System and method to determine thermophysical properties of a multi-component gas at arbitrary temperature and pressure

A method to determine the molecular weight of a subject gas mixture having both hydrocarbon and diluent components, and having known temperature, pressure, speed of sound, and diluent concentration values, comprising the steps of:

• selecting a set of reference gas mixtures, at least some of the gas mixtures containing diluents;
• determining the density and speed of sound for each of the reference gas mixtures, at the known temperature and pressure, thereby obtaining a set of reference speed of sound and reference density values;
• modeling the molecular weight of a gas mixture as a function of its speed of sound, a number of coefficients, and its concentrations of diluent components, thereby obtaining a model equation;
• using the reference speed of sound and reference density values to determine values for the coefficients;
• substituting the coefficient values and the speed of sound and concentration values of the subject gas into the model equation;
• and
• solving the model equation to determine the molecular weight of the subject gas mixture.

A method to determine a heating value of a subject gas mixture having both hydrocarbon and diluent components, and having known temperature, pressure, speed of sound, and diluent concentration values, comprising the steps of:

• selecting a set of reference gas mixtures, at least some of the gas mixtures containing diluents;
• determining the density and speed of sound for each of the reference gas mixtures, at the known temperature and pressure, thereby obtaining a set of reference speed of sound and reference density values;
• modeling the molecular weight of a gas mixture as a function of its speed of sound, a number of coefficients, and its concentrations of diluent components, thereby obtaining a model equation;
• using the reference speed of sound and reference density values to determine values for the coefficients;
• substituting the coefficient values and the speed of sound and concentration values of the subject gas into the model equation;
• solving the model equation to determine the molecular weight of the subject gas mixture;
• determining the speed of sound of the subject gas at standard temperature and pressure;
• modeling a heating value of the subject gas as a function of its speed of sound at standard temperature and pressure, a number of coefficients, and its concentrations of diluent components, thereby obtaining a model equation;
• and
• solving the model equation to determine the heating value of the subject gas mixture.

A method to determine density, at standard temperature and pressure, of a subject gas mixture having both hydrocarbon and diluent components, and having known temperature, pressure, speed of sound, and diluent concentration values, comprising the steps of:

• selecting a set of reference gas mixtures, at least some of the gas mixtures containing diluents;
• determining the density and speed of sound for each of the reference gas mixtures, at the known temperature and pressure, thereby obtaining a set of reference speed of sound and reference density values;
• modeling the molecular weight of a gas mixture as a function of its speed of sound, a number of coefficients, and its concentrations of diluent components, thereby obtaining a model equation;
• using the reference speed of sound and reference density values to determine values for the coefficients;
• substituting the coefficient values and the speed of sound and concentration values of the subject gas into the model equation;
• solving the model equation to determine the molecular weight of the subject gas mixture;
• determining the speed of sound of the subject gas at standard temperature and pressure;
• modeling the density, at standard temperature and pressure, of the subject gas as a function of its speed of sound at standard temperature and pressure, a number of coefficients, and its concentrations of diluent components, thereby obtaining a model equation;
• and
• solving the model equation to determine the density, at standard temperature and pressure, of the subject gas mixture.