Emissions tradeoffs associated with cofiring forest biomass with coal: A case study in Colorado, USA

Cofiring forest biomass residues with coal to generate electricity is often cited for its potential to offset fossil fuels and reduce greenhouse gas emissions, but the extent to which cofiring achieves these objectives is highly dependent on case specific variables. This paper uses facility and forest specific data to examine emissions from cofiring forest biomass with coal ranging up to 20% substitution by heat value in southwest Colorado, USA. Calculations for net system emissions include five emissions sources: coal mining, power plant processes, forest biomass processes, boiler emissions, and forest biomass disposal. At the maximum displacement of 20% of heat demand using 120,717 t of forest biomass per year, total system emissions are projected to decrease by 15% for CO2, 95% for CH4, 18% for NOX, 82% for PM10, and 27% for SOX. PM10 and CH4 emissions benefits are closely tied to reducing open burning for residue disposal. At maximum displacement, 189,240 t of CO2 emissions equivalent to the annual CO2 emissions from 36,200 passenger vehicles, 440,000 barrels of oil, or nearly 990 railcars of coal are avoided. When forest biomass is not cofired, emissions equivalent to144,200 t of CO2 are emitted from open burning. In addition to exploring the details of this case, we provide a methodology for assessing the emissions tradeoffs related to using forest biomass for cogeneration that incorporates the operational aspects of managing forest treatment residues, which are frequently omitted from similar analyses.