Discussion: Seeking advice on heat exchange issues in heat exchangers
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As shown in the figure, 8 kilograms of steam is cooled through a condenser, with the requirement that the temperature of the condensate be below 50 degrees. However, in actual operation with the control valve fully open and the circulating water flow at 1000 cubic meters per hour, the temperature of the condensate remains above 60 degrees. The inlet temperature of the circulating water is 30 degrees, while the outlet temperature is only 33 degrees; clearly, the heat exchange efficiency is very poor. Is this because the steam, after condensing, is discharged directly through vertical pipes without staying in the condenser long enough? As I understand it, the condensate pipe should be made into a U-shaped configuration upward, creating a water seal for the condensate from the condenser; this will increase the time that the condensate stays in the heat exchanger, thereby improving the heat exchange efficiency. I’m not sure if my understanding is correct; please correct me if I’m wrong! ! ! Thank you! !
Your analysis is correct, but implementing it with a water seal might not be feasible. After the steam condenses, the condensate flows rapidly into the lower tube bank; it does not stay long enough inside the heat exchange tubes, so it cannot be supercooled to below 50°C. Adding a water seal does not ensure the formation of a liquid level inside the heat exchange tubes. A valve can be added; by reducing the valve opening, the liquid level can be kept high.
I think the method used upstairs is not as effective as a water seal. I believe this is due to an insufficient heat exchange area; if the heat exchange area cannot be increased, making some adjustments to the process conditions may not yield any results. For example, a liquid seal can be added to raise the liquid level so that it can come into contact with the heat exchange tubes, allowing the liquid to continue exchanging heat with water. This might solve the problem, or it might cause new problems. In one of my previous experiments, I used chilled water as a medium for condensation; the normal bottom temperature was around 13 degrees. If the liquid level rose to the level of the heat exchange tubes, the bottom temperature could drop to roughly the same level as that of the chilled water
You mentioned that there are several reasons for this: 1. Design error – the heat exchange area was calculated too small; you need to recheck this. 2. The steam flow rate is too high; the diameter of the pipes needs to be reviewed. 3. It might be advisable to implement a liquid seal
The heat exchanger is fixed; no matter how much you increase the residence time, the amount of steam condensate (the input) will decrease. Is this operation permissible? If allowed, then increase the stay time. There is something wrong with the design of this heat exchanger; the circulating water does not make full use of the temperature difference. The main problem remains the insufficient heat exchange area; relying solely on an increase in the ΔT between the circulating water and steam (an increase in water volume and a decrease in the temperature of the return water) is not enough to compensate for this lack of heat exchange area.
The actual device is different from the experimental equipment; a U-shaped liquid seal can be used to maintain a liquid level, but it isn’t possible to make adjustments to it again. Moreover, if the equipment’s large tube box is long, the liquid seal will be long as well.
My feeling is that a liquid seal won’t solve the problem if the steam flow remains unchanged. Consider adding a circulation pump on the cooling water side to increase turbulence and improve heat transfer.
There are two manual valves and a water transfer device before the collection tank, which I did not draw. Will closing the valve on the water inlet device affect my amount of condensate? Adding a water seal won’t restrict the flow path for the amount of condensate, right? The amount of condensate won’t decrease, will it?
This steam is primarily used to balance and regulate the pressure in the steam distribution cylinder; no specific requirements are placed on its flow rate. However, under special circumstances, it is necessary to relieve the pressure in the distribution cylinder.
8 kilograms of steam represents high-quality energy, and its heat can be considered for recovery. The temperature dropping to 60°C is mainly due to the slow flow rate in the supercooled section and insufficient area.