MATHEMATICAL MODEL OF COOLING OF A STOPPED POT AND ITS VALIDATION Mohamed I. Hassan 1 , Ayoola T. Brimmo 1 , M. O. Ibrahiem 2 , and Youssef Shatilla 1 1 Mechanical Engineering Department, Masdar Institute of Science and Technology. Masdar City, Abu Dhabi, 54224, UAE 2 Emirates Aluminum (EMAL), Al Taweelah, Abu Dhabi, P.O.Box 111023, UAE Keywords: aluminum reduction pot, potshell, potshell cooling, potshell modeling Abstract In aluminum reduction pot technology, the potshell is used for several generations. After each shut down the potshell is cooled by free convection and radiation. This cooling takes from five to nine days depending on the surrounding temperature. Cooling by spraying water on the potlining is used in some aluminum plants; this reduces the cooling time to less than one day but this method can be harmful for the potshell and for the environment. The aim of this study is to develop a heat transfer model of the aluminum reduction pot in a free convection and radiation environment. A commercial finite element code (FEM), ANSYS®, was used to create the 3D model and solve both the steady state and transient temperature distribution. All material properties and heat transfer coefficients were modeled as functions of temperature. The solidification of aluminum at its phase transformation temperature was included in the model to investigate the behavior of the cooling curve of the various components of the pot during this phase change. The resulting cooling curves are in good agreement with experimental data. This model will be used to design an optimum pot cooling environment. Introduction Ideally, an aluminum reduction pot should be kept in operation as long as possible. During pot operation, chemical and abrasive forces wear the bottom carbon lining down to the cast iron around the collector bars. By normal standards this may take 3000 days [1]. This is, however, often not the case. Earlier, long pot life was not considered a critical parameter as long as it was above 1200 days but nowadays a potlife of less than 2000 days is considered not to be acceptable. All smelters make a considerable effort to increase pot life by improving pot design with high quality lining materials, correct construction, smooth start up and good operation. EMAL is approaching a point where a replacement cycle is forthcoming for the Phase 1 pots, and thus consideration of a delining facility is necessary to carry out the required operation and to achieve consistent production capacity. The cooling area in the delining building for Phase 1 pots is considered large for Phase 1 pots only. The main aim of this study is to reduce the cooling time of a stopped pot enough to accommodate Phase 2 potshells in the same building as well without any extension. Lalonde et al. [2] established a method for obtaining temperatures of molten aluminum as it solidifies in a reduction pot after it has been removed from line current. The temperatures were used to develop cooling curves and models were created to predict the effect of time of anode removal, size of metal pad and distance from the cell center on the cooling rate of the untapped aluminum. However, the study did not focus on the potshell and the model considered the pot contents as a single entity. Many other studies had paid an extensive attention to the potshell sides in operating pots; see [3-6]. One study, however, modeled pot cooling after the power interruption in order to determine the pot condition for subsequent potline restart after a few hours [7]. None of these studies established a long term cooling model for a permanently stopped pot. Even though some of the hitherto published cooling techniques can be considered for shutdown pots, the implementation of any of these may not fit the delining room design. The main goals of the study are to build and validate a full scale 3-D FEM model to be used, first, to map the temperature distribution inside the stopped pot after pot cutout and, second, to study and design an appropriate cooling system to reduce the shutdown cell cooling time without damaging the potshell. This paper shall focus upon the first goal associated with building and validating the FEM model. The model is based on ANSYS® commercial code and set up for a DX pot. The validation was done with measurements made on a stopped DX pot at DUBAL. The DX pot technology has been described previously [8]. Experimental Advances in FEM software such as ANSYS and availability of the very fast computers with large memory made it possible to build a full scale 3-D model of one quarter of DX pot with very detailed representation of the potlining and of the potshell steel structure. The objectives are: to build the 3-D FEM model for an operating pot design, perform onsite measurements on a stopped pot of that design, validate the model using these measurements, and use the model to map the temporal and spatial thermal contours in the pot at similar experimental environment and boundary conditions. The following two sections will explain the onsite measurements and results followed by the FEM model. Plant measurements on a stopped DX pot at DUBAL The onsite measurements were made on a stopped DX pot in Dubai Aluminium (DUBAL). The temperature measurements started just after the pot cutout and continued for almost seven days throughout different stages of the pot movement from the potroom to the delining room space. Bath temperature was measured at two locations, before and after tapping. Evolution of temperatures with time was measured in the metal on the potshell surface (on the upstream and downstream of the potshell side, and at the tap end), on the deckplate, and on the bottom of the