At any P and T along this line the system can be all solid, all liquid or a mixture of the two depending on the energy level. The energy change occurring along line HD is called the heat of fusion. Line HD can have a positive or negative slope depending on whether the liquid expands or contracts on freezing. Ice water at 0☌ and atmospheric pressure occurs on this line. Line HD is the equilibrium line between solid and liquid. The use of "dry ice" for cooling is an example of this. Point H, the triple point, is the only combination of pressure and temperature at which all three phases can exist together.Īlong line FH no liquid phase is ever present and solid sublimes to vapor. At equilibrium, one can change phase, by simply adding or removing energy from the system. Lines HD, HC, and FH are the equilibrium lines - combinations of pressure and temperature at which the adjoining phases are in equilibrium. Depending on the component’s pressure and temperature, it may exist as a vapor, a liquid, or some equilibrium combination of vapor and liquidįigure 2-1 P-T Diagram for pure component. Intermediate-weight hydrocarbons may condense from rich gases upon cooling.Ī pure component of a natural gas system exhibits a characteristic phase behavior, as shown in Fig. Lean gases burn with a low air-to-gas ratio and display a colorless to blue or yellow flame, whereas rich gases require comparatively higher amounts of air for combustion and burn with an orange flame. In addition, operators may intentionally add odorants, tracers (such as helium), or other components.ĭry, or lean, natural gas systems have high concentrations of the lighter hydrocarbons (methane and ethane), while wet, or rich, gas systems have higher concentrations of the intermediate-weight hydrocarbons. These constituents may occur naturally in gas reservoirs, or they may enter the system as contaminants during production, processing, and transportation. Natural gas systems can also contain non-hydrocarbon constituents, including hydrogen sulfide (H2S), carbon dioxide (CO2), nitrogen (N2), and water vapor. These components are commonly referred to as pentanes-plus, condensate, natural gasoline, and natural gas liquids (NGL). The intermediate-weight hydrocarbons (pentane through decane) exist as volatile liquids at atmospheric conditions. These are the primary components of liquefied petroleum gas, or LPG. Propane (C3H8), butane (n-C4H10 and i-C4H10), and heavier hydrocarbons may be extracted from the gas system and liquefied for transportation and storage. Methane and ethane exist as gases at atmospheric conditions.
#Depriester chart dew temperature series#
Natural gas systems are composed primarily of the lighter alkane series of hydrocarbons, with methane (CH4) and ethane (C2H6) comprising 80% to 90% of the volume of a typical mixture. Phase diagrams illustrate the phase that a particular substance will take under specified conditions of pressure, temperature, and volume. Pure substance (single-component systems),.One needs to know the phase or phases that exist at given conditions of pressure, volume, and temperature so as to determine the corresponding energy level, to do this we need to study the phase diagram or phase behavior, but first we have to separate components into three classifications: Additional energy will cause the liquid to vaporize. Our primary concern in this section is the difference in energy level between phases.Įnergy is added to melt a solid to form a liquid. Vapor molecules possess more energy than liquids (very active) and are less dense than liquids. Vapors do not have a definite volume or shape and will fill a container in which they are placed. By virtue of the energy, there is more space between molecules, and liquids are less dense than solids. Liquid molecules possess more energy than a solid (allows movement from place to another).
Liquids assume the shape of the container but will not necessarily fill that container.
Liquids have a definite volume but no definite shape. They are composed of molecules with very low energy that stay in one place even though they vibrate. Solids have a definite shape and are hard to the touch. The matter has three phases, the simplest example is water.
Phase defines any homogeneous and physically distinct part of a system that is separated from other parts of the system by definite bounding surfaces: Prediction and Inhibition of Gas Hydrates Bookīasics of Corrosion in Oil and Gas Industry Bookīefore studying the separation of gases and liquids, we need to understand the relationship between the phases. Fundamentals of Oil and Gas Processing Book
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