plant. Also of concern is the reagent requirement for sulfur removal and the resulting solid waste generation. As elaborated later in this chapter (see "Emission Control Technologies"), increasingly stringent requirements for SO₂ removal are becoming more difficult or more costly to achieve with fluidized-bed systems, which also generate larger quantities of solid waste than new PC plants with FGD. An increase in solid waste generation is inconsistent with DOE's goals for advanced power systems, which seek sizeable reductions in solid waste. Thus, there is a need to demonstrate efficient environmental designs and to address potential by-product markets for spent reagent in order to reduce solid waste impacts.

AFBC systems are a mature commercial technology, and, as such, DOE is no longer pursuing additional R&D on this technology. Significant performance improvements are expected for PFBC systems, which are now beginning to be commercialized. The DOE performance goals for the PFBC program appear to be reasonable for the first- and second-generation systems. The capital cost goals for all generations appear to be optimistic, especially as the number of components and complexity of the system are increased for the second-generation and improved second-generation systems. A major uncertainty still facing PFBC systems is the reliability and cost of hot gas particulate controls. Reduction of solid wastes, economical high SO₂ removal efficiencies, and generation of supercritical steam in a fluidized-bed are other issues to be addressed.

Coal gasification is a method of producing a combustible gaseous fuel from almost any type of coal. The current status of gasification technology and opportunities for efficiency enhancement have been discussed in Chapter 6. Gasification is a key step for advanced conversion of coal to electricity using IGCC systems. An IGCC power plant is a gasification facility coupled to a gas-fired combined-cycle unit. Based on current environmental control capabilities, IGCC offers a coal-based power technology with low emissions, high thermal efficiency, and the potential for phased construction—that is, building simple-cycle natural-gas-fired combustion turbines first, then converting to combined-cycle, and finally adding coal gasification as gas prices increase or gas availability deteriorates. Future advances in gasification-based power production are linked to increases in gas turbine firing temperature, hot gas cleanup of the fuel gas, coproduction of both chemicals and electricity, improved gasifier designs, and integration of gasification with advanced cycles and fuel cells.