July 1, 2009

Designing an Ultrasupercritical Steam Turbine

Heinrich Klotz,Ken Davis, and Eric Pickering

First U.S. Ultrasupercritical Project

American Electric Power (AEP), one of the largest electric utility power producers and distributors in the U.S., recognizes the need to continue to develop new coal-fired generation to meet projected load growth in its service territories, including west Arkansas and east Texas. To that end, construction on the John W. Turk, Jr. Power Plant (TPP), a 600-MW net coal-fired project that will introduce USC technology into the U.S., began in November 2008 (Figure 1). Integrated gasification combined-cycle (IGCC) was also explored as an alternative, although the supplier guarantees were stronger from the vendor supplying the USC plant. Table 1 illustrates the slight difference in CO ₂ emissions from IGCC, subcritical, and USC plant designs considered by AEP.

1.    One of a kind. AEP’s John W. Turk, Jr. Power Plant will be the only ultrasupercritical power plant in the U.S. when the $1.5 billion project enters commercial service in 2012. Shown is an artist’s concept of the project at completion. Courtesy: AEP


Table 1.    CO2 from various technology options. AEP’s evaluation of John W. Turk, Jr. Power Plant emissions for different combustion technologies. The fuel used in the evaluation is subbituminous coal. Source: AEP

Another key metric that persuaded AEP to adopt USC technology is its efficiency. A USC plant operates with steam conditions above 3,500 psia and 1,100F (593C). For comparison, a conventional supercritical unit operates at steam temperatures of 1,000F to1,050F (538C to 566C) and pressure typically up to 3,500 psia, levels that require careful equipment configuration decisions.

The design for TPP’s steam turbine efficiently optimizes steam cycle and operating parameters, uses the best advanced materials to operate reliably under these pressures and temperatures, uses a welded rotor design to match materials with the extreme operating environment, and includes new high-pressure (HP) and intermediate-pressure (IP) turbine design. Also, an Alstom Gigatop generator with direct hydrogen-cooled rotor and stator core and water-cooled stator windings, rated at 840 MVA, was selected.