The term "fuel gas" here refers to combustible gases that are by-products or specifically prepared in production processes such as petroleum refining, chemical manufacturing, and metallurgy. The main components of these gases include carbon monoxide, hydrogen, methane, small amounts of hydrocarbons, or other combustible gases. After collection, purification, and blending, such fuel gases can be used as energy sources in thermal and power systems such as boilers, heaters, and gas turbines, or as feedstock gases for chemical synthesis in reuse processes.