Biomass fuels: Municipal solid waste
1.3 Municipal Solid Waste
Municipal solid waste (MSW) in not technically a biomass fuel, but because of its
alternative nature and “waste” status, MSW is often included in biomass discussions
and statistics. The organic portion of the MSW is a biomass fuel, but it is impossible
to completely sort and filter MSW to obtain only organics.
MSW can be converted to energy in three different ways:
- Mass burn MSW combustion
- Processing of MSW into refuse-derived fuel (RDF), and combustion of the
RDF
- Landfilling of MSW and collection and combustion of the landfill gas (LFG).
MSW- and RDF-fueled waste-to-energy facilities may not qualify for the same tax treatment or subsidies as true biomass-to-energy facilities. Waste-to-energy facilities that burn MSW or RDF typically have higher levels of emissions and ash compared with other pure biomass fuel combustion facilities, and permitting and public acceptance of these facilities can be more difficult.
RDF is created from MSW by sorting and processing to eliminate as much noncombustible material as possible, and thus RDF has a higher energy value than MSW and will produce less ash. To create RDF, the MSW is shredded, separated by density to remove heavy noncombustibles, magnetically filtered to remove small ferrous metals, screened to redirect oversized materials back for re-shredding, and screened to remove undersized materials. The RDF may be compacted for transportation. It takes about 1.27 tons of MSW to create 1 ton of RDF. LFG is produced by decomposing MSW. The landfill actually serves as the biomass conversion facility. LFG contains between 30 and 55 percent methane, which is then flared or converted to electricity. Although conversion of LFG to electricity is gaining popularity because the source of the gas is free and flaring the gas is wasted energy, conversion of MSW to LFG has one of the lowest conversion efficiencies and one of the slowest conversion rates of all biomass technologies. In approximate numbers, 1 ton of MSW in a landfill will take 20 years of LFG recovery to produce just 40 percent of the energy that the same ton of MSW will produce in a matter of minutes through RDF combustion. One reason for the difference in the energy recovery is that some non-organic portions of the MSW, such as plastics, will release substantial amounts of energy when combusted as RDF, but will not break down into LFG.
One advantage of MSW as a fuel is that Yakima County already has control over this waste stream. Also, MSW can command high tipping fees. For MSW waste-toenergy projects, the revenues generated by the tipping fees will normally exceed the revenues from production of electricity or steam. Tipping fees for MSW waste-toenergy can run as high as $100 or $200 per ton, or higher. Yakima County landfills currently charge a comparatively low $24.05 per ton, which would limit the revenues an MSW biomass project could obtain through tipping fees. Another benefit of using MSW is that this type of project would redir
by Yakima County Public Works, Solid Waste Division
From 'Review of Biomass Fuels and Technologies', 2003
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