Regarding the hot water circulation pump of the external heat exchanger
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The gas generation rates of both the external heat exchanger of my catalytic unit and the slurry drum are around 2*40 t/h. But the external heat exchanger is equipped with a hot water circulation pump – why?
Because a catalyst is always present for external heat extraction, the flow of hot water used for heat extraction cannot be stopped; otherwise, over-temperature conditions will occur. For the steam generators in the oil slurry system, we can control the flow rate as well as the temperature by using control valves, manual valves, etc., based on speculation.
The oil slurry evaporator requires less heat extraction; internal circulation alone is sufficient to achieve an optimal level of heat extraction. In contrast, a higher rate of external heat extraction is needed, and a pump must be used to facilitate forced external circulation in order to achieve good heat extraction results
The temperature of the heat catalyst in the external heat exchanger is too high; if natural circulation occurs, localized overheating can lead to vaporization and dry burning. Therefore, forced circulation is necessary, with the circulation rate to production rate ratio needing to be above 14:1. In many cases, tube failures in external heat exchangers are caused by an insufficient circulation ratio
For external heat extraction, forced circulation is used because natural circulation can lead to localized dry burning; it is not simply for extracting heat from the heat exchanger. This is also for the long-term safe operation of the heat exchanger.
Forced circulation increases the water vapor ratio, which can effectively prevent localized heating in the tube bundle and extend its service life； At the same time, the adjustable heat extraction range is expanded, increasing the operational flexibility of the device.
This post was last edited by dqkwb on 2017-5-14 21:07. The person above is correct. The elevation of the external heat extraction drum in a natural circulation system must be much higher than that of the external heat exchanger, which requires more pipelines and steel, and the feed water pump also needs to have a higher head pressure. You can tell by seeing how much higher the drum temperature of your unit is than the external heat extraction temperature. If it is a drum with forced circulation, it doesn’t need to be that high, but an additional forced circulation pump will be required.