An Equation Of State For The CO₂-H₂O System Under Low To Intermediate Temperatures

The pressure–volume–temperature–composition?PVTx?and other thermodynamic properties of CO₂,H₂ O and their fluid mixtures play a significant role in many related geological,environmental and industrial processes.The function relation between the PVTx properties?i.e.,equation of state?is one of the most commonly used ways to simulate fluid thermodynamic properties.Considering that cubic equations of state has simple form,fewer parameters,analytic expression of volume roots and is easy to extend to the mixture,a five-parameter cubic equation is used in this work to model the PVTx property of the CO₂-H₂ O system.The main work in this thesis is as follows:?1?Fit the parameters in the new equation with high-precision PVT reference data of CO₂ and H₂ O.?2?Finalize the new cubic equation of state by optimizing co-volume parameter and the relations between parameters and temperature through a series of tentative fitting and calculation.?3?Check the accuracy of the new equation within and outside the pressure-temperature range of the parameter fitting.?4?Extend the equation of state for pure fluids to CO₂-H₂ O mixtures with a new mixing rule,where the fitting and optimization of the mixing parameters are carried out with only the elaborately assessed high-precision experimental PVTx data of mixtures.?5?Check and analyze the accuracy of the mixture equation.?6?Compare the new equation for mixtures with some accurate virial equations of state.For water at 273.16–423 K and 0–70 MPa,the maximum volume deviation?MDV?of the new equation is 0.94%,and the average volume deviation?ADV?is 0.19%;The MDV and ADV of liquid are 0.095% and 0.0068%,respectively.For carbon dioxide at 320–540K and 0–60 MPa,the MDV of the new equation is 0.96%,and the ADV is 0.08%.For water and carbon dioxide,the new equation can be extrapolated to higher temperatures and pressures.For CO₂-H₂ O mixtures at 320–423 K and 0–60 MPa,the MDV of the new equation is less than 0.93%,and the ADV is only 0.06%.The MDV of the liquid mixtures is less than 0.14%,and the ADV is less than 0.02%.The MDV of the gas mixtures is lessthan 0.93%,and the ADV is only 0.08%.