Iranian Journal of Oil and Gas Science and Technology

Abstract Understanding gas hydrate formation conditions is crucial for designing natural gas transmission pipelines. These compounds are studied from both thermodynamic and kinetic perspectives. Despite significant advances in the thermodynamic aspect of hydrates, kinetic investigations still demand further research. Accordingly, in order to determine the equilibrium conditions of natural gas hydrate formation, six independent experiments were conducted using natural gas samples from the NF unit of the Bandar Imam Petrochemical Complex. The tests were carried out in a fixed-volume reactor at temperatures of 278.3, 278.6, 284.8, 290.3, 279.3, and 280.6 K, and pressures of 37.8, 19.3, 28.4, 52.2, 32.7, and 16.2 bar, respectively. The experimental results showed that the mass transfer coefficients were 0.343, 0.236, 0.200, 0.314, 0.297, and 0.166 m/s, while the molecular diffusion coefficients were 2.5968 ×10^(-9), 6.2866×10^(-9), 3.3931×10^(-9), 1.49×10^(-9), 4.28×10^(-9), and 7.42×10^(-9) m²/s, respectively. These findings indicate that an increase in reactor temperature leads to a decrease in mass transfer coefficient and an increase in molecular diffusion coefficient, whereas an increase in pressure results in a rise in mass transfer coefficient and a decrease in molecular diffusion coefficient. These trends are consistent with established empirical correlations

Abstract Gasoline obtained from the fractionation of indigenous natural gas condensate has low octane number (78) and is therefore of limited uses. Lead-based octane boosting and catalytic reforming are not the viable methods for many fractionation plants. This study was therefore aimed to develop an inexpensive conceptual alternative method for boosting the octane number of gasoline. Natural gas concentrated in methane having high octane number (more than 100) was absorbed in the gasoline to boost the octane number partially (86). Selective additives i.e. ethanol, tert-butyl alcohol, methylcyclopentane, toluene, iso-octane and xylene were blended first with the gasoline to aid the absorption of natural gas molecules. The loss of absorbed gas molecules from gasoline with the increase in temperature was also observed. It is therefore required to try for avoiding any increase in temperature in the finished gasoline. The developed conceptual method is promising. The findings of this simulation study would be useful for more studies towards the development of an affordable alternative method for fractionation plants for boosting the octane number of gasoline derived from natural gas condensate.

Abstract In this paper, exergy and exergoeconomic analysis is performed on the recently proposed process for
the coproduction of liquefied natural gas (LNG) and natural gas liquids (NGL) based on the mixed
fluid cascade (MFC) refrigeration systems, as one of the most important and popular natural gas
liquefaction processes. To carry out this analysis, at first, the proposed process is simulated, and then
the exergy analysis of the process equipment is performed; finally, an economic model is used for the
exergoeconomic analysis. The results include cost of exergy destruction, exergoeconomic factor,
exergy destruction, and exergy efficiency. The results of the exergy analysis demonstrate that the
exergy efficiency of the proposed process is around 53.83%, and its total exergy destruction rate is
42617.5 kW at an LNG and NGL production rates of 68.99 kg/s and 27.41 kg/s respectively. The
results of exergoeconomic analysis indicate that the maximum exergoeconomic factor, which is
69.53%, is related to the second compressor in the liquefaction cycle and the minimum
exergoeconomic factor, which is 0.66%, is related to the fourth heat exchanger in the liquefaction
cycle. In this process, demethanizer tower holds the highest relative cost difference (100.78) and the
first air cooler in liquefaction cycle has the lowest relative cost difference (1.09). One of the most
important exergoeconomic parameters is the cost of exergy destruction rate. The second heat
exchanger has the highest exergy destruction cost (768.91 $/Gj) and the first air cooler in the
liquefaction cycle has the lowest exergy destruction cost (19.36 $/Gj). Due to the high value of fuel
cost rate (as defined in exergoeconomic analysis) in heat exchangers, their exergy destruction cost is
much higher than other devices.

Abstract A value chain is a series of events that takes a raw material and with each step adds value to it. Global interest in the application of natural gas (NG) in production and transportation has grown dramatically, representing a long-term, low-cost, domestic, and secure alternative to petroleum-based fuels. Many technological solutions are currently considered on the market or in development, which address the challenge and opportunity of NG. In this paper, a decision support system (DSS) is introduced for selecting the best fuel to develop in the value chain of NG through four options, namely compressed NG (CNG), liquefied NG (LNG), dimethyl ether (DME), and gas-to-liquids (GTL). The DSS includes a model which uses the technique for order performance by similarity to ideal solution (TOPSIS) to select the best fuel in the value chain of NG based on the attributes such as market situations, technology availability, and transportation infrastructure. The model recommends some key guidelines for two branches of countries, i.e. those which have NG resources and the others. We believe that applying the proposed DSS helps the oil and gas/energy ministries in a most effective and productive manner dealing with the complicated fuel-related production and transportation decision-making situations.

Abstract In this study, mass transfer coefficients (MTC’s) of natural gas components during hydrate formation are reported. This work is based on the assumption that the transport of gas molecules from gas phase to aqueous phase is dominant among other resistances. Several experiments were conducted on a mixture of natural gas at different pressures and temperatures and the consumed gas was monitored and measured over time. The driving force is the difference between the solubility of hydrate former components at operating pressure and the corresponding equilibrium pressure. It was found that MTC is a function of pressure and temperature during hydrate growth stage. Consequently, an equation was proposed to calculate the mass transfer coefficient based on the experimental data.