Features of a kiln for heat-treating fired pitch-containing refractories

Abstract

Heat-processing tarred refractories has certain special features compared with the firing of ordinary refractories, such as the need to create special atmospheres, the release of the pitch and gaseous matter from the tar in the goods, and the difficulties of making these substances harmless.Tarred refractories are divided into two groups, i.e., fired and unfired. The first includes corundum and magnesia goods for stopperless steel casting, and the second-dolomite and magnesia for converter production.This classification is important in principle in choosing the heating atmosphere. For fired goodsthe concentration of water vapors is not limited in the atmosphere, and oxygen concentrations of up to 2% are permitted; for unfired goods the water vapor and oxygen contents are limited, respectively, to 0.2 and 1.0%.This article deals with the principles and development of a project for a furnace suitable for heating fired tarred refractories, in particular corundum tiles for the gate valves used in steel casting, prefired and then impregnated with coal-tar pitch. The design of this furnace was perfected by the East Institute of Refracteries in a project for a workshop making refractories for the stepperless casting of steel at the Novomoskovsk Refractories Factory.* The demands that are common to any technology and specific in the particular case were considered in developing the kiln design.The overall requirements of the kiln are a large specific output, high quality of product, the necessary level of mechanization and automation, low specific fuel consumption, good gas sealing, mining capital and working costs, and clean air provision.The specific requirements due to the features of the heat processing of fired tarred refractories are: the existence of a special or controllable atmosphere, maximum gas sealing, and the ability to render the tar and gaseous substances harmless.A continuous-action kiln best meets these demands. This type of kiln has certain advantages, including the controllable atmosphere, maximum gas sealing, and the capacity for rendering harmless the tar and gaseous matter from the pitch, which amount, respectively, to 2.3-3.6 and 0.2-0.4% of the weight of the heat-processed refractories.Continuous-action kilns have not been employed in Soviet practice for heating refractories that are first fired and then impregnated with tar. But in an adjacent industry -the manufacture of electrodes -there is a tendency to use tunnel kilns in which the atmospheres can be controlled; it consists of a mixture of combustion products from organic fuel and volatiles from the carbonization of the binder in the carbon products (ware). The composition of the mixture is 20-80% N2, 10-40% H2, 8-29% CO, 2-15% CO2, 2-20% H20 , 1-5% CH 4 and less than 1% other gases. The maximum temperature of the isothermal soaking in the kilns is 800-1000~ [1, 2].The requirements of a kiln for heating gate-valve tiles are best satisfied by a continuous-action kiln of the tunnel-annular type.The main plan of the kiln with illustrations of t...

Technical solutions on designs of the elements of the kiln channel of a circular tunnel kiln

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The kiln channel of a circular tunnel kiln for heat treatment of refractories is formed by a circular tunnel and a rotating hearth.The channel is the main element of the kiln and, in turn, consists of individual elements including the shell of the kiln channel, the circular hearth, the hearth drive, the hydraulic seal, and the lining of the kiln channel.The optimum designs of the elements are their technical solutions* [1][2][3][4][5].Shell of the Kiln Channel.The shell serves as the base of the kiln channel, the supporting portion' of the circular tunnel, and the base for the support and thrust rollers and the base of the rotating hearth, that is, it receives all of the static and dynamic loads occurring in operatin of the kiln channel.The general form of the shell and its cross section are shown in Fig. i.

The basis of development of the technical solutions on design of the shell was a module system of dimensions in the horizontal plane along the axis of the kiln channel and similarity of the elements in all cross sections and along the length of the channel.

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Investigation of the aerodynamics of a tunnel circular kiln

“…In the experiment the gas flow in a length of five positions of a tunnel circular kiln built for heat treatment of burnt sand-containing corundum refractories was simulated [6] on a cold model according to the rule Re m = Re k = idem [7,8], where Rem = Re k = 24,700-37,100 are the Reynolds numbers of the gas flows of the model and the kiln.…”