February 1, 2012

Enhanced Load Dispatch Rate and Furnace Protection Through Model Predictive Control

By Don Andrasik and John McNulty, GenOn Morgantown and Don Labbe, Invensys Operations Management

Intermediate Boiler Temperatures Following MPC Upgrade

Following the expansion of the MPC system to include north/south steam temperature distribution, the boiler supercritical north/south steam temperature profile became more balanced, as shown in Figure 4, particularly at intermediate and higher loads. However, at lower loads the allowable range of air distribution and other variables was restricted, compromising the ability to impact north/south temperatures.

4. Striking a better balance after MPC upgrade. This chart represents the Unit 2 water/steam temperature profile after incorporating model predictive control–based control upgrades. The boiler supercritical north/south steam temperature profile became more balanced, particularly at intermediate and higher loads. The benefit is fewer incidences of high desuperheater inlet temperature and a lower average temperature, promoting longer tube life. Courtesy: GenOn Energy

The north/south split is nearly eliminated at intermediate and high loads but exists at lower loads. The mean north/south waterwall split decreased to a 7F split, and the desuperheater split was lowered to 31F, with nearly balanced conditions at intermediate and high loads. The benefit is fewer incidences of high desuperheater inlet temperature and a lower average temperature, promoting longer tube life.

Using Control Technology to Enhance Plant Performance

The value of control technology is significant when it provides continuous improvement in approaching the theoretical best that the mechanical limitations allow. It ensures improved economics in utilizing what is currently available and helps meet performance and component protection goals, while corrective mechanical changes can proceed as economics and circumstances allow.

In this case, significant value was gained at the Morgantown plant by the major improvement in balancing the desuperheater temperatures for waterwall control on both units at intermediate and high loads. This, along with the other enhancements, resulted in higher ramp rates over an expanded generation range.

The authors wish to acknowledge the assistance of the following people in the drafting of this article: Tom Turk, Morgantown Generating Station plant manager; Jurgen Brat, Morgantown Generating Station engineering manager; and John Gay with PowerMax Consulting.