This pressure was termed the “Convergence Pressure” of the system and has been used to correlate the effect of composition on K-values, thus permitting generalized K-values to be presented in a moderate number of charts. In each chart the pressure range is from 70 to 7000 kPa (10 to 1000 psia) and the temperature range is from 5 to 260 ✬ (40 to 500 ✯).Įarly high pressure experimental work revealed that, if a hydrocarbon system of fixed overall composition were held at constant temperature and the pressure varied, the K-values of all components converged toward a common value of unity (1.0) at some high pressure. In these charts, K-values for individual components are plotted as a function of temperature on the x-axis with pressure as a parameter. One of the earliest K-value charts for light hydrocarbons is presented in reference. There are several forms of K-value charts. EoS approach requires use of a digital computer. The widely used approaches are K-value charts, Raoult’s law, the equation of state (EoS) approach (f), activity coefficient approach (?) or combination of EoS and the EoS and ? approaches.
Depriester chart plus#
The components making up the system plus temperature, pressure, composition, and degree of polarity affect the accuracy and applicability, and hence the selection, of an approach. In general K-values are function of the pressure, temperature, and composition of the vapor and liquid phases. This “Tip of the Month” presents a history of many of those graphical methods and numerical techniques. Alternatively, there are several graphical or numerical tools that are used for determination of K-values. Obviously, experimental measurement is the most desirable however, it is expensive and time consuming. Equation (2) is also called “Henry’s law” and K is referred to as Henry’s constant. For the more volatile components the Kvalues are greater than 1.0, whereas for the less volatile components they are less than 1.0.ĭepending on the system under study, any one of several approaches may be used to determine K-values. Alternatively, the compressibility factor for specific gases can be read from generalized compressibility charts that plot as a function of pressure at constant temperature.Ki is called the vapor–liquid equilibrium ratio, or simply the K-value, and represents the ratio of the mole fraction in the vapor, yi, to the mole fraction in the liquid, xi. For a gas that is a mixture of two or more pure gases, the gas composition must be known before compressibility can be calculated. Compressibility factor values are usually obtained by calculation from equations of state (EOS), such as the virial equation which take compound-specific empirical constants as input. In general, deviation from ideal behaviour becomes more significant the closer a gas is to a phase change, the lower the temperature or the larger the pressure. It is a useful thermodynamic property for modifying the ideal gas law to account for the real gas behaviour. It is simply defined as the ratio of the molar volume of a gas to the molar volume of an ideal gas at the same temperature and pressure. In thermodynamics, the compressibility factor ( Z), also known as the compression factor or the gas deviation factor, is a correction factor which describes the deviation of a real gas from ideal gas behaviour. Read this K-value off the chart (approximately 21.3). Note where the line crosses the methane axis.Connect the points with a straight line.On the right-hand vertical axis, locate and mark the point containing the temperature 60☏.On the left-hand vertical axis, locate and mark the point containing the pressure 100 psia.Exampleįor example, to find the K value of methane at 100 psia and 60 ☏. Many DePriester charts have been printed for simple hydrocarbons. "K" values, representing the tendency of a given chemical species to partition itself preferentially between liquid and vapor phases, are plotted in between. These nomograms have two vertical coordinates, one for pressure, and another for temperature. DePriester in an article in Chemical Engineering Progress in 1953. ( December 2018)ĭePriester Charts provide an efficient method to find the vapor-liquid equilibrium ratios for different substances at different conditions of pressure and temperature. Please introduce links to this page from related articles try the Find link tool for suggestions. This article is an orphan, as no other articles link to it.