(93b) Furnace Tube Temperature and Monitoring

Managing furnace tube life is critical to achieving an efficient and safe process. As tubes accumulate damage from various process events such as fouling or flame impingement, the metallurgical characteristics are altered which can affect the expected life of the tube thereby leading to premature failure. In order to monitor and track tube condition, vision systems can be employed to view banks of tubes and provide data for each tube along it's length and surface area which becomes valuable not only as a live feedback on tube condition, but can also provide historical data for analysis of tube condition during shutdown which can then be used to create control loops in the software to predict current tube condition based on previous process conditions experienced. This allows operators to have a more complete knowledge of the tube status and make conservative judgments regarding current and future operations. The vision system works in a similar fashion to other temperature monitoring instruments in that it reacts to changing incident intensities over it's range of applicability, which is the visual spectrum. As metals are heated they begin to emit peak radiation in the IR and then near IR range. The near IR is visible to CCD cameras at approximately 750 F. With increasing temperature the radiation intensity increases and changes color from red to orange to white. Calibration to temperature allows the vision system to continually monitor the tube status in a substantially linear fashion as the emissivity of most metals in question is approximately constant in this temperature range.. An added feature of these systems is their ability to monitor the entire field of view which means that measurements are not made at single points but along the entire tube surface that is in view of the camera thereby allowing the system to monitor the tube surface to detect and locate hot spots. The software can also monitor tube distortion and displacement if desired and provide operators with a continuous, live process view.