H. Behjati Rad - Department of Chemical Engineering, Gas and Petroleum, Semnan University, Iran
F. Varaminian - School of Chemical, gas and petroleum Engineering, Semnan University, Iran

In this work, satbility calculations and determination of gas hydrate structure in equilibrium conditions by using minimization of TPD function for methane-water system (SI), propane-water system (SII) and methane-methyl cyclo pentane-water system (SH) were performed. Based on results, at 274 K and 275 K temperatures, the liquid phase of methane-water system at 27 bar and 30 bar pressures, propane-water system at 1.7 bar and 2.5 bar pressures and methane-methyl cyclo pentane-water system at 9.6 bar and 10.1 bar pressures was decomposed. As a result of decomposition of liquid phase for these systems, two new phases, a new liquid phase and hydrate phase were formed. Subsequently, multiphase flash calculations in order to determine the amount and composition of stable phases in equilibrium state were performed. For minimization of TPD function, Algorithm Genetic was used. The results Show good accuracy with data of Heriot Watt university hydrate model (HWHYD).

Tangent plane distance, Multiphase flash calculation, Gibbs energy minimization, Gas Hydrate