The cooling effect of the vent tower in the coking workshop is poor – what’s the reason?
Thread Content
The overhead coolers in the vent tower of our plant’s coking workshop often get clogged, causing the temperature after cooling to exceed 105 degrees, whereas the design specification allows for no more than 40 degrees; this has a significant impact on the flare gas tank! Analysis shows that it is mainly the reprocessing of waste oil from the entire plant that causes the quality of the oil at the bottom of the vent tower to deteriorate; the waste oil contains impurities, particularly as a result of the influence of energy sludge from the reprocessing process. The method used in the workshop is to regularly purge the air coolers and use additional fans to lower the temperature of the circulating water. I would like to ask if there are any better methods?
Steam purging inside the air cooler, with the air cooler fins being washed from the outside
Scaling occurs on the inner wall of the heat exchange tubes in air coolers; the finned tubes need to be regularly flushed as part of routine maintenance
Before switching to venting, the bottom pump of the vacuum tower is activated in advance to prevent excessive heavy oil from entering the air cooler; after the oil at the bottom of the tower is discharged daily, new wax oil is introduced for replacement. The air cooler is frequently purged with steam.
It is normal to have soot buildup; that’s well understood. The key is to regularly clean the tubes of the air coolers. For multiple units, they can be cleaned one by one while still in operation, and the units that are still running can be subjected to regular steam cleaning, although the results are not very good； Also, the cooler needs to be purged separately, and the circulating water should be backwashed regularly. Given the high temperatures you mentioned, it’s likely that the design of the circulating water system plays a role as well! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! Another measure is to increase the circulation rate in the air vent tower, so as to keep as much material as possible inside it
There are two methods; you can give them a try. First, replace the conveyor belt for the air cooler fan with a new one. Prolonged use causes the conveyor belt to loosen, which reduces the fan’s speed and affects the cooling effect. Or simply replace the fan motor with one that has a higher speed. Second, steam is used for purging at the air-cooled inlet to ensure timely cleaning, preventing dirty oil from adhering to the pipe walls and thus reducing the cooling efficiency.
Our company regularly transfers the dirty oil at the bottom of the vent tower to the oil product stream, and then recovers fresh wax oil to replenish it; we also conduct regular tests on the density of the oil at the bottom of the tower.
I think a buffer tank should be added after air cooling; after use, it should be purged with steam, and then hot water should be used for circulation in a single system (with the hot water from the buffer tank heating the fluid before it returns to the air cooling stage). After the hot water circulation is complete, oil and water separation takes place in the buffer tank. Water flushing can sometimes be cleaner than steam.
This phenomenon is likely to be quite common in coking units; the main reason is that coke dust blocks the heat exchange tube bundles of the after-cooler or the air-cooling tubes, resulting in poor heat exchange efficiency.
You can discharge oil into the vent tower during the preheating of the coke tower. After changing the overflow, shake off all the oil. Frequently replacing the oil in the vent tower can also help alleviate the problem of air cooler blockage. It is also possible to modify the cold reflux inlet distributor; consult a design institute for a design. That will solve the problem.
Why hasn’t anyone suggested adding another set of filters before the air cooling units? For those in better conditions, an automatic switching system would be useful; it’s so difficult to clean out blockages in the air cooling tubes!