The results of numerical experiments concerning the process of calcination of small grained limestone particles in contact with the gas phase of a fluidized bed of inert grainy material for obtaining a high-performance sorbent are given. The character of the change of the basic qualitative parameters of the obtained sorbent – droopiness, surface area, mass is presented depending on the time of residence of the initial limestones with a diameter of 80–200 nm with initial porosity e0 = 0,03–0,1 and pore diameter dpor = 3,84–17 nm in the high-reaction zone when the temperature of the gas phase of the fluidized bed is changed within 900–1200 °С. The obtained results allow further in the design stage to determine the optimum hardware and process design of the process of calcination, depending on the initial parameters of the limestone, which will provide the desired quality of the limestone sorbent in accordance with the given power installation. Bibl. 1, Fig. 10.
In the article the comparative analysis of energy consumption in the process of combustion of solid fuel containing sulfur compounds, while simultaneously feeding directly into the fire space of the boiler of carbonate sorbents (CaCO3, Ca(OH)2, CaO) for the absorption of formed sulfur dioxide, as is the case in dry methods of flue gas desulphurization, was presented. The calculations were made when supplying sorbents in a stoichiometric ratio and with a triple excess sorbent. It was shown that the energy costs for decomposition and heating of CaCO3 and Ca(OH)2 or only the heating of CaO when applied in the dry method desulphurization are practically compensated by the secondary reactions of the sequestration of sulfur dioxide. A simple and practical method for determining the temperature of a stationary state with simultaneous flow of coal combustion processes and sulfur dioxide chemisorption by carbonate sorbents was proposed, which is essential for choosing a temperature range in which sulfur is actively absorbed without decomposition of CaSO4 formed. Bibl. 6, Fig. 3, Tab. 1.
Porous thermal-insulation materials are widely used in building industry, the advantages of which are cheapness and efficiency. Their commercial appearance is also important in their implementation. Porous thermal-insulation materials to prevent sticking can be packaged only after cooling and after the main thermal processes and classification. The process of cooling porous hydroaluminosilicate materials by the method of modeling with the subsequent check on the laboratory equipment with a fluidized bed is investigated in the work. The main thermal process takes place at a temperature of about 300°C. The cooling time of the porous material to a temperature of 20°C, which is about 20 seconds, is calculated, and the need to ensure this time in its classification is indicated. This model allows you to determine with sufficient accuracy the cooling time for particles of different diameters and temperatures. The process of cooling the obtained thermal insulation material in the production technology occurs simultaneously with its hydrodynamic classification in the cascade classifier of the fluidized bed. It is important to determine the required cooling time of the spherical hydroaluminosilicate material to temperatures close to 20°C and to ensure the presence of particles in the apparatus during this time. Comparison of experimental data with the results of the mathematical model shows the results with an error of 10%. There is a slight increase in the minimum residence time of a single granule obtained experimentally compared with the calculated.
A detailed mathematical description of the endothermic process calcination of limestone particles is presented while they are passing high temperature zone of fluidized bed inert particles. When constructing a mathematical model of thermochemical conversion of limestone particles, are made the following key assumptions: large-grained inert particles are in the mode ideal mixing, they are acting as a thermostat, and limestone particles are removed from the fluidization bed with the heating gas in the mode piston flow; calcium oxide particles formed as a result of thermochemical processing, retain the original amount of limestone particles with a corresponding change in the current volumetric particle porosity; pressure and density of the carbon dioxide produced in the calcination process on the surface of unreacted CaCO3 and which are determining the reaction rate of calcination are equal to the value of these parameters in the radial pores of particles; particle heating is provided only due to the thermal conductivity of the solid phase and by intensity of heat exchange «limestone particles — inert particles of fluidized bed». Bibl. 7.
The possibility of obtaining perspective geopolymer materials for use in the building industry was shown. Geopolymer materials are used with such advantages as high strength, density, water resistance, heat and heat resistance, environmental friendliness, durability, and high corrosion resistance. The raw material is rottenstone, a rock with a high silica content, which is widespread in Ukraine. Rottenstone is characterized by a ratio of SiО2:Al2O3 equal to 16… 20, which provides a high strength of the final material. It was indicated that physico-chemical processes that take place during polymerization are similar to those that take place in thin pellicles of the released SiO2 gel, cements the particles, and thus promotes hardening. As a result of the treatment of raw materials with alkali solution at temperatures of 80-120 °С, a monolithic solid material of olive color with a density of 1200-1700 kg/m3, humidity of 30-45% was formed. Precipitations were observed on the surface of the material due to the presence of non-chemically bound sodium and potassium cations in the pores of the geopolymer. When dried, they diffuse to the surface of the geopolymer and are subjected to atmospheric carbonization. It was indicated that in order to obtain a high-strength geopolymer material, it is necessary to carry out final heat treatment at temperatures close to 100 °С. The behavior of geopolymer samples aged over time at room temperature during their heating was investigated. The samples of the material are melted due to the presence of Na2O×SiО2×8Н2O and Na2O×SiО2×5Н2O crystal hydrates, which melt at relatively low temperatures at 48°С and 72°С, respectively. The formation of building geopolymer materials should take into account this melting by placing it in molds was concluded. Indicators of moisture loss at a temperature of about 100°С depending on the heat treatment time were obtained.
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