may not be significantly more expensive than first-generation systems if the turbine development effort is successful.

As noted previously, integrated gasification fuel cell systems offer the highest efficiencies and emission controls. Systems using molten carbonate or solid oxide fuel cells incorporate a steam bottoming cycle to maximize efficiency. Molten carbonate and solid oxide fuel cells operate at high temperatures (650 °C [1200 °F] and 980 °C [1800 °F], respectively). Since the maximum voltage produced by a fuel cell decreases with increasing temperature, the higher-temperature solid oxide fuel cell produces a smaller fraction of the total system power. However, the potentially lower costs of the solid oxide fuel cell provide incentives for continued research on these systems. The potential market for fuel cell technologies is quite large, especially for distributed power generation. However, fuel cell systems may still not be cost competitive with gas turbine systems without environmental incentives for higher efficiencies.

Gas turbine and fuel cell activities are currently funded under the natural gas portion of DOE's FE R&D program. However, gas turbines and fuel cells could be used with coal-derived gas, with the addition of gasification and gas cleanup facilities. The principal operating difference between natural gas and coal-derived fuel gas in these applications relates to the contaminants in coal-derived gas. Cold gas cleanup is capable of removing contaminants to a negligible level; however, there is an efficiency penalty of about two percentage points, along with the production of liquid waste streams that must be treated, adding to system complexity and cost. Hot gas cleanup is potentially more efficient but at the expense of less complete removal of contaminants, especially volatilized species that are not captured in current hot gas cleanup designs.

The requirements for cleanup of coal-derived fuel gas are expected to differ for fuel cell and gas turbine systems. System optimization will be required and needs to be established as part of the DOE coal program. For the molten carbonate fuel cell, ammonia, hydrogen sulfide, chlorine compounds, trace metals, and particulates would interact with the electrodes and with the carbonate electrolyte, necessitating electrolyte replacement and disposal of resulting water-soluble solid waste. For high-temperature gas turbines, damage to the blades is of greatest concern, and a discussion of research aimed at mitigating this concern can be found in Chapter 9 (Advanced Research Programs). Degradation caused by contaminants would limit maximum turbine inlet temperature, thereby limiting attainable system efficiency.

Thus, for fuel cell systems, the major development challenge is to reduce both fuel cell costs and balance-of-plant costs. For gas turbines, the major goal is to maximize turbine inlet temperature. Increasing turbine inlet temperature from the current maximum of 1290 °C (2350 °F), beyond the 1370 °C to 1425 °C (2500 °F to 2600 °F) proposed for integrated gasification advanced-cycle systems, to the 1540 °C to 1650 °C (2800 °F to 3000 °F) used in high-performance turbines would bring system efficiencies to a level approaching that expected for



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