OCR Text |
Show fluid, thus avoiding the expense of hot gas cleanup and/or the corrosion of turbine blades by coal ash. Because the gas turbine working fluid (air) is heated indirectly, the highest air temperature that can be reached by coal combustion is limited by heat exchanger materials and will fall short of the ideal turbine inlet temperature for highest efficiency. T o achieve the desired turbine inlet temperature (approximately 2500°F) the program allows for up to 3 5 % use of a premium fuel (e.g., natural gas or no. 2 heating oil) in a topping cycle. The design is still required to have a growth path to all coal as improvements in materials allow for a high temperature, corrosion/ resistant heat exchanger. For the near term (<5 years) it is unlikely that there will be structural ceramics available that can withstand molten coal ash at temperature >2700°F for long times (10,000 hours). Therefore the present design must be based on materials available n o w or by the year 2000 and accept temporary limitations on the m a x i m u m air temperature from coal combustion. The program devised by DOE has three phases: Phase I - Concept Definition and Preliminary R & D , begun in 1992; Phase II - Engineering Development and Testing, which started in 1995; and, Phase DI - Prototype High Performance Power Plant, planned to start in 2000. The HIPPS designs are required to meet or exceed the goals listed in Table 1. Table 1. Phase I Phase II NSPS Pollutant Emissions N O x (lbs N 0 2/MBTU fuel) S O x (lbs S 0 2/MBTU fuel) Particulates (lbs/MBTU fuel) 0.15 0.15 0.0075 0.06 0.06 0.003 0.6 0.6 0.03 Thermal efficiency (HHV) w 4 7% All solid wastes benign Coal must w 6 5 % total fuel (and path to 9 5 % coal) C O E v 9 0 % present cost for NSPS plant Approach The U T R C team has developed a design based on a thermodynamic optimization study of a combined cycle 300 M W plant, using an advanced aeroderivative gas turbine and a commercially available steam turbine. The working fluid is heated, using both radiative and convective air heaters. The convective air heater is constructed of ferritic alloy and a radiative air heater that is constructed from Ni-based superalloy protected by a ceramic refractory coating. The three major elements of the system are the High Temperature Air Furnace (HTTAF), the gas turbine, and the steam turbine. The H T T A F supplies 5 5 % of the temperature rise required by the gas turbines, bringing the compressor discharge air to 1700°F. The air then goes to a duct burner, |