Production of gypsum and improvement of its quality properties using additives. Gypsum production business

Gypsum is widely used in construction in the production of various products and mortars. Gypsum is a white or white with a gray tint substance that hardens very quickly, but has very low water resistance. The technology for the production of gypsum comes down to firing natural gypsum in industrial furnaces, and the resulting gypsum gypsum stone crushed.

Contents of the article:

♣ Technology of gypsum production in rotary kilns.

♣ Production of gypsum using a method of combined grinding and firing of gypsum.

♣ Gypsum production in digesters.

Gypsum is a fast-acting and fast-setting air binder. Gypsum binders are divided into:

♦ High-strength gypsum,

♦ Construction gypsum,

♦ Anhydrite binder.

Gypsum binders are made from gypsum stone CaSO4 * 2H2O, CaSO4 anhydrite and some chemical industry wastes that contain anhydrous or dihydrate calcium sulfate. Natural gypsum usually does not contain admixtures of clay, limestone, sand and other substances. Gypsum is produced by firing natural gypsum dihydrate at high temperatures, resulting in the reaction CaSO4*H2O =CaSO4*0.5H2O+1.5H2O.

Construction gypsum.

♦ Natural gypsum usually contains impurities of the following rocks: sand, limestone, clay, which reduce the strength and quality building gypsum. Therefore, to obtain high-quality gypsum, which can be used in construction, medicine and other fields, it must be processed thermally. Today, gypsum is processed in several ways, which differ in the method of firing in ovens.

Plaster is fired:

1. In shaft furnaces, ring, chamber and rotary kilns. After firing, the resulting gypsum stone is crushed.

2. In digesters with preliminary grinding of gypsum stone.

3. Simultaneously with grinding in one machine.

Picture 1. Technological scheme for the production of building gypsum in rotary kilns

1-tray feeder, 2-gypsum stone hopper, 3-belt conveyor, 4-hammer crusher, 5-elevator.

6 - augers, 7 - gypsum crushed stone bunker, 8 - disc feeders, 9 - coal bunker, 10 - firebox, 11 - rotary kiln type drying drum.

12-hopper of burnt crushed stone, 13-dust settling chamber, 14-fan, 15-hopper of finished gypsum, 16-ball mill.

Depending on the size of the pieces of the initial raw material (gypsum stone), as well as on the size of the required sizes of the pieces sent to the furnace for the purpose of firing, the raw materials are crushed according to single-stage scheme or by two-stage scheme in crushers-4. To do this, the raw materials are loaded into the gypsum stone hopper-2, then, using a tray feeder-1, the raw materials are continuously supplied to the belt conveyor-3, which directs it to the crusher-4.

Crushers can be hammer or jaw and they crush the original gypsum stone into crushed stone with particle sizes from 0 ... 20-35 mm.

The gypsum crushed stone obtained in this way (if necessary) is subjected to screening in order to obtain fractions 0...10; 10…20; 20…35 mm. After screening, the fractions of gypsum crushed stone are sent further to the gypsum crushed stone bunker-7 located above the firing furnace-11. Crushed stone of different fractions is fired separately because each fraction requires a separate, appropriate firing mode.

From hopper -7, crushed gypsum is fed continuously into the rotary kiln using a disc feeder. Depending on the design of the rotary kiln, firing of crushed gypsum can be carried out using two methods:
1. In direct contact with hot gases that are formed during fuel combustion.
2. Or due to external heating of the walls of the rotary kiln drum.
Drum-drying type rotary gypsum kilns can operate on liquid, gaseous or solid fuel. Depending on the type of fuel used, firing technologies are also developed. For example, at the entrance to the furnace, the temperature of the gases with direct flow is -950...1000 °C, with counterflow - 750...800 °C. When leaving the furnace, the temperature of the gases with direct flow is 170...220°C, with counterflow - 100...110°C.

The fired gypsum crushed stone then comes from the drying drum (from the kiln) into the burnt crushed stone bunker -12 using an elevator, or, depending on the design, the supply bins can be located directly under the drying drum. Uniform feeding of the ball mill is provided by a tray-type feeder-8, which is located under the fired crushed stone hopper-12.

Burnt crushed stone enters the ball mill at a temperature of 80...100°C. In the ball mill -16, burnt gypsum crushed stone is ground and the material composition of gypsum is leveled due to the transition of overburn and underburning into hemihydrate. Next, from the ball mill the finished product is sent to the finished gypsum bin -15 using an elevator.

From the finished gypsum bin, the product is sent to storage bins or packaging. In the process of producing gypsum stone, dust settling chambers -13 are used, which ensure high air purification from dust.

Construction gypsum production technology

♦ It is believed that the most perfect method for producing building gypsum is based on the method of combined grinding and firing of gypsum stone, which allows mechanizing the production process.

Figure-2. Scheme of combined grinding and firing of gypsum

With combined grinding and firing of gypsum, the gypsum raw material is crushed in one or two stages. Figure -2 shows a diagram of combined grinding and firing of gypsum where the gypsum stone goes through two stages of crushing. At the beginning, gypsum raw materials are loaded into the hopper -2 from where the feeder continuously supplies gypsum stone to the jaw crusher -21, where the material is crushed for the first time to a fraction of 20-60 mm.

In a hammer crusher, the gypsum crushed stone is crushed a second time until the desired faction for example 10-20 mm. Next, using the elevator -3 crushed gypsum crushed stone enters the supply hopper -17, from where using a feeder -16 continuously fed into the tube mill - 15 .

In a pipe mill, fine grinding and drying of gypsum stone occurs due to gases that flow through the -4 according to the principle of co-current or counter-current, they are supplied at a temperature of 600-700 C. During the rotation of the pipe mill -15, the raw material moves along its entire length, is dried and crushed. During the firing of gypsum stone, it dehydrates to form beta hemihydrate.

Next, the crushed roasting product is fed into the through separator -5 , where the largest unfired gypsum particles are separated and then returned back to the mill for reprocessing through an air chute 14 . The crushed gypsum powder, separated to a residue of no more than 2-5% on sieve No. 02, is carried by a dust-air flow into the dust-settling system -6 and 10.

The gas-dust mixture, after leaving the tube mill, passes through the separator into the system of dust settling devices -6 and 10, where the final dehydration of the crushed mixture occurs. The movement of gases in the system is forced and is carried out due to work centrifugal fans -9. Passing through a system of dust settling devices (cyclones, electric precipitators, bag filters), the crushed product is fed using a screw conveyor -11 to the receiving hopper -12. Further by conveyor -13 the crushed product enters the elevator -8, which sends it to the receiving hopper finished products-7.

Technology for the production of gypsum in digesters

with preliminary grinding of gypsum stone.

The boiler is designed for dehydration of dihydrate ground gypsum into semi-hydrous gypsum and is a vertical steel cylinder with a vertical bottom-2 (see Figure -3). The boiler is assembled from cast iron elements and the joints between them are sealed with asbestos mass. The boiler is heated through the bottom and its side surface.

Figure-3. Plaster boiler

In order to increase the heating surface, a metal jacket is suspended inside the boiler, which also serves as a casing for the auger.
In the horizontal direction, four flame tubes-3 pass through it, located in two rows (one above the other). The boiler body-4 rests on three cast iron supports with a concrete foundation underneath.

A slide valve -9 located inside the boiler allows you to close the window in the housing. The window is used to unload the finished gypsum along the flow. The shutter is equipped with an electric drive that opens and closes it as needed. The top of the boiler is used to create a steam space. The top of the boiler is a cylinder consisting of two halves and closed with a lid.

On the cylinder cover there are two pipes for connecting loading augers-8 to them, as well as a pipe for connecting the steam exhaust pipe, two level gauges, two inspection hatches for maintenance and inspection internal space boiler and two loading sensors installed on the inlet pipes used to control the supply of gypsum to the boiler.

At the lower end vertical shaft Four blades are installed to move the gypsum mass during the cooking process. The rotation of the blades of the vertical shaft is carried out using an electric motor through a gearbox. The technological process of the boiler operation occurs in a continuous automated mode.

Fresh gypsum powder continuously enters the boiler throughout the entire processing process. Due to this, a high degree of saturation of the material with air and water vapor is constantly maintained, which leads to an improvement in the properties and modification composition of the final gypsum product.

The technological process of gypsum production based on a gypsum boiler can be described in the following way:

1. First, the gypsum stone in large pieces enters the jaw crusher using a transport system. In a crusher it is crushed into crushed stone of a fraction of 20-60 mm. The fraction size of the final product, gypsum crushed stone, can be adjusted depending on the design of the crusher.
2. Next, the crushed gypsum stone, after passing through the iron separator, enters a fine grinding mill, where the mill turns the gypsum crushed stone into powder. Different mills can be used, for example ball, hammer, roller-pendulum, shaft and others. In the mill, the material is crushed into powder and also heated and dried due to hot gases.

The grinding fineness of the material and the productivity of the mill play a role important role and depend on the speed of the gas flow that is supplied to the mill. Flue gases from gypsum boilers are used as a coolant. Depending on the gypsum chosen during firing thermal regime flue gases are supplied at a temperature ranging from 300 to 500 °C.

In the mill, no more than 2-5% of the gypsum crushed into powder and separated to a residue on sieve No. 02 is carried into the dust deposition system by the dust-air flow. Just as in the method described above, after leaving the mill, the gas-dust mixture passes through a system of dust collection devices (cyclones, bag filters, etc.).

The movement of gases in the system is forced and is carried out due to the operation of centrifugal fans. Passing through a system of dust settling devices (cyclones, electric precipitators, bag filters), the crushed product is fed into the supply hopper. The temperature of the powder depends on the temperature of the gases leaving the mill (85...105 °C) and can range from 70...95 °C.

3. In the boiler, gypsum powder is cooked using flue gases at a temperature of 800-900 °C. Hot gases are supplied through flame tubes and external channels created by the boiler lining. The coolant can be natural gas or another type of fuel. During the process of cooking gypsum, the gypsum mixture is constantly mixed with the help of blades and lasts 1...2 hours or more. In a digester, gypsum does not come into direct contact with hot flue gases, and its temperature can range from 100-180 °C. Combustion of gaseous or liquid fuel occurs in a special boiler heating furnace.

In the first period, the operating temperature in the boiler reaches 110...120°C. The gypsum powder is heated to 110...120°C and intensive dehydration of the gypsum occurs. Next comes the second period when the hydration water evaporates and the dehydration process begins, or as it is also called boiling of the mass. In the third period, a rapid rise in temperature and a sharp decrease in the intensity of the dehydration reaction are observed. As the density increases and vaporization of the resulting dehydration products ceases, the gypsum mass becomes denser and its mass in the boiler decreases.

This stage is called the first precipitation of the powder.
The second precipitation of gypsum powder occurs during the last period of cooking when the dehydrated calcium sulfate hemihydrate turns into anhydrite. Next, the finished product is unloaded from the boiler into a receiving hopper and transferred to silos using mechanical or pneumatic transport.

Purpose of the plant

Equipment for production of building gypsum intended for obtaining a binder that meets the requirements of GOST 125-79: Gypsum binders. Technical conditions.

Thermal unit at production of building gypsum Our installation is equipped with a TOS165 gypsum boiler.

Depending on the compressive strength of the finished product, the following grades of building gypsum can be produced in a gypsum boiler: G-4, G-5, G-6, G-7.

By adjusting the technological parameters of gypsum cooking, it is possible to obtain quick-hardening gypsum with index A, beginning of setting no earlier than 2 minutes, end no later than 15 minutes, and normal hardening B, beginning of setting no earlier than 6 minutes, end no later than 30 minutes.

Depending on the degree of grinding, medium grinding gypsum with a residue on a 0.2 mm sieve of no more than 14% and fine grinding with a residue on a 0.2 mm sieve of no more than 2% can be obtained.

When obtaining a product with a fine grind of less than 2%, equipment productivity decreases.

Plant productivity by production of building gypsum with an average grinding of 5-8%, the residue on a 0.2 sieve is 8 t/hour.

Plant equipment production of building gypsum placed on a technological shelf inside an unheated production premises.

During the construction of a new plant for the production of gypsum binder, sandwich panels are used as the enclosing structures of the production building.

Dimensions in terms of production shelving may vary depending on the customer’s technical specifications and available free space. The standard overall dimensions are 4.5 x 30 m and 9.0 x 18 m. The maximum height of equipment inside the production room is 16 m.

As a rule, the dimensions of the production shelter include equipment for the crushing and transportation of gypsum stone and silo banks intended for storing and simmering the finished gypsum binder.

Requirements for the source material - gypsum stone

It is produced using grade 1 gypsum stone that meets the requirements of GOST 4013-82 with a CaSO4 x 2H2O content of at least 95% and grade 2 gypsum stone with a CaSO4 x 2H2O content of at least 90%. High-quality binder in a gypsum boiler of at least G4 grade can be obtained using grade 3 gypsum stone with a CaSO4 x 2H2O content of at least 80% on solid gypsum stone.

To obtain gypsum binder, gypsum stone of fraction 60 - 300 mm is used in a gypsum boiler. The stone of the coarse fraction is the purest without inclusions of foreign material. In fine crushed stone of the 0-60 mm fraction, there are more inclusions of non-gypsum rock, which reduces the properties of the finished gypsum binder during gypsum cooking.

Construction gypsum production technology

Technology production of building gypsum with a gypsum boiler TOS165 consists of three main technological stages: 1- Crushing gypsum stone, 2- Drying and grinding gypsum crushed stone, 3- Cooking building gypsum in a gypsum boiler TOS165.

Crushing gypsum stone

Crushing of gypsum stone of fraction 60 - 300 mm occurs in a jaw crusher.

The stone is loaded into the receiving hopper of the crusher by a front-end or grab loader from the storage warehouse.

For smooth operation gypsum production A 15-day supply of raw materials should be stored in the warehouse.

The gypsum stone is fed into the jaw crusher by an oscillating feeder.

The size of the gypsum crushed stone fraction after the crusher is controlled by the size of the crusher exit slot. After the crusher, the gypsum crushed stone is sent for further processing to the grinding department and dried on a conveyor belt.

The crushing department is usually located outside the closed production room in which the drying, grinding and cooking of gypsum is carried out.

The crushed material, after passing through the iron separator, is fed into an axial hammer mill.

The axial hammer mill is designed for fine grinding of medium-hard gypsum crushed stone with its simultaneous drying. The material is fed into the mill by a swing feeder from the feed hopper.

Gypsum powder, ground and dried in a mill, enters the dust and gas purification system in a stream of hot gases. Axial hammer mills belong to the group of high-speed hammer grinding machines. Crushed stone is fed into the mill in the direction of rotation of the rotor. As a result of the blows, the crushed stone is crushed into powder. The fineness of grinding of the material depends on the feed speed, the volume of the ventilating agent and the angle of installation of the blades of the built-in separator. The exhaust flue gases of the gypsum boiler are used as a coolant and ventilation agent.

The temperature of the flue gases at the entrance to the mill, depending on the selected thermal regime for firing gypsum in the boiler, can range from 250 to 500 0 C.

Crushed, dried and separated to a residue of no more than 5-8% on sieve No. 02, the gypsum powder is carried in the dust-air flow into the dust deposition system. Cyclones are used as the first cleaning stage, and two-section TOC 3.8 bag filters are used as the second cleaning stage. To eliminate material hanging in the cyclone hopper, pneumatic impact devices are installed. The cyclone and bag filter are thermally insulated.

Regeneration of the bag filter is carried out by back-blowing the bags with compressed air when the automation system turns off one of the sections. The fabric used for the sleeves is Metaaramid type fabric. The fabric can withstand operating temperature up to 230 0С. In the event of an unplanned increase in the temperature of the waste coolant above the specified temperature, the dilution damper installed in front of the filter opens automatically and outside air enters the aspiration system. Compressed air is supplied at a temperature exceeding the dew point temperature by at least 5-10 0 C.

A smoke exhauster Dn is used as a traction unit.

The powder collected by cyclones and bag filters by conveyors through a screw conveyor system enters a heat-insulated raw material bunker. To eliminate leaks in cyclones and bag filters, sluice valves are used.

Cooking of building gypsum - dehydration of gypsum powder occurs in a gypsum boiler with flue gases at a temperature of 600-950 0 C, supplied through external channels created by the boiler lining and flame tubes. The coolant in these passages is combustion products gaseous fuel in the combustion chamber adjacent to the lining.

The coolant, having passed through the channels in the boiler lining and flame tubes with a temperature of 250-500 0 C, without coming into contact with the material, is removed from the boiler. The gypsum in the digester does not directly come into contact with gases; its temperature is 121-160 0 C. The process of firing gypsum is accompanied by intense release of water of crystallization. During this period, boiling of the gypsum powder is observed.

The gypsum boiler is a vertical steel drum, equipped with a stirrer and closed on top with a lid, equipped with pipes for loading powder and removing a mixture of steam and gypsum particles.

The residence time of the material is regulated by the loading and unloading mode, depending on the required temperature of the material inside the boiler. The material is supplied to the boiler by a screw conveyor from the raw material bunker. Loading capacity is regulated by changing the speed of the screw conveyor. In continuous mode, raw gypsum is loaded continuously above the level of the material in the boiler through a pipe installed on the boiler lid. The vertical discharge chute, located inside the boiler, is open at the bottom.

The material is unloaded continuously by overflow from the top of the discharge chute. To improve the transport of gypsum from the bottom of the discharge chute to the top, bottom part supply compressed air with a pressure of 2 atm

Vacuum in smoke ducts The boiler is created by a smoke exhauster, which is also a traction unit for an axial hammer mill. Water vapor and gypsum particles formed during gypsum hydration in the boiler, as well as excess dust-air mixture from the simmering bunker are removed from the boiler. The semi-aqueous gypsum obtained in the gypsum boiler is unloaded into the simmering bunker.

Automated control system

Automated control system production of building gypsum ensures the operation of all elements of technological equipment in automatic, semi-automatic and manual modes to ensure technological process production of building gypsum.

The system is a complex of hardware and software that jointly perform the task of controlling the technological process.

System architecture

The control system can be divided into three levels:

The lower (field) level is represented by sensors and actuators. The system contains temperature and pressure sensors, level switches, motor current monitoring devices, inductive sensors, limit position switches and additional contacts signaling the status and operating mode of the motors.

The actuators of the system are motors with contactors for direct starting, motors with variable speed, controlled by variable frequency drives, electromechanical positioners for controlling the throttle valves of smoke exhausters and a switch for the direction of gypsum supply to the silo.

At the average level, the system is represented by a programmable logic controller (PLC) with input/output modules for analog and discrete signals. The PLC is responsible for receiving signals from sensors and issuing control signals to actuators in accordance with the program embedded in it.

At the top level, the system is represented by a human-machine interface device. This is a computer connected to a controller industrial network, and with specialized software installed on it.

Controller equipment, switching and ballast equipment are supplied mounted in cabinets industrial use. The instrumentation is supplied separately in original packaging.

All ballasts, circuit breakers, contactors and VFDs are manufactured by Siemens.

Programmable logic controller

The system uses a Siemens Simatic S7 300 controller as a PLC with a set of discrete and analog inputs and outputs, sufficient to connect all sensors and actuators, and with a reserve determined at the design stage.

The controller must be mounted in a cabinet, which must be installed in a switchboard room with a temperature range of 0-50 °C.

A brief description of the algorithms embedded in the controller will be discussed below.

Human-machine interface

An operator station (OS) with installed operating system Microsoft Windows XP and Siemens Simatic WinCC SCADA system. This station is connected to the PLC via the MPI industrial network to obtain information about the progress of the technological process.

The main functions of the OS are:

• Displaying the state of the technological process and equipment in the form of mnemonic diagrams, tables, trends and messages on a computer monitor.
• Providing the operator with the opportunity to configure the technological operating modes of the installation.
• Manual control of some installation elements.
• Display and archiving of emergency and service messages.
• Storing historical process data with the ability to view it.

Depending on natural mining and geological factors, the production and extraction of gypsum is carried out underground or open method.

The production of gypsum, or rather the process of processing natural rocks into gypsum material that meets the technical parameters, is carried out by qualified personnel at special enterprises. As a rule, industrial facilities are built in the area of ​​gypsum deposits.

Open-pit mining and production of gypsum

The open-pit mining method is characterized by high labor productivity, which, while minimizing losses of gypsum raw materials, is an undeniable advantage process. The technological focus of production is based on the extraction, transportation and grinding of gypsum stone.

The technology for the production of gypsum is ensured by work in several stages:

• Crushing gypsum rocks. Today, the explosive method is used at this stage of work.
• Grinding Achieved by grinding gypsum to the required consistency, which helps convenient use material in the future.
• Drying and firing. The final stage of production associated with heat treatment of the material.

Open-pit mining of the material is carried out using continuous surface miners, which crush the gypsum with a rotating cutting drum. The mechanism of the device consists of segments fixed with bolts and holders with built-in cutters, which are equipped with durable carbide inserts.

Feeding of the mined gypsum stone into the combine and subsequent transportation of the material to the primary conveyor is ensured by segments arranged in the form of a screw. Adjustment of the size of loaded rock pieces, the size of which should not exceed 300 mm, is carried out thanks to design features drum of surface miners.

The operation of the mechanism is based on the principle of free arrangement of segments, coupled with different configurations and sizes of teeth. The leader among manufacturers is the German engineering concern Wirtgen.

The dimensions of the gypsum stone after the first crushing stage are 30-50 mm. IN further material crushed to a grain state. It is worth noting that in Lately Hammer crushers are widely used, thanks to which the process of grinding gypsum is carried out in one stage.

The next stage of gypsum production is the transformation of gypsum crushed stone into powder, which occurs in roller pendulum mills. Due to the impossibility of processing wet gypsum, the material is dried at this stage. The adjustable speed of the gas flow from the flue boilers allows the gypsum to be crushed with high precision. In this case, an increase in flow speed makes the material rougher and vice versa. Gypsum is subjected to heat treatment for 1-3 hours at a temperature of 130-160 °C.

Underground method of mining and production of gypsum

Despite the fact that open-pit mining is carried out in most gypsum deposits, more than half of the total volume of material obtained is provided by enterprises whose activities are based on the underground mining method.

The technology of the underground method for the extraction and production of gypsum is based on the extraction of minerals from a rock formation by autonomous cameras while maintaining the roof. Cleaning activities are provided by core drills, scraper winches, deep drilling machines, dump trucks and self-propelled trolleys. Exhausted cavities are used to store various materials.

As a rule, the useful layer of gypsum deposits is a layer of heterogeneous quality and different grades, often containing various admixtures of clay, sand or carbonate rocks. Therefore, during processing it is necessary to enrich the material. The method is a variant of selective grinding, which is based on different degrees of crushing of strong and weak components.

The greatest efficiency of the selective grinding process occurs in impact mills and crushers. The advantage of this method is to ensure the maximum difference between the energy costs for crushing weak mineral components and strong crushed materials. The main parameter of the selective crushing process is the speed of the working rotor of the crusher or mill.

Loading of raw gypsum into the boiler is carried out using a screw conveyor. Water vapor is removed through special pipes. As a result of grinding and drying, the gypsum enters the bunker. The final material, ready for subsequent use, is a binder that is used as a component in.

An important factor in the production of gypsum is the installation of a multi-stage cleaning system. This is a mandatory requirement for any plant whose personnel work in conditions of dust emitted during material processing that is harmful to the human lungs.

The photo below shows a gypsum adit near Moscow. The volume of production is so large that all the tunnels of the adit are several times larger than the Moscow metro.

GYPSUM

(gypsum binder) - binder construction material, which can be obtained from natural gypsum dihydrate (CaSO 4 ∙ 2H 2 O), called gypsum stone, natural anhydride CaSO 4 and some industrial wastes (phosphogypsum, as well as calcium sulfate formed during chemical cleaning flue gases from sulfur oxides using limestone).

Depending on the temperature of heat treatment of raw materials, gypsum binder is divided into two groups:

• low-annealing (up to 250 o C)
• high-annealing (over 450 o C)

BUILDING GYPSUM

Construction gypsum is made by annealing gypsum rock in digesters with preliminary grinding. At the same time, it loses part of the chemically bound water, turning into semi-aqueous calcium sulfate CaSO 4 ∙ 0.5H 2 O [β - modification (β-hemihydrate). The main problem and disadvantage of building gypsum (β-hemihydrate) is the presence large quantity free water in hardened plaster.

The fact is that to hydrate gypsum* you need about 20% of its mass of water, and to obtain plastic gypsum dough - 50-60%. Accordingly, after hardening of such a solution, 30-40% of free water (by weight of gypsum) remains in it. This volume of water forms pores that are temporarily occupied by water, and this, in turn, affects the strength characteristics of the material. To increase strength (1.5-2 times), finished gypsum products are dried.

Our company offers its customers construction gypsum produced by: Peshelansky Gypsum Plant (G6 BII), Samara Gypsum Plant, Gypsobeton (Vidnoye, Moscow region), Ust-Dzhegutinsky Gypsum Plant (grade G5 BII) .

* Hydration of gypsum- gypsum hardening process

High-strength gypsum is obtained by heat treatment high-grade gypsum stone in sealed apparatus under steam pressure (autoclave). In this case, the problem of reducing the water demand of gypsum is solved, and accordingly, during hardening, a less porous and more durable stone is formed. The gypsum obtained in this case has another crystal modification of semi-aqueous gypsum (α-hemihydrate) with a water requirement of 35-40%.

Currently, in Russia and the CIS the leader in the production of high-quality high-strength gypsum is Samara Gypsum Plant CJSC (SGK). Produced grades: GVVS-13 gypsum, GVVS-16 gypsum, Gypsum for artistic stucco molding ( GVVS-19).

In addition, SGK, based on high-strength gypsum, produces specialized gypsum mixtures SCULPTOR and STONEMAKER. These are compositions where, as binder material high-strength gypsum with the additive white cement, and a certain amount of mineral filler and chemical additives to improve the consumer properties of these mixtures and the technical characteristics of finished products.

OOO GeoStyle is the main distributor in the Moscow region for the distribution and sale of gypsum products from Samara Gypsum Plant CJSC.

In addition, as an alternative option for high-strength gypsum, we offer G-19 grade gypsum produced by LLC « CherkesskStroyProdukt.

Molding gypsum is obtained by a certain mechanical “refinement” of building gypsum, subjecting it to additional grinding and sifting. As a molding gypsum, we offer our customers gypsum for pouring molds, price produced by LLC Peshelansky Gypsum Plant (grade G6 BIII) and CJSC Ust-Dzhegutinsky Gypsum Plant (grade G5 BIII).

The name of this gypsum implies the possibility of its use for medical purposes. These are dentistry (temporary dentures and dummy casts) and traumatology (fixing plaster bandages). The main requirement for medical gypsum is its purity (the absence of impurities), and therefore, for the production of such gypsum, only grade 1 gypsum stone is used (the content of impurities in the rock should not exceed 5%). And so, in fact, both construction and molding or high-strength gypsum can act as medical gypsum. The only question is obtaining the appropriate permits from the certification authorities. Due to the rather expensive cost of these procedures and the relatively small volume of consumption of this product, many gypsum factories do not obtain such certificates.

At the same time, the most convenient for use for medical purposes are normally hardening (start of setting - from 6 minutes) molding and high-strength finely ground plaster.

We offer our Customers one of the highest quality Russian medical plaster - medical gypsum for traumatology and dentistry produced by Samara Gypsum Plant CJSC.

Gypsum brand

The grade of gypsum is determined by compression and bending tests of standard beam samples 4x4x16 cm 2 hours after their molding. During this time, hydration and crystallization of the gypsum ends. According to GOST 129-79, 12 grades of gypsum are established in terms of strength from G2 to G25 (the figure shows lower limit compressive strength of a given grade, unit of measurement MPa).

Setting time

For gypsum binder, the determining factors are: the beginning and end of setting. According to these parameters, gypsum is divided into three groups (A, B, C).

Grinding fineness

According to the fineness of grinding, determined by the maximum remainder of the gypsum sample when sifting on a sieve with 0.2 mm holes, gypsum binders are divided into 3 groups:

Color

The color of gypsum depends on the presence of impurities in it, in particular iron oxide.

Density

True density 2650-2750 kg/m 3

Bulk density 800-1100 kg/m 3

Density of hardened gypsum stone 1200-1500 kg/m 3

Normal thickness

Normal density is expressed as a percentage.

Marking

Marking of gypsum binder is carried out according to three main indicators - setting speed, grinding fineness and strength, for example:

Gypsum binder G7 AII - fast-hardening (A), medium grinding (II), compressive strength of at least 7 MPa.

To prepare a homogeneous mass of creamy consistency, in cold water Gradually add gypsum and mix quickly. Depending on the type of gypsum, the following amount of water is used per 1 kg of gypsum binder.

It is allowed to increase the amount of water up to 10% by weight of the binder.

The best quality of work is achieved when applying the solution before setting begins. A strongly frozen mass cannot be re-diluted with water and used for work. Extending the setting time of the solution is achieved by adding to the water before mixing: glue solution (carpentry, wallpaper), sulfate-alcohol stillage (SAB), technical lignosulfonates (LST), keratin retarder, boric acid, borax and polymer dispersions (for example PVA). To reduce the setting time of the solution it can be used in small quantity salt. The amount of additives is determined experimentally. It all depends on the type of binders, their normal thickness and the desired result.

Comparative characteristics of technical parameters of gypsum

Construction gypsum is an airy binder consisting mainly of semi-hydrous gypsum and obtained by heat treatment of gypsum stone at a temperature of 150-160 ° C. In this case, CaSOi > 2H2O contained in gypsum stone is dehydrated according to the reaction: CaSO4 2H2O - "- CaSOi 0, 5H2O + 1.5H2O - q.

The production of building gypsum consists of crushing, grinding and heat treatment (dehydration) of gypsum stone

There are several technological schemes for the production of building gypsum; according to some, preliminary drying and grinding of raw materials into powder precedes firing, according to others, grinding is carried out after firing, and according to others, grinding and firing are combined in one apparatus. Last method called suspended firing.

Heat treatment of gypsum stone can be carried out in digesters, drying drums, shaft or other mills. The choice of one or another kiln depends on the scale of production, raw materials, the required quality of the finished product and a number of other factors. Most common technology system using digesters.

Gypsum stone, arriving at the plant in large pieces, is first crushed in jaw, cone or hammer crushers, then, while simultaneously drying, it is crushed in a mill. It is advisable to combine the drying and grinding process in one apparatus, for example, in a shaft, air crushing or ball mill. The most widespread is the shaft mill (consisting of a hammer mill and a shaft 12-15 m high located above it. In the lower part of the shaft there are channels supplying coolant (flammable gases) with a temperature of 300-500 ° C from the furnaces of the digesters. The hammer mill is located slightly lower. Gypsum stone in the form of crushed stone 3-4 cm in size is fed into the mill by a disc feeder through a chute in the upper part of the chamber, meets on its way the rapidly rotating beats of the mill and is crushed into a fine powder. In the mill, some of the crystallization water is also removed from the gypsum.

The batch digester (33) is a brick-lined steel drum / with a spherical bottom 2 facing the convex side inside the cylinder. To mix the gypsum, the boiler has a stirrer 3 driven by an electric motor 4. Hot flue gases heat the bottom and walls of the boiler, and also pass through flame tubes 5 inside the boiler and, when cooled, are removed along chimney. Cooking duration is 90-180 minutes, and holding for 3-4 hours at 140-150° C helps reduce the water requirement of gypsum and increase its strength. Water requirement is significantly reduced when cooking it with the additive table salt. The resulting semi-aqueous gypsum is released from the boiler through hatch 6 into the holding bunker, where it is cooled and its quality is slightly increased, and then the gypsum is sent to the finished product warehouse. When cooked in a boiler, gypsum does not come into contact with flue gases, which... allows you to obtain clean products not contaminated with fuel ash. In the drying drums of rotary kilns (34), gypsum is obtained by firing gypsum stone in the form of crushed stone with a grain size of up to 20 MAI..

The firing part of the drying drum is an inclined steel cylinder with a diameter of up to 2.5 and a length of up to 20 m, mounted on roller supports and continuously rotating. Gypsum crushed stone is fed into the drum from its raised side and moves downward when the drum rotates. From the furnace, hot flue gases with a temperature of 600-700 ° C enter the drum, which are removed by a fan from the opposite side of the drum with a temperature of about 100 ° C. When moving along the drum, the gases meet the gypsum stone and burn it. Burnt gypsum is crushed in one- or two-chamber ball mills, producing construction gypsum, which is usually stored in round silos with a diameter of 6-10 m.

When firing gypsum in suspension, two operations are combined - grinding and firing. According to this scheme (35), the sequence of operations is as follows. The gypsum stone arriving from the warehouse is first crushed in a jaw crusher, and then in a hammer crusher until grains measuring 10-15 mm are obtained. The crushed material is fed by the elevator through a supply hopper into a ball mill, in which the combined grinding and firing of crushed gypsum is carried out. Flue gases with a temperature of 600-700 ° C enter the ball mill from a special furnace. The gypsum particles formed during the grinding process are carried away from the mill by the flow of hot flue gases, dehydrate in this flow to a semi-aqueous modification and enter through the separator into dust settling devices. In the separator, large gypsum grains are separated, which are returned to the mill for additional grinding. In dust settling devices, dewatered gypsum is separated from the gas stream and sent to the finished product bunker, and the purified gases are released into the atmosphere. The production of gypsum by combined grinding and firing differs mainly in the types of mills and crushers, as well as in the fact that sometimes the mills operate with recirculation of gases that have passed through dust settling apparatuses.

Construction gypsum is used for the production of gypsum and gypsum concrete building products for internal parts buildings: - partition slabs, panels, dry plaster, for the preparation of gypsum and mixed solutions, as well as the production of decorative and finishing materials, such as artificial marble

Magnesium binders.

Varieties of magnesium binders are caustic magnesite and caustic dolomite.

Caustic magnesite is obtained by firing rock magnesite MgCO3 in shaft or rotary kilns at 700-800° As a result, magnesite decomposes according to the reaction MgCOe-^MgO + CO. The decomposition action of MgCO3 is reversible, therefore, when firing magnesite, it is necessary to intensively remove CO2 from the furnace using natural or artificial draft. The remaining solid, magnesium oxide, is ground into a fine powder and packed into metal drums. It is advisable to grind burnt magnesite in a ball mill with a separator.

Caustic magnesite hardens relatively quickly: its setting should occur no earlier than 20 minutes, and the end should occur no later than 6 hours from the moment of mixing. Grades of caustic magnesite according to SNiP 1-V.2g62 according to the compressive strength of cube samples made of rigid rammed mortar with a composition of 1:3 by weight after 28 days of air hardening are set to 400, 500 and 600.

Caustic dolomite MgO CaCO3 is produced by firing natural dolomite MgCO3 CaCO3 at 650-750° C, followed by fine grinding of the product. At the firing temperature, CaCO3 does not decompose and remains in an inert form as ballast, which makes the astringent activity of caustic dolomite lower than that of caustic magnesite.

Caustic dolomite contains a significant amount of calcium carbonate: it must contain at least 15% magnesium oxide and no more than 2.5% calcium oxide, therefore its quality is lower than caustic magnesite and its grade is only 100-300.

\ Magnesium binders are mixed not with water, but with aqueous solutions of salts of magnesium sulfate or magnesium chloride. The most common sealer is a solution of magnesium chloride MgCb, as it provides greater strength. Magnesium binders have little resistance to water and can only be used when curing in air with a relative humidity of no more than 60%. Caustic magnesite easily absorbs moisture and carbon dioxide from the air, resulting in the formation of magnesium oxide hydrate and magnesium carbonate. Therefore, it must be stored in a tight, airtight container.

Based on magnesium binders, xylolite (a mixture of binder with sawdust) is used for flooring, fiberboard and others. thermal insulation materials. Magnesia binders are also used in the production of products for internal lining premises, production of foam concrete, bases for clean floors, sculptural products.

Related information.