CHEMICAL ENGINEERING TRANSACTIONS VOL. 53, 2016 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Valerio Cozzani, Eddy De Rademaeker, Davide Manca Copyright © 2016, AIDIC Servizi S.r.l., I SBN 978-88-95608-44-0; I SSN 2283-9216 Simulation of Pipeline Depressurization in the Transportation of Oil&Gas with High CO 2 and H 2 S Content Luigi Raimondi Process Simulation Services, Via Piave 17, 20027 Rescaldina, Italy luigi.raimondi@xpsimworld.com The problem of a reliable simulation of relief condition of a fluid (flow rate, pressure and temperature) is a preliminary and fundamental step to the calculation of dispersion effects. The evaluation of the mass discharged from pipelines in cases of leaks or abnormal operating conditions is largely based on the use of commercial simulators for safety analysis like PHAST or more specialized codes developed for oil&gas transportation such as OLGA and Ledaflow. However all these codes use a simplified thermodynamic approach since physical and transport properties are calculated on the basis of fixed fluid compositions and stored in tables. To avoid these limitations vapour-liquid equilibrium and fluid dynamics equations should be coupled and solved at the same time. This paper presents the implementation of two-fluid model fluid dynamics equations in a process simulator (XPSIM) providing an integrated tool which allows the simulation of vapour-liquid flows taking into account also the changes in the chemical composition. Since in this field experimental data are almost not available the validation of simulations is very difficult and different results are to be expected with different codes. The first case considered is the fast discharge of a rich CO2 mixture obtained in a small experimental flow-loop: the simulated results are described and compared with experimental values. The second case presents the results of the depressurization of a pipeline used to transport a hydrocarbon fluid with high hydrogen sulfide content in the case of an emergency through a control valve. 1. Introduction In the complex field of flow assurance the transportation of hydrocarbon fluids containing high amounts of acid gases is considered a critical topic. This paper is dealing with simulation aspects in two cases: the first is related to CO 2 transportation as usually required by “Carbon dioxide capture and storage” (CCS) projects, i.e. where carbon dioxide emitted from industrial or energy-related sources before entering the atmosphere, is recovered, compressed, transported and injected in geological formations with the scope of mitigation of greenhouse effects and the reduction of related global warming and climate changes. The second examines the importance of the evaluation of hydrogen sulphide content in the vapour phase discharged a when either a leak or abnormal conditions are met. Simulation required for both engineering design and operating analyses are usually carried out by means of commercially available process simulators (HYSYS, AspenPlus, ChemCad, etc.) and fluid-dynamics simulators (OLGA, LedaFlow, etc.). The results obtained using these tools are not always reliable, in particular the fluid dynamic codes are bases on the use of property tables calculated using a fixed initial composition. The simulation of the transport of almost pure carbon dioxide streams is very sensitive with respect to thermodynamic methods and equations of state used: the selection of reliable calculation methods for vapour-liquid equilibrium, enthalpy, entropy, density and viscosity play a key role in the fluid-dynamic calculations required by for safe and cost-effective pipeline design. This general problem has been described by the author in a previous event series (Raimondi, 2014) where some examples taken from industry projects have been discussed. The fluid-dynamic implementation considers most important two-phase flow patterns: stratified, annular, slug and bubble flows are considered even in cases of fast depressurization where most published papers apply a homogeneous no-slip flow model. DOI: 10.3303/CET1653057 Please cite this article as: Raimondi L., 2016, Simulation of pipeline depressurization in the transportation of oil&gas with high co2 and h2s content, Chemical Engineering Transactions, 53, 337-342 DOI: 10.3303/CET1653057 337