Why are the upper and lower tubes of the steam drum and waste heat boiler curved?
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Why are the tubes that carry water from the steam drum to the waste heat boiler, and the tubes that carry steam from the waste heat boiler to the steam drum, both curved? Why is it set up this way?
Reply to 1# zgm728: It is mainly to take into account the thermal expansion and contraction of the riser and downcomer in cold and hot conditions.
Reply to 1# zgm728: There are two reasons: 1. Mainly, it is to ensure that the drop in water level in the drum boiler and the rise in steam generated by the waste heat boiler do not affect each other； 2. Eliminate thermal stress in the pipes. The boiler water enters the waste boiler from the bottom of the drum; to avoid interfering with the upward movement of steam, it can only enter the waste boiler from its side ； The steam generated by the waste boiler emerges from the top of the waste boiler and enters the drum. To avoid affecting the drop in water level in the drum, this steam can only enter from the side of the drum, not from its bottom ； As a result, the positions of the inlet ports of the rising and descending tubes in the waste boiler and the drum shift, and bending is necessary in order to enable them to be connected ； For the installation elevation difference of the drum in a natural circulation boiler, it is necessary to calculate the head pressure and the resistance in the pipes to determine whether natural circulation can be achieved. To reduce pipe resistance, both the rising and falling tubes are designed with integral bends rather than welded elbows.
It’s mainly due to the principle of thermal expansion and contraction, I guess.
Thermal expansion and contraction in main pipelines, especially those under high temperature and pressure
I think what was said on the 3rd floor makes some sense; the boilers and steam drums in our factory that are connected in such a curved manner all operate using natural circulation. And the others are forced circulation. One thing that is not clear to me is that, in order to reduce the resistance in the pipes, both the rising and descending pipes are bent as a whole, rather than using welded elbows. The pipe is bent; that’s probably why the resistance has increased. If you say it’s to reduce resistance, why not just use straighter upper and lower tubes?
Reply to 6# zgm728: The rising and falling pipes cannot be straight pipes; as already explained, the purpose of bending them is, first, to eliminate thermal stresses in the pipes, and second, to prevent interference between the downward flow of furnace water and the upward movement of steam； The resistance to bending of the pipe certainly increases; with overall bending, its curved shape results in a much lower resistance coefficient compared to welded elbows.