Infrared Thermography Improving Process, Performances, and Maintenance of Furnaces
IR Thermography Improving Process, Performances, and Maintenance of Furnaces
Infrared Thermography is suitable for inspection and process improvements. Petroval experts carry-out comprehensive surveys of the furnace working parameters such as burning plan, flame shape/deviation, tube cleaning, air supply/distribution among others. On strategic furnaces the Infrared Thermography service can bring important improvements in terms of process, performances, and maintenance. This service can be tailor made to the refiner or petrochemical site requirements.
How would you react when tube skin thermocouple readings are constantly showing alarms when operating at max throughput? When tube skin thermocouples indicate high values and alarms are on all the time, the operation department must reduce the severity on the process in order to operate below the alarm level. The level of the alarms is set by the inspection department to ensure safe and long-term operation based on several criteria such as tube material and thickness, process conditions and operating pressure. Ideally, you want to be able to ensure that your alarm is correctly indicating a real problem, rather than just a mechanical issue with the thermocouple (e.g., a loose thermocouple). One of the features of IR thermography inside the furnaces is to verify the readings of the tube skin thermocouples by measuring the tube temperatures in the area where the thermocouples are welded.
Several situations can then be identified
CASE 1 : The tube is not showing any hot area and the tube temperature measured by IR thermography in the area ofthe thermocouple is in the range of the expected tube skin temperature during normal operation. Then that thermocouple reading may be disregarded (based on the IR measurements) and operation may continue at maximum throughput knowing the thermocouple readings are wrong. Thermocouple maybe replaced during the next shutdown (see figure 1).
CASE 2: The tube is showing a hot area (only visible by an IR scanner properly calibrated) and that hot area is measured at a similar level of temperature than the thermocouple reading, then the issue is real, and the tube mechanical condition is endangered. Operation must reduce the firing on the furnace (at least in the problem area) in order to avoid a severe issue such as a tube rupture. It is then recommended to follow the hot areas regularly until a decoking shutdown is performed and confirmed by instrumented pigging or IR thermography at startup (see figure 2).
CASE 3: The tube is showing a hot area, but the tube temperature is significantly different from the thermocouple reading. Then the difference of temperature between tube temperature measured by IR and the thermocouple value can be used to offset the thermocouple reading on the furnace monitoring to stick to the reality of the operation. A safety margin of 10 to 20°C may be used to account for the potential error of measurement (depending on the tube condition and calibration parameters). The corrected thermocouple value will consequently be significantly lower than before, and the alarm level may not be reached anymore. It is then recommended (until a decoking shutdown is performed) to follow the hot areas regularly in order to check the deviations between skin thermocouples and IR measurements, so as to adjust the offset as necessary (figure 3).
Conclusion
For 2 out of the 3 cases, the severity of the operation may be maintained at the maximum level and the validity of the thermocouple value is the real issue. The confirmation by IR thermography is provided instantly during the survey and the operation can be informed in real time. The opportunity to maintain the high level of operation when required, represents an instant payback compared with turndown operation for wrong reasons.
