Agenda - Council - 11/25/1980 - Laserfiche WebLink

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- 19 - ENERGY RECOVERY Energy recovery methods include production and processing of re~use-derived fuel, and use of waterwall furnaces and modular incinerators. The following descriptions o~ energy recovery technologies are from the Minnesota Resource Recovery Plan (MPCA, 1979). a. Refuse-Derived Fuel (RDF) The basic RDF system processes municipal solid waste to pro- duce a transportable alternative solid fuel for use in fossil- fuel-fired energy systems. RDF fuel may be classified as coarse, fluff or dust, depending on the degree o~ processing. Coarse RDF can be used in boilers equipped with grates, fluff RDF can be used in Suspen- sion-fired boilers, and dust RDF can be burned alone or emulsi- fied with oil to form a slurry ~or use in conventional boilers. Each o~ the fuels can be substituted for others that have received less processing. Coarse RDF is prepared by shredding raw refuse. During t~is stage of processing, the nominal size of the incomxng re~use is reduced, resulting xn partial homogenxzation of the waste. Coarse RDF contains large quantities of grit. All the unde- sxrable components o~ the refuse (91ass, grit, metal, chlor- inated plastics) that present corrosion, erosion, and material- handling problems are contained in the fuel. Coarse RDF bridges easily (hangs up in hoppers and will not flow) in stor- age. Coarse RDF has the same thermal properties as raw solid waste; that is, 4,600 Btu/lb., and burns to 26 percent moisture and 29 percent ash. Fluff RDF is prepared by air-classifying and screening coarse RDF to remove most of the grit and large inerts such as cans, rocks and metal debris. Air-classification vacuums off light material, separating it ~rom most of the chlorinated plas- tics. Unfortunately, large wood fragments are also separated, thus causing the loss of a desirable fuel component. Removal of screenable dirt, grxt and glass ~ragments to decrease fuel ash content further increases the heating value of the 'fuel while reducing'the amount of material to be handled in the boiler's ash handing system. Fluff RDF has a nominal shelf life of about five days. Longer storage encourages spon- taneous combustion. The material has the same bridging and flow characterxstics as coarse RDF. Unscreened fluff RDF has a heating value of 5,000 Btu/lb., burns to 26 percent mois- ture and 22 percent ash. Screened material has a higher heat- ing value of 5,550 Btu/lb. and and burns to 12 percent ash. It must be recognized that less total tonnage of screened fluff RDF is made because of grit removal; hence, while screen- ing improves the fuel product, some recoverable energy is sacrificed.