HEAT TRANSFER IN A ROTARY KILN DURING INCINERATION OF SOLID WASTE

A rotary kiln incinerator consists of a refractory lined cylindrical shell mounted at a slight incline from the horizontal plane. The solid combustible waste is fed into the kiln at the upper end and burning occurs as the material moves to the lower end where the ash is discharged.; The rotation of the kiln continuously mixes the solids and therefore, the heat transfer rate is not limited by the conductivity of the solids. In addition, the heat is transferred from the refractory wall to the solid waste in the region of contact. Due to rotation, the refractory wall is alternately heated and cooled by the combustion atmosphere and solid waste.; In the present study, a heat transfer model is developed for the rotary kiln incinerator which includes radiation from the flame, transient conduction in the wall and chemical reactions in the solid material. The objective of this investigation is to determine the length of the kiln required to burn the waste filled to a certain fill-angle.; To compute the radiation heat transfer, the wall and the waste surface are divided into twenty elements that form an enclosure. The shape factors between the elements are determined and the net radiation exchange is computed using the absorption factor method. Heat conduction in the refractory wall is determined using the finite difference technique and assuming heat conduction only in the radial direction. Convective heat transport due to kiln rotation is included in the energy balance of the wall elements. The thermal decomposition rate of the solid waste is modeled assuming that the chemical reaction is governed by the Arrhenius equation.; The circumferential temperature distribution of the inner kiln wall shows that an element of the wall as it emerges from the contact with the waste is progressively heated by the combustion gases. Also, except at locations very close to the inner wall, there is not much variation in the temperature in the radial direction of the kiln. The temperature of the waste increases almost linearly for most of the length of the kiln except at the end where the temperature tends to become constant.