 Corresponding author: Phone: +44(0)1314 513797 Fax +44(0)1314 513 797 E-mail: antonin.chapoy@pet.hw.ac.uk EFFECT OF COMMON IMPURITIES ON THE HYDRATE STABILITY OF CARBON DIOXIDE RICH SYSTEMS Ibrahim Alsiyabi, Antonin Chapoy*, Bahman Tohidi Hydrates, Flow Assurance & Phase Equilibria Research Group, Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK ABSTRACT CO 2 produced by carbon capture processes is generally not pure and can contain impurities such as N 2 , H 2 , CO, CH 4 and water. The presence of these impurities could lead to challenging flow assurance issues. The presence of water may result in ice and/or gas hydrate formation and cause blockage. The aim of this communication is to evaluate the risk of hydrate formation in a rich carbon dioxide stream. The three phases HLV equilibria of the ternary CO 2 + (N 2 or CH 4 or O 2 or Ar or H 2 or CO) + water systems were determined at a constant composition (4.56% N 2 , 7.09% H 2 , 5.85% CH 4 , 5.87% CO, 5.03% Ar, and 5.34% O 2 in dry basis). The tests were determined by standard constant-volume isochoric equilibrium step-heating techniques. A thermodynamic approach was employed to model the phase equilibria. The thermodynamic model was used to predict the hydrate dissociation conditions of CO 2 and CO 2 rich streams in the presence of free water. Keywords: Gas Hydrates; Carbon dioxide; Water; Thermodynamic Model. NOMENCLATURE List of symbols P Pressure T Temperature y Composition Abbreviations AAD Absolute Average deviation CPA Cubic Plus Association EoS Equation of State H Hydrate phase L liquid phase I Ice phase V vapour phase Subscript Cal Calculated property exp Experimental property W Water property Sat Saturation INTRODUCTION Hydrates are ice-like solid component formed mainly from water and other small molecules. To form hydrate, three things are required: a sufficient amount of water (host), a former (guest) and the right combination of pressure and temperature. Light gases such as CH 4 , N 2 , O 2 , Ar, H 2 S and CO 2 can form hydrate in the presence of water. There are basically three common types of hydrate, structure I (SI), structure II (SII) and structure H (SH). Primary, the hydrate structure depends on the size of the gas molecules. The mixture of light gasses can result in a change on both the structure and the hydrate stability zone. Suitable thermodynamic conditions of forming hydrate can be found in pipelines; therefore both experimental and modelling works should be carried-out to define the fluid hydrate zone. With regard to carbon emissions, the most promising solution currently on the table is CO 2 capture and subsurface storage, primarily by injection into ageing oil/gas reservoirs (where it can be used to improve oil/gas recovery) or deep saline aquifers. Conventionally, pipelines are used Proceedings of the 8th International Conference on Gas Hydrates (ICGH8-2014), Beijing, China, 28 July - 1 August, 2014