Effect and principle of fluidization air regulation in the external heat exchanger on the material level of the external heat exchanger in catalytic cracking
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In the external heat exchanger, the catalyst in the dense phase of the regenerator enters it through the inclined tubes at its top; downstream, it passes through a slide valve for throttling before entering the coking tank. At the top of the external heat exchanger, there is also an outlet for the fluidization air used in the exchanger, which enters the regenerator’s dilute phase without any throttling mechanism. Explain the principle behind how the level of material in the external heat exchanger changes when the fluidization air is increased or decreased
In my understanding, there should be 2–3 streams of fluidizing air: some that assist in fluidization, and others that regulate the material level. By increasing the flow rate of these airs, an upward force is generated that counteracts part of the catalyst’s downward gravity, thereby reducing the amount of catalyst that flows. This allows for adjustment of the material level for external heat extraction, and thus changes the capacity for heat extraction through external means.
Increasing the fluidization air flow reduces the external heat storage capacity; a decrease in storage capacity leads to an increase
Generally, the external heat exchanger is of the bubble bed type; when the opening degree of the external downflow valve remains constant, an increase in fluidization air leads to a reduction in the flow rate of material passing through the bed via the valve, resulting in a slight increase in the amount of material stored and thus an increase in the heat absorbed. The opposite is true as well. However, due to the bubble bed configuration, the fluidization air can be adjusted within acceptable limits, so its overall impact on the storage capacity is minimal; the main influencing factor is the opening degree of the slide valve.
What the guy on the fourth floor said is correct; the fluidizing air in the external heat exchanger serves mainly to fluidize the catalyst, thereby preventing it from accumulating and causing blockages in the external heat transfer pipes. The adjustment method mainly relies on the opening degree of the external heat extraction slide valve. However, for an external heat exchanger with lift air, the magnitude of the lift air can affect the material level in the external heat exchanger.