Problems with the vent tower in delayed coking units

1. The vent tower is also known as a contact cooling tower. Some vent towers have integrated trays inside them, while ours is divided into upper and lower sections, with trays present in both parts. Recirculation pumps are installed in both the upper and lower sections to control the temperature. 2. Whether it operates continuously depends on the number of coke towers in the system; generally, systems with two towers alternate in use – they come into operation only after minor gas injection in one tower and subsequent steam supply to the other, while the cold coke water is stopped from flowing before it overflows from the coke tower. 3. The material that enters consists of unreacted dirty oil in the coke tower, along with a small amount of oil vapor remaining after minor gas injection, plus a large quantity of steam. 4. The inlet is located below the trays in the middle and upper parts of the vent tower, and the dirty oil after venting can be used as quench oil for the coke tower

This post was last edited by lyhgchem on 2011-5-19 20:34. Thank you to the teacher in post 3. Is cold heavy oil injected at the top of the vent tower? (If it’s one furnace with two towers, is injection done intermittently or continuously?)

The last edit to this post was made by linweihua6 on 2011-5-20 at 14:25. Reply to 1# lyhgchem: What is a vent tower (are there trays inside it)? Is a vent tower connected to a contact cooling tower? There are trays; it’s a contact-type exhaust cooling tower. 2. Is it operated continuously? It is discontinuous and is used during the venting operation of the coke tower. 3. What materials mainly enter the venting tower? Do they enter from the top or from the bottom? (Steam and oil-gas, especially during heavy steam injection, enter the bottom of the venting tower.) Where do these vapors end up? Bottom of the single tower inlet ； The operation of the two towers is adjusted according to temperature: hot oil enters the lower tower while cold oil enters the upper tower. At the bottom of each tower, there are 4 outlets. What kind of oil is extracted from the bottom of the vent tower? Where did you go? Why must the oil at the bottom of the tower be replaced regularly? Venting heavy oil, reprocessing it, and periodically (i.e., intermittently injecting) wax oil to prevent the system from becoming too heavy and viscous and thus getting clogged. 5. What is vent washing? Is it the injection of cooled heavy oil at the top of the vent tower? (What kind of oil is it? Is it injected continuously?) ) What is its function? Heavy oil washing to remove coke powder, gums, and other impurities from the heavy oil. 6. Why does the air cooling at the top of the tower tend to get clogged? Due to improper design operations, heavy oil and coke powder ended up in the air cooler. 7. What are the typical temperatures at the bottom and top of the vent tower? The temperature at the bottom of the tower should be around 250 degrees, while it’s best to keep the temperature at the top of the tower below 150 degrees. I would like to learn more about delayed coking; please help me out with your expertise. Thank you!

Thank you so much! I’ve learned it! The temperature at the bottom of the tower is around 250 degrees. Since the vent tower operates intermittently, what heat source is used each time to raise the temperature to 250 degrees?

This post was last edited and replied to by walter029 on 2011-5-27 at 22:12. Reply to 1# lyhgchem: I’ve been looking at information online regarding delayed coking, but it’s not detailed enough. There are a few questions that I hope fellow users can help answer. Regarding your questions, I’ll share my views one by one for everyone to discuss together. 1. What is a vent tower (are there trays inside it)? Is the vent tower connected to a contact cooling tower? Answer: A contact cooling tower is simply a tower for venting air. It contains trays, which primarily serve to disrupt the flow of fluid and facilitate heat exchange through contact cooling; hence the name contact cooling tower. 2. Is it continuous operation? Intermittent operation, absolutely intermittent operation. We have three furnaces and six towers, and the 24-hour coking cycle remains a batch operation. By \"batch\" here, it is meant that the raw materials entering the vent tower do so in batches; after water supply to the last tower is completed, hardly any material enters the vent tower anymore, and what remains is just the material that continues to circulate. The control valve below our oil-water separator shuts off periodically; the pump used to draw out the contaminated oil at the top of the tower is controlled via frequency conversion, as is the pump at the bottom of the tower. After the water supply to the last tower is completed, the air cooling is shut down. 3. What materials mainly enter the vent tower? Do they enter from the top or from the bottom (is the steam and oil-gas used during intense steam injection entering the bottom of the vent tower)? Where does this steam end up? Materials: the oil and gas emitted from the coke tower during large-scale steam injection, along with large amounts of steam ； The large amount of steam generated during water supply, along with a small amount of dirty oil, enters the middle to lower part of the vent tower. The steam naturally condenses into water; initially, it undergoes oil-water separation in the contact cooling system. The oil-containing and sulfur-containing wastewater then enters the oil separator tank, after which the remaining dirty oil and wastewater go to the oil tank in the coking unit for further oil-water separation. 4. What type of oil is extracted from the bottom of the vent tower? Where did you go? Why must the oil at the bottom of the tower be replaced regularly? The oil drawn from the vent tower is mainly paraffin oil and heavy paraffin oil. Most of it goes to the oil sludge tanks and then into the coke tower for reprocessing as quench oil. Regular replacement is carried out to prevent the bottom of the tower and the entire contact cooling system from being clogged by coke powder. 5. What is vent washing? Is it about injecting cooled heavy oil at the top of the vent tower? (What kind of oil is it? Is it injected continuously?) ) What is its function? Our plant does not have a dedicated system for washing the vent tower, and there are no problems during a single major maintenance cycle. 6. Why do the air coolers at the top of the tower tend to get clogged? The medium entering the vent tower has a high sound intensity and a heavy composition (wax oil); it is prone to condensation. 7. What are the typical temperatures at the bottom and top of the vent tower? The top temperature should not exceed 190℃

Reply to 1# lyhgchem as follows: 1. The vent tower is also known as a contact cooling tower; it is equipped with herringbone baffles or duckbill trays (in China), while abroad, spray systems are used directly, usually with two stages of spraying； 2. In China, operation is generally not continuous; it is mainly used during the phase of high-pressure steam injection in the coke tower and at the beginning of coke cooling. In foreign countries, Conoco uses continuous operation, and the advantage of this approach is that it solves the problem of fluctuations in the pressure acting on the safety valves of the coke tower. Additionally, waste oil can be used as quenching oil, eliminating the need to use wax oil as a supplement ； 3. Primarily, the oil and gas released during the steam and cold coke blowing stages enter the vent tower and reach its bottom; eventually, the steam is cooled by the cooler at the top of the vent tower and then separated in a sedimentation tank, with the aqueous phase being sent to the acidic water stripping unit ； 4. The heavy contaminated oil at the bottom of the tower can be discharged; it can be used as quench oil, sent back to the raw material buffer tank for reprocessing, or removed from the plant ； 5. The so-called vent washing is a process of mass and heat transfer through gas-liquid contact; the gas phase coming from the coke tower enters at the bottom of the tower, while the heavy contaminated oil enters at the top. Through this reverse contact, the heavy contaminated oil is washed out. As long as there is oil and gas entering the vent tower, heavy contaminated oil will be continuously injected into it ； 6. Since the gas phase arriving is the one from the large-scale steam injection in the coke tower as well as that from the early stage of cold coke removal, when the gas flow rate is not properly controlled, it is very easy for coke powder to be carried into the vent tower, thus leading to blockages ； 7. The top temperature during operation should be around 200°C, not exceeding 230°C; the bottom temperature during operation can reach up to around 380°C. I hope this answers your question

I’ve benefited a lot from it; I hope everyone will keep communicating more

Another function of the vent tower is to allow the oil and gas from the coke tower to be cooled and washed in this tower after the safety valves of the coke tower activate due to excessive temperature or pressure, before they are sent to the flare system

The vent tower can also reprocess contaminated oil, using the reprocessed heavy oil as quench oil for the coke tower.

The vent tower is essentially a contact cooling tower; it has 8 trays. Wax oil serves as the liquid phase inside the tower, and it is used only during the process of forced steam injection and later in the cold coking stage, to recover the oil components from the gas stream. This oil can be recycled and used as quench oil. So it is used intermittently. At temperatures below 150 degrees Celsius, we promptly discharge the oil and gas from the vent tower, to prevent the water present in the oil and gas from condensing and ending up in the waxy oil, which could affect the pumping capacity during steam injection. But some condensation will still occur, so it needs to be replaced regularly