G. A. Tarakanchikov

Drying magnesia refractories with the flue gas of the tunnel kiln

ConclusionsExperiments at the Magnezit Plant confirmed the feasibility of drying magnesia refractories with the flue gas in the first positions of a tunnel kiln. Drying the refractories in the section where the flue gas is tapped off does not result in more rejects or in degradation of the properties of the fired products.Compounding the processes of drying and firing magnesia refractories in a single unit, viz., the tunnel kiln, makes it possible to dispense with the driers the freed floorspace of which can be used for installing equipment for mechanizing the loading of the products on the kiln trucks.

A circular tunnel kiln for firing of refractories

ConclusionsThe first high-temperature circular tunnel kiln in the country, in which firing of mullite-corundum refractories with a phosphate binder at 1400–1500°C has been introduced, has been placed in service.The operation of the kiln is characterized by the high service reliability of its design elements, including the hearth system, and insignificant costs for routine repairs of the kiln equipment.

Tunnel kiln for firing refractories at 1850°c

ConclusionsThe refractories industry of the Soviet Union has designed and is now operating a tunnel kiln for firing refractories at 1850–1900°C. The kiln works with high cost-benefit indices and is used for firing high-grade magnesite-spinel goods on the basis of fused and sintered materials.

Furnace truck with channeled base

ConclusionsChanneled furnace truck linings have been devised and industrially tested; they greatly reduce the vertical temperature drop in the furnace channel and improve the annealing quality of the refractories.

Combustion of natural gas in high-temperature tunnel kilns

ConclusionsThe positions in the firing zone of a tunnel kiln can be divided into transfer, principal, and fume-laden types in accordance with the characteristics of the combustion of gaseous fuel. Each type of position requires its own system of heating in which account is taken of the characteristics of the heating process. The GTP-3-type burner can be used to advantage in the principal positions because it permits the fuel distribution across the kiln space to be regulated.

Accelerated heating of magnesia refractories in the tunnel kiln

ConclusionsExperiments demonstrated the advantages of reducing the length of the preheating zone of high-temperature tunnel kilns by eight positions, a section which can then be used for drying the product on kiln trucks so that existing driers can be dispensed with and the vacated space be used for equipment for the mechanization of the loading operation.

Heat engineering tests on high-temperature tunnel kilns with setting heights of 700 and 1100 mm

ConclusionsRoof refractories can be fired in a setting 600–700 mm high; increased height of the setting leads to the development of substantial loss of products (fusion and deformation) in the lower courses. High-grade firing of roof products is achieved in a high-temperature tunnel kiln with a working space 0.75 m high.The low tunnel kiln designed by the All-Union Institute of Refractories compared with the standard tunnel kiln for firing single-grade settings of roof refractories gives better uniformity of product firing, close control of the process of improved cooling of the products, and lower loss. The specific consumption of heat for firing the goods in the low kiln is higher than in the standard.Improvements in the low tunnel kiln should be continued so as to permit the injector devices for feeding low-pressure air to the burners and intermediate burners to be cut off and to develop a lining for the cars and the kiln roof with higher thermal shock resistance, as well as improved systems of sealing the kiln.

Firing roof refractories by setting products of a single grade

ConclusionsA study was made of the firing process in a high-temperature tunnel kiln set with roof refractories of one and two grades. The firing loss when the products were placed in 3–4 rows (on edge) is slight but sharply increases in the two lower rows of the lattice setting using products of a single grade. The setting of the roof refractories over the height should consist of no more than four rows (on edge) which with a kiln channel height of 1.1 m is possible by using a setting of periclase-spinel refractories with an undersetting of chrome-magnesite products.The firing of the roof refractories should be done in a 7-column setting using products of two grades with a column thickness of 0.23 m and a length of 2.6 m.The possibility of using lattice settings in specialized kilns with a low channel height should be considered separately.

The ratio of zone lengths in high-temperature tunnel kilns

ConclusionsThe ratios of the heating zone lengths existing in high-temperature tunnel kilns for firing magnesia refractories are not optimal. There are reserves for improving the operation of the kilns by optimizing the ratio of the zone lengths.The operation of the preheat zone in a high-temperature tunnel kiln is characterized by perfect heat-exchange and the presence of a reserve section. This zone can be reduced without damage to the furnace operation, as a result of which it is possible to elongate the cooling zone.Further treatment of the question of optimization of the ratio of zone lengths in a high-temperature tunnel kiln should be continued in the new kiln design developed by the All-Union Institute of Refractories, which is equipped with burner assemblies from the 19th position.

Firing Savinsk magnesite in rotary kilns

ConclusionsSavinsk magnesite (lump and briquetted from the concentrate) can be thoroughly fired in rotary kilns of different sizes at a flame temperature of 1700–1750°C. The porosity of the powder is proportional to the size of the charge of raw material. During the firing of lump magnesite of all grades and briquette from ground concentrate it is possible to obtain powder with a porosity of 5–7%. When magnesite is being fired in a rotary kiln with a preparatory grid and when the raw materials charged amount to 1.5–2.0 times greater than when firing is done without the grid, a moderate-porosity powder is obtained. Thus, the fitting of a preparatory grid may increase the output of the furnace, and improve the quality of the product. During the firing of Savinsk lump and briquetted magnesite in rotary kilns in semiindustrial and industrial conditions, there is no bear formation, ringing, or crust formation on the lining of the furnace.