Rapid cooling of catalytic cracking settlers
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Our company’s 600,000 tons per year heavy oil catalytic cracking unit is shut down for maintenance. During this shutdown period, it has been difficult to reduce the temperature inside the settler; even after three days, the temperature remains around 230°C. The air-change bridge has little effect on reducing temperature; it can only introduce a small amount of low-pressure steam – too much steam would risk condensation into water, which could lead to the accumulation of catalyst and sludge inside the regenerator – in order to prevent the temperature from rising. Is there any manufacturer that modifies the \"nitrogen bridge\" during shutdowns (by introducing nitrogen into the steam pipeline and sending it into the settler; P?), or are there any better cooling methods (other than using water)?
I’m not sure how you manage to cool things down. Here, we open the manholes to allow natural cooling, but we have to prevent the coke inside from catching fire. Usually, it’s possible to enter after 2 days
It is best to increase the steam flow for cooling; the temperature in the settler should be 200 degrees Celsius, which will result in not much condensate water. It’s best to reduce the steam flow when the temperature is below 150. You can try using nitrogen; a fair amount is needed. At this temperature, the manhole opens directly; air present there may catch fire spontaneously, so it is necessary to monitor the temperature of the settler inside. When rising quickly, use steam first; if that doesn’t work, use water. We did it that way, and indeed the inclined tubes got clogged with mud; it took a lot of effort!
To date, spontaneous combustion of coke lumps still occurs from time to time in the settler of our equipment; a dedicated person is assigned to monitor it and spray water immediately whenever such combustion takes place.
We are all filling water, so we can remove the plug valve first.
Have you considered using stripping steam to control the temperature in the tower? The steam used in ordinary settlers is at 1.0 Mpa, with a temperature of around 200°C; this provides a certain cooling effect while also reducing air contact. However, at this time it is recommended to increase the flow rate of the two vents at the top of the tower to accelerate the displacement process; once the temperature stabilizes, the flow rates can be reduced appropriately!
Water cooling is not recommended; usually, natural ventilation is sufficient to create the necessary conditions for entry two days after the catalytic converters are removed through the manholes. In the case described by the original poster, nitrogen could be used to cool down the area, but access should be restricted to prevent unauthorized entry. Even so, after cooling, it is still necessary to test the oxygen level before allowing anyone to enter – this represents an additional step compared to natural cooling. In my opinion, once the manhole is opened, natural ventilation (with appropriate measures to prevent natural drafts such as steam) is more than sufficient to meet the entry requirements. Personal opinion