The uniformity of firing and fuel economics in tunnel kilns

Abstract

Following the introduction of new developments in the last few years [1][2][3][4][5][6][7] it has become possible to improve the thermal operation of tunnel kilns. However, the required uniformity of firing the goods is not always provided. This article assesses certain design and regime factors that influence this parameter. The influence of the shape of the setting and the properties of the goods being fired is not considered.Let us examine the irregularity of the firing, which is connected with the cooling of the products of combustion during movement along the kiln channel in the section between the two adjacent side burners. We shall use the following scheme for the heat work in the i-th section.At the exit of the port, combustion products are formed from the fuel whose temperature t com equals i the maximum permitted in the firing conditions for the stated type of article. The combustion products are exhausted into the burner chamber (gap in the setting opposite the burner), where they are mixed with the departing flow. As a result of the blending process, products are formed with an average temperature [cc 1 ' filling the entire volume of the combustion chamber. We consider that in the combustion chamber there is thermal equilibrium, i.e., [cc is constant for the entire volume. As the combustion products move they 1 give up heat to the material, and compensate for heat losses. As a result of this, the temperature of the combustion products is reduced.Let us call the section between the columns of the setting opposite the burners the combustion section. The section in which the combustion products are cooled shall be called the setting section. We note that the boundaries of the combustion section necessarily coincide with the boundaries of the combustion chamber. The minimum of the mean temperature of the combustion products'~. TM does not coincide with the boundaries 1 of the section of the setting, but is displaced by a distance Al because of the axial radiation of the neighboring combustion chamber.The value of Al depends on many factors and is selected on the basis of experimental data. In firing Dinas the value of •l can be taken as 0.2-0.3 of the length of the column.The heat-work scheme is illustrated in Fig. 1 in which the longitudinal section through the tunnel kiln is shown schematically. Fuel is fed into the combustion chamber with a consumption B i and primary (cold} air ' The secondary, hot air with a consumption V'.' with a consumption V i.1 moves from the cooling zone. At each section the fuel combustion uses up a certain amount of hot air V". The consumption of combustion products formed as a result of the burning of the fuel in each section we denote by V cp. cThe total consumption of combustion products passing from the section (the removal current) we indicate by VZi. The combustion products move toward the material. The length of the combustion section is l c, and of the setting section l s.We consider all the temperatures as average and constant in the transverse section of the kiln...

Means of cutting fuel consumption in kilns of the refractories industry

“…These factors, e.g., include [10] the temperature heterogeneity in firing the goods across the length of the setting, depending on the corresponding drop in temperature of the gases At in the latter (before the start of cooling) positions of the high-temperature soaking. The factors governing the consumption of fuel, needed to ensure the required temperatures of gases in the chambers, also affect the magnitude of At.…”