To: Dr. Jo Mackiewicz
From: B. J. Excellent Student

Thermocouple of a combustion turbine power plant
Date: April 9, 2003

Introduction

This purpose of this paper is to update you on my progress of completing the final recommendation report. I am still studying to find the best thermocouple to be implemented into a combustion turbine power plant. In my proposal, the criterion for evaluating thermocouples was a very long list. In researching, I have narrowed down the factors important to recommending a thermocouple. The most important value is temperature range. I have considered 5 types of thermocouples(Type E, J, K, N, and T). These thermocouples have a combined range of -330 to 2300 degrees Fahrenheit [1].

I will also search for differences in reading accuracy. When combustion turbines are running, temperatures can exceed 900degrees Fahrenheit. The exact measurement of the temperatures is crucial to an efficient power plant. When the exact temperature is known, machine part-life is maximized, turbine efficiency is optimized, and fuel sacrifice is minimized. Each of these factors reduces cost to the company, and to the utility cooperative.

Similar to accuracy, is reading drift. Drift involves the microstructure of the different alloys that compose the different thermocouple types. When exposed to temperature cycles of 0 to 900 degrees Fahrenheit, the alloys of a thermocouple start to break down [2]. The breakdown results in measurement drift in thermocouples.

One criterion I have decided to throw out is cost. I have decided that cost will not be a major issue for this topic. The quality and attributes of the recommended thermocouple are of utmost importance. As stated before, the thermocouple is directly related to the life of the turbine parts. When the turbine parts are in the millions of dollars, correct temperature reading becomes crucial, and cost can be overlooked.

I am still re-evaluating my criteria as I progress. I am finding some data that is helping narrow my recommendation, and some data that is confusing my results. I am finding difficulty in coming up with good numbers and statistics. However, I believe I will be able to narrow the recommendation to at least two thermocouples.

Discussion

Work Completed. I have completed most of my secondary source research. This involves searching for books in the UMD Library, and also searching the online databases at UMD’s Indexes and Databases webpage. I am still waiting on my primary source data. This data is an email-interview that I conducted with an operator of a combustion turbine power plant located in Pleasant Valley, MN.

Through my research I have found that many different thermocouple types will suffice for a combustion turbine. However, Type T thermocouples donot have a large enough range for effective temperature reading. Type T’s range of useful application is -330 to 660 degrees Fahrenheit [1]. The precision of Type K, E, J, and T’s are the same. They are within 2 degrees Fahrenheit of the standards set by theAmerican National Standards Institute (ANSI) [4]. Type E has the best accuracy of the five thermocouple types at 1/2% degree Fahrenheit of the ANSI standards [4]. However, on efunda’s website, they stated that the Type T thermocouple has the least error in readings, +/- .75 degrees F [5].

Since thermocouples increase the life of turbine parts, they may prolong time between plant outages. A plant outage is any time the plant cannot be operated. To show the effects of a plant outage, an example is needed. If the price per Megawatt (MW) of electricity is currently $100, and a plant can produce 500 MW’s per hour, a power outage of 5 days will cause the following:

5 days = 5x24 hr = 120 hours down time.

120 hrs x (500 MW/hr) x $100/MW = $6,000,000 in lost profit.

This does not take into consideration that the power plant will have to pay for the power they owe their customers who expect and demand power [3]. By reading precise and accurate temperatures, thermocouples have a great impact on the daily operations of a power plant. They save a lot of money by preventing damage.

Work in Progress. My work in progress is processing the information I get from my primary and secondary research. I will also keep searching for data sets or facts that will enable me to recommend the best thermocouple for turbine applications. Presently, I am still juggling the data to make a final recommendation on the best thermocouple based on temperature range, drift, accuracy, and precision.

Work Remaining. I would like to use the PleasantValley power plant as a case study for what one company is doing with their existing thermocouple use. Also, I will begin drafting my final recommendation report on April 2, when all research is completed. I still would like to find the types of thermocouples that are used in other combustion turbines. I will also research different thermocouple vendors to see if there is any substantial difference in prices of the different thermocouples. Although not being evaluated, I would just like to mention price in the final recommendation paper to possibly narrow my choice in the event of a tie.

Work completed, work in progress, and work remaining schedules are shown below in Figure 1.

Task / Feb. 23-29 / Mar. 1-7. / Mar. 8-14. / Mar. 15-21. / Mar. 22-28. / Mar.29–Apr. 4. / Apr. 5-16.
Conduct Primary Research.
Conduct Secondary Research.
Analyze research sources.
Begin rough draft.
Revise, review, edit draft.
Meet with inst. for final changes.

Figure 1. Gantt Chart for completion of the final recommendation report.

  • Work Completed. . .
  • Work in Progress. . .
  • Work Remaining. . .

Conclusion

My progress thus far is slightly behind my scheduled progress previously stated in my proposal. This is due to my irregular findings of data that are not exactly concrete. I do haveenough sources and am very close to completing the research and beginning the drafting process. To compensate for being behind, I will draft the paper in one week. When I scheduled my time, I gave myself two weeks to write the draft, and now I will have oneweek. This will enable me to have my final recommendation paper done at the scheduled time. I am very optimistic that I will have a very thorough and beneficial final recommendation paper on April 16, 2004. The final recommendation report will benefit those dealing with combustion turbine power plant applications. They will be looking for the best thermocouple to implement into their turbines. I will relay and compare my results with a combustion turbine power plant in Pleasant Valley, MN.

Works Referenced

1.Thermocouple Technical Reference Data, Instrumentation Central [online], (Accessed: 16 March 2004)

2.Temperature Measurement Using Thermocouples: The Theory Behind., OregonState [online], (Accessed” 16 March 2004)

3.Willis, H.L., Scott, W. G., Distributed Power Generation, New York: Marcel Decker, Inc., 2000.

4.Baukal, E.B. Jr., Heat Transfer in Industrial Combustion, Tulsa, OK: CRC Press, 2000.

5.Chambers, A., Natural Gas & Electric Power, Tulsa, OK: PennWell Books, 1999.

6.Thermocouples: Introduction., efunda, Engineering Fundamentals[online] , 2004, (Accessed: 16 March 2004)