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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 11 Saturated steam regenerative cycle.<br />

Limits to the level <strong>of</strong> superheating that can be used are primarily<br />

determined by the properties <strong>of</strong> boiler materials, specifically the creep and<br />

thermal fatigue resistance <strong>of</strong> the superheater tube materials used. Higher<br />

pressures that result with higher superheat temperatures also result in<br />

thicker tube walls, which slow unit startup and load changing and greatly<br />

affect the thermal fatigue life <strong>of</strong> the component.<br />

Typical supercritical unit conditions are 23.13 MPa (3500 psia) and<br />

538 8C/538 8C (1000 8F/1000 8F) for single reheat and 23.13 MPa (3500 psia),<br />

538 8C/551 8C/565 8C (1000 8F/1025 8F/1050 8F) for double reheat units.<br />

Turbine Efficiency and Overview <strong>of</strong> Losses<br />

Fundamental to understanding the effect <strong>of</strong> many <strong>of</strong> the damage<br />

mechanisms in steam turbines is understanding how the damage creates<br />

efficiency losses in the turbine. At some stage in the analysis <strong>of</strong> repair and<br />

prevention strategies, an economic analysis will be required. Being able to<br />

Copyright © 2003 Marcel Dekker, Inc.

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