Calculating the distribution of heat carrier over the length of the firing zone in tunnel kilns

Abstract

The distribution of fuel and air consumption at various positions in a tunnel kiln and the proper arrangement of the combustion process affect the quality of firing and the consumption of fuel for the kiln as a whole. A method was developed for calculating the rational distribution of gas and air consumption at various positions in a tunnel kiln [1]. In [1] equations are given for computing the heat load and volume of flue gases at different kiln positions for a stated gas temperature at that position. In this case it is assumed that the coefficient of consumption of primary air is known.The proposed method is suitable for computing the fuel consumption and also the primary and secondary (channel) air at each position of the firing zone, starting from the conditions for obtaining the minimum consumption of fuel at the position Bmi n (task 1) and a stated change in the temperature of the products of combustion over the length of the position Ats (task 2). It is assumed that the firing temperature of the material is given, the temperature of the combustion products in the soaking zone tcp is 10-20~ higher than the firing temperature, and the consumption of hot air moving along the channel from the cooling zone is stated.The formulas were obtained by using the following simplified scheme for the heat work at the position. Tentatively we can divide the position lengthwise into two sections: the combustion section and the section for which there is a fall in the temperature of the combustion products. We shall consider that in the combustion section the total heat absorption is compensated by the chemical heat separation, i.e., the temperature of the combustion products is constant. In the temperature-fall section the process of combustion is complete, and the temperature of the combustion products falls smoothly over the path of movement as a result of heat absorption for the material and the heat loss.The maximum change in the temperature of the combustion products in this section is indicated through At. The fall in the combustion product temperature causes a corresponding fall in the temperature of the setting over the gas path, as a result of which there forms an irregularity of firing of the goods in an a~ial direction. Since the firing irregularity is proportional to the magnitude At we shall tentatively consider At as the parameter characterizing the uniformity of firing over the length of the setting. We note that the firing uniformity over the setting length depends on the dimensions and thermophysical properties of the goods, the conditions of heat exchange, and the duration of heating. However, the scheme used permits, as a first approximation, an assessment of the firing uniformity without resorting to cumbersome calculations.The consumption of fuel at the n-th position in an oxidizing or neutral gaseous medium (~ >-1) may be determined from the heat balance for the combustion section from the equation ( 1) where B n is the consumption of fuel, m3/h; QZ = QK + QM + Qa + QO kJ/h (QK heat lost through the s...

Firing dinas goods in an oxidizing atmosphere in a tunnel kiln

“…The specific volume of combustion products increases linearly with a rise in a' and a" and ensures a more urAform distribution of temperature of the gas flow in the working channel of the kiln, which favorably affects the quality of the goods being fired [4].…”