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DCU preservation

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This topic contains 3 replies, has 3 voices, and was last updated by  Mike Kimbrell 2 years, 4 months ago.

  • Author
  • #31292

    Hedewandro Lucredi

    Due to the quarantine (COVID-19) the fuel market fell and because that we stopped our DCU. In order to preserve the unit, we are inerting (N2) the gas recovery area. The heaters are shutdown completely. We are in doubt whether it is better to stop the heaters completely or let steam pass with some burners on in order to prevent any corrosion or even any collapse of some coke inside the heaters coils by temperature. In this case during the start up it would be plugged. Also if only inerting the gas recovery area and the main tower would be enough.

  • #31305

    Mike Kimbrell

    The duration of the shutdown is important to how the unit should be laid up. Removing the hydrocarbon from the main tower and blanketing it with nitrogen is a good practice. Similarly, doing the same thing in the gas plant should allow the unit to return to service with the minimum number of issues.

    I would normally have steamed the heater coils out into the main tower and then blinded the fuel and pilot gas and any waste gas streams that are routed to the heaters. You will likely spall some coke off of the heater tubes with these actions and that coke will end up in the main tower. Removing coke from the heaters is typically a good thing. As long as you have good steam flow during the heater steam out, the heater should come back on-line with limited issues.

    The only time I have left pilots on while the unit was down was when the duration of the outage was expected to be short, only a few days. If it were to go beyond that time, I would steam out the heater and blind off the fuel gas.

  • #31767


    Lines running from the VDU to the Delayed Coker feed section, which are under vacuum residue service, are preserved/put on layup by displacing the service fluid with diesel. Is this the best way to go?

  • #31768

    Mike Kimbrell

    It is very common to flush the vacuum residue line from the vacuum unit to the Coker with a lighter hydrocarbon that will not set up. Diesel is commonly utilized for this service. Light cycle oil from the FCC is sometimes used to flush the lines in this service.

    If the line is adequately heat traced, it would not need to be flushed. There is process risk in leaving vacuum residue in the line and hoping the heat tracing prevents the line from setting up. If it does set up, temporary heat tracing using electric resistance coils have been used to heat the line up enough to get the residue flowing again.

    For an extended outage, I would prefer to flush the line with diesel.

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