Correlation Accurately Predicts Hydrate Forming Pressure of Pure Components

Abstract

Abstract Gas hydrates are a well-known problem in the oil and gas industry when they agglomerate and plug pipelines and process equipment. This paper presents a new correlation that predicts hydrate formation pressure of pure alkanes, acid gases and nitrogen as a function of molecular weight at a given temperature. This correlation covers a temperature range between 263 and 293 K. The results show an average absolute deviation of 3.06% from typical experimental data for light alkanes and 1.4165% for non-hydrocarbons. The average absolute deviation for all data used in this work is 2.24%. The new correlation can be improved if more experimental data will be available in future. Introduction Gas hydrates are ice-like crystalline structures that form when a mixture of water and gas molecules exist under favourable conditions, especially at low temperatures and high pressures. In the hydrate formation process, gas molecules are entrapped into cavities formed by water molecules. Usually light molecules such as methane, ethane, propane, isobutene, nitrogen, carbon dioxide and hydrogen sulfide will form hydrates, however, several heavy hydrocarbons such as benzene, cyclopentane, isopentane, methylcyclohexane and 2,3-dimethylbutane have been recently identified as hydrate formers(1). Gas hydrates are a serious problem in the oil and gas industry because they plug production and gas transmission pipelines and damage process equipment. It is possible to keep the operating conditions at a level where hydrate formation cannot occur by applying heat, insulating the pipelines and using chemical additives as inhibitors. To prevent the problems caused by hydrates, it is important to predict the hydrate formation temperature and pressure accurately. Hammerschmidt(2) first discovered that the formation of clathrate hydrates could block natural gas transport pipelines. After this discovery, the oil and gas industry has been more interested in investigating the problem. This paper presents a new correlation that can predict the gas hydrate formation pressure of pure alkanes, acid gases and nitrogen as a function of molecular weight and temperature. The developed correlation is applicable to a range of temperatures from 263 K to 293 K. The results show an average absolute deviation of 2.24% from typical experimental data. Methodology for Correlation Development The required data to develop this correlation include experimental temperature and pressure(3–13) for different pure components with different molecular weights. In previous work(14), a numerical method was applied to analyze gas hydrate formation in a multi-component system, and in this work, hydrate formation pressure for pure gas components is predicted accurately by proposing a new and simple correlation. The following methodology has been applied to develop this correlation. First of all, hydrate formation pressure is correlated as a function of hydrate formation temperature for different pure alkane components. Then, the calculated coefficients for these polynomials are correlated as a function of molecular weight. The derived polynomials are applied to calculate new coefficients for Equation (1) to predict the hydrate formation pressure of different pure alkane components as a function of temperature. Table 1 shows the tuned coefficients for Equations (2) to (5).