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11ЭФФЕКТИВНОЕ УПРАВЛЕНИЕ ФУНКЦИОНИРОВАНИЕМ ТЕХНОЛОГИЧЕСКОГО ОБОРУДОВАНИЯ В ПРОИЗВОДСТВЕ СТРОИТЕЛЬНОГО ГИПСА
Иванова О.В.
Уфимский государственный нефтяной технический университет,
доцент, канд. тех. наук Короткова Л.Н.
Уфимский государственный нефтяной технический университет,
доцент, канд. хим. наук Фаттахов М.М.
Уфимский государственный нефтяной технический университет,
профессор, д-р тех. наук Халиков Р.М.
Уфимский государственный нефтяной технический университет,
доцент, канд. хим. наук
EFFECTIVE MANAGEMENT OF THE FUNCTIONING OF TECHNOLOGICAL EQUIPMENT IN
THE PRODUCTION OF BUILDING GYPSUM
Ivanova O.,
Ufa State Petroleum Technological University, associate Professor, Ph. D.
Korotkova L.,
Ufa State Petroleum Technological University, associate Professor, Ph. D.
Fattakhov M.,
Ufa State Petroleum Technological University,
Professor, Sc. D. Khalikov R.
Ufa State Petroleum Technological University, associate Professor, Ph. D. DOI: 10.5281/zenodo.6882682
Аннотация
Оптимальная разработка технологической схемы производства гипсовых вяжущих требует необходимость учета химико-минералогические характеристики гипсового сырья, рентабельность и другие факторы при выборе типов аппаратов для измельчения и термообработки. Качественное управление бесперебойным функционированием технологического оборудования в производстве строительного гипса основывается на совмещение помола и термообжига сырьевых минералов. Abstract
Optimal elaboration of the technological scheme for the production of gypsum binders requires the need to take into account the chemical and mineralogical characteristics of gypsum raw materials, profitability and other factors when choosing types of devices for grinding and heat treatment. High-quality management of the smooth functioning of technological equipment in the production of construction gypsum is based on the combination of grinding and thermal combustion of raw minerals.
Ключевые слова: строительный гипс, технологическое оборудование, управление качеством. Keywords: building gypsum, technological equipment, quality management.
Building materials based on gypsum binders in comparison with Portland cement materials are characterized by low energy consumption in production and the best environmental performance [1, 2]. Gypsum products have hygiene, low thermal conductivity, good fire resistance, sound insulation ability, as well as a fast set of strength characteristics. It is gypsum composite nano-binders that will become the basis for the development of additive 3D technologies in the resource-saving construction industry [3-5].
The use of gypsum binders in the modern building industry has increased markedly as a result of the widespread use of dry mixes and the mechanization of plastering. Technological production of building gypsum is
carried out in devices for combined grinding and firing, in rotating furnaces etc. Currently, the special relevance of import substitution of foreign devices to replace worn-out equipment and the search for new technological solutions arose due to the destruction of logistics as a result of the coronavirus pandemic and interstate sanctions.
The purpose of this work is to consider technological schemes for the production of gypsum binders with high-quality control of the functioning of the equipment.
The main sources of raw materials for the production of gypsum binders are natural deposits of gypsum rocks, anhydrite and gypsum-containing waste from
chemical industries. In the gypsum raw materials of the developed natural deposits, the amount of impurities: sand, clay, limestone, etc. should not exceed 2-5%. Large deposits of gypsum mineral raw materials of the Russian Federation with reserves of more than 25 million tons are deposits of sedimentary type - layers with a capacity of up to 15 m or more.
Depending on mining and geological factors, the production and extraction of gypsum raw materials is carried out underground or open-pit. The open-pit mining method is distinguished by high labor productivity, but is associated with the formation of quarries. Innovative reclamation technology is a nature-saving method of restoring eroded landscape lands as a result of quarrying gypsum-containing raw materials [6].
The Republic of Bashkortostan, as well as neighboring regions: Perm Krai, Sverdlovsk, Chelyabinsk, Orenburg and Samara regions, the Republic of Ta-tarstan has quite large deposits of gypsum minerals. Uninterrupted and economical transportation of gypsum raw materials for processing from a quarry or mine is carried out by certified road [7], rail, etc. transport.
In natural gypsum, a mineral of CaSO4-2H2O composition, two anionic sulfate groups SO42- are bound to calcium cations Ca2+ and form double layers between which water molecules are located. The production of gypsum binders is based on the ability of gypsum dihydrate CaSO4-2H2O to dehydrate during heating - partially or completely give off crystallization water:
CaSO4-2 H2O ^ CaSO4^,5 H2O + 1,5 H2O
Gypsum dihydrate at a temperature from 110 to 175°C gradually loses part of the bound water molecules and transforms into gypsum semi-hydrate, and after fine grinding of the firing product, a gypsum binder for building, construction purposes is obtained [8].
According to the conditions of heat treatment, on which the properties of the obtained building materials depend in the future, gypsum binders are divided into:
♦ low-burning;
♦ high-burning.
Low-burning gypsum binding building materials, in turn, are divided into:
o building;
o molding;
o high strength.
Gypsum low-burn binders quickly set and harden; consist mainly of gypsum semi-hydrate: ^-modification CaSO4-0.5H2O (from the point of view of physical chemistry, 2CaSO4^2O is more correct), which is the basis of construction and molding gypsum binders; and a-form CaSO4-0.5H2O, which is part of high-strength construction gypsum and gypsum binder for medical purposes.
Gypsum building is traditionally produced by the technology of heat treatment of gypsum-containing raw materials - natural rock minerals at a temperature of 140-160°C. The technological process of production
of gypsum binders at the first stage consists in crushing gypsum minerals (crushing and grinding) extracted in quarries or mines and transported to the place of processing. The degree of grinding of gypsum raw materials before heat treatment is determined by the type of heat apparatus: gypsum-containing minerals are fed into the steamers in pieces up to 400 mm in size, into rotary kilns 10-35 mm, and into digesters - in the form of powder.
The technological schemes used for quality management of gypsum binders differ in the type and sequence of the main production operations in industrial installations:
1. Crushing ^ grinding ^ cooking.
2. Crushing ^ drying ^ grinding ^ burning.
3. Crushing ^ drying + grinding ^ cooking.
4. Crushing ^ grinding ^ cooking ^ grinding.
5. Crushing ^ drying + grinding ^ cooking ^ grinding.
6. Crushing ^ hot ^ grinding.
7. Crushing ^ firing + grinding.
8. Crushing ^ steaming ^ grinding.
The first five schemes are used in the production of gypsum binders in boilers, where heat treatment is carried out - cooking gypsum-containing raw materials. If the gypsum raw material is dry, then a simple scheme 1 is used; if the moisture content of the raw material exceeds 5%, then it must be dried before grinding (scheme 2). Sometimes it is advisable to combine two drying and grinding operations in one technological apparatus (scheme 3).
To improve the quality of construction gypsum, secondary additional grinding of gypsum semi-hydrate CaSO4 ^,5H2O coming out of digesters is desirable (schemes 4 and 5). Scheme 6 is used both in the production of high-burning and low-burning gypsum binders in rotating furnaces, and scheme 7 is used in combined grinding and firing apparatuses. Scheme 8 is designed to produce a gypsum binder of increased strength based on the a-modification of the semi-hydrate.
The traditional production of gypsum binders in digesters and quality management has become the most widespread. Gypsum raw materials are pre-crushed in a jaw crusher; hammer and cone crushers can also be used for grinding. The gypsum boiler is a technological equipment: a cylindrical apparatus with a concave spherical bottom, made of heat-resistant steel and lined with heat-resistant brick masonry. Under the boiler there is a heating furnace, the vault of which is the bottom of the boiler, and inside the boiler metal heat pipes pass one above the other in pairs. Fuel combustion products heat the bottom of the boiler; then its side walls are heated, and then removed through the chimney. As a result, uniform heating and dehydration of gypsum-containing raw materials and full use of thermal gases are ensured (Fig. 1).
Figure 1 - Technology for the production of building gypsum using a digester (1 - receiving hoppers of ground gypsum; 2 - screw conveyor; 3 - vertical steel drum;4 - spherical bottom; 5 - heat-resistant ceramics; 6- heating furnace; 7 - agitator with blades;8 - gypsum cooling tank)
Gypsum raw materials in the technological cycle are mixed by a vertical shaft with upper and lower agitators. The preheated boiler is loaded from above with gypsum-containing raw materials through a hole in the lid during continuous operation of the agitator, and after loading the first portion, "boiling" caused by the release of water vapor is expected. Then they continue gradually filling the gypsum powder and monitor that the gypsum dihydrate is in a "boiling state" all the time.
The duration of the process of technological dehydration of gypsum powder in boilers (from 50 min to 2.5 h) depends on their capacity, the fineness of powder grinding, etc. In boilers, for example, with a volume of 7 m3, the temperature of the raw material rises rapidly from 80 to 119 ° C. Then, despite the arrival of heat, the temperature remains constant for some time due to the release of crystallization water molecules from the raw gypsum and transformation into steam.
As the amount of calcium sulfate dihydrate decreases in the powder, heat begins to be consumed not only for the physico-chemical processes of dehydration, but also for heating the resulting CaSO4^,5 H2O semi-hydrate. Too high a temperature (170-180°C) can cause secondary secondary boiling due to excessive dehydration of gypsum semi-hydrate; at the same time, undesirable formation of raw material sediment is possible, which makes it difficult to unload building gypsum from the boiler.
In the article [9], the most optimal parameters of quality management of gypsum raw materials firing in a digester were determined: temperature of 120°C with exposure for 14-15 minutes and 125°C for 7 minutes. As a result of the production experience, it was possible to obtain a gypsum binder with a minimum content of gypsum dihydrate (~ 0.1%) and a maximum amount of building gypsum.
At the end of cooking in the processing equipment, gypsum raw materials are unloaded into a holding tank for gradual cooling for 20-30 minutes. The volume of the hopper is usually twice the volume of the boiler, and aging improves the quality of the binder: the remains of the dihydrate due to the heat of the discharged material turn into gypsum semi-hydrate. At the same time, under the action of water vapor, CaSO4 anhydrite is hydrated to semi-hydrate and as a result, the composition of the gypsum binder is leveled, its water demand decreases and the quality of the building material increases
The gypsum binder obtained in digesters mainly consists of a modification of ^-gypsum semi-hydrate; however, the amount of a-semi-hydrate can be increased by feeding small amounts of salts into the digester, for example 0.1% NaCl. A solution of sodium chloride reduces the elasticity of steam at the surface of the grains, as a result, the cooking process accelerates and the quality of the gypsum binder increases. The
content of the modification of a-semi-hydrate also increases in large-capacity boilers, since the height of the material layer increases in them and the removal of dehydration water molecules becomes difficult.
The choice of technological scheme and type of apparatus for heat treatment depends on the scale of production, chemical and mineralogical characteristics of gypsum raw materials, the required product quality and other factors. At many factories producing building gypsum, the cooking process in boilers is automated: loading the boiler with raw materials to a certain level, maintaining a set temperature at the end of cooking, unloading is carried out by appropriate actuators. As a result, manual labor costs are reduced, the probability of overheating of boiler bottoms is reduced, the cooking process is stabilized and the quality of building gypsum products is improved.
In the technology of gypsum binder production and quality management, digesters are distinguished by the convenience of regulating and controlling the firing mode. However, the technology using digesters has some disadvantages: the frequency of operation, the rapid wear of the bottom of the boilers, the difficulty of capturing gypsum dust. Further improvement of gypsum welding boilers is their transfer from a periodic mode of operation to a continuous one: finely ground gypsum is loaded into the boiler continuously below the level of the heat treatment surface.
The gypsum semi-hydrate formed during the firing process has a lower density, therefore it is displaced from the lower zone of the apparatus by the raw gypsum powder continuously entering the boiler. After heat treatment, the gypsum semi-hydrate rises and
flows by gravity through the upper hole into the holding hopper. The performance of continuous boilers is 2-3 times higher than that of batch boilers, however, the structural complexity reduces the reliability of their operation and limits their use.
The production of building gypsum in rotary kilns is quite widespread in domestic and foreign technologies for quality management of building materials. A rotating furnace is an inclined metal drum through which crushed gypsum raw materials slowly move. For firing gypsum dihydrate into semi-hydrate, technological equipment with a length of 8-14 m and a diameter of 1.6-2.2 m is used. The fuel is burned in a special furnace, and a mixing chamber is often placed between the furnace and the furnace, in which, in order to avoid burning the gypsum product, the temperature of the gases coming out of the furnace is slightly lowered by mixing them with cold air. The speed of movement of hot gases in the furnace is 1-2 m/s: exceeding these values causes a strong entrainment of small particles of gypsum semi-hydrate.
Currently, drying drums are used as rotary kilns for firing gypsum dihydrate (Fig. 3), which are a metal cylinder 1 mounted with a 5% slope on roller supports 2 and driven into rotation through a drive 3. Gypsum raw materials up to 35 mm in size are fed into the drum through a loading pipe 4 and moves to the lowered to the end as a result of its rotation. From the heating furnace 5, hot flue gases with a temperature of 800-900°C enter the drying drum, which pass inside the drum and burn the raw materials. The burnt building gypsum is unloaded from the drum along tray 6 and sent for further grinding.
Figure 2 - Diagram of the production of building gypsum with firing in rotary kilns (drying drums) (1 - drying drum; 2 - roller supports; 3 - drum drive; 4 - loading tube;5 - heating furnace; 6 - unloading tray)
The productivity of a rotating furnace depends on the volume of the inner part, the angle of inclination and the frequency of rotation of the furnace, the temperature and speed of the heating gases, the quality of gypsum raw materials and amounts to 125-250 kg of burnt gypsum semi-hydrate per hour per 1 m3 of furnace volume. The production of gypsum binders and
quality management in rotating furnaces of technological equipment makes it possible to produce cheaper building gypsum at lower costs.
The building gypsum obtained in rotary kilns has higher strength characteristics, which makes it possible to reduce its consumption by 20-25% in the preparation
of mortars and gypsum concrete. Continuously operating rotary kilns ensure the compactness of the technological scheme, allow automating the process of firing raw materials. However, the disadvantage of rotating furnaces is the difficulty of regulating the process, the need to ensure the stability of technological parameters, as well as increased entrainment of small particles of building gypsum.
The firing of gypsum raw materials in fluidized bed furnaces is carried out in special reactors, called de-hydrator boilers, in which hot flue gases with a temperature of 800-950°C are fed under a layer of natural gypsum dihydrate pre-crushed in a mine mill. The gypsum dihydrate layer is in a suspended, "boiling" state; the duration of firing gypsum raw materials by this method is reduced to 40 minutes.
It should be noted that the heat treatment of gypsum raw materials is carried out by the method of both direct flow and counterflow: the temperature of the hot gases entering the furnace with direct flow should be 950-1000°C, with counterflow - 750-800°C. With direct flow, a more uniform firing of gypsum dihydrate is achieved and, consequently, its better quality. At the same time, a kind of self-regulation of the heat treatment process occurs: small, rapidly dehydrating particles are transported by gases to the cold end of the furnace the faster the smaller their size. But at the same time there is a disadvantage of the direct-flow method of firing gypsum raw materials - in this case, the fuel consumption is higher.
The production of gypsum binders in rotary kilns can be intensified by improving the heat exchange between the coolant and gypsum raw materials and increasing the loading coefficient of firing units. Such modernization of technological equipment makes it possible to increase the productivity of furnaces, improve the firing mode of gypsum dihydrate, increase the uniformity of composition and quality, as well as reduce heat losses with waste gases. The article [10]
considers the structure of a software and hardware complex for controlling the thermal regime of natural gypsum firing and monitoring the operating parameters of a rotary kiln.
In recent years, combined grinding and firing of gypsum binders has been used to control the quality of technological firing, when heat treatment takes place in the grinding unit itself as a result of intensive heat exchange between hot gases and the crushed material. In the technological equipment of the mill, a pre-furnace is additionally constructed, in which fuel is burned and gases with a temperature of 700-800°C enter the mill; at the same time, the consumption of conventional fuel is 40-50 kg per 1 ton of gypsum binder. Technological mills are equipped with flow-through separators, after which the crushed and dehydrated construction gypsum enters the dust collectors.
In the technological scheme of combined grinding and firing of gypsum raw materials, two stages of crushing take place: in a jaw and hammer crusher, and then, in the form of particles of 10-15 mm in size, it enters a ball mill, where flue gases from the pre-furnace are also fed. The gypsum semi-hydrate dehydrated during the grinding process is carried out by the gas stream into the separator, where large particles are separated from it and returned to the mill. Fine fractions of construction gypsum are captured in dust collectors, after which the purified gases are released into the atmosphere.
The schemes for the production of gypsum binders with combined grinding and heat treatment differ mainly in the type of mills used (shaft, ball, etc.), as well as the fact that in some cases the mills work with a single use of coolant, and in others with the return of part of the gases to the mill after dust cleaning. The use of gas recirculation during combined grinding and firing increases energy consumption, but reduces fuel consumption. One of the options for the production of gypsum binders when combining their grinding and firing in technological equipment is shown in figure 3.
Figure 3 - Combined grinding and firing technological scheme for the production of gypsum binders (1 - receiving hopper, 2 - conveyor belt, 3 - jaw crusher, 4 - hammer crusher, 5 - elevator,6 - dispenser, 7 - ball mill, 8 - heating furnace, 9 - return screw, 10 - separator, 11-the first stage of deposition, 12- bunker
of ready-made construction gypsum)
The production cycle for the production of gypsum binders in combined grinding and firing mills is the shortest, and the number of aggregates is minimal. The advantage of such installations is their compactness and high productivity, but due to the short duration of exposure to gases, the largest particles do not have time to completely dehydrate, and some of the small particles are burned out, as a result, the resulting gypsum binder quickly sets and has reduced strength. Heat treatment of gypsum raw materials in digesters, rotary kilns and mills occurs at atmospheric pressure; The crystallization water is removed from the gypsum stone in the form of steam and as a result, the heat treatment product consists mainly of ^-CaSO4-0,5H2O.
To qualitatively improve the production of gypsum binders, the technology of obtaining a-modification of gypsum semi-hydrate in a vapor-saturated environment is also used. To obtain a high-strength building gypsum consisting mainly of a-semi-hydrate, it is necessary to create such conditions that the crystallization water is removed from the gypsum dihy-drate in a drip-liquid state.
Two main methods are used to control the quality of obtaining high-strength gypsum: 1) autoclave, based on the dehydration of gypsum raw materials in hermetic apparatuses in an environment of saturated steam under pressure above atmospheric; mechanochemical activation of raw materials reduces the duration and temperature of autoclave treatment [11]; 2) heat treatment in liquid media, dehydration of natural gypsum by boiling in aqueous solutions of salts.
The autoclave method for producing gypsum binders can be implemented in various devices: for example, the steamer is a sealed vertical metal tank with hatches and gates for loading and unloading. In the
lower part of the apparatus there is a dewatering sieve through which condensate flows, and when purging, flue gases are discharged; steam is fed into the apparatus from above into a perforated pipe located in the center.
In the patent [12], the processing of gypsum raw materials in an autoclave is carried out at a temperature of about 124°C and a pressure of 0.13 MPa for 5-7 hours with saturated steam. Then, in the same apparatus, the material is dried with gases at a temperature of 120-160°C for 3-5 hours; then the dried building gypsum is ground. Note that the autoclave method of producing gypsum binders has its drawbacks: uneven drying, high fuel and energy consumption.
Autoclaving technology is also used for the production of high-strength gypsum binders of a-modification, in which excess pressure is created by evaporation of a part of the crystallohydrate water from the gypsum raw materials. Crushed natural gypsum is loaded into a hermetically sealed rotating "autoclave", which is supplied with flue gases with a temperature of about 600°C. Passing through the pipes inside the apparatus, these gases heat the gypsum raw materials; as a result, the gypsum dihydrate is dehydrated, and the released molecules of vaporous water create excessive pressure in the apparatus.
It should also be noted that the dehydration of gypsum raw materials takes place in a steam environment under a pressure of 0.23 MPa for 5-5.5 hours, and excess water vapor is periodically released. After steaming, the material is in the same. the apparatus is dried, reducing the pressure to 0.13 MPa for 1.5 hours, and then to atmospheric; then the resulting building gypsum is crushed in mills. Gypsum binders obtained in a va-
por-saturated medium are characterized by greater homogeneity of the structure of a-semi-hydrate gypsum, less water demand and increased strength.
Further prospects for the development of technological equipment in the production of building gypsum are associated with an intensive search for technologies to increase the water resistance and durability of composite building materials based on gypsum binders [13, 14]. An effective solution to the problems of designing water-resistant gypsum nanocomposites is carried out using polycarboxylate superplasticizers [15], hydro-phobic coatings of gypsum concrete [16] and other innovative technologies. Modern production and eco-friendly [17] use of gypsum materials [18, 19] are in demand by the construction industry of the XXI century.
Thus, technological schemes of innovative production of gypsum binders with high-quality control of the functioning of the equipment make it possible to obtain building gypsum with improved physical and mechanical characteristics.
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