"Tail gas" is a general term that refers to the gases that exit a process, typically after the primary products have been removed. It's often used in industrial contexts, and the specific composition of the tail gas can vary depending on the process.

Here are some examples of where you might find "tail gas" mentioned:

* Chemical Manufacturing: In a chemical plant, the tail gas might be the gases remaining after the desired product has been extracted. It could contain unreacted starting materials, byproducts, and inert gases.

* Combustion Processes: In power plants or furnaces, tail gas can refer to the flue gas after it's passed through the heat recovery systems. It might still contain pollutants like sulfur dioxide or nitrogen oxides.

* Petroleum Refining: In oil refineries, tail gas can be the gas left after the desired hydrocarbons have been extracted. It often contains lighter hydrocarbons like methane, ethane, and propane.

* Gas Processing: In natural gas processing facilities, tail gas can refer to the gas left after the valuable components like methane and ethane have been removed.

Key points to remember:

* Tail gas is not necessarily a waste product. It may contain valuable components that can be recovered or used as fuel.

* The composition and treatment of tail gas will depend on the specific process and its environmental impact.

* Tail gas is often treated to remove pollutants before it's released into the atmosphere.

To understand the exact meaning of "tail gas" in a specific context, you need to look at the process being described.