In this statistical exergy study of a conventional power plant, the concept of statistical exergy analysis as an alternative to common engineering approaches is examined. The statistical aspect is drawn from conducting Analysis of Variance (ANOVA) factorial design on the components of a proposed system. The exergy aspect comes in the extension of the typical energy analysis on engineering systems to include the limitations on the system imposed by the second law of thermodynamics.
To test this approach, a steam power plant discussed in an example exercise in Cengel and Boles’ 5th Edition Thermodynamics textbook was used as the subject of analysis. Effects of three input parameters on 13 responses were closely examined.
While using only 8 data points, the analysis still showed highly reliable and predictable results with square of residuals (R2) values of almost 100%. Predicted R2 values ranged between 88% and 99% with one outlier of 14.36%, depending on the input parameters.
Derived from the results, a new plant design concept was proposed and analyzed. This design eliminated all theoretically unnecessary drivers of exergy destruction in the plant. It also utilized the force of gravity to achieve the desired power output. The design showed an increase of 3.85% to 18% in kilowatts of work output and 5% to 7% in first and second law efficiencies. In this case, the derived design was shown to be impractical due to difficult maintenance as well as the difficulty in reaching the required pressures without a pump. However, this method of statistical exergy analysis is still valuable, as practicality of application will vary from one proposed system to another.
Second-Law Analysis of Irreversible Losses in Gas Turbines