INFRARED THERMOMETRY FOR FIRED HEATERS

For over three decades, the utilization of infrared (IR) thermometry has remained a stalwart practice in refining and chemical industries, serving as a reliable means to monitor tube metal temperatures within furnaces. The crux of this technology lies in its capacity to track temperature variations, thereby enabling the assessment of performance limits and ensuring the longevity of tubes. Yet, the potential of IR thermometry has occasionally been hampered by operator-related factors, leading to inaccuracies in data interpretation and application.

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Enhancing Diagnostic Precision

In essence, IR thermometry serves as a powerful diagnostic tool, unveiling critical insights such as tube hot spots resulting from internal fouling or uneven heat distribution in fired heaters. To harness the full potential of IR thermometry, operators must employ the appropriate instruments and adopt a well-established methodology to consistently measure accurate temperatures. Through the implementation of a robust IR thermometry health monitoring program, operators not only safeguard the mechanical integrity of fired heaters but also streamline production rates.

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Instrumental Diversity for Holistic Insights

Central to the success of an IR thermometry health monitoring program is the strategic amalgamation of two primary instrument types: thermal imaging cameras and pyrometers. Each instrument type boasts unique strengths and limitations, necessitating a comprehensive approach that combines both methodologies.

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Thermal Imaging Cameras: Renowned for generating two-dimensional thermal images of target surfaces, thermal imaging cameras offer dual benefits. Firstly, they provide meaningful images and measurements, facilitating the establishment of a historical record. This record proves invaluable in assessing tube creep damage rates and observing long-term performance changes. Additionally, thermal imaging cameras spotlight irregularities that might evade notice, guiding operators toward timely interventions and optimized maintenance schedules.

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Pyrometers: In contrast, pyrometers excel in delivering real-time measurements and swift troubleshooting. Their pinpoint accuracy proves invaluable for comparative assessments of specific tubes and immediate identification of performance anomalies. Pyrometers serve as an essential asset in troubleshooting scenarios, enabling prompt resolutions and the mitigation of unscheduled downtime.

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Mastering Measurement Factors

In the pursuit of accurate and repeatable measurements, operators must comprehend various measurement factors that influence IR thermometry. These factors include the target tube's emissivity, target reflectance, and the impact of flue gas on temperature measurements. Moreover, instrument-related factors, such as wavelength, calibration, and size of source effect, play pivotal roles in the accuracy of temperature readings.

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Emissivity (ε): As an environmental factor, emissivity refers to the ratio of radiation flux emitted by the target tube in comparison to that emitted by a blackbody at the same temperature. A thorough understanding of emissivity is vital to achieving precise measurements, as it affects the radiation wavelength and thus influences measurement accuracy.

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Reflection and Flue Gas Effect: Reflection errors arise due to the emissivity of the target tube, necessitating correction techniques to eliminate inaccuracies. Additionally, the presence of flue gas introduces absorption and emission errors, demanding the selection of appropriate instruments to mitigate their impact.

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Instrumental Factors: The choice of instrument wavelength and setting of instrument emissivity value further affect temperature measurements. By meticulously addressing these factors, operators can enhance measurement accuracy and minimize deviations.

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A Proven Methodology

To guarantee reliable and repeatable results, a robust field data collection approach is crucial:

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Instrument Setup: Begin by configuring the instrument emissivity to 1.00 and the background to ambient conditions.

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Flue Gas Effect Evaluation: Assess the impact of flue gas absorption or emission on thermometer readings by measuring the same tube from two different sight doors with varying path lengths.

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Short-Term Fluctuations: Record short-term temperature fluctuations in a selected tube, providing insights into real-time performance changes.

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Radiance Temperature Measurement: Accurately measure radiance temperatures of target tubes, considering focus, avoidance of flame interference, and sufficient coverage of target tubes within the field of view.

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Surrounding Object Measurements: Capture radiance temperatures of surrounding objects, improving the accuracy of target tube temperature calculations.

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Unleashing Precision Through Corrections

Following the meticulous field data collection, operators must apply rigorous calculations to correct measurement factors. Correction calculations encompass emissivity and reflection error, size of source effect, flue gas emissions, and other instrument and environmental variables. This process culminates in precise temperature measurements, enabling operators to achieve reliable and consistent results.

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Paving the Path Forward

Infrared thermometry for fired heaters is not merely a technology; it's a methodology that demands adept understanding, meticulous implementation, and strategic instrumentation. By embracing this approach, industries can elevate the reliability and efficiency of their fired heaters, fostering optimal operational performance and safety standards. As innovation propels industries forward, the marriage of technology and methodology takes center stage, steering organizations toward a future where excellence and precision intertwine seamlessly.