Economy in natural gas together with an increase in the quality of fired parts are basic problems in the production of refractories.A large quantity of natural gas is consumed in the refractory industry in kilns.The use of most progressive types of thermal equipment for firing parts and optimization of the firing system will lead both to significant economy in natural gas and to acceleration of the firing processes.In recent years there has been an increase in the production of high-quality oxide refractories, which makes improvement in the method of their production, in particular the method of firing important.For firing these parts, more and more use is being made of batch furnaces, in the working space of which it is possible to obtain the required high temperatures.However, significant disadvantages, the primary of which is the large fuel requirement per unit of production, are inherent in firing in batch furnaces.For example, at Magnesite Combine 1250 kg of standard fuel is consumed in batch furnaces for firing one ton of magnesite inserts for the plates of slide valves.Firing of such parts in continuous furnaces requires several times less fuel.The use of continuous kilns is restrained by the fact that in them it is not possible to obtain temperatures of 1750-1850~ and to maintain the required firing cycle.Recently small tunnel kilns with an ejector system of firing [1][2][3], which are promising both from the point of view of obtaining high firing temperatures and in respect to flexibility in regulation of the thermal cycle, have been used.These furnaces are capable of replacing batch furnaces.It should be noted that kilns with an ejector system of firing require further improvement and optimization of the thermal cycle.In Snigirevka Division of Vnukovo Refractory Part Plant corundum parts are fired in small kilns with an ejector system of firing.The length of the kilns is 15 and 17 m. The temperature in them did not exceed 1650-1680~ Attempts to increase the temperature for the purpose of higher quality firing did not provide positive results.In the construction of a new high-temperature tunnel kiln the disadvantages of the thermal operation of existing small kilns were taken into consideration.Individual portions of the equipment were modernized, which made it possible to substantially improve the technical and economic indices of the kiln.For example, the use of the controllable gas burners developed in the All-Union Scientific-Research Institute for the Utilization of Gas made it possible to more flexibly control the thermal operation of the kiln. The installation, in addition to the lower burners, of an upper row of burners led to more uniform heating of the parts through the height of the charge.The thermal losses to the atmosphere in the high-temperature portion of the kiln were decreased by additional insulation of the roof.The height of the sand seals was increased, as the result of which gas exchange of the working area of the furnace with the atmosphere was decreased. The length of the kiln is ...
An analysis of operation of existing high-temperature shaft kilns for firing of refractory raw material showed that it is insufficiently effective and it is necessary to search for means of intensification of the thermal operation for the purpose of increasing the productivity of the kilns, improving the quality of the fired material, and reducing specific fuel consumption.Investigation of production shaft kilns for firing of refractory raw material is difficult as the result of the high temperatures in the working space and the high static pressure in the shaft (about 12-15 kPa) in the case of forced supply of air for cooling of the fired raw material.One of the effective means of studying the complex processes of heat and mass exchange and gasdynamics occurring in the working space of the kiln is simulation.The processes of mixing of the fuel with the air supplied to the burners and that rising from the cooling zone and the degree of combustion of the natural gas across the shaft cross section are the determining factors from the point of view of providing uniform firing and obtaining the required temperatures in the reaction zone.In turn, the process of mixing of the fuel with oxidizing agent depends upon several factors including the method of supply of fuel and air to the kiln, the type of gas burners used, their number and location, the ratio of primary and secondary air, the particle size of the charge, etc.The above processes may be studied with sufficient reliability on an isothermal mass exchange model.It is also necessary to observe geometric similarity and self-modeling conditions of operation of the model.Investigations of the hydraulics and complex processes of transfer of a quantity of movement and mass have decisive value for intensification of thermal operation and development of the optimum parameters of the gas burners.A model of a shaft kiln was constructed in the experimental plant of "Soyuzpromgaz" All-Union Scientific and Production Union (Fig. i). The height of the working space of the kiln is 3.0 m. The cross section has the form of an ellipse with short axes of 0.74 and 0.612 m and long axes of 1.21 and 1.08 m. The basis of development of the design of the model was the shaft kiln for firing of high-alumina granules built at "Kazogneupor" Plant using the design of the All-Union Institute for Refractories.The model was loaded with a total weight of 4 tons of corundum granules and equipped with 16 burners located at two levels at heights of 1.3 and 1.7 m from the level of the grate (sections II-II and IV-IV).To the burners were supplied natural gas and primary air and under the charge secondary air in quantities necessary for the condition of autosimulation.To take samples from the charge there are holes with connections at the sections III-III,
An ejection system for firing of tunnel kilns is promising from the point of view of effectiveness in utilization Of natural gas and also inhreasing the temperature potential in the working space of the kiln, increasing the quality of highly refractory parts, and increasing the productivity of the equipment. Determination of the capabilities of an ejection system for firing and optimization of the thermal operation of tunnel kilns has been delayed by the fact that until the present there have not been detailed investigations of such a system and, as a consequence, reliable methods of calculating it.Existing methods of calculation of ejection devices in recirculating furnaces of the metallurgical and machine building industries [1][2][3] provide results differing significantly, as will be shown below, from the experimental data.A distinguishing feature of an ejection system for firing of tunnel kilns is the presence of a positive static pressure in the channel connecting the cooling zone with the ejectors in the firing zone.To determine the ejection capacity of such a system the operation of burners with ejectors was simulated. The plan of the model of the ejection system for firing of a small high-temperature tunnel kiln is shown in Fig. i. In form and dimensions the model agrees with the ejection system for firing the tunnel kiln of Snigirevka Plant of Vnukovo Refractory Part Plant, which operates on natural gas [4]. The scale of the model was i:i with the exception of the model length. The length of the ejection channel of the model was equal to two positions of the firing zone.The gas burners, which were developed in the All-Union Scientific-Research Institute for the Gas Industry, are tube-in-tube type burners but with significant deepening of the gas nozzle within the housing of the burner for the purpose of providing partial preliminary mixing of the gas with the primary air supplied to the burner. In the simulation the gas was imitated by cold air. Fig. i. Plan of the ejection system model: ejection channel; 3) discharge chamber; tor; 6) coordinate spacer; 7) suring the static pressure; 9) heaters. I) burner; 2) 4) rotameters; 5) ejecPrandtl tube; 8) holes for mea-U-shaped manometer; i0) electric Union Gas Industry All-Union Scientific and Production Union. V. V. Kuibyshev Moscow Engineering and Construction Institute.
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