Journal of Mechanical Science and Technology 27 (10) (2013) 3191~3197 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-013-0841-0 Lifter design for enhanced heat transfer in a rotary kiln reactor † Hookyung Lee and Sangmin Choi * Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Korea (Manuscript Received February 5, 2013; Revised April 26, 2013; Accepted May 9, 2013) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract Rotary kiln reactors are frequently equipped with an axial burner with which solid burden material is directly heated. The burner flame provides the heat required for the vaporization of the water and the reaction of the solid phase. Lifters are commonly used along the length of the system to lift particulate solids and increase the heat transfer between the solid bed and the combustion gas. The material cascading from the lifters undergoes drying and reacting through direct contact with the gas stream. In this study, volume distribution of materials held within lifters was modeled according to the different lifter configuration and appropriate configuration was used for the design purpose. This was applied to the simplified one-dimensional heat balance model of a counter-current flow reactor, which contrib- utes to the increase of the effective contact surface, and thereby enhances the heat transfer. Keywords: Direct heating reactor; Counter-current flow; Heat transfer; Lifter design ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction The usable material in solid particles, such as ferrous or non-ferrous metal, cement, corn, food, and chemical products, initially was in a raw state composed of different contents and impurities in nature. Therefore, continuous processing of the raw material is necessary to make the particulates useful. There are drying and reaction processes that can separate the useful element from the raw material via mass transfer be- tween the solid phase and the gas phase as a reacting agent. Since the thermo physical and chemical reactions, such as vaporization of the water, roasting of the corn, calcining of the petroleum coke, and reduction of the oxide ore, are activated in a high temperature environment, the corresponding heat should be in the system. One of the methods to make a high temperature environment in the system is to use flue gas from the combustion of hydrocarbon fuel (direct heated), while another method heats the wall of the system using electric energy (indirect heated) [1]. For sufficient and stable heat supply from a hot gas phase to a solid phase, rotary kiln reactors have often been used during a long residence time of typically greater than one hour. Cur- rently, rotary kilns are employed by the industry to carry out a wide array of material processing operations as mentioned above [2]. The system has a long cylindrical shape and is slightly horizontally inclined to induce the solids flow from one end of the reactor to the other. The reactors are frequently equipped with an axial burner with which solid burden mate- rial is directly heated. The most common configuration is a counter-current flow for better heat exchange efficiency whereby the solid bed and combustion gas flows are in oppo- site directions [1, 3]. However, the co-current flow may be utilized in some instances, for example, rotary driers. Rotary kiln reactors are heat exchangers in which energy from a hot gas phase is extracted by the bed material. During its passage along the kiln, the bed material undergoes various heat ex- change processes, which is a typical sequence for long kilns being dried and heated, and chemical reactions that cover a broad range of temperatures. Therefore, an efficient use of heat is a matter of major concern in designing the rotary kiln reactors. The rotary kiln reactors that process the particulates com- monly use lifters (or called flight) along the length of the sys- tem to lift solids [4]. This involves lifting the material from the bottom of the system, up along the walls, and then allowing the material to fall back to the bottom of the system. The ma- terial cascading from the lifters undergoes heating and drying via direct contact with the gas stream. This increases the con- tact between the hot gaseous medium and the granular mate- rial and results in improved heat and mass transfer [4]. In other words, this process contributes to the heat and mass transfer activation of the bed material at the bottom and the economic effects from decreasing the length. This study presents a modeling approach to lifter design with lifter hold up volume distribution according to the angle of rotation of the kiln and various lifter configurations. In a * Corresponding author. Tel.: +82 42 350 3030, Fax.: +82 42 350 3210 E-mail address: smchoi@kaist.ac.kr † Recommended by Associate Editor Ji Hwan Jeong © KSME & Springer 2013