A debutanizer is a type of fractional distillation column used to separate butane from natural gas during the refining process. Distillation is the process of heating a liquid to vapor and condensing the vapors back to liquid in order to separate or purify the liquid. Examples include distilling water to purify it and distilling liquor to make it stronger. Fractional distillation, as occurs in a debutanizer, is the separation of a fraction — a set of compounds that have a boiling point within a given range — from the rest of the mixture.
Raw natural gas can be drilled from natural deposits or released as a byproduct from petroleum distribution. In either case, it is not the nearly pure methane used by consumers. As much as 20 percent of raw natural gas is various heavier hydrocarbons, which are chemical compounds made up of hydrogen and carbon, such as butane, propane and ethane. Additionally, oxygen, nitrogen, hydrogen sulfide and trace amounts of the noble gases might be mixed within the gas.
These other substances are removed in the production phase as the natural gas is refined. Huge fractionating columns — industrial towers that are 2-20 feet (0.61-6.1 m) across and 20-200 feet (6.1-61 m) high or sometimes more — vaporize the gas in an expansion turbine and then condense it with multiple valve trays. Depending on which hydrocarbon is being removed from the natural gas liquids (NGL), the column might be a debutanizer, a depropanizer or a deethanizer. When the process is finished, the natural gas is almost pure methane. Trace amounts of mercaptan, which is the source of the rotten egg smell associated with natural gas, are actually added to the methane to make leaks more detectible.
Different refineries might refine the gas in different orders. Most commonly, the NGL flows first through a depropanizer to remove the heavier propane from the mix and then through the debutanizer next to siphon off the butane. Other refineries use a debutanizer to remove a mix of butane and propane, also referred to as a C3/C4 mix, from the NGL and later use a depropanizer to separate the butane and propane from each other.
Studies have suggested that updating debutanizers for greater efficiency would be both profitable and eco-friendly. Normal petroleum refinery operation allows the light hydrocarbon gases to become dissolved into the petroleum. Siphoning off these gases gives the oil company another energy source to market but makes the petroleum more efficient by decreasing plugging and fouling of burner tips.