Refuse-derived fuel
Refuse-derived fuel (RDF) is a type of solid fuel produced from the processing of municipal solid waste (MSW). Unlike raw MSW, which often has high moisture and low heat content, RDF aims to improve combustion efficiency by reducing moisture, achieving uniform size, and lowering ash content. The production process typically involves screening to remove inert materials, shredding larger particles, and separating metals and lightweight fractions. The shredded organic material can be used as fluff RDF or compressed into high-density pellets known as densified RDF, which are easier to transport and store.
One significant advantage of RDF over traditional coal is its lower sulfur and nitrogen content, which can help mitigate environmental issues like acid rain. However, RDF has a lower calorific value compared to coal, necessitating higher quantities for equivalent energy output. Additionally, the use of RDF in combustion can present challenges, including potential impacts on air pollution control systems and increased chlorine content compared to coal. Concerns about odors, dust production, and emissions during combustion also warrant consideration. Overall, while RDF presents a more sustainable alternative to coal, it is not entirely free from environmental impacts.
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Subject Terms
Refuse-derived fuel
DEFINITION: Solid fuel material created from the processing of municipal solid waste
The burning of refuse-derived fuel has some advantages over the burning of coal in terms of reducing damage to the environment, but this alternative energy source is not completely clean.
Raw (MSW) is a notoriously poor fuel because of its high moisture and low heat content. In addition, mass-burn of MSW produces a broad range of atmospheric pollutants, and the produced may become concentrated in potentially toxic elements, such as cadmium or arsenic. One goal of the production of refuse-derived fuel (RDF) is to improve the combustion of MSW by producing a fuel of lower moisture content, more uniform size, greater density, and lower ash content than raw MSW. Another goal is to reduce the amount of material in landfills.
A typical process for the production of RDF involves passage of raw wastes through a screen to remove small, inert materials (such as stones, soil, and glass), pulverization of larger particles in a shredding device, separation of ferrous metals by magnetic extraction, and segregation of the lightweight, mostly fraction in an upward airstream (this step is known as air classification). The shredded organic fraction can be used directly as a fuel (fluff RDF), or it can be compressed into high-density pellets or cubettes (densified RDF). The latter material is popular because it is easy to transport and store and because of its adaptability in handling and combustion.
RDF can be utilized as a cofuel with or fired separately. A major advantage of RDF over coal is that its sulfur content is markedly lower (0.1 to 0.2 percent compared with 5 percent or more for some coal samples), as is its nitrogen content. Both sulfur and nitrogen are among the more notorious atmospheric precursors to acid rain. Also, as a result of processing, RDF contains smaller amounts of potentially toxic metals than does MSW.
RDF possesses only 50-60 percent of the calorific value and 65-75 percent of the of typical bituminous coals. As a consequence, considerably larger weights of RDF must be burned to obtain performance similar to that of coal. The use of RDF in a boiler may therefore have an adverse impact on the performance of the boiler’s systems for air-pollution control and ash removal. In addition, the chlorine content of RDF is higher than typical coal. Other problems sometimes associated with the use of RDF concern odors and dust production in storage and particulate, carbon monoxide, and hydrogen chloride discharges during combustion.
Bibliography
Hickman, H. Lanier, Jr. “Refuse-Derived Fuel and Energy Recovery: Fulfilling the Resource Recovery Promise.” In American Alchemy: The History of Solid Waste Management in the United States. Santa Barbara, Calif.: Forester Communications, 2003.
Mateus, Maria Margarida, et al. "Refused-Derived Fuels as an Immediate Strategy for the Energy Transition, Circular Economy, and Sustainability." Business Strategy and the Environment, vol. 32, no. 6, Sept. 2023, doi.org/10.1002/bse.3345. Accessed 22 July 2024.
Niessen, Walter R. “Refuse-Derived Fuel Systems.” In Combustion and Incineration Processes. 3d ed. New York: Marcel Dekker, 2002.
Shehata, Nabila. "Role of Refuse-Derived Fuel in Circular Economy and Sustainable Development Goals." Process Safety & Environmental Protection, vol. 163, July 2022, pp. 558-573, doi.org/10.1016/j.psep.2022.05.052. Accessed 22 July 2024.