Gas Turbine Research Development

Gas turbine research and development (R&D) efforts are currently focused on the continued development of alternative cycles, including regeneration, intercooling, power augmentation with steam injection, and NOx controls without injection of steam or water. Component development technology has centered on ceramics, advanced alloys for high temperature, coatings, efficiency enhancements in compressor and turbine designs, and control technology.

Because specific capacity, pressure ratios, and cycle efficiency are closely tied to increased firing temperatures, materials technology has become a limiting factor. Additional aggravating factors include combustion hot spots, fuel and air purity, and the mechanical strength of high-temperature materials to withstand rotational and other mechanical stresses concurrently with high temperatures at the target operation temperature. Primary focus for new technology development is combustor and hot gas path parts associated with the turbine.

At turbine inlet temperatures of about 2,800°F (1,538°C) and a pressure ratio of about 50:1, potential simple-cycle efficiency could approach 50%. However, material and cooling technology is currently limited to about 2,300°F (1,260°C), with component cooling to maintain metal temperatures well below this. Without component cooling, conventional materials cannot withstand long-term operating temperatures exceeding 1,800 or 1,900°F (982 or 1,038°C). With state-of-the-art cooling techniques and other material treatment, achievable inlet temperatures are about 2,300°F (1,260°C). Current R&D is aimed at up to 2,600°F (1,427°C). The relationship between inlet temperature and pressure ratio to efficiency is shown in Figure 10-89.

Increasing material strength and operating temperature tolerance of turbine components can improve cycle efficiency in two ways. First, firing temperatures can be increased. Second, cooling air requirements can be reduced, decreasing parasitic loads and increasing net capacity.

Currently available advanced cooling systems have brought the high-end limit for turbine inlet temperature to about 2,350°F (1,288°C). New developments in turbine design are targeting parts in the path of the hot gas with blade cooling and improved air delivery systems and airfoil internal passage design.

Fig. 10-89 Effect of Turbine Inlet Temperature and Pressure Ratio on Thermal Efficiency. Source: Solar Turbines
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