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- 15 - <br /> <br />recovery of reusable waste materials, resource recovery," as used in <br />this report, refers to those strategies that recover resources through <br />various processing methods--for example, incineration or biological <br />treatment. <br /> <br />1. ENERGY RECOVERY <br /> <br />Energy recovery methods include production and processing of <br />refuse-derived fuel, and use of waterwall furnaces and modular <br />incinerators. The following descriptions of energy recovery <br />technologies are from the Minnesota Resource Recovery Plan (MPCA, <br />1979). <br /> <br />a. Refuse-Derived Fuel (RDF) <br /> <br />The basic RDF system processes municipal solid waste to <br />prgduce a transportable alternative solid fuel for use in <br />fossil-fuel-fired energy systems. <br /> <br />RDF fuel may be classified as coarse, fluff or dust, depending <br />on the degree of processing. Coarse RDF can be used in <br />boilers equipped with grates, fluff RDF can be used in sus- <br />pension-fired' boilers, and dust RDF can be burned alone or <br />emulsified with oil to form a slurry for use in conventional <br />boilers. Each of the fuels can be substituted for others that <br />have received less processing. <br /> <br />Coarse RDF.is prepared by shredding raw refuse. During this <br />stage of processing, the nominal size of the incoming refuse <br />is reduced, resulting in partial homogenization of the waste. <br />Coarse RDF contains large quantities of grit. All the unde- <br />sirable components of the refuse (glass, grit, metal, chlori- <br />nated plastics) that present corrosion, erosion, and material- <br />handling problems are contained in the fuel. Coarse RDF <br />bridges easily (hangs up in hoppers and will not flow) in stor- <br />age. Coarse RDF has the same thermal properties as raw solid <br />waste; that is, 4,600 Btu/lb.,and burns to 26 percent moisture <br />and 29 percent ash. <br /> <br />Fluff RDF is prepared by air-classifying and screening coarse <br />RDF to remove most of the grit and large inerts such as cans, <br />rocks and metal debris. Air-classification vacuums off light <br />material, separating ~t from most of the chlorinated plastics. <br />Unfortunately, large wood fragments are also separated, thus <br />causing the loss of a desirable fuel component. Removal of <br />screenable dirt, grit and glass fragments to decrease the fuel <br />ash content further increases the heating value of the fuel <br />while reducing the amount of material to be handled in the <br />boiler's ash handing system. Fluff RDF has a nominal shelf <br />life of about five days. Longer storage encourages spon- <br />taneous combustion. The material has the same bridging and <br />flow characteristics as coarse RDF. Unscreened fluff RDF has <br />a heating value of 5,000 Btu/lb., burns to 26 percent <br />moisture and 22 percent ash. Screened material has a higher <br />heating value of 5,550 Btu/lb. and and burns to 12 percent <br /> <br /> <br />