Estimating the effects of ethane and heavier components recovery on the heat content of residue gas

Recovery of natural gas liquids (NGL) components in gas not only may be required for hydrocarbon dew point control in a natural gas stream (to avoid the unsafe formation of a liquid phase during transport), but also yields a source of revenue, as NGLs normally have significantly greater value as separate marketable products than as part of the natural gas stream. One of the key parameters in the recovery of ethane and heavier products from natural gas is the effect of the extraction on the heat content of the residue gas. In this work a simple-to-use generalized correlation is developed for the ethane recovery limit to attain a minimum higher heating value (HHV) for various feed gas compositions. As can be seen from this correlation results, the quantity of inerts in the feed gas has an impact on the ethane recovery level which can be targeted in a plant design. A simple correlation is also developed here to estimate the propane and butanes recovery percent as a function of ethane recovery percent. The tool developed in this study can be of immense practical value for petroleum and gas engineers to have a quick check of the heat content of the residue gas after recovery of ethane and heavier components from natural gas at various conditions without opting for any experimental trials. In particular, engineers would find the approach to be user-friendly with transparent calculations involving no complex expressions.