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DCU reliability and yield

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This topic contains 2 replies, has 3 voices, and was last updated by  Anonymous 3 years, 9 months ago.

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  • #29513

    Hedewandro Lucredi

    What are the process variables and analysis in the DCU Stream that we need to check everyday or even hours in order to keep the DCU reliability and yield , like salt in the desalter, heater TMT, heater temperature, feed quality (Na, API, etc), main tower temperature, drum outlet temperature.

  • #29818

    Mike Kimbrell

    This is an important subject and can lead into a long discussion. There are a number of items that require constant monitoring and immediate corrective action as necessary to prevent a reliability or availability problem with the unit. There are items that need to be monitored to prevent a reliability or availability problem that take several days to a few weeks to present. Additionally, their are items to monitor that could take even longer to manifest. There are similar items to monitor that could cause a short term yield or quality issue or a longer term yield or quality issue.

    As the fired heater is the heart of the unit, monitoring the coil outlet temperatures, tube metal temperatures, drum inlet temperature, drum outlet temperature before quench are all important and need immediate corrective action if they are outside of the prescribed limits.

    The off-line drum cycle steps are important as the coke drum and heater are both the thermal reactor in the technology and the reboiler for the fractionator. Many of the serious process safety incidents in Delayed Coking have been associated with the coke drums, which is why safety rated interlocks have become the standard for managing the drums. Still, ensuring that the off-line drum steps are proper from a process stand point are important. Each of the steps; little steam, big steam, little water, big water, venting, draining, all have to be accomplished to safely move to the next step and then to routine coke removal. There are a number of mechanical pieces that are required in the off-line drum operations that can result in a reduction in feed rate if they do not perform when required. All of these items need to be monitored during each coke drum cycle.

    The fractionator and the wet gas compressor manage the portion of the unit that operates continuously so they need to be monitored to ensure that portion of the unit is within the normal operating range. The yields of the various liquid products are controlled in the fractionator, similarly to a crude unit atmospheric tower, a FCC or Hydrocracker main fractionator.

    As the bottom portion of the Coker fractionator serves as the feed surge drum for the heater feed pumps, the tower serves multiple purposes. Managing coke formation in the lower portion of the fractionator sets the Coker tower apart from some of the other complex fractionators.

    These key operating variables should have a safe operating range defined. Consequences of deviation from these pre-defined ranges should be listed and have appropriate corrective actions associated with the deviations. The operating variables that are associated with short term consequences should have a higher priority than those that are associated with medium or longer term consequences. If all the variables are set to the same priority, there are too many to respond to in a meaningful manner and that dilutes the overall monitoring effort. The lower priority items have to have a method to highlight deviations in a manner that does not get in the way of addressing deviations to the short term issues.

    As I indicated earlier, this is an important and large subject.

  • #30148


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