Decoking preparation

[Hedewandro Lucredi]

After the draining of the coke drum, during the opening of the bottom delta valve the coke collapsed and produced a lot of steam that affect the operator. We observed that the feed was very light, the furnace was 495 Celsius, RR +/- 10 %, drum pressure 2.4 Kgf/cm2. We became very concerned about this problems. Is there any analysis that is possible to do in the feed to know and avoid this problem ? Which process conditions can I avoid this problem ?

[Mike Kimbrell]

Anytime there is a significant change to the feed slate, a review of the operating variables is needed. Light feed normally means a low concarbon value. Those types of feeds can require more energy per unit mass than heavier feeds to fully convert the feed to lighter products and coke. This can be done by increasing the heater outlet temperature or by extending the cycle time or some combination of both. The drum outlet temperature is an indicator if the heater outlet temperature is high enough. A drum outlet temperature of 440 C (825 F) is needed to fully thermally decompose the feed into lighter products and to cross link the coke to make it hard and mechanically stable.

With a light feed, the temperature drop from the drum inlet to the drum outlet is higher than with heavy feed. This requires the heater outlet temperature to be higher with light feed than with heavy feed.

Anytime there is a significant feed change, the first few drums should be closely monitored to ensure the operating conditions are suitable for the feed.

[Hedewandro Lucredi]

In order to avoid the operator goes to the drum bottom during the drum opening to pinned the bottom unheading valve opened, we intend to improve the SIS interlock that we do not need to do this operation. What is the risk of this proposal ? Damage to the automatic bottom drum valve ? Damage to the decoking drim stem ? Is this proposal (operate de drum bottom unheading opened with no pinned) usual ?

[Mike Kimbrell]

The locking pin is a part of the layers of protection on the operation of the DeltaValve. It prevents the inadvertent operation of the valve, which is a good thing. I am aware of a site that had an operator injured when they were attempting to install the locking pin with the bottom head in the open position. I believe they elected to leave the locking pin out when the valve was in the open position. As far as I know, that is the only site that has elected to keep the locking pin out while the unheading device is open. In all cases, the locking pin is installed when the unheading device is closed.

I am also aware of other sites that have installed a hydraulic cylinder to remove and install the locking pin remotely. That is my preference as the locking pin provides positive limitation on the valve being able to move. Removing and installing the locking pin remotely prevents the personnel hazard. I know that both DeltaValve and IMI Z&J have provided remote actuation of the locking pins.

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