Study On The Densities And Viscosities Of CO₂-CH₄ Binary System（for CO₂-EGR Technology）

CO₂ enhanced gas recovery（CO₂-EGR）technology is a"green"technology,which can not only capture CO₂ but also enhance natural gas recovery.The basic data such as the density and viscosity of CO₂-CH₄ mixture in CO₂-EGR process is of great significance in the application of CO₂-EGR technology.In order to reduce the experimental consumption and provide basic data for CO2-EGR technology,the thermodynamic model was proposed and used to calculate the density and viscosity of the CO₂-CH₄ binary mixture under the supercritical state in this work。The existing reported literatures were consulted and studied systematically,the density and viscosity data of the CO₂-CH₄ binary system were collected and analyzed.The PR-EOS was chose to calculate the density of the CO₂-CH₄ binary system.The binary interaction parameter k_ij in the PR equation with mixing rule was changed with the reduced pressure,the reduced temperature and the composition.The four different modified models of k_ij(PR-k_ij（1）,PR-k_ij（2）,PR-k_ij（3）,and PR-k_ij（4）)were proposed.The experimental data of the supercritical CO2-CH4 binary system in the literature were classified into training set and testing set.The parameters of the four correlation equations were obtained by fitting the the training set.The average absolute relative deviations（AAD）of PR-k_ij（1）,PR-k_ij（2）,PR-k_ij（3）,and PR-k_ij（4）for the training set were 0.9597%,0.634%,0.4351%and 0.1703%,respectively.The testing set was predicted and the AAD were 1.9877%,0.6735%,0.628%and 0.4811%,respectively.The accuracy and applicability of each model were verified.In addition,the parameter of the volume correction HTHPVT-PR equation was optimized by using the experimental density data of the binary system from the literature.The density data of the binary system were calculated by using the new parameters,and the accuracy was greatly improved.The relationship of viscosity,temperature,pressure,and composition of the supercritical CO₂-CH₄ binary system was analyzed.And a new correlation was proposed.The AAD of the training set are 2.25%.The AAD of the testing set are 2.86%.The results proved that the new model has a higher accuracy and reliability Four models of viscosity including the REFPROP,TRAPP,Chung,and Lucas models were used to calculate the viscosity of the binary system.The AAD were 5.54%,5.38%,6.50%and6.96%,respectively.The applicability of different models were analyzed and evaluated.A new modified method was proposed based on the LBC model.The viscosity data of CO₂–CH₄ binary system with low CO₂ concentration were calculated by this new model.The AAD of the model and the modified model were 8.70%and 2.14%,respectively.And the calculation accuracy was greatly improved.