Tunnel kiln for firing large refractory products

Conclusions A tunnel kiln has been put into operation for firing large products in which cycles were worked out for firing blocks for the glass industry. When these products are being fired in the tunnel kiln loss is reduced by a factor of 10 compared with loss obtained when firing them in round furnaces. There are appreciable reductions in labor expenditure, and the working conditions are improved. Setting and unloading are mechanized.Location of the kiln under an open roof hinders operations.Translated from Ogneupory, No, 5, pp. 7–10, May, 1969.     

Firing heavy silica products in a tunnel kiln

Conclusions It was shown to be possible to fire heavy dinas products weighing up to 25 kg for coking ovens and weighing up to 45 kg for glass tank furnaces in a tunnel kiln. Firing cycles and setting arrangements were developed.It is necessary on the basis of experimental data and experience that was gathered to design and build a new tunnel kiln for firing heavy silica products.Translated from Ogneupory, No. 6 pp.10–19, June, 1968.     

Temperature field in the setting of mullite corundum products in a tunnel kiln

Conclusions Investigations of the temperature field of the setting in a tunnel kiln of the high-alumina products section of the Zaporozhe Refractories Factory revealed individual features of the firing cycle for mullite-corundum articles; the low temperature of the setting in the first heated positions of the firing zone (Nos. 24–26) working without automatic regulation of the gas consumption according to the prescribed temperature of the kiln; the irregularity of the temperature field over the height and width of the setting; the variability of the linear dimensions and quality factors of the finished goods over the setting volume. Certain measures were worked out and used to eliminate these drawbacks.We obtained the general relationship for developing temperature fields in settings in actual kilns present in the department making aluminous, fireclay, and magnesia goods: when ensuring that t_kiln=const in the leading positions for burning the fuel in the firing zone we noted the extreme behavior of the temperature at the surfaces of the heated goods with a maximum at one or two positions.On the basis of the analysis of the processes of heat and body exchange occurring in the tunnel kiln, we note methods for improving its heat work and also the quality of the goods.Translated from Ogneupory, No. 5, pp. 15–20, May, 1981.     

An ejection system for firing a small high-temperature tunnel kiln

Conclusions An ejection system for firing a tunnel kiln differs from an ejection system for firing metallurgical and machine building industry furnaces.Investigations were conducted on a model of the ejection equipment of small high temperature kilns.Results were obtained on the change in the coefficient of ejection in relation to the geometric parameters of the ejectors and the burners, the distance between them, the pressure in the ejection channel and the working space of the kiln, and the temperature of the air ejected.A method of calculation of ejectors used in tunnel kilns is proposed.Translated from Ogneupory, No. 2, pp. 40–43, February, 1984.     

Tunnel kiln for firing refractories at 1850°c

Conclusions The 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.Translated from Ogneupory, No. 4, pp. 17–22, April, 1979.     

Firing roof refractories by setting products of a single grade

Conclusions A 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.Translated from Ogneupory, No. 1, pp. 11–19, January, 1971.     

Conditions of operation of a tunnel kiln with injection burners

Conclusions The injection burners ensure jet combustion of the gas with the generation of an oxidizing atmosphere in the tunnel kiln. The firing of dense ladle brick and brick for blast furnaces in such kilns must last for 50–60 h.In discussion series [see Ogneupory, No.5, 11 (1968)].Translated from Ogneupory, No. 5, pp. 10–13, May, 1969.     

Rapid firing of silica

Summary It was shown to be possible to fire silica in 200-ton periodic kilns in 160–170 h without worsening their properites.Experiments on the rapid heating and cooling of silica need to be continued both in test and in industrial furnaces.In an experimental furnace the firing time was reduced by about 80%, but this schedule was not proven in an industrial kiln.The obtained thermal-physical properties of the green goods permit a more accurate calculation of the permitted rated of heating. It is necessary to explain the influence of grading, batch composition and pressing conditions on the thermal-physical properties of green silica goods.     

Improving the production technology for chrome-magnesite products

Conclusions With the incorporation of finely milled magnesite into the batch of chrome-magnesite there are significant improvements in the sinterability of the brick, and increases in strength after firing. Changing the setting scheme for the products on the kiln cars yields more uniform distribution of the temperature over the height of the kiln, improves the firing conditions, and reduces the loss. The roofs of the furnaces also have a longer life.Translated from Ogneupory, No. 2, pp. 5–6, February, 1969.     

Production technology of high-density periclase-spinel roof materials

Conclusions High-density periclase-spinel refractories can be produced from a body of magnesite powder containing 94–96% magnesium oxide and Kempirsai chromite by high-pressure molding and high-temperature firing in a tunnel kiln. The product is strong with good thermal stability and high onset temperature of deformation under a load. The structure of the refractory is improved as a result of the formation of a large proportion of direct intergranular bonds between the periclase and spinel.It is planned to produce experimental industrial-scale batches of periclase-spinel roof refractories and to subject them to trials in the roof of open-hearth furnaces in continuous operation.Translated from Ogneupory, No. 8, pp. 39–44, August, 1973.     

Drying magnesia refractories with the flue gas of the tunnel kiln

Conclusions Experiments 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.Translated from Ogneupory, No. 4, pp. 15–21, April, 1976.     

Investigating temperature cycles for firing magnesite — Chromite products in a tunnel kiln

Conclusions Distribution of flue-gas temperatures in the cross section of the preheat zone of a tunnel kiln depends in particular on the reliability of sealing the roof and the hearth system.Variations in the temperatures of the flue gases in the firing zone depend mainly on the distribution of fuel and air in the cross section of the working region of the kiln, which is associated with the design of the burners, their arrangement, and their working conditions.The nature of the changes in the temperature of the surface at the settings is mainly the same as for the flue gases.A serious variation in temperature develops over the cross section of the setting column during heating, which reaches 100–150°C when no soak is provided.To level out the variations in temperature over the thickness of the column it is necessary to arrange a soaking at constant surface temperature at the end of the firing zone. Its duration depends on the material being fired, the thickness of the column, the heating rate, and the value of the stated final variation in the temperature.It is necessary to carry out an investigation to select the optimum burner design and arrangement.Translated from Ogneupory, No. 8, pp. 14–22, August, 1968.     

Cause-And-Effect Relations with Respect to Defects in Brick Firing in Tunnel Kilns

The cause-and-effect relations in firing brick in tunnel kilns are investigated and the causes of defects depending on the rate of heat treatment of brick in the kiln are identified. Current gas burners do not satisfy the requirements imposed on firing velocity regimes. The kiln has to be upgraded: Vulkan-gaz burners should be replaced by state-of-the-art gas burners with automatic control of the heat regime of the kiln, and the thermal regime in the preparation zone of the tunnel kiln has to be improved.__________Translated from Steklo i Keramika, No. 3, pp. 26 – 28, March, 2005.     

Firing of large intricately shaped Dinas products

Conclusions The large, complex-shaped Dinas refractory products for coke ovens should be fired in a specialized tunnel kiln equipped with burners (of the roof or wall type) which will ensure a high degree of firing uniformity. The effective height of the kiln charge should preferably be about 700 mm. The charge should be set up in well-spaced columns and the products should be placed predominantly on their ends. The lining of the floor of the kiln or kiln trucks should be constructed of lightweight refractories and heat-insulating materials.Complex-shaped Dinas products should be produced from compositions with a maximum grain size of 2 mm and the grain-size distribution given earlier in this article.The mineralizing additive should be ferrous lime with CaO/FeO=1.8/0.7, and the amount added to the composition should be 2.5±0.1%.To maximize the precision of the dimensions of the product and to minimize its aftergrowth the proportion of unconverted quartz should not exceed 2%. This condition can be ensured by using a fine-grained molding mix and the correct amount of an additive of the correct composition and by optimizing the firing conditions in the specialized kiln.Translated from Ogneupory, Vol. 18, No. 8, pp. 9–16, August, 1977.     

Speeding up the firing of silica in gas-chamber furnaces

Conclusions Speeding up the firing of silica products in gas-chamber furnaces does not lead to an increase in loss. It is most desirable to accelerate the firing of silica in gas-chamber furnaces with supplementary gas feed into the second preheat chamber in a period of 10–18 h. Under these conditions it is necessary to reduce the gas feed into the chamber working on the high-temperature schedule.     

A small tunnel kiln for firing corundum refractories

Conclusions The special features of the small (working volume capacity 6. 8 m³) tunnel kiln for firing corundum refractories are: firing with a gas-air mixture, absence of combustion chambers between the charges, absence of end doors, and slow kiln truck speed (13 cm/h). The corundum bricks are fired in the kiln for 136 h at 1660°C.The gaseous medium of the firing zone contains oxidizing and reducing components.The faults of the kiln are: nonuniformity of the firing of the bricks, inadequate firing temperature level, and unsatisfactory performance of the first six positions of the heating zone where heating takes the form mainly of a thermal shock in the region of the last two (in the direction of the gas flow) pairs of connections for the extraction of the combustion productsTo improve the quality and economics of the firing process, it will be necessary to improve the heat insulation of the kiln channel, to provide channels in the floor, and to modify the heating and gas extraction systems.Translated from Ogneupory, No. 7, pp. 8–15, July, 1977.     

A circular tunnel kiln for firing of refractories

Conclusions The 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.Translated from Ogneupory, No. 2, pp. 40–44, February, 1985.     

Upgrading burner devices in tunnel furnaces

Conclusions Gas and air flows have been measured at burners in existing tunnel furnaces by means of diaphragms, throttle washers, and flowmeter tubes, which substantially facilitates adjusting and regulating the thermal conditions.Cylindrical and conical nozzles can be replaced in burners on working furnaces by nozzles with peripheral holes, which improve the gas-air mixing and raise the flame temperature.Intermediate burners with a pitch of 1.5 m substantially improve the firing quality and enable one to increase the loading mass in a wagon.Translated from Ogneupory, No. 3, pp. 34–37, March, 1988.     

Calculation of the thermal operating conditions of a tunnel-type kiln with the use of the computer

Conclusions With the use of an ES computer, magnesite part firing parameters providing an improvement in technicoeconomic indices of the firing process have been developed and introduced in the tunnel kiln of Magnesite Combine. A production test showed satisfactory adequacy of the model developed of the tunnel kiln heating process to the object simulated.Translated from Ogneupory, No. 3, pp. 27–30, March, 1982.     

Emission during the firing of chrome-magnesite products in tunnel kilns

Conclusions When chrome-magnesite products are fired in tunnel furnaces, the concentration in the effluent gas of dust is 110–150; of Cr₂O₃, 5–7; NO_x, 20–35; CO, 100–125; SO₂, 25–40; and SO₃, 30–70 mg/m³. The emission dust is finely dispersed. The average size of the particles of dust is 0.3, the minimum 0.05, and the maximum 1 m. There is no hydrogen sulfide, NO₂, or CrO₃ in the emission.Dust and nitrogen oxides are formed in the firing zone of the kiln. The formation of dust and NO₂ depends on the air-consumption coefficient.The use of the pipe-in-pipe type of ports does not provide good gas combustion. To improve the operation of the kiln and the combustion of the natural gas it is recommended that instead of the obsolescent tube-in-tube ports, the ports developed by the Eastern Institute of Refractories be installed since they have given good results in tests [7].To improve the scattering effect of the removal of dust in the existing equipment it is recommended that the height of the flue stacks be increased to 40–50 m.Translated from Ogneupory, No. 4, pp. 36–41, April, 1986.