Transitioning to Low Carbon Power Generation by Integrating Renewables with Fossil Energy

It is expected that environmental regulations will be enacted to restrict the amount of carbon emissions from today's power plants. As such, it is likely that carbon capture and sequestration (CCS) technologies will be added to both new and existing coal-fired power plants to achieve compliance. Conventional CCS technologies, however, consume a great deal of energy to operate and hence introduce a significant energy penalty to the net output of the plant. Most often the energy for CCS operation is proposed to come from fossil sources with a large CO2 emission rate. The Office of Systems, Analyses, and Planning at the National Energy Technology Laboratory is evaluating the integration of both biomass and solar energy into new and existing coal-fired power plants as a means to offset the power and emissions penalties associated with CCS. Adding renewable biomass as a fuel in power cycles can reduce lifecycle greenhouse gas (GHG) emissions without incorporating conventional CCS technologies. The reduction of power plant CO2 emissions resulting from co-utilization of biomass with coal is directly proportional to the amount of biomass fed to the plant, however this benefit is partially offset by the fossil-generated emissions associated with the fuel's production and transportation to the plant. This portion of the paper will discuss the overall GHG benefits of supplying and co-firing biomass along with coal in select state of the art greenfield power applications with varying degrees of carbon capture. Carbon capture technologies included in this examination are Pulverized Coal (PC) plants with amine-based post-combustion carbon capture, PC oxy-fired combustion and pre-combustion capture in Integrated Gasification Combined Cycle (IGCC) systems. Each plant type will have multiple combinations of biomass feed percentage and overall carbon capture percentage. This paper will also discuss ways to reduce the power plant derate associated with incorporating CCS technology into existing plants. In this section it is proposed that the capacity derate associated with retrofitting a PC plant with CCS be overcome via the integration of a supplemental, low-carbon energy source. The two sources considered are solar thermal energy to regenerate CO2 capture solvents, thereby absolving a large portion of the parasitic penalty associated with the technology, and biomass combustion to supply the auxiliary steam and power loads associated with amine-based CCS. For purposes of this study, monoethanol amine (MEA) was selected as the CO2 capture solvent. The intent of this study is to determine the technical, economic and environmental performance of different power generation technologies when supplemented with low carbon, solar and biomass energy resources. The value of the renewable resource will be presented in the context of its contribution to: plant efficiency, overall fuel usage, level of lifecycle GHG mitigation, resultant power cost, and cost of mitigating GHGs. The study will also contribute to the discussion of how the nation's limited biomass resource can best be used to help reduce GHG emissions.