Numerical calculation of tertiary air duct in the cement kiln installation Borsuk G., Wydrych J., Dobrowolski B. Department of Thermal Engineering and Industrial Facilities Opole University of Technology, Prószkowska 76, 45-578 Opole, Poland e-mail: g.borsuk@po.opole.pl Key words: pneumatic transport, particle concentration, tertiary air, rotary kiln Abstract During cement production process, part of the fuel can be burned in preheater, so it is necessary to supply additional air (tertiary air), which should be taken from the clinker cooler [1]. Trouble at the tertiary air conveying make clinker particles which are entrained from the cooler and settle in the duct [2,3,4]. For optimization of kiln, it is necessary to understand the detailed process which takes place in the kiln. The specific requirements of the process is designing the burner system and provide a burner design that will deliver efficient and reliable combustion. Yet, extensive use of this form of transportation may bring about some problems that need to be eliminated. For describe the complex process of cement production a numerical calculation object were built. As for subsequent analyses only flow distribution through the kiln head was important, authors decided to build a part of cement kiln installation. Fig. 1 shows general view of the rotary kiln system with connection between head and preheater. Fig. 1 Rotary kiln general view Part of the installation inside a dotted line was cut and then had the opportunity to build a computing system of tertiary air duct. Figure 2 shows head of rotary kiln with base tertiary air duct connection, in figure 3 we see selected particle trajectories. Flow parameters for the system are set out the following assumptions: constant velocity in the inlet cross- section depends of the gas flow rate to the kiln head, at the outlet of the kiln and pipeline constant pressure value determined for the basic variant for the appropriate distribution of gas on kiln and tertiary air duct. Pressure drop between inlet to head and outlet from tertiary air pipe was treated as a base information for calculation proper distribution of gas. The primary step of setting the numerical calculation was the pressure at the outlet to the kiln, as the flow distribution is the same as at the start of the analysis. Over 70% of the incoming flow to the head is transported through the kiln. The rest is transported through the tertiary air installation. For the particle calculation authors used Rosin-Rammler-Sperling distribution, separated 10 fraction of particle with the range from 15 to 600 µm. The calculations assume the same number of intake point for all particle fraction. Such adopted boundary conditions gave the result of the expected pressure drop. Calculation were made by using ANSYS Package [5]. For the boundary conditions obtained from the initial calculations, special settler was used as one of the tertiary air installation sections located just behind the outlet from the kiln head.