form innocuous solids that do not attack the turbine blades. If the problem turns out to be more severe, blade coating has been identified as the most promising approach for current designs. For higher-temperature advanced turbines (e.g., 1430 °C [2600 °F]), requirements for contaminant removal from coal-derived fuel gas are not yet established.
Issues of system integration for coal-based power plants also remain to be addressed. At the present time, the concept of phased construction is widely viewed as a flexible strategy that can be a cost-effective way to transition the modest capital investment in a combustion turbine from peaking application to mid-load and eventually to baseload. However, there are significant technological and regulatory hurdles to overcome in such a conversion, which must be addressed. For example, a combustion turbine optimized for simple- or combined-cycle gas firing is not optimal for coal-based IGCC operation. Overall, converting to gasified coal lowers the net power plant efficiency by 5 to 10 percentage points—depending on gasifier and cleanup system design—relative to natural gas, primarily due to losses upstream of the turbine (Gilbert/Commonwealth, Inc., 1994).
Finally, turbine design modifications may be needed to take full advantage of integration issues that are unique to coal-based systems. For example, conceptually, integration of coal gasification with gas turbines that have been modified for operation on compressed humidified air from a storage reservoir have the potential to reduce gasification power plant costs by 20 percent. Another advantage to this cycle is that low-level waste heat energy can be reinjected into the cycle through the evaporation of hot water to humidify the high-pressure air. Expensive development efforts, however, will be required to modify existing aeroderivative turbines for this cycle. Systems studies are needed to identify the most promising options, as well as associated risks.
DOE's Advanced Turbine Systems (ATS) program—housed in the natural gas program of the Office of Fossil Energy—is a major effort to develop and design high-efficiency combined-cycle combustion turbines. The FY 1994 authorization for this program was $21.9 million; the FY 1995 DOE request has more than doubled to $44.9 million. The research is aimed at potential barrier issues, focusing on two primary areas: higher firing temperatures, mainly from improved cooling concepts and materials, and high-efficiency cycles, aimed at steam cooling, interstage compression cooling, and chemical recuperation. The program aims to provide technology ready for commercial baseload application by 2000 that will be applicable to coal and biomass systems as well as natural gas. DOE is also involved in other cooperative programs with industry, notably the Collaborative Advanced Gas Turbine program involving DOE, EPRI, GRI, and turbine manufacturers.