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. 2019 Jul 21;19(14):3211.
doi: 10.3390/s19143211.

Application of Sapphire-Fiber-Bragg-Grating-Based Multi-Point Temperature Sensor in Boilers at a Commercial Power Plant

Shuo Yang  1 , Daniel Homa  2 , Hanna Heyl  2 , Logan Theis  3 , John Beach  4 , Billy Dudding  4 , Glen Acord  4 , Dwyn Taylor  4 , Gary Pickrell  2 , Anbo Wang  3
Affiliations

Application of Sapphire-Fiber-Bragg-Grating-Based Multi-Point Temperature Sensor in Boilers at a Commercial Power Plant

Shuo Yang et al. Sensors (Basel). .

Abstract

Readily available temperature sensing in boilers is necessary to improve efficiencies, minimize downtime, and reduce toxic emissions for a power plant. The current techniques are typically deployed as a single-point measurement and are primarily used for detection and prevention of catastrophic events due to the harsh environment. In this work, a multi-point temperature sensor based on wavelength-multiplexed sapphire fiber Bragg gratings (SFBGs) were fabricated via the point-by-point method with a femtosecond laser. The sensor was packaged and calibrated in the lab, including thermally equilibrating at 1200 °C, followed by a 110-h, 1000 °C stability test. After laboratory testing, the sensor system was deployed in both a commercial coal-fired and a gas-fired boiler for 42 days and 48 days, respectively. The performance of the sensor was consistent during the entire test duration, over the course of which it measured temperatures up to 950 °C (with some excursions over 1000 °C), showing the survivability of the sensor in a field environment. The sensor has a demonstrated measurement range from room temperature to 1200 °C, but the maximum temperature limit is expected to be up to 1900 °C, based on previous work with other sapphire based temperature sensors.

Keywords: boiler; distributed sensing; femtosecond laser; fiber Bragg gratings; single-crystal sapphire fiber; temperature sensing; wavelength multiplex.

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Conflict of interest statement

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe on privately owned rights. Reference to any specific commercial product, process, or service by trade name, trade mark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Figures

Figure 1
Figure 1
(a) Fabrication procedure for wavelength-multiplexed SFBGs via point-by-point method [15]. (b) Configuration of the fabricated sensing fiber. Note: SFBG = sapphire fiber Bragg grating.
Figure 2
Figure 2
Working principle of wavelength-multiplexed-SFBGs temperature sensor and their spectra after fabrication at room temperature. Note: SFBG = sapphire fiber Bragg grating.
Figure 3
Figure 3
Design and picture of the sensor packaging.
Figure 4
Figure 4
Scheme for the interrogation system. Note: SLED = superluminescent light emitting diode; OSA = optical spectrum analyzer; MM = multimode; FC/APC = Ferrule Connecter/Angled Physical Contact.
Figure 5
Figure 5
(a) Calibration of the temperature response of the SFBGs, where λ (nm) is the measured wavelength, λ0 (nm) is the Bragg wavelength at room temperature, and T (°C) represents the temperature. (b) Evolution of the demodulated temperature during the 110-h isothermal test. The insert shows the configuration of the FBGs during the test. Note: SFBG = sapphire fiber Bragg grating. FBG = fiber Bragg grating.
Figure 6
Figure 6
(a) Evolution of the reflection spectrum during the 110 h test. The spectra at selected moments are shown (b–e).
Figure 7
Figure 7
Sensor deployment in a coal-fired boiler: (a) scheme for the configuration of the sensor (thermocouple not shown); (b) picture of the deployment site.
Figure 8
Figure 8
Temperature response of the sensor in a commercial coal-fired boiler over 42 days.
Figure 9
Figure 9
Sensor deployment in a gas-fired boiler: (a) scheme for the configuration of the sensor (thermocouple not shown); (b) picture of the deployment site.
Figure 10
Figure 10
Temperature response of the sensor in a commercial gas-fired boiler over 48 days.
Figure 11
Figure 11
Picture of the physical appearances of the packaging and thermocouple before and after the test.
Figure 12
Figure 12
(a) Picture of the onsite interrogation system packaged in a weather-proof enclosure. (b) Onsite user interface. (c) Remote user interface.
See this image and copyright information in PMC

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