ABSTRACT
The irreversible condensation of calibration gases due to trace amounts of C6+ hydrocarbons can be important to the calibration of calorimeters but is not likely to be significant in the calibration of devices for composition measurement. Gas samples in general and calibration gases in particular are subject to the possibility of condensation during storage and transit. Gaseous hydrocarbon mixtures, whether natural gases or man-made mixtures, will typically contain traces of the heavier hydrocarbons. These trace materials can raise the hydrocarbon dew point of the mixture and thereby alter the heating value of the sample if the condensation process is not fully reversible. This chapter discusses the composition and heating values of hydrocarbon mixtures. It uses the Soave/Redlich/Kwong equation of state to calculate the dewpoints of these mixtures and the equilibrium composition of their vapors at temperatures below the dew points.
