Drum downcomer size
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In ethylene plants, the rising and falling tubes of the heavy oil boiler’s drum have the same diameter; whereas in the light oil boiler, the falling tube has a diameter of 8” while the rising tube has a diameter of 10”. Why is this design chosen? It’s easy to understand why the falling tube should have a smaller diameter – as the volume expands after preheating, it’s necessary to increase the tube diameter in order to maintain the flow rate. But why isn’t the same approach used in heavy oil boilers? If we consider flow rate and heat transfer coefficients, the feedwater flow rate in heavy oil boilers is higher, so a higher heat transfer coefficient would be expected, which would imply that a smaller tube diameter would be necessary. This is confusing; I would appreciate everyone’s insights
I don’t know what the dimensions of the rising and falling tubes in the heavy oil furnace drum are. It’s possible that when calculating the diameter of the rising tube, the value came out to be somewhere between two different numbers, so the larger value was chosen; as a result, the diameter of the falling tube was set to be the same as that of the rising tube. This post was last edited by WSL01218 on 2009-2-3 at 09:35
Both the rising and falling tubes of the heavy oil furnace are 10", and there is no similar calculation document available; thus, only speculation is possible
The diameter selection of the rising and falling tubes in a steam drum is related to many factors, such as the circulation rate of the boiler water, the evaporation capacity of the boiler, the specific gravity of the boiler water, the positions of the rising and falling tube openings, and the height difference between the boiler and the steam drum. The original poster can conduct a comprehensive comparison of these factors to try to identify the cause.
Is it because the temperature of the heavy oil furnace changes little, that the pipe diameter remains unchanged? /
Thank you all for your help. I’ll compare them carefully before discussing them with everyone:D