Future innovations in coal gasifier and combustor design will depend largely on an improved quantitative understanding of the interactions between coal ash, carbon oxidation, and emissions. The committee identified this topic as being of importance for DOE's coal-related advanced research activities, given its relevance to improved coal-based systems for power generation and fuel production.
Advanced research on coal liquefaction has the potential to achieve significant cost savings, either through improvements in current processing chemistry and technology or through processes based on new chemistries. There is currently very little industrial research on coal liquefaction; most activities are funded by DOE.
The operating environment in a coal-gas-fired turbine is more corrosive than that in a natural-gas-fired turbine, due primarily to the presence of sulfur and alkali metals. Evaluation of existing and emerging turbine material systems is needed to determine their suitability for advanced coal gasification-based power generation systems. This evaluation will require appropriate test rigs and methods for accelerated long-term testing in corrosive environments. Subsequent materials development will likely be necessary to optimize substrate and coating materials. The need for improved corrosion-resistant turbine materials is dependent on the ability of hot gas cleanup systems to reduce contaminant levels in coal-derived gas to acceptable levels for advanced gas turbines. The more successful the hot gas cleanup, the less demanding are the materials requirements, and vice versa.
The performance of high-temperature, high-pressure heat exchangers for EFCC power generation systems is currently limited by the properties of available materials. In particular, the maximum operating temperature of approximately 1090 °C [2000 °F] would not provide efficiencies significantly higher than state-of-the-art pulverized coal systems. The corrosive environment resulting from coal combustion imposes additional severe demands on materials. The ability to reach operating temperatures of 1370 °C to 1425 °C (2500 °F to 2600 °F)—corresponding to the inlet temperatures of future advanced gas turbines—represents a major materials challenge and is far from the current state of the art.
Inorganic membranes with high separation efficiencies and long-term resistance to high-temperature corrosive environments have the potential to improve the economics of power generation from coal, particularly for systems using advanced turbines. Materials development is required to improve the separation efficiency of ceramic membranes used for hot gas and flue gas cleanup. Improvements in durability at elevated temperatures in corrosive environments are also needed. Additional research opportunities exist to investigate membrane separation of methane from very dilute coalbed methane streams.