NUMERICAL SIMULATION OF POOL HYDROCARBON FIRES AND THEIR EFFECT ON ADJACENT TANKS

Christina Goula – Chrysoula Malkotsi v ABSTRACT Tank fire incidents take place mainly in petroleum refineries, oil terminals or storage tanks and they can prove to be catastrophic. During the last years, engineering societies (American petroleum institute, National Fire Protection Association etc) have published strict engineering guidelines and standards for the construction, material selection, design and safe management of storage tanks. Nevertheless, tank fire incidents are increasing in the last decades. The problem addressed in this thesis is the thermal response of steel fixed roof oilstorage cylindrical tanks that are heated during pool fires. The first objective is to identify the parameters that describe the burning tanks and the geometric characteristics of flames are calculated. Numerical models are developed which include both burning tanks and the heated tank. The problem is solved numerically using the Finite Element method. The general purpose Finite Element code MSC Marc, which is optimized for non-linear problems, is used for the simulation. The three-dimensional models are developed through four-node shell elements. The behavior of the heated tank is examined for multiple pool fire scenarios. First, the case of one unique burning tank is examined. In rest scenarios, the fire spreads to adjacent tanks. Thus, in those scenarios the examined tank is heated by multiple sources (burning tanks). Parametric numerical analyses are conducted to study the influence of a combination of various parameters: diameter of the burning tank, type of stored fuel (gasoline or ethanol), incidence of wind, separation distance between tanks and the number of burning tanks involved. Furthermore, the study aims to propose an index for the evaluation of risk for fuel’s autoignition in the heated tank It is also examined if the safety distances that are recommended in current regulations (NFPA30:2012) are safe or not. The material properties of steel at elevated temperatures are according to EN 1993-1-2. It is found that the temperature distribution on the tank wall of the adjacent tank is not uniform. The temperature rise takes place on the side of the tank wall which is on the face of the source tank while the opposite side is not affected by the pool fire. This pattern becomes more complicated as more burning tanks are added. In both fuel types Ethanol and Gasoline the rate of reduction of the maximum temperature, as the separation distance increases, is more affected by the presence of wind than of the diameter of the burning tank. Under wind conditions, in smaller diameters of the source tank the rate of temperature reduction with the increase of the separation distance is not affected by the fuel type. In bigger burning tank diameters it has an effect. Under no wind conditions, the rate of temperature reduction with the separation distance is more influenced by the fuel type. According to the recommendations of NFPA30:2012, almost 62.5% of the case studies are on the unsafe side. It is concluded that the wind is the most critical parameter that should be considered for the determination of separation distance between tanks. Concerning the risk index that is defined in this thesis, the results of analyses indicate that under wind conditions, for both fuel types, at large diameters, the fire risk rate declines in a linear way. In small diameters for both fuel types the fire risk rate shows a rapid reduction in closer separation distances. When the two tanks become more separated, the fire risk becomes zero. Finally, the risk of autoignition in the heated tank increases as the number of burning tanks rises and, moreover, the risk in case of Ethanol is bigger in Gasoline models under both wind conditions. Institutional Repository Library & Information Centre University of Thessaly 27/05/2019 04:01:41 EEST 54.70. 40.1