was used in the reaction:

From the previous calculation, the mass of water required to humidify the mixture is 248 kg. Therefore, during the carbonation process, the following amount of water will be released as a result of the exothermic reaction during heating:

248-132.81=115.19 kg.

During brick carbonation, not all the water will be released as free water; some will be absorbed by the brick material, remaining in its pores. Experiments have shown that the moisture content of laboratory test samples and wall products (bricks) after forced carbonation is 2%, meaning the mass of the products after carbonation is 3,309.48...1.02 = 3,375.66 kg. They contain 3,375.66 - 3,309.48 = 66.18 kg of water. Therefore, the final amount of water released will be:

115.19 - 66.18 = 49.01 kg.

Carbonate hardening mode of bricks.

The forced carbonization mode of products in the chamber takes place in an artificially created environment with an increased concentration of CO2 in three stages:

1st stage - active carbonate hardening:

- duration - 30 min,

- the amount of CO2 that needs to be supplied to the chamber is 200 kg;

2nd stage - moderate carbonate hardening:

- duration - 90 min,

- the amount of CO2 that needs to be supplied to the chamber is 100 kg;

Stage 3 - exposure to carbon dioxide:

- duration - 120 min,

- the amount of CO2 that needs to be supplied to the chamber is 100 kg.

Characteristics of gas mixture and flow.

Temperature (min-max values) - 20-30°С.

CO2 concentration (min-max values) - 80-90% vol.

The flow rate when feeding into the chamber is 1.2 m/s.

Pressure - 101505 Pa.

Operations performed.

1. Feeding pallets with bricks into the carbonization chamber with a capacity of 8 pallets.

2. Forced carbonization of bricks.

3. Removing pallets with bricks from the carbonization chamber.

4. Feeding pallets with bricks to the brick packaging and packing station.

EXAMPLES OF IMPLEMENTATION

In practice, the construction and launch of production at a facility implementing a group of inventions was implemented.

Basic technological rules for performing operations:

Bricks placed on a pallet are fed into the carbonization chamber immediately after they have been molded.

The CO2 gas flow is fed into the carbonation chamber after the chamber has been filled with 8 brick trays and the carbonation chamber gates have been closed.

The CO2 gas flow should be supplied during the time period from the start of the carbonization process:

- from 0 to 30 minutes - at a speed of 1.2 m/s;

- from 30 to 120 minutes - at a speed of 0.2 m/s;

- from 120 to 240 minutes - at a speed of 0.15 m/s.

After 240 minutes of carbonization, the supply of CO2 gas mixture to the carbonation chamber is stopped. To displace the CO2 from the carbonation chamber, atmospheric air is introduced through the air ducts at a speed of 1.2 m/s for 10 minutes.

After the carbonation chamber has been purged with air, the gates of the carbonation chamber are opened and the pallets with bricks are removed from the carbonation chamber using a manipulator complex and fed to the stacking station (pushing the bricks into a tight stack) and packaging.

Control.

The temperature, CO2 concentration, gas pressure in the carbonation chamber and the gas flow rate at the entrance to the carbonation chamber are controlled by the laboratory technician by taking readings from the instruments.

The rate of gas supply to the chamber can also be controlled by the CO2 concentration in the outgoing streams.

If the CO2 concentration in the exhaust streams equals the CO2 concentration in the gas streams fed into the chamber, the gas supply can be stopped. However, the carbonization process should not be stopped; instead, the products should be held in the chamber for the period specified in the process documentation, as holding the products in an environment with a higher concentration is necessary for the formation of the carbonized material structure.

At low CO2 concentrations in exhaust gases (≤ 5% vol.), the exhaust gases can be discharged into the atmosphere.

If the concentration of CO2 in the exhaust gases is higher, it is advisable to re-introduce the latter into the process by mixing them into the gas mixture, preferably after first passing them through a CO2 separation unit.

The CO2 concentration in the chamber must be controlled in at least three zones:

- the lower part (below the pallets with products);

- at the level of the top row of products placed on pallets;

- in the upper part of the chamber (under the ceiling).

Depending on the CO2 concentration at the level of the top row of products, the rate of gas supply to the chamber should be adjusted, thereby maintaining a constant concentration of carbon dioxide in the area where the products are located.

CO2 monitoring is performed using gas analyzers that detect gas within the chamber. Measurements are continuous. An analog signal of 4.20 mA continuously outputs a value, where 4 mA is the minimum gas concentration, and 20 mA is the maximum gas concentration.

Three control zones: lower, middle, and upper. The lower and upper zones are controlled by sensors. The middle cavity is controlled by linear interpolation between the readings of the upper and lower sensors.

The chamber allows for a controlled carbonization process, achieving optimal building material properties. A conveyor system, consisting of a frame and drive elements used to move, load, and unload loads (pallets) along a horizontal surface, can also be integrated into the carbonization chamber.

When compiling the material balance for a production line for carbonate-cured wall products using nepheline slurry, the stoichiometric equations of chemical reactions and the compositions of the feedstock and finished product were taken into account. The material balance was calculated for the production of 1,000 carbonated bricks.

The material balance was calculated for two variants of brick compositions based on ground nepheline slurry, differing in the type of filler:

1) nepheline waste sludge was used as a filler;

2) crushed limestone screenings were used as filler.

Calculation of the material balance of the production of 1000 pieces of carbonate hardening bricks.

The mass of one dry carbonized brick measuring 250 x 120 x 65 mm is 3.3 kg. Therefore, after the final stage (stage #5), the output should be 3.3 x 1000 = 3300 kg of bricks.

We begin the raw material calculation with the carbonation stage, since by this stage the mass of the raw mixture increases due to the carbonization of the active minerals in the sludge. These transformations are described by the following chemical reaction equations:

According to X-ray phase analysis data, the content of active minerals in the sludge before carbonization was:

after carbonation:

According to equation (1), the mass of β-Ca2SiO4 increases by 200/172 = 1.163 times when converted to CaCO3. Accordingly, after carbonization, 35.4×1.163=41.2% of β-Ca2SiO4 remains. Then, 85.7 - 41.2 = 44.5% of β-Ca2SiO4 was carbonized.

The composition of the raw mixture is given in Table 1.

Table 1. Compositions of raw mixtures for brick production.

Name of raw materials and ingredients Composition of raw mixtures, % by weight. Nepheline sludge, crushed to a specific surface area of 2800 to 3400 ^cm2 /g 46 Nepheline waste sludge 46 Water 8 TOTAL 100

When entering the mixer, 1 ton of raw mix will contain 460 kg of nepheline slurry crushed to a specific surface area of 2800 to 3400 cm2/g (hereinafter NSS), 460 kg of nepheline waste slurry (hereinafter NSS), and 80 kg of water. To produce 1,000 bricks, 3.1 tons of raw mix will be required, consisting of 1426 kg of NSS, 1426 kg of NSS, and 248 kg of water.

Thus, the NSHI sludge contains the following minerals:

γ-Ca2SiO4: 1426 kg * 0.445 = 634.57 kg;

the rest: 1426 - 634.57 = 791.43 kg.

In terms of studying the operational properties and durability of carbonized building products based on TOM, tests were conducted on: resistance to decay (silicate decay);

During the tests, the following analysis methods were used to study the structure of the product material and its changes during the tests:

- differential thermal and thermogravimetric;

- X-ray phase;

To compare the properties of the final products, samples were used that were produced using the same process, but without using the water generated in the carbonation chambers as a binding agent. In this case, ordinary tap water was used.

The results obtained during testing of samples for resistance to decay are presented in Tables 2 and 3.

Table 2. Test results of samples after 30 days of storage in a container with distilled water before steaming.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength reduced to cylinder, MPa A b Samples of tiles based on electric steelmaking slag 1 7 7 41125 8.3 82.3 66.7 2 7 7 40750 8.3 81.5 66.1 3 7 7 41250 9.3 82.5 66.8 Average 8.6 82.1 66.5 Samples of tiles based on steel slag 1 7 7 49500 6.7 99.0 75.2 2 7 7 53625 6.7 107.3 81.5 3 7 7 48000 6.6 96.0 73.0 Average 6.7 100.8 76.6 Samples of bricks based on nepheline mud 1 25 12 110500 10.1 36.8 - 2 25 12 109675 10.2 36.6 - 3 25 12 111250 9.9 37.1 - Average 10.1 36.8 -

Table 3. Test results of samples after 30 days of exposure in a container with distilled water and subsequent three steaming cycles.

No.
p/p Geometric dimensions, cm Breaking load, kgf Water absorption by weight, % Sample strength, MPa Strength reduced to cylinder, MPa A b samples of tiles based on electric steelmaking slag 1 7 7 36625 9.1 73.3 59.4 2 7 7 41625 8.9 83.3 67.5 3 7 7 42750 9.5 85.5 69.3 Average 9.2 80.7 65.4 samples of tiles based on steel slag 1 7 7 45,000 6.8 90.0 68.4 2 7 7 54000 6.2 98.2 74.6 3 7 7 47125 6.9 94.3 71.7 Average 6.6 94.2 71.6 samples of bricks based on nepheline mud 1 25 12 115750 9.6 38.6 - 2 25 12 117,000 9.9 39.0 - 3 25 12 116250 9.7 38.7 - Average 9.7 38.8 -

During silicate decomposition tests of tile and brick samples, no processes (cracking, surface peeling) indicating material degradation were detected. As can be seen from Tables 2 and 3, the water absorption by weight of the samples before and after steaming remains virtually unchanged, and the variation in values is within the experimental error. If silicate decomposition occurs within the material (the polymorphic transformation of 2CaO⋅SiO2 from one form to another), its water absorption should increase significantly. As can be seen from Tables 2 and 3, the average compressive strength of the tile samples based on electric steelmaking slag remains virtually unchanged before and after steaming. However, the average compressive strength of the tile samples based on electric steelmaking slag decreased from 100.8 MPa to 94.2 MPa after steaming. In case of silicate decomposition (polymorphic transformation of 2CaO⋅SiO2 from one form to another), the compressive strength should decrease more significantly, up to complete spontaneous destruction of the samples during steaming cycles. In this case, it should be taken into account that in Table 2, sample No. 2 showed a strength of 107.3 MPa, and in Table 3, sample No. 1 - 90.0 MPa, which led to the difference in the indicators in the calculation of the average value (100.8 and 94.2 MPa, respectively). If these samples are excluded from the calculation of the average value, the difference in the strength indicators is virtually absent (97.5 and 96.3 MPa, respectively). The classical nature of the destruction of the tile samples (in the form of two pyramids, see Figure 4, h) also indicates the homogeneity and coherence of the material structure after steaming cycles, and a uniform distribution of stresses in the volume of the material during its loading. These signs also indicate the absence of silicate decomposition processes. Thus, the test data demonstrated the resistance of the obtained carbonized material of tiles and bricks to silicate decomposition.

After testing the samples for compression (see Figure 4-g, Figure 4-z), samples of the material were taken for X-ray phase, thermal, and microscopic analysis.

An analysis of X-ray diffraction patterns (Figures 5-7) revealed that the mineralogical composition of the steelmaking and electric arc furnace slag samples is based primarily on aggregate minerals introduced into the raw mix during tile production, namely, albite, clinochlore, and quartz. Residual minerals in the slags include silver dolskite, merwinite, strontium silica sulfide, and titanium, magnesium, and iron oxides of varying oxidation states. Calcite was identified as a product of forced carbonation in all samples, and aragonite, a metastable polymorph of calcite, was also found in the nepheline mud brick sample. The quantitative distribution of these minerals is presented in Table 2.4. It should be noted that during the production of tile samples under industrial conditions, the filler:slag ratio was 60:40. The results of quantitative X-ray fluorescence analysis (see Table 2.4) confirm this ratio for the steelmaking and electric steelmaking samples (61.7 and 63.1%, respectively), taking into account the error of this type of analysis. In turn, the 40% slag (in the form of mineral-forming phases) in the composition of the original raw mixture after carbonization decreased to values 18.5 and 25.3% for steelmaking and electric steelmaking, respectively. This decrease is due to the occurrence of a chemical carbonation reaction between the active minerals of the slag and gaseous CO2 with the formation of the reaction product - calcium carbonate in the form of calcite and aragonite minerals. It is also evident that in all X-ray diffraction patterns the highest intensity of diffraction reflections is inherent to the minerals albite and calcite, which indicates their highest content in the sample and good crystallinity, which is especially important for artificially obtained CaCO3 in the form of calcite and aragonite.

Table 4. Mineralogical composition of material samples based on various TOMs after tests for resistance to decay

Item No. Name Formula Quantity in sample, % wt. steelmaking electric steelmaking nepheline Filler minerals 1 Albite NaAlSi3O8 42.2 46.1 - 2 Clinochlor (Mg,Fe,Al)6(Si,Al)4O10(OH)8 10.2 10.0 - 3 Quartz SiO2 9.3 7.0 - TOTAL 61.7 63.1 - Minerals of the original slag/sludge 1 Srebrodolskite Ca1.94Na0.06Fe2O5 9.8 - - 2 Merwinite Ca3Mg(SiO4)2 - 11.8 - 3 Strontium silica sulfide Sr2SiS4 5.0 9.7 - 4 Hongkwiit TiO1.27 2.0 2.0 - 5 Iron magnesium oxide (MgO)0.432(FeO)0.568 1.7 1.8 - 6 Larnite β-Ca2SiO4 - - 30.1 TOTAL 18.5 25.3 30.1 Minerals formed by forced carbonation 1 Calcite CaCO3 19.8 11.7 58.9 2 Aragonite CaCO3 - - 11.0 TOTAL 100.0 100.1 100.0

The mineralogical composition and the nature of phase transformations during heating of the test samples were also studied using combined differential thermal analysis and thermogravimetric analysis. The DTA and TGA results for the test samples are presented in Figures 8-10.

The results of combined thermal analysis of material samples from various TOMs confirm the presence of chemically bound water in the system, characterized by a gradual mass loss in the temperature range from 30 to 440°C. It is noteworthy that the mass loss for steelmaking and electric arc furnace slag samples in this temperature range does not exhibit clear endothermic effects on the DTA curve (red), which may indicate an amorphous (gel-like) state of the hydrated phases containing chemically bound water. Furthermore, the amount of this water is extremely insignificant: 2.071% and 3.982% for steelmaking and electric arc furnace slag samples, respectively. An exception is the nepheline mud-based brick sample, which exhibits two distinct endoeffects within the same temperature range, with extremes at 114 and 204°C. The total amount of chemically bound water reaches 5.188%, indicating more intense hydration of this type of TOM and good crystallinity of the hydrated phases. Sample mass loss in the temperature range from 440 to 800°C corresponds to the decomposition of CaCO3. This temperature range is characterized by a pronounced endoeffect between 700 and 800°C, a weak endoeffect between 600 and 700°C, and virtually no endoeffect between 440 and 600°C. The indicated temperature ranges with the corresponding endoeffects characterize the decomposition of crystalline calcite (700 - 800°C), aragonite (600 - 700°C) and weakly crystalline or amorphous CaCO3 (440 - 600°C). Summary data on the quantitative determination of H2O and CO2 are presented in Table 5.

Table 5. Quantitative loss of mass of material samples in the studied temperature range based on various TOM

Name Temperature range (°C) Total mass loss (%) 30 - 440 440 - 600 600 - 700 700 - 800 Weight loss (%) H2O CO2 Sample of material from steelmaking slag tile 2,071 2,276 3.0 4.5 2,071 9,776 Sample of material from electric steelmaking slag tile 3,982 2,301 3.04 3,874 3,982 9,184 Sample of nepheline mud brick material 5,188 3,869 4,211 6,832 5,188 14,912

Electron microscopy results show that the material from steelmaking and electric arc furnace slag tile samples is a fairly dense structure consisting of dense aggregate grains and the resulting carbonate matrix with inclusions of the original unreacted slag minerals. The carbonation products (calcite and aragonite) are represented by rhombohedral and acicular crystals with an average crystal size of 1 to 3 µm. It should be noted that the contact zone between the aggregate and the carbonate matrix is quite dense, resulting in the high strength properties of the resulting material.

The sample material of the nepheline mud brick is a rather loose structure in which pores ranging in size from 2 to 30 μm, as well as calcite and aragonite crystals ranging in size from 1 to 5 μm, are clearly visible. Unlike the samples of steelmaking and electric steelmaking slag, this sample contains flocculent formations characteristic of the tobermorite phase, which is a product of β-Ca2SiO4 hydration, which correlates with the results of thermal analysis in terms of determining chemically bound water.

Thus, the silicate decomposition tests carried out on products based on various TOMs and the subsequent comprehensive analysis of the structure of the product material allow us to conclude that there are no signs of material destruction as a result of the polymorphic transformation of 2CaO⋅SiO2 from one form to another, accompanied by a significant increase in the volume of the solid phase and, accordingly, destructive phenomena.

Claims (10)

1. A method for producing carbonized building materials, which includes preparing raw materials, which are mineral raw materials and man-made metallurgical waste, by drying, grinding and sorting, wherein man-made metallurgical waste and mineral filler are used as raw materials, mixing and homogenization, adding water, molding, pressing, stacking, forced carbonization in a carbonation chamber at atmospheric pressure, room temperature and a _CO2 concentration of at least 80 vol.% for 4-6 hours, wherein condensate from the carbonation chamber is returned to the molding stage and is involved as impregnation in a ratio of fresh water to recirculated water of 5:1, and the carbonate hardening process occurs without forced circulation of the gas mixture in the chamber. 2. The method according to paragraph 1, in which additional components - coloring pigments - are added during mixing and homogenization. 3. The method according to paragraph 1, in which, when stacking products before carbonization, a 5 mm thick polymer mesh is placed between the rows of products to ensure access of the gas medium to all surfaces of the products. 4. The method according to paragraph 1, in which a manipulator complex is used to move raw materials and products between operations, which is a mechanical device that ensures transportation. 5. A plant for the production of carbonized building materials, including a raw material preparation unit, a molding unit, a carbonate curing unit, installed in a technological sequence, including at least one sealed carbonation chamber with technological lines for the supply and removal of carbon dioxide, a carbon dioxide preparation unit, a product packaging section, while from the carbonate curing unit a recirculation line for reaction water goes to the molding unit. 6. The plant for the production of carbonized building materials according to paragraph 5, in which the raw material preparation unit includes, installed in the process sequence, a drum dryer for drying sludge/slag and mineral raw materials; a crushing, grinding and sorting complex for processing sludge/slag and mineral raw materials; belt and screw conveyors for feeding prepared raw materials for processing and storage; pneumatic transport for transporting ground raw materials to a silo; a silo for storing ground raw materials; feed bins for storing mineral filler. 7. An installation for the production of carbonized building materials according to paragraph 5, in which the molding unit includes a high-speed mixer-activator with dispensers installed in the process sequence; hydraulic presses for semi-dry pressing; robots for placing molded products on pallets; a water tank; belt and screw conveyors for transporting raw materials and molding mixture. 8. An installation for the production of carbonized building materials according to paragraph 5, in which the carbon dioxide preparation unit includes mechanical cleaning filters, an amine cleaning apparatus for flue gases, and a gas holder for storing _CO2 . 9. An installation for the production of carbonized building materials according to paragraph 5, in which the carbonization chamber includes a housing, a door that ensures the tightness of the internal volume of the chamber, process pipelines for the supply and removal of _CO2 as a working medium in the chamber, a space for placing carbonized products subject to carbonate hardening, in which a false floor and a gas supply chamber under the false floor are provided for supplying _CO2 to the lower part of the chamber, and a false ceiling is also provided, and a vacuum space in the intake area, which is located in a niche above the level of the false ceiling at the top of the rear wall of the chamber, made sloping from the rear wall to the door. 10. An installation for the production of carbonized building materials according to paragraph 5, in which the carbonization chamber of the invention includes a housing, a door that ensures the tightness of the internal volume of the chamber, pipelines for supplying and removing the working gas - _CO2 and a false ceiling, wherein the pipeline for supplying the working gas is located at the top, above the false ceiling, above which a gas accumulation space is organized, and the false ceiling is a porous structure that ensures the filling of the chamber with the working gas under the action of gravity.