The vapour from the separators is cooled, compressed and dehydrated by counter-current contact with glycol. It is chilled by refrigeration and routed to a series of fractionation towers. These include a de-ethaniser which separates the methane (CH4) from ethane (C2H6). There is a depropaniser to remove propane (C3H8) and a debutaniser to remove butane (C4H10). Some of the gases – the methane and ethane – are used as fuel gas on the site, the rest is compressed, odorised (with tertiary butyl mercaptan) and is routed via a 8-inch (0.2 m) pipeline to Sopley near Christchurch where it enters the National Gas Grid. Propane and butane (known collectively as LPG or liquefied petroleum gas) are maintained as liquids, they are odorised (with ethyl mercaptan) and stored in horizontal vessels on the site. LPG is sold and transported from the site by road tanker.