A nitrogen rejection unit (NRU) selectively removes nitrogen from a gas. The name can be applied to any system that removes nitrogen from natural gas. For high flow-rate applications, typically >15 MMSCFD, cryogenic processing is the norm. This is a distillation process which utilizes the different volatilities of methane (boiling point of −161.6 °C) and nitrogen (boiling point of −195.69 °C) to achieve separation. In this process, a system of compression and distillation columns drastically reduces the temperature of the gas mixture to a point where methane is liquified and the nitrogen is not. For smaller applications, a series of heat exchangers may be used as an alternative to distillation columns.