Simulating the Heat Transfer Process of Horizontal Anode Baking Furnace

Abstract

IntroductionLarge amounts of carbon anodes are consumed in the aluminum industry. Anodes are made of petroleum coke held together by a pitch binder. They must be baked to a given temperature of about 1000 to 1200°C at a very low heating rate (10-15"Ch) in order to obtain the appropriate mechanical and electrical properties required for their use in electrolync cells [l, 21. This baking process occurs in a horizontal or vertical ring h a c e , which is built as a chain of sections arranged in a ring shape. The uniformity and stability of the balung temperature in the anodes during baking determines the anodes final qualities, and directly affects aluminum production When baking, air is blown into the flue from the cooling manifold (right hand side of Figure 1) and flows from right to lefl. It picks up heat from cooling the baked anodes and the burner, and gives up part of its heat to the solids in the heating zone before exhausting. During baking, the anodes are stationary in their pits. However, the burner, cooling manifold and exhaust manifold are displaced from one section to the next, moving from right to left at regular time intervals called firing cycle times (range 25-45 hours). The entire process corresponds to a counterflow semi-continuous heat exchanger [l]. The thermal behavior of the baking process in a ring furnace is too complicated to be described completely. Presently, the design of an anode baking furnace strongly depends on the experience of the designers. Thls would inherently induce some defects such as more fuel consumption, asymmetrical heating temperature in the anodes interior, cracking phenomena in anodes, etc. Furthermore, because of the large size and long time constant (in the order of 2 or 3 months) of a bakmg furnace, a real furnace experiment is impractical due to cost and time constraints. It is obvious that new theories and thermal simulation studies on anode baking furnaces are required.The purpose of this paper is to simulate the heat transfer in the horizontal baking furnace, and to identify optimal operating conditions, in order to support the required data for designing a baking furnace. 428Simulating the Heat Transfir Process of Horizontal Anode Baking Furnace Model DescriptionModeling of an anode balung furnaces started about 20 years ago. In an actual furnace, the burners are moved stepwise by one section after each firing cycle. All the burners are then tumed off and the cooling manifold, burners and exhaust manifolds are moved forward by one section. The burners are turned on again and the process is continued. The same process is repeated for another firing cycle time through all the sections from heating to cooling (1P to 1OP in Figure 1). However, it is very difficult to build such a model, which is able to simulate the actual operation of a ring fusnace, since the initial value and boundary conditions at each section are very different. Furthermore, huge amount of CPU time are required to use such models to calculate different firing configurations and to estimate th...

Sensitivity of Carbon Anode Baking Model Outputs to Kinetic Parameters Describing Pitch Pyrolysis

“…Since for most outputs of interest, linearity was satisfactory, it is possible to use Eq. (18) to predict the outputs of interest for a given set of inputs, as well as the variance of the outputs for given variances of the inputs.…”

“…The second category is 'overall models' where the ABF is treated as a counterflow heat exchanger: the gas is flowing from inlet to outlet and the solids are "moving" in the opposite direction at a speed corresponding to a section length divided by the fire time (roughly 5m/24h) [8][9][10][11][12][13][14][15][16][17][18] . The core of these models gas along the furnace.…”

Structural and thermal analysis of an innovative baking furnace for carbon anode production

“…11 It is reported that the spatial temperature distributions during the baking process in ABF would determine the properties of anode. 12 The structure of the typical ABF is shown in Figure 1. 13 In this layout, the anode blocks are placed in the pits and covered by the packing coke, as shown in Figure 1B.…”

“…Among the aforementioned processes, the baking process in the anode baking furnace (ABF) has the huge influence on the anode quality 11 . It is reported that the spatial temperature distributions during the baking process in ABF would determine the properties of anode 12 …”

Use of Mathematical Modelling to Study the Behavior of a Horizontal Anode Baking Furnace

“…In mid-1990's, a full 3D transient model was reported [10]. Later on, many models of varying complexity, but similar in nature to these early works have been published [11][12][13][14]. Mathematical modelling has become a key tool in the improvement furnace operation and design.…”