Analysis of Gas-Turbine Blade Air Cooler and Supporting Systems

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Sponsor: University of Texas Utilities and Energy Management

Date: Fall 2007

Requirements:

To perform a successful analysis, it was important to properly outline what was specifically required of the model, what measurement points were available, and what limitations we faced while working around an operating gas turbine. The blade air cooler is essentially a large heat exchanger which removes heat from the gas-turbine and converts it into steam sent to a deaerator. The primary result of the blade air cooler analysis must be a discrete value of the rate of energy transfer based on current operating parameters, in units of mmBTU’s per hour. Associated with this heat transfer will be the mass flow rate, both on the turbine side and the steam side. These flow rates will be necessary outputs for use in further analysis of the steam system and the gas-turbine cycle efficiency. A limited number of data points is continuously logged by the power plant, giving the ability to look back at a specific instance in time. Ideally, the model would utilize only these measurements to provide the most comprehensive analysis possible. However, some inputs will rely on physical gauges or results interpolated from operating specifications. Any necessary data points that are not data logged require a method with which to calculate their assumed value based on data points that have been recorded.

For the duration of this project, Gas Turbine #8 had to remain fully operational; all measurements could only occur with the currently available instrumentation. Also, we were not able to vary any normal operating parameters in order to measure their resulting impact on associated process parameters.

Problem:
Our formal project problem statement is to “design and verify methods to assess the heat transfer and energy recovery of a blade air cooling process on a gas turbine generator.” In other words, our goal was to analyze and understand the blade air cooling process, ultimately providing quantitative measurements of the flow rates and energy transferred through the heat exchanger. By generating a computer model of the heat transfer based on known operating conditions, we could utilize the results in the ongoing efforts to model and understand the efficiency of the gas turbine cycle, as well as to understand the effect on supporting systems such as the deaerator.

Solution:

With our completed model and semester worth of analysis of the blade air cooler for Gas Turbine #8, we have concluded our research and formulated many recommendations. With a verified blade air cooler model integrated into the ASME PTC-22, our main computational model objective was completed. Verification for our model was completed with respect to the limited scope of the project. Two different atmospheric conditions were tested within the model both producing positive results with respect to energy saved. Monetary savings given our best conditions over a given year are calculated to be in the hundred thousands of dollars.

The repercussions of improper cooling coupled with a “perplexing” stuck bypass valve are obviously too costly to overlook. Also, an understanding of the reasons behind the minimum position of the bypass valve should be uncovered. Alll releveant diagrams should be replaced with updated versions that incorporate the blade air cooler system.

In conclusion, UT Utilities has successfully analyzed the gas turbine cycle for turbine #8 along with its subsystems, the blade air cooler and dearator. A working Excel file was created to model these systems for integration into the AMSE PTC-22 code. With our results and recommendations, this project has been and will continue to augment the understanding of the turbine and overall goal of the University of Texas Utilities and Energy Management Department to increase energy efficiency.

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