Refinery gas is a mixture of gases generated during refinery processes which are used to process crude oil into various petroleum products which can be traded or sold. The composition of this gas varies, depending on the composition of the crude it originates from and the processes it has been subjected to. Common components include butanes, butylenes, methane, ethane, and ethylene. Some products found in refinery gas are subject to controls as a result of programs which are designed to address climate change.
When crude oil is brought to a refinery, it is taken through a number of processes to refine it into component parts. Refining includes distillation, reforming, cracking, and other processes. Typically, in addition to producing end products which can be sold, the refining process also produces products which require further refining, and refinery gas. To some extent, the byproducts produced can be controlled with adjustments to the settings at the refinery, including adjustments to the mixture of components refined together.
In some cases, refinery gas can be packaged and sold as a final product on the open market. In others, it can be used as a fuel. It can also be used as feedstock for other processes in the refinery. Use as a feedstock allows refineries to operate highly flexibly, adjusting what they produce easily by changing the processes and feedstock they use to meet demand for various petroleum products.
To determine what it contains, refinery gas is subjected to gas chromatography, which creates a chemical profile. Chromatography profiles are used by refinery officials as they decide what they want to do with refinery gas. These profiles can also be used to create reference profiles which help refinery officials keep up with the quality and constituency of the various crude oils they use. Higher grade crudes tend to more desirable and thus more expensive, and it is useful to be able to confirm which grade of crude is being used.
Release of refinery gas is tightly controlled. One reason for this is a desire on the part of the refinery to maximize profits; releasing potentially salable products would not be advised. Another reason is concerns about the environment which restrict the types of materials which can be released by companies which process chemicals and gases which can cause environmental harm. Companies can be fined or severely penalized in other ways for violating laws which are designed to limit harmful pollution.