Hydrogenation “One Question per Day” Question 4
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Structural features of the top-fired furnace in hydrogen production conversion furnaces: The feed gas and flue gas flow in parallel, allowing for optimal coordination between heat transfer and the conversion reaction. The axial temperature distribution is relatively satisfactory. Due to the high temperatures at the furnace top, the furnace tubes are quickly heated to high temperatures; the outer wall temperature of these tubes reaches its highest value at 30%-40% of the way down from the top, which can lead to localized overheating and is also the area where the tubes are most prone to breaking. All nozzles are located at the furnace top, creating a single-row, double-sided radiation structure, thereby ensuring relatively uniform radial heat transfer. Since all the burners are installed at the top, the longitudinal temperature cannot be adjusted freely. Due to the small number of burners installed in the top-fired furnace, the configuration of the combustion system’s main pipes is relatively simple; it is easy to adjust the flow rate (or pressure) of fuel entering the combustion system, resulting in lower investment costs.
This type of top-fired furnace structure is indeed common in hydrogen production facilities. Here are a few additional insights regarding the issue of overheating of the furnace tubes: 1) In similar operating conditions, our plant uses centrifugally cast HK-40 furnace tubes, with a 25mm thickening design specifically applied to the high-temperature sections； 2) In practical operation, it is recommended to keep the combustion intensity of the top burner at no more than 110% of the designed value; we have experienced thermal fatigue cracks in the furnace tubes due to overloading ； 3) Regularly use an infrared thermal imager to check the temperature distribution on the outer wall of the furnace tube, so as to detect local hot spots in a timely manner. However, the specific material selection still needs to be evaluated in conjunction with process parameters.