CCS and Power Systems
Advanced Energy Systems - Hydrogen Turbines
Materials Issues in Supercritical Carbon Dioxide
Performer: ORNL - Oak Ridge National Laboratory
Project No: FWP-FEAA112
Program Background and Project Benefits
Turbines convert heat energy to mechanical energy by expanding a hot, compressed working fluid through a series of airfoils. Combustion turbines compress air, mix and combust it with a fuel (natural gas, coal-derived synthesis gas [syngas], or hydrogen), and then expand the combustion gases through the airfoils. Expansion turbines expand a working fluid like steam or supercritical carbon dioxide (SCO2) that has been heated in a heat exchanger by an external heat source. These two types of turbines are used in conjunction to form a combined cycle— with heat from the combustion gases used as the heat source for the working fluid— improving efficiency and reducing emissions. If oxygen is used for combustion in place of air, then the combustion gases consist mostly of carbon dioxide (CO2) and water, and the CO2 can be easily separated and sent to storage or used for Enhanced Oil Recovery (EOR). Alternatively, the CO2/steam combustion gases can be expanded directly in an oxy-fuel turbine. Turbines are the backbone of power generation in the US, and the diverse power cycles containing turbines provide a variety of electricity generation options for fossil derived fuels. The efficiency of combustion turbines has steadily increased as advanced technologies have provided manufacturers with the ability to produce highly advanced turbines that operate at very high temperatures. The Advanced Turbines program is developing technologies in four key areas that will accelerate turbine performance, efficiency, and cost effectiveness beyond current state-of-the-art and provide tangible benefits to the public in the form of lower cost of electricity (COE), reduced emissions of criteria pollutants, and carbon capture options. The Key Technology areas for the Advanced Hydrogen Turbines Program are: (1) Hydrogen Turbines, (2) Supercritical CO2 Power Cycles, (3) Oxy-Fueled Turbines, and (4) Advanced Steam Turbines.
Supercritical CO2 power cycles have the potential to provide a low-cost advanced fossil fuel combustion option with carbon capture. The cycle envisioned for the first coal-based application is a non-condensing closed-loop recuperated Brayton cycle. The cycle is operated above the critical point of CO2 so that it does not change phases (from liquid to gas), but rather undergoes drastic density changes over small ranges of temperature and pressure. This allows a large amount of energy to be extracted at high temperature from equipment that is relatively small in size. The temperature profiles of typical heat sources, like oxy-fueled pressurized fluidized bed com¬bustors (PFBCs), are a better fit to those of the supercritical CO2 working fluid than a typical steam cycle. SCO2 research will improve the data available for CO2 properties that will exist at the conditions within the proposed cycles and conduct system studies to identify development needs that will result in a roadmap to a demonstration of a high efficiency robust power cycle at a commercially relevant scale.
Oak Ridge National Laboratory will build and validate a materials testing rig and test a variety of alloys to increase understanding of the applicable corrosion mechanisms in SCO2 as a function of temperature and establish temperature limits for various classes to enable materials selection and design of SCO2 systems. Increasing the understanding of materials issues will enable an increase the efficiency of commercial power production from scaling up SCO2 systems to higher temperatures.