Dangers of operating a steam reboiler (shell-and-tube type) at excessive flow rate
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This post was last edited by chuan21206 on 2017-1-8 at 22:32. Our facility has a reboiler that uses steam as the heating medium (steam is condensed to provide heat). Over the past 12 years, there have been two instances of leakage, and in both cases the leaking tubes were located in the same area – at the steam inlet. After the first leakage, we replaced the heat exchanger; yet two years later, leakage occurred again in the same area. Since the heat exchanger was not disassembled, no leakage points in the tube bundle were detected, but I saw that the anti-impact baffles were still intact. During my own investigation, I found that the steam flow rate of this heat exchanger had consistently exceeded the design value over a long period of time. But it’s not clear whether excessive flow rates will cause corrosion and leakage in the tube bundle at the steam inlet; the mechanism of this corrosion is not understood. I hope that senior colleague can help me analyze this issue, or recommend some relevant books for me to consult. During actual operation, there is a phenomenon of excessive steam flow; the designed maximum flow rate is 1.5 t/h, but the actual flow rate often exceeds the maximum value indicated by the instrument (FIC-2010), reaching 1.7 t/h. The attached drawings are respectively a flow chart, a diagram of pipe plugging for bundle leakage, and the specific parameters of the heat exchanger:
If the steam boiler has a capacity of over 10 tons, a deaerator is required; moreover, an anti-overflow plate is definitely not suitable
The leaked tubes are the first and second rows of tubes at the steam inlet; it is possible that vibrations at the bundle entrance caused this.
Is it near the junction where the heat exchange tube meets the tube sheet? If so, it is possible that the heat exchange tubes are joined to the tube sheet by expansion jointing, creating a gap between them; when steam condenses, scale forms in this gap, leading to corrosion and subsequent leakage
Due to the lack of detailed description, only the following preliminary conclusions can be drawn: 1) If saturated steam is used, the moisture content in the steam may cause cavitation at the inlet of the reboiler； 2) If superheated steam is used, uneven heating may cause stress, leading to localized deformation and damage ； 3) The presence of water hammer can also cause problems ； 4) The method of turning steam on and off is also related to the temperature control method. For more information, please visit Fred’s official website or its WeChat official account... Fred Steam Energy Saving
The flow rate must be very high; 1.7 t/h is merely the maximum range for the steam flow rate – any higher value cannot be displayed. Therefore, it’s not clear by how much the flow rate actually exceeds this value.
This possibility should not exist; other steam reboilers with the same structure all have similar performance, but none of them has such a high leakage rate. Generally, there are no problems within 10 years.
Other steam reboiler designs are the same; they do not exhibit such high leakage rates, and generally there are no problems over a period of 10 years
It’s not the case that identical forms always mean identical properties; it also depends on the temperature of the medium and the size of the heat exchanger