The Net CO2 Emissions and Energy Balances of Biomass and Coal-Fired Power Systems

To determine the environmental implications of producing electricity from biomass and coal, life cycle assessments (LCA) have been conducted on systems based on three power generation options: 1) a biomass-fired integrated gasification combined cycle (IGCC) system, 2) three coal-fired power plant technologies, and 3) a system cofiring waste biomass with coal. Each assessment was conducted in a cradle-to-grave manner to cover all processes necessary for the operation of the power plant, including raw material extraction, feed preparation, transportation, and waste disposal and recycling. Each study was conducted independently and can therefore stand alone. However, the resulting emissions, resource consumption, and energy requirements of each system can ultimately be compared. Although the studies conducted quantified resources consumed, as well as several air, water, and solid waste emissions, this paper will pay particular attention to net CO2 emissions and energy balances. The biomass IGCC system emits only 4.5 % of the CO2 produced by the average coal power system. This is due to the absorption of CO2 from the power plant by the growing biomass. Cofiring residue biomass at 5 % and 15 % by heat input reduces greenhouse gas emissions on a CO2-equivalent basis from the average coal system by 6.7 % and 22.4%, respectively, per unit of electricity produced. The life cycle energy balance of the coal systems is significantly lower than the biomass system because of the consumption of a non-renewable resource. Not counting the coal consumed by these systems, the net energy produced is still lower than from the biomass system because of energy used in processes related to flue gas clean-up. Cofiring biomass reduces total system energy consumption by 6.4 % and 19.9 % for the 5 % and 15 % cofiring cases, respectively. 1