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Session 2005-1222

Excel™ Analysis of Combined Cycle Power Plant

Michael R. Maixner

United States Air Force Academy

A key issue in student design projects in thermodynamics is the necessity to modify property values during iteration and/or redesign. This is particularly true when dealing with two working fluids (e.g., air, water) in a combined cycle. The necessity to manually ascertain these values at all points of the cycle can inhibit the pedagogic purpose of the project: to allow students to view how overall system parameters (efficiency, specific fuel consumption, horsepower, etc.) may vary in response to changes in one or several input parameters (turbine pressure ratio, ambient air temperature, barometric pressure, cooling water temperature, boiler pressure, etc.).

A separate paper1 to be presented at this conference describes the details of an Excel™ spreadsheet add-in that relieves the student of the laborious updating of these property values as cycle modifications are made. This paper presents the application of this Excel™ add-in to analyze a baseline combined cycle plant (including cogeneration), and how various sensitivity analyses and optimization problems may be used to enhance students’ understanding of the basic design. Additional plants that could be analyzed are suggested.

INTRODUCTION Although they have learned the essential elements of various power plants and other thermodynamics systems in their studies of thermodynamics, fluid mechanics, and heat transfer, students frequently graduate without having analyzed a more complicated design which incorporates elements from all of these disciplines. Cadets at the United States Air Force Academy who elect to take a course in energy conversion are required to analyze an existing or hypothetical plant which encompasses a higher degree of complexity including, perhaps, elements of a combined cycle, cogeneration, etc. In the past, the complexity of this plant precluded more than a rudimentary “first-pass” analysis, due in large part to the requirement to read thermophysical properties from tables and insert them into the calculations—this left little or no time for more meaningful design studies of the plant, “what-if” scenarios, parametric studies, and the like. The development of the Thermal Fluids Toolbox by SpreadsheetWorld, Inc. and its distribution as “freeware,” has removed much of the tedium from analyses such as this, freeing the students to conduct more productive and instructive investigations of plant design. Cadets have learned the rubrics of table-reading and interpolation in previous courses; at

“Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition Copyright © 2005, American Society for Engineering Education”

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Maixner, M. (2005, June), Excel Analysis Of Combined Cycle Power Plant Paper presented at 2005 Annual Conference, Portland, Oregon. 10.18260/1-2--14287