External heat exchanger issue
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For a pneumatically controlled external circulation type external heat extractor, how is the heat extraction amount adjusted? The adjustment by increasing the air flow rate did not have a significant effect; we felt that circulation was poor. As a result, we had to use the air flow rate for fluidization in order to extract heat, in a manner similar to the operation of a back-mixing type external heat extractor. What is the reason for this?
It works pretty well for us; by adjusting the fluidization air separately, it’s possible to remove heat, but it certainly won’t reach maximum capacity, which will limit the processing volume of the device. I think the fluidization air flow shouldn’t be set too high; if it is, the catalyst will only remain in a fluidized state at the upper part, with only a small amount reaching the bottom. Even if the air flow is increased further, the catalyst won’t be fluidized without sufficient airflow, and thus the effect will be minimal. It is recommended to check the external extraction density and the return tube density; it would be ideal if both are around 500. Personal opinion, for reference only.
The heat removal capacity of the heat extraction tube has reached its maximum; that is, the heat transfer coefficient remains constant. No matter how large the catalyst circulation rate is, it is not possible to remove any more heat. The only way to increase the heat removal amount is by altering the fluidization air and thereby raising the heat transfer coefficient. To further increase the heat extraction amount, the air circulation rate can be increased further, as well as the catalyst circulation volume.
It’s likely a problem with the adjustment of your fluidization system. Under normal conditions, fluidization based on density differences works fine; however, if the fluidization air flow is too high, it affects circulation as well. In such cases, increasing the lift air flow doesn’t help either. It is recommended to adjust the density to the proper level and then use the lift air flow to control the circulation rate for heat extraction
We use a downflow external heat removal method; once the lift air flow is adjusted to an appropriate value, no further adjustments are made, as it is mainly the fluidization air that plays a key role. At first, the performance wasn’t good, but after adding a ring-shaped air duct at the bottom to draw in heat from the outside, the performance improved significantly, and the adjustability was also satisfactory.