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1、 1.2 Equation of state for natural gases1 Ideal gas The volume of the gas molecules is insignificant compared with the total volume enclosing the gas;No attractive or repulsive forces exist among the molecules or between the molecules and the container walls;All molecule collisions are perfectly ela
2、stic;i.e.,there is no loss of internal energy upon collision.2 Equation of state for ideal gasnRTPVR:universal gas constantRTpMg3 Compressibility equation of state for natural gasznRTpVz:z-factor/gas deviation factor/gas compressibility factor idealactualVVz Vactual:volume occupied by a gas at given
3、 pressure and temperature Videal:volume the gas that would occupy at the same pressure and temperature if it behaved like an ideal gas4 Principle of corresponding state Pure,but similar,gases have the same Z factor at the same values of reduced pressure and reduced temperature.For pure substance:Red
4、uced temperature:crTTTReduced pressure:crppp4 Principle of corresponding stateFor mixture:the pseudoreduced pressurethe pseudoreduced temperaturepseudoreduced temperature:pseudoreduced pressure:pcprTTTpcprpppjcjjpcTyTjcjjpcpyppseudocritical pressure:4 Principle of corresponding stateStanding-Katz co
5、rrelation5 Calculation of Z-factorWhen gas composition is known-Stewart et al.Mixing Rules(1)To calculate the pseudocritical parameters(2)To calculate the pseudoreduced parameters(3)To check Standing-Katz correlation and get Z-factorjcjjpcTyTjcjjpcpyppcprTTTpcprppp5 Calculation of Z-factorWhen gas s
6、pecific gravity is known-Suttons method Where Ppch-pseudocritical pressure of the hydrocarbon components,psia;Tpch-pseudocritical temperature of the hydrocarbon components;h=specific gas gravity of the hydrocarbon components.26.30.1318.756hhpchp20.745.3492.169hhpchT0.57h1.68.5 Calculation of Z-facto
7、rWhen N2 great then 5:)1(NNNgyzyzCzz-the compressibility factor of the mixture zg-the z-factor of the hydrocarbon fraction of the mixture;zN-the compressibility factor of nitrogenyN-mole fraction of nitrogen in the mixture C-correction factor,1CEx.2 The composition of the natural gas is given as fol
8、lows,calculate the Z-factor of the natural gas under the condition of 35、10.2MPa？ComponentMole fraction(%)Pci(MPa)Tci(k)N243.53.399126.1CH444.54.604190.55C2H66.24.880305.43C3H83.94.249369.82C4H101.93.797425.165 Calculation of Z-factor5 Calculation of Z-factorSolution:(1)To calculate the mole fractio
9、n of hydrocarbon component in pure hydrocarbons Niiyyy1 (2)To calculate the pseudocritical parameters of pure hydrocarbons jcjjpcTyTjcjjpcpyp5 Calculation of Z-factor (3)To calculate the pseudoreduced parameters of pure hydrocarbons (4)To check Standing-Katz correlation and get Z-factor of pure hydrocarbonspcprTTTpcprpppZg=0.725 Calculation of Z-factor (5)To check the fig.of compressibility factor for N2 and get ZN ZN=1.02 (6)To calculate the the Z-factor of the natural gas 85.0)435.01(72.0435.002.1)1(NgNNyZyZZ5 Calculation of Z-factorThank you for your attention!