July 1, 2009

Designing an Ultrasupercritical Steam Turbine

Heinrich Klotz,Ken Davis, and Eric Pickering

Carbon emissions produced by the combustion of coal may be collected and stored in the future, but a better approach (in the near term at least) is to reduce the carbon produced through efficient combustion technologies. Increasing the efficiency of new plants using ultrasupercritical technology will net less carbon released per megawatt-hour using the world’s abundant coal reserves while producing electricity at the lowest possible cost.

Pushing the technology envelope to simultaneously minimize pollutants and fuel consumption through improved plant efficiency is the goal of every utility with an environmental conscience. One approach to achieving these goals is selecting coal-fired steam generation equipment operating at ultrasupercritical (USC) steam conditions. At these extremely high pressures and temperatures, a coal-fired power plant can operate with a net plant thermal efficiency over 44% based on the higher heating value of coal. Future development efforts target net plant efficiencies at or above 48% within the next decade.

In this article, we show the effects of increasing the steam turbine operating conditions for a new USC project in the U.S. and quantify the potential CO₂ reductions this advanced design makes possible.

Coal Conundrum

Coal is a very attractive resource in the U.S. for power generation due both to its availability and the estimated 250 years of reserves still in the ground. As utilities strive to keep up with rising demand for electricity, coal-fired generation remains exceedingly economical and the preferred fuel source for 50% of the U.S. electricity consumed.

The bad news is that coal-fired power plants are under heavy scrutiny, and there is strong political pressure to further limit pollutant emissions and begin regulating greenhouse gasses. Currently, 30% of worldwide CO ₂ emissions come from power plants, and most U.S. plants average more than 30 years of age. Alstom estimates that if all existing plants in the world were replaced by the latest, most-efficient plants, two gigatons of CO ₂ emissions would be avoided every year. If all coal-fired units in the U.S. were replaced by state-of-the-art coal combustion technology, the coal power sector’s CO ₂ emissions could drop by 25%, or almost 500 million metric tons annually.