Sensitivity Analysis

A sensitivity analysis was conducted on each system to determine which parameters had the most influence on the results and to pinpoint opportunities for reducing the environmental burden of the system. In general, parameters associated with increasing the system efficiency and reducing the fossil fuel usage had the largest effects. Additionally, for the biomass systems, variables associated with growing a dedicated feedstock and factors affecting how much CO₂ and CH₄ are avoided by using biomass residue significantly affected the GWP of the system. Overall, however, the sensitivity analyses demonstrated that the conclusions that can be drawn from these studies remain relatively constant as different parameters are varied.

Summary and Conclusions

It is evident that biomass power systems reduce the environmental burden associated with power generation. The key comparative results can be summarized as follows:

• The GWP of generating electricity using a dedicated energy crop in an IGCC system is 4.7% of that of an average US coal power system.Figure 6.16 Total amount of nonrenewable resources consumed by the systems.
• Cofiring residue biomass at 15% by heat input reduces the GHG emissions and net energy consumption of the average coal system by 18 and 12%, respectively.
• The life cycle energy consumption of the coal and natural gas systems are significantly lower than those of the biomass systems because of the consumption of nonrenewable resources.
• Not counting the coal and natural gas consumed at the power plants in these systems, the net energy consumption is still lower than that of the biomass systems because of energy used in processes related to flue‐gas cleanup, transportation, and natural gas extraction and coal mining.
• The biomass systems produce very low levels of particulates, NOx, and SOx, compared to the fossil systems.
• System methane emissions are negative when residue biomass is used because of avoided decomposition emissions.
• The biomass systems consume very small quantities of natural resources compared to the fossil systems.
• Other than natural gas, the natural gas IGCC consumes small amounts of resources.

These results demonstrate that overall, biomass power provides significant environmental benefits over conventional fossil‐based power systems. In particular, biomass systems can significantly reduce the amount of GHGs that are produced, per kilowatt‐hour of electricity generated. Additionally, because the biomass systems use renewable energy instead of nonrenewable fossil fuels, they consume very small quantities of natural resources and have a positive net energy balance. Cofiring biomass with coal offers an opportunity to reduce the environmental burdens associated with the coal‐fired power systems that currently generate over half of the electricity in the United States. Finally, by reducing NO_x, SO_x, and particulates, biomass power can improve local air quality over coal‐fired power generation.