Is there any delayed coking unit that, upon the wax oil being converted into residue, still requires a closed-loop circulation of the residue?
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Is there any delayed coking unit that, upon the wax oil being converted into residue, still requires a closed-loop circulation of the residue? Our plant has never done this before; after the wax oil turns into residue oil, we use an open-loop circulation system to replace the wax oil. Once it’s clean, we raise the temperature quickly and switch to a four-way circulation system. We have never switched to a closed-loop circulation system using residue oil after introducing it – I’ve heard that some plants do do that.
It shouldn’t happen, right? At 420 degrees, the residue starts to react; at such a temperature, part of the residue has already begun to react. If a closed-loop circulation of the residue is to be carried out, the oil discharge tank may experience coking, and neither the oil discharge pump nor the cooling tank will be able to handle it.
If the wax oil is converted into residue and a closed-loop circulation of the residue is still to be carried out, it is necessary to remove water or steam and then cool it down to 300 degrees.
The initial operation plans for some units do not specify consistently the temperature and timing required to convert wax oil into residue oil; in some cases, wax oil is replaced at a constant temperature of 350 degrees, while in other cases heating is used for this purpose. In my opinion, the temperature should be increased rapidly once residue oil starts flowing into the unit, as there will be no way to reverse this process once coking begins. To avoid coking, it is best to increase the temperature quickly and switch the four-way valve accordingly.
Without using dewaxing oil, the residue oil is circulated to quickly raise the temperature to 460 degrees for switching; the wax oil used at startup can be fed into the storage area together with the coking wax oil.
After introducing the residue oil, the unit should start to heat up. At this point, the wax oil does not meet the requirements and should be sent to the heavy residue oil stream. Once the unit is operating properly and the quality of the oil meets the standards, it can then be sent to downstream units.
I agree with the opinions from the 2nd and 4th floors: during the wax oil circulation heating process, the make-up oil valve should be opened to allow oil to flow in through the main oil-gas line to the bottom of the distillation tower, thereby supplying heat to the tower and reducing the load on the oil rejection pump. Circulating residue can cause coking in the large oil and gas lines. After introducing residue oil into the unit, the furnace temperature should be raised promptly to 450, and preparation should be made to cut off the feed; once the temperature reaches 480, the four-way valve should be switched and the make-up oil valve closed. Scanning lines, normal production.
Generally, after switching from wax oil to residue oil, a closed-loop dehydration and temperature-raising process is required, including isothermal thermal compression. Isothermal heat tightening at each stage plays a significant role in the smooth commissioning of the device, as well as its long-term operation after commissioning. The residue is heated in a closed loop to 450 degrees, then gas is injected, followed by a rapid temperature increase to return to normal conditions!
We start with residue oil; after completing the open-loop cycle, it switches to a closed-loop mode.
Further discussion is needed. I’ll keep learning*