Coking at the top outlet of the coking tower
Thread Content
At the inlet of the oil and gas line at the exit of the coking tower in our company’s coking unit, coking occurs frequently; it is necessary to disassemble and clean it once every 3 months on average (two diagonal oil injection nozzles at a 45-degree angle are used at the top of the tower). Has your company encountered such a problem? Please discuss.
Our company has encountered this issue as well; after that experience, we now inject antifoaming agents at the top of the coke tower to prevent coking in the large gas lines； Generally, to prevent coking in large gas columns, it is necessary to control the vertical height of the coke tower, which is usually between 4 and 5 meters, measured as the vertical tangent height.
This is a characteristic common to all coking units; it can only prevent and delay the rate of coking but cannot stop it entirely. Our company has also encountered similar situations – in those cases, the safety valves at the top of the carbon tower would activate for no apparent reason, while the pressure gauge on the production tower showed normal readings (the gauge was installed at the top of the gas pipeline). Various investigations revealed that coking had occurred in the pipelines, specifically at the inlet pipes, that is, before the pressure-taking pipes, which is why the issue was not detected. At that time, the diameter of the gas pipelines was only about DN80. After applying various technical solutions, such as installing the pressure gauge in front of the safety valves, using defoamers, and changing the location of the quench oil inlet from the previous oil-gas pipeline to the top of the carbon tower, the situation improved, and both the time required for coking removal and the frequency of such occurrences were reduced.
The friends upstairs are having a great conversation; this is indeed a difficult issue
The main solutions are to reduce the height of the foam layer and minimize the entrainment of coke dust. These methods include injecting defoamers, adding quench oil at the top of the tower, increasing the steam injection volume (which can reduce the height of the foam layer), preventing the coke tower from being overloaded, and avoiding overpressure in the tower.
If more air is injected, will it blow the oil foam upward?
No, steam still needs to be supplied to the small unit after the tower is replaced. Similarly, it’s just that the small puff of air is introduced earlier. Increasing the steam injection rate by 1–2 tons per hour is just enough to break the foam.
We used to do the same, cleaning regularly. Open again and insert the quench oil inlet at the top of the tower, not on the oil and gas pipeline – that’s it!
This method is very effective. Similar phenomena have also occurred at Guangdong Petrochemical in the past. To summarize what everyone has said, fluctuations in system pressure also have a significant impact. The cold coke gas supply volume value should not be too high.