Waste fuel accounted for 29% of U.S. manufacturing fuel use in 2010, according to EIA’s latest Manufacturing Energy Consumption Survey (MECS). Waste fuels are usually byproducts of onsite production processes; most have little to no economic value and are generally not able to be economically transported. Waste fuels accounted for 4,160 trillion British thermal units (Btu) in 2010 and were used in a wide variety of manufacturing industries.
Waste fuels are generally used where they are created because they are readily available to use for manufacturing heat and power needs. Most such fuels are principally derived from the onsite production process and cost little or nothing to use, lowering overall fuel costs by displacing purchased fuels. Using solid waste fuels also decreases the volume of waste disposal needed, lowering disposal cost for manufacturers.
Typically, the industries producing the most waste fuels are energy intensive and can readily use them, and doing so is less expensive than marketing and transporting them to a buyer. However, for some waste fuels, such aspetroleum coke (pet coke), the producing industry cannot make use of the waste fuel, while other industries can. Pet coke is produced by petroleum refineries as a waste product and sold to cement plants and paper mills to be used as a fuel and to aluminum smelting plants to be used for anodes, which are consumed in the electricity-intensive smelting process.
The petroleum and coal products industry uses waste fuels for most of its fuel consumption. Similarly, the paper and wood products industries use available biomass products from trees and production derivatives like black liquor. Chemical facilities use available waste gas. Iron and steel industries use mostly blast furnace gas, a smaller but still significant source.
Waste gas, the largest class of waste fuels, is derived primarily from petroleum and coal products, mostly from petroleum refining, and chemicals. Small amounts of waste gases are found in food and beverage manufacturing. In the refining industry, waste gas is known as still gas, which is a mixture of refined hydrocarbons such as ethane, propane, and normal butane, among others. The petroleum and coal products industry (mostly refineries) uses waste fuels for 59% of its fuel use. Blast furnace and coke oven gases are connected to the iron and steel industry, which uses waste fuels for 23% of its fuel use. The heat from blast furnace and coke oven gas is sometimes used to generate electricity in a combined heat and power (CHP) plant.
The other large class of waste fuel, biomass products, is principally used in the paper and wood products industries. The paper industry uses waste fuel for 58% of its fuel use. The paper industry is the exclusive user ofblack liquor, a byproduct of the kraft paper making process, which uses pulping (cooking) liquor to extract pulp from wood chips in a digester that cooks the mixture for several hours. Black liquor contains leftover cooking liquor and lignin, which is a substance found in wood that yellows paper over time and is undesirable in high-quality paper. The black liquor is concentrated and can be burned to provide process heat, refined to be reused as pulping liquor, or used for CHP. Nearly 3,900 megawatts of black liquor-fired CHP capacity was in service in 2012.
Waste materials used as fuels are very diverse. Wood and paper industries, chemicals, petroleum and coal products, plastics, and cement all use waste materials. Waste materials are waste oils and tars, waste paper, and anything else that can be used to provide heat and power in an industrial facility. For example, the cement industry uses a variety of delivered waste materials to provide heat for its kilns, including old tires (whole or processed), municipal solid waste, scrap fabrics, paints, and inks. Because of the inconsistent quality and heat content of waste products, they cannot be used for more than 10%-30% of a cement kiln’s heat output.