Logistics, Costs, and GHG Impacts of Utility Scale Cofiring with 20% Biomass

Abstract

The basis for selecting a cofiring rate of 20% biomass centers on the assumption that this level of substitution for coal can be accomplished when providing a biomass feedstock that is compatible with the existing power plant coal conveyors, grinders, pneumatic feed lines/injectors, and burner arrangements. Untreated biomass is does not pulverize effectively with coal. Torrefaction is one method of improving the milling and grinding characteristics of biomass. Although additional work is needed to confirm this assumption, preliminary measurement of the grindability of torrefied biomass and coal indicate wood and switchgrass can be pulverized in existing coal milling operations. Higher percentages of biomass cofiring may also be possible, but are not considered in this assessment. Details about the feedstock logistics and cost models, power plant model development and validation, LCOE and LCA calculations, and a comparison with a similar cofiring study completed by the National Energy Technology Laboratory (NETL) are provided in Appendices to the report. The main body provides a summary of the key assumptions, modeling results, and general observations. Some key outcomes of the simulation predictions are tabulated here. Scenario Biomass for 20% Cofire (dry ton/yr) Lowest Biomass Supply Cost

Optimal Level of Woody Biomass Co-Firing with Coal Power Plant Considering Advanced Feedstock Logistics System

“…There have been additional efforts to analyze torrefaction as the feedstock upgrading technology to overcome the challenges of biomass supply network [23][24][25]. Svanberg et al [23] studied the supply cost of torrefied biomass for a pellet-fired combined heat and power (CHP) plant.…”

“…Another study by Boardman et al [25] carried out transportation and logistics analyses for the torrefied biomass co-firing with coal power plant. They suggested using the advanced woody feedstock logistics with torrefaction process and applied the logistics system as an alternative of conventional woody biomass logistics.…”

“…When received at the power plant, the chips are cleaned, dried, and fed into the conversion process through combustion. As an alternative to the conventional system, the Idaho National Laboratory (INL) suggested advanced woody feedstock logistics [25]. A key feature of this advanced design is the integration of a local biomass-processing depot where the biomass is torrefied and densified prior to transportation to the plant, as shown in Figure 1.…”

“…Constraints (20)-(21) make sure that no more than one facility (for terminal and depot, respectively) can open at a given location. Constraint (22)- (25) ensure that biomass is stored at intermediate facility only if it is open while, at the same time, dictating the maximum annual storage capacity for the facility. In our study, three annual capacity levels (Q l ) of terminal/depot were assumed; 45, 91 and 136 million kilograms (50, 100 and 150 thousand tons) per year.…”

“…Adapted from Boardman et al[25]. Individual plant results of biomass co-firing ratios and cost savings by advanced logistics system.…”