(28c) A CFD Study Comparing Different Feed Nozzle Arrangement within an Empty Spray Section in a Coker Fractionator

Recent study was developed to evaluate the vapor distribution and its influence on the heat and mass transfer process considering coker fractionator designs with only one feed inlet nozzle. In these cases, high vertical velocities can be observed near the wall opposite to the inlet nozzle and large recirculation on the flash and washing zone, causing less efficiency on the heat and mass transfer between liquid and vapor phases. The vapor maldistribution on this section must be avoided since this behavior increases the probability of undesirable coke formation. The main purpose of this study is to predict the fluid dynamic behavior in a coker fractionator washing zone and analyze the influence of vapor distribution on the heat and mass transfer efficiency, considering different number of feed inlet nozzle. In general, licensors are used to design coker fractionator with only one feed inlet nozzle. However, recently, in new coker designs, specially those with four coke drums, it has been used a different design concept on the transfer line from the coke drum to the fractionator and two feed inlet nozzles has been used in these cases. For the coke drum process design, the most important criteria is the maximum vapor velocity and the number of coke drums are determined by the unit capacity and the maximum diameter limit that it can be manufactured. Depending on the unit capacity, six or more coke drums may be necessary. Six coke drums unit has become quite common recently and a new configuration of transfer lines from the coke drums to the fractionator and multiple inlet nozzles can be developed. A study comparing different number of inlet feed device was carried out in a coker fractionator washing zone considering a empty spray section instead of a conventional liquid-vapor contact device as tray and/or packing. Equipment with empty spray section takes some advantage such as lower: pressure drop, height, total costs and tendency of coke formation in high temperature sections. The results of this work are based on a steady state, three-dimensional, gas-liquid model with an Eulerian-Lagrangian approach of spray distributors using computational fluid dynamics techniques (CFD). A non-ideal Soave-Redlich-Kwong equation of state was applied to model the liquid phase equilibrium and fluid properties calculation within the condensation and evaporation models. The CFD model was capable to predict the fluid dynamic behavior of multiple inlet nozzles in a coker fractionator, and has proved to be a powerful tool to help engineering decisions. KEYWORDS: Coker fractionator, washing zone, empty spray section, multiphase flow, CFD.